Shift Conversion Catalysts - Operating Manual

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Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance
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GBH Enterprises, Ltd.
Shift Conversion
Catalysts - Operating
Manual

Contents
Introduction
High temperature shift catalysts
Low temperature shift catalysts
Catalyst storage, handling, charging and discharging
Health and safety precautions
Reduction and start-up of high temperature shift catalysts
Operation of high temperature shift catalysts
Reduction and start-up of low temperature shift catalysts
Operation of low temperature shift catalysts
Information contained in this publication or as otherwise supplied to Users is
believed to be accurate and correct at time of going to press, and is given in good
faith, but it is for the User to satisfy itself of the suitability of the product for its
own particular purpose.
GBH Enterprises, Ltd., Catalyst Process Technology gives no warranty as to the
fitness of the Product for any particular purpose and any implied warranty or
condition (statutory or otherwise) is excluded except to the extent that exclusion
is prevented by law. GBH Enterprises, Ltd., Catalyst Process Technology accepts
no liability for loss or damage, resulting from reliance on this information.

INTRODUCTION
The water-gas shift reaction plays a major role in ammonia and hydrogen plant
design and operation. Good performance of the shift catalysts, and attainment of
a close approach to equilibrium and hence minimization of the CO slip from the
catalyst system is critical to the efficient and economic operation of the plant and
ensures maximum hydrogen production from the hydrocarbon feedstock. The
water gas shift (or shift reaction) is highlighted below.
CO + H2O ⇔ CO2 + H2
The reaction is exothermic and high conversions are favoured by low
temperature and high steam ratio.
Ammonia plants usually operate a two stage system – a High Temperature Shift
(HTS) followed by a Low Temperature Shift (LTS) – with a suitable form of inter-
bed cooling.
Hydrogen plant designs feature a number of differing shift conversion sections.
Commonly there is a high temperature shift stage followed by a PSA unit to
recover the product hydrogen. On occasions an intermediate temperature shift
(ITS stage) is used in preference to high temperature shift. On older hydrogen
plants, a two-stage system is often utilized in which an HTS is followed by an
LTS stage with suitable inter-bed cooling.
Modern catalysts for the high temperature shift stage operate typically in the
temperature range 300-450o
C (570-840o
F).
Corresponding operating temperatures for the low temperature shift section are
180-270o
C (355-520o
F).
This manual discusses the principles of start-up, operation and shut-down of shift
converters, and the information provided is sufficient for the preparation of the
detailed operating instructions which of necessity will be plant-specific.

High temperature shift catalysts
GBH Enterprises, Ltd., Catalyst Process Technology supplies its HTS catalyst
VULCAN Series VSG-F101 in two sizes. The catalysts are formulated from iron oxide,
chromia and copper oxide, and feature enhanced activity and efficient operation at low
steam to carbon ratios.
Composition
VSG-F101 iron oxide, chromium oxide, copper oxide
Physical and Chemical Properties
Appearance brown cylindrical pellets
Diameter 9 & 6 mm
Length 5 & 3 mm
Bulk Density ~1.5 kg/l
Radial crushing strength (before reduction)
196(long), N/cm
100(short), N/cm
S content 200 ppm
Fe2O3 80 %
Cr2O3 5.0-9.0 %
CuO 2.0 %
Ignition Loss 10.0 %

Low temperature shift catalysts
VULCAN VSG-C111 catalysts are based on copper oxide supported on a matrix
of zinc oxide and alumina. The established product, VSG-C111 is also available
in a smaller pellet size, to allow optimization of performance and pressure drop.
GBH Enterprises also offers VSG-C111 which is based on the standard catalyst
but is promoted with alkali oxides to minimize methanol by-product formation. A
smaller pellet size is also available.
In all cases, the copper oxide must be reduced to its active metal state before
use. This critical step in catalyst activation is highly exothermic and the
temperature of the bed must be strictly controlled to ensure maximum catalyst
activity. An inert gas such as natural gas or nitrogen should be used to dilute the
hydrogen used for the reduction reaction. All gases used in the reduction must be
free of catalyst poisons. The use of steam as an inert diluent during reduction
must be avoided as steam sinters the copper crystallites and therefore
deactivates the catalyst.
Composition:
VSG-C111 Copper oxide, zinc oxide, and alumina (W/ proprietary promoters)
Chemical and Physical properties (typical)
Appearance black cylindrical pellets
Diameter 5.0~6.0 mm
Length 2.5 & 5 mm
Bulk Density 1.2 - 1.4 kg/l
Radial Crushing Strength (before reduction)
65 (long), N/gr
60(short), N/gr
CuO 40±2.0 %
ZnO 43±2.0 %

