Sulfiding of Sour Shift Catalyst

Sulfiding of Sour Shift
Catalyst
VULCAN Series
VIG SGS-201/202/203
Gerard B. Hawkins
Managing Director

Introduction to Sour Shift Catalysts
VIG SGS-201/202/203
 Feedstock's from the gasification of coal or heavy oil
contain high levels of sulfur.
 Conventional iron-chrome catalysts are not suitable
 “Sour” or “Dirty” shift catalysts were developed.
 These catalysts achieve maximum activity in the
sulfided state.
 Require treatment with Sulfur prior to start-up.
 Can only be used in streams that contain sufficient
sulfur to maintain them in this state

Introduction to VULCAN Catalysts
Sulfiding VIG SGS-201/202/203
 Sulfur can be supplied from the process gas stream or a
separate sulfiding agent.
 Sulfiding agents are typically H2S, COS, or CS2
 Sulfiding agent to be added at 60kg of Sulfur per tonne
of catalyst at a uniform rate over 24-36hrs.
 The process is typically carried out at 200-300oC
 Initial heating carried out in dry inert gas
 The end of sulfurization is determined by a high
increase of H2S outlet of the reactor.

CoO + H2S ↔ CoS + H2O ∆H = -
13.5kJ/mol
MoO3 + 2H2S + H2 ↔ MoS2 + 3H2O ∆H = -
48.3kJ/mol
CS2 + 4H2 ↔ CH4 + 2H2S ∆H = -242.6kJ/mol
COS + H2O ↔ CO2 + H2S ∆H = -35.3kJ/mol

CO + H2O ↔ CO2 + H2 ∆H = -
41.2kJ/mol
CO + 3H2 ↔ CH4 + H2O ∆H = -
215.7kJ/mol
• The shift reaction starts when process gas is introduced
at temperatures around 200oC.
• Methanation occurs at higher temperatures and
pressures.

 The aim is to add sufficient sulfur to fully
activate the catalyst without generating
excessive heat.
 The control of temperature is essential!
 The sulfiding is usually carried out using the
main process stream itself.
 However, it is possible to use a separate
recycle system.

 Probability of methanation reaction is high,.
Especially at higher pressures.
 Reactor should be nitrogen purged and heated to
220oC at a rate of 50oC/hr, at a pressure of 10bar
 Wet gas is added to the nitrogen, 25% Wet
gas:75% Nitrogen.
 After 15-30 minutes a temperature rise is
observed due to the starting of the shift reaction
(1) Using process gas

 Once conditions are stable the wet gas rate can
be increased by a factor of 2 and the nitrogen
rate decreased proportionally to maintain the
linear gas velocity.
 At this point additional sulfur compounds can be
added to speed up the sulfiding process
 Sulfur concentration exit the bed should be
carefully monitored throughout.

 The reactor should be purged free of oxygen
and heated to about 220oC in a stream of inert
carrier gas containing 10% hydrogen.
 The temperature rise due to the sulfiding
process must be limited to 20oC.
 Sulfur is added at 50% of the required rate to
begin with until the condition settle then the
rate can be increased.
 Significant break through of sulfur at the exit
of the last bed indicates sulfiding is close to
completion.
(2) Using a recycle loop

 At this stage the temperature should be
increased at a rate of 15oC/h to 280-300oC.
 In multi-bed systems it may be necessary to
increase Bed 1 inlet temperature to above 300oC
 Temperatures above 350oC should be avoided.

VULCAN Catalysts Sulfiding
Experience
– Ammonia plant East Asia
– The plant is being adapted to accept a coal
slurry feedstock via a single gasification unit.
– New shift train comprising 3 reactors using the
more active sulphur tolerant shift catalyst.
– Two beds of VULCAN Catalysts followed by two
beds of a local competitors catalyst.
Introduction

Experience
SHE
 Site safety systems were none existent
 Limited use of PPE
 No safety induction
 House keeping was poor by any standards
 There was no evidence of a permit to work
system

Experience
– The Reactors were heated in a recirculating
stream of nitrogen to 220oC over a period of
22hours.
– The procedure stated that the reactors should
be heated to 120oC and held at that
temperature for 4 hours.
– Process gas from the POX unit (H2:CO ratio
1:1) was introduced to produce 10% H2 at the
outlet of the Nitrogen blower.
The Sulfiding Process – Take 1

Experience
– Beginning with a targeted rate of 60kg/h, CS2
was added to the recirculating gas.
– A purge from the recycle loop was used to
keep the CH4 content to <20% of the N2
content.
– Water generated from the sulfiding process
was periodically drained from the knockout
drum
It quickly became apparent that:
•The CO content of the loop was low
•The H2S at the inlet of bed 1 was high
•The H2 content was quickly decreasing

Experience
The client then communicated that the CS2 flow meter was
faulty and the laboratory analysis was unreliable.
Further analysis indicated low CO, high CO2 and a very low
H2 content.
Conditions were proving to be particularly unstable and the
laboratory analysis look increasingly unreliable.
The sulfiding was abandoned after convincing the customer
to sulfide using make-up gas instead of process gas!

Experience
– Recycle loop purge to reduce the CO2 and H2S
levels in the loop.
– A make-up gas stream (75% H2) was
introduced to maintain a H2 content of >10%.
– A new CS2 flow meter was also installed which
also turned out to be faulty.
– Once conditions were stable, bed 1
temperature was increased to 240oC and CS2
addition increase to around 90kg/hr.
– Temperature continued to be increased until
Bed 2 temperature reached 280oC.
The Sulfiding Process – Take 2

Experience
– The sulfiding was completed over 33hours.
– The total CS2 consumed was 5.4Te, the
catalyst required 2600kg CS2.
– Upon completion the client was advised to
purge the loop, lower the bed temperatures to
approx. 60oC and store under positive N2
pressure.
– The client was also advised that a process
stream which does not contain Sulfur should
not be passed over the catalyst.

Experience
 The sulfiding was believed to be successful
based upon consumption of CS2, the control of
bed temperatures, the control of the H2
content and the duration.
 The client was concerned about how future
catalyst sulfiding would be carried out as the
MUG used would not be available.
 Two options were discussed: the use of
bottled H2 and using process gas without
recycling.

Sulfiding of Sour Shift Catalyst

Sulfiding of Sour Shift Catalyst

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