The document discusses the fertilizer industry in India. It notes that there are 32 major fertilizer complexes in India that produce over 53 million and 145 million tons of nitrogenous and phosphate fertilizers respectively. These complexes can be classified into 5 categories based on their products. The liquid and gaseous discharges from these complexes contain various pollutants like nitrogen, urea, arsenic, oil, and fluoride. The document then describes the various treatment processes used to remove these pollutants from effluents and emissions before they are discharged. These include scrubbers, separators, adsorption, and precipitation. The venturi scrubber is highlighted as an effective device for reducing dust levels in fertilizer plant emissions.

1. FERTILISER INDUSTRY

2. INTRODUCTION
Fertilizer is defined as any substance which is organic
or inorganic, natural or artificial supplies one or more of the
chemical elements required for plant growth . The fertilizer
industries are playing a crucial role in the production of food
grain to meet the requirements of increasing population.
Today there are 32 major fertilizer complexes in
India with production capacity of 53,80,000 and 1,45,09,000 tones
of nitrogenous and phosphate fertilizers respectively .Pollution due
to these fertilizer industry is found in air ,water and soil.

3. CLASSIFICATION OF FERTILISER PLANTS
Fertiliser plants in India can be classified into
following five categories.
 Ammonia and urea plants
 Ammonia, nitric acid and ammonium nitrate plants
 Ammonia, urea , phosphoric acid and complex fertilizer plants
 Ammonia, urea , ammonium sulphate and sulphuric acid plants
 Ammonia, urea, phosphoric acid, nitric acid , sulphuric acid and
complex fertilizer plants

4. POLLUTANTS IN LIQUID AND
GASEOUS DISCHARGES
A typical analysis of the total liquid waste from a fertiliser
complex giving out an average liquid effluent flow of 20,000
tonnes/day gives the following results
The chief gaseous pollutants are sulphur dioxide , oxides of
nitrogen ,fluorine and particulate matter of different sizes and
natures.
TOTAL NITROGEN 400-1000mg/l
UREA NITROGEN 400-800mg/l
PHOSPHATES 70-500mg/l
FLUORIDE 10-20mg/l
ARSENIC 1-2.5mg/l

5. POLLUTANT SOURCE
POLLUTION
EFFECTS
TOLERANCE
LIMITS
1. Ammonia Ammonia and urea
plants
Toxic to fish and other
aquatic organisms,
eutrophication
1.2 mg/l as nitrogen
in receiving water
2. Urea Urea plant eutrophication 1.2 mg/l as nitrogen
in receiving water
3. Arsenic Gas purification
plant in ammonia
and urea
manufacture.
Causes black-foot
disease , affects plants
and crops
1.0 mg/l in
industrial effluents
individually or
along with other
metals.
4.Oil Gas compressor
houses in ammonia
and urea
manufacture
Suppresses dissolution
of oxygen in water
10 mg/l
5.Fluoride Scrubber effluents in
phosphoric acid and
superphosphate
manufacture
Causes dental and
skeletal fluorosis,
affects hatching of
fish eggs
2 mg/l as F

6. Effluents from each units in a fertilizer complex needs to be
treated before it get discharged into atmosphere. Treatment
processes associated with each unit separates the pollutants or by –
products and uses it for other purposes.

7. The main constituents from an ammonia plant are
 Carbon particles
 Oil droplets
Hydrogen sulphide
 Nitrogen –wash tail gases

8. Removal of carbon
 Synthesis gas(a mixture of CO and H2 produced industrially especially
from coal and used to produce various synthetic chemicals) produced
by the cracking of naphtha , fuel oil and other hydrocarbons in
several fertilizer units contain soot particles along with the
gaseous products.
 Soot particles should be removed before the purification and
separation of gases. This is done by scrubbing the gases with
water in venturi scrubbers.
 The soot particles thus get removed from the gaseous mixture
into the water to form a slurry.

9.  The fine carbon particles in water do not settle easily during
primary treatment and can reduce bacterial activity in the secondary
treatment. When let into water bodies ,they adversely affect aquatic
life by blocking sunlight and oxygen.
 Failure of primary treatment (for the separation of carbon particles
from the slurry)is due to the fine particle size.
 The most commonly used method for the separation of carbon
particles is by mixing the slurry with mineral oil. The carbon
particles moves to the oil phase which is separated by gravity.
 Distillation of oil helps to recover carbon . The carbon obtained
by this method always contains a small amount of mineral oil and
can be used as a fuel.

