FROM OXYGENATION OF TURBINE DISCHARGES FORT PATRICK HENRY DAM Ri. J. RUANE Tennessee. Tennessee Valley Authority, Chattanooga, DR. SVEIN VIGANDER Tennessee Valley Authority, Norris, Tennessee. ABSTRACT the use of oxygen injection The Tennessee Valley Authority is investigating oxygen concentrations in through fine-pore diffusers for increasing dissolved Dam. Oxygen injection is the turbine discharges from Fort Patrick Henry from the turbine intakes, being considered either immediately upstream into the turbines, or immedi- so that the oxygenated water is drawn directly ately downstream from the "boil" area in the tailrace. ) selection of a diffuser for Research is being conducted in.two phases: (1 best location for injecting the *injecting the oxygen, and (2) selection of the are being evaluated for oxygen. In Phase I, various commercial diffusers efficiency. Field and * possible plugging problems and for oxygen absorption apparently is not a significant laboratory tests indicate that diffuser-plugging approaching 100 percent can problem and that oxygen absorption efficiency with several commercially be achieved in a 42-foot height of bubble rise system will be evaluated available diffusers. In Phase II, a large-scale diffuser fall of 1973. at Fort Patrick Henry Dam during the summer and if results of this research A full-scale system will be installed at the dam and economically feasible. show this method of reaeration to be technically INTRODUCTION through fine-pore diffusers TVA is investigating the use of oxygen injection in the turbine dis- for increasing dissolved oxygen (DO) concentrations charges from Fort Patrick Henry Dam. River at river mile 8.2 in The dam is located on the South Fork Holston from Kingsport, Ten- Sullivan County, Tennecssee, about 2.5 miles upstream Boone Dam (Figure 1). At nessee, and 10.4 river miles downstream from reservoir extends 10.3 miles normal maximum pool (elevation 1,263), the 291 Docket# 5' '3't-@ /3Ve Control #7 7i 70 112. Date 5!!/ 77 of Document. REGULATO1Y DOCKET FfLE tz' is:. 16 - 12 X D,8 , 4 0F JAN Flour. by the Stal that exists After an *servoir relc or oxygen correcting methods tL could be c dam. This Figure l Map of Project Area voir and p: Oxygen upstream and has a total volume of 27,100 acre-feet. The reservoir has 4,300 of the higl acre-feet of useful controlled storage between normal maximum pool level high initiaI and normal minimum pool level (elevation 1,258). Average streamflow at diffused a Kingsport was 2,522 cubic feet per second during the period 1925-1970. plants (4 The dam is equipped with two hydraulic turbines, each of which has a such an il generating capacity of 18,000 kw. Normal maximum discharge through each the needc turbine is 4,400 cfs. in.r.-wage The maximum depth of the pool immediately upstream from the dam is about 101 approximately 70 feet. The thermocline during summer and early fall is us- creasing: ually 5 to 20 feet below the surface of the pool. oxygen iT Low concentrations of DO occur in the turbine releases from Fort Pat- 000 for, rick Henry Dam duringtthe summer and fall each year (Figure 2). This prob- $220,00( lem is the combined result of water low in DO that enters Fort Patrick Henry sidered e Reservoir through low-level power intakes at Boone Dam upstream and an aeration additional depletion of oxygen in the hypolimnion of the stratified Fort Pat- This I. rick Henry Reservoir. This low DO problem adversely affccts a reach of Scale 0: stream immediately below the darn that has been classified as a trout stream fusers, ( 1* 292 t I 'I ~ CONCENTRATION SATURATION i 4/-MEAN i I i I5•1 I AI 1 o (960-71 NOV DEC JUN JUL AUG SEP OCT JAN FEB MAR APR MAY in the Turbine Discharge from FIGURE 2. Dissolved Oxygen Conditions Fort Patrick Henry Dam problem also compounds a water pollution by the State of Tennessee and that exists downstream from Kingsport. in re- methods for increasing DO levels After an evaluation of various air aeration in the tailrace (5), it was concluded that diffused servoir releases for are the most promising methods or oxygen injection into the releases aeration Patrick Henry Dam. Only those correcting this problem at Fort of the turbine releases not increase the temperature that would from the SBanCmethods of the cold-water fishery downstream could be considered because reser- eliminated destratification of the dam. This consideration automatically might be more economical. voir and possibly other methods that investigation, primarily because injection was selected for further Oxygen five percent of the plant output) and the high power requirements (about of DO by 4,300 of to achieve high concentrations has high initial investment cost required pool level air aeration in sewage treatment aeration. Using data on diffused diffused air estimated that amflow