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Ammonia Synthesis
Flowsheet
Operator Training
By
Gerard B. Hawkins
Managing Director, CEO
Introduction
 Most modern ammonia processes are
based on steam-reforming of natural
gas or naphtha.
 The 3 main technolo...
Simplified - NH3 PlantH2O
H/C
feed
H/C
purification
Removes
impurities (S,
Cl, metals)
Primary
reforming
Converts to
H2, C...
Ammonia Synthesis Loop
 Synthesis reaction is equilibrium limited,
typically 15 – 20% NH3 at converter exit.
 Therefore ...
Simplified Flowsheet for a Typical Ammonia
Plant
Natural
Gas
Steam
superheater
Air
Steam
30
bar
Steam
Steam
raising
350 C
...
Ammonia Plant Steam & Power
System
 Waste Heat recovery is used to raise
HP steam, 100 – 120 bar
 Steam is used to drive...
Ammonia Flowsheet Variations
1. Uhde
 Top fired reformer
• Cold outlet manifold design
 Secondary reformer with internal...
Ammonia Flowsheet Variations
2. KBR
 Top-fired reformer
• With internal risers
 Several synthesis loop options:
• Conven...
Ammonia Flowsheet Variations
3. Topsøe
 Side-fired reformer
 Radial flow converter
• S-100 2 bed quench
• S-200 2 bed in...
Ammonia Flowsheet Variations
4. Linde LAC (Linde Ammonia
Concept)
 Hydrogen plant + N2 addition from
air separation unit
...
Ammonia Flowsheet Variations
5. ICI (JM)
 AMV
• Large-scale process with excess air,
low pressure loop (80 – 110 bar)
 L...
Ammonia Synthesis Mechanism
 Dissociative adsorption of H2
Dissociative adsorption of N2 -
Believed to be the Rate Determ...
Typical Uhde Synthesis Loop
Uhde Dual-Pressure Process
C.W.Make up gas
from frontend
C.W.
Steam
Once
through
converter
Synthesis
Loop
Purge
NH3
NH3
NH...
Effect of Pressure on Ammonia
Equilibrium Concentration
0
10
20
30
40
50
60
50 75 100 125 150 175 200 225 250 275 300
NH3c...
Ammonia Equilibrium Diagram
300
(572)
350
(662)
400
(752)
450
(842)
500
(932)
550
(1022)
600
(1112)
650
(1202)
0
10
20
30
...
Effect of Catchpot Temperature on
Ammonia VLE
0.0
2.0
4.0
6.0
8.0
10.0
12.0
50 75 100 125 150 175 200 225 250 275 300
NH3c...
Synthesis Loop Principles:
Mass Balance
 Overall Loop Mass Balance
• On a mass basis:
NH3 = MUG – Purge
• On a molar basi...
Synthesis Loop Principles:
Mass Balance
 Converter Molar balance:
NH3 = Circ Flow x (NH3out- NH3in)
1 + NH3out
NH3in is s...
Synthesis Loop Principles:
Effect of Purge
 Circulating composition is the same
as the purge composition (like a
stirred-...
Synthesis Loop Principles:
H2 : N2 ratio example
H / N = 3 : 1
MUG NH3 Purge
H2 3000 2700 300
N2 1000 900 100
H / N 3.0 3....
Synthesis Loop Principles :
Inerts Balance
 Inerts (CH4 + Ar) concentrate in the loop,
typically by a factor of about 10....
Synthesis Loop Principles :
Effect of H2 Recovery
 Most modern loops have H2 recovery.
 2 systems are used, cryogenic or...
Synthesis Loop Principles :
Control of Catalyst Bed Temperatures
 Multi-bed design :
 2, 3, or 4 catalyst beds with
inte...
Synthesis Loop Principles :
Converter Heat Balance
 Older converter designs usually had an
interchanger after the final b...
3 Bed Converter Example
450 C
1. Optimum Catalyst
Temperatures
410 C
520 C
415 C
480 C
410 C
3 i/c design
‘Cold’ Converter
410 C
520 C
415 C
480 C
410 C
450 C
120 C
335 C
2 i/c design
410 C
520 C
415 C
480 C
410 C
450 C
‘Hot’ Converter
235 C
1 i/c design
410 C
520 C
415 C
480 C
410 C
450 C
‘Split’ Converter 305 C
Converter Heat Recovery Example
 In all cases the amount of heat recovered
is the same, only the available
temperatures a...
