DEPARTMENT OF TE TRANSPORT 662 .A3 OCT 2 - 197Z leport No. FHWA-RD-72-15 no.FHWA- LIBRARY RD-72-15
Tunnel Ventilation and
Air Pollution Treatment
S. J. Rodgers, F. Roehlich, Jr., and C. A. Palladino
Mine Safety Appliance Research Corporation Evans City, Pennsylvania 16033
" 4 *r5 ov
June 30, 1970
This document is available to the public through the National Technical Information Service, Springfield, Virginia 22151.
Prepared for
FEDERAL HIGHWAY ADMINISTRATION
Office of Research
Washington, D.C. 20590 NOTICE
This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof.
The contents of this report reflect the views of the contracting organization, which is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policy of the Department of Transportation. This report does not constitute a standard, specification, or regulation. — , , ot TE "department \{\Jnv+*y Aolm.'n.'str^^n. TRANSPORTATION u.S. ^e^er^l •; .A3 no- FHWA- ^ "ECHNICAL REPORT tTANTD^ T$T CE l|Q(?2. 1. Report No. 2. Government Accession No. 3. Recipient's CataloglNo. .-/r FHWA-RD-72-15, LIBRARY
4. Title and Subtitle 5. Report Dote \s * QctOl Tunnel Ventilation and Air Pollution Treatment Date of Preparation 6. Performing Organization Code
7. Author's) 8. Performing Organization Report No. Sheridan J. Rodgers , Ferdinand Roehlich, Jr., Cataldo A. Palladino MSAR-71-187
9. Performing Organization Name and Address 10. Work Unit No. Mine Safety Appliance Research Corporation FCP 33F3012 Evans. City, Pennsylvania 16033 11. Contract or Grant No. FH-ll-7597 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Final Report U.S. Department of Transportation June 30, 1970 Federal Highway Administration Washington, D. C. 20590 14. Sponsoring Agency Code Ab 2980
15. Supplementary Notes
16. Abstract The dangers such as harmful physiological effects and nuisances for various tunnel air impurities for occupants were usually negligible, especially because of limited exposure periods. Only carbon monoxide, hydrocarbons, nitrogen oxides, and particulates pose any significant problems. From the foregoing analysis, standards of American Conference of Government and Industrial Hygienists, Federal ambient air and occupational safety and health regulations, and tunnel occupancy, tentative limits include: Safety for Unmanned Tunnels Carbon Monoxide 500 ppm Nitric Oxide 37.5 ppm Nitrogen Dioxide • 5 ppm Particulates lOmg/meter"
A computer program was developed and validated to predict various significant air contaminants. Instrumentation to monitor tunnel air quality was proposed. Treatments of tunnel air for either discharge to the surroundings or recycling were examined. Economic and processing constraints such as dilute concentrations were probed. Limited laboratory tests were conducted. Removal of carbon monoxide appears to be impractical. Adsorption of nitrogen dioxide and more noxious hydrocarbons by activa- ted carbon showed promise. Particulates can be largely removed by electrostatic precipitation, filtration, and wet scrubbing.
17. Keywords 18. Distribution Statement TnTinel f Mr pollutants Availability unlimited. Ventilation Instrumentation, Air Purifica' The public can obtain this document through tion, Air Quality Standards the National Technical Information Service, Springfield, Virginia 22151.
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 267
Form DOT F 1700.7 ABSTRACT This study, funded by the Department of Trans- portation, Federal Highway Administration, was aimed at evaluating current air quality in existing tunnels and determining means of upgrading air quality in existing and future tunnels. The study consisted of six phases: 1. Identify the types and quantities of impurities in vehicular tunnels. 2. Evaluate the physiological effects of these impurities on tunnel workers and transients. 3. Establish air quality criteria for vehicular tunnels. 4. Determine available methods for improving air quality in vehicular tunnels. 5. Perform laboratory tests to demon- strate the applicability of selected purification procedures. 6. Recommend instrumentation for vehicular tunnels. Phase 1 consisted primarily of a literature survey of past tunnel studies as well as vehicle emission rates as a function of various driving modes. Those of major concern are CO, N0 X , HC and particulates. A computer program was developed which adequately predicts the concen- tration of various impurities as a function of driving mode and ventilation rates. Some on-site sampling was performed to verify the validity of the computer program. Phase 2 involved a survey of the literature to determine both short term and long term effects on humans exposed to specific tunnel impurities. These effects were considered in terms of both safe levels and comfort levels with respect to tunnel employees and tunnel transients. The work of Phase 3 evolved as a result of the findings in Phase 2. Criteria for tunnel impurity levels were established with the basic guidelines being the Recommended Levels of the American Conference of Governmental Industrial Hygienists, the EPA standards as set forth 1n the Federal Register and other references on the effects of air impurities on safety and comfort. Phase 4 involved a review of current literature on methods and procedures for purification of contaminated atmospheres. Typical purification systems which were reviewed included catalytic combustion, adsorption, absorp- tion, wet scrubbing and electrostatic precipitation. These methods were considered within the constraints imposed by tunnel atmospheres (i.e., low impurity levels and large gas volumes). An economic evaluation of selected systems was made. Phase 5 reguired laboratory evaluation of the most promising methods of tunnel atmosphere purification. Small scale testing was performed in a chamber containing actual automobile exhaust gases. Parameters which were studied included temperature, space velocity, residence time and so on. Hopcalite at 225°F to 250°F reduced the CO to zero. Activated carbon proved to be effective in the removal of NO2 and heavy hydrocarbons. Phase 6 reguired the recommendation of impurity monitors which should be used in tunnels. For tunnels where the air guality is maintained by ventilation, the recommen- dation was made that CO continued to be monitored and used as the primary indicator of tunnel ventilation rates. It was also recommended that smoke meters be installed in tunnels, particularly those which have heavy diesel traffic. TABLE OF CONTENTS Page No INTRODUCTION 1 RESULTS OF THE PROGRAM 3 Identification of Types and Quantities of Impurities in Vehicular Tunnels 3 Literature Survey 3 Computer Model 21 Emission Rates for CO, H-C, N0 X and Particulates 38 Verification of Computer Model 45 PHYSIOLOGICAL EFFECTS OF TUNNEL CONTAMINANTS 69 Contaminants Which Have Been Found in Tunnel Atmospheres 69 Selected Contaminant Levels for Vehicular Tunnels 72 Specific Limits for Manned Tunnels 72 Unmanned Tunnels 76 Summary of Recommended Levels 79 EVALUATION OF POLLUTANT REMOVAL METHODS 81 State of the Art - Applicable Control Technology 81 Applicable Tunnel Pollution Control Technology 83 Carbon Monoxide and Hydrocarbons 84 Catalytic Oxidation 87 Thermal Afterburning 93 Adsorption 94 Wet Scrubbing 97 Nitrogen Oxides 101 Source Control 105 Particulates 108 Tunnel Pollution Control - Feasibility and •Economic Evaluation 113 Tunnel Pollution Control Strategies 116 Exhaust Emission Projections 119 Tunnel Air Treatment: Problem Statement 125 Tunnel Ventilation Costs 130 Process Feasibility: CO and Hydrocarbons 134 Process Feasibility: Hydrocarbons 139 Process Feasibility: Particulates 143 Process Feasibility: Water Solubles 150 General Feasibility: Recycle & Compart- mentali zation 151 iii TABLE OF CONTENTS (Continued) Page No. Conclusions of Alternative Control Technologies 155 Selection of Control Techniques to be Evaluated 158 General Discussion 158 Carbon Monoxide Removal Systems 159 Hydrocarbons 159 Oxides of Nitrogen 159 Particul ates 160 Purification Test System 160 Run No. 1 - Blank 162 Run No. 2 - Cold Hopcalite 164 Run No. 3 - Activated Carbon 164 Run No. 4 - Purafil 166 Run No. 5 - Hot Hopcalite 166 Run No. 6 - Silica Gel -Hopcal i te 166 Run No. 7 - Hopcalite 167 Runs 8 and 9 - Filter Media 167 Run No. 10 - Mn02-Cu0 167 Run No. 11 - Charcoal Plus Hopcalite 167 Run No. 12 - Charcoal Plus Moisture Tolerant Hopcal i te 168 Purification Systems for Tunnels 168 TUNNEL INSTRUMENTATION 171 Carbon Monoxide ' 171 Smoke or Haze 173 Other Monitors 174 Hydrocarbons 174 Nitrogen Oxides 174 Total Aldehydes 174 Carbon Dioxide and Oxygen 174 Recommendations for Tunnel Instrumentation 174 CONCLUSIONS 177 REFERENCES 181 BIBLIOGRAPHY 191 A. Specific Tunnel Studies 191 B. General Tunnel Studies 192 C. Emission Rates 194 D. Traffic Surveys and Studies 197 E. Ventilation Requirements and Equipment 199 F. Physiological Effects 201 G. Emission Control 204 H. Pollutant Monitoring 205 TABLE OF CONTENTS (Continued) Page No. APPENDIX I - Final Report - IHF 209 APPENDIX II - Pollutant Removal Proceas Calculations 241 from Final Report — Patent Development Associates, Inc. LIST OF ILLUSTRATIONS Figure No. Page No m ii 1 Mean Hourly Traffic Flow Through Sumner Tunnel , By Time and Type of Day, Sept. 14-20, 1961 Mean Carbon Monoxide Concentration in Sumner Tunnel by Time and Type of Day, Sept. 14-20, 1961 Peak Carbon Monoxide Concentration 1n Sumner Tunnel, by Time of Day, July and September 1961 Mean Soiling Index at Sumner Tunnel Stations on Week Days, by Time of Day, Sept. 14-20, 1961 8 Mean CO Concentration at Sumner Tunnel Stations by Time of Day, April 20 Through 28, 1963 11 Mean Daily Concentration of Gaseous Pollutants in the Sumner Tunnel by Sampling Stations, April 20 Through 28, 1963 13 7 Carbon Monoxide Profile - Squirrel Hill Tunnel-North Tunnel 19 8 Carbon Monoxide Profile - Squirrel Hill Tunnel-South Tunnel 20 9 Carbon Monoxide Profile - Fort P1tt Tunnel-East Tunnel 22 10 Carbon Monoxide Profile - Liberty Tubes- West Tube 23 11 Effect of Air-Fuel Ratio on Automotive Exhaust Components 27 12 CO Output vs Vehicle Velocity 29 13 Multiplication Factor for Gradient /'Increase" For Gasoline Powered Cars 30 \Pecrease. vii 1 LIST OF ILLUSTRATIONS (Continued) Figure No. Page No 14 Multiplication Factor for Gradient Increases For oiesels 31 Gdecrease/ 15 CO Emission at 5500 Ft. Compared with That at 500 ft. 32 16 Ventilation Rates and Roadway Gradient for Baltimore Harbor-East Tube 47 17 Actual Trace of CO Monitor Readings in The Baltimore Harbor Tunnel 48 18 Computer Predicted CO Profile-Baltimore Harbor Tunnel-East Tube 50 19 Calculated and Actual CO Concentration For Baltimore Harbor Tunnel-East Tube 51 20 Ventilation Rates and Roadway Gradient For Allegheny-North Tube 53 21 Computed Traffic Conditions for Armstrong Mountain Tunnel 54 22 Carbon Monoxide Profile Lincoln Tunnel- North Tube 56 23 Actual and Calculated CO Values for the Lincoln Tunnel-North Tube 57 24 Actual and Calculated CO Values for the Lincoln Tunnel -Center Tube 59 25 Actual and Calculated CO Values for the Lincoln Tunnel-2 Way Traffic 60 26 Carbon Monoxide Profile of Fort Pitt Tunnel-West Tube 62 27 Measure of CO Values for the Naturally Ventilated Armstrong Tunnel 67 28 Schematic Diagram Proposed by Sir Bruce White 82 29 Emissions of Carbon Monoxide vs. Vehicle Speed 117 VI i LIST OF ILLUSTRATIONS (Continued) Figure No. Page No 30 Projected Average Exhaust Emissions, Period 1970-1980 126 31 Automotive Exhaust Purification Test Chamber 161 32 Removal of Hydrocarbons by Activated Carbon 165 33 Effect of Catalyst Temperature on CO Concentration 169 1 x LIST OF TABLES Table No. Page No. 1 Suspended Particulate Parameters in Sumner Tunnel Outlet and Inlet Air, Sept. 14-20, 1961 10 2 Comparison of Mean Concentrations of Particulate Pollutants at Sumner Tunnel as Two-Way Tunnel, Sept. 14-20, 1961 With Operation as One-Way Tunnel April 20-28, 1963 12 3 Results of Tunnel Experiments, Summer 1958 15 4 Pollution in Blackwall Tunnel, May 14, 1959 16 5 Average Annual Amounts of Smoke and 7 Polycyclic Hydrocarbons Per 1000 Cubic Meters of Air at the Mersey Tunnel 17 6 Average Annual Amounts of Selected Impurities at the Mersey Tunnel 18 7 Exhaust Gas Emission Rates (ft^/min 25 8 Carbon Monoxide Production as a Function of Carburetor Adjustment (Cubic Feet CO per Foot of Travel 26 9 CO Emissions Reported in Reference 22 Emission Rate gm CO/veh-mi 40 10 Grams of Pollutant Emitted per Mile For Fixed Mode of Operation (gm/veh-mi) 41 11 Carbon Monoxide Emission, gm CO/Vehicle- Mi. 42 12 Analysis of Material Collected From Ventilation Building of The Fort Pitt Tunnel 63 13 Fort Pitt Tunnel Test Data April 7, 1971 65 14 Measured Tunnel Contaminants 70 XI LIST OF TABLES (Continued) Table No. Page No. 15 TLV and STL for Selected Pollutants 77 16 Tentative Pollution Levels for Tunnels 79 17 Comparative Process Capabilities 85 18 Combustion-Related Vehicular Emissions 86 19 Removal Process Summary Catalytic Oxidati on 89,90 20 Scrubber Capabilities (Imperato) 98 21 Results of a Typical Analysis of Automobile Exhaust Gases 103 22 Simplified Reaction Scheme for Photo- cehmical Smog 104 23 Suspended Particulate Parameters in Sumner Tunnel Outlet and Inlet Air, Sept. 14-20, 1961 110 24 National Air Quality Standards Proposed by EPA Primary Standards 120 25 Exhaust Emission Standards and Goals 122 26 Automobile Longevity 124 27 Tunnel Pollutant Loadings 127 28 Preliminary Single-Pollutant Optimum Process Indication 129 29 Estimated 1970 Tunnel Ventilation Blower Capital Costs as Function of Head Regui rement 132 30 Operating Costs of Tunnel Ventilation Blower as Function of Head Reguirement 133 31 Summary of Catalytic Oxidation Costs 139 32 Spray Holdup Time & Chamber Volume as Function of Dust Particulate Size 148 xii LIST OF TABLES (Continued) Table No. Page No 33 Influence of Recycle on CO Concen- trate on 154 34 Process Cost and Feasibility Summary 156 35 Summary of Purification Systems 163 36 Application of Continuous Monitoring Instruments to Tunnel Atmospheres 172 x i i i INTRODUCTION This is the final report on Contract FH 11-7597 with the U. S. Department of Transportation, Federal Highway Administration. The work which covered Tunnel Ventilation and Air Pollution Treatment was performed by MSA Research Corporation and covered a period of 16 months. The basic objectives of the program were to identify the impurities and the level of these impurities in vehicular tunnels, establish the toxicity levels of these impurities and rec- ommend desirable time-concentration limits for the Impurities, determine and test applicable processes for removal of the impurities, and recommend air pollution monitoring devices for tunnels. The work statement as presented in the contract is quoted below: "The contractor shall furnish the necessary facilities, materials, personnel and such other services as may be re- quired, and in consultation with the Government, conduct a research and development project entitled Tunnel Ventilation and Air Pollution Treatment. The contractor shall direct its best efforts toward achieve- ment of the program objective to the extent that time and funds are provided. The objective is to conduct research on the feasibility of removing impurities from the air with- in vehicular tunnels and to maintain a purity level so as to relieve the discomfort and eliminate the dangers to the traveling public without exhausting vitiated air to surround- ing areas. To fulfill the above objective, the contractor shall obtain through comprehensive literature surveys and other sources, pertinent information and analyze this material to: Recognized variables include traffic conditions and vehicle mix under various circumstances such as speed, load and, fuel type-, road conditions including gradient, pavements, and elevation above mean sea level; and atmospheric conditions such as ambient temperature and winds at portals. 3. Establish criteria for desirable and allowable time- concentration limits of the pertinent impurities for the maintenance of a safe and comfortable tunnel atmosphere for various conditions and with due consideration to operating personnel as well as the traveling public. Reasoning be- hind the criteria shall be formulated. 4. Determine available methods, processes, and mechanisms for removing contaminants from the tunnel air which may in- clude but not be limited to cooling, scrubbing, electro- static precipitation, and deacidi fi cation. The interplay of natural additions and flow, vehicle induced air movement, internal ventilation patterns, and exhausting to the atmos- phere shall be considered. Physical feasibility of the systems including power, space, and disposal problems shall be included in the analyses. Cost effectiveness, and other economic factors will be involved in arriving at practical and practicable systems for various tunnel conditions. 5. Investigate and establish the adequacy, practicability, reliability, and costing of available air pollution gauges and detection devices (and systems of these) in the tunnel environment. The local concentrations as well as the large scale concentrations of pollutants shall be subject to me asurement. 6. Perform laboratory tests as required to demonstrate the applicability of chosen clean up procedures. This phase of the work must be carefully considered so that unnecessary work is not expended." Two subcontractors were used in the performance of the program. The Industrial Health Foundation of Pittsburgh, Pennsylvania contributed in evaluating the physiological effects of tunnel impurities. Patent Development Associates, Inc. of Glenshaw, Pennsylvania reviewed current impurity control technology and performed feasibility and economic evaluations of the current technology. RESULTS OF THE PROGRAM This section presents the results of the various phases of the program. One of the more difficult tasks was to recommend desirable time-concentration limits for vehicular tunnels. These recommendations were to cover three general categories - safe levels for tunnel personnel (Maintenance men or police officers) who would spend hours per day 1n a tunnel, safe levels for transient users who would spend 5- 15 minutes In a tunnel and comfort levels for the transient users. Identification of Types and Quantities of Impurities in Vehicular Tunnels Literature Survey - All artificially ventilated tunnels have instrumentation for continuous monitoring of CO. In almost every case, the type of instrument which is used to monitor CO 1n vehicular tunnels is the Hopcallte type where the change 1n temperature due to the heat of catalytic oxidation of CO can be related to the CO concen- tration in the air samples. Although a wealth of data exists on CO concentration as a result of this continuous monitoring, it is difficult to relate the CO concentration to the traffic density, type of vehicles (gasoline or diesel), vehicle velocity and so on since these parameters are not routinely measured. Furthermore, the monitoring systems 1n tunnels measure only CO, while this program is directed toward establishing typical concentration values for other Im- purities which are present 1n vehicular tunnels. One addi- tional shortcoming to this Information is that 1t represents point concentrations either at the site of the analyzer or an average concentration for a complete tunnel section when the monitoring station is located 1n a ventilation duct. A number of studies have been made on the concen- tration of impurities other than CO 1n vehicular tunnels. Some studies have been devoted to measuring the complete CO profile throughout the length of a tunnel. These studies were helpful 1n trying to determine typical and maximum values of Impurities in tunnels, but again 1n many cases the studies failed to present real time data on traffic patterns and ventilation rates. Two studies were made on the 1.1 mile long Sumner Tunnel in Boston, Massachusetts. The first study was made in 196l(U when the Sumner Tunnel was a single tube carrying two way traffic. .A second study on the Sumner Tunnel was performed in 1963(2) when a sister tunnel, the Callahan Tunnel was opened and the Sumner Tunnel was converted to a two lane, one way traffic pattern. The Sumner Tunnel has intake and exhaust fans located at both the Boston and East Boston ventilation buildings. The ventilation rate ranged from 73,000 cfm to 613,000 cfm. During the f i rs t s tudy, the num ber of ve hi cles using t he tunnel was a bout 3 5,000 per day The mi nlmum vehi cle flow was 200 v ehi cle s per hour at 5 A.M. a nd the maximum flow was 2,200 vehic les pe r hour during th e morning and eve ning rush hours (8 A. M. and 4 P.M. ). Figur e 1 is a plot of traffic flow v ersus time o f day f or a typi cal week- day, we ekend and weekl y aver age fo r the w eek of Se ptember 14 to Sept ember 20, 1961. Figu re 2 s hows th e mean CO concen- tration in the t unnel exhaus t stac k for t he same p eriod of time, Figure 3 shows the pe ak CO concent ration fo r the week of Septembe r 14-2 0, 196 1 as w ell as the week of July 27- August 2, 1961. The h ighest insta ntaneou s peak co ncentration during the study was 2 56 ppm . The tunnel is essen tlally a closed system an d thus offer s the opportu nity to d etermine the amo unt of po llutio n emit ted pe r vehic le mi le u sing the equatio n: (Outlet - Amount measured = cone. Inlet cone. )(Vo1ume of ventilation air) /i \ (No. of veh1cles)(0.55 mile of tunnel length) * ' ' The term 0.55 mile was used since only half of the tunnel served by the Boston ventilation building was used in the calculation. From 1 A.M. to 5 A.M. the calculated emission rate for CO was 35 gm per vehicle mile. During the remainder of the day, the values for emission rate were approximately twice this value. The higher rate is due to the effect of traffic modes, varying periods of idle, acceleration and deceleration as a result of traffic tie-ups. The mean soiling index was measured, also, and is shown in Figure 4. The highest mean coefficient of haze and smoke (Cons) per 1000 feet of air was 6.5 Cohs. In Allegheny County, Pennsylvania the following classifications are used for soiling index:(3) 0-1.0 Cons/1000 ft slight pollution 1.0-2.0 Cohs/1000 ft moderate pollution 2.0-3.0 Cohs/1000 ft heavy pollution 3.0-4.0 Cohs/1000 ft very heavy pollution Thus, in terms of this arbitrary assignment of pollution values, the 6.5 Cohs/1000 ft measured in the Sumner Tunnel would correspond to very heavy pollution. Suspended particulates were measured over a sampling period of 8 hrs with the maximum concentration being observed during the period from 9 A.M. to 3 P.M. The total particulate ' ' 3000 I i 1 1 i .A A f\ k f\\\ .^A — uj 2000 / \ \ J \\\syi v WEEKDAY —, .r--v\ l/s. \ y.\ i 1 \ 1 **zzf 5r /'/ WEEK— / If s VV :/ __•' ^—WEEKEND v~\ 1000 r \ 1 *\ * 1 / ^\*S\ * ^v ^v s*VJl 1 1 1 i i 12 IS 20 24 HOUR OF DAY FIGURE 1 - MEAN HOURLY TRAFFIC FLOW THROUGH SUMNER TUNNEL, BY TIME AND TYPE OF DAY, SEPT. 14-20, 1961 J 12 16 ?0 2» HOUR OF DAY FIGURE 2 - MEAN CARBON MONOXIDE CONCENTRATION IN SUMNER TUNNEL BY TIME AND TYPE OF DAY, SEPT. 14-20, 1961 300 SEPTEMBER 14-20 A7 £Vv JULY 27-AUGUST 2 \ ' 20 24 HOUR OF DAY FIGURE 3 - PEAK CARBON MONOXIDE CONCENTRATION IN SUMNER TUNNEL, BY TIME OF DAY, JULY AND SEPTEMBER 1961 * ^ TUNNEL CENTER if x -- — \ TUNNEL OUTLET AIR — HOUR OF DAY FIGURE 4 - MEAN SOILING INDEX AT SUMNER TUNNEL STATIONS ON WEEK DAYS, BY TIME OF DAY, SEPT. 14-20, 1961 8 conce ntrati on durtn g that peri od wa solub le mat erial (o rganic s) ac count mg/m3 ) of t he total parti culat e inv 3 for 7 .5% (. 045 mg/m ) of. the t otal The b alance of the parti c ulate s wer metal s othe r than 1 ead. Cadmi urn, a cern due to its tox icity, was qui te 1 11s ts the composi tion o f the coll Using equat ion (1) emissi on ra tes w ere calculated for par- ticul ates ( 0.36 gm/ vehicl e mi 1 e) , o rganic particulates (0.16 gm/ve hide mi le) an d lea d (0. 031 gm/vehicle mile). The secon d Sumne r Tunn el stu dy in volve d a total of 6 samp ling stati ons thr oughou t the tunne 1.(2) This study was made afte r the t unnel had be en co nvert ed to a two lane, one way t raffic c o n f i g uratio n wi t h an average daily tra ffic densi ty of 2 2,000 vehicl es pe r day . A sig- nif icant decrease i n impur ity le vel s w as no ted ; the decrease was attri buted to o peratio n of t he tun nel i n a o ne way traffic mode and a decrease of 36% i n mo tor ve hide traf fie. Figure 5 shows t he CO cone entrati on as a f unc tion of ti me of day. Mean morn ing rush h our con centra tions for t he tw o way mode ranged fr om 100-120 ppm CO , whil e the one w ay mo de mean con- centratio n was ^90 ppm CO. The s o i 1 i n g ind ex wa s also lower showing 3 .5 Cohs fo r one w ay tra ffic v ersus 6 5 Cohs for two way t raffic. T able 2 compar es the mean part iculate con- centratio n for the two mod es of traffi c. Additional pollutants including SO2, N0«, aldehydes and NO were measured during the second study. The concen- trations of these impurities are shown in Figure 6. It was concluded that automotive exhaust does not contribute sig- nificantly the S0 to 2 content of tunnel air. The results showed that the ratio of NO/NO2 was approximately 5/1. Finally, the aliphatic aldehydes ranged from about 0.01 to 0.1 ppm. An early study on the CO and particulate levels in the Holland Tunnel was performed by the Bureau of Mines. (4) The data in this report is probably of limited value due to the difference in emission rates from gasoline powered ve- hicles, gasoline composition and the number of diesel powered vehicles of today compared with the types of vehicles in use at that time. Standard operating procedure at that time was to allow the CO concentration to rise to 250 ppm with no change in ventilation rate. If the level remained at 250 ppm for longer than 5 minutes, then additional fans were acti- vated. The authors noted at that time that the CO concen- tration was highest on the upgrade sections of the tunnel. 1 T3 a OJ O «3 3 h n a o m cm "*! *"1 "! **? ftg -3 1 •b| ~ _ £ n r» o» «-• o» <-" "> r» oo i o © o o 3 S •oeo - jo g a § 2 n 2 » 32 *2 ^ > 88 a ^ ^ e- h > u a) a: S > w O Q> " s: VD a> zo O^ l- H a> a; c/> r~ ^ an a a ** oo o n <# n a o» «o *" i-< o «o r* _, S3 i-< C5 H i-» •-< r-< T3 3 1— O II C\J os OO 1 a a: «d- So*- g ® LU r— a ft u. TJ g l— 00 53 c +»O" LU • a 3 M V CO «5 >-< * JET h- N M O * H O H « * i-J H ^ p !>; •4* © a> 1 o ocJooocicooJeo •hncSw © LU q: i—• f- HgN«t»o«»n eo to «5 I—i _J H- ^ § * «-* *« * C£ >-H oo oo co c* ** H rf 5 I oo * « I CM »* «o § i 7* >» ^* t*» *H ^ D- Q as as" at a3 a P 3 a S < a o « >, LU .2 to t- ^ ^ o» Q I— -^ pi 51 03 * - 3^ ^aS58!SS88S5 15 3 8 8 9 is £ 8 Q- t— oo r3 8 ft rD o 3 oo g^saagssssssEgs 1 •^ i —I frO * p © t-t N 14 >U H H H « N C4 3 of rf «f S3 o a S3! a « § ft CO 1 i os a . « 2 3< S1 a,* 3 g § § s * X3* 2 § 3fi I V 4> to 3 -— .3 <-> tr oj O ® Si. ^ o U s - 31 1O w a 3 2 >• ^ 5 iJ 0J « W g o >» <-» S »-" a Q Oh a a -d » "O a 1|S 5 3 "So335J2oSJ300p "SO o ca H > N 10 r 130 i T 1 1 I 1 1 1 1 i—— 120 - BOSTON LAND SECTION BOSTON HARBOR SECTION . •--' EAST BOSTON HARBOR SECTION ••-••EAST BOSTON LAND SECTION K »~» 100 E Q- CL 90 e 80 o •r- 4-» 70 ro i. 4-> 60 C O! o 50 c o o 40 o o 30 20 10 ! I 8 10 12 14 16 18 20 22 24 26 Time of Day FIGURE 5 - MEAN CO CONCENTRATION AT SUMNER TUNNEL STATIONS BY TIME OF DAY, APRIL 20 THROUGH 28, 1963 11 TABLE 2 - COMPARISON OF MEAN CONCENTRATIONS OF PARTICULATE POLLUTANTS AT SUMNER TUNNEL AS TWO-WAY TUNNEL, SEPT. 14-20, 1961 WITH OPERATION AS ONE-WAY TUNNEL APRIL 20-28, 1963 Concentration, ug/cu m Two -Way One-Way* Tunnel Tunnel Outlet Inlet Outlet Inlet Pollutant Air Air Air Air Total particulates 588 104 424 86 Benzene-soluble organic substances 225 11 144.2 8.3 Sulfates 29 22 18.1 0.3 Nitrates 2.4 3.4 0.3 0.9 Lead 44.5 1.1 9 0.1 *36% decrease in traffic 12 45 Station Locations 40 1 - toll booth, E. Boston 2 - 1/3 of distance into tunnel 3 - center of tunnel - 2 4 2/3 of distance into tunnel t/( 35 5 - Boston ventilation bldg., o (inlet air) re 6 - Boston ventilation bldg., (outlet air) SO - U.o to UJo oUJ X >- o 25 X oUJ to l~ UJ c 20 o u CDo X c o < o X o 0. -J 15 UJo < o CC UJo li X 10 - o -, * J U. ;D i-J. . 23456 123456 123456 12 3456 Sampling Stations FIGURE 6 MEAN DAILY CONCENTRATION OF GASEOUS POLLUTANTS IN THE SUMNER TUNNEL BY SAMPLING STATIONS, APRIL 20 THROUGH 28, 1963 13 5 Work d one by Katz and Frevert^ ' led to an estimate of CO emissi on rate of 10 cu ft per car while traversing the tunnel This would correspond to an em ission rate of 220 g CO per vehicle mile, a factor of approx imately 10 higher than t he currently accepted average emi ssion rate. Par- 3 ticul a te concentration in the tunnel ra nged up to 1 .88 mg/m with a mean particle diameter of less t han 1 micron. Analyses of the particulates showed lead and ars enic to be present, but it was concluded on the basis of in let air concentrations that a rsenic was not contributed by aut omotive exhaust. One other point of interest in this study w as a reference to S i n g s t ad's work(6) on the induced pisto n effect of auto- motive traffic in vehicular tunnels. S ingstad stated that 1000 v ehicles per hour produced longitu dinal air velocities of 880 ft/min. Assuming a free cross-s ectional area of 2 370 ft , this is equivalent to a volume trie flow of 315,000 cfm. Waller, et an?) studied the impurity levels of the Blackwall and Rotherhithe Tunnels in London during a period of high traffic density. Table 3 summarizes the concentration of CO, smoke and hydrocarbons which were found in the two tunnels. Table 4 summarizes additional tests which were made in the Blackwall Tunnel only and in- cludes lead, NO and N0o in addition to the previously men- tioned contaminants. it was reported that the mass median diameter of the smoke particles was 1 micron. Stocks et a! W studied the concentration of seven polycyclic hydrocarbons and 13 trace metals in the Mersey Tunnel in England. Table 5 shows the average annual con- centration of smoke and selected hydrocarbons found in the Mersey Tunnel. Table 6 lists the average annual concen- trations for the 13 metals which were analyzed. A rece nt st udy was perform ed on the three arti - fi cal ly ve n t i 1 a t ed ,tu n n e 1 s i n Pittsb urgh by th e Mic hael Baker , Jr. Compa ny(9" 11). A 1 though this study was 1 imi ted to me asure ment o f CO only, i t is of inter est b ecaus e the CO prof i le th rougho ut ea ch tunn el was m easur ed ex perim ental ly and o ne ca n comp are t he CO 1 evels at vari ous p o i n t s in the tunne 1 wit h the level s indie ated by the p erman ently i n- stall ed CO monit oring system s . F i g u re 7 shows the C0 pro- file of th e 4225 ft 1 ong Squ irrel Hi 1 1 we stbou nd tu nnel - d u r i n g the early morn ing rus h hour, The maxim urn va 1 u e i n d i c a t ed by the t unnel CO mon itors wa s 100 ppm CO wh ereas level s as high a s 160 ppm we re measu red n ear t he ce ntetr of the t unnel . Fig ure 8 shows the effe ct of two way t raff ic in a tunne 1 wher ein t he pi st on effec t is negat ed. Again the m aximu m CO m oni to r readi ng (145 ppm C 0) wa s sig nifi- 14 > 3 Ms© «»"*> ^ ©rs»r» ©\r~© so — x> in O — f r» •> © oo w-> i-» MOMOV>^lrt. £Os «s r-os «n — oo c> — «o «s 09 0© (N vs OS ©s « 1^ $ 1*- r5 CO in s© vo»soo so cc UJ ' w*s — s© v> O *"* — «sm or~ m-OONON- to • oo ^ I- oo oo ad UJ , ©s ©-* • f K 00 o • r»> vo w> l« r4 — s© .- 0>0 — r> — «s T5 I < — — ©S so + «"VsO «r» m r- O ft f» * \e »»» — so vi f~ oo o> *> r* «> ts o 1^ — * Ooooorsr- — r-ONr»o>serj — — — ©n«N . \OOn»~ — N^Oom *r^©f»> •o. irt t*\ * + v\ —• r* Os — oo — so oo o so «<"> v> •* 5*^2^ ^2 ^ ri — — >- — fv oo © On so »»> 00 SO C4 W1 O 00 00 oo — so— «s«s gs-oo©^^© * rl — UJ 9 O so^©«"i — — ©oop-r^ w> o\ rA r» on — «>•> •* *t oo r~ r- so so On ^* 00 ""• ^ f*> r» o> O oo rf © so t n —<^t — v> ^ v> On **< — so *t * so w> c* v» »» w% © oo r- r% t~ r» *">00,i,,l.l«"">SO,iON 00 — so — — o t» <*> r-> o •* ts V% 00 »^ ^t 00 — 00 •-" f"^ c-"* W N — 00 — IS C v. u u 84 e V c 2d w w SE be C >.c OS u u «* v h u 4? S v i- s t> *- 2jr3'5 ? Q. >, n o. K n a C N 4S .C lis s o £m;c S c 5 5 b v a o w 1a-?g8 .2E u _ o •£ — •«* •"-. — •«• E »* .2 •• 5. o c •• •• c .. .. >U1 En w w «-o <-r-> (/}H c/i-JZZ 16 — — —- — t — 0) c I 0) 4-> J= vo CO cr> r— ^t- a> CO c -•-> <; c to 1 o Qi s- c WD CO CO CM O id o o ID O c c_> ^: o 1 c —I zo C\J N 0) cm . i— uj < c CJ o I c UJ o "S3- IM CO i— «3- CO CT> ID r>- ro CD 1 •• C S- ro ro ro <• «3- ro ID < CO OJ >-, Di Di CO oJ UJ UJ > C- 17 — 4 r— CO CM 00 :-, E 10 *-' m U 3 • • « 0) -r- O O '13 1— O in CO CO 1— t— o in in in in in o t— en m- CM «d- en O CJ co CJ CM co CM in DC o E « 1^ r-» ,— en UJ 1- 3 £1 •r- IT) 10 •* in CM u C <0 E in O in in o c 3l co CO co m CO CO in r~ •"" CM CM m ,_ • • • • t in r— <• I— ,— CM '~ r— r" r- CM c in O en CO CTl in Id co r-» r— in CTl 1 O- OJ co co r- 1— 1— UJ cm O I- UJ t/5 in r— ID «*• co ID o <•> \- «3. C 00 Ol CO -t-> 3 "3- ID 1— co o *d- 10 O rv r— O in "3- t-^ in «r «st" CM CM =3 O C o ID ID o CM CD CTi O co o cr CO at D> «J C +j t- r— O l/l (0 0) •r* - 0. ta c +J co +J CU c +j O en O TO CJ u _i n O >> n CJ to CO 1" Q) T) a* l/l X) • •a HH »— ai Di 18 UJ en O" I i—i LU o ^ UJ 31 Q I— o ox z o CO en o CD 19 LU en cr LU O ZD z£ LU t— Q rD »-H O ox en o CD o CO LU C3 20 cantly lower than the actual maximum in the tunnel (290 ppm CO). Figure 9 shows the CO profile of the 3613 ft long Fort Pitt Tunnel durinn the early morning rush hour. In this case, the maximum reading of the CO monitor was 150 ppm CO while the maximum CO concentration in the tunnel was 195 ppm CO. Figure 10 is a CO profile of the Liberty Tunnel during the evening rush hour. The Fort Pitt and Sguirrel Hill Tunnels have a longitudinal distributive type of venti- lation while the Liberty Tunnel has a basic longitudinal type of ventilation. Specifically, fresh air is drawn in through the entry portal and exhausted at the center for the first half of the tunnel, then fresh air is injected about 50 ft beyond the center and exhausted through the exit portal. This mode of ventilation accounts for the CO peak at the center of the tunnel . Computer Model - After havino reviewed the pertinent literature, two facts became obvious. First, the bulk of the work on tunnel impurity levels had been limited to the measure ment of CO, and second the bulk of the data which had been reported represented averages over time periods ranging from 1 hr to 24 hr with little or no information on ventilation rates as well as traffic density, traffic mix, road grade and so on. As a result of these deficiencies in the studies which had been made, it was concluded that a computer model should be developed which would predict concentration levels of any exhaust impurity at any point in a tunnel. The quantity of each component emitted from a particular vehicle at a specific time is dependent upon a number of factors : Type of engine (gasoline, diesel, etc) Size of engine (displacement, horsepower) Condition of engine Type of fuel (octane rating, additives) Adjustment of carburetor Driving mode - acceleration - crurrnuinni si ng - idling - deceleration 7 Velocity 8 Rate of acceleration 9 Road grade 10 Elevation above sea level 11 Ambient temperature and relati.ve humidity 12 Vehicle load 13 Condition of control devices such asa PCV valve and gasoline tank vapor suppr essors 21 CD UJ to _J o J u_ ro z o * ^ ° Z cr O < a. UJ uj !0 £ ui UJ cr < ob o o a. o to o CO x cr o _l o CO Z UJ < O I 2 o Z «1 v- < m Z U. 3-> _j !Z cvj a: 0- o o O ui cr CD (- bJ uj q: cr co o z < o < < o o u. uj o CD O c o z: cr ^ ro a. id to ro i—i W) x <: O LU O CO cr o cr (_) z < x< o O O o O O o ro cvj 22 i CO CO ZD >- »— CC Ul CQ I— _J I O CC LU O. CQ ZD X CO O LU O CQ o CXL C3 23 i 1 When considering the total pollution generated within a given tunnel, the following additional parameters must be considered: 1. Vehicle mix - cars, diesel trucks, busses, 2. 