CA1313088C - Steam generator and method of operating same utilizing separate fluid and combined gas flow circuits - Google Patents
Steam generator and method of operating same utilizing separate fluid and combined gas flow circuitsInfo
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- CA1313088C CA1313088C CA000573297A CA573297A CA1313088C CA 1313088 C CA1313088 C CA 1313088C CA 000573297 A CA000573297 A CA 000573297A CA 573297 A CA573297 A CA 573297A CA 1313088 C CA1313088 C CA 1313088C
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Abstract
A STEAM GENERATOR AND METHOD OF OPERATING SAME
UTILIZING SEPARATE FLUID
AND COMBINED GAS FLOW CIRCUITS
Abstract of the Disclosure A steam generator and method for operating same in which two beds of combustible particulate material are established and air is introduced to each of the beds for fluidizing the beds to promote combustion of the fuel.
The flue gases and entrained fine particulate material from each bed are combined and the particulate material then separated from the flue gases externally of the beds and introduced to a third bed. Air is passed through the material in the third bed to fluidize same. Independent fluid circuits are established for independently controlling the steam generation rate and the temperatures of the superheat steam and the reheat steam.
UTILIZING SEPARATE FLUID
AND COMBINED GAS FLOW CIRCUITS
Abstract of the Disclosure A steam generator and method for operating same in which two beds of combustible particulate material are established and air is introduced to each of the beds for fluidizing the beds to promote combustion of the fuel.
The flue gases and entrained fine particulate material from each bed are combined and the particulate material then separated from the flue gases externally of the beds and introduced to a third bed. Air is passed through the material in the third bed to fluidize same. Independent fluid circuits are established for independently controlling the steam generation rate and the temperatures of the superheat steam and the reheat steam.
Description
~3~.308i!3 A STEA~ GENERATOR AND METHOD OF OPERATING SAME
UTILIZING SEPARATE FLUID
AND COMBINED_ AS FLOW CIRCUITS
-~ackqround of_the Invention 5This invention relates to a steam generator and a method of operating same in which heat is generated by the combustion of fuel in a plurality of fluidized heds.
Steam generating systems utilizing fluidized beds as the primary source of heat generation are well known. In these arrangements, air is passed through a bed of particulate material, including a fossil fuel such as coal and an adsorbent for the 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. The heat produced by the fluidized bed is : utilized to convert water to steam which results in an ~ attractive combination of high heat release, high sulfur '.
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adsorption, low nitrogen oxides emissions and fuel flexibility.
The most typical fluidized bed combustion system is commonly referred to as a bubbling fluidized bed in which a bed of particulate materials is supported by an air distribution plate, to which combustion-supporting air is introduced through a plurality of perforations in the plate, causing the material to e~pand and take on a suspended, or fluidized, state. In a steam generator environment, the walls enclosing the bed are formed by a plurality of heat transfer tubes, and the heat produced by combustion within the fluidized bed is transferred to water circulating through the tubes. The heat transfer tubes are usually connected to a natural water circulation circuitry, including a steam drum, for separating water from the steam thus formed which is routed to a turbine or to another steam user.
In an effort to extend the improvements in combustion efficiency, pollutant emissions control, and operation turn-down afforded by the bubbling bed, a fluidized bed reactor has been developed utilizing a circulating fluidized bed process. According to this process, fluidized bed densities between 5 and 20% volume of solids are attained which is well below the 30% volume of~solids _3_ ~3~3~88 typical of the bubbling fluidized bed. The formation of the low density circulating fluidized bed is due to its small particle size and to a high solids throughput, which require high solids recycle. The velocity range of a ci~culating fluidized bed is between the solids terminal, or free fall, velocity and a velocity beyond which the bed would be converted into a pneumatic transport line.
The high solids circulation required by the circulating fluidized bed makes it insensitive to fuel heat release patterns, thus minimizing the variation of the temperature within the steam generator, and therefore decreasing the nitrogen oxides formation while increasing sulfur dioxide adsorption. Also, the high solids loading results in an increase in sulfur adsorbent and fuel residence time, which reduces the adsorbent and fuel consumption.
However the circulating fluidized bed process is not without problems, especially when used in a steam generation environment. For example, it normally lacks a method of independently controlling the outlet temperature of the reheat as compared to the temperature of the main steam and~or superheat, especially when it is necessary to heat both of these fluids to temperatures of 950F or ' ~4~ ~3~3~88 higher and maintain these temperature levels over a wide control range without excessive attemperation.
United States Patent Number 4,665,864 dated May 19, 1987 addresses this problem by providing a steam generator and a method of operating same in which a flow circuit is provided for the reheat steam which is independent of the circuitry for the other steam stages. In this arrangement, an independently fired fluidized bed is provided to directly control the temperature of the reheat steam, and separate fluidized beds are provided for controlling the steam generation rate and the temperature of the superheat steam.
Summary~of the Invention The object of the present invention is to provide a steam generator and method which further improves the steam generator and method disclosed in the above-identified patent by reducing the amount of heat exchange surface required in the circulating fluidized bed for a given heat input to that bed by removing heat from the recycled fly ash.
It is another object of the present invention to provide an improved steam generator and method of the above type in which a greater percentage of combustion : ' `; :
13~L3~)8~3 takes place in the circulating bed portion of the generator to allow a reduction in the firing rate of the bubbling bed section to take advantage of the better fuel combustion and limestone utilization inherent in the circulating bed.
It is a further object of the present invention to provide an improved steam generator and method of the above type in which the overall immersed tubing required b~ the fluidized bed is reduced by utilizing an unfired bed operating at a low fluidizing velocity.
A still further object of the present invention is to provide a steam generator and method of the above type in which the size and firing rate of the bubbling bed section of the steam generator is reduced so that the generator has a broader tolerance to small fuel and limestone particle sizes.
It is a still further object of the present invention to provide a steam generator and method of the above type in which a greater percentage of combustion and sulfur capture occurs in the circulating fluidized bed section of the steam generator where fuel and limestone fine particulate can be retained to reduce the calcium-to-sulphur ratio required to achieve sulphur dioxide emissions.
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It is a still further object of the present invention to provide a steam generator and method of the above type in which the circulating fluidized bed section is relatively large to improve the fuel carbon utilization.
It is a still further object of the present invention to provide a steam generator and method of the above type in which the overall height of the furnace may be reduced by virtue of cooling the recycled fly ash in an unfired fluidized bed.
Toward the fulfillment of these and other objects, two beds of particulate material containing fuel are established in a vessel and the fuel is combusted in each of the beds while air and additional fuel is added to the beds to fluidize the beds and promote combustion of the fuel. A mixture of flue gases and the entrained particulate material from the beds are combined and the entrained particulate rnaterials are separated from the flue ~ases. The separated particulate material is passed to a third bed in the vessel and air is introduced to the latter bed to fluidize the separated material. This air along with any immersed heat exchange surface located in the said third bed cools the separated particulate material.
