(WGS) Water Gas Shift - Loading & Unloading High Temperature Shift & Low Temperature Shift Fixed Beds: Catalyst Discharge

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