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Theory and Operation of
Secondary Reformers
By:
Gerard B. Hawkins
Managing Director, CEO
Introduction



Purpose
Key to good performance
Problem Areas
• Catalysts, heat shields and plant up-rates
• Burner Guns



Development of High Intensity Ring
Burner
Case Studies
Conclusions
Secondary Reformer Purpose

Reduce methane slip to very low
levels
• Around 0.3-0.5 % mol dry

For ammonia plants provide feed
point for nitrogen required for
ammonia synthesis
• And thereby Ensure optimal H/N ratio

Generate heat for transfer for HP
steam in Waste Heat Boiler
Typical Reforming Configuration
Steam + Gas
500°C
Air / Oxygen
450°C
Steam
Reformer
Secondary
Reformer
Steam
1200°C
Steam
780°C
10% CH
4
950°C
0.5% CH
4
Secondary Reformer Mechanical
Details
Refractory lined pressure shell
Fixed Catalyst bed in lower region
Combustion section in upper region
Water jackets to keep shell cool
Catalyst supported on brick arch
Keys to Good Performance
Air/Oxygen

–
–
–
Three key
components
Burner Design
Mixing Volume
Catalyst
All must be designed
correctly to maximize
performance
Steam Reformer
Effluent
To Waste
Heat Boiler
Keys to Good Performance
Note: Oxygen - Methanol Plant Design

Again three key
components
• Burner Design
• Mixing Volume
• Catalyst - VSGZ201/202/203
540`C
780°C
1300°C
1500°C

Since using O2 as 1100-1200°C
oxidant, flame
temperature is
higher
• Failures are much
faster
2500°C
1500°C
1100-1200°C
975°C
Secondary Reformer Operation
•Burner determines mixing performance
•Air injected at high velocity
•Forces mixing of air and process gas
•Combusts only 20% of process gas
•Must also mix in other 80%
•Should achieve a uniform mixture
•Catalyst bed can affect flow patterns
Secondary Reformer Combustion
Gas feed very hot > 630oC
Gas feed contains hydrogen
Gas ignites automatically
Autoignition >615oC
No need for spark or pilot
Must maintain gas above 615oC
Secondary Reforming Reactions
CH4
+
2H2 +
heat
2CO
O2
=
=
CO2
2H2O
+
2H2O
Exothermic - gives out
Flame 2500oC mixed gas 1500oC
Steam reforming
CH4 + H2O = 3H2 + CO
down gas
Endothermic - cools
Water gas shift
CO + H2O = CO2 + H2 Slightly exothermic
Key Components: Catalyst
Problems

Catalyst can
• Exhibit poor activity

Unlikely
• Break up in service

Usually linked to a plant upset
• Suffer physical blockage

Alumina vaporization
• Become overheated and fuse

Causes increased pressure drop and gas maldistribution
Key Components: Catalyst Activity



Catalyst is exposed to very high
temperatures
• Therefore nickel sinters
However once sintered it is very stable
Since catalyst operates at high temperature
it is difficult to poison
• Poisons will not stick
• For ammonia plants will pass through to
HTS and then LTS
• For methanol plants will pass through to
methanol synthesis loop
Key Components: Catalyst Activity

VULCAN Series range of
catalysts VSG-Z201/202/203
• Size - Mini and Standard plus
Elephant
• Use as a heat shield
• Shape
 5-Hole
 Quadralobe
 Quadralobe has +20% more
activity than 4-hole
• Well proven catalysts that are
high stable and strong
• Long lives
Key Components: Catalyst Appearance




White - loss of nickel
Coated in white - alumina vaporization
Glazed or blue - very high temperatures
Pink crystals - synthetic ruby formation
• Cause by high temperatures
• A mixture of refractory and transition
metals
Key Components: Mixing Performance




Good mixing is absolutely essential
Poor mixing in mixing zone gives high approach
and high methane slip
Poor mixing can be due to
• Poor burner design
• Insufficient mixing volume
• Burner gun failure
Root cause can be checked with CFD but will not
detect burner gun failure
Key Components: Burner Gun



If burner gun fails then can lead to
• Wall refractory damage
• Loss of vessel containment
Poor mixing can lead to zones of high
temperature
• Leads to high rate of catalyst sintering
• Reduction in catalyst activity
• Increase in approach to equilibrium (ATE)
Poor mixing can lead to high flow zones
• Movement/damage of target tiles or catalyst
bed
• Increased ATE
Key Components: Burner Guns

Standard Ammonia secondary burners have
• Small number of large holes
• Give poor mixing at high rates
• High risk of overheating bed
• Methane slip rises rapidly at high rates
• Burner can be plant limit
Key Components: Burner Guns





