Circulating Fluidized Bed Reactor

The present invention relates to a circulating fluidized bed reactor in which solid particles are separated from the flue gas and recycled to the reactor chamber. The invention may also be used in gasifiers.

In known circulating fluidized bed reactors, flue gas is removed from the upper end of the reactor chamber through a duct to a cyclone separator. Entrained ash, unburned solid fuel, and other relatively coarse particles, are separated from the hot flue gas and are returned to the lower part of the reactor chamber. Before the flue gas is discharged through a stack, it is passed through a dust collector of suitable design for removal of fine particles. Previously, the separation and collection of dust particles have been achieved by various apparatus which have required substantial space and multiple flow lines interconnecting their various elements. Integrating these various elements and functions into a substantially compact system has not heretofore been achieved.

In accordance with the present invention, there is provided a reactor having integrated therewith in a single vessel vertical filtration tubes for separating solids from the solids-entrained gases. These tubes are made of porous super alloys or ceramics, and which tubes are disposed in a filter housing located in back-to-back relation with the reactor chamber. The filtration tubes are used to clean the flue gas.

In certain applications, a pre-separator is located above the filter housing in direct communication with the flue gas discharge outlet. The pre-separator is thus located in back-to-back relation with the upper end of the reactor chamber. The pre-separator is used to separate relatively coarse particles from the flue gas and return them to the reactor chamber before the gas enters the filtration tubes. The smaller sized solid particles separate from the solids-entrained gas as the gas passes through the porous tubes. Such solids remain within the tubes along the inner walls thereof and are transported by the residual gas flow through the tubes for return to the reactor chamber. The structure and function of the filter apparatus which affords a thorough cleaning of the gas as it passes through the porous walls of the tubes are described in U.S. Pat. No. 4,584,003, the disclosure of which is incorporated herein by reference.

Further, in accordance with the present invention, two different types of pre-separators may be used in keeping with the compact nature of the reactor hereof. In a first type, the filtration tubes project above an inclined wall into an area in communication with the flue gas discharge outlet. The upper ends of the tubes are partially closed. In this manner, the change of direction of the flue gas causes separation of the coarse particles which are deposited on an inclined wall forming the top of the filter housing for conveyance back to the reactor chamber. The gas with the smaller size solids flows into the filtration tubes and through a plurality of compartments formed in the housing. Each compartment is connected with a clean gas outlet for flow out of the vessel.

In another form hereof, the pre-separator may comprise a cyclone separator disposed on top of the filter housing. An inlet duct is in communication with the gas discharge outlet for tangentially introducing gas into the cyclone separator. An inner tube of the separator extends upwardly into the cyclone and opens through an inclined wall into a chamber in communication with the filtration tubes. The solids fall onto the inclined wall for return to the reactor chamber, whereas the gas flows into the upwardly projecting tube for flow through and separation from the solids entrained therein by the filtration tubes.

From the foregoing, it will be appreciated that the reactor chamber and the filter housing, together with the pre-separator on top of the filter housing in certain applications, lie in back-to-back relation one to the other, thereby affording a compact unitary vessel. In this manner, the combined and integrated reactor and filter housing may be enclosed within a pressurized vessel.

In another form of the present invention, a pair of filter housings may lie on opposite sides of the reactor chamber. Thus, each filter housing lies in back-to-back relation with the centralized reactor chamber. Each may have a pre-separator of either of the foregoing described type, depending upon the application. Each filter housing has outlet conduits for transporting the clean gas from the space between the filtration tubes and the housing externally to the vessel. The solids which are separated in any pre-separator fall by gravity along the inclined wall into the central reactor chamber while the solids separated from the solids-entrained gas in the filtration tubes flows toward the base of the reactor chamber for return thereto.

In a further form of the present invention, whether the reactor chamber and filter housing lie in back to back relation or the filter housing straddles the reactor chamber, the coarse solids may be recirculated through discrete pipes which form part of the filter assembly. The coarse solids exiting the discrete filter assembly pipes may be recombined with the finer dust particles flowing through the other filter pipes for combined flow into the combustion chamber. Alternatively, the coarse and fine solids may be introduced into the combustion chamber separately.

