Title of Invention	A SORBENT CONDITIONING AND DIRECT FEED APPARATUS FOR A STEAM GENERATOR AND A METHOD FOR RETROFITTING A STEAM GENERATOR WITH SAME .
Abstract	A sorbent conditioning and direct feed apparatus for direct feeding of a conditioned solid sorbent to a fluidized bed combustor (12) comprising raw solid sorbent storage means (102); particle size reducing means (112) for reducing the particle size of solid sorbent supplied thereto from the raw solid sorbent storage means from a relatively coarse particle size to a relatively smaller fine particle size; transport means (118) for transporting to the combustor (12) solid sorbent that has been conditioned by the particle size reducing means in a separate particle size reduction operation prior to the supply thereof to the transport means in a manner in which most of the conditioned solid sorbent are delivered from the particle size reducing means (112) to the combustor (12) within a predetermined time period following their size reduction whereby conditioned solid sorbent is fed to the combustor with substantially no intermediate storage of the solid sorbent between the raw solid sorbent storage means (102) and the transport means (118); characterized in the control means (122) being operatively connected to the raw solid sorbent storage means (102) and the particle size reducing means (112) for controlling the feed of conditioned solid sorbent in the fluidized bed combustor; and in the means for sensing a sulfur concentration (132) in the fluidized bed combustor being operatively connected to the control means (122), the control means being operable to control the feed of conditioned solid sorbent to the fluidized bed combustor (12) in response to a sensed sulfur concentration condition of the fluidized bed combustor.

Title of Invention

A SORBENT CONDITIONING AND DIRECT FEED APPARATUS FOR A STEAM GENERATOR AND A METHOD FOR RETROFITTING A STEAM GENERATOR WITH SAME .

Abstract

A sorbent conditioning and direct feed apparatus for direct feeding of a conditioned solid sorbent to a fluidized bed combustor (12) comprising raw solid sorbent storage means (102); particle size reducing means (112) for reducing the particle size of solid sorbent supplied thereto from the raw solid sorbent storage means from a relatively coarse particle size to a relatively smaller fine particle size; transport means (118) for transporting to the combustor (12) solid sorbent that has been conditioned by the particle size reducing means in a separate particle size reduction operation prior to the supply thereof to the transport means in a manner in which most of the conditioned solid sorbent are delivered from the particle size reducing means (112) to the combustor (12) within a predetermined time period following their size reduction whereby conditioned solid sorbent is fed to the combustor with substantially no intermediate storage of the solid sorbent between the raw solid sorbent storage means (102) and the transport means (118); characterized in the control means (122) being operatively connected to the raw solid sorbent storage means (102) and the particle size reducing means (112) for controlling the feed of conditioned solid sorbent in the fluidized bed combustor; and in the means for sensing a sulfur concentration (132) in the fluidized bed combustor being operatively connected to the control means (122), the control means being operable to control the feed of conditioned solid sorbent to the fluidized bed combustor (12) in response to a sensed sulfur concentration condition of the fluidized bed combustor.

Full Text	BACKGROUND OF THE INVENTION The present invention relates to a sorbent conditioning and direct feed apparatus which is suitable for use in association with a fossil fuel-fired steam generator including, in particular, a circulating fluidized bed steam generator in a new utility unit application or a retrofit application in an existing utility unit. Limestone is a natural mineral principally comprised of calcium carbonate, CaCO3, and limestone is used as a desulfurizing or scrubbing medium in fluidized bed combustion units. In these units, combustion materials such as coal and the like are fluidized and combusted in a combustion vessel by contact with upflowing high temperature gasses. Limestone can be mixed with the combustion materials pnor to feeding of the combined fuel-sorbent mixture into the unit and the desulfunzation process takes place during combustion. Since the scrubbing or desulfunzation process is a chemical reaction, the proper stoichiometric ratio of limestone containing calcium carbonate to flue gas will produce the most efficient reaction. In order for the desulfunzation reaction to proceed efficiently and with minimal waste, the limestone must be conditioned such as by gnnding to produce a defined panicle size prior to use and it is particularly important in the fluidized bed combustion process to control limestone panicle size distribution so as to thereby ensure an efficient desulfunzation process. If the particles are too large, the desulfurization process will not be efficient because there is insufficient limestone panicle surface area to react with the flue gas. On the other hand, if the particles are too small, the limestone will be earned out of the vessel with the flue gas before it can react to remove the sulfur. Conventional limestone preparation systems often include a drying system having a cyclone or baghouse and typically comprise as well storage hoppers, conveyors, crushing and grinding machines and, in some configurations, vibrating screens. Such conventional systems effect particle size reduction of the limestone in discrete steps including, for example, multiple passes of the limestone particles through size reduction units which is typically performed to progressively reduce the particle size from a relatively larger or coarse panicle size to a relatively smaller or fine particle size suitable for introduction into the combustion vessel. Thus, it can be appreciated that such conventional limestone preparation systems generally have a complexity which contributes significantly to their cost and the number of processing operations and transport paths between the various components adds to the operational complexity and maintenance costs of such systems. Conventional limestone storage and feed systems also typically require separate preparation and/storage facilities for the raw sorbent and these facilities add to the capital cost of the utility unit. Also, such facilities may be sited several hundred meters from the combustor of the utility unit, thus adding to the overall space requirements of the utility unit. SUMMARY OF THE INVENTION To thus summarize, a need has been evidenced in the prior art for a sorbent conditioning and direct feed apparatus that would be particularly suited for use in effecting the pulverization of sorbent material such as, for example, limestone, and the feed thereof directly to a steam generator including, in particular, a circulating fluidized bed steam generator. It is, therefore, an object of the present invention to provide a new and improved sorbent conditioning and direct feed apparatus that is particularly suited for use in effecting the pulverization of sorbent material such as, for example, limestone, and the feed thereof directly to a steam generator including,in particular, a circulating fluidized bed steam generator. Yet a further object of the present invention is to provide such an improved sorbent conditioning and direct feed apparatus which is suitable for installation in new steam generator facilities including, in particular, a circulating fluidized bed steam generator facility. Yet another object of the present invention is to provide such an improved sorbent conditioning and direct feed apparatus which is capable of being retrofitted in connection with existing steam generator facilities including, in particular, a circulating fluidized bed steam generator facility. In accordance with one aspect of the present invention, these and other objects of the present invention are achieved by an improved sorbent conditioning and direct feed apparatus which is suitable for installation in new steam generator facilities including, in particular, a circulating fluidized bed steam generator facility and which is capable of being retrofitted in connection with existing steam generator facilities including, in particular, a circulating fluidized bed steam generator facility. In accordance with the present invention, there is thus provided a sorbent conditioning and direct feed apparatus operable to effect the direct feeding of a conditioned solid sorbent to the combustor. The apparatus includes a raw solid sorbent storage means and a particle size reducing means for reducing the particle size of solid sorbent supplied thereto from the raw solid sorbent storage means from a relatively larger coarse particle size to a relatively smaller fine particle. Also, the apparatus includes transport for transporting solid sorbent which has been conditioned by the particle size reducing means to the combustor in a manner in which, on average, at least ninety percent (90%) of the conditioned solid sorbent are delivered from the particle size reducing means to the combustor in less than thirty (30) minutes) following their size reduction, whereby conditioned solid sorbent is fed to the combustor with substantially no intermediate storage of the solid sorbent between the raw solid sorbent storage means and the transport means. According to one aspect of the