Catalyst storage, handling, charging and discharging
Before charging, discharging and handling shift catalysts any potential risk to
health during these activities should be assessed and appropriate precautions
taken. In addition the GBH Enterprises Catalysts brochure on “Catalyst
Handling” should be consulted.
Drum storage
Shift catalysts are generally supplied in mild steel drums, fitted with polythene
liners, and having the following packaging details. Precise information will be
recorded in the documentation covering the goods when supplied.
Drums must not be stacked on their sides or stacked more than four drums high,
even when held on pallets. Taller stacks tend to be unstable and there is the risk
that the top drums may fall off the stack, and the lower drums can be crushed
due to the weight of the drums above them. The metal drums are usually suitable
for outside storage for a few months but should be protected against rain and
standing water. If prolonged storage is expected, they should be kept under
cover and away from damp walls and floors. The lids should be left on the drums
until just before the catalyst is to be charged. If the lids are removed it is
important that they should be replaced as soon as possible, so that
contamination of the catalyst is avoided. If the drum lid cannot be replaced, then
the catalyst should be redrummed without delay. If any contamination occurs it is
difficult to assess the extent of any damage without full examination of the
catalyst. If there is any doubt about the state of the catalyst it is best not to
charge it to the reactor.
Drum handling
Catalyst drums should be handled as carefully as possible. They must not be
rolled. Catalyst drums are often supplied on pallets, which reduces the likelihood
of damage in transit but requires suitable fork-lift trucks and a paved area to
handle the pallets. The fork-lift truck to be used for dismantling the pallets should
be fitted with rim or body clamps to avoid damage to the drums. The use of
shipping containers for either catalyst drums or palleted drums eases shipment
and further reduces the likelihood of damage in transit. It is important not to use
standard forks to lift the drums under the rolling hoops, as damage to the drums
and catalyst is almost inevitable.

Sieving catalyst
Shift catalysts are screened before they are packed into drums for dispatch,
hence sieving on site is not usually required, but in some instances attrition can
occur in transit if the drums are roughly handled. In this case some form of
screening is advisable before charging, especially if the catalyst appears to
contain dust on delivery. A good method of sieving is to pass the catalyst over a
simple inclined screen. This is often the most satisfactory method, since vibrating
screens can cause additional unnecessary damage and loss. The screen should
contain provision to collect the dust, and at the same time avoid generating a
dusty atmosphere. The mesh spacing should be about half the smallest
dimension of the catalyst pellet. While the catalyst is being poured over the
screen, the use of a vacuum system situated close to the sieve will control the
dust effectively.
Pre-charging checks
Before the catalyst is charged it is important that the condition of the catalyst
support grid in the vessel and any supporting materials such as inert balls are
checked. Any support or hold down material in the HTS converter should be of a
low silica type to prevent the possibility of silica poisoning of the HTS catalyst.
Some form of light metal shield or “spider” fitted into the discharge manhole
prevents an uncontrolled discharge of catalyst, when the manhole cover is
removed. The vessel should be clean, dry and free from loose scale and debris.
It is important to ensure that the charging level is clearly defined, so as to avoid
under filling or overfilling. The desired level can be marked with chalk before
charging is commenced.
It is strongly recommended that the operation of the thermocouples is checked
and their position noted to allow for temperature profile analysis during operation
of the catalyst. This can be done before charging commences by warming them
in turn to ensure that the correct indication is given on the instrument panel.

Charging the shift converter
The catalyst may be loaded directly from the drums or from intermediate bulk
containers. The general rules for charging catalysts into vessels are:
• The catalysts should have a free fall of between 50 and 100 cm (20-40
inches) to ensure a suitable packed density is achieved. (More than 100
cm/40 inches may damage the catalyst)
• The catalyst must be distributed evenly as the bed is filled, with a
maximum height difference of 15 cm (6 inches) across the bed when
completed.
Special procedures are required for loading tubular isothermal reactors. GBH
Enterprises, Catalysts Process Technology will advise on these procedures
on request.
Discharge of high temperature shift catalyst
The catalyst is usually discharged with large mobile vacuum extraction units.
Occasionally it may be discharged by gravity flow from the bottom of the
converter.
No special oxidation procedure is required before discharge. After cooling in
steam the catalyst is not pyrophoric although water hoses should be available in
case the catalyst overheats for any unexpected reason.
If catalyst has been operated in the fully sulfided state care will be needed during
discharge because iron sulfide is pyrophoric. The sulfur must either be removed
by steaming, which may take 2-7 days, or the catalyst should be discharged
under nitrogen or after drenching with water.
The normal shut-down procedure for inert discharge is as follows
1 Reduce pressure in the reactor at a maximum rate of 1-2 bar (15-30 psi)
per minute, or as governed by the mechanical design of the equipment.
Purge the reactor free of process gas with steam and cool to 150o
C
(300o
F).
2 Replace steam with inert gas and cool to ambient temperature that is to
say below 40°C (105°F).

3 Discharge the catalyst under a positive pressure of inert gas.
Alternatively the procedure is as follows:
1 Reduce pressure in the reactor at a maximum rate of 1-2 bar (15-30 psi)
per minute. Purge the reactor free of process gas with steam and cool to
150o
C (300o
F)
2 Replace steam with inert gas and cool to ambient temperature. That is to
say below 40°C (105°F)
3 Fill vessel with water and immediately drain off. Air can then be allowed to
enter the vessel as required in order to achieve an atmosphere where life
support is not required.
Discharge of intermediate or low temperature shift catalyst
The catalyst is usually discharged with large mobile vacuum extraction units or
by gravity flow from the bottom of the converter.
Reduced LTS catalyst is potentially pyrophoric and care must be taken when it is
to be discharged from the reactor. The usual procedure is as follows:
1 Reduce the pressure in the reactor at a maximum rate of 1-2 bar (15-30
psi) per minute, or as governed by the mechanical design of the
equipment.
2 Purge the vessel with nitrogen and cool to less than 40o
C (100o
F).
3 Discharge the catalyst under a positive pressure of nitrogen. This may be
done by vacuum extraction or by gravity flow from the bottom of the
converter. In the latter case as catalyst falls from the bottom manhole it is
sprayed with water, collected and dumped on a suitable site where it is
allowed to oxidize slowly.
In plants where there is insufficient available nitrogen for it to be used during
catalyst discharge air must not be allowed to enter the converter when it contains
reduced catalyst otherwise gross or localized overheating will take place. In
these situations it may be convenient to fill the converter with water, drain and
discharge the catalyst wet.

