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Pollution Prevention and Abatement Handbook WORLD BANK GROUP Effective July 1998

Nitrogenous Plants

Industry Description and Practices tion of solids by prilling (pelletizing liquid drop- lets) or granulating; cooling and screening of sol- This document addresses the production of am- ids; coating of the solids; and bagging or bulk monia, , ammonium sulfate, ammonium ni- loading. The dioxide for urea manufac- trate (AN), calcium ammonium (CAN), ture is produced as a by-product from the am- and ammonium sulfate nitrate (ASN). The manu- monia plant reformer. facture of nitric used to produce nitrogenous typically occurs on site and is there- Ammonium Sulfate fore included here. Ammonium sulfate is produced as a caprolac- tam by-product from the petrochemical indus- try, as a by-product, and synthetically

Ammonia (NH3) is produced from atmospheric through reaction of ammonia with . and from a hydrocarbon Only the third process is covered in this docu- source. Natural gas is the most commonly used ment. The reaction between ammonia and sulfu- hydrocarbon feedstock for new plants; other ric acid produces an ammonium sulfate solution feedstocks that have been used include naphtha, that is continuously circulated through an evapo- oil, and gasified coal. Natural gas is favored rator to thicken the solution and to produce am- over the other feedstocks from an environmen- monium sulfate crystals. The crystals are tal perspective. separated from the liquor in a centrifuge, and the Ammonia production from natural gas in- liquor is returned to the evaporator. The crystals cludes the following processes: desulfurization of are fed either to a fluidized bed or to a rotary the feedstock; primary and secondary reforming; drum dryer and are screened before bagging or carbon monoxide shift conversion and removal bulk loading. of carbon dioxide, which can be used for urea manufacture; methanation; and ammonia synthe- , Calcium Ammonium Nitrate, sis. Catalysts used in the process may include and Ammonium Sulfate Nitrate , molybdenum, , /chro- mium oxide, oxide/ oxide, and iron. Ammonium nitrate is made by neutralizing nitric acid with anhydrous ammonia. The result- Urea ing 80–90% solution of ammonium nitrate can be sold as is, or it may be further concentrated to Urea fertilizers are produced by a reaction of liq- a 95–99.5% solution (melt) and converted into uid ammonia with carbon dioxide. The process prills or granules. The manufacturing steps in- steps include solution synthesis, where ammo- clude solution formation, solution concentration, nia and carbon dioxide react to form ammonium solids formation, solids finishing, screening, coat- carbamate, which is dehydrated to form urea; ing, and bagging or bulk shipping. The process- solution concentration by vacuum, crystalliza- ing steps depend on the desired finished product. tion, or evaporation to produce a melt; forma- Calcium ammonium nitrate is made by adding

353 354 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES calcite or dolomite to the ammonium nitrate melt higher if a fuel other than natural gas is used. before prilling or granulating. Ammonium sul- Energy consumption ranges from 29 to 36 fate nitrate is made by granulating a solution of gigajoules per metric ton (GJ/t) of ammonia. Pro- ammonium nitrate and ammonium sulfate. cess condensate discharged is about 1.5 cubic meters per metric ton (m3/t) of ammonia. Am- Nitric Acid monia tank farms can release upward of 10 kg of ammonia per ton of ammonia produced. Emis- The production stages for nitric acid manufac- sions of ammonia from the process have been ture include vaporizing the ammonia; mixing the reported in the range of less than 0.04 to 2 kg/t vapor with air and burning the mixture over a of ammonia produced. / catalyst; cooling the result- In a urea plant, ammonia and particulate mat- ant (NO) and oxidizing it to nitrogen ter are the emissions of concern. Ammonia emis- dioxide (NO2) with residual ; and absorb- sions are reported as recovery absorption vent ing the in in an absorp- (0.1–0.5 kg/t), concentration absorption vent tion column to produce nitric acid (HNO3). (0.1–0.2 kg/t), urea prilling (0.5–2.2 kg/t), and Because of the large quantities of ammonia and granulation (0.2–0.7 kg/t). The prill tower is a other hazardous materials handled on site, an source of urea dust (0.5–2.2 kg/t), as is the granu- emergency preparedness and response plan is lator (0.1–0.5 kg/t). required. are the principal air pollutant emitted from ammonium sulfate plants. Most of the Waste Characteristics particulates are found in the gaseous exhaust of the dryers. Uncontrolled discharges of particu- Air Emissions lates may be of the order of 23 kg/t from rotary dryers and 109 kg/t from fluidized bed dryers. Emissions to the atmosphere from ammonia plants Ammonia storage tanks can release ammonia, include (SO2), nitrogen and there may be fugitive losses of ammonia from

