5 Agricultural

Chemicals:
Fertilizers

5.1 Overview of Fertilizers Nitric acid is a powerful oxidizing agent and is

used primarily to manufacture ammonium
Ammonia and Sulfuric Acid Are Key nitrate. Its minor uses include the manufacture
Chemicals In Fertilizer Production of adipic acid, nitroglycerin, trinitrotoluene
(TNT), nitrobenzene, and other chemicals.
Approximately 85 percent of the ammonia
After World War II, the chief use of ammonium
produced worldwide is used to make agricultural
nitrate was as an explosive. Although it is still
fertilizers. While ammonia can be applied
used in the manufacture of more than 75 percent
directly to the soil, it is usually first converted to
of all explosives, its primary use today is as a
a solid by reacting it with carbon dioxide or
fertilizer because of its high nitrogen content.
certain acids. Ammonia is also used as a raw
Nitric acid and ammonium nitrate ranked
material in the manufacture of polymeric resins,
explosives, nitric acid, and other products (see
Figure 5-1).
Production of Major
Agricultural Chemicals (1997)
Ammonia is ranked seventh among the top fifty
chemicals, with an annual production of 28.4 Ammonia (28.4 billion lbs)
billion pounds, and has ranked among the top ten Nitric Acid (13.5 billion lbs)
chemicals for the last thirty years. Ammonia is Ammonium Nitrate ( 12.3 billion lbs)
derived from methane, an organic feedstock, but Urea (11.8 billion lbs)
has traditionally been grouped with inorganic Ammonium Sulfate (4.1 billion lbs)
chemicals because its primary derivatives are Sulfuric Acid (71.4 billion lbs)
Phosphoric Acid (9.9 billion lbs)
inorganic. Many of its derivatives are also
Ammonium Phosphates (18.9 billion lbs)
among the top fifty chemicals, including nitric Super Phosphates (3.4 billion lbs)
acid, ammonium nitrate, ammonium sulfate, and
urea (Chenier 1992, CMA 1998). Source: CMA 1998, TFI 1999.

141
 Figure 5-1. Agricultural Chemicals: The Fertilizer Chain

seventeenth and eighteenth, respectively, among Sulfuric acid is an essential input to the
the top fifty chemicals in 1997 (Chenier 1992, manufacture of agricultural chemicals. In 1997,
CMA 1998). it was the chemical produced in the second
largest amount in the United States, at over 71
Although urea is considered an organic billion pounds annually. About 65 to 70 percent
compound, it is usually grouped with other of the sulfuric acid produced is used to
ammonia-derived synthetic nitrogen compounds manufacture phosphoric acid. The remainder is
because of its importance to the fertilizer used in chemical processing, petroleum refining
industry. About 53 percent of the urea produced (alkylation), pulp and paper production, plastics
is used in solid fertilizers, 31 percent is used in manufacture, and in non-chemical applications.
liquid fertilizers, and the rest is found in other Since its primary use is for fertilizer production,
products, including animal feed, formaldehyde it is often grouped with agricultural chemicals
resins, and adhesives. Urea is often combined (Chenier 1992, CMA 1998).
with other fertilizers, such as the commonly used
urea-ammonium nitrate mixture. Formaldehyde Phosphoric acid is the primary feedstock for
resins made from urea are found in dinnerware producing phosphate fertilizers. Of the nearly
and other consumer products (e.g., Formica®). 10 billion pounds of phosphoric acid produced
in 1997, about 9 billion pounds were used to
Ammonium sulfate, which ranked thirty-two on produce ammonium phosphates, normal
the top-fifty list in 1997, is used almost entirely superphosphates, and triple superphosphates.
as a fertilizer. Minor uses include water Ammonium phosphates contain both nitrogen
treatment, fermentation, and leather tanning and phosphorus, important fertilizer ingredients.
(Chenier 1992). The two most frequently used compounds are

142
monoammonium phosphate and diammonium has been weak prices in urea markets, which
phosphate (EPA 1997f, CMA 1998). may not improve unless China resumes
importing this product (CHEMWK 1999).The
Superphosphates are fertilizers containing use of fertilizers in the United States has grown
relatively large amounts of phosphorus. Normal steadily over the last ten years and is now
superphosphates contain up to 22 percent relatively stable. Rates of application range from
phosphorus; triple superphosphates contain about 140 to 270 pounds of fertilizer per acre
over 40 percent phosphorus (EPA 1997f). (see Table 5-2).

Demand for Fertilizers Is Closely Linked The United States is currently the largest
to Export Markets exporter of ammonium phosphates, providing
over 70 percent of the world’s supply. New
The production of fertilizers and their precursor capacity additions in Morocco, Australia, and
chemicals has declined significantly in recent India will create an oversupply of this fertilizer,
years, showing, for example, a drop of 20 to 30 however, and may force reductions in U.S.
percent from 1996 to 1997. This is due in part to production in the future (CHEMWK 1999). A
the growing capacity for manufacturing number of firms have shut down high-cost
fertilizers in Third World countries such as Asia capacity for phosphoric acid over the past few
and Mexico, which have previously been major years, which should help improve margins for
importers of U.S. products. Trends in U.S. phosphorus and a number of its derivatives
exports of major products are shown below in (CHEMX 1997).
Table 5-1.
Ammonia production is closely tied to
China has affected the demand for urea by agriculture and the demand for fertilizers. In the
banning its importation beginning in mid-1997, past, ammonia plants have sometimes operated
although it is the world’s largest consumer of this at close to 100 percent capacity to meet demand.
fertilizer. China is striving to become self- Today, oversupply and depressed margins are
sufficient in fertilizer production and continues affecting this trend, and forcing producers to
to bring new capacity on-line. India has also look for cheap ways to increase capacity. Some
reduced its urea imports following government analysts predict there will be a 1.4 million
controls on selected fertilizers. The result ton/year surplus in ammonia supplies this year
(CE 1996). Production decreased by a
substantial 20 percent between 1996 and 1997,
Table 5-1. Export Trends of U.S.
reflecting primarily decreased margins and
Fertilizers (1000 tons)
changes in export demand for fertilizers.
1994 1995 1996 1997
Ammonia 288 426 584 561 Table 5-2. Percentage of U.S. Acres
Receiving Fertilizer
Ammonium 840 1011 909 957
Sulfate Phos-
Total Nitro- pho-ic
Urea 1005 971 1621 1028 Crop lb/acre gen Acid Potash

Phosphoric 308 342 339 323 Corn 268 99 84 72

Acid
Cotton 202 90 67 58
Super- 882 787 752 766 Soybeans 163 20 28 33
phosphates
Wheat 139 87 63 18
Di- 10135 11088 8727 10405
ammonium
Phosphate Source: TFI 1999.

Source: TFI 1999.

143
Similar decreases of over 25 percent were noted this country has been steam reforming of natural
for sulfuric acid, the primary input to phosphoric gas. About 2 percent of the hydrogen required
acid and phosphate fertilizer production. Future for the Haber process is obtained from
production trends will be quite dependent on electrolysis of brine at chlorine plants.
export markets, particularly those in the Asia-
Pacific region. A typical process configuration for production
of ammonia is shown in Figure 5-2. Natural gas
5.1.1 Ammonia Manufacture is mixed with steam and charged to a primary
reformer, where it is passed over a nickel
Ammonia Is Still Produced by the Haber catalyst. In the primary reformer, which
Process operates at around 1300oF–1500oF
(700oC–815oC), most of the gas is converted to
Commercial synthesis and use of ammonia hydrogen, carbon monoxide, and carbon
originated in Germany’s need for nitrogen-rich dioxide. The exiting gas is mixed with air and
compounds for explosives manufacture during charged to a secondary reformer operating at
World War I. In the early 1900s, German higher temperatures, 1650oF-1700oF
chemist Fritz Haber developed an ammonia (900oC–925oC), where the remaining natural gas
synthesis process based on an iron catalyst that is converted. The gas leaving the secondary
enabled large-scale production of ammonia. reformer contains nitrogen, hydrogen, carbon
By1913, the German chemical company BASF1 monoxide, and carbon dioxide.
was making ammonia using this process at the
rate of 30 metric tons per day. The new The reformed gas is cooled in a waste heat
technology enabled greater, more rapid boiler where high-pressure, super-heated steam
production of explosives and extended the war is generated. The cooled gas is then charged to
for many years. Haber, however, received the high- and low-temperature shift converters
Nobel prize for his work in 1918, amidst containing different catalysts to convert the
objections from those who denounced his carbon monoxide into carbon dioxide to obtain
contributions to the war effort (Bristol 1999). additional hydrogen.

