(hts) high temperature shift catalyst (vsg-f101) - comprehensiev overview
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Performance & Operation Improvements using VULCAN Series
VSG-F101 High Temperature Shift Catalysts
By:
Gerard B. Hawkins Managing Director, CEO
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
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
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
From Steam Reformer HTS LTS Methanation
LTS (optional)
H2
Introduction How to include a Shift Section ?
Liquid CO2
Removal
PSA HTS From Steam Reformer H2
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 !
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
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
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
High Temperature Shift Catalyst Issues
Over-reduction at low steam/dry gas ratio
Cr6+ content Sulfur content Activity Strength
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 SO42-
• typically < 50 (Cr) & < 300 ppmw (S) or better
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
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
50-700 A pore o
Chrome Oxide Crystal
Iron Oxide Crystals
High Temperature Shift Catalyst Structure
Cu Crystals
Amorphous Structure (achieved in VSG-F101)
Microstructure of HTS Catalysts
Crystalline Structure (Competitor)
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
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
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
HTS Catalyst - Addition of Copper 2. Over-reduction
CO2/CO phase equilibrium Cu increases activity
• rapidly increases p[CO2]/decreases p[CO]
300 350 400 450 500 5500.5
0.70.91.11.31.51.71.9
Temperature (oC)
P[CO2]/P[CO]
Fe
Fe3O4
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 5500.1
0.20.3
0.50.7
1
Temperature (oC)
P[H2O]/P[H2]
Fe
Fe3O4
FeO
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)
Low Cr6+ High Cr6+
High Temperature Shift Chromium (VI) Issues
High Cr6+ Low Cr6+
Boiling water test Water soak test
Low Cr6+ : typically < 10 ppmw
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
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
Improvements in High Temperature Shift Catalysts
The high temperature shift duty HTS catalyst characteristics Typical HTS operational problems Improved catalysts and loading
regimes Summary
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)
1st Steam Introduced
0 20 40 60 80 100
250
300
350
400
450
500
600
700
800
Time, minutes
Tem
pera
ture
(°C
)
Tem
pera
ture
(°F)
Inlet
Top
Mid
Bot
Exotherm on Steam New HTS Catalyst
Large European Plant
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
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
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)
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
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
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
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
Improvements in High Temperature Shift Catalysts
The high temperature shift duty HTS catalyst characteristics Typical HTS operational problems Improved catalysts
VSG-F101 Series
Summary
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%
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)
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
Structural promoter
Micrograph showing catalyst enlarged x140,000
VSG-F101 Series Modified Microstructure
Rad
ial C
rush
Str
engt
h (K
g/cm
)
VSG-F101 Competitor A Competitor B Competitor C 0
2
4
6
8
10
12 VSG-F101 Series Reduced Strength
Crush strength after 2
weeks operation
Months on Line 0
0
10
20
30
40
50
10 20 30
Start of Leak
Comp. A
VSG-F101
Limit
VSG-F101 Comparison Boiler Leak
Months in Operation
Cat
alys
t Act
ivity
2
3
4
5
6
7
8
9
10 20 30 40 0
Design for VSG-F101
Expected for VSG-F101
Measured Activity
VSG-F101 in a Large Syngas Plant in China
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
Improvements in High Temperature Shift Catalysts
The high temperature shift duty HTS catalyst characteristics Typical HTS operational problems Improved catalysts and loading regimes Summary
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
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