PROCESS AND APPARATUS FOR WITHDRAWING SOLIDS FROM A VESSEL

Abstract: Process and apparatus for withdrawing solids from a vessel utilizing a nozzle (5) to introduce transport fluid via the outer tube (12) into the solids pick-up area (4) and withdrawing solids and fluid via an inner tube (11), which comprises withdrawing a slurry of transport fluid and solids via a retracted inner tube (11).

Description: The present invention relates to a process and apparatus for withdrawing a slurry of solids and a transport liquid from a vessel. It is known to withdraw solids, such as catalyst particles which gradually have become deactivated, e.g. during operation of hydrocarbon processes in which they are employed, from vessels, especially reactors which are equipped with a movable catalyst bed. Such vessels usually comprise one or more screen sections for separating the reactor effluent from the catalyst, the vessel being provided with separate outlet means for effluent and catalyst in a lower part of the vessel. Fresh and/or regenerated catalyst can be fed continuously or at intervals at the top and spent catalyst is removed from the bottom of the vessel via an outlet system containing a rotating valve as for instance as described in US patent specification 4,590,045. Since catalyst fines and smaller (broken) catalyst particles have a tendency to accumulate near the reactor bottom they will block the rotating valve and thus reduce the withdrawal flow of spent catalyst. It has now been found that the problem encountered with the use of rotating valve systems can be solved in a different manner. In FR-A-2 579 573 an apparatus is depicted in figure 2 comprising a conduit situated on top of the mass of particles and through which conduit gas and/or liquid is introduced, and another conduit for withdrawing the fluidized particles thus obtained, which inlet is depicted to be somewhat higher than the outlet of the first mentioned conduit. From US-A-2 762 658 a pneumatic system is known comprising a tubular sleeve concentrically surrounding the lower end portion of a lift pipe providing an annular passage for lift gas, which annular passage is closed at its upper end. Further, a tubular vessel concentrically encloses and extends below the sleeve to provide an outer annular passage. A major amount of lift gas is introduced into the annular passage, while a minor amount is introduced into the outer annular passage. The lift gas introduced into the outer annular passage is to carry the catalyst upwardly, while the lift gas introduced into the outer annular passage is to regulate the catalyst flow. The present invention now relates to a process for withdrawing solid particles from a pick-up area in a vessel utilizing an inserted nozzle comprising one or more retracted inner tubes which are located inside an outer tube, which process comprises the use of a transport liquid split up into an entrainment flow which is introduced into the vessel upstream of the pick-up area and a dilution flow which is led to the pick-up area via the outer tube of the inserted nozzle, thereby withdrawing a slurry of transport liquid and solid particles through the one or more retracted inner tubes. It should be noted that it is known from Journal of Pipelines ( 5 , 1985, 67-75) to unload ships in an economically attractive way with an air-driven withdrawing system comprising a suction nozzle which consists of two tubes mounted co-axially, wherein the inner conveying tube has to protrude from the outer tube in order to obtain meaningful results. The invention will now be illustrated by way of Figures 1-5, wherein Figure 1 schematically shows a part of a longitudinal cross-section of a conventional reactor vessel comprising a rotating valve system. Figure 2 schematically shows a longitudinal cross-section of a part of a reactor vessel utilized in the process according to the invention. Figure 3 schematically shows the pick-up vessel and inserted nozzle in more detail. Figure 4 schematically shows a further embodiment of the present invention, wherein the withdrawal system comprises two inner tubes located inside the outer tube. Figure 5 schematically shows a preferred embodiment of the present invention. Throughout Figures 1-5 the same reference numerals have been used for similar purposes, and accessories such as valves, pumps and control instruments not necessary for the purpose of understanding the present invention are not (all) shown. In Figure 1 the bottom part of a normally vertically extending reactor utilized in a conventional process, such as hydroconversion, is depicted, comprising the lower part of the reactor side wall 1 and the bottom end shell 2 which is provided with reactor effluent outlet means 3. In Figure 2 the bottom part of a normally vertically extending reactor utilized in a process according to the invention is depicted wherein the bottom end shell 2 is provided with a catalyst pick-up vessel 4 including an inserted nozzle 5. The reactor (see Figures 1 and 2) is provided with internals for supporting catalyst particles, said internals consisting of a downwardly converging conical surface 6 terminating at the lower end thereof in a substantially vertical outlet channel 7 for the passage of catalyst particles and reactor effluent. To direct catalyst particles from channel 7 towards catalyst pick-up vessel 4, a lower conical segment 8 is arranged between the lower end of outlet channel 7 and the upper end of the catalyst pick-up vessel 4 via tube 9. The angle with the vertical axis of the lower conical segment 8 should be such that the catalyst can smoothly pass through this segment 8 towards the catalyst pick-up vessel. The conical surface 6, the outer channel 7 and the lower conical segment 8 are supported at the inner surface of the reactor wall 1. Part or all of the outlet channel 7 is provided with a cylindrical screen section 10, for separating the reactor effluent, which passes through the screen section from the catalyst