The Haber process is still the primary method Shift Converter Reaction
for ammonia synthesis used today, and requires
hydrogen, which can be produced from a variety CO + H2O 6 CO2 + H2
of hydrocarbon sources, and nitrogen, which is
supplied from air. The production of ammonia
from coal-derived synthesis gas is considered one
of the chemical engineering achievements of this The mixture of gases is then charged to a carbon
dioxide removal plant. Methods most
commonly used for this purpose include
absorption or wet scrubbing (e.g., with hot
Ammonia Formation potassium carbonated or methyl
diethanolamine). Outlet gas from the recovery
N2 + 3H2 ! 2NH3 plant is further purified through methanation
(Iron) and drying. The resulting pure synthesis gas is
compressed and fed through heat exchangers to
ammonia converters containing iron oxide
century. Since the 1930s, however, the primary catalysts (the Haber process). The gas stream is
source of hydrogen for ammonia production in refrigerated to condense ammonia, and
unreacted gases are recycled. The resulting
product is anhydrous ammonia.

1
BASF, or Badashe Analine und Soda Fabrik

144
 Figure 5-2. Manufacture of Ammonia (EPA 1997a, Orica 1999, HP 1999)

Key Energy and Environmental Facts - Ammonia Manufacture

Energy Emissions Effluents Wastes/Byproducts

Net Energy use: Largest source - fugitive Largest source - process water Carbon dioxide
emissions of ammonia
Process Energy: 12,150 Btu/lb
(includes fuel and feedstock)

While all plants use a process similar to that beverage markets. Excess carbon dioxide may
described above, configurations will vary with also be vented to the atmosphere (Process
respect to feedstocks (natural gas, hydrocarbon Description: EPA 1997a, Orica 1999, HP
gases, naphtha), operating temperatures, 1999).
pressures, and other parameters. In most cases,
the natural gas feedstock will need to be 5.1.2 Urea Manufacture
desulfurized to prevent poisoning of the nickel
catalyst used in steam reforming. Most Urea Is Produced by Solution Synthesis
ammonia plants use activated carbon fortified of Ammonia and Carbon Dioxide
with metallic oxide additives for this purpose.
About 50 percent of the ammonia
Carbon dioxide is produced as a byproduct of manufactured is used to produce urea (also
the ammonia manufacturing process, and is known as carbamide or carbonyl diamide) in
utilized in various ways–as a feedstock for urea both solid and liquid forms. Most solids are
production, or liquified and sold to food and produced as prills or granules, and are used as

145
fertilizers, protein supplements in animal feed, If a solid product is being manufactured,
and in plastics. additives are often used to reduce the caking of
solids and formation of urea dust during its
A typical flow diagram for production of urea is storage and handling.
shown in Figure 5-3. The actual configuration
will depend on whether urea is to be produced Concentration produces a urea “melt” that can
in solid (crystalline) or liquid form. In the then be used to produce solid urea through
solution synthesis process, ammonia and carbon prilling or granulation methods. Prilling
dioxide are first reacted under high pressure, produces solid particles directly from molten
140–250 atmospheres, and moderate urea; granulation, the process used more
temperatures, 350oF–400oF (175oC–200oC). The frequently, builds solids by creating layers of
resulting mixture is about 35 percent urea, 8 seed granules that are started by cooling
percent ammonium carbamate, 10 percent water, (Process Description: EPA 1993d, Orica 1999,
and 47 percent ammonia. Enviro-Chem 1999c, HP 1999).

The ammonia is distilled, and the solution is 5.1.3 Nitric Acid Manufacture
dehydrated to form a 70–77 percent aqueous
urea solution. The urea solution can be used in Nitric Acid Is Made by Direct Oxidation
this form, or it can be further concentrated using of Ammonia
vacuum concentration, crystallization, or
atmospheric evaporation. Nitric acid was made years ago by the reaction
of sulfuric acid and salt peter (a common name
for potassium nitrate or sodium nitrate).

Figure 5-3. Manufacture of Urea

(EPA 1993d, Orica 1999, HP 1999, Enviro-Chem 1999c)

Key Energy and Environmental Facts -Urea Manufacture

Energy Emissions Effluents Wastes/Byproducts

Net Energy use: Largest source - fugitive emissions Largest source - process Inert gases
(ammonia, formaldehyde, water
Process Energy: 732 Btu/lb methanol) and particulates

146
Today, most nitric acid is produced by high- The resulting mixture from this reaction is then
pressure and -temperature catalytic oxidation of sent to a waste heat boiler where steam is
ammonia. A typical process flow for nitric acid produced. In the second step, nitric oxide is
production is shown in Figure 5-4. oxidized by passage through a cooler/condenser,
where it is cooled to temperatures of 100oF
While configurations may differ somewhat (38oC) or less, at pressures of up to 116 psia.
between plants, three essential steps are During this stage, the nitric oxide reacts with
commonly employed. In the first step, ammonia residual oxygen to form nitrogen dioxide and
is oxidized to nitric oxide (NO) in a catalytic nitrogen tetroxide.
convertor over a platinum catalyst (90 percent
platinum, 10 percent rhodium gauze). The The final step introduces this mixture of
reaction is exothermic (heat-releasing) and nitrogen oxides into an absorption process
produces nitric oxide in yields of 93–98 percent. where the mixture flows countercurrent to
The reaction proceeds at high temperatures deionized water and additional liquid dinitrogen
ranging from 1380oF–1650oF (750oC–900oC). tetroxide. The tower is packed with sieve or
bubble cap distillation type trays. Oxidation

Figure 5-4. Manufacture of Nitric Acid

(EPA 1997b, Orica 1999, EFMA 1999, Enviro-Chem 1999a)

Key Energy and Environmental Facts -Nitric Acid Manufacture

Energy Emissions Effluents Wastes/Byproducts

Net Energy Exporter: Largest source - fugitive Largest source - process water Nitrogen oxides, spent
emissions (oxides of nitrogen, catalysts, inert gases
Net Steam: 311 Btu/lb nitric acid mist, ammonia)

147
takes places in between the trays in the tower; atmosphere (Process Description: EPA 1997b,
absorption occurs on the trays. An exothermic Orica 1999, EFMA 1999).
reaction between NO2 and water occurs in the
tower to produce nitric acid and NO. Air is 5.1.4 Ammonium Nitrate
introduced into the tower to re-oxidize the NO
that is being formed and to remove NO2 from Neutralizing Nitric Acid with Ammonia
the nitric acid. A weak acid solution (of 55–65 Produces Ammonium Nitrate
percent, although this varies) is withdrawn from
the bottom of the absorption tower. Ammonium nitrate is produced by neutralizing
nitric acid with ammonia. The final product can
To produce high strength nitric acid, the weak be liquid, or a solid in the form of prills, grains,
nitric acid solution is concentrated using granules, or crystals, depending upon whether
extractive distillation with a dehydrating agent. the end-use is for fertilizers or explosives.
Concentrated sulfuric acid is often used as the High-density solids are generally used as
agent. During this process, the sulfuric acid and fertilizers, while low-density grains are typically
weak nitric solution are fed to the top of a used in explosives manufacturing.
packed dehydrating column at atmospheric
pressure. Concentrated nitric acid leaves the top Figure 5-5 illustrates the processing of both
of the column as 99 percent vapor, with small liquid and solid ammonia nitrate. Ammonia and
amounts of NO2 and oxygen. The concentrated nitric acid are first introduced into a stainless
vapor is sent to a bleacher and condenser system steel reactor, where the heat of neutralization
to condense the strong acid and separate oxygen boils the mixture and concentrates it to about 85
and any nitrogen oxide byproducts, which are percent nitrate. If a liquid product is desired, it
recycled. Inert gases are vented to the is drawn off at this time.

Figure 5-5. Manufacture of Ammonium Nitrate (EPA 1993c, Chenier 1992)

Key Energy and Environmental Facts - Ammonium Nitrate Manufacture

Energy Emissions Effluents Wastes/Byproducts

Net Energy use: Largest source - particulates Largest source - process negligible
(ammonium nitrate and coating water
Process Energy: 341 Btu/lb materials), ammonia and nitric acid

148
About 60 percent of ammonium nitrate is 5.1.5 Ammonium Sulfate Production
currently produced in solid form. To create the
solid, the 85 percent nitrate solution is further Ammonium Sulfate Can Be Synthesized
concentrated through vacuum evaporation or in Directly or Produced as a Byproduct
a concentrator. The resulting “melt” contains
from 95 to 99.8 percent ammonium nitrate. The Ammonium sulfate was one of the first popular
melt can then be used to produce a solid product fertilizers, primarily because it was produced as
in prill towers or rotary drum granulators. a byproduct of coke ovens as early as 1893.
While it is still widely used, it has been
Additives such as magnesium nitrate or supplanted somewhat by urea and other
magnesium oxide may be introduced into the fertilizers that promote green growth in plants.
melt prior to solidification to raise the It is still often used as a component in many
crystalline transition temperature, act as a fertilizer blends.
desiccant (removing water), or lower the
temperature of solidification. Products are Ammonium sulfate can be produced as a
sometimes coated with clays or diatomaceous byproduct of caprolactam (see Section 4, The
earth to prevent agglomeration during storage BTX Chain), as a coke oven byproduct, or by
and shipment, although additives may eliminate direct synthesis. A typical flow diagram for the
the need for coatings. The final solid products synthetic process is shown in Figure 5-6. In this
are screened and sized, and off-size particles are process, anhydrous ammonia and sulfuric acid
dissolved and recycled through the process are combined in a pipe reactor. A highly
(Process Description: Chenier 1992, EPA exothermic reaction occurs, producing
1993c). ammonium sulfate and a bisulfate solution.