For methanol plants remember that
oxidant used in oxygen
Gives higher flame temperatures
If jet impinges on refractory then
refractory will be damaged much more
quickly
Vessel will fail rapidly
As oxidant flow is lower than for an
ammonia plant use a different design of
burner
Key Components
High Intensity Ring Burner

The high intensity burner differs from the
standard burners
• Large number of small holes: Small flames
• High degree of mixing: Short mixing distance
• Oxidant fed evenly into process gas: Good
Mixing
• Insensitive to rate increases
• Used in ICI Ammonia plants
Effect of Operational Changes
Air Rate
Name
Units
Plant Rate
Air Rate
Exit Pressure
Steam to Carbon to Primary
Outlet Temperature
Methane Slip
H/N Ratio
Approach to Equilibrium
%
%
Bara
n/a
°C
mol %
n/a
°C
Base
Case
100
100
39
2.88
1000
0.41
3.00
14.2
Increased Air
Rate
100
105
39
2.88
1026
0.41
2.86
45.1
Effect of Operational Changes
Pressure
Name
Units
Plant Rate
Air Rate
Exit Pressure
Steam to Carbon to Primary
Outlet Temperature
Methane Slip
H/N Ratio
Approach to Equilibrium
%
%
Bara
n/a
°C
mol %
n/a
°C
Base
Case
100
100
39
2.88
1000
0.41
3.00
14.2
Increased
Exit Pressure
100
100
40
2.88
1000
0.41
3.00
11.3
Effect of Operational Changes
Steam to Carbon Ratio
Name
Units
Plant Rate
Air Rate
Exit Pressure
Steam to Carbon to Primary
Outlet Temperature
Methane Slip
H/N Ratio
Approach to Equilibrium
%
%
Bara
n/a
°C
mol %
n/a
°C
Base
Case
100
100
39
2.88
1000
0.41
3.00
14.2
Decreased
Steam to Carbon
100
100
39
2.78
1002
0.41
3.00
12.2
Key Components: Effect of Poor
Mixing

Poor mixing can be illustrates by assuming
a secondary reformer with a high zone of
high air flow and a zone with low flow
Poor
Name
Units
Temperature
o
C
Methane slip Mol %
Approach
o
C
Too
Too little
much air
air
1034
902
Mixed
Good
971
957
0.13
1.89
0.9
0.62
10
10
53
10
Key Components: Catalytic Heat Shield




Bed has to be protected
against disturbances
Conventional target tiles or
alumina lumps used
Even these can be moved
No longer required: can
replace with active catalyst
• Additional activity improves
reforming performance

Use – VULCAN Series AST
Advanced Support Technology
• Large (35mm) 4-hole shape
Key Components
Use of CFD for Secondary Reformers




CFD modelling very good for secondary
reformers
BUT time consuming and expensive
Building up a library of case studies
VULCAN Series Catalysts VSG-Z201/202/203
has extensive experience with CFD for
secondary reformers
•
•
•
•
Troubleshooting problems
Designing burner guns
Validation of modifications
Optimization of catalyst quantity
Case Study 1:
Insufficient Mixing Volume
Air
Gun
Air
gun
Recirculation
zones
Catalyst
Bed
Catalyst
Bed
<1200 C
1200 C 1400 C
1400 C
1500 C 1600 - 2100 C
Case Study 1:
Insufficient Mixing Volume
Case Study 2 Burner Guns


In this case, secondary operated well up to 1450 mtpd
At rates above this, methane slip rose rapidly
Limiting further plant rate increases
Methane slip

0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1100
1200
1300
1400
1500
Plant rate, mtpd
1600
1700
Case Study 2:
High Intensity Ring Burner
Burner
Rings
Burner
Rings
Recirculation
Zone
Catalyst
Bed
Catalyst
Bed
<1200 C
1200 C
1300 C
1400 C
1500 C
1600 - 2100 C
Secondary Catalyst Conclusions


All three components must be designed
correctly
If there are problems then can change catalyst
type to high activity catalyst – VULCAN Series
VSG-Z201/202/203 5-hole or Quadralobe
• Can achieve large reduction volumes
• Allows increase in mixing space
• VSG-Z201/202/203 catalysts are well proven,
stable and reliable



Good mixing above the catalyst bed is essential
Poor mixing gives high methane slip
Mixing performance critically depends upon
burner
Secondary Reforming Conclusions

CFD useful for
• Troubleshooting
• Design, modifications and optimization
• VULCAN Series Catalysts can offer this service

GBHE Catalyst Process Technology can
recommend the appropriate burner type
•
•
•
•
•
Eliminates problems caused by poor mixing
Optimum burner type opposite plant configuration
But still needs designing correctly
Continued process of improvement to design
Contact your GBHE Catalysts representative for
details