Fluidized bed combustion system and method having multiple furnace and recycle sections

Abstract: A fluidized bed combustion system (10) and method in which a plurality of enclosures (12a,12b), each having a furnace section (30a,30b) and integral recycle section (32a,32b) are joined using common walls (60). Openings (64,66) are provided in lower portions of the common walls for permitting the fluidized bed material to flow between adjacent or opposing furnace sections and between adjacent recycle sections. Openings (62) are also provided in upper portions of the common walls for equalizing the gas pressure between the adjacent or opposing furnace sections.

Description: This invention relates to a combustion system and method, and, more particularly, to such a system and method in which a plurality of adjacent and opposing enclosures including furnace sections and recycle sections are provided for receiving fluidized beds. Fluidized bed combustion systems are well known and include a furnace section in which 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 of the fuel at a relatively low-temperature. These types of combustion 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 and fuel flexibility, high sulphur adsorption and low nitrogen oxides emissions. A typical fluidized bed utilized in the furnace section of these type systems is commonly referred to as a "bubbling" fluidized bed in which the bed of particulate material has a relatively high density and a well-defined, or discrete, upper surface. Other types of systems utilize a "circulating" fluidized bed in which the fluidized bed density is below that of a typical bubbling fluidized bed, the fluidizing air velocity is equal to or greater than that of a bubbling bed, and the flue gases passing through the bed entrain a substantial amount of the fine particulate solids to the extent that they are substantially saturated therewith. Circulating fluidized beds are characterized by relatively high internal and external solids recycling which makes them insensitive to fuel heat release patterns, thus minimizing temperature variations and, therefore, stabilizing the sulfur emissions at a low level. The external 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 sulphur adsorbent and fuel residence time reduces the adsorbent and fuel consumption. U.S. Patent No. 5,040,492 and No. 5,054,436 disclose systems in which the separated solids are recycled back to the furnace. U.S. Patent No. 4,609,623 and No. 4,809,625 disclose a fluidized bed reactor in which a dense, or bubbling, bed is maintained in the lower portion of the furnace, while the bed is otherwise operated as a circulating bed. This hybrid arrangement results in several advantages not the least significant of which is the ability to utilize fuel and adsorbent over a relatively large particle size range. In designing fluidized bed combustion systems of the above types, increases in furnace capacity from a given design are usually achieved by increasing the height of the furnace walls. However, this is expensive and there are certain limits to the height of the walls. It has therefore been suggested that the size of the furnace, and therefore its capacity, be increased by increasing the size of the furnace in "plan view" i.e., increasing the width and/or the depth of the furnace. However, this usually requires a common wall, or the like, to be placed in the furnace section to divide the area into two or more fluidized beds which requires separate operating controls, etc. which is expensive. Also, the common wall is subjected to lateral loading, especially when the multiple beds operate differently or if one bed is rendered inoperable due to equipment failure. This lateral loading can cause damage to the wall and attendant reduction in operation and efficiency. Increases in furnace capacity also lead to the use of larger cyclone separators which permit increasing amounts of fine, unburnt fuel particles to escape with the separated flue gases. This escape of unburnt fuel particles reduces fuel efficiency, thereby increasing fuel consumption. Our EP-A-506 342 describes a fluidised bed combustion system and method in which there are a plurality of furnace sections having a common wall. Openings are provided through a lower portion of this to permit fluidized bed material to flow between the furnace sections and through an upper portion of this to equalize gas pressures. According to the invention in one aspect there is provided a fluidized bed combustion system comprising a first enclosure having a first furnace section, a first recycle section adjoining the first furnace section, means for forming a fluidized bed of particulate material including fuel in the first furnace section, means for forming a fluidized bed of particulate material in the first recycle section, means for passing particulate material from the first recycle section to the first furnace section, a second enclosure having a second furnace section, means for forming a fluidized bed of particulate material including fuel in the second furnace section, the first and second enclosures being disposed adjacently and sharing a common wall which divides the first furnace section from the second furnace section, the first furnace section being disposed adjacent the second furnace section, the common wall having at least one aperture extending through an upper portion of the common wall and registering with the first and second furnace sections for permitting gases to pass between the first and second furnace sections to equalize pressure in the furnace sections, and the common wall having at least one aperture extending through a lower portion of the common wall and registering with the first and second furnace sections for permitting particulate material to pass between the first and second furnace sections, characterised in that a second recycle section adjoins the second furnace section, means are provided for forming a fluidized bed of particulate material in the second recycle section, the common wall divides the first recycle section from the second recycle section, the first recycle section is disposed adjacent the second recycle section and the common wall has at least one aperture extending through a lower