GAURAV SONIChemical engineering departmentIIT Roorkee

National Fertilizers Limited

Bathinda

AMMONIA PLANT

UREA PLANT

STEAM GENRATION

PLANT

BAGGING PLANT

Four Sections

Desulphurization section

Reforming section

Shift section Carbon dioxide removal section

Methanation section

Ammonia synthesis section

1 2

3 4

5 6

Ammonia Plant

(900MT/Day)

Desulphurization Section

General Information:

• Natural gas contains up to 10 vol ppm sulphur compounds.

• Gas contains both H₂S and organic sulphur compounds.

• Desulphurization takes place in two stages.

1. Hydrogenation 2. H₂S absorption

TK- 250

HTZ – 5 catalyst

TK- 250

HTZ – 51 catalyst

Hydrogenation

In case if Natural gas containing CO and CO₂ is fed to the hydrogenator, the following reactons will take place

CO₂ + H₂ ↔ CO + H₂O

CO₂ + H₂ ↔ COS + H₂O

(400˚C)(38 Kg/cm2)

35˚C(39 Kg/cm2)

(395˚C)

(351˚C)

C2H6- 9C3H8- 3C4H10- 2C6H12- 0.25CH4 – 84.50N2 – 1.25

TK-250 must not get into contact with HC’s without presence of hydrogen. This will increase sulphur slip to reforming section.

CoMo or NiMo based catalyst.(Pyrophoric)

TK- 250

HTZ – 51 catalyst

H₂S absorption

• The hydrogenated natural gas is fed to the Sulphur Absorbers ( R 202 A/B).

• Zinc oxide catalyst is in the form of 4 mm extrudates.

• Operating temperature is approx. 395˚C.

ZnO + H₂S ↔ ZnS + H₂O ZnO + COS ↔ ZnS + CO₂

• Sulphur content in the natural gas = less than 0.1 ppm by weight

(351˚C)Ar – 0.02, CH4 – 79.68, CO – 2 ppm, CO2 – 0.24, H2 – 4.09, N2 – 2.54, C2H6 – 6.48, C3H8 – 2.63, C4H10 – 1.88, C6H12 - 0.24

C2H6- 9C3H8- 3C4H10- 2C6H12- 0.25CH4 – 84.50N2 – 1.25

TK- 250

(400˚C)(38 Kg/cm2)

35˚C(39 Kg/cm2)

(395˚C)Does not react with Oxygen and hydrogen, Not pyrophoric. Steam operation should not be carried out.Operating temp – 350-400’CZnO = More than 95%Al2O3 = Less than 5%Shape- Cylindrical Extrudates

Reforming Section

General Information: Desulphurized gas is converted into synthesis gas by catalytic reforming of the hydrocarbon mixture with steam and the addition of air.

CnH2n+2 + 2H₂O ↔ Cn-1H2n + CO₂ + 3H₂ - heatCH₄ + 2H₂O ↔ CO₂ + 4H₂ - heatCO₂ + H₂ ↔ CO + H₂O - heat

Reactions take place in two steps1. Primary reforming2. Secondary reforming

Primary Reforming• Heat is transferred by radiation from a number of

wall burners to the catalyst tubes.• Hydrocarbon in the feed converted to CO₂ and

H₂ with 13.3 mole% of methane(dry)

• Reformer tubes is loaded with catalyst RK-211 (prereduced) followed by a layer of RK-201, while the bottom part of the reformer tubes is loaded with catalyst R-67_7H.

