ammonia production from natural gas
DESCRIPTION
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National Fertilizers Ltd.Bathinda
AJAY NAGAR
10112001
Sections
Ammonia Plant
Urea Plant
Steam Generation Plant
Bagging Plant
Ammonia Plant
Desulphurization Section
Reforming Section
Shift Section
Carbon Dioxide Removal Section
Methanation Section
Ammonia Synthesis Section
HYDROGENATOR:
• Reactions involved in Hydrogenator are:
RSH + H2 → RH + H2S
R1SSR2 + 3H2 → R1H + R2H + 2H2S
R1SR2 + 2H2 → R1H + R2H + H2S
COS + H2 → CO + H2S
• If some content of CO2 is also exist in Natural Gas feed then:
CO₂ + H₂ ↔ CO + H₂O
CO₂ + H S₂ ↔ COS + H₂O
• CoMo or NiMo based catalyst is used in Hydrogenator.
Desulphurization Section
Natural Gas Feed
Recycle Hydrogen
Feed Gas Preheater
Hydrogenator
Sulphur Absorber No. 1 Sulphur
Absorber No. 2
400oC38 Kg/cm2
395oC
351oC395oC
Natural Gas With Recycle Hydrogen
Desulphurization Section
H₂S ABSORBER:
• The Hydrogenated Natural Gas is fed to the Sulphur Absorbers.
• Zinc oxide catalyst is in the form of 4 mm cylindrical extrudates.
• Operating temperature is approx. 395˚C.
ZnO + H₂S ↔ ZnS + H₂O
ZnO + COS ↔ ZnS + CO₂
• Sulphur content in the natural gas is less than 0.1 ppm by weight.
Reforming Section
Desulphurized gas is converted into synthesis gas by catalytic reforming of the hydrocarbon mixture with steam and the addition of air.
Reactions involve in Reformer Section:
CnH2n+2 + 2H₂O ↔ Cn-1H2n + CO₂ + 3H₂ - heat
CH₄ + 2H₂O ↔ CO₂ + 4H₂ - heat
CO₂ + H₂ ↔ CO + H₂O – heat
Reactions take place in two steps
1. Primary reforming
2. Secondary reforming
Primary Reformer
Desulphurized Gas
Process Steam
Preheater
PrimaryReformer
SecondaryReformer
Process Air
785-795oC
520oC
34 - 31 kg/cm2 g
Steam Carbon Mole Ratio=3/1
Composition of catalyst (% w/w)1. Nickel Monoxide, NiO (17)2. Calcium Oxide, CaO (7)3. Potassium oxide, K2O (4)4. Aluminum Oxide, Al2O3 (Balance)
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
As we have seen that we are getting around
12.86 mole % of methane and we don’t want
it to be exist in stream just because it will be
acting as inert in whole further processes.
So we have to remove it.
`For removing this access of methane we
use Secondary Reformer.
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Process Gas
Secondary Reformer
• The process gas is mixed with air with keeping the ratio of H2/N2 Ratio: 3.0.• Partial combustion takes place in the top of reactor.• Methane concentration is 0.60 mole%.• Outlet gas contains about 13.05mole% CO and 7.24mole% CO₂ that are removed further because catalyst may get poisioned.
550oC791oC
1100-1200oC
958oC
30 kg/cm2 g
Catalyst composition(%mole):NiO = 8 – 10%Al2O3 = 87 – 90 %Cao = < 0.05 %
Gas inlet composition (mole%)Ar – 47 ppmCH4 – 12.86CO – 9.5CO2 – 10.70H2 – 66.20N2 – 0.74
Gas outlet composition (mole%)Ar – 0.27CH4 – 0.60CO – 13.37CO2 – 7.65H2 – 55.61N2 – 22.47
CO Shift Section
• Exothermic reaction which occurs in this section is:
CO + H2O ↔ H2 + CO2 + heat
• Shift reaction takes place in the two CO converters:
1. HT CO-Converter.
2. LT CO- converter with process gas cooling after each converter.
Methanator trimheater
HT/LT CO Convertors
Process gas from Reformer Section
HT COConvertor
Waste heatboiler
BFW Preheater 1 BFW Preheater 2
360oC29.6kg/cm2
432oC205oC
205oC28.6kg/cm2
227oC 160oC
LT COConvertor
Catalyst’s composition (mole%) which is available in pellet form. Fe2O3 - 85- 95 % Cr2O3 - 7-9 % CuO - 1-2% Al2O3 - 1.0%
Catalyst consist the oxides of Cu, Cr and Al, Which is most active in between 170-250oC.
Composition (mole%) of inlet stream of HT CO Converter is:Ar – 0.27, CH4 – 0.60, CO – 13.37, CO2 – 7.65, H2 – 55.61, N2 – 22.47
Composition (mole%) of outlet stream of HT CO Converter is:Ar – 0.24, CH4 – 0.55CO – 3.22, CO2 – 15.94H2 – 59.59, N2 – 20.48
Composition (mole%) of outlet stream of LT CO Converter is:Ar – 0.24, CH4 – 0.53CO – 0.30, CO2 – 18.32H2 – 60.73, N2 – 19.88
340oC
CO2 Removal Section
• Outlet gas from CO converter contain 18.32 mole% CO2• 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.
• These are the reactions occurs in CO2 removal section.