In a preferred embodiment of the present invention, the reactor chamber and filter housing are enclosed in a pressure-proof vessel, preferably cylindrical. Also, the reactor is supplied with compressed air and the cleaned flue gas is used in a gas turbine. It will be further appreciated that the principles of the present invention can likewise be applied to a gasifier rather than a fluidized bed reactor.

In certain fluidized bed reactor applications, solid particles may adhere to the inner surface of the filtration tubes, tending to clog the tubes and inhibit the flow of gas through the tubes. While a pressure pulse may be provided in the gas outlet pipes to momentarily change the direction of the gas flow through the porous tubes and thereby loosen the particles adhering to the inner surfaces of the tubes, it has been recognized that such solid particles afford a beneficial scrubbing effect on the tubes. Consequently, in certain applications, the scrubbing effect of the solid particles as they move through the tubes tend to clean the tubes and keep the pores free of clogging material. Thus, in certain applications, a pre-separator may not be used and the larger particles, separated in other applications by the pre-separator, are particularly directed for flow through the filtration tubes to scour the inside of the tubes and maintain such surfaces clean. More particularly, this is achieved by providing enlarged inlet openings to the porous tubes such that additional quantities, particularly of the larger materials, may flow through the tubes to clean the latter and for ultimate return to the fluidized bed combustion chamber.

In a still further form of the present invention, the filter housing is comprised of a plurality of porous plates. The plates may have ribs projecting from one side thereof. When the plates are aligned generally vertical one with the other, the free edges of the ribs engage the back side of the adjacent plate to form a plurality of passageways. Certain of the passageways communicate with the filter housing gas inlet at the top of the filter such that gas may flow through the passageways and through the porous plates into other passageways formed by the juxtaposition of the plates. These latter passageways are closed at both the top and bottom of the filter housing and have communicating conduits for collecting the filtered clean gas flowing into such passageways for flow to a clean gas outlet. Alternatively, the filter housing may be formed of solid porous material having a plurality of bores formed therein whereby gas flows into those bores in communication with the gas inlet at the top of the housing and through the porous filter housing into those bores closed at the top and bottom of the housing for flow of clean gas to the clean gas outlet.

In accordance with a specific preferred embodiment of the present invention, there is provided a circulating fluidized bed reactor comprising means defining an upright reactor chamber having at least one gas discharge opening adjacent its upper end and at least one inlet opening for solids separated from the gas adjacent its lower end. There is also provided a filter housing and means defining a plurality of generally vertically extending horizontally spaced passageways, these passageway defining means in part formed of porous material and disposed in the housing. The housing and the reactor chamber are arranged in back-to-back relation one with the other. The housing has a gas inlet in communication with the gas discharge opening and the passageways, a solids outlet in communication with the solids inlet opening, at least one clean gas outlet, and means in the housing in communication with the one clean gas outlet for communicating gas flowing through the porous material of the passageways with the one clean gas outlet.

In a preferred form of the invention for certain applications, the gas inlet includes means defining larger inlet openings for the passageways than the internal diameter of the passageways to provide a solids scrubbing action along the inside surfaces of the passageways to minimize clogging. Preferably, the inlet opening means are generally funnel-shaped elements, thereby increasing the quantity of solids flowing through the passageways in comparison with the quantity of solids which would flow through the passageways if the inlet openings were of the same diameter as the passageways. That is to say, the inlets for each of the passageways have combined cross-sectional areas greater than the combined cross-sectional areas of the passageways to provide enhanced scrubbing of the solids along the interior surfaces of the passageways.

In a further aspect of the present invention, there is provided a method for separating solids entrained in a gas from a fluidized bed reactor comprising the steps of forming a filter comprised of a plurality of spaced passageways of porous material, disposing the filter in a housing, disposing the housing in back-to-back relation with the reaction chamber, flowing the gas with entrained solids through a gas discharge opening in the reactor and into the passageways for flow of the gas through the porous material to clean the gas, collecting the clean gas flowed through the porous material and returning solids separated from the gas within the passageways to the reactor chamber.

