(hts) high temperature shift catalyst (vsg-f101) - comprehensiev overview
DESCRIPTION
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 SummaryTRANSCRIPT
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Performance & Operation Improvements using VULCAN Series
VSG-F101 High Temperature Shift Catalysts
By:
Gerard B. Hawkins Managing Director, CEO
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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
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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
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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
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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
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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 !
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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
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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
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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
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High Temperature Shift Catalyst Issues
Over-reduction at low steam/dry gas ratio
Cr6+ content Sulfur content Activity Strength
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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
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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
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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
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50-700 A pore o
Chrome Oxide Crystal
Iron Oxide Crystals
High Temperature Shift Catalyst Structure
Cu Crystals
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Amorphous Structure (achieved in VSG-F101)
Microstructure of HTS Catalysts
Crystalline Structure (Competitor)
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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Improvements in High Temperature Shift Catalysts
The high temperature shift duty HTS catalyst characteristics Typical HTS operational problems Improved catalysts and loading
regimes Summary
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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)
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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
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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
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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
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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)
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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
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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
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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
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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
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Improvements in High Temperature Shift Catalysts
The high temperature shift duty HTS catalyst characteristics Typical HTS operational problems Improved catalysts
VSG-F101 Series
Summary
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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%
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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)
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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
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Structural promoter
Micrograph showing catalyst enlarged x140,000
VSG-F101 Series Modified Microstructure
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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
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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
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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
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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
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Improvements in High Temperature Shift Catalysts
The high temperature shift duty HTS catalyst characteristics Typical HTS operational problems Improved catalysts and loading regimes Summary
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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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