Methane Steam Reformer Re-Tube Evaluation

By Gerard B. Hawkins

Managing Director, CEO

Contents

Design methodology applied • Mechanical design • Process design

Case studies Why work with GBHE ?

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

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

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

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

Design Methodology

Average Reported Stress

Design Curve 80% of Average Reported Stress

Temperature

Stre

ss

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

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

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

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

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

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

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

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%

Example - Methanol Plant

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

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

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

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

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

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 ?

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

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

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