Pressurized fluidized bed combustion system and method with integral recycle heat exchanger

Abstract: The recycle heat exchanger (38) includes a plurality of stacked sections (68,70,72,74,76,78) for receiving the recycled solids and are arranged in such a matter that the recycled solids are introduced into an upper level of the sections and pass through these sections to a lower level of sections before returning to the furnace. A portion (68,70,74,76) of the stacked sections contain heat exchange surfaces for removing heat from the solids therein while another portion (72,78) does not. The solids in the various sections are selectively fluidized to control the flow of the solids through the sections to control the temperature of the solids accordingly.

Description: This invention relates to a pressurized fluidized bed combustion system and method and, more particularly, to such a system incorporating a integral heat exchanger for recycling solids from the combustor. According to prior art fluidized bed combustion systems and methods, air is passed through a bed of particulate material, including a fossil fuel, such as coal, and a sorbent for the oxides of sulfur generated as a result of combustion of the coal, to fluidize the bed and to promote the combustion at a relatively low temperature. These types of systems are often used in steam generators in which water is passed in a heat exchange relationship to the fluidized bed to generate steam and permit high combustion efficiency, fuel flexibility, high sulfur adsorption and low nitrogen oxides emissions. These types of systems often utilize a "circulating" fluidized bed in which the entrained solid particles of fuel and sorbent (hereinafter referred to as "solids") from the furnace are separated from the mixture of fluidizing air and combustion gases (hereinafter referred to as "flue gases") and are recycled back to the furnace. In these circulating beds, the fluidized bed density is relatively low when compared to other types of fluidized beds, the fluidizing air velocity is relatively high, and the flue gases passing through the bed entrain a substantial amount of the fine solids to the extent that they are substantially saturated therewith. The relative high solids recycling is achieved by disposing a cyclone separator at the furnace section outlet to receive the flue gases, and the solids entrained thereby, from the fluidized bed. The solids are separated from the flue gases in the separator and the flue gases are passed to a heat recovery area while the solids are recycled back to the furnace. This recycling improves the efficiency of the separator, and the resulting increase in the efficient use of sulfur adsorbent and fuel residence times reduces the adsorbent and fuel consumption. Also, the relatively high internal and external solids recycling makes the circulating bed relative insensitive to fuel heat release patterns, thus minimizing temperature variations and, therefore stabilizing the sulfur emissions at a low level. When the circulating fluidized bed combustors are utilized in a steam generating system, the combustor is usually in the form of a conventional, water-cooled enclosure formed by a welded tube and membrane construction so that water and steam can be circulated through the wall tubes to remove heat from the combustor. However, in order to achieve optimum fuel burn-up and emissions control, additional heat must be removed from the system. This heat removal has been achieved in the past by several techniques. For example, the height of the furnace has been increased or heat exchange surfaces have been provided in the upper furnace to cool the entrained solids before they are removed from the furnace, separated from the flue gases and returned to the furnace. However these techniques are expensive and the heat exchange surfaces are wear-prone. Other techniques involve the deployment of an additional, separate heat exchanger between the outlet of the separator and the recycle inlet of the furnace. Although heat can be removed from the recycled solids in this separate heat exchanger before the solids are passed back into the furnace, these type of arrangements are not without problems. For example, it is difficult to precisely control the heat transfer rates in the recycle heat exchanger. Also, during startup or load low conditions, it is often difficult to bypass the heat exchange surfaces in the recycle heat exchanger. Further, in situations when the recycle heat exchanger is formed integrally with the furnace, there is often an increase in boiler plan area which adds to the cost of the system. WO-A-90/05020 discloses a method of operating a fluidized bed combustion system. The flue gases comprise the fluidising air and entrained material, which is then separated. The separated material is provided to a heat exchanger which includes a plurality of sections. A cooling medium is passed through at least one of the sections to remove heat from the portion of the separated material passing through that section. Another portion of the separated material is not cooled, and thereby maintains a substantially constant temperature. According to a first aspect of the present invention, a fluidised bed combustion system comprises a furnace, means for establishing a fluidized bed containing particulate material including fuel in the furnace whereby flue gases produced as a result of combustion of the fuel entrain a portion of the particles, means for separating