portion of the common wall and registering with the first and second recycle sections for permitting particulate material to pass between the first and second recycle sections. According to the invention in another aspect there is provided a method of operating such a fluidized bed combustion system comprising fluidizing particulate material in the furnace sections and the recycle sections, equalizing the heights of the material in adjacent furnace sections, equalizing the pressure in the adjacent furnace sections, and equalizing the heights of the material in the recycle sections. In accordance with the present invention it is possible for the separate furnace sections to be operated without the need for separate controls. Equally the separate integral recycle sections may be operated without the need for separate controls. Because the common walls are vented to equalize the pressure across the walls, this minimizes or eliminates lateral loading and enables the fluidized beds in each furnace section to maintain substantially the same height. Also the common walls are vented to enable the fluidized beds in the integral recycle sections to maintain substantially the same height. Thus one maintains substantially identical dense bed heights in the furnace sections and substantially identical dense bed heights in the recycle sections. In a fluidized bed combustion system and method according to the invention fuel efficiencies are increased by reducing losses of fine, unburnt fuel particles. The invention will be more fully described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation depicting the system of the present invention; Fig. 2 is an enlarged cross-sectional view taken along the line 2-2 of Fig. 1; Fig. 3 is a reduced cross-sectional view taken along the line 3-3 of Fig. 2; Fig. 4 is a cross-sectional view taken along the line 4-4 of Fig. 2; and Figs. 5 and 6 are views similar to Fig. 2 but depicting alternate embodiments of the system of the present invention. Referring to Figs. 1 and 2 of the drawings, the fluidized bed combustion system of the present invention is referred to in general by the reference numeral 10. The system 10 includes two upright water-cooled enclosures 12a and 12b which are substantially identical. For the convenience of presentation, only enclosure 12a will be described in detail. The enclosure 12a has a front wall 14a, a rear wall 16a and two sidewalls, one of which is referred to by the reference numeral 17 and the other of which is formed by a common wall extending between the enclosures 12a and 12b, which will be discussed in detail later. The upper portion of the enclosure 12a is closed by a roof 18a and the lower portion includes a floor 20a. A distribution plate or grate 22a extends across a lower portion of the enclosure 12a. The plate 22a is spaced from the floor 20a to define a plenum area between the floor 20a and the plate 22a which is adapted to receive an oxygen-containing gas such as air from an external source (not shown). A partition 24a is disposed in the enclosure 12a and extends between the side walls, including side wall 17a. The partition 24a includes a lower, substantially vertical portion 24a' which extends upwardly from the floor 20a, through the distribution plate 22a, and into the enclosure 12a. The partition portion 24a' is disposed parallel to the front and rear walls 14a and 16a. The partition 24a also includes an upper portion 24a'' which angles upwardly and rearwardly from the lower portion 24a' of the partition to the rear wall 16a. The partition 24a thereby divides the plenum area into plenum chambers 26a and 28a and further divides the enclosure 12a into a furnace section 30a disposed above plenum chamber 26a and a recycle section 32a disposed above plenum chamber 28a. At least one opening 34a is provided in a lower portion of the vertical partition portion 24a' for reasons to be described. A plurality of air distributor nozzles 36a are mounted in corresponding openings formed in the portion of the plate 22a extending under the furnace section 30a for passing air through the plate 22a, for reasons to be described. A feeder system 38a is provided adjacent the front wall 14a-for introducing particulate material into the furnace section 30a. The particulate material includes fuel and may also include other components including an adsorbent, such as limestone. The particulate material is fluidized in the furnace section 30a by the air from the plenum 26a as it passes upwardly through the plate 22a. This air promotes the combustion of the fuel, generating combustion gases which combine with the air to form flue gases which rise in the furnace section 30a by convection and which entrain a portion of the particulate material as will be described. A cyclone separator 40a extends adjacent the enclosure 12a. As shown in Fig.1, a duct 42a extends from an outlet opening provided in the rear wall 16a of the enclosure 12a to an inlet opening provided through the wall of the separator 40a. The separator 40a receives flue gases and entrained particulate material from the furnace section 30a in a manner to be described and operates in a conventional manner to disengage the particulate material from the flue gases. The separated flue gases in the separator, which are substantially free of solids, pass, via a duct 44a located immediately above the separator, into a heat recovery section 48, via an inlet provided through a wall thereof. The heat recovery section 48 includes a plurality of heat exchange surfaces 50 which may serve as heaters, reheaters, superheaters, and economizers, all of which are formed by a plurality of heat exchange tubes extending in the path of the gases as they pass through the heat recovery section 48. After passing across the heat exchange surfaces 50, the gases exit the heat recovery section 48 through an outlet 52. It is preferred that a number of separators associated with additional enclosures be connected to a single heat recovery section 48. It is understood that a number of different embodiments of heat recovery sections may be used. For a more detailed discussion of a preferred embodiment of a heat recovery section, see U.S. Patent No. 5,040,492 and No. 5,054,436. The disclosure of these references is