Figure 5-6. Manufacture of Ammonium Sulfate (EPA 1997d, Orica 1999)

Key Energy and Environmental Facts -Ammonium Sulfate Manufacture

Energy Emissions Effluents Wastes/Byproducts

Net Energy use: Largest source - particulates Largest source - process water negligible
(ammonium sulfate)
Process Energy: 4,000 Btu/lb

149
Ammonium sulfate crystals are formed by The contact process utilizes the techniques of
circulating the solution through an evaporator interpass absorption or double absorption. The
where it thickens. A centrifuge separates the typical flow diagram for this process is shown in
crystals from the mother liquor. The crystals Figure 5-7. Molten sulfur is burned at high
contain 1 percent to 2.5 percent moisture, and temperatures (>1800oF, or >980oC) in excess
are dried in a fluidized bed or rotary drum dryer. dry air to produce sulfur dioxide. The sulfur
Dryer exhaust gases are sent to a particulate dioxide is cooled in a waste heat boiler (that
collection system (e.g., wet scrubber) to control produces high-pressure steam and usually
emissions and recover residual product. Coarse powers a turbine for electricity generation).
and fine granules are separated by screening
before they are stored or shipped (Process After cooling, the sulfur dioxide is sent along
Description: EPA 1997d, Orica 1999). with oxygen to a staged converter with a set of
chambers containing a vanadium catalyst. After
5.1.6 Sulfuric Acid Manufacture passing through the third chamber, about 95
percent of the sulfur dioxide has been converted
Most Sulfuric Acid Is Made by Oxidation to sulfur trioxide. The mixture is then charged
of Sulfur to a two-stage absorption process where it
combines with water to form sulfuric acid. The
Historically, sulfuric acid2 has been an exiting sulfuric acid can be passed over the
important chemical, at least as far back as the vanadium catalyst again to attain a 99.7 percent
tenth century. Processes for making sulfuric conversion if desired. After the second
acid were first described in the fifteenth century, absorption stage, the final concentration of
when chemists told of burning sulfur with sulfuric acid is 98 percent or greater.
potassium nitrate (sometimes called salt peter).
The lead chamber process was introduced in the If oleum is produced (a mixture of excess sulfur
eighteenth century, which involved the trioxide and sulfuric acid), sulfur trioxide from
oxidation of sulfur to sulfur dioxide by oxygen, the converter is passed to an oleum tower that is
further oxidation to sulfur trioxide with nitrogen fed with 98 percent acid from the absorbers.
oxide, and hydrolysis of sulfur trioxide to The gases from this tower are then pumped to
achieve the final product. Nineteenth century the absorption column where sulfur trioxide is
modifications made the early process removed. Various concentrations of oleum can
economical until the 1940s, when it was be produced. Common ones include 20 percent
displaced by the contact process. oleum (20 percent sulfur trioxide in 80 percent
sulfuric acid, with no water), 40 percent oleum,
Today, 99 percent of sulfuric acid is made using and 60 percent oleum.
the contact method, an oxidation process based
on the burning of elemental sulfur (brimstone) The sulfuric acid conversion process is highly
with dry air (see Figure 5-7) or the roasting of exothermic, providing opportunities for energy
pyrite ore. Sources of elemental sulfur include recovery in many areas (e.g., after the sulfur
mining or oxidation of hydrogen sulfide (via the burner, after the converter pass, and in the
Claus process) from “sour”natural gas wells or absorption towers). Energy recovered is used
petroleum refineries. for process heating and/or electricity generation
(Process Description: Chenier 1992, EPA
1992a, Enviro-Chem 1999b, Orica 1999).

2
A colorless, odorless, heavy, oily liquid that was once
referred to as ”oil of vitriol”

150
 Figure 5-7. Manufacture of Sulfuric Acid
(EPA 1992a, Enviro-Chem 1999b, Orica 1999)

Key Energy and Environmental Facts - Sulfuric Acid Manufacture

Energy Emissions Effluents Wastes/Byproducts

Net Energy Exporter : Largest source - sulfur Largest source - process water Spent catalysts
dioxide, acid mist
(1,047 Btu/lb product)

5.1.7 Phosphoric Acid Manufacture form of phosphorus pentoxide, or P2O5). The

thermal process (sometimes called the furnace
Wet and Thermal Processing Methods process) accounts for about 10 percent of
Produce Different Grades of Phosphoric production, and is used to make high purity
Acid phosphoric acid for use in manufacturing
specialty chemicals, pharmaceuticals,
Phosphoric acid is the most important detergents, food products, and beverages.
derivative of sulfuric acid. It has been used as
fertilizer for hundreds of years, and is a key In the wet process (see Figure 5-8), sulfuric acid
ingredient in today’s phosphate fertilizers. The is reacted with naturally occurring phosphate
wet process is used to produce fertilizer-grade rock. The rock usually contains a high
phosphoric acid, and accounts for more than 90 percentage of fluorine, and if this is the case, the
percent of phosphoric acid production (in the mineral is called fluorapetite. It is mined in

151
 Figure 5-8. Manufacture of Phosphoric Acid - Wet Process (Chenier 1992, EPA 1997e)

Key Energy and Environmental Facts - Phosphoric Acid Manufacture

Energy Emissions Effluents Wastes/Byproducts

Net Energy use: Largest source - gaseous Largest source - acidic cooling Fluorosilicate salts,
fluorides (SiF4 and HF) and water with high concentrations uranium oxides, gypsum
Process Energy: 1,810 Btu/lb particulates of phosphorus and fluoride slurry, silicon fluoride

Florida, Texas, North Carolina, Idaho, and subsequently recycled back to the reactor for
Montana; 30 percent of world reserves are in the heat control and recovery.
United States.
U.S. plants typically use dihydration to produce
The phosphate rock is dried, crushed, and fed gypsum in the form of calcium sulfate with two
continuously into a reactor along with sulfuric water molecules attached (calcium sulfate
acid. During the reaction, calcium from the dihydrate). Hemihydration processes are
phosphate rock is combined with sulfate, popular in Japan and produce calcium sulfate
forming calcium sulfate (gypsum) and with a half molecule of water, which yields
phosphoric acid. Sulfuric acid with a phosphoric acid with a higher phosphorus
concentration of 93 percent is used to decrease pentoxide concentration and fewer impurities.
evaporation costs and ensure production of the In recent years, some U.S. firms have switched
strongest possible phosphoric acid. The four to to the hemihydration process.
eight reactors are heated to about 175oF (80oC)
for four to eight hours. Considerable heat is After the gypsum crystals are formed, filtration
generated in the reactors. A portion of the is used to separate them from the solution. The
reactor slurry is cooled by vacuum flashing and separated crystals are washed to yield 99
percent or better recovery of filtered phosphoric

152
acid. The final wet phosphoric acid product of phosphoric acid with anhydrous ammonia in
contains about 26 to 30 percent P2O5, and is ammoniation-granulation plants. In the United
further concentrated to 40 to 55 percent by States, 95 percent of ammoniation-granulation
vacuum evaporation to make it suitable for plants use a slightly inclined open-end rotary
fertilizer production. drum mixer for this process.3

After washing, the gypsum slurry is sent to a The ammoniation-granulation process is shown
pond for storage. Water from this pond is in Figure 5-9. Phosphoric acid is first mixed in
recycled back to the phosphoric acid process. a surge tank with 93 percent sulfuric acid and
Water storage requirements are substantial: recycled acid. The acids are neutralized with
approximately 0.7 acres of cooling and settling liquid or gaseous anhydrous ammonia in an acid
pond area are required for every ton of P2O5 reactor with a brick lining. The reactor
produced per day. produces a slurry of about 22 percent
ammonium phosphate and water, which is sent
Side products from the reaction include through steam-trace lines to the rotary drum
fluorosilicate salt (H2SiF6) and uranium oxides ammoniator-granulator.
(U3O8). Both silicon oxide and uranium occur in
many phosphate rocks in small percentages. The reactor slurry is distributed on a bed in the
Fluorosilicate salts are used in ceramics, granulator, while the remaining ammonia is
pesticides, wood preservatives, and concrete sparged underneath. Granulation occurs
hardeners. Processes for extraction of uranium through agglomeration and by coating particles
are available (MEAB 1999), but it is often not with slurry. Part of this process occurs in the
economical to recover the uranium. rotary drum, and is completed in a rotary
concurrent dryer.
During the thermal process, liquid elemental
phosphorus is burned in ambient air to form Ammonia-rich off-gases are produced, and these
P2O5. The P2O5 is then hydrated to produce are passed through a wet scrubbing system
strong phosphoric acid. Demisting is used to before venting to the atmosphere. Cooled
remove the phosphoric acid mist from the granules pass to a screening unit, where
combustion gas stream before it is released to oversized and undersized granules are separated
the atmosphere (Process Description: Chenier out and recycled back to the granulator (Process
1992, EPA 1997e). Description: EPA 1993e, EPA 1997f).