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- 6A - ~3~8~
More particularly the invention in one aspect comprehends a method of operating a steam generator comprising the steps of forming at least two beds of particulate material containing fuel in a vessel, combusting the ~uel in each of said beds, introducing air and additional fuel into each of said beds to fluidize said beds to promote the combustion of said fuel, establishing a first flow circuit for passing water in a heat exchange relation to at last one of said beds for converting said water to steam, combining a mixture of flue gases and the entrained particulate material from both of said beds, separating said entrained particulate material from the flue gases of said combined mixture, passing said separated particulate material to a third bed in said vessel, and introducing air to said third bed to fluidize and cool said separated particulate material.
Another aspect of the invention pertains to a steam generator comprising a vessel, means of forming at least two beds of particulate material containing fuel in said vessel, means for introducing air and fuel into ea~h of said beds to fluidize said beds and combust said fuel, A~
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`- ~3~3~88 first flow circuit means for passing water in a heat exchange relation to one of said beds for converting said water to steam, means for combining the flue gases and the entrained particulate material from both of said beds, means for separating said entrained particulate materials from the flue gases of said combined mixture, means for forming a third bed, means for passing said separated particulate material into said third bed, means for introducing air to said third bed to fluidize said separated parti.culate material, and means for cooling said separated particulate material.
_7_ ~3~3~
Brief Description of the Drawinqs The above brief description as well as further objects, features and advantages of the method of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawing in which:
Fig. l is a schematic side elevation view of a forced circulation steam generator employing features of the present invention; and Figs. 2-~ are schematic plan views of a portion of the steam generator of Fig. l depicting alternate embodiments of the present invention, with portions of the steam generator being deleted for the convenience of presentation.
Description of the Preferred Embodiment Referring specifically to Fig. l of the drawing, the ; 20 reference numeral 10 depicts, in general, a forced circulation steam generator according to the present invention including a plurality of elongated vertically-extending steel support columns such as shown -8- ~3~3~8 by reference numerals 12, 19, and 16 extending from the floor 18 of the generator to a plurality of spaced horizontally-extending beams, one of which is shown by the reference numeral 20, which define the ceiling of the generator. A plurality of hangers ~2 extend downwardly from the beam 20 for supporting a steam drum 24 having a plurality of downcomers extending downwardly therefrom, one of which is shown by the reference numeral 26. A
plurality of additional hangers 28 extend downwardly from the beam 20 for supporting a heat recovery portion of the generator 10 which will be described in detail later.
Two fluidized bed chambers A and B are supported in the lower portion of the generator 10 by a bottom support system (not shown) of a conventional design.
Two air distribution plates 30 and 31 extend horizontally through the entire width of each of chambers A and B, respectively. Air plenums 32 and 39 extend immediately below the chambers A and B, respectively, for introducing air upwardly through the corresponding portions of the air distribution plates 30 and 31, respectively, into the chambers.
The chamber A is defined by the air distribution plate 30, a pair of vertically-extending spaced walls 36 -9- ~L313~8~
and 38 and a diagonally-extending roof 40 while the chamber B is defined by the air distribution plate 31, the wall 38, and a vertically-extending wall 42 disposed in a spaced relation to the wall 38.
A third chamber C is defined by a vertical wall 44 extending in a spaced relation to the wall 42, a distribution plate 45 and an upper, diagonal roof 46. An air plenum 47 extends below the plate 45 for directing air upwardly through the plate into the chamber C. It is understood that a pair of spaced sidewalls (not shown) are provided which, together with the walls 36, 38, 42, and 44 form an enclosure, and that these sidewalls, along with the latter walls are formed by a plurality of vertically-extending waterwall tubes connected in an air-tight relationship.
Bundles of heat exchange tubes 48 and 50 are provided in the chambers A and C, respectively for circulating Eluid through the chambers as will be described in detail later.
The walls 38 and 42 extend for substantially the entire height of the generator 10 and an opening 52 is provided through the wall 38 in order to permit the flue gases from the chamber A to flow to the chamber B where - 1 o - ~313~8 !3 they mix with those from the chamber B. The flue gases then pass upwardly in the chamber B before passing through one or more openings 53 provided in the wall 92 and into a cyclone separator 54 disposed above the chamber C. The separator 54 includes a funnel portion 56 having a dipleg 58 connected to its lower outlet end and extending through the roof 46 and into the lower portion of the chamber C for reasons to be described later. It is understood that additional separators 54 can be provided as needed.
A heat recovery area, shown in general by the reference numeral 64, is disposed adjacent the upper portion of the chamber B on the side thereof opposite that of the cyclone separator 54. The heat recovery area 64 is defined by a vertical wall 66 extending in a spaced relationship to the wall 38 and a substantially horizontal roof 68 which spans the heat recovery area, the chamber B, and the cyclone separator 54.
A wall 69 extends across the top of the cyclone separator 54 and the top of the chamber B and, together with the wall 68, defines a duct for passing gases from the cyclone separator 54 to the heat recovery area, as will be described later. The walls 66, 68, and 69 may ~3~3~)~8 also be formed by a plurality of waterwall tubes connected in an air tight manner.
A gas control damper system 70 is disposed in the lower portion of the heat recovery area 64 and controls the flow of gas throuqh the heat recovery area in a manner to be described, before the gas passes over a tube bundle 72 and exits from a flue gas duct 74 to an air heater (not shown) in a manner also to be described in detail later.
A pump 76 is connected to the lower portion of the downcomers 26 of the steam drum 24. Since more than one downcomer 26 and pump 76 can be provided, manifolds 78 are connected to the inlet and-outlet of the pump(s) 76 for supplying water from the steam drum 24 to a plurality of substantially horizontally and vertically extending water lines, one of each of which are shown by the reference numerals 80 and 82.
A plurality of vertical feeders 83, one of which is shown in the drawing, extend from the water lines 80 and are connected to a header 84 which supplies water to a water tube wall 85 disposed in the heat recovery area 64, it being understood that other vertical feeders are connected to the water lines 80 for supplyinq water to the ~5 , - ., '~
-12- ~313~8 sidewalls (not shown) of the heat recovery area 64.
A plurality of feeders 86 extend from the water lines 80 and are connected to headers (not shown) forming portions of a pair of seal assemblies 88 associated with each wall 38 and 42. The seal assemblies 88 function to accommodate relative differential expansion between the lower portion of the steam generator 10 supported from the floor 18 and the upper portion of the steam generator top-supported by the hangers 22 and 28. Since the seal assemblies 88 are fully disclosed in co-pending CDN. Patent Application Serial No. 499,894 filed on Jan-uary 20, 1986 and assigned to the same assignee as the present invention, they will not be described in any further detail. It is understood that the headers associated with the seal assemblies 88 supply water to the waterwall tubes forming the upper portions of the walls 38 and 42.
