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Ammonia
Introduction
• Ammonia (NH3) is a compound of nitrogen
and hydrogen. It is a colorless gas with a
characteristic pungent s...
World consumption of Ammonia -
2011
China
33%
Russia
11%
India
9%
Pakistan
1%
America
11%
Others
35%
Uses
• Ammonia is major raw material for fertilizer
industries
• It is used during the manufacture of Nitro
compounds, Fer...
Uses
20% is used in
manufacturing:
• Plastics
• Synthetic fibres
• Explosives
• Dyes
• Pharmaceuticals
• Industrial refrig...
History
• Gaseous ammonia was first isolated by Joseph Priestley in 1774 and was
termed as "alkaline air". Claude Louis Be...
Production of Ammonia (kt) in
Pakistan
0
20
40
60
80
100
120
140
160
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
Process
• Ammonia is synthesized from nitrogen and hydrogen by the
following reaction:
N2 + 3H2 ⇌ 2NH3
• The best availabl...
Steam reforming of NG
A) Synthesis gas
production
– Feedstock
pretreatment and gas
generation
– Carbon monoxide
conversion...
Hydro-desulfurization
Raw materials
• Air, natural gas (or other
hydrocarbons) and steam.
• Removal of sulfur from feedsto...
Primary reformer
• After the removal of sulfur compounds, the gas is mixed
with superheated steam and fed into a primary r...
Primary reformer
The burners primary reformers can be classified as top-fired, side-
fired, terraced-wall, or, less common...
Primary reformer
• The mixture is heated to 770oC in the
presence of a nickel catalyst and
these reversible reactions occu...
Primary reformer
• Primary reformer has been identified as bottle-neck in increasing
the capacity of existing natural-gas-...
Secondary reformer
• Only 30-40% of the hydrocarbon is
reformed in the primary reformer
because of the equilibrium reactio...
Uhde combined autothermal reformer (CAR)
a) Sandwich type tubesheet; b) Enveloping tube;
c) Reformer tubes; d) Tubesheet; ...
Shift conversion
• Any remaining carbon monoxide in the gas
mixture is converted to carbon dioxide in the shift
section of...
Purification
• CO2 containing synthesis gas is scrubbed under pressure with a solvent
capable of dissolving carbon dioxide...
Purification
• Physical solvent e.g. polyethylene glycol dimethyl ether,
polyethylene glycol methyl isopropyl ether, polyp...
Purification
Methanation
• Any remaining amounts of CO and CO2 must be removed before the NH3
synthesis stage as they woul...
Effect of catalyst on reaction rate
• A catalyst has no effect on equilibrium. It speeds up
both forward and backward reac...
Effect of pressure on reaction rate
• Collision theory
– High pressure - More successful collisions
• Increase rate of rea...
Le Chatlier’s Principle
• If a chemical system at equilibrium experiences a change
in concentration, temperature, volume, ...
Compression
• Centrifugal compressor for make-up and
recycle gas compression of an ammonia plant
a) Air cooler; b) Separat...
Compression
Advantages over reciprocating compressors:
– Lower investment (single machines even for very
large capacities)...
Ammonia synthesis
Ammonia synthesis
• The synthesis of NH3 takes place on
an iron catalyst at pressures usually
in the ran...
Ammonia synthesis
• The synthesis reaction is limited by the unfavorable position of the
thermodynamic equilibrium, so tha...
Ammonia synthesis
Schematic flow diagrams of typical ammonia synthesis loops
A) Synthesis loop for pure and dry make-up ga...
Ammonia synthesis
a) Locus of
temperatures
resulting in
maximum
reaction rate
space velocity (per hour)  1/ contact time
...
Influence of the different variables on
the Synthesis Loop
• Pressure: increasing pressure will increase conversion
due to...
Ammonia converter
Commercial Ammonia Converters
• Commercial converters can be classified into two main
groups:
– Internal...
Ammonia converter
• Assignment
– Historical evolution of ammonia converter
technology.
• 15 hand written pages
• Deadline ...
Complete Ammonia Production Plants
Modern integrated single-train ammonia plant based on steam reforming of natural gas (U...
Complete Ammonia Production Plants
M.W. Kellogg's low energy process
Complete Ammonia Production Plants
Haldor Topsøe's low energy process
a) Desulfurization; b) Primary reformer; c) Secondar...