10. Oil removal
Another liquid stream coming from a typical
ammonia plant contains oil from the compressor bay. An oil
separator followed by adsorption by coke helps reduce the oil
content to a value lower than 10 mg/l.

11. Hydrogen sulphide removal
 The feedstock for the production of synthesis gas contains
naphtha, fuel oil, hydrocarbons e.t.c. Most of all the feed stokes
contain some quantity of sulphur. During cracking sulphur gets
converted to H2S (hydrogen sulphide),which is recovered and
burnt.
 SO2 (Sulphur dioxide) obtained from the combustion of H2S can
be converted to H2SO4 ( sulphuric acid) or to sulphur by Claus
process (Claus process is the most significant gas desulphurizing
process, recovering elemental sulphur from gaseous hydrogen
sulphide)

12. Nitrogen- wash tail gas
 Carbon monoxide, which is a major component of synthetic gas
can be removed by using nitrogen.
 The exit nitrogen wash gas contains approximately 45% by
volume of CO, 5% H2, 5% CH4, and the rest (45% ) N2.
 The exit stream can be used for the catalytic reduction of oxides
of nitrogen in the exit stream associated with a nitric acid plant
,this is because of its high calorific value.

13.  For every tone of ammonium sulphate produced from natural
gypsum or phospho gypsum, about 0.75 tone of chalk is
produced as a by -product.
 The chalk thus produced contain impurities like ammonium
sulphate, ammonium hydroxide and unreacted gypsum.
 After removing undesirable impurities followed by proper
conditioning and treatment, chalk can be utilized in the
production of cement.

14. Solid waste
 The important solid product of phosphoric acid plants is
gypsum and its quantity varies from 4-6 tonnes/ tonne of P2O5
produced as phosphoric acid.
 The gypsum thus produced contains fluorine (1-1.5 %) and
P2O5 (1- 2%). Their presence makes its use undesirable in cement
manufacture.
 The method of phosphoric acid manufacture has now been
changed to the dihydrate –hemihydrate process, making it
possible to get pure grades of gypsum containing low quantities
of fluorine and P2O5.

15. Liquid Effluent
The liquid effluent contains acidic and fluoride bearing
chemicals which can be removed by neutralization and
precipitation processes using lime solution.
Gaseous discharge
 The chief gaseous pollutant from phosphoric acid plant is
fluorine. It has harmful effects on the health of living beings
as it leads to bone decay and smarting of skin.
Fluorine from the effluent gas can be removed by scrubbing
the gas containing fluorine with silicic acid in a high pressure
venturi scrubber.

16.  The recovered hydrofluoro-silicic acid is a starting
material for a manufacture of cryolite and other fluorine
bearing compounds.
The recovery of fluorine from gases from phosphoric
acid plant is an important example of pollution abatement
combined with recovery and production of important
chemicals.

18. Liquid Effluent
 The liquid effluent from the complex fertilizer plant consists of
ammoniacal nitrogen, fluoride, and phosphates.
 The effluent is first reacted with lime at a pH of 7-8 and then
at a pH of about 11 in the second stage of treatment.
At the end of each of the stages a clariflocculator is used. The
chemically –dosed effluent enters the centre of the clariflocculator
and moves radially outwards in the circular unit. Gentle agitation
by means of a paddle agitator helps the particle to grow in size
and moves downwards. The deposited sludge is racked towards the
inner wall and discharged into sludge lagoons and dried. The
water flows upwards into a peripheral launder and is collected in
a vessel where a final adjustment of pH is done before discharge
or reuse.

19. Gaseous Emissions
 The gaseous emissions from a complex fertilizer unit contains dust
produced from the granulation or prilling units.
 As per industry specifications, the particulate matter emitted
through stacks should not exceed 0.5mg/l of product for single super
phosphate plants and 4kg/tonne of product in the case of triple
super phosphate plants.
 A wide variety of collection equipment with varying collection
efficiencies are available for the removal of particles from granulation
and prilling units.

20. VENTURI SCRUBBER
 venturi scrubber is one of the most
important wet scrubbers used to
remove particulate matter.
 A venturi scrubber consists of a
convergent portion where the
velocity of the gas increases up to
the throat where the liquid enters.
 Throat, the narrowest portion in the
length of the venturi scrubber,
accelerates the gas velocity.
 The kinetic energy of the gas breaks
the liquid entering at the throat into
a very fine spray.
 The particles carried by the gas are
separated onto the liquid droplet
surface by diffusion and
interception.
 venturi scrubber can reduce the dust
level in fertilizer plants to 0.06mg/l