Design methodology applied Mechanical design Process design Case studies Why work with GBHE ?

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