An additional feeder 94 extends from each of the water lines 80 and supplies a header 96 for circulating water through a water tube wall 98 which, together with the walls 42 and 69, and the sidewalls (not shown), enclose the cyclone separator 59.
-13- ~3~3088 The vertical water lines 82 are respectively connected to horizontal water conduits 100 each of which has a plurality of vertically-extending feeders 102 extending therefrom which are connected to headers 104 connected to the lower ends of the walls 36, 38 and 42 for supplying water to the wall 36 and the lower portions of the walls 38 and 42. Additional feeders 106 supply water from the water conduits 100 to corresponding headers 108 for the bundle of water tubes 48 in the chamber A.
A pipe 110 extends from a boiler feed pumping and preheating system (not shown) to an inlet header 112 for the tube bundle 72. The outlet of the tube bundle 72 is connected, via a header 114, a transfer line 116, and an inlet header 118 to a bundle of water tubes 120 disposed within the heat recovery area 64 and functioning as a economizer. The outlet of the tube bundle 120 is connected, via a header 122 and a transfer line conduit 124, to the inlet of the steam drum 24. Water flow through the circuit of the present invention is established from the pumping and preheating system into and through the tube bundle 72, the tube bundle 120, and into the steam drum 24. This water is mixed with the water separated from the water/steam mixture supplied to the .
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-14- ~313~8~
drum 24 and the resulting water passes through the downcomer 26 and, via the pump(s) 76, into the manifold 78. The water then passes from the manifold 78 through the water lines 80, the feeders 83 and 94, and to the waterwalls 66, 85, 38, 42, and 98. The water lines 82 supply water, via the conduits 100 and the feeders 102 and 106 to the walls 36, 38, and 42, and to the tube bundle 48.
The reference numeral 130 refers to a plurality of headers disposed at the upper end portions of the 10 walls 66, 85, 38, 42, and 98, it being understood that the side walls associated with the heat recovery area 64, the chamber B and the cyclone separator 54 would have similar type headers. A plurality of risers 132 extend upwardly -from the headers 130 and connect with a conduit 133 which 15 extends from the endmost riser 132 to the steam drum 24 to transfer the fluid from the various headers in the wall into the steam drum.
The water passing through the walls 36 and 38 is partially converted to steam and passed to a pair of headers 134 while the water passing through the tube bundle 98 is also partially converted to steam and passed to a plurality of outlet headers, one of which is shown by -15- 13~3~
the reference numeral 135. The steam from the header 135 passes into a conduit 136 and the steam from the headers 134 is passed, via conduit 137, to the conduit 136. The conduit 136 is connected to the steam drum 24 so that the steam from the headers 134 and 135 mixes with the steam entering the steam drum 24 from the conduit 133 in the manner described above.
The superheat circuitry includes a bundle of tubes 140 functioning as a primary superheater disposed in the heat recovery area 64 and having an inlet header 142 connected, via a conduit 149, to the outlet of the steam drum 29. After passing through the tube bundle 140 the superheated steam exits, via a header 146. Although not shown in the drawing it is understood that a spray attemperator, or the like, is connected to the header 146 to reduce the temperature of the steam as necessary before the steam is introduced to a finishing superheater.
Although not shown in the drawings in the interest of clarity, it is understood that the finishing superheater may be formed by an additional tube bundle in the chamber A or by a tube bundle in the chamber C. ~fter passing through this superheater, the steam is then passed to the inlet of a turbine. Thus the finishing superheater -16- ~3~3088 circuit is independent of the steam generating circuit described above.
A plurality of tubes forming bundles 150 and 162 are provided in the heat recovery area 64 and each bundle functions as a reheater. One or two conduits, one of which is shown by the reference numeral 1~4, extend from the high pressure turbine (not shown) and is connected to an inlet header 166 which is connected to the tubes forming the tube bundles 160 and 162. After passing through the tube bundles 160 and 162 the reheated steam is passed to an outlet header 172 which, in turn, is connected, via one or two conduits 174, to a low pressure turbine (not shown). It is noted that this reheat flow circuitry is entirely independent from the steam generating flow circuitry and superheat circuitry described above.
Air from one or more forced draft fans 180 is passed, via a duct 182 and a plurality of vertical ducts 184 to the plenums 32, 34 and 47 e~tending below the chambers A, B, and C, respectively. Although omitted from the drawings in the interest of clarity, it is understood that a bed of particulate material is disposed in each of the chambers A, B, and C which is fluidized in respons~e to the -17- ~3~
air passing upwardly from the plenums 32, 34 and 47, respectively, through the air distribution plates 30, 3L, and 45 and into the latter chambers. It is also understood that each chamber A, B, and C may be subdivided by partitions, or the like (not shown), into segments that are used during start-up and for load control of the steam generator 10.
The fluidizing velocity of the air introduced into the bed in the chamber A is regulated in accordance with the size of the particles in the bed so that the particulate material in the chambers A and B is fluidized in a manner to create a "bubbling" bed with a minimum of particles being entrained by the air and gases passing through the bed. The velocity of the air introduced into the chamber B relative to the particle size in the bed is such that a "circulating" bed is formed, i.e. a bed in which the particulate material in the bed is fluidized to an extent that the combustion gas is very near saturation solids capacity for the entire length of the chamber B.
Chamber C is an inactive, or unfired, bed in that there is no introduction o particulate fresh fuel or adsorbent into the bed and no ignition of the fuel so that the air passing through the bed serves to cool the particulate material forming the bed, as will be explained.
-18- ~3~ 8 The fuel introduced to the beds in the chambers A and B is ignited and additional fuel and adsorbent is added to the beds by conventional feeders (not shown). The resulting flue gases, which include the gaseous products of combustion and the air passing through the beds, entrain a small portion of the relatively fine particulate material in the latter chambers. The resulting mixture of flue gases and particulate material in the chamber A
passes through the opening 52 in the wall 38 and into the chamber B where it combines with a similar mixture in the latter chamber. As indicated above, the velocity of the air passing, via the plenum 34, into the chamber B is such relative to the size of the particles in the latter chamber such that the particles are suspended in the flue gases and eventually transported up~ardly through the length of the chamber B. The flue gases with the entrained particles exit through the opening 53 formed in the upper portion of the wall 42 before passing into the cyclone separator 59. It is noted that, by virtue of the fact that chamber B is located between the chambers A and C, the fluidized bed in the chamber A is thermally isolated from the fluidized bed in the chamber C.
- 1 9 - ~3~
The particulate material is separated from the gases in the cyclone separator 54 and the gases pass upwardly into the conduit defined between the walls 68 and 69, through openings formed in the walls 42 and 38 and into the heat recovery area 64. A portion of the gases in the heat recovery area 64 passes through the wall 85 which has openings formed therein for this purpose, before the gases pass over the tube bundles 140 and 120 forming the primary superheater and the economizer, respectively. The remaining gases pass over the tube bundles 162 and 160 forming the reheaters.
