Hydroprocessing
catalyst manual
Guides you through handling, loading, start-up,
and operation of our hydroprocessing catalysts
www.topsoe.com
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Hydroprocessing catalyst manual
Table of Contents
1
Introduction
3
2
Catalyst application
4
3
Catalyst handling
5
3.1
Safety
6
Reactor internals
7
4.1
Distribution tray types
7
4.2
Sieve tray (perforated plate)
9
4.3
Simple chimney tray
9
4.4
Separate vapor and liquid chimney tray
10
4.5
Multi-port chimney tray
10
4.6
Bubble cap tray
10
4.7
Topsoe vapor-lift tray
11
4.8
Quench mixing assemblies
11
4.9
Scale catcher
12
4
5
6
4.10 Liquid phase scale catcher
12
4.11 Gas phase scale catcher
12
4.12 Reactor inspection and preparation
12
4.13 Inspection and cleaning of reactor internals
13
Catalyst loading
15
5.1
Support material and topping layers
15
5.2
Sock loading
18
5.3
Dense loading
18
Catalyst activation and start-up
20
6.1
Catalyst drying
21
6.2
Sulfur-donating agent
23
6.3
Sulfiding procedure for hydrotreating catalyst
26
6.4
Sulfiding procedure for hydrocracking catalyst liquid phase
30
6.5
Sulfiding procedure for hydrocracking catalyst vapor phase
36
6.6
Feed introduction after vapor phase sulfidation
40
6.7
Sulfiding of replacement catalyst after skimming
42
6.8
Start-up after planned shutdown
43
6.9
Start-up of tail gas treating catalysts
45
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7
8
9
10
Noble metal aromatic saturation catalysts
46
7.1
In-situ reduction
46
7.2
Transition to normal operation
46
Troubleshooting
48
8.1
Off-spec product – high sulfur
48
8.2
Off-spec product – high hydrogen sulfide
49
8.3
High reactor pressure drop
50
Planned shutdown
51
9.1
Temporary shutdown
51
9.2
Shutdown for catalyst unloading
52
Emergency shutdown
54
10.1 Hot hydrogen without hydrogen sulfide or oil
54
10.2 Hot oil without hydrogen
54
10.3 Contact with water
54
10.4 Backflow
54
10.5 Loss of feed
55
10.6 Loss of recycle gas
55
10.7 Loss of make-up gas
55
10.8 Loss of amine flow
56
10.9 Loss of wash water
56
10.10 Emergency depressurization
56
Catalyst unloading
57
11.1 Catalyst skimming and sampling
58
11.2 Catalyst dumping
59
11.3 Catalyst screening
59
11.4 Nickel carbonyl
60
Catalyst regeneration
60
12.1 Ex-situ versus in-situ regeneration
61
13
Liability
62
14
Contact addresses
63
11
12
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1
Introduction
This Hydroprocessing catalyst manual is intended to provide general guidelines for the handling and
operation of the Topsoe TK series of hydrotreating, hydrocracking, and hydrodewaxing catalysts.
When applying the guidelines in this manual, please refer to the limitations in liability as detailed in
Section 13.
The guidelines included in this manual cover:
−
−
−
−
−
−
−
−
Catalyst handling
Reactor internals
Catalyst loading
Catalyst activation and start-up
Troubleshooting
Shutdown procedures
Catalyst unloading and sampling
Catalyst regeneration.
Unit-specific, detailed operating procedures based on information described in this manual should be
developed by either the refiner or their engineering contractor. Such procedures are based on a
combination of unit design specifications, experience gained from previous turnarounds, and similar
applications in other plants. The detailed procedures should incorporate the guidelines from this
manual to form the basis for the operating procedures, taking into account the proper operation of
the unit for optimal catalyst activation, utilization and product recovery, while at all times maintaining
plant safety.
Topsoe engineers are available to assist in reviewing the preliminary and final versions of detailed
procedures generated by the refiner or engineering contractor for a specific unit. In cases where the
guidelines in this manual are in conflict with detailed plant procedures, Topsoe should be consulted.
Topsoe uses the term “hydroprocessing” to encompass hydrotreating, hydrocracking,
hydrodewaxing, and hydrogenation reactions and catalysts. The TK series of catalysts include a
number of specialized active hydroprocessing catalysts containing one or more of the metals cobalt,
nickel, molybdenum, tungsten, platinum, and palladium on alumina-based carriers. The start-up
guidelines in Section 6 of this manual apply to catalysts containing cobalt, nickel, molybdenum, and
tungsten. The start-up guidelines in Section 7 of this manual apply to catalysts containing platinum
and/or palladium.
March 2017
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2
Catalyst application
The TK series of catalysts are comprised of shape-optimized inert material, rings, and shaped
extrudates (threelobes, quadralobes, cylindrical). Inert and ring material are most often used for the
Topsoe graded bed system installed in the top section of hydroprocessing reactors. The extrudates
are mainly used as bulk catalysts and in some cases as intermediate grading catalysts.
Graded bed systems provide the following benefits:
A high void fraction in the top section is obtained by applying shape-optimized inert material (such as
TK-10, TK-15, TK-26 TopTrap™) and ring-shaped catalysts that allow the accumulation of large
amounts of foreign particles (i.e. dust and particulates) in order to minimize pressure drop build-up.
A gradual decrease in catalyst particle size to distribute particulates, contaminants, and reactions
over a larger part of the catalyst bed.
A variety of active topping materials provides the technology to gradually increase catalyst activity
from the top to the bottom of the catalyst bed. This results in better control of reaction rates and thus
exotherm for the hydrogenation of the most reactive, possibly fouling compounds and spread the
reactions over a larger portion of the catalyst bed.
The main bed hydroprocessing catalysts are produced in threelobe, quadralobe, and cylindrical
extrudate shapes. Typical sizes are 1/10”, 1/12”, 1/15”, 1/16”, and 1/20”. The larger size catalysts are
used for size transition and/or pressure drop control in units that have been expanded to operate at
higher rates.
The catalyst color is an indication of the active metals. The cobalt-molybdenum type catalysts are
typically greyish-blue. The nickel-molybdenum type catalysts are typically greenish-yellow. This is
not the case for Topsoe BRIM® and HyBRIM™ catalysts, which are black, dark brown, or dark blue.
Catalysts containing molybdenum or noble metals alone have the same color as the carrier (i.e.
white).
Regardless of type, all ex-situ presulfided catalysts are dark grey or black, and dependent on the
method of presulfiding, they may smell of organic solvent. The TK series, including our high-activity
BRIM® and HyBRIM™ catalysts are suitable for ex-situ presulfiding. Presulfided catalysts have been
either coated with a sulfur-donor, and thus partially activated, or they have been preactivated where
all the metal sites have been fully converted from metal-oxides to metal-sulfides.
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3
Catalyst handling
Typically, Topsoe’s TK catalysts are supplied either in removable lid drums, with nominal capacity of
200 liters (55 gallons), or big bags, holding approximately 1 m3 (35 ft3). Ex-situ presulfurized or
preactivated TK catalysts are packed and delivered in United Nations (UN) certified steel drums,
rental flow bins, or big bags (wrangler bags) to meet customer requirements.
Catalyst big bags, drums, and bins should always be handled with care, ensuring they are not
dropped or rolled, in order to avoid breaking the catalyst or the container.
Big bags – sometimes referred to as “super sacks” – are equipped with lifting straps and placed on
pallets for easy handling. UV light and time can lead to deterioration of the straps leading to a loss of
strength. The maximum recommended storage time for catalyst and big bags varies. Catalyst may
be kept for several years in airtight containers and maintain excellent integrity.
However, big bags integrity may be compromised after one year or less, especially if left exposed to
the elements. Any big bag that has been holding catalysts for more than one year should have the
lifting strap integrity checked before initiating the loading. For uncompromised safety, all four lifting
straps must be used when moving around the big bags.
Sometimes, the catalyst may appear solid or hard (i.e. not free flowing) in the big bags. This may
occur in case the catalyst in production is packed warm, resulting in a vacuum effect upon closing
the bag. This occurrence has no consequence on catalyst integrity, and as soon as the bag is
opened, the catalyst will appear free flowing again.
Discharge of catalyst must be done through the discharge chute in the bottom of the bag, using the
strips to open the chute. The bags should not be cut open. It is important that big bags are always
handled according to instructions, i.e. all lifting straps must be used at the same time, no open hooks
to be used etc.
Drums and big bags are equipped with internal polyethylene bags and, in some cases, aluminum
foil, which protects the catalyst from dust, water, and moisture. Topsoe recommends that the catalyst
drums and big bags be stored indoors. In cases where it is necessary to store the catalyst outside
short-term, the drums or big bags must be placed upon pallets or boards and securely covered with
heavy plastic or canvas sheets to protect them from rain/moisture and UV light.
The reason for having the catalyst protected from water and moisture is to ensure optimal catalyst
performance and a long cycle. Since the catalysts are hygroscopic in nature, large amounts of water
can be absorbed in the catalyst pore system, and during catalyst activation, this water may cause
reduction of the catalyst strength and potentially impact catalyst activity.
The range of water contents observed coming off the catalyst during the drying phase varies with
environmental conditions during loading. A level of 1 wt% water is typical.
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TK catalysts have a high porosity with a well-defined pore structure and a large surface area.
Despite the high porosity, TK catalysts have high crush strength specifications in order to cope with
mechanical stress on the catalyst during handling and operation. Nevertheless, improper handling
can result in breakage of any catalyst particle and the formation of catalyst fines. This may result in
pressure drop issues, which can eventually limit the cycle length. Hence, crushing of the catalyst
must be avoided.
Topsoe recommends that big bags are not be stacked at any time and only be placed in single
layers for shipping and storage. Drums can be stored in stacks up to a safe level. In the field or
laydown yard, drums are recommended to be stored in a single layer.
3.1
Safety
TK catalysts contain alumina and in some cases silica. These catalysts may also contain nickel,
cobalt, molybdenum, tungsten, platinum, and palladium as well as small amounts of other elements
and compounds. Some of these elements and compounds have been found to be carcinogenic and
may also cause various respiratory illnesses and complications.
It is critical and of utmost importance that all persons that could be exposed to catalyst dust directly
or indirectly during catalyst handling, loading, and unloading are adequately protected from any
catalyst dust or fines, including the following without limitation:
Respiratory protection:
Use approved respirator with particle filter type P3
(EU-Standard) / P100 (US-standard), when
exposure may exceed recommended limits
Hand protection:
Gloves recommended
Eye protection:
Goggles recommended. Contact lenses should not
be worn when working with TK catalysts
Other protection:
Change work clothing daily. Safety shoes
recommended when handling heavy containers.
Wash hands thoroughly after handling
Any personnel inside a reactor during handling, loading, and unloading of the catalysts must wear
gloves, full-body protective clothing, and self-contained breathing equipment at all times.
All work in an inert atmosphere must only be performed by trained and certified personnel. Great
care should be taken during all operations by all personnel near where inert entry work is required
and performed.
Safety Data Sheets (SDS) are available for each type of catalyst and should be consulted prior to
any catalyst handling, loading, or unloading. Be sure to obtain copies of the most recent applicable
SDS for each catalyst to be handled.
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The precautions in the latest SDS, which accompany the catalysts and describe how the specific
catalysts should be handled, should be followed carefully in all aspects and situations.
In case of ex-situ presulfided TK catalysts, the loading operation normally should be carried out in an
inert atmosphere (i.e. nitrogen) to avoid self-heating of the catalysts. Furthermore, ex-situ presulfided
catalysts may, dependent on which method of ex-situ presulfiding has been applied, emit
hydrocarbon vapors, or, in case of contact with (even small amounts of) water, emit sulfur dioxide.
All personnel inside a reactor during handling and loading of the presulfided catalyst must wear a
self-contained breathing apparatus or fresh air mask, gloves, and protective clothing at all times.
The user should refer to the most recent applicable SDS and other precautions as provided by the
company performing and delivering the ex-situ presulfiding of the catalysts.
4
Reactor internals
During the last 30 years, Topsoe has gained knowledge about and expertise in our own highefficiency reactor internals as well as older types of liquid distribution trays and quench mixing
assemblies still used in the industry.
The following general guidelines for maintenance of reactor internals are provided to ensure optimal
performance of the catalysts installed in hydroprocessing reactors. Should the guidelines given
below deviate from the guidelines given by the tray supplier, the guidelines from the tray supplier
must govern. The guidelines are provided separately according to the different type of trays and
mixers typically encountered. Should the distributor tray or mixer type in question not be
represented, please contact Topsoe for guidelines covering the specific type.
4.1
Distribution tray types
When the unloading of the reactor has been completed, the reactor internals must be inspected with
special attention to the following:
−
−
−
−
−
Contamination, dirt, dust, and/or accumulation of debris
Damage to tray parts
Missing or loose bolts
Missing, loose, or damaged packing or seals
Levelness.
Corrosion products, coke, scale, dust, or other solid particles entering the reactor with the feed may
settle and deposit on the top distribution tray plates, in risers, and/or in scale baskets.
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Depending on the tray design and amount of contaminants, performance of the distribution tray may
be affected. Thus, the tray must be carefully cleaned of all dust and debris. It is especially important
to observe that all weep holes, notches, and/or slots are perfectly clean. In case of severe
contamination, it may be necessary to dismantle the tray plates and have these cleaned outside the
reactor. Alternatively, cleaning by use of high-pressure water jet equipment can be done inside the
reactor. Before using a water jet, the water quality should be checked for chloride content. Levels
should be low enough to prevent chloride stress corrosion cracking of stainless steel parts inside the
reactor.
After completion of the loading, it is also necessary to perform a final inspection and cleaning to
remove any remaining catalyst particles and/or dust from the tray.
It is important to visually inspect the tray for damage, such as bent nozzles or corrosion on the tray
plates. In order to ensure optimal performance of the distribution tray, it is necessary that repair of all
damaged parts is carried out. In case of severe damage, replacement of the damaged sections of
the tray, or possibly a complete replacement of the tray, may be necessary.
It is commonly observed that bolts are missing from various parts of the reactor internals. It must be
kept in mind that the supplier of the reactor internals has provided the necessary bolting to withstand
load and stress at normal operating conditions. The reactor internals, even with some missing bolts,
may look correctly installed at ambient conditions. However, the situation may be completely
different when the internals are exposed to high temperatures, liquid load, and gas flow. Under these
conditions, the missing bolts may result in leak of liquid at places where it is not desirable, e.g. along
the reactor wall. Therefore, it is important that all missing bolts are replaced with new bolts of the
correct metallurgy and type. Places of special attention are the fastening of the reactor internals to
the reactor wall (in some tray designs done by J-bolts) and the manway covers.
In general, all ceramic fiber rope packing or seals must be replaced in open manways and other
sections that have been opened during each turnaround to prevent leak of liquid. Topsoe
recommends that the packing or seals around the manway covers are always replaced with new
gasket material after completion of the catalyst loading. In case inspection of the packing or seals
shows that they are in good shape, replacement may be postponed until the next turnaround.
Certain types of trays (see below) are very sensitive to levelness. Such trays must be carefully
checked, and if the levelness is found not to be within the tolerances specified by the tray vendor,
corrective actions must be taken. Some tray types may be difficult to adjust during and after
installation, and in case the levelness is found to be outside the tolerances as specified, it is
recommended to replace such a tray with a modern tray type (like the Topsoe Vapor-Lift Tray),
which can be adjusted. In case the tray is found to be out of level due to bent tray plates or beams,
these should be replaced with new straight pieces or brought to the workshop for repair.
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Distributor trays can significantly impact utilization of the installed catalysts, and thus the required
catalyst bed temperatures, catalyst deactivation rate, and, ultimately, the cycle length. If a tray is not
performing properly (as evident from significant radial variation of reactor bed temperatures), options
for improvement include repairs, new gasketing, or a full replacement of the distributor tray.
Performance estimates can be prepared by Topsoe to quantify the impact and justify the expense.
Specific information for each of the common types of reactor internals is given below.
4.2
Sieve tray (perforated plate)
This type of tray has a large number of distribution
points (holes) and is very sensitive to non-level
installation. Furthermore, deposits on the tray (fouling)
will severely affect the liquid and gas distribution.
For this tray type, it is very important to perform a
careful cleaning. The tray plates must be perfectly
clean and have the right design diameter for good performance. Levelness is also very important for
this tray type, and the tight tolerances must be observed. The levelness of each tray plate and
support beam must be checked to ensure that there are no local cavities. This type of tray is often
mounted to the support ring with J-bolts. It is very important that all these J-bolts are in place and
correctly tightened.
