Steam Reforming - Practical Operations

Steam Reforming
Practical Operation
C2PT Catalyst Process Technology
By Gerard B Hawkins
Managing Director, CEO

Contents
Reaction Chemistry
Typical Reformer Configurations
Catalyst Design Criteria
Carbon Formation and Prevention
Catalyst Deactivation
Steaming Reforming Catalysts
Monitoring Reforming Catalysts
Catalyst Loading
Reduction & Start-Up
Tube Wall Temperature Measurement

Steam Reforming Reactions
The conversion of hydrocarbons to a mixture of CO,
CO and H2
Two reactions: Reforming and Shift
Water gas shift (slightly exothermic)
CO + H2O CO2 + H2
Steam Reforming (very endothermic)
CH4 + H2O CO + 3H2
CnH(2n+2) + nH2O nCO + (2n+1)H2
Overall the reaction is highly endothermic

Equilibrium Considerations
 Both reforming and shift reactions are reversible
 Rate of shift is fast compared to reforming
 Methane conversion favoured by:
low pressure
high temperature
high steam to carbon ratio
 CO conversion to CO2 favoured by:
low temperature
high steam to carbon ratio
 GBHE kinetics developed using full size reformer
tube with whole pellets under industrial conditions

Primary Reformer
 The Primary Reformer is a heat exchanger
 Its function is to heat up process gas
 Catalyst and reaction in the tubes
 Combustion on the shell side
 Dominant heat transfer by radiation
 Multiple fuel supply points

Reformer Furnace
 3 major types of reformer
 Each tackles the duty in different ways
 No clear best choice
 Choice dictated by Contractor history
 Terrace wall - Foster Wheeler
 Side Fired - Topsoe, Selas, Chiyoda
 Top Fired - H & G, Davy, Toyo, Howe Baker, Kellogg,
KTI etc

 Many reformers now heat transfer limited
 Catalyst not limiting reformer size or operation
 Especially the case for hydrogen & methanol
plants
 Important for design and uprating
 Fluegas exit flow and temperature often limits
 Heat exchange must not be ignored
 Claims of +30% capacity treated with caution
Reformer Furnace

Heat Transfer - Top Fired
 Nearly all heat transfer is by radiation
 Radiation from the fluegas to the tubes
 Little direct radiation from refractory to tube
 Refractory acts as a reflector
 Radiation from flame to tube at tube top

Heat Transfer - Top Fired
Radiative
heat flows

Heat Transfer - Side Fired / Terraced
 Same for side fired and terrace walled
 Nearly all heat transfer is by radiation
 Radiation from the fluegas to the tubes
 Major direct radiation from refractory to tube
 Significant heat transferred from flame to wall
 Carried out by convection
 Radiation from flame to tube all down

Typical Reforming Configuration
Steam
Steam
Steam + Gas
Steam
Reformer
500°C
870°C
1200°C
3% CH4

Reformer Firing Balancing
 Must have an even heat input to the furnace
 Same reasons as for an even process gas flow
 Exit temperature variations give high average
approach
 Need to keep exit temps the same
 Trim air and fuel flows to individual burners
 Monitor tube wall temps and exit temps
 Must be done as air ducting, tunnels etc may have
a systematic effect upon heat input

Reformer Firing Balancing
 Usual problems for uneven heat input:-
 Burner problems
 Burner fouling with liquid fuels or offgas
 Air leaks around burners or tube tops
 Tunnel problems (mods or collapses)
 Air ducting problems (internal refractory)

Typical Primary Reformer Catalyst
Loading
LoadedLength-12.98m
HalfLoadDip-7.38m
Tubes 352
Tubes id : 95 mm
Loaded Length : 12.98 m
Catalyst Types : 50% VSG-Z101
50% VSG-Z102
Loaded density : VSG-Z101 0.857 kg/l
VSG-Z102 0.828 kg/l
Total volume loaded 32.38m3
Full Tube Dip
0.89m
Catalyst
Support Grid
VSG-Z102
6.49m
VSG-Z101
6.49m
Ammonia Plant

Primary Reformer
 Reforming involves heating the process gas
 The position of equilibrium is constantly changing
 The catalyst tries to react the gas to equilibrium
 The catalyst is essentially chasing the heat input
 Top of tube: slow reaction rate, high heat flux
 Bottom of tube: high reaction rate, low heat flux
 High approach to equilibrium at top of tube, low
approach at bottom of tube
 Can never achieve a zero approach to equilibrium

0
100
200
300
400
500
600
700
800
900
0 0.2 0.4 0.6 0.8 1
Fraction down tube
Temperature(°C)
Gas T
Eqm. T
ATE
Approach to Equilibrium

Primary Reformer Catalyst
Requirements
 High and Stable Activity
 Low Pressure Drop
 Good Heat Transfer
 High resistance to Carbon Formation
 High Strength
 Robust Formulation / Simple Operation

High and Stable Activity
 Low methane slip
 Lower tube wall temperature
 Reduced Fuel usage

Low Pressure Drop
 Savings in Compression Power / Fuel
 Possible Throughput increase

Improved Heat Transfer
 Reduced tube wall temperatures
 Increase firing /higher throughput
 Smaller catalyst particles improve heat transfer
from wall to bulk gas
 Smaller particles increase pressure drop
 Catalyst shape should be optimised for high heat
transfer with low PD

Steam Reforming Catalysts
 Nickel on a ceramic support
 Three key factors in catalyst design:
i) geometric surface area
ii) heat transfer from tube to gas
iii) pressure drop
 Also of concern:
i) packing in the tube
ii) breakage characteristics

