Catschool 1: Prereforming catalysts
Pia Elholm, Product manager for prereforming catalysts
Outline
• History
• Use of prereforming technology
• Topsøe prereforming catalysts
• Handling and installation of prereforming catalysts
• Evaluation and operational precautions
• Summary
• Quiz
Topsøe prereforming catalyst changes in operation
worldwide
100
90
80
No. of references
70
60
50
40
30
20
10
0
1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012
Year
Hydrogen plant
H2O
Hydrocarbon
feed
Steam reforming
Hydrogenation
temperature
Pre-reforming
absorption
Medium
Sulphur
shift
Off gas
H2
Pressure swing absorption
CnHm + nH2O → nCO + (n+m)/2 H2
CO + H2O ↔ H2 + CO2
CO + 3H2 ↔ CH4 + H2O
GTL/MeOH frontend with ATR
H2O Recycle O2
Feed H2O
H2
Feed Pre-
purification reformer
ATR
Ammonia plant
Desulphurisation Reforming Shift
Prereforming
Process steam
Natural gas
Process air
Fuel
Stack
Purge gas
CO2-
removal
Ammonia Process
product Ammonia synthesis Methanation cond.
Benefits of prereforming technology
• Feedstock flexibility – Natural gas, naphtha, butane, LPG, Off-gas or
mixed
• Optimize steam to carbon ratio:
• Down to 1.6 with naphtha feedstock
• Down to 0.52 with light natural gas
• All higher hydrocarbons will be converted - Exit gas is H2, CO, CO2 and
CH4
• In new plants:
• In large capacity new plants savings can be made on the tubular reformer
• In revamp situations:
• Plant load can be increased if part of revamp
• Energy consumption can be lowered by reheat of the prereformer exit gas in
connection with a plant revamp
Catalyst characteristics
• AR-401 • RKNGR
• Suitable for reforming of natural gas, • Suitable for reforming of heavy
LPG and naphtha hydrocarbon feedstocks
• High activity • High resistance towards carbon
• Resistance towards sintering formation
• High resistance to carbon formation at • Resistance towards sintering
low steam to carbon
• Pre-reduced for easy start-up
• Unique ability to tolerate condensing
steam
• Pre-reduced for easy start-up
Catalyst AR-401 RKNGR
Carrier MgAl2O4 MgO/Al2O3
Nickel, wt% >30 >20
Shapes 7-hole 11×6 and cylinders 4.5×4.5
Prereformer
Inert material Alumina
Shape Sphere
Diameter, inch ½
Alumina balls
Diameter, inch 1
Al2O3, wt % >99
SiO2, wt % <0.2
AR-401 or RKNGR
Alumina balls
Benefits of prereforming catalysts
• Protection of downstream equipment and catalysts:
• Lower tube skin temperatures in the tubular reformer, resulting in a longer
lifetime of the tubes compared to operation without prereforming catalyst
• Installation of standard reforming catalyst in tubular reformer
• Risk of carbon formation in the tubular reformer can be excluded
• Extended lifetime of the catalyst in the tubular reformer
• Longer lifetime of MTS and LTS catalysts
Handling of Topsøe prereforming catalysts
• Installation
• All Topsøe prereforming catalysts are skin-passivated securing easy
handling
• Hose loading
• Avoid “chimney” effect
• Unloading
• The prereforming catalyst is pyrophoric due to chemisorbed H2
• Unloading from bottom dump chute to drums with lids in order to minimize
ingress of air
• Avoid “chimney” effect
Loading of catalyst
Loading of catalyst
Loading of catalyst
Loading of catalyst
Evaluation of prereforming catalysts
• Follow DP across reactor
• Visual monitoring of performance
with Z90 plot
• Measure slip of HHC
T
T
T
Temperature
Naphtha
T
LPG
Natural gas
0 Bed depth, % 100
Poisoning
Temperature
0 Bed depth, % 100
Z90, %
Age
Calculation of Z90 in a naphtha based plant
495
T90
TExit
490
DT90
DT
485
Temperature (°C)
480
TMin
475
Z90
470