With this technique catalyst should not be allowed to sit in water for any length of
time otherwise catalyst breakdown can occur. Under these circumstances it is
advisable to drain the vessel as soon as possible after filling.
Also note that when reduced catalyst is wetted hydrogen will be generated;
hence ensure that precautions are taken to ensure an explosive atmosphere
cannot occur and that sources of ignition are controlled.
Special procedures are required for the discharge of tubular isothermal reactors.
GBH Enterprises, Catalysts Process Technology will advise on the
procedures on request.
Disposal of discharged catalyst
GBH Enterprises, Catalysts Process Technology offers advice on the
environmentally safe disposal of its complete product range.
Health and safety precautions
Before charging, discharging and handling shift conversion catalysts any
potential risk to health during these activities should be assessed and
appropriate precautions taken.
Entry into inert gas atmospheres
Extreme care is needed during a shut-down when an entry has to be made into a
vessel containing an inert gas. Such atmospheres do not support life and
personnel entering must wear a suitable breathing apparatus. Failure to do so
will result in loss of consciousness within seconds of breathing the atmosphere
followed within minutes by death. To avoid accidental entry of the vessels
openings must be kept closed. When personnel have to work inside the vessel,
prominent warning notices must be displayed. Everyone working within the area
should be made aware of the nature and dangers of asphyxia. They should know
how to affect a rescue and resuscitation of anyone who may be overcome. An
integrated life support system is essential with adequate back up. If a company
has no experience in such activities then the work is often best done by a
specialized service firm.

Discharged pyrophoric catalysts
Catalysts discharged in the pyrophoric state must be kept separate from
flammable materials. Transport of such catalyst should only be in metal
containers or metal-sided trucks. Dumps of the catalyst should be within reach of
water hoses so that any overheating that occurs can be controlled. High
temperatures can build up in heaps of discharged catalyst and it is a prudent
precaution to spread the catalyst thinly over the ground until the oxidation is
complete and under no circumstances should personnel be allowed to walk over
the catalyst until it has been fully stabilized.
Dust exposure
Short term exposure to the metals and metal oxides used in catalysts may give
rise to irritation of the skin, eyes and respiratory system. Over-exposure can give
rise to more serious effects. Material Safety Data Sheets (MSDS) should be
consulted for information. Catalysts should be handled as far as possible in well
ventilated areas and in a way that avoids the excessive formation of dust.
Operators who handle catalyst must wear suitable protective body clothing,
gloves and goggles. Inhalation of dust should be avoided, and the appropriate
occupational exposure limits should be strictly observed. If these limits are likely
to be exceeded then respiratory protection should be used. Everyone involved in
the handling operation should clean up afterwards and, in particular must wash
before eating. Clothing should be changed at the end of each shift, and more
frequently if contamination is heavy.
Ergonomics
Physical hazards arise from the handling of drums, material and lifting
equipment. Personnel should be aware of these and appropriate precautions
taken.

Reduction and start-up of VULCAN Series VSG-F101
When the reactor has been charged the high temperature shift catalyst must be
reduced before it can be used. The reduction of high temperature shift catalyst is
invariably carried out with process gas under conditions that allow the haematite
to be converted to magnetite without further reduction to metallic iron. Reduction
also converts any of the small quantity of residual hexavalent chromium (CrO3) to
trivalent chromium (Cr2O3).
3Fe2O3 + H2 → 2 Fe3O4 + H2O ΔH = -16.3 kJ/mol
3Fe2O3 + CO → 2 Fe3O4 + CO2 ΔH = +24.8 kJ/mol
2CrO3 + 3H2 → Cr2O3 + 3H2O ΔH = -684.7 kJ/mol
2CrO3 + 3CO → Cr2O3 + 3CO2 ΔH = -808.2 kJ/mol
It is very important that steam should be present during the reduction procedure
in order to prevent over-reduction of the catalyst. It can be shown that if the
H2O/H2 ratio exceeds 0.18 at 400o
C (750o
F) or 1.0 at 550o
C (1020o
F) then the
desired magnetite is the stable phase. Similarly, the CO2/CO ratio should exceed
1.16 at 400o
C (750o
F) or 1.0 at 550o
C (1020o
F). The graph below summarizes
the conditions necessary to prevent the reduction of Fe3O4 to metallic iron in
hydrogen and steam mixtures.
Figure 1 Minimum H2O to H2 Ratio for HTS Catalyst Reduction

