Fertiliser Plants

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353

Nitrogenous Fertilizer Plants

Industry Description and Practices

This document addresses the production of am-monia, urea, ammonium sulfate, ammonium ni-trate (AN), calcium ammonium nitrate (CAN),and ammonium sulfate nitrate (ASN). The manu-

facture of nitric acid used to produce nitrogenousfertilizers typically occurs on site and is there-fore included here.

Ammonia

Ammonia (NH3) is produced from atmosphericnitrogen and hydrogen from a hydrocarbonsource. Natural gas is the most commonly usedhydrocarbon feedstock for new plants; otherfeedstocks that have been used include naphtha,oil, and gasified coal. Natural gas is favored

over the other feedstocks from an environmen-tal perspective.Ammonia production from natural gas in-

cludes the following processes: desulfurization ofthe feedstock; primary and secondary reforming;carbon monoxide shift conversion and removalof carbon dioxide, which can be used for ureamanufacture; methanation; and ammonia synthe-sis. Catalysts used in the process may includecobalt, molybdenum, nickel, iron oxide/chro-mium oxide, copper oxide/zinc oxide, and iron.

Urea

Urea fertilizers are produced by a reaction of liq-uid ammonia with carbon dioxide. The processsteps include solution synthesis, where ammo-nia and carbon dioxide react to form ammoniumcarbamate, which is dehydrated to form urea;solution concentration by vacuum, crystalliza-tion, or evaporation to produce a melt; forma-

tion of solids by prilling (pelletizing liquid drop-lets) or granulating; cooling and screening of sol-ids; coating of the solids; and bagging or bulkloading. The carbon dioxide for urea manufac-ture is produced as a by-product from the am-monia plant reformer.

Ammonium Sulfate

Ammonium sulfate is produced as a caprolac-tam by-product from the petrochemical indus-try, as a coke by-product, and syntheticallythrough reaction of ammonia with sulfuric acid.Only the third process is covered in this docu-ment. The reaction between ammonia and sulfu-ric acid produces an ammonium sulfate solutionthat is continuously circulated through an evapo-rator to thicken the solution and to produce am-

monium sulfate crystals. The crystals areseparated from the liquor in a centrifuge, and theliquor is returned to the evaporator. The crystalsare fed either to a fluidized bed or to a rotarydrum dryer and are screened before bagging orbulk loading.

Ammonium Nitrate, Calcium Ammonium Nitrate,and Ammonium Sulfate Nitrate

Ammonium nitrate is made by neutralizingnitric acid with anhydrous ammonia. The result-

ing 8090% solution of ammonium nitrate canbe sold as is, or it may be further concentrated toa 9599.5% solution (melt) and converted intoprills or granules. The manufacturing steps in-clude solution formation, solution concentration,solids formation, solids finishing, screening, coat-ing, and bagging or bulk shipping. The process-ing steps depend on the desired finished product.Calcium ammonium nitrate is made by adding

Pollution Prevention and Abatement HandbWORLD BANK GRO

Effective July 1

of April 30 2007, this document is NO LONGER IN USE by theorld Bank Group. The new versions of the World Bank Groupvironmental, Health, and Safety Guidelines are available atp://www.ifc.org/ifcext/enviro.nsf/Content/EnvironmentalGuidelines


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354 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES

calcite or dolomite to the ammonium nitrate meltbefore prilling or granulating. Ammonium sul-fate nitrate is made by granulating a solution ofammonium nitrate and ammonium sulfate.

Nitric Acid

The production stages for nitric acid manufac-ture include vaporizing the ammonia; mixing thevapor with air and burning the mixture over aplatinum/rhodium catalyst; cooling the result-ant nitric oxide (NO) and oxidizing it to nitrogendioxide (NO2) with residual oxygen; and absorb-ing the nitrogen dioxide in water in an absorp-tion column to produce nitric acid (HNO3).

Because of the large quantities of ammonia andother hazardous materials handled on site, anemergency preparedness and response plan isrequired.