Diffusion Limitation
 The reforming reaction is very fast on the Ni sites
 Reaction limited to catalyst surface (<0.1mm)
 Reaction rate controlled by film diffusion
 High geometric surface area gives high activity

Diffusion into and out of Catalyst
Bulk
Gas
Gas
Fil
m
Ni
Sites
CO
H O2
H2
CH4
Catalyst Support

Key Reaction Steps
1. Fast
Diffusion of the molecules in the bulk gas
phase
2. Slow
Diffusion of the molecules through the gas
film
3. Slow
Diffusion through catalyst pores
4. Fast
Absorption of the molecules onto the Ni
sites
5. Fast
Chemical reaction to produce CO2 and H2

Reaction Rate
Reaction rate controlled by film diffusion
- Most of the reaction takes place on
the catalyst surface (<0.1mm)
- Pore diffusion not limiting as film diffusion
controls the overall rate
Catalysts with higher geometric surface area
(GSA) per unit volume of catalyst will have a
higher activity.
Pore size/distribution is not significant for most
commercial grades of reforming catalyst

Un-sintered Catalyst
0.001 mm (1/25 thou)

Sintered Catalyst
0.001 mm (1/25 thou)

Outside Tube Wall T 830°C
Fluegas T 1200°C
Inside Tube Wall T 775°C
Gas film
Tube
Wall
Heat Transfer
Bulk Process
Gas T 715°C

Catalyst Heat Transfer
 Reforming involves large heat flows into tubes
 Absolute requirement to keep tubes cool
 Major limitation is at the tube wall
 Need to minimize thickness of stationary gas film
at tube wall
 The catalyst acts as a heat transfer enhancer to
improve heat transfer from tube wall to gas
 Promotes turbulence at the wall
 Promotes gas mixing from walls to tube centre
 Smaller catalyst particles improve heat transfer
from wall to bulk gas and hence reduce tube wall
temperatures

Catalyst Heat Transfer
 Heat transfer to catalyst normally very good (high
GSA)
 Minor limitation is radially in the catalyst
 Catalyst also improves radial heat transfer
 Smaller pellets improve wall transfer
 Larger pellets improve radial transfer
 Smaller usually better overall
 BUT smaller particles increase pressure drop
 Catalyst shape needs to be optimized for high heat

Catalyst Shape
 The traditional catalyst shape is a ring
 Smaller rings give higher activity and heat transfer
but higher pressure drop
 Shape optimised catalysts offer high GSA and heat
 Important that shape also provides good packing
and breakage characteristics

Tube Wall Temperature Profile
Top Fired Reformer
660
680
700
720
740
760
780
800
820
840
860
0 0.2 0.4 0.6 0.8 1
Fraction Down Tube
TubeWallTemperature(°C)
Base case with twice GSA
Base case with twice heat transfer
Base case

Heat Transfer and Pressure Drop
1 2 3 4
1 2 3 4
Voidage 0.49 0.6 0.58 0.59
Relative PD 1 0.9 0.9 0.8
Relative HTC 1 1.3 1.1 1

Catalyst Design Criteria
Conclusions
Design of catalyst shape is a complex optimization of:
- Higher GSA (Needed for activity - diffusion control)
- Higher HTC (Needed for cooler reformer tubes)
- Lower Pressure drop (Plant Efficiency / Capacity)
Need also to consider breakage characteristics
and loading pattern inside the reformer tube

VULCAN
VSG-Z101
VULCAN
VSG-Z102

Catalyst Breakage
 Catalyst breaks up in service
 Main mechanism due to startup / shutdown
 The tube when cooling exerts massive forces
(several tonnes)
 Forces exerted by carbon formation immeasurable
 Pressure drop rises about 10% per year
 Minimum Catalyst strength for handling & charging
approx. 10 kgf
 The key is to ensure the catalyst does not fragment
into small bits/dust.
 Careful charging essential

Breakage Characteristics
Contraction of tube
- some readjustment
- some breakage
Cold ColdHot
Initial
catalyst level
Expansion of tube
- some settling
All catalysts show breakage with time
No support can withstand tube forces

Pressure Drop due to Catalyst Breakage
Relativepd(%)
% Breakage
100
200
0 5 10 15 20
pd limit
Shape with good breakage
characteristics
Shape with poor breakage
characteristics Conventional rings
Breakage Characteristics is an
Important Consideration

Packing Characteristics
Uniform loading of catalyst
- Uniform tube pressure drops
- Uniform tube temperatures (no hot spots)
Long cylinders with hole(s) through
the centre give good uniform
packing
Short cylinders (tablets) with hole(s)
through the centre can stack resulting
in poor gas distribution down the
reformer tube

Packing Characteristics
Extended External Surface Area - "Cogs"
Void

Catalyst Support
Three types commercially available
– Alpha Alumina
– Calcium Aluminate
– Magnesium Aluminate Spinel

Catalyst Support - Bulk Chemistry
Alpha
Alumina
Calcium
Aluminate
Magnesium
Aluminate
Spinel
Structure Corundum Spinel-like Spinel
Stability to
Sintering
Extremely
Stable
Relatively
Stable
Relatively
Stable
Chemical
Stability
(Hydrolysis)
Inert Stable ‘Free’ MgO
Hydration
under
Steaming
Conditions

Catalyst Support - Surface Chemistry
Alpha
Alumina
Calcium
Aluminate
Magnesium
Aluminate
Spinel
Surface Area Low Higher Higher
Basicity Inert Basic Sites Most Basic
Support
Surface
Interaction
with Ni / NiO
No Chemical
Interaction
Moderately
Reactive
Surface
Some
bonding of
Ni 2+
ions
Most
Reactive
Surface
Strongest
bonding of
Ni 2+
ions

