Manual for Topsoe
Hydroprocessing Catalysts
LIST OF CONTENTS
1.
INTRODUCTION
1
2.
APPLICATION
1
3.
CATALYST HANDLING
3
3.1.
4.
Safety
3
REACTOR INTERNALS
5
4.1.
4.2.
4.3.
5.
5
9
10
CATALYST LOADING
5.1.
5.2.
5.3.
6.
Distribution Tray Types
Reactor Inspection and Preparation
Procedure for Inspection of Internals
12
Support Material and Topping Layers
Sock Loading
Dense Loading
12
15
15
CATALYST ACTIVATION AND START-UP
6.1.
6.2.
6.3.
6.4.
17
Drying of Catalyst
Sulphiding by the Doped Feed Method
Sulphiding of Replacement Catalyst after Skimming
Start-up after Normal Shutdown
18
19
24
25
7.
NORMAL SHUTDOWN
28
8.
EMERGENCY SHUTDOWN
30
8.1.
8.2.
8.3.
8.4.
8.5.
8.6.
9.
Loss of Feed
Loss of Recycle Gas
Loss of Make-up Gas
Loss of Amine Flow
Loss of Wash Water
Emergency Depressurisation
CATALYST UNLOADING
9.1.
Catalyst Screening
10. CATALYST REGENERATION
10.1.
Ex-Situ versus In-Situ Regeneration
11. LIABILITY
30
31
31
31
31
32
33
33
35
35
37
HALDOR TOPSOE
Introduction
1. Introduction
This "Manual for Topsoe Hydroprocessing Catalysts" is intended to provide general
guidelines for the handling and operation of the Topsoe TK series of catalysts, except for
the TK-900 Series of noble metal hydrodearomatisation (HDA) catalysts. The guidelines
cover:
•
•
•
•
•
•
•
Catalyst Handling.
Reactor Internals.
Catalyst Loading.
Catalyst Activation and Start-up.
Shutdown Procedures.
Catalyst Unloading.
Catalyst Regeneration.
Normally, detailed procedures for each of the operations described in this manual are
developed by either the refiner or their engineering contractor. Such procedures are
based upon experience gained from previous turn-arounds or from similar applications in
other plants and are usually unit- or site-specific in the refinery. The detailed procedures
should incorporate the guidelines from this manual to form the basis for the operating
procedures, which take into account the proper operation of the unit for optimal catalyst
usage and product recovery while maintaining plant safety.
Topsoe is available for consultation on procedures for a specific unit. In cases where the
guidelines in this manual are in conflict with detailed procedures, Topsoe should be
consulted. On request, Topsoe will provide specific procedures for specialised catalysts
or services, such as hydrocracking or residual oil processing.
2. Application
The TK series encompasses a number of specialised hydroprocessing catalysts
containing one or more of the active metals cobalt, nickel and molybdenum on aluminabased carriers.
TM
The cobalt-molybdenum types are greyish blue, except for TK-558 BRIM , TK-574 and
TK-576 BRIMTM, which are often dark grey or black and the nickel-molybdenum are
greenish yellow, except for TK-559 BRIMTM, which is brown. Catalysts containing
molybdenum alone have the same colour as the carrier (white).
Irrespective of type, ex-situ presulphided catalysts are dark grey or black sometimes with
a slight smell of organic solvent dependent on the method of presulphiding. The TK series
HALDOR TOPSOE
1
Application
incl. our high active catalysts are suitable for ex-situ presulphiding. However, a minor
loss in final catalyst activity should be anticipated when applying ex-situ presulphided
catalysts compared to in-situ sulphided catalysts.
The TK series of catalysts comprise of inert materials, rings and shaped extrudates
(threelobes and quadralobes). Inert material and rings are most often used for the Topsoe
grading system installed in the top section of hydrotreating reactors. The shaped
extrudates are mainly used as bulk catalysts.
The grading system comprises the following benefits:
•
•
•
Shape-optimised inert material and ring-shaped catalysts with a high void fraction
installed in the top section of the reactor, thereby allowing the accumulation of large
amounts of particulates without plugging and causing pressure drop build-up.
Provides a step-wise decrease in catalyst particle size to spread out reactants and
contaminants over a larger part of the catalyst bed.
Selection of topping material to provide a gradually increasing catalyst activity from
the top to the bottom of the catalyst bed, resulting in a better control of the
hydrogenation of more reactive compounds, thereby spreading out the reaction
products over a larger part of the catalyst bed.
The TK series of catalysts are manufactured in the shapes and sizes mentioned below:
Shape
Size, inch
Size, mm
Tablets
Butterflies
Rings
Threelobes
Quadralobes
5/8
3/2x1x3/4
1/8 and 3/16
1/8, 1/16 and 1/20
1/2, 1/10, 1/12, 1/15 and 1/20
16x11
38x25x19
3.2 and 4.8
3.2, 1.6 and 1.3
13, 2.5, 2.1, 1.7 and 1.3
HALDOR TOPSOE
2
Catalyst Handling
3. Catalyst Handling
All TK catalysts are supplied in either drums of 200 litres (53 gallons) nominal capacity
with a removable lid or big bags holding approximately 1 m3 (35 ft3). Packing in
specialised catalyst containers can be made on request. Ex-situ presulphided TK
catalysts are packed and delivered in UN-certified steel drums, rental flow bins or big
bags (wrangler bags) to meet customer requirements.
It is important that the catalyst containers are handled carefully without bumping and
that the containers are never rolled to avoid disintegration of the catalyst particles.
However, if the catalyst containers have been subjected to rough handling, it may be
necessary to screen the catalyst before installation.
Big bags are equipped with lifting lugs and placed on pallets in order to make handling
easy. Discharge of catalyst must be done through the discharge chute in the bottom of
the big bag.
Drums and big bags are equipped with internal polyethylene bags which protect the
catalyst from ingress of water and moisture. Topsoe recommend that the catalyst is
stored indoors. If it is necessary to store the catalyst outside, the drums or big bags must
be placed upon pallets or logs and securely covered with plastic or canvas sheet to
protect them from rain. Big bags must be placed in single layers (no stacking).
The reason for having the catalyst well protected from water and moisture is the
hygroscopic nature of the catalyst carrier. Large amounts of water can be absorbed in
the catalyst pore system and this water may, during activation of the catalyst, cause
reduction of the catalyst strength and activity. Reduction in strength could cause
disintegration of the catalyst particles and consequently result in increased pressure drop
over the catalyst bed.
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 strength in order to cope with
mechanical influences on the catalyst during handling and operation. Nevertheless,
improper handling can result in breakage of catalyst particles and formation of catalyst
fines. This may result in pressure drop problems, which can eventually limit cycle length
rather than catalyst activity. Hence crushing of the catalyst must be avoided by use of
walking boards/planks possibly laid out on a soft material or by use of “snow shoes”.
3.1.
Safety
Some TK catalysts contain nickel. Nickel has been found to be potentially carcinogenic.
The work force engaged in catalyst handling and loading operations must be adequately
HALDOR TOPSOE
3
Catalyst Handling
protected from catalyst dust or fines. For those working outside the reactor, gloves and
suitable masks must be worn. For those working inside the reactor, self-contained
breathing apparatus or fresh-air masks and protective clothing must be worn.
Material Safety Data Sheets are available for each type of catalyst.