Comparison of 74 & 35 Series
30
40
50
60
70
80
90
100
110
120
0 2 4 6 8 10 12 14
Time on line (years)
RelativeActivity
Sev...
Effect of Size on Activity
Particle Diameter (mm)
14121086420
RelativeActivity
120
100
80
60
40
0
20
Effect of Size on Activity
 Smaller pellets = high activity
 Therefore high production rate or
smaller catalyst volume
...
Deactivation
 Clean Gas
• Thermal sintering
 Contaminated Gas
• Both Temporary and Permanent
Poisoning
• Oxygen induced ...
Typical Operating Conditions
 Temperature (o
C) 360-520
 Pressure (bar) 80-600
 Space velocity (hr-1
)1000-5000
 Poiso...
Catalyst Size
Grade Size
A 1.5-3.0 mm
B 3.0-4.5 mm
C 3.0-6.0 mm
D / E 6.0-10.0 mm
G 14.0-20.0 mm
Catalyst Reduction
Max water in outlet gas during
reduction (ppm)
Formation of water during
reduction of 1te of Catalyst (...
End
Ammonia Converter
Designs
Converter Designs
Objectives for modern designs are;
- low pressure drop with small catalyst
particles.
- high conversion ...
Uhde
 Uhde design a range of converters:
 Modern designs use radial flow
with inter-cooling & 'split
converters' with he...
Uhde 3 bed
NH3 Converter
M W Kellogg Converter Types
 'Conventional' make-up gas and loop
layout, refrigeration to low temperature (-
25 C),
 loo...
Kellogg Ammonia Quench Converter
Outlet
Inlet
Kellogg Horizontal Converter
Bed 1Bed 2ABed 2B
Inlet
Outlet
KBR KAAP
 Converter is made up of 4 beds
 First bed uses magnetite catalyst
 Ru can not be used since
temperature rise ...
Braun Converter Types
 Purifier Process gives pure make-up gas
 - low levels of poisons; H2O, CO, CO2
 - Low inerts; no...
Haldor Topsøe S- Series
 S-100 :Radial flow 2-bed quench
 S-200 :Radial flow 2-bed inter cooled
 S-250 : S-200, heat re...
Topsøe S-200 Converter
Inlet
Outlet
Cold
Bypass
Ammonia Casale
 Ammonia Casale - 'axial-radial'
concept
- radial flow without a top cover on
the beds
- simpler mechanica...
ICI Types
 Lozenge quench converter :
• single bed divided into 3 parts by quench
addition
• simple concept but suffered ...
ICI Lozenge Quench Converter
ICI Tube Cooled Converter
ICI TCC Equilibrium Plot
300
(572)
350
(662)
400
(752)
450
(842)
500
(932)
550
(1022)
600
(1112)
650
(1202)
0
10
20
30
40
...
Ammonia Synthesis Flowsheet - Operator training
Ammonia Synthesis Flowsheet - Operator training
Ammonia Synthesis Flowsheet - Operator training
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Ammonia Synthesis Flowsheet - Operator training

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Most modern ammonia processes are based on steam-reforming of natural gas or naphtha.

The 3 main technology suppliers are Uhde (Uhde/JM Partnership), Topsoe & KBR.

The process steps are very similar in all cases.

Other suppliers are Linde (LAC) & Ammonia Casale.

Publicada em: Tecnologia, Negócios
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Ammonia Synthesis Flowsheet - Operator training

  1. 1. Ammonia Synthesis Flowsheet Operator Training By Gerard B. Hawkins Managing Director, CEO
  2. 2. Introduction  Most modern ammonia processes are based on steam-reforming of natural gas or naphtha.  The 3 main technology suppliers are Uhde (Uhde/JM Partnership), Topsoe & KBR.  The process steps are very similar in all cases.  Other suppliers are Linde (LAC) & Ammonia Casale.