Catalyst Support - Solid Solutions
Magnesium Aluminate Spinel
NiO / MgO
Solid solution
NiAl2O4
formed
NiO / Ni
Fresh catalyst
High surface area
Heat
In use - Low surface area
Difficult to reduce NiO
Important to consider in-service activity
and ease of catalyst reduction

Catalyst Support - Reduction
Temperatures
AlphaAlumina
CalciumAluminate
Temperature (°F)
Temperature (°C)
800 1000 1200 1400 1600
400 500 600 700 900
Magnesium aluminate
spinel material usually
supplied pre-reduced
MagnesiumAluminateSpinel

Tube Wall Temperature Stability
0 200 400
820
840
860
880
900
920
940
DAYS ON LINE
ICI RINGS
COMP A
SHAPE
COMP B
SHAPE
COMP B
SHAPE 2
ICI SHAPE
POWEROUTAGE
CATALYSTCHANGE
AT584DAYS
REDUCED
CATALYSTCHANGE
AT280DAYS
PDLIMITRATE
REDUCED
CATALYSTCHANGE
AT421DAYS
0 0 0 0200 400200 200 200
TWT
LIMIT
RATE25%
CATALYSTCHANGE
AT258DAYS
600 700 800 900
MAXIMUMTUBEWALLTEMPERATURE(°C)

Carbon Formation and Prevention
 Carbon formation is totally unwanted
 Causes catalyst breakage and deactivation
 Leads to overheating of the tubes
 In extreme cases carbon formation causes a
pressure drop increase

 Cracking
CH4 ⇔ C + 2H2
C2H6 ⇔ 2C + 3H2 etc
 Boudouard
2CO ⇔ C + CO2
 CO Reduction
CO + H2 ⇔ C + H2O
If carbon formation rate is faster than removal
rate then carbon will be deposited

Carbon Formation - Heavy Feeds
Hydrocarbon
Feed
Intermediates
(Olefins, Paraffins,
CH4, & H2)
Carbon
CH4, H2, CO2
& CO
Catalyzed
Partial
Decomposition
Thermal
Cracking
Polymerization
Steam
Reforming
Carbon
Gasification
H2O
H2O

Effect of Carbon Formation
1. Physical poisoning
-Carbon covers the catalyst surface
2. Pressure drop increase
- Usually only in severe situations
- Carbon fills catalyst bed voids
-Carbon formed in catalyst pores will weaken
or break catalyst
3. Hot tubes
- Carbon laydown on the inside of the tube
wall
- Lower catalyst activity

Giraffe
Necking
Hot TubeHot Band
Reformer tube appearance - Carbon laydown

 Under normal conditions carbon gasification by
steam and CO2 is favored
i.e. gasification rate > C formation rate)
 Problems of carbon formation may occur when:
i) steam to carbon ratio is too low
ii) catalyst is not active enough
iii) higher hydrocarbons are present
iv) tube walls are too hot (high flux)
v) catalyst has poor heat transfer characteristics

 Methods of preventing carbon formation:
– Use more active catalyst
– Use better heat transfer catalyst
– Reduce levels of higher hydrocarbons
– Increase the steam ratio
– Use a potash doped catalyst (VULCAN-
series) which reduces probability of carbon
formation

 Alkali greatly accelerates carbon removal
 Addition of potash to the catalyst support reduces
carbon formation in two ways:
a) increases the basicity of the support
b) promotes carbon gasification (aids
adsorption of water)
C + H2O ⇔ CO + H2
 Potash is mobile on the catalyst surface
 Level of potash required depends on feed and heat
flux
 Potash doped catalyst is only needed in the top half
of the reformer tube
OH
-

 Increasing the content of alkali (potash) allows:
Higher heat flux for light feeds
Heavier hydrocarbons in feed
Lower steam to carbon ratios
Faster carbon removal during steaming

Increasing potash
addition
Methane feed/Low heat flux
Methane feed/High heat flux
Propane, Butane feeds (S/C >4)
Propane, Butane feed (S/C >2.5)
Light naphtha feed (FBP < 120 °C)
Heavy naphtha feed (FBP < 180 °C)
K2O wt%
0
2-3
4-5
6-7

Methane Cracking
100
10
1.0
0.1
Temperature (°C )
(pH2) 2
pCH4
Carbon Formation
Zone
No Carbon
Formation
CH4 2H2 + C
550 600 650 700 750 800

Methane Cracking - Kinetic Limitation
Carbon Formation
Zone
No Carbon
Formation
Deposition rate
< removal rate
Promoted by alkali
Deposition rate
> removal rate
Promoted by acid
550 600 650 700 750 800
Temperature (°C )
100
10
1.0
0.1
(pH2) 2
pCH4

Methane Cracking - Kinetic Limitation
0.6
0.5
0.4
0.3
Fraction of
tube length
from top
550 600 750 800
Temperature C
100
10
1.0
0.1
Carbon Formation
Zone
No Carbon
Formation
Deposition rate
< removal rate
Deposition rate
> removal rate
650 700650 700
O
(pH2) 2
pCH4

Methane Cracking - Basic Catalyst
Support
0.6
0.5
0.4
0.3
0.25
More basic
support
550 600 800
Temperature C
100
1.0
0.1
No Carbon
Formation
650 700 750
10
Carbon Formation
Zone
O
(pH2) 2
pCH4

Methane Cracking - Increased Potash
Content
Carbon
Formation Zone
Increasing
Potash
Content
550 600 800
Temperature C
100
1.0
0.1
No Carbon
Formation
650 700 750
10
0.6
0.5
0.4
0.3
0.25
O
(pH2) 2
pCH4