In case of ex-situ presulphided TK catalyst, loading preferably should be carried out in
inert atmosphere (nitrogen) to avoid self-heating. Furthermore, ex-situ presulphided TK
catalysts may, dependent on which ex-situ presulphiding method has been applied, emit
hydrocarbon vapours or, in case of contact with (even small amounts of) water, sulphur
dioxide. The personnel working inside the reactor therefore must wear self-contained
breathing apparatus or fresh air masks, gloves and protective clothing.
The user should refer to the Material Safety Data Sheets and other precautions provided
by the company performing the ex-situ presulphiding of the catalysts.
HALDOR TOPSOE
4
Reactor Internals
4. Reactor Internals
In modern hydrotreating units, optimal performance of the reactor and reactor internal is
critical to ensure that the product specifications can be achieved in the most efficient and
economical way. Especially in units producing ultra low sulphur diesel fuels, proper
performance of the reactor is mandatory to reach the very low product sulphur
requirements.
Topsoe has more than 20 years of experience in the development and supply of high
efficiency reactor internals to the refining industry. Topsoe has gained a lot of knowledge
and expertise in this area, not only with our own high efficiency internals but also with
other older types of liquid distribution trays and quench mixing boxes.
The following general guidelines for maintenance of reactor internals are provided to
ensure optimal performance of the TK catalysts installed in hydrotreating units. Should
the guidelines given below deviate from the guidelines given by the tray supplier, the
guidelines from the tray supplier must be governing. The guidelines given below are
divided according to the different type of trays and mixers typically encountered. Should
the tray and/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 always
be inspected with special attention to the following:
•
•
•
•
•
Contamination, dirt or debris accumulation.
Damage.
Missing bolts.
Missing 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 the inlet
diffuser basket.
Depending on the tray design and amount of contaminants, performance of the
distribution tray may be affected. Thus, the tray must be carefully cleaned and all dust
and debris must be removed. It is especially important to observe that all weep holes,
notches 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. After completion
HALDOR TOPSOE
5
Reactor Internals
of the loading, it is also necessary to perform a final inspection and cleaning before
reactor closure to remove any remaining catalyst particles and dust from the tray.
It is important to visually inspect the tray for damage like bent nozzles, corrosion on the
tray plates, etc. 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.
According to Topsoe experience bolts are often 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 loads and stresses under normal operating conditions.
The reactor internals, even with some missing bolts, may look correctly installed under
ambient conditions. However, the situation may be completely different when they are
exposed to high temperatures, liquid loads and streaming gasses. Under these conditions
the missing bolts may result in leakage of liquid at places where it is not desirable, i.e.
along the reactor wall. It is therefore important that all missing bolts are replaced with
new bolts of the right 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 packing or seals must be replaced during each turn-around to prevent
leakage of liquid. Should a careful inspection of the packing or sealing show that it is in
good shape a replacement may be postponed to the next turn-around. However, Topsoe
recommend that the packing or sealing around the manway covers is always replaced
with new after completion of the catalyst loading.
Certain types of trays (see below) are very sensitive to levelness. Such trays must be
carefully checked for levelness, and if the levelness is not found to be within the
tolerances specified by the tray vendor, corrective actions must be taken. Some tray
types may be difficult to adjust and in case the levelness is found to be outside the
specified tolerances, it is recommended to replace such a tray with a modern type (like
the Topsoe Vapour 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.
HALDOR TOPSOE
6
Reactor Internals
Specific information for each of the common types of reactor internals is given below:
1)
Sieve Tray (Perforated Plate)
This type of tray is a rather old and not very common type in modern
hydrotreating units. It is recognised by a very large number of distribution points
but also a very high sensitivity 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. Especially the
holes on the tray plates must be perfectly clean and have the right design
diameter. 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 very poor flexibility for changes in operating conditions concerning
this type of tray the refiner should consider a replacement with a more modern
type (like the Topsoe Vapour Lift Tray), especially in high severity units.
2)
Simple Chimney Tray
This type of tray also is a rather old and not very common type in hydrotreating
units today. This tray type is recognised 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.
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 or notches are perfectly clean. 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.
3)
Multi-port Chimney Tray
This tray type is a further development of the simple chimney tray mentioned
above. This type of tray is recognised 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.
HALDOR TOPSOE
7
Reactor Internals
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)
Separate Vapour and Liquid Chimney Tray
This type of tray is a variant of the chimney tray. It is recognised 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 may have weep holes at different levels. Compared to the older types of
chimney trays, this type 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, again it is
important that all weep holes, especially the lower ones, are perfectly clean.
5)
Bubble Cap Tray
The bubble cap tray is using the vapour-assist principle (siphon) and is often
applied in high severity units like hydrocrackers or FCC pretreater units. The
bubble cap trays are usually very flexible with respect to changes in liquid and
vapour 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 square metre/foot.
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.
6)
Topsoe Vapour Lift Tray
Topsoe’s own high performance Vapour Lift Trays are unique as 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 utilisation is greatly improved. Additionally, the Topsoe trays
have many drip points (nozzles) in the outer 20% of the tray area close to the
reactor wall. The high utilisation of the catalyst installed in the reactor will result
in a reduced reactor average temperature for the required product specifications
and eventually in a longer catalyst cycle length.
The Vapour Lift Trays show superior performance at all liquid loads. The trays
have a very broad operating range and flexibility regarding temperatures, feed
composition and different vapour/liquid loads.
HALDOR TOPSOE
8
Reactor Internals
Additionally, 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.
7)
Quench Mixing Assemblies
A number of different designs exist for quench mixing assemblies, which will not
be discussed in this manual. However, general guidelines for inspection of the
quench mixing assemblies and re-distribution trays are included.
As the quench mixing assembly and re-distribution trays are protected from
contamination by the catalyst bed(s) above, this section of the reactor will
normally be clean. However, Topsoe recommend that the quench mixer is
inspected for damage, broken bolts and corrosion and that any packing or seals
are intact and in good shape.
The re-distribution tray(s) must be checked as described for the top distribution
tray.
4.2.
Reactor Inspection and Preparation
Prior to loading of catalyst the reactor must be inspected to ensure 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:
1)
Ensure all contractor equipment and extraneous hardware have been removed.
2)
Verify that support beams are intact, straight and level.
3)
Check that screens (wire mesh) on the support grids and outlet collector are
properly mounted and are all clean and intact (no corrosion).
4)
Gaps between support grid sections and between grid sections and reactor wall
must be sealed with ceramic fibre rope packing to prevent catalyst migration.
5)
The outlet collector is checked for gaps at the reactor head. It is also checked
that all holes and slots are clean.
6)
The quench line nozzles must be clean.
7)
Check that thermocouple nozzles are clean and free from catalyst particles.
HALDOR TOPSOE
9
Reactor Internals
8)
4.3.
Thermocouples must be correctly positioned and firmly attached to their
supports. Furthermore, we recommend that the thermocouples are properly
calibrated after each reactor shutdown.
Procedure for Inspection of Internals
A general step-by-step procedure for inspection of reactor internals in hydrotreating units
in connection with catalyst replacement is given below:
1)
The unit is shut down following the normal shutdown procedure and is prepared
for opening of the manway at the top of the reactor.
2)
The inlet basket is inspected and if necessary cleaned.
3)
Following a normal shutdown some liquid could remain on the distribution tray.
Do not drill holes in the plate to remove the liquid; use vacuum instead. Holes in
the tray will lead to maldistribution upon restart.
4)
The distribution tray is inspected for signs of possible leakage. Potential areas of
leakage are around the tray manway cover (for instance due to poor or missing
packing fibre rope), 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 poor or missing packing fibre rope).
5)
The distribution tray manway cover is removed.