High-purity phosphoric acid (in a concentration Normal superphosphates are made by reacting
of up to 50 percent and greater) can also be ground phosphate rock with a 65 to 75 percent
recovered from the wet process by using concentration of sulfuric acid. Both virgin and
selective solvent extraction. A new membrane spent (recycled) sulfuric acid from other
process was developed recently that does not industrial processes may be used, although spent
require the use of solvents (KEMWorks 2000). acid may impart unusual colors, odors, or
toxicity to the product. The amount of iron and
5.1.8 Phosphate Fertilizers aluminum present in the rock is also a
consideration, as they can impart a condition of
Ammonium Phosphate and extreme stickiness to the superphosphate and
Superphosphates Are Processed make it difficult to handle.
Differently
In this process, ground phosphate rock and acid
Ammonium phosphate is the most widely used are mixed in a reaction vessel, stored until the
phosphate fertilizer, and is found in both solid
and liquid forms. Granular ammonium
phosphate fertilizer is produced by the reaction 3
Developed and patented by the Tennessee Valley
Authority (TVA)

153
 Figure 5-9. Manufacture of Ammonium Phosphate (EPA 1993e, Brown 1996)

Key Energy and Environmental Facts - Ammonium Phosphate Manufacture

Energy Emissions Effluents Wastes/Byproducts

Net Energy use: Largest source - gaseous Largest source - acidic Gypsum slurry, fertilizer
ammonia, fluorides (SiF4 and wastewater dust
Process Energy: 206 Btu/lb HF) and particulate
ammonium phosphate

reaction is completed (about 30 minutes), and removed and distributed onto dried, recycled
transferred to a storage pile for curing. These fines, where the granular surfaces become
processes are all conducted in enclosed areas to coated and increase in size.
prevent venting of toxic emissions. After
curing, the superphosphate is typically used as Rotating drum granulators are often used for
an additive to granular fertilizers, or it can be granulation. They are open-ended, slightly
granulated in a rotary drum granulator/dryer/ inclined rotary cylinders with a cutter mounted
cooing system. inside. A bed of dry material is maintained in
the unit, while slurry is introduced through pipes
Triple superphosphates are usually produced under the bed. The granules are wetted by the
using the Dorr-Oliver granular process (see slurry and discharged to a rotary dryer to
Figure 5-10). In this process, ground phosphate evaporate water and accelerate the chemical
rock or limestone is reacted with low- reaction to completion. Screening is used to
concentration phosphoric acid in a reactor(s). A remove off-size particles, which are recycled
sidestream of the resulting slurry is continuously Process Description: Brown 1996, EPA 1997a).

154
 Figure 5-10. Manufacture of Triple Superphosphates
(EPA 1993e, Brown 1996)

Key Energy and Environmental Facts - Triple Superphosphates Manufacture

Energy Emissions Effluents Wastes/Byproducts

Net Energy use: Largest source - gaseous Largest source - acidic Rock dust, fertilizer dust
fluorides (SiF4 and HF), rock wastewater
Process Energy: 690 Btu/lb dust, particulates

4.2 Summary of Inputs/Outputs

The following summarizes the essential inputs
and products, wastes and byproducts of the
chemicals and chemical products included in the
Agricultural Chemicals chain.

Ammonia Urea

Inputs: Outputs: Inputs: Outputs:

Natural Gas Anhydrous Ammonia Ammonia Solid Urea

Air Carbon Dioxide Carbon Dioxide Urea Solution
Catalyst Export Steam Additives Process Water
Steam/Fuel Recycle Gases Process Water
Electricity Process Water Steam/Fuel
Electricity

155
Nitric Acid Phosphoric Acid

Inputs: Outputs: Inputs: Outputs:

Ammonia Weak Nitric Acid Phosphate Rock Phosphoric Acid
Deionized Water High Strength Nitric Acid 93% Sulfuric Acid Fluorosilicate Salts
Sulfuric Acid Process Water Process Water Uranium Oxide
Catalyst Steam Steam/Fuel Silicon Fluoride
Air/Oxygen Spent Catalyst Electricity Export Steam
Bleaching Agent Nitrogen Oxides Gypsum Slurry
Process Water Inert Gases Process Water
Steam/Fuel
Electricity
Ammonium Phosphate

Ammonium Nitrate
Inputs: Outputs:

Inputs: Outputs: Phosphoric Acid Ammonium Phosphate

Sulfuric Acid Fertilizer
Ammonia Solid Ammonium Anhydrous Process Water
Nitric Acid Nitrate Ammonia Gypsum Slurry
Additives Air Gypsum Pond Water
Electricity Process Water
Gypsum Pond Water
Ammonium Sulfate Scrubbing Liquor
Steam/Fuel
Electricity
Inputs: Outputs:
Ammonia Ammonium Sulfate Normal Superphosphates
Sulfuric Acid Scrubber Products
Cooling Water Vent Gas
Steam/Fuel Process Water Inputs: Outputs:
Electricity Ground Phosphate N-Superphosphates
Rock Rock Dust
Sulfuric Acid Sulfuric Acid
Air
Electricity
Inputs: Outputs:
Elemental Sulfur Sulfuric Acid Triple Superphosphates
Dry Combustion Air Sulfur Dioxide
Catalyst Process Water Inputs: Outputs:
Cooling Water Export Steam
Steam/Fuel Export Electricity Ground Phosphate Triple Superphosphates
Electricity Spent Catalyst Rock Process Water
Air Rock/Fertilizer Dust
Process Water
Steam/Fuel
Electricity

156
5.3 Energy Requirements For every category, energy use for process heat is
distributed according to the various fuel types
Process Energy for Some Agricultural used throughout the industry. Fuel distribution for
Chemicals Is Relatively High 1997 was as follows: fuel oil and LPG - 3
percent; natural gas - 77 percent; coal and coke -
The process and feedstock energy used for the 10 percent; other - 10 percent (CMA 1998). The
production of agricultural chemicals are shown “other” category includes any other fuel source
in Tables 5-3 through 5-12 (PNNL 1994, Brown (e.g., byproduct fuel gases).
1996, HP 1997d, Enviro-Chem 1999a, HP
1999). Each table provides net processing Processing energy consumption for heat and
energy, which is the energy used to provide heat power associated with the production of ammonia
and power for the process, in the form of fuels, is relatively high, on the order of 12,000 Btu/lb.
electricity, or steam. Each table also shows Most of this energy is in the form of steam used
Total Process Energy, which includes for the reforming of methane, ammonia
processing energy for the final product, minus conversion, and vent gas stripping. The large
any steam or fuel generated by the process, plus energy input results primarily from the need for
electricity losses. Electricity losses are those multiple passes over the catalyst to achieve
incurred during the generation and transmission acceptable product yields.
of electricity (regardless of whether it is
purchased or produced on-site). Thus, Total Feedstock energy in the form of natural gas or
Process Energy is the total primary energy mixed hydrocarbon gases is required for ammonia
consumption associated with production of the production, and is included in the processing
individual chemical. energy since it is normally reported this way in

Table 5-3. Estimated Energy Use in Ammonia Manufacture- 1997

Specific Energyd Average Specific Total Industry
Energy (Btu/lb) Energy (Btu/lb) Usee (1012 Btu)
Electricitya 885 - 953 919 26.1

Energy for Steam/Process Heatd

Fuel Oil and LPGb 121 - 130 126 3.6

Natural Gas 9,888 - 10,649 10,269 291.6

Coal and Coke 403 - 434 418 11.9

Otherc 403 - 434 418 11.9

NET PROCESS ENERGY 11,700 - 12,600 12,150 345.1

Electricity Losses 1,838 - 1,979 1,908 54.2

Energy Export 0 0 0.0

TOTAL PROCESS ENERGY 13,538 - 14,579 14,058 399.3

a Does not include losses incurred during the generation and transmission of electricity.
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values are based on
published fuel use and electricity requirements for licensed technologies, including those licensed by ICI Katalco/Synetix,
Linde AG, and Kellogg, Brown & Root, Inc. (EEA 1983, HP 1999, EFMA 1999).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values for ammonia (28.4 billion lbs) (CMA 1998).

