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.

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