Purpose Key to good performance Problem Areas Catalysts, heat shields and plant up-rates Burner Guns Development of High Intensity Ring Burner Case Studies Conclusions

1. Theory and Operation of
Secondary Reformers
By:
Gerard B. Hawkins
Managing Director, CEO

2. Introduction
 Purpose
 Key to good performance
 Problem Areas
• Catalysts, heat shields and plant up-rates
• Burner Guns
 Development of High Intensity Ring
Burner
 Case Studies
 Conclusions

3. Secondary Reformer Purpose
 Reduce methane slip to very low
levels
• Around 0.3-0.5 % mol dry
 For ammonia plants provide feed
point for nitrogen required for
ammonia synthesis
• And thereby Ensure optimal H/N ratio
 Generate heat for transfer for HP
steam in Waste Heat Boiler

4. Typical Reforming Configuration
Steam
Secondary
Reformer
Steam
Steam + Gas
Steam
Reformer
Air / Oxygen500°C
780°C
450°C
1200°C
950°C
10% CH
4
0.5% CH
4

5. Secondary Reformer Mechanical
Details
Refractory lined pressure shell
Fixed Catalyst bed in lower region
Combustion section in upper region
Water jackets to keep shell cool
Catalyst supported on brick arch

6. Keys to Good Performance
 Three key
components
– Burner Design
– Mixing Volume
– Catalyst
All must be designed
correctly to maximize
performance
Air/Oxygen
Steam Reformer
Effluent
To Waste
Heat Boiler

7. Keys to Good Performance
 Again three key
components
• Burner Design
• Mixing Volume
• Catalyst - VSG-
Z201/202/203
 Since using O2 as
oxidant, flame
temperature is
higher
• Failures are much
faster
780°C
540`C
2500°C
1500°C
1100-1200°C
975°C
1500°C
1100-1200°C
1300°C
Note: Oxygen - Methanol Plant Design

8. Secondary Reformer Operation
•Burner determines mixing performance
•Air injected at high velocity
•Forces mixing of air and process gas
•Combusts only 20% of process gas
•Must also mix in other 80%
•Should achieve a uniform mixture
•Catalyst bed can affect flow patterns

9. Secondary Reformer Combustion
Gas feed very hot > 630oC
Gas feed contains hydrogen
Gas ignites automatically
Autoignition >615oC
No need for spark or pilot
Must maintain gas above 615oC

10. Secondary Reforming Reactions
CH4 + 2CO = CO2 + 2H2O
2H2 + O2 = 2H2O Exothermic - gives out
heat
Flame 2500oC mixed gas 1500oC
Steam reforming
CH4 + H2O = 3H2 + CO Endothermic - cools
down gas
Water gas shift
CO + H2O = CO2 + H2Slightly exothermic

11. Key Components: Catalyst
Problems
 Catalyst can
• Exhibit poor activity
 Unlikely
• Break up in service
 Usually linked to a plant upset
• Suffer physical blockage
 Alumina vaporization
• Become overheated and fuse
 Causes increased pressure drop and gas mal-
distribution

12. Key Components: Catalyst Activity
 Catalyst is exposed to very high
temperatures
• Therefore nickel sinters
 However once sintered it is very stable
 Since catalyst operates at high temperature
it is difficult to poison
• Poisons will not stick
• For ammonia plants will pass through to
HTS and then LTS
• For methanol plants will pass through to
methanol synthesis loop

13. Key Components: Catalyst Activity
 VULCAN Series range of
catalysts VSG-Z201/202/203
• Size - Mini and Standard plus
Elephant
• Use as a heat shield
• Shape
 5-Hole
 Quadralobe
 Quadralobe has +20% more
activity than 4-hole
• Well proven catalysts that are
high stable and strong
• Long lives

14. Key Components: Catalyst Appearance
 White - loss of nickel
 Coated in white - alumina vaporization
 Glazed or blue - very high temperatures
 Pink crystals - synthetic ruby formation
• Cause by high temperatures
• A mixture of refractory and transition
metals

15. Key Components: Mixing Performance
 Good mixing is absolutely essential
 Poor mixing in mixing zone gives high approach
and high methane slip
 Poor mixing can be due to
• Poor burner design
• Insufficient mixing volume
• Burner gun failure
 Root cause can be checked with CFD but will not
detect burner gun failure

16. Key Components: Burner Gun
 If burner gun fails then can lead to
• Wall refractory damage
• Loss of vessel containment
 Poor mixing can lead to zones of high
temperature
• Leads to high rate of catalyst sintering
• Reduction in catalyst activity
• Increase in approach to equilibrium (ATE)
 Poor mixing can lead to high flow zones
• Movement/damage of target tiles or catalyst
bed
• Increased ATE

17. Key Components: Burner Guns
 Standard Ammonia secondary burners have
• Small number of large holes
• Give poor mixing at high rates
• High risk of overheating bed
• Methane slip rises rapidly at high rates
• Burner can be plant limit