Due to the poor flexibility for changes in operating conditions concerning this type of tray, the refiner
should consider replacement with a modern type (like the Topsoe Vapor-Lift Tray), especially in high
severity units.
4.3
Simple chimney tray
This type of tray is characterized by having separate paths
for the liquid and gas. Typically, this tray type will have
chimneys spread in a regular pattern over the cross
section. Each chimney has single weep holes or notches at
the same level.
The tray will have some capacity for deposition of
contaminants on the tray plates without negatively affecting
the liquid distribution. However, it is important that all weep holes or notches are perfectly clean.
Levelness is also very important for this tray type, and tight tolerances must be observed. The
levelness of each tray plate and support beam must be checked to ensure that there are no local
cavities.
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4.4
Separate vapor and liquid chimney tray
This type of tray is a variant of the chimney tray. It is characterized by having nozzles for liquid and
chimneys for gas. The nozzles and chimneys are spread in a regular pattern over the cross sectional
area of the reactor. Each nozzle or chimney often has weep holes at different levels. This type of
chimney tray often has more distribution points and also lower sensitivity to levelness. These trays
will have some capacity for deposition of contaminants on the tray plates without negatively affecting
the liquid distribution. However, it is important that all weep holes, especially the lower ones, are
perfectly clean.
4.5
Multi-port chimney tray
This tray is characterized by having separate
paths for liquid and gas. Typically, these trays will
have chimneys spread in a regular pattern over
the cross section. Each chimney has several
weep holes at different levels in order to reduce
the sensitivity to levelness.
This tray type will have some capacity for deposition of contaminants on the tray plates without
negatively affecting the liquid distribution. However, it is important that all weep holes and especially
the lower weep holes are perfectly clean.
4.6
Bubble cap tray
The bubble cap tray makes use of the vapor-assist principle (siphon) and is often applied in highseverity units, like hydrocrackers or FCC pretreater units. The
bubble cap tray is usually flexible with respect to changes in liquid
and vapor loads and composition of feed. The drawback is the
large size of the bubble cap nozzles, which limits the number of
nozzles (distribution points) that can be installed per area.
This type of tray will have some capacity for deposition of
contaminants on the tray plates without negatively affecting the liquid distribution. Due to high gas
velocities, the slots in the bubble cap tend to stay clean even after extended time in service on
contaminated or cracked feedstocks. In order to prevent loose or improper placement of bubble
caps, new pins should be installed at each unit turnaround.
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4.7
Topsoe vapor-lift tray
Topsoe-designed, high-performance vapor-lift trays apply
the vapor-assist principle. They have a large number of
distribution points spaced at a close pitch. The closer the
distance between the distribution points, the better the
catalyst is wetted, and, as a result, the catalyst utilization is
greatly improved. The high utilization of the catalyst
installed in the reactor will result in a reduced reactor
temperature for the required product specifications and
eventually in a longer cycle length.
The vapor-lift trays show superior performance at all liquid loads and thus can be successfully
applied in all types of hydrotreating units. The trays have a wide operating range and flexibility
regarding temperatures, feed composition, and vapor/liquid loads. The gas velocity through the slots
of the vapor-lift tray chimneys is high, thus minimizing the risk of fouling.
The trays are designed to hold back scale (e.g. corrosion products) that may enter the reactor with
the feed, thus avoiding the need for installation of scale baskets. As for other trays, any debris,
scale, and contamination that may have accumulated on the tray plate below the chimneys must be
removed during each turnaround.
4.8
Quench mixing assemblies
A number of different designs exist for quench mixing assemblies. In multi-bed, two-phase
hydroprocessing reactors with interbed quench, a mixing device is required between the catalyst
beds in order to contact the quench fluid with the vapor and liquid effluent from the above catalyst
bed for efficient heat and mass transfer.
The purpose of the mixer is to obtain a uniform mixture regarding temperature and composition
before the two-phase mixture is redistributed over the next catalyst bed. Any irregularity will result in
loss of reactor efficiency.
The “vortex-type” mixing chamber receives the
gas and oil equally from all quadrants of the
quench collection tray through 2 or 4 slide
nozzles. There, the fluids reach the dispersed
flow regime, forcing the mixed media into a
centrifugal path where the mixed gas and oil
interchange with each other until they reach the
orifice of the mixer, where the mixed liquid and
vapor are reaccelerated, reaching the dispersed
flow regime, again ensuring that the mixture is
mixed sufficiently to reach an equilibrium temperature before it is redistributed onto the next catalyst
bed. The vortex mixer principle is illustrated in the sample photo above.
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As the quench mixing assembly and distribution trays of subsequent catalyst beds are protected
from contamination by the catalyst bed above, this section of the reactor will normally be clean.
However, Topsoe recommends that the quench mixer is inspected for damage, broken/missing
bolts, corrosion, and that all packing or seals are intact and in good shape.
The distribution trays of subsequent catalyst beds must also be inspected and cleaned, if needed.
4.9
Scale catcher
In some cases, where the feed contains fines, scales, inorganic matter, corrosion products, etc., it is
recommended to install a scale catcher above the top distributor tray. The scale catcher will collect
these solid materials in order to avoid plugging of the distributor tray and the catalyst bed below.
4.10
Liquid phase scale catcher
Topsoe’s High Efficiency Liquid Phase scale catcher
(HELPsc™) is designed with a dual-stage system,
combining sedimentation and filtration. The
sedimentation chambers of HELPsc™ provide
extended residence time for the liquid and thereby
allow the heavier particles to settle at the bottom of
the chambers. After the sedimentation section the
liquid will enter the catalyst filter elements, where the
smaller particles are captured. This leaves the liquid
almost particle free, when passing down to the distributor tray.
4.11
Gas phase scale catcher
Naphtha gas phases can also contain significant
amounts of particles. The particles are often very fine,
stemming from processes and equipment prior to
hydrotreating. The particles can be of organic nature like
coke and gums or inorganic like salts or iron
components. Topsoe’s gas phase scale catcher can
efficiently remove these particles from the gas stream, to
prevent pressure drop build up by plugging.
4.12
Reactor inspection and preparation
Prior to catalyst loading, the reactor must be inspected
to ensure that all maintenance work is complete, the
internals are properly installed (with the exception of the
manways), and the reactor is clean and dry. Areas of
particular importance are as follows:
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1) Ensure that all contractor equipment and extraneous hardware have been removed.
2) Verify that support beams are intact, straight, and level.
3) Check that screens (stainless steel) on the support grids and outlet collector are properly
mounted and are all clean and intact (no corrosion or brittleness).
4) Gaps between support grid sections and between grid sections and reactor wall must be sealed
with ceramic fiber rope packing to prevent catalyst migration. Note that fiber rope will disintegrate
in time, and thus fiber ropes must be replaced if they appear worn.
5) The outlet collector is checked for gaps at the reactor head. It is also important to check that all
holes and slots of the outlet collector are clean.
6) The reactor outlet elbow, the quench line nozzles, and all associated piping must be clean.
7) Check that thermocouple nozzles are clean and free from catalyst particles.
8) Thermocouples must be correctly positioned and firmly attached to their supports. It is
recommended that the thermocouples are properly calibrated and validated following each
shutdown.
4.13
Inspection and cleaning of reactor internals
A general step-by-step procedure for inspection, cleaning, and installation of reactor internals in
hydrotreating units in connection with catalyst replacement is given below:
1) The unit is shut down following the planned shutdown procedure and is prepared for opening of
the manway at the top of the reactor.
2) The reactor inlet diffusor is inspected and, if necessary, cleaned or repaired.
3) Following a planned shutdown, some liquid could remain on the distribution tray. Although most
trays are designed with drain holes, if liquid remains then vacuuming may be required. Additional
holes should never be drilled to remove the liquid, as they may lead to mal-distribution upon
restart. Be sure to consult with the tray design experts for possible drain-hole modifications.
4) The panels of the distribution tray manway are removed.
5) The top of the catalyst bed is inspected for signs of uneven liquid or gas distribution, such as
difference in degree of contamination, color differences, or catalysts that have shifted position
since initial loading and start-up. In case scale baskets are installed, differences in the amount of
dust in these baskets or any other irregularities could indicate that conditions have not been
uniform throughout the cross section of the catalyst bed. If such differences are identified, it
could be useful to reinspect the distribution tray above to check if any obvious faults are
observed on the tray directly above the specific section of the catalyst bed.
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6) Especially for naphtha hydrotreating units operating at high gas rates, emphasis should be given
to check for possible milling (dust formation) of the top layer of inert material. In case milling
appears to be an issue, Topsoe should be contacted for advice on future loading.
7) The catalyst is dumped through the dump nozzle (refer to Section 11, Catalyst unloading, in this
manual), the reactor walls are passivated with caustic wash, and the reactor atmosphere is
changed to air.
8) After having unloaded the catalyst, all the reactor internals (including distribution trays, catalyst
support grids, and the outlet collector) are carefully cleaned, making sure that the guidelines
mentioned above are observed. Special attention should be devoted to checking the condition of
the chimneys (risers) of the trays and cleaning as required. Furthermore, the size and suitability
of the wire mesh, screens, slots, and holes of the support grids and the outlet collector must be
compared with the sizes of ceramic balls to be used.
9) After completion of the cleaning, inspect for poor welding or other visible faults or damage. All
seals, packing, wire mesh, screens, etc. must be inspected and, if necessary, replaced. The
levelness of the distribution tray in all directions must be checked in different sections of the tray.
Any fault, damage, poor packing or seals, and/or non-levelness must be repaired or corrected.
10) The distribution tray is inspected for signs of possible leaks. Potential areas of leaks are around
the tray manway cover (for instance, due to damaged or missing fiber rope packing), in the joints
between the different tray section plates, around the nozzles (in case these are not seal-welded
but only rolled), or along the reactor wall due to damaged or missing fiber rope packing.
11) Prior to catalyst loading, in order to improve loading efficiency, marking the reactor wall with
chalk at the upper level of each layer of inert material and catalyst will reduce the time for
measurements and overall load time. An intrinsically safe, laser leveling device may also be
helpful during the loading. Both of the above-mentioned methods (or combinations of the
methods) will facilitate leveling of the different layers of catalyst and inert.
12) The new charge of catalyst is carefully loaded as recommended by Topsoe. Such loading must
be done by an experienced loading company (refer to Section 55, Catalyst loading, in this
manual for further details). In case any cleaning of the top distribution tray is performed following
the loading, the installed catalysts must be covered in order to prevent any dust and particulates
on the top of the catalyst bed. Make sure to remove all foreign material from the reactor prior to
closing.
13) The tray manway panels are installed. Great care must be used to install the panels correctly
and with new and suitable fiber rope packing or gasket tape. The entire circumference of each
panel must be packed. A final cleaning of the tray from the top is necessary before the reactor is
closed.
14) The unit is started up, and the catalyst is activated in accordance with the recommendations
given by Topsoe (refer to Section 6, Catalyst activation and start-up, in this manual).
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5
Catalyst loading
Refer to Section 3.1 in this manual and the latest SDS for the catalysts to be loaded prior to catalyst
loading.
Correct installation and subsequent activation of the TK catalysts are very important in order to
obtain optimal catalyst performance. Therefore, these operations must be carefully monitored, so
that the catalyst is not harmed in any way.
Loading of fresh catalysts can be performed in atmospheric air. However, air should be able to enter
the reactor only through the top of the reactor for the purpose of exchanging air in the void space
above the catalyst bed. Typically, a hose is lowered down to the level where workers are present.
The air is vacuumed out of the reactor, creating natural ventilation.
In order to avoid a chimney effect in the reactor, all potential air entry points below the top of the
loaded catalyst should be closed via appropriate blinds or flanges. The list of entry points includes,
but is not limited to, the reactor bottom elbow, manways, dump nozzles, and entry taps for
instrumentation, such as thermocouples and pressure indication meters.
On some sites, the safety requirements mandate that air movers or ventilators be used. In our
experience, using a vacuum hose system works better and more completely to ensure air flow
throughout the entire working void space.
Since catalysts are extremely hygroscopic, the reactor top and catalyst loading area have to be
protected with tarpaulins during rainy or snowy weather in order to keep the catalyst dry at all times
during the loading. If protection from precipitation is not possible, catalyst loading must be postponed
until it can be completed without the catalyst getting wet.
When TK catalysts are delivered in the ex-situ presulfided form, loading in rainy weather must not
take place due to the risk of sulfur dioxide formation. Furthermore, the loading will often have to be
carried out in inert atmosphere (i.e. nitrogen) to avoid self-heating. The company supplying the
presulfiding should be contacted for detailed guidelines on handling and loading.
In order to avoid uneven flow distribution (channeling) in the catalyst bed, it is important that loading
of the catalyst is done correctly. Uneven flow distribution may have a significant influence on the
performance of the unit, and, in the worst case, it may not be possible to meet product specifications.
5.1
Support material and topping layers
Ceramic balls (inert material) are used for catalyst support at the bottom of each catalyst bed. The
support is graded in size to prevent migration of the relatively small main bed catalyst particles
through gaps in the support grids and outlet collector. The heights and sizes of the ceramic balls are
specified in the loading diagram or in the reactor specification.
Make sure that the integrity of the ceramic balls is acceptable. Structurally weak balls have been
observed, and they may break upon loading or during service at elevated temperatures.
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The following general guidelines should be followed:
1) Refractory fiber is inserted into the bottom dump nozzles, and ceramic balls are carefully loaded
in the reactor head until the outlet collector/screen is covered to a depth as specified in the
loading diagram. For tall reactors, it is recommended using an elbow connected to the sock in
order to allow the balls to change direction and let them roll into the reactor head. This avoids
direct impact with the outlet collector or the bottom of the reactor. The recommended minimum
layer of the large size ceramic balls to be loaded at the bottom of the reactor should be 150 mm
(6”) over the top of the outlet collector. The size of the ceramic balls in the bottom of the reactor
(as well as in the dump nozzles) must be larger than the width of the slots in the outlet collector.
Typically, a nominal 1” or ¾” diameter ceramic ball is specified.
2) When 1/10” or larger size bulk catalysts are used, two layers of ceramic balls are used on top of
the 1” or 3/4” ceramic balls in the bottom of the reactor. A layer of minimum 75 mm (3”) of a
nominal 1/4” diameter ceramic ball is loaded on top of a layer of minimum 75 mm (3”) of a
nominal 1/2” diameter ceramic ball. Please refer to the loading diagram B on the following page.
3) When 1/12” or smaller size bulk catalysts are used, in addition to the two layers of
ceramic balls (1/4” and 1/2”) on top of the 1” or 3/4” ceramic balls in the
bottom of the reactor, a layer of minimum 75 mm (3”) of a 1/10” quadralobe-shaped catalyst or a
nominal 1/8” diameter ceramic ball is loaded on top of the layer of 1/4” ceramic balls. Please
refer to the loading diagram A on the following page.
4) If the reactor has more than one catalyst bed, the layer of support material at the bottom of each
bed should be minimum 150 mm (6”) of a combination of 1/4” ceramic balls and a 1/10”
quadralobe-shaped catalyst or 1/8” balls, depending on the size of the bulk catalyst as well as
the screen size of the catalyst support grid.
5) When the reactor is equipped with internal dump nozzles in between the catalyst beds, these are
normally filled with ceramic balls in sizes 1/4”, 1/2”, or 3/4”. The dump
nozzles must be designed to extend through the support grid, the mixer section, the
distribution tray, the void below the tray, the top inert material, and 300–600 mm (12–24”) into
the bulk catalyst in the catalyst bed below. The dump nozzles may include stainless steel plates
to minimize on-stream oil and gas flow through the nozzles.
6) At the top section of the reactor, a high void inert material is usually installed. The target height of
the layer of high void material (preferably TK-10 or TK-15) is 150 mm (6”). If the reactor has
more than one catalyst bed, a similar target of 150 mm (6”) layer of inert material is normally
installed on top of each subsequent bed. Alternatively, 1” or 3/4” ceramic support can be installed
on top of these lower beds.
7) The remaining grading system, normally consisting of different types and sizes of TK rings and
extrudates, is installed between the top layer of inert material and the bulk catalyst. The rings
and ceramic support material are always sock loaded. The personnel inside the reactor should
minimize time standing on the catalyst and avoid stepping directly on the ring-shaped catalysts.
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For exact loading heights of the grading catalysts, refer to the specific Topsoe technical
recommendation, catalyst specification, or the loading diagram.