6)
The top of the catalyst bed is inspected for signs of uneven liquid or gas
distribution like for instance difference in degree of contamination or colour
differences. 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 area of the catalyst bed. If such
differences are identified, it could be useful to re-inspect the distribution tray
above to check if any obvious faults are observed on the tray directly above the
specific section of the catalyst bed.
7)
Especially for naphtha hydrotreating units operating at high gas rates special
emphasis should be given to check for possible milling (dust formation) of the
top layer of inert material. Contact Topsoe for advice on future loading.
8)
The catalyst is dumped through the dump nozzles and normal atmosphere is
established in the reactor vessel (refer to section 9, Catalyst Unloading, in this
manual).
HALDOR TOPSOE
10
Reactor Internals
9)
After having unloaded the catalyst, all the reactor internals (including catalyst
support grids and/or the outlet collector) are carefully cleaned making sure that
the guidelines mentioned above are observed. Furthermore, the size and
suitability of the wire mesh, screens, slots and holes of the support grids and/or
the outlet collector must be compared with the sizes of ceramic balls to be used.
10) After completion of the cleaning, the reactor internals must be checked for leaks,
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. A Topsoe engineer should participate in this final inspection of the
reactor and the reactor internals prior to catalyst loading.
11) The new charge of catalyst is carefully loaded as recommended by the catalyst
vendor. Such loading must be done by an experienced loading company and
most often under supervision of a Topsoe engineer on site (refer to section 5,
Catalyst Loading, in this manual for further details).
12) The tray manway cover is installed. Great care must be used to install the cover
correctly and with new and suitable packing fibre ropes. The entire
circumference of the cover must be packed. A final cleaning of the tray is
necessary before the reactor is closed.
13) The unit is started up and the catalyst is activated in accordance with the
recommendations given by the catalyst vendor (refer to section 6, Catalyst
Activation and Start-up, in this manual).
HALDOR TOPSOE
11
Catalyst Loading
5. Catalyst Loading
Correct installation and subsequent activation of the TK catalysts are extremely important
in order to obtain optimum catalyst performance and life. Therefore, these operations
must be carefully monitored so that the catalyst is not degraded in any way.
In case of rainy weather, the top of the reactor and catalyst loading area have to be
protected with tarpaulins in order to keep water off the catalyst during the loading
operation. If protection from rain is not possible, catalyst loading must be postponed until
it can be executed without getting the catalyst wet.
When the TK catalysts are delivered ex-situ presulphided the loading in rainy weather
must not take place due to the risk of SO2 formation. Furthermore, loading of ex-situ
presulphided catalysts preferably should be carried out in inert atmosphere to avoid selfheating. The TK series incl. our high active catalysts are suitable for ex-situ
presulphiding. However, a minor loss in final catalyst activity should be anticipated when
applying ex-situ presulphided catalysts compared to in-situ sulphided catalysts.
In order to avoid uneven flow distribution (channelling) in the catalyst bed, it is important
that loading of the catalyst is done in a proper way. Uneven flow distribution may have a
significant influence on performance of the unit and in the worst case, it may not be
possible to meet product specifications. This can force an unscheduled shutdown for
rectification of the situation.
It is recommended that the reactor wall is marked with chalk at the upper level of each
layer of inert material and catalyst. A laser levelling device also may be helpful during the
loading. Both of the above mentioned methods (or combinations of the methods) will
facilitate levelling of the different layers of catalyst and inert.
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 catalyst through gaps in the
support grids and outlet collector. The heights and sizes of the balls are specified in the
reactor specification or in the loading diagram. The following general guidelines should
be followed:
1)
Ceramic balls are carefully loaded into the bottom of the reactor head until the
outlet collector/screen is covered to a depth as specified in the reactor
specification. Minimum distance of the large balls above the top of the outlet
collector is 150 mm (6 inch). Topsoe recommend that the bulk catalyst is loaded
in the reactor head only to 90% of the reactor diameter. The size of the ceramic
HALDOR TOPSOE
12
Catalyst Loading
balls in the bottom of the reactor must be larger than the width of the slots in the
outlet collector. Typically a nominal 3/4 inch diameter ceramic ball or pellet is
specified.
2)
When 1/10 inch or larger size catalysts are used, the layer on top of the 3/4 inch
balls in the bottom of the reactor consists of nominal 1/4 inch diameter balls.
The depth of the layer is minimum 150 mm (6 inch). Refer to the following
loading diagram shown on the right hand side.
3)
When 1/12 inch or smaller size catalysts are used, two layers of balls are used
on top of the 3/4 inch balls in the bottom of the reactor. A layer of minimum 75
mm (3 inch) of a nominal 1/8 inch diameter balls is loaded on top of a layer of
minimum 75 mm (3 inch) of a nominal 1/4 inch diameter balls. Refer to the
following loading diagram shown on the left hand side.
4)
If the reactor holds more than one bed, the layer of ceramic balls at the bottom
of each bed is minimum 150 mm (6 inch) of 1/4 inch and/or 1/8 inch balls
depending on catalyst size.
5)
At the top section of the reactor, usually a high void inert material is installed.
The minimum height of the layer of high void material (TK-10 or TK-15) is 150
mm (6 inch). If the reactor holds more than one catalyst bed, normally a similar
150 mm layer of inert material is installed on top of each bed. Alternatively,
ceramic balls can be installed on top of the subsequent beds. However, it is not
recommended to install ceramic balls on top of the first bed.
6)
The remaining grading system, normally consisting of different types and sizes
of TK rings, is installed between the top layer of inert material and the bulk
catalyst. The rings (and inerts) are always sock loaded. For exact loading heights
of the grading catalyst, reference is made to the technical recommendation,
catalyst specification, reactor specification or loading diagram.
Examples of loading diagrams are found on the following page.
HALDOR TOPSOE
13
Catalyst Loading
300-500 mm (1' 0"-1' 8") free space
from distribution tray to top of
catalyst
300-500 mm (1' 0"-1' 8") free space
from distribution tray to top of catalyst
Min. 150 mm (6") TK-10 or TK-15
inert material
Min. 150 mm (6") TK-10 or TK-15
inert material
Topsøe grading of two or
more layers of TK-rings
Topsøe grading of two or
more layers of TK-rings
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") 1/8" ceramic balls
Min. 75 mm (3") 1/4” ceramic balls
Min. 150 mm (6") 3/4” ceramic balls
above outlet collector
Min. 150 mm (6") 1/4” ceramic balls
Min. 150 mm (6") 3/4” ceramic balls
above outlet collector
Note that the ceramic balls must be sock loaded and care must be taken to avoid
breakage during loading resulting in risk of pressure drop. Dropping of the ceramic balls
from the top of the reactor or bed also may cause damage to the outlet collector or dump
nozzles.
As mentioned above (item 1) it is recommended that the bulk catalyst is loaded in the
reactor head only to 90% of the reactor diameter. The remaining volume in the bottom
reactor head is filled with large size ceramic balls.
HALDOR TOPSOE
14
Catalyst Loading
5.2.
Sock Loading
The TK catalysts can be either sock or dense loaded. It is specifically indicated in the
technical recommendation, the catalyst specification, the reactor specification or in the
loading diagram which method to be applied for each catalyst layer or bed.
Sock loading is done through a vinyl or canvas hose attached to a hopper. The hopper is
placed on the inlet flange on top of the reactor with the hose extending from the bottom
of the hopper to the top of the catalyst bed. The hose must be filled with catalyst at all
times.