incorporated herein by reference. As shown in Fig. 1, the lower portion of the separator 40a is conically shaped and is connected to a dip leg 54a which, in turn, is connected to a J-valve 56a. A conduit 58a connects the outlet of the J-valve 56a to the recycle section 32a to transfer the separated particulate material from the separator 40a to the recycle section 32a. The J-valve 56a functions in a conventional manner to prevent back-flow of solids from the furnace section 30a and the recycle section 32a to the separator 40a. It is understood that a substantially identical separator, dip leg, J-valve and inlet conduit are associated with each enclosure and all function in a substantially identical fashion. It is also understood that other types of separators may be used, and the separators may pass the separated particulate material to the recycle sections in any conventional manner. As shown in Fig. 2, the enclosures 12a and 12b are disposed adjacent one another and share a common wall 60 which extends from front walls 14a and 14b to rear walls 16a and 16b and which extends from the enclosure floors 20a and 20b to the enclosure roofs, including roof 18a. A furnace section 30b is formed in the enclosure 12b and is disposed adjacent the furnace section 30a, and a recycle section 32b located adjacent the furnace section 30b and is disposed adjacent the recycle section 32a. As shown in Fig. 3, a plurality of openings 62 are provided in the upper portion of the common wall 60 and a plurality of openings 64 and 66 are provided in the lower portion of the common wall 60, for reasons to be described. Figs. 2 and 4 depict the adjacent recycle sections 32a and 32b in greater detail. For convenience of presentation, the recycle section 32a will be described in detail, it being understood that the description also applies to the recycle section 32b, as well as to additional recycle sections such as those in Figs. 5 and 6. A partition 68a is disposed in the recycle section 32a and extends between the side wall 17a and the common wall 60 and parallel to the vertical partition portion 24a'. The partition 68a also extends from the distribution plate 22a to the angled portion 24a'' of the partition 24a to define a channel 70a between the partitions 24a and 68a. A plurality of openings are provided in an upper portion of the partition 68a for reasons to be described. The front wall 14a, the rear wall 16a, the sidewalls, the roof 18a, the partitions 24a and 68a, and the walls of the separator 40a and heat recovery section 48 are all formed by a plurality of vertically-extending, spaced, parallel tubes 72 with adjacent tubes being connected by continuous fins 74 along their lengths to form airtight structures. As shown schematically in Fig. 1, a portion of the tubes 72 forming the rear wall 16a are bent out of the plane of the latter wall, towards the partition section 24a'' to form a partition 76a, and back to the rear wall 16a to form a partition 78a. The partitions 76a and 78a thus help support the partition section 24a''. A pair of vertically-spaced secondary air inlets 80a and 82a register with openings in the rear wall 16a for introducing a secondary, oxygen-containing gas such as air into the-enclosure 12a at two levels, one between the points of intersection of the partitions 76a and 78a with the rear wall 16a and another above the point of intersection of the partition 78a with the rear wall 16a. Although not clear from the drawings, it is understood that the tubes 72 forming the partition 76a have no fins so that secondary air from the inlet 80a can pass therethrough, while the tubes 72 forming the partition 78a are finned to prevent the passage of air therethrough and thus form a roof for the recycle section 32a. As shown in Fig. 1, four rows of nozzles 84a extend through the partition portion 24a'', with two rows located above the partition 78a and two rows located below the partition 78a. As a result, secondary air from the inlet 80a is directed through the lower two rows of nozzles 84a, and secondary air from the inlet 82a is directed through the upper two rows of nozzles 84a. As best shown in Figs. 2 and 4, partitions 88a and 90a are disposed within the recycle section 32a and extend between the rear wall 16a and the partition 68a, substantially parallel to the side wall 17a and the common wall 60. The partitions 88a and 90a extend upwardly from the distribution plate 22a to a desired height within the recycle section 32a. Referring to Fig. 4, the partitions 88a and 90a divide the lower portion of the recycle section 32a into three compartments 92a, 94a and 96a. As shown in Fig. 2, the inlet conduit 58a registers with an opening in the rear wall 16a communicating with the compartment 94a. Within the recycle section 32a, a plurality of rows of nozzles 98a extend through the perforations in the plate 22a above plenum chamber 28a. Each nozzle 98a consists of a central portion extending through the perforation and a horizontal discharge portion registering with the vertical portion. The nozzles 98a in the compartments 92a and 96a are disposed in parallel rows with their discharge portions facing away from the compartment 94a. Two parallel rows of nozzles 98a are provided in the compartment 94a with their discharge portions facing towards the partitions 88a and 90a, respectively. A single row of nozzles 100a is also located in the compartment 94a and extends between the two rows of nozzles 98a. The nozzles 100a are taller than the nozzles 98a for reasons to be explained. A manifold 102a is located in the plenum 28a and is connected to the nozzles 100a for supplying air to the nozzles 100a independently of the flow of air from the plenum 28a, through the plate 22 and to the nozzles 98a. As shown in Fig. 4, a bank of heat exchange tubes 104a are disposed in each of the compartments 92a and 96a. The tubes 104a are bent into a serpentine pattern and extend between headers for circulating fluid through the tubes 104a in a conventional manner. Three horizontally-spaced, elongated slots or openings 106a, 108a and 110a (Fig. 4) are provided through a portion of the partition 68a defining the compartments 92a, 94a and 96a, respectively. The opening 108a extends at an elevation higher than the openings 106a and 110a