Accordingly, it is a primary object of the present invention to provide a novel and improved compact circulating fluidized bed reactor design with separator, particularly a circulating fluidized bed reactor design with separator suited for use in pressurized combustion or other processes, as well as a method of operating the reactor.

These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.

FIG. 1 is a schematic vertical cross-sectional view of a circulating fluidized bed reactor constructed in accordance with a preferred embodiment of the present invention;

FIG. 2 is a fragmentary enlarged cross-sectional view of a portion of the pre-separator forming a part of the reactor illustrated in FIG. 1;

FIG. 3 is a cross-sectional view of the reactor taken generally about on line A--A in FIG. 1;

FIG. 4 is a view similar to FIG. 1, illustrating a further embodiment of the present invention;

FIG. 5 is a cross-sectional view thereof taken generally about on line C--C in FIG. 4;

FIG. 6 is a view similar to FIG. 1, illustrating a still further embodiment of the present invention;

FIG. 7 is a cross-sectional view thereof taken generally about on line D--D in FIG. 6;

FIG. 8 is a view similar to FIG. 1, illustrating still another embodiment of the present invention;

FIG. 9 is a cross-sectional view thereof taken generally about on line E--E in FIG. 8;

FIG. 10 is a view similar to FIG. 1 illustrating still a further embodiment of the present invention;

FIG. 11 is a still further embodiment of the present invention;

FIG. 12 is a view similar to FIG. 1 illustrating another embodiment of the present invention; and

FIG. 13 is enlarged cross-sectional view thereof taken generally about on line A--A in FIG. 12.

Reference will now be made in detail to the present and preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.

Referring now to the drawing figures, particularly to FIG. 1, there is illustrated a circulating fluidized bed reactor 1. Reactor 1 comprises a substantially vertical reactor chamber 2. The reactor chamber has a front wall 3 having a multi-sided angular shape, best illustrated in FIG. 3, and a planar rear wall. Front and rear walls 3 and 4, respectively, are water-cooled and are formed of vertically extending tubes in a conventional manner. A filter housing 5 is disposed in back-to-back relation to reactor chamber 2. The rear wall 4 of the reactor thus forms a wall of the filter housing. A semi-circular wall 6 having a multi-sided angular shape, similar to but reverse from wall 3, forms the remaining water-cooled wall of housing 5. Filter housing 5 includes a wall or plate 8 which closes the upper end of the housing. Wall 8 is disposed below the top wall 9 of reactor 1 and is inclined downwardly towards the reactor chamber. Wall 8 is provided with a plurality of openings and serves as a mounting plate for the upper end of a plurality of filtration tubes 10 defining gas passageways or channels. As illustrated, tubes 10 are vertically disposed in housing 5. The lower end of housing 5 is provided with a generally funnel-shaped bottom part 11 having an outlet 12 through which solids are discharged from housing 5. The lower end of filtration tubes 10 are connected to a lower structural tube plate 16. Housing 5 is divided into a plurality of superposed compartments by intermediate tube sheets 13, 14 and 15. The upper ends of filtration tubes 10 protrude through the inclined plate 8 and the openings of the tubes are covered by caps 17, as illustrated in FIG. 2, to avoid direct access of the solids into the tubes. Openings 33 are formed in the sides of the upper ends of the tubes below caps 17 to enable entry of gas into the tubes and the tubes are therefore partially closed at their upper ends.

Tubes 10 are formed of sintered ceramic material and are porous except for the upper portion between the tube plates 8 and 13. The tubes at that location are not permeable to gas. Compartment 18, 19 and 20 between the tube sheets 13-16 are provided with gas outlets 21, 22 and 23, respectively.

An inlet opening 24 for recycled solids is provided in the lower part of the reactor chamber. A standpipe 25 and a loop seal 26 connect the outlet 12 in the bottom part of the filter housing with the solids inlet opening 24 in the reactor chamber.

Air from a conduit 27 connected to an air plenum 28 below a grid 29 supplies compressed air from an external source to the plenum. Feeders, shown schematically by the reference numerals 30 and 31, are adapted to feed fuel, such as coal, and additives, such as limestone, into the reactor chamber above grid 29.