  3. 3. Simplified - NH3 PlantH2O H/C feed H/C purification Removes impurities (S, Cl, metals) Primary reforming Converts to H2, CO, CO2 + H2O + CH4 CO Shift WGS reaction Secondary reforming Combustion + Adiabatic Reforming + Adds Nitrogen Air Ammonia synthesis NH3 Converts N2 + H2 => NH3 Syngas compression Purification CO2 Removal & Methanation
  4. 4. Ammonia Synthesis Loop  Synthesis reaction is equilibrium limited, typically 15 – 20% NH3 at converter exit.  Therefore recycle in a ‘loop’ is required.  Multi-stage complex converters are required to control bed temperatures.  Various designs are used depending on contractor.  Liquid Ammonia is recovered by refrigeration.
  5. 5. Simplified Flowsheet for a Typical Ammonia Plant Natural Gas Steam superheater Air Steam 30 bar Steam Steam raising 350 C 200 C Heat Recovery Steam raising Cooling Cooling Reboiler CO Cooling Preheater Heat Recovery Steam Boiler Process Condensate Quench Quench Liquid Ammonia H Hydrodesulphuriser Primary Reformer Secondary Reformer High Temperature Shift Low Temperature Shift Ammonia SynthesisMethanator Carbon Dioxide Purge Gas Cooling 400 Co 390 Co 2 790 C o 550 Co 1000 Co o 420 Co 150 C o 400 Co 470 C o o 220 C o 290 Co 330 Co 2 CO Removal2 220 bar Refrigeration Condensate Cooling Ammonia Catchpot
  6. 6. Ammonia Plant Steam & Power System  Waste Heat recovery is used to raise HP steam, 100 – 120 bar  Steam is used to drive the main compressors • Process air • Syn gas compression + circulator • Refrigeration  Pass-out steam is used for process.
  7. 7. Ammonia Flowsheet Variations 1. Uhde  Top fired reformer • Cold outlet manifold design  Secondary reformer with internal riser  H P loop (200 bar) with radial flow converter • 1 or 2 converters  Once-through synthesis section upstream of main synthesis loop for very large capacities (dual pressure Uhde process)
  8. 8. Ammonia Flowsheet Variations 2. KBR  Top-fired reformer • With internal risers  Several synthesis loop options: • Conventional 140 bar loop with 4bed quench converter • Higher pressure for large-scale plants • Horizontal converter on modern plants. • KAAP design – 100 bar loop with Ru/C catalyst  Braun Purifier flowsheet • Excess air with cryogenic ‘purifier’ to remove excess N2 and inerts from MUG
  9. 9. Ammonia Flowsheet Variations 3. Topsøe  Side-fired reformer  Radial flow converter • S-100 2 bed quench • S-200 2 bed intercooled • S-250 = S-200 + boiler + 2nd converter (1 bed) • S-300 3 bed intercooled
  10. 10. Ammonia Flowsheet Variations 4. Linde LAC (Linde Ammonia Concept)  Hydrogen plant + N2 addition from air separation unit  Ammonia Casale synthesis loop
  11. 11. Ammonia Flowsheet Variations 5. ICI (JM)  AMV • Large-scale process with excess air, low pressure loop (80 – 110 bar)  LCA • Small-scale plant based on GHR technology  AMV / LCA technology is now part of JM’s ‘background in ammonia’
  12. 12. Ammonia Synthesis Mechanism  Dissociative adsorption of H2 Dissociative adsorption of N2 - Believed to be the Rate Determining Step (RDS) Multi-step hydrogenation of adsorbed N2 Desorption of NH3
  13. 13. Typical Uhde Synthesis Loop
  14. 14. Uhde Dual-Pressure Process C.W.Make up gas from frontend C.W. Steam Once through converter Synthesis Loop Purge NH3 NH3 NH3 1 2 3 R C.W.Make up gas from frontend C.W. Steam Once through converter Synthesis Loop Purge NH3 NH3 NH3 1 2 3 R
  15. 15. Effect of Pressure on Ammonia Equilibrium Concentration 0 10 20 30 40 50 60 50 75 100 125 150 175 200 225 250 275 300 NH3concentration% Pressure bara 380 C 400 C 420 C
  16. 16. Ammonia Equilibrium Diagram 300 (572) 350 (662) 400 (752) 450 (842) 500 (932) 550 (1022) 600 (1112) 650 (1202) 0 10 20 30 40 Equilibrium Max Rate Temperature °C (°F) Ammoniacontent%
  17. 17. Effect of Catchpot Temperature on Ammonia VLE 0.0 2.0 4.0 6.0 8.0 10.0 12.0 50 75 100 125 150 175 200 225 250 275 300 NH3concentration% Pressure bara 0 C minus 20 C
  18. 18. Synthesis Loop Principles: Mass Balance  Overall Loop Mass Balance • On a mass basis: NH3 = MUG – Purge • On a molar basis: NH3 = (MUG – Purge) / 2 because 4 mol -> 2 mol in the NH3 reaction.  Converter balance, on a molar basis: NH3 = Inlet gas – Outlet gas
  19. 19. Synthesis Loop Principles: Mass Balance  Converter Molar balance: NH3 = Circ Flow x (NH3out- NH3in) 1 + NH3out NH3in is set by P & T of final separator + position of MUG addition (before or after separator).
