Element for ejecting gas into a regenerator of a fluid catalytic cracking unit

Abstract

An injection element (10) for a gas injection system (1) inside a regenerator of a fluid catalytic cracking unit, said injection element defining a flow passage (12) and being arranged so as to be able to be fastened to a support (11) so that said flow passage opens on one side into a cavity and on the other side into a fluidized catalyst bed, characterized in that said injection element is made of ceramic material.

Claims

1. An injection element for a gas injection system inside a regenerator of a fluid catalytic cracking unit, the gas injection system comprising a support defining at least one orifice, this support comprising a wall defining at least one portion of a cavity and having a first face intended to be in contact with the gas contained in this cavity, and the support comprising a second face, opposite the first face, intended to be in contact with a fluidized catalyst bed, wherein the injection element comprises a flow passage and is arranged so as to be able to be firmly attached to the support, at the orifice, so that gas from the cavity can circulate via the flow passage to the fluidized catalyst bed, characterized in that the injection element is made of a ceramic material comprising a ceramic matrix and carbon and/or ceramic fibres incorporated into this ceramic matrix, wherein the ceramic material comprises silicon carbide in a majority amount.

2. The injection element according to claim 1, in which the ceramic material is a Ceramic Matrix Composite (CMC).

3. A gas injection system for injecting gas into a regenerator of a fluid catalytic cracking unit, the gas injection system comprising: at least one injection element, and a support defining at least one orifice, this support comprising a wall defining at least one portion of a cavity and having a first face intended to be in contact with the gas contained in this cavity, and the support comprising a second face, opposite the first face, intended to be in contact with a fluidized catalyst bed, in which the injection element defines a flow passage and is arranged so as to be able to be firmly attached to the support, at the orifice, so that gas from the cavity can circulate via the flow passage to the fluidized catalyst bed, characterized in that the injection element is made of a ceramic material comprising a ceramic matrix and carbon and/or ceramic fibres incorporated into this ceramic matrix, wherein the ceramic material comprises silicon carbide in a majority amount.

4. The gas injection system according to claim 3, in which, for at least one injection element, the injection system comprises a device for fastening the injection element to the support, the fastening device being capable of absorbing a difference in expansion between the material of the support and the ceramic material of the injection element.

5. The gas injection system according to claim 4, in which, for at least one injection element, the fastening device comprises at least one pressing element capable of exerting a force on this injection element in order to press this injection element against the support.

6. The gas injection system according to claim 5, in which the pressing element comprises a tab welded via one end to the support and of which the other end is capable of exerting an elastic bearing force on the injection element when the injection element is installed on the support.

7. The gas injection system according to claim 3, in which the support comprises a perforated plate arranged to cover the whole of a cross section of a chamber of the regenerator in order to support the fluidized catalyst bed.

8. The gas injection system according to claim 3, wherein the ceramic material comprises silicon carbide SiC, preferably in a majority amount.

9. The gas injection system according to claim 3, wherein the ceramic material is a Ceramic Matrix Composite (CMC).

10. A process for manufacturing a gas injection element for a regenerator of a fluid catalytic cracking unit, so that this element defines a flow passage for the gas, intended to open on one side into a cavity and on the other side into a fluidized bed, the process being characterized in that the injection element is made of ceramic material comprising a ceramic matrix and carbon and/or ceramic fibres incorporated into this ceramic matrix, wherein the process comprises: 1) shaping a fibrous ceramic material over a supporting material that could be removed without excessive effort, in order to obtain a fibrous shape that can be assimilated to the backbone of the final device to be obtained, in the presence of a first resin, 2) coating the shape obtained at step (1) with finely divided ceramic powder and at least a second resin, in the presence of finely divided carbon powder, to obtain a coated shape, 3) repeat steps (1) and (2), 4) heating the coated shape of step (2) or (3) under vacuum and/or under inert atmosphere in order to transform the resins of step (1), (2) and (3) into a carbon-rich structure, essentially deprived of other elements to obtain a carbon-rich coated shape, 5) introducing a gas within the carbon-rich coated shape of step (4) under conditions efficient to transform the carbon-rich structure into carbide containing carbon-rich structure, 6) removing the supporting material of step (1), when present, wherein carbon fibers are present at least at step (1), (2) and/or (3) within the fibrous ceramic material, within the finely divided ceramic powder, within the finely divided carbon powder, and/or within the first and/or second resin.