520˚C

791˚C

Operating parameter1. Inlet temperature : 520 ºC2. Exit temperature : 785 - 795 ºC3. Pressure: 34 - 31 kg/cm2 g4. Steam/carbon ratio: 3.0 mole/mole

RK-211

RK-201

R-67_7H

ContentsNickel(Ni) Calcium Oxide(CaO)Potassium oxide(K2O) Aluminum Oxide(Al2O3 )

Nickel Monoxide(NiO) Calcium Oxide(CaOPotassium oxide(K2O) Aluminum Oxide(Al2O3 )

Nickel Monoxide(NiO) Calcium Oxide(CaOAluminum Oxide(Al2O3 ) Ni-S + H2O = NiO + H2S

C+O2 = CO2

Composition : (Mole %)(At Inlet of Catalyst Tubes)Ar – 0.02CH4 – 79.68CO – 2 ppmCO2 – 0.24H2 – 4.09N2 – 2.54C2H6 – 6.48C3H8 – 2.63C4H10 – 1.88C6H12 - 0.24

Composition: (Mole %)(At Outlet of Catalyst Tubes)Ar – 47 ppmCH4 – 12.86CO – 9.5CO2 – 10.70H2 – 66.20N2 – 0.74Higher HC - Neglegible

Primary Reformer Inlet & Outlet

Secondary Reforming

520˚C

791˚C

• The process gas is mixed with air.• Partial combustion takes place in the top

of R 203.• Methane concentration is 0.60 mole%

(dry).• Outlet gas contains about 13.05mole%

(dry) CO and 7.24mole% (dry) CO₂.• Loaded with RKS-2-7H, and RKS-2 catalyst.

H2+O2=H2O CH4+O2= CO2+2H2O 958˚C

(550 ˚C)

(1100-1200˚C )

Operating Pressure: 30 kg/cm2 gH2/N2 Ratio: 3.0

Ar – 0.27CH4 – 0.60CO – 13.37CO2 – 7.65H2 – 55.61N2 – 22.47

Ar – 47 ppmCH4 – 12.86CO – 9.5CO2 – 10.70H2 – 66.20N2 – 0.74

NiO = 8 – 10%Al2O3 = 87 – 90 %Cao = < 0.05

RKS-2

RKS-2-7H

RKS-2

CO Shift Section

General Information:CO + H2O ↔ H2 + CO2 + heat• Shift reaction takes place in the two CO

converters: • HT CO-Converter( R 204) • LT CO- converter (R 205) with process gas

cooling after each converter

HT CO-Converter(R 204)

• Contains SK-201-2 catalyst installed.• The catalyst is Cu promoted

iron/chromium based, in the form of pellets.

• Can operate continuously in the range of 320-480˚C.

• Chlorine and inorganic salts are poisons to the catalyst. (Below 1ppm)

360˚C

432˚C

340˚C

205˚C

(29.6 kg/cm2)

(SK-201-2)

1. Mechanical stability2. Low Steam to Carbon ratio3. Low byproduct formation

Fe2O3 - 85- 95 % Cr2O3 - 7-9 % CuO - 1-2% Al2O3 - 1.0%

Ar – 0.27, CH4 – 0.60, CO – 13.37, CO2 – 7.65, H2 – 55.61, N2 – 22.47

Ar – 0.24CH4 – 0.55CO – 3.22CO2 – 15.94H2 – 59.59N2 – 20.48

LT CO-Converter(R 205) 360˚C

432˚C

340˚C

205˚C

(29.6 kg/cm2)(28.6 kg/cm2)

227˚C 160˚C

• Loaded with a top layer of LSK and a bottom layer of LK-821-2.

• Can be operated within a temperature range of 170-250˚C.

• The activity of the catalyst increases with increasing temperature, but the life of the catalyst shortened

• LSK is installed to catch possible chlorine in the gas.

• Amount of CO (3.22 – 0.30), CO2 (15.94 – 17.72)

205˚C

(LSK)

(LK-821-2)

(SK-201-2)

Ar – 0.24CH4 – 0.53CO – 0.30CO2 – 18.32H2 – 60.73N2 – 19.88

Ar – 0.24CH4 – 0.55CO – 3.22CO2 – 15.94H2 – 59.59N2 – 20.48

Ar – 0.27, CH4 – 0.60, CO – 13.37, CO2 – 7.65, H2 – 55.61, N2 – 22.47

• Consist of oxides of copper, zinc, chromium or aluminium

• Temperature range - 170-250˚C.

• Top layer catches possible chlorine in the gas and also preventsliqvid droplets from reaching bottom layer.(Disintegration may takes place)

CO2 Removal Section

General Information:• Based on two stage activated

MDEA process• The solvent used for CO2

absorption is aMDEA(40%)• Consists of a two stage CO2

absorber, a CO2 stripper and two flesh vessels.