Waste Characteristics

Air Emissions

Emissions to the atmosphere fromammonia plantsinclude sulfur dioxide (SO2), nitrogen oxides(NOx), carbon monoxide (CO), carbon dioxide(CO2), hydrogen sulfide, volatile organic com-pounds (VOCs), particulates, methane, hydrogencyanide, and ammonia. The two primary sourcesof pollutants, with typical reported values, in ki-lograms per ton (kg/t) for the important pollut-ants, are as follows:

Flue gas from primary reformerCO2: 500 kg/t NH3NOx: 0.61.3 kg/t NH3as NO2SO2: less than 0.1 kg/tCO: less than 0.03 kg/t

Carbon dioxide removalCO2: 1,200 kg/t

Nitrogen oxide emissions depend on the pro-cess features. Nitrogen oxides are reduced, forexample, when there is low excess oxygen, withsteam injection; when postcombustion measuresare in place; and when low-NOxburners are inuse. Other measures will also reduce the totalamount of nitrogen oxides emitted. Concentra-tions of sulfur dioxide in the flue gas from thereformer can be expected to be significantly

higher if a fuel other than natural gas is used.Energy consumption ranges from 29 to 36gigajoules per metric ton (GJ/t) of ammonia. Pro-cess condensate discharged is about 1.5 cubicmeters per metric ton (m3/t) of ammonia. Am-

monia tank farms can release upward of 10 kg ofammonia per ton of ammonia produced. Emis-sions of ammonia from the process have beenreported in the range of less than 0.04 to 2 kg/tof ammonia produced.

In a urea plant,ammonia and particulate mat-ter are the emissions of concern. Ammonia emis-sions are reported as recovery absorption vent(0.10.5 kg/t), concentration absorption vent(0.10.2 kg/t), urea prilling (0.52.2 kg/t), andgranulation (0.20.7 kg/t). The prill tower is asource of urea dust (0.52.2 kg/t), as is the granu-lator (0.10.5 kg/t).

Particulates are the principal air pollutantemitted fromammonium sulfate plants. Most of theparticulates are found in the gaseous exhaust ofthe dryers. Uncontrolled discharges of particu-lates may be of the order of 23 kg/t from rotarydryers and 109 kg/t from fluidized bed dryers.Ammonia storage tanks can release ammonia,and there may be fugitive losses of ammonia fromprocess equipment.

The production of ammonium nitrate yieldsemissions of particulate matter (ammonium nitrateand coating materials), ammonia, and nitric acid.The emission sources of primary importance arethe prilling tower and the granulator. Total quan-tities of nitrogen discharged are in the range of0.0118.4 kg/t of product. Values reported forcalcium ammonium nitrate are in the range of 0.13.3 kg nitrogen per ton of product.

Nitric acid plants emit nitric oxide, nitrogendioxide (the visible emissions), and trace amountsof nitric acid mist. Most of the nitrogen oxidesare found in the tail gases of the absorption tower.Depending on the process, emissions in the tailgases can range from 215 to 4,300 milligrams per

cubic meter (mg/m3) for nitrogen oxides. Flowmay be of the order of 3,200 m3 per ton of 100%nitric acid. Nitrogen oxide values will be in thelow range when high-pressure absorption isused; medium-pressure absorption yields nitro-gen oxide emissions at the high end of the range.These values are prior to the addition of anyabatement hardware.


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355Nitrogenous Fertilizer Plants

Liquid Effluents

Ammonia plant effluents may contain up to 1kg of ammonia and up to 1 kg of methanol percubic meter prior to stripping. Effluent from

urea plants may discharge from less than 0.1kg to 2.6 kg nitrogen per ton product. Efflu-ents from ammonium nitrate plants have beenreported to discharge 0.76.5 kg nitrogen perton product. Comparable values for CAN plantsare 010 kg nitrogen per ton of product. Nitricacid plants may have nitrogen in the effluentof the order of 0.11.7 kg nitrogen per ton ofnitric acid.

Solid Wastes

Solid wastes are principally spent catalysts thatoriginate in ammonia production and in the ni-tric acid plant. Other solid wastes are not nor-mally of environmental concern.

Pollution Prevention and Control

Ammonia Plant

The following pollution prevention measures arerecommended:

Where possible, use natural gas as the feed-

stock for the ammonia plant, to minimize airemissions.

Use hot process gas from the secondary re-former to heat the primary reformer tubes (theexchanger-reformer concept), thus reducingthe need for natural gas

Direct hydrogen cyanide (HCN) gas in a fueloil gasification plant to a combustion unit toprevent its release.

