Steam Reforming - Common Problems

Gerard B. Hawkins
Managing Director
WWW.GBHENTERPRISES.COM

 The aim of this presentation is to
• Discuss some of the common problems that
occur on steam reformers
• Analyze problems associated with
◦ Catalyst
◦ Tubes
◦ Reformer Design

 Many ageing plants
 Problems generally
increase towards
end of plant life
 Loss of corporate
knowledge
 De-manning
 Result is that
number of problems
will increase
Plant Reliability
Life of Plant

• Many problems
• Varied causes and effects
• Not always easy to detect
• Can reduce efficiency significantly
• Can affect plant financial profitability

• Some typical ones include
◦ Poisoning
◦ Carbon formation
◦ Tunnel problems
◦ Air leaks
◦ Tube failures
• Less common ones include
◦ Tunnel Port Effect
◦ Flue gas Mal-distribution

• There are many poisons but most common is
sulfur - must not rule out
◦ Chlorides
◦ Heavy metals - Arsenic/Vanadium
◦ Phosphates
• Will reduce activity
• Raises tube temperatures
• Can lead to hot bands
• And hence carbon formation

• Hot bands are formed due to
◦ Loss of activity
◦ Poor heat transfer
◦ Localized high voidage
◦ Too low a steam to carbon ratio
• Once formed they will get worse
• On Top Fired reformers occur about 1/3 down the
tube
◦ Not so much of a problem on Terrace Wall or Side Fired
furnaces as inside tube temperatures are lower

Weld
Hot Band

• All combustion at top of furnace
• High heat transfer rate at this point
• Measured by heat fluxes
◦ Top fired between 80-140 kW/m²
◦ But some in range 140-160 kW/m²
• Side Fired/Terrace Wall have multiple fuel
combustion points
◦ Heat Fluxes are lower
• Therefore Top Fired more prone to carbon
formation

• Can remove by steaming
• Need exit temperature above 700°C = 1300°F
• No feed - Only steam
• Continue for at least 12 hours
• Monitor for CH4 and CO2 exit reformer
• Check process condensate for sulfites and
sulfates
• Add nitrogen as carrier if required
• If really bad may need an air burn
• If even worse - a new charge of catalyst

Hot Band Hot Tube SettlingGiraffe
Necking
Tiger
Tailing

• Can eventually lead to
tube failure of affected
tube
• Can run with failed tube
◦ Provided leak is not too
severe
◦ No direct impingement on
adjacent tubes
• Can nip each tube to
allow continued operation
Nipped
Tube

 Nipped tubes
run much hotter
 Eventually fail
 Normally fall
over
 Need to monitor
 Shut down if
there is a
problem
Coffin

 Occurs if nipping tubes but no firing adjustment
Single Tube Failure Failures spread along row
Failed tubes
Nipped Tubes

Continues to move along row Jumps across to adjacent rows
Spreads along adjacent rows

• Absolutely vital to get right in primary reformers
• If not right then will get a spread of temperatures
• A case is shown below - problems on loading
Poor Loading

• Next charge used a dense loading technique
• Achieved a very even loading
Good Loading - UnidenseTM

-20
-15
-10
-5
0
5
10
15
20
-20 -15 -10 -5 0 5 10 15 20
Pressure drop variation (%)
Flowvariation(%)
-50
-40
-30
-20
-10
0
10
20
30
40
50
TWTvariation(oC)

Catalyst Deactivation
 Physical processes
• Tube expansion/contraction
• Expansion during start-up
• Contraction during cooling stresses pellets
At shutdown
Stressed Pellets
After loading
During operation

Initial
catalyst level
Cold Hot
Expansion of tube
- some settling
Cold
Contraction of tube
- some readjustment
- some breakage
Hot Zone

• Catalyst will break in service during
◦ Trips
◦ Steaming
• Will lead to high resistance to flow
• Some tube will have less flow
◦ Therefore will appear hotter

Fluegas Fans

 Double Fan can lead to variation of TWT along
reformer

• This occurred on Methanol Plant in Western
Europe
• Plant ran for almost 30 years
• Tubes at the hot points had been replaced 3 times
during the plant life
◦ Average life of these tubes was 7years
• Tubes at the cold points were replaced once or
never at all !
◦ Average life of these tubes was 25-30 years
• Overall cost plant money since tube life not
utilized fully

