APPARATUS AND PROCESS FOR SOLIDS-FLUID SEPARATION

Abstract: An apparatus suitable for solids-fluid (e.g. cracking catalyst/­ hydrocarbon vapour) separation comprising a plurality of substantial­ ly vertical tubular elements (6) in a housing (1), inlet means (2) arrangement in the bottom section (3) of the housing (1) and communicating with the space (14) between the tubular elements (6) and the housing (1), a plurality of tubular fluid outlet means (10) of which the lower sections (7) are arranged substantially co-axially within the upper sections of said tubular elements (6) defining annular spaces wherein swirl imparting means (9) are arranged and of which fluid outlet means (10) the upper sections cooperate with opening(s) in the upper section (11) of the housing (1), and solids outlet means (4) communicating with the lower sections (7) of the tubular elements (6) and with opening(s) in the bottom (3) of the housing (1). The invention further relates to a process for separating fluid cracking catalyst particles from gaseous hydrocarbon conversion products and/or flue gases using said apparatus.

Description: The invention relates to an apparatus and a process for solids-fluid separation and to products obtained by such a process. It is known to separate solids from gases by imparting a rotating movement to a solids-gas mixture which is entered substantially horizontally and tangentially in a vertical cylindrical body (e.g. a cyclone) from which gas is discharged at the top and solids are discharged from the bottom. In order to attain substantially complete removal of small solid particles (e.g. catalyst fines) from gases, as desired in e.g. catalytic cracking processes, a number of cyclones is usually required even when the bulk of the solids has already been removed in a preceding separation stage (e.g. by means of deflection plates or cyclones). As a consequence of the horizontal feed inlet means extending tangentially from each cyclone body, a housing (e.g. a reactor vessel) having substantial dimensions would be needed to accommodate a number of cyclones. Alternatively, such cyclones could be placed outside a reactor vessel, thus requiring complex bracing in order to withstand the prevailing pressure differentials at relatively high operating temperatures (e.g. 400-600 °C inside the cyclones). Moreover, in both cases undesired coke- and hydrogen formation (i.e. after-cracking) may take place in the various dead spaces at said high temperatures during the substantial residence time in such a large apparatus of e.g. hydrocarbon-containing catalyst particles which are being separated from heavy hydrocarbon vapours. It is further known to use cylindrical cyclones with axial downward entry for solids-gas separation. In conventional multiple cyclone designs a solids-containing feed stream enters the cyclone assembly horizontally or under a slight angle (e.g. less than 45 degrees) with a horizontal plane from one side which would require additional space in case such an assembly is arranged inside a reactor vessel, as discussed hereinabove for cyclones with tangential feed entry. Moreover, such an arrangement would lead to a pressure difference between the cyclones near the feed inlet side and the downstream cyclones, which would cause unequal distribution of solids-containing fluid over the various cyclones. It has now been found that the aforementioned disadvantages which are inherent to the various types of cyclones can be overcome by particularly arranging tubular elements and inlet- and outlet means in a housing, resulting in a very compact apparatus for a given solids-fluid separation capacity. The invention therefore relates to an apparatus suitable for solids-fluid separation which comprises a plurality of substantially vertical tubular elements in a housing, inlet means arranged in the bottom of the housing and communicating with the space between the tubular elements and the housing, a plurality of tubular fluid outlet means of which the lower sections are arranged substantially co-axially within the upper sections of said tubular elements defining annular spaces wherein swirl imparting means are arranged and of which fluid outlet means the upper sections cooperate with opening(s) in the upper section of the housing, and solids outlet means communicating with the lower sections of the tubular elements and with opening(s) in the bottom of the housing. The apparatus according to the invention can be employed in processes wherein solids have to be separated from fluids (in particular gases at elevated temperatures and pressures) such as catalytic cracking, shale conversion processes and coal- or heavy oil gasification. An advantage of the apparatus according to the invention is the relatively short residence time of the solids and fluids to be separated, which is of particular importance when the apparatus is applied in a fluid catalytic cracking process for separation of catalyst (fines) from hydrocarbon vapours; as a consequence of short residence times after-cracking of hydrocarbons (and thus carbon-formation on the catalyst particles) will be reduced, resulting in better product yields and less catalyst deactivation. Moreover, the spread in residence times will be relatively narrow, which leads to the production of less undesired products and a longer catalyst life, in comparison with the use of separation apparatuses in which the residence