3. 4. Du ring th e early part of the program an evaluation of each of t hese fa ctors and parameters was initiated with the ult imate goal i n mind of establishing a mathematical model represe n t i n g any tu nnel. Such a model would then enable calcula tion of poll ution levels expected in any existing tunnel or proposed tunnel and thereby serve as the basis both fo r det e rm i n i n g pollutant removal system requirements and for the e s t a bJ i shment of pollution monitoring system speci f c a t i o ns. (A preliminary summary of the study of the c o n d i t i ons a ff ectin g exhaust emission is given below followed by the descr i ption of a computer program for calculating p o 1 1 u t i on co ncentra tion. A Ithough the exhau engi nes are simi lar to those prop ortions of thes e constit a ga sol ine powered automobi carb on mono xide emi tted duri wher eas a d i e s e 1 bti s may emi Howe ver, th e hydroc arbon emi engi ne may be seven times th gas powered automob i le. Tab emi s si ons o f four e xhaust co vehi cle ope namely ac dece le ratio An important factor in exhaust emission rates aside from the engine is the carburetor. This is particularly so with larger vehicles as illustrated in Table 8 which com- pares CO emission of cars and trucks as a function of car- buretor adjustment. (1 3) Another exhaust factor is crankcase ventilation. The control device introduced in 1963 reduces pollution rates considerably when it is in proper condition. The concentrations of other exhaust pollutants - nitric oxide and hydrocarbons as well as CO - are influenced by the fuel/ air ratio delivered to the engine as shown in Figure 11.^4) 24 3 TABLE 7 - EXHAUST GAS EMISSION RATES (ft /min) Mode Accel eration Crui se Idle Deceleration, Gas auto 6.000 0,700 0,400 0.400 CO Diesel bus 0.200 0,080 0.025 0.040 Gas auto NO* 0.050 0.020 <0.001 <0.001 Diesel bus 0.400 0,083 0,007 0.009 Gas auto 0.016 0,006 0.005 0.024 HC Diesel bus 0.100 0.030 0,045 0.100 Gas auto R-COH 0.002 <0.001 <0.001 0.001 Diesel bus 0.008 0.003 0.001 0.009 25 TABLE 8 - CARBON MONOXIDE PRODUCTION AS A FUNCTION OF CARBURETOR ADJUSTMENT (Cubic Feet CO per Foot of Travel) Cars Trucks Adjustment of 18.8 mi/ 9.4 mi/ 5.6 mi/ Carburetor qal 1 on qal Ion qal 1 on r/" Good /.•5 0.000248 H2.\ 0.000494 %C.o 0.000829 Average 0.000646 . S^ 0.001292 0,002152 5*; 3 5"% 7 Bad -5 0.001033 }7f,& 0.002066 0.003358 26 r— oi VO u 00 Ul oz 2: o cove <- cm c oo«ott cm o «»»• AM01N3? yjd anniOA - noiiiimhoo s*o isnvmo <: X Ul o I- o o u_ 1 o oc c M c < IT) Wdd-»0N u_ - UJ X u. u. Z UI KUl t- U» 1 KUl 3 r— t-X 2 Ul O e; "3 < H uidd ( H»0SV) 'NOUVUlNaDNOD NOOHVDOMQAH 27 : r, 1 rs . ( Another factor, particularly in hydrocarbon concentration,cone 1 s the timing adjustment of the ignition spark .(15) Exh aust emission rates in units of weight per unit distance trav eled for a slow moving vehicle are generally much greater than for one cruising at speeds in excess of 50 miles/hrl Several experimental studies have been reported in the litera ture which correlate carbon monoxide emission with 16-19) vehicle veloc i ty and acceleration. ('4, /\ summary of some of these results is given in Figure 12. A least-mean squares equat ion of the combined data was calculated as fol lows rvT° J v = 1.478xlO + 10.43 is r?-o6 (2) 4-b in, ik *& fs.^n where v = spe ed in miles per hour So 3^.?? 55 37- 3 ° y = CO emission in gms/veh-mi &o 3£T, (s Other studies have been reported in which the exhaust emission of pollutants other than CO have been related to vehicle ope- rating mode ( velocity, acceleration, etc). E xhaust emi ssi on is a 1 o aff ected by t he gr ade of the r a d , i . e . , i n c 1 i n a t ion of th e roa dway The effe ct of an up -grade on th e exhau st emissi on ra te is s i m i lar t that of ac celera t i o n , that is , it i n c eases the exhau st vo 1 ume. Conve rsely the e ffect o f a down- grade i s s i m i 1 a r to that of decel erati o n. Th e effec t of grad e on exhau st vo 1 ume may be state d as a mul ti pi i cat i on coeffi c i e n t appl ied t o the points obtai ned f om Equ ation 2 J The gr aphs of Fi gures 13 a nd 14 give the gr ade co ef f i cie nts for C emi s s i o n of c ars a nd di ese 1 true ks. F or exam pie, Figu re 13 show s tha t a c ar cl imb ing a 2% gra de wi 1 emi t 1,4 time s as much CO as it norma 1 ly wo uld on a flat (0-grade ) roa dway while the same car d escend ing a 3% grad e will em it on ly 70 % as much CO as it wo u 1 d w i th zer o grade Coeffi c i e n t s can be s i m i 1 a rly estab 1 i shed for o ther ex haust pol 1 utan ts.U 8) Another exha ust p arame ter is the elevation above sea 1 eve! of the roadw ay. The e xhaust emi s si on of an auto- m o b i 1 e who se carb ureto r i s ad jus ted fo r sea level conditions will be co n s i d e r a bly g reate r at higher elev ations. An examp le of this i s giv en in Figu re 1 5 for C emissions at 16 5500 feet e 1 e v a t i on co mpare d wit h thos e at 500 feet. ) When coup! ed with the fact that the CO tole ranee of the human body decrea ses a salt i t u d e i ncre ases , this parameter 2 prese nts a seriou s pro blem i n a high a ltitu de tunnel. ( °) A few expe rimenta 1 stu dies of th e al ti tude effect have been repor ted, primari ly th ose m ade i n conn e c t i o n with a proposed tunne 1 nea r Denve r whi ch wi 11 be locat ed at an elevation of about 11 ,0 00 feet abov e sea leve 1.(21 J 28 180 1 ' 1 1 160 (*] 140 — ELEVATION Acceleratl O »— u. y • o to £> E * Deceleration 60 o o Deceleration Deceleration 20 O - Surgeon General Report, 1958 Study - Cars © - Stern, Los Angeles & Cincinnati, 1965 - Cars D - 0TT, 1962 Study - All vehicles - Tlppetts, JFK Airport study 1 I I i J L 10 20 30 40 50 60 Vehicle speed (m1/hr; FIGURE 12 - CO OUTPUT VS VEHICLE VELOCITY 29 % Grade (x) A = 1 .00 + 0.0542 x where x = percent grade A = CO emission multiplication factor for cars on grade (t wpDCflccX DECREASE/ F0R GASOLINE POWERED CARS 30 % Grade (x) B = 1 + x/2 for grades >-0.25% B = 0.91 + 0.11 x for grades <-0.25% where x = percent grade B = CO emission multiplication factor for diesels on grade F0R diesels FIGURE 14 - MULTIPLICATION FACTOR FOR GRADIENT (deCREASe) 31 180 r r i t—i I 160 140 120 E 100 I -C >. «/> E o» - v~ 80 •o o» 4-> +> •f- E Ul o 40 20 10 20 30 40 50 60 Vehicle speed (mi/hr) FIGURE 15 - CO EMISSION AT 5500 FT COMPARED WITH THAT AT 500 FT 32 Available data has been correlated in order to establish an altitude coefficient for our mathematical model Two regression lines have been computed as follows: CO emission vs altitude with zero grade _8 F = 1.0 + 0.166 A - 0.7035xl0 h 2 (3) 1000 where h = altitude above sea level in feet F = CO emission multiplication factor for altitude b. CO emission vs grade at elevations exceeding 7500 ft above sea level 2 y = 92.99 + 28. 2x + 6.924x (4) where x = percent grade y = CO emission in gms/vehi cl e-mi 1 e. (jhe com puter progr am wh ich was developed included van abl es such as emi s s i o n r ates , ventilation rates, vehicle mix , vehi cle velo city, road grade induced ventilation and so o n) ther fac tors such a s eng i ne displacement and horse- powe r, th e condit ion o f the e n g i n e, age of the vehicle, car- bure tor a djustmen t and so on coul d not be included since thes e are unknown vari ables whi ch exist in any traffic mix. This is t o say th at th ere i s no s uch thing as an "average car" . De velopmen t of the co mpute r program was rather stra ightf orward w hile select i on o f emission rates proved to be a diff i c u 1 1 t a sk in terms of s electing an appropriate emis si on rate. The expected concentration level of a gaseous pol- lutant in a given tunnel may be calculated if the following data are known: a. Quantity of pollutant generated (cfm/vehi cl e) b. Traffic load (vehi cles/hr) c. Fan air flowrate (cfm/mile) d. Traffic speed (miles/hr) e. Ambient air pollutant concentration (ppm) The average pollutant concentration within the tunnel (f is then calculated by the equation: f(ppm) = axbxl06 + e (5) cxd 33 In order to calculate a more definitive profile of a given pollutant through the length of the tunnel, the following elementary model was derived. The assumptions made in the derivation are minimal hence the chief possible source of error is the accuracy of the input data. The assumptions made are: a. There is no appreciable removal of oxygen nor production of CO2, or water vapor. b. The gas composition at a given tunnel point has constant access to the tunnel cross section. c. Longitudinal diffusion is low. Assumption a is implied by the mass volume balance for air flow. It states, essentially, that the net gain or removal (of these substances) is small when compared with the quantity of ventilating air passing through the tunnel. The combustion process is 3N + 2 + CH >NC0 (N + 1)H °2 M 2)N — 2 + 2 (6) where the second term represents the saturated hydrocarbon. This process does produce a slight increase in air volume. The second assumption (uniform composition at a given cross section) is based on turbulence induced by traffic. Since the axial air velocity differs from the vehicle velocity, a turbulent swirl is produced behind each vehicle which tends to homogenize the tunnel air. Also the inlet and outlet air flow patterns minimize the possibility of stagnant air pockets. In the third assumption the pure axial diffusion is extremely low. The axial diffusion caused by the swirls in the wake of the vehicles is larger. How- ever for long tunnels it is small when compared with the axial transport of pollutants. If these assumptions are applied, the differential equations for pollutant concentration become simple air and pollutant mass balances. The differential equation for air is v (7) $ M o where Q = quantity of air flow in axial direction 1 = length v v = in (quantity per unit length). i » o cross flow and out 34 The differential equation for pollutant is 4|^£l = v.c r \ c+z (8) where C = pollutant concentration q = ambient pollution concentration G = pollution generated per unit length of tunnel. The above equations are subject to the boundary conditions: Q(0) = Q (9) and C(0) = C in (10) where Q - inlet axial flow = Cj n pollution concentration at tunnel inlet. The above equations can best be cast in a "finite difference" form. Several forms are available of which the following are the simplest: Q(n) = (n-1) + (V (n)-v (n))dl Q i (11) = i ( C Q(n-1 )c(n-l )+G(n) " ) -,- 1 + ( c(n) V d 12 ) where V n and G are evaluated at the mid point between (n-1) and (n). These equations require that Q be always positive and are always stable. The computer program solves the above set of equations "stepwise from tunnel entrance to tunnel exit. The step length (dl) may be selected as desired. The program is written so as to check the direction of axial air flow at each step and will stop if Q becomes negative. For tunnels in which air flow direction in some segments is opposite that in other segments, the program would be applied to the individual tunnel segments so as to keep Q positive. Since the exit air flow is given the tunnels or tunnel segments may be conveniently linked. A print out of the program is presented on page 36. The program is normally read from magnetic tape, however a punched tape recording of the program has also been prepared and will be forwarded with this report. A glossary of input and readout data is given on page 37. This lists the units and encoding symbols used for each of the variables used in the program. 35 L C P IS GU FT/VEH MILEJ QTI/O IS CFM/MILEJVI IS CFM C TUNNEL LENbTH AND DELT IS MILESJVEH IS VEH/HH;CONC ARE PPM DIMENSION GTK5>*QT0C5> 24 TYPE I 1 FORMAT ACCEPT 2* P1*P2 2 FORMAT •p- •p- OI .»» E E E r— 3 r- i- t- p— E a> O) O > Ol p— 01 01 0) >> u +j +-> 4J -O p- 3 3 3 >— jC C C C 0) •r— •p" •p- i- c > E E E 3 o o •P" fc. J- J- U x: p- 01 0) Oi Ol p- D- O- c o. •p- OI E +J 4-> +> •-» a. 01 o> 01 OI t- ^~» ^~» 01 OI OI OI to Ol p— p— M- «4- «4- «r- OI O- o o OH p"» > > CD t/> U o u u to to u to to ^-^ ^-* © 1— •p- •P" •p- T- OI OI •p- •-» Ol oc M X) -O -Cl J3 p— p— .e i- p— E s: E a. z: 3 3 3 3 •p- •p- 0) «a c •p- ta u_ ta r: U u u U E E > a. o E t_> to. oc •r- LU to CO •p- E Ol c o o o •p* u o: 3 to o o Ol _j c r- o • =) CO O II O. s: 1—1 o IE z I— >- 1— r- »— _J _J LU o P-" 3 to O. cr o- > CQ o > o 1 O 37 . ' An actual data computation is presented on page 39. Output data consists of columns showing concentration levels for a given pollutant at incremental distances along various sections of the tunnel. Section boundaries are usually de- termined by blower shaft locations and changes in road grade level (or percent inclination). The exhaust air flow from the section is given below the concentration/location columns followed by the average concentration of the given pollutant in the exit air duct (where applicable). Emission Rate s for CO H-C, N0_£ and Particulates As stat ed befo re, selec ting app ropriate emission rates proved to be a di f f i c ult and f strating task. The XIII World Con- gress o n Road Tunnel s I 51 showed that a great discrepancy existed in reg ard to em ission rates. Some of the data re- ported in this ref erenc e dated back to 1919, and it was found later t hat in some case s this data is still being used to predict emissi on rates. Table 7 shows the emission rates of d f CO, N0 X , HC an R-COH rom gasoline and diesel engines as a f u n c t i o n of mo de of ope ration as reported in 1965. This same re ference also rep orts emission rates of CO as a function of carb uretor adjustmen t for cars and trucks (Table 8). Table 9 lists the emission rates for CQ^s sum- 22 marized in XIII World Congress on Road Tunnels. ( ' This table represents the best data available in 1957 and is com- posed primari ly .of resul ts reported by the Coordinating Re- 23 search Ci:ouncil. ( ' 24 The Surgeon General's Report of 1962< ) lists the emission rates for late 1950 automobiles, Table 10 lists in table the results; values for H-C and N0 X are shown this also and will be discussed later. Over the past few years, the emission rate of CO from gasoline powered vehicles has been decreasing. Table 11 shows the emission rates for pre-1966, 1966-1969 and 1970 . 25 25 passenger cars and light trucks as well as heavy duty trucks! » ' 2 Stormont' ^) reports emission rates of 65 g CO/veh- mi for 1965-1967 models, 35 gm CO/veh-mi for 1968 models, 25 gm CO/veh-mi for 1969 and 1970 models. A target of 4.7 gm CO/veh-mi is set for 1975 models. Federal Regulations for CO emissions as reported in Environmental Science and Technology( 28 ) are: Year gm CO/veh-mi 1968 35.1 1970 23.0 1972 39.0 1975 4.7 38 0.7209 0.3341 TRANS AIR IN TRANS AIH OUT 0.4684E6 0.264E6 to end aih in tunnel lenbth tunnel delt l28600 0.235 0.02 vehicles/hr; inlet* anient conc 11&0 352 CONT-I TUNNEL POS CONC 0.200000E-1 0.850087E+1 0.400000E-1 0.142818E+2 Section N4 0.599999E-1 0.1&3770E+2 40 ppm 0.800000E-1 0.213752E+2 CO Monitor Chart Reading 0.999999E-1 0.236307E+2 0.119999E+0 0.253666E+2 0.139999E+0 0.267267E+2 0.159999E+& 0.27815SE+2 0.179999E+0 0.2869S4E+2 0.199999E+0 0.294170E+2 0.219999E+0 0.300154E+2 0.2350O0E+0 0.304023E+2 DISCRAKbE PLOW -766339E+5 AVb CONC 0.235749E+2 TUNNEL CONC POL. COEFS 0.9876 0.86 TRANS AIR IN TRANS AIH OUT0.6011E6 0.6266E6 end aih in tunnel lenuth tunnel delt l 0.76634e5 0.4868 0.05 vehicles/hr; inlet* ambient conc 1180 352 30.4 CONT-l TUNNEL POS CONC 0.5000U0E-1 0.333033E+2 0.1Uu)kJt3t3L + kJ 0.3S41 40E+2 0.1S000WE+0 0.369414E+2 Section N3 0.200000E+0 0.3b0414fc;+2 0.250000E+0 0.3bb298E+2 50 ppm 0.3000O0E+0 0.393920E+2 CO Monitor Chart Reading 0.35O000E+0 0.39790911+2 0.399999E+0 0.400723E+2 0.449999E+0 0-40269bE+2 0.466600E+0 0.403804E+2 DISCHARbE PLOW 0.642205E+5 AVO CONC 0.381655E+2 TUNNEL CUNC POL. COEFS 1.1944 2.7607 TRANS AIH IN TRANS AIH OUT 0.&786E6 0.&76E6 END AIH IN TUNNEL LENbTri TUNNEL DELT L 0.642205E5 0.4621 0.05 VEHlCLES/HH; INLh.T# AMBIENT CONC 1 1 bo 352 40.38 CONT-l PORTION OF COMPUTER PRINTOUT FOR LINCOLN TUNNEL-WESTBOUND TUBE 39 ) TABLE 9 - CO EMISSIONS REPORTED IN REFERENCE 22 Emission Rate gm CO/veh-mi Speed (mnh Downgrade Level Accelerati on Upgrade ?£ £ 3 y 20 56 78 311 128 «5 ?! i? 2. f 15 74 99 410 159 ?*- Z-7 /<£S ^ 10 106 128 573 214 40 : ) TABLE 10 - GRAMS OF POLLUTANT EMITTED PER MILE FOR FIXED MDDE OF OPERATION (gm/veh-mi Mode CO Gross HC Mx Cruise: 20 miles per hour 72 9.1 30 miles per hour 57 6.4 2.7 40 miles per hour 47 5.4 50 mi les per hour 40 7.7 5.2 Acceleration : to 60 miles per hour 381 28 to 25 miles per hour 240 29 15 to 30 miles per hour 120 14 10.2 Decelerati on 50 to 20 miles per hour 26 6.8 30 to 15 miles per hour 40 5.9 30 to miles per hour 60 7.7 40 to 20 miles per hour 30 5.0 41 ol o $. 4- SJte c o o «a- t— c ro o •— *a- in o u . o CO CVJ r- r- E o c CM •r- 1/1 V) •p- E 3: CD o1 o:=> O o C o o in CO ro , *o r>. i— ro o> o o CM CM r— CO rmm * ^i o o U CM 3 S- J— > s o -l-> I > o 3 o o O o «— CO CO O f— o o vo o I-** C7> > "O CM i— r— > ID O «o A .£ o 2=1 ^~I co co o o UJ ZJ r>. CO «S- o Q J- cr> CM CM r— >— r— oX •f CTi -J ve 1 O ©a CO If) ic CM in cn CO fe? CO CM to CT. o S- O(O I s- 0J U3 ex CO c CT> i— f»» •3- o» 4 Ol r— i— CO If) CO i/1 1 ^~ CO CO CJ T3 CL) 01 O. CO Ctt 42 This applies only to light duty vehicles. Many other references were reviewed and are in- cluded in the Bibliography section of this report. For the current mixture of model years we have selected an average CO emission rate from gasoline powered vehicles of 40 gm CO/ yeh-mi . If the Federal Standards are met and as older models are phased out of operation, this value will decrease. Less information was found on CO emission from diesel powered vehicles, and again some of this information was contradictory. For example, all references on CO emis- sion from diesel engines listed some positive values, whereas the Surgeon General's Report of 1962(24) listed an emission rate of zero for CO. Rispler ('2) reported a CO emission rate for diesel engines at 40 mph cruise of 4.3 gm/veh-mi. Rose(29) reported an emission rate of CO from diesels of about 3.5 gm/veh-mi under crui se, condi tions . From this limited data, we conclude that under cruise conditions, the CO emission rate from diesels is M gm/veh-mi. Emission rates of CO from diesels for the effects of road grade can be ad- justed using. the data in Figure Ik. Hydrocarbon emissions have been studied by a number of investigators. In the case of hydrocarbons, emissions are much more dependent upon the condition of the car and the emission control devices installed on cars than are CO emission rates. The Surgeon General's report(24) listed the emission rates as a function of mode of operation. (Table 10). This same reference reports diesel emission of H-C as 4.5 gm H-C/veh-mi at 30 mph (cruise), 20.5 gm H-C/ veh-mil under acceleration and 17.3 gm H-C/veh-mi under 'decelerati on. Stormont(27) reports H-C emissions according to the year of the automobile under cruise conditions. The values are: Year gm H-C/veh-mi 1965-1967 12 1970 6 1972 2 1975 0.5 (Projected) The Federal Standards (28, 30) for H-C emissions from passenger vehicles are as follows: Year gm H-C/veh mi 1972-1974 3.4 1975 0.46 43 These values apply to light duty vehicles only. In 1965, Rose'29) reported H-C emission for gaso- line and diesel engines under cruise conditions as 5.8 gm H-C/veh-mi 1 and 6.2 gm H-C/veh mi, respectively. On the basis of the data which were compiled on H-C emissions, we selected an average emission rate of 2.7 gm H-C/veh-mi for gasoline powered vehicles and 3.4 gm H-C/veh-mi for diesels. Hydrocarbon emission by diesels are about 8.0 gms/veh-mi under accelerating conditions and 10.5 gm/veh-mi under decelerating conditions. The emission of oxides of nitrogen from motor ve- is in of N0 , i.e., hicles exhaust generally reported terms X the total of NO plus N0 . Studies have shown that approxi- 2 mately 80% of the N0 X emitted is in the form of NO. In tunnels, where the residence time of the exhaust gases is of the order of seconds, there is little time for NO to con- vert to NO2, hence approximately 80% of the N0 V in tunnels is there as NO. The Surgeon General's Report lists NO emissions of 2.6 gm NO /veh-mi at 30 mph and 5.2 gm NO /veh-mi at 50 x x mph cruise. The same reports lists the emission from diesels as 8.9 gm NO x /veh-mi and 8.8 gm NO/veh-mi under acceleration. Stormont reported N0 X emissions according to the vehicle year: Emission Rate Year (gm NO y /veh-mi) 1960 6 1965-1971 5 1972 4 1973 3 1975 1 The values listed for 1972-1975 are projected values. Rose reported an emission rate of 3.9 gm NO /veh-mi x for gasoline engines in the cruise mode. Diesels in a cruise mode emitted 10.0 gm N0 x /veh-mi. to N0 Although the data are limited with respect X emission, the reported values are in relatively good agree- ment. We have selected an emission rate of 4.0 gm NO/veh-mi for gasoline engines and 8.0 gm NO/veh-mi for diesel engines. It must be recognized that various driving modes will change these emission rates, but the data on N0„ emissions as a function of driving mode is limited. 44 The data on particulates are even more limited 31 than for other exhaust contaminants. Frey and Corn^ ' studied the particle size and concentration in vehicle ex- haust gases. The particle size ranged from 0.01 to 5 u. Gasoline engines were reported to emit 0.4 gm/veh-mi while diesel engines emitted 5.0 gm/veh-mi. The Environmental 32 Protection Agency' ) has set standards for particulate emissions for 1975 model cars - 0.1 gm/veh-mi. In summary, it has been difficult to select standard emission rates for gasoline and diesel powered vehicles under various driving modes, with the possible exception of CO. However, by limiting the selection of emission rates reported 960 during the 1 ' s only, we believe the selected rates are representative of the gasoline and diesel powered vehicle mix which is currently on the road The emission rates which we have selected are as follows: Type of Mode of Emission Rates (gm/veh-mi) Vehicle Operation CO, HC N0 Particulates -xV Gasoline Cruise* 40 2.7 4.0 0.4 Diesel Cruise 4.0 3.4 8.0 5.0 Gasoline Projected 1970 23 2.2 Gasoline Projected 1975** 4.7 0.5 0.9 0.1 Emission rates for CO can be corrected for grade by using factors given in Figures 13 and 14. Federal Standards 1. Baltimore Harbor Tunnel 2. Allegheny Mountain Tunnel 3. Lincoln Tunnel 4. Fort Pitt Tunnel 5. Armstrong Tunnel In most cases, the CO levels of the tunnel were taken from the continuous monitoring data while in one case CO, H-C, NO and/or particulates were measured. 45 The Baltimore Harbor Tunnel is a 6700 ft long dual tube tunnel which is part of an expressway circling the city of Baltimore. The Harbor Tunnel is located beneath the Patapsco River. The northern portal and ventilation building are surrounded by industrial plants while the southern one lies in rather open country. Tolls are collected at booths located about 0.7 miles from the south portal. Each tube is staffed by 3 or 4 patrolmen on a continuous basis with a shift change every two hours. Each tunnel patrolman spends a total of 4 hours per day inside the tunnel - most of the time in semi- enclosed shelter booths. The traffic load varies from 55,000 to 75,000 vehicles per day. Transverse ventilating is used and CO is continuously monitored in the exhaust stacks. One of the chief reasons for selecting the Harbor Tunnel for our survey was the fact that complete records are maintained which include the following: • Traffic counts and traffic type, according to number of axles • Continuous ventilation rate data • Detailed accounting of all traffic stoppages in the tunnel • Complete set of engineering drawings • Ambient weather conditions. During the visit spot checks were taken of traffic count and mix and vehicle residence time or speed. Particulate samples were also obtainedby portable MSA mine samplers placed on the tunnel catwalk. The weight per unit-volume of sample collected was about 0.6 mg/m^ which is the same concentration as the sample taken at the Fort Pitt Tunnel. The average CO concentration in the tunnel, as recorded by monitors sampling exit air, averaged about 75 ppm over a three day period and rarely exceeded 180 ppm during peak traffic periods. Traffic counts were made of both gasoline and diesel powered vehicles in the east tube over a period of about 15 mins. The CO traces for this period were then ob- tained from the Baltimore Harbor Tunnel authorities. Figure 16 shows the road grade of the tunnel and the reported ventilation rates for the period during which traffic counts were made. Figure 17 is an actual trace of the CO monitors in the tunnel during the period when traffic counts were made. The inputs to the computer program included: 1. Ventilation pattern and flow rates, road gradient and tunnel section lengths are shown in Figure 16. 2. Traffic count and mix: 1260 gas/hr 268 diesel/hr I 5 l 46 ' 41 UJ 00 CO I OQ£ CO E E u: «- «*- «C U k. O i- O' x: •r- CO ©on o +-> •— o «*- C — Q «* «t sz oc +J CD a> c >- o c o c c err O => • O I© CO J- oo E a: *- «J cc o z »-> o o 0J CM o o e— r— * CM C rt I— i-. O CM o I o o" Co 70 ID CD 47 CO Concentration (parts per 10,000) 1 2 AM / \ 1 1 AM • 10 AM Ol -1— f^h 12 AM 1 \ 11 AM- , 10 AM 1 FIGURE 17 - ACTUAL TRACE OF CO MONITOR READINGS IN THE BALTIMORE HARBOR TUNNEL 48 3. Vehicle velocity: 42-50 mph 4. Ambient CO level : 2 ppm assumed 5. Piston effect: ^23% of fan rates (50,000 cfm) 6. Emission rate for CO as a function of the above conditions. The CO concentration profile calculated by the mathematical model method is presented in Figure 18. The sharply defined maximum and minimum values are similar to the pattern obtained by other investigators. These peaks are caused by the combined effects of ventilation patterns and CO emission rate differentials. Since the tunnel CO monitor's sampling probes are installed in the exit air ducts instead of at road level, a direct comparison with calculated results at a given point in the tunnel can only be obtained by actual CO measurement at a given point. However, an average CO concentration calcu- lated from the profile values should agree with the CO levels indicated by the permanent tunnel CO monitors. Hence an additional step was added to the computer program which yields average CO concentration values at the end of each tunnel section and a cumulative average value for a series of com- bined tunnel sections. Average CO concentration values ob- tained were: a. 71.1 ppm for Section (1 and 2) b. 75.9 ppm for Sections (3,4, 5 and 6) Actual values taken from the recorders in the control room during the time of this test were, respectively: a. 60 i 15 ppm (1 and 2) b. 65 + 15 ppm (3, 4, 5 and 6). Figure 19 is a plot of these average results. The results indicate that the computed CO level falls within the measured CO concentration. Th e Alleg heny Mounta in Tunnel is a dual tube tunnel locat ed on t he Penn sylvania Tu rnpike. It differs from all of the o ther tu nnels w hich we vis ited in that it is located in a rural area w hi le th e others we re all urban tunnels. Each tube is 61 00 ft 1 ong and has an ave rage grade of t 0.5%. The tunne 1 s are venti 1 a ted in a lo ngitudinal distributive fashion, Venti lati on is prov ided by ove rhead ducts and fans mounted at ei the r porta 1 of ea ch tube. F lowrates may be adjusted in four steps from 4 50,000 cfm/tube to 1,200,000 cfm/tube. Vitiated air i s exhau sted th rough the t raffic portals. Anemometer readi ngs of wind ve locity insi de the duct of the south tube 49 i oex. < ZTLU UDLU CO o~l— OH- co o«c <_>UJ I <;lu or> o«=c uj a: h- a: o yielded values of 600 ft/min at a point 30 ft from the intake fan and 390 ft/min at duct midpoint. Traffic and gas/diesel mix was rather constant throughout the day and was nearly identical in both directions 295 ± 10 gasoline vehicles/hr 105 ± 5 diesel vehicles/hr Average speed for the vehicles was determined by telephone communications at each portal 9 and was 55 to 60 mph for cars and 50 mph for large trucks. Carbon monoxide monitoring instruments are located in the ventilation building control rooms. Air inlet probes are located in three niches in the wall of each tube. The CO levels indicated by the center tunnel monitors are gen- erally higher than those of the other monitors. However, the concentration ranges of all six monitors were below 40 ppm throughout the day of our visit. (Fig. 20) Input parameters: Traffic count and mix: 291 gas/hr 110 diesel/hr Ventilation flow rate: 450,000 cfm/duct (see Fig. 20) Ambient CO level : 1 . ppm assumed Road gradient: See Fig. 20 Tunnel length: See Fig. 20 The CO level was quite low and nearly constant throughout the length of the tunnel during the period that the traffic counts were made. Monitors located in niches at three points inside the tunnel each showed CO levels averaging 20 ppm. Since the response accuracy of the moni- tors is I 10 ppm the computed result (15 ppm CO) is considered in agreement with actual. If a 20% factor is added for piston effect the calculated average CO concentration drops to 12 ppm which is still in agreement with the monitors. Other potential conditions for the Allegheny Tunnel were computed (Figure 21). These included: 1. 1000 cars/hr @ 40 mph with 450,000 cfm forced and 50,000 cfm natural and piston ventilation (Curve A). 2. A complete power failure with 1000 cars/hr @ 40 mph with a 180,000 cfm piston effect (Curve B). 52 i•1 CO ttttt ££ O •HV U*3 z= 1 >- 2: III o g. o o vo UJ _J —I «-, - >- JCZ r— a E CM 1 < o o CVJ *» o utv U*3 Hill 53 — . 11 o IS) CO -i o c 1 o o «* o -a c to fO 1— Z to Z i- 3 0) •-> to c c E s- o *— **- 3 •r— +> E +J o => *> O 1 u o a. oO V: CVJ Of ZD CD 1 o CD o o o in o o o CM cvj IT) (uidd) 'ouoq 03 54 . 3. A traffic jam with a forced ventilation rate of 600,000 cfm (Curve C). 4. A traffic jam with a forced ventilation rate of 450,000 cfm (Curve D). With 1000 cars traveling at 40 mph and a ventilation rate of 450,000 cfm, the average CO concentration would be 35 ppm. Under a traffic jam condition, the CO would be 160 ppm with a 600,000 cfm ventilation rate and 225 ppm with a 450,000 cfm ventilation rate. With a power failure where the only ventilation would be due to the piston effect, the CO profile would range from zero at the entry portal to 150 ppm at the exit portal. Traffic counts were made at the Lincoln Tunnel in New York City and CO data from the permanent monitors in the tunnel were acquired. This information was used to predict the CO level in various sections of the tunnel and to compare the predicted with the actual concentration. A mat hematica 1 mod el of tunnel vent ilatlon was de- veloped in 1965 by the R&D D i v i s i o n of t he Po rt of N ew York Authori ty-Engi n eering D epart ment The p urpos e of th is model was to predict the amou nt of any c ontami nant in the Lincoln and Hoi land Tun nels. T he mo del wa s form ulate d by ba lancing air and contami nant i n f 1 ows and ou tf lows for each se ctional length of tunne 1. Inst ead o f the finite diff erence equations used in the MSA R model , the PNYA m odel e mploy s diffe rential - equatio ns which are der i ved for bo th ven til at ion and contami nant pr ofi les. The dat a gen erated by bo th me thods s hould be identic al if a suf ficie ntly smal 1 length deri v a t i v e (dl) is chosen, The MS AR model does not r equi re deri v a t i o n of differe ntial eq u a t i o n s . The carbon monoxide profile of the Lincoln Tunnel- north tube was calculated using the PNYA model. The results were then compared with observed CO values as shown in Figure 22. Agreement between observed and calculated CO profiles is good except at the tunnel portals. 55 •i O o CO oO o cr: vO o o ZD o H- o «/"> O—J H ?* W •— __! o o 5S UJ o M —J St »— o U- 7S (_) < Dl wH 0_ M lil £4 Q t— o X o o H CO o o o m o on o 1 evi UJ i o CXL _) o o H wto "•UKJWMtfW** 1 — 4-> i 4-> U C E «*- | •r- a> o c o ^ 1 1 O 0) »- 4-> 4-» <*- 1 T- M- l/l C i J3 «3 •r- o E i | .. CL E u o. o *-> 1 | 0) »- o vt o. I O 10 i ^-^ c w> •r- cr> i i C 1 ' y 4. -r- i — O X> 1 ' / i 1 i / I 1 i 1 '/ Z i > CO i ' O h- i 0)f7ij «0 4J o 1 ' J3 «- yt — o «o iif ' c_> 1— | Q J- JZ ID . I / i UJ C£ o 1 a. 1— O I 1/ <: z _j i // ' =3 _J 1 O SI O UJ 4-> CO 1 — o _J Z cr CD i 1 f 1 I Q i l i— z z c 1 / c o 1 3 _J o ; — o O 1- < z «s- ID l-H 1— -J : i i o 1 <: I o i 1 — o mo ro 1 UJ I a: CM I ZD CO z 1 o —1 1 — o o u_ CM 1 i 1 i 1 i i i i 1 1 I z i I i 1 1 . 