Complete Ammonia Production Plants
The Braun purifier ammonia process
a) Sulfur removal; b) Primary reformer; c) Convectio...
Complete Ammonia Production Plants
ICI AMV process
a) Desulfurization; b) Natural gas saturation; c) Process air compressi...
Complete Ammonia Production Plants
ICI LCA process (core unit)
PAC, purified air compressor; HDS, hydrodesulfurization; IP...
Complete Ammonia Production Plants
KBR KAAPplus Process
a) Air compressor; b) Sulfur removal; c) Process heater; d) Automa...
Complete Ammonia Production Plants
Ammonia production based on heavy fuel oil (Linde flow scheme with Texaco gasification)...
Ammonia Industries
Ammonia Industries
Ammonia Industries
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Ammonia Industries

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Lecture Slides by Prof. Imitaz Ali at Ghulam Ishaq Khan Institute for Engineering Sciences and Technology (GIKI).

Published in: Engineering

Ammonia Industries

  1. 1. Ammonia
  2. 2. Introduction • Ammonia (NH3) is a compound of nitrogen and hydrogen. It is a colorless gas with a characteristic pungent smell of 'wet nappies' − this is because urine can decompose to ammonia. Year Million tonnes of Ammonia 2005 148 2006 153 2007 159 2008 158 2009 158 2010 159
  3. 3. World consumption of Ammonia - 2011 China 33% Russia 11% India 9% Pakistan 1% America 11% Others 35%
  4. 4. Uses • Ammonia is major raw material for fertilizer industries • It is used during the manufacture of Nitro compounds, Fertilizers e.g. urea, ammonium sulfate, ammonium phosphate etc. • It is also used in manufacture of Nitric acid, Hydroxylamine, Hydrazine, Amines and amides, and in many other organic compounds
  5. 5. Uses 20% is used in manufacturing: • Plastics • Synthetic fibres • Explosives • Dyes • Pharmaceuticals • Industrial refrigerant • Industrial and domestic cleaning agent
  6. 6. History • Gaseous ammonia was first isolated by Joseph Priestley in 1774 and was termed as "alkaline air". Claude Louis Berthollet ascertained its composition in 1785. • The Haber-Bosch process to produce ammonia from the nitrogen in the air was developed by Fritz Haber and Carl Bosch in 1909 and patented in 1910. Prior to the availability of cheap natural gas, hydrogen as a precursor to ammonia production was produced via the electrolysis of water or using the chloralkali process.
  7. 7. Production of Ammonia (kt) in Pakistan 0 20 40 60 80 100 120 140 160 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
  8. 8. Process • Ammonia is synthesized from nitrogen and hydrogen by the following reaction: N2 + 3H2 ⇌ 2NH3 • The best available source of nitrogen is from atmospheric air. The hydrogen required can be produced from various feedstock but currently it ias derived mostly from fossil fuels. • Depending of the type of fossil fuel, two different methods are mainly applied to produce hydrogen for ammonia production: – steam reforming CnHm + nH2O  nCO + (n+ m/2) H2 H > 0 – partial oxidation CnHm + n/2 O2  nCO + m/2 H2 H < 0 • Steam reforming of light hydrocarbons is the most efficient route, with about 77% of world ammonia capacity being based on natural gas.
  9. 9. Steam reforming of NG A) Synthesis gas production – Feedstock pretreatment and gas generation – Carbon monoxide conversion – Gas purification B) Compression C) Synthesis
  10. 10. Hydro-desulfurization Raw materials • Air, natural gas (or other hydrocarbons) and steam. • Removal of sulfur from feedstock, e.g. natural gas, involves these chemical reactions: R-CH2SH + H2  H2S + RCH3 H2S + ZnO  ZnS + H2O • zinc oxide beds are typically not regenerated but are replaced with new absorbent once exhausted
  11. 11. Primary reformer • After the removal of sulfur compounds, the gas is mixed with superheated steam and fed into a primary reformer. • To achieve the required stoichiometric hydrogen/nitrogen ratio for ammonia synthesis, the reforming reaction is split into two sections. • In the first section, the primary reformer, the reaction proceeds to achieve a partial conversion only [in conventional plants 65 % based on methane feed, leaving around 14 mol % methane (dry basis) in the effluent gas]. • In the secondary reformer— the gas is mixed with a controlled amount of air. • The steam/carbon ratio used in modern commercial primary reformers for natural gas is between 2.8 and 3.5.