The flue gas with entrained solids leaves reactor chamber 2 through an opening 32 formed between its top wall 9 and the inclined upper tube plate 8. The gas then flows into the passageways or channels defined by filtration tubes 10. When flowing into tubes 10, the gas flows through openings 33 below cap 17, and abruptly changes direction, which causes separation of the coarse fraction of the solids from the gas. These coarse solids collect on the inclined tube plate 8, slide down along the surface of the plate under the influence of gravity, and fall down into the reaction chamber along the rear wall 4.

A portion of the flue gas, which after having entered the filtration tubes for flow in a downward direction along the passageways or channels defined thereby, passes through the porous tube walls in the first gas compartment 18 while the solids remain along the inside of the tubes.

Another portion of the flue gas passes through the porous tube walls in the second gas compartment 19. Remaining portions of the flue gas pass through the porous tube walls in the third gas compartment 20. The gas in the space between the exterior of the tubes and the interior of the filter housing compartments is removed through clear gas outlets 21, 22 and 23 and transferred through a conduit 32 to a gas turbine, not shown.

The fine particles which are separated from the gas fall down or are moved by the downward flow of the gas or coarser particles to the bottom part of the filter housing and are discharged through the solids outlet 12. The solids are returned to reactor chamber 2 through standpipe 25 and the loop seal 26. Particulate material which mainly consists of ash can be removed from the loop seal or the lower end of the reactor chamber through conduits 34 and 35. The material removed is cooled in an ash cooler 36.

The entire reactor chamber 2, filter apparatus 37, standpipe 25, loop seal 26 and the ash cooler 36 are encased by and within a pressure-proof vessel 7. The vessel is pressurized by the same air which is introduced into the reactor chamber. As the inner and outer pressures acting on these parts are equal, they do not have to be pressure-proof. Also, the walls of the filter housing are formed of water wall tubes, thereby affording a high heat resistance.

FIGS. 4 and 5 illustrate another embodiment of the invention which is generally similar in structure and operation to the embodiment shown in FIGS. 1 through 3. Only those structural and operational features which serve to distinguish this embodiment from that shown in FIGS. 1 through 3 will be described below. The same reference numerals have been used in FIGS. 4 and 5 to identify elements identical or substantially identical to those depicted in FIGS. 1 through 3.

The embodiment of the invention shown in FIGS. 4 and 5 includes a filter housing 5 and a reactor chamber 2 disposed in back-to-back relation one with the other. The walls of the reactor chamber and the filter housing form a vessel having a cylindrical cross-section, as best illustrated in FIG. 5. Two parallel cyclone separators 40 are mounted on the filter housing which operatively connect the reactor chamber with the filter apparatus 37. Each cyclone separator comprises a circumferential wall 41 defining an annular separator chamber 42. A gas inlet duct 43 is tangentially connected to each separator chamber. The inlet ducts 43 of the separators are connected to two discharge openings 44 formed in the rear wall 4 of the reactor chamber for discharging gas from the reactor chamber. The upper end of separator chambers 42 are closed by top wall 9. An inclined wall or plate 46 mounted on the filter housing forms the bottoms of the separator chambers. A central pipe 47 extends into each separator channel and is connected to the bottom. An opening 48 in the circumferential wall of the separator chamber and rear wall 4 located near the bottom of the separators forms an outlet for separated solid material. A plurality of parallel filtration tubes 10 defining gas passageways or channels are disposed vertically in the filter housing. The ends of the tubes are connected to an upper tube sheet 13 forming structural connections for supporting the tubes 10. Additional intermediate tube sheets 14 and 15 divide the filter housing into compartments. The top part of the filter housing below inclined wall or plate 46 forms an inlet chamber 49 which distributes the gas from the cyclone separator to the filtration tubes 10.

In operation, the flue gas with entrained solids is discharged through the reactor chamber gas discharge openings 44 at the upper end of the reactor chamber. A coarse fraction of the solids material is separated at the periphery of the separator chamber and falls down to the bottom wall 46 of the chamber. The material collected on bottom wall 46 slides down its inclined surface under the influence of gravity and falls down into the reactor chamber through the solids opening 48.