• Outlet gas from CO converter contain 17.7 mole% CO2.

R3N + CO2 + H2O ↔ R3NH+ + HCO3-

2R2NH + CO2 ↔ R2NH2+ + R2N-COO-

(65˚C)

Process Condensate

Process gas

(F-304 CO2 Stripper) (50˚C)

(76˚C)

IMTP-50

IMTP-25

Purified gas

0.59 Kg/cm2 5.1 Kg/cm2

Ar- 0.24CH4- 0.53CO- 0.30CO2- 17.7H2- 80.75N2- 19.89

CH4, CO, CO2, H2, N2

Ar- 0.29CH4- 0.65CO- 0.36CO2- 0.05H2- 74.29N2- 24.36

(72˚C)

(82˚C)

(45˚C)

99.88% CO2

(50˚C)

0.35 Kg/cm2

IMTP

-50

(95˚C)Process gas(160˚C)

27.8 Kg/cm2

(131˚C)

(65˚C)

(65˚C)

27 Kg/cm2

26.7 Kg/cm2(60˚C)

(50˚C)

Methanation Section

General Information:• Methanation, a process in which the residual

corbon oxides are converted into methane. • Methane acts as an inert in the ammonia

synthesis section CO + 3H2 ↔ CH4 + H2O + heat

CO2 + 4H2 ↔ CH4 + 2H2O + heat

• Low temperature, high pressure and a low water vapour content favours the methanation equilibrium.

• Methanator (R 301) has one catalyst bed loaded with PK-7R catalyst

(300˚C)

(322˚C)

PK-7R

(90˚C)

(285˚C)

(100˚C)

26.7 Kg/cm2(60˚C)

• Temperature range of methanator- (280˚C - 420 ˚C )

• Catalyst sensitive to sulphur, chlorine compounds.

• PK-7R is Nikel based catalyst.

Deactivation of catalyst can be caused by:• Thermal ageing• Gradual poisoning by

impurities in the feed gas such as potassium, sulphur or arsenic. • CO & CO2 conc. Should be below 1 mole% to minimize temperature increment.

• Now pressure of gas is increased from 25 to 187 Kg/cm2 in various stages with Synthesis gas compressor, gas booster.

• At every stage temperature gets increases, to maintain low temperature Syngas compressor chillers are installed in between.

25 Kg/cm2Ar- 0.29, CH4- 1.08, H2- 73.95, N2- 24.88

Ar- 0.29, CH4- 0.65, CO2-0.05,CO-0.36, H2- 74.29,N2- 24.36

Ammonia Synthesis Section

General Information• In ammonia converter R-501: 3H2 + N2 = 2NH3 + heat• High pressure and low

temperature favours equilibrium conc. of ammonia.

• About 20% of N2 and H2 is converted to ammonia.

• Unconverted remainder is recycled back.

187 Kg/cm2

(130˚C)

(354˚C)183.6 Kg/cm2

• Ammonia Synthesis catalyst - KM1/KM1R

• High concentration of oxygen compounds at the converter inlet, even for short periods of time, should be avoided.(permanent deactivation takesplace).

Features of the catalyst

1. Stable pressure drop2. Long operating life3. High resistance to poison

• Normal operating temperature for First bed : 370-510 Second bed: 425-480 Third bed: 420-460

KM1/KM1R

Non pyrophoric upto 90-100’C Temperature range – 530-550’C

Features of the catalyst : 1.Stable pressure drop 2. Long operating life 3.High resistance to poison

Iron based catalyst with some non reducible oxides.

