Slide Valve Intended for Flow Control in a Fluid Catalytic Cracking Unit

Abstract

The invention relates to a slide valve (200) comprising:

a body (201) having a through-duct (202) for the passage of a fluid, the flow rate of which is to be controlled,

at least one gate (203) slidably mounted inside said body (201), crosswise to said duct (202), and partially or completely closing off said duct (202), said gate (203) being movable between a position in which the duct is partially or completely closed off and a position in which the duct is open,

in which the following are defined as portions subject to erosion: portions of the body that delimit the duct (202), at least one portion of said at least one gate (203) located across the duct (202) when said at least one gate partially or completely closes off said duct, characterized in that at least said portions subject to erosion are made of metal covered with a layer of ceramic material or are entirely made of ceramic material.

Claims

1.-10. (canceled)

11. A slide valve comprising: a body having a through-duct for the passage of a fluid, the flow rate of which is to be controlled, at least one gate slidably mounted inside the body, crosswise to the duct, and partially or completely closing off the duct, the gate being movable between a position in which the duct is partially or completely closed off and a position in which the duct is open, in which the following are defined as portions subject to erosion: portions of the body that delimit the duct, at least one portion of the at least one gate located across the duct when the at least one gate partially or completely closes off the duct, characterized in that at least the portions subject to erosion are made of metal covered with a layer of ceramic material or are entirely made of ceramic material and the ceramic material comprises a ceramic matrix selected from the group consisting of silicon carbide SiC, boron carbide B.sub.4C, silicon nitride Si.sub.3N.sub.4, aluminium nitride AlN, boron nitride BN, alumina Al.sub.2O.sub.3, and mixtures thereof, wherein carbon fibres or ceramic fibres are incorporated in the ceramic matrix.

12. The slide valve according to claim 11, characterized in that the ceramic fibres comprise crystalline alumina fibres, mullite fibres, crystalline or amorphous silicon carbide fibres, zirconia fibres, silica-alumina fibres, or mixtures thereof.

13. The slide valve according to claim 11, characterized in that, when the portions of the slide valve subject to erosion are made entirely of ceramic material, the ceramic material is a sintered ceramic material.

14. The slide valve according to claim 11, characterized in that, when the portions of the slide valve subject to erosion are made entirely of ceramic material, the ceramic material is a Ceramic Matrix Composite (CMC).

15. The slide valve according to claim 11, characterized in that the body, or at least the portions of the body delimiting the duct, and the at least one gate are entirely made of ceramic material.

16. The slide valve according to claim 11, characterized in that a portion entirely made of ceramic material is made of several separate parts assembled together by welding or brazing.

17. The slide valve according to claim 11, characterized in that a portion entirely made of ceramic material is made of several separate parts assembled together and in that the separate parts have ends that are shaped in order to be assembled by interlocking or screwing.

18. The slide valve according to claim 11, characterized in that the portions subject to erosion are made entirely of ceramic material, the rest of the slide valve being made of a material other than ceramic, the portions of the slide valve made of material other than ceramic being connected to the portions made of ceramic material of the slide valve by fastening means capable of absorbing a difference in expansion between the non-ceramic material and the ceramic material.

19. Catalytic cracking unit comprising at least one slide valve according to claim 11.

20. A method of preparation of a slide valve, comprising a preparation step for portions of the slide valve subject to erosion made entirely of ceramic material which is Ceramic Matrix Composite (CMC), the step comprising: 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 portion 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.

Description

[0087] The invention is now described with reference to the appended, non-limiting drawings, in which:

[0088] FIG. 1 is a schematic representation of an FCC unit;

[0089] FIG. 2 is a schematic representation, in longitudinal cross section, of a slide valve according to one embodiment of the invention;

[0090] FIG. 3 is a schematic representation of a slide valve according to another embodiment of the invention;

[0091] FIGS. 4a and 4b are axial cross-sectional views of the ends of two assembled parts. The assembled parts are separated in FIG. 4b for greater clarity;

[0092] FIG. 5 shows an example of assembling a metal plate to a valve body made of ceramic material.