particles, said screen section 10 forming part of the wall of the outlet channel 7. In Figure 3 the pick-up vessel 4 is depicted in more detail. The inserted nozzle comprises an inner tube 11 which is located inside the outer tube 12 and a dilution supply pipe 13. The inner tube 11 and the outer tube 12 normally have diameter ratios in the range of between 0.30 and 0.90, and in particular 0.40-0.65. The inner tube 11 can be retracted inside the outer tube up to 5.0 times the outer tube diameter, and in particular in the range of between 0.5 and 1.5 times the outer tube diameter. Catalyst pick-up vessel 4 includes an entrainment liquid supply pipe 14 through which part of the transport flow (primary flow) can be introduced into the bottom area of the reactor upstream of the pick-up area for entrainment purposes. A further part of the transport liquid flow (secondary flow) or a different transport liquid is led controllably into the pick-up area of the reactor through the outer tube. By splitting up the transport liquid flow in two parts the velocity and concentration of the slurry to be withdrawn through an inner tube can be independently controlled. In this arrangement the slurry is entirely entrained by the primary flow passing through the pick-up vessel 4. The secondary dilution flow introduced via the outer tube 12 does not substantially influence the entrainment flow. This complete separation of entrainment and dilution is one of the advantages of the easily controllable system. The process according to the present invention thus provides the possibility to pick-up the solids and make up the slurry to be transported simultaneously and to feed transport liquid to the system without disturbance of the slurry flow in the reactor. In Figure 4 an optional embodiment of the reactor utilized in a process according to the invention is depicted wherein the withdrawal system comprises an outer tube 12 and two inner tubes 11a. Alternatively the withdrawal system may comprise an outer tube 12 and more than two inner tubes 11a. In Figure 5 a preferred embodiment of the reactor utilized in a process according to the invention is depicted wherein in the bottom part outlet channel 7 is directly connected to a pick-up means 15 which includes an inserted nozzle 10 comprising an inner tube 17 which is located inside the outer tube 18 and a dilution pipe 19. An entrainment pipe 20 is connected to the pick-up means 15 upstream the pick-up area from where the slurry is to be withdrawn. This embodiment is not limited to two inserted nozzles as depicted but the number of inserted nozzles may range from two to for example 12, depending on the size of the individual outlet channels 7 chosen. It will be understood, especially with a large number of inserted nozzles, that the inserted nozzles can terminate at their lower ends in a single catalyst withdrawal pipe passing through an opening in the bottom of the vessel thereby forming a single catalyst outlet instead of all the individual inserted nozzles extending through openings in the bottom of the vessel. For detailed description of bottom internals reference is made to US patent specification 4,568,523. During operation of the reactor, catalyst and reactant can be supplied into the upper part of the interior of the reactor. Having passed the conical surface 6 (see Figure 2) catalyst particles and reactor effluent enter the outlet channels(s) 7 where reactor effluent is separated from catalyst particles via screen section 10. The catalyst moves downwardly through the outlet channel 7 and via the interior of the lower conical segment 8 and tube 9 into the catalyst pick-up vessel 4. Via entrainment pipe 14 which is connected with the catalyst pick-up vessel 4 a transport liquid, preferably an oil, is fed to the catalyst pick-up vessel 4 to sustain the flow entraining catalyst from the pick-up area and to prevent effluent which passed with catalyst particles screen section 10 from flowing downwards into the catalyst pick-up vessel 4. Dilution pipe 13 (see Figure 3) is connected to the outer tube 12 via which part of the same or a different transport liquid is introduced into the pick-up area to withdraw a slurry of transport liquid and catalyst particles through an inner tube 11. The hydroconversion processes which can be carried out suitably according to the present invention comprise hydrogenation, hydrodesulphurization and hydrodemetallization of hydrocarbon oil residues. The invention also relates to an apparatus suitable for carrying out the process as described in any one of claims 1-11, comprising a normally vertically extending substantially cylindrical vessel with one or more inlet means for fresh and/or regenerated catalyst and/or liquid and/or gas, containing catalyst bed supporting and guiding means in the shape of one or more downwardly converging conical surfaces, one or more vertical outlet channels connected to the lower end(s) of the conical surface(s), the supporting and guiding means comprising one or more screen sections for withdrawal of vessel effluent from the catalyst, separate outlet means for vessel effluent and catalyst, which comprises a withdrawal system including an inserted nozzle containing a retracted inner tube for withdrawing a slurry of transport liquid and solids which inner tube is located inside an outer tube, and which withdrawal system further comprises a dilution supply pipe connected with the outer tube, and an entrainment liquid supply pipe upstream of the pick-up area. The inner/outer tube diameter ratio preferably ranges between 0.30 and 0.90, and in particular between 0.40 and 0.65. An inner tube can be retracted inside the outer tube up to 5.0 times the outer tube diameter, and in particular in the range of between 0.5 and 1.5 times the outer tube diameter. The withdrawal system is preferably provided with means to vary the extent of retraction of the inner tube 11 inside the outer tube 12 in order to comply with different slurry concentrations.

