Methane Steam Reformer Re-tube Evaluation Wsv

8/14/2019 Methane Steam Reformer Re-tube Evaluation Wsv

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Methane Steam Reformer

Re-Tube EvaluationBy

Gerard B. HawkinsManaging 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 keyconsumable

Different to the majority of hardware on asynthesis 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 minimumperformance 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 andchange size

Simulate re-tube case Determine pressure and temperature profile

Determine stress (σ) and use Larsen-Miller plot todetermine design temperature



Design Methodology

Must be careful with stress data

Some tests have been conducted over a shortperiod 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 stressdata



Design Methodology

Average Reported

Stress

Design Curve

80% of Average

Reported Stress

Temperature

S t r e s s



Design Methodology

Deduct off a margin to give Maximum AllowableOperating Temperature (MAOT)

Check if MAOT is greater than maximumpredicted 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 pressuredrop below that of base case

Or install a larger pellet and generate largepressure drop benefits



Typical Tube Compositions

HK40 Alloy HK40 20% Ni 25% CrIN519 Alloy IN519 24% Ni 24% Cr 1% Nb36X Manaurite 36X (Pompey) 33% Ni 25% Cr 1% NbH39W Alloy H39W (APV) 33% Ni 25% Cr 1% Nb

H39WM Paralloy H39WM 35% Ni 25% Cr 1% Nb + TiXM 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 sincethe reduction in tube thickness is smaller



Options for Catalyst Optimization

A re-tube can allow for an optimization of thecatalyst loading since the tube ID can beincreased

If tube wall temperature are limiting

• Re-tube will reduce peak tube walltemperatures since there is more catalyst andhence more reaction

• Can install a smaller shape - no increase inpressure drop



Options for Catalyst Optimization

Pressure drop will be reduced

• Can reduce even further by installing largercatalyst 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 catalystcombination, 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 2.2

Exit Temperature °C 869 869 869 869 Approach to Equi libr ium °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 and15% extra capacity worth US$330,000-1,000,000per year

Reduce pressure drop by 1/3rd

Increase radiant reformer efficiency



Why Work with GBHE ?

GBHE has operating experience of steamreformers

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 uniqueposition to help with reformer re-tubes



Why Work with GBHE ?

This model includerigorous modelling of

• Heat transfer onfluegas and process

gas side• Kinetic models for

• Carbon prediction

• Pressure drop

• Full tube stress



Details of VULCAN REFSIM

Also includes effect of

• Process conditions changes on tube life

• Coffins

• Tunnel port effects• Naphtha feeds

This means that VULCAN REFSIM is becoming a

leading primary reformer simulation package



Other Issues

If the re-tube allows for a plant rate increasethen must consider other parts of the plant

Fluegas rate will increase

• Can the fluegas duct coils cope with theincreased duty ?

Process gas rate through the reformed gascooling train will rise

• Can the reformed gas cooling train cope ?



Other Issues

What will the effect be on the downstreamcatalytic 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 isdesign and operation of steam reformers

GBHE has project management experience ofre-tubes

GBHE can determine the effect of a revampusing the world leading VULCAN REFSIMsimulation model.

GBHE can optimize the catalyst loading usingthe world leading large matrix catalyst

GBHE can determine effect of re-tube ondownstream and associated unit operations

Methane Steam Reformer Re-tube Evaluation Wsv

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