During catalyst reduction it is preferable to avoid the condensation of water in the
catalyst bed. If possible, therefore, the catalyst should be heated in an inert gas
stream to a temperature that will prevent the condensation of steam before
process gas is admitted to the reactor.
All HTS catalysts contain a small amount of residual sulfate that is converted to
H2S during the reduction procedure. Low temperature shift catalysts and some
CO2 removal systems are sensitive to sulfur and it may be necessary to include a
desulphurization step during the start-up of some HTS catalysts.
The level of residual sulfur is so low in VSG-F101, that no special
desulphurization step is usually needed.
Reduction and start-up
In plants based on steam reforming of hydrocarbons no separate reduction
procedure is required for the HTS catalyst as the introduction of process gas
serves to activate, desulfurize and commission the catalyst bed. It is therefore
convenient to bring the catalyst on-line as follows:
1 Purge the reactor free of air with an inert gas and heat the catalyst above
the condensation temperature at a rate of about 50o
C (90o
F) per hour.
2 Care should be taken to ensure that the catalyst is not dried excessively
prior to reduction. This can occur if the catalyst is held in hot nitrogen
circulation for an excessive period (24 hrs+), for example if there are
problems elsewhere in the plant during start-up. When wet process gas is
introduced to the dried oxidized catalyst, structural changes that are
exothermic can be initiated, leading to temperatures in excess of 450o
C
(840o
F).
To avoid this phenomenon, introduce process gas as soon as possible
after the catalyst is hot enough, or suspend nitrogen circulation whilst
problems elsewhere are attended to once the bed is up to temperature.
Should an exotherm occur when process gas is admitted, continue
introducing feed to remove the heat generated, and keep the vessel at low
pressure. If excessive drying is suspected, it is possible to rehydrate the
catalyst by controlled addition of steam, obviously monitoring
temperatures carefully whilst small amounts of steam are introduced.

It should be noted that this phenomenon only occurs on the initial start up
of the HTS catalyst and does not occur on subsequent start-ups.
3 Establish a flow of process gas or steam through the reactor at a wet gas
space velocity in the range 200-1000 h-1
. Allow any water that does
condense on the catalyst to drain from the vessel. VSG-F101 reduction
will start at about 150o
C (300o
F), if hydrogen is present and so process
gas can be utilized at an early stage during heating.
4 Increase the catalyst inlet temperature at a rate of 50o
C (90o
F) per hour
until the bed temperature reaches 300o
C (570o
F). Reduction will continue
gradually until the normal operating temperature is reached.
5 The high temperature shift reaction will gradually begin at temperatures in
the range 300-320o
C (570-610o
F) and a temperature profile will develop
through the bed. The temperature rise will be about 13.5o
C (24o
F) for
every 1% of carbon monoxide (in dry process gas) that is converted. It is
important, therefore, to restrict the amount of carbon monoxide and/or the
bed inlet temperature to prevent the bed outlet temperature exceeding
500o
C (930o
F) during the reduction procedure.
6 If required any residual sulfur in the catalyst will be converted to hydrogen
sulfide at bed temperatures in the range 350-400o
C (660-750o
F). It is
therefore necessary to maintain the catalyst bed at these temperatures for
a period long enough for the sulfur to be completely reduced. Bed inlet
temperature should be increased to at least 370o
C (700o
F). VSG-F101
contains less than 0.025% w/w sulfur and the desulphurization period
should be only about 4 hours from the first introduction of process gas. It
is usual to bring the catalyst on line without the need for a special
desulphurization step. It may be prudent to check the sulfur content in the
outlet stream before bringing the LTS on-line.
7 Increase the process gas rates and adjust the bed inlet temperature to the
start of run operating value.
The above procedure is chosen as a reasonable compromise between energy
use and stress on the plant equipment. It should be used during the first
reduction of a new catalyst in order to avoid condensation on the catalyst, which
can leach any soluble chromium (Vl) from the catalyst, weakening its structure
and reducing its life. During subsequent start-ups, plant equipment permitting,
steam or normal process gas can be used to warm up the catalyst from cold, and
heating rates of 100-150o
C/h (180-270o
F/h) can be employed without any
detrimental effect to the catalyst.

Greater care must be taken if the catalyst has been wetted during the shut-down,
and in this case the catalyst must be warmed up slowly at first to allow the pellets
to dry out. Once this has been achieved, heating rates can be increased to 100-
150o
C/h (180-270o
F/h).
Operation of VULCAN Series VSG-F101
Plants based on steam reforming usually incorporate an HTS stage followed
either by a PSA unit or a LTS, CO2 removal and methanation stages. Whatever
the plant design, it is usual to operate the HTS catalyst to give maximum carbon
monoxide conversion. In plants with more than one shift reactor, a more flexible
operation is possible and bed temperatures must be carefully optimized.
Optimum conditions can usually be determined by trial and error. When
requested, GBH Enterprises, Ltd., Catalyst Process Technology will give advice
based on calculations using its own specialized computer programs.
The HTS reactor is integrated with the process heat recovery system. It is usually
preceded by, and in many modern plants also followed by, a waste heat boiler.
The flexibility of the HTS inlet temperature can therefore be limited by steam
requirements and boiler performance so that operation under optimum conditions
will not always be possible.
The normal life of HTS catalysts in ammonia and hydrogen plants is 3-5 years
although in some cases it can be longer. End of life may be indicated by an
increase in carbon monoxide slip and the end of the temperature profile moving
towards and through the end of the bed. It is normal practice, at the start of life,
to take advantage of the high initial activity of these catalysts by running at a low
inlet temperature (around 300o
C/570o
F), although in some cases this cannot be
achieved due to limitations with the upstream or downstream heat recovery
requirements. As the catalyst ages and loses activity over its operational life, it is
necessary to raise the inlet temperature gradually to maintain the minimum CO
slip, which corresponds to the maximum CO conversion and maximum
temperature rise across the bed. Over the life of the catalyst the inlet temperature
would typically rise 30-40o
C (54-72o
F) depending on the initial inlet bed
temperature.
Catalyst operating life may also be shortened as a result of high pressure drop
caused by the accumulation of deposits on the top of the catalyst bed.
Depending upon the position of the deposits in the bed, it is sometimes possible
to remove these deposits by using a vacuum device during a convenient plant
shut-down.