entrained particles from the flue gases, a heat exchanger disposed adjacent the furnace for receiving the separated particles, characterised in that the heat exchanger comprising a first series of compartments including a first inlet compartment for receiving the separated particles, a first additional compartment disposed adjacent the first inlet compartment and a first outlet compartment disposed adjacent the first additional compartment, a second series of compartments extending underneath the first series of compartments and including a second inlet compartment, a second additional compartment disposed to the side of the second inlet compartment and a second outlet compartment disposed to the side of the second inlet compartment, first heat exchange means associated with the first additional compartment and a second heat exchange means associated with the second additional compartment, first passage means connecting the first inlet compartment with the first additional compartment to enable the separated particles to pass to the first additional compartment to exchange heat with the first heat exchange means, second passage means connecting the first additional compartment with the first outlet compartment to enable the separated particles to pass from the first additional compartment to the first outlet compartment, third passage means connecting the first outlet compartment with the second inlet compartment to permit the separated particles to pass from the first outlet compartment to the second inlet compartment, fourth passage means connecting the second inlet compartment to the second additional compartment to enable the separated particles to pass from the second inlet compartment to the second additional compartment to exchange heat with the second heat exchange means, and fifth passage means connecting the second additional compartment to the second outlet compartment to enable the separated particles to pass from the second additional compartment to the second outlet compartment, and sixth passage means connecting the second outlet compartment to the furnace to permit the separated particles to pass from the second outlet compartment to the furnace. According to a second aspect of the present invention, a method of operating a fluidized bed combustion system comprises the steps as claimed in claim 5. The present invention gives a system which allows the amount of heat removed from the recycled solids to be precisely controlled. The recycled heat exchanger can be bypassed during start-up and low load conditions. In a preferred embodiment of the invention, a pressurised system using an outer pressure vessel is used to achieve the benefits of the present invention without requiring an increase in the size of the enclosing pressure vessel. The above objects and summary, as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the presently preferred, but nevertheless illustrative, embodiments of the present invention when taken in conjunction with the accompanying drawings wherein: Fig. 1 if a schematic representation depicting the combustion system of the present invention; Fig. 2 is a cross-sectional view taken along the line 2-2 of Fig. 1; Figs. 3 and 4 are cross-sectional views taken along the lines 3-3 and 4-4, respectively, of Fig. 2; and Fig. 5 is a cross-sectional view taken along the line 5-5 of Fig. 3. The drawings depict the fluidized bed combustion system of the present invention used for the generation of steam and including an upright pressure vessel 10 in which is disposed a water-cooled furnace enclosure, referred to in general by the reference numeral 12. The furnace enclosure 12 includes a front wall 14, a rear wall 15 and two sidewalls 16a and 16b (Fig. 3). As shown in Fig. 1, the lower portions 14a and 14b of the walls 14 and 15, respectively, converge inwardly for reasons to be explained. The upper portion of the enclosure 12 is enclosed by a roof 18a and a floor 18b defines the lower boundary of the enclosure. An air inlet duct 19 connects to the lower portion of the pressure vessel 10 for introducing pressurized air from an external source, such as a compressor driven by a gas turbine or the like. A plurality of air distributor nozzles 20 are mounted in corresponding openings formed in a horizontal plate 22 extending across the lower portion of the enclosure 12. The plate 22 is spaced from the floor 18 to define an air plenum 24 which is adapted to receive air contained in the vessel 10 and selectively distribute the air through the plate 22 and to portions of the enclosure 12, as will be described. It is understood that a fuel feeder system (not shown) is provided for introducing particulate material including fuel into the enclosure. The particulate material is fluidized by the air from the plenum 24 as it passes upwardly through the plate 22. The air promotes combustion of the fuel and the flue gases thus formed rise in the enclosure 12 by forced convection and entrain a portion of the solids to form a column of decreasing solids density in the enclosure to a given elevation, above which the density remains substantially constant. A cyclone separator 26 extends adjacent the enclosure 12 inside the vessel 10 and is connected to the enclosure by a duct 28 extending from an outlet provided in the rear wall 15 of the enclosure to an inlet provided through the separator wall. The separator 26 receives the flue gases and the entrained particulate material from the enclosure in a manner to be described