[0093] FIG. 1 represents a fluid catalytic cracking unit equipped with a reactor having an essentially ascending flow. This unit is of a type known per se. It comprises in particular a column-shaped reactor 1, referred to as a feedstock riser or riser, supplied at its base via a duct 32 with regenerated catalyst grains in a predetermined amount. A riser gas, for example steam, is introduced into the column 1 through the line 4, by means of a diffuser 5.

[0094] The feedstock to be cracked is introduced at the injection zone 6, which comprises injectors 2 and 3. The column 1 opens, at its top, into a chamber 9, referred to as a disengager, in which the separation of the cracking products and the stripping of the deactivated catalyst particles are carried out. The cracking products are separated from the spent catalyst particles in a cyclone 10, which is housed in the chamber 9, at the top of which a line 11 is provided for discharging the cracking products, whilst the deactivated catalyst particles move by gravity to the base of the chamber 9. A line 12 supplies fluidizing gas injectors or diffusers 13, uniformly arranged at the base of the chamber 9, with stripping fluid, generally steam. One or more other cyclones may be provided inside the chamber 9.

[0095] The deactivated catalyst particles thus stripped are discharged at the base of the chamber 9 to a regenerator 14, through a duct 15, along which a control valve 16 is provided. In the regenerator 14, the coke deposited on the catalyst particles is burnt using air, injected at the base of the regenerator via a line 17, which supplies uniformly spaced injectors or diffusers 18. The treated catalyst particles, entrained by the flue gas, are separated by cyclones 19, from which the flue gas is discharged through a line 20, whilst the catalyst particles are discharged to the base of the regenerator 14, from where they are recycled to the feed of the riser 1 via the duct 32, equipped with a control valve 33.

[0096] The control valves 16 and 33 are generally slide valves.

[0097] A slide valve according to the invention may be arranged in accordance with any one of the slide valves known in the prior art.

[0098] Some of these slide valves are described with reference to FIGS. 2 and 3. The invention is not however limited to these embodiments.

[0099] FIG. 2 represents a slide valve 200 comprising a body 201 having a through-duct 202 for the passage of a fluid, the flow rate of which is to be controlled. The slide valve also comprises a gate 203 slidably mounted inside the body 201, crosswise to the direction F of the flow. This gate 203 is conventionally in the form of a plate connected to a rod 204 itself connected to an actuating device 205 which controls the movement of the rod 204 and of the adjoining gate 203. This actuating device 205 is for example a hydraulic actuating device, such as a piston.

[0100] This actuating device 205 may thus move the gate 203 between a position in which the duct 202 is closed off (as represented in FIG. 2) and a position in which the duct 202 is open (not represented).

[0101] Certain portions of the slide valve 200 are subject to erosion. These are the portions of the body delimiting the duct, namely the sidewalls 206 of the duct located upstream of the gate 203 with respect to the direction of circulation F of the fluid through the slide valve 200 and also at least one portion of the sidewalls 207 of the duct located downstream of the gate 203. In the example represented, the sidewalls 206 upstream comprise a cylindrical portion 206a, followed by a conical portion 206b then again by a cylindrical portion 206c, from upstream to downstream in the direction of the gate 203. The sidewalls 207, downstream, are essentially cylindrical 207a and partially conical 207b in the vicinity of the rod 204 of the gate 203.

[0102] Of course, the invention is not limited to the shape of the duct 202 represented.

[0103] Certain portions of the gate 203 are also subject to erosion. These are at least the portion of the gate 203 located across the duct 202 when the gate partially or completely closes off the duct 202. Thus, in the example, these are the upstream surface 203a (facing upstream) of the gate, its end 203b (parallel to the flow of the stream F) and a portion of the downstream surface 203c (pointing downstream).