time spread is relatively wide. Furthermore, the apparatus according to the present invention is very efficient in separating relatively small solid particles from gases in which said particles are present in relatively small amounts due to the symmetrical flow pattern in the apparatus which results in substantially equal loading of each tubular element. Therefore, the amount of solids carry-over into the separated gases will be very small, which makes it possible to eliminate recycle of slurry oil (e.g. catalyst fines in liquid hydrocarbons) recycle in a fluid catalytic cracking operation from a downstream hydrocarbon fractionator to the cracking reactor, thus again improving product yields. Preferably, the inlet means (through which a mixture of solids and fluid enters the apparatus) is (are) centrally located in the bottom of the housing below the tubular elements, in order to ensure optimal distribution of the upwardly flowing solids-fluid mixture over all tubular elements in which, to a large extent, the actual separation takes place. A suitable number of tubular elements and separation means belonging thereto may lie between 3 and 80, especially between 5 and 20, more especially between 6 and 12. The tubular elements are preferably situated in one or more (concentric) circles. Various embodiments of the apparatus according to the invention are described hereinafter, using Figures 1-4 in which reference numerals relating to corresponding parts are the same. In Figure 1 a longitudinal section of a fully enclosed individual separating apparatus is shown. Figure 2 represents a longitudinal section of an integrated apparatus of which the upper separating means is identical to that depicted in Figure 1. In Figures 3 and 4 cross sections are shown at AA′ and BB′, respectively, of the apparatus depicted in Figure 2. The apparatus depicted in Figure 1 comprises a housing (1) provided with an inlet (2) for an upwardly flowing mixture of solids and fluid in its bottom section (3), a plurality of separate solids outlets (4) and a combined fluid outlet (5). A number (eight according to Fig. 3) of substantially vertical tubular elements (6) are symmetrically arranged in the housing, preferably in such a manner that they can be easily removed from said housing through an opening (2 or 5); the lower sections (7) of the tubular elements (6) are suitably downwardly converging. Preferably, vortex stabilizer means (8) are arranged in the lower sections of the tubular elements (6) in which, during operation, the mixture of solids and fluid is subjected to a helical movement. Swirl imparting means (9) (suitably outwardly curved swirl vanes) are located in the upper sections of said tubular elements, and are preferably attached to tubular fluid outlet means (10) which are arranged substantially co-axially within said upper sections. Alternatively, inwardly extending swirl imparting means can be attached to the upper sections of tubular elements (6). Preferably, only a small number (e.g. 1, 2 or 3) of tubular elements (6) cooperate with a common solids outlet (4), in order to avoid fluid and/or solids surging effects ("cross-talk") between different tubular elements. The length:diameter ratio of the tubular elements (6) is suitably from 1-10, and preferably from 2-5. The ratio of the diameters of the tubular elements (6) and the tubular fluid outlet means (10) is suitably from 1.5-4, and preferably from 2-3. The upper section (11) of the housing (1) is preferably provided with a central downwardly extending fluid deflection means (12); suitably an inverted truncated cone) arranged in wall (13) separating the space (14) between the tubular elements (6) from fluid collecting space (15). The presence of fluid deflection means can substantially reduce erosion problems which might otherwise arise due to impingement of solids with a relatively high velocity on wall (13) when the upward flow of the solids-fluid feed mixture is reversed before said mixture enters the annular spaces between the tubular elements (6) and the tubular fluid outlet means (10). Moreover, the presence of fluid deflection means (12) will in some cases lead to a reduced pressure drop during operation of the apparatus. The apparatus according to the present invention advantageous­ ly further comprises lower pre-separation means (as depicted in Figure 2 and Figure 4) suitable for the separation of larger (e.g. catalyst) particles from fluids. This embodiment is particularly preferred for application in a fluid catalytic cracking process. The lower separation means comprises a domed upper section (16), upwardly directed feed inlet means (17) cooperating substantially tangentially with said domed upper section, a central section (18) provided with outlet means (19) in communication with the space (14) between the tubular elements (6) and the housing, and a solids outlet opening (20) in the lower section (21) of the separation means. Preferably, the domed upper section (16), the central section (18) and the lower section (21) together form a substantially spherical body having two vertically flattened sides to provide spaces (22) between the central section (18) and the housing (1), through which spaces (22) space (14) is in communication with (preferably tubular) outlet means (19). In such a substantially spherical body an optimal flow pattern of the solids and fluid streams will be attained which results