preferred embodiment of the present invention, the combustor is a fluidizcd bed combustor. According to another aspect of the preferred embodiment of the present invention, the transport means is a fuel feed transport means operable to transport as well conditioned solid fossil fuel to the fluidized bed combustor, whereby the conditioned solid sorbent and the conditioned solid fossil fuel are fed as a mixture to the fluidized bed combustor. Additionally, the sorbent conditioning and direct feed apparatus preferably comprises control means operativcly connected to the raw solid sorbent storage means, the particle size reducing means, and the transport means for controlling the feed of conditioned solid sorbent to the fluidized bed combustor in accordance with a predetermined sorbent feed regime. According to yet another aspect of the preferred embodiment of the present invention, the sorbent conditioning and direct feed apparatus further comprises means for sensing an operating condition of the fluidized bed combustor operatively connected to the control means, the control means being operable to control the feed of conditioned solid sorbent to the fluidized bed combustor in response to a sensed operating condition of the fluidized bed combustor. The means for sensing an operating condition of the fluidized bed combustor can be operable to sense a sulfur concentration in the fluidized bed combustor. According to a further additional aspect of the preferred embodiment of the present invention, the particle size reducing means is a roller mill. Alternatively, the particle size reducing means is a roll crusher. Also, according to a supplemental aspect of the preferred embodiment of the present invention, the conditioned solid fossil fuel is subjected to a separate particle size reduction operation prior to the supply thereof to the transport means and the fluidized bed combustor is supplied by the transport means with a mixture of conditioned solid fossil fuel and conditioned solid sorbent. The transport means may alternatively be configured as a pneumatic transport assembly operable to pneumatically transport conditioned sorbent to the steam generator from any air swept mill or crusher or as a mechanical transport assembly. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 is a side elevational view of a circulating fluidized bed steam generator of the type with which the sorbent conditioning and direct feed apparatus of the present invention can be operatively associated to feed conditioned sorbent thereto; Figure 2 is a side schematic view of one embodiment of the sorbent conditioning and direct feed apparatus of the present invention; Figure 3 is an enlarged side view in partial section of the gravimetric feed device of the one embodiment of the sorbent conditioning and direct feed apparatus shown in Figure 2; Figure 4 is an enlarged side elevational view of a roll crusher for use with the one embodiment of the sorbent conditioning and direct feed apparatus shown in Figure 1; Figure 5A is a side schematic view of one variation of an embodiment of the sorbent conditioning and direct feed apparatus of the present invention having the roll crusher shown in Figure 4; Figure 5B is a side schematic view of another variation of an embodiment of the sorbent conditioning and direct feed apparatus of the present invention having the roll crusher shown in Figure 4; and Figure 6 is a side schematic view of a further embodiment of the sorbent conditioning and direct feed apparatus of the present invention for use with a direct fired pulverized coal combustor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to Figure 1 there is shown a typical circulating fluidized bed steam generator to which the sorbent conditioning and direct feed apparatus of the present invention has particular application. Crushed fuel and sorbent are normally fed to the lower portion of a combustor 12. Typically the fuel and sorbent material are fed to a chute (not shown) that is disposed at approximately a 60 degree angle from horizontal. Thus, the fuel and sorbent pass along the chute and into the combustor 12. Primary air is supplied to the bottom of the combustor through an air distributor 14 with secondary air fed through one or more air ports at various elevations in the lower part of the combustor. Combustion takes place throughout the combustor 12 which is filled with bed material. Flue gas and entrained solids leave the combustor 12 and enter one or more cyclones 16 where the solids are separated and fall to a seal pot 18. From the seal pot 18, the solids are recycled to the combustor 12. Optionally, some solids may be diverted through an ash control valve 20 to a fluidized bed heat exchanger 22. Flue gas leaving the cyclone 16 passes to a convective pass 24 and then to an air heater, a bag house or an electrostatic precipitator, and fan (not shown). The solids in the combustor 12 are periodically allowed to pass out of the combustor 12 by draining these hot solids through an ash cooler 30 or, in lieu of the ash cooler 30, an ash screw may be provided to periodically remove the hot solids. One preferred embodiment of the sorbent conditioning and direct feed apparatus of the present invention is illustrated in the schematic arrangement of Figure 2 in which limestone, which has not yet been subjected to a particle size reduction treatment, is conditioned into a final particle size distribution in which the conditioned limestone can be fed into a steam generator. The steam generator can be, for example, a circulating fluidized bed steam generator such as the one illustrated in Figure 1 having a combustor 12. Limestone is supplied from a conventional limestone storage facility 102 to a feed hopper 104. Limestone is then fed by the feed hopper 104 onto a weigh scale belt 106 which is part of a gravimetric feeder device 108 and is moved thereby to fall through a chute 110 into the selected particle size reducing apparatus 112 which may be configured as, for example, a roller mill or a roll crusher. The particle size reducing apparatus 112 is driven by a conventional prime mover (not shown) which is controllable as will be presently described. A conventional rotary valve 114 controls the supply of the conditioned limestone having a size below a predetermined size which has exited the particle size reducing apparatus 112 via an outlet 116. The rotary valve 1 14 controls the supply of conditioned limestone to a pneumatic transport assembly 118 which transports the conditioned limestone to feed inlets of the combustor 12. One configuration of the panicle size reducing apparatus 112 which can advantageously make use of a transport arrangement of the type including the rotary valve 114, the outlet 116. and the pneumatic transport assembly 118 could be, for example, a roll crusher. Alternatively, in accordance with a variation of the sorbent conditioning and direct feed apparatus of the present invention, an air swept arrangement having conventional features may be deployed in lieu of the rotary valve 114, the outlet 116, and the pneumatic transport assembly 118 to effect the transport of the conditioned sorbent from the particle size reducing apparatus 112 to the combustor 12. One configuration of the particle size reducing apparatus 112 which can advantageously make use of a transport arrangement of the type including an air swept arrangement could be, for example, a roller mill. This air swept arrangement could include, for example, a suitable conventional heated air take-off duct assembly to convey heated air from the combustor 12 to the particle size reducing apparatus 112 and a suitable conventional return duct assembly to convey the heated air, with the conditioned sorbent entrained therewith, from the particle size reducing apparatus 112 to the combustor 12. Conditioned solid fuel such as, for example, crushed coal, is supplied separately to the combustor 12 from a solid fuel feed supply 120. A limestone feed system, control unit 122 controls the limestone feed operation through the various assemblies just noted to ultimately feed conditioned limestone to the circulating fluidized bed steam generator. The limestone feed system control unit 122 is connected via a connector 124 to the drive motor which drives the belt of the weight scale belt 106 of the gravimetric feeder device 108 and is connected via a connector 126 to the weight assessment sub-assembly of the gravimetric feeder device 108 for receiving from the connectors 124 and 126 signals relating to the output rate and the quantity (i.e., volume by weight) of the limestone being fed by the gravimetric feeder device 108 to the particle size reducing apparatus 112. A connector 128 connects the limestone feed system control unit 122 to the dnve motor of the particle size reducing apparatus 1 12 and a connector 130 connects the limestone feed system control unit to an optional rotary valve 114. The limestone feed system control unit can. thus, in connection with selected particle size reducing scenarios, control the operation of the particle size reducing apparatus 112 and the supply rate of the rotary valve 1 14. In accordance, for example, with one typical control regime, as the limestone feed system control unit 122 controls the speed of the particle size reducing apparatus 112 to thereby increase the output of the conditioned limestone, the rotary valve 114 is controlled to increase the supply rate of conditioned limestone to the fuel feed transporter 118. A conventional sulfur level sensing device 132 is located relative to the