Fraction Down TubeTop Bottom
Non-Alkalised
Catalyst
Ring Catalyst
Optimised Shape
(4-hole Catalyst)
Inside Tube Wall
Temperature
920°C
820°C
720°C
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Alkalised
Catalyst
Carbon Forming
Region

For light feeds and LPG etc. using lightly
alkalized catalyst (VSG-Z102)
- Potash is chemically locked into catalyst
support
- Potash required only in the top 40-50% of
the reformer tube
- Catalyst life influenced by
Poisoning
Ni sintering
Process upsets etc.
VSG-Z101
VSG-Z102

For heavy feeds, potash needs to be mobile
Utilize VSG-Z101 series catalyst
Removes carbon on the catalyst surface and
inside of the tube wall
Potash slowly released by a complex reaction
VSG-Z101
VSG-Z102

Potash release mechanism (VSG-Z102 series)
K2O-Al2O3-SiO2
CaO-Al2O3
MgO-Al2O3
CO2 + H2
CaO-Al2O3-SiO2
CaO-MgO-SiO2
K2CO3
H2O
2KOH + CO2
Note:- MgO is chemically
locked into catalyst support
material
Catalyst Support Material

VSG-Z102 Series catalysts
 Catalyst life determined by residual potash
remaining in the catalyst
 Minimum amount typically 2-3 %wt at bottom of
potash promoted catalyst bed - but minimum
level depends on feedstock type and
operational severity

 Carbon formation by polymerization
– Suppressed by having NiO / MgO solid
solutions as the active catalyst component
– Need to increase total NiO content to
overcome loss of steam reforming activity
– Zirconia addition also further enhances
catalyst activity

Potash promotion
 Lowers hydrocarbon carbon cracking rate
 Increases carbon removal rate
 VSG-Z102 series can remove carbon from tube
wall ("mobile" potash)
 VSG-Z102 series contain some NiO/MgO solid
solutions to lower polymerisation activity
 Greatly facilitates carbon removal during
steaming operation (after severe carbon
formation)
Summary

Natural Gas
Reforming
Catalysts
Associated Gas
Reforming
Catalysts
Dual Feedstock
Reforming
Catalysts
Naphtha
Reforming
Catalysts
Un-alkalised Lightly Alkalised Moderately
Alkalised
Heavily
Alkalised
VSG-Z101 VSG-Z102 VSG-Z102 VSG-Z102
Naphtha 3.0 – 3.5
Light Naphtha 6.0 – 8.0 3.0 – 4.0 2.5 – 3.0
Butane 4.0 – 5.0 2.5 – 3.5 2.0 – 3.0
Propane / LPG 3.0 –4.0 2.5 – 3.0 2.0 – 2.5
Refinery Gas 6.0 – 10.0 3.0 – 4.0 2.0 – 3.0 2.0 – 2.5
Associated Gas 5.0 – 7.0 2.0 – 3.0 2.0 – 2.5
Natural Gas 2.5 – 4.0 1.5 – 2.0 1.0 – 2.0
Pre-reformed
Gas
2.0 – 3.0 1.0 – 2.0 1.0 – 2.0

Catalyst Activity Die Off
2 major factors:
 Poisoning by sulfur
Affects upper tube and tube temperatures
 Thermal sintering
Affects lower tube and approach
Some effect on upper tubes and tube
temperatures

Poisons
 Many poisons affect reforming catalysts
 Halides, phosphates, sulfur
 Heavy metals, alkali metals etc
 Major poisons are:
Sulfur ex feedstock
Phosphate ex BFW
Metals ex BFW or liquid feed

Sulfur Poisoning
 Nickel is a very good sulfur adsorbent
 Sulfur sticks to the nickel surface
 Do not need a lot of sulfur to give problems
 Can totally deactivate a reforming catalyst

Sulfur Poisoning
Pellet
S
SS
S
S
S
S
S
S S
Nickel
CH4
H2O

Sulfur Poisoning
 Depends upon the catalyst temperature
 Occurs in the cooler regions
 Upper section of tubes vulnerable
 Also depends upon sulfur exit the HDS

Effect of sulfur coverage on activity
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Coverage
Activity

Sulfur Poisoning
 Sulfur poisoning is reversible
 Steam the catalyst for 24 hours
 Steam slowly strips off the sulfur
 Re-oxidizes the catalyst in addition
 May lose some activity permanently

Steaming Reforming Catalysts
 Steaming of the catalyst is required when there is:
 Severe carbon formation
Loss of steam
Incorrect steam to carbon ratio operation
sulfur poisoning
 sulfur poisoning
Poor performance of the desulfurization
system

 Isolate hydrocarbon feed
 Maintain steam flow at highest possible level
 Adjust reformer firing to achieve 750°C reformer
exit temperature or higher if possible
 Monitor carbon oxides or H2S in the exit gases
 Addition of a small amount of nitrogen into the
steam facilitates reliable sample analysis

Potash promoted catalyst
 Accelerates carbon gasification during
steaming
 Required since carbon laydown often occurs in
the top section of the reformer tubes where high
temperatures needed for steaming are not
easily achieve
 Design of catalyst needs to ensure potash
release is controlled during steaming
 Release rate for VSG-Z102 series is
approximately double the normal rate during
steaming (24 hours of steaming ages the
catalyst by 48 hours)

Effect of Steaming - Alkalized Catalyst
Steaming Temperature °C (equivalent to 1 year operation)
Potash Retention - Steaming Test
500 550 600 650 700 750
0
0.5
1
1.5
2
2.5
3
Residualwt%ofpotash
VSG-Z102
Comp. A
Comp. B

Carbon Removal By Steaming
50
0
100
150
200
1.2
0
0.2
0.4
0.6
0.8
1
1.4
1.6
Time (hours)
0 5 10 15 20
ResidualCarbon(%)