in high solids separation efficiency, a relatively short solids residence time (in order to avoid undesired reactions) and a low pressure drop in the apparatus. Suitably, the lower section (21) comprises at least one fluid ventilation opening (23) which is in communication with space (24) wherein during operation relatively large solid particles separated from fluid in the lower separation means are collected together with relatively small particles (fines) flowing through solids outlets (4) into said space (24). A more detailed description of this separation apparatus is given in European patent application No. 86201003. When the apparatus depicted in Figures 2-4 is employed in a fluid catalytic cracking process, feed inlet means (17) suitably form the upper part of a fluid catalytic cracking riser reactor (25), whereas in space (24) optionally stripping of hydrocarbons from cracking catalyst particles may be carried out by means of steam or other stripping gases which are suitably introduced through gas feed means (not shown) into one or more lower sections of the housing (1). Through fluid ventilation opening (23) vapours evolving from (pre-) stripped catalyst particles can flow into the domed separation means. However, the (pre-)stripper vapours can also be kept separate from the vapours originating from the riser reactor, if desired, by providing a separate vapour outlet for the (pre-)stripper vapours in an apparatus without said opening. The integrated apparatus according to the invention comprises one or more, preferably substantially horizontal, outlet means (19) for fluid containing some (catalyst) fines, from which the larger particles have been separated. Suitably, the outlet means (19) forms a tube extending through central section (18) and comprising at least one opening (26) preferably located at the lower central part of the tube, in order to avoid entrainment of catalyst particles by hydrocarbon vapours during start-up of the catalytic cracking process when the velocity of the catalyst particles in the dome is relatively low. During normal operation of the apparatus according to the invention the (catalyst) particles follow a flow path in a substantially vertical plane along the inner wall of domed section (16) and leave section (18) through solids outlet opening (20). In order to avoid a flow of solids together with fluid directly from feed inlet means (17) via lower section (21) to solids outlet opening (20), the latter opening is suitably provided with a shim (27) which is preferably inclined at an angle from 15 to 45 degrees with respect to a vertical plane for optimal solids deflection (see in particular Figure 2). The ratio of the maximum internal widths of the dome and the feed inlet means (17) is suitably from 1.5-6, and preferably from 2-4. The invention further relates to a process for separating solid particles from fluid, in particular for separating fluid cracking catalyst particles from gaseous hydrocarbon conversion products which comprises passing a mixture of solid particles and fluid upwardly into a space between tubular elements and subsequent­ ly downwardly into annular spaces provided with swirl imparting means, which annular spaces are defined between the upper sections of the tubular elements and the lower sections of tubular fluid outlet means arranged substantially co-axially within said upper sections, imparting a helical movement to the solids-fluid mixture (e.g. catalyst fines-containing gases) in the tubular elements to separate solids from fluid, removing solids through the lower sections of the tubular elements and removing fluid upwardly through the upper sections of the tubular fluid outlet means. Preferably, a mixture of solid cracking catalyst particles and hydrocarbon-containing gases emanating from a fluid catalytic cracking zone is pre-separated by passing said mixture upwardly and tangentially into a substantially spherical pre-separation zone, wherein the mixture is subjected to a rotating movement in a substantially vertical plane, removing catalyst particles through an opening in the lower section of the pre-separation zone and passing catalyst fines-containing gases from the central section of the pre-separation zone upwardly through the space between the tubular elements of the next separation zone. Apart from gaseous hydrocarbon conversion products, other gases such as flue gases or gases obtained in shale conversion processes and coal- or heavy oil gasification process can also be separated from solid particles in the above-described manner. Preferably, catalyst particles and/or -fines which have been separated by means of said process are passed to at least one stripping zone which is in gaseous communication with the first and/or second separation zone, and contacted in the stripping zone(s) with a stripping gas (e.g. steam). Moreover, the invention relates to hydrocarbon conversion products separated by a process as described hereinbefore. The invention will be further elucidated by means of the following Example. EXAMPLE A feed stream of hydrocarbon vapours and cracking catalyst particles in a weight ratio of 40 enters feed inlet (2) of a separation apparatus as depicted in Figure 1 at a temperature of 520 °C, a pressure of 2 bar gauge and a vapour velocity of 6 m/s. Catalyst particles are removed through solids outlets (4) with a separation efficiency of more than 95% on a weight basis.