The gases passing through the heat recovery area 64 in the foregoing manner then pass through the damper system 70, which can be adjusted as necessary to control the fraction of the total gas flow that is to flow across the tube bundle 140 forming the primary superheater and the tube bundle 120 forming the economizer. The gases then pass across the tube bundle 72 and through the outlet duct 74. It is understood that the duct 74 can be connected to an air heater (not shown) where the gases give up heat to the air from the forced draft fan 180 before the gases exit to a dust collector, induced draft fan, and/or stack (not shown). The air from the fan 180 ZS
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-20- ~3~308~
is thus preheated before passing to the duct 182, as described above.
The solid particulate material separated in the cyclone separator 54 falls into the funnel portion 56 of the separator before discharging, via the dipleg 58, into the chamber C. Thus, a bed of the relative hot separated particulate material from the sepafator 54 is formed in the chamber C and is cooled by the cooling air passing from the plenum 47 through the plate 95 and fluidizing the material. Also, water from an external source, water from the previously mentioned boiler feed pumping system or steam from the superheat circuitry, is circulated through the tubes 50 to further cool the separated particulate material in the chamber C.
The method of the present invention provides several advantages. For example, the reheat circuitry is entirely independent of the steam generating circuitry and the superheat circuitry depicted. Moreover, the use of the three separate fluidized beds in the chambers A, B and C
enables the temperatures in each bed to be controlled independently. Also, by removing heat from the separated particulate material in the unfired bed C, the amount of heat exchange surface required in the chamber B per unit . . };
-21- 13~3~8 heat input to chamber B is reduced. ~urther, since the amount of heat exchange surface per unit heat input to chamber B is reduced, it becomes practical to increase the firing rate of chamber B. This allows a reduction in the firing rate, area and surface of the bubbling fluidized bed in chamber A. Further, the use of the unfired bed of particulate material in chamber C operating at a relatively low fluidizing velocity and consisting of relatively fine particles of the separated particulate material, results in a much higher in-bed tube heat transfer coefficient, thus reducing the overall immersed tubing required by the fluidized beds in chambers A and C. Also, since the reaction performance of the bubbling fluidized bed in chamber A is more sensitive to small particle sizes, the reduction in area and firing rate for this chamber enables the steam generator of the present invention to be more tolerant to small fuel and limestone particle sizes.
Still further, by allowing a greater percentage o combustion to occur in the circulating fluidized bed in chamber B, where relatively fine particulate fuel material can be used, the e~ficiency of sulfur capture by adsorbent : is increased to reduce the percentage of sulphur dioxide ' ~ , ' ' '~''~ ' '.
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emissions. Also, the method of the present invention improves the fuel carbon utilization as a result of the larger circulating fluidized bed area in chamber B.
Finally, the overall height of the furnace can be reduced by virtue of the cooling of the separated particulate material in bed C.
Figures 2-4 depict alternate embodiments of the present invention and, for the convenience of presentation, only top plan views showing the chambers A, B and C, the funnel portion 56 of the cyclone separator 54 and the dipleg 58 are shown. According to the embodiment of Fig. 2, the dipleg 58 of the funnel portion 56 of the cyclone separator 54 tnot shown) is located in a corner of the chamber C. A dipleg 58' of another funnel portion 56' of another separator is located in another corner of the chamber C to provide for the introduction of the separated particulate material from two cyclone separators.
According to the embodiment of Fig. 3, chambers A and B are in a side-by-side relationship as in the embodiment of Figs. 1 and 2, but the unfired chamber C is located in a plane behind that of chamber B. As in the previous embodiment, the two diplegs 58 and 58' of the funnel portions 56 and 56' of two cyclone separators are located in two corners of the chamber C.
1313~8~3 According to the embodiment of Fig. 4, there are two unfired chambers Cl and C2 disposed to the side of chamber B and spaced apart in a front-to-rear relationship as shown. The funnel portion 56 of the cyclone separator 54 is positioned over the chamber Cl with its dipleg 58 extending slightly in front thereof. A funnel portion 56' of another cyclone separator is provided with its dipleg 58' extending between the two chambers, and still another separator and funnel portion 56" is disposed over the chamber C2 with its dipleg 58" located slightly to the rear of chamber C2.
It is understood that the funnel portions 56, 56', and 56" are located relative to the opening 53 in the wall ~2 and to the walls 68 and 69 so that the mixture of flue gases and particulate material in the chamber B passes into each of their corresponding separators and so that the separated gases pass from the separators to the conduit defined between the walls 68 and 69, as discussed above.
It is understood that several other variations rnay be made in the foregoing without departing from the scope of the invention. For example, the cyclone separator 54 can extend between the heat recovery area 64 and the chambers A, ~ and C, and the diplegs 58 do not have to extend -2q- ~3~3~38 directly into the chamber C but can go through a conventional seal pot or the like disposed externally of the chamber C and another dipleg can be provided that extends from the seal pot into the chamber C.
Other modifications, changes, and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention therein.
UTILIZING SEPARATE FLUID
AND COMBINED_ AS FLOW CIRCUITS
-~ackqround of_the Invention 5This invention relates to a steam generator and a method of operating same in which heat is generated by the combustion of fuel in a plurality of fluidized heds.
Steam generating systems utilizing fluidized beds as the primary source of heat generation are well known. In these arrangements, air is passed through a bed of particulate material, including a fossil fuel such as coal and an adsorbent for the 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. The heat produced by the fluidized bed is : utilized to convert water to steam which results in an ~ attractive combination of high heat release, high sulfur '.
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adsorption, low nitrogen oxides emissions and fuel flexibility.
The most typical fluidized bed combustion system is commonly referred to as a bubbling fluidized bed in which a bed of particulate materials is supported by an air distribution plate, to which combustion-supporting air is introduced through a plurality of perforations in the plate, causing the material to e~pand and take on a suspended, or fluidized, state. In a steam generator environment, the walls enclosing the bed are formed by a plurality of heat transfer tubes, and the heat produced by combustion within the fluidized bed is transferred to water circulating through the tubes. The heat transfer tubes are usually connected to a natural water circulation circuitry, including a steam drum, for separating water from the steam thus formed which is routed to a turbine or to another steam user.
In an effort to extend the improvements in combustion efficiency, pollutant emissions control, and operation turn-down afforded by the bubbling bed, a fluidized bed reactor has been developed utilizing a circulating fluidized bed process. According to this process, fluidized bed densities between 5 and 20% volume of solids are attained which is well below the 30% volume of~solids _3_ ~3~3~88 typical of the bubbling fluidized bed. The formation of the low density circulating fluidized bed is due to its small particle size and to a high solids throughput, which require high solids recycle. The velocity range of a ci~culating fluidized bed is between the solids terminal, or free fall, velocity and a velocity beyond which the bed would be converted into a pneumatic transport line.