Consider using purge gases from the synthe-sis process to fire the reformer; strip conden-sates to reduce ammonia and methanol.

Use carbon dioxide removal processes that donot release toxics to the environment. Whenmonoethanolamine (MEA) or other processes,such as hot potassium carbonate, are used incarbon dioxide removal, proper operation andmaintenance procedures should be followedto minimize releases to the environment.

Urea Plant

Use total recycle processes in the synthesis pro-cess; reduce microprill formation and carryoverof fines in prilling towers.

Ammonium Nitrate Plant

The following pollution prevention measures arerecommended:

Prill tower: reduce microprill formation andreduce carryover of fines through entrainment.

Granulators: reduce dust emissions from thedisintegration of granules.

Materials handling: where feasible use coversand hoods on conveyors and transition points.Good cleanup practices must be in place to

minimize contamination of stormwater run-off from the plant property.

It is important to note that hot ammonium ni-trate, whether in solid or in concentrated form,carries the risk of decomposition and may evendetonate under certain circumstances. Suitableprecautions are therefore required in its manu-facture.

Ammonium Sulfate Plant

Ammonium sulfate plants are normally fitted withfabric filters or scrubbers as part of the process.

Target Pollution Loads

Implementation of cleaner production processesand pollution prevention measures can yield botheconomic and environmental benefits. The fol-lowing production-related targets can beachieved by measures such as those describedabove. The numbers relate to the production pro-cesses before the addition of pollution control

measures.

Ammonia Plant

New ammonia plants should set as a target theachievement of nitrogen oxide emissions of notmore than 0.5 kg/t of product (expressed as NO2


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at 3% O2). Ammonia releases in liquid effluentscan be controlled to 0.1 kg/t of product. Conden-sates from ammonia production should be re-used.

Nitric Acid Plant

Nitrogen oxide levels should be controlled to amaximum of 1.6 kg/t of 100% nitric acid.

Treatment Technologies

In urea plants,wet scrubbers or fabric filters areused to control fugitive emissions from prillingtowers; fabric filters are used to control dust emis-sions from bagging operations. These devices arean integral part of the operations, to retain prod-

uct. New urea plants should achieve levels ofparticulate matter in air emissions of less than 0.5kg/t of product for both urea and ammonia.

In ammonium sulfate plants,use of fabric filters,with injection of absorbent as necessary, is thepreferred means of control. Discharges of notmore than 0.1 kg/t of product should be attain-able for particulate matter.

In ammonium nitrate plants, wet scrubbers canbe considered for prill towers and the granula-tion plant. Particulate emissions of 0.5 kg/t ofproduct for the prill tower and 0.25 kg/t of prod-uct for granulation should be the target. Similarloads for ammonia are appropriate.

In nitric acid plants,extended absorption andtechnologies such as nonselective catalytic reduc-tion (NSCR) and selective catalytic reduction(SCR) are used to control nitrogen oxides in tailgases. To attain a level of 150 parts per million byvolume (ppmv) of nitrogen oxides in the tail gases,the following approaches should be considered:

High-pressure, single-pressure process withabsorbing efficiency high enough to avoid ad-ditional abatement facilities

Dual-absorption process with an absorptionefficiency high enough to avoid additionaltreatment facilities

Dual-pressure process with SCR Medium-pressure, single-pressure process

with SCR.

Other effluents that originate in a nitrogenousfertilizer complex include boiler blowdown, wa-

ter treatment plant backwash, and cooling towerblowdown from the ammonia and nitric acidplants. They may require pH adjustment and set-tling. These effluents should preferably be re-cycled or reused.

Spent catalysts are sent for regeneration or dis-posed of in a secure landfill.Modern plants using good industrial practices

are able to achieve the pollutant loads describedbelow.

Emissions Guidelines

Emissions levels for the design and operation ofeach project must be established through the en-vironmental assessment (EA) process on the ba-sis of country legislation and thePollution Prevention

and Abatement Handbook,as applied to local con-ditions.The emissions levels selected must bejustified in the EA and acceptable to the WorldBank Group.

The guidelines given below present emis-sions levels normally acceptable to the WorldBank Group in making decisions regardingprovision of World Bank Group assistance. Anydeviations from these levels must be describedin the World Bank Group project documenta-tion. The emissions levels given here can beconsistently achieved by well-designed, well-

operated, and well-maintained pollution con-trol systems.

