Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including internal mixing or stirring means
Reexamination Certificate
1999-07-09
2001-08-07
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including internal mixing or stirring means
C422S139000, C422S140000, C422S227000
Reexamination Certificate
active
06270734
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a multizone downcomer for a three phase liquid slurry. More particularly the invention relates to a downcomer for producing at least two different solids and gas reduced slurries from a hydrocarbon synthesis slurry comprising gas bubbles and particulate solids dispersed in a hydrocarbon liquid.
2. Background of the Invention
Slurry hydrocarbon synthesis (HCS) processes are known. In a slurry HCS process a synthesis gas (syngas) comprising a mixture of H
2
and CO is bubbled up as a third phase through a slurry in a reactor in which the slurry liquid comprises hydrocarbon products of the synthesis reaction and the dispersed, suspended solids comprise a suitable Fischer-Tropsch type hydrocarbon synthesis catalyst. Reactors which contain such a three phase slurry are sometimes referred to as “bubble columns”, as is disclosed in U.S. Pat. No. 5,348,982. Irrespective of whether the slurry reactor is operated as a dispersed or slumped bed, the mixing conditions in the slurry will typically be somewhere between the two theoretical conditions of plug flow and back mixed. The catalyst particles are typically kept dispersed and suspended in the liquid by the lifting action of the syngas bubbling up through the slurry and by hydraulic means. Mechanical means such as impellers and propellers and the like are not used, because they will quickly erode and also cause attrition of the catalyst particles. One or more vertical, gas disengaging downcomers may be used as hydraulic means to assist in maintaining more uniform catalyst dispersion, by providing a vertical catalyst circulation in the slurry, as is disclosed in U.S. Pat. No. 5,382,748. The larger catalyst particles tend be more concentrated at the bottom of the slurry. It would therefore be advantageous in maintaining a more uniform vertical catalyst concentration to circulate a catalyst lean slurry to the bottom of the reactor and a catalyst rich slurry at the top. Further, the slurry liquid hydrocarbon product of the HCS reaction must be separated from the catalyst particles. This is typically accomplished by mechanical filtration in which the slurry is fed to one or more porous filter media which permit the liquid to pass through, but not the catalyst particles. The hydrocarbon liquid filtrate is then sent to further processing and upgrading. The build-up of a catalyst particle cake and plugging of the filters could be reduced if some of the catalyst particles were removed from the slurry before it is filtered. Hence, there is a need for a means of reducing the catalyst concentration in slurry being fed to the bottom of the reactor and to filtration.
SUMMARY OF TIE INVENTION
The present invention relates to a means and a process for simultaneously producing slurries of two or more different compositions from a three phase slurry and is useful in a hydrocarbon synthesis (HCS) process. The slurry comprises gas bubbles and particulate solids in a slurry liquid. The means comprises two or more successive gas and solids disengaging zones, and at least one slurry transfer conduit. The process comprises passing the slurry successively through at least two gas and solids disengaging zones to form a solids and gas reduced slurry, which is then passed to a desired location by means of a fluid conduit, such as a downcomer. This invention is useful for removing gas bubbles and solid catalyst particles from an HCS slurry being fed to the bottom of the slurry body to improve vertical catalyst distribution, to slurry filtration for recovering the slurry liquid produced by the HCS reaction and also for feeding a gas reduced and catalyst increased slurry to rejuvenation. By successive zones is meant that slurry passes from the outer zone to an adjacent downstream zone and then to successively adjacent downstream zones, until it finally passes into the inner or last zone, which is furthest downstream. Adjacent zones are in fluid communication with each other, by which is meant that slurry passes from each zone into the next successive zone downstream. Gas reduced slurries may be produced which have a solids concentration both greater and less than that in the slurry body which feeds the means. As slurry successively passes from one zone to the next, adjacent downstream zone, the gas concentration in the slurry is reduced. Each zone also has downcomer means for feeding slurry from that zone to a desired location such as the top or bottom of the slurry, to filtration, to a zone or vessel external of the slurry, etc. Depending on the configuration of the zone and the means that separates it from an adjacent downstream zone, the solids concentration of the slurry fed into its downcomer may be greater than that in the slurry fed into the adjacent downstream zone. The gas and solids disengaging zones may simply be upward open cups having a respective one or more downcomers depending from the bottom, in which gas and solids are disengaged from the slurry passing through. In one embodiment, the process of the invention is achieved by means which comprises a downcomer immersed in a slurry body, with the top of the downcomer opening into a multizone gas and solids disengaging means comprising an inner zone peripherally surrounded by an outer zone and separated from the outer zone by weir means. Slurry from the slurry body surrounding the downcomer passes into the outer zone in which a portion of the gas bubbles and solids are disengaged to form two slurries which are; (i) a solids and gas reduced slurry which passes over the weir means into the inner zone, and (ii) a gas reduced and solids increased slurry which is passed out the bottom of the outer zone to a desired location. In the inner zone, additional gas is disengaged from the solids and gas reduced slurry which enters it from the outer zone, to form a gas and solids depleted slurry which is passed to and through one or more inner zone downcomer conduits to the desired location.
With particular regard to a slurry HCS process for forming hydrocarbons, at least a portion of which are liquid, the invention comprises the steps of:
(a) contacting a synthesis gas (syngas) comprising a mixture of H
2
and CO with a solid, particulate hydrocarbon synthesis catalyst in a slurry body comprising the catalyst and gas bubbles in a hydrocarbon slurry liquid under reaction conditions effective to form hydrocarbons from the syngas, at least a portion of which are liquid at the reaction conditions and comprise the slurry liquid;
(b) passing a portion of slurry from the slurry body into a first zone to disengage and remove a portion of the gas bubbles and form a first gas and catalyst reduced slurry;
(c) passing said first gas and solids reduced slurry into at least one adjacent zone downstream of the first zone to disengage and remove more gas bubbles in each zone and form successive gas reduced slurries, and
(d) passing slurry from at least one zone into a fluid conduit by which it is passed to a desired location.
In one embodiment, solids are removed from the slurry in at least one zone, so that the slurry in the innermost or downstream zone is reduced in both gas and solids. In the embodiment referred to above in which a two zone, gas and solids disengaging means is used, a portion of the slurry body is passed into the outer zone in which a portion of the gas bubbles and solids are disengages from the slurry to form a solids and gas reduced slurry which is passed over a weir means to the inner zone, in which more gas is disengaged from the slurry to form a solids and gas reduced slurry. The solids and gas reduced slurry is then passed into and through at least one downcomer depending from at least one orifice in the bottom of the inner zone, and from there to a desired location, such as to the bottom of the slurry or to filtration means. The slurry removed from the bottom of the outer zone has less gas bubbles and more catalyst than the surrounding slurry body, and more gas bubbles and catalyst than the slurry passing out of the inner zone
Exxon Research and Engineering Company
Foss Norby L.
Provoost Jonathan N.
Tran Hien
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