and operates in a conventional manner to disengage the particulate material from the flue gases due to the centrifugal forces created in the separator. The separated flue gases, which are substantially free of solids enter a duct 30 projecting upwardly through the upper portion of the separator 26 and the vessel 10 for passage into a hot gas clean-up and a heat recovery section (not shown) for further treatment. The lower portion of the separator includes a hopper 26a which is connected to a conventional "J valve" 32 by a dip leg 34. A heat exchanger 38 is located adjacent the enclosure 12 and within the vessel 10, and is connected to the outlet of the J valve 32 by a duct 39. The heat exchanger 38 includes an enclosure 40 formed by a front wall 42, a rear wall 43, two sidewalls 44a and 44b (Fig.2), a roof 46a and a floor 46b. As shown in Fig. 1, the front wall 42 forms a lower extension of that portion of the rear enclosure wall 15 that extends just above the converging portion 15a. As shown in Figs 1 and 5, the plate 22 extends to the wall 42 to form a solids return channel 50 defined above the latter extension and between the converging portion 15a of the enclosure rear wall 15 and the front wall 42 of the enclosure 40. Two horizontally-extending, vertically-spaced, plates 54 and 56 (Figs. 1 and 2) are disposed in the enclosure 40 and receive two groups of air distributor nozzles 58a and 58b, respectively. A third horizontally-extending plate 60 is disposed in the enclosure 40 and extends between the plates 54 and 56 to generally divide the enclosure into an upper portion and a lower portion. As shown in Fig. 2, a plenum section 61 is defined between the plates 54 and 60 for supplying air to the nozzles 58a, and a plenum section 62 is defined between the plate 56 and the floor 46b for supplying air to the nozzles 58b. As shown in Figs. 2 and 3, a pair of spaced, parallel vertical plates 64 and 66 extend between the rear wall 43 of the enclosure 40 and the wall 15 (and the wall 42) in a spaced parallel relationship to the sidewalls 44a and 44b. The plates 64 and 66 thus divide the upper portion of enclosure 40 into two heat exchange sections 68 and 70, respectively extending to the sides of a inlet/bypass section 72 (Figs. 2 and 3). The plates 64 and 66 also divide the lower portion of the enclosure 40 into two heat exchange sections 74 and 76 respectively extending to the sides of a bypass section 78 (Figs. 2 and 4). As shown in Fig. 2, three openings 64a, 64b, and 64c are formed in the plate 64 and three openings 66a, 66b and 66c are formed in the plate 66 to permit the flow of solids between the upper sections 68, 70, and 72, as well as between the lower sections 74, 76 and 78 as will be described. The plates 64 and 66 also divide the plenum 61 into three sections respectively extending below the sections 74, 76, and 78 and, in addition, divide the plenum 62 into three sections respectively extending below the sections 74, 76, and 78. It is understood that pressurized air from the vessel 10 is selectively introduced into the aforementioned plenum sections at varying velocities in a conventional manner, for reasons to be described. As shown in Fig. 3, a vertical partition 80 extends from the horizontal plate 60 (Fig. 2) to the roof 46a and divides the inlet/bypass compartment 72 into two sections 72a and 72b. Although not shown in the drawings, it is understood that openings are respectively formed in the plates 54 and 60 that are aligned with the compartment section 72b to connect the latter section with the section 78 for reasons that will be described. Four bundles 82a, 82b, 82c, and 82d of heat exchange tubes are disposed in the heat exchange sections 68, 70, 74, and 76, respectively and are connected in a conventional manner to a fluid flow circuit (not shown) to circulate cooling fluid through the tubes to remove heat from the solids in the sections, in a conventional manner. With reference to Fig. 5, an opening 80a is provided in the partition 80, an opening 42a is provided in the wall 42 and an opening 15b is provided in the wall 15. The opening 80a is in the upper portion of the enclosure 40 and the opening 42a is in the lower portion of the enclosure at a higher level than the opening 15b, for reasons to be described. Also, an optional opening 15c can be provided in the upper portion of the wall 15a for venting the fluidizing air to the furnace at a higher level than the level of the opening 15b, as will be described. It is understood that all of the foregoing walls, plates and partitions are formed of a conventional welded membrane and tube construction shown and described in U.S. Patent No. 5,069,171 assigned to the assignee of the present application, the disclosure of which is incorporated by reference. It is also understood that a steam drum is provided adjacent the vessel and a plurality of headers, downcomers and the like are provided to establish a fluid flow circuit including the foregoing tubed walls. Thus, water is passed in a predetermined sequence through this flow circuitry to convert the water to steam by the heat generated by the combustion of the fuel solids in the furnace enclosure 12. In operation, the solids are introduced into the furnace enclosure 12 in any conventional manner where they accumulate on the plate 20. Air is introduced into the pressure vessel 10 and passes into the plenum 24 and through the plate 20 before being discharged by the nozzles 22 into the solids on the plate 