The high solids circulation required by the circulating fluidized bed makes it insensitive to fuel heat release patterns, thus minimizing the variation of the temperature within the steam generator, and therefore decreasing the nitrogen oxides formation while increasing sulfur dioxide adsorption. Also, the high solids loading results in an increase in sulfur adsorbent and fuel residence time, which reduces the adsorbent and fuel consumption.
However the circulating fluidized bed process is not without problems, especially when used in a steam generation environment. For example, it normally lacks a method of independently controlling the outlet temperature of the reheat as compared to the temperature of the main steam and~or superheat, especially when it is necessary to heat both of these fluids to temperatures of 950F or ' ~4~ ~3~3~88 higher and maintain these temperature levels over a wide control range without excessive attemperation.
United States Patent Number 4,665,864 dated May 19, 1987 addresses this problem by providing a steam generator and a method of operating same in which a flow circuit is provided for the reheat steam which is independent of the circuitry for the other steam stages. In this arrangement, an independently fired fluidized bed is provided to directly control the temperature of the reheat steam, and separate fluidized beds are provided for controlling the steam generation rate and the temperature of the superheat steam.
Summary~of the Invention The object of the present invention is to provide a steam generator and method which further improves the steam generator and method disclosed in the above-identified patent by reducing the amount of heat exchange surface required in the circulating fluidized bed for a given heat input to that bed by removing heat from the recycled fly ash.
It is another object of the present invention to provide an improved steam generator and method of the above type in which a greater percentage of combustion : ' `; :
13~L3~)8~3 takes place in the circulating bed portion of the generator to allow a reduction in the firing rate of the bubbling bed section to take advantage of the better fuel combustion and limestone utilization inherent in the circulating bed.
It is a further object of the present invention to provide an improved steam generator and method of the above type in which the overall immersed tubing required b~ the fluidized bed is reduced by utilizing an unfired bed operating at a low fluidizing velocity.
A still further object of the present invention is to provide a steam generator and method of the above type in which the size and firing rate of the bubbling bed section of the steam generator is reduced so that the generator has a broader tolerance to small fuel and limestone particle sizes.
It is a still further object of the present invention to provide a steam generator and method of the above type in which a greater percentage of combustion and sulfur capture occurs in the circulating fluidized bed section of the steam generator where fuel and limestone fine particulate can be retained to reduce the calcium-to-sulphur ratio required to achieve sulphur dioxide emissions.
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It is a still further object of the present invention to provide a steam generator and method of the above type in which the circulating fluidized bed section is relatively large to improve the fuel carbon utilization.
It is a still further object of the present invention to provide a steam generator and method of the above type in which the overall height of the furnace may be reduced by virtue of cooling the recycled fly ash in an unfired fluidized bed.
Toward the fulfillment of these and other objects, two beds of particulate material containing fuel are established in a vessel and the fuel is combusted in each of the beds while air and additional fuel is added to the beds to fluidize the beds and promote combustion of the fuel. A mixture of flue gases and the entrained particulate material from the beds are combined and the entrained particulate rnaterials are separated from the flue ~ases. The separated particulate material is passed to a third bed in the vessel and air is introduced to the latter bed to fluidize the separated material. This air along with any immersed heat exchange surface located in the said third bed cools the separated particulate material.
'' '' "
', . .
- 6A - ~3~8~
More particularly the invention in one aspect comprehends a method of operating a steam generator comprising the steps of forming at least two beds of particulate material containing fuel in a vessel, combusting the ~uel in each of said beds, introducing air and additional fuel into each of said beds to fluidize said beds to promote the combustion of said fuel, establishing a first flow circuit for passing water in a heat exchange relation to at last one of said beds for converting said water to steam, combining a mixture of flue gases and the entrained particulate material from both of said beds, separating said entrained particulate material from the flue gases of said combined mixture, passing said separated particulate material to a third bed in said vessel, and introducing air to said third bed to fluidize and cool said separated particulate material.
Another aspect of the invention pertains to a steam generator comprising a vessel, means of forming at least two beds of particulate material containing fuel in said vessel, means for introducing air and fuel into ea~h of said beds to fluidize said beds and combust said fuel, A~
.
.
`- ~3~3~88 first flow circuit means for passing water in a heat exchange relation to one of said beds for converting said water to steam, means for combining the flue gases and the entrained particulate material from both of said beds, means for separating said entrained particulate materials from the flue gases of said combined mixture, means for forming a third bed, means for passing said separated particulate material into said third bed, means for introducing air to said third bed to fluidize said separated parti.culate material, and means for cooling said separated particulate material.
_7_ ~3~3~
Brief Description of the Drawinqs The above brief description as well as further objects, features and advantages of the method of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawing in which:
Fig. l is a schematic side elevation view of a forced circulation steam generator employing features of the present invention; and Figs. 2-~ are schematic plan views of a portion of the steam generator of Fig. l depicting alternate embodiments of the present invention, with portions of the steam generator being deleted for the convenience of presentation.
Description of the Preferred Embodiment Referring specifically to Fig. l of the drawing, the ; 20 reference numeral 10 depicts, in general, a forced circulation steam generator according to the present invention including a plurality of elongated vertically-extending steel support columns such as shown -8- ~3~3~8 by reference numerals 12, 19, and 16 extending from the floor 18 of the generator to a plurality of spaced horizontally-extending beams, one of which is shown by the reference numeral 20, which define the ceiling of the generator. A plurality of hangers ~2 extend downwardly from the beam 20 for supporting a steam drum 24 having a plurality of downcomers extending downwardly therefrom, one of which is shown by the reference numeral 26. A
plurality of additional hangers 28 extend downwardly from the beam 20 for supporting a heat recovery portion of the generator 10 which will be described in detail later.
Two fluidized bed chambers A and B are supported in the lower portion of the generator 10 by a bottom support system (not shown) of a conventional design.
Two air distribution plates 30 and 31 extend horizontally through the entire width of each of chambers A and B, respectively. Air plenums 32 and 39 extend immediately below the chambers A and B, respectively, for introducing air upwardly through the corresponding portions of the air distribution plates 30 and 31, respectively, into the chambers.
The chamber A is defined by the air distribution plate 30, a pair of vertically-extending spaced walls 36 -9- ~L313~8~
and 38 and a diagonally-extending roof 40 while the chamber B is defined by the air distribution plate 31, the wall 38, and a vertically-extending wall 42 disposed in a spaced relation to the wall 38.
A third chamber C is defined by a vertical wall 44 extending in a spaced relation to the wall 42, a distribution plate 45 and an upper, diagonal roof 46. An air plenum 47 extends below the plate 45 for directing air upwardly through the plate into the chamber C. It is understood that a pair of spaced sidewalls (not shown) are provided which, together with the walls 36, 38, 42, and 44 form an enclosure, and that these sidewalls, along with the latter walls are formed by a plurality of vertically-extending waterwall tubes connected in an air-tight relationship.
