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
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
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