1 _i __ i o o o o o oo vo CM (uicJd) 03 57 . a o concentrations deviated somewhat from the measured concen- trations. This was also true in the case where two-way traffic was used in the center tube (Figure 25). However, with the two-way traffic pattern the calculated and measured CO con- centrations followed the same general trend. Deviations of the actual values from calculated values could be due to in- - correct ventilation rate data, incorrect CO readings, incorrect inlet air CO concentrations or an error in the computer pro- gram. However, the latter reason is unlikely since good agree- ment between actual and calculated values were found in all other tunnels tested as well as the north tube of the Lincoln Tunnel . The Fort Pitt Tunnel is a dual-tube urban tunnel which carries Interstate Route 1-76 into downtown Pittsburgh, Pa. Each tube is 4900 ft long and has a road level grade of Mo except at one end of the West tunnel which has a 3.5% up grade for about 400 ft. (The North portals are on two differ- ent levels which correspond to the decks of the approach bridge.) Atmospheric conditions were cloudy, light rain all day, very little wind, temperature 50 to 54°F during the day when actual measurements were made. A s eries of 30-minute counts were taken at various times t hrough out a typical week day. Results showed that the traf f i c rate varied from 1500 to 1900 vehicles per hour per tube be tween 9 A.M. and 4 P.M. and 3200 to 3400 vehicles per hour at peak times (4 to 6 P.M. outbound tube and 7 to 9 A.M. inbound ). Du ring the night the rate is usually down to 200- 400 per hour except when a sports or civic event is scheduled, The rat i o of gasoline engine powered to diesel powered vehicles varied from 1 3/1 in late morning to 66/1 during the evening rush ho ur. T raffic normally moved through the tunnel at 45 to 55 mph. At p eak periods speeds fall to 20-25 mph. Since the average s p a c i ng between vehicles is about 20 ft, the maximum tunnel popul tion is 250 vehicles per tube. The population den si ty may i ncrease, of course, in case of a stoppage. In the Fo rt Pit t Tunn el , a s in most tunnels which empl oy semi -t ravers e or s emi -1 n g i t u dinal ven t i 1 a t i o n with intake fans b ut no exhaus t fans , the air samp ling intake lines for the CO mo ni tori ng equ ipmen t are mou nted in niches in the tunnel wal 1 about 9 ft a bove roadway 1 e v e 1 . This tunnel employ ed two moni t ors pe r tub e ; each o ne located about 350 ft in fro m the portal sort unnel ends. T he recorded signal s from each o f the four H opcal i te-type detectors are m o n i t o red by operat ing pe rsonne 1 in the contr ol room. During the n i ght the CO le vel is norma lly a bout 10 p pm. During the day it rises to abo ut 50 ppm ex cept at peak p eriods when it rises to 100 ppm. Peak p e r i o d level may rise to 250 ppm if fan sp eeds ar e not i n c r e a s e d in adva nee of po llution emission i ncrea ses 58 !-» C 0) A f-H- •«J c E«t- O C o "^. a> (_> 0) u M u •-> «*- " r" •^ . M c o • £J3 1- •t_ u O I o oi as H- o. a» O +J o e o.«c oa: < CM UJ CC (uidU) 03 59 — c o c o (_> CJ •• EJ3 •t- o V o 00 UJ ZD _l o o< Q I- LU >- -J 13 CM <£ LU CJ Z Q ID 2= I— I— Z O i-h «C -J If) CM I r i LU i CM <_> l_> o1 o c CM (wdu) 03 60 Spot checks of CO content at catwalk levels were made with a portable detector. Readings during off-peak hours agreed with the CO values recorded in the control room. At peak traffic hours, however, the spot check values ranged about 60 ppm higher than .those recorded. In a more complete analysis of CO level variations in the Fort Pitt tunnel, it was demonstrated that the CO level in the central portion of the tunnel may be considerably higher than that at the ends (Figure 26). Each tube contains six fans - three at each end. Only two of the three are used as fresh air input fans. The third fan is used as an emergency exhaust. Fresh air is supplied through ceiling ducts from either end of each tube. Vitiated air is exhausted through the traffic portals. Considerably more air is exhausted via the traffic exit portal due chiefly to the addition of the piston effect. The magnitude of this difference was measured by taking anemometer readings on the catwalk. Air velocity at the inlet portal ranged from about 820 ft/min compared with 1210 ft/min at the exit portal. Air flow rates are adjusted manually from the con- trol room according to traffic demand. Flow rates range from 121,000 cfm (night-downgrade) to 535,000 cfm (peak-upgrade) with a maximum fan capacity of 714,000 cfm (upgrade tunnel). Each fan can provide for up to 85% of the normal requirement for its particular duct. Ten-minute observations were carried out at various hours along the tunnel catwalk. Results showed an average noise level of 97 dBC with peaks up to 106 dBC. The peaks were produced by the passage of large trailer and cab type trucks. Operating and maintenance personnel are normally not exposed to these sound levels for extended time periods. A constant volume air sampler was placed in operation at a point 264 ft from the south portal of the east tube on the catwalk with the sampling inlet away from the stream of traffic. A filter paper disc (MSA Part No. 25310) was used with a sampling flow rate of 15 cfm. The sampler was operated for 5 hours during the off-peak hours (11 A.M. to 4 P.M.). A total of 68 mg of particulates were collected which represents a density of 0.6 mg/m3. A 3.2 gm sample of particulates was collected from the floor of the room housing the Fort Pitt tunnel south portal ventilation fans. An analysis of this sample was performed by an emission spectroscopy method. The results are shown in Table 12. Extraction with benzene showed that the sample was 9355 benzene soluble (organic). 61 tn o> <* c 73 ro O (U CT> CO oi or o o o a. ox o CO I VD CM LU a: ID cu 62 TABLE 12 - ANALYSIS OF MATERIAL COLLECTED FROM VENTILATION BUILDING OF THE FORT PITT TUNNEL* Component Concentration Iron 7.5% Aluminum 3.6% Magnesium 1% Silicon 14% Boron 90 ppm Cobalt 10 ppm Manganese 8000 ppm Tin 150 ppm Lead 2000 ppm Chromium 400 ppm Titanium 1000 ppm Nickel 500 ppm Molybdenum 200 ppm Vanadium 200 ppm Sodium 1500 ppm Niobium <100 ppm Calcium <100 ppm Zinc 1000 ppm *This is an analysis of the benzene in soluble fraction of the collected material. 63 . Samples were taken for total hydrocarbons and NO, also. The total hydrocarbon samples were taken in glass sampling bombs and ultimately transferred to the laboratory and analyzed. Samples for NO were collected and analyzed by the Saltzman Method. (33) Vehi cle co unts we re made in bot h the no rthbo und and south bound tub es and sample s were c o 1 1 e c t ed at tw o loc a t i o n s in ea ch tu be. Venti 1 a t i o n rates we re obt ained fr om th e con- trol room oper ators and the i nf orma t i o n w as used to ca 1 cul ate the p redi c ted level s based on the c ompute r model and t he selec ted e miss ion ra tes. T he resul ts are shown i n Tab le 13. The p redi c ted and ac tual CO values agree quite we 11 (± 20%). The N B-l s amp! es for NO and HC did not ag ree well wi th the predi cted leve Is. H owever, since t hese a re point sour ce measu remen ts a nd wer e made near the entry of the tunne 1 , some diffe rence s co uld be expect ed. In al 1 ca ses, the pred i cted NO le vel s were equal to or higher t han th e measur ed va 1 ues This may i ndi c ate th at NO e mission factor s are in corre ct. In gener al , h owev er , mo st of t he resul ts agr ee rathe r wel 1 , but could prob ably be im proved if bette r em is s i o n rat es we re known for t he cu rren t car populat ion. One naturally ventilated tunnel, the Armstrong Tunnel in Pittsburgh, was visited and data were collected on CO con- centration and noise level. This two-tube tunnel is located near downtown Pittsburgh, Pa. It carries city traffic a distance of 1350 ft and lies beneath the campus of Duquesne University. Traffic lights are located at the intersections at either end of the tunnel. Since this tunnel has no venti- lating fans, it was selected as an ideal location to study piston effect. The tunnel is also used by pedestrians (in one tube only). The number of vehicles admitted to the tunnel is limited by the cycle of the traffic control lights. In the west tube approximately 18 vehicles/min are admitted while in the east tube the number is about 33 per minute.. Traffic speed is maintained at about 30 mph. Backing does occur at the traffic lights. This normally involves 6 to 12 vehicles for times of 30 seconds. Gas/diesel ratio ranges from 10:1 to 20:1. Pedestrian traffic averages 8 per hour with an average walk-through time of approximately four minutes. Readings taken with a portable Hopcalite detector averaged 50 ppm inside the tunnel with an increase to 200 ppm at the portal at which backed-up traffic occurs,. Anemometer determinations of air movement showed that a velocity of 370 ft/min was maintained at sidewalk level with an intermittent flow of 1050 vehicles per hour. Assuming a tunnel cross- 2 section of 435 ft , the volumetric flow rate could be as high as 150,000 cfm. The CO output for 18 cars at 30 mph is 18 x 64 X — -'>•-' 1 .-'"•v *-^ . s 4J »= co i^O CJ O CM -t~ KT :/) Q. • • • w E CJ c. r 00 10 o i r>- co h-^-- 1 sz • 1 ac id cm > -i— «*^ »— 1 s > "D l/» ^^ ^^ O 3 t- ° +-> E CO CO en CO C 1— E ro -—» +-> C C E c r— C f— CO CM r— •r- ••— ^ ^"^ +-> C7> tu •»— 1 1 1 1 CO CO V) C V) 0) O CO CO co CO ~ 00 UJ CU r— a. 2^ zz 00 00 3 CL— - E r— CM ro in — o ,-, CM co «* z~z 65 60 gms/mile or 270- gm per tunnel length (1/4 mi). Since vehicles require 30 sec to pass through the tunnel the CO emission rate is 540 gms/min or 15.3 cfm. Assuming a ven- tilation rate of 150,000 cfm (4,860,000 gms/min) yields a possible average tunnel CO concentration of 110 ppm. Figure 27 shows the measured CO profile. Traffic noise ranged from 88 to 93 dBC. In conclusion, the computer program appears to adequately predict the pollution level of CO in tunnels as a function of the variables which are fed into the program. Computed values for hydrocarbons and NO appear to be reliable in some cases and unreliable in others. However, emission rates for the contaminants are not as well defined as are emission rates for CO and vary considerably depending upon the mechanical condition and age of the car. 66 O ID id o rD COM- lu -z. rs o < I— o ct o < U_ Q M- O O LiJ C y£) \- "^ a. -o in o (13 a: o -- cn O «- oo I— , CM- r— 4-> 3 o o in o CM 67 PHYSIOLOGICAL EFFECTS OF TUNNEL CONTAMINANTS The objectives of this phase of the program were to evaluate the effects of vehicle tunnel impurities on both in-tunnel workers and the transient public, and to set limits for maximum allowable concentrations for manned tunnels as well as safety and comfort levels for unmanned tunnels. Selection of the impurities for which limits were set was based on the contaminants which were found in tunnels and the concentration levels at which these contaminants were present in vehicular tunnels. The Industrial Health Foun- dation, Inc. of Pittsburgh served as a subcontractor on this phase of the program. The final report from Industrial Health Foundation is included as Appendix I of this report. The selection of specific limits was the responsibility of MSAR and selected limits along with the criteria for se- lection of these limits were submitted to and reviewed by the Environmental Protection Agency. Table 14 is a composite listing of ranges of tunnel contaminants measured in a number of different tunnels. These values serve to compare relative concentrations and therefore provide a basis on which to select those contaminants for which limits should be set. Carbon monoxide levels in tunnels frequently exceed the Threshold Limit Value (50 ppm) and occasionally exceed the Short Term Limit Value (400 ppm/15 min). Since CO is the major health hazard impurity in automobile exhaust, limits will be set for this contaminant. 69 TABLE 14 - MEASURED TUNNEL CONTAMINANTS Contaminant Range CO 54-170 ppm N0 2 0.05-0.43 ppm 0.2-1 .63 ppm ' Aldehydes** ! 0.05-0.12 ppm SO2 0.04-<0.05 ppm Tota 1 pa rticul ates 0.424-2.350 mg/m Poly cycl ic hydrocarbons Pyre ne 0.04-1.20 yg/m 3 Benz o(a )pyrene 0.03-0.69 yg/m 3 Coro nene 0.03-0.53 yg/m 3 Benz perylene 0.09-0.99 yq/m 3 Metals Lead 9.5-44.5 ug/m 3 Iron 9.5-23.4 yg/m 3 Zinc 2.2 yg/m 3 3 Cadm i urn 0.04-0.6 yg/m (1) It has been estimated that formaldehyde accounts for 70-80% of the total aldehyde emissions. 70 . Oxides of nit rogen are p resent i n t unnel atmospheres as a resul t of ox i d a t i o n of a tmosp h e r i c ni tro gen du ring fuel combu st ion . The N0/N0 ratio vari es ace ordi n g to t he mode 2 of op erati on but on the avera ge th e rati o is in the range of appro ximat ely 4/1 to 5/ I in q a s o 1 i ne eng i nes . Howe ver, the oxide s of ni troge n emi t ted by dies el eng ines are hi gher than emi tt ed by a s o 1 i n e engi nes Of th e two oxide s, N0 is that g 2 the m ore t o x i c an d more i rri t a t i n . The TLV f or N0 is 5 ppm, g 2 where as th e TLV f or NO is 25 ppm. Altho ugh t hese c ontami - nants appe ar to b e pres ent in 1 eve Is bel ow th e safe ty limits and o dor t hreshol d 1 imi ts , at the presen t tim e , the re are plans to u se cert a i n t u nnel s for d i e s e 1 traff ic onl y. For examp le, t he Pitt sburgh Port Autho rity T r a n s i t inte nds to conve rt an e x i s t i ng tro Hey t unnel into a mas s tran sit bus tunne 1. T hese bu ses wi II be d i e s e 1 powe red a nd one woul d predi ct an increa sed le vel of ox id es of ni tro gen in that tunne 1. I n antic i p a t i o n of t hese probl e ms , i t was decided that level s would be se t for NO an d N0 . 2 The other impurity in tunnels which has been ob- served to exceed the irritation or odor threshold limit is formaldehyde. The irritation threshold for HCHO has been reported to be as low as 0.05 ppm while levels of 0.12 ppm have been reported in tunnels. Authorities on odor have frequently attributed the objectionable odor of auto exhaust to the aldehyde content. Therefore, limits have been se- lected for formaldehyde which is the major aldehyde emitted from auto exhaust. Other impurities present in tunnel atmospheres in- clude, as two general categories, partially burned hydrocarbons and metals. Benzo(a )pyrene has been of particular concern to the environmental health personnel because of its carcinogenic properties. However, the maximum value measured has been only 0.5% of the TLV. All metals which have been detected are well below the TLV. Lead is the metal that has been measured in highest concentrations and it is only 20% of the TLV. With the advent of unleaded gasolines, the concentration will un- doubtedly decrease. 71 p This covers all of the contaminants which have been detected in vehicular tunnels except for S0«. A cursory com- parison of the concentration level versus tne odor level would suggest that limits should be set for SO?. However, the work which provided these values showed that the S0« level was present in the intake air rather than as a result of auto- motive exhaust. Therefore, no limits will be set for SO2. Selected Contaminant Levels for Vehicular Tunnels In manned tunnels, police officers are located at three or four locations in the tunnel. These officers spend two hours in the tunnel and two hours out of the tunnel , so that during an 8 hr work day, they are exposed to the tunnel atmosphere for a total period of four hours. Personal in- terviews with these employees revealed that they frequently experience headache, tiredness and eye irritation. Personal observation of these officers as they came off duty during or immediately following rush hour traffic indicated that they did indeed have eye irritation. Ma intenance personnel represent another work group whi ch is e x osed to tunnel atmospheres. Routine maintenance such as repl acement of lights, repair or replacement of tile and w ashing of the tunnel walls is scheduled during off-peak perio d s . In dual tube tunnels such as the Pennsylvania Turnp i ke Tun nels, Baltimore Harbor Tunnel and others, two way t raff ic is shunted through one tube during the late eveni ng and early morning hours while the other tube is being washed or repaired. Emergency maintenance within the t u n n e 1 i s not frequently required and in general requires that mai nten ance personnel be present in the tunnel for only a sho rt time Three of the studies were directly pertinent to setting of limits for manned tunnels in that the studies in- volved clinical examination of personnel who had spent greater than 10 years working in tunnels. One of the reports stated: "No mortality or morbidity from primary lung cancer was found among a group of 97 retired tunnel police officers who had worked within 72 1 , i . the H oil and Li nco 1 n Tunne Is, a nd had been in re ti rement for at leas t 10 years after 25 years of activ e serv ice. No c ase of primary lung cancer wa s foun d amo ng th e 25 r etired pol ic e officer s stud ied w ho ha d died during this same reti rement peri od. Among the 16 1 i v i n g nontunn el ret ired pol ic e offi cers in- cl ude din this study , the re is one w ith pri- mary lung cane er sue cessf ul ly resect ed 11 years ago. Th e inte rval betwe en i n tial ex- posur e in the tunnel s and the time o f this study was at east 1 8 yea rs an d as 1 ong as 37 ye arsrs ; in 8 9.7%, the i nterv al was over 30 ye a rs."(34l The second article stated: "Resul ts are pre sented of a n epi demiol og i c i nvest igatio n of the r e s p i r atory sympton s and pulmon ary fu ncti ons of a gr oup o f men ex posed to aut omobi e ex haust in a road tunnel . Chroni c nonspe ci f i c resp i rator y dis ease was more preva- lent i n men who had wo rked in th e tunnel for more t han 10 yea rs tha n in those with a shorter time o f empl oyme nt. C hest colds were al so more freque nt in thi s group . Th e siz e of the sample did no t perm it p roper asses sment of the effect of age or ci gare tte sm o k i n g on t his popu 1 a t i o n The ma ximal expi ratory flow rate , as mea sured with t he Wri ght peak f lowme ter was sign ifi- cantly lower in the wo rkers with chronic non- speci f ic res pi ra tory d iseas e tha n in the rest of the worke rs s tudied "(35 A third stated that: "Examination of a group of 156 Holland Tunnel traffic officers exposed throughout a period of 13 years to an occupational carbon monoxide exposure averaging 70 ppm did not reveal any evidence of injury to health contri butable to carbon monoxide exposure. "(36) On the basis of the work by Speizer, one may conclude that some adverse effects on the respiratory system are imposed by exposure to tunnel impurities. In spite of the large volume of information avail- able on physiological effects of air contaminants on the human being, it is still extremely difficult to select firm standards for employees in manned tunnels due to the con- flicting data which are presented. However, this dilemma 73 e has apparently been solved by the Occupational Safety and Health Act of 1970, Public Law 91-596.(37) This Act sets standards "to assure safe and healthful working conditions for working men and women". As part of this Act, concen- trations are set for air contaminants including CO, NO, NO2, HCHO and particulates (oil mist). These values are: Al lowable Time Weighted Contaminant Concentrati on Avg. Limi ts(38) CO 50 ppm 75.0 ppm NO 25 ppm 37.5 ppm N0 2 5 ppm 10.0 ppm HCHO 3 ppm 6.0 ppm _ Particul ates (oil mist) 5 mg/m 3 10.0 mg/rrr Although the Act does not make allowances for less than 8 hr exposure periods, the TLV levels do provide for a time weighted average. By definition, time weighted averages permit ex- cursions above the TLV provided they are compensated by equiv- alent excursions below the limit during the work day. In some instances it may be permissible to calculate the average weekly concentration for a workweek rather than a workday. The degree of permissible excursion is related to the magnitude of the TLV of a particular substance as shown below: Permi ssi bl TLV (ppm) Excursion Factor 0-1 3 1-10 2 10-100 1.5 100-1000 1.25 It is therefore recommended that these time weighted average limits be adopted as standards for manned tunnels since tunnel personnel are not exposed for a full 8 hr workday. Most tunnels are designed to maintain CO levels at less than 100 ppm and in general, a warning light is activated in the fan control room when the level goes above 250 ppm. During rush hour traffic, CO levels in the range of 350 ppm are not unusual in some tunnels. It is obvious that these levels significantly exceed the above recommended values for manned tunnels. In such cases, the workers are exposed to levels exceeding the Occupational Safety and Health Act of 1970 and some remedial action must be taken to bring these tunnels within the limits as set forth by the Act. 74 The Act does allow these limits to be exceeded "in cases where protective equipment or protective equipment in addition to other measures" are provided. Alternatives to maintaining levels at less than the specified limit should be considered since with appropriate fan operation these levels can be maintained in most tunnels for 18-20 hrs of a 24 hr day. Some tunnel authorities have already considered alternatives : 1. Baltimore Harbor Tunnel Authority con- sidered the use of closed circuit tele- vision surveillance as an alternative to having personnel in the tunnel. In the event of an accident or breakdown as in- dicated by the closed circuit television system, maintenance men, firemen or police officers would immediately enter the tunnel to rectify the problem. However, the authority ultimately rejected the idea with the reasoning being that men stationed in the tunnel could react more rapidly to potentially hazardous situations such as accidents, fires and so on. 2. The Port Au t h o r i ty of N ew Yo rk Ci ty has i nst ailed c losed circui t tel evisi on in the Line oln Tun nel . Howeve r, th ey st ill main- tai n police offi cers in the tunne 1 for rapi d respo nse t o fires , bre akdow ns, etc. They are cu rrent ly buil ding a pro totype trol ley car whic h would be c onsta ntly mann ed by a pol i ce offi cer a t eac h portal, In t he even t of a probl em wi tness ed on the closed ci rcu it tele v i s i o n , th e car woul d be ra P i d 1 y d i s p a t ched to th e scene of t he prob 1 em. Al thou gh th e off icer will not be stat ioned i n the tunn el , it is h ighly 1 i k e 1 y that h e wi 1 1 be exposed to c oncentr ation s above the speci fied 1 i mi t at th e exi t porta Is as a re suit of the piston ef fee t of ca rs ex haust ing con- tami nants t hroug h the p ortal s. These two aforementioned measures involve removing the offi- cers from the tunnel, and it must be admitted that this does increase the reaction time to an incident in the tunnel. Other measures which would be feasible would in- elude: 1. A direct air supply to the officers' cubicle to provide clean, outside air 75 e was tried in at least one tunnel, but the inlet vents were plugged up by the offi- cers during the winter due to the chill factor of the cold air blowing in. 2. In summ ary, the re commen dati on i s ma de tha t lm- puri ty limit s i n manne d tunn el s co nf orm to the Occup a t i o n a 1 Health and S afety Act of 197 with the a ddi tio nal pr o v i s i o n that th e tim e-wei ghted limit s esta b 1 i s h e d by t he Ame r i c a n Conf ere nee o f Gov ernme ntal a nd Ind u s t r i a 1 Hygi e n i s t s be used, It is reco g n i z e d that these limit s are curren tly ex- ceeded durin g rus h hou rs in all tu nnel s and ev en dur i n g n o n peak ho urs i n som e tun nel s. If th ese re commen dati on s are adopted , the n rem edi al actio n must be ta ken to bri ng the tunnels with in al lowab 1 e 1 i m its. These action s may i nclude traffic cont rol , chang es in tunnel venti lation proce dures , puri fie a t i o n of t unnel air o r indi v i d u a 1 respi ratory pro- tection Unmanned Tunnels min/day) of the t n i f i c a n t ly less t police o fficers i premise is made t should b e set to safety 1 evel must be h i g h r than th of expos ure to th shorter, Safety separate ly in the The pollutants which are considered in unmanned tunnels are the same as those considered in manned tunnels, the resi- i.e., CO, NO, N0 2? HCHO and particulates. Since dence time of an individual in a tunnel is relatively short (5-15 min), then safe levels for most of the contaminants can be increased over those limits set for manned tunnels. It must be remembered that if one contaminant is allowed to increase, then all other contaminants increase proportionately according to their relative concentrations in auto exhaust. However, if internal purification which is being studied as part of this program proves to be feasible, removal of selected contaminants would be possible. 76 Prior to setting safe limits for unmanned tunnels, "safe limits" must be defined. The definition used in this case refers to levels at which short term exposure will not create any physiological effects on the individual. One of the problems in setting short term safe limits is that limited work has been done in this field, and no systematic rationale has been developed for relating Threshold Limit Values, which are set for long term exposures, to short term exposures. The American Industrial Hygiene Association, The Pennsylvania Department of Health and the Aero Medical Association have attempted to set tentative standards and at this time this is the only established information which can be reliably quoted. Table 15 lists Threshold Limit Values and Short Term Limits (AIHF) which have been set for the selected tunnel pollutants. It is obvious from Table 15 that the number of Short Term Limits which have been set are signifi- cantly fewer than the number which have not been set. How- ever, the tunnel engineer needs values to design to and other data exist which can be used to set tentative limits. TABLE 15 - TLV AND STL FOR SELECTED POLLUTANTS STL (ppm) Polluta nt TLV 5 mm 10 min 1 5 mi n 30 min CO 50 ppm _ _ 1500 1000 800 NO 25 ppm — -- -- N0 2 5 ppm 35 25 20 HCHO 2 ppm 5 -- -- 3 Particulates 5 mg/m ------ The assumption is made that during rush hour traffic with a stop and go situation, the time to traverse a tunnel could be of the order of 15 min. The standard curves for effects of various carbon monoxide exposures as a function of time shows that at 500 ppm no perceptible effects occur within 15 min. Nitric oxide (NO) is a simple asphyxiant and therefore levels significantly higher than the TLV should be tolerable. However, in the absence of any firm values to support this conclusion, it is .recommended that the STL for NO be set at 37.5 ppm. The STL for N0 (15 min) has been 2 tentatively set at 5 ppm. This could cause temporary eye and nasal irritation but no permanent physiological damage. Short Term Limits for formaldehyde has been set at 5 ppm for 5 min. The literature states that levels above 5 ppm are severely irritating and therefore a 5 ppm STL is recommended for 15 min. exposures. Particulates are the only non-gaseous 77 impurities which are being considered for STL values. We do not recommend a level higher than the TLV for particulates, i.e., 10 mg/m^. In summary, it is difficult to set Short Term Limits for tunnel pollutants due to the lack of specific data on short term effects. However, using the data which are available along with what is believed to be reasonable extrapolations of related data, the limits which have been selected are as follows: CO 500 ppm NO 37.5 ppm NO2 5 ppm HCHO 5 ppm 3 Particulates - 5 mg/m* Comfort level, as used in this case, is defined as that level of contaminant which produces no irritation, sense of unpleasant odor or physiological effect such as minor headache. The "comfort level" varies from person to person depending upon his sensitivity to a given contaminant. Individuals with certain allergies may be particularly sensitive to specific contaminants. Some individuals are more sensitive to odors than are others. These are normal differences that exist among the human population, so in general, odor threshold levels or irritation levels have been selected on the basis of the sensitivity experienced by the major portion of the public. Carbon monoxide is colorless and odorless and there- fore creates no sensation odor or eye or nasal irritation. Significant levels of carbon monoxide over certain periods of time can cause headache. However, assuming a maximum again of 15 minutes residence time in a tunnel, a level of 1000 ppm is certainly well within the tolerable range. Nitric oxide (NO) is also a colorless gas with a slightly sweetish taste or odor at high concentrations. No data were found on either the odor threshold limit or the irritation threshold limit, hence for the present time the TLV of 25 ppm will be used as the comfort limit for NO. NO? exhibits an undesirable odor and is a strong irritant. Trie odor threshold limit has been reported to be 1-3 ppm and the odor is characteristic and distinct at 5 ppm. The recommended comfort limit for tunnels should be 1-3 ppm. Formaldehyde is also an odorous and irritating compound. Most references quote an odor threshold limit of ^1 ppm, although this seems to vary greatly among individuals. Eye and nasal irritations have been reported at levels of 2-3 ppm HCHO. For a comfort level in tunnels, we recommend a level of 1 ppm. 78 Particulates in tunnels can be odorous due to their own chemical composition or from odorous gases absorbed on the particulate surface. Particulates can also have an irri- tation effect particularly through deposition in the eyes. However, the most significant effect on comfort is probably due to the haze effect of particulates. Mo data was found on the correlation of particulate concentration versus visi- bility in tunnels. Spot checks made by MSAR personnel at the Baltimore Harbor Tunnel and the Fort Pitt Tunnel showed particulate concentrations of approximately 0.6 mg/m 3 with the particle size ranging from <1 micron to about 5 microns. 3 At this concentration level (0.6 mg/m ), the "haze level" was low and the visibility was quite good. However, we hesitate to select this concentration as a firm value for tunnel comfort. In the absence of sufficient data, we have decided that a satisfactory level cannot be chosen at this time. Summary of Recommended Levels Tentative pollutant concentration levels have been chosen for manned tunnels and for unmanned tunnels. In the latter case, both safe and comfortable levels have been chosen. These levels are summarized in Table 16. TABLE 16 - TENTATIVE POLLUTION LEVELS FOR TUNNELS Manned Unmanned Tunnels Pol 1 utant Tunnel s Safety Level Comfort Level CO 75 ppm 500 ppm 1000 ppm NO 37 5 ppm 37.5 ppm 25 ppm N0 ? 10 PPm 5 ppm 1 ppm hcro 6 PPm 6 ppm 1 Parti cul ates 10 mg/m J 10 mg/m J N.R. W (1) N.R. No recommendation due to insufficient i n format ion. The levels which have been set for manned tunnels were dic- tated by the Occupational Safety and Health Act of 1970; there would seem to be little reason to question these values since they are required standards set by the Federal Government. The safety and comfort levels which were chosen are, of course, subject to some question since little data exists on short term exposure limits. 79 EVALUATION OF POLLUTANT REMOVAL METHODS There are two potential reasons for development of methods and systems for purification of tunnel atmospheres. One of these reasons is to purify the atmosphere within the tunnel itself, while the other reason is to improve the quality of the exhaust air from the tunnel. In relation. to purity 39 of the air within the tunnels, one reference* ' which was found involves recycle of tunnel air. This system catalyti- cally oxidized CO to CO2 with Hopcalite followed by condensation of CO2 and water at liquid nitrogen-liquid oxygen temperatures (Figure 28). The boil-off of the liquid air during cooling provided fresh air for the tunnel. No claim was made for re- moval of hydrocarbons , particulates and so on. One other reference was found on recycle of tunnel air. (4°) This system incorporated wet scrubbing for particulate removal, catalytic oxidation for CO removal, a deacidi f ication unit to remove CO2 and a condenser. This article claimed that Neutrotecni cia Italiana S.R.L., Milan manufactured these units commercially. MSA Italiana is located in Milan and one of the MSA repre- sentatives in the Milan office was requested to procure in- formation from the referenced company. The MSA representative reported that the company stopped its activity in November 1968. Patent Development Associates, under subcontract to MSAR, reviewed the state-of-the-art of applicable control technology. PDA also made an economic evaluation of selected control measures which might be adaptable to purification of tunnel atmospheres. The result of this study is presented as part of this section. It should be noted that the PDA study was made mid-way through the overall program and therefore some of the emission standards or criteria which are quoted may have changed since that time. It must also be kept in mind that the economic evaluations which are presented are for hypothetical cases and do not necessarily apply to any specific existing or planned tunnel; these economic evalu- ations are presented merely to show the relative cost of tunnel air purification or recycle versus direct ventilation. As a result of the survey, certain control tech- niques were selected for evaluation. The test system and the control techniques which have been tested are also presented in this section. State of the Art - Applicable Control Technology Historically, emission control technology was devel- oped as a set of empirical solutions to specific industrial problems in diverse industries and areas. The acceleration of technical and industrial interest in pollution control per se 81 VENTILATING DEVICE AT \i,2m (SOO It.) INTERVALS ALONG TUNNEL DUCT FPESH arfe 8 Q B P DISCHARGE HOPCALtTE CATALVST FOR OXIDISING CARBON MONOXIDE TO CARBON DIOXIDE RFLF.ASE FLOAT VALVE WATER LIOUID CARBON DIOXIDE CARBON DIOXIDE PUMP FIGURE 28 - SCHEMATIC DIAGRAM. PROPOSED BY SIR BRUCE WHITE(39) 82 d in the last two decades has forced continuing collection and critical examination of the technology available for accom- plishing such control, and several comprehensive reviews have recently appeared. The Air Pollution Engineering Manual j ./1s an ex- tensive compilation by the Air Pollution Control district of the County of Los Angeles of control problem hardware solu- tions and design approaches by type of industrial emission and industry. This reference includes in-depth review of the supporting theory for the design and selection of control method and equipment for particulate removal (inertial separ- ators, baghouses, electrical precipitators) and gaseous pollutants (thermal and catalytic incineration, adsorption, condensation, scrubbing). Perhaps t he best basic text in ew po lluti on (42)" control technology field is Air Pollution Vol urn e III Sources of Air Poll ution and Their Contro 1 of this prima ry work con tains the m ost com plete and d e t a i Ted r eview of e quip- ment des ign prccedu res and c a p a b i 1 i t ies . Anot her s tate- of- artt reyi ew is Vol urn e II: C ontrol Equ i pmen t of the A i r Po 1 1 u t i o n 4 Ma nuaiv 3) which co vers in d u s t r i a 1 c ontroT equ i pmen t in the same tec hnology cat e g o r i e s of inerti al se parat ors , bagho uses , etc. g i v en above, An abbr eviated tr eatme nt of theo ry an d design p rocedures i n d i c a t e s the empi ricis m of 1 arge area s of curre nt equipmen t selec tion proce dures . Th e sta temen t made in this refere nee tha t "when th e pro cess is on the drawing board and t he coll e c t o r is t be speci fied as pa rt of the p lant design , the p rime recou rse i s to exper i e n c e , on similar plants and process es" is a r e a 1 i s tic a pprai sal o f many are as of prese nt cont rol techno logy art. Much of t he informat ion obtaine d by "e xperience" has been and i s con f i ned to equip ment vendor or i n us trial fi 1 es , but t he in creas e in enforcem ent efforts and in dependent resea rch a nd pu b 1 i c a tion should e ventually f orce su c h data in to th e ope n lit eratu re. At the p resent time , much of control equi pment desi gn ar t and tech no logy is h eld by vendors on a co nf i de n t i a 1 basi s. One resu It of this s i t u a t i on is freq uent equi p ment over- design t o compensat e for p erformance unce rtain ty, w i th attendan t cost and space e xcesses , a nd th is si tuati on ap plies to some of the appl i c a b 1 e control te chnol ogy f or th e tun nel problem. Applicable Tunnel Pollution Control Technology Control technology possibly applicable to the problem of pollutant removal in the ventilation of vehicular tunnels must be evaluated in the context of the probable system constraints. Initial review of tunnel -contained dilute automotive exhaust pollution indicate the following parameters 83 i 1 : to be potentially significant: 1. Mul ti -poll utant removal requirements. 