Ceramic Injector for Fluid Catalytic Cracking Unit

Abstract

The invention relates to a feedstock injector (2′) for injecting an atomized hydrocarbon feedstock into a tubular-type reactor with substantially upward or downward flow that is intended to be used in a fluid catalytic cracking unit, having: at least one hollow cylindrical body (41); at least a first and a second inlet openings (40, 42) for respectively injecting a liquid hydrocarbon feedstock to be cracked and an atomizing gas into said cylindrical body (41); at least one contact chamber (46) arranged inside said hollow cylindrical body, in which said liquid hydrocarbon feedstock to be cracked and said atomizing gas are intended to be brought into contact in order to atomize said liquid hydrocarbon feedstock to be cracked; and at least one outlet opening (44) that opens on the inside of said reactor in order to eject said liquid hydrocarbon feedstock thus atomized. According to the invention, each element of the injector (2′) is formed of a ceramic material.

Claims

1.-14. (canceled)

15. A feedstock injector for injecting an atomized hydrocarbon feedstock into a tubular-type reactor (1) with substantially upward or downward flow that is intended to be used in a fluid catalytic cracking unit, having: at least one hollow cylindrical body; at least a first and a second inlet openings for respectively injecting a liquid hydrocarbon feedstock to be cracked and an atomizing gas into the cylindrical body; at least one contact chamber arranged inside the hollow cylindrical body, in which the liquid hydrocarbon feedstock to be cracked and the atomizing gas are intended to be brought into contact in order to atomize the liquid hydrocarbon feedstock to be cracked; and at least one outlet opening that opens on the inside of the reactor in order to eject the liquid hydrocarbon feedstock thus atomized, characterized in that each element of the injector is formed of a ceramic material, and the ceramic material comprises a ceramic matrix selected from 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, or mixtures thereof, incorporated in which ceramic matrix are carbon fibres or ceramic fibres.

16. The feedstock injector according to claim 15, characterized in that the ceramic fibres are selected from crystalline alumina fibres, mullite fibres, crystalline or amorphous silicon carbide fibres, zirconia fibres, silica-alumina fibres, or mixtures thereof.

17. The feedstock injector according to claim 15, characterized in that the ceramic material is a sintered ceramic material.

18. The feedstock injector according to claim 15, characterized in that the ceramic material is a Ceramic Matrix Composite named CMC.

19. The feedstock injector according to claim 15, characterized in that it is formed as one part.

20. A riser or downer tubular-type reactor for use in a fluid catalytic cracking unit equipped with at least one feedstock injector according to claim 15.

21. The reactor according to claim 20, characterized in that it is equipped with at least two feedstock injectors, and in that at least one of the injectors is oriented so as to inject a liquid hydrocarbon feedstock counter-currently inside the reactor with respect to a flow direction of the stream of catalyst grains.

22. The reactor according to claim 20, characterized in that it is made of metal, and in that the injector is connected to the reactor by fastening means capable of absorbing a difference in expansion between the metal of the reactor and the ceramic material of the injector.

23. The reactor according to claim 20, characterized in that it is made of ceramic material and in that the injector is connected to the reactor by welding, brazing, screwing or interlocking.

24. A catalytic cracking unit comprising at least one injector according to claim 15.

25. The catalytic cracking unit of claim 24, further comprising at least one reactor according to claim 19.

26. A fluid catalytic cracking process comprising an injection of hydrocarbon feedstock into a riser or downer tubular-type reactor, characterized in that the injection of feedstock comprises a prior step of bringing a liquid hydrocarbon feedstock to be cracked into contact with an atomizing gas in order to atomize the liquid hydrocarbon feedstock using at least one injector according to claim 1, and in that the atomizing gas consists of a compound that does not comprise any oxygen atoms.

27. The fluid catalytic cracking process according to claim 26, characterized in that the compound is hydrogen sulphide H.sub.2S.

28. The fluid catalytic cracking process according to claim 26, characterized in that the liquid hydrocarbon feedstock is injected into the reactor counter-currently with respect to a flow direction of the stream of catalyst grains.

29. A method of preparation of a feedstock injector made of Ceramic Matrix Composite (CMC), comprising: 1) shaping a fibrous ceramic material eventually 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, eventually 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, eventually in the presence of finely divided carbon powder, to obtain a coated shape, 3) eventually 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 eventually (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) eventually 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

[0084] Other distinctive features and advantages of the invention will emerge on reading the description given below of one particular embodiment of the invention, given by way of indication and non-limitingly, with reference to the appended drawings, in which:

[0085] FIG. 1 illustrates a schematic representation of an FCC unit;

[0086] FIG. 2 illustrates a schematic cross-sectional representation of an injector, the subject of the invention according to a first variant;

[0087] FIG. 3 illustrates a schematic cross-sectional representation of an injector, the subject of the invention according to a second variant;

[0088] 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; and

[0089] FIG. 5 shows an example of assembling an injector according to the invention to a reactor, in particular a metal reactor, FIG. 5a showing a detail from this FIG. 5.

[0090] FIG. 1 represents a fluid catalytic cracking unit equipped with an essentially ascending flow reactor. 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 determined amount. A riser gas, for example steam, is introduced into the column 1 through the line 4, by means of a diffuser 5.

[0091] The feedstock to be cracked is introduced at the injection zone 6, which comprises injectors 2 and 3 that will be described in detail below. The column 1 opens, at its top, into a chamber 9, referred to as a disengager, which is for example concentric with it and 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 towards 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.

