Process of Urea Plant:

The raw material required for the process of Urea plant is

ammonia (NH3) and carbon dioxide (CO2).

Plant Description:

1) Urea synthesis and high pressure recovery.

2) Urea pressure and low pressure recovery.

3) Urea concentration

4) Urea prilling

5) Waste water treatment

1)Urea synthesis and high pressure recovery:

Compressor K-1

compress carbon-di-oxide comming from ammonia

plant at 0.65 kg/cm2g to 157 kg/cm2g pressure . Air

is added in CO2 before compressor to provide oxygen

for passivating the equipment to avoid corrosion.

Liquid ammonia is received in receiver and its

pressure is boosted up by means of the pump p-5 .

part of the ammonia isi sent to medium pressure

absorber c-1 and the remaining is pumped by high

pressure ammonia pump p-1 to a pressure of

240kg/cm2g . liquid ammonia from p-1 isii used as

motive fluid in ejector in which carbomate coming

from separator (MV-1) is recycled to reactor.

In reactor R-1 ammonia and carbon-di-oxide reacts to

form ammonium carbomate , a portion of which

dehydrates to form urea and water.

About 65% of the total CO2 entering the reactor is

converted into urea.

The reaction product goes to steam heaed falling film

bimetallic stripper E-1 , where the carbon-di-oxide

content of the solution is substantially reduced by the

stripping action of ammonia as it boils out of

solution . The overhead gases and the solution

recovered from medium pressure absorber C-1 , flow

to high pressure condenser E-5 where the total

mixture except for a few inerts is condensed and

recycled via a carbomate seperator MV-1 to the

reactor by means of ejector.

L.P steam is generated n the shell side of E-5 and is

used to supply the decomposition and concentration

heat required in the downstream section .

From the top of carbomate separator MV-1 iert gases

with small quantity of ammonia and carbon-di-oxide

are sent to the bottom of medium pressure

docomposer.

2)M.P purification and recovery:

E-1 bottom solution which

contain around 23% ammonia 5% carbon-di-oxide and

45% urea is expanded to a pressure of 17kg/cm3g and

enters the medium pressure separator where the

released flash gases are removed next it enters the

falling film exchanger E-2 where most of the residual

carbomate is decomposed . The required heat is

supplied by steam condensate coming from the

stripper.

The ammonia and carbon-di-oxide rich gases leaving

the top of the separator are sent to M.P condenser

and then liquid/gas mixture from E-7 goes to medium

pressure absorber.

The upper part of the absorber I fitted with four no.

bubble cap trays for CO2 absorber and NH3

rectification . Here a reflux of ammonia drawn from

the ammonia receiver eliminates residual carbon-di-

oxide and H2O . The bottom solution is recycled by

pump P-2 to the H.P carbomate condenser .

Ammonia vapour leaving the top of absorber are

condensed in ammonia condenser before entering

ammonia receiver.

The innert gas leaving the receiver are scrubbed with

condensate in ammonia absorber . From bottom of

the water ammonia solution is recycled back to

medium pressure absorber by mean of ammonia

solution pump.

3) L.P purification and recovery:

The solution which

contain around 6.5% NH3 , 1.5% CO2 and 62% urea

leaving he bottom of MP decomposer is expanded to

a pressure of 3.5 g/cm3g and enters LP separator .

The required heat of decomposition is supplied by 3.5

kg/cm2 LP steam which is generated in E-5.

The vapours leaving the top of the separator ,

together with the recoverd solution from waste

water section are condensed in LP condenser (E-8) .

Heat of the condensation is recoverd by cooling

water. The solution from E-8 is sent to carbomate

solution tank V-3 to be recycled to the medium

pressure suction by pump P-3

4) Solution concentration and prillilng:

Vaccum section is in

two stage to get 99.7% wt urea melts for

prilling .The 70% wt. solution of urea leaving the

bottom of E-3is sent to 1st stage vaccum separator

MV-6 through 1st stage vaccum preconcentraror E-

14 and E-15 operating at a pressure of 0.3ata.

After 1st stage vacccum sepertor 95% wt. urea is

sent to second stage vaccum concentrator E-15 and

separator working at 0.03ata. Heat required in E-14

and E-15 are met by L.P section . The vapour leavin

the vaccum evaporator are condensed in vaccum

system.

Urea melt is sent to prilling spinning bucket which

distributes the urea melt in small droplets over the

crossection of natural draught circulling prilling

tower .Cold air entering the bottom of prilling

tower causes urea droplets solidify.

The solid urea collected at the bottom of the

prilling tower and sent to the bagging plant for

further activity.

5) Process condensate treatment:

The waste coming from vaccum

system containing NH3 5%, CO2 , and urea 1% is

collected in buffer waste water tank from where it

pumped by P-16 to waste water distillation tower

C-2 through distillation tower preheater operating

at a pressure of 1.5kg/cm2g column C-2 is divided

into two part by chimney tray located at a suitable

height. From upper part of chimney tray located at

suitable height . From upper part of the chimney

tray the solution containing water urea and small

amount of NH3 and CO2 is pumped by hydrolyser

R-2 through hydrolyser preheater . In R-2 urea is

quantitatively decomposed into CO2 and NH3.

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