 Can also get mal-distribution due to
• Poor fuel header design
◦ Causes fuel mal distribution between cells
• Poor feed header design
◦ Causes feed mal distribution between cells
• Also affects side fired type reformers

Poorly
Balanced
Cell 1
55
869
1596
1.5
11
20
Cell 2
45
810
1490
3.7
11
20
Well
Balanced
100
842
1548
2.3
12
21
Mixed
Gas
100
840
1544
2.6
16
29
Fuel flow (% of average)
Exit temp (oC)
Exit temp (oF)
Exit CH4 (mol % dry)
ATE (oF)
ATE (oC)
Parameter

• Used to collect flue gas in Top Fired reformers
• Used to collect the flue gas such that furnace
operates in ‘Plug Flow’ regime
• Have proven to be a problem
◦ Mechanically - they have collapsed
◦ Damage can lead to localized mal-distribution
◦ Tunnel port effect
• Some plants have removed them !
◦ Reduces flue gas side pressure drop
◦ Allows uprate of plant

Effect on Flow
Effect on Temperature

• Kellogg plant in India
• Coffin collapsed
• Side wall and roof bricks rested on the manifold
• Manifold deviated from normal position
• Induced additional stresses
• Manifold did not fail - problem rectified at shut
down just after failure

With Coffins
Fluegas flow patterns
Tubes Coffins
Without Coffins
Area of Hot tubes

• Due to preferential flow of flue gas to the
extraction end
◦ Have more flow
◦ Therefore more heat available
◦ Therefore high temperatures
Distance
Temperature

• Common problem on uprated plants
• Lack of ID (Fluegas) fan capacity leads to high
box pressures
◦ -2 or -3 mm water gauge
◦ Normally -10 mm
◦ Safety issue - flames can pass out of box
• Lack of FD (Combustion Air) fan capacity can lead
to low excess air/oxygen levels
◦ Leads to afterburning
◦ In worst case high CO levels in duct

• Classic example is a South American Methanol
Plant
◦ Tightly designed plant - 2000 mtpd but operating at
2200 mtpd +
◦ Both fans limited
◦ One end of reformer was at positive (+) pressure
◦ Flames emitted from peepholes
• Outer lane cool - inner’s hot
• Afterburning in centre
• CO inlet duct
• CA ducting symmetrical
• Poor CA distribution

• Tube Failures - covered in Tube Design
◦ Can nip the tube
• Tunnel Port Effect
◦ Can be overcome by
 Installation of appropriate catalyst - high heat transfer/activity
 Design of the tunnel ports
• Weld position - on top fired reformers avoid the
hottest point of tube
• Movement of coffin walls

• All streams should be
symmetrical
• Including
◦ Feed, fuel, effluent and combustion
air headers/ducts
◦ Prevents mal distribution of process
flows
◦ Prevents variations in operating
conditions
 Tube and exit temperatures
Preferential Flow Path

Flow prefferentially
passing to this end of reformer
Flow starved
at this end
Distance Down Reformer
Temperature

• Must ensure good sealing
between the tube and the
refractory
• Otherwise air will be
sucked into the furnace
• Increased excess O2
levels
• Inefficient plant operation
• Normally pack with
refractory rope and
blankets

• Mainly affects Top Fired furnaces
• Two types
◦ #1 - direct impingement of flame on tube
 This is the worst since tube wall temperatures will be raised
the most
 Can lead to rapid tube failure
◦ #2 - impingement of hot flue gas on tube
 Normally observed as shimmering on tube surface
 Will lead to premature failure in ‘long term’
• Both raise tube wall temperatures

• Causes
◦ Fluegas Mal-
distribution
◦ Poor burner design
◦ Blockage of ports in
burners
◦ Mis-alignment of burner
• Can remove burners
on line
• Allows for repair
• Must be careful

• Cause by a localized lack of combustion air
• The fuel is not fully combusted
• Fuel moves on and when it meets oxygen is
combusts
◦ The flue gas/fuel mixture is above auto-ignition
temperature
• Usually observed on surface of the tubes
◦ Can damage tubes

