Principles of Pre-reforming Technology

Principles of Pre-reforming
Technology

Contents
 Pre-reforming
 Flow-schemes
• Feed-stocks
• Catalyst handling, loading & start-up
 Benefits of a pre-reformer
• Case studies
• Effects upon primary reformer
• Data analysis
• Reactor temperature profiles
• Catalyst management
 Summary

Markets
 Towns Gas
• Naphtha => Town Gas, reforming &
methanation
• Market declining due to NG availability
 Hydrogen
• Utility/chemical/refinery
• C1 though to naphtha => H2
• Feedstock flexibility/smaller primary
• Growing market for pre-reforming

Markets (contd)
 Methanol
• Retrofits, increase output/efficiency
• Growing market, technology enabler, big
reactors
 Ammonia
• Retrofits only
 GTL
• 1,2 stage
• Very big reactors

Contents
 GBHE pre-reforming background
• Markets
• Flow-schemes
• Feed-stocks
• Catalyst handling, loading & start-up
 Benefits of a pre-reformer
• Case studies
• Effects upon primary reformer
• Data analysis
• Reactor temperature profiles
• Catalyst management
 Summary

Flow-schemes - what does
Pre-Reforming do?
What is the aim of a pre-reformer?
 To react hydrocarbon feed with steam to give a methane
rich product suitable for further downstream reforming.
 Pre-reforming works as an adiabatic steam reforming
step over a Ni based catalyst.
 The basis for the reforming may be considered
as the reaction between a hydrocarbon and steam
• steam / methane reaction
• water / gas shift reaction

Prereformer Installation
Pre-
Heating
Re-
Heating
Gas/Steam
VSG-Z101
Pre-reformer
500ºC
500ºC
450ºC

Flow Scheme -
Desulfurization
 Pre-Reforming catalyst is poisoned by sulfur.
 The performance of the sulfur removal
system is important for the pre-reformer.
 The sulfur removal system may be designed
in accordance with any well proven system
but must achieve less than 0.1 ppm wt sulfur
throughout the catalyst life.
 Ultra-purification recommended for natural
gas applications

Advantages of Pre-reforming
 Fuel savings over stand alone primary reformer
 Reduced capital cost of reformer
 Higher primary reformer preheat temperatures
 Lower involuntary steam production
 Increased feedstock flexibility
 Higher activity primary reforming catalyst for
naphtha based plants
 Lower overall steam to carbon ratios
 Provides protection for the main reformer
 Reliable and easy operation

Feedstock
Following feeds may be fed to a pre-
reformer reactor
• Natural gas
• Refinery Off Gas
• Synthesis Gas derived from coal/oil
gasification
• LPG’s
• Naphtha (up to FBP 240°C)
• Kerosene
• Methanol
• Ethanol

Feedstock
Feed Specification
 Poisons in feed
Sulfur < 0.1 ppm wt
Chloride < 1.0 ppm wt *
Total heavy metals < 1.0 ppm wt (inc Lead) *
Lead < 0.2 ppm wt *
* - inlet purification section
 Steam Quality
Sodium < 0.2 ppm wt
Chloride < 0.1 ppm wt
Sulphide < 0.1 ppm wt
Silica < 0.1 ppm wt

Feedstock contd
For naphtha feeds over pre-reforming
catalyst there are limits on
• Aromatic content – normally 10 wt%
• Naphthene content – normally 25 wt%
• When considered together < 40 wt% has
been applied

Feedstock contd
Following feedstock data is
required for assessment of
performance:
•Gas and LPG feeds
•Full composition
•Level of impurities
•For Naphtha feeds
•PONA analysis
•Level of impurities
•C/H ratio and molecular weight
•FBP

Pre Reformer Loading
 Extremely important to achieve a uniform
loading
 Any zones of low or high voidage will
reduce catalyst life
• Check man-way plugs
 No meshes should be used in the vessel
 Thermocouples must be positioned
correctly and height recorded
 Loading procedure will be provided
 Loading assistance may be provided

Prereformer Installation
 Adiabatic Pre-Reformer
 Axial flow with Thermowell
 Bed of pre-reforming catalyst.

Pre-reformer Start-up
 Drying
 Heating
 Start-up
 Reduction

Catalyst Drying
For catalyst subjected to low temperature
(ie <0oC)
 Dry using Nitrogen
 175 to 250°C
 NG can be used below 200°C
 4 to 24 hours
 Dry air, not suitable for prereduced
 First start-up of prereduced

Catalyst Heating
 Normally heated using nitrogen
 Absorbed moisture
 Initial heating rate, 50°C per hour
 Max temp differential in bed 100°C
 At 200°C, 70°C per hour
 Heating till peak 400°C, min 370°C
 High circ rate, max pd 2 bar

Catalyst Heating continued
Warm-up rates
 Rapid warm-up minimises energy usage/time
 Traditional constraints of equipment
 Controllability
 Limited by mechanical considerations of vessel
 Catalyst, 150-170oC per hour

Catalyst Heating contd
Limits on impurities *
 Oxygen 1% vol
 Carbon Dioxide 1% vol
 Carbon Monoxide 1% vol
 Methane 1% vol
 Hydrogen 1% vol
 Ethane 100 ppm vol
 Sulfur 0.1 ppm wt
* For the initial warm up.
Lower limits for already activated or prereduced
catalyst

Catalyst Heating contd
Holding at temperature
 Not recommended
 2% hydrogen added
 Temperature reduced to 350°C

