water-gas-shift reactor loading & unloading considerations
Post on 18-Dec-2014
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by: Gerard B. Hawkins
Managing Director, CEO
Water-Gas-Shift Reactor Loading & Unloading
Considerations
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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