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
afterwards distributed evenly, as this will result in segregation of particle sizes and
improper catalyst particle orientation, easily leading to channelling. It is recommended to
have trained personnel inside the reactor to observe and guide the loading and ensure
that the top of the catalyst bed is reasonably level at all times.
The personnel inside the reactor must not stand or step directly on the catalyst. It is
recommended to use walking planks or "snow shoes" for distribution of weight over a
larger area.
The top layers of inerts and TK rings are always sock loaded. When loading inerts, care
must be taken to prevent particles from filling the hose. The weight of inerts may cause
the hose to break or separate from the hopper and thereby endangering the personnel
inside the reactor.
5.3.
Dense Loading
Dense loading is performed using a special dense loading apparatus. The various designs
for dense loaders all use the principle of dispersing the catalyst over the cross sectional
area of the reactor in such a way that the catalyst level is evenly increased. Loading rate
is controlled such that each catalyst layer comes to rest before being covered by the next
layer, thereby minimising bridging and particle size segregation.
The catalyst loading company always should refer to the instructions or manual which
are relevant for the particular dense loading apparatus they have elected to employ.
The dense loading apparatus is mounted on the inlet flange of the reactor or in the
manway of the distribution tray in multibed reactors. In the latter case, a vinyl or canvas
hose typically transfers catalyst from a hopper above the reactor to the dense loader.
HALDOR TOPSOE
15
Catalyst Loading
When using the dense loading technique, it is very important to periodically stop the
loading and measure the level and density of the catalyst bed. Depending on the
apparatus, there are various adjustments that can be made to correct the loading
patterns. If the bed density is high, it may be an indication that the dense loader throws
the catalyst particles at the reactor wall, which causes breaking of the particles.
Furthermore, adjustments have to be made as the level of catalyst rises to maintain an
even distribution of the catalyst over the reactor cross sectional area.
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 weight of catalyst loaded in order to
check that the required loading density has been achieved. The target loading densities
are provided by Topsoe and can be found in the technical recommendation, the catalyst
specification or in the product sheet of each catalyst.
It is recommended that dense loading is done by a company specialising in catalyst
loading and unloading. The proper operation of the dense loader is a matter of equipment
and experience with the actual equipment. A list of experienced companies will be made
available upon request.
HALDOR TOPSOE
16
Catalyst Activation and Start-up
6. Catalyst Activation and Start-up
Hydroprocessing catalysts as manufactured consist of an alumina (aluminum oxide)
carrier impregnated with oxides of different metal combinations. The metal oxides have
to be converted to sulphides to be in the active state.
The activation step is very important for the subsequent performance of the catalyst
charge and therefore requires careful monitoring. During the activation, the catalyst will
pick up 5-13 weight per cent sulphur depending on the amount of active metal present in
the catalyst.
The sulphur uptakes of some of the TK catalysts are shown below:
Catalyst
Sulphur Uptake (wt%)
Catalyst
Sulphur Uptake (wt%)
TK-431
8.0
TK-574
11.9
TK-527
5.3
TK-575 BRIMTM
12.3
TM
TK-558 BRIM
11.9
TM
TK-576 BRIM
11.9
TK-559 BRIMTM
11.1
TK-605 BRIMTM
12.3
TK-565
12.3
TK-753
5.3
TK-573
12.3
TK-773
7.9
There are several methods available for sulphiding/activation of the catalyst. The method
recommended by Topsoe (and the method described in this manual) is the doped feed
method where an easily decomposable sulphur compound/agent (such as DMDS,
SulfrZol 54, TNPS or TBDS) is mixed with the oil upstream the reactor.
On request, Topsoe will provide start-up procedures and recommendations for other
sulphiding methods, such as gas phase activation, presulphiding and native (oil) sulphur
activation.
The TK series including our high activity catalysts are suitable for ex-situ presulphiding.
However, a minor loss in final catalyst activity should be anticipated when applying exsitu presulphided catalysts compared to in-situ sulphided catalysts.
For units/reactors that are limited in activation temperature to around 300°C (570°F) it is
recommended to have the catalyst ex-situ pre-activated (truly sulphided) by a specialised
company prior to loading and start-up.
HALDOR TOPSOE
17
Catalyst Activation and Start-up
As mentioned in section 3, Catalyst Handling, the TK catalysts are very porous, having
surface areas of 150-250 m²/g. This is an important feature of the catalyst. Such porous
catalyst is hygroscopic, i.e. water or moisture from the atmosphere surrounding the
catalyst is readily absorbed. As delivered, the catalyst may contain some water, normally
about 1-2% of the catalyst weight. Furthermore, the catalyst may absorb additional
moisture during the loading.
To avoid breakage of catalyst particles during the heat-up and to obtain maximum
activity, the catalyst must be carefully dried before the activation/sulphiding is carried
out.
6.1.
Drying of Catalyst
Drying of fresh or regenerated catalyst prior to activation is preferably carried out using
hydrogen containing treat gas or nitrogen.
If a liquid phase, e.g. a kerosene or gas oil fraction, is present during the drying phase,
the sulphur compounds present in the kerosene or gas oil will be adsorbed on the metal
oxides inside the catalyst. This is not sulphiding, but simple adsorption. By this
adsorption, the sulphur compounds hold or lock the metals together.
If the metals are "locked" by the adsorbed sulphur compounds, the metal dispersion is
reduced as the water evapourates and the activity is adversely affected. Our researchers
have estimated that 10 to 20% reduction in activity can occur, if the metals are bound by
adsorbed sulphur compounds. Thus, we recommend drying of the catalyst in vapour
phase.
The dispersion of the active metals is strongly effected by the presence of water. During
the drying of the catalyst, as the water is gradually evapourated, the metals dispersion
increases and a high activity is obtained.
When hydrogen containing gas is used for the drying, the reactor temperature should be
kept at 150°C (300°F). Refer to the table below for time frames at different temperatures
when hydrogen and no hydrogen sulphide or oil is present. This is due to the risk of
reducing the catalyst oxides to free metals, which will result in permanent reduction of
the catalyst activity. If the drying is conducted in nitrogen atmosphere, the maximum
allowable temperature is 250°C (480°F).
Highest temperature, °C (°F)
Time frame, hours
200 (390)
250 (480)
300 (570)
24
6
1
HALDOR TOPSOE
18
Catalyst Activation and Start-up
In case some equipment upstream or downstream the reactor has been leak tested with
water prior to drying and activation of catalyst, the entire system must be properly
drained before commencing the drying procedure.
A step-by-step drying procedure is provided below:
1)
If the catalyst loading has been carried out in normal atmosphere, the reactor
must be purged with nitrogen so that the oxygen content of the high pressure
loop is less than 0.5 vol% before hydrogen containing gas is introduced. Purging
avoids the risk of forming explosive mixtures of hydrogen and oxygen.
2)
Pressurise the reactor to normal operating pressure. Be aware of any pressure
limitations at low temperature as some reactor material is brittle at ambient
temperatures. The actual constraint is informed by the reactor vendor. If limited
in pressure, the reactor temperature must be increased to the value specified
before pressure is increased.
3)
At the same time, start the flow of gas at maximum flow rate. The nitrogen or
hydrogen containing gas used for the drying of catalyst may be recycled, if
desired. Since the amine circulation must be stopped or the amine absorber
bypassed during the subsequent activation, this also is applied during the drying
phase.
4)
Light the heater according to refinery procedure and raise the reactor
temperature to 150°C (300°F). To minimise the risk of leaks due to thermal
expansion, the recommended maximum rate for heating up the catalyst is
30°C/hr (50°F/hr).