Catalyst Start-up
When operating temperature has been achieved
 Check for build-up of carbon oxides and hydrocarbons
 Addition of 10 mol % Hydrogen
 Followed by steam
 Introduce process feed, maintain safe S:F ratio
 Ensure feed lines are drained and warmed
 Vent steam to atmosphere before cutting in

Heating using Natural Gas
Using NG as heating medium
 No impurities
 Immediate start-up
 50°C per hour, max differential 100°C
 At 200°C introduce steam
• Min S:C 0.3kg/kg at 200°C
• Min S:C 0.5kg/kg at 400°C to 450°C
• Increase to design feed and S:F

Process benefits of pre-reforming
 Moves reforming load from
Primary
 Better reformer design
• Higher thermal efficiency in radiant box
• Raises pre-heat temps before carbon formation
issues
• Feedstock flexibility
 Reduced steam export
• Heat is recovered from duct
 Demonstrated using case studies

Process Benefits- Case Study
 Case 1 – Base Case – no pre-reformer installed
 Case 2 – Pre-reformer installed
 Case 3 – Pre-reformer installed and plant rate
increased until firing on the reformer is the same
as Case 1

Effect of a Pre-reformer on Primary
Reformer Performance
Parameter Units Case 1
Plant rate % 100
Methane slip mol % (dry) 12.84
ATE °C 1.8
Pressure drop bar 1.26
Maximum TWT °C 809
Fluegas temperature °C 898
Radiant efficiency % 68.7
Fuel rate change % 0
Case 2
100
12.76
1.1
1.28
803
885
69.4
-8.8
Case 3
109
12.79
1.3
1.49
807
898
68.7
0

Reformer Performance
 For new plants, there are CAPEX benefits
• Can reduce tube count on a new hydrogen plant by over
5%
• Fuel usage can be reduced by 8%
 For existing plant, excellent revamp opportunity
• Additional throughput or feedstock flexibility
 In summary
• Significant potential economic benefits
• Overall benefits plant specific

Reformer Performance contd
 Good performance depends on good design and
preparation of the reactor
 It is not simply another catalyst bed
 Guaranteed operation assumes plug flow
through the bed
 Guaranteed operation relies on good catalyst
management

Travelling
(or multi-point)
thermocouple
Catalyst
Graded
Ceramic Balls
Catalyst
discharge
nozzle
(alternative)
Catalyst discharge
nozzle (typical)

Good performance is achieved
through
 Even gas distribution
 Adequate temperature
measurement
 Thorough pre-commissioning
 Correct catalyst charging
procedures
 Good operating practices

Pre Reforming Data Analysis
 Good data is key to understanding
performance of the pre reformer
 Data includes
• Temperatures inlet and outlet the bed
• Temperatures through the bed
• Gas analysis inlet and outlet bed
• Feedstock and steam flows inlet bed
• Bed pressure drop trend

Pre Reforming Data Analysis
 Careful monitoring of
temperatures inlet, outlet and
through the bed allows
• Problems to be detected early on
 Sulfur poisoning, wetting etc
• Problems to be resolved before
there has been too much damage
caused
• Estimation of residual life

Reaction Profile
Reaction Zone Length
End Of Reaction Zone
Thermoneutral
Point
Minimum
Reaction
Temperature
Beginning Of
Reaction Zone
Preheat
Temperature
Temperature°C
Distance through bed

Reaction Profile
end of
reaction
zone
methanation and shift
reactions dominate
bed shrinkage
or deactivation
Temperature°C
endotherm
steam reforming reaction dominates

Reaction Profile
 By monitoring relative movement
of specific points on the profile,
• See if there is sulfur poisoning
• See if there is excessive sintering
• See if there is mal-distribution
 But rate changes will affect
positions of profiles

Temperature Profiles
Natural Gas - Effect of Plant Rate
 Changes in plant rate affect
profile
• Increases in rate
 Increases the length of profile
 Decreases the gradient
• Can be mistaken for sintering

Temperature Profiles -
Changes in Inlet Temperature

Changes in Inlet Temperature
 Increases in inlet temperature
• Shorten profile length
• Steeper profile gradient
• Change exit temperature

Maldistribution
TI
Maldistribution due to
wetting/agglomeration

Maldistribution
Maldistribution

Natural Gas
Temp
Position along Bed
Std NG
Sintering
(Lazy profile)
Poisoning
(Flat inlet)

Naphtha
Temp
Position along Bed
Std Naphtha
Sintering
(Lazy profile)
Poisoning
(Flat inlet)
Polymeric Carbon
(deepen endotherm)

Catalyst Management
 Draw the pre-reformer catalyst profile
weekly
 Examine profile and check for
• poisoning
• carbon polymer formation
• sintering
 Plot “end of reaction zone” (EOZ or
Z90) against time

Catalyst Management - EOZ
Temperature





Predicting End-of-Life
 The EOZ (or Z90) plot is the most useful tool
 Waiting for ethane or higher hydrocarbon
slip is too late
 Ultimate limits are
 when feed preheat limitations are
reached
 when C2
+ slip is unacceptable for
reforming catalyst
• EOL of VSG-Z101 catalyst often taken to
be when C2
+ slip of 2000 ppm v/v of the
wet rich gas.

Summary
Successful Pre-reforming requires
• A good catalyst
• Careful Operation/Procedures
GBHE VSG-Z101 catalysts are well suited
to withstand operating rigors
And come with the GBHE Experience - the
learning which is so essential to well
advised operation

Principles of Pre-reforming Technology

Principles of Pre-reforming Technology

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