5 10 15 20 25 30 35
2.5
0
3
3.5
4
4.5
Time on line (months)
HDS
Problem
Catalyst
Steamed
Methaneslip(mol%dry)
Design

Sulfur removal
 Catalyst performance can be restored
 High reformer inlet temperature during
steaming is important for successful sulfur
removal
 Need to monitor the H2S slip during steaming

Sulfur Levels in Discharged Catalyst
0
100
200
300
0 10 20
Distance Down Reformer Tube (m)
sulfur(ppmwt)
Before Steaming
After Steaming

Steaming Reformer Catalyst
 MgO in catalyst support must not be "free"
otherwise during steaming, the MgO will
hydrolyse
MgO + H2O Mg(OH)2
 Hydration of the MgO causes rapid loss of
catalyst strength and severe catalyst break-up
and high reformer pressure drop
 VSG-Z102 series catalyst contain MgO that is
chemically locked into the the catalyst support -
No hydration

Reformer Catalyst Monitoring
Monitor frequently (daily)
 Exit Methane
 Tube Wall Temperature (TWT)
 Tube Appearance
Monitor Less Frequently
 Pressure Drop
 Approach to Methane Steam Equilibrium

 Methane Slip
– Dependant on throughput, heat load & catalyst
activity
– If these conditions vary then exit CH4 will vary
 Approach to Equilibrium
– ATE defined as Difference between Actual
Temperature & Equilibrium Temperature
– Better guide to catalyst activity
– ATE increases as catalyst activity decreases

 Tube Wall Temperature
– Dependant on catalyst loading, catalyst
activity & physical catalyst condition
– As maximum TWT is approached, rate must be
reduced. In worst case catalyst will need to be
changed
 Appearance
– A good indication of how reformer is operating
– Tubes should look cool. Poor catalyst
performance will mean tubes looking hot.
.

Pressure Drop
–PD will increase with time due to physical
blockage/breakage of catalyst
–Too high PD will result in throughput
limitation
–Should back-calculate PD at design
conditions (independent of throughput)
Since PD α (velocity) 2
Normalised PD = Measured PD 100
% design( (2

Approach to Equilibrium (ATE)
 The approach to equilibrium (ATE) at any point
along the catalyst bed is the difference between
the actual gas temperature and the equilibrium
temperature corresponding to the gas
composition.
 The ATE can be used as a good measure of the
performance of the catalyst when the operating
temperature of the reactor is held constant, and
when the reaction is equilibrium limited, such as
with primary reforming.

Calculation of ATE
Steam Reforming Reactions
CH4 + H2O ⇔ CO + 3H2 Methane Steam (MS)
CO + H2O ⇔ CO2 + H2 Water Gas Shift (WGS)
Since the WGS reaction is so fast it can be
assumed to be at equilibrium under reformer exit
conditions
This means then the equilibrium temperature for
this reaction (TWGS) can be used as a reliable
estimate of the actual reformer exit temperature
(Measurements are unreliable)

For the WGS reaction the equilibrium constant
(KWGS) can be calculated
Then equilibrium tables can be used to determine
the equilibrium temperature for this reaction (TWGS)
For the MS reaction the equilibrium constant (KMS)
can also be calculated and equilibrium tables then
used to determine the equilibrium temperature for
this reaction (TMS)

The ATE can then be calculated as the difference
between TWGS (equal to the actual reformer exit
temperature) and TMS
GBHE uses a computer program to calculate ATE

Example Calculation of ATE
Reformer Exit Composition
% v/v
H2 68.0
N2 1.6
CH4 9.6
CO 10.2
CO2 10.6
Total 100.0 Dry
H2O 76.6
Total 176.6 Wet
Reformer Exit
Pressure = 31.6 ata
Reformer Exit
Temperature
(TWGS) = 796°C

pCH4 = 9.6 x 31.6 = 1.7178 ata
176.6
pH2 = 68.0 x 31.6 = 12.1676 ata
176.6
pH2O = 76.6 x 31.6 = 13.7065 ata
176.6
pCO = 10.2 x 31.6 = 1.8251 ata
176.6

Example Calculation of ATE
KMS = pCH4 . pH2O
pCO . (pH2)3
= 1.7178 x 13.7065
1.8251 x (12.1676) 3
= 7.161 x 10-3
From Tables TMS = 792°C
ATE = 796 - 792 = 4°C

Catalyst Handling
 Catalysts are expensive & should be treated with
care at all stages of:
– Handling on arrival
– Storage
– Charging
– Storage in vessel before start-up
 Careful & detailed supervision at all stages is
essential
 Safety: proper equipment is essential both for the
safety of workers & to prevent damage to catalyst

Handling & Storage
 On Arrival
– Use suitable fork lift truck or crane to transfer to
storage
– Don't drop drums off tail board of lorry
– Don't roll drums
– Inspect drums for damage & repair broken lids
 Storage
– Store under cover (long term storage)
– Avoid damp / wet conditions
– Store drums in upright position
– Stack no higher than 4 drums
– Catalyst not affected by extremes of
temperature
– (-50°C to +50°C) provided kept dry.