157
 Table 5-4. Estimated Energy Use in Urea Manufacture- 1997
Specific Energy Average Specificd Total Industry Usee
Energy (Btu/lb) Energy (Btu/lb) (1012 Btu)

Electricitya 23 - 188 106 1.2

Energy for Steam/Process Heatd

Fuel Oil and LPGb 19 - 25 22 0.3

Natural Gas 483 - 652 567 6.7

Coal and Coke 63 - 85 74 0.9

Otherc 63 - 85 74 0.9

NET PROCESS ENERGY 650 - 1,035 843 9.9

Electricity Losses 48 - 390 219 2.6

Energy Export (94) - (127) (111) (1.3)

TOTAL PROCESS ENERGY 604 - 1,298 951 11.2

a Does not include losses incurred during the generation and transmission of electricity.
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values are based on published
fuel use and electricity requirements for licensed technologies, including CO2 and NH3 stripping, isobaric double recycle, and
advanced processes (EFMA 1999, HP 1999).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values for urea (11.8 billion lbs) (CMA 1998).

Table 5-5. Estimated Energy Use in Manufacture of Nitric Acid - 1997

Specific Energyd Average Specific Total Industry Usee
Energy (Btu/lb) Energy (Btu/lb) (1012 Btu)

Electricitya 2-3 3 0.0

Energy for Steam/Process Heatd

Fuel Oil and LPGb 7-9 8 0.1

Natural Gas 178 - 229 203 2.7

Coal and Coke 23 - 30 26 0.4

Otherc 23 - 30 26 0.4

NET PROCESS ENERGY 233 - 300 267 3.6

Electricity Losses 4-6 5 0.1

Energy Export (594) - (561) (578) (7.8)

TOTAL PROCESS ENERGY (255) - (357) (306) (4.1)

a Does not include losses incurred during the generation and transmission of electricity.
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values based on published
fuel and electricity requirements for licensed technologies (Enviro-Chem, Inc.,1999a).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values (13.5 billion lbs) (CMA 1998).

158
 Table 5-6. Estimated Energy Use in Ammonium Nitrate Manufacture- 1997
Specific Energy Average Specificd Total Industry Usee
Energy (Btu/lb) Energy (Btu/lb) (1012 Btu)

Electricitya 55 - 187 121 1.5

Energy for Steam/Process Heatd

Fuel Oil and LPGb 5-8 7 0.1

Natural Gas 127 - 212 169 2.1

Coal and Coke 17 – 28 22 0.3

Otherc 17 - 28 22 0.3

NET PROCESS ENERGY 220 - 462 341 4.2

Electricity Losses 114 - 388 251 3.1

Energy Export 0 0 0.0

TOTAL PROCESS ENERGY 334 - 850 592 7.3

a Does not include losses incurred during the generation and transmission of electricity.
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values are based on
published fuel use and electricity requirements for licensed technologies (EFMA 1999).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values (12.3 billion lbs) (CMA 1998).

Table 5-7. Estimated Energy Use in Manufacture of Ammonium Sulfate - 1997

Average Specificd Energy Total Industry Usee
Energy (Btu/lb) (1012 Btu)

Electricitya 720 3.0

Energy for Steam/Process Heatd

Fuel Oil and LPGb 98 0.4

Natural Gas 2,526 10.4

Coal and Coke 328 1.3

Otherc 328 1.3

NET PROCESS ENERGY 4,000 16.4

Electricity Losses 1,495 6.1

Energy Export 0 0.0

TOTAL PROCESS ENERGY 5,495 22.5

a Does not include losses incurred during the generation and transmission of electricity.
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values are based on published
fuel use and electricity requirements for licensed technologies (PNNL 1994).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values (4.1 billion lbs) (CMA 1998).

159
 Table 5-8. Estimated Energy Use in Manufacture of Sulfuric Acid - 1997
Average Specificd Energy Total Industry Usee
Energy (Btu/lb) (1012 Btu)

Electricitya 28 2.0

Energy for Steam/Process Heatd

Fuel Oil and LPGb 1 0.1

Natural Gas 23 1.7

Coal and Coke 3 0.2

Otherc 3 0.2

NET PROCESS ENERGY 58 4.1

Electricity Losses 58 4.2

Energy Export (1,047) (74.8)

TOTAL PROCESS ENERGY (931) (66.5)

a Does not include losses incurred during the generation and transmission of electricity.
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values are based on published
fuel and electricity requirements for licensed technologies (Enviro-Chem, Inc.,1999b).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values (71.4 billion lbs) (CMA 1998).

Table 5-9. Estimated Energy Use in Manufacture of Phosphoric Acid (Wet Process) - 1997
Specific Energy Average Specificd Total Industry Usee
Energy (Btu/lb) Energy (Btu/lb) (1012 Btu)

Electricitya 186 - 464 325 3.1

Energy for Steam/Process Heatd

Fuel Oil and LPGb 17 - 73 45 0.4

Natural Gas 424 - 1,863 1,143 10.9

Coal and Coke 55 - 242 149 1.4

Otherc 55 - 242 149 1.4

NET PROCESS ENERGY 736 - 2,884 1,810 17.2

Electricity Losses 386 - 963 675 6.4

Energy Export 0 0 0.0

TOTAL PROCESS ENERGY 1,122 - 3,847 2,485 23.6

a Does not include losses incurred during the generation and transmission of electricity. Does not include electricity for grinding
phosphate rock, which requires about 4,180 Btu/lb (Brown 1996).
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values are based on published
fuel and electricity requirements for wet process technologies (EFMA 1999, Brown 1996).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values (9.5 billion lbs) (CMA 1998). The wet process is
used for about 96 percent of phosphoric acid manufacture.

160
 Table 5-10. Estimated Energy Use in Manufacture of Phosphoric Acid
(Furnace Process) - 1997
Average Specificd Energy Total Industry Usee
Energy (Btu/lb) (1012 Btu)

Electricitya 14,581 58.0

Energy for Steam/Process Heatd

Fuel Oil and LPGb 3 0.0

Natural Gas 82 0.0

Coal and Coke 24,003 9.6

Otherc 21 0.0

NET PROCESS ENERGY 38,690 15.5

Electricity Losses 30,277 12.1

Energy Export 0 0.0

TOTAL PROCESS ENERGY 68,967 27.6

a Does not include losses incurred during the generation and transmission of electricity. Includes electricity for grinding
phosphate rock..
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values are based on
published fuel and electricity requirements for furnace process technologies (Source: Brown 1996).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values (0.4 billion lbs) (CMA 1998). The furnace
process is used for about 4 percent of phosphoric acid manufacture.

the literature (see Table 5-3). Feedstock compressors and pumps. Steam consumption is
requirements usually comprise about 50–60 somewhat higher in plants utilizing dual-pressure
percent of combined processing energy. Despite (rather than single-pressure) operations.
their origin in hydrocarbon feedstocks, ammonia-
derived compounds are generally considered The sulfuric acid plants are large net steam
inorganic. Thus, any organic feedstock energy exporters. Large amounts of high-pressure steam
embodied in the ammonia input is not considered are used to power a turbo-alternator for
in the remainder of the energy tables. electricity generation. The waste heat boiler used
for cooling sulfur dioxide is the largest source of
Process energy requirements for manufacture of export steam, although energy may be recovered
urea, ammonium nitrate, and ammonium in many places throughout the process. Steam
sulfate are relatively low. The bulk of energy is export values range from about 1,000 Btu/lb to
in the form of steam used for process heating. over 2,600 Btu/lb of sulfuric acid in well-
Electricity is used mostly for the centrifuging and optimized, state-of-the art plants. Optimizing
screening of solid products. energy recovery from plants lowers production
costs, and improvements are continually being
Processes used for manufacturing nitric acid are made in this area. With advanced technology,
generally net steam exporters, requiring very net steam export values can reportedly double in
small amounts of electricity for driving air amount (Enviro-Chem 1999d, EFMA 1999).

