Module V

Fertilizers
 Fertilizer industry in India
• Second largest consumer after China.
• Third largest producer (China, USA)
• Total fertilizer production in India is 39 MMTA
• 22.6 MMTA urea
• 7.7 MMTA SSP
• 3.2 MMTA DAP
• 6.2 MMTA NPK
• 47 MMTA is the total consumption
• 80% of urea is indigenously produced and 20%
we imported.
• 50% of DAP imported.
• 100% of MOP is imported.
• 16 elements required for plant growth.
• N,P,K primary nutrients
• Ca,Mg, S are called secondary nutrients
• Fe, Zn,Co,Bo etc called micro nutrients.
• NPK ratio required is 4:2:1
• Actual ratio is 7:2.7:0.1
• Nutrient based subsidy (NBS)
• Direct benefit transfer (DBT)
• Fertilizer subsidy is around 60000 crore.
• Under the make in India scheme GOI is now investing
50000 crore to revive 4 closed urea plants.
• FCI Gorokhpur (UP) 2200 T ammonia, 3850 T urea per day.
• FCI Sindri (Jharkhund)
• HFC Barouni (Bihar)
• FCI Thalchar (Orissa) Coal gasification technology.
• Gas pipe line to eastern India.
• Total 128 fertilizer plants in India
• 57 large fertilizer plant.
• 1906, EID parry is the first fertilizer plant, Chennai.
• 1943, FACT Udl – wood gasification.
• Bengal famine in 1943, 4 million peoples were dead.
• 1952 our food production is 52 mmt, now it is 260 mmt.
• 18 grades of NPK are available for different soil, different
crops.
• 25% of our GDP from agriculture, 80% of peoples are
engaged in the agriculture.
 Fertilizer Industries
• 1. Public sector Units (PSU)
• NFC
• FACT
• RCF
• MFL
• NLC
• FCI
• HFC
• PPL
• SAIL
• GSFC
• 2.Private sector units
• Chambal fertilizers
• Deepak fertilizers
• Coromondal fertilizers
• GNFC
• Indo Gulf fertilizers
• MCFL
• Godavari fertilizers
• SPIC
• Zuari agro
• Oswal fertilizer
• 3. cooperative sector
• IFFCO having 4 units.
• KRIBHCO
• 31 urea plants in India
• 28 are using gas as a feed stock.
• 3 still using Naphtha are MFL, MCFL and SPIC.
• Ministry of Chemicals and fertilizers, GOI is planning
self sufficiency in urea production at 2022.
• Soil health card
• Oman India fertilizer company jointly owned by Oman
oil, IFFCO and KRIBHCO at Oman.
 Classification of fertilizers
• Based on origin:-
• Organic fertilizer- manure, compost etc.
• Inorganic fertilizer – Chemical fertilizer
• Bio fertilizer
• Based on Nutrients:-
• Nitrogenous – N2
• Phosphatic- P2O5
• Pottasic- K2O
• Complex
• Mixed
 Process licensors for ammonia
• Halder Topsoe
• Linde
• Thyssenkrupp
• KBR – Kellog Brown Root
• Casale
• Fauser Monte Catini
• Udhe
• Halder topsoe developed a new technology
called Syncore Ammonia.
• NG-> PDS->Syncore (autothermal reforming
using O2) -> CO shift-> CO2 removal-> N2
wash-> Ammonia synthesis.
• S/C ratio = 0.6
• Kellog developed another technology called
green ammonia or sustainable ammonia using
solid oxide electrolytic cell (SOEC).
 Green Ammonia technology

Electri Ammo
Sy gas NH3
SOEC nia
Air Steam Synthes
H2O
is
 Ammonia
• Base of Nitrogenous fertilizer.
• Coal/NG/Naphtha/FO
• During ammonia production we will get CO2
as a by product, ammonia and CO2 are the
feed stock for urea manufacture.
• Haber bosch process for ammonia synthesis.
• Reforming process for production of syn gas.
• Coal gasification process also used.
Manufacture of Ammonia
• Hydrodesulphurisation
• Reforming- Primary and secondary reformer.
• CO shift reactors- HTS and LTS
• CO2 removal
• Methanation
• Synthesis
• Recovery.
Ammonia Synthesis
Ammonia synthesis
 Types of ammonia converters
• Axial flow
• Radial flow
 Urea
• Urea is a white, odorless, hygroscopic solid. It is non-
corrosive.
• Urea is a major nitrogenous fertilizer (46% N) in the
form of granules or prills.
• It is a solid with a specific gravity of 1.335 and a
melting point of 132.7C
• Casale
• Snamprogetti process
• Montecatini
• Stamicarbon
• Toyo engineering company.
 Urea(NH2.CO.NH2)
• Uses
Fertilizers
Animal feeds
Plastics,adhesives,coatings
• About 56 % of Urea manufactured is used in
solid fertilizer.
• • About 31 % of Urea manufactured is used in
liquid fertilizer.
• • Urea-formaldehyde resins have large use as
a plywood adhesive.
• • Melamine-formaldehyde resins are used as
dinnerware & for making extra hard surfaces.
 Method of production