combustor 12 for continuously sensing or monitoring the sulfur level in the flue gas, whereby the sulfur level sensing device 132 may be located, for example, on the flue gas outlet stack. The sulfur level sensing device 132 is connected via a connector 134 to the limestone feed system control unit 122 for providing signals thereto concerning the sensed sulfur level in the flue gas. A moisture control assembly 136 is provided to control the moisture content of the conditioned limestone to a desired level. The moisture control assembly 136 preferably selectively effects drying of the raw limestone upstream of the panicle size reducing apparatus 112 by, for example, drying the raw limestone stored in the limestone storage facility 102 to a predetermined feed moisture of, say, 1 to 10 such that the conditioned limestone fed to the combustor 12 has the desired moisture content. The moisture control assembly 136 can be configured with a conventional externally powered or fueled drying device such as, for example, a gas-fired drying device which applies heated air to the raw limestone to effect drying thereof. Preferably, however, the moisture control assembly 136 is configured to use process heat generated in connection with the operation of the steam generator and, to this end, the moisture control assembly 136 may include an optional externally powered heater 138 or a duct and damper sub-assembly which communicates the particle size reducing apparatus 112 with the combustor 12 such that process heat from the combustor 12 can be selectively applied to the limestone in the particle size reducing apparatus 112 to effect the drying thereof. The sorbent conditioning and direct feed apparatus of the present invention advantageously permits a process heat arrangement of this type to be used in a cost effective manner in that the sorbent conditioning and direct feed apparatus can be located sufficiently proximate to the combustor 12 - that is, typically less than 50 meters therefrom - to permit process heat to be transferred to the particle size reducing apparatus 112 in a cost favorable manner. In contrast, in a conventional limestone storage and conditioning arrangement, the limestone storage facility which performs the limestone storage function of the limestone storage facility 102 is typically located several hundred meters from the combustor and it is thus not cost justifiable to deliver process heat from the combustor over the several hundred meter distance. The operation of the particle size reducing apparatus 112 to effect a size reduction of the limestone is controlled in response to certain signals received by the limestone feed system control unit 122 from the various components connected thereto. Thus, for example, in accordance with one exemplary limestone feed control regime, the limestone feed system control unit 122 receives signals from the sulfur level sensing device 132 concerning the sensed sulfur level in the flue gas and the limestone feed system control unit 122 evaluates these signals to determine the need for feeding limestone to the combustor. When the limestone feed system control unit 122 determines a need to supply the prepared limestone particles to the combustor 12. the limestone feed system control unit 122 controls the feed hopper 104 to feed raw untrammeled limestone onto the gravimetric feed device 108. The operation of the gravimetric feed device 108 is also controlled by the limestone feed system control unit 122 to effect the supply of a predetermined volume (by weight) of raw untrammeled limestone to the particle size reducing apparatus 112. The particle size reducing apparatus 112 then performs a size reduction operation on the limestone supplied thereto and the thus conditioned limestone panicles exit the particle size reducing apparatus 112 into the pneumatic transport assembly 118. If the particle size reducing 112 is configured, for example, as a conventional roller mill, the optional rotary valve 114 is omitted and the conditioned limestone particles will exit the roller mill directly to the pneumatic transport assembly 118 as a function of the classification operation of the roller mill. The thus supplied limestone particles are then transported to the combustor 1 2. In connection with a sensing operation by the sulfur level sensing device 132 which indicates that the desired sulfur level in the combustor 12 has been achieved, the limestone feed system control unit 122 controls the system to reduce or increase the supply of prepared limestone. As shown in Figure 3, the gravimetric feed device 108 is preferably configured as a single belt feeder 240 for sorbent. Disposed at spaced intervals along the belt feeder 240 is a first belt scale 242. Disposed upstream respectively from the belt scale 242 is the feed hopper 204 which feeds sorbent to the belt feeder 240. A programmable logic controller 250 receives inputs from the first belt scale 242. The sorbent will be dumped off the belt feeder 240 at the right (as shown in the drawing) hand end of the belt feeder 240. A programmable logic controller 250 is optionally provided to which is supplied an input (the weight) from the belt scale 242. The supply of sorbent to the belt feeder 240 from the feed hopper 204 is controlled by a rotary valve 254. The rotary valve 254 is controlled by a motor 256 which is in turn controlled by the programmable logic controller 250. The control of the motor 256 driving the rotary valve 254 determines the actual amount of sorbent delivered to the belt feeder 240. The programmable logic controller 250 compares the actual feed rate to the intended or desired gravimetric feed rate. It will be understood that a motor 260 is provided to drive the continuous belt feeder 240 and that this motor 260 is driven at a speed and/or periods of time corresponding to the desired rate of delivery of sorbent to the limestone conditioning operation and from there, to the combustion process in the circulating fluidized bed steam generator. More specifically, the belt scale 242 sends a signal to the motor 260 and thus controls the motor 260. The signal from the programmable logic controller 250 to the motor 260 is a function of the weight of the sorbent added to the belt feeder 240 per unit of time. It will also be seen that the relative rate of sorbent feed is controlled by the motor 256 controlling the valve 254 and that this control is achieved by the programmable logic controller 250. In some forms of the invention, the programmable logic controller 250 may be a dedicated programmable logic controller. The programmable logic controller 250 is a common commercial commodity and typical dedicated programmable logic controllers. In other forms of the invention the programmable logic controller 250 may be part of the distributed control system of the plant in which the fluidized bed steam generator is located. Thus, the one embodiment of the sorbent conditioning and direct feed apparatus illustrated in Figure 2 is operable to effect the direct feeding of a conditioned solid sorbent to the combustor 12. The apparatus includes a raw solid sorbent storage means in the form of the limestone storage facility 102 and a particle size reducing means for reducing the particle size of solid sorbent supplied thereto from the raw solid sorbent storage means from a relatively larger coarse particle size to a relatively smaller fine particle size in the form of the particle size reducing apparatus 112. Also, the apparatus includes transport means in the form of the fuel feed transporter 118 for transporting solid sorbent which has been conditioned by the particle size reducing means to the combustor in a manner in which, on average, at least ninety percent (90%) of the conditioned solid sorbent are delivered from the particle size reducing means to the combustor in less than thirty (30) minutes) following their size reduction, whereby conditioned solid sorbent is fed to the combustor with substantially no intermediate storage of the solid sorbent between the raw solid sorbent storage means and the transport means. Thus, it is contemplated that the present invention encompasses (a) those material feed apparatus configured to deliver the entirety of the conditioned solid sorbent directly to the combustor without any diversion enroute of a portion of the conditioned solid sorbent; and (b) those material feed apparatus configured to permit an insubstantial enroute diversion of the conditioned solid sorbent during its travel between the particle side reducing means and the combustor. An example of an insubstantial enroute diversion of the conditioned solid sorbent is the removal of a sample size portion of the conditioned solid sorbent to permit testing or quality control measures to be performed on the removed sample size portion. Another example of an insubstantial enroute diversion of the conditioned solid sorbent is the creation of an operational reserve of the conditioned solid sorbent designed to accommodate inline feed variations in the mass flow of the conditioned solid sorbent and this volume of this operational reserve is considered to be many orders of magnitude less than the storage volume of conditioned solid sorbent which is typically stored in a dedicated large volume silo or other structure in connection with conventional conditioned solid sorbent preparation and feed arrangements. As shown in Figure 4 in conjunction with, respectively, Figures 5A and 5B, a roll crusher can be provided as the preferred configuration of the particle size reducing apparatus 112 for effecting the