Steam Reforming - Poisons

Steam Reforming - Poisons
Gerard B. Hawkins
Managing Director
WWW.GBHENTERPRISES.COM

 The aim of this presentation is to
• Introduce the various poisons
• Indicate actions that need to be taken if
catalyst is poisoned
• Effect of ultra purification

 Common poisons include
• Sulfur
• Chlorides and other halides
• Metals including arsenic, vanadium, mercury,
alkali metals (including potassium)
• Phosphates
• Organo-metalics

 Reduced catalyst activity
 In primary reformer this means
• Reduced reaction
• Reduced reaction heat load
• High tube/process gas temperatures
• More susceptible to carbon formation
• Hot bands

Hydrocarbon
Feed
Hydrogenation
Chloride
Removal
Sulfur
Removal

 Steam reforming catalyst requirements
 Poison Limit Effect
Sulfur <0.1 ppmv Poison
Chlorides <0.1 ppmv Poison
As/V/Pb/Hg <5ppbv Poison
Olefins <1-2 vol% Carbon
• Process gas feed to reformer (dry basis)
• Excludes Pre Reforming catalysts

 For Pre Reformers must be lower than for
primary reformers
 Sulfur specified at 25 ppb or less
 But needs to be checked using a space
velocity calculation
 Chlorides and Sodium are also poisons
 Silica is also an issue

• Sulfur Feedstock
• Chlorides/halides Feedstock
• Arsenic Vetrocoke
• Vanadium Benfield
• Mercury Feedstock
• Alkali metals Steam/BFW
• Phosphates Steam/BFW

Natural
Gas
Associated
Gas/LPG
Refinery Off
Gas (ROG)
Naphtha
Hydrogen Sulfide X X X X
Mercaptans (low) X X X X
Carbonyl Sulfide X X X
Mercaptans (high) X X
Thiophenes X

• Vast majority of poisoned
reformers are affected by Sulfur
• Many problems with sulfur
analysis
• At more than 5 ppm will cause
severe and rapid deactivation
• At 20-30 ppb will lead to slow
deactivation
• Nickel is excellent sulfur
absorbent
• At high enough levels will
completely de-active catalyst
Pellet
S
SS
S
S
S
S
S
S S
Nickel
CH
H O
4
2

 Sulfur less ‘sticky’ at high temperatures
 Only affects upper parts of tube
 Little affect lower down - usually hot bands are
so bad that catalyst is changed out prior to
affecting bottom part of tube
 Poisoning is generally reversible - can steam
 May lose some activity
 Particularly if low inlet temperature

 Sulfur can be passed to reformer if
• ZnO saturated - difficult to test
• COS in feed gas and not hydrolyzed over
ZnO
• Organics in feed with no CoMo/NiMo
• Plants with NG bypass to secondary
• Bypass around HDS/ZnO
◦ DP Tappings
◦ Bypass lines
◦ Incorrect valves open
• Leaks on HDS interchangers

COS not as common as H2S, mercaptans
COS + H2O H2S + CO2
Reacts over CoMo/NiMo at typical conditions
or
Over ZnO that contains some alumina
NOTE: COS is not removed by amine systems

 Zinc Oxide will remove some COS provided
that there is alumina in support
 As with VSG-S201- series
 Competitors have no alumina
 Organic sulfur compounds (mercaptans)
pass through zinc oxide

• Difficult to set up analysis
• Tests are difficult
• Tests not accurate
• Looking at low levels
• Generally looking for sulfur at detection limit
of the laboratory equipment
• Limit is 10 ppb
• ZnO will slip about 10 ppb

• Problems of sampling
• Pipe work must be of stainless
• Sulfur absorbs into Carbon Steel
• Will absorb into stainless but at lower rate
• Short pipe runs
• Prevent absorption
• Sample keeps for four hours
• In a stainless steel sample bomb
• Use plastic sample bags if sample to be
transported

• Some sulfur is removed during shut down
• All shut downs include a steam out
• Bulk and surface different readings
• use surface
• Better to conduct full steam out
• Test condensate for sulfur compounds
• Or smell condensate (beware)

 Of benefit to most plants
 Effect most pronounced in tough conditions
◦ Low S/C operation where Carbon formation is likely
◦ Prereformers which are very sensitive
◦ GHRs where deactivation impacts heat transfer
◦ Heavy feed reforming where poisoning and carbon
formation determine life
◦ Heavily stressed reformers

 Together with ZnO at regular
operating conditions
◦ ZnO to remove bulk of sulfur (H2S)
◦ Followed by a layer of
Ultrapurification for polishing
 Cannot replace ZnO completely since
it has a lower saturation capacity
 Catalyst requires reduction prior to
use
 Can be pyrophoric on discharge -
similar to LTS

 Unfortunately, measuring low ppbv levels of
sulfur is difficult
 So proof has to come from lab/field work
 We wanted to test the concept
 So we chose a plant where we can measure
the effect of deactivation, a reformer we
know suffers from deactivation, and where
LTS catalysts are known to pick up sulfur

• Smaller, slower
decrease of GHR UA
expected in theory with
Cu/Zn
• Historical evidence
from plant that UA
settles to lower than
SOR value
UA v Days online
0.8
0.85
0.9
0.95
1
1.05
0 200 400 600
Without With

 Arsenic is a very virulent poison
 If a reformer has been poisoned by arsenic
then must clean tubes thoroughly
 If this is not done then arsenic will poison
then next batch of catalyst
 And continue to do so

• Most common as HCI or highly mobile ion
• Remove less than 5ppb
• Accelerates sintering in catalyst metal
crystallites
• Found in:
• Feed storage locations
• Crude and distillate oils
• Certain refinery processes

Effect of Chloride on ZnO Sulfur Removal Catalyst
1. Fresh ZnO 2. Poisoned ZnO
HCl
ZnO
Crystallites
Catalyst
Pores
ZnCl2 blocks
catalyst surface
and pores to
prevent sulfur
absorption

Location Elemental
Mercury
Concentration
(Micrograms/m3
)
South America 69 –119
Far East 58 –193
North Africa 0.3-130
Groningen 180
Middle East 1-9
Eastern US
Pipeline
0.019-0.44
Midwest US
Pipeline
0.001-0.10
North America 0.005-0.040

 Most steam reforming catalysts can handle
olefins
 Typically between 1-2%
 Can lead to rapid formation of hot bands
 If more than this then need to be treated in
HDS

Steam Reforming - Poisons

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