8) The void space between the top of the catalyst bed material and the bottom of the lowest point of
the tray section should often be minimized and must be no more than 500 mm (20”). However,
for some tray designs, up to 400 mm (16”) void space is required in order to ensure proper
wetting of the catalyst.
Examples of loading diagrams:
A
B
Normally 300–500 mm (1'0"-1'8")
free space from distribution tray to
top of catalyst
Normally 300–500 mm (1'0"-1'8")
free space from distribution tray to
top of catalyst
Minimum 150 mm (6") TK-10 or
TK-15 high void inert material
Minimum 150 mm (6") TK-10 or
TK-15 high void inert material
Topsøe grading of two or more
layers of TK rings and extrudates
Topsøe grading of two or more
layers of TK rings and extrudates
Bulk catalyst in sizes
1/12", 1/15", 1/16" and 1/20"
threelobes or quadralobes
Bulk catalyst in sizes
1/8" and 1/10" threelobes
or quadralobes
Min. 75 mm (3") 1/10" quadralobes
or 1/8" ceramic balls
Min. 75 mm (3") 1/4" ceramic balls
Min. 75 mm (3") 1/2” ceramic balls
Min. 150 mm (6") 1" or 3/4” ceramic
balls above outlet collector
Min. 75 mm (3") 1/4" ceramic balls
Min. 75 mm (3") 1/2” ceramic balls
Min. 150 mm (6") 1" or 3/4” ceramic
balls above outlet collector
Please note that the ceramic balls must be sock loaded and care must be taken to avoid breakage
during loading. Additionally, dropping of the ceramic support from the top of the reactor may cause
damage to the reactor internals, outlet collector, dump nozzles, thermocouples, etc.
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In order to minimize pressure drop, it is recommended that the bulk catalyst be loaded in the reactor
head only to 90% of the full reactor diameter. The remaining volume in the bottom reactor head is
carefully filled with ceramic balls, as described above.
5.2
Sock loading
The TK catalysts can be either sock or dense loaded. It is specifically indicated in the technical
recommendation, catalyst specification, reactor specification, or loading diagram which method is to
be applied for each catalyst layer or catalyst bed.
Sock loading is done through a vinyl or canvas hose. A hopper is placed on the inlet flange on top of
the reactor. A hose or a pipe is connected to the bottom of the hopper. For multiple bed reactors, the
pipe is extended from the hopper through the empty catalyst beds. The hose is only used in the
catalyst bed being loaded. Additionally, the free fall of catalyst from the hose to the top of the
catalyst bed should be limited to a maximum of 1 meter (3 ft).
During the loading, the hose is progressively shortened in order to keep it close to the top of the
catalyst bed at all times. The catalyst must not be poured into a heap and distributed evenly
afterwards, as this can lead to segregation of particle sizes and improper catalyst particle orientation,
leading to channeling. Instead, the loading personnel should continuously move the sock in order to
ensure even distribution of the catalyst in the reactor.
After loading of each layer (or part of the layer) of catalyst, it is recommended to determine the depth
of the catalyst bed and the amount of catalyst loaded in order to check that the required loading
density has been achieved or is otherwise consistent. The target loading densities are provided by
Topsoe and can be found in the technical recommendation, the catalyst specification, or in the
product sheet for each type of catalyst. It is recommended to perform density checks at around 25%,
50%, and 75% of each sock loaded layer.
It is recommended to always have trained personnel on location during the loading process to
observe and guide the loading to ensure that the top of the catalyst bed is reasonably level at all
times. The loading sock cannot be left hanging in the center of the reactor with the catalyst pouring
out, as this will lead to maldistribution and subsequent less than optimal performance of the reactor
system once in operation.
NOTE: When loading ceramic balls, care must be taken to prevent filling the hose. The weight of a
sock filled with the ceramic support material may cause the hose to break or separate from the
hopper, thereby endangering the personnel inside the reactor.
5.3
Dense loading
Dense loading is performed using a special dense loading device/machine. The various designs for
dense loaders all use the principle of dispersing the catalyst over the entire cross sectional area of
the reactor in such a way that the catalyst level is evenly increased. Loading rate is controlled so that
each catalyst layer comes to rest before being covered by the next layer, thereby minimizing bridging
and particle size segregation.
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The catalyst loading company should always refer to the instructions or manual which are relevant
for the particular dense loading device they have selected. Operators for specific dense loading
methods must have regular (annual) certification.
The dense loading device is mounted in the manway of the distribution tray or on the reactor inlet
flange if there is no distribution tray installed in the reactor. A vinyl or canvas hose typically transfers
catalyst from a hopper above the reactor to the dense loader inside the reactor – for multi-bed
reactors, hard pipe should be used.
When applying dense loading techniques, it is very important to periodically stop the loading and
measure the level (outage) and density of the catalyst bed to ensure even loading density
throughout the catalyst layer. Depending on the device, there are various adjustments that can be
made to correct the loading patterns. A bed level that is not increasing evenly is an indication that
the dense loader is distributing the catalyst particles unevenly over the cross section of the reactor
and possibly into the reactor wall, which could result in particle breakage or cause an uneven
catalyst bed density profile, possibly leading to maldistribution upon start-up.
Any unlevelness should be leveled by modifying the operation of the dense loader. The motor speed
and/or catalyst flow pathways (dense loader shutter openings) should be adjusted to improve the
distribution profile (filling in center sections, outer rings, or inner rings as necessary).
As the loading progresses and the level of catalyst rises, adjustments of the dense loader are
needed in order to maintain an even and level distribution of the catalyst over the entire reactor cross
sectional area. The angle of deviation should be less than 5° at all times.
After loading of each layer (or part of the layer) of catalyst, it is recommended to determine the depth
of the catalyst bed and the amount of catalyst loaded in order to check that the required loading
density has been achieved or is otherwise consistent. The target loading densities are provided by
Topsoe and can be found in the technical recommendation, the catalyst specification, or in the
product sheet for each type of catalyst. The dense loading contractor will often run tests and make
an estimate as to the expected loading density for the catalyst to be loaded. If multiple catalysts are
being used in the unit, the loading contractor can make an estimate for each type of catalyst. Topsoe
recommends density checks at a minimum of 10%, 25%, 50%, 75%, and 90% of each dense loaded
layer. Additional checks for the loading density can be made by the dense loading contractor as
desired.
Finally, it is recommended that dense loading is performed by a company specializing in dense
loading. Although the final results of the dense loading are going to depend on the equipment, the
proper operation of the dense loader, and thus the quality of the dense loading, is highly dependent
on the experience of the dense loading personnel with the actual equipment.
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6
Catalyst activation and start-up
Hydroprocessing catalysts as manufactured consist of an alumina carrier impregnated with oxides of
different combinations of metals. For the metal oxides to be in the active state, they have to be
converted to sulfides.
The activation step is critical for the subsequent performance of the catalyst charge and therefore
requires careful attention and monitoring. During the activation, the catalyst will typically pick up
sulfur, 5-13 percent by weight, depending on the amount of active metals present in the catalyst.
The sulfur uptake of some of our TK catalysts is shown below.
Catalyst
Sulfur uptake (wt%)
TK-220
6.3
TK-611 HyBRIM™
11.8
TK-222
7.8
TK-743
5.3
TK-224
5.1
TK-773
7.9
TK-431
8.0
TK-921
8.7
TK-453
5.3
TK-925
3.4
5.3
TK-926
8.7
11.6
TK-931
8.7
TK-565 HyBRIM™
8.2
TK-939
8.7
TK-568 BRIM®
9.3
TK-941
8.7
TK-569 HyBRIM™
TK-527
TK-562
BRIM®
Catalyst
Sulfur uptake (wt%)
10.1
TK-943
8.7
TK-570
BRIM®
11.6
TK-947
9.3
TK-578
BRIM®
12.9
TK-951
8.7
12.3
TK-961
12.0
TK-609 HyBRIM™
There are several methods available for sulfiding of the catalyst. The method recommended by
Topsoe (and the method described in this manual) is the in-situ sulfiding method, where an easily
decomposable sulfur-donating agent (such as DMDS or TBPS) is mixed with the oil upstream of the
reactor. The sulfur-donating agent should not be added to the feed surge drum, as this prevents
control of the concentration of sulfur-donating agent in the oil being fed to the reactor.
On request, Topsoe will provide start-up procedures and recommendations for alternative methods,
such as native (oil) sulfur activation and start-up of ex-situ presulfided catalysts. For units/reactors
that are limited in reactor inlet temperature to around 300°C (570°F) or lower during the activation
step, it is recommended having the catalysts ex-situ preactivated by a specialized company prior to
loading and start-up. In some cases, catalysts can be sulfided at lower temperatures than normally
recommended. However, longer hold times are required to complete the sulfiding. Topsoe
representative should be contacted for guidelines.
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6.1
Catalyst drying
TK catalysts have a high porosity and a large surface area. Such catalysts are hygroscopic in nature,
and moisture from the air can be readily absorbed in the catalyst pore system. This water can be
easily removed by routine procedures in order to avoid reduction of the catalyst strength and
potential impact on catalyst activity.
The range of water content observed coming off the catalyst during the drying phase varies with
environmental conditions during loading. A level of 1 wt% water is typical. Careful drying must be
performed prior to catalyst activation/sulfiding.
Drying of fresh or regenerated catalyst prior to activation is preferably carried out in gas phase using
hydrogen-rich treat gas or nitrogen. The gas for drying should be low in hydrogen sulfide (preferably
less than 50 ppm) and low in carbon monoxide (less than 10 ppm). Vapor-phase drying of the
catalyst is recommended, as the gradual evaporation of water gives the highest possible catalyst
activity.
A fast heat-up can lead to steam formation, and the corresponding rapid volume expansion inside
the catalyst particles can lead to sufficient pressure to break the catalyst. The broken catalyst can
lead to pressure drop issues and, in severe cases, require a skim or complete replacement of
catalysts. During an oil-phase drying, water can be trapped to a greater extent in the catalyst pores.
The potentially higher temperatures can convert the water to steam and lead to structural changes
and a loss of porosity and, in some cases, loss of catalyst activity.
For the catalyst drying (as well as the sulfiding), a straight-run kerosene or light diesel or gas oil
stream can be used. The recommended maximum feed end point is 380°C (720°F) using D2887
(simulated distillation). This end point is selected in order to keep heavy aromatics out of the feed,
since these aromatics can impact the quality of the catalyst sulfiding.
When hydrogen-rich gas is used for the drying, the reactor inlet temperature should be kept around
150°C (300°F). The catalyst should not be exposed to hot hydrogen for prolonged periods of time
due to the risk of reducing the catalyst oxides to free metals, which can result in permanent reduction
of the catalyst activity. Refer to the table below for time frames when hydrogen and no hydrogen
sulfide or oil are present.
The following table shows the maximum time at temperature for oxidic catalysts:
Highest temperature, °C (°F)
Maximum time, hours
150 (300)
175 (350)
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For larger reactors, the catalyst drying step needs to be slower and more gradual. It is recommended
to start drying at a reactor inlet temperature of 130°C (270°F) instead of 150°C (300°F). Water
liberated from the top catalyst bed may be reabsorbed by catalyst below, resulting in excessive
levels of water being accumulated in latter catalyst beds. This water may evaporate and cause
breaking of catalyst particles and subsequent risk of pressure drop. Unloading catalyst to rectify the
situation can be time-consuming and expensive.
Hydrogen-rich treat gas should be circulated prior to any oil introduction. In situations where
equipment upstream or downstream the reactor has been leak tested with water during the
turnaround, the entire system must be properly drained before commencing the drying and activation
procedures. Ensure that all low point drains are purged.
A step-by-step catalyst drying procedure is provided below.
1) In case the catalyst loading was carried out in atmospheric air, the reactor must be purged with
nitrogen to the extent that the oxygen content of the high-pressure loop is less than 0.5 vol%
before hydrogen-rich gas is introduced. Purging avoids the risk of forming explosive mixtures of
hydrogen and oxygen. It is recommended by Topsoe to apply the method of pressurizing with
nitrogen followed by depressurization, and repeat the procedure until oxygen levels are
consistently lower than 0.5 vol%. Depending on the method, this would normally require 2–4
pressurization/depressurization steps.
2) Pressurize the reactor to normal operating pressure or a maximum of 70 barg (1,000 psig). Be
aware of any pressure limitations at low temperature, as some reactor material is brittle at
ambient temperatures. If limited in pressure, the reactor skin and/or flange temperature must be
increased to the value specified before pressure is increased. Sites should use the unit specific
Mechanical Pressurization Temperature curves to determine when the pressure can be raised.
Pressurization of some units is limited by heat exchangers and not the reactors. Every unit needs
to be thoroughly checked prior to pressurization. The pressurization should preferably be done in
steps with holding period for pressure test to verify that the unit is tight.
3) At the same time, start the flow of gas at maximum flow rate. The nitrogen or hydrogen-rich gas
used for the catalyst drying may be recycled, if desired. The amine circulation must be stopped
or the amine absorber bypassed during the drying and the catalyst activation.
4) Light the heater according to refinery procedure and increase the reactor inlet temperature to
150°C (300°F), or 130°C (270°F) for larger reactors or systems with multiple reactors in series.
The temperature should not exceed 175°C (350°F) at any time during the catalyst drying
operation.
5) In order to minimize the risk of leaks due to thermal expansion, the recommended maximum rate
for heating up the catalyst is 30°C/hr (50°F/hr). For low LHSV units (i.e. less than 0.6
hr-1), the heat-up rate may need to be reduced to around 20°C/hr (35°F/hr). Topsoe
representative should be consulted for advice.
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6) Maintain the reactor inlet temperature at 150°C (300°F), and maximize cooling of the reactor
effluent. Check and drain water from the high-pressure separators.
7) Regardless of the amount of water being collected in the separators, the drying of the catalyst
should be performed for a minimum of 4 hours at reactor bed temperatures of 120–150°C (250–
300°F). Please note that, in some cases, no water will appear in the separators. As described
above, for large reactors, the water will be moved from the upper beds and may be readsorbed
in the lower beds. The absence of water in the early phase of drying does not necessarily mean
that all of the catalyst is dry. Once the catalysts near the reactor outlet start to heat up, any water
present will start to be released and show up in the separators.
8) Generally, a drying period of 6 hours at reactor bed temperatures in the range of 120 (250°F) to
150°C (300°F) will be more than sufficient for catalyst drying. If the drying is taking longer than
anticipated, please check the system for other sources of water, such as water wash or amine
scrubbing systems in operation.
9) When no more water accumulates in the separators, the catalyst drying is complete. However,
drying the catalysts for longer than 6 hours should be avoided.
6.2
Sulfur-donating agent
Hydrogen sulfide (H2S) is required to convert the metal oxides to catalytically active metal sulfides.
Most sites use a sulfur-donating agent to facilitate a controlled catalyst sulfiding operation. An easily
decomposable sulfur-donating agent (such as DMDS, TBPS, or DPDS) is added to the start-up feed.
Recommendations for the start-up feed are the following:
−
−
−
−
A light, straight-run fraction, such as kerosene or gas oil (diesel)
For naphtha units, straight-run naphtha should be used
Final boiling point less than 380°C (720°F) using ASTM D2887 (simulated distillation)
Maximum specific gravity of 0.85, equivalent to an API gravity higher than 35.
Generally, use of vacuum gas oil fractions as start-up feed should be avoided. However, in some
cases, straight-run vacuum gas oil must be used. It is recommended to contact Topsoe for advice on
a specific feed and unit in question. The guidelines for the start-up feed have been selected in order
to keep heavy aromatics out of the feed, since these aromatics can impact the quality of the catalyst
sulfiding.
Properties of two of the most commonly used sulfur-donating agents are listed below.
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Unit
DMDS
(Di-Methyl Di-Sulfide)
TBPS
(Di-Tert-Butyl PolySulfide; SulfrZol 54®)
kg/l
1.06
1.09
lbs/gal
8.9
9.1
wt%
68
54
lbs S/gal
6.0
4.9
°C
170–210
160–220
°F
340–410
320–430
°C
15
100
°F
60
210
g/mole
94
248
Density
Sulfur content
Decomposition
temperature*
Flash point
MW**
* The decomposition temperatures are in the presence of catalyst.