for reasons to be described. The openings are shown schematically in Fig. 4 for the convenience of presentation, it being understood that they actually are formed by cutting away the fins 74, or bending the tubes 72 out of the plane of the partition 68a. A plurality of openings 112a and 114a are formed in the lower portions of the partitions 88a and 90a, respectively, to communicate the chambers 92a and 96a with the chamber 94a. As shown in Fig. 2, the common wall 60 extends to the rear wall 16a to separate the recycle sections 32a and 32b and the plurality of openings 66 are provided in the extended portion of the common wall 60, for reasons to be described. It is understood that the particular design of recycle sections 32a and 32b is shown as an example only and that a number of different embodiments of recycle sections may be used. For example, U.S. Patent No. 5,054,436 and No. 5,040,492 disclose a number of different recycle section configurations that may be employed with the present invention. The disclosure of these references is incorporated herein by reference. It is understood that the above description of the enclosure 12a is equally applicable to the enclosure 12b and identical structure in the latter embodiment is indicated by the same reference numerals but with a "b" suffix. Therefore, the enclosure 12b will not be described in detail. A steam drum 116 (Fig. 1) is located above the system 10 and, although not shown in the drawings, it is understood that a plurality of headers are disposed at the ends of the various water-tube walls described above. As shown in general by the reference numeral 118, a plurality of downcomers, pipes, etc. are utilized to establish a flow circuit for circulating a cooling fluid such as water or steam or a water and steam mixture through these headers, the steam drum 116, and the various tubed walls, partitions, and heat exchange surfaces, with connecting feeders, risers, and headers being provided as necessary. Thus, water is passed in a predetermined sequence through this flow circuitry to convert the water to steam and to heat the steam by the heat generated by combustion of the particulate fuel material. For ease of presentation, the operation of the present system will be described with reference to enclosure 12a. In operation, particulate material including fuel and sorbent material are introduced into the furnace section 30a through the feeder system 38a. Alternately, sorbent may also be introduced independently through openings formed through one or more of the enclosure walls. Air from an external source is introduced at a sufficient pressure into the plenum 26a extending below the furnace section 30a, and the air passes through the nozzles 36a disposed in the furnace section 30a at a sufficient quantity and velocity to fluidize the particulate material in the furnace section 30a. Each nozzle 36a is adjusted so that the velocity of the air discharged therefrom increases from right-to-left as viewed in Fig. 1, i.e., the nozzles 36a closest to the front wall 14a discharge air at a relatively high velocity while the nozzles 36a closest to the partition 24a discharge air at a relatively low velocity. A lightoff burner (not shown), or the like, is provided to ignite the fuel material, and thereafter the fuel material is self-combusted by the heat in the furnace section 30a. Combustion of the fuel material generates combustion gases which mix with the air introduced through the plate 22a, which mixture is hereinafter referred to as flue gases. The flue gases pass upwardly through the furnace section 30a and entrain, or elutriate, a portion of the particulate material. The quantity of particulate material introduced into the furnace section 30a and the quantity of air introduced, via the air plenum 26a, through the nozzles 36a and into the interior of the furnace section 30a is established in accordance with the size of the particulate material so that a dense bed is formed in the lower portions of the furnace section 30a and a circulating fluidized bed is formed in the upper portions thereof, i.e. the particulate material is fluidized to an extent that substantial entrainment or elutriation thereof is achieved. Operated in the above manner, the density of the particulate material is relatively high in the lower portion of the furnace section 30a, decreases with height throughout the length of the furnace section 30a and is substantially constant and relatively low in the upper portions of the furnace section 30a. Since the operation in the enclosure 12b is identical to that in the enclosure 12a, the former will not be described in detail. As best shown in Figs. 3 and 4, the openings 64 in the lower portion of the common wall 60 are sized to permit adequate flow of the particulate material between the furnace sections 30a and 30b so that the respective heights of the solids in the furnace sections 30a and 30b section are substantially the same. Referring again to Fig. 1, the flue gases passing into the upper portion of the furnace section 30a are substantially saturated with the particulate material and pass, via the outlet opening in the upper portion of the rear wall 16a, into the cyclone separator 40a. The openings 62 (Fig. 3) in the upper portion of the common wall 60 equalize the gas pressure in the furnace sections 30a and 30b and thus eliminate any pressure drop across the common wall 60. In the separator 40a, the particulate material is separated from the flue gases, and cleaned flue gases pass to the heat recovery section 48 for passage across the heat exchange surfaces 50. The separated particulate material passes from the separator 40a, through a dipleg 54a, J-valve 56a, and conduit 58a, and into the recycle section 32a as described above. With reference to Figs. 2 and 4, the separated solids from the conduit 58a enter the compartment 94a of the recyle section 32a. Assuming normal operation, the plenum chambers 26a and 28a selectively distribute the air through the nozzles 36a and 98a, respectively, to the furnace section 30a and the recycle section 32a. Each nozzle 36a and 98a is of conventional design and, as such, includes a control device to enable the velocity of the air passing therethrough to be controlled. During such normal