The guidelines are expressed as concentrationsto facilitate monitoring. Dilution of air emissionsor effluents to achieve these guidelines is un-acceptable.

All of the maximum levels should be achievedfor at least 95% of the time that the plant or unitis operating, to be calculated as a proportion ofannual operating hours.

Air Emissions

The emissions levels presented in Table 1 shouldbe achieved.

Liquid Effluents

The effluent levels presented in Table 2 shouldbe achieved.


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357Nitrogenous Fertilizer Plants

Ambient Noise

Noise abatement measures should achieve eitherthe levels given below or a maximum increase inbackground levels of 3 decibels (measured on theA scale) [dB(A)]. Measurements are to be takenat noise receptors located outside the projectproperty boundary.

Maximum allowable log

equivalent (hourly

measurements), in dB(A)

Day Night

Receptor (07:0022:00) (22:0007:00)

Residential,institutional,

educational 55 45

Industrial,

commercial 70 70

Monitoring and Reporting

Frequent sampling may be required during start-up and upset conditions. Once a record of con-

sistent performance has been established, sam-pling for the parameters listed in this documentshould be as described below.

Air emissions should be monitored annually,except for nitrate acid plants, where nitrogen

oxides should be monitored continuously. Efflu-ents should be monitored continuously for pHand monthly for other parameters.

Monitoring data should be analyzed and re-viewed at regular intervals and compared withthe operating standards so that any necessarycorrective actions can be taken. Records ofmonitoring results should be kept in an accept-able format. The results should be reported tothe responsible authorities and relevant parties,as required.

Key Issues

The key production and control practices that willlead to compliance with emissions requirementscan be summarized as follows:

Choose natural gas, where possible, as feed-stock for the ammonia plant.

Give preference to high-pressure processes orabsorption process in combination with cata-lytic reduction units.

Use low-dust-forming processes for solids for-mation.

Reuse condensates and other wastewaters. Maximize product recovery and minimize air

emissions by appropriate maintenance andoperation of scrubbers and baghouses.

Sources

Bounicore, Anthony J., and Wayne T. Davis, eds. 1992.Air Pollution Engineering Manual. New York: VanNostrand Reinhold.

European Fertilizer Manufacturers Association.

1995a. Production of Ammonia. Booklet 1 of 8.Brussels.

. 1995b. Production of Nitric Acid. Booklet2 of 8. Brussels.

. 1995c. Production of Urea and Urea Am-monium Nitrate. Booklet 5 of 8. Brussels.

. 1995d. Production of Ammonium Nitrateand Calcium Ammonium Nitrate. Booklet 6 of 8.Brussels.

Table 1. Air Emissions from Nitrogenous

Fertilizer Plants

(milligrams per normal cubic meter)

Parameter Maximum value

Nitrogen oxides (as NO2) 300

Urea 50

Ammonia (NH3) 50

PM 50

Table 2. Effluents from Nitrogenous Fertilizer Plants

(milligrams per liter, except for pH and temperature)

Parameter Maximum value

pH 69

TSS 50

Ammonia (as nitrogen) 10

Urea 1

Temperature increase < 3oCa

Note: Effluent requirements are for direct discharge to

surface waters.

a. The effluent should result in a temperature increase of

no more than 3C at the edge of the zone where initial

mixing and dilution take place. Where the zone is not

defined, use 100 meters from the point of discharge.


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European Union. 1990. Best Available TechnologiesNot Entailing Excessive Costs for Ammonia Produc-tion. Technical Note. Brussels.

Sauchelli, Vincent. 1960. Chemistry and Technology ofFertilizers. New York: Reinhold Publishing.

Sittig, Marshall. 1979. Fertilizer Industry: Processes, Pol-lution Control and Energy Conservation. Park Ridge,N.J.: Noyes Data Corporation.

UNIDO (United Nations Industrial Development Or-ganization). 1978. Process Technologies for NitrogenFertilizers. Vienna.

World Bank. 1995. Industrial Pollution Prevention andAbatement: Nitrogenous Fertilizer Plants. DraftTechnical Background Document. EnvironmentDepartment, Washington, D.C.

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