size reduction of the limestone particles. As seen in one variation of such a roll crusher embodiment shown in Figure 5A, this variation of the one embodiment of the sorbent conditioning and direct feed apparatus includes a roll crusher 412 for effecting the particle size reduction of the limestone. The roll crusher 412, as seen in more detail in Figure 4, comprises a feed area 414 for feeding raw untrammeled limestone from a raw material feed arrangement 416, a first pair of grinding rolls 418, 420 and a second pair of grinding rolls 422, 424. The first pair 418, 420 of grinding rolls and the second pair 422, 424 of grinding rolls are each driven by independent drive means (not shown) such as electric motors. The raw untrammeled limestone is fed from the feed area 414 by gravity. The first pair of grinding rolls 418, 420 comprises opposing rotating rolls 418, 420 which each rotate about a horizontal axis in a respective direction of rotation opposite to that of the other grinding roll. The rolls 418, 240 form therebetween a first nip 430, which is adjustably or fixedly set in dependence upon the raw untrammeled limestone particle size. The second pair of grinding rolls 422, 424 comprises opposing rotating rolls which each rotate about a horizontal axis in a respective direction of rotation opposite to that of the other grinding roll. The rolls 422, 424 are separated by a second nip 434, which is based upon the final product particle size distribution desired. A preferred particle size distribution is comprised of particles smaller than 2 mm and, generally, smaller than J mm, and having a mean size of about 300 microns. Preferably, the panicle size distribution is produced with the nip 434 between the second set of rolls 422, 424 in the range of about 2 to 3 mm. Each of the grinding rolls of the first pair 418, 420 and the second pair 422, 424 of grinding rolls rotate at different velocities relative to its opposed paired grinding roll to produce a shear in the particles as they pass into and through the nip 430 and the nip 434. Raw untrammeled limestone is fed by the raw material feed arrangement 416 into the feed area 414. The limestone then falls into the nip area 430 of the first pair of rolls 418, 420. Grinding of the limestone particles occurs in the nip 430 and, as the limestone travels therethrough, the compression and shear imparted by the rolls 418, 420, on the limestone causes the particles to work against each other thereby breaking down or fracturing the crystalline structure. The particle size distribution of the product is controlled in that, the larger the nip, the less the work that is done on the limestone particles, while, the smaller the nip, the greater the work that is done on the limestone particles. As the limestone passes beyond the first nip 430, it falls into the second nip 434 at which it is subjected to further size reduction by the second pair of grinding rolls 422, 424. The one variation of the roll crusher embodiment of the sorbent conditioning and direct feed apparatus shown in Figures 4 and 5A also includes, in lieu of the pneumatic transport assembly 118 described with respect to Figure 2, a fuel feed transporter 436 for feeding the conditioned limestone to the circulating fluidized bed steam generator along with raw or conditioned solid fuel such as. for example, raw untrammeied coal or crushed coal, which is supplied from a solid fuel feed supply. The fuel feed transporter 436 may be configured, for example, as a conventional mechanical transporter in the form of, for example, an endless belt conveyor. The conditioned limestone particles exiting the second pair of grinding rolls 422, 424, having thus been reduced in size to achieve the desired particle size distribution, are then released into the pneumatic transport stream of the pneumatic transport assembly 436 in a metered manner by means, for example, of a conventional rotary valve arrangement, and supplied thereby along with the solid fuel into the circulating fluidized bed steam generator. As seen in another variation of such a roll crusher embodiment shown in Figure 5B, this variation of the one embodiment of the sorbent conditioning and direct feed apparatus includes all of the features of the one roll crusher embodiment variation shown in Figure 5A with the addition, in this other variation, of a drying arrangement 438 for effecting at least some reduction in the moisture content of the raw limestone prior to its feed into the roll crusher. The drying arrangement 438 may be configured, for example, as a conventional tempered air drying arrangement which diverts a portion of the air heated in the circulating fluidized bed steam generator and, by means of a conventional rotary dryer, passes the heated air into contact with the raw limestone with the now cooler heated air being returned via a return loop to the steam generator. A further preferred embodiment of the sorbent conditioning and direct feed apparatus of the present invention is illustrated in the schematic arrangement of Figure 6 in which limestone, which has not yet been subjected to a particle size reduction treatment, is conditioned into a final particle size distribution in which the conditioned limestone can be fed into a direct fired steam generator such as a pulverized coal combustor having comer mounted or wall mounted burners for directly injecting pulverized coal and conditioned limestone into the combustor. The steam generator shown in Figure 6 is exemplarily illustrated as a conventional pulverized coal direct fired boiler 500. Limestone is supplied from a conventional limestone storage facility 502 to a feed hopper 504. Limestone is then fed by the feed hopper 504 onto a weigh scale belt 506 which is part of a gravimetric feeder device 508 and is moved thereby to fall through a chute 510 into the selected limestone size conditioning apparatus such as, for example, a roller mill 512. The roller mill 512 is driven by a conventional prime mover (not shown) which is controllable as will be presently described. The roller mill 512 may optionally include a dynamic classifier or a static classifier for classifying the limestone particles conditioned by the roller mill. Merely for the purpose of illustrating such an option, the sorbent conditioning and direct feed apparatus shown in Figure 6 is provided with a dynamic classifier 514, whose rate of rotation is controllable as will be presently described, which classifies the limestone in the roller mill 512 such that a portion of the conditioned limestone having a size below a predetermined size are permitted to exit the roller mill 512 via an outlet 516 while another portion of the limestone having a size above the predetermined size are returned to the grinding area of the roller mill 512 for further size reduction. The outlet 516 communicates with a conventional pneumatic transport assembly 518 operable to pneumatically transport conditioned limestone from the roller mill 512 to the plurality of burners at which the conditioned limestone is mixed with pulverized coal during direct firing thereof into the pulverized coal direct fired boiler 500. The conditioned limestone travels from the outlet 516 via the pneumatic transport assembly 518 to the pulverized coal direct fired boiler 500 at which it is combined with the pulverized solid fuel such as, for example, pulverized coal, which is supplied from a solid fuel feed supply 520. The pulverized coal is itself supplied to the solid fuel feed supply 520 in a separate solid fossil fuel preparation process which may include, for example, size reduction of raw untrammeled coal in a conventional pulverizer 521. The conventional pulverizer 521 uses some combination of impact, attrition and crushing to reduce a solid fuel to a particular particle size. Several types of pulverizer mills can be employed for the pulverization of the solid fuel, which may be, for example, coal, to a particulate size appropriate for firing in a furnace. These can comprise, for example, ball-tube mills, impact mills, attrition mills, ball race mills, and ring roll or bowl mills. Most typically, however, bowl mills are employed for the pulverization of the solid fuel to allow for direct firing of the pulverized fuel entrained in an air stream. A limestone feed system control unit 522 controls the limestone feed operation through the various assemblies just noted to ultimately feed conditioned limestone to the pulverized coal direct fired boiler 500. The limestone feed system control unit is connected via a connector 524 to the drive motor which drives the belt of the weight scale belt 506 of the gravimetric feeder device 508 and is connected via a connector 526 to the weight assessment sub-assembly of the gravimetric feeder device 508 for receiving from the connectors 524 and 526 signals relating to the output rate and the quantity (i.e., volume by weight) of the limestone being fed by the gravimetric feeder device 508 to the roller mill 512. A connector 528 connects the limestone feed system control unit 522 to the grinding bowl drive motor of the roller mill 512 and a connector 530 connects the limestone feed system control unit to the dynamic classifier 514. The limestone feed system control unit thus controls the speed of the roller mill 512 and the speed of the dynamic classifier 514. In accordance, for example, with one typical control regime, as the limestone feed system control unit controls the speed of the roller mill 512 to thereby increase the grinding capacity of the limestone, the speed of the dynamic classifier 514 is