(130˚C)187 Kg/cm2

(354˚C)

(270˚C)

(180˚C)

(10˚C)

(10˚C)

(10˚C)

178.9 Kg/cm2

27 Kg/cm2

25 Kg/cm2

(11˚C)

(12˚C)

Ar- 2.49CH4- 8.38H2- 82.48N2- 20.82NH3- 5.82

Ar- 3.16CH4- 16.12H2- 38.06N2- 15.76NH3- 26.88

Ar- 0.01CH4- 0.16H2- 0.06N2- 0.04NH3- 99.73

Ar- 2.11CH4- 7.14H2- 52.84N2- 17.61NH3- 20.30

Ar- 1.82, CH4- 6.18, H2- 65.95, N2- 21.99, NH3- 4.06

(10˚C)178.9 Kg/cm2

27 Kg/cm2(11˚C)Ar- 3.16

CH4- 16.12H2- 38.06N2- 15.76NH3- 26.88

Ar- 2.49CH4- 8.38H2- 82.48N2- 20.82NH3- 5.82

(61˚C)20 Kg/cm2

Ar- 64ppmCH4- 0.03H2- 0.06N2- 0.02NH3- 99.88

Ar- 2.71CH4- 9.46H2- 65.73N2- 22.08NH3- 0.01

(45˚C)

25 Kg/cm2

(248˚C)

Ammonia Recovery

Synthesis section Decomposition section

Recovery section Crystallizations and Priling Sections

1 2

3 4

Urea Plant

(1550MT/Day)

MITSUI-TOATSU Total Recycle ‘C’ Improved Process

• Urea is produced by the highly exothermic reaction of Ammonia and carbon dioxide to form ammonium Carbamate with slightly endothermic dehydration of ammonium Carbamate to form urea.

The reactor temperature is controlled by the combination of the following factors:

1. Excess ammonia to the reactor 2. Recycle solution rate to the reactor 3. Pre-heat temperature of liquid ammonia

to the reactor.

Synthesis Section

Decomposition Section

1. Here Carbamate is decomposed to ammonia and carbon dioxide gasses.

NH2COONH4 = CO2 + 2NH3

2. Decomposition is usually achieved at temperature of 1200C to 165oC

Decreasing pressure favors decomposition as dose increasing temperature.

3. During decomposition, hydrolysis of urea becomes an important factor. Hydrolysis proceeds as per the following reaction: 

NH2 CONH2 +H2O = CO2 + 2NH3

At low partial pressure of ammonia and temp. Above 900C

Urea converts to form ammonia and biurate as in the overall reaction below: 

2 NH2CO NH2 = NH2 CONHCO NH2 +NH3

Recovery Section

1. The unreacted ammonia and CO2 can not be compressed in practical instead of this we do 1. Separate and recycle as gasses.2. Recycle in a solution or slurry

form.

NFL Bathinda uses second one.

2. The mixture of ammonia CO2 gasses from the decomposers are absorbed in water and urea solution in the respective absorbers and recycle back to the urea synthesis reactor.

3. The excess ammonia is purified in high-pressure absorber and recycled separately to the reactor through ammonia condensers

Crystallization Section

1. The urea solution leaving the Carbamate decomposes is vacuum crystallized and urea crystals are separated by centrifuge.

2. Crystals formed in the vacuum crystallizer are centrifuged and then dried to less than 0.3% moisture by hot air.

3. The biurate is converted back to urea in presence of excess ammonia.

NH2 CONHCONH2 +NH3 = 2NH2CONH2

4. Dry crystals are conveyed to the top of prilling tower passing through Fluidizing dryer

Prilling Section

• Dry crystals of urea collected in the air dryer in which it is dried by passing dry air from F.D. fan.

• Attain a temperature less than melting point of urea i.e. 1200C.

• Dry crystals are conveyed to the top of prilling tower passing through pneumatic duct and send to the melter via cyclone and screw conveyor to melter.

• In melter dry urea crystals are melted by using 7K steam and finally reaches to the Head tank . In melter temperature of molten urea control up to 1370C to avoid the biuret formation.

Prilling Section

• Molten urea solution comes from head tank to acoustic granulator and then sprayed in the form of prills form a rising column of prilling tower.

• These prills get cooled down by F.D. fan air which take suction from atmosphere and send it through continuous fluidized dryer.

• After cooling of prills not less than 450C, it is conveyed to bagging plant via passing through trommel and belts and finally stored in the silos.

Thank you