** MW for TBPS is an approximate average molecular weight.
Note that when TBPS is applied as the sulfur-donating agent, caution should be taken to avoid
conditions where oil with dissolved TBPS is heated to temperatures in excess of 250°C (480°F)
without hydrogen present. When sufficient hydrogen is not available, e.g. in units where hydrogen
gas is added downstream the feed heater, there is a risk of polymerization reactions and subsequent
plugging in furnace tubes, heat exchangers, etc. This may require downtime for cleaning. In this
case, and for units where vapor-phase sulfiding is applied, TBPS should be injected at the reactor
inlet for immediate decomposition. Topsoe recommends consulting the vendor of TBPS for any
additional requirements.
When applying DMDS at low temperatures, the DMDS will first decompose to DMS and then
hydrogen sulfide. The formation and possible build-up of DMS can create contamination issues in
slop systems and with butane storage. To avoid these issues, sites should maximize the hydrogen
purity of the treat gas and operate the unit in full recycle mode (recycle feed and gas) until the
temperatures are sufficiently high to ensure full decomposition of DMS to methane and hydrogen
sulfide, i.e. above 220°C (430°F). Sometimes local conditions and unit constraints make the use of
DMDS difficult or even impossible. In such a case, it is recommended to apply a polysulfide, such as
TBPS, for the activation, or contact Topsoe for advice.
The stoichiometric requirement of sulfur-donating agent for a given catalyst loading is most often
provided by Topsoe and included in the product sheet, the technical recommendation, or in the
catalyst specification sheet. It is recommended to have a general excess of 20% sulfur-donating
agent available on site. In case the activation is done using once-through gas and/or once-through
feed, it is recommended to have an additional 30% available on site, resulting in a total of 50%
excess sulfur-donating agent.
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For activation of units, where relatively small catalyst volumes are installed, and the
stoichiometric sulfur requirement is thus low, we recommend a greater excess of sulfur-donating
agent due to higher relative losses. Refer to the tables below for guidelines.
For catalyst systems having an average sulfur uptake lower than 9 wt%, we recommend the
following guidelines:
Bulk catalyst volume
m3
0–25
25–50
50–75
75–100
ft3
0–900
900–1,800
1,800–2,700
2,700–3,600
100
70
50
30
Excess sulfur-donating agent, %
For catalyst systems having an average sulfur uptake higher than 9 wt%, we recommend the
following guidelines:
Bulk catalyst volume
Excess sulfur-donating agent, %
m3
0–15
15–25
25–35
35–50
ft3
0–500
500–900
900–1,300
1,300–1,800
100
70
50
30
The recommended amounts of excess sulfur-donating agent, as included in the tables above,
assume that gas and oil feed are recycled during the activation procedure. If they are once-through,
an additional 30% should be added. On request, Topsoe will provide recommendations for a specific
unit, service, and start-up procedure.
It should be ensured that a correctly sized sulfur-donating agent injection pump is available for the
operating flow range to match the required rates for the catalyst sulfiding.
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6.3
Sulfiding procedure for hydrotreating catalyst
A step-by-step procedure, including a graph of the reactor inlet temperature profile during a typical
catalyst sulfiding operation, is shown below.
1) At this point, it is assumed that the unit has been purged, pressurized to normal operating
pressure, or a maximum of 70 barg (1,000 psig), and heated to 150°C (300°F) as described in
Section 6.1 in this manual. Furthermore, gas circulation has been established, and the catalyst
drying has been completed. It must be ensured that the hydrogen purity of the treat gas is higher
than 60 vol% at all times. For sites that do not have an online analyzer for recycle gas purity, it is
recommended to verify purity by gas chromatography every 4 hours. In general, hydrogen purity
should be maximized. Treat gases that contain carbon oxides should be avoided. Carbon oxides
can be an issue with catalytic reformer units and with refineries processing renewable diesel. In
some cases, carbon oxides can interfere with the catalyst sulfiding process. It is thus
recommended to purify the hydrogen stream in a PSA unit or similar membrane unit.
2) Once-through start-up oil is introduced at around 50% of the design feed flow rate. The liquid
feed must be introduced at reactor temperatures below 175°C (350°F). Normally, due to heat of
adsorption (heat of wetting), an exotherm will be observed when oil is first introduced to the
catalyst. Monitor the reactor temperatures and pressure drop and adjust the rates, if necessary.
NOTE: The overall effect from introducing oil is often a drop in reactor bed temperatures. In general,
the heavier the feedstock, the more pronounced the effect.
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3) The feed rate is increased to 60–100% of design (or normal) feed flow rate. The reactor is
flushed with start-up oil, corresponding to around three times the reactor volume or maximum 6
hours at full design rate, in order to remove dust and particles that would otherwise be trapped
in the reactor section. Prior to initiating recycle of oil, a sample of the product is visually checked
in order to verify that it is non-hazy and free of particles. A reactor flush may not be necessary
when sulfiding is performed with once-through oil. In case sulfiding is performed with
recirculated oil (which is typically the case), a reactor flush is required prior to initiating the oil
recirculation.
4) After flushing and stabilization of flows, temperatures, and pressures in the unit, the start-up oil
can be circulated from the stripper or fractionation section back to the unit feed pump, if desired.
This significantly reduces the quantity of start-up oil needed and thus reduces the amount of offspecification material produced. It is suggested that the oil recycle is not processed through
storage/product tanks, because the unstripped oil may contain hydrogen sulfide, partially
decomposed sulfur-donating agents, and/or ammonia which may accumulate in the tanks.
Furthermore, the product salt dryer should be bypassed in order not to bring salts back to the
top of the catalyst bed.
5) The reactor inlet temperature is increased to 190°C (375°F) at a rate of 25°C/hr (45°F/hr), and
the hydrogen content of the recycle gas is measured. In case the hydrogen content drops below
60 vol% at any time during the catalyst sulfiding, the high-pressure loop must be purged/vented,
and hydrogen-rich make-up gas is introduced to the unit.
6) Injection of sulfiding agent at the feed pump suction side is started. As a guideline, the average
injection rate is obtained by dividing the total stoichiometric requirement of sulfiding agent into
16 hours, which is the approximate duration of the activation. Until the reactor exotherm has
stabilized (normally after 1–2 hours), it is recommended to apply half of the average injection
rate of sulfiding agent. Doping with a sulfur-donating agent should result in a total sulfur
concentration in the oil not exceeding 2.5 wt%, as this could result in excessive reactor
exotherm during the first stage of sulfiding – this is especially relevant when LHSV is lower than
0.6 hr-1. The maximum catalyst temperature should be kept below 250°C (480°F) during this
phase.
CAUTION: If an issue arises with the initiation of sulfur-donating agent injection, the
reactor inlet temperature ramping should be suspended until the sulfur-donor injection
can be started. The reactor temperatures should be maintained below 190°C (375°F).
7) When the injection rate of sulfur-donating agent has been verified, the reactor inlet temperature
is increased toward 225°C (440°F) at a rate of 25°C/hr (45°F/hr). When the decomposition
temperature of the sulfur-donating agent is reached, hydrogen sulfide (H2S) and light
hydrocarbons are produced, resulting in reactor exotherms. The gas and oil feed rates are
maximized in order to control the temperature increase.
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8) If desired, the injection rate of sulfiding agent may be doubled during the first stage of
sulfiding (until breakthrough of hydrogen sulfide), corresponding to dividing the total
stoichiometric requirement of sulfiding agent into 8 hours. However, exotherms and
maximum temperatures must be closely monitored as described below.
9) Water is formed from the sulfiding reactions. Check the high-pressure separators at regular
intervals for water accumulation throughout the catalyst sulfiding and drain, when necessary.
10) During the first phase of sulfiding, the reactor inlet temperature is maintained at 225°C (440°F)
until breakthrough of hydrogen sulfide. Due to the risk of coking, the reactor bed temperatures
during this period should not exceed 250°C (480°F). The injection rate of sulfur-donating agent,
and possibly the reactor inlet temperature, are adjusted accordingly. In hydrocracking pretreat
units, it is advised to apply interbed quench in order to maintain temperatures of the downstream
catalyst beds at or below 200°C (390°F).
11) Hydrogen purity of the recycle gas is checked during the first stage of sulfiding. Accumulation of
light hydrocarbons (from decomposition of the sulfur-donating agent) in the recycle gas may
result in low hydrogen purity and an increase in recycle gas density, which can cause issues
with the recycle gas compressor operation. Thus, it may be required to purge the high-pressure
loop as described above.
12) In order to ascertain breakthrough of hydrogen sulfide, the high-pressure separator off-gas (i.e.
recycle gas) must be checked for concentration of hydrogen sulfide using Dräger tubes or an
appropriate online GC system at hourly intervals. The check of hydrogen sulfide should be
commenced around 2–3 hours after the initiation of the sulfur-donating agent injection. When an
online analyzer is applied, Dräger tube assessment may only be needed for instrument
validation. Breakthrough is defined as the point when two consecutive measurements of
hydrogen sulfide show levels above 3,000 ppmv. When using an online analyzer, breakthrough
is defined as sustained indications of hydrogen sulfide concentrations above 3,000 ppmv, with a
single verification by Dräger. Breakthrough typically occurs after 30–60% of the stoichiometric
amount of sulfur-donating agent has been injected. However, for naphtha service activations or
other small-size reactors, the breakthrough may not occur until 60–80% of the stoichiometric
amount of sulfur-donating agent has been injected. Breakthrough indicates completion of the
first phase of sulfiding.
13) In some cases, breakthrough has been observed early in the process. The source of
breakthrough may be due to an exchanger leak, poor distribution when using low liquid feed
rates, or uneven distribution through multiple reactors oriented in parallel. In any case, it is
recommended to maintain temperatures below 250°C (480°F) until at least 40% of the
stoichiometric amount of sulfur-donating agent has been injected.
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14) Following confirmed breakthrough of hydrogen sulfide, the reactor inlet temperature is increased
to target catalyst bed temperatures of 330°C (625°F) at a rate of 20°C/hr (35°F/hr). The injection
rate of sulfur-donating agent is adjusted to ensure sufficient quantity is available for injection
through the end of the high-temperature hold period. The recycle gas is checked for levels of
hydrogen sulfide every hour and for hydrogen content every 2-3 hours. Once verified by Dräger,
an online analyzer can be used to monitor the levels of hydrogen sulfide. Peak bed
temperatures should be kept below 350°C (660°F), and the reactor inlet temperature is adjusted
accordingly, if necessary. During the second stage of the catalyst sulfiding, the heating is
adjusted in order to maintain the H2S concentration above 3,000 ppmv. In case the H2S
concentration drops below 3,000 ppmv, the heat ramp should be stopped until a hydrogen
sulfide concentration of 3,000 ppmv or greater is measured. Alternatively, the rate of sulfurdonating agent may be increased.
NOTE: Excessive recycle gas H2S concentrations can be corrosive. This is especially
important for the compressor and associated parts and piping. Investigate design limits
and tolerances of equipment to avoid corrosion and subsequent compressor or piping
failure. If no limits are given, the recycle gas H2S content should preferably be less than
1.0 vol% and shall not exceed 2.0 vol%.
15) During the final stage of catalyst sulfiding, the reactor inlet temperature should be adjusted such
that the reactor bed temperatures are maintained at 330-350°C (625–660°F). At this time, if
applied, interbed quench should be reduced. When the final hold temperatures have been held
at reactor bed temperatures of at least 330°C (625°F) for a minimum of 4 hours, and when a
sulfur balance shows that no less than 100% of the stoichiometric amount of sulfur has been
added, the activation/sulfiding is considered completed. The addition of sulfur-donating agent
can be terminated after once-through, fresh straight-run feed flow has been established.
16) During the second stage of sulfiding, if the maximum temperatures are less than 320°C (610°F),
it is recommended that a Topsoe representative is contacted for advice. A longer hold
temperature may be implemented.
17) Pressure is adjusted to normal unit pressure, and straight-run feed is stabilized at normal feed
flow rate. If the start-up oil is circulated, this recirculation is stopped, and the oil is routed to
product tanks. If installed in the unit, amine circulation is started, and the recycle gas scrubber
and associated equipment are put into service. The product stripper and/or fractionation section
are brought to normal operating conditions according to refinery procedures. Typically, the initial
product will not meet all specifications, and laboratory analyses have to be performed to verify
that the product meets target specifications.
18) Wash water injection is commissioned to the reactor effluent at normal rate.
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19) The reactor inlet temperature is adjusted at a rate of 30°C/hr (50°F/hr) to the temperature
required to reach the product specifications. After 5–6 hours, feed and product samples should
be analyzed to verify the operation and performance of the catalysts.
20) In order to condition the catalyst and to ensure optimal activity, it is recommended that the unit is
fed with straight-run feedstock for a minimum of 48 hours upon completion of catalyst sulfiding.
After that, cracked stocks and/or renewable feeds may be gradually introduced.
21) In the event that the refinery needs to process cracked stock or renewable feeds prior to the end
of the 48-hour break-in period, Topsoe representative should be contacted for advice.
22) Operating conditions are checked in order to ensure that the pressure, gas rates, recycle gas
purity, and hydrogen sulfide removal specifications are met. Reactor temperatures, stripper
operation, etc. are adjusted in order to meet product specifications.
6.4
Sulfiding procedure for hydrocracking catalyst liquid phase
Fresh or regenerated zeolitic catalysts have a very high cracking activity due to the acidic nature of
the zeolite. During normal operation, the high activity is moderated by adsorption of basic
compounds, principally ammonia. Until the catalyst equilibrates with the ammonia level in the reactor
environment, its high activity can result in significant hydrocracking, even at very low temperatures.
Some sulfiding procedures use addition of aqueous or anhydrous ammonia during the latter stages
of the sulfiding to passivate the cracking catalyst. However, anhydrous ammonia handling has safety
concerns.
This sulfiding procedure describes a method where native nitrogen in the feed passivates the
cracking catalyst. Light feed hydrocrackers that do not have the possibility to add a feed containing
minimum 400 wt ppm nitrogen in the Phase II of the sulfiding will need to follow a different
procedure.
The start-up feed used for the Phase I of the sulfiding must be a straight-run petroleum fraction, such
as atmospheric gas oil (diesel). The start-up feed should have the following properties:
−
−
ASTM D2887 or TBP final boiling point maximum 380°C (720°F)
Maximum specific gravity of 0.85, equivalent to an API gravity higher than 35.
For the Phase II final high-temperature sulfiding, while the reactors are being heated, the start-up
feed is changed to a heavier material that contains more nitrogen. The heavier material is preferably
straight-run vacuum gas oil (VGO) with the following properties:
−
−
−
Specific gravity maximum 0.91 (gravity minimum 24°API)
ASTM D7213 or TBP distillation endpoint below 530°C (990°F)
Total nitrogen minimum 400 wppm.
The catalyst sulfiding guidelines for hydrocracking catalyst are similar to those of the hydrotreating
catalysts. A step-by-step procedure, including a graph of the reactor inlet temperature profile during
a typical catalyst sulfiding operation, is shown below.
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1) At this point, it is assumed that the unit has been purged, pressurized to normal operating
pressure or a maximum of 70 barg (1,000 psig), and heated to a reactor inlet temperature of
175°C (350°F) as described in Section 6.1 in this manual. Furthermore, gas circulation has been
established, and the catalyst drying has been completed. It must be ensured that the hydrogen
purity of the treat gas is higher than 60 vol% at all times. For sites that do not have an online
analyzer for recycle gas purity, it is recommended to verify purity by gas chromatography every
4 hours. In general, hydrogen purity should be maximized. Treat gases that contain carbon
oxides should be avoided. Carbon oxides can be an issue with catalytic reformer units and with
refineries processing renewable diesel. In some cases, carbon oxides can interfere with the
catalyst sulfiding process. It is thus recommended to purify the hydrogen stream in a PSA unit or
similar membrane unit.
2) Once-through start-up oil is introduced at around 50% of the design feed flow rate. The liquid
feed must be introduced at reactor temperatures below 175°C (315°F).
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3) Normally, due to heat of adsorption (heat of wetting), an exotherm will be observed when oil is
first introduced to the catalyst. Monitor and anticipate the temperature wave through the catalyst
beds. If unmitigated, the heat of adsorption can bring catalyst beds into a cracking temperature
regime. The following progression will keep bed exotherms within acceptable limits to
compensate for the heat of adsorption:
a) Set all quench valves to Manual mode. In Auto or Cascade modes, the Process Control
responses programmed for normal operation are too slow to counteract the heat release
from wetting.
b) As the heat wave approaches the bottom of each bed, open the corresponding quench
valve to preemptively cool the stream going into the following bed. Do not wait for the inlet
temperature of the subsequent bed to show an increase in temperature – an action at this
time can be too late. On occasion, a quench valve opening of 60% or more may be required
to compensate for a maximum temperature rise.
c) Once the temperature wave starts to wane, close the corresponding quench valve to
prevent the catalyst bed temperatures from falling too low. Ensure temperatures are
maintained above the Mechanical Pressurization Temperature limits.
d) This sequence of opening and closing quench valves is repeated for subsequent beds until
the entire reactor has experienced the temperature wave from heat of adsorption.
