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Nitrogenous Fertilizer Plants Pollution Prevention and Abatement Handbook WORLD BANK GROUP Effective July 1998 Nitrogenous Fertilizer 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, urea, ammonium sulfate, ammonium ni- loading. The carbon dioxide for urea manufac- trate (AN), calcium ammonium nitrate (CAN), ture is produced as a by-product from the am- and ammonium sulfate nitrate (ASN). The manu- monia plant reformer. facture of nitric acid used to produce nitrogenous fertilizers typically occurs on site and is there- Ammonium Sulfate fore included here. Ammonium sulfate is produced as a caprolac- Ammonia tam by-product from the petrochemical indus- try, as a coke by-product, and synthetically Ammonia (NH3) is produced from atmospheric through reaction of ammonia with sulfuric acid. nitrogen and hydrogen 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- Ammonium Nitrate, Calcium Ammonium Nitrate, sis. Catalysts used in the process may include and Ammonium Sulfate Nitrate cobalt, molybdenum, nickel, iron oxide/chro- mium oxide, copper oxide/zinc 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. platinum/rhodium catalyst; cooling the result- In a urea plant, ammonia and particulate mat- ant nitric oxide (NO) and oxidizing it to nitrogen ter are the emissions of concern. Ammonia emis- dioxide (NO2) with residual oxygen; and absorb- sions are reported as recovery absorption vent ing the nitrogen dioxide in water 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. Particulates 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 sulfur dioxide (SO2), nitrogen oxides 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 cyanide, 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 Nitrogen oxide 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 hydrogen cyanide (HCN) gas in a fuel and pollution prevention measures can yield both oil gasification plant to a combustion 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.
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