Manual for Topsoe Hydroprocessing Catalysts

Transcription

1 Manual for Topsoe Hydroprocessing Catalysts

2 LIST OF CONTENTS 1. INTRODUCTION 1 2. APPLICATION 1 3. CATALYST HANDLING Safety 3 4. REACTOR INTERNALS Distribution Tray Types Reactor Inspection and Preparation Procedure for Inspection of Internals CATALYST LOADING Support Material and Topping Layers Sock Loading Dense Loading CATALYST ACTIVATION AND START-UP Drying of Catalyst Sulphiding by the Doped Feed Method Sulphiding of Replacement Catalyst after Skimming Start-up after Normal Shutdown NORMAL SHUTDOWN EMERGENCY SHUTDOWN Loss of Feed Loss of Recycle Gas Loss of Make-up Gas Loss of Amine Flow Loss of Wash Water Emergency Depressurisation CATALYST UNLOADING Catalyst Screening CATALYST REGENERATION Ex-Situ versus In-Situ Regeneration LIABILITY 37 HALDOR TOPSOE

3 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. The cobalt-molybdenum types are greyish blue, except for TK-558 BRIM TM, TK-574 and TK-576 BRIM TM, which are often dark grey or black and the nickel-molybdenum are greenish yellow, except for TK-559 BRIM TM, 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

4 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 38x25x and , 1.6 and , 2.5, 2.1, 1.7 and 1.3 HALDOR TOPSOE 2

5 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 m 3 (35 ft 3 ). 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 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

6 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

7 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 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

8 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

9 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

10 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

11 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 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

12 Reactor Internals 8) 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

13 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

14 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 SO 2 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 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

15 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

16 Catalyst Loading 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 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 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

17 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 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

18 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

19 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 TK TK TK-575 BRIM TM 12.3 TK-558 BRIM TM 11.9 TK-576 BRIM TM 11.9 TK-559 BRIM TM 11.1 TK-605 BRIM TM 12.3 TK TK TK TK 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

20 Catalyst Activation and Start-up As mentioned in section 3, Catalyst Handling, the TK catalysts are very porous, having surface areas of 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 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) 200 (390) 250 (480) 300 (570) Time frame, hours HALDOR TOPSOE 18

21 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 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

22 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, m 3 (ft 3 ) 25 (900) 50 (1800) 75 (2700) 100 (3600) Excess sulphur agent, % 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 H 2 S 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) (374) 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) (320) * The decomposition temperatures are in the presence of catalyst. HALDOR TOPSOE 20

23 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: Reactor Inlet Temperature, C Typical Catalyst Sulphiding using DMDS Reactor Inlet Temperature Profile during Activation Drying Catalyst Sulphiding 25 C/hr (45 F/hr) 150 C (300 F) Analyse H 2 S with 1 hr interval after 2-3 hours at 225 C (440 F) First stage of sulphiding: Hold temperature until H 2 S breakthrough when H 2 S > 5000 vol ppm - usually after 6-8 hours of DMDS addition Feed introduction: When no more water accumulates in the separators, drying is complete and SR feed can be introduced 225 C (440 F) 15 C/hr (30 F/hr) DMDS injection is started at 180 C (360 F) Addition of DMDS to straight run kerosene or gas oil 4 hrs hold at 350 C (660 F) Normal Operation Adjusting to Normal Operation - Remove DMDS - Introduce fresh feed (once-through) - Purge remaining H 2 S in recycle gas or start amine flow to the absorber - Adjust reactor inlet temperature to the predicted SOR value Reactor Inlet Temperature, F 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

24 Catalyst Activation and Start-up because the unstripped oil may contain H 2 S and/or NH 3, 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 H 2 S). 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 H 2 S. 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 H 2 S, the high pressure separator off-gas (recycle gas) must be checked for H 2 S 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 H 2 S are above HALDOR TOPSOE 22

25 Catalyst Activation and Start-up 5,000 vol. ppm H 2 S, 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). H 2 S 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 H 2 S 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 H 2 S 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 H 2 S content in the recycle gas should be vol.%. The target H 2 S 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

26 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 H 2 S removal specifications are being met. Reactor temperatures, stripper operation, etc. are adjusted according to product specifications 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 H 2 S 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