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.

1. Ammonia Synthesis
Flowsheet
Operator Training
By
Gerard B. Hawkins
Managing Director, CEO

3. 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.

4. 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

6. 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.

7. 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

8. 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.

9. 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)

10. 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

11. 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

12. Ammonia Flowsheet Variations
4. Linde LAC (Linde Ammonia
Concept)
 Hydrogen plant + N2 addition from
air separation unit
 Ammonia Casale synthesis loop

13. 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’

14. 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

15. Typical Uhde Synthesis Loop

16. 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

17. 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

18. 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%

19. 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

20. 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

21. 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).

22. 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.

23. 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

24. 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.

25. 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.

26. Synthesis Loop Principles :
Control of Catalyst Bed Temperatures
 Multi-bed design :
 2, 3, or 4 catalyst beds with
intermediate cooling.

27. 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.

28. 3 Bed Converter Example
450 C
1. Optimum Catalyst
Temperatures
410 C
520 C
415 C
480 C
410 C

29. 3 i/c design
‘Cold’ Converter
410 C
520 C
415 C
480 C
410 C
450 C
120 C
335 C

30. 2 i/c design
410 C
520 C
415 C
480 C
410 C
450 C
‘Hot’ Converter
235 C

31. 1 i/c design
410 C
520 C
415 C
480 C
410 C
450 C
‘Split’ Converter 305 C

32. 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

33. 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

34. Effect of Size on Activity
Particle Diameter (mm)
14121086420
RelativeActivity
120
100
80
60
40
0
20

35. 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

36. Deactivation
 Clean Gas
• Thermal sintering
 Contaminated Gas
• Both Temporary and Permanent
Poisoning
• Oxygen induced sintering
• By water, CO and CO2
• Site blocking/Sintering

37. 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

38. 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

39. 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

40. End

41. Ammonia Converter
Designs

42. 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)

43. 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.

44. Uhde 3 bed
NH3 Converter

45. 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

46. Kellogg Ammonia Quench Converter
Outlet
Inlet

47. Kellogg Horizontal Converter
Bed 1Bed 2ABed 2B
Inlet
Outlet

48. 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

49. 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

50. 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

51. Topsøe S-200 Converter
Inlet
Outlet
Cold
Bypass

52. 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.

53. 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.

54. ICI Lozenge Quench Converter

55. ICI Tube Cooled Converter

56. 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%