Bundles of heat exchange tubes 48 and 50 are provided in the chambers A and C, respectively for circulating Eluid through the chambers as will be described in detail later.
The walls 38 and 42 extend for substantially the entire height of the generator 10 and an opening 52 is provided through the wall 38 in order to permit the flue gases from the chamber A to flow to the chamber B where - 1 o - ~313~8 !3 they mix with those from the chamber B. The flue gases then pass upwardly in the chamber B before passing through one or more openings 53 provided in the wall 92 and into a cyclone separator 54 disposed above the chamber C. The separator 54 includes a funnel portion 56 having a dipleg 58 connected to its lower outlet end and extending through the roof 46 and into the lower portion of the chamber C for reasons to be described later. It is understood that additional separators 54 can be provided as needed.
A heat recovery area, shown in general by the reference numeral 64, is disposed adjacent the upper portion of the chamber B on the side thereof opposite that of the cyclone separator 54. The heat recovery area 64 is defined by a vertical wall 66 extending in a spaced relationship to the wall 38 and a substantially horizontal roof 68 which spans the heat recovery area, the chamber B, and the cyclone separator 54.
A wall 69 extends across the top of the cyclone separator 54 and the top of the chamber B and, together with the wall 68, defines a duct for passing gases from the cyclone separator 54 to the heat recovery area, as will be described later. The walls 66, 68, and 69 may ~3~3~)~8 also be formed by a plurality of waterwall tubes connected in an air tight manner.
A gas control damper system 70 is disposed in the lower portion of the heat recovery area 64 and controls the flow of gas throuqh the heat recovery area in a manner to be described, before the gas passes over a tube bundle 72 and exits from a flue gas duct 74 to an air heater (not shown) in a manner also to be described in detail later.
A pump 76 is connected to the lower portion of the downcomers 26 of the steam drum 24. Since more than one downcomer 26 and pump 76 can be provided, manifolds 78 are connected to the inlet and-outlet of the pump(s) 76 for supplying water from the steam drum 24 to a plurality of substantially horizontally and vertically extending water lines, one of each of which are shown by the reference numerals 80 and 82.
A plurality of vertical feeders 83, one of which is shown in the drawing, extend from the water lines 80 and are connected to a header 84 which supplies water to a water tube wall 85 disposed in the heat recovery area 64, it being understood that other vertical feeders are connected to the water lines 80 for supplyinq water to the ~5 , - ., '~
-12- ~313~8 sidewalls (not shown) of the heat recovery area 64.
A plurality of feeders 86 extend from the water lines 80 and are connected to headers (not shown) forming portions of a pair of seal assemblies 88 associated with each wall 38 and 42. The seal assemblies 88 function to accommodate relative differential expansion between the lower portion of the steam generator 10 supported from the floor 18 and the upper portion of the steam generator top-supported by the hangers 22 and 28. Since the seal assemblies 88 are fully disclosed in co-pending CDN. Patent Application Serial No. 499,894 filed on Jan-uary 20, 1986 and assigned to the same assignee as the present invention, they will not be described in any further detail. It is understood that the headers associated with the seal assemblies 88 supply water to the waterwall tubes forming the upper portions of the walls 38 and 42.
An additional feeder 94 extends from each of the water lines 80 and supplies a header 96 for circulating water through a water tube wall 98 which, together with the walls 42 and 69, and the sidewalls (not shown), enclose the cyclone separator 59.
-13- ~3~3088 The vertical water lines 82 are respectively connected to horizontal water conduits 100 each of which has a plurality of vertically-extending feeders 102 extending therefrom which are connected to headers 104 connected to the lower ends of the walls 36, 38 and 42 for supplying water to the wall 36 and the lower portions of the walls 38 and 42. Additional feeders 106 supply water from the water conduits 100 to corresponding headers 108 for the bundle of water tubes 48 in the chamber A.
A pipe 110 extends from a boiler feed pumping and preheating system (not shown) to an inlet header 112 for the tube bundle 72. The outlet of the tube bundle 72 is connected, via a header 114, a transfer line 116, and an inlet header 118 to a bundle of water tubes 120 disposed within the heat recovery area 64 and functioning as a economizer. The outlet of the tube bundle 120 is connected, via a header 122 and a transfer line conduit 124, to the inlet of the steam drum 24. Water flow through the circuit of the present invention is established from the pumping and preheating system into and through the tube bundle 72, the tube bundle 120, and into the steam drum 24. This water is mixed with the water separated from the water/steam mixture supplied to the .
' ' ' ` ' , . . . .
-14- ~313~8~
drum 24 and the resulting water passes through the downcomer 26 and, via the pump(s) 76, into the manifold 78. The water then passes from the manifold 78 through the water lines 80, the feeders 83 and 94, and to the waterwalls 66, 85, 38, 42, and 98. The water lines 82 supply water, via the conduits 100 and the feeders 102 and 106 to the walls 36, 38, and 42, and to the tube bundle 48.
The reference numeral 130 refers to a plurality of headers disposed at the upper end portions of the 10 walls 66, 85, 38, 42, and 98, it being understood that the side walls associated with the heat recovery area 64, the chamber B and the cyclone separator 54 would have similar type headers. A plurality of risers 132 extend upwardly -from the headers 130 and connect with a conduit 133 which 15 extends from the endmost riser 132 to the steam drum 24 to transfer the fluid from the various headers in the wall into the steam drum.
The water passing through the walls 36 and 38 is partially converted to steam and passed to a pair of headers 134 while the water passing through the tube bundle 98 is also partially converted to steam and passed to a plurality of outlet headers, one of which is shown by -15- 13~3~
the reference numeral 135. The steam from the header 135 passes into a conduit 136 and the steam from the headers 134 is passed, via conduit 137, to the conduit 136. The conduit 136 is connected to the steam drum 24 so that the steam from the headers 134 and 135 mixes with the steam entering the steam drum 24 from the conduit 133 in the manner described above.
The superheat circuitry includes a bundle of tubes 140 functioning as a primary superheater disposed in the heat recovery area 64 and having an inlet header 142 connected, via a conduit 149, to the outlet of the steam drum 29. After passing through the tube bundle 140 the superheated steam exits, via a header 146. Although not shown in the drawing it is understood that a spray attemperator, or the like, is connected to the header 146 to reduce the temperature of the steam as necessary before the steam is introduced to a finishing superheater.
Although not shown in the drawings in the interest of clarity, it is understood that the finishing superheater may be formed by an additional tube bundle in the chamber A or by a tube bundle in the chamber C. ~fter passing through this superheater, the steam is then passed to the inlet of a turbine. Thus the finishing superheater -16- ~3~3088 circuit is independent of the steam generating circuit described above.