2. Blower head loss limitations, particularly in existing tunnels. 3. Large air volume handling requirements. 4. Relatively low pollutant concentrations. 5. Relatively low pollutant emission rates. Thu s, app 1 i c a b 1 e co ntrol te c h n i q u e s sho uld have 1 ow or zero p ol luta nt th resho Id s e n s tivity, be c apab le of being d e s i g n e d into hi gh -thro ughput , 1 ow-1 os s equ ipme nt conf i gu ration s , and pref erabl y be fun cti onal for more than one com ponent or ty pe of poll utant. Unfortu natel y, m ost process es cap able o f tre a t i n g large v ol umetr ic fl ows at wery dilute pol 1 ut ant co ncent ratio ns are n ormal ly sing 1 e-p urpose operati ons , a s typi fied by el ectrosta tic pre c i p i t atio n. For the gas eous c ompone nts , the c ontrol p rocesse s tha t ap pear likely to sat isfy t he ab ove-n oted gen eral cr i teri a ar e adsorpt ion, c atalyt i c ox i d a t i on, and absorpt ion. For the particu lates , a p p 1 i cable proc esses in elude e lectr osta ti c, precipi tation , and inert i al o r wet-sc rubbing . It i s obvious that a comb in ati on of co ntrol operati ons w i 1 be need ed to cover t he spe ctrum of po lluta nts and concent ratio n le vel s present in di luted autom oti ve exhaust gas. Table 17 presents a summary of the comparative process capabilities for the probably-applicable control technology as they apply to the tunnel pollution problem. An inspection of Table 17 shows that \/ery few of the stand- ard control operations appear to have unqualified applica- bility to the tunnel' pollutants within the general constraints of the problem. The two operations that appear to be tech- nically applicable without apparent limitations or additional research are electrostatic precipitation for the particulates, and adsorption for the hydrocarbons. The state of the art of available control technology will be reviewed below with respect to the principal classes of pollutants, and the processes that would normally be used for removal of each pollutant. Because of the mul ti -function- ality of several of the operations considered, process dis- cussion emphasis will be placed on the primary pollutant applicability as shown in Table 17. Carbon Monoxide and Hydrocarbons In terms of the relative magnitude of pollutant loadings, CO and unburned (including partially-oxidized) hydrocarbons are the major constituents in auto exhausts, as shown in Table 18, taken from Stern' 42 ). In addition to the emissions shown as contributed by blow-by and exhaust, the 84 ) Satn. disposal problem Liquid Gas 4-> 0) X >e X X X X 3. X +> (1 (2) -t-> «/>o I_ *J o >> Ul I. X X X C >. O u c n> «J OS O u» 8- X X X X X X X t- -o O o. X 44 CD O- c CO 10 8- i/i o i. f- -r- 3 3 T3 •M +) cr 1= D. IO 01 "O 01 00 S- Ut i-f-r- UJ o 3 .£> +J WOCTO .Q c u u IO o3 ••- f- < HI a: oa j a > X X X X X X c X o •— CM CO CQ o a: D- 1 at a> o > 8- o ••- a. »> c *- a> o CD 8- 8- C i- 01 *J OI 3 4-> Q. C7> CTi— •!- 8- X X X X X as c O of o: («- o >U 8- u m .i- C 01 3 ai o; er •r- OI O I— OS •f- IO 85 i1 O CVJ ^- CO CT>CVJ OOMO CO VD o co r- r»» r— O CM CO vo CVJ o o oo r- O O CO • o o o o o o o 5 o (A to 86 evaporative losses from the fuel tank and carburetor add another 20 to 40 percent to the hydrocarbon content of the total emission. Nevertheless, Table 18 indicates the various pollutant contributions, exclusive of the particulates, and CO and hydrocarbons are the most significant. These two pollutant components are usually grouped together by reason of the fact that they are present because of incomplete oxidation, and completion of oxidation by secondary means will eliminate them from the exhaust. It should be pointed out, however, that for non-oxidati ve techniques such as adsorption, these two components will not behave similarly. The two general methods of oxidative disposal of carbon monoxide and hydrocarbons are. (a) Catalytic oxidation (b) Direct thermal or flame incineration These two methods of combustion completion have been used as source control techniques for automotive emissions, and sufficient experience has been obtained on their use to provide a guide to their possible use on tunnel air. Catalytic Oxidation Basic researc h on the s uscepti bi 1 i ty of homolo gous series of hydrocarbons talyt ic oxidation has been 45 ) carried out by Accomazz and Caretto^ , while the industrial aspects of d , eco nomics and operation ha ve been reviewed by Brewer nir and W erner(47). Werner clas s i f i e s the commercial catalyti c aft erbur ning (CAB) catalysts as (a) active metal /metal 1 ic ca r r i e r , (b) active oxide/oxid e carrier, and (c) active meta 1 / o x i de carrier. Poisoning or loss of activity is one of t he ma jor problems with CAB materials and both Brew er an d Wer ner provide information on the nature of poisons f or th e var ious types of catalysts Miller(47a) reported th e res ults of laboratory tests of the effect of support g eomet ry on oxidation performance over a volumetric space velo city (gas volume/bed volume) rang e of 1 30,000 to 175,000 hr." , con c 1 u d i ng that an open-structu red geometrically regular s uppor t was optimum. However, lar ge volume costs for this c ataly st ($ 300/cu.ft.) appear to b e prohibitive. Further w ork o n sup port geometry was repor ted by Leak(48) w ho tested alumi na-co ated steel wool filamen tary catalytic mufflers on a uto e xhaus t. A dual-catalyst sys tern of vanadia plus copper chrom ite o n the alumina had the h ighest activity for CO and hyd rocar bon r emoval. Industrial and economic data on CAB in stall a t i o n s is provided by Lauber (49) and Krenz(50) while des ign p roced ures are given by Dey(5 1). 87 e , Research on a wide variety of possible exhaust has been published including vanadium-alumina promoted uranium oxides(54) an d combinations of vanadium a nd copper oxides with noble metals(55) a /\ large amount of relevant background art on catalytic mufflers is contai ned in the U. S. Patent Office, Class 23/Subclass 2. This file has been reviewed, and it was found that most of the develo pment effort in this area has been undertaken either by chemical companies manufacturing tetraethyl lead or petrole urn companies. Table 19 summarizes the features of several of the recent catalytic muffler patents for treatment of auto exhaust. Cata lytic o x i d a tion n ormal ly i n vol ve s tempe ratures in the ra n g e o f 400 °-800° F.C5.6). Muc h of the c n v e n t i onal techno logy of catal ytic o x i d a t i on de ri ves from commer cial a p p 1 i c a t i o n to the remova 1 of o rgani c vap ors f rom ind ustrial proces s emissi ons a t thes e el ev ated tempe ratur es(57), and automo t i v e e x h aust cataly st tern perat ures are o f the o rder of 600 °F. In tunne 1 gas proces sing, the opera tion of a cataly tic o x i d a t i o n proce ss at tempe ratur es ab ove amb ient will i ncur an econo m i c b u rden p ropor t i o n a 1 to the deg ree of temper ature el evati on. T he the rmal penal ty in the ca se of a recy cle gas opera t i o n i s doub led, becau se th e gas n ot only has to be heat ed to react ion t e mpera ture it h as to b e re- cool ed to ambi ent c i rcul a tion t emper ature . Th us, wit h large circul a t i n g a i r vol umes , an opt imum syste m wi 1 1 requi re a parti c ularly 1 ow, o r pref erenti ally ambie nt-te mperatu re cataly St. Heat evolution in catalytic oxidation application does not appea r to be a potential problem at the low com- b u s t i ble cone entration levels expected in tunnel gas. On the o ther hand , combustible levels are too low to support react ion at t mperatures above ambient. The ambient-temp- eratu re requi r ement delineates an operational area in which only limited w ork has been done. Low-temperature catalytic o x i d a nts for C and hydrocarbons consist of hopcalite, suppo rted nob! e-metal catalysts, and some newly developed trans i t i o n and noble-metal /activated carbon combinations. Low- temperature catalytic oxidation of CO and unbur ned hydro carbons at simulated auto exhaust conditions was s tudied by Cannon and Welling(58) for a very wide range of metal and support combinations at temperatures below 350°C. While a large group of catalysts appeared to have satisfact ory activity in this temperature range, only one catalyst, a commercial 60% manganese oxide/40% copper oxide , had a t hreshold oxidation temperature of 25°C and a com plete oxi dation (100%) efficiency at an operating tempe rature le vel of 25°C for an hourly space velocity of 10,80 0. All o ther catalytic materials tested had threshold 88 — — — — sz o •— o c U3 CO -M lo to O 1— 1- •-• LO p-» re CM o r^ i— i— re re * CO lo s_ co .n CSJ •- • • C Q) C * • o - o •o o to oo o to o vo CO ex CO CJ * CO o O) en ..- Q) •!- CO CM S- en «/> lO r— o co+ja+j *r ^- O -* «3- O -i- * IO w c • re c o •c- • 4-> O U c o ID o QJ r- c ««- J- *->•!- O 4-> U 1 E o o o c 3 C CJ O cj cj +J CO Q •a o o cj •r- 1/1 c a> 0) •!- C 2C 4-> D •o T3 3 o > o; --j a> (O c c C re ex o 1 U WcOTI re re re x: E E xre ai •^ X c a> o a> v- o X o O o ct lu cj ct: s: i- 0.0 o cj CJ a: <: s: co _J -J re " o I 1 o J-T3 re CJ CJ r— 4-» $- "O OJ • 1 3 re 3 cx-o a> re re >> re o to -o re •r* •r- cx re M re •r* >> •^ 0.1 r- -M * X cx ai c r— 0J CJ +-> r— x-o u en u O) o o o o U E c u s- re o •1— •r* re s- u •r- »»- o re re 4-* X -M CD o CJ X E O eS "O M- CX +-> re o o >> C 4-> to CJ o 3 at E J- CA u >r. r— j- •f— to 0) 0) i. •r- M re re +j 3 3 re >> 4J u re a* N >>+J c 3 $-T S- c c i. to C to c .1 •p- - »^- X c •r- 4-> •r" r— •r- re cx a* CJ re O •r* r o CJ •r— re o re fc. re J- "O re 1 CD o CX J— cx E E cx-o 4-> -C E +> "O -O cx o $- •r- +J o c -o •r- CX «— cx 3 3 cx •r- re CD 3 re HI o 3 re X re aj re c X o re 3 r— r— 3 X i— •r- ^™ o 0£ o u re u o o M E re o CJ cx to re to o cx jz re +J 4-> to to 1/) to to 3 3 3 3 3 •»-> re « re re re c f .e JC JZ f OJ X X X X X c LU LU LU LU LU o D. O O O o O E +J +J +» •»-> M o 3 3 3 3 3 o «C «c •a: 89 c o •r- fO 4-> CT> i© ©^ «o in m je in s- r». +j t£> U « o * c « J- t/1 in o. CM © er> c o c C_> o •M 0J "CI X w 01 V) o •o -o r- c a> •o w eO X • to .O 0) ai O to +> O.T3 E 01 c ace +J «o o. c 3 u> E •p- en o o V) «o c o M 4-> 4-> 10 10 (A (/I 3 3 3 4-> «3 RS to c J= JE SZ w X X X c Ui UJ UI o o. o o o E M p +J o 3 3 3 CJ 90 v c , oxida tion temp erat-u res well in ex cess o f 100°C a nd 100% effic iency lev els o ver 200°C . It shoul d be note d here that one of th e cri terion fo r aut omoti e catalyt ic muffler use - retentio n of catalytic acti vity a t elevate d temper- ature s -is no t rel evant to conti nuous ambient-t emperature opera tion on t unnel venti lat ion g as. T h u s , w h i 1 e the man- ganes e-copper oxide combi nat ions were d owngraded by Cannon and W elling be cause of high- tempe rature loss of acti vi ty the a bility of thes e catalys ts to o x i d i ze both C and un- burne d hydroca rbons at room tempe rature in the p resence of wa ter vapor is e xtremely s i g n i f i cant in terms of the objec tives of the t unnel ven til at ion pr ogram, an d high- tempe rature st ructu ral and a c t i v i ty cha nges are not pert- inent Becaus e of this chan ge in cri te r i a of a ceptabi 1 i ty , prior work on the c atalytic oxida tion o f automot ive exhaust fumes has to b e re- examined or re peated Th e usual low-tempe rature CO ca talysts such as hopcal ite, a re susce ptible to poi son ing w ith water vapor, It is bel iev ed that a part of this w ater- caused loss in activi ty may be due to c a p i 11 ary con densa tion and blockage of por e f 1 ow •at lo\, temperatu res, wh ich p henomenon would also b e expe cted to be operat iveon any f ine-pore, high- area c atalys t. Howe ver, Sutt (59) re porte d two new cata- lysts suppor t on act i vated-ca rbon wh i ch w ere claimed to be res istant to wate r-vapor p o i s o n i n g. f the two cata- lysts tested , a copp er II chl oride/p latin um group com- oinati on on carbon w as found to be f u n c t i onal for CO oxidat ion at lower t emperatur es (25° C) th an a transition- metal oxide catalyst (150°C). When teste d on ammonia synthe sis g a s at 25° C at a sp ace vel o c i ty of 200, the Cu/Pt/ carbon catalys t gave 10 0% CO o x i d a t ion at a CO select ivity (in the presence of Ho) v a ry i ng from 0.86 to 1.0 . Bee ause the syngas u sed has a re lative humidity of 80% , exce llent re sistance to wate r poi son ing is indi- cated , al tho ugh conf i rmati on of this beha vior at higher space veloci ties wou Id be des i rable. In 1 964, the sta te of Ca 1 if orni a cert ified a s number of cata lytic muffle r system s as be ing ca pable o f meetin g their proje cted 19 66 emiss ion sta ndards of 275 ppm hydroc arbons a nd 1. 5% carb on monox i d e , a v eraged over 1 2,000 mi les. Howeve r, th e autom obile ma nuf actu rers c hose to meet the em ission s tanda rds by air i n j e c t i o n i nto th e exhau st manifo Id (manu al tr a n s m i s s ions) or by mod ificat ion of the fuel-a ir ratio . sp ark t i m ing and other a spects of eng ine design As a resul t, none of the catalyt i c d e v ices we re ever u sed, and furt her res earch on these reacto rs virt ual ly ceased in 1964 . Th e u 1 1 i m ate capa b i 1 i t i e s of c atalyti c muffle rs are t he su bject o f some s pecul at ion, b ut ther e is eviden ce that they can mee t the mo re stri ngent emissio n standa rds proj ected for th e mid- a nd late -1970' s. Imp rove- 91 . , i . , ments are required. to meet the di sadvantages shown in the 1964 test campaign: a. Short life-time of 6,000 to 12,000 miles b. Susceptibility to lead and particulate poisoning (a contributing factor to the short life). c. Susceptibility to inactivation by temper- atures in excess of 1700°F, a level occasionally reached in the exhaust. d. Relatively high initial cost of $75 to $100, with frequent maintenance and replacement costs. One of the prim a ry c a u s es of short cataly st life in the 19 64 Ca 1 i forn i a te sts was the co a t i n g of the catalyst surface w ith 1 ead(60 ). T he use o f a no n-lea ded gas oline would obviously remo ve thi s cau se of fa i 1 ure and also wo u 1 d yield a smaller and less-s luggi sh conve rter. With the ad vent of in ere as in g sup plies of un leaded g a s o 1 i n es , e xhaust catalysts have been cl as si f i ed acco rding to a p p 1 i c a b i 1 leaded or unleaded p o i. s o n i n n - o i s o n a s o 1 i How- ( g or no p ing) q ») ever, the othe r de-a c t i v a tion mec h a n i s m of o ver-hea ting would still rem ain. For t hese reasons , it ha s bee n state d by the Ameri can Chemi cal So ciety that "d i f f i cu 1 1 i e s thus r emain in the devel opmen t of a cata lytic co nverte r tha t could meet even the 1968 or 19 70 fed eral standard s for hydro carbons and ear- bon . monox i de a t reas onabl e cost a nd wit h rea sonable 1 i fetime 162)' The outl ook f or the p o s s i b le use of ca talyt 1 c o x i d a t i o n tec h n i q u es fo r the removal of CO and u nburn ed hydrocar bons at th e con d i t i o n s speci fie to proje cted tunnel gas appl i c a t i on is not encour aging, There are n o known i nstance s of i ndus tri al a p p 1 i cation of cata lytic ox id a t i o n at the 1 arge gas f 1 ow v ol umes , 1 ow c ombusti ble c oncen tration , and most impo rtant , at the re 1 ati vel y low t emper ature s in- volved i n tun nel a i r tr eatmen t. Mor e to th e poi nt , t here are no known succ essfu 1 i nd us tri a 1 i n s t a 1 1 ati on s i nv o 1 v i n g any one of t he th ree s peci f i c par ameters sti pul a t e d Alt hough the new 1 ow-t emper ature catal yst lab oratory data revi ewed above ap pears hope ful p arti cu larly f or CO o x i d a t i on a great deal of a d d i t i o n a 1 deve 1 opmen t work is o b v ously requ i red for the full evalu ati on of th e large -scale u t i 1 i z a t i o n of such tec hnolo gy. Feasi bili ty determ i n a t i o n requ i res further inf ormat ion o n al 1 owabl e spac e veloc ity, po s s i b 1 e tra ce metal p o i s o n i n g, ca talys t lif e , cos ts and a v a i 1 a b i 1 i ty , and the present 1 abor atory data fall short o f these asse ssmen t re- qui remen ts Again , the pract ical i ty of try inq t o ace ompl i sh at ambie nt tu nnel condi t i o n s what ha s not b een c ommer c i a 1 1 y accompl i shed at th e mor e f avo rable c oncentr a t i o n and temp- e rat ure condi t i o n s prev alent in the source exhau st , m ust be 92 i seriously questioned. Should low-temperature oxidation of the major pollutant, CO, prove feasible, then a secondary operation, such as adsorption, will be required for removal of the hydrocarbon content. Such dual processing is certain to be costly, even if probably feasible. it shoul d be no ted t hat i ndustrial appl icati on of catalyti c oxi d a t i o n has n ot be en fo und accep for hydro' carbon o x i d a t ion u se in t he Lo s Ang eles area (635. In reviewin g the use of cata lytic afte rburners for s ol ven t emission cont rol , Krenz s tated that permi ts are n o 1 on qer being is sued by th e Los A ngele s Cou nty APCD for t hese units because "sour ce te st data i ndi cate that thes e cat alyti c afterbur ners could not me et th e 90 percent e ffici ency re- quiremen t of Rule 66". T here are o ther, and conf li cti ng, reports in th e lit erature on t he su ccess of comme r c i a 1 in- s t a 11 a t i ons o f cat alytic oxi da ti on units. F or ex ample , the successf ul us e of a CAB o n an a cry! ic monome r vap or in several diffe units a t Joh nson Wax Compa ny pi ants has (Mf. been rep orted Conve rsely , onl y partial oxid ation of a mineral solve nt fu me was obtai ned a t a GAF C orpor ation vinyl fl oor c o v e r i ng plan t wit h CAB , and th s pro cess was din favor of a c onden s a t i o n-mist el i m i n a tor s ys- Information privately available to PDA on catalytic oxidation uses indicates that CAB is highly effective for situations where the material to be oxidized is either a single component or an homologous group of compounds. Fur- ther, for an efficient design, the concentrations and ex- haust conditions must be known in detail. For most applica- tions involving a wide range of combustible materials at variable concentrations, CAB will not yield adequate effic- iency levels. Thermal Afterburning All of the development work on thermal afterburning of the residual CO and hydrocarbons in vehicle exhaust has been done as source control work. Early efforts to complete the combustion of the unburned hydrocarbons and CO leaving the cylinders involved both air injection into the exhaust manifold and direct flame afterburners (42) . Air injection and/or engine design changes appear to be sufficient to meet the 1970 federal standards for CO and hydrocarbon emissions, but for the pro- jected lower emission levels, more advanced systems are required. One such system under active development is the exhaust manifold thermal reactor, a unit which has been ex- tensively developed by DuPont (66) (67) . Exhaust reactors 93 are suitable for use with leaded gasolines, and their use would permit continuation of present gasoline formulations. The exhaust manifold reactors mount on the engine in place of the conventional exhaust manifolds. Air is injected into the exhaust ports, using the air injection system now standard on most production autos. The reactor consists essentially of an initial mixing chamber, followed by baffled passageways to provide adequate retention time at high temperature. The DuPont units use concentric annular baffles surrounding the central mixing tube. Development efforts have been directed at finding suitable low-cost materials that will endure the 1700°F reaction temperatures and also have adequate erosion resistance to the high- velocity lead compounds impinging with the exhaust. In an initial 100,000 mile test, an early DuPont Type I reactor^6) held average emissions to 27 ppm hydro- carbons and 0.65% CO, but suffered from baffle. rosion. 7 An improved later version, Type V, was claimed'- ' to yield emission levels of 0.2 g/mile HC and 4.5 g/mile CO, both well below the 1974 California standards. Thermal incineration of small quantities of com- bustibles in air requires temperatures of the order of 1100 o -1500°F. Because of the virtually trace quantities of oxidizable material, none of the heat requirements can be internally derived, and must therefore be completely supplied externally. Even where a fraction of the thermal energy was internally derived, the economic penalty attached to the higher temperatures of direct incineration was cal- culated by Heinle) to be from 150 to 600% of the cost of an equivalent catalytic oxidation temperatures of 500° to 800°F lower than for thermal incineration. The external fuel and cooling costs for thermal cycles of the order of magnitude required for direct incineration of the CO and HC in the bulk tunnel air thus appears to be insupportable. Adsorption S elective removal of hydrocarbons from a gas stream can be effected by the process of physical adsorption, Al thou gh ac tivated carbon is the usual sorbent employed for the va por-p hase adsorption of organic molecules, other high- surfac e are a media, such as synthetic zeolites, silica gel and al umina , have been used for selective removal of or- g a n i c and i norganic, contaminants. The synthetic zeolites genera y h ave better sorption efficiencies than the car- 11- bonsH bu t they do not have as great an equilibrium- h o 1 d i n g cap acity. They are therefore occasionally used as the fi nal c leanup bed in a two-adsorbent system to remove the la st tr aces of pollutant. 94 i i Activa ted car bon i s the sorbent of general i n- dustrial use, an d "this mater i a 1 w i 11 adsorb, by means of Van der Waal's f orces , all c ompone nts from a ir with mo le- ti cular we ights gr eater t han N 2 or 2. The te rm "carbon » is somet h i n g of a m i s n o mer, inasmu ch as acti vated carb on contains ,2 to 25 % oxyge n and c o n s i derable qu a n t i t i e s o f hydrogen (69). A c t i v a t e d car bon ma y be more properly viewed a s a comp lex org anic polyme r with a 1 arge inter nal surface, A fair ly volu i nou s lite rature on acti vated car- bon exis ts. Has slerwO J pre sents a detailed review of the prior 1 terature , h i s t o ry, a nd cur rent appli cations in his book, wh ile some prel im inary engin eering des ign theory and practi ce is cove red i n two s tandar d referenc Barry(73 ), after review ing p u b 1 i s h ed informa t i o n , cone 1 uded that ade quate de sign an d pro cess s caleup pro cedures we re not sati sfactory at tha t tim e. Co nfirming t his find in g, the Los Angeles County AFCD and th e U. S. Pu blic Healt h Service undertoo k the e valua t i o n o f sorption design me thods and obta ined and p u b 1 i s hed u pdated design da ta(74). N ever- theless , valid d e s i g n r equi r es rel i a b 1 e 1 a b o ratory dat a for the speci f i c organi c or organi c mix, a r equi rement seldom s a t i s f i e d i n adv ance. Va por-ph ase a dsorption over activated crbon is a gas- solid equi 1 brium process where the rate of dsorption is pro p o r t i o nal to the displacement from equilibrium (driving force) . The equi 1 i b r i u m driving force is favored by low temper atures and h igh p ressure, and in many cases, by smal le r carb on par tide sizes. Because activated carbon costs are in the r ange of $0.75/lb, adsorption beds are normal ly reg enerat ed wi th steam or hot inert gas to per- mit re -use. Physi cal a dsorption is an exothermic operation and he at mus t be s uppl i ed in regeneration to overcome the energy of ad sorpti on. Steam is a convenient source of therma 1 ener gy and beca use of its low (ambient) vapor pressure and co ndensa bility , it is the regenerant of choice. However, the no rmal t empera ture range of saturated steam is not suff ic i e n 1 1 y high to co mpletely strip an adsorbed phase from t he car bon , a nd st eam-regenerated carbon cannot normally be emp loyed for ve r w concentrations of organic pollutants. 56? For ex ample , Matti aif states that 3.5 lbs of steam/lb of stripp ed org anic i s req uired when the vapor-containing air in the sorpt ion cy cle i s 0.2%, while over 30 lb of steam/lb of org anic m ay be requi red when the pollutant concentration level is red uced t o 200 ppm. Adsorption techniques have been applied to the control of evaporative emissions from automobile fuel tanks and carburetors. Vapor-capture systems, employing activated carbon canisters or foamed polyurethane, serve as storage systems for the vapors released during engine shutdown. The 95 1 , i 1 . ) stored vapors are purged from the sorbent on engine startup into the intake system of the engine^'5), j^e main problem with such adsorption/desorption systems had been the up- setting of carburetion by over-enrichment of the engine feed on startup, but automatic valve control appears to have solved this particular problem. The technical feasibility" of such evaporative control systems has been demonstrated v42 and it is expected that they will be incorporated in 1972 producti on model s. The use of a c t i v a t ed carb on adso rptio n for the continuous removal o f hydroc arbons from tu nnel air a p pears to be technically fe a s i b 1 e , i nasmuc h as th is is norma 1 ly an ambient temperature operatic n. In terms o f the tunne 1 ven- ti ation probl em , ac ti vated carbon adsorpt ion h as pot e n t i a 1 only with respect to the org a n i c co ntent o f the gas, al though in combination with other so rbents , i t may al so parti ally cover N0 X . It will be d e f i c i e n t w i th resp ect t o CO r emoval , the major const ituen t of the pol lut ant i n p ut , a nd can there- a s a 1 fore be considered only partia or su pplem entary , con- trol process for thi s a p p 1 i c ation. The ma jor o bjecti on to activated carbon tre atment o f large f 1 ows of ga s typi cal of the projected tunnel a p p 1 i c a t i o n is one of capi tal co st. Exclusive of erectio n costs, total install ed co sts fo r - carbon sorption syst ems us in g steam regene ratio n , are e s t i mated to be $32.50/1 b of con t ami nan t capac ity p er eye le(43). Operating costs depe nd on th e frequ ency an d len gth of re- generation life of b ed, cont ami n ant concen trati on lev el , and necessity for pr e-f i 1 tra t i o n an d secon d-sor bent s ystems Given the wery dilut e org an c conta m i n a n t 1 eve! in tu nnel air and the nature o f the po 1 utant mix, a c t i v a ted ca rbon sorption may have to be supp lemente d with a cle anup o per- ati on employing a di fferent sorbent , thus compo u n d i n g the cost problem. T o meet some of the cost o bjections to ca rbon sorpti on sy stems as app lied to 1 ow c oncentrat ion 1 e vel " system s (20 ppm) , Matt ial56) propos ed the "Z orbci n pro- cess , in wh ich th e stri pped or ganic obtai ned during regen- erati o n i s i n c i n e rated to prov ide bo th the he at and inert gas ne eded for re genera tion. In the event th at org anic recove ry ra ther t h a n in ci nerat ion is indi cate d s Mat tia propos ed a "Casca de" op e r a t i o n in wh ich a p a i r of p ri ma ry adsorb ers i n para lie! f eed a s ingle secondary adsor ber. An eco nomi c compa r i s o n of vari ous mo des of so rption and/or i n c i n e rati o n syst ems in d i c a t e that t he "Casca de" ar rangement had th e low est an nual iz ed cost , i n c 1 u d i n g an apprec i a b 1 e credit for the re covere d solve nt. W ithout th is rec overed sol ven t ere dit, t he "Zo rbci n" arrang ement was the m ost ec- onomic . Ho wever if a low-con centra tion and ambien t-temp- eratur e cat alyti c oxida tion te c h n i q u e is avai lable , there 96 r, . would be no point -to sorbing organic pollutants prior to an elution and burning sequence. Th e presen ce of part i c u 1 a t es in an air stream being proces sed by a cti va ted c arbon sorption poses several probl ems. I f the pa rticu lates are s olid, then the carbon bed m ay act as a fil ter a nd th e flow resistance of the unit will in crease o r it may p lug. Very fine solids or aeros ols may also po ison the s orpti o n abilities of the carbo n , and a sorpti on be d mus t usua lly be protected from parti culate effects by su itabl e pre- filtration means. If the a erosol size and bed depth is su ch that bed penetration occur s, then aerosol bui 1 dup i n the gas will occur in a recyc le syst em, unle ss an effi c i e n t particulate collection techn ique su ch as el ectro s t a t i c prec ipitation or filtration is us ed in s e r i e s w i th th e ads orpti o n unit. Wet Scrubbing "Wet s crubb ing" in the f ield of pol lution control has tw o differen t mea n i n g s It is appl ied to both p articu- late r emoval and gas absor p t i o n , a nd de spite the dis parity of fun cti on, dis t i n c t ion b etween t he tw o appl i cation areas and ty pes of equ i pmen t is sometime s not made A cas e in point is Table 2 tak en f om a rec ent r eview. Of th e eight types of equipme nt li sted only tw o , th e pack ed and spray towers , are conv entio nal m ass tran sfer or gas -absorp tion device s. As is o b v i o us fr om the p artic ulate- removal eff ic- iencie s for thes e two type s of equ ipmen t list ed in T able 20, they, as well as the prima r i 1 y d u s t-scr ubber units, have some d egree of d ual-f u n c t i onal i ty. How ever, for mas s trans- fer co ntactors , dust col le c t i o n is usua lly in c i d e n t a 1 and vice v ersa, and becau se of the ext reme di ffer ences i n design theory and objec ti ves , sep a r a t i o n by pr imary functio n is desi ra ble. 97 — 1 M o l/l I. 0) 10 M- t- •> c ^~ O 0J *-> • •/> o> •r- xi •M M- -M c c s- E l/> c f- u> •r* 6 •r- o O i~ 3 o •0 E 3 t- •c— +* 3 i- «/» o "O •f-" -o 3 •*-> «/> r— M- -M *t- •M t- -o M re •0 *»- C ••-> ID a> -r- •— C u o 4J <0 s- c i- «/> +> u re at 1— $- «- «/) 1— a> at +J r— O 3 O- x; E c t— a> u co D. 0J "O i/) • »- $. Ca- p c s- to 0) a) 5 05 c M o re •!-> 4-> «- S- •r- -o »-» IM -o o J- UDIMQ r= >, •M c rtJ •!- >> oj c u re 3 fc- V) <0 O- O- 3 x: f— s- u re CL c re "o a» re u t- o D-.i- (O <0 >> 0) i— c •1— c o O- (/> +J E c j<: > at OlO (Ui- a> C- o «/> E O J- •r- i- o IC c >»a. e u E >j J- XI o J= *S E >, 3 O E c + + •i- en X •!