The document discusses improvements in high temperature shift catalysts. It describes the characteristics and operational issues of traditional HTS catalysts and how the new VULCAN Series VSG-F101 catalyst has addressed these issues through modifications to its microstructure and composition. The VSG-F101 has shown improved activity, strength, and resistance to thermal and mechanical stresses during plant upsets compared to previous catalysts.
2. Improvements in High Temperature
Shift Catalysts
The high temperature shift duty
introduction and theory
HTS catalyst characteristics
developments over time
Typical HTS operational problems
Improved catalysts
VULCAN Series VSG-F101 Series
Summary
3. Improvements in High Temperature
Shift Catalysts
The high temperature shift duty
Introduction and theory
HTS catalyst characteristics
Typical HTS operational problems
Improved catalysts and loading regimes
Summary
4. Introduction
What is the Shift Reaction ?
Water gas shift reaction has two effects:
• generates hydrogen from carbon
monoxide & steam
• converts CO to CO2
CO + H2O <=> CO2 + H2
5. From Steam
Reformer
HTS LTS Methanation
LTS
(optional)
H2
Introduction
How to include a Shift Section ?
Liquid
CO2
Removal
PSAHTS
From Steam
Reformer
H2
6. Theory - Equilibrium
CO + H2O CO2 + H2 (+ heat)
• Reaction is reversible
• Forward reaction - moderately exothermic
– equilibrium at lower temperature favors
• more CO converted
• more H2 produced
• Cannot beat equilibrium !
7. Theory - Reaction Rate
Reaction Rate depends on
• distance from equilibrium
further from equilibrium =>
larger driving force
• catalyst formulation/activity
• operating temperature
Catalyst enables reaction to proceed
Higher temperature drives rate
Ideal catalyst promotes rate to achieve
equilibrium at low temperature
8. Improvements in High Temperature
Shift Catalysts
The high temperature shift duty
HTS catalyst characteristics
developments over time
Typical HTS operational problems
Improved catalysts and loading regimes
Summary
9. High Temperature Shift
Operating Conditions
Inlet CO 8 - 15 % / outlet CO 2 - 4 %
(dry)
Bulk of CO conversion > 75 %
Typical inlet temp of 335 - 360OC (640 -
680OF)
• recent improvements down to 300oC
(575oF)
Temperature rise 55 - 65OC (100 - 120OF)
Typical lives 3 - 5 years
10. High Temperature Shift
Catalyst Issues
Over-reduction at low steam/dry gas
ratio
Cr6+ content
Sulfur content
Activity
Strength
11. High Temperature Shift
Modern Catalyst Features
Iron/chromium/copper oxides catalyst
• typical composition 87 % / 10 % / 3% (wt)
Active phase is magnetite, Fe3O4
• supplied as haematite, Fe2O3
• requires reduction
Activity supplemented by Cu
• helps avoid over reduction of Fe3O4
Low Cr6+ and SO4
2-
• typically < 50 (Cr) & < 300 ppmw (S) or better
12. High Temperature Shift
Catalyst Features
To overcome the catalyst issues
• Over-reduction
copper promotion
• Cr6+ content and sulfur content
production route
• High stable activity & high strength
dispersion of iron oxide, Cr2O3 and Cu crystallites
low hexavalent chromium
copper promotion
micro-structure, particularly iron oxide
catalyst pellet size options
VULCAN Series VSG-F101 incorporates all the
required features
13. High Temperature Shift
Catalyst Structure - General
Small crystals of magnetite
high surface area => high activity
Good dispersion of Cr2O3 (Cr3+)
gives strength to resist breakage in process
upsets (eg wetting)
gives high thermal stability
prevents sintering of Cu and Fe3O4
slows activity loss & increases life
Good dispersion of Cu
small crystallites => high Cu surface area =>
high activity
slows Cu sintering
14. 50-700 A pore
o
Chrome Oxide
Crystal
Iron Oxide Crystals
High Temperature Shift
Catalyst Structure