operation, fluidizing air is introduced, via the plenum 28a, to the nozzles 98a in the compartments 92a, 94a and 96a of the recycle section 32a, while the air flow to the manifold 102a, and therefore to the nozzles 100a, is turned off. Since the two rows of nozzles 98a in the compartment 94a are directed towards the partitions 88a and 90a, the particulate material passes from the compartment 94a into the compartments 92a and 96a. The particulate material mixes and builds up in the compartments 92a and 96a and thus gives up heat to the water/steam in the tubes 104a in those compartments. The cooled particulate material then passes through the openings 106a and 110a in the partition 68a through the channel 70a (Fig. 1), through the openings 34a in the partition 24a, and back into the furnace section 30a. As shown in Figs. 3 and 4, the openings 66 in the common wall 60 are sized to permit adequate flow of particulate material between the compartments 96a and 92b of the recycle sections 32a and 32b, respectively, so that the respective heights of the particulate material in the compartments 92a, 96a, 92b, and 96b are maintained substantially the same. Since, during the above operation there is no air introduced into the nozzles 100a in the compartment 94a, very little, if any, flow of particulate material occurs through the compartment 94a and opening 108a. During initial start up and low load conditions, the fluidizing air flow to the plenum 28a is turned off and the air flow to the manifold 102a, and therefore to the nozzles 100a, is turned on. As a result, the volume of particulate material in the compartments 92a and 96a slump and therefore seal these compartments from further flow. Thus, the separated particulate material from the conduit 58a passes directly through the compartment 94a and, after building up to the level of the opening 108a, passes through the opening 108a, through the channel 70a, through the openings 34a in the partition 24a, and back into the furnace section 30a. Since the compartment 94a does not contain heat exchange tubes 104a, start up and low load operation can be achieved without exposing the banks of tubes 104a to the hot recirculating particulate material. If desired, secondary air may be introduced into the enclosure 12a via inlets 80a and 82a, the secondary air from inlet 80a passing through the spaces in the partition 76a and through the recycle section 32a before exiting through the lower two rows of nozzles 84a leading into the furnace section 30a. The secondary air from the inlet 82a is prevented from passing into the recycle section 32a by the partition 78a and therefore passes through the upper two rows of nozzles 84a leading into the furnace section 30a. The fluidizing air that is introduced into the recycle section 32a is controlled to entrain fine fuel particles in the recycle section. In this manner, fine fuel particles of approximately 1 to 10 micrometers in diameter are exposed to the secondary air from the secondary air inlet 80a and pass with the secondary air through the nozzles 84a into the furnace section 30a. The high oxygen content in the latter air promotes the combustion of these entrained fine fuel particles as they pass from the recycle section 32a, through the lower two rows of nozzles 84a and into the furnace section 30a. Feed water is introduced into the flow circuit described above and is circulated therethrough in a predetermined sequence to convert the feed water to steam and to reheat and superheat the steam. Also, drain pipes (not shown) may be provided for the furnace section 30a and recycle section 32a and for each furnace section and recycle section as desired for discharging spent particulate material, in a conventional manner. The system and method of the present invention have several advantages. For example, in the embodiment of Figs. 1-4, the use of two adjacent enclosures sections 12a and 12b sharing a common wall 60 enables the size of the system 10, and therefore the load capacity, to be increased without increasing the height of the system. Moreover, the provision of openings 64 and 66 provided in the lower portion of the common wall 60 equalizes the heights of the respective dense beds in the furnace sections 30a and 30b and recycle sections 32a and 32b, thus correcting for imbalances in the fuel feed from the feeder systems 38a and 38b, or the like. Further, since the adjacent enclosures 12a and 12b are substantially the same, a single control scheme can be utilized which controls the operation in both enclosures. Moreover, the provision of the openings 62 in the upper portion of common wall 60 enables the respective gas pressures in the furnace sections 30a and 30b to be equalized, thus minimizing or eliminating any lateral loading across the common wall 60 and possible damage. Also, the openings 62 enable a predetermined gas pressure drop to be set across the furnace sections 30a and 30b and enable the entrainment and circulation to be substantially the same in each furnace section 30a and 30b. Also, the provision of the openings 62 enables substantially the same combustion environments to be established above the dense bed in both furnace sections 30a and 30b. Although the embodiment described above utilizes a single common wall 60 shared between two substantially identical enclosures 12a and 12b, it is understood that multiple common walls can be used in a similar manner to join additional enclosures. As examples of this, Figs. 5 and 6 depict alternate embodiments of the present invention in which adjacent and opposing enclosures are joined by common walls. According to the embodiment of Fig. 5, two more enclosures 12c and 12d, which are substantially similar to enclosures 12a and 12b, are joined with enclosures 12a and 12b. Enclosure 12c is disposed opposite enclosure 12a and adjacent enclosure 12d, and enclosure 12d is disposed opposite enclosure 12b. Enclosure 12a and enclosure 12c share a common wall 120, and enclosure 12b and enclosure 12d share a substantially identical common wall 122. As shown in Fig. 7, common wall 122 (and common wall 120) has a plurality of openings 124 in an upper portion for permitting flue gases to pass between the furnace sections joined thereby. The openings 124 equalize gas