20, with the air being at sufficient velocity and quantity to fluidize the solids. A lightoff burner (not shown), or the like, is provided to ignite the fuel material in the solids, and thereafter the fuel portions of the solids is self-combusted by the heat in the furnace enclosure 12. The flue gases pass upwardly through the furnace enclosure 12 and entrain, or elutriate, a quantity of the solids. The quantity of the air introduced, via the plenum 24, through the nozzles 22 and into the interior of the enclosure 12 is established in accordance with the size of the solids so that a circulating fluidized bed is formed, i.e., the solids are fluidized to an extent that substantial entrainment or elutriation thereof is achieved. Thus, the flue gases passing into the upper portion of the furnace enclosure are substantially saturated with the solids and the arrangement is such that the density of the bed is relatively high in the lower portion of the furnace enclosure 12, decreases with height throughout the length of this enclosure and is substantially constant and relatively low in the upper portion of the enclosure. The saturated flue gases in the upper portion of the furnace enclosure 12 exit into the duct 28 and pass into the cyclone separator 26. The solids are separated from the flue gases in the separator 26 in a convention manner, and the clean gases exit the separator and the vessel 10 via the duct 30 for passage to hot-gas clean-up and heat recovery apparatus (not shown) for further treatment as described in the above-cited patent. The separated solids in the separator 26 fall into the hopper 26a and exit the latter, via the dip leg 34 before passing through the J-valve 32 and, via the duct 39, into the enclosure 40 of the heat exchanger 38. The separated solids from the duct 39 enter the inlet/bypass compartment section 72a of the enclosure 40 as shown by the flow arrow A in Fig 3. In normal operation, air is introduced at a relatively high rate into the sections of the plenum 61 extending below the heat exchange sections 68 and 70 while air at a relatively low rate is introduced into the section of the plenum extending below the section 72a. As a result, the solids from the section 72a flow through the openings 64b and 66b (Fig. 2) in the partitions 64 and 66, respectively, and into the sections 68 and 70, as shown by the flow arrows B1 and B2 in Figs 2 and 3. The solids flow under and up through the heat exchange tube bundles 82a and 82b in the sections 68 and 70, as shown by the arrows C1 and C2 in Figs. 2 and 3. The solids thus build up in the sections 68 and 70 and spill through the openings 64a and 66a in the partitions 64 and 66 respectively, into the inlet/bypass compartment section 72b, as shown by the flow arrows D1 and D2 in Figs. 2 and 3. The solids then fall, by gravity through the openings in the plates 54 and 60, respectively, and into the lower section 78, as shown by the flow arrows E in Fig. 2. Air at a relatively high rate is introduced into the sections of the lower plenum 62 extending below the lower heat exchange sections 74 and 76 while air at a relatively low rate is introduced into the section of the plenum 62 extending below the section 78. This promotes the flow of the solids from the section 78, through the openings 64c and 66c in the partitions 64 and 66, and into the heat exchange sections 74 and 76, as shown by the flow arrows F1 and F2, respectively, in Figs. 2 and 4. The solids thus flow up through the tube bundles 82c and 82d in the sections 74 and 76, respectively, to transfer heat to the fluid flowing through the latter tubes. As shown in Figs. 4 and 5 by the flow arrows H1 and H2, the solids exit the sections 74 and 76 via openings 42a in the wall 42 and pass into the return compartment 50 where they mix before passing, via openings 15b in the lower portion of the wall 15, back into the furnace enclosure 12. The fluidizing air from all of the heat exchange sections 68, 70, 74 and 76 also flows into the furnace enclosure 12 through the openings 42a and 15b. Feed water is introduced into, and circulated through, the flow circuit described above including the water wall tubes and the steam drum described above in a predetermined sequence to convert the water to steam and to superheat and reheat (if applicable) the steam. During low loads, emergency shutdown conditions or start-up a bypass operation is possible by terminating all air flow into the sections of the plenums 61 and 62 extending below the sections 68, 70, 74 and 76 and thus allowing the solids to build up in the inlet section 72a until their level reaches that of the weir port 80a in the partition 80, as shown in Fig. 5. Thus, the solids spill over into the section 72b of the inlet/bypass compartment 72 and fall down through the openings in the plates 54 and 60 and into the section 78. The solids thus build up in the section 78 until their level reaches that of the weir port 42a in the wall 42 and enter the channel 50 before passing, via the opening 15b, back to the enclosure 12 at substantially the same temperature as when the solids entered the heat exchanger 38. By selective control of the respective velocities of the air discharging into the heat exchange sections 68, 70, 74 and 76, the respective heat exchange with the fluid passing through the walls and partitions of the enclosure 40 can be precisely regulated and varied as needed. For example, in the bypass operation described above, instead of completely defluidizing the