Cu Crystals
16. HTS Catalyst - Addition of Copper
1. Activity
Activity increase due to Cu addition
• much higher intrinsic activity than Fe3O4
• increases shift activity
Benefits are
• at same SOR inlet temperature, maintain
equilibrium for longer - extend life
• achieve equilibrium at lower SOR inlet
temperature - lower CO slip, higher H2 make,
slower sintering (deactivation)
• for same SOR inlet temperature and life -
decrease catalyst volume
17. HTS Catalyst - Addition of Copper
1. Activity
Cu issues - overcome by catalyst design
• Cu sinters rapidly at HTS operating
temperatures
• high Cu levels weaken catalyst structure
=> stabilize by the Fe3O4/Cr2O3 micro-
structure
• Pore diffusion controls overall reaction rate
cannot achieve full benefit of Cu intrinsic
activity
=> optimize pore structure to maximize
benefit
18. HTS Catalyst - Addition of Copper
2. Over-reduction
Fe3O4 => FeO => Fe
• causes increased Fischer-Tropsch activity
• C laydown (2CO <=> C + CO2)
For over-reduction to occur
• need R ~ 1.5 or higher
• corresponds to S/C approx 2.8 in reformer
Reducing (CO)+ (H2)
Oxidising (CO2) + (H2O)
= Pc = R
20. HTS Catalyst - Addition of Copper
2. Over-reduction
H2O/H2 phase equilibrium
• rarely close to boundary
• Cu tends towards lower temperature
operation
300 350 400 450 500 550
0.1
0.2
0.3
0.5
0.7
1
Temperature (oC)
P[H2O]/P[H2]
Fe
Fe3O4
FeO
21. High Temperature Shift
Chromium (VI) Issues
Cr6+ content must be low
• Cr6+ can form during manufacture
means less Cr2O3 so affects stability
• Cr6+ is a Category 1 carcinogen
• Cr6+ is water soluble
can be washed out of catalyst into
condensate system (particularly during
start-ups)
loss of catalyst strength
• upon reduction, Cr6+ gives an exotherm
40OC (72OF) per 1%
danger of over-temperature (catalyst;
vessel)
22. Low Cr6+ High Cr6+
High Temperature Shift
Chromium (VI) Issues
High Cr6+Low Cr6+
Boiling water testWater soak test
Low Cr6+ : typically < 10 ppmw
23. High Temperature Shift
Sulfur Removal Issue
Sulfur source
• residual sulfate from metal salts used in
catalyst manufacture
Sulfur problem during initial reduction
• liberate H2S during initial catalyst reduction
• poison for LTS catalyst or PSA absorbent
vent exit gas to prevent poisoning
if not, consumes up to 1 volume LTS catalyst
per 20 volumes HTS catalyst
• duration depends on catalyst sulfate level
• prolongs commissioning
24. High Temperature Shift
Sulfur Removal Issue
Sulfur level
• depends on manufacturing route
sulfate route (older) ~ 5000 ppmw
nitrate route (newer) ~ 200 ppmw
Effect of de-sulfiding on reduction time
• duration depends on catalyst type
nitrate route: complete in ~4 hours
after process gas
sulphate route: hold for 5 - 10 hours
extra
25. Improvements in High
Temperature Shift Catalysts
The high temperature shift duty
HTS catalyst characteristics
Typical HTS operational problems
Improved catalysts and loading
regimes
Summary
26. HTS Operational Problems
Catalyst Start Up
Exotherm on steam addition
• Temperature “spike” sometimes observed
new HTS catalyst; all vendors
• often 100 oC (180 oF) and up to 250oC (450oF)
Root cause analysis
• not understood for many years
• correlated with long hold on N2 flow at >> 200 oC
• catalyst surface becomes “super dry”
• steam re-hydrates surface (heat of hydration)
27. 1st Steam
Introduced
0 20 40 60 80 100
250
300
350
400
450
500
600
700
800
Time, minutes
Temperature(°C)
Temperature(°F)
Inlet
Top
Mid
Bot
Exotherm on Steam
New HTS Catalyst
Large European Plant
28. HTS Operational Problems
Catalyst Start Up
Exothermic Rehydration Case Study
• VSG-F101 Series installed
• subsequent performance unaffected
• demonstrates good catalyst thermal
stability
Rehydration phenomenon
• avoid by controlling drying conditions