[0092] The deactivated catalyst particles thus stripped are discharged at the base of the chamber 9 to a regenerator 14, through a duct 15, on 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 where 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.

[0093] The reaction effluents are transported via the line 11 to a fractionating column 25, which makes it possible to separate them by distillation, in order to obtain: [0094] through the line 26, the gaseous products (C1 to C4 hydrocarbons); [0095] through the line 27, a petrol cut; [0096] through the line 28, a diesel or LCO cut; [0097] and finally, through the line 29, a distillation residue or slurry cut, which contains significant amounts of fine particles.

[0098] The ceramic injectors 2, 3 according to the invention may be installed, for example, in the lower portion of the riser 1.

[0099] FIG. 2 schematically represents an injector according to a first embodiment of the invention. The injector 2′ is an injector commonly referred to as a “Venturi” type injector, having a hollow cylindrical body 41. The injector 2′ has a first opening 40 and a second opening 42, each opening into a contact chamber 46 arranged inside the cylindrical body 41. The injector 2′ additionally has an outlet opening 44 that opens into the reactor 1 (not presented in FIG. 2).

[0100] The contact chamber 46 has a first introduction chamber 47 and a second outlet chamber 49, which communicate with one another via a neck 48 having a diameter substantially smaller than that of the first and second chambers 47, 49.

[0101] The first opening 40 and the second opening 42 are respectively provided for injecting the liquid hydrocarbon feedstock to be cracked, and for injecting an atomizing gas into the injector. In this case, the atomizing gas may be steam but may be replaced by another gas, for example hydrogen sulphide H.sub.2S, hydrogen H.sub.2 or refinery gas.

[0102] A refinery gas generally contains C1 to C5 hydrocarbons, hydrogen, and sometimes H.sub.2S.

[0103] When the liquid hydrocarbon feedstock C is introduced through the first opening 40, the liquid is guided by a path 50 that opens into the first chamber 47. At the same time, the atomizing gas G introduced through the second opening 42 reaches the first chamber 47 in order to be mixed with the liquid hydrocarbon feedstock. Next, the mixture of the atomizing gas and of the hydrocarbon liquid reaches sonic velocities at the neck 48 owing to the Venturi effect. The increase in the velocity and the shear caused by the atomizing gas cause the jet of liquid hydrocarbon feedstock to break up into fine droplets.

[0104] The injector 2′ may be sized in order to operate with a stream of liquid at the neck of the order of 5000 kg/m.sup.2s. The atomization of the liquid hydrocarbon feedstock essentially takes place at the neck 48.

[0105] FIG. 3 schematically represents an injector according to a second embodiment of the invention. The injector 2″ is an injector commonly referred to as an “impactor” type injector, which also has a hollow cylindrical body 141, arranged in which is a contact chamber 146. Structurally, the impactor type injector 2″ differs from that of Venturi type by the fact that: [0106] the contact chamber 146 has a substantially constant internal diameter, that is to say that it does not have a neck; and [0107] the injector 2″ has a target 143 that juts out from an inner wall 145 of the contact chamber 146 opposite the opening 142 for introducing the atomizing gas G and through the passage of the liquid hydrocarbon feedstock C.

[0108] The liquid hydrocarbon feedstock C is projected against the target 143, as soon as it enters the contact chamber 146 through a first opening 140. The jet of liquid breaks up and is carried in the form of droplets by a stream of atomizing gas G introduced through a second opening 142 at high speed. The atomization of the liquid hydrocarbon feedstock in this type of injector 2″ is carried out in two parts. A first part takes place at the target 143 via a breakup of the jet of liquid hydrocarbon feedstock. The second atomization takes place at an outlet opening 144 of reduced diameter, where the narrowing of the diameter accelerates the fluids. By way of example, the outlet opening 144 has a diameter of the order of 18 to 23 mm.

[0109] According to the invention, the injectors 2′, 2″ are formed entirely from a ceramic material, preferably from 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 injectors 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.

[0110] According to the invention, the injector 2 is made from one or more parts made of ceramic material. For example, the hollow cylindrical body 41, 141 and the second inlet opening 42, 142 may be separate parts, it being possible for the hollow cylindrical body 41, 141 and the first inlet opening 40, 140 to be made from a single part.

[0111] The elements 41 and 42 may then be interlocked, as represented schematically in FIG. 4a by interlocking of conical end portions of complementary shape, or assembled by screwing of their ends (FIG. 4b), or else welded or brazed (not represented). Similarly, the hollow cylindrical body 41, 141 may consist of several separate portions that are assembled, it being possible for this assembling to be carried out as described above, by assembling cylindrical or conical sections, or else by assembling parts resembling bricks by interlocking and/or welding/brazing.

[0112] The injector 2 may be connected directly to an outer wall 1a of the tubular reactor 1 as represented schematically in FIG. 5. When the tubular reactor 1 is made of metal, its outer wall 1a may have a fastening face 1b, firmly attached to which are at least two metal tabs 1c shaped in order to bear against an edge 2c of the injector 2 in order to keep this edge 2c bearing against the fastening face lb of the reactor. This edge 2c may be located at one end of the injector 2. The fastening face 1b and the edge 2c may extend over the entire periphery of the ends to be assembled. They may be flanges.

[0113] As a variant that is not represented, the reactor may also be made of ceramic material and the fastening to the injector may then be carried out as described above for the assembling of the elements of the injector.

[0114] The invention has been described with reference to an FCC unit operating with a riser reactor, the injectors according to the invention may however also be used in FCC units operating with a downer reactor.