pressure in the joined furnace sections and thus eliminate any pressure drop across the common wall 122. The common wall 122 (and common wall 120) also has a plurality of openings 126 in a lower portion for permitting particulate material to flow between the furnace sections joined thereby. The openings 126 are sized to permit adequate flow of particulate material between the furnace sections joined thereby so that the respective heights of the dense beds in the furnace sections are substantially the same. The common wall 128 between enclosure 12c and enclosure 12d is substantially identical to common wall 60. Separators 40a, 40b, 40c, and 40d are associated with the respective enclosures 12a, 12b, 12c, and 12d in a substantially identical fashion as separator 40a is associated with enclosure 12a in the embodiment described in detail above. The separators 40a, 40b, 40c and 40d function in a substantially identical manner as separator 40a in the embodiment described in detail above. The embodiment of Fig. 5 thus functions in the same manner as described above in connection with the embodiment of Figs. 1-4 while enjoying the added capacity and flexibility of the additional enclosures. According to the embodiment of Fig. 6, two additional enclosures 12e and 12f, which are substantially similar to enclosures 12a, 12b, 12c, and 12d, are joined with enclosures 12a, 12b, 12c, and 12d. Enclosure 12e is disposed adjacent enclosure 12b and opposite enclosure 12f, and enclosure 12f is disposed adjacent enclosure 12d. Common walls 130 and 132, dividing enclosures 12b from 12e and 12d from 12f, respectively, are substantially identical to common walls 60 and 128. Similarly, common wall 134 dividing enclosure 12e from enclosure 12f, is substantially identical to common walls 120 and 122. Separators 40a, 40b, 40c, 40d, 40e, and 40f are associated with enclosures 12a, 12b, 12c, 12d, 12e, and 12f, respectively. The embodiment of Fig. 6 functions in the same manner as described above in connection with the embodiment of Figs. 1-4 and the embodiment of Fig. 5 while enjoying the added capacity and flexibility of the additional enclosures.

Claims: A fluidized bed combustion system comprising a first enclosure (12a) having a first furnace section (30a), a first recycle section (32a) adjoining the first furnace section (30a), means for forming a fluidized bed of particulate material including fuel in the first furnace section (30a), means for forming a fluidized bed of particulate material in the first recycle section (32a), means for passing particulate material from the first recycle section (32a) to the first furnace section (30a), a second enclosure (12b) having a second furnace section (30b), means for forming a fluidized bed of particulate material including fuel in the second furnace section (32b), the first and second enclosures (12a, 12b) being disposed adjacently and sharing a common wall (60) which divides the first furnace section (30a) from the second furnace section (30b), the first furnace section (30a) being disposed adjacent the second furnace section (30b), the common wall (60) having at least one aperture (62) extending through an upper portion of the common wall (60) and registering with the first and second furnace sections (30a, 30b) for permitting gases to pass between the first and second furnace sections (30a, 30b) to equalize pressure in the furnace sections, and the common wall (60) having at least one aperture (64) extending through a lower portion of the common wall (60) and registering with the first and second furnace sections (30a, 30b) for permitting particulate material to pass between the first and second furnace sections (30a, 30b), characterised in that a second recycle section (32b) adjoins the second furnace section (30b), means are provided for forming a fluidized bed of particulate material in the second recycle section (32b), the common wall (60) divides the first recycle section (32a) from the second recycle section (32b), the first recycle section (32a) is disposed adjacent the second recycle section (32b) and the common wall (60) has at least one aperture (66) extending through a lower portion of the common wall (60) and registering with the first and second recycle sections (32a, 32b) for permitting particulate material to pass between the first and second recycle sections (32a, 32b). A system as claimed in Claim 1 in which the common wall (60) is formed by a plurality of spaced cooling tubes connected by continuous fins to form an airtight structure, each of the apertures (62, 64, 66) in the common wall (60) being provided by omitting the fins from between portions of the spaced tubes. A system as claimed in Claim 1 or Claim 2 in which each enclosure (12a, 12b) has a partition (24a) dividing the respective enclosure (12a, 12b) into the respective furnace section (30a, 30b) and a recycle section (32a, 32b). A system as claimed in Claim 3 in which the partition (24a) has a first portion (24a 1 ) extending substantially vertically and a second portion (24a 11 ) angling upwardly and rearwardly from the first portion (24a 1 ) and extending to a rear wall (16a, 16b) of the enclosure (12a, 12b). A system as claimed in Claim 4 further comprising a fifth partition (76a, 78a) having a lower portion (76a) of angling upwardly into the respective recycle section (32a, 32b) from the rear wall (16a) of the enclosure to the second portion (24a 11 ) of the partition (24a), and an upper portion (78a) angling upwardly and rearwardly from the second portion (24a 11 ) of the partition (24a) to the rear wall (16a), the said lower portion (76a) of the fifth partition having at least one aperture. A system as claimed in Claim 5 further comprising a plurality of nozzles (84a) extending through the second portion (24a 11 ) of the partition (24a) and into the recycle section (32a, 32b) below a point of intersection of the said fifth partition (76a, 78a) with the second portion (24a 11 ) of the partition (24a), means for introducing an oxygen-containing gas through the rear wall (16a) and into the recycle section between the points of intersection of the upper and lower portions (78a, 76a) of the fifth partition (78a, 76a) with the rear wall (16a) so that the gas may create oxidizing conditions in