  20. 20. Synthesis Loop Principles: Effect of Purge  Circulating composition is the same as the purge composition (like a stirred-tank reactor).  Inerts (CH4 + Ar) build-up in loop.  Circulating gas H / N ratio is very sensitive to MUG H / N ratio because the reaction consumes gas in a 3 : 1 ratio.
  21. 21. Synthesis Loop Principles: H2 : N2 ratio example H / N = 3 : 1 MUG NH3 Purge H2 3000 2700 300 N2 1000 900 100 H / N 3.0 3.0 3.0 H / N = 2.95 : 1 H2 2950 2700 250 N2 1000 900 100 H / N 2.95 3.0 2.50
  22. 22. Synthesis Loop Principles : Inerts Balance  Inerts (CH4 + Ar) concentrate in the loop, typically by a factor of about 10.  Note that some of the inerts (10 – 20% of the total) dissolve in the product NH3.  A few loops with purified make-up gas have a ‘self-purging loop’ where all the inerts are removed in solution in the product.  The NH3 content of the purge at the flowmeter position is required to check the loop mass balance.
  23. 23. Synthesis Loop Principles : Effect of H2 Recovery  Most modern loops have H2 recovery.  2 systems are used, cryogenic or membrane.  The overall effect is similar, typically 90% H2 recovery at 90% purity.  Overall loop H2 conversion to NH3 increases from about 92% to 98%.  MUG H / N ratio changes from 3.0 to approx. 2.85, and returns to 3.0 after H2 addition.
  24. 24. Synthesis Loop Principles : Control of Catalyst Bed Temperatures  Multi-bed design :  2, 3, or 4 catalyst beds with intermediate cooling.
  25. 25. Synthesis Loop Principles : Converter Heat Balance  Older converter designs usually had an interchanger after the final bed to contain high temperatures within the converter.  Modern designs typically have no ‘overall’ interchanger because this gives better heat recovery (heat available at a higher temperature)  ‘Split converter designs’ further increase the heat recovery temperature.
  26. 26. 3 Bed Converter Example 450 C 1. Optimum Catalyst Temperatures 410 C 520 C 415 C 480 C 410 C
  27. 27. 3 i/c design ‘Cold’ Converter 410 C 520 C 415 C 480 C 410 C 450 C 120 C 335 C
  28. 28. 2 i/c design 410 C 520 C 415 C 480 C 410 C 450 C ‘Hot’ Converter 235 C
  29. 29. 1 i/c design 410 C 520 C 415 C 480 C 410 C 450 C ‘Split’ Converter 305 C
  30. 30. Converter Heat Recovery Example  In all cases the amount of heat recovered is the same, only the available temperatures are different.  In all cases, the catalyst bed temperatures are the same: Bed 1 410 – 520 dT = 110 Bed 2 415 – 480 dT = 65 Bed 3 410 – 450 dT = 40 Total Bed dT = Converter dT = 215
  31. 31. Comparison of 74 & 35 Series 30 40 50 60 70 80 90 100 110 120 0 2 4 6 8 10 12 14 Time on line (years) RelativeActivity Severnside LCA Standard Catalyst
  32. 32. Effect of Size on Activity Particle Diameter (mm) 14121086420 RelativeActivity 120 100 80 60 40 0 20
  33. 33. Effect of Size on Activity  Smaller pellets = high activity  Therefore high production rate or smaller catalyst volume  But pressure drop will rise  Either axial-radial or radial flow beds are used to minimise pressure drop  Radial flow is the basis of many converter internal retrofits
  34. 34. Deactivation  Clean Gas • Thermal sintering  Contaminated Gas • Both Temporary and Permanent Poisoning • Oxygen induced sintering • By water, CO and CO2 • Site blocking/Sintering