4) The feed rate is increased to 60–100% of the design feed flow rate or the maximum rate allowed
by the fractionator bottoms pump capacity, and the reactor is flushed with start-up oil,
corresponding to around three times the reactor volume or maximum 6 hours at full design rate,
in order to remove dust and particles that would otherwise be trapped in the reactor section.
Dependent on the liquid hourly space velocity, the flushing oil will often be sufficiently free of
particles within a period of 4 hours. Prior to initiating recycle of oil, a sample of the product is
visually checked in order to verify that it is non-hazy and free of particles. Completing a reactor
flush may not be necessary if sulfiding will be performed with once-through oil.
5) After flushing and stabilization of flows, temperatures, and pressures in the unit, the start-up oil
can be circulated from the stripper or fractionation section back to the unit feed pump, if desired.
This significantly reduces the quantity of start-up oil needed and thus reduces the amount of offspecification material produced. It is suggested that the oil recycle is not processed through
storage/product tanks, because the unstripped oil may contain hydrogen sulfide, partially
decomposed sulfur-donating agents, and/or ammonia which may accumulate in the tanks.
6) The reactor inlet temperature is increased to 190°C (375°F) at a rate of 25°C/hr (45°F/hr), and
the hydrogen content of the recycle gas is measured. In case the hydrogen content drops below
60 vol% at any time during the catalyst sulfiding, the high-pressure loop must be purged/vented,
and hydrogen-rich make-up gas is introduced to the unit.
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7) Injection of sulfur-donating agent at the feed pump suction side is started. As a guideline, the
average injection rate is obtained by dividing the total stoichiometric requirement of sulfurdonating agent into 18 hours, which is the approximate duration of the activation. Until the
reactor exotherm has stabilized (normally after 1–2 hours), it is recommended to apply half of
the average injection rate of sulfur-donating agent. Doping with a sulfur-donating agent should
result in a sulfur concentration in the oil not exceeding 2.5 wt% totally, as this could result in
excessive bed exotherms during the Phase I of the sulfiding – this is especially relevant when
the overall LHSV is lower than 0.6 hr-1. The maximum catalyst temperature should be kept
below 250°C (480°F) during this phase.
CAUTION: If an issue arises with the initiation of sulfur-donating agent injection, the
reactor inlet temperature ramping should be suspended until the sulfur-donor injection
can be started. The reactor temperatures should be maintained below 190°C (375°F).
8) The reactor inlet temperature is increased toward 225°C (440°F) at a rate of 25°C/hr (45°F/hr).
When the sulfur-donating agent decomposition temperature is reached, hydrogen sulfide (H2S)
and light hydrocarbons are produced, resulting in bed exotherms. The gas and oil feed rates are
maximized in order to control the temperature increase.
9) If desired, the injection rate of sulfur-donating agent may be doubled during the Phase I of
sulfiding (until breakthrough of hydrogen sulfide), corresponding to dividing the total
stoichiometric requirement of sulfur-donating agent into 9 hours. However, exotherms and
maximum observed catalyst bed temperatures must be closely monitored as described below.
10) Water is formed from the sulfiding reactions. Check the high-pressure separators at regular
intervals for water accumulation throughout the catalyst sulfiding and drain, when necessary.
11) During Phase I of the sulfiding, the reactor inlet temperature is maintained at 225°C (440°F) until
breakthrough of hydrogen sulfide. Due to the risk of coking, the reactor bed temperatures during
this period should not exceed 250°C (480°F). The injection rate of sulfur-donating agent, and
possibly the reactor inlet temperature, are adjusted accordingly. It is advised to apply interbed
quench in order to maintain temperatures of the downstream catalyst beds at or below 200°C
(390°F).
12) Hydrogen purity of the recycle gas is checked during the whole sulfiding. Accumulation of light
hydrocarbons (from decomposition of the sulfur-donating agent) in the recycle gas may result in
low hydrogen purity and an increase in recycle gas density, which can cause issues with the
recycle gas compressor operation. Thus, it may be required to purge the high-pressure loop as
described above.
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13) In order to ascertain breakthrough of hydrogen sulfide, the high-pressure separator off-gas (i.e.
recycle gas) must be checked for concentration of hydrogen sulfide using Dräger tubes or an
appropriate online GC system at hourly intervals. The check of hydrogen sulfide should be
commenced around 2–3 hours after the initiation of the sulfur-donating agent injection.
Breakthrough is defined as the point when two consecutive measurements of hydrogen sulfide
show levels above 3,000 ppmv. This typically occurs after 30–60% of the stoichiometric amount
of sulfur-donating agent has been injected. However, for small-size reactors, the breakthrough
may not occur until 60–80% of the stoichiometric amount of sulfur-donating agent has been
injected. Breakthrough indicates completion of the first phase of sulfiding.
In some cases, breakthrough has been observed early in the process. The source of
breakthrough may be due to an exchanger leak, poor distribution when using low liquid feed
rates, or uneven distribution through multiple reactors oriented in parallel. In any case, it is
recommended to maintain temperatures below 250°C (480°F) until at least 50% of the
stoichiometric amount of sulfur-donating agent has been injected.
14) Following confirmed breakthrough of hydrogen sulfide, start the addition of fresh start-up VGO to
the feed surge drum and reduce recirculation from the fractionation section to maintain levels.
Gradually convert to once-through operation with the start-up VGO feed at the normal fresh feed
rate or lower, if limited by the fractionator bottom pump rate. During the sulfiding heat-up
following the H2S breakthrough, many hydrocrackers will be limited in charge rate by the
available duty in the charge heater. This is a consequence of the limited heat release by low
reaction rates at low temperatures.
15) The hydrotreating reactor inlet temperature is increased to 260°C (500°F) at a maximum rate of
15°C/hr (27°F/hr). The recycle gas is checked for levels of hydrogen sulfide every hour and for
hydrogen content every 2–3 hours.
16) When increasing the hydrotreating reactor inlet temperature with fresh start-up VGO, a
temperature rise may develop. Activate quench gas control and establish a slightly descending
temperature profile of about 3°C (5°F) per catalyst bed (i.e. the outlet temperature of a
successive catalyst bed is 3°C below the outlet temperature of the previous catalyst bed). The
reactor quench gas should be maintained under active control throughout the final heat-up
phase of presulfiding.
17) Stop the heat-up if any temperature rise in the hydrocracking catalyst beds exceeds 10°C
(18°F). Hold temperatures until the rise falls below 10°C (18°F). If the temperature rise
continues to increase above 10°C (18°F) in any hydrocracking bed, use quench to rapidly
reduce all hydrocracking bed inlet temperatures until the increasing rise is stopped. If any
hydrocracking catalyst bed temperature rise exceeds 30°C (54°F), the unit should be
immediately depressurized according to the emergency shutdown procedures.
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18) At the higher temperatures, the catalyst consumes more sulfur. In case the levels of hydrogen
sulfide drop below 3,000 ppmv, the heating should be stopped until a level of hydrogen sulfide
greater than 3,000 ppmv is achieved. Alternatively, the rate of sulfur-donating agent can be
increased.
NOTE: Excessive recycle gas H2S concentrations can be corrosive. This is especially
important for the compressor and associated parts and piping. Investigate design limits
and tolerances of equipment to avoid corrosion and subsequent compressor or piping
failure. If no limits are given, the recycle gas H2S content should preferably be less than
1.0 vol% and shall not exceed 2.0 vol%.
19) When the hydrotreating reactor inlet reaches 260°C (500°F), decrease the heat-up to 10°C/hr
(18°F/hr) and increase the hydrotreating reactor inlet to 330°C (625°F). At this stage, the startup gas oil has been replaced 100% by start-up VGO.
20) Start wash water to the reactor effluent air cooler at normal rates.
21) Continue to use quench to maintain a descending temperature profile of 3°C (5°F) per bed while
increasing the hydrotreating reactor inlet temperature. Continue to monitor temperature rise in
the hydrocracking catalyst beds and limit rise to less than 10°C (18°F) in these beds.
22) At higher temperatures, sufficient H2S is probably generated by conversion of sulfur in the feed,
and injection of the sulfur-donating agent can be reduced or stopped. Maintain the sulfurdonating agent supply connection to enable injection to the feed pump suction if necessary.
23) During the final phase of catalyst sulfiding, the hydrotreating reactor inlet temperature should be
adjusted such that all reactor bed temperatures are maintained at 330–350°C (625–660°F).
Peak bed temperatures should be kept below 350°C (660°F). When all catalyst bed
temperatures have been at or above 330°C (625°F) for a minimum of 4 hours, and when a sulfur
balance shows that no less than 100% of the stoichiometric amount of sulfur has been added,
the activation/sulfiding is considered completed. Addition of sulfur-donating agent can be
terminated if this has not already been done.
24) During the second phase of sulfiding, if the maximum temperatures are less than 320°C
(610°F), it is recommended that a Topsoe representative is contacted for advice. A longer hold
temperature may be implemented.
25) Amine scrubber is put into service.
26) Raise system pressure to normal operating level while following the Mechanical Pressurization
Temperature curves.
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27) If the unit normally operates with recycle of fractionator bottoms unconverted oil, start the
recirculation and line out at the normal operating rate. Depending on the capacity of the
fractionator bottoms pump and rundown cooling capacity for unconverted oil, it may be
necessary to limit recycle rate until the conversion of fresh feed is established in the reactor
section.
28) When the normal recycle oil rate (if any) has been established, begin gradually increasing
hydrocracking catalyst bed temperatures at a maximum rate of 5°C/hr (9°F/hr) to start lining out
conversion. Allow hydrocracking catalyst bed temperature profiles to stabilize after each
increase in temperature. Adjust hydrocracking bed temperatures by quench gas addition to
maintain approximately equal cracking bed temperature rises and outlet temperatures. Monitor
bed temperature rises and do not allow them to increase above normal levels during the heatup. Changes in hydrocracking conversion can take significant time to appear; therefore, be sure
to make gradual adjustments in the reactor temperatures in order to prevent overshooting the
desired conversion level.
29) Bring the fractionation section on line and adjust parameters to obtain the desired product splits.
30) Check operating conditions to ensure that the operation meets the design pressure, gas rates,
recycle gas purity, and H2S removal specifications. Adjust the pretreater reactor operating
temperatures to achieve the desired nitrogen conversion target.
31) In order to precondition the catalyst to the operation, it is recommended that the unit is fed with
straight-run feedstocks for a minimum of 48 hours upon completion of catalyst sulfiding. After
that, cracked stocks or renewable feeds may be gradually introduced. In the event that the
refinery needs to process cracked stock or renewable feeds prior to the end of the 48-hour
break-in period, Topsoe representative should be contacted for advice.
6.5
Sulfiding procedure for hydrocracking catalyst vapor phase
In this procedure, a sulfur-donating agent is added to the treat gas. For sour gas, please consult with
your Topsoe representative. The approved sulfur-donating agents include DMDS, DMS, and
polysulfides. DMDS is the most commonly applied agent. Note that if a polysulfide is used for vapor
phase activation, then the polysulfide will need to be introduced into the gas stream as close as
possible to the reactor inlet.
It is advisable to do a sulfur balance as a check on the level of sulfiding. Ideally, this will be done by
measuring the amount of sulfur-donating agent injected into the system and subtracting the sulfur in
the product streams, as well as the content of hydrogen sulfide in the purge/vent stream and any
other sour gas streams leaving the unit. This requires that flow meters for these streams are zeroed
and calibrated for the atypical operating conditions found during start-up conditions. We recommend
having a minimum of 50% excess of the sulfur-donating agent on site.
Following the gas phase sulfiding, the catalyst beds are cooled down prior to feed introduction. A
graph of the reactor inlet temperature profile during a typical vapor phase catalyst sulfiding operation
is shown below.
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Below is shown two examples of how to calculate the rate of DMDS for obtaining 0.5% H2S in the
treat gas going into the first reactor.
0.5
𝑘𝑘𝑘𝑘
𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 � � =
∗
100
ℎ𝑟𝑟
𝑘𝑘𝑘𝑘 𝑆𝑆
𝑁𝑁𝑁𝑁3
𝑡𝑡𝑡𝑡𝑒𝑒𝑎𝑎𝑎𝑎 𝑔𝑔𝑔𝑔𝑔𝑔 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 �
� ∗ 32 �𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘�
ℎ𝑟𝑟
𝑘𝑘𝑘𝑘 𝑆𝑆
𝑁𝑁𝑁𝑁3
22.41 �
∗ 0.68 �
𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘�
𝑘𝑘𝑘𝑘 𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷�
𝑘𝑘𝑘𝑘 𝑆𝑆
𝑁𝑁𝑁𝑁3
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝑔𝑔𝑔𝑔𝑔𝑔 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 �
� ∗ 32 �𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘�
𝑔𝑔𝑔𝑔𝑔𝑔
0.5
ℎ𝑟𝑟
𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 �
∗
�=
𝑙𝑙𝑙𝑙𝑙𝑙 𝑆𝑆
ℎ𝑟𝑟
100 22.41 𝑁𝑁𝑁𝑁3 ∗ 0.4536 𝑘𝑘𝑘𝑘 ∗ 6.0
�𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘�
�𝑙𝑙𝑙𝑙𝑙𝑙�
�𝑔𝑔𝑔𝑔𝑔𝑔 𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷�
1) In preparation for catalyst activation activities, the site should ensure that the appropriate
logistics and supplies are available and on hand: adequate laboratory coverage, sample
containers, and increased frequency of sample pick-up for spot and special analyses of treat
gas/recycle gas and product oil streams; a sufficient supply of Dräger tubes if Dräger readings
are taken. The sulfur-donating agent injection equipment should be prepared and ready for
injection.
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2) At this point, it is assumed that the unit has been purged, pressurized to normal operating
pressure or a maximum of 70 bar g (1,000 psig), and heated to 175°C (350°F) as described in
Section 6.1 in this manual. Furthermore, gas circulation has been established, and the catalyst
drying has been completed. It must be ensured that the hydrogen purity of the treat gas is higher
than 60 vol% at all times. Prior to the introduction of the sulfur-donating agent, the treat gas
purity should be maximized to minimize the need for recycle gas purge when H2S concentration
in the recycle gas is elevated. For sites that do not have an online analyzer for recycle gas purity,
it is recommended to verify purity by gas chromatography every 4 hours. In general, hydrogen
purity should be maximized. Treat gases that contain carbon oxides should be avoided. Carbon
oxides can be an issue with catalytic reformer units and with refineries processing renewable
diesel. In some cases, carbon oxides can interfere with the catalyst sulfiding process. It is thus
recommended to purify the hydrogen stream in a PSA unit or similar membrane unit.
3) The reactor inlet temperature is increased to 200°C (390°F) at 15°C/hr (27°F/hr), and recycle gas
flow rate is maximized.
4) Injection of sulfur-donating agent is initiated. The injection rate should start at a low level due to
the risk of undesirable high bed temperatures resulting from a high exotherm. As a guideline, the
injection rate should correspond to having 0.5% H2S in the treat gas to the first reactor. The initial
injection rate should be half of this value and remain at that rate until the reactor exotherm has
stabilized (normally after 1 hour). Note that during the catalyst activation, the injection rate of
sulfur-donating agent may be changed but it should never exceed 1%. The exact rate should be
agreed on by the refinery and a Topsoe representative.
5) In case the injection of sulfur-donating agent cannot be started or the injection has stopped, the
reactor temperatures should be lowered and should not exceed 200°C (390°F) before the
injection is commenced or reestablished.
6) When the injection of sulfur-donating agent is initiated the purge can be opened to bleed out the
methane gas formed during the sulfiding. The site should confirm whether bleed gas scrubbing is
required based on its disposition. Fresh make-up gas should be added continuously to maintain
a high H2 content of the recycling gas.
7) Water is formed during the sulfiding. This will accumulate in the separators, and the water boot
level should be maintained in the normal operating range.
8) The inlet temperature of the first bed in the first reactor is increased to 225°C (440°F) at 15°C/hr
(27°F/hr). The maximum bed temperature rise should not exceed 30°C (50°F), and peak
temperatures of the first bed should not exceed 250°C (480°F). The temperature of the
subsequent beds should be kept at 175–200°C (350–390°F) as long as the reactor inlet
temperature remains above the minimum decomposition temperature for the selected sulfurdonating agent.