  12. 12. Primary reformer The burners primary reformers can be classified as top-fired, side- fired, terraced-wall, or, less common, bottom-fired reformers
  13. 13. Primary reformer • The mixture is heated to 770oC in the presence of a nickel catalyst and these reversible reactions occur: CH4 + H2O ⇌ CO + 3H2 ∆H=+206kJmol−1 CnHm+ nH2O ⇌ nCO + (n+ m/2) H2 CO + H2O ⇌ CO2 + H2 ∆H=−41kJmol−1 Overall reaction: CH4 + 2H2O ⇌ CO2 + 4H2 ∆H=+165kJmol−1 • The mixture that emerges is called synthesis gas • The overall reaction (CH4 and steam to CO2 and H2) is highly endothermic. • Therefore, maintaining a high reaction temperature moves the position of equilibrium to the right.
  14. 14. Primary reformer • Primary reformer has been identified as bottle-neck in increasing the capacity of existing natural-gas-based ammonia plants. • This can be addressed by – having pre-reforming, installed at the up-stream • to transfer part of the conversion duty to the secondary reformer with application of an superstoichiometric amount of air.
  15. 15. Secondary reformer • Only 30-40% of the hydrocarbon is reformed in the primary reformer because of the equilibrium reactions. The synthesis gas is cooled slightly to 735 oC, mixed with air and passed into the secondary reformer. Highly exothermic reactions happen such as: CH4 + 2O2  2H2O + CO2 ∆H=−82kJmol−1 • With the energy released and further heating a temperature of about 1000oC is reached and up to 99% conversion to methane to hydrogen achieved. • Nitrogen (from the air) is used later in the synthesis of ammonia.
  16. 16. Uhde combined autothermal reformer (CAR) a) Sandwich type tubesheet; b) Enveloping tube; c) Reformer tubes; d) Tubesheet; e) Refractory lining; f) Water jacket Alternate technologies Kellogg reforming exchanger System (KRES) exchanger reforming + noncatalytic partial oxidation
  17. 17. Shift conversion • Any remaining carbon monoxide in the gas mixture is converted to carbon dioxide in the shift section of the process: CO + H2O ⇌ CO2 + H2 ∆H = −41 kJ mol−1 • The shift conversion happens in two stages: –HTS | High temperature shift (iron oxide/chromium oxide based catalyst at about 400 oC) that lowers the CO content from 12-15% to about 3%. –LTS | Low temperature shift (copper oxide/zinc oxide - based catalyst at about 200-220 oC) which lowers the CO content further to about 0.2-0.5%.
  18. 18. Purification • CO2 containing synthesis gas is scrubbed under pressure with a solvent capable of dissolving carbon dioxide in sufficient quantity and at sufficient rate, usually in countercurrent in a column equipped with trays or packing • The CO2-laden solvent is flashed, often in steps, to around atmospheric pressure, and the spent scrubbing liquid is subsequently heated and regenerated in a stripping column before being recycled to the pressurized absorption column • CO2 is removed by chemical or physical absorption. • Chemical Absorption – Tertiary amines methyldiethanolamine (MDEA) together with an activator. Approximately 80 percent of the ammonia plants use this process to aid in removing CO2 – The potassium carbonate with an activator, corrosion inhibitor • Benfield LoHeat System (UOP) • Catacarb Process • Giammarco -Vetrocoke process • LRS 10 of British Gas • Exxon's Flexsorb process
  19. 19. Purification • Physical solvent e.g. polyethylene glycol dimethyl ether, polyethylene glycol methyl isopropyl ether, polypropylene carbonate etc – Selexol Process (UOP) – Sepasolv MPE process (BASF) – Fluor Solvent Process • After bulk removal of the carbon oxides has been accomplished by shift reaction and CO2 removal, the typical synthesis gas still contains 0.2 – 0.5 vol % CO and 0.005 – 0.2 vol % CO2. These compounds and any water present have to be removed down to a very low ppm level, as all oxygen-containing substances are poisons for the ammonia synthesis catalyst • The gas mixture is further cooled to 40°C, water condenses out and is removed.