11. The manufacturing process according to claim 10, comprising a step of sintering silicon carbide SiC particles.

Description

(1) The invention will be better understood with reference to the figures, which show exemplary embodiments of the invention.

(2) FIG. 1 shows an example of a portion of a regenerator with an example of an air injection system according to a first embodiment of the invention.

(3) FIGS. 2A and 2B are views, respectively in perspective and in cross section, of an example of an air injection element according to the first embodiment of the invention, when installed on a plate-type support.

(4) FIG. 3 is a cross-sectional view of an example of an air injection element according to a second embodiment of the invention.

(5) Identical references may be used from one figure to the next to denote elements that are identical or similar in their shape or in their function.

(6) With reference to FIG. 1, a regenerator 100 is part of a fluid catalytic cracking (FCC) unit not represented in its entirety. In this regenerator, the combustion of coke deposited on catalyst resulting from a reactor of the FCC unit is carried out.

(7) The catalyst in the chamber 101 of the regenerator 100 forms a fluidized bed 102.

(8) An injection system 1 makes it possible to inject air into this fluidized catalyst bed 102, and therefore the oxygen needed for the combustion of the coke.

(9) This injection system 1 comprises a support, here a perforated plate 11, occupying the whole of a cross section of the chamber 101, and supporting the fluidized bed 102. This plate defines, with the bottom walls of the chamber, an air cavity 103. A duct 104 that opens into this cavity 103 makes it possible to provide pressurized air.

(10) The plate thus comprises a first face 105 in contact with the air of the cavity 103 and a second face 106 in contact with the fluidized bed 102.

(11) The perforated plate 11 is made of steel. An anti-erosion coating made of concrete, not represented, additionally makes it possible to protect the plate from the abrasion linked to the catalyst present in the regenerator. For example, concrete is poured onto a steel mesh, not represented, for example having a honeycomb shape comprising a plurality of hexagonal cells firmly attached to one another by their sides (hex mesh), or other mesh.

(12) Mounted on each orifice (reference 19 in FIG. 2B) of the plate 11 is a gas injection element, here an air injection nozzle 10, with the aid of tabs 14, or flanges, welded to the plate 11.

(13) The injection nozzle 10 is made of ceramic, for example made of silicon carbide SiC. It is for example formed by injection moulding or extrusion. Injection moulding or extrusion are conventionally carried out using ceramic powders or precursors of ceramics with a binder. According to another manufacturing method, the ceramic nozzle 10 is formed by compression and heating of a ceramic powder, it being possible for the compression to be maintained during the heating step, the heating step being a step of sintering the ceramic powder. This technique is particularly well suited to the manufacture of solid elements made of silicon carbide according to the invention. The ceramic powder used optionally comprises ceramic fibres in order to increase the mechanical strength of the parts produced. The ceramic fibres, when they are present, generally represent from 0.1% to 10% by weight of the part produced.

(14) Such a nozzle, made of solid ceramic, has a relatively low manufacturing cost and does not result in a significant additional cost with respect to a steel having a surface treatment, or a special steel having an improved abrasion resistance.

(15) With reference to FIGS. 2A and 2B, the injection nozzle 10 defines a flow passage 12 in which air is intended to circulate from the air cavity to the catalyst bed, according to the arrows 13.

(16) Pressing elements 14, here steel tabs welded to the plate 11, make it possible to exert a pressing force on a bearing surface 15 of a flange 16 of the injection nozzle 10.

