Gas separation: processes – Solid sorption – Moving sorbent
Reexamination Certificate
1999-12-30
2002-04-23
Smith, Duane (Department: 1724)
Gas separation: processes
Solid sorption
Moving sorbent
C095S109000, C095S111000, C095S148000, C095S269000, C095S272000, C096S130000, C096S132000, C096S143000, C096S150000, C055S315000, C055S331000, C055S419000, C055S447000, C055S474000
Reexamination Certificate
active
06375715
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the separation of solid particles and gaseous fluids. More particularly its objective is a device and a procedure that make it possible to separate solid particles in an intimate mixture with gaseous fluids in a manner that is both fast and efficient.
The invention applies in particular to procedures of the thermal or catalytic type in which solid particles with an essentially coolant and/or catalytic effect, move in suspension within gaseous fluids, from which they must later be rapidly separated in order to be regenerated prior to being reused.
In the following, the invention is described in reference to procedures used in the oil industry, and in particular to the fluid-bed catalytic cracking procedure (commonly called FCC procedure from the English Fluid Catalytic Cracking), in which the gas/particle separation processes must be carried out in a fast and efficient manner. It must however be understood that the invention applies to any procedure that requires a fast separation phase of solid particles and gaseous fluids.
In the FCC procedure, a hydrocarbon charge, pulverized in the form of fine droplets, is put in contact with cracking catalyst grains at a high temperature that circulate in the reactor in the form of a diluted fluidized bed, meaning in suspension within a gaseous fluid that ensures or assists their transportation. When in contact with the hot catalyst, there is a vaporization of the charge, followed by the cracking of the hydrocarbon molecules on the active catalyst sites. After having reached the desired range of molecular weight, with a corresponding reduction of the boiling points, the gaseous effluents of the reaction are separated from the catalyst grains. These catalyst grains, deactivated because of the coke that has deposited on their surface, are then stripped, in order to recuperate the hydrocarbons that were entrained, then regenerated by combustion of the coke, and lastly are put back in contact with the charge to be cracked.
The reactors used are generally vertical reactors of the tubular type, in which the catalyst diluted fluidized bed moves following a flow that is essentially upward (the reactor is then called “riser”) or following a flow that is essentially downward (the reactor is then called “dropper” of “downer”).
As known in the art, the efficiency of the separation process of the solid particles of the catalyst and the gaseous fluids in which they that are put in suspension is a key factor in the catalytic cracking procedure.
In particular, when exiting the tubular reactor, it is important to separate the catalyst particles from the gaseous reaction fluids in a manner that is both complete and fast. Indeed, it is fundamental not to prolong, within the separation and stripping enclosure, the time of contact between the reaction effluents and the catalyst, as this inevitably leads to an over-cracking of these effluents, which results in an increased coking of the catalyst along with the formation of products that are too light such as dry gases (methane, ethane, ethylene), to the detriment of the sought-after intermediary hydrocarbons (gasoline, gas-oil). A separation that is either too slow or too incomplete (gaseous effluents entrained in the stripper), is thus penalized by a significant loss in terms of performance and selectivity of the procedure.
Today, various devices are used to separate the solid particles from a gaseous fluid in which they are dispersed. These separation devices, that may or may not be directly connected to the output of the reactor, are essentially separators of the ballistic type, that impart a rotary motion to the suspension, so that the particles separate from the gas through a centrifugal effect.
Among the various devices in existence, the ones most used at this time are those known to the man of the art under the name of “cyclones”. These devices usually consist of a enclosure that is essentially cylindrical, in which the flow of gas and particles is introduced tangentially, and put in rotation around a winding axle that is more or less vertical. The particles thus concentrated on the walls of the separator fall into the lower part of the latter where they are discharged, through a first conduit that generally directs them toward the bottom, in the direction of an area where they are collected. The gaseous fluid concentrates in the upper part of the separator, from where it is discharged by a second conduit, that carries it toward an appropriate treatment system.
This device has the advantage of carrying out a separation of very high quality: the separated particles contain a very low quantity of gaseous fluids, and vice versa. However, such a system of separation lacks speed. Indeed, the particles make several full circles in the cylindrical enclosure, which prolongs by as much and in an undesired fashion, the period of time during which they are in contact with the gaseous fluids.
The various improvements that have been proposed in the prior art aim at improving even more the actual quality of the separation by cyclone, but do not solve, or may even aggravate, the problem of the slowness of this process.
Thus patent U.S. Pat. No. 4,446,107 proposes to improve the performances of the cyclones by providing the output of the discharge conduit of the separated particles with a sloped valve that opens regularly under the weight of the particles when the latter have accumulated in a sufficient quantity. This valve, when in a closed position, establishes a counter-pressure in said conduit, so that the gaseous fluids are less aspirated in this direction. It results in an improvement of the degree of separation.
Nevertheless, the repeated openings and closings of the valve result in significant variations of the counter-pressure exerted in the discharge conduit of the separated particles. These instabilities disturb the separation process and, in the end, strongly damage the quality of the latter.
In order to remedy the instability of the above-mentioned system, patent U.S. Pat. No. 5,055,177 proposes to install, around the output of the discharge conduit, outside the separated particles cyclone, a container equipped at its base with a drain of rather restricted size. This container is designed to collect the separated particles that pile up around the output of said conduit and thus act as a real stopper gasket. The particles escape from the container through the drain, and possibly by overflow (depending on the size of the drain and the flow of separated particles arriving from the conduit). The container can possibly be equipped with a vapor injection system so as to avoid coking inside said system.
The particles that are thus piled up around the output of said conduit carry out the same type of counter-pressure as the sealing valve described in U.S. Pat. No. 4,446,107 A, but this time in a constant manner, so much so that the quality of the separation is improved (better rate of separation). However, there again, the improvement takes place to de detriment of the speed of the separation: the watertight plug made by the accumulation of the catalyst at the output of the conduit, while achieving a significant counter-pressure, slows down by as much the speed at which the particles separate toward the lower part of the cyclone, and such a system therefore only prolongs further the time of separation that is already too long.
To compensate for the lack of speed of the cyclonic type separation systems, other techniques of ballistic separation have been proposed, in particular separators with a horizontal winding axis, directly connected to the reactor's output, as for example, those proposed in EP 332 277 A or in FR 2 758 277 A.
The separator described in EP 332 277 A imparts a half turn around a horizontal axis, to an upward flow of gas and particles. The particles projected against the walls are discharged toward the lower part whereas the gaseous fluid is extracted by means of a conduit arranged in the axis of rotation. This device has the undeniable a
Mauleon Jean-Louis
Mirgain Cyrille
Greene Jason M.
Smith Duane
Total Raffinage Distribution , S.A.
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