- 00 00 er> o> d en o> a> re o a: LU in o ui * CvJ *— i/) t- irt ai r— O •»-> INI l£> in 00 iO a> o o re _i re CO r-» h-i CO E s ^t" r^ CVJ C\J 1 i *- *-> vo in »- «C OU- • • a. ST re c CO 00 C' =) •«- V> ooc o in a> o*1— enm c c re 0) o o © in in in o in in et p— t_ o o o o INJ CVJ CVJ CVJ o o j— •r- 1— re 4-» s: 3 $- IA re => O. fc. t- t- 3 i- 0) u >> 3 vo re O X) E J- +J re l*- Cl T> a> c o 1/1 "O 0J u >> a> at TJ •r- -o G) c j* O +-> o oJ 0) V 4-> O •r- +» C o >> a. re O) t- 0J a* »- o a. O 3 98 , . The primary function of any piece of absorption equipment is to provide a large active area of contact between the gas and liquid phases. This is accomplished by dispersing the liquid phase over a geometric packing material or as droplets by spraying. Packed tower absorbers may be used in three modes of two-phase flow operation: (a ) countercurrent, (b) cocurrent and (c) crossflow. The maximum degree of absorption efficiency (most number of transfer units, or NTU) is obtained with countercurrent contact, and for difficultly-soluble gases, or maximum degree of removal , this is the preferred type of contact unit. In an absorber, the completeness of solute removal fr om the gas stream is a sensitive function of the time of c ontact or height, Because the gas pressure loss through the packing is directly proportional to the height o f packing, this latter factor controls efficiency and affect s gas blowing costs. For this reason, a large variety of 1 ow-loss, high-efficiency packings have been developed commerci ally. Because any packing shape represents a compromise between the conflict- ing requirements of high fluid disper si on and low gas pressure losses, each tower packing h as its particular optimum area of application. The key en gi neer i ng es timate l n pa eking sele c t i o n and c olumn des ign is asses sment of the requi red v ol ume of - packi ng for a given amount of tr ansfer. To make this e s t i mate some typ e of p acking perfo rmance index , in the f orm of ei ther a vo lgmetr ic coe ff i cie nt, Kg a , or heigh t of a trans fer unit, (HTU) , must be em ployed, Des pi te the r api d advan ces in fu ndamen tal tr ansfer theory in r ecent year s, the b ody of de sign i nf orma t i o n a v a i 1 a b 1 e to the e ngine er has n ot reflec ted th ese ad vances The di ff i cul ty is t hat , even for a giv en sys tern, an d pack ing, th e coe ffici ents are not i nvari ant prope r t i e s , but d epend o n flo w rat es an d opera tive port ion of the e q u i 1 i b rium cu rve. The stand ard proce dure is t herefo re to select desi gn perf orman ce da ta whose conditio ns or determ i n a t i o n most cl ose iy ap proxi mate those of the a ppl ica t i o n For t race co ntami nant remov al this inf ormati on i s u n a v a i 1 abl e. 99 r Spray chambers or towers may be used for gas absorption in cases where only a few transfer units are required, i.e., for soluble gas components. These units have the advantages of very low gas-phase pressure drop and inexpensive construction, but do not offer counter- current contact. Four types of spray systems are used commercially: (a) simple spray columns, (b) cyclonic spray towers, (c) venturi scrubbers, and (d) jet scrubbers. The spray chamber is a contacting device that is frequently used in situations where a contaminated gas stream contains both particulates and a highly soluble gas component. Particle collection in spray towers is discussed below, but the mass transfer characteristics of this equipment is pertinent to the removal of the oxygenated, partially- oxidized, hydrocarbons in the exhaust. These include such components as acrolein and formaldehyde, which are object- ionable from the point of view of odor and irritation effects. Spray scrubb ers c an remo ve hyd rocar bons f rom a gas s tream by th ree me chani sms(79) : (a) d i s s o 1 u t i o n of the vapor comp onent in the 1 iqu id, (b) conde n s a t i on by temper- ature diff erenti a 1 , in the same ma nner t hat a i r is de- humid i f ied by co Id wat er sp rays , a nd (c) vapo r mol e cules may a dsorb on pa rticul ate m atter w h i c h i s sub sequen tly remov ed by impi n gement on t he liqu id dro ps. Design data are a v a i 1 a ble pr imari 1 y for the so lubili ty me c h a n i s m, and a f ul ly va lid d e sign w ould undoubt edly r equi r e pre! i m i n a ry - test data, With respe ct to the so lubili ty me c h a n i s m , 1 i t eratu re da ta for spray towe rs(80) showed that the n umber of tr ansfe r unit s was propo rtional to th e 1 iq u i d r a te, and was i ncrea sed by a fin er sp ray (hi gher 1 i q u i d power input) . The r ate o f mass trans fer w as most rapid near the s pray nozzl e , ow ing to the f ormat ion of fresh 1 i q u i d surf ace and col le ction of sp ray by the chamber wal 1 s . En trai nm ent is a pro bl em with s pray t ower use, pa rticul arly at the higher gas f lows , al tho ugh th is pr oblem m ay be resol ved by the use of su i tab! e mist el imi nator s or cy clonic flow spray towers. Appl ica tion of we t scrub b i n g g as ab sorption technique s to rem oval of co ntamina nts f om tu nnel ventilation air poses several probl ems. If an organ ic so Ivent is em- ployed as a solve n t , even i f a hig h-mol e cul ar weight material is employ e d , its vapor pres sure wi 1 1 una v o i d a bly be at least the same order of magnitude as som e of t he po llutants, so that the net effe ct could b e subst i t u t i o n of one pollutant, the solve nt, for another, t he solu te. A s i m i lar problem exists wi th water as a solv ent, si nee re cycle of gas through an aqueou s phase system wil 1 tend to adi a b a t i cally saturate the air. C o n t i n u ous operat ion of a tunn el at 100% relative humidity is not d esirable , and app 1 i c a t i on of wet scrubbing 100 i i . techniques would require the use of a downstream condensing system to remove solvent vapors. If the absorber is operated at ambient temperatures, then the downstream solvent-removal condenser must be operated at low, or refrigerant, tempera- tures in order to remove solvent. This, in turn, means that the bulk tunnel air must be thermally cycled between refrig- erant and ambient temperatures, adding a thermal cooling and heating cost to the base operation of the absorption. I t appe ars that the humidi f ication or saturation proble m wi 1 1 prob ably prevent in situ tunnel application of absorp tion proces ses. However, the possibility remains of using such a proc ess on the exhaust air from the tunnel, While the w ashed air may generate a steam plume under certain atmosp heric condi tions, exhaust processing would prevent local accum u 1 a t i o ns of pollutants, and the possibility of contam i n a n t recyc le in situations where the intake fan is locate d nea r the exhaust fan. A number of tunnels already have s pray chambe rs installed to protect the exhaust fans in the even t of t unnel fires, and their use as exhaust con- trol d evice s woul d represent only an operating cost increment. While the d i sposa 1 of the polluted water resulting from wet scrubb ing m ay be a problem, this can be minimized by the use of wate r recy cle operation, with a small amount of make- up and blee d 1 i q u id. The recycle mode of operation would al so p ermi t use o f exhaust wet scrubbing in tunnels without ready acces s to 1 arge amounts of water. Nitrogen Oxides Combustion of a hydrocarbon fuel with air normally results in the combination of part of the nitrogen and oxygen to form nitric oxide (NO) at the higher temperatures. Sub- sequent to its formation, NO is oxidized by residual or atmospheric oxygen to nitrogen dioxide, NO2: 2N0 + Oo = 2N0, (13) The x i d a t i n of ni trie x i de is a si ow exot dermic reaction, 1 iber ating 2 4,250 B tu/lb mo le , a nd is favore d by low temper- ature s. The x i d a t ion reac tion in a r is ma rkedly concen- trati on-depe ndent. When th e r i g i n a 1 concen tration of NO is 2% by vol ume, it requi re s 10 secon ds for half the NO to oxidi z e , w h i le it t akes nea rly 6 hou rs for a similar degree of ox i d a t i n when t he i n i t al NO cone entrati on is 1 ppm' Kinet ically, the ox idation react ion i s third -order, .and the 2 rate constan ts have been th oroug hly e xplored by Rao^° ) for the h omogene ous gas -phase r eacti on. This la tter investigation al so explore d the c atalyzed ox id a t i n of nit ric oxide, using both a c t i v a t ed carb on and s i 1 i c a gel as cata lysts 101 g . - Th e van able mix ture of NO and NO? (plus minor amount s of o ther n i trogen oxide s ) is commonly designated as fix- NO. fo rmatio n is fav ored by nig h combustion tempera- tures and ex cess o xygen, s tha t for internal combustion engi ne s , the h i g h e st emiss ions are as sociated with air-fuel ratios s 1 i g h tly on the lea n si d e of s toi chi ometri c. High speeds and h eavy a ccelerat ions produc e the major portion of the NO x , and level s of N0 X emi s s in typical urban traffic range betwee n 800 and 3000 ppm( w Data published by the Los An geles County Air Pol 1 u t i o n Cont rol District, as pre- sented by Fa 1th(83 ) and g i ven i n Tabl e 21 show the effect of d r i v i n g vari ations on NO emiss ions. At \/ery low concentrations of N0 , the reaction 2 with water is: 5 2 N0 + H = HN0 + HN0 (K = 10 2 2 2 3 ) (15) and in warm water, the HN0 is unstable: 2 3 HN0 = HNO3 + 2N0 + H 2 2 (16) The NO released in any of the above dissolution reactions must be re-oxidized to N0 2 . Ni troge n d i x i d e i s a s trong abso rber f ultra- violet light and is the i ni t i ator comp ound for th e chain reacti ons re s u 1 1 i ng in the f ormat ion f ozo ne and photo- chemi c al smo g. A simp! if ied reac ti on schem e for the for- mation of ph otoch emical smog (62) indie a t i n g the t rigger role f is i n . Th e fir st N0 2 , g iven Tab Te 22 two reactions show t he pro babl e prima ry ox idant (ozo ne) f ormati on mechan- ism, w hi le t he su bseque nt re actio ns in d i c a t e the f ormati on of sec ond a ry i r r i t a n t s and p ol lut ants. A f ew ten ths of a ppm of N0 X a nd 1 e ss tha n 1 p pm of reac ti ve hydroc arbons (unsat urated ) are suf f i c i e n t to i n i t i a te th e reac tion chain, but va 1 ues a s hi h as .7 pp m N0 X and 3 ppm hydro carbons have b een fo und f or amb lent atmos phere on s moggy days Al thou gh ul t ravio let ra d i a t i on is not avail able i n vehicular tunnel s , F a i th(33 ) stat es th at ex perie nee i n the gas i n dustry shows that oxide s of ni tro gen i n ext remely smal 1 102 1 i 4-> cn oo c LU •r" «d" «* Id «3- *3" CTi 4-> oo U) in cc O cc < U h- O to oo •r- => Q Z • • c 103 TABLE 22 SIMPLIFIED REACTION SCHEME FOR PHOTOCHEMICAL SMOG N0 + Light —*~ NO +0 2 Nitrogen Nitric Atomic dioxide oxide oxygen + °2 T °3 Molecular Ozone oxygen + NO — N0 + 3 2 2 + He — HcO Hydrocarbon Radical HcO + 2 _^ HcOj Radical Hc0 + He — Aldehydes, 3 ketones ,etc. Hc0 + NO -— Hc0 3 — Radical? Hc0 + m- + Hc0 3 2 3 2 HcO x + N0 2 —— Peroxyacyl Radical nitrates This reaction scheme is intended to be illustrative, not definitive. Research is still in progress on the detailed chemistry of the smog-forming process. 104 i , quantities will react with hydrocarbons to form particulate matter, even in the dark. This latter role of N0 X with respect to in situ particulate matter generation in tunnels has apparently not been investigated, so that based on present data on concentration levels, the primary objection to tunnel N0 V concentrations would be with respect to ex- baust to the ambient atmosphere. Source Control De sign change s made on in ternal- combust ion engines for the purp ose o f redu c i n g t h e emi ssion o f unbur ned hydro- carbons and carbo n mono xide th rough more e f f i c i e n t com- b u s t i o n gene rally have the opp o s i t e effect on nit rogen oxide product ion. The higher combus tion tempera tures a nd excess oxygen atten dant on mor e effic ient combust ion or secondary oxidati on ar e exa ctly t he cond i tion s servi n g to i ncrease the deg ree o f nit rogen f i x a t i o n. C onverse ly, red uction of the com b u s t i on te mperat ure and the amount of oxyg en avail- able at this temp eratur e serve s to reduce the N0 X level s and thi s pro vi des the b as is fo r the most c ommon a pproach to control : exh aust gas re c i r c u 1 a tion. The exhaus t gas reci r c u 1 a t i on sys tern d eveloped by Esso Resea rch and En gi nee ri ng C ompany (85) u t i 1 i z es a system which recy cles gas f ro.m t he exh aust t hrottl e pla te. A simpl e vac uum-operat ed on -off v alve s huts o ff th e recircu- latio n at idle to g ve sm ooth e n g i n e operat ion a nd also at wide- open throttle t o pre vent 1 oss i n vehic 1 e pe rformance. Dynam omete r tests fo r 50, 000 mi les at a rec ircul at ion rate of ab out 1 5 percent showe d cons i s t e n t reduc ti on of N0 X level s to the 1974 C al i fo rnia s tandar ds of 1.3 g rams of N0 X per m ile. Theoretic ally, 90 pe rcent NO'x re on will requi re 30 percent e xhaus t gas recycl e Teve ) but the decre ase i n power ge nerat ion at this recycl e lev el may not be ac cepta ble. N0 X emissions from vehicles can also be controlled by catalytic reduction in the exhaust stream. However, such 105 . r . h a reduc tion op e ratio n requi res t he pres ence f a re d u c i n g gas sue h as CO or a hydroca rbon , and th is is b v i u sly i n c o n s i stent w i th 1 her exh aust control objec t i v e s For this re ason, m ost pr oposed catal ytic mu f f ler system s for control of N0 X call for two sepa rate re actors or ca talyst - o a t i n at ti r beds, ne oper g redu cing condi ons fo NO X reduct- ion, an d the ther a t oxidi zing condi ti ons fo r C0 a nd HC removal A ca se in point i s pre sented by T ay lor, 1 969, in U. S . Paten t No. 3,429.6 56, a ssigned to Es so Res earch 8 1 and Eng i n e e r i n g Comp any^ °) . Ta ylor s two- st age ex haust treatme n t call s for a prima ry ox i d a t i n bed t remo ve 02, f ol lowe d by a reduci ng bed conta i n i n g a steam -refor ming catalys t to re act CO and th e hyd rocarbo ns wit h H 2 to form CO2 and , an d reac tion of the N0 the hydrog en thus Ho2 V with produce d. (87)KO/ A recent news announcement 3 disclosed the development of a new "ni ckel -copper" catalyst claimed to be 90% effective for N0 X reduction in automotive exhaust. It was also indicated that the new catalyst for N0 X removal would be part of a dual -catalyst system, with the second catalyst capable of oxidative removal of CO and hydrocarbons However, the development of exhaust catalytic converters for N0 X does not appear to have progressed to the same feasibility point as the exhaust recycle units. 88) Har di son and Fletc her(89 ) have reviewed both elevate d and atmospher i c pr e s s u r e cata lytic p rocesses for the red ucti on of N0 X i n the tail gases from i n d u s t r i al nitric acid p lants. W hen t he em i s s i n limit is of t e order f 200 ppm Europ ean p racti ce is to use a two-st age reduc ti on sys tern. The firs t sta ge is used to remove practi c al ly a 11 of the oxyg en f om the gas st ream to secure the nee essary complete redu c t i n in th e secon d stage, Oper- ating t empera ture 1 i mi ts ar e fro m 900° to 1 °F, and this type of reduc tion oper a t i n does not a ppear t be fea s i b 1 e for the tunne 1 ventila tion probl em, be cause f both t he tempera ture 1 eve! and the xygen -remov al feat ure. Th e normal atmosp heric con centr a t i n of ox ygen in tunnel re- cycle a i r , an d the obv ious neces s i ty f mai nt a i n i n g t his level , preclu des the u se of any reduct i v e cat alytic t ech- n i q u e w hich c ould cons ume xygen . Thu s , the only pot e n t i a 1 for cat alytic reductio n app 1 i c a t ion to NO ha s to ste m from the pos s i b i 1 i ty of sel ecti v e rea c t i n with a reduci ng agent such as CO in the pres ence of 0? . Thi s 1 atte r reacti on has 11*91) been st u d i e d by both B akerv 90) a nd Rya so , at the 1 aborat ory le vel It is anticipated that removal of nitrogen oxides from tunnel air by any conventional technique, including catalytic reduction may be the most difficult objective to achieve. Thermodynami cal ly , the decomposition of NO into 106 g 1 i and N is uite fa vorab le , b ut no cataly st has b een 2 2 q found that w i 1 effec t thi s dec omposi tion a t reason able rates or tempe ratures (92). Whi le the destr uctive c ata- lytic oxidatio n of CO and hydro carbon s requ ires an excess ic remo val o f N0 from a n of 2 , catalyt X gas stream ormal ly employ s reduci ng cond i t i o n s. fi owever , the use of t wo or more d if ferent cataly sts w i th d i s s i m i lar se lecti vi t ies at reacti on condi tions o ften al low s the cataly sis of i ncom- p a t i b 1 e reacti ons. E ven i n the prese nee of excess °2» a cataly st with the cap a b i 1 i ty of adsor b i n g b oth CO a nd N0 X " select ively, c o u 1 d y i eld a n "in ternal redu ctive re action. (91) Ryason stu died th e cat alyze d reac tion o f N0 X wi th CO at hi h space veloci t ies a nd te mperat ures a nd found alumina suppor ted cata lysts t o be effec ti ve. Howev er, temp eratures of 100 0°F were requi r ed, p lus s toichi ometri c quanti ties of reacta nts, so that th is ap proac h to t unnel gas clea n u p is not ap parently promis ing. An extremely comprehensive and detailed body of work on N0 2 adsorption was developed in connection wi t b the Wisconsin process for the production of nitric add'93j t This process employed shallow fluidized beds of silica gel of N0 and for the adsorption 2 , this process was demonstrated on an industrial scale. Silica gel contacting was also used in this process for the catalytic oxidation of NO to N0 2 . The published data on this si 1 ca-gel -based oxi dati on-sorption operation show the following specific points: a. Sorber design was based on operation at 10°F at a gel: N0 2 ratio of 14. Poor recovery was indicated at temperatures above 10°, regardless of gel flow. b. Catalysis of NO oxidation to N0 2 by silica gel required a gas dewpoint of -60°F. It is obvious that both of the above specifications are outside the range of probable tunnel application with respect to utilization of ambient temperatures and in-tunnel dewpoints. The sorption concept is nevertheless of con- tinuing interest; Sundaresan(94) reported that a commercial zeolite (molecular sieve) was more efficient than silica gel for removing very low concentrations of N0 X from a nitric acid plant tail gas. N0 X selectivity in the presence of organic contaminants has not been explored for zeolite or carbon adsorption, and laboratory studies of such selectivity at the low levels of N0 X concentration indicated for tunnel air must be made before actual application can be seriously considered. 107 : As sh own ab ove i n the bri e f rev i ew of the d i s- sol lit ion r e a c t i ons of N0 wet scrub bi ng of M0 part icu- 2s X , larly at 1 ow CO ncentr a t i n s, is nei t her a strai g htf or ward nor e ff ici ent a bsorpt ion s i t u a t ion. Fort her, ot her s ol uble gas c ompon ents likely to b e pre sent in tu nnel ga s , su ch as CO2 a nd SO 2 , wi 11 int erfer e wit h N0 y solu tion eq u i 1 i b ria. A det ailed revi ew of the d i ff ic ul tie s ass ociated with the sorpt ion f low conce ntrat i ons of NO x fco m oower pi an t stack gase s has been recen tly p u b 1 i s fiedO conn ection wi th this 1 atte r revi ew, a pape r by Barto ndi ca ted that absor ption (wi th chem i cal react ion) appeare d to be the m ost p romi s i n g p tenti al te c h n i q ue f r the r emova 1 of N0 f rom pi ant and th e use of X p ower stack gas, sugge sted recyc le li mewat er or magne sium hydro xide s 1 u t i n. H ow- " ever, the poten tial promi se" f thi s abs orption tech n i q u e was b ased on tw cond i t i n s tha t wou Id no t neces s a r i 1 y be b t a i ned i n the case of tu nnel venti 1 a 1 1 n a. Cost-benefit calculations on a complex magnesium hydroxide absorption flow sheet showed absorption to have the lowest annual costs only because by- product credits offset the high capital charges for installation. b. It was assumed that equimolar con- of NO N0 centrations and 2 (N2O3) could be obtained in the gas in order to optimize absorption. The assumption of equimolar NO and NO? gas con- tents finds some support in the literature; Radnakri shna'96) s t u d i e d the removal of N0 X with dilute sodium, potassium and ca lcium hydroxide solutions, and found that when the alkali was in excess, equal amounts of nitrate and nitrite were f ormed. However, this may be a liquid-phase reaction, rather than a catalyzed gas-phase displacement. In any event, N0 X removal from tunnel air by wet scrubbing means appare ntly requires intensive development effort prior to feasib i 1 i ty determination, and this operation does not appear to be susceptible to design or installation at present. Particulates The government has estimated that current vehicles emit approximately 0.3 g/mile of particulate matter(67). Although particulate matter has not as yet been clearly de- fined, and neither measuring techniques nor test cycle con- ditions have been specified, a standard of 0.1 g/mile has been proposed for 1975, and a 1980 level of 0.03 g/mile. According to Stern(42), automotive exhaust emissions contain 70% by count of extremely fine particles in the size range 108 i , of 0.02 to 0.06y. However, on a mass distribution basis, particles less than 1 . 0y in size account for less than 5% of the total weight of the particulate matter in the ex- haust. Exhaust particulates contain both inorganic and organic compounds of high molecular weight, with the most significant fraction consisting of lead compounds deriving from the tetraethyl lead antiknock compounds. Approximately 75% of the lead burned in the engine is exhausted to the atmosphere, with the total amount of lead particulates dis- charged being proportional to the concentration of tetra- ethyl lead in the gasoline. It is worth noting that the current introduction of low-lead and non-leaded gasolines at the fuel pumps will directly yield significant reduc- tions in the total particulate emission. In a dditi on to the lead salt s , the e xhaust partic- ulates may als o rep resen t carbon, i ron rust, t a r s and oil mists. Furthe r , tu nnel air also conta ins part iculates derive d from t i re a brasi on, salt (from winter salting operat ions) an d fug i ti ve dust. T he pr imary pa r t i c u 1 a t e contri b u t o r is exha ust , both from gaso line and d i e s e 1 engine s. The latte r exh a u s t is p artic ularly h igh in smoke and od or compo unds (part ial ly-oxi di zed hydroca rbons), and the us e of bar ium-b ased smoke sup press ant a d d i tives may give rise t o a uniq ue se t of particula te em i s s i o n p roblemsW). Bari urn sul fate has low t oxici ty and t here is usual ly enough sulfur in d esel fuel to y ield this inn ocuous com- pound in the e xhaus t ash Howeve r , wa ter-sol u ble barium salts are toxi c , an d com plete sul fatio n may no t always be certai n. 109 1 i u l/l c CD 4- 0J © > o r— •u 0) CD CVJ U0 u p— c C o o c c r-». in Ol NOOCr-wi-ncoOfonr-NMr) I— U0 (U o o o c 00 00 CVJ t— i— "Si" r-rOO I 00tWC«tW «3" a: fj~> • OH H- -l-> 3 UJ Cu 10 O «x r>» ro r- UJ J- ->»^ • » CVJ UJ tn 4-> V) o c © o CVJ <5J" p— (T3- c o © o Ch CT) CO r». cocvjcvji»^ct>Op— fOujkniNN^ a: in *-. CD • C tflp- 0J u o &. •r- e/> >>*—« CD C CL-P- E CD 3 «J 0J—~- * CD >)3 E in C E E OJ O) O C fi £ C C •«- X: £ 3 CD CD 3 3 CD t— 4-»-»->l-CD",^--*CDCD Op— -M 3 «p- +* $- r— c -o •p- •p- *t- "D 3 t0 (O O N O OVp— C E •— 3 T- E •— CD CD «e xi C X) O C U »r-l- CN«--'>,CD «/>•!- >>£EO«JO-C"OJ* Oi >> A3 to u CD -r- i-i-+Jr-(UCOS»Cr-Pl.WDl.J3aO«0 c r— c M c e: mZ:+J>-'fiQ C 0.i.p no . 64,000 mile test as against a normal emission rate of 0.2 to 0.3 g/mile. In a 26,000 mile test on an improved version of the trap system, lead salt emissions were reduced to 0.03 g/ mile. Perhaps even more significant were the reductions in the BaP emission rates. At 3,000 miles, the trap system reduced BaP emissions from 66 to 24 mi crograms/gallon of fuel, while at 18,000 miles traveled, the reduction was from 228 to 6 micrograms/gallon. Studies are continuing, but the last test data showed that total particulate emission could be maintained at the 0.03 to 0.04 g/mile level, with a lead salt content running from 50 to 75% of the total partic- ulates. The D uPont exhaus t trapping system described above utilize d the fl ow energy an d high velocity inherent in auto- motive exhaust to agglomera te and centrifugal ly separate the particl es from the exhaust gases. Any similar external system of parti culate remov al must include means for imparting the sam e flow e nergy to the total gas: exhaust plus the much larger venti lat ion flow. F urther, while agglomeration may be easi ly accom plished at h igh particle population density, it beco mes infi nitely more difficult with a very disperse populat ion dens ity. For cy clones, therefore, dust collection eff i cie ncy deer eases with d ecreasing dust loadings (42) Collect ion effi ciency for i nertial separators also depends on part i c 1 e s i z e distributi on, particle density and other particl e proper ties. As po inted out above, information on the nat ure of p articul ates in gasoline and diesel engine ex- haust i s still sketchy, and does not yet provide the basis for pro per sele ction of col lector type. Inasmuch as cyclones and oth er inert ial devices show high efficiencies for particles in the plus-10 micron size range, such data are of extreme prel imi nary imp ortance. Fu rther, relatively high pressure drops a re regui red for high efficiencies, and these will be at leas t of the same order of magnitude as the initial tunnel ventila tion sys tern itself. Some of the pressure drop characteristics of wet collectors, as well as the gas and liquid velocity ranges were given in Table 20. Again the humidi f ication problems existing with any type of wet contactor mitigate against the use of an internal wet scrubber, but such units may have application to the exhaust air. Most of the wet collectors listed also have a pressure drop range that would necessitate a doubling of the fan horsepower for most existing tunnels in order to operate the scrubbing equipment. Notably, the spray chamber is the sole device with an inherent resistance less than 1 inch. W.G. Aqueous spray scrubbing is capable of a high degree 9/ of particulate removal in a well-designed unit. Hangebrauclo ) 111 i , 1 has re ported that spray scrubbing removed 98% of the benzo- (a)pyr ene emi ssion from a municipal incinerator. Similar level s of con trol were achieved on the polynuclear hydro- carbon emi ssi on from hot asphalt blowing plants. Because polynu clear c arcinogens are associated with the particulate f racti on, the se data indicate excellent potential for tunnel exhaus t contr ol for the most dangerous health hazards in the emi ssi on. In addition to the organic carcinogens, wet scrubb i n g has capability for the removal of most oxygenated o r g a n i c s , w h i ch are usually water-soluble, and a portion of the NO x« One of the few industrial control units which appea rs to be readily applicable to the tunnel air control probl em is th e electrostatic precipitator. In mechanical col le ctors , s uch filters (baghouses) and cyclones, energy is ap plied to the entire gas stream. In the electrostatic preci pi t a tor the energy used for collection is applied only to the p articles. The collection process consists of charg i n g the particulates by means of a hioh-voltaqe corona d i s c h arge and then electrostatically depositing them on a groun ded coll ecting electrode. The electric power required to ma i n t a i n t he corona ranae from 50 to 500 watts/1000 CFM(J2) and v ol tages of from 50,000 to 100,000 volts are required^ 98 ), Becau se of th e highly selective energy input mechanism, press ure loss through the electrostatic precipitators is very low, fro m 0.1 to 0.5 inches W.G. However, gas flow throu gh the u nit must be held tc low velocities (2 to 8 ft/ sec) so that these devices are usually fairly large. In addi tion to the volume trie requi rement s, other d i s a d v antage s inc 1 u d e hi gh ca pi to! costs and p o s s i b le dust expl os ion ha zards in the case s of c umbus tible dusts . Effic- i e n c i e s of c ommer c i a 1 u n its n ow bei ng so 1 d ar e i n e xcess of 99%(99 ) and submi cron pa rti cl es may be c ol lee ted wi th almost equal f aci 1 ty as 100-rni cron parti c les. Fact ors co ntroll i ng design i n c 1 u de (a ) dust re si s ti vi ty (b) gas t empera tures (c) f low di stri b u t i o n a nd (d ) mo is ture conte nt of gas. For high e ff 1 cie ncy p artic! e remo val , t he el e c t r i cal re si sti vi ty 4 should be i n the range o f 10 to 10 10 oh m-cm; actua 1 particle 3 resist i vi ty range s from lO" to 1 0l 4 ohm -crow 9). H i gh parti - cle re s i s t i v i t i e s can le ad to col le c t i o n elec trode insulation by a t hick p artic le laye r and subse q u e n t back d i s c h arge of a corona from the c ol ecti ng el ectrod e , in terfe ring w i th the normal perf o rmanc e of th e u n i t. An excellent review of both design and- application of electrostatic precipitators is presented in the Air Pollu - 99 ) tion Engineering Manual (41) while Walker( $ nas updated the cost and efficiency data for this equipment. A simpler, and potentially cheaper form of electrostatic unit, is the 112 v 1 , . s p a c e-charae" precipitator, described by Faith^ ^) and by Ha nsonHOl). in the space-charge precipitator, the parti culates are charged by a conventional corona, and then charg ed droplets of liquid are introduced into the gas in the f orm of a spray froma charged nozzle. Particles and 1 i q u i d droplets are then collected by grounded wire mesh col le ctors. This unit combines the best features of spray absor ption with the electrostatic efficiency levels of parti culate removal, while avoiding the complexity and high capital cost of conventional precipitators. Unfort- unate ly, this type of equipment is in the devlopment stage and w ill require extensive work before becoming commercially avail able. Tunnel Pollution Control - Feasibility and Economic Evaluation T he objective of this study was to determine the techn i c a 1 a nd economic feasibility of available processes for r emovi n g pollutants from vehicular tunnel atmospheres, The p ol uta nts are those originating in automotive exhausts, and i CO, N0 nclude X , unburned and partially-oxidized hydro- carbo ns , an d. particulates. Early in the program, it was real i zed th at adaptation of existing industrial pollution contr ol tec hnology for processing tunnel air was only one of se veral possible control strategies that might be employed, The o ther p ossible strategies include auto exhaust source contr ol and tunnel ventilation augmentation. The cost and ef fee tivene ss of these latter control strategies were explored to a degree sufficient to establish a basis for comparison for the i n situ secondary pollution control approach. The present state of the pollution control tech- nology art potentially applicable to the tunnel problem has been covered. This section deals with the preliminary tech- nical design and cost evaluations for selected systems. The base model used for the feasibility studies is a 1-mile long, 250,000 CFM ventilation rate tunnel. D esign a nd ec onomi c studi es hav e been ma de of indust rial pol luti on co ntrol proces ses po t e n t i a 1 1 y appl icable to the remo val of pol lu tants from v e h i c u 1 ar tunnel atmospheres In add i tion , a stu dy ha s bee n made of the effect o f automotive exhaus t sou rce con trol measu res pro gramme d to go i nto effect in the deca de of 1 970-1 980, on the averag e CO and hydrocarbon emissi on , c orrecte d for auto mobi le popula tion age. The result s of this la tter study i n d i c a te tha t a four- fold re- d u c t i o n in CO and hydro carbo n emiss ion 1 e vel swill result from p resen tly-man dated vehi cle exh aust c ontrol s and that the tu nnel polluti on pr oblem wi 11 c orresp ondi ngly diminish in s e eri ty unless ambi ent s tandard s are changed. At minimum, it app ears that tu nnel venti 1 at ion design must mak e allowance 113 c i 1 for the transi ent nature of the pollutant loadings, and at maximum, there is a good possibility that source control will eliminate the tunnel atmosphere problem. A compara tive fe a s i b i 1 ty and econ dy of tunnel v e n t i 1 ati on bl ower augment a t i o n vs . v arious s econdary poll uti on co ntrol p rocesse s has s hown t hat b lower ad dition or revi sio n is the mos t techn i c a 1 1 y and ec onomi cally fe a s i b 1 e route t all e v i at i n q the t unnel a tmosph ere n ollution burden at this time . Of a 11 of t he cont rol op erati ons, tha t of - catalyt i c ox i d a t i o n , uti 1 zing a 60% Mn 02/40 % CuO am b i e n t tempera ture catalys t, appe ars mos t prom i s i n g for in si tu tunnel use. Howeve r, desi gn was extrap ol ate d from 1 aboratory data, a nd fu rther d irect d evelopm ent wo rk is requi re d and recomme nded. From a techn i c a 1 v i ewpoin t, th ere are seri ous operabi lity q u e s t i o ns for catalyt i c o x i d a t i o n , a c t i v ated carbon adsor p t i o n a nd elec trostat ic pre c i pit a t i o n be cause the pol 1 utan t or pa rti cul a te cone entrat ion i n each c a s e is well be 1 ow t he lowe r limit of any known indu s t r i a 1 a ppl i cation Economi cally , only catalyt i c o x i d a t i o n appea rs to be near- competi ti ve with a u gmented bl ower capac ity. Spray s c rubbing was ass essed • as a p o t e n t i a 1 exhau st tre atmen t method for control of t he gros s tunne 1 emiss ion, a nd wa s found to be t e c h n i c ally feasibl e and e conomi c ally p romi s i n g , alt hough di rect test veri f i a t i o n i s d e s i r able. A short study of recycle air operations around the tunnel or tunnel section was made, and it was found that any degree of recycle would give rise to an increase in tunnel pollutant concentration above the level obtained in once- through air operation. The detailed review of the state-of-the-art for both source control and tunnel ventilation air treatment technology yields a number of significant conclusions which bear directly on the technology feasibility determination. In summary: 1. Control technology available for the removal of vehicle-derived pollutants comprises two distinct categories: (a) Source control technology already developed for removal of pollutants from automotive exhaust at exhaust conditions. (b) Industrial technology which must be adapted or extrapolated to tunnel air pollutants and concentration levels, as well as to ambient temp- erature operating conditions. 114 V e h f c u 1 a r pol lutant so urce controls are al ready parti ally in o peration and an e s c a 1 a t i ng de gree of a pplication and e f f i c i e n cy. is now mand ated by law for the imme di ate fi ve-yea r period. Some proven c ontro I equipme nt meeting pro- posed fu ture emi ssion standards already exists, and a choice o f competitive t e c h n i q u es wi II appare ntly become avail able in the n ear futur e. Significant decrease s i n vehicular emissions have al ready occur red. In most cases, the adaptation of con- ventional industrial control technology to the tunnel air treatment will require experimental development and field tests This required preliminary work has not been done, and no present tunnel treat- ment installations exist. 4. 