18. Key Components: Burner Guns
 For methanol plants remember that
oxidant used in oxygen
 Gives higher flame temperatures
 If jet impinges on refractory then
refractory will be damaged much more
quickly
 Vessel will fail rapidly
 As oxidant flow is lower than for an
ammonia plant use a different design of
burner

19. Key Components
High Intensity Ring Burner
 The high intensity burner differs from the
standard burners
• Large number of small holes: Small flames
• High degree of mixing: Short mixing distance
• Oxidant fed evenly into process gas: Good
Mixing
• Insensitive to rate increases
• Used in ICI Ammonia plants

20. Effect of Operational Changes
Air Rate
Name Units Base
Case
Increased Air
Rate
Plant Rate % 100 100
Air Rate % 100 105
Exit Pressure Bara 39 39
Steam to Carbon to Primary n/a 2.88 2.88
Outlet Temperature °C 1000 1026
Methane Slip mol % 0.41 0.41
H/N Ratio n/a 3.00 2.86
Approach to Equilibrium °C 14.2 45.1

21. Effect of Operational Changes
Pressure
Name Units Base
Case
Increased
Exit Pressure
Plant Rate % 100 100
Air Rate % 100 100
Exit Pressure Bara 39 40
Steam to Carbon to Primary n/a 2.88 2.88
Outlet Temperature °C 1000 1000
Methane Slip mol % 0.41 0.41
H/N Ratio n/a 3.00 3.00
Approach to Equilibrium °C 14.2 11.3

22. Effect of Operational Changes
Steam to Carbon Ratio
Name Units Base
Case
Decreased
Steam to Carbon
Plant Rate % 100 100
Air Rate % 100 100
Exit Pressure Bara 39 39
Steam to Carbon to Primary n/a 2.88 2.78
Outlet Temperature °C 1000 1002
Methane Slip mol % 0.41 0.41
H/N Ratio n/a 3.00 3.00
Approach to Equilibrium °C 14.2 12.2

23. Key Components: Effect of Poor
Mixing
 Poor mixing can be illustrates by assuming
a secondary reformer with a high zone of
high air flow and a zone with low flow
Name
Temperature
Methane slip
Approach
Poor
Units Too
much air
Too little
air
o
C 1034 902
Mol % 0.13 1.89
o
C 10 10
Mixed
971
0.9
53
Good
957
0.62
10

24. Key Components: Catalytic Heat Shield
 Bed has to be protected
against disturbances
 Conventional target tiles or
alumina lumps used
 Even these can be moved
 No longer required: can
replace with active catalyst
• Additional activity improves
reforming performance
 Use – VULCAN Series AST
Advanced Support Technology
• Large (35mm) 4-hole shape

25. Key Components
Use of CFD for Secondary Reformers
 CFD modelling very good for secondary
reformers
 BUT time consuming and expensive
 Building up a library of case studies
 VULCAN Series Catalysts VSG-Z201/202/203
has extensive experience with CFD for
secondary reformers
• Troubleshooting problems
• Designing burner guns
• Validation of modifications
• Optimization of catalyst quantity

26. Catalyst
Bed
Air
gun
Recirculation
zones
Case Study 1:
Insufficient Mixing Volume
1200 C 1400 C 1500 C 1600 - 2100 C
Air
Gun
Catalyst
Bed
<1200 C 1400 C

27. Case Study 1:
Insufficient Mixing Volume

28. Case Study 2 Burner Guns
 In this case, secondary operated well up to 1450 mtpd
 At rates above this, methane slip rose rapidly
 Limiting further plant rate increases
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1100 1200 1300 1400 1500 1600 1700
Plant rate, mtpd
Methaneslip

29. Catalyst
Bed
Recirculation
Zone
Burner
Rings
1200 C 1300 C 1400 C 1500 C 1600 - 2100 C
Catalyst
Bed
Burner
Rings
<1200 C
Case Study 2:
High Intensity Ring Burner

30. Secondary Catalyst Conclusions
 All three components must be designed
correctly
 If there are problems then can change catalyst
type to high activity catalyst – VULCAN Series
VSG-Z201/202/203 5-hole or Quadralobe
• Can achieve large reduction volumes
• Allows increase in mixing space
• VSG-Z201/202/203 catalysts are well proven,
stable and reliable
 Good mixing above the catalyst bed is essential
 Poor mixing gives high methane slip
 Mixing performance critically depends upon
burner

31. Secondary Reforming Conclusions
 CFD useful for
• Troubleshooting
• Design, modifications and optimization
• VULCAN Series Catalysts can offer this service
 GBHE Catalyst Process Technology can
recommend the appropriate burner type
• Eliminates problems caused by poor mixing
• Optimum burner type opposite plant configuration
• But still needs designing correctly
• Continued process of improvement to design
• Contact your GBHE Catalysts representative for
details