(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