5. It does not appear reasonable to expect exhaust control techniques developed to operate at the high-temperature, high- pollutant concentration exhaust conditions to function at the 150- fold dilution, ambient-temperature tunnel air conditions. In pollution control design a prime rule is to treat at the point of maximum con- centration prior to dilution - a rule based on both economic and efficiency considerations, as well as functional feasibi 1 i ty. The above preliminary conclusions strongly indicate that tunnel air treatment is not likely to prove to be a tenable control strategy at this time, should alternate means of control be available. On the other hand there are a few standard tech- nologies such as electrostatic precipitation, which appears to be more suitable for tunnel air processing than for source control 115 application. This section will be concerned with the evalu- ation of the capabilities of all potentially applicable tech- nology in the context of available alternates and the changing nature of the source emissions. Tunn el Pollution Con trol Strategie s I. I . I ! ..! ..II. , — II..!.. »— — ! I — » ! ~ I— ~ ~ ^t- — The application of pollution control equipment for the removal of pollutants from tunnel air is only one of several control approaches open, and it is necessary to con- sider these alternates, if only from the point of technical and economic perspective. There are four apparent tunnel pollution control strategies: A. Control of traffic loadings and speed within tunnel. B. Increased ventilation rates. C. Exhaust source controls. D. Tunnel air treatment. Pragmatically, the first two control strategies are standard present control modes for tunnel pollution problems, although recent studies'^ 8 ) indicate that these techniques are not yet fully realized. Se veral of the newer E uropean tu nnels , such as the Mon t Bla nc Tun nel an d Great St. Bernha rd Tun nel , o pened in the I960' s , ut1 lize t raffic f low contro 1 as a means of 1 1 mi tin g in- tunnel emi ss ions (20) The Mon t Blan c Tunn el utilize s a s ystem of con trol lig hts for ve hides in an d e n t e r i n g the tunne 1 to c ontrol s peed betwe en 25 and 37 mph. The Gre at St . Bern hard T unnel us es traffic count ers to con- ti nuous ly mo ni tor the nu mber of vehicles i n the tunnel , and enterin g tra ffic i s stop ped when the maxim urn num ber of vehi cle s is reache d. Wh lie t h e s e are non- urban tunnel s , the Lincoln Tunn el und er the Hudson River, is report edU8) to be install ing t raff i c flow control s utilizing traff i c c o u nters tied in to a comput er whi ch will in turn co ntrol traffi c sig- nal s. The o bjecti ve i s to simul taneously reduce the n umber of vehi cles in the tunne 1 at any one time by inc reasin g the average vehi cul ar speed in the t unnel. F i gure 2 9, tak en from Ot t U 02 ) show s the reductio n in CO em is si on with in- crease in av erage vehi cl e speed and it is appare nt tha t in ere as ing a verage vehic le speed is a dire ct CO contro 1 measure 18 Information supplied by Kyle' ) on the Sumner Tunnel in Boston Harbor showed that the total longitudinal air speed in the tunnel was 14.7 mph, of which the ventilation air speed constituted only 1.3 mph, while the vehicle sweep effect contributed 13.4 mph. It should be noted that the 116 If) UJ 1 c x o z 1 o i 5 o to SPEED 0TT(I9 DC CARBON X 29 5 to VS. UJ OF SOURCE FIGURE VEHICLE if) CM UJ -J EMISSIONS o X >UJ u. o o CJ Q ^*^*. UJ UJ 0. 0) UJ < UJ ID > < _ lO o lO o IT) O to o to ro CM CM o 6 o O o O <5 6 \W21 l (3311HN3 3QIX0N01N N09HV0 117 , 1 . i h Re serve capaci ty and fan spee d con trol are i nvar- i a b 1 y built into t unnel v e n t i 1 a t i o n sys terns in order to hand! e peak traf fi c 1 oad i n g s , with out i ncurr i n g the a d d i t i o n a 1 opera ting ex pense of con stantly ru nning at m aximum ve n t i 1 a t i o n capac ity. T heoret i c a 1 1 y , this des ign a pproa ch could be carri ed one step f urther by adding fans to a ugment pe ak venti- 1 a t i o n capac i ty Howeve r, v e n t i 1 a ti on ducts in exist ing tunne 1 s are of a f i x e d s ize, and t he pr essur e head of the v e n t i 1 a t i o n blower s is s i m i 1 a r 1 y f i xed by th e peak fl ow re- qui re ments f or tha t duct size. Be cause the blower he ad re- 2 qui re ment is a fun c t i o n of (gas ma ss fl ow ra te) thro ugh the f i xed -size d uct , a n atte mpt to dou ble t he pe ak ventil a t i o n flow rate wi 1 1 cau se a f our-fold i ncrea se in the head 1 oss . Depen ding on the h ead-ca pacity cha racte r i s t i cs of the original fan it is p robabl e this higher he ad wi 1 1 no t permit the o r i g i nal fan to de vel op any more t han a frac t i o n of i ts low- head flow ca paci ty Thu s reductio n of pol 1 u tant cone en t rati on by fl ow augm en tat i on for an e x i s t ng tu nnel will depe nd on the d egree , if any , of o ver-design i n t he or iginal ve n t i 1 a t i o n syste m , and the he ad-cap acity char acter i s t i c s of the original bl owe r. Thi s comb i n a t i o n of facto rs wi 11 ob viously b e differ- ent f or each tunne 1 , and would req ui re check i n g of t e initial v e n t i 1 ati on system d e s i g n. Altern ately , it may be po s s i b 1 e to re place t he bl a des on the o r i g i nal f an to yield he ad com- p a t i b i 1 i ty w ith th e a d d i t i o n a 1 h i g h-hea d uni t. The a d d i t i o n of i n termedi ate ve nti lat ion shafts is a nothe r possibi 1 ity but t his w i 1 be f e a s i b 1 e only for spec i f 1 c tunnels , and this c o n s i d e r a t i o n is b eyond the scope of th i s re port. Direct vehicular exhaust control techniques have received the major share of attention and implementation. There appears to be no question that every possible effort has been, and will be made, to protect the present industrial 118 o h i1 , , , , and private investment in the internal combustion vehicular engine by the further development of source controls. Present differences between Federal authorities and the automotive industry concern timetables for emission reduction, rather than the degree. In a re cent paper (103) rev iewi n g the pr ogress of the a utomo t i v e in d u s t ry in control 1 ng em i s s i o n s , i t was claim ed th at 1971 model pas senqer ca rs ha d 85% le ss hydro- carbo n emi ssi ons and 65% le ss CO emi s s i o n than ea r 1 i e r uncon troll ed mode Is. Jense n also in d i c a t ed that similar reduc tion in N0 X emi ssi ons could be expec ted for 1973 model cars. No data we re introdu ced to su pport the mag n i t u d e of the c laime d emiss ion reduct i ons , but neve rtheless , e n q i n e d e s i g n cha n g e s in recent mo del years have al ready produced signi f i can t reduc t i o n s in e xhaust em i s s i o n. Whil e previous intro ducti on of 1 ow-emissio n vehicle s i s now affe cting "aver- age" v e h i c le emis si ons, and will con t i n u e to lowe r this avera ge as the ve hide popu 1 a t i o n in cl ude s a grea ter pro- porti on of these low- emi ssi on v e h i c es , p redi ctio n of the quant i t a t i ve effe ct of the programme d red u c t i o n s is desirable, and t his w ill be done below Be cause source contr ol te c h n i q ues appear to be succeed ing, proje cted em i s s i o n stan dards and air q u a 1 i ty cri teri a goa Is th at form erly a ppear ed un atta i n a b 1 e are now p o s s i b 1 e, if not probabl e. Tu nnel v e n t i lati on syst em design must ta ke in to ac count t he new Fede ral a i r q ual i ty cri teri a which a re 1 i kely to be c onsi de rably more str i n g e n t than pre- sent al lowab 1 e po 1 1 utant conce ntrat ion 1 i m i t s. The most recent i nfor mati o n on pr imary stand ards ( 104) is giv en in Table 2 4, an d the propos ed CO level (max imum 1 -hour concen- tration once a ye ar) of 17.2 p pm is part i cul a r 1 y i m portant when co mpare d to present d e s i g n 1 im its o f 10 to 20 ppm CO. In view of t he pr oposed Federa 1 sta ndard s f o r autom oti ve emi ssi n red u c t i o n in t e 1971 -1980 peri od it appe ars cer- tain th at th e ave rage CO emi ss ion 1 evel wi 11 c o n t i n ue to decline , and with respec t to t his p ollut ant al 1 owa nee must be made in v entil a t i o n d e s i g n for t his d ecre ase. H owever it is a lso v i rtua lly cer tain t hat , as ex haus t contr 01 tech- nology prove s to be effe cti ve in re ducti on o f peak pol 1 utant 1 oading s, th e all owable i n - 1 u n nel a mbi en t po 1 1 u t i o n concen- tration 1 i mi ts wi 11 also be 1 o wered Exhaust Emission Projections The design basis for the ventilation of vehicular tunnels is the peak traffic load (exhaust emission rate) plus a maximum CO concentration limit. It should be noted that prevailing vehicular CO emission data obtained from test data at the time of the ventilation design are now used as the 119 TABLE 24 NATIONAL AIR QUALITY STANDARDS PROPOSED BY EPA PRIMARY STANDARDS Air Pollutants pg/m3 ppm CO Max. 8-hr. cone, once a year 10, 000 11.4 Max. 1-hr. cone, once a year 15,000 17.2 HC Max. 3-hr. cone, from 6 am. to 9 am. once a year 125 -- NOx Annual arithmetic mean 100 0.19 (as NO2) 24-hr. cone, once a year 250 0.47 (as NO2) SOx Annual arithmetic mean 80 0.21 (as SO2) 24-hr. cone, once a year 365 0.96(asSO2) Particulate matter annual geo. mean 75 Max. 24-hr. cone, once a year 260 -- Photochemical oxidants Max. 1-hr. cone, once a year 125 Adapted from Pollution Engineering, 1971 120 v v 1. , . 1 basis for estimating ventilation needs. Thus, for the Straight Creek Tunnel ventilation system des1gn(l05) f CO emission test data obtained in 1964 road tests were utilized, Ventilation needs for the year 1990 were also calculated based on these 1964 emission data. Because 1964 is a year representative of virtually uncontrolled exhaust emissions, it may serve a conservative design base, but a 26-year ex- trapolation in the light of the success of source control techniques represents an unknown degree of over-design. u- In order to pr operly d e f i n e the tunne 1 air pol 1 tion problem in a t i m e - v a r i a n t frame work it is nece ssary to re view and quant ify t he effe cts f man dated autom otive sourc e contro Is on f utur e emiss ions, Exh aust s ource control techn iques ha ve bee n ope r a t i v e for s evera 1 year s , an d will be in creasing ly imp lemen ted at highe r eff i c i e n c ies i n the immed iate f i e-year peri od. Th e que s t i o n is: h ow mu c h will this control strate gy af feet tu nnel envi r onment s i n the next 10 ye ars, and will furth e r i n - unnel cont rol be nece ssary? As no ted abov e , tun nel v e n t i 1 a t ion s ystem s appe ar to be d e s i g ned for the em i s s i o n s e x i s ting at th e time of d esign i n i t i at ion, b ut are then wri tte n off over a 20 to 30 year p e r i o d of dec reasin g emi s s i o n s Sys terns amorti zed o ver this period s hould be so design ed as to t ake ad vanta ge of a decre a s i n g v e n t i 1 a t ion 1 oad. W ith t he re cent d evelo pment of val id predi ct ive mo dels, togeth er wi th th e firm ing o f emi ssi on contr ol timet abl es , it i s now p o s s i b le to predi ct th course of fu ture aut omoti e emi ssi ons. Table 25 lists the e xhau st emiss i on st andards pro- posed by both the Federal gove rnme nt and th e Sta te of C al ifor- ni a. These standa rds mus t be cons idered te n t a t i v e , i n a smuch as Fe deral standar ds are prese ntly beinq fo rmul a ted, an d are expec ted to be ann ounced some time in 1971. If Califor nia stand ards prevai 1 , then 1 975 m ode! cars w i 1 sho w a dec rease of 77 .3% in hydroc arbons 47.8 % in 75% i n N0 i n , CO, and X exhau st emissions compare d to 1971 model s Alth ough Ta ble 25 sizes the Cal iforni a stan dard s , recent news announ cements indicate tha t the E nvi ro nmen tal Prote c t i o n Agency may accel erate the Cal i form* a time tabl e in its own F ederal schedule. Shoul d this be the case , then the schedule indie ated in Table 25 wi 11 prove to b e conse rvati ve, assuming of CO urse, f ull compl iance by the automot ive i ndus try. The data of Tab le 25 may b e combined wi th pass enger car (and tru ck) p opul ati on compo si tion data t o gener ate a qua nti tat ive pred i c t i o n of f utur e emissions,, a n d t h i s typ e of analysis has been de veloped in de tail by Blum' 107) in hi s Mode 1 I prese n t a t i on. Previous estimates of future automotive exhuast emi ssions (1 °8) have made allowance for the projected increase in the total automobile population. This is a necessary approach when computing the net effect of control technology 121 TABLE 25 EXHAUST EMISSION STANDARDS AND GOALS Emission Levels, Grams per Mile Year HC CO NOx Particulate 1970 2.2 23.0 1971* 2.2* 23.0* 4.0* 1972* 1.5*. 23.0* 3.0* 1973 2.2 23.0 3.0 1974* 1.5* 23.0* 1.3* 1975* 0.5* 12.0* 1.0* 1975 0.5 11.0 0.9 0.1 1980 0,25 4.7 0.4 0.03 Evaporation Losses - 6.0 grams per test in 1970 in California and 1971 nationwide. California only. 122 a on atmospheric pollution in urban areas, and where total emissions are of prime interest. However, vehicular tunnels have a finite length, and a design base maximum traffic capacity at a fixed emission level. Emissions in tunnels will thus be affected only by the age-composition of the automobile and truck population, and not by the expansion or gross numbers of the car and truck populations. Age-composition data have been calculated by Blum^O?) f r om figures published in Automobile Facts and Figures (' 09) and these data on automobile longevity are presented in Table 26. In the absence of information on changes in ownership patterns or automobile longevity with economic conditions, it may be assumed that Table 26 repre- sents a composition that will be relatively stable with time, and that the age distribution of 1963-1964 will con- tinue to hold for the 1970-1980 period. Blum derived a statistical model relating the total rate of vehicular emissions to driving characteristics and vehicle emission controls, and while this model is best projected by computer, Table 26 does allow arithmetic approximation of Blum's Model I analysis, using the emission control schedules of Table 25. As Blum points out, T able 26 indicates t hat, while the averag e age of the automobi le population is ap proximately 6 years, t he media n life of an individual vehicle is 11 years Further, w hile car s 16 years an d older constitute 1 to 2% of the tot al car p opulation in any given year, 10% of the cars produ ced in a model year a re still in use 16 years later. Be cause of this longevi ty characteristics, there is a time- lag in the effect of any change in emission on over- all emissi on level s. Thus, eve n if all cars produ c e d in 1972 were to have little or no emissions, it would be 1978 (6-year av erage ag e) before the 1972 and later mod el cars would make up 50% of the total car population, 198 1 before they would make up 75% of the p opulation, and 1986 before they would have re placed .95% of the older cars. T ruck re- 10 placement is even slower'' / w i th a 50% replaceme nt age of 7 years, 7 5% repla cement time o f 1 3 years , and a 9 5% re- pi acement of 18 ye ars. These d ata make no allowan ce for any in ere se in th e rate of pro duction of new mode Is, and are thus c onservat ive in terms of the effects of e xhaust controls . Any inc reases in the rate of new model producti on (with cont rols) wi 11 be reflect ed in a decrease in average age and a greater influence on total emissions of the new vehicles. Combining the above data with the projected control timetables enables a stepwise arithmetic calculation of com- parative CO and HC emissions for the years 1970, 1975 and 1980. These calculations are presented in the Appendix II 123 TABLE 26 AUTOMOBILE LONGEVITY Fraction of Cars (A-l) Years Old in Fraction of Cars "A" Preceding Year Originally Produced Age of Car Surviving to Become that had Survived (Years) "A" Years Old iin: "A" Years in: 1963 1964 1963 1964 2 - 3 .999 1 .000+ 3 - 4 .999 .991 .999 .991 4 - 5 .990 .990 .990 .981 5 - 6 .974 .975 .964 .956 6 - 7 .957 .952 .922 .910 7 - 8 .936 .916 .863 .834 8 - 9 .906 .909 .781 .758 9 - 10 .856 .859 .669 .651 10 - 11 .813 .822 .544 .535 11 - 12 .780 .770 .424 .412 12 - 13 .764 .753 .324 .310 13 - 14 .769 .752 .249 .234 14 - 15 .752 .757 .187 .177 15 - 16 .773 .731 .145 .129 16+ .797 .825 .116 .107 Median Automobile Life = 11 Years (Approx.) Average Age of Automobile Population = 6 Years (Approx.) 124 and the results are plotted in Figure 30. It is obvious that, despite the time-lag effect, the degree of control programmed is so sharp that the indicated reductions in average emissions are considerable. The average hydro- carbon emission will be reduced from 660 ppm in 1970 to 156 ppm in 1980, and the average CO emission will decrease from 25,790 ppm to 6,120 ppm over this same period. This calculation makes no assumptions concerning the nature of the exhaust control technology to be employed, but should it be of a non-integral nature, such as a catalytic con- verter, which can be added to older models, then the decrease in emissions would be even more marked than shown in Figure 30. The i ndicated four-fold reduction in CO and hydro carbons in the immediate decade resulting from the i m p o s i t i o n of e xhaust controls is substantially equivalent to a four-fol d increase in tunnel ventilation capacity over origi n a 1 design levels (discounting the decreases in average emi ss ion levels that have already occurred in the 1964-1971 p e r i o d). The q uestion naturally arises as to whether or not a u x i 1 i a ry t unnel ventilation or pollutant removal measures are, o r w i 1 1 be , required in view of the apparent effective- ness of the exh aust control approach. The only answers that can b e ventured at this time are: 1. If no changes are made in the allowable ambient tunnel co ncentration levels used as the initi al ventilation system design basis, the n additional controls will not be requi red, and source con- trol will elimina te any excessive tunnel pollutant loading problems, 2. Tunnel control te chnology will be needed only in the event that ambient quality criteria call for pollutant reductions in excess of thos e presently scheduled via source exhaus t controls. Because national primary ambient air quality criteria are still in preparation, it will be necessary to review the control problems at the time these standards have been formulated and accepted. Tunnel Air Treatment: Problem Statement The design base used in assessing the feasibility of various tunnel air treatment techniques was a 1-mile long, single-tube tunnel with a ventilation air rate of 250,000 CFM Data on the gaseous pollutant volumetric emission rates for this base tunnel are listed in Table 27. These values are 125 iI Wdd**NONOO NOSUVOOUaAH 1S0VHX3 39VU3AV O o o o O o o o o O CO *0 o CO oI en o o I— LU a. o •— en reX LU UJ CD o LU o a: o CO cr CD ._0IX Wdd VN0N00 00 !SnVHX3 39VU3AV 126 TABLE 27 TUNNEL POLLUTANT LOADINGS Basis: 1 Mile Tunnel Length Level Single Tube, 2,000 Vehicle/Hr. 40 Mile/Hr. Average Speed a b Component Ft. 3/Hr.< ) ppm Lbs./Hr.< ) Carbon Monoxide 2 ,260 150 163.5 Ethylene 28 1.86 2.02 Acetylene 28 1.86 1.88 c Hydro carbon 68 4.53 17.6 < > Nitrogen Dioxide 8 0.53 0.95 Nitric Oxide 28 1.86 2.17 Acrolein 10 0.67 1.44 Formaldehyde 22 1.47 1.70 Sulfur Dioxide 16 1.07 0.26 Carbon Dioxide 10, 170 678 1,156 (a) Letter from F. Roehlich, MSA Research, March 19, 1971 to B. Lerner, Patent Development Associates (b) Based on 70°F. tunnel temperature (c) Assumed mol. wt. = 100 Assumed Ventilation Air Rate = 250, 000 cfm. 127 g . - also stated in terms of parts per million (volumetric) and mass rates to provide comparisons with normal industrial pollution equipment capabilities. With the exception of CO, the ppm pollutant concentrations listed in Table 27 are representative of treated gaseous effluent concentration levels for most gas processing operations, rather than concentration inputs to such processes. A prel imi nary me as ure of the very small mag ni tude of the pol 1 u tion lo ading rat es may be obtain ed by com paring the lo a d i n g s to the assumed v e n t i 1 a t i o n air rate, w h i ch is rel ati vely 1 ow. Th e ventila tion a ir rate of 250,000 CFM is equi va lent t o a wei ght rate of 1 ,1 25,000 lbs /hr. Thu s , if total air t r eatment is to be c o n s i dered, the n it will be necess ary to proces s more th an 500 tons/hr o f air in order to rem ove le ss than 25 Ibs/h r of p ol lutants other tha n CO and CO * n the ca se of the i n d i v idual poll utants, t he Z' select i vi ty requi re ment is m uch mo re extreme For ex ample , to rem ove th e eye i rri tants , acrol ein and fo rmal dehyd e , in- vol ves the r emoval of 3.2 lb s/hr from the t otal 1 ,12 5,000 and r lbs/hr air , for NO x 3.0 Ibs/h Th e com binati on of high total gas proces sing i capaci ty wit h the extre mely low CO ncent ratio n leve Is i n d cated in the Tabl e 27 d ata, cal 1 s for a remo val se lecti vi ty which is h i hly u n i q u e for i ndustr i al a 1 r tr eatmen t tech- n i q u e s , and even for mo st sp e c i f i c ally s e n s i tive p ollution contro 1 oper ati on s such as a dsorpt ion. The cl oses t pro- cessin g anal og wi t h s i m 1 lar select i vi ty requ iremen. ts is extrac tive m etal 1 urgi ca 1 ope rati on s i nv o 1 v i n g the removal of a rare metal such as ur a n i u m from a low -cone entrat ion ore, typi ca lly 0. 5% fo r uran ium o x i d e . In t he la tter c ase ? not only i s the conce ntrati on 50 to 1 000-f old h 1 g h e r than for i n d i c a ted po 1 1 uta nt con centr a t i o n level s i n tunnel venti la- t i o n a i r , b u t the cost- benef it rel a t i o n ships for u ranium are qu i t e d i f fere nt tha n for pol lu tants , whe re the health b e n e f i ts are stil 1 not fully d e f 1 n ed. The tunnel air treatment problem becomes even more complex when each pollutant is matched against the re- moval process judged to be most applicable under normal cir- cumstances. This has been done in Table 28, which briefly summarizes the results of an evaluation of the current opti- mum control process art with respect to each pollutant. Also given in Table 28 are particulate data. The process selections listed are preliminary and "apparent" from an engineering point of view; they should not be considered feasible or recommended at this point. It is obvious from Table 28 that a combination of processes will be required for the removal of most or all of the pollutants. Essentially, the 1,125,000 lbs/hr of tunnel air must be processed several 128 - TABLE 28 PRELIMINARY SINGLE -POLLUTANT OPTIMUM PROCESS INDICATION Component ppm Process Indication Carbon Monoxide 150 Catalytic Oxidation Ethylene 1.86 Catalytic Oxidation Acetylene 1,86 Catalytic Oxidation Hydrocarbons 4.53 Carbon Adsorption Nitrogen Dioxide 0.53 Water Absorption Nitric Oxide 1.86 Zeolite Adsorption Acrolein 0.67 Water Absorption Formaldehyde 1.47 Water Absorption Sulfur Oxide 1.07 Water Absorption Carbon Dioxide 678 Water Absorption a Particulates( ) /Vnr Electrostatic Precipitation (including benzene 500 soluble organics) (150) (a) Letter of December 30, 1970 from F. Roehlich, Jr , MSA Research to B. J. Lerner, Patent Development Associates, Inc. 129 , , . g i 1 1 , - times to yield multi -pol lutant removal capability. One of the hidden difficulties in Table 28 is the fact that each process was selected for the individual pollutant, neglecting the interference and interaction effects known to exist. For example, gas absorption of NO2 in water is a standard operation for this component, but it is doubtful if this soluble acid-gas can be absorbed in the presence of much higher concentrations of another acid-gas: CO2. Further, even when considered alone, the concentrations of NO2 in tunnel gas are far below the concentrations normally treated in sorption operations, and indeed, below usual effluent treated gas concentrations. T he sele c t i n s listed i n T able 28 a re bas ed entirely on con s i d e r a t i n f the nature of th e si ngle pol lut ants with- out re feren ce to t heir tunnel s i te f generat ion. Addi ng this 1 atter factor lead s direct ly to f easi bi i ty de termina- t i n s , whic h will be co nsidered i n d e t a i 1 b e 1 ow. H owever i it may be n oted he re th at the c losed -system a spect of a p p 1 cation of t unnel a ir tr eatment in si tu immedi ately rules out some f the standa rd tr eatment proce sses of T able 2 8 , such as aqu eous a.bsorpt ion. Re-use of we t-scrubbe d air within a tunn el wi 11 not be pe rmi ssi bl e bee ause of t he 100 % humidity charac teri s tic of such treated air. This p i nts up one of the pa rticu larly u n i q u e aspects of t he tunnel venti 1 a t i n proble m; th e conce ntrat ion of p ol 1 ut ants is s low that im- puri ty -cont ri butio n or s u b s t i t u tion by a trea tment operation c n s t i tutes a seco ndary p 1 1 u t i on pr oblem. Tunnel Ventilation Costs As i ndi ca ted a bove an al t ernate t tunnel a i r - treat ment for pol 1 u tant remova 1 is i ncreased tunnel ven t i 1 a tion by m eans of fa n add i t i n Al th u g h th s latter me thod may i nvol ve po s s i b 1 e rec onstru ction problems for existi ng tunne 1 s such recon struc tion i s much more p r b a b 1 e in t he case of p ollut i on c ontro 1 e q u i pment i nstal 1 a tion. This factor aside , th e ass essme nt of i ncre mental tunnel ventilation costs provi des a yar d s t i c k aga i n s t w h i c h t he compa rative capi tal and pera ting costs of a ny ind i v i d u a 1 pollut ion control method can b e me asure d. W hi le such c ost c ompari so ns are by n means di rec t, t hey c an se rve a s a pr e 1 i m i n ary guid e , until s u ff i cient data beco me av a i 1 a b 1 e to permi t v a 1 i d cost-b enefit calc u 1 a t i n s Tunne 1 ve n t i 1 a ti on base costs provi d e a cons ervative me asure i n a s m uch as a 100% incre a s e in venti 1 a t i n f low theoret ically provi ded for a 50% decre a s e in conce nt rati on for all ai r pol 1 u tant s i n the t unnel air. On th e other hand, ~Tn~e p Dilution contr ol t e c h n i ques c n s i dered be! ow are gene rally selec ti ve for ne r two spec i f i c c n t a m i n a n t s T h i s limited s e ecti vi ty prope rty is pa rtly of f se t by t he h i her effi ciency of t he pol 1 u tion cont rol p roces s , so that d irect co st comparis ons 130 ., : r . d at this stage of changing ambient standards becomes uncertain Tabl e 29 pre sents a tabul a t i o n of ca p i t a 1 costs of fan a nd motor combi nat i ons to yield a ne ak ven t i 1 a t i on air rate of 250,00 CFM ag a i n s t di f fere nt he ad 1 os ses It should be no ted that this is an ar bi tra ry examp le and does not - neces sarily ap ply to a 11 ty pes of t unnel s and tunnel v e n t i 1 a ti on systems These c al cul ations w ere b ased o n the data con- t a i n e d in Proj ect No. 170-3 (212) (1 966) Report on Ve n t i 1 a t i o n Studi es of the Col orad o Dep artment of Hi ghways for t he 1 .6 mi le Strai ght Creek Tu nnel . These latte r data were corrected to se a level h orsepowe r req ui rement s and corre cted f or the cost index c h a nges bet ween 1964 and 1970 . The basi s for Table 29 was t he use o f thr ee fans 1 su pply , 1 exha ust and 1 sta ndby, eac h of 250 ,000 CFM rati ng, a c h o i c e deli berately made to provid e a maxi mum ( and thus cons ervati ve ) co st basis. Add it ional ly extrapol ated unit p r i ces o f the motor- fan corn- b i n a t ions in T able 29 were known to be i n t r i n s ic a 11 y high; di rec t q u o t a t i on from a man ufacture r on two 12 5,000 CFM vane- " axi al motor-fa n comb in a t i o n s at 1.5 sta tic he ad i n i cated a cos t of $11 , 250 for the p air. T h is co mpares with the Table 29 value of $18, 500 f or the s ame f low ca pa city at 1" stati c head. Ta ble 2 9 pro v i d e s a base cost of the bl owe r aug- men tat i on ro ute o f pro v i d i n g e i t h e r i ncr emental vol urn e or static head (or b oth). Thus , to pr ovi de an i n c ement al 250,000 CFM f 1 ow for a n i n i t i a 1 250 ,000 CFM tunn el pe ak venti 1 a tion rate at a 2" stati c pre ssure head, w oul d requi re a total capi tal c harge for the addi t i o n a 1 blower s of $102,600. The new head of 4 .2" W .G. woul d sat i s f y the squa rinq of the origina 1 hea d req ui rem ent, and the annua 1 capita 1 cha rges for the adde d sys tern o n a 30-y ear a morti z a t i o n s chedu le would be $6,6 80. Addit ional ly, Tabl e 29 may b e used t o est imate the cap ital costs i ncu rred in incre a s i n g the sta tic h ead at constan t del i vere d vol ume, a s i t u a t ion t hat woul d res ult from the use of a f i xe d-bed p o 1 1 u t i on co ntrol unit in a ve nti 1 ati on 3" tunnel . Tab le 29 show s that a n inc remen tal W .G. h ead would in vol ve a ca pita! cost increme nt of $26, 100, and an a n n u a 1 i z e d charge incre ment of $1 ,700. The tunnel ventilation fan operating costs were also adapted from the Straight Creek Tunnel Design report, and the electrical energy costs were assumed to be the same as in the report. In the absence of a specific reference tunnel location, the electrical power cost data for any location may be used as a reference case, provided the detailed cost break- down is provided, as was the case in the Straight Creek Tunnel report. The calculated data are summarized in Table 30, and attention is called to the assumed operating rate of half-peak load for 365 days/year plus peak load of 44 hours per week. 131 1 1 4 i1 2l TO o © O •a s! &> oo in OO 3 •t! H ON cs vO CX ed •» s rt 43 vo NO < O U *«- •ao a o o o •r-l o o o in o vO 12 73 4J vO vO to CO o o Ov CSo u O p E- U 54 o o TO 3 o •3 H in c h— a cs o TO * S*H I-H % in O 2 *-> o o o vO r— TO o o I o o ME o o o 73 4-» O 4-J 8 ex. « OWER TO 8 TO O to CM CM u IRE —jCJ o CO «5- .?? o Pi > § B S RE 5 a CO J CM PS 08 0) s CO TO o HEAD T3 <— o w to o <=> 73 O VENTILATION o e S S O o u fa ° S o u «™i m o vo 5° £ o cd TO OF o 4-1 in in i— 73 o o in r- CO 4-> « s ««- »• feG- 2 g <4H § a, N o cd in 3* HPz to vO O u oj H o p< 132 4 « —t i 4 i CO 1/5 ON CO 0) o CO 13 u, o CM a* Q ° CN O S3 vO cn u CO o cm <§> 4-> o "* o\ ->* 6 CO o o o ^ m oo o n u £ o CO o•* J-l t^ 3 t— o d 43 « •^ 133 , 1 , i1 s , It s hould be o b v i o u s at t his p o i n t t h at if l nse rtion of a pol 1 u t i o n control u nit i n the tunnel v e n t i 1 a t i o n sys tern 1" incu rs a head loss of or m ore , t hen ad d i t i o n al fa n cap a- city wi 1 be r equi red. Howev er , th e use of thi s fan al on e, with out i nstal 1 a t i o n of the p o 1 1 u t i on con trol u nit, is it self capa ble o f red u c i n g the pol 1 u tant c oncent ration 1 eve Is. Thus , the cost- benef it p o t e n t al of pol lu t i o n c ontrol unit wi th sign i f i ca nt he ad loss mu st ou twei gh not o nly th e cap ital and oper a t i n g cost s of the a dditi onal f anpowe r requ i r e d , but al so the pol 1 u ti on improvemen t ben efit o f the v e n t i 1 ati on pote n t i a 1 pres ented by t he fan inc remen t i t s e If. W hile t his w ill d epend on t he he ad-ca pa city cur ves o f the origin al fan s i n exist ing tunn els pragm a t i c a 11 y t h i s w o u 1 d i n d i c a t e that the head 1 oss aero ss th e pol 1 u t i o n con trol equipm ent be held to le ss th an the norma 1 hea d rating o f the o r i g i nal fa n , and pref erabl y to a ne g i i g i ble h ead loss. Ther e are very f ew pol 1 utio n con trol proc esses that have an i nhere ntly 1 ow or n e g 1 i g i ble press ure loss char acter istic, but in v iew of the i ncreme ntal v e n t i 1 a t i o n al te mate to h i g h h e a d - oss e quipme nt , th e 1 ow- 1 oss equip ment will poss ess a two-fold econo m i c ad vantag e. Process Feasibility: CO and Hydrocarbons Be cause the pres ence of CO and hydroca rbons , in- c 1 u d i ng oxyg enated hy droca r b o n s , i s the r esult o f inc omplete combu sti on completi o n of combusti on is a n o b v i o us me thod of remov ing the se pollut ants from tun n e 1 air Howe ver al though CO an d hydro carbons c n s t i tute the major f racti o ns of the pol 1 u tant lo ad, and o x i d a t ive remo val of these f racti o n s is i i the p referre d i n d u s t r ial t reatment method 9 n s p e c t o n of Table 27 led to the p rel im i n a ry j u dgement that t herma 1 o x i d a tion wa s not fea s i b 1 e This concl us ion is based on the fact that th e concent ratio n 1 eve! of com b u s t i b 1 es in the tunne 1 air a re severa 1 ord ers of m a g n i t u d e lower than any known feed s tream to a the rmal inc i n e r a t i on proc ess and that the a mbient temperatu re of the tun n e 1 air presen ts no thermal advan tage fo r such a proce ss. All of the energy i npu t and remov al for the requi red t hernial c ycle mu st be e xtern ally suppl i e d , an d thermal i n c i nerati on was no t c o n s i dered fea si ble 134 1 i . or treated in depth. However, some preliminary calculations were carried out to assess the magnitude of the economics of a hypothetical heat/cooling cycle. Ther e are two types of th ermal o x i d a t i o n pra c t i c e d ; di rect flame a nd i n di re ct hea ting, Becaus e the p roduc ts of combus tion of di rec t fl a me in c i n e r a tion wo uld pro bably add to the tunnel air p ollu tant c oncent rations of the same or greate r concen trati on 1 evel s as tho s e o r i g i n a 1 1 y prese nt in the tu n n e 1 air , thi s me thod w as jud ged not a p p 1 i c able . Assumi n g , ther ef ore , in di rect heati ng, and a temp eratu re increm ent of 1 000°F , Pr e 1 i m i n ary he a t i n g a nd cool ing c ost e s t i m a tes have been mad e. Fo r the heating p o r t i o n of the cycle, using a ther mal e f f i c i ency 1 evel of 5 0%, n atura 1 gas requir ements o f 5.5 6 x 10 5 CF H are indicat ed. If a co nser- vati ve estimat e of cool ing cy cl e op era ting costs is ma de, taking these a s equ al t o the n a t u r a 1 gas c osts fo r hea ting, then t he minim al an nual opera ting c osts fo r the t herma 1 cycle operat ion w o u d be $99, 200, b ased o n a tot al annu al op erating time o f 2,288 hours . E ven wi thout system capital char ges, this f igure is far i n e xcess of the a u x i 1 i ary ven ti lat ion costs. Fur the r, it sho ul d be noted that t he use of 5. 