Gas, from which the coarse particles have been separated, is discharged from the separation chambers 42 through gas outlet pipes 47 to inlet chamber 49 of the filter apparatus which distributes the gas to the filtration pipes. The gas flows through the porous filtration pipes for collection external to the apparatus, with the smaller sized particles being returned with a portion of the gas to the reaction chamber, as previously described in connection with the embodiment of FIGS. 1 through 3.

Referring now to the embodiment of the invention hereof illustrated in FIGS. 6 and 7, which is generally similar in structure and operation to the embodiments of FIGS. 1-3 and 4-5, only those structural and operational features which serve to distinguish this embodiment from the other embodiments will be described below. Similar reference numerals are used in FIGS. 6 and 7 as used in FIGS. 1-3 to identify identical or substantially identical elements.

In FIG. 6, the reactor chamber 2 is illustrated as a central chamber or column which has a lower grid 29 to which feeders 30 and 31 feed coal or other fuels for burning in the chamber. Below grid 29, there is provided a plenum 28 and the upper portion of reactor chamber 2 is closed by a wall 9.

In accordance with this embodiment of the present invention, disposed on opposite sides of the reactor chamber 2 are a pair of filtration housings 5, which are identical in construction and mirror-images of one another. Each filtration housing 5 has a plurality of upstanding filtration tubes 10 supported at their upper ends by inclined wall or plate 8, the upper ends of which tubes 10 are closed by cap 17 in the manner illustrated in FIG. 2. The filtration housings 5 are separated into discrete superposed compartments 18, 19 and 20, separated by plates 13, 14, 15 and 16. The space about the filtration tubes 10 and within housing 5 communicates with a clean gas outlet 21, 22 and 23. The lower portions of the filtration housings 5 communicate with the reactor chamber through a bottom part 11 with outlet 12, which in turn communicate with the chamber through the standpipe 25 and loop seal 26.

The operation of this form of the invention is similar to that described with respect to the previous embodiments. Importantly, the filtration housings are disposed in a straddling relation to the reactor chamber 2, with each filtration housing lying in back-to-back relation with the reactor chamber 2. In this manner, a compact housing is provided for the entirety of the apparatus.

Referring now to the embodiment of the invention hereof illustrated in FIGS. 8 and 9, which is generally similar in structure and operation to the embodiments of FIGS. 1-3 and 4-5, only those structural and operational features which serve to distinguish this embodiment from the other embodiments will be described below. Similar reference numerals are used in FIGS. 8 and 9 as used in FIGS. 1-3 to identify identical or substantially identical elements.

In FIG. 8, the reactor chamber and filter housing 5 are arranged in back to back relation similar as the embodiments of FIGS. 1-3 and 4-5. The cyclone separators 40 mounted on top of inclined wall 46 are structurally and operationally similar to the cyclones of the embodiment of FIG. 4. In this embodiment, the inclined wall of plate 46 mounted on the filter housing forms the bottoms of the separator chambers. A plurality of parallel filtration tubes 10 defining gas passageways or channels are disposed vertically in the filter housing similarly as in the previous embodiment of FIGS. 4-5 except that a pair of enlarged diameter or area tubes 100 formed of similar porous material as the remaining tubes 10 extend the full length of the housing. The upper ends of the tubes 10 and 100 are connected to an upper tube sheet 13 forming structural connections for supporting the tubes 10. Additional intermediate tube sheets 14 and 15 divide the filter housing into compartments. The top part of the filter housing below inclined wall or plate 46 forms an inlet chamber 49 which distributes the gas from the cyclone separator to the filtration tubes 10. The upper ends of the enlarged area tubes 100 open through the inclined wall 46 to receive the coarse solids sliding down wall 46. The lower ends of tubes 10 and 100 exit into a common hopper 11 with an outlet 12 which, in turn, communicates with the chamber through standpipes 25 and loop seal 26.

In operation, the flue gas with entrained solids is discharged through the reactor chamber gas discharge openings 44 at the upper end of the reactor chamber. A coarse fraction of the solids material is separated at the periphery of the separator chamber and falls down to the bottom wall 46 of the chamber. The material collected on inclined wall 46 slides down its inclined surface under the influence of gravity into the upper open ends of filtration tubes 100.