Claims: A process for withdrawing solid particles from a pick-up area in a vessel utilizing an inserted nozzle comprising one or more retracted inner tubes which are located inside an outer tube, which process comprises the use of a transport liquid split up into an entrainment flow which is introduced into the vessel upstream of the pick-up area and a dilution flow which is led to the pick-up area via the outer tube of the inserted nozzle, thereby withdrawing a slurry of transport liquid and solid particles through the one or more retracted inner tubes. A process according to claim 1, which comprises the use of an oil as transport liquid. A process according to claim 1 or 2, which comprises the use of an inner tube and an outer tube having diameter ratios in the range of between 0.30 and 0.90, and in particular 0.40-0.65. A process according to any one of claims 1-3, which comprises the use of an inner tube which is retracted inside the outer tube up to 5.0 times the outer tube diameter, and in particular between 0.5 and 1.5 times the outer tube diameter. A process according to any one of claims 1-4, which comprises the use of a movable catalyst bed reactor. A process according to claim 5, which comprises the use of a movable catalyst bed reactor wherein hydroconversion processes are carried out. A process according to claim 6, which comprises hydrogenation, hydrodesulphurization and hydrodemetallization of hydrocarbon oil residues as hydroconversion processes. A process according to claim 7, which comprises the use of catalyst particles to be withdrawn which contain one or more metals having hydrogenation activity on a carrier. A process according to any one of claims 1-8, which comprises the use of solids containing spent catalyst particles. A process according to any one of claims 1-9, which comprises the use of two or more inserted nozzles to withdraw a slurry of solids and transport liquid from appropriate area(s) from where the slurry is to be withdrawn. An apparatus suitable for carrying out the process as described in any one of claims 1-10, comprising a normally vertically extending substantially cylindrical vessel with one or more inlet means for fresh and/or regenerated catalyst and/or liquid and/or gas, containing catalyst bed supporting and guiding means in the shape of one or more downwardly converging conical surfaces, one or more vertical outlet channels connected to the lower end(s) of the conical surface(s), the supporting and guiding means comprising one or more screen sections for withdrawal of vessel effluent from the catalyst, separate outlet means for vessel effluent and catalyst, which comprises a withdrawal system including an inserted nozzle containing a retracted inner tube for withdrawing a slurry of transport liquid and solids which inner tube is located inside an outer tube, and which withdrawal system further comprises a dilution supply pipe connected with the outer tube, and an entrainment liquid supply pipe upstream of the pick-up area. An apparatus according to claim 11, which comprises an inner tube and an outer tube having diameter ratios in the range of between 0.30 and 0.90, and in particular 0.40-0.65. An apparatus according to claim 11 or 12, which comprises an inner tube which is retracted inside the outer tube up to 5.0 times the outer tube diameter, and in particular between 0.5 and 1.5 times the outer tube diameter. An apparatus according to any one of claims 11-13, which comprises a withdrawal system including two or more inner tubes located inside the outer tube. An apparatus according to claim 14, which comprises a withdrawal system including means to vary the extent of retraction of an inner tube inside the outer tube. An apparatus according to any one of claims 11-15, which comprises two or more inserted nozzles capable of withdrawing a slurry of solids and transport liquid from appropriate area(s).

Inventors: POLDERMAN, HUGO GERARDUS
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1987
Main classification: B01J4
IPC codes: B01J8, B01J4, B65D90, C10G49