Catalyst Loading
 If loading is poor, variety of flows in tubes
 Each tube has different exit temperature
 Each tube has a close approach
 Methane slip not linear with temperature
 Mixture of all tubes far from equilibrium
 Made worse by the flow imbalance

Base Case
Reformer Exit: 20 ata 870°C design
10 °C approach to equilibrium
Maldistribution
10 °C approach to equilibrium
Tube 1: 105% flow 850°C Exit T
Tube 2: 95% flow 890°C Exit T

Base Case Maldistribution Case
Tube 1 Tube 2
Exit Temperature (°C) 870 850 890
Relative Flow (%) 100 105 95
Approach to Equilibrium (°C) 10 10 10
Methane Slip (% dry) 3.583 4.698 2.687
Average Methane Slip (% dry) 3.583 3.743
Average Approach to Equilibrium (°C) 10 13.1

Catalyst Charging - Tubes
 Inspect empty tubes
 Check pressure drop on tubes both empty and
full
 'Sock' or 'Unidense' method recommended
 Avoid excessive hammering and vibration
 Final PDs should be within 5% of mean
 Better to discharge tubes with high PDs rather
than over-vibrate tubes with low PDs
 Weighing is a useful check on charged bulk
density, but not essential

 Catalyst supplied in pre-weighed socks

 Sock slightly narrower than tube bore
 End of sock folded over

 Lowered down tube on rope
 ‘Tugged’ to release fold
 Free fall <0.5m allowable

 Vibrated with hammer after each sock

 PD measured empty / ½ full / full
 Adjusted to ± 3 - 5%

 Norsk Hydro technology
- available through Hydro Agri Europe
 Simple & fast loading technique
 No pre-socking and no tube vibration required
 Applicable to a range of catalyst types & reformer
designs
 Offers high uniform catalyst density
Catalyst Charging - Unidense Method

Charging Technique
 Weighed amount of catalyst is poured into the
tube & the loading rope is gradually pulled out of
the tube as the catalyst layer builds up.
 The brushes with flexible springs reduce the
speed of the catalyst particles so that breakage
is avoided.
 This results in a loading without bridges & voids,
hence there is no need for tube vibration /
hammering.
Catalyst Charging Unidense Method

Support grid
Charging
chute
Loading rope with
flexible springs

Benefits
 Reduced loading time
 Reduced possibility of bridging / less hot spots
 Contributes to lower tube wall temperatures and
prolonged tube life
 Narrow pressure drop variation in tubes
 Slightly higher PD than sock method
 Minimal further settling / PD increase

Precommisioning / Periods of Shutdown
 Completely close reactor after charging
 Box up under N2 if necessary
 After commissioning leave temperature points
connected and check regularly during shutdown
periods
 Check drains regularly
 After shutdown keep under positive N2 pressure
(natural gas OK for sulfur removal catalysts)
 On decommissioning Nickel containing catalysts
must be purged free from carbon oxides before
temperature falls below 250°C

Normally
 Process feed on flow control
 Process steam on ratio control from feed
rate
 Purge fuel / flash gas to fuel header
 Fuel header on pressure control
 Fuel to reformer on flow control
◦ Adjusted to maintain reformer exit temperature

 Introduction
 Start-up Procedures
 Warm-up
 Catalyst Reduction
 Feed Introduction
 Shut-down
 Case Studies
Contents

 Steam reformer is complex
 heat exchanger
 chemical reaction over catalyst
 combustion, leading to steam generation
 Common symptoms of poor performance
 high exit methane slip
 high approach to equilibrium
 high tube wall temperature
 high pressure drop
Need properly active catalyst
Introduction

As supplied - NiO on support
Active species - Ni Crystallites
Reduction process needed:-
NiO + H2 ⇔ Ni + H2O
Introduction - Catalyst Reduction

400 500 600 700 800
100
200
300
500
700
Temperature °C (°F)
Partial Pressure of H2O / Partial Pressure H2
EquilibriumConstant
Reducing Conditions
Oxidising Conditions
(752) (932) (1112) (1292) (1472)

 Faster at high temperature
 Slower in presence of steam
 Thermodynamically, very little hydrogen needed
 Support also affects ease of reduction

Extreme danger of local overheating!
 Requires high temperature
- fire steam reformer
 Requires reducing conditions
- supply H2 or reducing gas
- re-circulation or once-through
 Since little or no steam reforming is taking place,
less heat is required to warm up gas
 50% steam rate, with 5:1 steam:H2 ratio requires
1/7 fuel of normal operation

 Introduction
 Start-up Procedure
 Warm-up
 Shut-down
 Case studies
Start-Up Procedure

Air warm-up possible, but not for previously
reduced catalyst (possible carbon)
 Purge plant of air with N2
(Care: must be free of hydrocarbons and carbon
oxides)
 Heat reformer above condensation temperature
 Add steam when exit header temperature 50°C
above condensation temperature
(low pressure favours good distribution and
lowers this temperature)
 Increase steam rate to 40 - 50 % of design rate
(min 30%)
 Stop N2 circulation
Start-Up Procedure - Warm Up

 Rapid warm-up minimises energy usage / time
 Limited by mechanical considerations of steam
reformer
 Assess effect on plant equipment
 thermal expansion of inlet/exit pipes
 reformer tube tensioners
 reformer tubes
 refractory linings
Traditionally: 50°C per hour
Modern material: 100°C per hour
Catalyst: 150 - 170°C per hour

 If upstream pipe-work cold, good practice to warm
up by steam flow to vent to prevent carry-over of
water.
Steam Steam
Reformer
Cold Pipe-work

 Temperatures referred to are true catalyst
temperatures at exit of tube
 Measured temperatures during normal operation are
10 -100°C cooler due to heat losses
 Most catastrophic failures of tubes in top-fired
furnaces occur during start-up
 Cannot rely on plant instrumentation during start-up
lower flows than normal
higher heat losses than normal
fewer burners can give severe local effects
Frequent visual inspection of reformer tubes and
refractory essential during start-up

Effect of Pressure and Temperature
1
10
100
1,000
10,000
100,000
1,000,000
10,000,000
Tube Wall Temperature °C (°F)
TubeLife(hours)
800 900 1000 1100 1200
(1500) (1650) (1830) (2010) (2200)
5 bar30 bar
Start-Up Procedure - Tube Life