Gas, from which the coarse particles have been separated, is discharged from the separation chambers 42 through gas outlet pipes 47 to inlet chamber 49 of the filter apparatus which distributes the gas to the filtration pipes 10. The gas flows through the porous filtration pipes 10 and 100 for collection external to the apparatus, with both the smaller and larger sized particles being returned with a portion of the gas to the reaction chamber through the hopper 11, outlet 12, standpipe 25 and loop seal 26. Alternatively, the coarse and fine solids can be introduced into the combustion chamber separately.

It will be appreciated with respect to both the embodiments illustrated in FIGS. 4-5, 6-7 and 8-9 that the apparatus may be enclosed within a pressure vessel similar to the vessel illustrated with respect to the embodiment of FIG. 1.

It will also be appreciated that the invention can be carried out without any pre-separator which separates the coarse fraction from the gas. Consequently, the pre-separators, whether they be cyclone separators as in the embodiments of FIGS. 4-5 or the capped filtration tube arrangement illustrated in the embodiment of FIGS. 1-3, may be eliminated and the coarse material may flow through the filtration tubes, scouring the filtration surfaces, thus keeping the filtration tubes clean.

For those applications where a pre-separator is not necessary or desirable, and in keeping with a still further embodiment of the present invention, there is illustrated in FIG. 10 a fluidized bed reactor generally similar to the reactor illustrated in FIG. 1. In the embodiment hereof in FIG. 10, an enhanced scouring or scrubbing effect of the particles or solids as they flow downwardly through the filtration tubes 110 is afforded by providing an inlet and tube construction enabling a considerably larger quantity of particles to flow through the porous tubes. In this form, the reactor chamber 102 and filter housing 105 are arranged in back-to-back relation similarly as in FIG. 1, separated by the wall 104. The filtration housing 105 includes an upper inclined wall or plate 108. Plate 108 is provided with a plurality of openings 133 and serves as a mounting plate for the upper end of the filtration tubes 110. The openings 133 which deliver the combined gas and solids to the interior of the tubes 110 are generally funnel-shaped, with their larger openings at their upper ends. The smaller downward openings of the generally funnel-shaped openings 133 fit the porous tubes 110. By this orientation and disposition of funnel-shaped openings, larger quantities of solid particles are enabled to flow into the tube and drywash or scrub the interior surfaces of the tubes to substantially minimize or eliminate clogging of the porous tubes by the particulate matter. Preferably, the larger openings at the upper ends of the funnels 133 lie flush with the inclined wall 108, although it will be appreciated that the enlarged funnel-shaped portions of the tube inlets may project above the inclined wall 108. Suffice to say, the generally funnel-shaped openings 133 increase the cross-sectional area extent for receiving the gas and solid particles as compared with the combined cross-sectional area of the tubes at locations downstream from the generally funnel-shaped inlet openings 133. This increases flow velocity and the quantity of solid particles flowing through the filtration tubes and hence the scouring or scrubbing action of the particles along the interior surfaces of the tubes.

It will be appreciated from a review of FIG. 10 that plate 108 is inclined such that particles flowing by gravity therealong are returned to the combustion chamber of the fluidized bed reactor 102. The plate 108 could, of course, be horizontal or inclined in the opposite direction in the event that it is desirable to flow all particles from the combustion chamber of the reactor into the filtration tubes.

As in the previous embodiments, gas outlets 121 and 122 lie in communication with a chamber defined by the space or area between the filtration tubes 110. Thus, a portion of the gas flowing through the porous tubes enters the chamber between the tubes for egress from the reactor via gas outlet passages 121 and 122. The solids flowing through the tubes flow into a funnel-shaped bottom part 111 for egress into a standpipe 125 and loop seal. As in the previous embodiments, the apparatus described is encased within a pressure-proof vessel.