reduced. In lieu of the sulfur level sensing performed by the sulfur level sensing device 132 described with respect to the one embodiment of the sorbent conditioning and direct feed apparatus shown in Figure 2, the further embodiment of the sorbent conditioning and direct feed apparatus shown in Figure 6 does not perform any real time sulfur sensing but. instead, operates to control the feed of conditioned limestone to the pulverized coal direct fired boiler 500 in accordance with a pre-programmed limestone feed regime. The limestone feed system control 522 is configured to increase, decrease, or maintain the feed rate of the conditioned limestone to the pulverized coal direct fired boiler 500 in accordance with a limestone feed program stored in the limestone feed system control. The stored limestone feed program is configured based upon empirical data concerning suitable limestone feed rates. The operation of the roller mill 512 for grinding limestone is subjected to certain signals received by the limestone feed system control unit 522 from the various components connected thereto. Thus, for example, in accordance with one exemplary limestone feed control regime, the limestone feed system control unit 122, in accordance with the stored limestone feed program, controls the feed hopper 104 to feed raw untrammeled limestone onto the gravimetric feed device 108 at a predetermined feed rate. The operation of the gravimetric feed device 108 is also controlled by the limestone feed system control unit 122 to effect the supply of a predetermined volume (by weight) of raw untrammeled limestone to the roller mill 512. The roller mill 512 then performs a size reduction operation on the limestone supplied thereto while the limestone feed system control unit 122 controls the operation of the classifier 514 to ensure that the limestone particles exiting the roller mill 512 onto the pneumatic transport assembly 518 conform to the desired particle size distribution. The thus supplied limestone particles are then transported by the pneumatic transport assembly 518 to the pulverized coal direct fired boiler 500. In connection with outputs from the stored limestone feed program, the limestone feed system control unit 522 controls the system to reduce or cease the supply of prepared limestone. While an embodiment and variations of the present invention have been shown, it will be appreciated that modifications thereof, some of which have been alluded to hereinabove, may still be readily made thereto by those skilled in the art. It is, therefore, intended that the appended claims shall cover the modifications alluded to herein as well as all the other modifications which fall within the true spirit and scope of the present invention. WE CLAIM: 1. A sorbent conditioning and direct feed apparatus for direct feeding of a conditioned solid sorbent to a fluidized bed combustor (12) comprising: raw solid sorbent storage means (102); particle size reducing means (112) for reducing the particle size of solid sorbent supplied thereto from the raw solid sorbent storage means from a relatively coarse particle size to a relatively smaller fine particle size; transport means (118) for transporting to the combustor (12) solid sorbent that has been conditioned by the particle size reducing means in a separate particle size reduction operation prior to the supply thereof to the transport means in a manner in which most of the conditioned solid sorbent are delivered from the particle size reducing means (112) to the combustor (12) within a predetermined time period following their size reduction whereby conditioned solid sorbent is fed to the combustor with substantially no intermediate storage of the solid sorbent between the raw solid sorbent storage means (102) and the transport means (118); characterized in the control means (122) being operatively connected to the raw solid sorbent storage means (102) and the particle size reducing means (112) for controlling the feed of conditioned solid sorbent in the fluidized bed combustor; and in the means for sensing a sulfur concentration (132) in the fluidized bed combustor being operatively connected to the control means (122), the control means being operable to control the feed of conditioned solid sorbent to the fluidized bed combustor (12) in response to a sensed sulfur concentration condition of the fluidized bed combustor. 2. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein the predetermined time period is less than thirty (30) minutes. 3. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein, on average, at least ninety percent (90%) of the conditioned solid sorbent are delivered from the particle size reducing means (112) to the combustor (12) in less than thirty (30) minutes following their size reduction. 4. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein the transport means (118) is a fuel feed transport means operable to transport as well conditioned solid fossil fuel to the fluidized bed combustor (12) whereby the conditioned solid sorbent and the conditioned solid fossil fuel are fed as a mixture to the fluidized bed combustor. 5. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein the control means is operatively connected to the transport means for controlling the feed of conditioned solid sorbent to the fluidized bed combustor. 6. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein the particle size reducing means (112) is a roller mill. 7. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein the particle size reducing means (112) is a roll crusher. 8. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein the particle size reducing means (112) is an impact mill. 9. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein the particle size reducing means (112) is a rod mill. 10. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein the particle size reducing means (112) is a hammer crusher. 11. The sorbent conditioning and direct feed apparatus as claimed in claim 1 wherein the transport means has a mechanical transport assembly and the conditioned solid sorbent is transported solely by mechanical transport to the fluidized bed combustor. A sorbent conditioning and direct feed apparatus for direct feeding of a conditioned solid sorbent to a fluidized bed combustor (12) comprising raw solid sorbent storage means (102); particle size reducing means (112) for reducing the particle size of solid sorbent supplied thereto from the raw solid sorbent storage means from a relatively coarse particle size to a relatively smaller fine particle size; transport means (118) for transporting to the combustor (12) solid sorbent that has been conditioned by the particle size reducing means in a separate particle size reduction operation prior to the supply thereof to the transport means in a manner in which most of the conditioned solid sorbent are delivered from the particle size reducing means (112) to the combustor (12) within a predetermined time period following their size reduction whereby conditioned solid sorbent is fed to the combustor with substantially no intermediate storage of the solid sorbent between the raw solid sorbent storage means (102) and the transport means (118); characterized in the control means (122) being operatively connected to the raw solid sorbent storage means (102) and the particle size reducing means (112) for controlling the feed of conditioned solid sorbent in the fluidized bed combustor; and in the means for sensing a sulfur concentration (132) in the fluidized bed combustor being operatively connected to the control means (122), the control means being operable to control the feed of conditioned solid sorbent to the fluidized bed combustor (12) in response to a sensed sulfur concentration condition of the fluidized bed combustor.

Full Text

BACKGROUND OF THE INVENTION
The present invention relates to a sorbent conditioning and direct feed
apparatus which is suitable for use in association with a fossil fuel-fired steam
generator including, in particular, a circulating fluidized bed steam generator in a
new utility unit application or a retrofit application in an existing utility unit.
Limestone is a natural mineral principally comprised of calcium carbonate,
CaCO3, and limestone is used as a desulfurizing or scrubbing medium in fluidized
bed combustion units. In these units, combustion materials such as coal and the
like are fluidized and combusted in a combustion vessel by contact with
upflowing high temperature gasses. Limestone can be mixed with the combustion
materials pnor to feeding of the combined fuel-sorbent mixture into the unit and
the desulfunzation process takes place during combustion.
Since the scrubbing or desulfunzation process is a chemical reaction, the
proper stoichiometric ratio of limestone containing calcium carbonate to flue gas
will produce the most efficient reaction. In order for the desulfunzation reaction
to proceed efficiently and with minimal waste, the limestone must be conditioned
such as by gnnding to produce a defined panicle size prior to use and it is
particularly important in the fluidized bed combustion process to control
limestone panicle size distribution so as to thereby ensure an efficient
desulfunzation process. If the particles are too large, the desulfurization process
will not be efficient because there is insufficient limestone panicle surface area to
react with the flue gas. On the other hand, if the particles are too small, the
limestone will be earned out of the vessel with the flue gas before it can react to
remove the sulfur.