A plurality of tubes forming bundles 150 and 162 are provided in the heat recovery area 64 and each bundle functions as a reheater. One or two conduits, one of which is shown by the reference numeral 1~4, extend from the high pressure turbine (not shown) and is connected to an inlet header 166 which is connected to the tubes forming the tube bundles 160 and 162. After passing through the tube bundles 160 and 162 the reheated steam is passed to an outlet header 172 which, in turn, is connected, via one or two conduits 174, to a low pressure turbine (not shown). It is noted that this reheat flow circuitry is entirely independent from the steam generating flow circuitry and superheat circuitry described above.
Air from one or more forced draft fans 180 is passed, via a duct 182 and a plurality of vertical ducts 184 to the plenums 32, 34 and 47 e~tending below the chambers A, B, and C, respectively. Although omitted from the drawings in the interest of clarity, it is understood that a bed of particulate material is disposed in each of the chambers A, B, and C which is fluidized in respons~e to the -17- ~3~
air passing upwardly from the plenums 32, 34 and 47, respectively, through the air distribution plates 30, 3L, and 45 and into the latter chambers. It is also understood that each chamber A, B, and C may be subdivided by partitions, or the like (not shown), into segments that are used during start-up and for load control of the steam generator 10.
The fluidizing velocity of the air introduced into the bed in the chamber A is regulated in accordance with the size of the particles in the bed so that the particulate material in the chambers A and B is fluidized in a manner to create a "bubbling" bed with a minimum of particles being entrained by the air and gases passing through the bed. The velocity of the air introduced into the chamber B relative to the particle size in the bed is such that a "circulating" bed is formed, i.e. a bed in which the particulate material in the bed is fluidized to an extent that the combustion gas is very near saturation solids capacity for the entire length of the chamber B.
Chamber C is an inactive, or unfired, bed in that there is no introduction o particulate fresh fuel or adsorbent into the bed and no ignition of the fuel so that the air passing through the bed serves to cool the particulate material forming the bed, as will be explained.
-18- ~3~ 8 The fuel introduced to the beds in the chambers A and B is ignited and additional fuel and adsorbent is added to the beds by conventional feeders (not shown). The resulting flue gases, which include the gaseous products of combustion and the air passing through the beds, entrain a small portion of the relatively fine particulate material in the latter chambers. The resulting mixture of flue gases and particulate material in the chamber A
passes through the opening 52 in the wall 38 and into the chamber B where it combines with a similar mixture in the latter chamber. As indicated above, the velocity of the air passing, via the plenum 34, into the chamber B is such relative to the size of the particles in the latter chamber such that the particles are suspended in the flue gases and eventually transported up~ardly through the length of the chamber B. The flue gases with the entrained particles exit through the opening 53 formed in the upper portion of the wall 42 before passing into the cyclone separator 59. It is noted that, by virtue of the fact that chamber B is located between the chambers A and C, the fluidized bed in the chamber A is thermally isolated from the fluidized bed in the chamber C.
- 1 9 - ~3~
The particulate material is separated from the gases in the cyclone separator 54 and the gases pass upwardly into the conduit defined between the walls 68 and 69, through openings formed in the walls 42 and 38 and into the heat recovery area 64. A portion of the gases in the heat recovery area 64 passes through the wall 85 which has openings formed therein for this purpose, before the gases pass over the tube bundles 140 and 120 forming the primary superheater and the economizer, respectively. The remaining gases pass over the tube bundles 162 and 160 forming the reheaters.
The gases passing through the heat recovery area 64 in the foregoing manner then pass through the damper system 70, which can be adjusted as necessary to control the fraction of the total gas flow that is to flow across the tube bundle 140 forming the primary superheater and the tube bundle 120 forming the economizer. The gases then pass across the tube bundle 72 and through the outlet duct 74. It is understood that the duct 74 can be connected to an air heater (not shown) where the gases give up heat to the air from the forced draft fan 180 before the gases exit to a dust collector, induced draft fan, and/or stack (not shown). The air from the fan 180 ZS
.
-20- ~3~308~
is thus preheated before passing to the duct 182, as described above.
The solid particulate material separated in the cyclone separator 54 falls into the funnel portion 56 of the separator before discharging, via the dipleg 58, into the chamber C. Thus, a bed of the relative hot separated particulate material from the sepafator 54 is formed in the chamber C and is cooled by the cooling air passing from the plenum 47 through the plate 95 and fluidizing the material. Also, water from an external source, water from the previously mentioned boiler feed pumping system or steam from the superheat circuitry, is circulated through the tubes 50 to further cool the separated particulate material in the chamber C.
The method of the present invention provides several advantages. For example, the reheat circuitry is entirely independent of the steam generating circuitry and the superheat circuitry depicted. Moreover, the use of the three separate fluidized beds in the chambers A, B and C
enables the temperatures in each bed to be controlled independently. Also, by removing heat from the separated particulate material in the unfired bed C, the amount of heat exchange surface required in the chamber B per unit . . };
-21- 13~3~8 heat input to chamber B is reduced. ~urther, since the amount of heat exchange surface per unit heat input to chamber B is reduced, it becomes practical to increase the firing rate of chamber B. This allows a reduction in the firing rate, area and surface of the bubbling fluidized bed in chamber A. Further, the use of the unfired bed of particulate material in chamber C operating at a relatively low fluidizing velocity and consisting of relatively fine particles of the separated particulate material, results in a much higher in-bed tube heat transfer coefficient, thus reducing the overall immersed tubing required by the fluidized beds in chambers A and C. Also, since the reaction performance of the bubbling fluidized bed in chamber A is more sensitive to small particle sizes, the reduction in area and firing rate for this chamber enables the steam generator of the present invention to be more tolerant to small fuel and limestone particle sizes.
Still further, by allowing a greater percentage o combustion to occur in the circulating fluidized bed in chamber B, where relatively fine particulate fuel material can be used, the e~ficiency of sulfur capture by adsorbent : is increased to reduce the percentage of sulphur dioxide ' ~ , ' ' '~''~ ' '.
.
-22- ~3~3~
emissions. Also, the method of the present invention improves the fuel carbon utilization as a result of the larger circulating fluidized bed area in chamber B.
Finally, the overall height of the furnace can be reduced by virtue of the cooling of the separated particulate material in bed C.
Figures 2-4 depict alternate embodiments of the present invention and, for the convenience of presentation, only top plan views showing the chambers A, B and C, the funnel portion 56 of the cyclone separator 54 and the dipleg 58 are shown. According to the embodiment of Fig. 2, the dipleg 58 of the funnel portion 56 of the cyclone separator 54 tnot shown) is located in a corner of the chamber C. A dipleg 58' of another funnel portion 56' of another separator is located in another corner of the chamber C to provide for the introduction of the separated particulate material from two cyclone separators.
According to the embodiment of Fig. 3, chambers A and B are in a side-by-side relationship as in the embodiment of Figs. 1 and 2, but the unfired chamber C is located in a plane behind that of chamber B. As in the previous embodiment, the two diplegs 58 and 58' of the funnel portions 56 and 56' of two cyclone separators are located in two corners of the chamber C.