Turning now to the embodiment hereof illustrated in FIG. 11, there is provided a reactor chamber 202 in back-to-back relation with a filter housing 205, separated by a common wall 204. In this application, pre-separation is achieved by centrifugal force as the gas is conveyed along a curved path 232 between the upper reactor wall 209 and the upper plate 208 of the filter housing. In this form, the upper plate 208 is inclined downwardly in a direction away from the reactor 202 and toward the side wall of the reactor in the flow direction of the gas. Thus, the coarse, solid particles flow along the curved wall 232 for passage with a portion of the gas through a passageway 239 for return to the combustion chamber of the reactor. Additionally, gas and solid particles also flow into and through funnel-shaped openings 233 formed in the inclined wall 208. The funnel-shaped openings 233 are arranged as in the previous embodiment with respect to the inclined wall 208. Gas outlet chambers 221 and 222 lie in communication with the chambers between the filtration tubes 210.

Thus, in operation, the gas is initially pre-separated by flow along the curved wall 232 such that the larger or coarser solid particles flow through the path 239 together with portions of the gas for return to the reactor 202. Another portion of the gas and particulate flow enters the funnel-shaped openings 233 for flow into the porous filtration tubes 210. As in the previous embodiment, gas flows along the passageways or channels defined by the tubes and through the porous tubes into the chambers separated by plates 214 and 215 for flow through gas outlets 221, 223 and 222. The particles flow along the interior surface of the filtration tubes, effecting a washing, scouring or scrubbing action in the course of their passage to maintain the pores of the porous tubes substantially clean of clogging material. As in the prior embodiment, the solids flowing through the tubes 210 flow into a funnel-shaped area 211 and through a standpipe and loop seal for return to the reactor.

The embodiment hereof illustrated in FIG. 11 is particularly suitable for processes with substantial amounts of particles circulating, whereas the embodiment of FIG. 10 is more suitable for processes with more limited quantities of circulating particles.

Turning now to the embodiment illustrated in FIGS. 12 and 13, instead of using porous filtration tubes, the filter is formed of a series of porous plates. In FIG. 12, there is illustrated the reactor chamber 302 in back-to-back relation with the filter housing 305. As in the prior embodiments, the lower end of the filter housing 305 has a solids collection chamber 311 and a standpipe 325 for feeding the solids back to the reaction chamber.

In this form, as illustrated in FIG. 13, the filter housing 305 encompasses a series of substantially vertically extend plates 334 each having laterally projecting ribs 337 projecting from one face of the plates. When the plates are juxtaposed vertically in lateral adjacent position one to the other, it will be appreciated that the free edges of the ribs 337 engage the back side of the adjoining plate, i.e., engage the side of the adjoining plate opposite its ribs 337. In this manner, a series of horizontally spaced passageways or channels 335 and 336 are formed between the plates and ribs.

Preferably, alternating rows of the channels are open at their upper ends, i.e., at 333 in FIG. 12, into the area of the gas inlet opening to the filter housing 305. The lower ends of the passageways 335 are open to the solids collection chamber 311. The other passageways 336, which alternate with passageways 335, are closed at both their top and bottom. Outlet conduits 321, however, communicate with each of the closed passageways 336 for removing clean gas from the passageways 336 and communicating it to a clean gas outlet, not shown. The upper surface defining the inlet to the plates is inclined as in the previous embodiment such that larger particles may be pre-separated for flow back into the reactor chamber 302.

In operation, the flue gas from the reaction chamber 302 flows through the gas inlet opening to the filter housing and particularly into the passageways 335 open at the upper end of the filter housing. The gas and solids separate by passage of the gas from passageways 335 through the porous vertical plates 334 into the passageways 336. The clean gas in passageways 336 is removed by conduits 321 to the clean gas outlet. The separated solids in the passageways 335 continue to flow downwards to the solids collection chamber 311 for return to the combustion chamber.

It will be appreciated that other forms of filter may be provided in keeping with the present invention as illustrated in FIGS. 12 and 13. For example, porous plates spaced one from the other without ribs and defining the passageways 335 and 336 alternately therebetween may be used instead. Also, porous plates with channels in the plates themselves for either the flue gas or the clean gas may be utilized. Blocks of porous material, for example, may be used with boreholes formed in the material whereby gas would flow from the gas inlet through certain ones of the boreholes and through the porous material into certain of the other of the boreholes for removal from the filter.

It will be appreciated that objects of the present invention are fully accomplished in that there has been provided a circulating fluidized bed reactor which is compact in construction and capable of use within a pressurized vessel.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.