If the deposits are lying in the top section of the bed then this technique can be
very effective, and an extension of the operating life may be achieved. If the
deposits have migrated down into the main body of the bed, then vacuuming will
be of limited use.
Loss of activity under normal conditions is usually caused by slow thermal
sintering, in which the small magnetite crystals agglomerate together in spite of
the stabilizing effect of the chromia. The larger magnetite crystals have a lower
active surface area, and hence the catalyst activity decreases. The higher the
temperature the greater the rate of sintering. In addition, the effects of certain
poisons such as silica can reduce catalyst activity and life.
Temperature profile
Performance of the catalyst may be monitored during operation by the slope of
the temperature profile together with the corresponding increase of outlet carbon
monoxide concentration towards the end of life. The temperature profile should
not move down the bed unless there are unusual problems. These may be
deposition of solids such as soda, silica, potash etc from upstream equipment
(such as a waste heat boiler leak or high silica refractory), which block the bed
and interfere with gas flow. The most common symptom of blockage is
increasing pressure drop.
Common problems can usually be identified from routine measurement of bed
temperatures, pressure drop through the bed and analysis of outlet carbon
monoxide concentration. Advice should be requested from GBH Enterprises as
soon as any unusual conditions are experienced.
Deposition of solids in the catalyst bed
If any solids are deposited on the top of the catalyst bed causing increased
pressure drop they should be removed. It is then possible to purge the reactor
with inert gas and vacuum extract any contaminated catalyst together with the
deposit from the top of the bed.
Caution: great care should be taken and procedures well defined before a person
enters a vessel containing an inert atmosphere.
Depending on the quantity of catalyst that has been contaminated by the deposit
it may be necessary to replace with an equivalent volume of new catalyst. No
special reduction procedure will be required for the new catalyst.

Sulfur
During use the catalyst will establish an equilibrium with any sulfur that is present
in the inlet gas. Any unexpected sulfur entering the catalyst vessel will be
retained by the catalyst as iron sulfide and then slowly released as normal
conditions are resumed. In steam reforming flowsheets the inlet sulfur level
should be much less than 1 ppm. However, a HTS catalyst may be used
downstream of coal-based or partial oxidation units where the sulfur levels may
be significantly higher. For concentrations of sulfur compounds less than 200
ppm in the inlet gas there should generally be no significant effect on the
catalyst. Above this level bulk FeS will be formed which has only about half the
activity of magnetite and allowance for this must be made in the initial design
calculations. Frequent cycling between sulfiding and non-sulfiding conditions
should be avoided although the catalyst is strong enough to withstand occasional
cycling during plant mal-operation.
GBH Enterprises can also offer VULCAN Series VIG SGS201/202/203, a
cobalt molybdenum catalyst, which has been developed for shift conversion in a
high sulfur environment. Details are available from GBH Enterprises, Ltd.
Catalyst Process Technology’s web site, at www.gbhenterprises.com
.
Shut-down
During a short shut-down VSG-F101 may be left in an atmosphere of process
gas or steam at operating pressure and temperature. This can result in a partial
oxidation of the catalyst that will be reduced rapidly during restart.
If the vessel is likely to cool during the shut-down period it should be purged with
an inert gas to prevent condensation of water. In addition the vessel drains
should be checked and any accumulation of condensate within the vessel
drained off.

Reduction and start-up of VULCAN VSG-C111 catalysts
LTS catalysts must be reduced with hydrogen before use. This procedure
converts the stable copper oxide component of the new catalyst into reactive
copper metal. During reduction and operation both the zinc oxide and alumina
components are unchanged and act as a support, which stabilizes the copper
metal crystallites and as a reservoir for poisons.
CuO + H2 → Cu + H2O ΔH = -81 kJ/mol
Since the reaction is exothermic, the reduction generates large quantities of heat
and depends on having equipment available to pass diluent inert gas through the
LTS reactor.
The easiest procedure is to pass a continuous stream of inert gas, usually
methane or nitrogen, through the catalyst bed on a “once through” basis.
Although this method can be relatively expensive it has the advantage of allowing
a high space velocity during reduction, which will complete the procedure in
about 12-24 hours. The alternative procedure is to recycle inert gas, usually
nitrogen, through the catalyst bed via a special reduction loop, which also
includes a recycle compressor and start-up heater. Space velocity will be limited
by the capacity of the recycle compressor but should preferably be at least 300 h-
1
Care should be taken to ensure that the inert carrier gas is free from reducing
components (such as hydrogen or CO) and oxidizing components (oxygen). In
the event that natural gas is used as the inert carrier the quantity of heavier
hydrocarbons should be minimized as such hydrocarbons can crack over copper
catalysts. The carrier gas should also be free of catalyst poisons such as sulfur
or chloride.
With recycle systems there are several important points to remember
1 If the reformer is being used as the start-up heater, then carbon dioxide,
evolved from residual carbonates in the LTS catalyst, may methanate and
the product methane can crack on the nickel based reforming catalyst in
the reformer and thereby deposit carbon. There are various procedures to
prevent this from happening and GBH Enterprises, Ltd. Catalyst
Process Technology can provide recommendations if required.
2 The concentration of hydrogen entering the LTS catalyst bed should not
exceed 0.5% v/v during the early stages of reduction in order to limit the
temperature rise if unreacted hydrogen builds up in the recycle loop.