9) The catalyst is sulfided at a reactor inlet temperature of 225°C (440°F) until breakthrough of H2S.
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10) In order to ascertain breakthrough of hydrogen sulfide, the high-pressure separator off-gas (i.e.
recycle gas) must be checked for concentration of hydrogen sulfide using Dräger tubes or an
appropriate online GC system at hourly intervals, starting 2–3 hours after the initiation of the
sulfur-donating agent injection. Breakthrough is defined as the point when two consecutive
measurements of hydrogen sulfide show levels above 3,000 ppmv. This typically occurs after
30–60% of the stoichiometric amount of sulfur-donating agent has been injected. Breakthrough
indicates completion of the first phase of sulfiding. If breakthrough occurs at a point when less
than 30% of the stoichiometric amount of sulfur-donating agent has been injected, then pay
attention to reactor bypass and anticipate a longer hold period.
11) Following confirmed breakthrough of H2S, the reactor inlet temperature is increased to target
catalyst bed temperatures of 330°C (625°F) at a rate of 15°C/hr (27°F/hr). Continuous addition of
sulfur-donating agent is critical at this point, and it must be ensured that the levels of H2S in the
gas downstream the reactor is in the range from 3,000 ppmv up to 1% at all times. Heating is
paused if the H2S content of the treat gas drops below 3,000 ppmv. Alternatively, the rate of
sulfur-donating agent may be increased up to 1%.
12) Monitor the H2 purity of the recycle gas every 2–3 hours, assuring that it does not drop below 60
vol%.
NOTE: Excessive recycle gas H2S concentrations can be corrosive. This is especially
important for the compressor and associated parts and piping. Investigate design limits
and tolerances of equipment to avoid corrosion and subsequent compressor or piping
failure. If no limits are given, the recycle gas H2S content should preferably be less than
1.0 vol% and shall not exceed 2.0 vol%.
13) During the final phase of catalyst sulfiding, the reactor inlet temperature and rate of sulfurdonating agent should be adjusted such that the reactor bed temperatures are maintained at
330–350°C (625–660°F). Peak bed temperatures should be kept below 350°C (660°F).
14) When all catalyst bed temperatures have been at or above 330°C (625°F) for a minimum of 4
hours, the activation/sulfiding is considered completed.
15) At this point, the addition of sulfur-donating agent can be terminated as long as the recycle gas
H2S remains above 3,000 ppmv. Do not disconnect the sulfur-donating injection facilities until
after once-through, fresh straight-run feed flow has been established, and HDS is occurring
(producing H2S).
16) The reactor bed temperatures are reduced to maximum 175°C (350°F) or 14°C (25°F) above
Mechanical Pressurization Temperature (whichever is higher) for operation at 70 barg (1,000
psig). Cool down rate should be limited to a maximum of 30°C/hr (50°F/hr) in preparation for feed
introduction. Cool down rates can be increased based on the equipment temperature stress
analysis.
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6.6
Feed introduction after vapor phase sulfidation
Feed introduction will result in catalyst bed exotherms due to the heat of adsorption (heat of wetting).
In the case where the catalyst bed temperatures are too high, this exotherm may bring the reactor
temperature up to a level where reactions start to take place. Kinetically-controlled reactions, such
as aromatic saturation, can lead to additional heat release and exotherm in the catalyst bed,
resulting in excessive cracking and a temperature runaway. The freshly sulfided hydrocracking
catalyst is very active, as it has not yet been subjected to ammonia or nitrogen, which passivates the
active cracking sites. Therefore, caution is required when introducing the liquid feed.
The start-up feed should be a straight-run atmospheric gas oil or light vacuum gas oil (VGO) to
reduce catalyst exposure to heavy aromatics that can lead to premature coking. The feed must not
contain any cracked material. The start-up feed should have the following properties:
−
−
Specific gravity maximum 0.91 (gravity minimum 24°API)
ASTM D7213 or TBP distillation endpoint below 530°C (990°F).
1) At this point, it is assumed that the unit is pressurized to normal operating pressure or a
maximum of 70 barg (1,000 psig), and all reactor bed temperatures are maximum 175°C
(350°F). Furthermore, the catalyst sulfiding has been completed, and the addition of sulfurdonating agent has been terminated. It must be ensured that the hydrogen purity of the treat gas
is higher than 60 vol% at all times. In general, hydrogen purity should be maximized.
2) Once-through start-up oil is introduced at around 50% of the design feed flow rate.
3) Normally, due to heat of adsorption (heat of wetting), an exotherm will be observed when oil is
first introduced to the catalyst. Monitor and anticipate the temperature wave through the catalyst
beds. If unmitigated, the heat of adsorption can bring catalyst beds into a cracking temperature
regime. The following progression will keep bed exotherms within acceptable limits to
compensate for the heat of adsorption:
a) Set all quench valves to Manual mode. In Auto or Cascade modes, the Process Control
responses programmed for normal operation are too slow to counteract the heat release from
wetting.
b) As the heat wave approaches the bottom of each bed, open the corresponding quench valve
to preemptively cool the stream going into the following bed. Do not wait for the inlet
temperature of the subsequent bed to show an increase in temperature – an action at this
time can be too late. On occasion, a quench valve opening of 60% or more may be required
to compensate for a maximum temperature rise.
c) Once the temperature wave starts to wane, close the corresponding quench valve to prevent
the catalyst bed temperatures from falling too low. Ensure temperatures are maintained
above the Mechanical Pressurization Temperature limits.
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d) This sequence of opening and closing quench valves is repeated for subsequent beds until
the entire reactor has experienced the temperature wave from heat of adsorption.
4) The feed rate is increased to 60–100% of the design feed flow rate or the maximum rate allowed
by the fractionator bottoms pump capacity.
5) For units with recycle oil operations, the reactor is flushed with once-through start-up oil,
corresponding to around three times the reactor volume in order to remove catalyst dust and
particles that would otherwise be trapped in the reactor section. Dependent on the liquid space
velocity, flushing oil will often be sufficiently free of particles within a period of 4 hours.
6) If the unit normally operates with recycle of fractionator bottoms unconverted oil, start the
recirculation after the flushing period.
7) Temperatures and pressures can be increased concurrently with catalyst flushing. Start
temperature increase towards 230°C (450°F) at 25°C/hr (45°F/hr). Start increasing the pressure
to the normal operating pressure at increments that ensure stable operation and according to the
mechanical pressurization temperature curves.
8) When increasing the hydrotreating reactor inlet temperature, a temperature rise may develop.
Activate quench gas control and establish a slightly descending temperature profile of about 3°C
(5°F) per catalyst bed (i.e. the outlet temperature of a successive catalyst bed is 3°C below the
outlet temperature of the previous catalyst bed).
9) Stop the heat up if any temperature rise in the hydrocracking catalyst beds exceeds 10°C (18°F).
Hold temperatures until the rise falls below 10°C (18°F). If the temperature rise continues to
increase in any hydrocracking bed, use quench to rapidly reduce all hydrocracking bed inlet
temperatures until the increasing rise is stopped. If any hydrocracking catalyst bed temperature
rise exceeds 30°C (54°F), the unit should be immediately depressurized according to the
emergency shutdown procedures.
10) When the hydrotreating reactor inlet temperature reaches 230°C (450°F), decrease the heat
ramp rate to 15°C (27°F) and continue to heat the reactor inlet to 260°C (500°F).
11) When the hydrotreating reactor inlet temperature reaches 260°C (500°F), switch to the normal
feed without cracked material in case the start-up feed is lighter than the normal feed. The heatup process can continue while feed is being transitioned.
12) At 260°C (500°F), decrease the heating ramp rate to 10°C/hr (18°F/hr) and continue to heat the
reactor inlet to 28°C (50°F) below the expected start of run (SOR) temperatures.
13) Start wash water to the reactor effluent air cooler at normal rates.
14) Amine scrubber is put into service.
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15) Begin gradually increasing reactor bed temperatures for conversion target. Raise temperatures
in 2°C (3°F) increments every 15–20 minutes (approximately 5°C/hr or 9°F/hr). Allow
hydrocracking catalyst bed temperature profiles to stabilize after each increase in temperature.
Adjust hydrocracking bed temperatures by quench gas addition to maintain approximately equal
cracking bed temperature rises and outlet temperatures. Monitor bed temperature rises and do
not allow them to increase above normal levels during the heat up. Changes in hydrocracking
conversion can take significant time to appear; therefore, be sure to make gradual adjustments in
the reactor temperatures in order to prevent overshooting the desired conversion level.
16) Bring the fractionation section on line and adjust parameters to obtain the desired product splits.
17) Check operating conditions to ensure that the operation meets the design pressure, gas rates,
recycle gas purity, and H2S removal specifications. Adjust the pretreater reactor operating
temperatures to achieve the desired nitrogen conversion target.
18) In order to precondition the catalyst to the operation, it is recommended that the unit is fed with
straight-run feedstocks for a minimum of 48 hours upon completion of catalyst sulfiding. After
that, cracked stocks or renewable feeds may be gradually introduced. In the event that the
refinery needs to process cracked stock or renewable feeds prior to the end of the 48-hour
break-in period, Topsoe representative should be contacted for advice.
6.7
Sulfiding of replacement catalyst after skimming
In some cases, refiners have to interrupt a run to skim off the top catalyst bed to alleviate pressure
drop problems or to replace contaminated catalyst from unexpected feed variations. In these cases,
new catalyst and/or grading are installed to replace the skimmed catalyst. The remaining catalyst in
the reactor is in the sulfided state, which means that only sulfiding of the replacement catalyst is
required.
In this situation, an abbreviated sulfiding procedure is typically applied. If a large percentage (more
than 10%) of the bulk catalyst in the reactor is replaced, we suggest applying the recommended
method described for fresh or regenerated catalyst, which can be found in Sections 6.3, 6.4, or 6.5 of
this manual, as appropriate.
Therefore, the following procedure is for activating a small portion (less than 10%) of fresh catalyst
loaded on top of the catalysts that have previously been in operation.
The procedure assumes that the catalyst in the reactor is under nitrogen atmosphere and that the
reactor is kept at ambient temperature. Furthermore, it is assumed that the fresh make-up catalyst
as delivered is in the oxidic state – and not presulfided or preactivated.
1) Start heating the reactor towards an inlet temperature of 175°C (350°F) at around 25°C/hr
(45°F/hr).
2) The unit is pressurized to normal operating pressure (unless limited by the Mechanical
Pressurization Temperature curves (as described in Section 6.1 in this manual).
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3) While raising system pressure, the recycle gas compressor is started, and circulation of treat gas
is established at normal flow rate. It must be ensured that the hydrogen purity of the treat gas is
higher than 60 vol%. In order to conserve hydrogen sulfide during the sulfiding step, the amine
absorber must be bypassed or the amine circulation stopped, and any purging/venting should be
minimized.
4) Straight-run feed is gradually introduced and increased to design rate. Monitor the reactor
pressure drop and adjust the feed rate and reactor inlet temperature, if necessary. In case the
feed is a cracked stock or contains cracked components, apply a straight-run feedstock in the
same boiling range as the normal feed or the straight-run components of the blend. To be
effective, the start-up feed must contain minimum 0.5 wt% sulfur.
5) Reactor inlet temperature is increased towards 330°C (625°F) at 20°C/hr (35°F/hr).
6) Normally, desulfurization reactions begin around 275–300°C (525–570°F). H2S will be generated
from the feed, and water formation is to be expected and will be observed in the separator(s).
7) Maintain the inlet temperature above 330°C (625°F) for 4 hours, after which the sulfiding of the
make-up catalyst is considered complete.
8) Amine circulation is initiated, and the amine absorber is put into service. Typically, the product
will have to be sent to the normal off-spec disposition until laboratory analyses indicate that the
product meets target specifications.
9) The reactor inlet temperature is adjusted at 30°C/hr (50°F/hr) to the required temperature to
meet product specifications.
10) If the unit normally treats cracked or renewable feedstock, it is recommended to continue feeding
the unit with straight-run material (containing no less than 0.5 wt% sulfur) for a minimum of 48
hours in order to condition the catalyst. After that, cracked or renewable feedstock may be
gradually introduced.
11) Operating conditions are checked to ensure that the pressure, gas rates, recycle gas purity, and
hydrogen sulfide removal specifications are met. Reactor temperatures, stripper operation, etc.
are adjusted according to product specifications.
6.8
Start-up after planned shutdown
The start-up procedure described below is applied following a planned shutdown, where no changes
have been made to the state of the catalyst. All of the catalyst is still in its active/sulfided form and
thus does not require additional sulfur.
If any high-pressure equipment or piping has been opened, the high-pressure section must be
purged with nitrogen in order to bring the oxygen content to a safe level (typically below 0.5 vol%)
prior to introduction of hydrogen. The reactor temperatures should be maintained below 150°C
(300°F) during the shutdown to minimize the risk of catalyst reduction.
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1) The unit is pressurized to normal operating pressure (unless limited by the Mechanical
Pressurization Temperature of the reactor – as described in Section 6.1 in this manual).
2) While pressurizing the unit, the recycle gas compressor is started, and circulation of process gas
is established at normal flow rate. Amine circulation is initiated, and the amine absorber is put
into service.
3) Fresh straight-run feed oil is introduced and gradually increased to design rate. For heavier,
more viscous feeds, reactor temperatures may need to be raised to 150°C (300°F) or higher prior
to feed introduction. Monitor the reactor pressure drop and adjust the feed rate, if necessary. In
case the feed is normally a cracked feedstock or has cracked components, use a straight-run
feed in the same boiling range as the normal feed or the straight-run components of the blend.
4) After stabilizing flows, temperatures, and pressures, the start-up oil can be circulated from the
stripper or fractionation section, if desired. This reduces the quantity of start-up oil needed and
may reduce off-specification material produced. However, it must be ensured that some sulfur
remains in the oil, either by fresh feed make-up or sulfur-spiking agent, in order to maintain the
exotherm, and thus the hydrogen sulfide, in the reactor and thus prevent removal (stripping) of
sulfur from the catalyst. The preferred method to avoid this is to check that the level of hydrogen
sulfide in the recycle gas leaving the high-pressure separator remains above 0.05 vol% (500
ppmv). Use Dräger tubes to check. A more conservative method is recycling only 80–90% of the
product and adding sulfur components from 10–20% fresh feed. It is recommended that the oil
recycle is not done through storage/product tanks, because the unstripped oil may contain
hydrogen sulfide and/or ammonia, which may accumulate in the tanks.
5) Start wash water injection (if applicable) to the reactor effluent at normal rate.
6) The reactor inlet temperature is increased at 30°C/hr (50°F/hr) towards the temperature specified
as the start-of-run temperature or to the required temperature to meet product specifications. At
no point should the reactor inlet temperature be more than 100°C (212°F) higher than any
reactor bed temperature.
7) In case the normal feed contains cracked material, it may be gradually introduced as soon as the
reactor outlet temperature is above 250°C (480°F). Prepare for increased hydrogen consumption
and exotherm that will result from the addition of the cracked material.
8) At this time, any product recirculation should be stopped. As the reactor temperatures approach
the normal operating temperatures, laboratory analyses should be initiated in order to verify
product specifications.
9) Operating conditions are checked in order to ensure that the pressure, gas rates, recycle gas
purity, and hydrogen sulfide removal specifications are met. Reactor temperatures, stripper
operation, etc. are adjusted according to product specifications.
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6.9
Start-up of tail gas treating catalysts
The procedure outlined below should be followed for Topsoe tail gas treating catalysts.
1) The catalyst loading is performed in air according to the general guidelines listed in Section 5 of
this manual.
2) Before starting the actual sulfiding step, the unit needs to be purged to the extent that the oxygen
content is less than 0.5 vol%. Purging avoids the risk of forming explosive mixtures of hydrogen
and oxygen.
3) The purging is normally carried out using nitrogen but can also be accomplished by operating the
burner at a sub-stoichiometric ratio.
4) At these conditions, there will also be some hydrogen present in the treat gas. In order to avoid
reduction, prolonged exposure of the catalyst without hydrogen sulfide in the treat gas should be
avoided.
5) The catalyst bed is heated to 200°C (390°F) at a maximum rate of 25°C/hr (45°F/hr). Care
should be taken to ascertain that hydrogen sulfide is available for the catalyst activation.
Impaired catalyst activity can also result from exposure to hydrogen sulfide for extended periods
without the presence of hydrogen.