Conventional limestone preparation systems often include a drying system
having a cyclone or baghouse and typically comprise as well storage hoppers,
conveyors, crushing and grinding machines and, in some configurations, vibrating
screens. Such conventional systems effect particle size reduction of the limestone
in discrete steps including, for example, multiple passes of the limestone particles
through size reduction units which is typically performed to progressively reduce
the particle size from a relatively larger or coarse panicle size to a relatively
smaller or fine particle size suitable for introduction into the combustion vessel.
Thus, it can be appreciated that such conventional limestone preparation systems
generally have a complexity which contributes significantly to their cost and the
number of processing operations and transport paths between the various
components adds to the operational complexity and maintenance costs of such
systems.
Conventional limestone storage and feed systems also typically require
separate preparation and/storage facilities for the raw sorbent and these facilities
add to the capital cost of the utility unit. Also, such facilities may be sited several
hundred meters from the combustor of the utility unit, thus adding to the overall
space requirements of the utility unit.
SUMMARY OF THE INVENTION
To thus summarize, a need has been evidenced in the prior art for a sorbent
conditioning and direct feed apparatus that would be particularly suited for use in
effecting the pulverization of sorbent material such as, for example, limestone,
and the feed thereof directly to a steam generator including, in particular, a
circulating fluidized bed steam generator.
It is, therefore, an object of the present invention to provide a new and
improved sorbent conditioning and direct feed apparatus that is particularly suited
for use in effecting the pulverization of sorbent material such as, for example,
limestone, and the feed thereof directly to a steam generator including,in
particular, a circulating fluidized bed steam generator.
Yet a further object of the present invention is to provide such an
improved sorbent conditioning and direct feed apparatus which is suitable for
installation in new steam generator facilities including, in particular, a circulating
fluidized bed steam generator facility.
Yet another object of the present invention is to provide such an improved
sorbent conditioning and direct feed apparatus which is capable of being
retrofitted in connection with existing steam generator facilities including, in
particular, a circulating fluidized bed steam generator facility.
In accordance with one aspect of the present invention, these and other
objects of the present invention are achieved by an improved sorbent conditioning
and direct feed apparatus which is suitable for installation in new steam generator
facilities including, in particular, a circulating fluidized bed steam generator
facility and which is capable of being retrofitted in connection with existing steam
generator facilities including, in particular, a circulating fluidized bed steam
generator facility.
In accordance with the present invention, there is thus provided a sorbent
conditioning and direct feed apparatus operable to effect the direct feeding of a
conditioned solid sorbent to the combustor. The apparatus includes a raw solid
sorbent storage means and a particle size reducing means for reducing the particle
size of solid sorbent supplied thereto from the raw solid sorbent storage means
from a relatively larger coarse particle size to a relatively smaller fine particle.
Also, the apparatus includes transport for transporting solid sorbent which
has been conditioned by the particle size reducing means to the combustor in a
manner in which, on average, at least ninety percent (90%) of the conditioned
solid sorbent are delivered from the particle size reducing means to the combustor
in less than thirty (30) minutes) following their size reduction, whereby
conditioned solid sorbent is fed to the combustor with substantially no
intermediate storage of the solid sorbent between the raw solid sorbent storage
means and the transport means.
According to one aspect of the preferred embodiment of the present
invention, the combustor is a fluidizcd bed combustor. According to another
aspect of the preferred embodiment of the present invention, the transport means
is a fuel feed transport means operable to transport as well conditioned solid fossil
fuel to the fluidized bed combustor, whereby the conditioned solid sorbent and the
conditioned solid fossil fuel are fed as a mixture to the fluidized bed combustor.
Additionally, the sorbent conditioning and direct feed apparatus preferably
comprises control means operativcly connected to the raw solid sorbent storage
means, the particle size reducing means, and the transport means for controlling
the feed of conditioned solid sorbent to the fluidized bed combustor in accordance
with a predetermined sorbent feed regime.
According to yet another aspect of the preferred embodiment of the
present invention, the sorbent conditioning and direct feed apparatus further
comprises means for sensing an operating condition of the fluidized bed
combustor operatively connected to the control means, the control means being
operable to control the feed of conditioned solid sorbent to the fluidized bed
combustor in response to a sensed operating condition of the fluidized bed
combustor. The means for sensing an operating condition of the fluidized bed
combustor can be operable to sense a sulfur concentration in the fluidized bed
combustor.
According to a further additional aspect of the preferred embodiment of
the present invention, the particle size reducing means is a roller mill.
Alternatively, the particle size reducing means is a roll crusher. Also, according
to a supplemental aspect of the preferred embodiment of the present invention, the
conditioned solid fossil fuel is subjected to a separate particle size reduction
operation prior to the supply thereof to the transport means and the fluidized bed
combustor is supplied by the transport means with a mixture of conditioned solid
fossil fuel and conditioned solid sorbent. The transport means may alternatively
be configured as a pneumatic transport assembly operable to pneumatically
transport conditioned sorbent to the steam generator from any air swept mill or
crusher or as a mechanical transport assembly.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is a side elevational view of a circulating fluidized bed steam
generator of the type with which the sorbent conditioning and direct feed
apparatus of the present invention can be operatively associated to feed
conditioned sorbent thereto;
Figure 2 is a side schematic view of one embodiment of the sorbent
conditioning and direct feed apparatus of the present invention;
Figure 3 is an enlarged side view in partial section of the gravimetric feed
device of the one embodiment of the sorbent conditioning and direct feed
apparatus shown in Figure 2;
Figure 4 is an enlarged side elevational view of a roll crusher for use with
the one embodiment of the sorbent conditioning and direct feed apparatus shown
in Figure 1;
Figure 5A is a side schematic view of one variation of an embodiment of
the sorbent conditioning and direct feed apparatus of the present invention having
the roll crusher shown in Figure 4;
Figure 5B is a side schematic view of another variation of an embodiment
of the sorbent conditioning and direct feed apparatus of the present invention
having the roll crusher shown in Figure 4; and
Figure 6 is a side schematic view of a further embodiment of the sorbent
conditioning and direct feed apparatus of the present invention for use with a
direct fired pulverized coal combustor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to Figure 1 there is shown a typical circulating fluidized
bed steam generator to which the sorbent conditioning and direct feed apparatus of
the present invention has particular application. Crushed fuel and sorbent are
normally fed to the lower portion of a combustor 12. Typically the fuel and
sorbent material are fed to a chute (not shown) that is disposed at approximately a
60 degree angle from horizontal. Thus, the fuel and sorbent pass along the chute
and into the combustor 12. Primary air is supplied to the bottom of the combustor
through an air distributor 14 with secondary air fed through one or more air ports
at various elevations in the lower part of the combustor. Combustion takes place
throughout the combustor 12 which is filled with bed material. Flue gas and
entrained solids leave the combustor 12 and enter one or more cyclones 16 where
the solids are separated and fall to a seal pot 18. From the seal pot 18, the solids
are recycled to the combustor 12. Optionally, some solids may be diverted
through an ash control valve 20 to a fluidized bed heat exchanger 22. Flue gas
leaving the cyclone 16 passes to a convective pass 24 and then to an air heater, a
bag house or an electrostatic precipitator, and fan (not shown). The solids in the
combustor 12 are periodically allowed to pass out of the combustor 12 by draining
these hot solids through an ash cooler 30 or, in lieu of the ash cooler 30, an ash
screw may be provided to periodically remove the hot solids.
