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(HTS) High Temperature Shift Catalyst (VSG-F101) - Comprehensiev Overview
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(HTS) High Temperature Shift Catalyst (VSG-F101) - Comprehensiev Overview

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The high temperature shift duty introduction and theory …

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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  • 1. Performance & Operation Improvements using VULCAN Series VSG-F101 High Temperature Shift Catalysts By: Gerard B. Hawkins Managing Director, CEO
  • 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
  • 15. Amorphous Structure (achieved in VSG-F101) Microstructure of HTS Catalysts Crystalline Structure (Competitor)
  • 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
  • 19. HTS Catalyst - Addition of Copper 2. Over-reduction  CO2/CO phase equilibrium  Cu increases activity • rapidly increases p[CO2]/decreases p[CO] 300 350 400 450 500 550 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 Temperature (oC) P[CO2]/P[CO] Fe Fe3O4
  • 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
  • 39. Structural promoter Micrograph showing catalyst enlarged x140,000 VSG-F101 Series Modified Microstructure
  • 40. RadialCrushStrength (Kg/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
  • 41. 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
  • 42. Months in Operation CatalystActivity 2 3 4 5 6 7 8 9 10 20 30 400 Design for VSG-F101 Expected for VSG-F101 Measured Activity VSG-F101 in a Large Syngas Plant in China
  • 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