6) As soon as the catalyst bed temperature has reached 200°C (390°F), the operation can be
switched to stoichiometric conditions by adjusting the gas entering the unit to contain 2-5 vol%
hydrogen. Hydrogen sulfide is added to target 1 vol% concentration in the gas with a maximum
of 2 vol% in the gas.
7) Once the system is stable, the reactor temperature is slowly increased towards 320°C (610°F).
The exotherm should be kept below 30°C (50°F) at all times. When a reactor temperature of
230°C (450°F) is reached and the exotherm has moved out of the reactor, heating can be
continued towards 320°C (610°F) at 15°C/hr (25°F/hr).
8) When all catalyst temperatures have been at or above 320°C (610°F) for a minimum of 4 hours,
the sulfiding is considered completed.
9) The reactor is cooled to less than 280°C (540°F), and normal operation is initiated.
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7
Noble metal aromatic saturation catalysts
The noble metal catalysts are hydrotreating catalysts with high activity for saturation of aromatics.
Before use, these catalysts must be activated by reducing the metals.
7.1
In-situ reduction
The catalyst is activated by reduction with high-purity hydrogen. The hydrogen gas can originate
from a platinum reformer or a hydrogen plant and should meet the following minimum requirements:
−
−
−
Hydrogen purity
Nitrogen
Chlorides
>80%
<0.1 ppm
<2 ppm.
1) The unit is pressurized to normal operating pressure using the hydrogen-rich reformer gas.
2) Start up the recycle gas compressor and circulate gas at the normal recycle gas rate. Quench
gas flow should be blocked out.
3) Increase the reactor inlet temperature to 315°C (600°F) with a maximum of 320°C (610°F) at a
maximum rate of 50°C/hr (90°F/hr).
4) Maintain the reactor inlet temperature at 315°C (600°F) with a maximum of 320°C (610°F) for
minimum 5 hours. The time is measured from when the reactor outlet temperature has reached
at least 290°C (555°F).
5) Decrease the reactor outlet temperature to 150°C (300°F) before introducing liquid feed.
When reduction is completed, transition to normal operation can be commenced. If time elapses
from the completion of the reduction until oil feed is introduced, the catalyst can be cooled down and
circulation stopped. The reactor should be kept under hydrogen pressure.
7.2
Transition to normal operation
After reduction of the catalyst, two situations can occur according to the above.
Situation 1: Transition to normal operation is commenced immediately after the reduction.
1) When the reactor outlet temperature has reached 150°C (300°F), the flow of oil can be started
at normal LHSV.
2) When temperatures have stabilized throughout the reactor(s), temperature is increased towards
200°C (390°F) by 15°C (27°F) per hour.
3) When temperatures have stabilized throughout the reactor(s), the product aromatics content is
measured.
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4) If the product aromatics content is higher than the specification, increase the reactor inlet
temperature by 15°C (27°F) and repeat Step 3. If product is on or better than the specification,
go to Step 5.
5) Start flow of quench gas if quench is available.
6) Adjust the reactor inlet temperature in order to meet product specifications.
Situation 2: The unit has been cooled down and left under hydrogen pressure with the flow of gas
stopped.
1) The unit is pressurized to normal operating pressure with hydrogen gas, and the flow of recycle
gas is established at the normal flow rate.
2) If the reactor maximum temperature is below 150°C (300°F), the flow of oil can be started at
normal LHSV. If not, follow the procedure from Situation 1.
3) Increase the reactor inlet temperature at a rate of maximum 15°C (27°F) per hour until a reactor
inlet temperature of 150°C (300°F) is reached.
4) When temperatures have stabilized, the temperature is increased by 15°C (27°F) per hour
towards 200°C (390°F).
5) When temperatures have stabilized throughout the reactor(s), the product aromatics content is
measured.
6) If the product aromatics content is higher than the specification, increase reactor inlet
temperature by 15°C (27°C) and repeat Step 5. If product is on or better than the specification,
go to Step 7.
7) Start flow of quench gas if quench is available.
8) Adjust the reactor inlet temperature in order to meet product specifications.
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8
Troubleshooting
During normal operation of a hydroprocessing unit, many operations and causes could be
responsible for a specific issue. The tables below include some of the main areas of concern and
their remedies.
8.1
Off-spec product – high sulfur
Possible causes
Actions
High sulfur or nitrogen (or otherwise increased
severity) feedstock.
Check feed quality (density, end point, nitrogen,
aromatics, etc.) and adjust operating conditions
until desired values are reached.
Low reactor temperatures.
Increase reactor inlet temperature by additional
firing of the feed furnace, adjusting heat exchanger
bypasses, and/or reduce the quench gas. Check
possible fouling of heat exchangers or fires heaters
by a duty evaluation.
Mal-distribution in reactors.
Evaluate with reactor thermocouples temperature
indication for radial temperature differences.
Perform tracer study or a variable feed rate test.
Contact Topsoe for advice.
Reduced catalyst activity.
Check feed for catalyst poisons and/or other
contaminants. Check the gas for carbon oxides.
Leak in reactor feed/effluent heat exchangers.
Perform a temperature pulse test.
Increase reactor inlet temperature. If the product
sulfur does not decrease by the expected amount,
it is likely that there is a heat exchanger leak.
Obtain product samples for sulfur species analysis.
A shutdown to repair the leak may be necessary.
Leak in product stripper feed/effluent heat
exchanger.
Check with lead acetate paper. In case of high H2S,
increase flow rate of stripping steam. If product H2S
is still high, there is likely a heat exchanger leak. A
shutdown to repair the leak may be necessary.
Low hydrogen partial pressure in the reactor.
Purge from high pressure loop to increase
hydrogen purity of the Recycle Gas. Check makeup gas purity. If possible, increase pressure of the
reactor loop to maximum allowable working
pressure.
Insufficient absorption of H2S in the recycle gas
scrubber.
Check amine system including amine regeneration
and filters.
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8.2
Off-spec product – high hydrogen sulfide
Possible causes
Actions
Low stripping steam rate in the product stripper, or
low reboiler duty.
Increase stripping steam flow or reboiler duty.
Low temperature of liquid feed to the product
stripper.
Adjust liquid feed temperature according to design
of the product stripper.
Low liquid level in the bottom of the product
stripper.
Increase liquid level to design/normal level.
Leak in product stripper feed/effluent heat
exchanger.
Check with lead acetate paper. In case of high H2S,
increase flow rate of stripping steam. If product H2S
is still high, there is likely a heat exchanger leak. A
shutdown to repair the leak may be necessary.
Low product stripper column efficiency.
Adjust temperature and pressure; Maintain top
temperature minimum 10°C (20°F) above water
dew point. Increase naphtha reflux; Shutdown for
tray maintenance if damage of the trays is
suspected.
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8.3
High reactor pressure drop
Possible causes
Actions
Coke formation in the reactor due to more severe
feedstock properties.
Ensure adequate hydrogen availability by
increasing hydrogen purity and recycle rate.
Adjust atmospheric and/or vacuum distillation
unit(s), coker unit(s), FCC unit(s), blending
operation to reduce hydrogen consumption.
Catalyst dumping and subsequent
regeneration/replacement may be required.
Coke formation in the reactor due to reactor maloperation (unit upsets, sub-optimal operation, etc.)
Hot hydrogen strip may be beneficial. Catalyst
dumping and subsequent
regeneration/replacement may be required.
Operating conditions and/or procedures may need
revision.
Iron sulfide formation at top layer of the catalyst
bed.
Iron dispersant or anti corrosion chemical injection
may be beneficial. Shutdown to skim top section of
the catalyst bed. Consider modifying grading
catalyst profile for increased contaminant capacity.
Consider installing Topsoe Scale Catcher
By-pass or breach of feed filter (if installed).
Check filter operation and replace feed filter
elements. Check backflush operation, if applicable.
Consider modifying grading catalyst profile for
increased contaminant capacity. Consider installing
new filters and/or a Topsoe Scale Catcher in the
reactor. Catalyst regeneration/replacement may be
required.
Deposition of dust, debris, or corrosion products
(spalled from upstream equipment) in the top of the
catalyst bed following a unit upset or shutdown.
Shutdown to skim top section of the catalyst bed.
Consider modifying grading catalyst profile for
increased contaminant capacity. Consider installing
Topsoe Scale Catcher.
Excess treat gas flow to the reactor section.
Check treat gas flowmeters, quench valves and
hydrogen balance. Adjust as required.
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9
Planned shutdown
A planned shutdown is a controlled cooling of the reactor and removal of feed from the unit.
Temporary shutdown without catalyst replacement and shutdown for catalyst unloading are
described separately in this section.
The shutdown can be a temporary occurrence during a catalyst cycle due to maintenance
requirements or a shutdown of upstream or downstream units. In this case, it is expected that the
reactor will be restarted without catalyst replacement.
On the other hand, a shutdown for catalyst unloading (or skimming) will occur typically at the end of
the catalyst life cycle. Section 11 in this manual describes the reactor unloading process.
9.1
Temporary shutdown
In case the shutdown is temporary (without catalyst replacement), the following procedure should be
applied:
1) The heat input to the unit is reduced at a maximum rate of 30°C/hr (50°F/hr) in order to cool the
reactor catalyst beds to 250°C (480°F).
2) Product rundown is switched to off-specification storage. The feed rate is gradually decreased to
around 50% of design (or normal) feed rate of the unit. If cracked feedstock is processed, the
cracked portions of the feed blend are removed first.
3) When the reactor inlet temperature reaches 250°C (480°F), it is recommended that the design
feedstock to the unit is replaced with straight-run gas oil, diesel, or lighter feed, as feasible.
4) Maintain hydrogen sulfide in the treat gas, shut down amine circulation, and take amine absorber
offline.
a) In case it is expected to restart the unit within 48 hours, cool further and initiate product oil
and gas recirculation when reactor temperatures are below 200°C (390°F). Until restart, no
further actions are required.
b) If the unit will be shut down for more than two days, the catalyst will have to be stripped by
treat gas sweeping in order to remove hydrocarbons from the reactor section.
5) The reactor should be flushed with a total volume of light straight-run feed corresponding to
approximately three times (3x) the catalyst volume. During light-feed flushing, the following
guidelines should be followed:
a) Maintain reactor inlet temperature around 250°C (480°F) in order to prevent (or limit)
vaporization of the feed.
b) Maintain the light feed rate at around 50% of design (or normal) unit feed rate.
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c) Monitor reactor pressure drop and reduce feed rate, if necessary.
d) Maximize treat gas rates and maintain hydrogen purity above 60%.
e) Maintain separators and downstream cooling at normal operating temperatures.
f)
Purge recycle gas as needed to prevent recycling of low-boiling hydrocarbons and avoid
operational issues with the recycle compressor.
6) After flushing with the recommended amount of light feed, treat gas is circulated at 250°C
(480°F) until no more liquid accumulation is observed in the separators. However, the treat gas
sweep should be limited to a maximum of 12 hours in order to prevent stripping sulfur from the
catalyst.
7) The catalyst beds are cooled to 150°C (300°F). At this point, the treat gas may be replaced with
nitrogen. Circulation of gas is maintained.
8) In case maintenance of the high-pressure loop is required, the reactor and catalysts are further
cooled in nitrogen or treat gas circulation. The unit pressure is reduced before cooling below the
Mechanical Pressurization Temperature.
9) Before opening, the high-pressure loop is depressurized and purged with nitrogen. In order to
avoid the risk of explosion or self-heating of the catalyst upon opening of the reactor section, it is
important to secure and maintain a constant supply of nitrogen. Please also refer to the warning
related to possible formation of toxic nickel carbonyl as included in Section 11.4 of this manual.
9.2
Shutdown for catalyst unloading
In case the shutdown is for catalyst unloading or skimming, the following procedure should be
applied, even if the catalyst load is going to be reloaded in the reactor following screening, or ex-situ
regenerated, and possibly treated by the Topsoe reactivation process ReFRESH™.
1) The heat input to the unit is reduced at a maximum rate of 30°C/hr (50°F/hr) in order to cool the
reactor catalyst beds to 320°C (610°F).
2) Product rundown is switched to off-specification storage. When the reactor inlet temperature
reaches 320°C (610°F), it is recommended that the design feedstock to the unit is replaced with
straight-run gas oil, diesel, or lighter feed, as feasible.
3) The reactor should be flushed at the highest possible feed rate for 4 hours in order to remove
any cracked and/or heavy oil from the catalyst. During light-feed flushing at 320°C (610°F), the
following guidelines should be followed:
a) Maintain the light feed rate at design (or normal) unit feed rate, if possible.
b) Monitor reactor pressure drop and reduce feed rate, if necessary.
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c) Maximize treat gas rates and maintain hydrogen purity above 60%.
d) Maintain separators and downstream cooling at normal operating temperatures.
e) Purge recycle gas as needed to prevent recycling of low-boiling hydrocarbons and to avoid
operational issues with the recycle compressor.
4) After flushing with light feed, stop liquid feed to the reactor circuit and maintain a reactor
temperature of 320°C (610°F) while sweeping the catalyst at maximum treat gas circulation and
normal operating pressure. Reduce purging and stop amine scrubbing.
5) Increase the reactor inlet temperature at 30°C/hr (50°F/hr) to a target of 360°C (680°F). Maintain
separators and downstream cooling at normal operating temperatures.
6) Hold the reactor inlet temperature at 360°C (680°F) for 12 hours.
7) Following the hold at 360°C (680°F), the reactor temperature is reduced to 150°C (300°F) or at
low as possible at a cooling rate of 30°C/hr (50°F/hr). Pay attention to any material restrictions,
as provided by the vendors of the reactor or high-pressure vessel, as well as potential presence
of nickel carbonyl in case the gas contains more than 10 ppmv carbon monoxide.
8) The unit is depressurized, and the reactor section is purged with nitrogen until hydrogen levels
are below 5 vol%. In order to reach this level of hydrogen in the recycle gas, it may be necessary
to repeat depressurization and addition of nitrogen several times.
9) Continue cooling the reactor to ambient temperatures in nitrogen. External cooling, liquid
nitrogen, or temporary coolers on the recycle compressor discharge can be used to expedite
reactor cooling.
10) Upon opening the reactor, it is important to secure and maintain a constant supply of nitrogen for
a slight positive pressure in the reactor to prevent ingress of air. Please refer to Section 11 in this
manual for guidelines of catalyst unloading.
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10
Emergency shutdown
Emergency shutdowns may be caused by failures of various kinds. The actions to be taken are
primarily dictated by personnel, equipment, and safety considerations. However, in order to best
protect the catalyst from damage, it should be noted that the catalyst may be damaged by:
10.1
Hot hydrogen without hydrogen sulfide or oil
Prolonged exposure at these conditions would tend to strip sulfur from the active sulfided catalyst
with the inherent risk of reducing the metal sulfides to free metals with a consequential, permanent
loss of catalyst activity and creating the risk for a temperature runaway. Refer to the table below for
time frames at different temperatures when hydrogen and no hydrogen sulfide or oil are present.
°C
200
250
300
350
°F
390
480
570
660
hrs
48
12
4
1
Highest temperature
Maximum time
Temperatures may be maintained at the higher levels for a longer period of time if H2S levels are
confirmed greater than 100 ppmv. However, for an extended period without H2S or oil (more than 48
hours), it is recommended to cool the reactor beds below 200°C (390°F) or as specified by the
Mechanical Pressurization Temperature.
10.2
Hot oil without hydrogen
Operating with hot oil on the catalyst without any hydrogen will result in coke formation on the
catalyst, leading to loss of catalyst activity and increased pressure drop.
10.3
Contact with water
Catalysts are stable with small amounts of water (less than 500 ppmw by Karl Fischer analysis)
contained in feeds that have removed the free water. Exposing the catalyst to liquid water or high
water vapor concentrations at elevated temperatures can result in loss of catalyst strength.
Therefore, any slugs of water in the reactor inlet streams must be avoided. A slug of water entering
the hydroprocessing unit can create a steam surge that can spall coke and scale from the
exchangers and pipes. This can lead to pressure drop issues.
10.4
Backflow
Backflow through the reactor must be avoided due to the risk of lifting of the catalyst bed and
support.
The above focus points should be kept in mind during all unit operation procedures.
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10.5
Loss of feed
If the charge pump shuts down or feed is otherwise lost, treat gas flow will normally continue. The
heater will not respond quickly to the sudden loss in flow. To prevent overheating, the heater should
therefore automatically cut back to minimum fire or trip the fuel gas to the main burners. Pilot burners
are kept in service to facilitate returning the furnace to normal operation.