 Introduction
 Warm-up
 Shut-down
 Case studies
Start-Up Procedure - Catalyst Reduction

 Reduction with Hydrogen
 Reduction with Natural Gas
 Reduction with other sources of hydrogen
 Higher hydrocarbons
 Ammonia
 Methanol
Start-Up Procedure - Catalyst Reduction

 H2 or H2-rich gas can be added at any time to the
steam when plant is free of O2
 Steam : hydrogen ratio normally 6:1 - 8:1
 Get tube inlet temperature as high as possible
 Increase exit temperature to design value
>700°C
 Hold for 2-3 hours
Catalyst Reduction with Hydrogen

Hydrogen must be free of poisons (S, CI)
Special consideration must be given to the
 presence in impure hydrogen sources of:
carbon oxides
hydrocarbons
Also applies to nitrogen (or inert) source used for
purge/warm-up

 Recirculation loop may include HDS unit (at
temperature)
 Carbon oxides above 250°C (480°F) methanate over
unsulphided CoMo catalyst:
temperature rise 74°C per 1% CO converted
temperature rise 60°C per 1% CO2 converted
If H2 contains > 3 % CO or > 13 % CO2 or a mixture
corresponding to this then by-pass the HDS system

Natural Gas
 Will be converted to carbon oxides + hydrogen in
reformer
 May crack thermally to give carbon
Catalyst Reduction with Natural Gas

 Warm-up as before (N2 then steam)
 Introduce natural gas at 5% of design rate
 Slowly increase gas rate to give 7:1 steam:carbon
over 2-3 hours
 Simultaneously increase reformer exit temperature
to design level i.e. >700°C
 Increase inlet temperature as much as possible (to
crack natural gas to give H2)
 Monitor exit methane hourly
 Reduction complete when methane reaches low,
steady value (4 to 8 hours)
Catalyst Reduction with Natural Gas

E.g. propane
 Increased possibility of carbon formation
 Much greater care needed
 Longer time periods needed
 More precision in all measurements needed
 Hydrogen addition recommended if possible
 Purification issues
- Desulfurization
- Methanation of carbon oxides
Catalyst Reduction with Higher
Hydrocarbons
Not normally recommended

 Crack ammonia in ammonia cracker
 Crack ammonia in steam reformer
 inject liquid ammonia upstream of steam
reformer
 bypass HDS
 Procedure as for hydrogen reduction
 Exit temperature 800°C (1470°F) to maximise
ammonia cracking
Catalyst Reduction with Ammonia

 Uncommon Procedure
 Methanol decomposes to give H2 and CO
 Regulate flow of liquid methanol to give
6:1 - 8:1 steam:hydrogen ratio exit steam reformer
 Do not recycle exit gas (potential methanation of
carbon oxides)
Catalyst Reduction with Methanol

 Introduction
 Warm-up
 Shut-down
 Case studies
Start-Up Procedure - Feed Introduction

 Introduce feedstock at high steam:carbon ratio (5:1
for natural gas; 10:1 for higher hydrocarbons)
 Steam reforming will give small increase in inlet
pressure, cooling of tubes, and lower exit
temperature
 Need to increase firing to maintain exit temperature
 Then increase feedstock flow
 Increase pressure to operating pressure
 Adjust steam:carbon ratio to design

 Increase flow of natural gas to design
steam:carbon ratio (2 hours)
 Maintain exit temperature
 Check that exit methane stays low
(reducing steam:carbon ratio will increase
methane slip and heat load)
if not, hold at 7:1 steam : carbon for 2 hours
 Increase throughput to design level
 Increase pressure to design level
Always increase steam rate before feed rate

 Shorter re-reduction recommended
 Typically 4-6 hours for heavy feeds
 Not essential to carry-out reduction with natural
gas or light off-gas feedstock
 Start up at 50% design rate, high steam:carbon
ratio
Start-Up Procedure - Restart

 Introduction
 Warm-up
 Shut-down
 Case Studies
Case Studies

 Reduce tube exit temperature to 750°C
 Decrease feed and steam flows in stages to 40%
design
- always decrease hydrocarbon flow first
- adjust firing to keep exit temperature steady
 Keep steam flow constant, shut off hydrocarbon
feed
- adjust firing to maintain exit temperature
- purge system of hydrocarbons
 Decrease exit temperature to 550°C at 100°C per
hour
Shut-down

Add flow of N2 and continue cooling
Shut off steam 50°C above condensation
temperature
Continue cooling with N2 flow
When catalyst below 50°C tubes may be emptied
Shut-down

 Large modern top-fired steam reformer
 Significant tube failures during start-up
 Caused by overfiring at start-up due to a number
of coincident factors
Case Studies - No 1

 Site steam shortages requiring conservation of steam
 Pressure to avoid a shut-down (due to low product
stocks)
 Burner fuel usually from two sources, mixed:
one low calorific value
one high calorific value
 At time of incident, all high calorific value
(unexpectedly) fuel received
 Operators had seen many shutdown/start-ups during
past two years
Case Studies - No. 1

 Plant trip (loss of feedstock to reformer) due to
valve failure
 Feedstock to reformer not isolated adequately by
valve
 Setpoint on reformed gas pressure not reduced
 Steam introduced for plant restart at reduced rate
 All burners lit (deviation from procedure)
Reformer tubes remained at normal operating
pressure of 16 barg

 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"
Emergency Shutdown Activated!
30minutes Case Studies - No. 1

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

Ammonia Plant
 LTS reduction loop included steam reformer
 CO2 released from LTS reduction
 Carbon formed in steam reformer