Claims: 1. Apparatus suitable for solids-fluid separation which comprises a plurality of substantially vertical tubular elements in a housing, inlet means arranged in the bottom section of the housing and communicating with the space between the tubular elements and the housing, a plurality of tubular fluid outlet means of which the lower sections are arranged substantially co-axially within the upper sections of said tubular elements defining annular spaces wherein swirl imparting means are arranged and of which fluid outlet means the upper sections cooperate with opening(s) in the upper section of the housing, and solids outlet means communicating with the lower sections of the tubular elements and with opening(s) in the bottom of the housing. 2. Apparatus according to claim 1 wherein the inlet means is (are) centrally located in the bottom of the housing below the tubular elements. 3. Apparatus according to claim 1 or 2 wherein vortex stabilizer means are arranged in the lower sections of the tubular elements. 4. Apparatus according to any of the preceding claims wherein the lower section of a tubular element is downwardly converging. 5. Apparatus according to any of the preceding claims wherein the length:diameter ratio of a tubular element is from 1-10, and preferably from 2-5. 6. Apparatus according to any of the preceding claims wherein the ratio of the diameters of the tubular elements and the tubular fluid outlet means is from 1.5-4, and preferably from 2-3. 7. Apparatus according to any of the preceding claims wherein the lower sections of the fluid outlet means are provided with outward­ ly extending swirl vanes. 8. Apparatus according to any of the preceding claims which comprises a plurality of separate solids outlet means. 9. Apparatus according to any of the preceding claims wherein the upper section of the housing is provided with a central downwardly extending fluid deflection means around which the openings for the fluid outlet means are arranged. 10. Apparatus according to any of the preceding claims which further comprises in the bottom section of its housing a solids-­ fluid separation means comprising a domed upper section, upwardly directed feed inlet means cooperating substantially tangentially with said domed upper section, a central section provided with outlet means in communication with the space between the tubular elements and the housing, and a solids outlet opening in the lower section of the separation means. 11. Process for separating solid particles from fluid which comprises passing a mixture of solid particles and fluid upwardly into a space between tubular elements and subsequently downwardly into annular spaces provided with swirl imparting means, which annular spaces are defined between the upper sections of the tubular elements and the lower sections of tubular fluid outlet means arranged substantially co-axially within said upper sections, imparting a helical movement to the solids-fluid mixture in the tubular elements to separate solids from fluid, removing solids through the lower sections of the tubular elements and removing fluid upwardly through the upper sections of the tubular fluid outlet means. 12. Process according to claim 11 wherein fluid cracking catalyst particles are separated from gaseous hydrocarbon conversion products. 13. Process according to claim 12 wherein a mixture of solid cracking catalyst particles and hydrocarbon-containing gases emanating from a fluid catalytic cracking zone is pre-separated by passing said mixture upwardly and tangentially into a substantially spherical pre-separation zone wherein the mixture is subjected to a rotating movement in a substantially vertical plane, removing catalyst particles through an opening in the lower section of the pre-separation zone and passing catalyst fines-containing gases from the central section of the pre-separation zone upwardly through the space between the tubular elements of the next separation zone.

Inventors: BARNES, PETER HADDON
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1986
Main classification: B04C7
IPC codes: B04C9, B04C5, C10G11, B01J8