For hydroprocessing units, in case the charge pump cannot be restarted within 10 minutes, the
amine circulation in the absorber is stopped, and the reactor is cooled to below 200°C (390°F) at a
rate of 30°C/hr (50°F/hr). Treat and make-up gas flows are maximized during the cooling of the
reactor, and the feed/effluent heat exchanger(s) are bypassed, if possible.
Introduction of feed following a loss of feed should be carefully controlled. It is recommended to
reintroduce feed at reduced feed rate (around 25%) until reactor temperatures are stable. Usually
after 1–2 hours, the feed rate can be gradually increased to normal rates.
For hydrocracking units, even a few minutes after feed is lost, restarting of the feed pump can lead to
excessive heat build-up in the reactor through the heat of adsorption. The hydrocracking catalyst
beds will thus need to be cooled down to a safe level below 200°C (390°F) prior to restarting the
feed pump. This is to avoid a temperature excursion.
10.6
Loss of recycle gas
In the case of a recycle gas compressor shutdown, oil may stagnate in the reactor. The feed pump
must trip automatically, and the heater should cut back to minimum fire or trip the fuel gas to the
main burners. If at all possible, the make-up gas compressor must be kept at maximum to remove
(sweep) oil and cool the heater tubes and catalyst as fast as possible.
Stagnated oil in the reactor will increase the risk of hot spots, coke formation, excessive deactivation,
and potential temperature excursions. To make sure that oil is sufficiently removed from the catalyst,
it may be necessary to depressurize the unit by normal purge or emergency depressurization. In
case the gas circulation cannot be reestablished after 10 minutes, the unit should be depressurized
according to standard depressurization procedures.
The loss of recycle gas often means a loss of quench gas too. For hydrocracking and aromatic
saturation units, the loss of quench gas will often lead to a temperature excursion. Topsoe requires
that these units have an automatic depressurization system that will activate in the event of loss of
recycle gas.
10.7
Loss of make-up gas
In the case of a make-up gas compressor shutdown, the pressure will drop as the hydrogen is
consumed. If the make-up gas compressor cannot be restarted immediately, the feed must be
removed and the unit cooled, as described for planned shutdown in a previous section of this
manual.
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10.8
Loss of amine flow
In case the amine pump stops, the concentration of hydrogen sulfide in the recycle gas will increase,
and the catalyst activity will be inhibited. Products may go off-specification. Additionally, the
performance of the recycle gas compressor will be affected by the higher molecular weight of the
recycle gas. It should be possible to continue operation of the unit for a short time, although the
product may be off-spec.
The recycle gas purge is maximized until limited by the ability of the make-up gas compressor to
maintain reactor circuit pressure. Feed rate or total sulfur input to the unit may need to be reduced to
avoid off-spec product. Since the unit metallurgy is typically not designed for very high H2S
concentration in the recycle gas, the allowable time the related equipment can be exposed to
elevated H2S levels should be verified. Otherwise, if the amine system cannot be restarted and the
product specifications are not able to be met, the unit may have to be shut down, as described for
planned shutdown in a previous section of this manual.
10.9
Loss of wash water
If the wash water pump stops, operation can continue for a limited time period. However, ammonium
salts may start to precipitate in downstream locations, such as the heat exchangers. Some units can
run for 24 hours, while others require an immediate shutdown. Be aware of the amount of salts and
all of the potential accumulation points, which may lead to pressure drop or corrosion. Cleaning and
removing salts from unexpected locations can lead to a long downtime.
With the loss of wash water, ammonia will accumulate in the amine section and could potentially
cause an upset of the downstream sulfur plant. A reduction of the oil feed rate will reduce the
ammonia build-up.
10.10
Emergency depressurization
Hydrotreating, hydrocracking, and aromatic saturation units must be equipped with an emergency
depressurization system. Recommendations for design of the depressurization system can be found
in API 521. For hydroprocessing units, the design normally results in a valve system that reduces the
pressure from normal operating pressure to 50% of the design pressure in 15 minutes or the
standard initial depressurization rate of 7 bar/min (100 psi/min). The emergency depressurization
system is connected to the flare and is applied in emergency situations such as fire, power failure,
uncontrolled leak, and temperature excursions.
For higher pressure units, such as lube and hydrocracking units, an additional 21 bar/min (300
psi/min) emergency depressurization valve may be required. The higher pressure relief is applied
only in emergency situations.
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11
Catalyst unloading
CAUTION: Refer to Section 3.1 in this manual and the latest Safety Data Sheet (SDS) for the
catalysts to be unloaded prior to catalyst unloading.
A number of material protection and safety measures must be in place when catalysts are unloaded.
It is recommended as a safety precaution to have a fire hose or steam lance ready for use, if
necessary. The work force engaged in the unloading operations must be adequately protected from
getting into contact with the catalyst. In addition to conventional personnel protective equipment
(PPE), a suitable face mask should be used to protect workers from catalyst dust.
Before entering the reactor, it is mandatory to verify levels of hydrogen and oxygen, as well as
hydrocarbon content and lower explosive limit (LEL). Hydrogen and oxygen levels should both be
less than 0.5 vol%. National and local plant guidelines, requirements, and safe working practices
must be followed at all times.
Spent catalyst and iron sulfide deposits can be pyrophoric at temperatures above 60–70°C (140–
160°F) and therefore, the reactor should be cooled to less than 40°C (100°F) prior to unloading.
Respecting the local safety practices, a nitrogen purge should be maintained during the unloading in
order to minimize ingress of air. In particular, opening of more than one manhole/flange must be
avoided, as this could create a "chimney effect", leading to uncontrolled oxidation and possible
temperature excursion and/or fire in the catalyst bed.
The installed catalysts can either be vacuumed out from the top (skimming operation or reactor beds
without dump nozzles) or dumped via the dump nozzle. Generally, the vacuuming process is harsh,
resulting in dust formation and excessive catalyst breakage. Thus, catalysts that have been removed
by vacuum have high attrition and generally cannot be reused.
To minimize air exposure, the unloaded catalysts must be stored in sealed steel drums or preferably
in airtight catalyst bins. Nitrogen or dry ice may be used to reduce the oxygen content before sealing
the containers.
If the catalysts are screened before loading in drums, the screening should be carried out in inert
atmosphere to minimize the potential for oxidation and heat-up.
In any situation where a significant amount of iron sulfide (i.e. corrosion product) is present on the
catalyst, there is a potential for any catalyst to heat-up or ignite during the unloading or vacuuming
process. In order to prevent fire from occurring, it is recommended monitoring temperature in drums,
vacuum systems, etc. by temperature sensing guns or similar equipment.
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11.1
Catalyst skimming and sampling
When reactors require skimming due to excessive pressure drop build-up, additional expenses are
incurred. Sites will typically benefit from taking steps to ensure that these events are prevented in the
future. Recording data in every form can be valuable.
The reactor top elbow can be removed once the lower explosive limit (LEL) and levels of hydrogen
and oxygen have been verified, and all appropriate safety equipment is on location and properly
functioning.
Typically, an intrinsically safe video camera is applied to film all 360° of the top of the distribution
tray. Any debris, problem areas, damaged packing on tray sections or around the reactor walls
should be recorded. The outages and distances from the bottom of the distribution tray or top of the
inlet flange to top of the catalyst bed should be measured and compared with that recorded following
the initial catalyst loading. Samples from debris or other accumulated material should be taken.
As a general rule, in case anything abnormal is observed, a sample should be taken. A proper note
of sample location (position in catalyst bed, distance to distribution tray, etc.) should be added to the
label on the sample. If in doubt, it is recommended to take additional samples for later review and
analyses, as needed. The samples do not have to be immediately sent for analysis. However, in
case certain samples are not taken in time, it might be too late. Without a sufficient sample size, the
quality of the analytical results may be inadequate, and therefore impact the efforts required to
understand the root cause of the problem that led to the unit shutdown. Also, the sampling quality
can be affected if materials get mixed during unloading, handling, and transport. Thus, care should
be taken to attain high-quality samples.
The minimum sampling requirements when skimming are as follows: Each grading layer has to be
vacuumed individually, one layer at a time, with samples taken from the very top of the reactor bed
and from each grading layer, as well as the top of the bulk catalyst, with care taken to ensure the
sample is representative. Samples have to be collected in ½ liter/one-quart plastic or metal
containers and should be adequately labeled. In case the catalyst is dumped (refer to Section 11.2 in
this manual), a sample from the first drum is taken and then subsequent samples are taken at
intervals representing volumes of 20%, 40%, 60%, 80%, and 100% of the catalyst bed being
dumped. If fines, foulant, or scales are found on the distributor tray and/or scale catchers, these
samples should also be obtained for analysis.
The vacuumed catalyst has to be placed into suitable containers, such as steel drums. The drum
atmosphere should be inert to minimize the potential for oxidation and self-heating of the catalysts.
Appropriate safety precautions should be taken in which case dry ice or nitrogen blanketing can be
applied. The drum lining should be tightened, and the drum closed and sealed properly. The steel
drum should be labeled appropriately and include a suitable SDS label.
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11.2
Catalyst dumping
Following top skimming (refer to Section 11.1 in this manual), when the catalysts are dumped, a
sloped (usually a cone-shaped) profile is formed in the reactor, as the catalysts are flowing out
through the dump nozzle(s). Since most of the bottom ceramic support is dumped in the process,
small catalyst particles can reach the outlet collector area. Part of the catalysts, and especially fines,
can penetrate through the grid on the outlet collector or through openings or gaps, where the outlet
collector rests on the bottom head. Thus, particles may migrate to the outlet piping.
Migration of catalyst particles is a potential problem for downstream equipment and units having
multiple reactors. In order to avoid the catalyst particles, dust, and fines being transferred to the
downstream equipment, the outlet piping of each reactor should be cleaned. This will minimize the
risk of plugging the upper part of the downstream reactor or cause upsets in downstream equipment.
In a similar manner, for multiple bed reactors, dumping one of the upper beds will lead to small
catalyst particles reaching the bed support screens. Catalyst may migrate through the screens or
plug the screens and lead to additional pressure drop. The screens and interbed sections should be
cleaned to ensure trouble-free operations.
The dumped catalyst should be carefully sampled and collected in suitable steel drums, as described
above in Section 11.1 in this manual.
11.3
Catalyst screening
If the unloaded catalyst is to be reused, it should be screened before reloading. The catalysts are
screened through sieves according to catalyst size. The screen opening should be approximately
75% of the maximum catalyst diameter.
The amount of fines found during screening of unloaded (dumped) catalysts is normally around 2–3
wt%, and usually much higher for catalyst unloaded by vacuuming. The undersized material found
during screening is a mixture of catalyst fragments and coke.
It is difficult to screen mixtures of catalysts and ceramic support. A multiple screening process should
be employed. The first screening removes the larger, heavier ceramic supports and inert balls. If
possible, the mixture of ceramic support and catalyst should be dumped into separate drums or bins
for “individual” screening.
Attention should be taken to the self-heating nature of spent catalysts. The guidelines for safe
handling, as described above, should be followed at all times.
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11.4
Nickel carbonyl
Nickel carbonyl, an extremely toxic substance, may be generated any time a carbon monoxide
containing gas gets in contact with a nickel-containing catalyst at temperatures below about 200°C
(390°F). Strict operational and testing procedures must be followed to primarily avoid and secondly
check for the presence of carbon monoxide. If the atmosphere around the nickel-containing catalyst
measures more than 10 ppmv carbon monoxide, it must be assumed that nickel carbonyl is present.
Alternatively, nickel carbonyl can be detected by Dräger type 19501 or Sensidyne type 129 tubes.
12
Catalyst regeneration
All hydroprocessing catalysts will age and deactivate during the cycle. The deactivation rate varies
considerably and depends on feedstock and operating severity. Straight-run naphtha processing will
have a relatively low deactivation rate, and residual oil processing, on the other hand, will have
relatively high deactivation rate.
Carbon (coke) will deposit on the catalyst during normal operation, and as the run progresses, this
carbon and other deposits like metals, arsenic, silica, etc. will contribute to a loss of catalyst activity.
Normally, reactor temperatures are increased in order to compensate for this deactivation effect and,
in this way, still maintain product quality.
At a point in time, the inability to increase reactor temperatures further or failure to meet product
specifications will necessitate a unit turnaround and a catalyst change-out. For naphtha, kerosene,
and diesel hydrotreating services, as well as some vacuum gas oil and hydrocracking services, the
catalyst may be reused after it has been regenerated and possibly treated by Topsoe’s ReFRESH™
reactivation process.
When Topsoe’s TK catalysts are regenerated ex-situ, they will generally return to 80-85% of the
activity compared to fresh catalyst, if the deactivation is caused by coking. However, catalysts
deactivated by deposition of metals, arsenic, and silica or by maloperation that causes sintering, loss
of surface area, and/or poisoning of active sites are typically not good candidates for regeneration.
The TK rings and other catalysts used as grading material are unsuitable for regeneration and
should be replaced after each cycle.
Upon dumping, regeneration, screening, and reloading, the regenerated catalyst will typically have a
reduced length compared to that of fresh catalyst. This means that a slightly higher loading density
(around 5%) and a slightly higher start-of-run pressure drop (around 20%), as compared to fresh
catalyst, must be expected.
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12.1
Ex-situ versus in-situ regeneration
There are several advantages of ex-situ regeneration compared to in-situ regeneration:
1) Ex-situ regeneration can generally be made much more uniformly and more tightly controlled
than in-situ regeneration, especially in cases where poor flow distribution has been observed in
the reactor during the catalyst cycle;
2) The regenerated catalyst can be analyzed for physical and chemical properties, such as length
and strength, as well as catalyst poisons and activity, before it is reloaded;
3) Dust, solid contaminants, and broken catalyst particles will be removed during the screening of
the catalyst following the ex-situ regeneration. With in-situ regeneration, these particles
generated during the burn remain in the reactor and can lead to subsequent pressure drop
issues.
Typical losses during ex-situ regeneration of Topsoe’s hydroprocessing catalysts will be less than 5
wt%. However, it is recommended to have around 10 wt% fresh catalyst available (relative to the
original loading) when reloading of catalyst is performed. Because of breakage, regenerated catalyst
often will have around 5% higher loading density resulting in less reactor volume to be filled.
Ex-situ regeneration performed by companies who specialize in regeneration of catalysts is
recommended for all TK catalysts. Topsoe continuously discusses procedures and provides
guidelines to the companies performing the regeneration of TK catalysts.
At the request of the client, Topsoe can comment on the potential regenerated catalyst quality of a
specific batch of catalyst prior to shipment to the company doing the regeneration. The review will be
based on physical and chemical analysis of the spent catalyst in question. In order to minimize the
unit downtime, having a spare catalyst charge of (possibly regenerated) catalyst available at site can
be useful.
Since in-situ regeneration may be performed infrequently, the unit operators may not normally be
familiar with the required procedures and safety precautions associated with the catalyst
regeneration. Therefore, equipment damage caused by corrosion or overheating during the
regeneration process is an evident risk. If not all procedures are carefully followed, there is also a
risk of causing damage to the catalyst or performing an insufficient regeneration of the catalyst.
There are some locations where logistics prohibit the refiner from taking advantage of ex-situ
regeneration, and therefore, the catalyst must be regenerated in-situ. In cases where the refiner
needs an in-situ regeneration procedure, it will be provided by Topsoe.
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13
Liability
The guidelines contained in this manual have been prepared by Topsoe engineers and scientists
having thorough knowledge of the catalyst. However, any operating guidelines specified herein
should be considered to be of a general nature, supplied without detailed knowledge of the specific
plants and with the understanding that such recommendations shall not be relied upon by the
customer without independent verification of accuracy, validity, and applicability to a specific plant or
processing unit.
The guidelines are given without any liability on the part of Topsoe for upset or damage to the
individual plants or personnel. Nothing enclosed in this manual is to be construed as recommending
any practice or any product in violation of any patent, law, or regulation.
Topsoe technicians present on site are solely to be considered as advisors, who are in no way
responsible for the duties or responsibilities of the operation managers for operating the facility in a
careful and safe manner. These responsibilities remain with the customer.
We wish to underline the importance of the operating guidelines issued by Topsoe being carefully
reviewed by the plant personnel before use in a specific unit.
Any unclear points in the procedures or recommendations should be discussed and clarified with
Topsoe before start of operation.
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14
Contact addresses
Haldor Topsoe A/S
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Haldor Topsoe is a world leader in catalysis and surface science,
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