the nozzles (84a) for combusting fine particulate material passing through the nozzles. A system as claimed in any of Claims 4 to 6 in which the means for passing particulate material from the respective recycle section (32a, 32b) to the respective furnace section (30a, 30b) comprise a second partition (68a, 68b) disposed between side walls of the respective recycle section (32a, 32b) and extending upwardly to the second portion (24a 11 ) of the partition (24a) to form a channel (70a, 70b) between the partition (24a) and the second partition (68a, 68b), an upper portion of the second partition (68a, 68b) having an aperture (106a, 106b, 110a, 110b) for permitting particulate material to pass from the recycle section (32a, 32b) to the channel (68a, 68b) and a lower portion of the partition (24a) having an aperture (34a) for permitting particulate material to pass from the channel (70a, 70b) to the furnace section (30a, 30b). A system as claimed in Claim 7 in which the partition (24a) and second partition (68a, 68b) are formed by a plurality of spaced cooling tubes connected by continuous fins to form airtight structures, and each of the apertures (106a, 106b, 110a, 110b, 34a) in the partition (24a) and second partition (68a, 68b) are provided by omitting the fins from between portions of the spaced tubes. A system as claimed in any preceding claim in which a grate (22a, 22b) is disposed in a lower portion of the respective enclosure (12a, 12b) for supporting the particulate material in the respective furnace section (30a, 30b) and recycle section (32a, 32b) and means (36a) introduce an oxygen-containing gas through the grate and the furnace section (32a, 32b) for fluidizing the particulate material in the furnace section (32a, 32b). A system as claimed in any preceding claim further comprising a first separator (40a) disposed adjacent the first enclosure (12a) for separating particulate material from gases, means for passing particulate material and gases from the first furnace section (30a) to the first separator (40a), means for passing separated particulate material from the first separator (40a) to the first recycle section, a second separator (40b) disposed adjacent the second enclosure (12b) for separating particulate material from gases, means for passing particulate material and gases from the second furnace section (30b) to the second separator (40b) and means for passing separated particulate material from the second separator (40b) to the second recycle section (32b). A system as claimed in Claim 10 in which the first and second separators (40a, 40b) are cyclone separators. A system as claimed in any preceding claim in which the first recycle section (32a) is located within the first enclosure (12a) and the second recycle section (32b) is located within the second enclosure (12b). A system as claimed in any preceding claim further comprising a third enclosure (12c) having a third furnace section (30c), a third recycle section (32c) adjoining the third furnace section (30), means for forming a fluidized bed of particulate material including fuel in the third furnace section (30c), means for forming a fluidized bed of particulate material in the third recycle section (32c), means for passing particulate material from the third recycle section (32a) to the third furnace section (30c), a fourth enclosure (12d) having a fourth furnace section (30d), a fourth recycle section (32d) adjoining the fourth furnace section (30d), means for forming a fluidized bed of particulate material including fuel in the fourth furnace section (30d), and means for forming a fluidized bed of particulate material in the fourth recycle section (32d), the third enclosure (12c) being disposed opposite and sharing a second common wall (120) with the first enclosure (12a), the fourth enclosure (12d) being disposed opposite and sharing a third common wall (122) with the second enclosure (12b), and the fourth enclosure being disposed adjacent to and sharing a fourth common wall (128) with the third enclosure (12c), the second common wall (120) having at least one aperture (126) extending through a lower portion of the wall and registering with the first and third furnace sections (30a, 30c) permitting particulate material to pass between the first and third furnace sections (30a, 30c), and the second common wall (120) having at least one aperture (124) extending through an upper portion of the wall (120) and registering with the first and third furnace sections (30a, 30c) permitting gases to pass between the first and third furnace sections (30a, 30c), the third common wall (122) having at least one aperture (124) extending through a lower portion of the wall (122) and registering with the second and fourth furnace sections (30b,30d) for permitting particulate material to pass between the second and fourth furnace sections (30b, 30d), and the third common wall (122) having at least one aperture (124) extending through an upper portion of the wall (122) and registering with the second and fourth furnace sections (30b, 30d) for permitting gases to pass between the second and fourth furnace sections (30b, 30d), and the fourth common wall (128) having at least one aperture (126) extending through the lower portion of the wall (128) and registering with the third and fourth furnace sections (30c, 30d) for permitting particulate material to pass between the third and fourth furnace sections (30c, 30d), the fourth common wall (128) having at least one aperture in the lower portion of the wall and registering with the third and fourth recycle sections (32c, 32d) for permitting particulate material to pass between the third and fourth recycle sections (32c, 32d), and the fourth common wall (128) having at least one aperture (124) in an upper portion of the wall (128) and registering with the third and fourth furnace sections (30c, 30d) for permitting gases to pass between the third and fourth furnace sections (30c, 30d). A system as claimed in Claim 13 in which said first recycle section (32a) is disposed within the first enclosure (12a), the second recycle section (32b) is disposed within the second enclosure (12b), the third recycle section (32c) is disposed within the third enclosure (12c), and the fourth recycle section (32d) is disposed within the fourth enclosure (12d). A system as claimed in Claim 13 or Claim 14 further comprising a fifth enclosure (12e) having a fifth furnace section (30e), a fifth recycle section (32e) adjoining the fifth furnace section (30e), means for forming a fluidized bed of particulate material including fuel in the fifth furnace section (30e), means for forming a fluidized bed of particulate material in the fifth recycle section (32e), means for passing particulate material from said fifth recycle section (32e) to the fifth furnace section (30e), a sixth enclosure (12f) having a sixth furnace section (30f), a sixth recycle section (32f) adjoining the sixth furnace section (30f), means for forming a fluidized bed of particulate material including fuel in the sixth furnace section (30f), means for forming a fluidized bed of particulate material in the sixth recycle section (32f), the fifth enclosure (12e) being disposed adjacent the second enclosure (12b) on a side opposite the first enclosure (12a), and the fifth enclosure sharing a fifth common wall (130) with the second enclosure (12b), the sixth enclosure (12f) being disposed opposite the fifth enclosure (12e) and adjacent the fourth enclosure (12d), the sixth enclosure sharing a sixth common wall (134) with the fifth enclosure (12e) and sharing a seventh common wall (132) with the fourth enclosure (12d), the fifth common wall (130) having at least one aperture in a lower portion of the wall (130) and registering with the second and fifth furnace sections (30b, 30e) for permitting particulate material to pass between the second and fifth furnace sections (30b, 30e), the fifth common wall (130) having at least one aperture in a lower portion of the wall (130) and registering with the second and fifth recycle sections (32b, 32e) for permitting particulate material to pass between the second and fifth recycle sections (32b, 32e), and the fifth common wall (130) having at least one aperture in an upper portion of the wall (130) and registering with the second and fifth furnace sections (30b, 30e) for permitting gases to pass between the second and fifth furnace sections (30b, 30e), the sixth common wall (134) having at least one aperture in a lower portion of the wall (134) and registering with the fifth and sixth furnace sections (30e, 30f) for permitting particulate material to pass between the fifth and sixth furnace sections (30e, 30f), and the sixth common wall (134) having at least one aperture in an upper portion of the wall (134) and registering with the fifth and sixth furnace sections (30e, 30f) for permitting gases to pass between the fifth and sixth furnace sections (30e, 30f) and the seventh common wall (132) having at least one aperture in a lower portion of the wall (132) and registering with the fourth and sixth furnace sections (30d, 30f) for permitting particulate material to pass between the fourth and sixth furnace sections (30d, 30f), the seventh common wall (132) having at least one aperture in a lower portion of the wall (132) and registering with the fourth and sixth recycle sections (32d, 32f) for permitting particulate material to pass between the fourth and sixth recycle sections (32d, 32f), and the seventh common wall (132) having at least one aperture in an upper portion of the wall (132) and registering with the fourth and sixth furnace sections (30d, 30f) for permitting gases to pass between the fourth and sixth furnace sections (30d, 30f). A system as claimed in Claim 15 in which the fifth recycle section (32e) is disposed within the fifth enclosure (12e), and the sixth recycle section (32f) is disposed within the sixth enclosure (12f). A method of operating a fluidized bed combustion system as claimed in Claim 1 comprising fluidizing particulate material in the furnace sections (30) and the recycle sections (32), equalizing the heights of the material in adjacent furnace sections, equalizing the pressure in the adjacent furnace sections, and equalizing the heights of the material in the recycle sections (32). A method as claimed in Claim 17 in which the step of equalizing the heights in the adjacent recycle section (32) comprises permitting particulate material to flow between the adjacent recycle sections (32). A method as claimed in Claim 17 or Claim 18 in which the step of fluidizing results in a dense bed of particulate material being formed in each section and flue gases being formed which entrain a portion of the particulate material, the step of equalizing the heights in the adjacent furnace sections (30) comprises permitting particulate material to flow between the adjacent furnace sections (30) and the step of equalizing the pressure in adjacent furnace sections (30) comprises permitting the flue gases to flow between the adjacent furnace sections (30). A method as claimed in any of claims 17 to 20 further comprising further comprising passing a portion of flue gases and entrained particulate material from the furnace sections (30), separating the passed, entrained particulate material from the flue gases, and in which the step of introducing particulate material into the recycle sections (32) comprises passing the separated particulate material to the recycle sections (32). A method as claimed in Claim 20 further comprising removing heat from the separated particulate material in the recycle sections (32). A method as claimed in Claim 20 or Claim 21 in which the particulate material in the recycle sections (32) includes fine fuel particles and further comprising controlling the fluidizing gas introduced into the recycle sections to entrain the fine fuel particles from the dense beds in the recycle sections, passing a portion of the entrained fine fuel particles from the recycle sections (32) to the furnace sections (30), and introducing a secondary oxygen-containing gas into the recycle sections above the dense beds so that secondary gas creates oxidizing conditions for combusting the entrained fine fuel particles as they pass from the recycle sections (32) to the furnace sections (30).

Inventors: DIETZ DAVID HAROLD, DIETZ, DAVID HAROLD
Applicants: FOSTER WHEELER ENERGY CORP, FOSTER WHEELER ENERGY CORPORATION
Application year: 1993
Main classification: F23C11
IPC codes: F22B31, F23C10