56 x c 6 105 CF H of nat ural gas as f ue 1 prod uces a total o f 3.7 6 x 10 CFH of combust ion g ases with their own sec ondary pol lu tion 1 o a d i n g. Thes e wou Id h ave to be ve nted fr om the tunne 1 by a sepa rate flu e , bu t si nee th ey amo unt to about 2 5% of the total vent i 1 at ion a ir r ate , p rovi si on for this in exi s ting tunnel s would i n v o 1 ve c o n s i d e rabl e constru c t i o n Thus , both t e c h n i cal and econo mic i n d i c a ti ons for the rmal ox i da ti on appear to be n e g a t i ve. The norma 1 i n d u stri a 1 cataly tic ox idati on pr ocess employs o perat ing t empera tures several hundr ed de grees lower than thos e use d in therma 1 oxi d a t i o n t e c h n i q ues , but t hese neverthel ess w ould consti tute apprecia ble th ermal cycl ing costs for tunn el ai r trea tment . What is req ui red i s a n ambient , or ne ar-am b i e n t tempe rature c atalyt ic ox idati on operation , to avoid both therm al cycl i ng and the secon dary pol lutant prob 1 em o f auxi 1 i a ry fuel -bu r n i n g to su pply thermal - energy, While a 11 teratu re se arch fai led to find any i n d u s trial low -temp eratu re o x d a t i o n proces ses fo r pol lutan t re- moval , tw o rec ent 1 aborat ory d evelopme nts ap peare d to satisfy the low-t emper ature requi remen ts. The first of t hese is a v "commerci al" 6 0% Mn 02/40% CuO catalyst teste d by Canno n (58) on automo ti ve exhau st and repo rted to have a thre shold acti v- ity tempe ratur e of 25°C. Desp ite seve ral di rect i n q u i ries , no furthe r i nf ormat ion co uld b e elicit ed on this mater i al , which app ears to be s i m i 1 ar to Hopcal i te. B ecaus e the test condition s rep orted for t his c a t a 1 y s t were v ery e ncour aging , c a 1 c u 1 a t i ons o f the requi red c atalyst vol ume and heat loss - were made to d eterm i n e t h e fea si bi 1 i ty of la rge s cale a p p 1 i 135 cation to the 250,000 CFM base tunnel air case: Cannon Catalyst : 60 Mn02/40 CuO Test Conditions: Space Velocity = 10,880 hr Operating Temperature = 25°C Catalyst Density = 0.88 g/ml Volumetric Air Flow = 250,000 CFM a. Catalyst Volume Required Volume = {250,000)(60) = -, 380 CF 10,880 b. Pressure Drop Without information on the physical form of the catalyst, it is necessary to assume that it would be equiv- alent to 4-10 mesh granules in fixed-bed form. Assuming further a linear velocity of 80 ft/min, typical of granular fixed-bed gas processing: Case I : Face Velocity = 80 FPM Bed Area = (250,000 CFM)_ „ 3>125 ft 2 (80 FPM) .(Volume) Bed Thickness = = P?jj°? = 0.441 ft (Area) (3125) 5.3 inches Weight of Catalyst = (1380 CF) (0.88) (62.4 PCF) = 7,580 lbs From Figure 1, Appendix II: Pressure Drop/inch depth at 80 FPM = 0.725 in.W.G Pressure Drop through 5.3-inch bed = (0.725) (5.3) = 3.84 in. W.G. The above pressure drop calculation was based on a normal linear gas flow velocity through a fixed granular bed, and the AP of 3.84 in. W.G. may be excessive for ventilation blowers with limited heads. It is therefore desirable to calculate bed area and thickness for the case of limited blower head, and this latter value can now be assumed as not to exceed 1 inch W.G. 136 r Case II: Face Velocity = 45 FPM (Trial & error from Figure 1, Appendix II) 25 2 Bed Area = ( ?»??°? = 5,560 ft (45) Bed Thickness = -(^jj*Jg| = 0.2485 ft = (0.2485) (12) = 2.98 inches From Figure 1, Appendix II, at 45 FPM Pressure drop/ in. depth = 0.33 in. W.G. Total Pressure Drop = (2.98) (0.33) = 0.985 in. " The reduct i on in press u re dr op f om 3.8 to 1" W.G. is ac compl is he d by t he red u c t i o n in fa ce ve loci ty from 80 to 45 FP M, and a simul t aneous decrea se in bed t h i c k n ess f rom 5.3 to 3 inches, Howeve r , in order t con serve the i n i t i a 1 space vel oc ity value of 10 ,800 h r-1, th e bed f 1 ow area incre ases 2 2 from 3,125 ft to 5 , 560 ft . Thi s i s a 783 incre ase i n bed area , which wi 11 be ref lee ted in the c a p i t a 1 cost of t he unit in te rms of th e extr a bed constru c t i o n requ ired. Howe ver, the econo mic calcu lation s out! ined be 1 ow d e 1 i b e rately negl e c t this facto r, to pro vide t he mos t o p t i m i s t i c cost e s t i m ate f or oxi- d a t i o n. The o ptimum fixed -bed un it in term s of t he he ad-loss/ bed a rea cap it al cos t rel a t i o n s h i p can be d etermi ned f rom the c a p i t al and op eratin g cost s diffe rence for the bl owers in- vol ve d , from t he dat a of T ables 2 9 and 30, should this com- p a r i s on be req ui red. Whil e the ambien t-tem perature , MnOo/Cu catalyst appea rs to off er re asonabl e pro spects o f appiica bil ity to the t u n n e 1 air prob lem, pe n d i n g further developm ent effort, there are two a d d i t i o n a 1 a spect s to be considere d. First, the C annon tes ts we re made di re ctly on automoti v e exhaust, and t he concen trati ons of pol lu tants we re approx imately 150 times as great as t hose to be e ncounter e d in tun n e 1 air. Secon d, there is ev i d e n c e that complete oxidati o n of the hydro carbo n fractio n by ambient -temp erature catalytic oxidation may n ot be pos s i b 1 e , and c ertai n partia 1 ly-oxidi zed hydrocar- bons , such as acrol e i n and form al dehyde , are eye irri tants which are much more discern forti ng than their i n e rt precursors. The t e c h n i c a 1 feasi bil ity of ca t a 1 y t i c oxidation employing manga nese-copp er ox i d e cat alyst s may be consider ed to be ten- t a t i v ely promi sing, and fu rther di rect testing a t tunnel air pol lu tant cone entra t i o n s i s str ongly re commended One of the well-established feasibility factors for catalytic oxidation of automobile-derived pollutants is the susceptibility of the catalyst to poisoning by the lead salts and other particulates present in auto exhaust. Based on exhaust catalytic converter experience continuous long term 137 1 , , e o , use of a fixed -bed catalytic o x i d a tion p r ocess is not feasible w i t h o ut pr o v i s i o n f or pre -remova 1 of parti cul ates and a co st eva luati on must c n s i d e r the c ombin ed syste m. This con sidera ti on also appl ies to the se cond 1 ow- temperat ure ox i d a t i on ca'taly st dev eloped by Su wh\ch consi sts of a trans ition met al oxi de supp orted on acti vated carbon, When used on ammoni a synt h e s i s g as , t he lowes t temperat ure at whic h plus-90 % oxid at ion w as ob tained w as 120°C, a 1 thoug h the re were i n d i c a t ions t h at th i s was n ot the lowe st the rmal activity level a c h i e v a ble. While t his catalyst appea rs pr omi sing , the da ta prov i ded are labo ratory scale, w i t h s p ace v e 1 o c i t i e s of on ly 200 hr-1 at ambie nt pressure Tes ts at higher p ressur es (400 psi) and hi g her 1 space ve loci ti es of 4800 hr~ show ed only 503 c o n v e r s i on , so i that ext rapol a ti on to tunnel d e s g n i s un certa in. How ever , because of the acti vated car bon ba se for this o x i d a t i o n catalyst , i t i s pro bable tha t the feasibi lity and econ omics of its a p p 1 i c a tion will clos ely pa rallel that of a c t i v ated carbon a dsorpt ion , treated b el ow. Price information on the Mn02/Cu0 catalyst tested by Cannon was not available directly, and it was therefore assumed that this was a precipitated material. From published price data on the component oxides so prepared, it was esti- mated that the cost of the mixed oxides was approximately $1.80/1b. Provided that bulk quantities of this catalyst could be obtained at this price, the catalyst cost for the required 7,580 lbs would be $13,644. This latter figure involves considerable uncertainty because of the quantity involved and the. present lack of available information on commercial sources. Because of th e sirrn larity b etween f ixed- bed c ata- lyti c oxid a t i o n op erati ons an d a c t i v a ted carb on ad sorbe rs , i t w as fel t that a v a i 1 a ble ca pital co sts data for the 1 atter unit s coul d be app lied to the catalyt ic opera tion, wi th due corr e c t i o n for the cost of ca talyst a nd acces sorie s. B ecause adso rbers (and cat a lyti c oxid a t i o n u n its) 1 a r ger t han 5 0,000 CFM have n ot yet b een b u i 1 1 it is n cessary to ex trapo 1 ate from the 1 0,000 to 50,0 00 CFM range t o the 25 0,000 CFM 1 eve] of t unnel air flow of t he pre sent pro blem. F rom H EW, A P-68U12) the extrap olated i nstal 1 ed co st of an acti vat ed ca rbon adsorber trea ting 2 50,000 C FM of ai r i n c 1 u d i n g superh eater , con denser deca nter blower a nd mo tor, c ooling t ower, fi 1 ters , car bon f 11 er hou sing and vess el , wa s est i ma ted to b e $29 5,000 For cata lytic oxidatio n , it was a ssumed t hat the acces sory charges were equiv alent to 50% of the total i nstal led cost s giv i n g an e s t i mated capital cost of $14 7,000. However, this f igu re cont a i n s a carbon charg e of $ 0.45/lb, and cor recti ng f r the diff erence between this price and the $1.80/1 b cat alyst cost give s an i ncrement al co st of $10,233, for a t otal of $1 57,233. 138 Depending on catalyst life with and without pre-removal of particulates, a situation that should be experimentally determined for the low tunnel air particulate loading of 500 yg/m^, it probably would be cheaper to periodically replace the catalyst rather than install a suitable partic- ulate-removal device such as an electrostatic precipitator. Lack of catalyst cost and life data does not allow a firm estimate at this time, but assuming a 3-year replacement schedule at the above-estimated catalyst cost, plus 35% for the labor involved in change-over, the annualized catalyst charge would then be $4,775.40, and the particulate control unit is eliminated. The write-off period for pollution control equip- ment will vary with the potential corrosion severity of the process and system handled, but in any event will be faster than for a purely mechanical unit such as a blower and motor. For the comparatively mild conditions expected in ambient- temperature catalytic oxidation, a 20-year straight-line amortization period may be assumed. The capital and operating charges for catalytic oxidation may be summarized as follows: TABLE 31 - SUMMARY OF CATALYTIC OXIDATION COSTS 60% Mn0 2 /40% CuO Ambient-Temperature Catalyst Annual Unit Annualized Annual Fan Total Annual Total Capital Catalyst Capital Cost Capital Operating Charged) Replacement (Table 29) Charges Cost Cost (Table 30) $9,434 $4,775 $4,980 $19,189 $4,095 (a) Including 20% for taxes, insurance and maintenance. For the removal of small amounts of hydrocarbons from an air stream, activated carbon adsorption is the method of choice, primarily because of its selectivity and low-concen tration capability. A number of discussions were held with 139 1 engineering representatives of a major activated carbon supplier with reference to the practicality of a 250,000 CFM scale of operation, which was known to be roughly 10 times that of a large industrial installation. The con- sensus as to economic feasibility was negative, although technically, there was no indication of scale problems for adsorbable hydrocarbons, although capacity was questionable On a preliminary basis, removal of a single component or pollutant group from the air stream with a high-head loss fixed-bed operation is an expensive and less-than-i deal method of partial control. As shown in T abl e 27, t he con centr ation of hydro- carbo ns in tunnel air a t pea k loa ding, excl u si ve of acety- lene and e thylene, i s a bout 7 ppm Bas ed on adsorpti on i s o t h erm d ata supp lied by Pi ttsbu rgh Ac t i v a t ed Carbon Com- pany, ther e will b e no ads or pti on of et hylen e, acetylene or fo rmald ehyde at the 1 or 2 ppm conce ntrat ion levels at which thes e compon ents are p resen tint unnel air. Based on he xane adsorpti on da ta , a t 77° F and 1 psi a, 30 lbs hexane w i 1 be ad sorbed n er 10 lbs carb on , so hydr ocarbon adsorption 0-5 at 7 ppm ( 6.86 x 1 p si a) is pr obably feas ible, although at limit ed ca paci ty. In o rder to ta ke a c onser vative approach to th e pre 1 i m i n a ry desi gn, p arti c u 1 a r 1 y i n t he absence of data on th e hydroc arbon comp o s i t i on in tunne 1 air, it was deci d ed to utilize n-bu tane adsor p t i o n data, The n-butane i s o t h erms were sup plied by P i 1 1 s b urgh A c t i v a ted Carbon Compa ny, a nd an ex trapo 1 a t i o n of these i s o t h erms to the re g i o n of hydrocar bon c oncen t r a t i on in tunne 1 air is pre- sente d i n Figure 2 in A ppend ix II Fro m thi s basis: Activated Carbon Adsorber Design Part I: Adsorption Cycle : From Figure 2, Appendix II at 7 ppm HC: Capacity to saturation = 1.57 lb n-butane/100 lb carbon Working Charge, at 50% of saturation capacity = 0.785 lb n-butane/100 lb carbon From Lee (1970) and PACC0 data: Face Velocity = 80 FPM 2 Area of Bed Required = (250,000j. = 3 j 2 5 ft Bed Depth: In order to avoid the use of a two- bed system, and the extreme capital costs involved, bed depth was selected by trial and error to yield a single- 140 bed adsorber capable of operating, with steam regeneration, within a 24-hour cycle. Design is such that steam regeneration can be theoreti- cally accomplished in off-peak load time period. Bed Depth = 6 inches Volume of Bed = (3,125) (1/2) = 1,562 CF Weight of Carbon in Bed (at 30 Ib/CF bulk density) = (1 ,562) (30) = 46,860 lbs Weight of Adsorbate to Breakthrough = (46,860) (0.00785) = 368 lbs Lb/Hr of Hydrocarbon (Table 27) = 17.6 Ib/hr Duration of Adsorption Cycle 368 ) = 20.8 hours 17.6) From Figure 1, Appendix II: Pressure Drop/inch depth at 80 FPM = 0.725 in.W.G. Pressure Drop through 6-inch bed = (0.725) (6) = 4.35 in.W.G. The pressure loss through the fixed-bed adsorber is virtually the same as the head capacity of the 4.2" W.G. blower listed in Tables 29 and 30, and the operating costs of this unit may be added to those of the adsorption equip- ment (capital cost estimate for the activated carbon adsorber includes the blower). In the absence of actual system test data, steam regeneration cycle requirements for a uniquely low concen- tration of 7 ppm hydrocarbon of varying composition can at best be roughly approximated. Mattia(56) presents dsta for adsorption of a 20 ppm solvent from a 20,000 CFM stream, together with steam regeneration time curves for various blowdown rates. Taking a value of 128 minutes regeneration from the Mattia curve at a blowdown rSte of 2000 CFM, and estrapol ating linearly to the tunnel air adsorption conditions 141 1 CFM Blowdown Required = (20 ppm) (20,000 CFM) (2,000 CFM) (7 ppm) (250,000 CFM) = 8,760 CFM Lb Steam/Regeneration, assuming 110% blowdown for vessel heatup : = (8,760) (492)(128)(18)(1.1) (359)(7l0) = 42,900 lbs/cycle Assuming 50% operational time requirements: 3 5 No. Cycles/Year = ( ^ )p2) = 182 cycles where adsorption time = 20.8 hours, regeneration =' time 2.1 hours , and heating-cooling time = 1.1 hours While the s i m i 1 a r fixe d-bed proc esse s of ca talyti c oxidati on and adsor p t i o n b oth ap pear to be tec h n i c a 1 y feasible the high flow requi red in the co ntact beds may give r i s e to space req uirement p roblems . Thi s i s parti cul a rly tru e in the case of t he adsorpt ion ope ration whi c h req ui re s acces sory regenerat ion e q u i p.m ent sue h as a 1 arg e ste am b oiler, condenser and cooli ng water, etc. A 1 s o , w hi le catal yti c o x i d a t ion pro- duces no secondary p o 1 1 u t i on pro blem, stea m re generat ion/ condensat ion in an adsorpt ion cy cle p roduc es a hydroc arbon- contami na ted water st earn to d i s pose of. If h o t i n e r t-gas stripping is used, the hyd rocarb on ca n be burn ed but then thermal i ncineratio n costs must be ad ded. The sing! e -bed , conventi o nal steam- regener ated a dsorp ti on syst em out! ined above appears t o offer th e fewes t prob 1 ems in st rai g htforwa rd a p p 1 i c a t i on to tunn el air contro 1 , bu t the bas i c a d s o rption/ regenerat ion data r equi red for a more ri no rous determ i n a t i o n - of techni cal feasib i 1 i ty i n the const rai nt s of tunnel i n s t a 1 1 a tions are not avail able. As was noted in the economic workup on fixed-bed catalytic oxidation, the capacity of the adsorption system required, 250,000 CFM, far exceeds that of any unit yet built. Extrapolation of economic data to this range is ex- treme, and extremely uncertain. Again using HEW AP-68C12) curves for installed costs, and extrapolating: Installed Cost, 250,000 CFM Adsorber = $295,000 142 i i Capital Charges : Assuming 15-year life, 20% taxes and insurance Annualized Capital Charges = $23,600 Operating Charges : Steam Costs: Cost/cycle, at $1.00/M lb steam cost = $42.90 Cost/Year, 182 cycles = $7,808 Blower Cost From Table 30, 1" W.G. = $4,095 Total Operating Costs = $11,903 Total Annual Capital + Operating Charges = $35,503 Ac t i v a t e d carbo n adsor p t i o n systems are particularly susce pti ble to bind i n g an d deact i v a t i on by particulates, and the e conomi c s of pa rti cul ate rem oval equipment y_s_. periodic carbo n repla cement are in determi nate without information on 3 the r ate of loss of adsor p t i o n c a p a c i ty at the 500 yg/m parti cul ate loading How ever, t he ec onomics already indi- cated are no t encou raging , compa red w i th the costs of straight' f orwa rd vent i 1 a t i o n in ere ases as show n in Table 29 and 30. Addit i on a! ly , the c arbon system has t he limited capability of re movi ng only th e heav ier hyd rocar bon fraction from the pol lu tant sp ectrum, and n o sorpt ion c apability for the crit- ical 1 ow-wei ght hyd rocarb ons sue h as acetylene, ethylene and forma ldehyde . Thus , this proces s can not be recommended at this time. Process Feasibility: Particulates T he ca pa city an d eff l ci ency of e 1 ectros tatic pre- c i p i t a tors (ESP) are enti rely adequat e for treatm ent of tunnel - air. In co ntras t to the propo sed cat alyti c o x i d a tion or a d sorpti on me thods for tunn el po 1 1 u t i o n cont rol , 1 a rge-scale commer ci al high- voltage e 1 ectr o s t a t i c prec i pi tat on units handle gas f 1 ows in the 5 00,00 to 2, 000,0 00 rang e, so that a 250, 000 C FM ca pacity is not at all unusu al. Ho wever, when di rect inqu i r i e s were mad e of several vend ors of ESP equip- ment r e 1 a t i ve to the tunn el ai r probl em, t here wa s unanimous doubt expre ssed as to the appl i c a b i 1 i ty of their units to a gas st ream c o n t a i n i n g the 1 ow parti cu late concent ration of 3 500 ug /m . The reason fo r th s attit ude i s not d ifficult to 143 u i 3 determ i ne. In t he stan dard un its o f grains/CF, 500 ug/m is e q al to a va 1 ue of 0.00021 9 gr/ CF. HEW, AP-51 013) in their summa ry on Contro 1 Techn i q u e s for Particulate Air Pollut ants repor ted an extreme ly lo w exit loading from a commer ci al ESP u nit to be 0.00 5 gr/ CF. Thus, the concen- t r a t i o n of parti cul ates report ed in ambient tunnel air is only 4 % tha t of an unus ually 1 ow-co ncentration treated gas stream . It ther efore a ppears that the technical feasibility of ESP appl i c a t i on to p art cul ate r emoval at the loadings normal ly en count ered in tunnel ai r is very doubtful. Pre- 1 i m i n a ry te sting would be nece ssary to modify present nega- tive e n g i n e e r i n g judgme nt of t he fe asibility of ESP extra- p o 1 a t i on to the highly- dilute regi o n of particulate loadings Assuming a 150 to 200-fold dilution of automotive exhaust in tunnel air, the concentration of particulates in the exhaust itself will be of the order of 0.04 gr/CF. This latter concentration is in the range where agglomeration and inertia! removal are effective, and exhaust source control of particulates has already proven to be technically feasi- ble, and is most certain to be utilized when standards are formulated. The impetus for external control of particulates therefore would not seem to exist atthis time. Despite the present lack of any data on particulate collectibility by ESP, or the physical nature and properties of the particu- lates, an exploratory economic analysis of this operation was carried out. The economic workup of ESP was carried out using the procedures outlined in HEW, AP- 51 (113) and the cost data contained in this publication and in Walker(99) 4 Design Capacity (S), ACFM = 250,000 Assuming 50% onstream time requirement: Annual Operating Time (H) = 4,380 Hours Purchase Cost (High Efficiency Unit) = $180,000 Instal 1 ati on : Low Typical High Installation Factor, % 40 70 100 Installation Cost $ 72,000 $126,000 $180,000 Purchase Cost $180,000 $180,000 $180,000 Total Capital Cost $252,000 $306,000 $360,000 144 : Annual Capital Charges (C) The simplifying assumptions used in estimating the annualized capital costs, in HEW, AP-51 were: (a) Depreciation of purchase and installation costs over 15 years. (b) Straight-line depreciation of 6-2/3% on installed costs, plus (c) Capital charges of taxes, interest and insurance of 6-2/3% of initial capital costs, to give a total annual charge of 13-1/3%. Additionally, the 1968 equipment costs used in AP-51 were uncorrected to 1971 costs because of the preliminary nature of the cost estimates made. (C) = (0.133)(Cost) Low (C ) = (0. 1 = L 33) ($252,000) $33,516 (C = 1 = Medium M ) (0. 33) ($306 ,000) $40,698 High (C ) = ,000) = H (0.133) ($360 $47,880 Power & Maintenance Costs (assuming no extra fan power) Low Typi cal High Power Costs (K), $/kw-hr 0.005 0.011 0.06 Power Requi rements (J) , 10"3| Maintenance Costs(M), $/ACFM 0.01 0.04 0.06 G = S(JHK + M) where G = annual operating & maintenance costs S = design capacity, ACFM J = power requirements, kw/ACFM H = annual operating time, 4,380 hours K = power cost, $/kw-hr M = maintenance costs, $/ACFM 145 1 . Low(G L ), Typical (G M ), and High(Gu) annual operating and maintenance costs calculated as above are as follows:. G = G = 6 = L $3,540; M $13,130; H $41,230 and, Total Mean Annual Cost = C|^ + G = M $53,828 Using the square root of the sum of the squares of the differences, the high (V^) and low(V L ) cost variances are as follows: 2 V = + 2 1/2 L ( ($7,182) ($9,590) ) = $11 ,940 1/2 V = 2 + 2 H ( ($7,182) ($28,1 00) ) = $28,950 Therefore : Lower Cost Limit = $53,828 - $11,940 = $41 ,888 Higher Cost Limit* $53,828 + $28,950 = $82,778 The high cost variance amounts to more than 50% of the mean cost of $53,828, so that the chances of exceeding the mean cost is much better than a cost under-run. The annual ESP costs are a good deal higher than those of the treatment techniques previously estimated, and it may be con- cluded that, in addition to being technically doubtful, ESP is apparently prohibitively expensive for the single-compon- ent application. It s hould be n oted that high -vol ta ge ESP units are normal ly appl i ed to high ly co ncentrate d emis s i o n s , whereas two-stage , low -volt age u nits are used for di lute li quid aerosol s such as oi 1 smo kes a nd genera 1 air condi ti o n i n g units. I t was real i zed that the low-v ol tage units might be more appl i c a b 1 e to the t unnel parti cul ate pr oblem, but these units can not b e use d on solid s , w i t h o u t wash i n g a d a p t a t i o n . Further, the 1 arges t-cap aci ty two-stag e unit for wh ich cost data are avail able is 10 0,000 ACFM, an d the i nstal 1 ed cost of this u nit i s abo ut $3 30,00 0, as aga i n s t $ 190,000 for the h i g h - v o 1 age E SP un it of the same capa ci ty Theref ore, the cost situ a t i o n for the t wo- st age low-v ol tage preci p i t a t o r is even more nega ti ve than for t he ESP un it c a 1 cul ated in detail above, an d thi s uni t was not reviewed f urthe r. 146 . , , o , Based on data provided by Western Precipitation Division of Joy Manufacturing Company, a precipitator volume of 16,680 cubic feet was estimated as necessary to handle the requirement of 250,000 ACFM at a 5 ft/sec linear velocity. W h i 1 e a n umber of di ffere nt ty pes o f we t col 1 ectors can be used for par t i c u 1 a te co llect ion , a pre 1 imi nary survey of n ormal c a pa city ranges and head 1 osse s i nd icat e the spray cham ber to be the 1 owest head- loss , high est t hrou gh-pu t devi ce. Ba s i c a 1 1 y becau se of the humid i f i c a tion prob 1 em, wet col 1 ect ion devi ces of any sort canno t be used with in a tunn el for treatmen t of a i r w h i ch w ill b e re- i ntr oduce d into the tunnel . All we t scru b b i n g devi ces i nhere ntly cont ai n an i n i t i a 1 a d i a b a t i c gas s a t u r a t i o n zone , and thi s eva por- atio n mecha n i s m act ual ly h i n d e rs pa rti cu 1 ate coll e c t i o n be- caus e of th e diffus ion of wate r vap or aw ay fr om t he li quid drop s or su rface (s weep d i f f us ion). Bee ause of t he sa turation phen omenon associ at e d wit h wet cont actor s, th ese units can be e mpl oyed only fo r exha ust a i r tr e a t i n g , an d ca nnot be cons idered for cont rol of the i n - 1 u nnel atmos pher e. H owever many tunnel s have s pray c hambe rs to prot ect t he e xhaus t fans in t he even t of tun n e 1 f i res and i t is of di rect i nte rest to esti mate th e c a p a b i 1 i t i e s of s uch p resen t equ i pme nt f r gross tunn el emis s i o n con trol. This pres ent s e c t i o n i s 1 i m i ted to the c o n s i d e ration o f the a p p 1 i c a t i o n of spray cha mbers to part i cul ate removal only. A lthough t here are s everal e s t i m a tion t e c h n i q ues avail able f or calcul a t i o n of c rossf 1 ow spra y chamb er re 14 ) ments for p arti cul at e rem oval , the met hods of Ranz and Wongv' have been s uccessful ly em ploye d previo usly for i n d ustri al d e s i g n prob lems, and thes e wer e used t o obt a i n a p rel im i nary size esti ma te for sp ray c hambe r volume s. T hese ca 1 cul a t i o n s are g i v e n i n detail in th e App e n d i x II and the res ul ts are prese n t e d i n summary form in T able 32. The requi r ed ch amber hoi du p time depends on th e spr ay rate ratio of wat e r / a i r , the 1 i q u i d drop let size, aero sol p article size and the requ i red parti cul ate removal e f f i c iency For t he 50 0-mi cro n spr ay drops , the requi red res id ence contact time falls o ff ra p i d 1 y wi th the in crease in aero sol p article size, at any gi ve n ef f i c i ency 1 eve! . F or th e 90% removal leve 1 , the conta ct time decrea ses from 16.1 secon ds for a 2 -mi cron ae rosol part- 5- i c 1 e , to 1 75 second s for a micron p arti c le. Th e cor res- 3 p o n d i ng vol umetric c hambe r req ui rement s are 67,000 ft and 3 7,300 ft , respecti v ely. For a decrea se in ef f i ci ency from 90% t o 75%, the volu me re quire ments on a 5- micron parti cle 3 3 basis chang es from 7 ,300 ft t o 4,400 ft . As is obvious from Table 32, the governing variable for particulate removal in a spray system is the size of the particulate. As was indicated earlier, more than 95% of the mass of automotive exhaust fumes is in the plus-1 micron size 147 H JB o o o o I o o \r> »o es ~2 2 «sco o 1 oo lO > to o # $ a o S3 CO Q P ON o *W^ www CVJ JO JB o o W lO O NO u 2°° ° CN CO o >s • I a,cl ^5 CO t>» > CO U £ VO r-4 o o 1*1 CO in xi t-< d - S <=> ft h w vO CO es —i 33 Pi ^ m r^. m «* •>* o CO LO vO O -r-« Cd O 2; JE5 w CO O £2 COO 8 » 1-1 o —l CN CO "* IT) O 148 range. Further, a spray system tends to increase particle size by agglomeration, so that a degree of particle growth can be expected. Also, in the normal spray system, the liquid is colder than the gas, and a certain amount of condensation on the aerosol particulates will occur, increasing the particle size. The chamber sizes required for the removal of plus-3 micron particulates from 250,000 CFM of air in Table 32 are reasonable and, given the expected particle size distribution, the use of spray chambers for removal of particulates from tunnel exhaust air at good efficiency (75-90%) apnears to be technically feasible. Because water spray scrubbing was under consider- ation as a tunnel exhaust treatment technique, a detailed estimate was not attempted, and the preliminary costs were calculated under the assumptions and the data of HEW, AP- 51, as outlined previously. Using the wet scrubber cost data for a 250,000 CFM unit: Annual Capital Cost : Purchase Cost = $32,000 Installation Cost(0 100%) = $32,000 Total Installed Cost = $64,000 and Annual Capital Cost = (0. 1 33) ($64 ,000) = $8,512 Annual Operating and Maintenance Cost, (G) : G = S(0.7457HK(Z + Qh/1980) + WHL + M) where Val ue S = Design capacity, ACFM 250,000 H = Annual operating time, at 50%, hours/year 4,380 K = Power costs, $/kw-hr (typical) 0.011 Z = Contacting power, HP/ACFM (low) 0.0013 Q = Liquor circulation rate, gal /ACFM(low) 0.001 h = head required, ft of water (high) 60 W = Make-up water, gal/ACFM 0.0005 149 , = L Water cost, $/gal x 10~3(typi cal ) 0.50 M = Maintenance cost, $/ACFM(low) 0.02 now (Z .+ Qh/1980) = 0.00133 = 10" 3 and WHL (0.005) (4,380) (0. 5 x ) = 0.001096 G •= (250, 000)(0.7457)(4,380)(0.011)(0.00133) + (0. 0211) = $17,250 Total Annual Cost = $8,510 + $17,250 = $25,760 The annual operating and maintenance costs are on the high side because of the use of generalized wet scrubber cost data. The spray chamber is the simplest device of all wet contacting units, but the absence of specific unit operating cost information prevents a more rigorous analysis. If more definitive costs are required, a reassessment of operating costs is recommended for a specific tunnel location and a localized cost structure. Process Feasibility: Water Solubles I nspec ti on of Table 27 s hows that the water-soluble pol lut ants i n c 1 u de th e oxygen a ted hydrocarbons, primarily formal dehyd e and aero 1 e i n , n i troge n dioxide, sulfur dioxide and ca rbon d i o x i de. Other th an th e fact that the oxygenated hydroc arbon s are eye irritant s , th e use of a wet scrubbing operat ion w ould not a ppear to be w arranted for removal of these compo nents at t he conce ntrat ion levels indicated. How- ever, prope rly-d e s i g n ed spray cham bers have the capability of remova 1 of c a r c i nogen s of the benz o-(a)-pyrene typevllS) ancj they h ave a lso b een f ound to irly effective in the removal of eve n rat her i nsol u ble gase \hU ). The only valid basis for evalua tion of we t scr u b b i n g a s an exhaust pollution control t e c h n i que i s exp erime ntal wor k on the pollution system repre- sentat i ve o f dil uted automoti ve ex haust. For the present, feasi b i 1 i ty may be on 1 y indie ated not calculated. The primary indicators of the feasibility of wet scrubber or spray chamber application to tunnel exhaust cleaning are the size of the unit to be required, and its probable efficiency. Spray chamber capacities and efficiencies were investigated by Pigford(80) } an d mass gas flow rates of 2000 lbs/hr/ft^ were reported as being achievable in cyclonic 150 ah , ui u. . entra nee un its w it h c entra 1 core sprays, or in counter- curre nt or cross curre nt co ntactorsltactors withvnth good mist enmi-elimi- n a t i o n. Fo r air , the base ventilation flow rate of 15 x 106 C FH wou Id re qui re a cr o_)SS-sectional flow area of 562 sq ft to ma tch t he 20 00- lb /hr/ft^'hr/ft^ mass rate. This area i equi v al ent to a vesse 1 dia meter of about 27 ft, which is rough ly the size of a two- 1 ane tunnel . However, units of this size a re no t unc ommon in industry, and since it could be bu i 1 1 ex terna 1 to the t unnel proper, the diameter needed does not ap pear impra c t i c a 1. Again, the benefits of ex- haust pol 1 u tant remov al re qui re further definition both on a hea 1 th an d nui sance basi s 80 T he exten sive data of P igford^ ' on spray chamber absor ption show tha t from 1 to 3 transfer units are a v a i 1 a b 1 e in su ch equ i pment depending on t he design . Th is con tact ef f i c i ency is a d e q ate for s olubl e gases w i th f avorab le e q u i 1 i b r i u m r e 1 a t i o n s h i p s at the low conce ntrat ion 1 e vel s Cal cu 1 a t i o n s i n d i c a te that a 11 of the oxyg enate d hydr ocarbons can b e remo ved by w et scrubb ing , as can a s i g n i f i c a n t porti on of th e n i t r ogen and sul fur o x i d e s The ex tent of rem oval of the 1 atter compound s , as wel 1 as that of a dditi onal m ateri al , depen ds on the w a t e r/gas rat i o , t he liquid temp eratur e , and the d egree of water recycl e. Exp eri mental data are r equi red to de fine t he s p e c f i c pol 1 tant removal e ffici e n c i e s as a funct ion of these p arameters , and the pres ent f e a s i b i lity must be reg arded as uncertai n. The economics of spray scrubbing have been reviewed in the previous section. General Feasibility: Recycle & Compartmental i zati on un e of th l nves t i g a t i o n of th t i o n s , in w ich the in wh ole or part, t tunne 1 . Fun damenta the a ccumul t i o n an While a theo r e t i c a 1 more i n s t r u c t i v e to model , and t he 2260 the e ffect o f diffe trati on leve Is, as Assuming now a tunnel, or tunnel section, T, followed by a treatment process, P, for the removal of CO at an effici- ency of E r : 151 c c C c c c TUNNEL, T p i i t 1 W C E C 1 as* __ RECYCLE, R where F = fresh air rate, CFH R = recycle air rate, CFH Wc = rate of CO generation in T, CFH = P, ppm C c concentration of CO leaving process, C' = of CO entering tunnel, T, ppm c concentration = CJ1 concentration of CO leaving tunnel, T, ppm Assuming there is no CO content in fresh ambient air, and taking a process, effi ciency of 90%: b R + F = 15 x 10 CFH Let: x = R/F = Recycle ratio Substituting in the above equation: 6 F = 15 x 10 (1 + x) At steady-state conditions, CO input = CO output from system, so: FC = - E C W c (1 c ) and = - FC C 2260 (1 0.9) = C c 226/F 152 1 , cu Now from CO balance around the bleed point: (R + F) + W - E = (R + F) C C£ c (1 c ) c = 2 6 and (C C ' ppm c " c) 6 = 15-1 1 5 x l0 Assuming val ue s of t he re cycle r atio , x, the co ncentr ations of CO lea ving the tu nnel can now be ca 1 culated. This has been done for val ue s of x from 0.5 to 4, an d the res ul ts a re tabu- la ted in Table 33. Wit ho ut any recycl e air, t h e cone entration of CO lea ving the tu nnel is the base v alue of 1 50 ppm , which is simply the genera ti on rate (2 260 CF H ) divide d by t he tunnel 6 v e n t i 1 a t i on ra te of 15 x 10 CFH . It is o b v i o s that any and all val ue s of recycl e ser ves to increa se the CO conce ntrati on of t u n n e ai r above the b ase