161
 Table 5-11. Estimated Energy Use in Manufacture of Ammonium Phosphate - 1997
Average Specificd Energy Total Industry Usee
Energy (Btu/lb) (1012 Btu)

Electricitya 82 1.6

Energy for Steam/Process Heatd

Fuel Oil and LPGb 7 0.1

Natural Gas 186 3.5

Coal and Coke 24 0.5

Otherc 24 0.5

NET PROCESS ENERGY 323 6.1

Electricity Losses 170 3.2

Energy Export (117) (2.2)

TOTAL PROCESS ENERGY 376 7.1

a Does not include losses incurred during the generation and transmission of electricity.
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values are based on
published fuel and electricity requirements for licensed technologies (Brown 1996).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values (18.9 billion lbs) (TFI 1999).

The wet process is used for 96 percent of the Production of phosphate fertilizers requires very
phosphoric acid manufactured. This process is modest energy consumption, primarily in the
moderately energy-intensive, requiring about form of steam used for drying. Ammonium
6,130 Btu/lb. An alternative method, the furnace phosphate processes also generate export steam.
process, is used for the remaining 4 percent of Electricity is used for granulating, milling,
production and it is highly energy-intensive, crushing, and screening solid products.
consuming nearly 40,000 Btu/lb. This process is
used solely for producing high-quality, chemical-
grade phosphoric acid, not fertilizer-grade
product.

162
 Table 5-12. Estimated Energy Use in Manufacture of Superphosphates - 1997
Average Specificd Energy Total Industry Usee
Energy (Btu/lb) (1012 Btu)

Electricitya 340 1.2

Energy for Steam/Process Heatd

Fuel Oil and LPGb 11 0.1

Natural Gas 270 0.9

Coal and Coke 35 0.1

Otherc 35 0.1

NET PROCESS ENERGY 690 2.4

Electricity Losses 706 2.4

Energy Export 0 0.0

TOTAL PROCESS ENERGY 1,396 4.8

a Does not include losses incurred during the generation and transmission of electricity.
b Includes ethane, ethylene, propane, propylene, normal butane, butylenes, and mixtures of these gases.
c Includes net purchased steam, and any other energy source not listed (e.g., renewables).
d Steam/fuel use estimated based on current distribution of fuels in chemical plants (CMA 1998). Values are based on
published fuel and electricity requirements for granulated triple superphosphate processes (Brown 1996).
e Calculated by multiplying average energy use (Btu/lb) by1997 production values for normal and triple superphosphates (3.4
billion lbs) (TFI 1999).

5.4 Air Emissions fugitive emissions sources. Ammonia is released

during its manufacture as well as during its use in
other chemical processes. Releases of ammonia
Ammonia and Sulfur Compounds Are the are reported annually in the Toxic Release
Primary Source of Air Contaminants from Inventory (TRI). In 1996, nearly 110 million
Production of Agricultural Chemicals pounds of ammonia were released by the
chemical industry to the air, land, and water.
The primary sources of emissions in the Over 10 million pounds were also released from
agricultural chemicals chain are fugitive and petroleum refineries (EPA 1998, EPA 1997c).
point air source emissions of particulates and
volatile compounds emitted from equipment and Pollutants from ammonia manufacture are
process operations. Fugitive emissions of emitted from regeneration of the desulfurization
volatile compounds arise from leaks in valves, bed, heating of the catalytic steam, regeneration
pumps, tanks, flanges, and other similar sources. of carbon dioxide scrubbing solution, and steam
Particulates arise from granulation processes stripping of the process condensate. Emission
used for production of solid fertilizers, and from factors for each of these emission points are
rock dust during ore processing. given in Table 5-13. Nearly all U.S. ammonia
plants use activated carbon fortified with metallic
Ammonia is one of the top five toxic chemicals
oxide additives to desulfurize feedstocks. These
released every year, primarily from point air and

163
beds are regenerated about once a month. The those from concentrating the solution and vented
vented regeneration steam contains sulfur oxides through stacks. Particulate control is usually
and hydrogen sulfide, some hydrocarbons, and only carried out in the solids-producing areas;
carbon monoxide. other emissions of particulates are small by
comparison. In the solids-screening process, dust
Carbon dioxide is a byproduct of the reaction and is generated as urea particles collide and the
is removed from the synthesis gas by scrubbing screen vibrates. In urea manufacture, almost all
with hot potassium carbonate or similar the screening operations are enclosed or covered
compounds. Regeneration of this scrubbing to reduce emissions. Coating of the product may
solution liberates water, ammonia, carbon emit entrained clay dust during loading and
monoxide, and volatile scrubbing solution product transfer, but no emission factors are
compounds. Stripping of process condensate available to quantify this source (EPA 1993d).
yields steam, which is vented to the atmosphere
and contains ammonia, carbon dioxide, and Emissions from the manufacture of nitric acid
methanol. include mostly nitrogen oxides (NO and NO2),
and trace amounts of ammonia and nitric acid
The primary emissions from urea manufacture mist. The tail gas from the acid absorption tower
are ammonia and particulates. Small amounts of is the largest source of nitrogen oxide emissions.
volatile additive components (e.g., methanol, These emissions can increase when insufficient
formaldehyde) may also be emitted. Additives air is supplied to the oxidizer and absorber, under
like FormalinTM, for example, may contain up to low absorber pressure conditions, and during
15 percent methanol. Ammonia may be emitted high temperature conditions in the
during solution synthesis and production of solid cooler/condenser and absorber. Other factors
products. Particulates are emitted throughout the may contribute, such as high throughputs, very
process. Table 5-14 provides emission factors high-strength products, or faulty compressors or
for urea production. pumps. Emission factors for nitric acid plants are
shown in Table 5-15.
The recycling of carbamate gases or liquids
allows some emission control. Emissions from
the synthesis process are usually combined with

Table 5-13. Air Emissions from Ammonia Manufacture

Emission Point CO SO2 TOCa NH3 CO2
(lb/ton) (lb/ton) (lb/ton) (lb/ton) (lb/ton)
b
Desulfurization unit regeneration 13.8 0.0576 7.2 ND

Carbon dioxide regenerator 2.0 1.04c 2.0 2440

Condensate steam stripper 1.2d 2.2 6.8 (±60%)

a Total organic compounds.

b Intermittent source; regeneration is done every 30 days. SO2 is a worst case factor (all sulfur entering tank is emitted).
c 0.1 lb/ton is monoethanolamine.
d Primarily methanol.

Source: EPA 1997a.

164
Control of emissions from nitric acid plants is Particulate matter is the largest source and is
usually accomplished through either extended emitted throughout the process during the
absorption or catalytic reduction. Extended formation of solids. Prill towers and granulators
absorption works by increasing the efficiency of are the largest sources of particulates.
the absorption process. Catalytic reduction Microprills can form and clog orifices,
oxidizes nitrogen oxides in the tail gas and increasing fine dust loading and emissions.
reduces them to nitrogen. While catalytic
reduction is more energy-intensive, it achieves Emissions occur from screening operations by
greater emission reductions than the extended the banging of ammonium nitrate solids against
absorption method. Less-used control options each other and the screens. Most of these
include wet scrubbers or molecular sieves, both screening operations are enclosed or have partial
of which have higher capital and operating costs covers to reduce emissions. The coating of
than the other options (EPA 1997b). products may also create some particulate
emissions during mixing in the rotary drums.
The manufacture of ammonium nitrate This dust is usually captured and recycled to
produces particulate matter, ammonia, and nitric coating storage. Another source of dust is
acid emissions. Emission factors are shown in bagging and bulk loading, mostly during final
Table 5-16. Emissions from ammonia and nitric filling when dust-laden air is displaced from
acid occur primarily when they form solutions bags (EPA 1993c).
(neutralizers and concentrators), and when they
are used in granulators.

Table 5-14. Air Emissions from Urea Manufacture

Particulates (lb/ton) Ammonia (lb/ton)
Type of Operation
Uncontrolled Controlled Uncontrolled Controlled

Solution formation 0.021 18.46

a
and concentration

Nonfluidized bed 3.7 0.063 0.87

b
prilling

Fluidized bed 4.9 0.63 3.53 2.08

c
prilling
c
Drum Granulation 241 0.234 2.15

Rotary Drum 7.78 0.20 0.051

Cooler

Bagging 0.19

a Emissions from synthesis are usually combined with those from solution concentration and vented through a common stack.
In synthesis, some emission control is inherent in the recycle process where carbamate gases and/or liquids are recovered
and recycled.
b Controlled factors are based on ducting exhaust through a downcomer, then a wetted fiber filter scrubber (98.3% efficient), a
higher degree of control than is typical in the industry.
c Controlled factors are based on use of an entrainment scrubber.

Source: EPA 1993d.