3 In some cases the “minimum gas density limit” of the compressor may restrict
the maximum hydrogen concentration in recycle gas during the final stages of
reduction.
4 Water evolved from the catalyst during reduction must be removed from the
closed recycle loop and not be recycled through the catalyst bed.
5 Hydrogen and nitrogen streams need to be free from water and oxygen that
will interfere with the reduction. Nitrogen should be free of hydrogen as this
can lead to excess hydrogen being fed to the catalyst.
Reduction procedure
The following reduction procedure is recommended for use in plants with facilities
for either “once-through” or “circulating recycle” systems for catalyst reduction.
1 Purge the reactor with inert gas until all oxygen has been removed.
Establish a flow of inert gas and heat the catalyst bed to 120o
C (250o
F) at
a rate of 50o
C (90o
F) per hour or as governed by the mechanical design of
the equipment. Any convenient pressure, up to operating pressure, may
be chosen for the catalyst reduction. In a circulating system a high
pressure is normally preferred as it allows a higher gas flow to be
achieved in the system, and the higher partial pressure of hydrogen helps
the reduction.
2 Increase the inert gas flow rate to the maximum space velocity possible.
Ensure that both the hydrogen flow meter and analyzer are operating
satisfactorily as the temperature approaches 130o
C (265o
F). Continue
heating the catalyst until the top of the bed is at 180o
C (355o
F). The
temperature of the inert gas should not exceed 210o
C (410o
F) during the
initial heating. If the inert gas space velocity is less than 300 h-1
more care
is necessary as there can be poor gas distribution that can lead to
localized overheating. Start recording bed temperatures during warm-up to
confirm that the thermocouples are responding correctly and that the gas
is well distributed through the bed.
3 When at least the top third of the catalyst bed has reached 160o
C (320o
F)
hydrogen should be introduced into the carrier gas entering the bed up to
a maximum of 1.0% v/v. Once the reduction reaction has started it will be
necessary to record the temperature at different points in the catalyst bed
to determine the progress of the temperature profile at regular time

intervals. If the reduction reaction is slow with a bed inlet temperature of
180o
C (355o
F) then the inlet temperature should be raised cautiously to
190-200o
C (375-390o
F) and held steady at the temperature which gives a
satisfactory reduction rate.
4 Once reduction has started and a steady temperature profile has been
established, the hydrogen concentration should be increased. With
nitrogen as carrier gas the hydrogen concentration can be increased to
1.5% v/v and with natural gas as carrier gas the hydrogen concentration
may be increased to 2.0-2.5% v/v. The peak temperature in the bed
should not, however, exceed 230o
C (445o
F) and the hydrogen
concentration should be changed as necessary to control the temperature
rise and thereby limit the peak bed temperature. Once reduction has
started it may be possible to decrease the temperature of inlet gas
entering the catalyst bed to 180o
C (355o
F) or less. The temperature rise
for 1% hydrogen is typically 30o
C (54o
F) in nitrogen and 20o
C (36o
F) in
natural gas.
5 As the reduction proceeds, the temperature profile will move down the
catalyst bed. The temperature rise will decrease when most of the copper
oxide has been converted to copper. At this point the catalyst bed inlet
temperature may be raised to 200o
C (390o
F). The inlet hydrogen
concentration can also be increased to 3-5% v/v provided that the
maximum temperature limit of 230o
C (445o
F) in the catalyst bed is not
exceeded.
6 When the catalyst reduction appears to be complete the catalyst bed inlet
temperature should be raised to 225-230o
C (435-445o
F) and then if
possible, the inlet hydrogen concentration in the inert gas should also be
increased to 20% v/v. This procedure should take not less than two hours.
No temperature rise should be observed and the maximum catalyst
temperature should not exceed 230o
C (445o
F). Analysis should indicate
that the hydrogen concentration inlet and exit of the catalyst bed are within
0.2% of each other.
7 The catalyst reduction is complete and the reactor should be
commissioned.