(17) Thus, the other side of the flange 16 is pressed against the perimeter of the edge of the orifice 19 corresponding to this nozzle 10.

(18) If temperature variations lead to a variation in the dimensions of this orifice, the fastening of the injection nozzle 10 thus remains stable despite the possible expansion of the support 11 when the temperature varies.

(19) When it is present, the anti-erosion coating may cover the pressing elements 14, it is thus preferable to increase the height of the walls defining the flow passage 12 so that the concrete does not cover it. However, it may be advantageous for the anti-erosion coating not to cover the pressing elements 14 in order to allow a free expansion of the various materials. In this case, it is not necessarily useful to increase the height of the walls of the injection nozzles 10.

(20) The nozzle 10 additionally comprises an air inlet portion 17 intended to be received inside the orifice 19. This air inlet portion 17 has a cylindrical general shape in this embodiment.

(21) The diameter of this portion 17 is smaller than the diameter of the orifice 19, so that the expansion of the plate 11 does not lead to a fracture of the injection nozzle 10.

(22) The tabs 14 are welded to the plate 11, each tab 14 comprising an end 21 intended to exert an elastic bearing force on the flange 16. Each end 21 comprises a flat side 22 in order to avoid regions of excessively high stresses on the flange 16 of the nozzle 10.

(23) The tabs 14 act like a spring in order to press the nozzle 10 against the walls of the plate 11.

(24) In one embodiment that is not represented, the air inlet portion could have a conical shape in order to facilitate the pre-positioning of the nozzle during the installation of this nozzle.

(25) In the first embodiment, illustrated by FIGS. 1 to 2B, the air inlet portion 17 of the nozzle 10 defines oblique orifices 18. The flow path of the air thus forms bends, which is not really a hindrance in terms of pressure drop. On the other hand, the catalyst particles falling into the flow passage 12 from the catalyst bed will have a tendency to remain in the bottom 107 of the nozzle 10, this bottom being solid, rather than reaching the air cavity via these oblique orifices 18. This type of air inlet portion may be advantageous in so far as the walls of the air cavity may be devoid of abrasion-resistant concrete coating.

(26) The oblique orifices are positioned slightly offset from one another, so that the pressurized air entering the nozzle 10 has a tendency to form a vortex, with a view to discharging any possible catalyst particles present in the bottom 107 of the nozzle 10 to the fluidized bed.

(27) With reference to FIG. 3, the injection nozzle 10, here represented held on a plate 11 with the aid of tabs 14 bearing against a flange 16 of the nozzle, comprises a hat portion 201 covering a flow passage 12, so that the air circulating via this flow passage 12 is injected towards the catalyst bed via oblique outlet orifices 203, according to the arrows 203.

(28) This type of nozzle may make it possible to limit the entry of catalyst particles into the nozzle.

(29) The flow passage 12 may thus have a cross section of relatively large dimensions, which may be advantageous in the sense that the requirements in terms of pressurization of the air may then be lower than when the nozzles have cross sections of smaller dimensions, and/or in the sense that fewer injection nozzles than in the prior art could be provided.

(30) In one variant that is not represented, the air outlet portion from the second embodiment, with a portion that forms a hat, could of course be combined with the air inlet portion from the first embodiment.

(31) The invention may make it possible to design nozzles 10 with greater freedom of design as regards the shape in so far as it is less necessary than in the prior art to take into account the problem of erosion by the catalyst.

(32) In particular, a shape could be provided that makes it possible to optimize the injection of air, which may make it possible to improve the combustion quality, and therefore to further preserve the catalyst, which may be beneficial for the environment.

(33) In addition, the maintenance operations, capable of imposing shutdowns and/or of limiting catalytic cracking, may be carried out less frequently than in the prior art.

(34) Finally, this type of injection system may prove more reliable than in the prior art and therefore may make it possible to limit the risk of unscheduled catalytic cracking shutdown.