 LTS reduction with closed loop circulation
 Normally condenser, compressor and pre-heat coil
 This time included steam reformer, pre-heater and
waste heat boiler
 Steam reformer fired to TWT of 900°C
 LTS reduction liberates CO2
 By 2am, LTS reduction almost complete
- 50 % CO2 in recirculation gas
- also some H2 present

 Steam reformer pushed to give apparent LTS
temperature of 200°C
 Due to instrument error, in fact 380°C
 Between 5am - 7 am, steam reformer PD
increased
 Tubes looked hot
 Reformer steamed for 18 hours
 No reduction in PD
 Plant shutdown
Reformer catalyst black and badly broken up - due
to severe carbon formation

Check to ensure that recirculation loops do not
contain high levels of carbon oxides
 CO2 can shift in LTS to CO
CO2 + H2 CO + H2O
 CO in presence of H2 gives carbon
CO + H2 C + H2O
 CO can methanate in steam reformer (if some
catalyst reduction due to presence of H2 is seen)
forming CH4
CO + 3H2 CH4 + H2O
 This cracks to form carbon
CH4 C + 2H2

Importance of Tube Wall Temperature
Measurement
 Need accurate information
 Tube life
 Artificial limitation on plant rate

Effect of Tube Wall Temperature on
Tube Life
850 900 950 1000
(1560) (1650) (1740) (1830)
Temperature °C (°F)
TubeLife(Years)
Design
+ 20°C
20
10
2
5
1
0.5
0.2

Tube Wall Temperature Measurement
 Contact
- Surface Thermocouple
 "Pseudo-contact“
- Gold Cup Pyrometer
 Non-contact
Disappearing Filament
Infra Red Optical Pyrometer
Laser Pyrometer

Surface Thermocouples
 Continuous measurement, by conduction
 "slotting" can weaken tube wall
 Spray-welding leads to high readings
 Short, unpredictable lives (6 -12 months)
Not commonly used for steam reformer tubes

Disappearing Filament
 Hand held instrument
 Tungsten filament superimposed on image of
target
 Current through filament altered until it
"disappears“
 Current calibrated to temperature
 Range 800-3000°C
Very operator sensitive
Largely displaced by IR

Infra-red Pyrometer
 Easy to use
 Need to correct for emissivity and reflected
radiation
 Inexpensive

Laser Pyrometer
 Laser pulse fired at target and return signal
detected
 Can determine target emissivity
 Must correct for background radiation
 High spacial selectivity
 Very accurate for flat surfaces

Gold Cup Pyrometer
 Excludes all reflected radiation
 Approximates to black body conditions
 High accuracy / reproducibility
 BUT
- Limited access
- Awkward to use

Gold Cup Pyrometer
Tube Furnace Wall
Water
Cooling
To
Recorder
Gold Cup
Lance
*

Accurate Temperature Measurement
 Combination of IR pyrometer and Gold cup pyrometer
 Gold cup pyrometer allows calculation of emissivity
 Full accurate survey of reformer possible with IR
pyrometer

Temperature Measurement Corrections
epyrometer (Tm)4 = etube (Tt )4 + rtube (Tw)4
Measured True Averaged
target target background
temperature temperature temperature
e = emissivity
r = reflectance
= (1-e)

Accurate Temperature Measurement
(Tm)4 = etube (Tt )4 + (1 - etube) (Tw)4
- Set IR Pyrometer emissivity at 1
- Measure Tm and Tw with Pyrometer
- Measure Tt with Gold Cup
- Calculate etube

Background Temperature Measurement
NORTH
A
a
2
a
1

Comparison of Infra-red Pyrometer and
Calculated Tube Wall Temperature
MeasurementsTemperature(°C)
Temperature(°F)
Fraction Down Tube
0 0.2 0.4 0.6 0.8 1
950
900
850
800
750
1742
1652
1562
1472
1382
Uncorrected Pyrometer
Corrected Pyrometer
Calculated
= Gold Cup Measurements

Tube Wall Temperature Measurement -
Conclusions
 IR Pyrometer typically reads high
 Top-fired reformer 32°C
 Side-fired reformer 50°C
 IR Pyrometer with Gold Cup "calibration“
 Top-fired reformer 2°C
 Side-fired reformer 16°C

Classroom Exercise 2 - PROBLEM
Reformer exit gas composition (dry %)
 H2 73.19
 N2 + Ar 1.11
 CH4 3.04
 CO 15.55
 CO2 7.11
 Total (dry) 100.00
 H2O 41.34
 Total (wet) 141.34
Reformer exit pressure 18.11 barg
Reformer exit temperature 875°C
Calculate the approach to equilibrium

Classroom Exercise 2 - ANSWER
Exit Pressure (ata) = (18.11 / 1.013) + 1 = 18.88 ata
pCH4 = 3.04 x 18.88 = 0.4061 ata
141.34
pH2 = 73.19 x 18.88 = 9.7766 ata
141.34
pH2O = 41.34 x 18.88 = 5.5221 ata
141.34
pCO = 15.55 x 18.88 = 2.0771 ata
141.34
pCO2 = 7.11 x 18.88 = 0.9497 ata
141.34

KWGS = pH2 . pCO2
pH2O . pCO
= 9.7766 x 0.9497
5.5221 x 2.0771
= 8.09 x 10-1
From Tables TWGS = 875°C
Reformer exit temperature = 875°C

KMS = pCH4 . pH2O
pCO . (pH2)3
= 0.4061 x 5.5221
2.0771 x (9.7766) 3
= 1.15 x 10-3
From Tables TMS = 874°C
ATE = 875 - 874 = 1°C

Steam Reforming - Practical Operations

Steam Reforming - Practical Operations

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Steam Reforming - Practical Operations