0 20 40 60 80 100
Height of bed, %
Calculation of Z90 in a natural gas based plant
520
TInlet
500
480
Temperature (°C)
460 TExit
T9
0
440
0 20 Z9040 60 80 100
Height of bed, %
Graphical deactivation plot -
the Z90 method
80
60
40
20
Z90, %
0
0 20 40 60
Age, months
Graphical deactivation plot -
the Z90 method
80
60
Z70, %
40
20
0
0 10 20 30 40 50
Age, months
Significant change in Z90 plot
100
80
60
40
Z90, %
20
0
0 20 40 60 80 100
Age, months
Operational precautions
• Prevent poisoning from
• Sulphur
• Alkali
• Silica
• Prevent carbon formation
• Prevent oxidation
Prevent sulphur poisoning
Feed TK-250
H2
Hydro- Conversion of organic sulphur
genation R-SH + H2 → H2S + RH
Sulphur Absorption of inorganic sulphur
absorption ZnO + H2S ↔ ZnS + H2O
HTZ-5
Sulfur trap
Feed
H2
ST- 101
Hydro- Sulfur Sulfur
genation absorption absorption
Sulfur
trap
• Application • Properties
• CO2 or H2O in the feed • Pick-up of any H2S and organic
sulfur
• CO2 + H2 ↔ CO + H2O
• Cu-based
• ZnS + H2O ↔ ZnO + H2S
• Fluctuating sulfur levels
Boiler feed water requirements
Requirement Unit Specification
Generel Colourless, clear, free from nondisolved matter
pH value at 25ºC 9-10
Conductivity at 25ºC mS/cm < 0.2
Oxygen (O2) mg/kg < 0.1
Iron, total (Fe) mg/kg < 0.02
Copper, total (Cu) mg/kg < 0.003
Silicic acid mg/kg < 0.02
Sodium (Na) mg/kg < 0.01
Chlorine (Cl) mg/kg < 0.1
Sulphur (as SO42-) mg/kg < 0.2
KMnO4 consumption mg/kg <3
Mn(VII) -> Mn(II) as KMnO4
Oil, grease mg/kg <1
Prevent carbon formation
Whisker carbon formation depressed by:
Lower temperatures
High steam/carbon ratios
High H2 recycle
Gum formation depressed by:
High temperatures
High steam/carbon ratios
High H2 recycle
Catalytic carbon formation
• During start up:
- Dry hydrocarbons during nitrogen recycle
Leaking valves on feed line:
- Valves (always) leak!
- Use double block and bleed (or blind)
Hydrocarbons from DES section:
- NG: Purge system properly: < 0.05 – 0.2 %
- Heavy feeds: Never include DES section in
nitrogen loop
• During operation:
- Complete loss of steam
- Operation at very low steam to carbon ratio
Oxidation of un-poisoned catalyst
Consequences of oxidation of un-
poisoned catalyst
• Loss of activity
• Increased sintering
• Very low degree of re-reduction at
operating conditions
Special risk during start-up/shut-down/trip
Oxidation of sulfur poisoned catalyst
If the catalyst is oxidized Initial poisoning of top layer Oxidation of sulfur poisoned
some of the sulfur picked catalyst
up on the catalyst in the top
will be released
This sulfur will be picked up
by the catalyst further down
in the bed
The overall catalyst activity
will decrease when the
sulfur is distributed to a
larger part of the bed
Trouble-shooting
• Z90 deactivation rate increases, consider
• Poisoning
• Gum formation
• Increase in DP is measured, consider
• Whisker carbon formation
• Hydration
• Deposition of foreign material
• Milling
• Other considerations
• Steam quality
• Changes in feedstock
• Plant layout
• Catalyst quality
• Quality of inert materials
Summary
• Topsøe prereforming catalysts are high activity nickel catalysts on stable carrier
materials with excellent carbon resistance
• Topsøe prereforming catalysts are well-referenced for a all types of feedstock
• Loading and start-up is simple due to the prereduced, but skinpassivated
catalysts
• Deactivation is diminished by avoiding poisoning of the catalyst – caution against
sulphur poisoning is essential
• Following the development in temperature profiles with Z90 plot enables actions
against poisoning