sections 68, 70, 74 and 76 and thus allowing all of the solids to bypass through the sections 72b and 78 as described above, the sections 68, 70, 72a, 74 and 76 can be partially fluidized so that only a portion of the solids bypass directly through the sections 72b and 78, and thus pass directly into the enclosure. The remaining portion of the solids would thus pass in the standard manner through one or more of the sections 68, 70, 74 and 76 to remove heat therefrom, as described above, resulting in less heat removal from the solids when compared to the standard operation described above in which all of the solids pass through the sections 68, 70, 74 and 76. Also, the fluidization could be varied so that the solids bypass one of the sections 68 and 70 as described in the bypass operation, above, and pass through the other as well as bypass one of the sections 74 and 76 and pass through the other. Moreover, during the standard operation, the fluidization, and the resulting heat removal, can be varied between the sections 68 and 70 and between the section 74 and 76, especially if these sections perform different functions (such as superheat, reheat, and the like). For example, the respective fluidization can be controlled so that 70% of the solids pass through the section 68 and 30% pass through the section 70 and so that 60% of the solids pass through the section 74 and 40% pass through the section 76, with these percentages being variable in accordance with particular design requirements. In addition to providing the flexibility of operation discussed above, the present invention enjoys several other advantages. For example, a significant amount of heat can be removed from the solids circulating through the recycle heat exchanger 38 to maintain the desired temperature within the furnace for optimum fuel burn-up and emissions control. Also, the aforementioned selective fluidization, including the bypass modes, is done utilizing non-mechanical techniques. Moreover, the use of a pressurized system enables the separator to be relatively small, thus making room for the stacked heat exchange sections in the enclosure 40 to minimize the pressure vessel diameter. It is understood that several variations can be made in the foregoing without departing from the scope of the invention. For example, the optional opening 15c in the wall 15a permits the fluidizing air from all of the heat exchange sections 68, 70, 74 and 76 to be vented into the furnace enclosure instead of through the opening 15b with the solids. This venting of the air through the opening 15c would enable the air to enter the furnace at a higher level and function as secondary air. The solids would still be returned to the enclosure 12 through the opening 15b but would be allowed to build up to a sufficient level to balance the pressure difference between the openings 15b and 15c. Also, the number and location of the various other openings in the walls of the enclosures 12 and 40 can be varied, and more than one separator can be utilized.

Claims: A fluidized bed combustion system comprising a furnace (12), means for establishing a fluidized bed containing particulate material including fuel in the furnace (12) whereby flue gases produced as a result of combustion of the fuel entrain a portion of the particles, means (26) for separating entrained particles from the flue gases, a heat exchanger (38) disposed adjacent the furnace (12) for receiving the separated particles, characterised in that the heat exchanger (38) comprising a first series of compartments (68, 70, 72a) including a first inlet compartment (72a) for receiving the separated particles, a first additional compartment (68, 70) disposed adjacent the first inlet compartment (72a) and a first outlet compartment (72b) disposed adjacent the first additional compartment (68, 70), a second series of compartments (74, 76, 78) extending underneath the first series of compartments (68, 70, 72) and including a second inlet compartment (78), a second additional compartment (74, 76) disposed to the side of the second inlet compartment (78) and a second outlet compartment (50) disposed to the side of the second inlet compartment (78), first heat exchange means (82a, 82b) associated with the first additional compartment (68, 70) and a second heat exchange means (82c, 82d) associated with the second additional compartment (74, 76), first passage means (64b) connecting the first inlet compartment (72a) with the first additional compartment (68; 70) to enable the separated particles to pass to the first additional compartment (68, 70) to exchange heat with the first heat exchange means (82a, 82b), second passage means (64a) connecting the first additional compartment (68, 70) with the first outlet compartment (72b) to enable the separated particles to pass from the first additional compartment (68, 70) to the first outlet compartment (72b), third passage means connecting the first outlet compartment (72b) with the second inlet compartment (78) to permit the separated particles to pass from the first outlet compartment (72b) to the second inlet compartment (78), fourth passage means (64c) connecting the second inlet compartment (78) to the second additional compartment (74, 76) to enable the separated particles to pass from the second inlet compartment (78) to the second additional compartment (74, 76) to exchange heat with the second heat exchange means (82c, 82d), and fifth passage means (42) connecting the second additional