165
 Table 5-15. Air Emissions from Nitric Acid Plants
Control Efficiency Nitrogen Oxides
Source % (lbs/tona)
Weak Acid Plant Tail Gas

Uncontrolledb 0 57

Catalytic Reduction
Natural Gas 99.1 0.4
Hydrogen 97-98.5 0.8
98-98.5 0.9
Natural Gas/Hydrogen
95.8 1.9
Extended Absorption 2.1
Single-Stage
Dual-Stage
n/a 2.2
Chilled Absorption & Caustic
Scrubber

High Strength Acid Plant n/a 10

a Based on 100% nitric acid.

b Single-stage pressure process.

Source: EPA 1993b.

Table 5-16. Air Emissions from Ammonium Nitrate Manufacture

Process Particulate Matter (lb/ton) Ammonia Nitric Acid
(uncontrol lb/ton
a
Uncontrolled Controlled led) lb/ton
Neutralizer 0.090-8.6 0.004-0.44 0.86-36.0 0.084-2.0

Evaporation/concentration 0.52 0.54-33.4

operations

Solids Formation operations 298.8 2.2 58.5

Coolers and Dryersb 220.4 2.2 1.93

Coating Operations <4.0 <0.04

a Based on the following efficiencies for wet scrubbers: neutralizer, 95%; high density prill towers, 62%; low density prill towers,
43%; rotary drum granulators,99.9%; pan granulators,98.5%; coolers, dryers, and coaters,99%.
b Combined cooler and precooler emissions, and combined dryer and predryer emissions.

Source: EPA 1993c.

166
 Table 5-17. Air Emissions from Ammonium Sulfate Manufacture
Dryer Type Particulate (lb/ton) VOCa (lb/ton)
Rotary Dryers
(Uncontrolled) 46 1.48
(Wet Scrubber) 0.04 0.22

Fluidized-bed Dryers
(Uncontrolled) 218 1.48
(Wet Scrubber) 0.28 0.22

a VOC emissions occur only at caprolactam plants where ammonium sulfate is produced as a byproduct. The emissions
are caprolactam vapor.

Source: EPA 1997d.

Particulate ammonium sulfate is the air Acid mists may also be emitted from absorber
emission occurring in the largest amount from stack gases during sulfuric acid manufacture.
manufacture of this fertilizer. Dryer exhaust is The very stable acid mist is formed when sulfur
the primary source of the particulates, and trioxide reacts with water vapor below the dew
emission rates are dependent on gas velocity and point of sulfur trioxide. Acid mist emission
particle size distribution. Particulate rates are factors for controlled and uncontrolled plants are
higher for fluidized bed dryers than for the rotary shown in Table 5-19 and Table 5-20. Typical
drum type of dryer. Most plants use baghouses control devices include vertical tube, vertical
to control particulates of ammonium sulfate, panel, and horizontal dual pad mist eliminators
although venturi and centrifugal wet scrubbers (EPA 1992a).
are better suited for this purpose.
Major emissions from wet process phosphoric
Some volatile carbon emissions may be present acid manufacture are comprised of gaseous
in caprolactam plants where ammonium sulfate is fluorides in the form of silicon tetrafluoride
produced as a byproduct. Emission factors for (SiF4) and hydrogen fluoride (HF). The source
controlled and uncontrolled emissions of of fluorides is phosphate rock, which contains
ammonium sulfate are shown in Table 5-17 (EPA from 3.5 to 4.0 percent fluorine. The fluorine is
1997d). generally precipitated out with gypsum, leached
out with phosphoric acid product, or vaporized in
Sulfur dioxide is the primary emission from the reactor or evaporator.
sulfuric acid manufacture, and is found
primarily in the exit stack gases. Conversion of The reactor where phosphate rock is contacted
sulfur dioxide to sulfur trioxide is also with sulfuric acid is the primary source of
incomplete during the process, which gives rise emissions. Vacuum flash cooling of the reactor
to emissions. Dual absorption is considered the slurry will minimize these emissions as the
Best Available Control Technology (BACT) for system is closed. During acid concentration, 20
meeting new source performance standards to 40 percent of the fluorine in the rock may
(NSPS) for sulfur dioxide. In addition to stack vaporize. Emission factors for fluorides from
gases, small amounts of sulfur dioxide are wet processing are shown in Table 5-21.
emitted from storage and tank-truck vents during
loading, from sulfuric acid concentrators, and
from leaking process equipment. Emission
factors for sulfur dioxide from sulfuric acid
plants are shown in Table 5-18.

167
 Table 5-18. Air Emissions from
Sulfuric Acid Manufacture
SO2 to SO3 Conversion SO2 Emissions (lb/ton
Efficiency of product)
93 96

94 82

95 70

96 55

97 40

98 26

99 14

99.5 7

99.7 4

100 0.0

Source: EPA 1992a.

Table 5-19. Acid Mist Emissions from

Uncontrolled Sulfuric Acid Plants
Oleum Produced
Raw Material (% total output) Uncontrolled (lb/ton)
Recovered Sulfur 0-43 0.348-0.8

Bright Virgin Sulfur 0 1.7

Dark Virgin Sulfur 0-100 0.32-6.28

Spent Acid 0-77 2.2-2.4

Source: EPA 1992a.

Table 5-20. Acid Mist Emissions from

Controlled Sulfuric Acid Plants
Oleum Produced
Raw Material (% total output) Controlled (lb/ton)
Elemental Sulfur - 0.64

Dark Virgin Sulfur 0-13 0.26-1.8

Spent Acid 0-56 0.014-0.20

Source: EPA 1992a.

168
 Table 5-21. Air Emissions from Wet Process
Phosphoric Acid Manufacture
Controlled Controlled
Fluorine (lb/ton P2O5 Fluorine (lb/ton P2O5
Source produced) produced)
Reactor 3.8 × 10-3 0.38

Evaporator 0.044 × 10-3 0.0044

Belt filter 0.64 × 10-3 0.064

Belt filter vacuum pump 0.15 × 10-3 0.015

Gypsum settling and Site-specific Site-specific

cooling pondsa

a Acres of cooling pond required range from 0.1 acre per daily ton phosphoric acid produced in the summer in the
southeast U.S., to 0 (zero) in colder locations in winter months when cooling ponds are frozen. There are still
considerable uncertainties in measurement of fluoride from gypsum ponds.

Source: EPA 1997e.

Table 5-22. Emission Factors for Thermal Process

Phosphoric Acid Manufacture
Particulate Acid Mist
Source (lb/ton P2O5 produced)
Packed Tower 2.14

Venturi Scrubber 2.53

Glass fiber mist eliminator 0.69

Wire mesh mist eliminator 5.46

High pressure drop mist 0.11

Electrostatic Precipitator 1.66

Source: EPA 1997e.

Scrubbers (venturi, wet cyclonic, and semi-cross particles suspended in the gas stream, so most
flow) are used to control emissions of fluorine. plants attempt to control this loss. Control
Leachate fluorine may settle in settling ponds, equipment includes venturi scrubbers, cyclonic
and if the water becomes saturated, it will be separators with wire mesh mist eliminators, fiber
emitted to the air as fluorine gas. mist eliminators, high energy wire mesh
contactors, and electrostatic precipitators.
Thermal or furnace processing of phosphoric Emission factors for thermal processing are given
acid results in phosphoric acid mist, which is in Table 5-22.
contained in the gas stream exiting the hydrator.
A large amount of phosphorus pentoxide product Normal superphosphate manufacture produces
may be present as liquid phosphoric acid emissions of gaseous fluorides in the form of

169
silicon tetrafluoride (SiF4) and hydrogen fluoride ammoniator-granulator, dryers, coolers, product
(HF). Particulates composed of fluoride and sizing, material transfer, and the gypsum pond
phosphate material are also emitted. Sources (see Table 5-25). Silicon tetrafluoride (SiF4),
include rock unloading and feeding, mixing hydrogen fluoride (HF), gaseous ammonia, and
operations, storage, and fertilizer handling (see ammonium phosphate particulates are produced
Table 5-23 for emission factors). by the reactor and ammoniator-granulator. These
emissions are controlled by primary and
Sources of emissions for triple super- secondary scrubbers. Exhaust gases from the
phosphates manufacture include the reactor, dryer and cooler contain similar emissions and
granulator, dryer, screens, cooler, mills, and are passed through cyclones and scrubbers, as are
transfer conveyors (see Table 5-24). Particulates emissions from product sizing and material
may be emitted during unloading, grinding, transfer (EPA 1997f).
storage, and transfer of ground phosphate rock.
Baghouses, scrubbers, or cyclonic separators are Combustion of fuels in boilers to produce steam
used to control emissions. and in process heaters or furnaces also produce
criteria air pollutants that are regulated under the
Emissions from production of ammonium Clean Air Act. Current emission factors for
phosphate fertilizers come from the reactor, the process heaters and boilers are discussed in
Section 7, Supporting Processes.