at to tailwater conditions, it was plants (4) and extrapolating to drive 1970. require a minimum of 3,000 horsepower such an installation would used rich has a fine-bubble diffusers such as those the needed compressors and 15,000 each ough tailrace would cover an area plants. The diffusers in the estimates for in- e din sewage treatment 250 feet downstream. Preliminary about 100 feet wide and cost for he dam is to 6 mg/1 indicate the total annual creasing'DO in the turbine release fall is us-. , injection and $220,- between $120,000 for upstream is about oxygen injection ranges diffused air aeration in the tailrace Fort Pat- 000 for downstream injection; was con- ortiPatb- investment cost for oxygen injection $220,000. The lower initial on his prob- of the limited information available sidered especially important because ick Henry aeration of reservoir releases. Full- m and an main sections: (I) Proposed This paper is divided into the following Pat- Available Dif- Fort System, (2) Evaluation of Commercially Scale Oxygenation Conclusions. Lreach of Tests, (4) Discussion, and (5) fusers, (3) Field Oxygenation Ut stream 293 .... ....... PROPOSED FULL-SCALE OXYGENATION SYSTEM Oxygen can probably best be injected into the turbine rcleases from Fort Patrick Henry Dam by diffusing the oxygen through finc-pore diffusers. a Amberg et al. tested injection of oxygen into a turbine system by means of the perforated sparge ring that encircled the turbine above the runner blade; the maximum absorption efficiency obtained was only 40 percent (1). In proposed system, oxygen would be injected through diffusers placed either intakes, so that the oxygenated water immediately upstream from the turbine OXYC- is drawn directly into the turbines (Figure 3), or immediately downstream ox~ 0 0000oo U F from the "boil" area in the tailrace (Figure 4). The oxygen injection system through the turbines. 0 would only operate when water was discharged 00.01 The most economical location for diffuser injection appears to be upstream of from the turbine intakes. The greater depth of water has the advantages of allowing more contact time between the water and the gas bubbles and of increasing the ratio of the partial pressure of oxygen in the bubbles to that dissolved nitrogen so that oxygen transfers into the water faster than dissolved nitrogen transfe sure of oxygen t partial pressure HEADWATER dissolved nitrog of these factors thus reducing t' A disadvant- if all the oxygt 0 0 0 possible probic: 0 'o O.HYPOLIMNION turbine and thl 0 0 0 00 * 0 0 0 used to m,: 000- , ° :-OXYGEN0 taps Injecting w:: .............. BUBBLES affect the turi; 0o 00 0 0 0000 lower because injection inclu DIFFUSER: of gas (result oxygen per un injection), wC recirculation, depending on A liquid w Figure 3. Oxygen Injection Upstream from Turbine Intakes 294 0 -1 ases from Fort pore diffusers. by means of a incr blade; the it (I). In the ;placed either Igenatcd water ' downstream OXYGEN BUBBLES ýjection system bines. 000000 0 t0 0 0 0 0 0 00 D 0 be upstream o.oo%. o -oo o.0a 'dvantages of ubbles and of bles to that of Ian dissolved Figure 4. Oxygen Injection Downstream from Turbine Releases nitrogen transfers into the oxygen gas bubbles. The ratio of the partial pres- sure of oxygen to that of nitrogen increases with increased depth because the partial pressure of oxygen in a bubble increases with depth while that for dissolved nitrogen generally remains the same at all depths. The combination of these factors allows more gas to be injected through a unit area of diffuser, thus reducing the size of the required diffuser system. 'LINE A disadvantage of upstream injection is that several problems may develop if all the oxygen is not absorbed by the time it reaches the turbines. These IMNION possible problems include a reduction in turbine efficiency, corrosion of the turbine and the associated discharge system, and adverse effects on pressure taps used to measure turbine discharge. )XYGEN Injecting oxygen through diffusers downstream from the dam would not BUBBLES., affect the turbine discharge system, but oxygen absorption efficiency may be lower because of the shallower water. Other disadvantages of downstream injection include the need for a larger diffuser system to inject larger volumes of gas (resulting from both lower absorption efficiency and less mass of oxygen per unit volume of gas, because of less pressure compared to upstream injection), waste of oxygen to the atmosphere or the need for capture and recirculation, and perhaps a somewhat greater consumption of electric power depending on the number of vaporization units required. A liquid oxygen storage tank would be the source of oxygen gas because 295 An 0 0 Year 0 .- JI 1960 1961 0 3962 1.9634 .1965 MAY JUN JUL AUG SEP OCT NOV DEC 3.966 106 FIGuRE 5.