One preferred embodiment of the sorbent conditioning and direct feed
apparatus of the present invention is illustrated in the schematic arrangement of
Figure 2 in which limestone, which has not yet been subjected to a particle size
reduction treatment, is conditioned into a final particle size distribution in which
the conditioned limestone can be fed into a steam generator. The steam generator
can be, for example, a circulating fluidized bed steam generator such as the one
illustrated in Figure 1 having a combustor 12. Limestone is supplied from a
conventional limestone storage facility 102 to a feed hopper 104. Limestone is
then fed by the feed hopper 104 onto a weigh scale belt 106 which is part of a
gravimetric feeder device 108 and is moved thereby to fall through a chute 110
into the selected particle size reducing apparatus 112 which may be configured as,
for example, a roller mill or a roll crusher. The particle size reducing apparatus
112 is driven by a conventional prime mover (not shown) which is controllable as
will be presently described.
A conventional rotary valve 114 controls the supply of the conditioned
limestone having a size below a predetermined size which has exited the particle
size reducing apparatus 112 via an outlet 116. The rotary valve 1 14 controls the
supply of conditioned limestone to a pneumatic transport assembly 118 which
transports the conditioned limestone to feed inlets of the combustor 12. One
configuration of the panicle size reducing apparatus 112 which can
advantageously make use of a transport arrangement of the type including the
rotary valve 114, the outlet 116. and the pneumatic transport assembly 118 could
be, for example, a roll crusher. Alternatively, in accordance with a variation of
the sorbent conditioning and direct feed apparatus of the present invention, an air
swept arrangement having conventional features may be deployed in lieu of the
rotary valve 114, the outlet 116, and the pneumatic transport assembly 118 to
effect the transport of the conditioned sorbent from the particle size reducing
apparatus 112 to the combustor 12. One configuration of the particle size
reducing apparatus 112 which can advantageously make use of a transport
arrangement of the type including an air swept arrangement could be, for example,
a roller mill. This air swept arrangement could include, for example, a suitable
conventional heated air take-off duct assembly to convey heated air from the
combustor 12 to the particle size reducing apparatus 112 and a suitable
conventional return duct assembly to convey the heated air, with the conditioned
sorbent entrained therewith, from the particle size reducing apparatus 112 to the
combustor 12.
Conditioned solid fuel such as, for example, crushed coal, is supplied
separately to the combustor 12 from a solid fuel feed supply 120.
A limestone feed system, control unit 122 controls the limestone feed
operation through the various assemblies just noted to ultimately feed conditioned
limestone to the circulating fluidized bed steam generator. The limestone feed
system control unit 122 is connected via a connector 124 to the drive motor which
drives the belt of the weight scale belt 106 of the gravimetric feeder device 108
and is connected via a connector 126 to the weight assessment sub-assembly of
the gravimetric feeder device 108 for receiving from the connectors 124 and 126
signals relating to the output rate and the quantity (i.e., volume by weight) of the
limestone being fed by the gravimetric feeder device 108 to the particle size
reducing apparatus 112.
A connector 128 connects the limestone feed system control unit 122 to
the dnve motor of the particle size reducing apparatus 1 12 and a connector 130
connects the limestone feed system control unit to an optional rotary valve 114.
The limestone feed system control unit can. thus, in connection with selected
particle size reducing scenarios, control the operation of the particle size reducing
apparatus 112 and the supply rate of the rotary valve 1 14. In accordance, for
example, with one typical control regime, as the limestone feed system control
unit 122 controls the speed of the particle size reducing apparatus 112 to thereby
increase the output of the conditioned limestone, the rotary valve 114 is controlled
to increase the supply rate of conditioned limestone to the fuel feed transporter
118.
A conventional sulfur level sensing device 132 is located relative to the
combustor 12 for continuously sensing or monitoring the sulfur level in the flue
gas, whereby the sulfur level sensing device 132 may be located, for example, on
the flue gas outlet stack. The sulfur level sensing device 132 is connected via a
connector 134 to the limestone feed system control unit 122 for providing signals
thereto concerning the sensed sulfur level in the flue gas. A moisture control
assembly 136 is provided to control the moisture content of the conditioned
limestone to a desired level. The moisture control assembly 136 preferably
selectively effects drying of the raw limestone upstream of the panicle size
reducing apparatus 112 by, for example, drying the raw limestone stored in the
limestone storage facility 102 to a predetermined feed moisture of, say, 1 to 10
such that the conditioned limestone fed to the combustor 12 has the desired
moisture content. The moisture control assembly 136 can be configured with a
conventional externally powered or fueled drying device such as, for example, a
gas-fired drying device which applies heated air to the raw limestone to effect
drying thereof. Preferably, however, the moisture control assembly 136 is
configured to use process heat generated in connection with the operation of the
steam generator and, to this end, the moisture control assembly 136 may include
an optional externally powered heater 138 or a duct and damper sub-assembly
which communicates the particle size reducing apparatus 112 with the combustor
12 such that process heat from the combustor 12 can be selectively applied to the
limestone in the particle size reducing apparatus 112 to effect the drying thereof.
The sorbent conditioning and direct feed apparatus of the present invention
advantageously permits a process heat arrangement of this type to be used in a
cost effective manner in that the sorbent conditioning and direct feed apparatus
can be located sufficiently proximate to the combustor 12 - that is, typically less
than 50 meters therefrom - to permit process heat to be transferred to the particle
size reducing apparatus 112 in a cost favorable manner. In contrast, in a
conventional limestone storage and conditioning arrangement, the limestone
storage facility which performs the limestone storage function of the limestone
storage facility 102 is typically located several hundred meters from the
combustor and it is thus not cost justifiable to deliver process heat from the
combustor over the several hundred meter distance.
The operation of the particle size reducing apparatus 112 to effect a size
reduction of the limestone is controlled in response to certain signals received by
the limestone feed system control unit 122 from the various components
connected thereto. Thus, for example, in accordance with one exemplary
limestone feed control regime, the limestone feed system control unit 122 receives
signals from the sulfur level sensing device 132 concerning the sensed sulfur level
in the flue gas and the limestone feed system control unit 122 evaluates these
signals to determine the need for feeding limestone to the combustor. When the
limestone feed system control unit 122 determines a need to supply the prepared
limestone particles to the combustor 12. the limestone feed system control unit
122 controls the feed hopper 104 to feed raw untrammeled limestone onto the
gravimetric feed device 108. The operation of the gravimetric feed device 108 is
also controlled by the limestone feed system control unit 122 to effect the supply
of a predetermined volume (by weight) of raw untrammeled limestone to the
particle size reducing apparatus 112. The particle size reducing apparatus 112
then performs a size reduction operation on the limestone supplied thereto and the
thus conditioned limestone panicles exit the particle size reducing apparatus 112
into the pneumatic transport assembly 118. If the particle size reducing 112 is
configured, for example, as a conventional roller mill, the optional rotary valve
114 is omitted and the conditioned limestone particles will exit the roller mill
directly to the pneumatic transport assembly 118 as a function of the classification
operation of the roller mill. The thus supplied limestone particles are then
transported to the combustor 1 2. In connection with a sensing operation by the
sulfur level sensing device 132 which indicates that the desired sulfur level in the
combustor 12 has been achieved, the limestone feed system control unit 122
controls the system to reduce or increase the supply of prepared limestone.