  35. 35. Typical Operating Conditions  Temperature (o C) 360-520  Pressure (bar) 80-600  Space velocity (hr-1 )1000-5000  Poisons oxygen and oxygen compounds normally < 3ppm
  36. 36. Catalyst Size Grade Size A 1.5-3.0 mm B 3.0-4.5 mm C 3.0-6.0 mm D / E 6.0-10.0 mm G 14.0-20.0 mm
  37. 37. Catalyst Reduction Max water in outlet gas during reduction (ppm) Formation of water during reduction of 1te of Catalyst (kg) Pre-reduced Oxidized 1000 3000 25 280
  38. 38. End
  39. 39. Ammonia Converter Designs
  40. 40. Converter Designs Objectives for modern designs are; - low pressure drop with small catalyst particles. - high conversion per pass with high grade heat recovery. Principal types are designed by: Uhde Kellogg (KBR) - conventional, Braun, KAAP Topsoe Ammonia Casale JM (I C I)
  41. 41. Uhde  Uhde design a range of converters:  Modern designs use radial flow with inter-cooling & 'split converters' with heat recovery between, - Converter 1 : 2-bed, 1 interchanger - Heat recovery (boiler) - Converter 2 : 3rd bed.
  42. 42. Uhde 3 bed NH3 Converter
  43. 43. M W Kellogg Converter Types  'Conventional' make-up gas and loop layout, refrigeration to low temperature (- 25 C),  loop pressure typically 140 - 180 bar.  Converters:  4 bed quench ; conventional Kellogg design.  Horizontal converter ; • lower cost, low pressure drop, easier installation • 2 bed inter-cooled layout with small catalyst
  44. 44. Kellogg Ammonia Quench Converter Outlet Inlet
  45. 45. Kellogg Horizontal Converter Bed 1Bed 2ABed 2B Inlet Outlet
  46. 46. KBR KAAP  Converter is made up of 4 beds  First bed uses magnetite catalyst  Ru can not be used since temperature rise is too large  Lower beds use Ru catalyst  Ru catalyst has a carbon support  Catalyst developed by BP • Very high activity even at low pressure
  47. 47. Braun Converter Types  Purifier Process gives pure make-up gas  - low levels of poisons; H2O, CO, CO2  - Low inerts; no purge from loop  Converters :  Basically 2-bed intercooled with each catalyst bed in a separate vessel  Modern designs may use 3 converters &/or radial flow
  48. 48. Haldor Topsøe S- Series  S-100 :Radial flow 2-bed quench  S-200 :Radial flow 2-bed inter cooled  S-250 : S-200, heat recovery, 2nd converter with 1 radial flow bed  S-300 :Radial flow 3-bed inter cooled
  49. 49. Topsøe S-200 Converter Inlet Outlet Cold Bypass
  50. 50. Ammonia Casale  Ammonia Casale - 'axial-radial' concept - radial flow without a top cover on the beds - simpler mechanical design  No. of beds & type of inter-bed cooling varies; typically 3 bed, 2 interchanger.
  51. 51. ICI Types  Lozenge quench converter : • single bed divided into 3 parts by quench addition • simple concept but suffered high pressure drop  ICI AMV Process : • Low pressure loop with H2 recovery at loop pressure • range of converters in use • Terra: ICI 3-bed, 1 quench + 1 intercooler axial flow  ICI LCA Process : • Tube-cooled + adiabatic design.
  52. 52. ICI Lozenge Quench Converter
  53. 53. ICI Tube Cooled Converter
  54. 54. ICI TCC Equilibrium Plot 300 (572) 350 (662) 400 (752) 450 (842) 500 (932) 550 (1022) 600 (1112) 650 (1202) 0 10 20 30 40 Equilibrium Max Rate Converter Profile Temperature °C (°F) Ammoniacontent%

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