R3N + CO2 + H2O ↔ R3NH+ + HCO3-
2R2NH + CO2 ↔ R2NH2+ + R2N-COO-
CO2 to Urea
Condensate
StripperReboiler
HEL S Pump
Cooler
Chiller
L PFlash
HPPump
BFWPreheater
Semilean Soln
Lean Solution
Process gassaparator
CO2 Absorber
Output after CO2Absorption
Flash gas/ Inerts
Stripper160˚C27.8 Kg/cm2
131˚C
65˚C
65˚C
65˚C27.8 Kg/cm2
60˚C26.8 Kg/cm2
50˚C5.1 Kg/cm2
72˚C0.59 Kg/cm2
95˚C
Methanation Section
Methanation, a process in which the residual Carbon Oxides (CO, CO2) are converted into METHANE because it acts as inert in Ammonia Synthesis Section.
Reactions involve in Methanator are:
CO + 3H2 ↔ CH4 + H2O + heat
CO2 + 4H2 ↔ CH4 + 2H2O + heat
As we can see these reactions are exothermic so Low temperature, high pressure and a low water vapour content favours the methanation equilibrium.
After converting all Carbon Oxides into METHANE, product stream is pressurised from 25Kg/cm2 to 187Kg/cm2 by using compressors and gas boosters and for maintaining temperature, chillers are being used.
Gas/GasHE
Trimheater
Process gas fromHT CO Converter
Process gas forLT CO Converter
Synthesis Gas From CO2 Removal Section
Methanator
Synthesis gas to loop
60˚C26.8 Kg/cm2
285˚C
300˚C
322˚C
90˚C25 Kg/cm2
Nickel based catalystis used here in methanatorwhich consist around 27% wt Nickel. (280-420˚C)
Composition(%mole) at inlet is:Ar- 0.29, CH4- 0.65,CO2-0.05,CO-0.36,H2- 74.29,N2- 24.36
Composition(%mole) at inlet is:Ar- 0.29, CH4- 1.08, H2- 73.95, N2- 24.88
• High pressure and low temperature favourable equilibrium conditions of ammonia reaction.
• About 20% of N2 and H2 is converted into ammonia at given operating conditions. • Unconverted remainder is recycled back.
• There are three beds we use in Ammonia Convertor: First bed : 370-510 ˚C Second bed: 425-480 ˚C Third bed: 420-460 ˚C
Ammonia Synthesis Section
3H2 + N2 = 2NH3 + heat (ΔH = −92.4 kJ/mol) 130˚C187 Kg/cm2
354˚C183.6 Kg/cm2
Feed gas inlet
Feed gas inlet Outlet
Feed gas inlet
Fe Oxied (Fe3O4) % wt 93 ± 2CaO, Al2O4, K2O, SiO2, % wt 7 ± 2With the irregular shape beads with the size of 1.5-3mm Bulk density 2.8kg/l
130˚C187Kg/cm2
StartupHeater
Ammonia(Product)
Let DownGas
Product letDown tank
AmmoniaSeparator
Purge Gas
Makeup SynthesisGas
AmmoniaConverter
Cooler
SynthesisHotHeatExchanger
SteamBoiler HE
Chiller
Compressors
10˚C
10˚C
11˚C27Kg/cm2
12˚C25Kg/cm2
10˚C178.9Kg/cm2
354˚C 270˚C 180˚C
Composition(mole%) atOutlet of AmmoniaConverterAr- 2.11, CH4- 7.14H2- 52.84, N2- 17.61NH3- 20.30
Composition(mole%) ofPurge Gas of AmmoniaConverterAr- 2.49, CH4- 8.38H2- 82.48, N2- 20.82NH3- 5.82
Composition(mole%) of LetDown Gas of AmmoniaConverterAr- 3.16, CH4- 16.12H2- 38.06, N2- 15.76NH3- 26.88
Composition(mole%) of ProductStream of Ammonia ConverterAr- 0.01, CH4- 0.16H2- 0.06, N2- 0.04NH3- 99.73
Composition(mole%) atInlet of AmmoniaConverterAr- 1.82, CH4- 6.18, H2- 65.95, N2- 21.99, NH3- 4.06
Ammonia Recovery
Ammonia
AmmoniaReflux
AmmoniaOH Drum
DistillationColumn
Reboiler
Purge GasAbsorber
Lean Soln Cooler
Circulation Pump
Purge Gas
Let Down Gas
Steam
RichleanSoln
Exchanger
Fuel Gas
248˚C
11˚C27Kg/cm2
10˚C178.9Kg/cm2
61˚C20Kg/cm2
45˚C25Kg/cm2Composition(mole%) of
Purge Gas:Ar- 2.49, CH4- 8.38H2- 82.48, N2- 20.82NH3- 5.82
Composition(mole%) ofLet Down Gas:Ar- 3.16, CH4- 16.12H2- 38.06, N2- 15.76NH3- 26.88
Composition(mole%) ofFuel Gas:Ar- 2.71, CH4- 9.46H2- 65.73, N2- 22.08NH3- 0.01
Composition(mole%) ofProduct Gas:Ar- 64ppm, CH4- 0.03H2- 0.06, N2- 0.02NH3- 99.88
Conclusion
National Fertilizer Ltd. Bhatinda is producing 99.80% pure Ammonia by Using Natural Gas with the help of helder tropsch method for further production of Urea.
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Thank You !!!