• By Ammonium Carbamate decomposition

Chemical Reaction:

Raw materials:

CO2 from synthesis gas manufacture and ammonia

• Once through process.
• Partial recycle process.
• Total recycle process.
Montecatini total recycle process.
 Process description
• Liquid ammonia and CO2 are mixed in a molar ratio of
3 to 4 at a high pressure of about 200 Kg/cm2 and a
temp of 190C and sent to a urea reactor. Ammonium
carbamate will be formed in the reactor which will be
further converted into a urea and water as per the
second reaction.
• The product from the reactor is reduced in three stages
to 34 Kg/cm2, 2Kg/cm2 and 0.1 Kg/cm2 respectively.
The gases produced in the first stage and second stage
pressure letdown are compressed and sent back to the
urea reactor as a combined recycle ammonium
carbamate.
• The urea solution from the last separator is
evaporated under slight vacuum and the
product is pumped to the top of the prilling
tower. The liquid is sprayed from the top
against a counter current flow of air. The urea
prills get solidified, cooled and hardened. They
are collected in belt conveyors and sent to
storage for bagging and sale.
• The waste water from the urea plant will contain
2% urea and 3% ammonia. By using the
hydrolyzer this is reduced to 50ppm of urea and
ammonia each. The waste water collected is
pumped to a distillation column and ammonia is
distilled off. The solution taken out from the
middle of this column is heated to 160C and sent
to hydrolyzer which is maintained at 13Kg/cm2
pressure and temp of 195C for a period of 1hr.
The solution containing less than 50 ppm
ammonia is sent to the bottom section and then
sent to an effluent treatment plant.
 Parameters affects the autoclave
reaction.
• Temperature :- Process temperature (185 C)
favours equilibrium yield at a given pressure (180
atm).
• Pressure :- The main reaction is sufficiently slow
at atmospheric pressure. However, it starts
almost instantaneously at pressure of the order
of 100 atm and temperature of 150 C. There is
reduction in volume in the overall reaction and so
high pressure favors the forward reaction.
• Concentration :- Higher the concentration of
the reactants, higher will be the forward
reaction according to the law of mass action.
CO2 being the limiting reagent higher
NH3:CO2 ratio favours conversion. Since,
dehydration of carbamate results in urea
production, lesser H2O:CO2 ratio favours
conversion. Water intake to the reactor should
therefore be minimum.
• Residence time: Since, urea reaction is slow and
takes about 20 mins to attain equilibrium,
sufficient time is to be provided to get higher
conversion.
• Biuret formation :- A problem faced during
manufacture of urea is the formation of biuret
during the production of urea. It is not a desirable
substance because it adversely affects the growth
of some plants. Its content in urea should not be
more than 1.5 % by weight.
• Although the production of urea is high at high
pressure and high temperature, the reaction is not
operated at maximum temperature and pressure
because:
• 1) Increased pressure increases capital & operating
costs of compression and reaction equipment.
• 2) Increased temperature accelerates decomposition of
urea to biuret, a compound that adversely affects the
growth of some plants.
• 3) The above stipulated conditions produce intolerable
corrosion rates, and a compromise design must be
chosen.
MAJOR ENGINEERING PROBLEMS
• Carbamate decomposition and recycle:
• There are many processes that can be used for
the manufacture of urea. Main difference in
competing processes is in the recycle design.
Since, conversion is only 40-50 % per pass, the
unreacted off gases must be recirculated or used
economically elsewhere. Recompression of off
gases is virtually impossible because of corrosion
and formation of solid carbamate in compressors.
• Production of granular urea: Biuret formation
is another problem. Vacuum evaporation of
urea from 80% to about 99% ,spraying to air
cool and solidification must be done just
above the melting point of urea and with a
minimum residence time in the range of
several seconds.
• Heat dissipation in the autoclave: The exothermic heat
of reaction can be removed by coils or wall cooling.
• Corrosion: This has been the major reason why the
NH3-CO2 process was slow to develop. High cost silver
or tantalum liners are used in the autoclaves with
hastealloy C, titanium, stainless steel (321 SS), and
aluminium alloys used in other parts of the plant.
Minimum pressure and temperature conditions with
excess NH3 are desirable to reduce the severe
corrosion rates. Under these conditions, stainless
• steel can be used in the autoclave.
 Once-through urea process:
• The unconverted carbamate is decomposed to
NH3 & CO2 gas by heating the urea synthesis
reactor effluent mixture at low pressure. The
NH3 & CO2 gas is separated from the urea
solution and utilized to produce ammonium
salts by absorbing NH3, either in sulfuric or
nitric acid.
 Solution recycle urea process:
• The NH3 & CO2 gas recovered from the
reactor effluent mixture either in one or in
several pressure staged decomposition
sections is absorbed in water and recycled
back to the reactor in the form of an
ammoniacal aqueous solution of ammonium
carbamate.
 Internal carbamate recycle urea
process:
• The unreacted carbamate & the excess ammonia
are stripped from the urea synthesis reactor
effluent by means of gaseous hot CO2 or NH3 at
the reactor pressure, instead of letting the