compartment (74, 76) to the second outlet compartment (50) to enable the separated particles to pass from the second additional compartment (74, 76) to the second outlet compartment (50), and sixth passage means (15b) connecting the second outlet compartment (50) to the furnace (12) to permit the separated particles to pass from the second outlet compartment (50) to the furnace (12). The system of claim 1 further comprising an additional compartment (68, 70) in the first series of compartments and disposed adjacent the first inlet compartment (72a), heat exchange means (82a, 82b) disposed in the additional compartment (68, 70), passage means (64b) connecting the first inlet compartment (72a) to the additional compartment (68, 70) to enable a portion of the separated particles to pass from the first inlet compartment (72a) to the said additional compartment (68, 70) to exchange heat with the latter heat exchange means (82a, 82b), passage means (64a) connecting the additional compartment (68, 70) to the first outlet compartment (72b) to permit the portion of the separated particles to pass from the additional compartment (68, 70) to the first outlet compartment (72b). The system of claim 1 or 2, further comprising an additional compartment (74, 76) in second series of compartments and disposed adjacent the second inlet compartment (78), heat exchange means (82c, 82d) disposed in the additional compartment (74, 76), passage means (64c) connecting the second inlet compartment (78) to the additional compartment (74, 76) to enable a portion of the separated particles to pass from the second inlet compartment (78) to the additional compartment (74, 76) to exchange heat with the heat exchange means (82c, 82d), passage means (42) connecting the additional compartment (74, 76) to the second outlet compartment (50) to permit the portion of the separated particles to pass from the additional compartment (74,76) to the second outlet compartment (50). The system of any one of the preceding claims, further comprising passage means (80a) directly connecting the first inlet compartment (72a) to the first outlet compartment (72b) to enable the separated particles to pass directly from the first inlet compartment (72a) to the first outlet compartment (72b) in response to the height of the separated particles in the first inlet compartment (72a) exceeding a predetermined height. A method of operating a fluidized bed combustion system comprises the steps of supporting a bed of particulate material including fuel in a vessel (14), passing air through the bed to fluidize the material and promote the combustion of the fuel, whereby flue gases consisting of air and the products of combustion entrain a portion of the material, separating the entrained material from the gases, passing the separated material to a heat exchanger (38), passing the separated material to an inlet compartment (72a) formed in the heat exchanger and passing a first portion of the separated material from the compartment (72a) through at least one section (68, 70) formed in the heat exchanger, passing a cooling medium through said at least one of the sections (68, 70) to remove heat from the first portion of material while passing a second portion of the separated material from the compartment (72a) through a by-pass section (72b) formed in the heat exchanger to maintain a substantially constant temperature of the second portion of the separated material, passing the separated material to a second inlet/by-pass compartment (78), passing a portion of the separated material from the said second inlet/by-pass compartment (78) to at least one additional section (74, 76) formed in the heat exchanger and extending below the at least one section (68, 70), passing a cooling medium through said at least one additional section to remove heat from the latter material while passing a portion of the separated material through a second by-pass compartment (78) to maintain a substantially constant temperature of said portion of the separated material, and returning the portions of separated material from at least one of the additional sections (74, 76) back to the vessel (14), and varying the amount of material passed though at least one of the sections (68, 70) and at least one of the additional sections (74, 76) to vary the temperature of the material returned to the vessel (14) . A method of Claim 5, wherein each of the steps of passing comprises the step of selectively fluidizing the material in the respective sections (68,70,74,76). The method of Claim 5 or 6, further comprising the step of mixing the portions of separated material after the steps of passing and before the step of returning. The method of Claim 7, wherein the cooling medium and the first mentioned portion of the separated material passes through two sections (68,70; 74,76), and further comprising the steps of selectively fluidizing the separated material in each of the said two sections (68,70; 74,76) so that different quantities of heat are respectively removed from the separated material in each of the said sections (68,70; 74,76). A method of Claim 6, further comprising the step of controlling said fluidization to control the relative quantities of separated material passing through the respective sections.

Inventors: GOIDICH STEPHEN JOHN, GOIDICH, STEPHEN JOHN
Applicants: FOSTER WHEELER ENERGY CORP, FOSTER WHEELER ENERGY CORPORATION
Application year: 1995
Main classification: F23C10
IPC codes: F22B31, F22B1, F23C10