5)
Keep 150°C (300°F) at reactor inlet and maximise cooling of the reactor effluent.
Check and drain water from the high pressure separator. When no more water is
accumulated in the separator(s), the drying of the catalyst is complete.
6.2.
Sulphiding by the Doped Feed Method
In the doped feed method, an easily decomposable sulphur agent (such as DMDS,
SulfrZol 54, TNPS or TBDS) is added to the start-up feed, which must be a light straightrun fraction (e.g. kerosene or gas oil) that has a recommended boiling point (endpoint) of
maximum 370°C (700°F).
The injection rate of the sulphur agent must be adjusted to cover the entire activation
phase. The amount of sulphur agent needed for a given catalyst loading is provided by
Topsoe and included in the technical recommendation or in the catalyst specification.
HALDOR TOPSOE
19
Catalyst Activation and Start-up
Generally, we recommend having an excess of 15% available on site. In case the
activation is done with once-through gas, a total excess of 25% should be available.
For activation of our low density TK catalysts (such as TK-527) for naphtha service
(relatively low catalyst volume), we recommend an even higher excess of sulphur agent
due to higher relative losses. Refer to the table below for recommendation.
Volume of catalyst, m3 (ft3)
25 (900)
50 (1800)
75 (2700)
100 (3600)
Excess sulphur agent, %
90
70
50
30
It is advisable to do a sulphur balance as a check on the level of sulphiding by measuring
the amount of sulphur agent that has been added, the organic sulphur in the feed and
product streams (when oil recycle is not used) and the H2S content in the gas product
(purge) stream leaving the unit.
Properties of two of the most commonly used sulphur agents are listed below:
DMDS (Di-methyl-di-sulphide)
Density, kg/l
(lb/gal)
Sulphur Content, wt%
Decomposition
Temperature*, °C (°F)
MW, g/mole
Lbs S/gal
1.06 (8.9)
67.2
190 (374)
94.2
5.9
SulfrZol 54 (Di-t-butyl polysulphide)
Density, kg/l
(lb/gal)
Sulphur Content, wt%
Initial Decomposition
Temperature*, °C (°F)
MW, g/mole
Lbs S/gal
1.09 (9.1)
54
160 (320)
-
4.9
* The decomposition temperatures are in the presence of catalyst.
HALDOR TOPSOE
20
Catalyst Activation and Start-up
A step-by-step procedure including a graph of the temperature profile during a typical
doped feed sulphiding method using DMDS as sulphur agent is given below:
Typical Catalyst Sulphiding using DMDS
Reactor Inlet Temperature Profile during Activation
400
Drying
Catalyst Sulphiding
Normal Operation
700
Analyse H2S with 1 hr interval after 2-3 hours at 225°C (440°F)
350
300
550
Adjusting to Normal Operation
- Remove DMDS
- Introduce fresh feed (once-through)
- Purge remaining H2S in recycle gas or
start amine flow to the absorber
- Adjust reactor inlet temperature to the
predicted SOR value
250
25°C/hr (45°F/hr)
225°C (440°F)
15°C/hr (30°F/hr)
200
475
400
325
DMDS injection is started at 180°C (360°F)
150°C (300°F)
150
625
250
Feed introduction: When no more water
accumulates in the separators, drying is
complete and SR feed can be introduced
100
175
50
100
Addition of DMDS to straight run kerosene or gas oil
0
25
0
5
10
15
20
25
30
35
40
45
Approximate Duration, hours
1)
It is assumed at this point that the unit has been purged, pressurised and heated
to 150°C (300°F) as described in section 6.1, Drying of Catalyst, in this manual.
Furthermore, gas circulation has been established and the catalyst has been
dried.
2)
Start flow of start-up oil at normal feed flow rate. Monitor the reactor
temperatures and pressure drop and adjust the feed rate, if necessary. The
reactor is flushed with start-up oil, corresponding to 2-3 times the reactor
volume (or at least 4 hours), to remove dust and particles that would otherwise
be trapped in the reactor section.
3)
After flushing and stabilising of flows, temperatures and pressures in the unit,
the start-up oil can be circulated from the stripper or fractionator back to the
feed pump, if desired. This significantly reduces the quantity of start-up oil
needed and thus reduces the amount of off-specification material produced. It is
recommended that the oil recycle is not done through storage/product tanks
HALDOR TOPSOE
21
Reactor Inlet Temperature, °F
Reactor Inlet Temperature, °C
4 hrs hold at 350°C (660°F)
First stage of sulphiding: Hold
temperature until H2S breakthrough
when H2S > 5000 vol ppm - usually
after 6-8 hours of DMDS addition
Catalyst Activation and Start-up
because the unstripped oil may contain H2S and/or NH3, which may accumulate
in the tanks.
4)
The reactor inlet temperature is raised to 180°C (360°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%, the high pressure loop must be purged and
hydrogen rich make-up gas is introduced to the unit.
5)
When the reactor inlet temperature is 180°C (360°F), injection of sulphur agent
is started and the rate is adjusted to the value obtained by dividing the total
amount of sulphur agent (stoichiometric requirement) into 20 hours which is the
approximate duration of the sulphiding. Note that the rate of sulphur agent may
be changed during the activation.
6)
The heating is continued towards 225°C (440°F) at a rate of 25°C/hr (45°F/hr).
The sulphur agent will start decomposing at temperatures between 160°C and
190°C (see tables above). The decomposition of DMDS produces hydrogen
sulphide and methane and could result in exotherms in the reactor. The gas
rates are maximised to control the temperature increase.
7)
If desired, the injection rate of sulphur agent may be doubled during the first
stage of sulphiding (until breakthrough of H2S). However, exotherms and
maximum temperatures must be closely monitored as described below.
8)
Water is formed from the sulphiding reactions. Check the high pressure
separator at regular intervals for water accumulation throughout the catalyst
sulphiding and drain, if necessary.
9)
During the first stage of sulphiding the reactor inlet temperature is maintained at
225°C (440°F) until breakthrough of H2S. The reactor outlet temperature during
this period must not exceed 250°C (480°F) after the exotherm has passed
through the reactor.
10) Check hydrogen purity of the recycle gas during the hold period. Accumulation of
methane (from decomposition of DMDS) in the recycle gas may result in low
hydrogen purity and an increase in recycle gas density. Thus, it may be required
to purge the high pressure loop as described above.
11) In order to ascertain breakthrough of H2S, the high pressure separator off-gas
(recycle gas) must be checked for H2S concentration (using Dräger tubes) at
hourly intervals starting after 2-3 hours at 225°C (440°F). Breakthrough can be
defined as the point when two consecutive measurements of H2S are above
HALDOR TOPSOE
22
Catalyst Activation and Start-up
5,000 vol. ppm H2S, which typically occurs after addition of 40-60% of the
stoichiometric amount of sulphur agent needed. However, for naphtha service
activations, the breakthrough may not occur until 70-80% of the stoichiometric
amount of sulphur agent has been injected. Breakthrough indicates completion
of the first stage of sulphiding.
12) The reactor inlet temperature is raised towards 350°C (660°F) at a rate of
15°C/hr (30°F/hr) and the injection rate of sulphur agent is adjusted to ensure
enough sulphur agent for the remaining activation (approximately 12 hours). H2S
levels are checked each hour and the hydrogen content of the recycle gas is
measured every 2-3 hours.
13) At the higher temperatures the catalyst consumes more sulphur. If the H2S levels
drop below 3,000 vol.ppm, the heating should be decreased. Alternatively, the
rate of sulphur agent can be increased after a Topsoe engineer has been
consulted.