(NOx), carbon monoxide (CO), carbon dioxide process equipment.

(CO2), hydrogen sulfide, volatile organic com- The production of ammonium nitrate yields pounds (VOCs), particulates, methane, hydrogen emissions of particulate matter (ammonium nitrate , and ammonia. The two primary sources and coating materials), ammonia, and nitric acid. of pollutants, with typical reported values, in ki- The emission sources of primary importance are lograms per ton (kg/t) for the important pollut- the prilling tower and the granulator. Total quan- ants, are as follows: tities of nitrogen discharged are in the range of 0.01–18.4 kg/t of product. Values reported for • Flue gas from primary reformer calcium ammonium nitrate are in the range of 0.1– CO : 500 kg/t NH 2 3 3.3 kg nitrogen per ton of product. NO : 0.6–1.3 kg/t NH as NO x 3 2 Nitric acid plants emit nitric oxide, nitrogen SO : less than 0.1 kg/t 2 dioxide (the visible emissions), and trace amounts CO: less than 0.03 kg/t of nitric acid mist. Most of the nitrogen oxides • Carbon dioxide removal are found in the tail gases of the absorption tower. CO : 1,200 kg/t 2 Depending on the process, emissions in the tail emissions depend on the pro- gases can range from 215 to 4,300 milligrams per cess features. Nitrogen oxides are reduced, for cubic meter (mg/m3) for nitrogen oxides. Flow example, when there is low excess oxygen, with may be of the order of 3,200 m3 per ton of 100% steam injection; when postcombustion measures nitric acid. Nitrogen oxide values will be in the are in place; and when low-NOx burners are in low range when high-pressure absorption is use. Other measures will also reduce the total used; medium-pressure absorption yields nitro- amount of nitrogen oxides emitted. Concentra- gen oxide emissions at the high end of the range. tions of sulfur dioxide in the flue gas from the These values are prior to the addition of any reformer can be expected to be significantly abatement hardware. Nitrogenous Fertilizer Plants 355

Liquid Effluents Urea Plant

Ammonia plant effluents may contain up to 1 Use total recycle processes in the synthesis pro- kg of ammonia and up to 1 kg of methanol per cess; reduce microprill formation and carryover cubic meter prior to stripping. Effluent from of fines in prilling towers. urea plants may discharge from less than 0.1 kg to 2.6 kg nitrogen per ton product. Efflu- Ammonium Nitrate Plant ents from ammonium nitrate plants have been reported to discharge 0.7–6.5 kg nitrogen per The following pollution prevention measures are ton product. Comparable values for CAN plants recommended: are 0–10 kg nitrogen per ton of product. Nitric acid plants may have nitrogen in the effluent • Prill tower: reduce microprill formation and of the order of 0.1–1.7 kg nitrogen per ton of reduce carryover of fines through entrainment. nitric acid. • Granulators: reduce dust emissions from the disintegration of granules. Solid Wastes • Materials handling: where feasible use covers and hoods on conveyors and transition points. Solid wastes are principally spent catalysts that Good cleanup practices must be in place to originate in ammonia production and in the ni- minimize contamination of stormwater run- tric acid plant. Other solid wastes are not nor- off from the plant property. mally of environmental concern. It is important to note that hot ammonium ni- trate, whether in solid or in concentrated form, Pollution Prevention and Control carries the risk of decomposition and may even detonate under certain circumstances. Suitable Ammonia Plant precautions are therefore required in its manu- facture. The following pollution prevention measures are recommended: Ammonium Sulfate Plant • Where possible, use natural gas as the feed- stock for the ammonia plant, to minimize air Ammonium sulfate plants are normally fitted with emissions. fabric filters or scrubbers as part of the process. • Use hot process gas from the secondary re- former to heat the primary reformer tubes (the Target Pollution Loads exchanger-reformer concept), thus reducing the need for natural gas Implementation of cleaner production processes • Direct (HCN) gas in a fuel and pollution prevention measures can yield both oil gasification plant to a unit to economic and environmental benefits. The fol- prevent its release. lowing production-related targets can be • Consider using purge gases from the synthe- achieved by measures such as those described sis process to fire the reformer; strip conden- above. The numbers relate to the production pro- sates to reduce ammonia and methanol. cesses before the addition of pollution control • Use carbon dioxide removal processes that do measures. not release toxics to the environment. When monoethanolamine (MEA) or other processes, Ammonia Plant such as hot potassium carbonate, are used in carbon dioxide removal, proper operation and New ammonia plants should set as a target the maintenance procedures should be followed achievement of nitrogen oxide emissions of not