Table 5-23. Air Emissions from Normal Superphosphate Manufacture

Emission Point Particulates (lb/ton) PM 10c (lb/ton) Fluoride (lb/ton)
Rock unloadinga 0.56 0.29 -

Rock feedinga 0.11 0.06 -

Mixer and denb 0.52 0.44 0.20

Curing building 7.2 6.1 3.80

a Factors are for baghouses with estimated collection efficiency of 99 percent.

b Factors are for wet scrubbers with an estimated 97 percent control efficiency.
c Particulate matter 10 microns and above. Based on AIRS listing for criteria air pollutants.

Source: EPA 1997f.

Table 5-24. Air Emissions from Triple Superphosphate Manufacture

Emission Point Particulates (lb/ton) PM 10c (lb/ton) Fluoride (lb/ton)
Rock unloadinga 0.18 0.08 -

Rock feedinga 0.04 0.02 -

Reactor, granulator, dryer, 0.1 0.08 0.24

cooler, and screensb

Curing building 0.20 0.17 0.04

a Factors are for baghouses with estimated collection efficiency of 99 percent.

b Factors are for wet scrubbers with an estimated 97 percent control efficiency.
c Particulate matter of 10 microns and larger. Based on AIRS listing for criteria air pollutants.

Source: EPA 1997f.

170
 Table 5-25. Air Emissions from Ammonium Phosphate Manufacture
Emission Point Fluoride as F Particulate Ammonia SO2
(lb/ton) (lb/ton) (lb/ton) (lb/ton)
Reactor / ammoniator-granulator 0.05 1.52 ND

Dryer/Cooler 0.04 1.50

Product sizing and material 0.002 0.06

transfer

Total Plant Emissions 0.04 0.68 0.14 0.08

Source: EPA 1997f.

5.5 Effluents In phosphoric acid production, the fluorine

released from reactors and evaporators is usually
Wastewaters May Contain Phosphorus, recovered as a by-product that can be sold. The
Fluorides, Nitrogen Compounds, Carbon remainder is passed to the condenser that
Dioxide, or Acids produces a liquid effluent with mostly fluoride
and small amounts of phosphoric acid. Closed
Wastewaters from manufacture of agricultural systems recycle this effluent; in other cases, it is
chemicals consist mostly of wash water, scrubber discharged to open waters (EFMA 1999).
water, boiler and vaporizer blow down, or
stripper water. These may contain phosphorus, Limitations for toxic or hazardous compounds
fluorides, ammonia, carbon dioxide, or weak contained in these wastewaters are given by the
acids. Many of these waters are treated and U.S. Environmental Protection Agency in 40
recycled to the process. Valuable components CFR, Chapter 1, Part 418, which was originally
(e.g., ammonia) may also be recovered. Water promulgated in 1974 and has undergone several
scrubbing of the purge gases in ammonia revisions. The chemicals in the agriculturalchain
production, for example, creates an ammonia are covered under Subparts A-G.
water solution that can be used in another process
(e.g., urea production). In urea production, Specific limitations for restricted compounds and
ammonia, carbon dioxide, and urea are removed total suspended solids (TSS) are shown in Tables
from process waters by water treatment, and the 5-26 through 5-30. BPT indicates the use of best
gases are recycled to the synthesis process practicable control technology currently
(EFMA 1999). available; BAT refers to the best available
technology economically achievable.
Plants producing nitric acid and ammonium
nitrate produce waste waters containing these
compounds as well as ammonia. Wastewater
containing ammonia and nitric acid must be
neutralized to produce ammonium nitrate.

171
 Table 5-26. Effluent Pretreatment Standards: Phosphate Fertilizers
Maximum for any 1 day Maximum for Monthly
Effluent (micrograms/liter) Average (micrograms/liter)

Total Phosphorus (as P) 105 35

Fluoride 75 35

Total Suspended Solids 150 50

Source: 40 CFR Chapter 1, Part 418, Fertilizer Manufacturing Point Source Category, Subpart A.

Table 5-27. Effluent Pretreatment Standards: Ammonia

BPT Standards: Average BAT Standards: Average
Effluent Daily Value for 30 Daily Value for 30
Consecutive Days Consecutive Days
(lb/1000 lb product) (lb/1000 lb product)

Ammonia (as N) 0.0625 0.025

pH 6.0-9.0 -

Source: 40 CFR Chapter 1, Part 418, Fertilizer Manufacturing Point Source Category, Subpart B.

Table 5-28. Effluent Pretreatment Standards: Urea

BPT Standards: Average BAT Standards: Average
Daily Value for 30 Daily Value for 30
Consecutive Days Consecutive Days
(Micrograms/liter) (micrograms/liter)
Effluent
Solution Prills or Solution Prills or
Urea Granules Urea Granules

Ammonia (as N) 0.48 0.59 0.27 0.27

Organic Nitrogen 0.33 0.8 0.24 0.46

Source: 40 CFR Chapter 1, Part 418, Fertilizer Manufacturing Point Source Category, Subpart C.

Table 5-29. Effluent Pretreatment Standards: Ammonium Nitrate

BPT Standards: Average BAT Standards: Average
Effluent Daily Value for 30 Daily Value for 30
Consecutive Days Consecutive Days
(lb/1000 lb/product) (lb/1000 lb product)

Ammonia (as N) 0.39 0.04

Nitrate (as N) 0.37 0.07

Source: 40 CFR Chapter 1, Part 418, Fertilizer Manufacturing Point Source Category, Subpart D.

172
 Table 5-30. Effluent Pretreatment Standards: Nitric Acid
BPT Standards: Average BAT Standards: Average
Daily Value for 30 Daily Value for 30
Consecutive Days Consecutive Days
(lb/1000 lbs product) (lb/1000 lbs product)
Effluent
Gaseous Liquid Gaseous Liquid
Form Form Form Form

Ammonia (as N) 0.0007 0.008 0.00045 0.008

Nitrate as N 0.044 0.044 0.023 0.023

Source: 40 CFR Chapter 1, Part 418, Fertilizer Manufacturing Point Source Category, Subpart E.

5.6 Wastes, Residuals, and used to absorb solvent gas. A hydrocarbon

solvent is used in the unit, which breaks down
Byproducts into a hydrocarbon sludge during the process.
This sludge is usually combusted in another part
Spent Catalysts, Sludges, and Baghouse of the process. Sulfuric acid manufacture also
Dust Are Residuals of Agricultural produces a solid waste containing the heavy
Chemical Manufacture metal vanadium, when the convertor catalyst is
regenerated or screened. This waste is sent to an
The manufacture of agricultural chemicals off-site vendor for reprocessing. Additional solid
produces some solid wastes and byproducts, the wastes from sulfuric acid production may contain
majority from spent catalysts and particulates both vanadium and arsenic, depending on the raw
that have been trapped in various capture materials used, and care must be taken to dispose
systems. Solid wastes from ammonia of them properly in landfills (EFMA 1999).
production, for example, include spent catalysts
and molecular sieves that are removed and sent The production of solid fertilizers produces dust,
off-site for removal of valuable precious metals. some of which is collected in baghouses. It must
Sulfur may be recovered in plants that use partial be disposed of or is recycled to the process when
oxidation (EFMA 1999). possible. Some processes (e.g., thermal
processing of phosphoric acid) produce an acid
Solid wastes from nitric acid manufacture mist consisting of entrained acid particles in gas.
include spent catalysts that are either returned to This particulate acid is usually controlled and
the manufacturer or disposed of. Dust from the recovered as a valuable product.
catalyst may settle out in the equipment, but if it
contains precious metals, it is recovered and sent The manufacture of phosphoric acid produces a
for reprocessing to an outside vendor. Precious gypsum slurry that is sent to settling ponds to
metals (e.g., platinum) lost from the ammonia allow the solids to settle out. About 5 pounds of
oxidation catalyst are captured by a recovery phosphogypsum are generated per pound of
gauze (getter), which must be replaced phosphoric acid. This phosphogypsum contains
periodically and is reprocessed by a gauze trace elements from phosphate rock, such as
manufacturer. Filters used for ammonia/air cadmium and uranium. Pond systems are usually
filtration must also be replaced. They are often fitted with lining systems and collection ditches
disposed of, but can be recycled (EFMA 1999). to maintain control of trace elements and avoid
contamination of ground water (EFMA 1999).
During the production of sulfuric acid, a sludge
is produced in the carbon dioxide removal unit

173
174