1) GBHE has extensive experience designing and evaluating methane steam reformer tubes and can perform detailed simulations and modeling to optimize reformer performance during retube evaluations. 2) The methodology involves understanding current operations, simulating the existing reformer, selecting improved tube materials and catalysts, and modeling stress levels and temperatures to determine maximum operating conditions. 3) Case studies demonstrate how optimizing tubes and catalyst can increase production by 3-15% while reducing pressure drop, temperatures, and methane slip.

1. Methane Steam Reformer
Re-Tube Evaluation
By
Gerard B. Hawkins
Managing Director, CEO

2. Contents
 Design methodology applied
• Mechanical design
• Process design
 Case studies
 Why work with GBHE ?

3. Introduction
 The tubes in a primary reformer are a key
consumable
 Different to the majority of hardware on a
synthesis gas plant
 They have a limited life
 They fail due to creep damage

4. Design Methodology
 Understand present operation
 Base Case - simulate existing reformer
• At normal conditions
• Using existing tube design
• Determines the required minimum
performance for all other cases
• Determines the base line life for all other cases

5. Design Methodology
 Then select a tube material to use
• Always go for an improved metallurgy
 Select a catalyst type to give required benefits
• Initial select existing catalyst but ‘like for like’
catalyst change may not be optimal
• Look at effect of large matrix catalyst and
change size
 Simulate re-tube case
 Determine pressure and temperature profile
 Determine stress (σ) and use Larsen-Miller plot to
determine design temperature

6. Design Methodology
 Must be careful with stress data
 Some tests have been conducted over a short
period of time
• May not be representative
 GBHE has reviewed manufacturers stress data
and eliminated any dubious data
 There is still a large degree of variation
 Therefore use a percentage of the average stress
data

7. Design Methodology
Average Reported
Stress
Design Curve
80% of Average
Reported Stress
Temperature
Stress

8. Design Methodology
 Deduct off a margin to give Maximum Allowable
Operating Temperature (MAOT)
 Check if MAOT is greater than maximum
predicted temperature
 Increase/decrease tube wall thickness if required

9. Typical Options
 Typical to upgrade to a modified micro-alloy
 Such as H39WM, XM or KHR35CT
 Use minimum sound wall thickness of 8 mm
 Keep outside diameter constant
 Allow inside diameter to be increased
 Can install smaller catalyst and keep pressure
drop below that of base case
 Or install a larger pellet and generate large
pressure drop benefits

10. Typical Tube Compositions
HK40 Alloy HK40 20% Ni 25% Cr
IN519 Alloy IN519 24% Ni 24% Cr 1% Nb
36X Manaurite 36X (Pompey) 33% Ni 25% Cr 1% Nb
H39W Alloy H39W (APV) 33% Ni 25% Cr 1% Nb
H39WM Paralloy H39WM 35% Ni 25% Cr 1% Nb + Ti
XM Manaurite XM 33% Ni 25% Cr 1% Nb + Ti

11. Relative Allowable Stresses
700
720
740
760
780
800
820
840
860
880
900
920
940
960
980
1000
2
5
10
20
50
100
200
Temperature °C
HK40
IN519
H39W
36X
XM

12. Typical Tube Upgrades
 If using HK40 or similar
• Replace with HP or HP Mod
• Can get a large change in performance due to
large reductions in tube wall thickness
 If using HP
• Replace with HP Mod
• Can get smaller changes in performance since
the reduction in tube thickness is smaller

13. Options for Catalyst Optimization
 A re-tube can allow for an optimization of the
catalyst loading since the tube ID can be
increased
 If tube wall temperature are limiting
• Re-tube will reduce peak tube wall
temperatures since there is more catalyst and
hence more reaction
• Can install a smaller shape - no increase in
pressure drop

14. Options for Catalyst Optimization
 Pressure drop will be reduced
• Can reduce even further by installing larger
catalyst matrix
• Allows plant rate increases
 Reduce flue gas temperature
• Allows for plant rate increases
• Remove coil skin temperature limitations
 Reduced ATE
• Reduces methane slip

15. Example - Ammonia Plant
 By optimizing both the tube ID and catalyst
combination, achieved,
• Reduction in ATE
• Reduced pressure drop by 60%
• Reduced maximum tube wall temperatures by
40°C
• Increase radiant box efficiency
• And can increase through put by 3%

16. Example - Methanol Plant
Name Units Case 1 Case 2 Case 3 Case 4
Tube material n/a HK40 Microalloy Microalloy Microalloy
Plate Rate % 100 100 115 105
Wall Thickness mm 13.5 13.5 8 8
Methane Slip mol % 2.80 2.80 2.80 2.2
Exit Temperature °C 869 869 869 869
Approach to Equilibrium °C 7.3 7.3 5.5 5.6
Pressure Drop bara 5.2 5.2 3.4 3.44
Maximum Tube Temperature °C 921 921 910 925
Fluegas Temperature °C 1126 1127 1113 1125
Savings US$/yr n/a n/a 1,000,000 340,000

17. Example - Methanol Plant
 Can reduce ATE and hence methane slip
 Increase production to realise between 5 and
15% extra capacity worth US$330,000-1,000,000
per year
 Reduce pressure drop by 1/3rd
 Increase radiant reformer efficiency

18. Why Work with GBHE ?
 GBHE has operating experience of steam
reformers
 GBHE has design experience of steam
reformers and in particular re-tubes
 GBHE understands the problems and
issues associated with re-tubes
 This means that GBHE is in a unique
position to help with reformer re-tubes

19. Why Work with GBHE ?
 This model include
rigorous modelling of
• Heat transfer on
fluegas and process
gas side
• Kinetic models for
• Carbon prediction
• Pressure drop
• Full tube stress

20. Details of VULCAN REFORMER
SIMULATION
 Also includes effect of
• Process conditions changes on tube life
• Coffins
• Tunnel port effects
• Naphtha feeds
 This means that VULCAN REFORMER
SIMULATION is becoming a leading primary
reformer simulation package

21. Other Issues
 If the re-tube allows for a plant rate increase
then must consider other parts of the plant
 Fluegas rate will increase
• Can the fluegas duct coils cope with the
increased duty ?
 Process gas rate through the reformed gas
cooling train will rise
• Can the reformed gas cooling train cope ?

22. Other Issues
 What will the effect be on the downstream
catalytic units ?
• For example - HTS/LTS
 What will happen to plant production
 GBHE has models to perform this analysis
 Can simulate all unit operations in detail and
determine performance post re-tube

23. Middle Eastern Ammonia Plant
 During discussions re-tube was mentioned
 Conducted 3 phase approach
 Process design - US$ 10,000 : 1 days work
 Fluegas modelling - US$ 20,000 : 10 days work
 Detailed tube design - US$ 75,000
• Performed by a Engineering Contractor

24. Conclusions
 GBHE has an un-paralleled experience is
design and operation of steam reformers
 GBHE has project management experience of
re-tubes
 GBHE can determine the effect of a revamp
using the world leading VULCAN REFORMER
SIMULATION simulation model.
 GBHE can optimize the catalyst loading using
the world leading large matrix catalyst
 GBHE can determine effect of re-tube on
downstream and associated unit operations