val u e wit hout recy cle. Further , even if t he pr ocess remov al effi ciency is incre ased t o 100%, the tunne 1 CO concen t r a t i on then only becomes e qual t o the base 150 ppm v al ue. For any pro cess r emoval ef f i ci en cy of less than 100% , the tunne 1 conce ntrati on must i ncreas e above the base val ue of 15 ppm CO wit h any finite v a 1 ue fo r re- cycle. I f the re wer e no piston effect , it must be co nd uded that recy cle a ir ope rati o n in tu nnel v e n t i 1 a t i o n i s c ompletely impracti c al , a nd wou 1 d on ly resu It in higher p o 1 lutan t con- centratio ns th an wou Id be the ca s e wit hout recy cle. However, since a p i s t o n ef fee t doe s exist , and is in f a t impo s s i b 1 e to e 1 i m i n ate recycl e cou Id prov e to b e a feasi ble al though highly ex p e n s i ve pro cess. A glance at the model used for the above calculation will show that it applies equally well to internal recycle operations between sections of a tunnel as well as to a com- plete tunnel system. Thus, no matter where the recycle is placed, the pollutant concentration increase will occur. An examination of the assumptions made in the derivation of the data of Table 33 show that these are not limiting, and the above conclusions are general for any pollutant generated at any rate. In the lat ter p art of the fea si bi 1 ity prog ram, it was requeste d that t he po s s i b i 1 i ty of c ompar tmental i z a t i o n of sect i onal iza t i o n of tunne 1 air t reatmen t be exami ned One of the u n d e r 1 y i ng assum p t i o n s of th e contr ol pr ocesses previously cons idered i n this r eport was th at they woul d have t o operate with a (pol 1 u t e d ) a i r int a k e int ermedia te in tunnel location, Beca use it w ould mak e lit tie sen se for this air i n t a ke to be loca ted at t he norma 1 poi nt of m ax i mum pol 1 u tant con centration (too late) o r at the i nle t (too soon) , it wa s o b v i o u s that the loca t i o n wou Id be de termi ned by pol 1 uta nt co ncentrat ion gradient with d i s t a n c e, and t he de sired 1 i m i t i n g val u e. Howe ver, in any even t, the b a s i c ass umpti on of i ntake 1 o c a t i on was o ne of a two- sect ion comp artmenta 1 i z a t ion of the tun nel . The two -section 153 1 i « o in r-' ^ cn bo o i*» in o m o £ in in \o oo ej\ »rH I I i I CN a i t— •— i—I i— i— 581 O vO in in 3 * X in in CO CO TO .Jj pL, fa S < u fa 154 compartmental izati on requires the use of one control process installation, and generalizing, the breaking of the tunnel into r^ treating sections requires the use of (n_-l) process units. The estimated annual costs for the various pollution control processes evaluated in this study are summarized in Table 34. This tabulation permits a cost comparison of the alternate control techniques, and in purely economic terms, it appears that augmentation of tunnel ventilation is the most attractive control measure. This would be particularly true for existing low head-loss tunnel ventilation systems, in the range of 1" to 2" W.G. However, for the higher initial head- loss tunnel systems above 2" W.G. the increase in annual power costs required for significant flow augmentation would bring the total cost of this method above that of catalytic oxidation or spray scrubbing. As indicated in Table 34, when feasibility factors are added to the economic considerations, then there appears to be no secondary pollution control technique with the cost- effectiveness capability of ventilation blower addition or substitution at the present time. However, the desirability of additional development work on catalytic oxidation and spray scrubbing is definitely indicated by the data of Table 34, and it is recommended that additional laboratory and pilot work 155 i I "3 cg «/9- ir, CO lO CO oo m no oo o 1 co t< On o CM \o 4-> o eo CM in oo •a to *-> o oC —oo* cm* CO in CO in o ° * cm cm CO in cs <**- Ctf m CO in "Tn CO o o Os o oo On O CO in o 1—1 CM o ON CM t^t cm vo -* CO Q •a «=5- 3 «J £ u •J-> T3 -a < S o co o H Pm CO 00 «-> en u -a CO O CO 13 o •rH & T3 3 u o p-i 4-> CO rt o o (D § to -8 a) 8 to cT o 3 0-. Oh Q w in u CM o Oh- U Ph 3, o 3 O Oh Cm 8 CO Cm 0-. o C! Oh 1 o O bo • rH _ - - C $ ^ CO -=f •rH O O§ O •rH cu +J M •9i Q. Cm 0) & Oh *rt O O .8 O *w CO •a N—J -a 6 H o < CO X! •-H I § O O O 6 Jh r— *-> 13 J8 o CQ i H & l-H Oh 4 O u CO rt 156 on these operations be undertaken. Based on the process review and analyses carried out in this study, the following conclusions may be drawn: 1. Both exhaust source control and tunnel ventila- tion augmentation appear to be either more effective or more economical pollutant control strategies than secondary pro- cessing of vehicular tunnel atmospheres. Projections of exhaust emissions under presently-mandated standards and source controls and correcting for auto population age, in- dicates a reduction in average hydrocarbon emission from 660 ppm to 156 ppm in the period 1970-1980, and a corresponding reduction in average CO emission from 25,790 ppm to 6,120 ppm. Thus, the problem of tunnel atmosphere pollution appears to be one of decreasing severity, and secondary controls may not be reguired. 2. Tunnel ventilation augmentation appears to be economically and technically more attractive than any secon- dary pollution control process. Both catalytic oxidation, and carbon adsorption control operations are fixed-bed units reguiring supplemental blower head additions to force air through the process. This creates the anomaly that tunnel ventilation augmentation must be used in conjunction with any fixed-bed control process, but the potential direct ventilation increase benefits are nullified by the process use. 3. AmbieHfc temperature catalytic oxidation appears to be potentially the most attractive secondary control pro- cess. Further development is reguired to assess its capa- bility for CO and hydrocarbon removal at the low concentrations existing in tunnel air, and to yield more complete data for desi gn. 4. Spray scrubbing has apparent application to the control of gross tunnel exhaust emissions, and if localized control is necessary or desirable, further study of the full capability of this operation should be undertaken. This and other wet scrubbing methods are not suitable for in-tunnel use because of the accompanying gas saturation and the result- ant in-tunnel fog possibilities. 5. Investigation of conventional electrostatic precipitation for the removal of the particulates from tunnel air showed this process to be of doubtful feasibility because of the extremely low particle concentration. Further, cost studies showed it to be the most expensive control method of those reviewed. 157 r . r r 6. A study of recycle operations shows that any degree of processed air recycle around the tunnel or any part of the tunnel will yield higher in-tunnel pollutant concen- tration levels than would be the case for once-through air ventilation. However, the injection of fresh air into a tunnel by the piston effect could compensate for the build- up of pollutants. Selection of Control Techniques to be Evaluated - Gen era! Discussion A s i g n i f i c ant amou nt of work has been and is be i n g don e on pol 1 ut ion c ontrol t e c h n i ques and d e v i ces f or in d u s t r i a 1 ope ration s , po wer plan ts an d auto- mobile e xhaus t sys terns In th ese ty p,es o f pol 1 ut ant s ources , the effl uent gas s tream i s at an ele vated tempera ture and the concentr a t i o n of p ol 1 utan ts is high, As an examp le , m otor vehicle exhau st em i s s i o n conce n t r a t i on ra nges to 3% CO (30,000 ppm) and 0.5% H-C (5000 p pm) a nd tern perat ures ran ge f om 150°F to 1500° F. C onver sely, t unnel atmos phere s genera ily r ange to maximum pol 1 u ti on concent ratio ns of 250 p pm CO an d 50 ppm H-C, with n e a r amb ient tempera tures r a n g i ng f om 20°F to 90 °F. It is o b v i o us f om th is comp ari so n that many of the contr ol tech- ' niques w h i c h have been de vel op ed rec ently are not nece ssari ly a p p 1 i c a b le to tunn el poll u t i o n contr ol. The constraints imposed by a tunnel atmosphere dictates and limits the types of purification processes which can be used. These constraints include: 1. Relatively low ambient temperature 2. Relatively low pollutant concentration levels 3. High throughput rates 4. Low exit concentrations. Additonal constraints are imposed depending upon whether the tunnel atmosphere is to be recycled (either completely or in a compartmentalized fashion) or merely exhausted to the atmosphere. In recycle, consideration must be given to cooling, CO2 removal, water removal and perhaps oxygen make-up These constraints are not imposed where the air is to be puri- fied prior to exhaust to the atmosphere. On the basis of recommendations for allowable im- purity limits in tunnels along with the current Environmental Protection Agency national air quality standards, removal systems for the following pollutants must be considered: 1. CO 2. H-C 3. N0-N0 2 4. Particulates 158 p . n . The EPA has also established limits for SO2 and photochemical oxidants, but these do not appear to be problems in vehicular tunnels based on measurements which have been made. Ca rbon Monoxide Remo val Systems - A r e v l e w of the 1 i tera ture r eveal ed two potent i a 1 1 y p romi s i no m eans of CO re- moval , based on t empera ture re qui reme nts a nd th rough put rate. these two ge neral cl ass es of c a t a 1 y t i c oxi d i z e r s i nc 1 uded - mangan ese-co pper oxide and tra n s i t i n met a 1 oxi des n a c t i ( vated carbon . A revi ew by Can non and Well inq 58) 1 n d i c a t e d that 6 0% MnO 2-40% CuO c omplete 1 y x i d i zed a gas mixt ure con- t a i n i n 3% C H 1 i bal c e i 25°C g 0,1% 2 , .1% gas n e , an n troge n at ' with a stand ard s pace v e 1 c i ty of 18, 800 h r~ . The other cataly st res u 1 1 e d in on % x i d a t i n of CO a t 120 °C at a space v e 1 c i ty of 200 h r" ' . However , at s ace v e 1 c i ties of 4800 h r ' on ly 50 % conv ersi on of CO w as at t a i n e d. f these tWO C5 talyst s, th e Mn02 -CuO ca talyst appea red t be more promi s i n g on the basis of both temper ature and throu ghput rate and th erefor e was selec ted for smal 1 scale eval u a t i n of its effect i venes s on di 1 ute d auto exhaust Hydrocarbons Catalytic oxidation or the rmal after' burni ng bo th can be used to oxidize hydrocarbons, These metho ds mu st be ess e n t i a 1 ly 100% efficient otherwis e the parti ally oxidized hydroc arbons may be more toxic a nd/or n x i us th an the in i t i a 1 hydrocarbon. To assure 10 0% con- versi on , h igh tempe rature s must be used, hence oxid ation was felt to be an i n a p ropri a te means of hydrocarbon re moval Acti v ated carbon ap peared to be the most promising technigue for r emova 1 of hydr ocarbo ns. Activated carbon will remove the h e a v i e r and mos t of t he partially oxidized hydr ocarbons at am b i e n t temperat ures Activated carbon will als remove N0 2 , anoth er of the impur i ties selected for conside rati on for r emova 1 from tu nnel a tmospheres. An attractive feature of ac ti vat ed carbon is th at it can be regenerated, pre- ferab ly wi th steam, and t herefore the maintenance r re- place ment problems are mi nimized. Because of the p romi sing outl ok fo r a c t i v a t ed car bon for removal of both hy drocarbon and N 0. t was sel ected for study on diluted autom b i 1 e ex- h a u s t Oxi des of Nj trogen - As stated earlier, activated carbon will remove NTTjT However, it is ineffective for removal of NO, which accounts for ^80% of the total oxides of nitrogen emitted from auto exhaust. Thermodynami cally , the conversion of NO into O2 and N2 is favorable, but no catalysts have been found which will effect this decomposition at reasonable rates or temperatures. Unfortunately, catalytic removal of N0 X from gas streams requires a reducing atmosphere, a con- dition which does not exist in polluted tunnel air. Conversely, proprietary information exists which indicates that M0 can be 159 , . n or , cata lytic al ly ox i d i z e d t o the ni tr ate f rm. It ha sals been o x i d i t h repo rted that NO can be zed o N0 2 , whi c cou Id be sorbed on a c t i v a ted car bon, but the proce ss req u i r e s a ga s dew poi nt - of 60°F. The p s s i b i 1 i ty of 1 iqu id s c u b b i n q anp eared to be o f que s t i o n a b 1 e a p p 1 i c a b i 1 i ty i n 1 i g h t of the N con cen- trat ions in t u n el atmos phere s. I n summ ary the r emova 1 of - NO s eemed to be the majo r pro blem of tun nel p ollut ant p uri fi ca t i o n The D OT Techn i cal Offic er in d i s c u s s i o n with Marb on Ch emi cal Division of B org-W arner Corpo ratio n sug gested that Pura fil, a chemi sor bent imp re gnated with KMnO 4 mig ht remo ve NO x from the atmo spher e. I t shou Id be note d tha t this mate rial f unctio ns by ch emi ca 1 rea c t i o n rathe r tha n cat a 1 y t i c acti on an d would therefo re ha ve to be re pi ace d per iodic ally. Howe ver since o ther met hods seeme d impr a c t i c al an d sin ce MSAR had a sup ply of this mat e r i a 1 on h and, i t was deci ded t hat Pura f i 1 w ould be eval uat ed on di 1 u ted au to ex haust Parti culates Typical means of removal of par- ticulates from gas streams include mechanical separators such as cyclones, wet collectors, electrostatic precipitation and filtration. The efficiency of each of these methods depends upon such factors as particle size, density, concentration and electrical resistivity as well as moisture content of the gas and physio-chemical characteristics of the gas. Cyclone separators are not particularly efficient for the size range (<1 y to 5 y) of particles in tunnels and in general require large energy inputs with attendent high pressure drops. With the present state-of-the-art of wet collectors, efficiencies at the anticipated particulate levels and particle sizes in tunnels would likely be quite low. Electrostatic precipi- tation and filtration may be apolicable to the problem. How- ever, since manufacturer's data are available for these types of particulate removal systems as well as for wet scrubbing systems, it was decided that no laboratory work on particulate removal would be performed. Purification Test System 3 Figure 31 is a schematic diagram of a 4300 ft chamber at MSAR. The chamber is leak-tight and is made of carbon steel with the inside walls coated with aluminum paint. The chamber is fitted with an air blower with a capacity of 80 cfm. Minor modification to the chamber included installation of an inlet port for injection of auto exhaust. Major modifications to the chamber involved in- stallation of monitoring equi pment, test beds and a gas stream heater (Fig. 31). The monitors which were used included: 160 Temperature (§) Carbon dioxide Pressure (7) Oxygen Relative humidity (8) Particulates (4) Carbon monoxide (9) Nitrogen oxides (5) Total hydrocarbons Q) Air sample for GC Heater ®®O®0(5> Flow Meter Bed I ©- -Bed II ^)©0®®©® ©©®®®®®s>- © © © Test Chamber - 4300 ft 3 r^— Exhaust Inlet FIGURE 31 - AUTOMOTIVE EXHAUST PURIFICATION TEST CHAMBER 161 Impuri ty Instrument Range CO MSA Lira Model 200 (IR) 0-300; 0-500 ppm Ful 1 Seal e Total H-C MSA Total H-C Analyzer 0-5; 0-15; 0-3D; 0-60 ppm C0 2 MSA Lira Model 200 0-0.5% °2 Biomarine 0M-300 Analyzer 0-100°/ H2.O Motometer RH Indicator 0-100% Particulates Royco Model 200 PC 0-54 u to 5.0 u; 100 particles/cc NO-NO, Wet chemical; Saltzman 0.01-10 ppm Method A fan was installed inside the chamber to assure rapid mixing of the contaminated gas. In most runs, the auto exhaust was provided by a 1963 Chevrolet Impala with 103,000 miles on it; the source of auto exhaust for the first two runs was a 1967 Chevelle with 33,000 miles on it. A typical run was as follows: 1. Run automobile engine for 1.5 min; car in drive; accelerator slightly depressed; brakes on. 2. Circulate contaminated air for 5 min to assure complete mixing within the chamber. 3. Turn on blower and set to desired flow rate. 4. Collect monitor readings at various in- tervals depending upon the type of removal system and rate of removal. The first run was a blank run to determine whether the test chamber and associated equipment resulted in change in con- centration of any of the contaminants during circulation without any purification system on line. The results in- dicated no change in concentration with time except for the particulates. Table 35 is a summary of the runs which were made. Results of each run are discussed in the following subsections Run No. 1 - Blank Run No. 1 was a blank run although a fiber glass mat was placed in one of the purification canisters to provide a pressure drop across the system. The vehicle used for the pollutant source was a 1967 Chevelle and was run at idle for 5 min. Small differences can be seen in the CO inlet (300 ppm) versus the CO outlet (285 ppm) and the HC inlet (78 ppm) 162 1 4 TABLE 35 - SUMMARY OF PURIFICATION SYSTEMS Bed Res 1 Pres.s H-C NO HO CO, Bed Space dence , Vehicle CO 2 Run Type of Wt. Temp. Velocity Time Flow Drop 1n Run Time ppm ppm oom oom y No lii - Purification lbs °F hr-' sec. CFM Water Mln. Out (n Out In Out In Out In Out RH 1 Blank HA HA HA NA 82 3.3 5 300 285 78 61 0.051 0.048 0.029 0.011 0.10 0.10 85 1"! Hopcal 1 te 12.0 92 17,100 0.21 84 3.6 2.5 280 215 41 0.14 0.006 0.069 0.08 0.12 0.12 52 2 (Cold) 12.0 92 12,100 0.30 60 2.0 ... 205 190 41 41 0.04 0.02 0.10 0.12 0.12 0.12 52 Ac tt vated 3 Carbon 8.0 92 17,100 0.21 84 3.0 2.5 300 + 300 + 84 22 4.03 4.47 1.38 0.24 0.24 90 8.0 92 4,100 0.88 20 3.0 300 + 300 + 60 20 3.16 3.68 1.05 0.23 0.23 90 8.0 92 8,200 0.44 40 --- ... 300 + 300 + 60 20 0.23 0.23 90 Purafll 4 12.0 90 17,100 0.21 84 2.0 1.5 357 320 56 47 0.93 0.30 0.44 1.26 0.11 0.11 85 12.0 93 8,500 0.42 42 0.5 ... 320 320 48 38 0.26 0.10 0.63 0.57 0.11 0.11 85 20 hr total 12.0 95 17,100 0.21 84 2.0 ... 270 270 25 24 0.00 0.00 0.018 0.018 0.10 0.10 85 Hopcal 1 te 1 .0 95 9,500 0.04 38 18.2 1.5 287 230 til 53 1 .55 0.89 0.14 2.49 0.13 0.13 65 (Hot) 1.0 96 4,700 0.08 19 8.8 235 223 59 55 0.13 -.13 64 700 watts Input 1.0 175 4,700 0.08 19 10.7 220 30 O'l 38 1.43 0.15 0.30 0.66 -.13 0.16 63 1650 watts ... Input 1.0 240 4,700 0.08 19 12.0 117 3 50 29 1 .48 0.69 0.44 0.22 0.14 0.16 61 Hopca 1 i te 2.0 6 Silica gel 1.0 90 4,700 0.08 19 11.9 1 .5 500 480 61 61 0.56 0.52 0.12 0.23 0.09 0.08 89 Hopcal i te 0.25 167 18,800 0.02 20 3.6 1.5 203 147 50 47 0.10 0.10 86 1635 watts 275 18,800 0.02 20 6.0 147 20 43 30 0.91 l.Ot 0.20 0.02 0.11 0.12 life 4 2 o.ll 0.12 8b 7 1635 watts 227 28,200 0.015 30 6.1 141 63 36 2620 watts 260 28.200 0.015 30 6.4 124 38 31 29 0.99 1 .09 0.15 0.03 0.11 0.12 85 1080 watts 276 9,400 0.04 10 1.8 102 8 38 24 0.89 0.61 0.13 0.02 0.10 0.11 84 Parti cula te Filter Resu ts void; face vel >dty too h1g 8 65% effi- ciency Particulate Filter Res ilts void face ve oclt) too hi Jh 99.5% ef f 1 dency 60% Mn02 + 1 86 2,350 0.16 10 3.3 1.5 349 346 53 53 0.39 0.51 0.04 0.06 0.11 0.11 .. 40% CuO 750 watts 201 2.?50 0.16 10 4.0 i2!L ?97 52 5? 0.41 0.89 0.03 0.00 0.12 0.12 1700 watts 247 2,350 0.16 10 4.4 325 297 S3 52 0.47 0.94 0.02 0.00 0.12 0.12 Charcoal + 1 94 11 ,750 0.03 50 5.6 487 474 50 23 0.36 0.22 0.14 0.04 0.10 0.10 70" Hopcal 1 te 4"67J 0.22 0.11 0.10 750 watts 134 11 ,750 0.03 50 5.6 4 36 426 2 18 .... 0.10 0.10 4T4" T7 0.10 2620 watts 265 11,750 0.03 50 5.9 356 351 23 17 0.10 0.10 1 T37 T7 0.12 2620 watts 261 4,700 0.08 20 2.0 318 318 22 17 0.10 0.10 -*TJ- TE" 0.12 2700 watts 311 2,350 0.16 10 2.0 293 293 2? 15 0.16 0.10 0.08 0.00 0.10 0.10 T7" TT 0.22 0.02 Charcoal + 1 93 4,700 0.08 20 2.6 1.5 445 445 48 23 0.52 0.28 0.09 0.00 0.1 0.1 68 Moisture T59 23 o.n 0.41 o"7T Tolerant Hopcal 1 te 2 12 1700 watts 280 4,700 0.08 20 2.9 400 395 4 23 0.33 0.21 0.09 0.00 0.10 0.10 77 0,62 6.61 0.14 1100 watts 240 4,700 0.08 20 3.9 290 290 32 21 0.12 0.12 70" 071 600 watts 185 4,700 0.08 20 3.2 248 248 31 21 0.20 0.13 0.04 0.00 0.12 0.12 8 76" 0.03 O.o2 0.14 163 . . t i , versus the HC outlet (61 ppm). This could be attributed to physical sorption on the fiber glass mat. A slight reduction in NO and a large reduction in NO? concentration was also noted, but problems existed with the NO-NO2 analyses at that time, so these differences may not be real. The difference in the concentration of particulates greater than 1 micron, 550/cc versus 60/cc was probably due to the filtration effect of the fiber glass mat. Run No. 2 - Cold Hopcalite I nit i al ly , it was intend ed to use the 60% Mn02-40% . CuO c atalyst r eport ed by Can non an d Welling to be effective for C at 25°C (77° F). No c ommerc ial source of this catalyst could be 1 ocat ed so H p c a 1 i t e , a c oprecipitated 70% f1n02~ 30% C uO cataly st wa s s u b s t i t u t e d i n its place. The bed was run a t 92° F. Again , a 1967 Chevel le was used at idle, but idle time was 2.5 m in. At a space velocity of 17,100 hr" 1 (resi dence tim e of 0.21 sec) , no s ignificant reduction was obser ved for C or HC. The oxides of nitrogen did appear to under go x i d a ion i n that th e i n 1 e t NO was 0.14 ppm and the outl e t NO was 0.006 ppm. Th is w u Id indicate oxidation of NO to N0 2 . Fu rther veri f i ca t i n f this is the fact that 8 the utlet N0 2 (0.0 ppm) wa s high er than the inlet NO? (0.06 9 ppm). At a space vel oci ty of 12,100 hr"' (residence time of 0.30 s ec) the CO an d HC w ere not changed, but again it ap peared th at NO was b e i n g part ial 1 y oxidized to NO2. Run No. 3 - Activated Carbon In th s run , as in al 1 su bsequent runs, a 1963 Chevrolet Impal a was us ed as a pol 1 utant source and was run under load condi t i n s . Cocon ut bas ed activated charcoal was used as th e puri f icati n medi a. Th e CO concentration was off scale, but it is known that c harcoa 1 is ineffective for CO 1 removal At a s pace ve 1 oci ty of 17 ,100 hr" (RT = 0.21 sec), a s i g n i f i c ant re d u c t i n was bserve d in the H-C level and the NO2 level The H-C con centra tion w as reduced from 84 ppm to 22 ppm (74 % remo val ) an d the N0 co ncentration was reduced 2 from 1 . 38 ppm to zero p pm. T he str earn was tested upstream and downst ream f the t est be d for odor. The upstream odor was typica 1 of t he odor s in t unnel s while the downstream was odorless, F i g u r e 32 is a chr omatoq ram of an upstream and downstream sampl e showi ng tha t the heavy hydrocarbons (which are the mo re tox i c and more dorous ) had been removed. Addit- ional test s at s pace ve 1 c i t i es of 8,200 (RT = 0.44 sec) and 4,100 (RT = 0.88 sec) w ere ma de on the same pollutant charge, Again a ma jor fr action of the hydro carbons , 67% and 100% of the NO2 wa s remo ved. T he app arent reduced removal rate of hydrocarbo ns at these 1 ower s pace v elocities is due only to the fact t hat a portion of th e heav ier hydrocarbons had been 164 Chromatograph Hewlett Packard Model 5750 dual column. Columns - 6* x 1/0" stainless steel 10% UC-W98 Carrier gas - Helium 40 cc/mln Temperature - 30°C temp, program to 230*C at 20°C/min Hydrocarbons Light Sample - ^230 cc of air. Hydrocarbons trapped on 12" x 1/0" stainless steel pre-column at -197°C packed with 45-60 mesh Chromosorb P Detectors - Flame Ionization Light Hydrocarbons Start temperature program (Room temp, to 230°C) IL -*A- Start temperature program Sample Upstream of Carbon Bed Sample Downstream of Carbon Bed FIGURE 32 REMOVAL OF HYDROCARBONS BY ACTIVATED CARBON 165 i - removed during the earlier part of the test thus increasing the ratio of light to heavy hydrocarbons. Run No. 4 - Purafil Purafil acts as a chemisorbent using KMn04 on a -sub strat e of activated alumina. Purafil had no effect on the CO conce ntrat ion but did reduce part of the hydrocarbon fraction as we 11 as NO. At a space velocity of 17,100 hr" 1 (RT = 0.21 sec) hydro carbons were reduced by 18% and NO was reduced by 68%. At a space velocity of 8,500 hr"" 1 (RT = 0.42 sec) hydro carbo ns were reduced by 21% and MO was reduced by 61%. The s ystem was allowed to run overnight and the following morni ng , a fter a total run time of 20 hrs, the NO concen- trati on ha d been reduced to zero and the NO^ concentration was d own t o 0.018. After 20 hrs of operation, the Purafil did n ot ap pear to be removing any hydrocarbons, indicating that those hydrocarbons which are reactive with Purafil had been remov ed. Total reduction in hydrocarbon content was 57%. Run No. 5 - Hot Hopcalite Thi s run was m a d e wit h hot Hopcalite with the ef f i c iency me asure d at v ari ous temperatures. At 95°F, a smal 1 reducti on in CO (2 0%) and HC (13%) was observed, while NO wa s reduce d by 43%. At 175° F, the CO was reduced by 86% and t he hydro carbo ns wer e reduc ed by 30%. The NO was re- duced by 90%. At 240°F, the CO was nearly completely re- moved (97% re moval ) and the hyd rocarbons were reduced by 42%. The beh a v i o r of th e oxide s of nitrogen at this tempera- ture is diffi cult to exp lain si nce NO removal did not seem to be as e f f c i e n t How ever, t he removal of NO2 was observed i for t he first time indie a t i n g p ossible oxidation to the n trate . It sh ould be not ed that the significant reduction in CO an d HC res ulted in an i ncrea se of C0 9 from 0.13% to 0.16%. Run No. 6 - Silica Gel -Hopcal i te In this run, a silica gel bed was installed upstream of the Hopcalite bed in hopes that Hopcalite would be effec- tive at ambient temperature if the stream were free of moisture No significant improvement was noted in the removal of CO, HC or NO/NO2. More effective drying agents might be considered, but for a system to be economical, the dryer must be regen- erable. Those dryers which can be used only once and then discarded would increase both the replacement and maintenance costs. Of course, these costs have to be weighed against the cost of heating the air stream to ^225°F, in the case of Hopcalite. 166 R un No. 7 - Hopcalite This run was made with a 0.25 pound Hopcalite bed as opposed to the 1.0 pound beds used in earlier runs. At identical flow rates, the residence time was reduced by a factor of 4 while the space velocity was increased by a factor - of 4. At a space velocity of 4,700 hr 1 and a residence time of 0.08 seconds used in earlier runs, the exit concentration CO was <1.5% (3 ppm) of the inlet concentration (117 ppm); this was accomplished at a temperature of 240°F. In this run, with a lower residence time and a hiqher space velocity, the CO was reduced by only 86%. Runs 8 and 9 - Filter Media These two runs were made with particulate filter media with efficiencies of 67% and 99% for 0.3 micron particles The results from these two runs were considered unreliable be- cause of the high face velocity at the filter, and the face velocity could not be reduced due to the performance charac- teristics of the air blower. Therefore, manufacturers data will have to be used for prediction of filter performance. Inquiries were sent to manufacturers of electrostatic pre- cipitators, also. Run No. 10 - MnQ ? -CuQ This run was made using an admixture of 60% MnO and 40% CuO as described by Cannon and Welling. The two materials were mixed, about 10% water was added and the moist mix was pressed into a solid cake. The cake was dried and then sieved to 4-8 mesh granule size. The test showed little activity of the catalyst for CO. Run No. 11 - Charcoal Plus Hopcalite This run was made to de t e rm i n e the overall per- formanc e of tw o se 1 ecte d met hods of tunne 1 air purification, The cha rcoal b ed w as lo cated upst ream of the Hopcalite bed, but in actual prac tice, i t w ould be more sensible to locate the cha rcoal b ed d ownst ream of th e Hopcal ite bed since NO is conv erted t o NO 2 in the H opcal ite bed. However, since no cool ing was pr ovi d ed fo r the Hope a 1 i t e be d outlet stream, the opt imum co nf i g urati on co uld n ot be us ed in the test system, At 31 1°F, the CO wa s red uced by greater than 90% and the charco al r emove d ess entia lly 100% of the NO2. The charcoa 1 al so remo ved a frac ti on of the h ydrocarbons ; gas chromat ographi c an alyse s ind icate d that t he heavy hydrocarbons were re moved. 167 Run No. 12 - Charcoal Plus Moisture Tolerant Hopcalite This run was made with moisture tolerant Hopcalite since it is less susceptible to powdering than standard Hopcalite, thus providing a lower pressure drop across the system. Information was acquired during this run on the effect of temperature on CO removal and the results are shown in Figure 33. These results indicate that at a space velocity of 9400 hr"l, a residence time of 0.04 sec and a temperature of 225°F, complete removal of CO can be expected. Purification Systems for Tunnels Th e 1 ab orato ry wo rk perfo rmed under this program demo nstrated that the techn ology ex ists for purification of tunn el atmos phere s. A p p 1 i c a t i o n of these principals and meth ods to t unnel atmo spher e p u r i f i cation requires a signifi cant degree of sy stem scale -up as w ell as an economic eval- uati on of sy stems requ i red for hand ling large volumes of tunn el air. An e a r 1 i e r sec tion of this report includes an eval uation o f the cost requ i rements for such systems, but it shou Id be ke pt in mind that the fea sibility and economic stud ies were made prio r to the labo ratory studies. Because of t his fact , som e add i t i o n al comme nts are warranted. First, ambient temperature catalytic oxidation proved to be an unattainable goal. The laboratory studies indicated that a temperature of ^225°F would be required for oxidation of CO using the best commercially available catalyst. As a result of this temperature requirement, an engineering design estimate of size and heat requirements for a 200,000 cfm unit with a regenerative heat exchanger was made. The results were as follows: Heat requirements - 1.63x10^ Btu/hr No. of plates in heat exchanger - 200 Size of plates - 80 ft x 20 ft Spacing between plates - 1/8 in. Velocity through plates - 22 ft/sec AP across heat exchanger - 4.7 in. H2O The second comment concerns the use of electrostatic precipitators to remove particulates. Inquiries were sent to a number of manufacturers of electrostatic precipitation units requesting performance characteristics and price. In regard to performance characteristics, the answers varied from - "it cannot be done by electrostatic precipitation" to "our units will reduce the particulate loading from 5 mg/m 3 down to 3 0.1 mg/m . Prices ranged from ^$81,000 for a 50,000 cfm unit and $164,000 for a 250,000 cfm unit to $1,000,000 plus for a 250,000 cfm unit. 168 — « O) 1 u +* J- Q) 1- J= t/> i— 00 Left I I I I I I I I I I I I I I I I o CD CO o o O O O o o o o o o c O o o c o CM r— O <7» CO to If) «3- CO CM r— O en CO CM CM CM (Jo) 9Jn^PU3dmox o^iicodOH 169 M0 X and hydrocarbons - activated carbon The electrostatic precipitator would be periodically cleaned by back washing; this could be done during an off-peak time. Activated carbon would require periodic regeneration with steam. The catalyst should have a lifetime of several years if properly protected from particulate contaminant, particularly lead. The electrostatic precipitator upstream of the catalyst bed should provide this protection. The question arises as to the anticipated lifetimes of all the purification system components, as well as the re- generation frequency and maintenance requirements. These questions cannot be answered at this time. It is recommended that a small scale (perhaps 5000 cfm) system be fabricated and tested under actual tunnel conditions. The information acquired from such tests would reveal not only the removal efficiency of the system but also the lifetime of the com- ponents and the required maintenance and regeneration fre- quency. It i s appa rent as a result o f this study that the ini t ial c a p i t a 1 cost of a vehi cular tu nnel a i r p u r i f i c a t i o n syst em wi 11 be high, In addit ion to t he cap ital co st, the powe r req ui rem ents w ill a 1 so b e high d ue to the hea ting re- quir ement s and press ure d rop a cross th e syst em. Fo r main- tain ing t he qu a 1 i ty of ai r wit h i n the tunnel , i t wo uld be sign i f i c a ntly 1 ess e xpens i ve t o increa se the size o f the vent i 1 a t i ng ai r syst em. Howev e r , if i n the future , tunnel s must comp ly wi th EPA stan dards for emi s s i o n from st ationary sour ces , then p u r i f i c a t i o n sys terns on the ex haust s tack will be r equi r ed an d syst ems t o per form thi s trea tment h ave been esta blish ed as a res ul t o f thi s study. 170 TUNNEL INSTRUMENTATION The present emphasis on air quality and monitoring of atmosp heric pollutants has accelerated the development of i nstrumen t a t i o n capable of continuous monitoring of low level impuri tie s in the atmosphere. Many of these instruments have combined class ical, chemical and physical analytical techniques used in t he 1 a boratories with automated industrial process instrumen tati o n. The resulting array of available instru- mentati on runs the gamut of sophisticated computerized mass spectrome ters to simple rugged temperature indicators. The appl icabi lity of these instruments in monitoring the air quality o f veh icular tunnels must be considered within the f ol lowing cons traints : 1. adequate sensitivity and specific response to the pollutants of interest, 2. operation and maintenance requirements, 3. capabilities of operating and maintenance personnel , 4. real-time data output, 5. reliable and reproducible operation. Table 36 summarizes the types of instrumentation which are currently available for monitoring vehicular ex- haust impurities. This table shows the principle of operation along with approximate cost ranges for each type of monitoring system. Carbon Monoxide Two general types of instruments are available for continuous monitoring of CO. These are the Hopcalite type and the non-dispersive infrared type of instrument. In general, the Hopcalite type has been used almost exclusively in tunnel monitoring applications. This instrument is rugged, inexpensive, simple and requires very little maintenance. The non-dispersive infrared type of instrument is more expensive 171 I 1*» to «* UJ c C£ — moo — r>r> — M so — 0»*> — •> v> v> 2 ^M 4 «*— n —*AL+QTI<4))*AL+QTI(3>)*AL+QTH2))*AL+QTI