14) Note that high levels of H2S are corrosive to the equipment. This is especially
important for the compressor parts. Investigate the tolerance of the equipment to
avoid corrosion and subsequent compressor failure. If no specifications are given
for the tolerance, a maximum H2S content in the recycle gas should be 1-1.5
vol.%. The target H2S content during the sulphiding should be 5,000 to 10,000
vol.ppm.
15) Hold the reactor inlet temperature at 350°C (660°F). When all catalyst
temperatures have been at or above 330°C (625°F) for a minimum of 4 hours
and when at least 100% of the stoichiometric amount of sulphur has been
added, the final stage of sulphiding is considered completed. Addition of sulphur
agent can be terminated.
16) Normal straight-run feed is introduced to the unit at design rate. Amine
circulation is started and the recycle gas scrubber and associated equipment are
put into service. The product stripper and/or fractionators are commissioned
according to refinery procedure. If the start-up oil is circulated, this recycle is
stopped and the oil is routed to product tanks. Typically the initial product will
not meet all specifications and laboratory analyses have to be performed to
verify that the product meets design specifications.
17) Start wash water injection (if applicable) to the reactor effluent at normal rate.
18) The reactor inlet temperature is adjusted at a rate of 30°C/hr (50°F/hr) to the
temperature specified as the start-of-run temperature. After 4-6 hours at start-
HALDOR TOPSOE
23
Catalyst Activation and Start-up
of-run conditions, feed and product samples must be analysed to check the level
of activity.
19) It is important that the unit is fed only with straight-run components (start-up
feed) for a minimum of 2 days after start-up. After that cracked stocks can be
gradually introduced to the unit.
20) Operating conditions are checked in order to ensure that the pressure, gas rates,
recycle gas purity and H2S removal specifications are being met. Reactor
temperatures, stripper operation, etc. are adjusted according to product specifications.
6.3.
Sulphiding of Replacement Catalyst after Skimming
In some cases, refiners have had to interrupt a run to skim off the top catalyst bed to
alleviate pressure drop problems or to replace contaminated catalyst. In these cases,
new replacement catalyst (or a graded bed) could be installed after the skimming. The
bulk catalyst in the reactor is still in the sulphided state, which means that sulphiding is
only required for the new top layers of catalyst.
In this situation, an abbreviated sulphiding procedure is typically used. If a large
percentage of the catalyst in a reactor is replaced, use the recommended method
previously described for new or regenerated catalyst. The following procedure is for
activating a small portion (less than 10%) of new 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
catalyst as delivered is in the oxidic state.
1)
Heat the reactor to an inlet temperature of 150°C (300°F) over a period of 3-4 hours.
2)
The unit is pressurised to normal operating pressure (unless limited by the brittle
temperature of the reactor as described in section 6.1 in this manual).
3)
While pressurising the unit, the recycle gas compressor is started and circulation
of process gas is established at normal flow rate. In order to conserve H2S the
amine absorber must be by-passed or the amine circulation stopped during
sulphiding.
4)
Straight-run feed is introduced at design rate. Monitor the reactor pressure drop
and adjust the feed rate, if necessary. In case the feed is normally a cracked
stock or has cracked components, use a straight-run feed in the same boiling
HALDOR TOPSOE
24
Catalyst Activation and Start-up
5)
range as the normal feed or the straight-run components of the blend. The startup feed must contain enough sulphur (above 0.5 wt%), to make this procedure
effective.
Reactor inlet temperature is increased at 30°C/hr (50°F/hr) until desulphurisation
reactions begin and the resulting exotherm develops. Water formation also starts
which is seen by water starting to appear in the separators. Hold the inlet
temperature at this temperature for a minimum of 2 hours.
6)
After the 2-hour hold, reactor inlet temperature is increased to 350°C (660°F) at
30°C/hr (50°F/hr).
7)
Hold inlet temperature at 350°C (660°F) for 4 hours. The sulphiding of the
replaced catalyst is then considered complete.
8)
Amine circulation is initiated and the amine absorber (incl. amine regenerator) is
put into service. Typically the product will have to be sent to off-spec storage
until laboratory analyses indicate that the product meets design specifications.
9)
Reactor inlet temperature is lowered at a rate of 30°C/hr (50°F/hr) to the
temperature specified as the start-of-run temperature or to the temperature
needed to obtain the desulphurisation required.
10) If the unit normally treats cracked material, it is important to continue feeding
the unit with straight-run components or the start-up oil (having a sulphur
content of more than 0.5 wt%) for a minimum of 24 hours when the catalyst has
been conditioned to the operation. After that, cracked stocks can be charged to
the unit.
11) Operating conditions are checked in order to ensure that the pressure, gas rates,
recycle gas purity and H2S removal specifications are being met. Reactor
temperatures, stripper operation, etc. are adjusted according to product specifications.
6.4.
Start-up after Normal Shutdown
The start-up procedure described below is applied following a normal shutdown, where
no changes have been made to the state of the catalyst. The catalyst is still in its
active/sulphided form.
The procedure is also applicable if the catalyst has been dumped and reloaded under
inert conditions and the added volume of fresh (oxidised) catalyst is less than 10% of the
total catalyst volume (i.e. normal loss of catalyst during dumping/screening). Since the
catalyst is still in its sulphided state, it is not necessary to add additional sulphur.
HALDOR TOPSOE
25
Catalyst Activation and Start-up
If any high pressure equipment or piping has been opened, the high pressure section
must be purged with nitrogen. The reactor inlet temperature is kept below 150°C (300°F)
during the shutdown to minimise the risk of catalyst reduction.
1)
The unit is pressurised to normal operating pressure (unless limited by the brittle
temperature of the reactor as described in section 6.1 in this manual).
2)
While pressurising 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 (including amine regenerator) is put into service.
3)
Light the heater and start increasing the heater outlet temperature at 30°C/hr
(50°F/hr) to 150°C (300°F). Normal hydrogen flow must be established.
4)
When the heater outlet temperature has reached 150°C (300°F), fresh feed oil is
introduced and gradually raised to design rate. Monitor the reactor pressure drop
and adjust the feed rate, if necessary. In case the feed is normally a cracked
stock 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.
5)
After stabilising flows, temperatures and pressures in the unit, the start-up oil
can be circulated from the stripper or fractionator, if desired. This reduces the
quantity of start-up oil needed and may reduce off-spec material produced.
However, it must be ensured that some sulphur remains in the liquid feed to
maintain the exotherm in the reactor and thus prevent removal (stripping) of
sulphur from the catalyst. The preferred method to avoid this is to check that the
level of H2S in the recycle gas leaving the high pressure separator remains above
0.05 mol%. Use Dräger tubes to check. A more conservative method is recycling
only 80-90% of the product and adding sulphur 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 H2S and/or NH3, which may
accumulate in the tanks.
6)
Start wash water injection (if applicable) to the reactor effluent at normal rate.
7)
The heater outlet temperature is raised at 30°C/hr (50°F/hr) towards the
temperature specified as the start-of-run temperature or to the temperature
needed to obtain the desulphurisation required. At no point in time the heater
outlet temperature must be more than 100°C (210°F) higher than any reactor
temperature.
HALDOR TOPSOE
26
Catalyst Activation and Start-up
8)
In case the normal feed contains cracked material, it can be gradually introduced
as soon as the reactor outlet temperature is above 250°C (480°F). Prepare for
the increased hydrogen consumption and resulting exotherm, before adding of
the cracked material. Any circulation of product must be stopped when cracked
material is introduced.