reactor effluent down to a much lower pressure.
• The NH3 & CO2 gas, thus recovered at reactor
pressure, is condensed and returned to the
reactor by gravity flow for recovery.
• Montecatini Ammonia stripping process
• Stamicarbon CO2 stripping process.
 Ammonium chloride
• It has some agronomic advantages for rice;
nitrification is less rapid than with urea or
ammonium sulfate and, there-fore N losses
are lower and yields are higher.
• Although ammonium chloride is best known
as a rice fertilizer, it has been successfully
tested and used on other crops such as wheat,
barley, sugarcane, maize, fiber crops, and
sorghum in a variety of climatic conditions.
• Ammonium chloride is as highly acid-forming as
ammonium sulfate per unit of N, which can be a
disadvantage. Other disadvantages are its low N
content compared with urea or ammonium
nitrate and the high chloride content, which can
be harmful on some crops or soils.
• The fertilizer-grade product contains 25% N. The
product can be in the form of either crystals or
granules.
 Properties of Ammonium chloride
• Formula : NH4Cl
• Molecular weight :53.5
• Nitrogen content: 26%
• Color: white
• Density of solid, 20oC : 1.526
 Production Methods
• The dual-salt process, whereby ammonium
chloride and sodium carbonate are produced
simultaneously. (Solvay Process)
• NH3 + CO2 + H2O Amm.Carbonate
• Amm.carbonate + H2O +CO2 
Amm.Bicarbonate.
• Amm.Bicarbonate + Nacl  NaHCO3 + NH4Cl
• Direct neutralization of ammonia with
hydrochloric acid.
The Direct-neutralization Method
• The reaction is exothermic . In most cases,
neutralization is undertaken at reduced pressures
of 250-300mm of mercury in one or more
rubber-lined steel vacuum reaction vessels
protected with an additional inner lining of inert
brick.
• A reduced pressure of 250- 330mm of mercury
and a corresponding slurry temperature of 75-
80C represent typical operating conditions.
• Traces of free chlorine in the acid feed can lead to
disastrous explosions caused by the formation of
nitrogen trichloride in the saturator. Hence,
adequate safety precautions must be installed
whereby the HCl gas feed is monitored and the
flow discontinued when chlorine is detected.
• After separation and drying, the crystalline
ammonium chloride is bagged as quickly as
possible to minimize subsequent storage and
application difficulties.
 Manufacture of NH4Cl
• Gaseous ammonia is bubbled into 30%
hydrochloric acid solution in a reactor. The
reaction is controlled by addition of water. The
resulting solutions are then reacted with
ammonia. The slurry from the saturator is
centrifuged and the crystals are washed with
water and dried with warm air in a manner to
that used in ammonium sulfate.
 Advantages of NH4Cl
• Its low cost, as it is often directly available as a
by-product from important industries such as
the Solvay soda industry and potassium
sulfate industry .
• The fact that it combats certain plant diseases
and prevents others.
 Disadvantages
• Incompatibility of Cl - ions with the physiology
of many plants .
• The corrosive action which it exhibits owing to
the high degree of hydrolysis that it
undergoes.
• Difficult to store as it has tendency to cake.
 Ammonium Sulphate (NH4)2 SO4)
• The main advantages of ammonium sulfate are its low
hygroscopicity, good physical properties ,chemical stability
and good agronomic effectiveness. It reaction in the soil is
strongly acid forming, which is an advantage on alkaline
soils and for some crops such as tea; in some other
situations its acid forming character is a disadvantages.
• Its main disadvantages is its lower analysis (21%N), which
increases packaging, storage and transportation costs. As a
result, the delivered cost at the farm level is usually higher
per unit of nitrogen than that of urea or ammonium nitrate.
• Ammonium sulfate is available as a byproduct from the
steel industry.
 Manufacture
• By product from steel industry.
• Direct Neutralization
• Gypsum process.
 Production
1. Reaction of Ammonia and Sulphuric Acid:
• The stiochiometric quantities of preheated
gaseous ammonia and concentrated sulphuric
acid (98.5% wt/wt) are introduced to the
evaporator – crystalliser.
2. Crystallization
• The reaction takes place in the crystallizer where
the generated heat of reaction causes
evaporation of water making the solution
supersaturated. The supersaturated solution
settles down to the bottom of crystalliser where
it is pumped to vacuum metallic filter where the
A. S crystals are separated, while the mother
liquor is recycled to the crystalliser.
• 3.Drying of the wet Ammonium Sulphate
Crystals.
• The wet A.S crystals are conveyed (by belt
conveyors) to the rotary dryer to be dried
against hot air (steam heated) and then
conveyed to the storage area where it aturally
cooled and bagged.
 Phosphatic fertilizers
• Single Superphosphates.
• Triple superphosphates.
• Single superphosphate (SSP) was the first
commercial mineral fertilizer and it led to the
development of the modern plant nutrient
industry. This material was once the most
commonly used fertilizer, but other phosphorus
(P) fertilizers have largely replaced SSP because of
its relatively low P content.
• SSP is an excellent source of three plant nutrients
are P,S and ca.
 Calcium phosphate
• Two grades
1. Super phosphate: made by reacting
phosphate rock with sulfuric acid, contains
16-20% P2O5
2. Triple super phosphate: made by reacting
phosphate rock with phosphoric acid,
contains 42-50% P2O5
 Superphosphate
Chemical Reactions

