Slurry phase apparatus

Abstract

A method of operating a slurry phase apparatus includes feeding one or more gaseous reactants into a slurry body of solid particulate material suspended in a suspension liquid contained inside a vessel. The one or more gaseous reactants are fed into the slurry body through a gas distributor having downward facing gas outlets and are fed towards a fluid impermeable partition spanning across the vessel below the gas distributor. The partition divides the vessel into a slurry volume above the partition and a bottom volume below the partition. A differential pressure is maintained over the partition between predefined limits by manipulating or allowing changes in the pressure in the bottom volume by employing a pressure transfer passage establishing flow or pressure communication between the bottom volume and a head space above the slurry body.

Claims

1. A method of operating a slurry phase apparatus, the method including feeding one or more gaseous reactants into a slurry body of solid particulate material suspended in a suspension liquid contained inside a vessel, with a head space above the slurry body, the one or more gaseous reactants being fed into the slurry body through a gas distributor having downward facing gas outlets and being fed towards a fluid impermeable partition spanning across the vessel below the gas distributor, the partition dividing the vessel into a slurry volume above the partition and a bottom volume below the partition; and maintaining a differential pressure over the partition between predefined limits by manipulating or allowing changes in the pressure in the bottom volume by employing a pressure transfer passage establishing flow or pressure communication between the bottom volume and the head space above the slurry body.

2. The method according to claim 1, in which the partition is planar or flat and arranged perpendicular to a longitudinal vertical central axis of the vessel, thus defining a false floor or bottom for the vessel.

3. The method according to claim 1, in which the partition has a design pressure which is less than 600 kPa and in which the predefined differential pressure limits fall within the design pressure for the partition.

4. The method according to claim 1, in which the pressure in the bottom volume is allowed to change automatically in sympathy with pressure changes in the slurry volume or the head space thereby to maintain the differential pressure over the partition within said predefined limits.

Description

(1) The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which

(2) FIG. 1 shows a slurry phase apparatus, in the form of a slurry bubble column, which can be operated in accordance with one embodiment of the invention;

(3) FIG. 2 shows a plan view of a gas distributor of the apparatus of FIG. 1;

(4) FIG. 3 shows a slurry phase apparatus, in the form of a slurry bubble column, which is not in accordance with the invention; and

(5) FIG. 4 shows a slurry phase apparatus, in the form of a slurry bubble column, which is also not in accordance with the invention.

(6) Referring to FIG. 1 of the drawings, reference numeral 10 generally indicates slurry phase or suspension apparatus which can be operated in accordance with one embodiment of the method of the invention. The apparatus 10 includes an upright cylindrical Fischer-Tropsch synthesis slurry phase reactor vessel 12 and a gas distributor 14 located in a bottom portion of the vessel 12. A gaseous components outlet 16 is provided in an upper portion of the vessel 12, with a gaseous products withdrawal line 17 leading from and in flow communication with the gaseous components outlet 16. A solid planar partition or false floor 18 is provided in a bottom portion of the vessel 12. The partition 18 partitions the vessel 12 into a slurry volume 19 above the partition 18, and a bottom volume 36 below the partition 18. A liquid phase outlet 20 is provided below the gaseous components outlet 16 but above the partition 18. A bank 22 of cooling tubes is located above the gas distributor 14 but below the gaseous components outlet 16.

(7) The gas distributor 14 is in flow communication with a gaseous reactants feed line 26. The gas distributor 14 may be of any suitable design for feeding a gas into a slurry bed, provided it includes downward facing gas outlets. It may for example be made up of or include radially extending branch pipes connected to concentric rings or tubular toroids, or be made up of or include a system of horizontal distributor pipes branching into smaller horizontal pipes, or be made up of or include a pipe arranged in a spiral in a horizontal plane. In the embodiment illustrated in FIG. 2, the gas distributor 14 includes a header 27 in flow communication with a plurality of lateral pipes 28 and with the feed line 26. A plurality of diffusers 30 extend downwardly from the lateral pipes 28 with each diffuser 30 defining a downwardly facing gas outlet 32 spaced equidistantly from the partition 18. It is however to be appreciated that the particular design of the gas distributor 14 will vary from application to application and that fairly complicated designs may be employed. The various further design possibilities for a gas distributor for a three-phase slurry apparatus however do not fall within the scope of the invention and are not further discussed.

(8) The partition 18 is welded to the vessel 12 using a welding expansion ring in conventional fashion and may include further supports such as I-beams also welded to the vessel 12. The design and manufacture of a vessel 12 with a false floor or partition 18 fall within the knowledge of a person skilled in the art but outside the scope of the present invention and these aspects are not further discussed. Typically, the partition 18 includes at least one manhole (not shown) with a lid to allow access to the bottom volume 36 below the partition 18.

(9) In use, the slurry volume will hold a slurry bed 37. The slurry bed 37 will have an expanded height with an upper surface 38 above the bank 22 of cooling tubes but below the gaseous components outlet 16, leaving a head space 40 to disengage gaseous components from the slurry bed 37.

(10) A pressure transfer passage 34 is provided to manipulate or allow changes in the operating pressure in the bottom volume 36 thereby limiting the pressure differential across the partition 18. The pressure transfer passage 34 extends between the gaseous products withdrawal line 17 and the bottom volume 36, allowing in use the pressure in the bottom volume 36 to be equalised with the pressure in the gaseous products withdrawal line 17, i.e. in essence with the pressure in the head space 40.

(11) The apparatus 10 may include many additional features commonly found in or on slurry bubble columns or similar slurry phase apparatus, such as means for loading and withdrawing catalyst, means for draining spaces, means for filtering catalysts from liquid phase and the like. Such features would typically however be conventional and known to those skilled in the art and need not further be described.