[0104] In the example represented, these various portions 203, 206, 207 subject to erosion are formed of a metal wall 203m, 206m, 207m respectively, covered with a layer of ceramic material 203mc, 206mc, 207mc. As a variant, these metal walls could be entirely made of ceramic material, preferably made of silicon carbide SiC. They are 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 walls are 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.

[0105] FIG. 3 represents another embodiment of a slide valve 200, which differs from the preceding embodiment by: [0106] the presence of two gates 203 each connected to a rod 204 itself connected to an actuating device 205 [0107] the shape of the duct 202 downstream of the gates 203, which has a conical shape 207b followed by a cylindrical shape 207a from upstream to downstream starting from the gates 203.

[0108] In FIG. 3, the elements identical to the elements from FIG. 2 bear the same reference followed by a prime '. The gates 203 are not described in detail but are similar to the gate 203 described with reference to FIG. 2. A fluid may thus circulate through the slide valve 200 following the moving of the two gates 203 apart from one another, their coming together making it possible, on the contrary, to reduce the flow rate until all circulation of fluid is prevented in the position represented in FIG. 3.

[0109] Furthermore, the portions subject to erosion are the same as those from FIG. 2. In FIG. 3, only the portions of one of the gates 203 subject to erosion have been represented for the greater clarity. In the same way as for FIG. 2, the portions in question may be entirely made of ceramic material.

[0110] In one variant of the two embodiments described with reference to FIGS. 2 and 3, all of the body 201, 201 may be made of ceramic material, or at the very least the portions of the body forming the walls of the duct 202, 202. The body 201, 201 may be entirely made of ceramic material, produced from one part (without welding or assembling), for example by sintering. Or at least the portions of the body forming the walls of the duct 202, 202 may be entirely made of ceramic material, produced from one part, for example by sintering. In this case, the portions from FIGS. 2, 3 comprising a metal wall covered with a layer of ceramic material are replaced by walls entirely made of ceramic material.

[0111] These portions entirely made of ceramic material may also be produced from several separate parts assembled together. For example, the cylindrical portion 206a (or 206a) of the duct 202 (or 202) may be a separate part and may be assembled to the conical portion 206b (or 206b) of the duct 202 (or 202). The parts 206a and 206b may then be interlocked, as represented schematically in FIG. 4a by interlocking of conical end portions of complementary shape, or by screwing of their ends (FIG. 4b), or else welded or brazed (not represented). The other portions of the duct (206c, 207a, 207b) or (206c, 207a, 207b) may also be separate parts that are assembled as described above. Similarly, the body (201 or 201) may be made of several separate parts that are assembled as described above.

[0112] In FIGS. 2 and 3, the body 201, 201 comprises one or two support plates 208, 208 supporting the rod 204, respectively the rods 204. If the body is made of ceramic material, this support plate (208 or 208) may be made of metal. The connection between the plate 208, 208 and the body 201, 201 is then different from the screw connection represented in FIGS. 2 and 3, this connection being obtained by fastening means capable of absorbing a difference in expansion between the metal and the ceramic material.

[0113] By way of example, as represented schematically in FIG. 5, the plate 208 has a fastening face 208a, attached to which are at least two metal tabs 208b that are shaped to bear against an edge 201a of the body 201 in order to keep this edge 201a bearing against the fastening face 208a of the plate. This edge 201a may form a flange. A similar fastening may be made between metal plates 208 and a body 201 made of ceramic material.

[0114] Fastening means capable of absorbing a difference in expansion between the metal and the ceramic material, for example of the type described above, could also be used to fasten a slide valve, the body of which is made of ceramic material, to a metal duct in which the fluid, the flow rate of which must be controlled, circulates.

[0115] The invention has been described with reference to an FCC unit operating with a reactor having an ascending flow (riser), the valves according to the invention may however also be used in FCC units operating with a reactor having an descending flow (downer).