Raw materials:

Phosphate rock(30-35% P2O5) and dilute sulfuric acid ( 62-70%)

 Process description
• In this process ground phosphate rock is transported
from the storage site to automatic weight, by a system
of belt and screw conveyors and elevators, which feed
the continuous action double conical mixer. The
sulfuric acid is continuously diluted with water in a
batch mixer to a 75 % concentration, then fed to the
mixer to react with ground phosphate rock where a
first reaction takes place.
• This reaction ends in the reaction mixer in 30- 60
minutes, during the period of settling and hardening of
the superphosphate slurry, which is caused by the
relatively rapid crystallization of the low solubility
calcium sulphate.
• The next stage of the process is ageing of the
superphosphate, i.e. the formation and crystallization
of monocalcium phosphate in the den.
• The formed slurry is transported to the continuous-
action reaction den which has a very low travel speed
to allow for solidifying , where formation of
superphosphate takes place (settling and hardening of
the slurry in the first stage of ageing). Considerable
quantities of fluoride compounds are evolved from the
acidulation, they are sent to the scrubbers.
• The superphosphate powder, from the den, is
transferred for ageing by a belt conveyor, located
below the den, to the pile storage for curing, or
completion of chemical reaction, which takes 2-6
weeks to a P2O5 availability acceptable for plant
nutrient.
• During reaction of the phosphate with sulphuric
acid in the den, hydrogen fluoride evolves and
reacts with the silica contained in the phosphates
and forms gaseous silicon-tetrafluoride (SiF4) and
fluo slicic acid (H2SiF6).
• Superphosphate is granulated in drum
granulators to improve its physical properties.
In the granulator, the superphosphate powder
(after being cured for 2-6 weeks) is wetted
with water fed into the drum through nozzles,
and rolled into granules of different size which
are then dried, screened into size fractions
cooled and the product is bagged in plastic
(polyethylene) bags.
 Complex fertilizers
• The production and marketing of compound
fertilizers are unique compared with
commodity type fertilizers such as urea,
ammonium phosphates and potash.
• Complex fertilizer containing various ratios of
the primary nutrients (N+P2O5+K2O), they
contain certain secondary and micronutrients
specific to the crop needs in a particular agro-
climatic region.
 Role of complex fertilizers
• 1. Convenience.
• 2. Crop nutrient needs.
• 3. Government policy objectives.
• 4. Economics.
• Tank type neutralizers:-
• The use of an atmospheric or pressurized tank type
neutralizer offers maximum flexibility in managing the
acid/ammonia reactions and obtaining the critical
heat/liquid phase criteria needed for good granulation
when producing w wide variety of granular NPK grades.
• Because the acid/ammonia reactions are most often
only partially completed in these tank type
neutralizers, they are often referred to as “pre-
neutralizers”. Such pre neutralizers are commonly used
in most of today’s ammonium phosphate plants and in
many NPK plants.
• Pipe type reactors :- The pipe type reactor consists
basically of a length of corrosion resistant pipe (about
5-15 m long) to which phosphoric acid, ammonia and
often water are simultaneously added to one through a
piping configuration resembling a tee, thus the name
“tee reactor”.
• The acid and ammonia react quite violently,
pressurizing the unit and causing the superheated
mixture of ammonium phosphate slurry (“melt”) and
water vapour to forcefully discharge from the opposite
end of the pipe that is positioned inside the granulator.
• Granulation techniques
• – Drum granulation
• – Blunger/pugmill granulation
• – Spherodiser granulation
• – Prilling
Ammonium Phosphate
• Chemical reactions
• NH3 + H3PO4 NH4H2PO4 (MAP)