(12) The apparatus 10 can be used, for example, in a Fischer-Tropsch process to synthesise hydrocarbons from carbon monoxide and hydrogen using an appropriate catalyst, such as a supported iron or cobalt catalyst. Synthesis gas, comprising mainly carbon monoxide and hydrogen, thus enters the submerged gas distributor 14 from the gaseous reactant feed line 26 and is injected into the slurry bed 37 through the downward facing gas outlets 32, in order to maintain the slurry bed 37 in a churn turbulent state. The gas is thus injected downwardly through the diffusers 30 and out through the gas outlets 32, towards the partition 18.

(13) The slurry bed 37 comprises the catalyst particles suspended in liquid product, i.e. liquid wax produced in the vessel 12 on the action of the gaseous reactants. The catalyst particles are maintained in suspended state in the slurry bed 37 by means of the turbulence created therein by the gas passing upwardly therethrough.

(14) For Fischer-Tropsch reactions, the vessel 12 is typically maintained at an operating pressure of between about 10 bar and about 40 bar, more typically between about 20 bar and about 30 bar, and at an operating temperature of between 180 C. and 280 C., typically about 220 C. to 260 C. The operating pressure and the operating temperature selected may depend on the nature and spread of gases and liquid product required and the type of catalyst used. Naturally, the apparatus 10 is provided with suitable temperature control means such as the bank 22 of cooling tubes for controlling the reaction temperatures, as well as suitable pressure control means such as one or more pressure control valves.

(15) In the reactor vessel 12, as the synthesis gas passes through the slurry bed 37, the carbon monoxide and hydrogen react to form a range of products in accordance with known Fischer-Tropsch reactions. Some of these products are in gaseous form at the operating conditions of the vessel 12 and are withdrawn, together with unreacted synthesis gas, through the gaseous components outlet 16. Some of the products produced, such as the wax already mentioned, are in liquid form at the operating conditions of the vessel 12 and act as the suspension medium for the catalyst particles. As liquid product is formed, the level 38 of the slurry bed 37 naturally tends to rise and the liquid product is thus withdrawn, by means of the liquid phase outlet 20 to maintain the slurry bed level 38 and to ensure an adequate head space 40. Catalyst particles may be separated from the liquid phase either internally of the vessel 12, using suitable filters (not shown) or externally. Naturally, if separation occurs externally, the catalyst is preferably returned to the slurry bed 37.

(16) As a result of the pressure adjustment or manipulation or balancing through the pressure transfer passage 34, the partition 18 does not have to form part of the pressure envelope of the apparatus 10, as differential pressures over the partition 18 can be kept within predefined limits which are orders of magnitude less than the operating pressure of the vessel 12. The design pressure of the partition 18 is determined by the maximum differential pressure immediately above and below the partition 18 for various modes of operation (e.g. a slumped bed) in the upward and downward direction respectively. So, for example, the partition 18 will still have to be designed to carry the weight of the slurry bed under slumped conditions in the downward direction. Under normal operating conditions however, the differential pressure over the partition 18 can be limited, for example, to less than about 50 to 150 kPa by means of the pressure transfer passage 34.

(17) Referring to FIG. 3 of the drawings, reference numeral 100 generally indicates slurry phase or suspension apparatus which is not in accordance with the invention. The apparatus 100 has features in common with the apparatus 10 and unless otherwise indicated, the same reference numerals are used to indicate the same or similar parts or features.

(18) In the apparatus 100, a balancing flow conduit 102 extends between the feed line 26 and the bottom volume 36. In use, the balancing flow conduit 102 allows the pressure in the bottom volume 36 to be equalised with the pressure in the feed line 26.

(19) Referring to FIG. 4 of the drawings, reference numeral 200 generally indicates slurry phase or suspension apparatus which is also not in accordance with the invention. Again, the apparatus 200 has features in common with the apparatus 10 and unless otherwise indicated, the same reference numerals are used to indicate the same or similar parts or features.

(20) In the apparatus 200, the gaseous reactants feed line 26 leads into the bottom volume 36. The bottom volume 36 is also in direct flow communication with the gas distributor 14 by means of a feed pipe 202 passing through the partition 18. In use, the bottom volume 36 is thus pressurized to the pressure of the gaseous reactants flowing along the gaseous reactants feed line 26.

(21) The apparatus 100 and the apparatus 200 are thus in line with the teachings of CN 1233454 C and US 2010/0216896. However, as pointed out before, these approaches are believed to still suffer from the danger of slurry ingress below the partition 18, since a flow path exists from the slurry body 37 into the bottom volume 36. In addition, in the event of a blockage of the gas distributor 14, the partition 18 will be subjected to large differential pressures (consider e.g. the maximum synthesis gas supply pressure typically used in slurry bubble columns used for hydrocarbon synthesis) and will accordingly need to be mechanically designed with these large differential pressures in mind.

(22) A gas distributor with downward facing gas outlets, such as the gas distributor 14 with the downward facing gas outlets 32 defined by the diffusers 30 prevent catalyst lay-down. Advantageously, when a planar solid fluid impermeable partition 18 is employed below the gas outlets 32, the uncooled volume in the vessel 12 is minimised and equidistant spacing of the gas outlets 32 from the partition 18 is achievable in a simple manner. By ensuring that the partition 18 does not form part of the pressure envelope of the apparatus 10, the mechanical design of the partition 18 is much simplified leading to a reduction in capital costs. Advantageously, the partition 18 prevents gas jets being directed directly onto the wall of the vessel 12 thereby to inhibit erosion and the partition 18 can thus be used as a sacrificial component which is much easier to repair or replace than the wall of the vessel 12. In addition, the mechanical design of the partition 18 in the apparatus 10 is much simplified when compared to the apparatus 100 and 200, since blockages of the gas distributor 14 need not be considered.