during start-up
29. HTS Operational Problems
Catalyst Start Up
Exotherm due to H2 ingress
• passing valve allowed H2 entry
before reduction started
on hold at 200+ oC
• new VSG-F101 Series installed
• significant exotherm
• subsequent performance unaffected
on line > 4 years
• demonstrates good catalyst thermal
stability
30. HTS Operational Problems
Upstream Boiler Leaks
Boiler leaks
• relatively common
• more likely at high plant rates
Effects
• possible catastrophic catalyst failure due
to thermal shock
• pressure drop increase due to
boiler solids fouling of the catalyst
catalyst breakage (droplet
impingement)
31. HTS Operational Problems
Upstream Boiler Leaks
Boiler leak case study - background
• large new Syngas plant
• Vulcan Series catalysts throughout
including VSG-F101
• observed increase in HTS pressure drop
• data consistency check indicated showed
high steam ratio in the shift section
• boiler leak suspected
32. HTS Operational Problems
Upstream Boiler Leaks
Boiler leak case study - actions/outcome
• catalyst inspected
• boiler leak confirmed
• catalyst skimmed
• plant restarted at 100% rate with 40%
less HTS catalyst
space velocity increased to 9000 h-1
• catalyst still achieved maximum
conversion
33. HTS Operational Problems
Unplanned Catalyst Oxidation
Exothermic Catalyst Oxidation
• activated (reduced) catalysts
reacts with air rapidly and exothermically
catalyst oxidizes with possible thermal
damage
Case Study from a large syngas plant
• air machine delivery valve failed
• huge HTS catalyst temperatures increase
middle = 635oC (1175oF) and exit = 540oC
(1100oF)
• temperatures stayed high ~30 minutes
34. HTS Operational Problems
Unplanned Catalyst Oxidation
Catalyst Oxidation Case Study - outcomes
• catalyst activity impaired
flatter reaction profile
CO slip has increased from < 3% to
>4%
• VSG-F101 remains operable
capable of an acceptable
performance until a convenient
change is planned
despite significant over-temperature
35. Improvements in High Temperature
Shift Catalysts
The high temperature shift duty
HTS catalyst characteristics
Typical HTS operational problems
Improved catalysts
VSG-F101 Series
Summary
36. VSG-F101 Series
Step change improvement for HTS
Launched almost three years ago
Reformulated catalyst
• similar bulk composition to previous grades
• modified iron oxide pore structure
patented use of acicular iron oxide
Increased activity by 20%
• reduced diffusion limitation
Increased in-service strength +100%
37. VSG-F101 Series
Properties
Composition
Fe
Ni
Cu
(+ Al2O3 )
Form
VSG-F101 9 mm (dia) x 5 mm pellets
VSG-F101 5 mm (dia) x 8 mm spheres
Charged bulk density
0.8-1.1 kg/l (50-69 lb /ft3)
38. VSG-F101 Series
Improved HTS Catalyst
Structural promoter
• Improves strength
better able to withstand plant upsets such
as boiler leaks
higher strength through life
• Modifies pore structure
wider pore distribution
allows easier diffusion through wide pores
to high surface area active sites in small
pores
increases activity
43. VSG-F101 Large Size for Low Pressure
Drop
VSG-F101DG
• 14 mm dia x 5 mm height domed pellets
• pressure drop is 40 % lower than VSG-
F101
• larger pellet => stronger
better resistance to plant upsets
• activity ~90 % that of VSG-F101 at 360 oC
THUS exceeds that of VSG-F101
44. Improvements in High Temperature
Shift Catalysts
The high temperature shift duty
HTS catalyst characteristics
Typical HTS operational problems
Improved catalysts and loading regimes
Summary
45. Summary
Fundamentals of HTS Catalysis
HTS catalysts have improved
• VULCAN Series VSG-F101
Operational issues still affect HTS
catalysts
• start up exotherms; boiler leaks;
catalyst breakage; reoxidation
Active and robust VSG-F101 Series