  20. 20. Purification Methanation • Any remaining amounts of CO and CO2 must be removed before the NH3 synthesis stage as they would poison the catalyst. Methanation is the simplest method to reduce the concentrations of the carbon oxides well below 10 ppm and is widely used in steam reforming plants. • The reaction is carried out over a supported nickel catalyst at a pressure of 25 – 35 bar and a temperature of 250 – 350 °C. CO + 3H2 ⇌ CH4 + H2O ∆H = −206 kJ mol−1 CO2 + 4H2 ⇌ CH4 + 2H2O ∆H = −165 kJ mol−1 • The emerging gas must be completely dry so water produced in these reactions is removed by condensation. This is accomplished by passing the makeup gas through molecular sieve adsorbers, which can be positioned on the suction side or in an intermediate-pressure stage of the synthesis gas compressor.
  21. 21. Effect of catalyst on reaction rate • A catalyst has no effect on equilibrium. It speeds up both forward and backward reactions equally. • Provide an alternate pathway with lower activation energy • Increase rate of reaction
  22. 22. Effect of pressure on reaction rate • Collision theory – High pressure - More successful collisions • Increase rate of reaction
  23. 23. Le Chatlier’s Principle • If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established. N2 + 3 H2 ⇌ 2 NH3 + 92kJ – Decreasing the temperature of a system in dynamic equilibrium favours the exothermic reaction. 4 volumes ⇌ 2 volumes – an increase in system pressure due to decreasing volume causes the reaction to shift to the side with the fewer moles of gas.
  24. 24. Compression • Centrifugal compressor for make-up and recycle gas compression of an ammonia plant a) Air cooler; b) Separator; c) Silencer; d) Water cooler
  25. 25. Compression Advantages over reciprocating compressors: – Lower investment (single machines even for very large capacities) – Lower maintenance cost – Less frequent shutdowns for preventive maintenance – High reliability (low failure rate) Other compression duties in the plants are also performed by centrifugal compressors.
  26. 26. Ammonia synthesis Ammonia synthesis • The synthesis of NH3 takes place on an iron catalyst at pressures usually in the range 10-25 MPa and temperatures in the range 350- 550oC N2 + 3H2 ⇌ 2NH3 ∆H = –92 kJ mol−1 • The conditions used are a compromise between yield, speed & energy demands. Mittasch
  27. 27. Ammonia synthesis • The synthesis reaction is limited by the unfavorable position of the thermodynamic equilibrium, so that only partial conversion of the synthesis gas (25 – 35 %) can be attained on its passage through the catalyst. • Ammonia is separated from the unreacted gas by condensation, which requires relatively low temperatures for reasonable efficiency. • The unconverted gas is supplemented with fresh synthesis gas and recycled to the converter. • The concentration of the inert gases (methane and argon) in the synthesis loop is controlled by withdrawing a small continuous purge gas stream. • These basic features together with the properties of the synthesis catalyst and mechanical restrictions govern the design of the ammonia synthesis converter and the layout of the synthesis loop.
  28. 28. Ammonia synthesis Schematic flow diagrams of typical ammonia synthesis loops A) Synthesis loop for pure and dry make-up gas; B) Product recovery after recycle compression; C) Product recovery before recycle compression (four-nozzle compressor design); D) Two stages of product condensation a) Ammonia converter with heat exchangers; b) Ammonia recovery by chilling and condensation; c) Ammonia recovery by condensation at ambient temperature; d) Synthesis gas compressor; e) Recycle compressor Molecular sieve drying of make-up gas has increasingly been applied in order to realize the energy-saving arrangement of the synthesis loop corresponding to Figure A.