• Causes
◦ Lack of Forced Draft (Combustion Air) fan capacity
◦ Poor combustion air header design
◦ Poor burner design
◦ Fuel gas composition deviations
◦ Poor balancing of furnace combustion air
• Can rectify but must identify cause

 If distance from inlet of
tube to the surface of the
catalyst is too short then
can get milling of the
catalyst
 Allow 200 mm for top
entry
 Allow 150 mm for side
entry
Top entry Side entry

 From a South American
Reformer
 Had thoroughly wetted catalyst
 On restart pressure drop very
high
 Catalyst badly damaged
 Water had rapidly vaporised
inside pellets
 Blew them apart

 On heating catalyst can be a variety of colors
Carbon
Normal
Overheated

1200oC
1100oC
1000oC
900oC
800oC
700oC

 If tubes receive differential
amounts of heat from
adjacent burner rows
 Each side expands differently
 Tubes will bow
 This increases stress on
outside of bow
 GBHE recommends change
tube if more than ID outside
of the centre line of the lane

• Damage to refractory
◦ Flame impingement
◦ Poor installation
• Gas tracking behind refractory
◦ Usually due to anchor failure
◦ Refractory moves away from wall
◦ Casing becomes hot - cooling by steam lances
etc

• Condensation due to
◦ passing valves
◦ dead legs
◦ too early steam or feed introduction
• Ammonia formation
◦ Problems on demin train
◦ Environmental
• Boxing up reformer
◦ Avoid as can slowly cook tubes

• Stress Corrosion
Cracking
◦ Due to condensation - can
eliminate by design
modification
 Tube tops - insulation
 Tube bottoms - use hot
bottom design
Failure Point

• Over tensioning of tubes -
premature failure
• Pigtail failure
◦ Operate in creep regime - will fail
• Header failure - Again in creep
regime
• Poor burner maintenance
◦ Must clean regularly
• Metal dusting of burner tips
◦ Methanol plants only
Failure

• Modifications to coffins/ports in coffin
◦ Can lead to flow mal-distribution
• Wind changes
◦ Changes temperature - up to 20°C seen
• Leaks in air pre-heaters
◦ Worst on rotary air pre-heaters
◦ Have seen leaks on static heaters as well
• Fouling of duct coils
◦ High DP and low heat transfer

• Gas composition analysis has a number of
problems
• Sample shifting
◦ Normally affects only CO and CO2
◦ In worst case can increase CH4
◦ Problem if using CH4 as a constraint in a model
• Hydrogen by difference
◦ Errors in other components will be included in H2
• Inerts (N2 and Ar) poor measurement
◦ Can affect fitting programs

• Typical temperature losses are
• Exit tubes 1-3°C
• Sub headers 3-10°C
• Main headers 5-15°C
• Inlet secondary
• Top Fired Reformers 10-20°C
• Foster Wheeler Reformers 15-35°C
• Side Fired Reformers 15-35°C
• Inlet WHB,
• Top Fired Reformers 10-20°C
• Foster Wheeler Reformers 15-35°C
• Side Fired Reformers 15-35°C

 Main cause of catastrophic tube failure
• This one was at North American Methanol Plant
• Plant trip (loss of feedstock to steam reformer)
due to valve failure
• Feedstock to steam reformer not isolated
adequately by valve
• Set point on reformed gas pressure not reduced
• Steam introduced for plant restart at reduced rate
• All burners lit (deviation from procedure)
• Tubes at 16 bara

Steam reformer tubes "looked normal"
Nearly 3x as much fuel going to burners than there should have
been
High calorific value fuel added an extra 15% heat release
First tubes rupture
High furnace pressure (trip bypassed)
Oxygen in flue gas dropped to zero
Flames seen from peep holes
Normal furnace pressure
Visual inspection revealed "white hot furnace and tubes
peeling open"
30minutes

Reformer exit gas temperature on panel never
exceeded 700°C (1290°F)
Cannot use this instrumentation as a guide to tube
temperature
Reformer start-up at normal operating pressure
Tube failure temperature 250°C (450°F) lower than
normal for start-up
All burners lit
Far too much heat input resulted in excessive
temperatures

Steam Reforming - Common Problems

Steam Reforming - Common Problems

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