to minimize releases to the environment. more than 0.5 kg/t of product (expressed as NO2 356 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES

at 3% O2). Ammonia releases in liquid effluents ter treatment plant backwash, and cooling tower can be controlled to 0.1 kg/t of product. Conden- blowdown from the ammonia and nitric acid sates from ammonia production should be re- plants. They may require pH adjustment and set- used. tling. These effluents should preferably be re- cycled or reused. Nitric Acid Plant Spent catalysts are sent for regeneration or dis- posed of in a secure landfill. Nitrogen oxide levels should be controlled to a Modern plants using good industrial practices maximum of 1.6 kg/t of 100% nitric acid. are able to achieve the pollutant loads described below. Treatment Technologies Emissions Guidelines In urea plants, wet scrubbers or fabric filters are used to control fugitive emissions from prilling Emissions levels for the design and operation of towers; fabric filters are used to control dust emis- each project must be established through the en- sions from bagging operations. These devices are vironmental assessment (EA) process on the ba- an integral part of the operations, to retain prod- sis of country legislation and the Pollution Prevention uct. New urea plants should achieve levels of and Abatement Handbook, as applied to local con- particulate matter in air emissions of less than 0.5 ditions. The emissions levels selected must be kg/t of product for both urea and ammonia. justified in the EA and acceptable to the World In ammonium sulfate plants, use of fabric filters, Bank Group. with injection of absorbent as necessary, is the The guidelines given below present emis- preferred means of control. Discharges of not sions levels normally acceptable to the World more than 0.1 kg/t of product should be attain- Bank Group in making decisions regarding able for particulate matter. provision of World Bank Group assistance. Any In ammonium nitrate plants, wet scrubbers can deviations from these levels must be described be considered for prill towers and the granula- in the World Bank Group project documenta- tion plant. Particulate emissions of 0.5 kg/t of tion. The emissions levels given here can be product for the prill tower and 0.25 kg/t of prod- consistently achieved by well-designed, well- uct for granulation should be the target. Similar operated, and well-maintained pollution con- loads for ammonia are appropriate. trol systems. In nitric acid plants, extended absorption and The guidelines are expressed as concentrations technologies such as nonselective catalytic reduc- to facilitate monitoring. Dilution of air emissions tion (NSCR) and selective catalytic reduction or effluents to achieve these guidelines is un- (SCR) are used to control nitrogen oxides in tail acceptable. gases. To attain a level of 150 parts per million by volume (ppmv) of nitrogen oxides in the tail gases, All of the maximum levels should be achieved the following approaches should be considered: for at least 95% of the time that the plant or unit is operating, to be calculated as a proportion of • High-pressure, single-pressure process with annual operating hours. absorbing efficiency high enough to avoid ad- ditional abatement facilities Air Emissions • Dual-absorption process with an absorption efficiency high enough to avoid additional The emissions levels presented in Table 1 should treatment facilities be achieved. • Dual-pressure process with SCR • Medium-pressure, single-pressure process Liquid Effluents with SCR. Other effluents that originate in a nitrogenous The effluent levels presented in Table 2 should fertilizer complex include boiler blowdown, wa- be achieved. Nitrogenous Fertilizer Plants 357