  29. 29. Ammonia synthesis a) Locus of temperatures resulting in maximum reaction rate space velocity (per hour)  1/ contact time reaction rate v in m3 NH3 / (m3 cat alyst · s)
  30. 30. Influence of the different variables on the Synthesis Loop • Pressure: increasing pressure will increase conversion due to higher reaction rate and more favourable ammonia equilibrium. • Inlet temperature: there are two opposed effects as increasing temperature enhances reaction rate but decreases the adiabatic equilibrium concentration. • Space velocity: increasing the space velocity normally lowers the outlet ammonia concentration, but increases total ammonia production. • Inert level: increasing the inert level lowers the reaction rate for kinetic and thermodynamic reasons
  31. 31. Ammonia converter Commercial Ammonia Converters • Commercial converters can be classified into two main groups: – Internally cooled with cooling tubes running through the catalyst bed or with catalyst inside the tubes and the cooling medium on the shell side. The cooling medium is mostly the reactor feed gas, which can flow counter- or cocurrently to the gas flow in the synthesis catalyst volume (tube-cooled converters). – The catalyst volume is divided into several beds in which the reaction proceeds adiabatically. Between the individual catalyst beds heat is removed by injection of colder synthesis gas (quench converters) or by indirect cooling with synthesis gas or via boiler feed water heating or raising steam (indirectly cooled multi bed converter).
  32. 32. Ammonia converter • Assignment – Historical evolution of ammonia converter technology. • 15 hand written pages • Deadline : 8 November 2013
  33. 33. Complete Ammonia Production Plants Modern integrated single-train ammonia plant based on steam reforming of natural gas (Uhde process) a) Sulfur removal; b) Primary reformer; c) Steam superheater; d) Secondary reformer; e) waste-heat boiler; f) Convection section; g) Forced draft fan; h) Induced draft fan; i) Stack; k) HT and LT shift converters; l) Methanator; m) CO2 removal solvent boiler; n) Process condensate separator; o) CO2 absorber; p) Synthesis gas compressor; q) Process air compressor; r) Ammonia converter; s) High-pressure ammonia separator; t) Ammonia and hydrogen recovery from purge and flash gas
  34. 34. Complete Ammonia Production Plants M.W. Kellogg's low energy process
  35. 35. Complete Ammonia Production Plants Haldor Topsøe's low energy process a) Desulfurization; b) Primary reformer; c) Secondary reformer; d) Shift conversion; e) CO2 removal; f) Methanation; g) Main compressor; h) Recycle compressor; i) Heat recovery; j) Converter
  36. 36. Complete Ammonia Production Plants The Braun purifier ammonia process a) Sulfur removal; b) Primary reformer; c) Convection section; d) Secondary reformer; e) waste-heat boiler; f) Process air compressor; g) Gas turbine; h) High- and low- temperature shift converters; i) CO2 removal solvent reboiler; k) CO2 absorber; l) CO2 desorber; m) CO2stripper; n) Methanator; o) Driers; p) Purifier heat exchanger; q) Expansion turbine; r) Purifier column; s) Synthesis gas compressor; t) Synthesis converters; u) waste-heat boiler; v) High-pressure ammonia separator; w) Ammonia letdown vessel; x) Ammonia recovery from purge gas
  37. 37. Complete Ammonia Production Plants ICI AMV process a) Desulfurization; b) Natural gas saturation; c) Process air compression; d1) Primary reformer; d2) Secondary Reformer; e) Boiler; f) High temperature shift; g) Low temperature shift; h) Selexol CO2 removal; h1) CO2 absorber; h2) Regenerator; i) Single stage compression; j) Methanation; k) Cooling and drying; l) Circulator; m) Hydrogen recovery; n) Ammonia converter; o) Refrigeration system
  38. 38. Complete Ammonia Production Plants ICI LCA process (core unit) PAC, purified air compressor; HDS, hydrodesulfurization; IP, intermediate pressure; LP, liquefied petroleum; BFW, boiler feed water
  39. 39. Complete Ammonia Production Plants KBR KAAPplus Process a) Air compressor; b) Sulfur removal; c) Process heater; d) Automatic reformer (ATR); e) Reforming exchanger (KRES); f) Condensate stripper; g) CO2 absorber; h) Methanator; i) CO2 stripper; j) Dryer; k) Expander; l) Feed/effluent exchanger; m) Condenser; n) Rectifier column; o) Synthesis gas compressor; p) KAAP ammonia converter; q) Refrigeration compressor; r) Refrigeration exchanger
  40. 40. Complete Ammonia Production Plants Ammonia production based on heavy fuel oil (Linde flow scheme with Texaco gasification) a) Air separation unit; b) Soot extraction; c) CO2 absorption; d) Methanol/H2O distillation; e) Stripper; f) Hot regenerator; g) Refrigerant; h) Dryer; i) Liquid N2 scrubber; j) Syngas compressor; k) NH3 reactor

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