• NH3 + NH4H2PO4 (NH4)2HPO4 (DAP)

• NH3 + H2SO4 NH4HSO4

• NH3 + NH4HSO4 (NH4)2SO4
 Urea ammonium Phosphate
• Tank reactor
• Pipe reactor
• Urea solution + Ammonium phosphate slurry -
- UAP.
 Mixed fertilizer
• A mixed fertilizer is a mixture of two or more straight
fertilizers. A mixture of Nitrogen (N), Phosphorus (P)
and Potassium (K) or mostly known as NPK, three
elements that are critical to plant survival and growth
are added to the mixed fertilizer.
• Straight fertilizers: Straight fertilizers are those which
supply only one primary plant nutrient, namely
nitrogen or phosphorus or potassium. eg. Urea,
ammonium sulphate, potassium chloride and
potassium sulphate. 2. ... These fertilisers are usually
produced in granular form.
• 1.Suppliers of plant materials: These are the straight fertilizers added to supply the plant nutrients
mentioned in the grade, thus, are the primary materials most essential for preparing mixed
fertilizers.

2. Conditioners: These are the organic substances which prepare the fertilizer mixture in good
drilling condition and reduce caking. E.g.: Tobacco stems, Peat, Groundnut hulls and paddy hulls
(Husks), bone meal, oilcakes.

3. Neutralizers of residual acidity: The substances used to neutralize the residual effects are known
as neutralizers. For example, if the ‘N’-ous fertilizers used are acididic in nature like Amm. Sulphate,
Urea, a basic material like lime stone is added to counteract the acidity.

4. Filler: Filler is the make – weight material added to a fertilizer mixture. It is added to make up the
differences between the weight of the added fertilizers required to supply the plant nutrients and
the desired quantity of fertilizer mixture, such as sand, soil, ground coal ashes, sawdust and other
waste products.

5. Secondary and micro – nutrients: Some times, secondary and micro – nutrient carrying fertilizers
are added to correct its deficiency.
Incompatibilities in Fertiliser Mixture

• A detailed knowledge of the properties of

fertilisers is essential for preparing the
fertiliser mixture.
• Ammonium sulphate, ammonium nitrate etc.
should not mixed with basically reactive
fertilisers like basic slag, rock phosphate etc.,
because they may decompose to liberate
ammonia gas.
• Fertilisers like single super phosphate,
ammonium phosphate etc. which contain water
soluble phosphorus should not be mixed with
fertilisers then contain free lime because water
soluble phosphorus would be converted to water
insoluble phosphorus.
• Some hygroscopic fertilisers like urea and
sulphate of potash tend to form lumps after
mixing. Therefore, they should be mixed only just
before application.
• Urea should not be mixed with ammonium
nitrate because the mixture will readily
liquefy.
 Advantages of Mixed Fertilisers:

• Two or more fertiliser elements are added together to

make a mixed fertiliser to be applied to the field. Less
labour is therefore required for the application of a mixed
fertiliser.
• 2. The fertiliser elements can be more uniformly applied to
the field especially when they are required in small
quantities.
• 3. Mixed fertilisers can be easily drilled in the filed because
they are in a good physical condition.
• 4. When a mixed fertiliser has been prepared on a scientific
basis and compensates for the deficiency of nutrients in the
soils of the region, the farmer is assured of the right
proportion of plant nutrients in the soil.
 Disadvantages of a Mixed Fertiliser:

• The use of mixed fertiliser does not permit

application of individual fertiliser elements,
which may be required by the crop at specific
times.
• 2. The illiterate farmer cannot effectively
control the quantity of plant food present in
the mixture. He has to rely entirely on the
grade advertised by the firms.
• 3. The firms charge for mixing the fertilisers.