1313~8~3 According to the embodiment of Fig. 4, there are two unfired chambers Cl and C2 disposed to the side of chamber B and spaced apart in a front-to-rear relationship as shown. The funnel portion 56 of the cyclone separator 54 is positioned over the chamber Cl with its dipleg 58 extending slightly in front thereof. A funnel portion 56' of another cyclone separator is provided with its dipleg 58' extending between the two chambers, and still another separator and funnel portion 56" is disposed over the chamber C2 with its dipleg 58" located slightly to the rear of chamber C2.
It is understood that the funnel portions 56, 56', and 56" are located relative to the opening 53 in the wall ~2 and to the walls 68 and 69 so that the mixture of flue gases and particulate material in the chamber B passes into each of their corresponding separators and so that the separated gases pass from the separators to the conduit defined between the walls 68 and 69, as discussed above.
It is understood that several other variations rnay be made in the foregoing without departing from the scope of the invention. For example, the cyclone separator 54 can extend between the heat recovery area 64 and the chambers A, ~ and C, and the diplegs 58 do not have to extend -2q- ~3~3~38 directly into the chamber C but can go through a conventional seal pot or the like disposed externally of the chamber C and another dipleg can be provided that extends from the seal pot into the chamber C.
Other modifications, changes, and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention therein.
Claims (14)
1. A method of operating a steam generator comprising the steps of forming at least two beds of particulate material containing fuel in a vessel, combusting the fuel in each of said beds, introducing air and additional fuel into each of said beds to fluidize said beds to promote the combustion of said fuel, establishing a first flow circuit for passing water in a heat exchange relation to at least one of said beds for converting said water to steam, combining a mixture of flue gases and the entrained particulate material from both of said beds, separating said entrained particulate material from the flue gases of said combined mixture, passing said separated particulate material to a third bed in said vessel, and introducing air to said third bed to fluidize and cool said separated particulate material.
2. The method of claim 1 further comprising the step of passing said steam from said first flow circuit to a steam drum, establishing a second flow circuit for receiving steam from said steam drum, passing said separated flue gases in a heat exchange relation with said second flow circuit for superheating said steam, and passing said superheated steam to external equipment.
3. The method of claim 2 further comprising the steps of establishing a third flow circuit independent of said first and second flow circuits for receiving said steam from said external equipment, and passing said separated flue gases in a heat exchange relation with said third flow circuit for reheating said steam.
4. The method of claim 1 further comprising the step of controlling the velocity of air introduced to said two beds relative to the size of the particulate material in said beds so that said one bed operates as a bubbling bed and the other bed operates as a circulating bed.
5. The method of claim 1 wherein said first flow circuit includes water tubes forming walls defining said one bed, and heat exchange tubes disposed in at least a portion of said one bed.
6. The method of claim 1 wherein said separated particles are directly passed into said third bed without passing over any heat exchange surfaces.
7. The method of claim 1 further comprising the step of regulating the operating temperature of each of said beds independently of the operating temperature of the other beds.
8. The method of claim 1 wherein said step of combining comprises the step of directing a mixture of flue gases and the entrained particulate material from said one bed where it combines with the flue gases and entrained particulate from the other of said two beds.
9. A steam generator comprising a vessel, means of forming at least two beds of particulate material containing fuel in said vessel, means for introducing air and fuel into each of said beds to fluidize said beds and combust said fuel, first flow circuit means for passing water in a heat exchange relation to one of said beds for converting said water to steam, means for combining the flue gases and the entrained particulate material from both of said beds, means for separating said entrained particulate materials from the flue gases of said combined mixture, means for forming a third bed, means for passing said separated particulate material into said third bed, means for introducing air to said third bed to fluidize said separated particulate material, and means for cooling said separated particulate material.
10. The steam generator of claim 9 further comprising means for passing said steam from said first flow circuit means to a steam drum, second flow circuit means for receiving steam from said steam drum, means for passing said separated flue gases in a heat exchange relation with said second flow circuit means for superheating said steam, and means for passing said superheated steam to external equipment.
11. The steam generator of claim 10 further comprising third flow circuit means independent of said first and second flow circuit means for receiving said steam from said external equipment, and means for passing said separated flue gases in a heat exchange relation with said third flow circuit means for reheating said steam.
12. The steam generator of claim 9 further comprising means for controlling the velocity of air introduced to said beds relative to the size of the particulate material in said beds so that said one bed operates as a bubbling bed and the other of said two beds operates as a circulating bed.
13. The steam generator of claim 9 wherein said first flow circuit means comprises a plurality of water tubes forming walls defining said one bed and heat exchange tubes disposed in at least a portion of said one bed.
14. The steam generator of claim 9 further comprising means for regulating the operating temperature of said one bed independently of the operating temperature of the other beds.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US10051087A | 1987-09-24 | 1987-09-24 | |
| US100,510 | 1987-09-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1313088C true CA1313088C (en) | 1993-01-26 |
Family
ID=22280136
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000573297A Expired - Fee Related CA1313088C (en) | 1987-09-24 | 1988-07-28 | Steam generator and method of operating same utilizing separate fluid and combined gas flow circuits |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS6490901A (en) |
| CA (1) | CA1313088C (en) |
| ES (1) | ES2010371A6 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007224690A (en) * | 2006-02-27 | 2007-09-06 | Sumitomo Forestry Co Ltd | Balcony |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5749701A (en) * | 1980-09-10 | 1982-03-23 | Babcock Hitachi Kk | Fluidized bed boiler |
| CH652190A5 (en) * | 1981-04-23 | 1985-10-31 | Sulzer Ag | STEAM GENERATOR WITH FLUIDIZED BURN FIRING. |
| DE3133298A1 (en) * | 1981-08-22 | 1983-03-03 | Deutsche Babcock Ag, 4200 Oberhausen | STEAM GENERATOR WITH A MAIN BOILER AND A FLUID BURN FIRING |
| JPS5944506A (en) * | 1982-09-03 | 1984-03-13 | 石川島播磨重工業株式会社 | Reheating boiler |
| US4617877A (en) * | 1985-07-15 | 1986-10-21 | Foster Wheeler Energy Corporation | Fluidized bed steam generator and method of generating steam with flyash recycle |
| JPS6226401A (en) * | 1985-07-25 | 1987-02-04 | 三井造船株式会社 | Circulation type fluidized bed boiler |
-
1988
- 1988-07-28 CA CA000573297A patent/CA1313088C/en not_active Expired - Fee Related
- 1988-08-09 JP JP19728788A patent/JPS6490901A/en active Pending
- 1988-09-22 ES ES8802879A patent/ES2010371A6/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| ES2010371A6 (en) | 1989-11-01 |
| JPS6490901A (en) | 1989-04-10 |
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