9)
As the reactor temperatures approach the normal operating temperatures,
product circulation (if any) is stopped and laboratory analysis are initiated to
verify product specifications.
10) Operating conditions are checked in order to ensure that the pressure, gas rates,
recycle gas purity and H2S removal specifications are being met. Reactor
temperatures, stripper operation, etc. are adjusted according to product
specifications.
HALDOR TOPSOE
27
Normal Shutdown
7. Normal Shutdown
A normal shutdown is a controlled cooling of the reactor and removal of feed from the
unit.
The shutdown can be a short term occurrence midway through the life cycle of the
catalyst due to maintenance requirements or due to shutdown of upstream or
downstream units. In this case, it is expected that the reactor will be restarted without
catalyst change-out after the shutdown.
On the other hand, a long term shutdown will occur at the end of the life cycle of the
catalyst. Thus, the catalyst will be unloaded (as described in section 9, Catalyst
Unloading, in this manual) and be replaced or regenerated (as described in section 10,
Catalyst Regeneration, of this manual).
Both cases described above are anticipated in the procedure below.
1)
The heat input to the unit is reduced to cool the reactor at a maximum rate of
30°C/hr (50°F/hr).
2)
Product run down is switched to off-spec storage. The feed rate is gradually
decreased to nominally 50% of design. If cracked feedstock is processed, the
cracked portions of the feed blend are removed first.
3)
For complete flushing of heavy oil components from the distribution tray and
catalyst, it is recommended that the design feedstock to the unit is replaced with
naphtha, kerosene or light straight-run gas oil when the reactor inlet
temperature reaches 250°C (480°F). A total amount of light feed corresponding
to approximately 4-5 times the catalyst volume should be used for flushing.
During flushing with light feed the following guidelines should be followed:
ƒ
ƒ
ƒ
ƒ
ƒ
4)
Reactor inlet temperature is kept around 250°C (480°F) to prevent (or limit)
vapourisation of the feed.
Feed rate of light feed is maintained at normal feed rate of the unit. Monitor
reactor pressure drop and reduce feed rate, if necessary.
Recycle gas flow is maximised.
Cooling upstream of the separators is maximised.
Purge of recycle gas is initiated (as needed) to prevent recycling of lower
boiling hydrocarbons.
After flushing with the recommended amount of light feed, treat gas at 250°C
(480°F) is circulated until no more liquid accumulation is observed in the
HALDOR TOPSOE
28
Normal Shutdown
separators. However, the treat gas sweep should be limited to 6 hours to prevent
stripping sulphur from the catalyst.
5)
At further cooling, the treat gas is replaced with nitrogen (if possible) to avoid
risk of explosion or self-heating.
6)
If the shutdown will be temporary, the following should be done:
ƒ
ƒ
ƒ
7)
Cooling is continued until all reactor temperatures reach 175°C (350°F). If
not involved in the shutdown maintenance, there is no need for further
reactor cooling. Nitrogen or treat gas circulation is maintained.
The amine circulation is maintained and the amine regenerator kept hot
unless the shutdown is for an extended period.
If the reactor or associated equipment is to be worked on, cooling is
continued (as necessary) with nitrogen or treat gas. The unit pressure is
reduced before cooling below the brittle temperature (refer to section 6.1 in
this manual).
If the high pressure loop is to be worked on, the loop is depressurised and
purged with nitrogen. Refer to section 9, Catalyst Unloading, in this manual in
case the catalyst will be unloaded.
HALDOR TOPSOE
29
Emergency Shutdown
8. Emergency Shutdown
Emergency shutdowns may be caused by failures of various kinds. The actions to be
taken are primarily dictated by personnel and equipment safety considerations.
However, in order to best protect the catalyst from damage, it must be kept in mind that
the catalyst may be damaged by:
1)
Hot hydrogen without hydrogen sulphide or oil
This will tend to strip sulphur from the active/sulphided catalyst and at prolonged
exposure to these conditions, there is a risk of reducing the metal sulphides to
free metals with consequent permanent loss of catalyst activity. Refer to the
table below for time frames at different temperatures when hydrogen and no
hydrogen sulphide or oil is present.
Highest temperature, °C (°F)
Time frame, hours
200 (390)
250 (480)
300 (570)
48
12
2
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.
3)
Contact with water
Exposing the catalyst to liquid water or high water vapour concentrations at
elevated temperatures can result in loss of catalyst strength. Therefore, any
slugs of water in the reactor inlet streams must be avoided.
4)
Back-flow
Back-flow through the reactor must be avoided due to the risk of lifting of the
catalyst bed and support.
The above should be kept in mind during all unit operations procedures.
8.1.
Loss of Feed
If the charge pump shuts down or feed otherwise is lost, the compressors and thus treat
gas flow normally will continue. However, the heater will not respond quickly to the
sudden loss in flow. To prevent overheating, the heater therefore should automatically
cut back to minimum fires or trip the fuel gas to the main burners. Pilot burners are kept
in service to facilitate return to normal operation. If the charge pump cannot be restarted
HALDOR TOPSOE
30
Emergency Shutdown
within 15 minutes, continue to cool the reactor at a rate of 30°C/hr (50°F/hr) to 200°C
(390°F). Stop the amine circulation in the absorber. The recycle (and make-up) gas flow
is maximised during the cooling of the reactor.
8.2.
Loss of Recycle Gas
In case the recycle gas compressor shuts down, oil will stagnate in the reactor. The feed
pump must trip automatically and the heater should cut back to minimum fires or trip the
fuel gas to the main burners. The make-up gas compressor must be kept at maximum to
sweep off oil and cool the heater tubes and catalyst as fast as possible. To make sure
that oil is removed from the catalyst it may be needed to depressurise the unit by normal
purge or emergency depressurisation.
8.3.
Loss of Make-up Gas
If the make-up gas compressor shuts down, 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 normal short-term shutdown in
section 7 of this manual.
8.4.
Loss of Amine Flow
In case the amine pump stops, the H2S concentration in the recycle gas will increase and
the catalyst activity will be inhibited. 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 maximised until limited by the ability of the make-up
gas compressor to maintain loop pressure. Feed rate or total sulphur input to the unit is
reduced to avoid off-spec product. If the amine system cannot be restarted within 15-30
minutes and the unit metallurgy is not designed for H2S in the recycle gas, the unit has to
be shut down as described for normal short-term shutdown in section 7 of this manual.
8.5.
Loss of Wash Water
If the wash water pump stops, operation can continue up to 24 hours but be aware that
ammonium salts may start to precipitate in the heat exchangers operating below the
precipitation temperatures of the salts. Furthermore, ammonia will accumulate in the
amine section and could potentially upset the downstream sulphur plant. A reduction of
oil feed rate would reduce the ammonia built-up.
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Emergency Shutdown
8.6.
Emergency Depressurisation
The unit must be equipped with an emergency depressurisation system that will allow
the unit to be depressurised according to the recommendation in API 521. For
hydrotreating units, this normally results in a valve system that reduces the pressure
from normal operating pressure to 50% of the design pressure in 15 minutes. The
emergency depressurisation system is connected to the flare and should only be used in
case of fire, uncontrolled leak, etc.
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Catalyst Unloading
9. Catalyst Unloading
A number of material protection and safety measures must be taken when unloading
catalyst. It is recommended to use metal equipment for the unloading and, 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.
