Water-Gas-Shift Reactor Loading & Unloading Considerations
12 likes8,267 views
The document discusses considerations for loading and unloading catalysts in fixed bed reactors, including issues related to catalyst discharge, preparation methods, and handling techniques. Key procedures involve in situ oxidation, ensuring safety from hazards like evolved hydrogen, and managing catalyst types. Various loading methods, including manual and pneumatic techniques, are outlined to optimize catalyst distribution while minimizing damage.
Water-Gas-Shift Reactor Loading & Unloading Considerations
- 1. by: Gerard B. Hawkins Managing Director, CEO Water-Gas-Shift Reactor Loading & Unloading Considerations
- 2. Fixed Beds: Catalyst Discharge Issues to consider • reduced catalysts: self heating HTS, MTS, LTS and methanation • inert discharge or in situ oxidation/passivation • in situ oxidation with O2 or passivation with H2O • carbon contamination: self heating/pyrophoric possible for HDS and ZnO • inert or wet discharge if necessary • agglomerated catalysts cause usually fouling or wetting • physical breakage may be required Catalyst history affects procedure
- 3. Fixed Beds: Catalyst Discharge Preparation • select discharge method • cool and purge reactor • oxidize or passivate catalyst (if required) • water can be a weak oxidant and/or inerting medium beware of evolved H2 hazard • metal + H2O => metal oxide + H2 water fills catalyst pores • slows rate of O2 diffusion
- 4. Fixed Beds: Catalyst Discharge In situ oxidation with air • purge all combustibles from process • cool with steam or nitrogen at 600-1000 h-1 space velocity to 204 oC (400 oF) for HTS and 177 oC (350 oF) for LTS • meter 1% air into bed and monitor exotherm 31 oC (55 oF)/% air for HTS; 14 oC (25 oF)/% air for LTS or MTS • Once exotherm stable, slowly increase air up to 3 % initially and monitor exotherm hold peak temperature below hardware limits
- 5. Fixed Beds: Catalyst Discharge In situ oxidation with air (cont.) • continue to increase air level keep below vessel or piping temperature limitations • oxidation is complete when exotherm has passed through bed air level is 7-10% • replace steam or nitrogen flow with air flow • cool catalyst in air to discharge temperature below 38 oC (110 oF) for dry methods below 93 oC (200 oF) for wet method
- 6. Fixed Beds: Catalyst Discharge • Top discharge by vacuum – Man enters from top under vessel entry permit – Vacuum hose is 4 - 6” dia (10 - 15 cm) – Support material > 1” dia (2.5 cm) has to be removed by hand Man works evenly across and down bed For inert discharge, N2 is cooled and recycled
- 7. Fixed Beds: Catalyst Discharge Bottom discharge - dry • most common method • requires a proper dump chute and containers (bins or drums) for discharged catalyst • keep positive N2 pressure for inert discharge catalyst bins must be inerted • water hose available in case of heat generation wet catalyst during discharge if required
- 8. Fixed Beds: Catalyst Discharge Bottom discharge - wet • less common • cool catalyst below 93 oC (200 oF) • ensure suitable isolations for H2O • fill vessel with water • dump vessel contents through bottom drain valve • remove catalyst through bottom manway discharge of wet catalyst is very messy water may not completely oxidise the catalyst
- 9. Fixed Beds: Catalyst Handling & Loading Vessel inspection • inspect vessel for stress damage • thermocouples: check condition if present document T/C locations relative to fixed point • eg inlet flange or tangent line • support grids: check condition if present correct any damaged clips, grid blinding, etc • reactor clean and dry
- 10. Fixed Beds: Catalyst Handling & Loading Pre-loading checks • ensure vessel is free from rubbish • bottom manway door and spider in place • inspect reclaimed support/hold down materials remove broken or extraneous contaminants • inspect new catalyst type and condition • inspect new support/hold down materials type and condition ceramic versus alumina
- 11. Fixed Beds: Catalyst Handling & Loading Pre-loading checks (cont.) • appropriate personal protection available - and is used - inside and outside vessel eg dust masks • for vessel entry air tests breathing air and/or air movers usual stringent vessel entry precautions boards to support worker inside • minimises catalyst damage
- 12. Fixed Beds: Catalyst Handling & Loading Loading methods • manual most common by far • pneumatic specialised techniques (eg from Technivac) not considered further • dense loading specialised technique (eg from Petroval DENSICATTM) not considered further
- 13. Fixed Beds: Typical Loading 6” (15cm) of 1”- 2” balls (25 - 50mm) Catalyst/ absorbent 6” (15cm) of 0.5” balls (13mm) 4” (10cm) of 0.25”- 0.5” balls (6 - 13mm) 6” (15cm) of 1”balls (25mm) 1”- 2” balls (25 - 50mm) Support grid Spider
- 14. Fixed Beds: Manual Loading • Key points – use hopper or supersack with attached sock – move sock to ensure uniform distribution – catalyst freefall • maximum 3 ft (1m) • minimum 1 ft (0.3 m) – try to keep sock full – cut sock as vessel fills
- 15. Fixed Beds: Manual Loading Charging tube - fixed position More smaller particles: higher pressure drop Support Grid Catalyst Support More larger particles: lower pressure drop Distribution issue