Controlling the catalyst reduction
The reduction procedure has been designed to limit the temperature rise in the
catalyst bed by restricting the hydrogen concentration. This ensures that the
maximum temperature in the bed does not exceed 230o
C (445o
F) and the
maximum catalyst activity is achieved. The reduction reaction is indicated by the
temperature profile which moves from the inlet to exit of the catalyst bed at a rate
which depends on inert gas space velocity, hydrogen concentration and bed inlet
temperature.
During the whole of the reduction period it is important that operators should
determine the inlet and exit hydrogen concentration at regular intervals. The
difference between these two measurements during the time of the reduction
represents the volume of hydrogen consumed. Any oxygen present in carrier gas
will also react with hydrogen to form water. Normally the volume of hydrogen
required for the reduction is 185 Nm3
/m3
(195 scf/ft3
) for VULCAN Series VSG
C111 catalysts. A comparison of the hydrogen consumed against the theoretical
consumption should be made as a cross check against the progress of the
reduction.
The volume of water forming during the reduction procedure will also provide an
indication of the progress. Measurement of water produced should only be used
as a rough check on hydrogen uptake. VULCAN Series VSG C111 catalysts will
produce 240 kg water/m3
(15 lb water/ft3
) catalyst, from the reduction process.
Water formed from oxygen present in the inert gas should not be included in any
estimate. Again this can be used as a cross check against the progress of the
reduction.
Catalyst reduction is virtually completed when the inlet and outlet hydrogen
concentrations are the same and the whole bed is above a temperature of 225o
C
(435o
F). The volume of hydrogen consumed should confirm this. It may be
difficult to achieve exactly equal hydrogen concentrations at inlet and outlet of the
bed and reduction may be considered complete when the difference between the
two measurements has been less than 0.5% v/v for more than four hours.
Any complex copper-zinc basic carbonates present in the catalyst decompose
during reduction and release carbon dioxide. Carbon dioxide can be purged from
the recycle system but if for any reason the catalyst reduction procedure is
halted, or the catalyst bed isolated at reduction temperature, then any further
carbon dioxide evolution will lead to an increase in reactor pressure. Pressure
should therefore be monitored during the time that a reactor is isolated, when it
contains partially or freshly reduced catalyst, and any increase in pressure
controlled by venting.

In addition, if the reactor is to remain isolated for any length of time after the
reduction is completed but before it is commissioned, catalyst bed temperatures
should be monitored frequently. If any increase in temperature is detected the
reactor should be immediately purged with inert gas to avoid any rapid
temperature rise.
Hydrogen source
Almost any gas containing hydrogen is suitable for the reduction e.g. methanator
gas, carbon dioxide removal or high temperature shift reactor effluent gas.
Hydrogen should be free of sulfur or chlorine and, if any carbon monoxide is
present, allowance should be made for the extra temperature rise during
reduction.
Natural gas
Natural gas is used as the inert carrier gas during reduction in many natural
gas/steam reforming plants. Any high molecular weight hydrocarbons in the
natural gas can crack in the pre-heater at temperatures below 300o
C (570o
F) to
produce hydrogen. Most types of natural gas have been safely used at a
maximum catalyst temperature of 230o
C (445o
F) so it is recommended that care
should be taken in measuring the hydrogen concentration carefully at the catalyst
bed inlet and that the bed temperature be carefully controlled.
Start-up
If the catalyst has already been reduced but is cold, the bed should be warmed to
a temperature above the dew point with inert gas before process gas is
introduced to the reactor. When process gas first contacts the catalyst the bed
temperatures will usually increase rapidly as the reaction comes to equilibrium
with process conditions.
The peak temperature may reach 260o
C (500o
F) or higher at this stage but there
will be no damage to the catalyst because the peak will quickly pass through the
bed. The high temperature can be moved quickly through the bed by increasing
the flow of process gas to design rates as soon as possible. The catalyst bed
inlet temperature should also be held as low as possible provided that it is at
least 20o
C (35o
F) above the dew point. For most duties this corresponds to an
inlet temperature of about 200o
C (390o
F). If there are particular reasons for
avoiding a temperature peak there are several ways by which it can be
minimized.

1 By increasing reactor pressure to design level with inert gas before
introducing process gas.
2 Introducing process gas at low pressure while venting gas at the reactor exit.
This is particularly easy after reducing catalyst with a ‘once-through’ flow of
natural gas by gradually replacing the flow of natural gas by process gas and
then opening the inlet and exit valves fully while closing the vent to
commission the reactor.

Operation of VULCAN Series VSG-C111 catalysts
It is important to operate the LTS catalyst under optimum conditions to achieve
the potential savings in plant costs. The LTS catalyst is sensitive to changes in
operating conditions but it is not difficult to maintain fixed steam ratio, pressure
and gas composition so that the only real variable is the catalyst inlet
temperature. During the commissioning procedure the bed inlet temperature is
gradually increased until the carbon monoxide concentration in exit gas falls to
the minimum level for the conditions. This is the optimum level for maximum CO
conversion and at higher inlet temperatures the carbon monoxide level will again
increase. As the catalyst ages or is poisoned it will be necessary to increase the
inlet temperature to maintain the minimum carbon monoxide concentration in the
exit gas.
LTS catalysts often operate close to condensation conditions during the early
part of the catalyst life. To avoid condensation of water either in the catalyst
pores or onto the bed the inlet temperature should be at least 20o
C (35o
F) above
the dew point at all times. This may mean that operation will be at temperatures
higher than the optimum until catalyst activity has fallen sufficiently for the actual
and optimum operating temperatures to correspond. This is not a problem
because at temperatures in the range 200-205o
C (390-400o
F) the difference
between the equilibrium outlet carbon monoxide concentration and the optimum
will be very small and the actual outlet concentration will remain constant for a
long period.
During the normal operating life of the catalyst, optimum operating conditions can
be maintained by a gradual increase of the bed inlet temperature as soon as the
carbon monoxide level increases slightly. Whenever changes in steam ratio or
gas composition occur the bed inlet should be checked to ensure that it is still at
the optimum level. This should be done by increasing or decreasing the bed inlet
temperature by 5o
C (10o
F) and then checking the carbon monoxide concentration
at the bed outlet when conditions have stabilized. If a decrease in the carbon
monoxide concentration is detected the procedure is repeated until the minimum
level has been reached. A simple way of determining CO slip is to observe the
methanator temperature rise if the flowsheet features this reactor. Minimum CO
slip from the low temperature shift will correspond to the minimum temperature
rise across the methanator.
Towards the end of the catalyst life the bed exit temperature will often reach the
design level, which might occasionally correspond to the specified maximum
operating temperature of 250o
C (480o
F). This is however a conservative figure
and operation up to at least 270o
C (520o
F) will still be possible.