Table 1. Air Emissions from Nitrogenous sistent performance has been established, sam- Fertilizer Plants pling for the parameters listed in this document (milligrams per normal cubic meter) should be as described below. Parameter Maximum value Air emissions should be monitored annually, except for nitrate acid plants, where nitrogen

Nitrogen oxides (as NO2) 300 oxides should be monitored continuously. Efflu- Urea 50 ents should be monitored continuously for pH Ammonia (NH )50 3 and monthly for other parameters. PM 50 Monitoring data should be analyzed and re- viewed at regular intervals and compared with Table 2. Effluents from Nitrogenous Fertilizer Plants the operating standards so that any necessary (milligrams per liter, except for pH and temperature) corrective actions can be taken. Records of monitoring results should be kept in an accept- Parameter Maximum value able format. The results should be reported to pH 6–9 the responsible authorities and relevant parties, TSS 50 as required. Ammonia (as nitrogen) 10 Urea 1 Key Issues Temperature increase < 3oCa

Note: Effluent requirements are for direct discharge to The key production and control practices that will surface . to compliance with emissions requirements a. The effluent should result in a temperature increase of can be summarized as follows: no more than 3°C at the edge of the zone where initial mixing and dilution take place. Where the zone is not • Choose natural gas, where possible, as feed- defined, use 100 meters from the point of discharge. stock for the ammonia plant. • Give preference to high-pressure processes or absorption process in combination with cata- Ambient Noise lytic reduction units. • Use low-dust-forming processes for solids for- Noise abatement measures should achieve either mation. the levels given below or a maximum increase in • Reuse condensates and other wastewaters. background levels of 3 decibels (measured on the • Maximize product recovery and minimize air A scale) [dB(A)]. Measurements are to be taken emissions by appropriate maintenance and at noise receptors located outside the project operation of scrubbers and baghouses. property boundary. Sources Maximum allowable log equivalent (hourly Bounicore, Anthony J., and Wayne T. Davis, eds. 1992. measurements), in dB(A) Air Pollution Engineering Manual. New York: Van Day Night Nostrand Reinhold. Receptor (07:00–22:00) (22:00–07:00) European Fertilizer Manufacturers’ Association. Residential, 1995a. “Production of Ammonia.” Booklet 1 of 8. institutional, Brussels. educational 55 45 Industrial, ————. 1995b. “Production of Nitric Acid.” Booklet 2 of 8. Brussels. commercial 70 70 ————. 1995c. “Production of Urea and Urea Am- Monitoring and Reporting monium Nitrate.” Booklet 5 of 8. Brussels. ————. 1995d. “Production of Ammonium Nitrate Frequent sampling may be required during start- and Calcium Ammonium Nitrate.” Booklet 6 of 8. up and upset conditions. Once a record of con- Brussels. 358 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES

European Union. 1990. “Best Available Technologies UNIDO (United Nations Industrial Development Or- Not Entailing Excessive Costs for Ammonia Produc- ganization). 1978. Process Technologies for Nitrogen tion.” Technical Note. Brussels. Fertilizers. Vienna. Sauchelli, Vincent. 1960. and Technology of World Bank. 1995. “Industrial Pollution Prevention and Fertilizers. New York: Reinhold Publishing. Abatement: Nitrogenous Fertilizer Plants.” Draft Technical Background Document. Environment Sittig, Marshall. 1979. Fertilizer Industry: Processes, Pol- Department, Washington, D.C. lution Control and Energy Conservation. Park Ridge, N.J.: Noyes Data Corporation.