Spent catalyst and iron sulphide deposits can be pyrophoric at temperatures above 70°C
(160°F), and therefore the reactor should be cooled to less than 50°C (120°F) prior to
unloading. A purge of nitrogen must be maintained during the unloading in order to
minimise ingress of air. In particular, opening of more than one manhole/flange at a time
should be avoided as this could create a "chimney effect" leading to uncontrolled
oxidation and possible temperature run-away in the catalyst bed.
The installed catalysts can either be vacuumed out (top skimming) or dumped via the
dump nozzle (removal of all catalysts from the bed). Generally, the vacuuming process is
very harsh, resulting in a lot of catalyst breakage and dust. Thus, catalysts that have
been removed by vacuum, have high losses and generally cannot be reused.
To avoid exposure to air, the unloaded catalysts must be stored in sealed steel drums or
preferably in airtight catalyst bins. If the catalysts are screened before loading in drums,
the screening must be carried out in inert atmosphere.
When the catalysts are dumped, a slope (usually a cone) is formed in the reactor, as the
catalysts are flowing out through the dump nozzle. Since the ceramic balls are dumped,
the outlet collector gets in contact with the catalysts. Part of the catalysts and especially
fines often will penetrate through the grid on the outlet collector and migrate to the outlet
piping. This is a potential problem for units having multiple reactors. In order to avoid the
catalyst particles/dust being transferred to the downstream reactor, the outlet piping
should be cleaned to minimise the risk of plugging the upper part of the next reactor.
9.1.
Catalyst Screening
If the unloaded catalyst is to be reused, it must be screened before reloading. The
catalysts are screened on sieves according to catalyst size. The screen opening should
be approximately 75% of the maximum catalyst diameter.
The normal amount of fines found during screening of unloaded (dumped) catalysts is
approximately 1-2%. The undersize material found during screening is a mixture of
catalyst fragments and coke.
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Catalyst Unloading
It is difficult to screen mixtures of catalysts and inert ceramic balls, as the relatively
heavy ceramic balls tend to crush the catalysts on the screens and thus create a lot of
dust. The mixture of inert ceramic balls and catalyst is normally dumped into separate
drums/bins for “individual” screening.
Warning
Nickel carbonyl, an extremely toxic substance, may be generated any time a carbon
monoxide bearing gas contacts a nickel containing catalyst at temperatures below about
200°C (400°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 30 ppm carbon monoxide, it
must be assumed that nickel carbonyl is present.
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Catalyst Regeneration
10. Catalyst Regeneration
All hydroprocessing catalysts will age and deactivate during the cycle. The deactivation
rate varies considerably, depending upon feedstock and operating severity. Straight-run
naphtha processing will have a low deactivation rate and residual oil processing on the
other hand will have a high deactivation rate.
Some carbon (coke) will form on the catalyst during normal operation and as the run
progresses this carbon and other depositions like metals, silica, etc. will contribute to a
loss of catalyst activity. Normally, reactor temperatures are increased to compensate for
this deactivation effect and in this way still maintain product quality.
At some point in time, the inability to raise reactor temperatures further or failure to meet
product requirement will necessitate a plant turn-around. For many light services, the
catalyst may be reused after it has been regenerated and reactivated.
If the catalyst is regenerated ex-situ, in most cases it will regain 80-90% of the activity
compared to fresh catalyst. Catalyst deactivated by metals and silicon or by maloperation that causes sintering and loss of surface area will not regain the activity of
fresh catalyst after regeneration.
The TK rings used as grading material are unsuitable for regeneration and thus should be
replaced after each cycle.
10.1.
Ex-Situ versus In-Situ Regeneration
There are several advantages of ex-situ regeneration compared to in-situ regeneration.
First of all an ex-situ regeneration generally can be made much more uniformly than an
in-situ regeneration, especially in cases where poor flow distribution has been observed
in the reactor during the catalyst cycle. Secondly, the regenerated catalyst can be
analysed for strength and activity before it is reloaded. Finally, dust, solid contaminants
and broken catalyst particles will be removed during the screening of the catalyst during
the ex-situ regeneration. Typical losses during an ex-situ regeneration will be less than
10%.
Ex-situ regeneration performed by companies who specialise in regeneration of catalysts
is recommended for all TK catalysts. Topsoe continuously discuss procedures and advice
the companies that do the regeneration of TK catalysts. At the request of the client
Topsoe will provide an evaluation (catalyst analysis) of the regenerability of a specific
batch of catalyst prior to shipment to the company doing the regeneration.
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Catalyst Regeneration
In case the refiner has a spare charge of catalyst available at site (which is
recommended by Topsoe), less unit down time is required for ex-situ compared to in-situ
regeneration.
Since in-situ regeneration is done infrequently, the unit operators are not normally
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, and if all procedures are not carefully
followed, there is also a risk of causing damage to the catalyst.
Following an in-situ regeneration, dumping and screening of the catalyst is
recommended. The reason for this is to remove particulates that have accumulated in the
bed during normal operation and any agglomerated catalyst formed during the
regeneration. Iron sulphide that is deposited in the reactor during normal operation will
fuse catalyst pellets together during regeneration. This can result in subsequent high
pressure drop or hot spots inside the catalyst bed after restart of the unit.
As mentioned above the TK rings (grading), loaded at the top of the first bed of the
reactor, are unsuitable for regeneration and should be replaced with fresh TK rings and
the reactor topped with fresh catalyst to reach the original catalyst volume after reloading
the regenerated catalyst.
After dumping, screening and reloading, regenerated catalyst will normally have a lower
length/diameter ratio than fresh catalyst. This means that a slightly higher start-of-run
pressure drop as compared to fresh catalyst must be expected.
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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Liability
11. Liability
The recommendations contained in this manual have been prepared by Topsoe engineers
and scientists having thorough knowledge of the catalyst. However, any operating
recommendations should be considered to be of a general nature, given 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 and
validity.
The recommendations are given without any liability on the part of Topsoe for upset or
damage to the individual plants or personnel. Nothing enclosed is to be construed as
recommending any practice or any product in violation of any patent, law or regulation.
Topsoe technicians present at 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 recommendations
issued by Topsoe being carefully reviewed by the plant personnel before their adoption to
a specific unit.
Any unclear points should be discussed and clarified with Topsoe before start of
operation.
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Contact Addresses
Contact Addresses:
Haldor Topsoe A/S
Nymøllevej 55
DK-2800 Lyngby, Denmark
Telephone: +45 4527 2000
Telefax:
+45 4527 2999
Haldor Topsoe, Inc
17629 El Camino Real, Suite 300
Houston, Texas 77058, USA
Telephone: +1 281 228 5000
Telefax:
+1 281 228 5159
24-hour hotline: +1 281 228 5201
Haldor Topsoe, Inc.
770 The City Drive, Suite 8400
Orange, CA 92868, USA
Telephone: +1 714 621 3800
Telefax:
+1 714 748 4188
Haldor Topsoe A/S, Moscow Representative Office
Bryusov per, 11, 4th Floor
Moscow -125009, Russian Federal Republic
Telephone: +7 495 229 6350
Telefax:
+1 503 956 3275
Haldor Topsoe International A/S
Room 1008, 22 Jianguomenwai Dajie, Scitech Tower
Beijing-100 004, China
Telephone: + 86 10 6512 3620
Telefax:
+ 86 10 6512 7381
Haldor Topsoe International A/S
B-42 (First Floor), Panchsheel Enclave
New Delhi-110 017, India
Telephone: +91 11 5175 0081-85
Telefax:
+91 11 5175 0252
File No. 42211 – AKU/IGS, August 2006
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