At higher temperatures however the deactivation rate for partially poisoned
catalyst is faster and the carbon monoxide equilibrium level becomes
increasingly unfavorable. Operation with high outlet carbon monoxide
concentrations will become increasingly expensive. It is usually more economic
to plan a catalyst change before the performance deteriorates beyond the design
level.
By-product formation
Methanol and, to a lesser extent amines formed from methanol produced in the
LTS converter and any nitrogen compounds inlet the converter (such as
ammonia formed in the secondary reformer), are formed in low temperature shift
catalyst beds, particularly in the early stages of life when catalyst activity is at its
maximum. By-product formation is very sensitive to temperature and can be
minimized by running with a low inlet temperature. This is consistent with
maximizing CO conversion. As ageing occurs, by-product formation is reduced.
If operators require ultra-low methanol by-product formation, then GBH
Enterprises, Ltd. Catalyst Process Technology should be consulted.
Temperature profile
The temperature profile through the catalyst bed is a useful indicator to follow
changes in catalyst activity especially when the outlet carbon monoxide
concentration is at the equilibrium level. For a fresh catalyst most of the reaction
and the corresponding temperature rise will be at the top of the bed. Loss of
catalyst activity (or catalyst deactivation) during operation is largely due to
poisoning. Because the catalysts are “self-guarding” poisons accumulate at the
top of the catalyst bed. The temperature profile will therefore gradually move
from the inlet towards the exit of the catalyst bed as more poisons are absorbed.
Towards the end of the catalyst life when the reaction zone has reached the
bottom of the bed and the outlet carbon monoxide level has started to increase
from the equilibrium concentration, the catalyst should be changed.
Any variation from a typical temperature profile will indicate abnormal conditions.
1 A slow increase in bed temperature giving a flatter than average profile
can indicate that the whole catalyst bed has been partially deactivated.
This may be due to the presence of liquid water in the bed that would
block the catalyst pores and wash poisons from the top of the catalyst
down to the middle or bottom levels. The catalyst may also have been
overheated.

3 If the temperature profile appears to be normal but the outlet carbon
monoxide is higher than expected then gas may be bypassing part of the
catalyst bed.
Steam
The use of steam alone should be avoided as far as possible to prevent
condensation of water in the catalyst bed. During plant upsets, short periods of
steaming may be unavoidable but it is far better to isolate the low temperature
shift reactor and reduce pressure to depress the dew point. The reactor should
then be purged with an inert gas.
Shut-down
During an extended plant shut-down, when the reactor can cool down, process
gas must be purged from the reactor to avoid the condensation of water on to the
catalyst. This could damage the catalyst by washing poisons from the top to the
bottom part of the catalyst bed onto fresh unpoisoned catalyst lower down the
bed. Pressure should therefore be decreased to atmospheric, before the
temperature falls below the dew point, and the vessel purged with an inert gas to
remove all steam.
Catalyst poisons
Sulfur and chloride are the most serious poisons for LTS catalysts. Of the two,
chlorides are the more virulent; however, sulfur tends to be present in greater
concentrations in the process gas and therefore often determines the catalyst
life.
Chlorine compounds are often present in process gas streams in extremely small
concentrations that cannot be detected by typical analytical procedures. The
poisoning effect is cumulative so that any concentration of chlorine in process
gas will eventually poison the catalyst bed and detection is only possible by the
analysis of samples then from discharged catalyst.
The formulation of GBH Enterprises, VULCAN Series catalysts to provide
thermally stable structures also enhances the ability of these catalysts to absorb
poisons. VSG-C111 series catalysts can absorb chlorides at the top of the bed
and guard active catalyst in lower layers, and so extend operating time.

Strict attention is necessary however to maintain steam purity and to avoid
contamination of feedstocks or process air by chlorine compounds. Solvents
containing chlorine should not be used for cleaning any items of plant equipment.
If chloride poisoning is an issue then GBH Enterprises, Ltd. Catalyst Process
Technology should be consulted.
Sulfur compounds also affect the operation of VSG-C111 series catalysts but are
much less virulent poisons than chlorine compounds. GBH Enterprises, Ltd.
VULCAN Series catalysts are self-guarding against sulfur compounds provided
that the typical levels found in ammonia or hydrogen plants based on steam
reforming are not exceeded for long periods.
Silica is also present in most process gas streams and is absorbed by the
catalyst bed and gradually deactivates the catalyst. Small amounts of silica are
deposited on the catalyst surface but larger quantities react with the catalyst to
form zinc silicate. Silica is not a typical catalyst poison but has the effect of
decreasing the catalyst’s capacity for other poisons and therefore allows chlorine
and sulfur to pass further into the catalyst bed.
Hydrogen and ammonia plants should always be designed to include sufficient
catalyst volume to operate satisfactorily with average levels of poisons present in
feedstocks. Adjustments can be made when increased levels of poisons are
detected either by using extra catalyst volume or by installing appropriate guard
beds.

Shift Conversion Catalysts - Operating Manual

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Shift Conversion Catalysts - Operating Manual