As shown in Figure 3, the gravimetric feed device 108 is preferably
configured as a single belt feeder 240 for sorbent. Disposed at spaced intervals
along the belt feeder 240 is a first belt scale 242. Disposed upstream respectively
from the belt scale 242 is the feed hopper 204 which feeds sorbent to the belt
feeder 240. A programmable logic controller 250 receives inputs from the first
belt scale 242. The sorbent will be dumped off the belt feeder 240 at the right (as
shown in the drawing) hand end of the belt feeder 240. A programmable logic
controller 250 is optionally provided to which is supplied an input (the weight)
from the belt scale 242. The supply of sorbent to the belt feeder 240 from the feed
hopper 204 is controlled by a rotary valve 254.
The rotary valve 254 is controlled by a motor 256 which is in turn
controlled by the programmable logic controller 250. The control of the motor
256 driving the rotary valve 254 determines the actual amount of sorbent
delivered to the belt feeder 240. The programmable logic controller 250 compares
the actual feed rate to the intended or desired gravimetric feed rate. It will be
understood that a motor 260 is provided to drive the continuous belt feeder 240
and that this motor 260 is driven at a speed and/or periods of time corresponding
to the desired rate of delivery of sorbent to the limestone conditioning operation
and from there, to the combustion process in the circulating fluidized bed steam
generator. More specifically, the belt scale 242 sends a signal to the motor 260
and thus controls the motor 260. The signal from the programmable logic
controller 250 to the motor 260 is a function of the weight of the sorbent added to
the belt feeder 240 per unit of time. It will also be seen that the relative rate of
sorbent feed is controlled by the motor 256 controlling the valve 254 and that this
control is achieved by the programmable logic controller 250.
In some forms of the invention, the programmable logic controller 250
may be a dedicated programmable logic controller. The programmable logic
controller 250 is a common commercial commodity and typical dedicated
programmable logic controllers. In other forms of the invention the
programmable logic controller 250 may be part of the distributed control system
of the plant in which the fluidized bed steam generator is located.
Thus, the one embodiment of the sorbent conditioning and direct feed
apparatus illustrated in Figure 2 is operable to effect the direct feeding of a
conditioned solid sorbent to the combustor 12. The apparatus includes a raw solid
sorbent storage means in the form of the limestone storage facility 102 and a
particle size reducing means for reducing the particle size of solid sorbent
supplied thereto from the raw solid sorbent storage means from a relatively larger
coarse particle size to a relatively smaller fine particle size in the form of the
particle size reducing apparatus 112. Also, the apparatus includes transport means
in the form of the fuel feed transporter 118 for transporting solid sorbent which
has been conditioned by the particle size reducing means to the combustor in a
manner in which, on average, at least ninety percent (90%) of the conditioned
solid sorbent are delivered from the particle size reducing means to the combustor
in less than thirty (30) minutes) following their size reduction, whereby
conditioned solid sorbent is fed to the combustor with substantially no
intermediate storage of the solid sorbent between the raw solid sorbent storage
means and the transport means. Thus, it is contemplated that the present invention
encompasses (a) those material feed apparatus configured to deliver the entirety of
the conditioned solid sorbent directly to the combustor without any diversion
enroute of a portion of the conditioned solid sorbent; and (b) those material feed
apparatus configured to permit an insubstantial enroute diversion of the
conditioned solid sorbent during its travel between the particle side reducing
means and the combustor. An example of an insubstantial enroute diversion of
the conditioned solid sorbent is the removal of a sample size portion of the
conditioned solid sorbent to permit testing or quality control measures to be
performed on the removed sample size portion. Another example of an
insubstantial enroute diversion of the conditioned solid sorbent is the creation of
an operational reserve of the conditioned solid sorbent designed to accommodate
inline feed variations in the mass flow of the conditioned solid sorbent and this
volume of this operational reserve is considered to be many orders of magnitude
less than the storage volume of conditioned solid sorbent which is typically stored
in a dedicated large volume silo or other structure in connection with conventional
conditioned solid sorbent preparation and feed arrangements.
As shown in Figure 4 in conjunction with, respectively, Figures 5A and
5B, a roll crusher can be provided as the preferred configuration of the particle
size reducing apparatus 112 for effecting the size reduction of the limestone
particles. As seen in one variation of such a roll crusher embodiment shown in
Figure 5A, this variation of the one embodiment of the sorbent conditioning and
direct feed apparatus includes a roll crusher 412 for effecting the particle size
reduction of the limestone. The roll crusher 412, as seen in more detail in Figure
4, comprises a feed area 414 for feeding raw untrammeled limestone from a raw
material feed arrangement 416, a first pair of grinding rolls 418, 420 and a second
pair of grinding rolls 422, 424. The first pair 418, 420 of grinding rolls and the
second pair 422, 424 of grinding rolls are each driven by independent drive means
(not shown) such as electric motors. The raw untrammeled limestone is fed from
the feed area 414 by gravity. The first pair of grinding rolls 418, 420 comprises
opposing rotating rolls 418, 420 which each rotate about a horizontal axis in a
respective direction of rotation opposite to that of the other grinding roll. The
rolls 418, 240 form therebetween a first nip 430, which is adjustably or fixedly set
in dependence upon the raw untrammeled limestone particle size.
The second pair of grinding rolls 422, 424 comprises opposing rotating
rolls which each rotate about a horizontal axis in a respective direction of rotation
opposite to that of the other grinding roll. The rolls 422, 424 are separated by a
second nip 434, which is based upon the final product particle size distribution
desired. A preferred particle size distribution is comprised of particles smaller
than 2 mm and, generally, smaller than J mm, and having a mean size of about
300 microns. Preferably, the panicle size distribution is produced with the nip
434 between the second set of rolls 422, 424 in the range of about 2 to 3 mm.
Each of the grinding rolls of the first pair 418, 420 and the second pair
422, 424 of grinding rolls rotate at different velocities relative to its opposed
paired grinding roll to produce a shear in the particles as they pass into and
through the nip 430 and the nip 434. Raw untrammeled limestone is fed by the
raw material feed arrangement 416 into the feed area 414. The limestone then
falls into the nip area 430 of the first pair of rolls 418, 420. Grinding of the
limestone particles occurs in the nip 430 and, as the limestone travels
therethrough, the compression and shear imparted by the rolls 418, 420, on the
limestone causes the particles to work against each other thereby breaking down
or fracturing the crystalline structure. The particle size distribution of the product
is controlled in that, the larger the nip, the less the work that is done on the
limestone particles, while, the smaller the nip, the greater the work that is done on
the limestone particles. As the limestone passes beyond the first nip 430, it falls
into the second nip 434 at which it is subjected to further size reduction by the
second pair of grinding rolls 422, 424. The one variation of the roll crusher
embodiment of the sorbent conditioning and direct feed apparatus shown in
Figures 4 and 5A also includes, in lieu of the pneumatic transport assembly 118
described with respect to Figure 2, a fuel feed transporter 436 for feeding the
conditioned limestone to the circulating fluidized bed steam generator along with
raw or conditioned solid fuel such as. for example, raw untrammeied coal or
crushed coal, which is supplied from a solid fuel feed supply. The fuel feed
transporter 436 may be configured, for example, as a conventional mechanical
transporter in the form of, for example, an endless belt conveyor. The conditioned
limestone particles exiting the second pair of grinding rolls 422, 424, having thus
been reduced in size to achieve the desired particle size distribution, are then
released into the pneumatic transport stream of the pneumatic transport assembly
436 in a metered manner by means, for example, of a conventional rotary valve
arrangement, and supplied thereby along with the solid fuel into the circulating
fluidized bed steam generator.
As seen in another variation of such a roll crusher embodiment shown in
Figure 5B, this variation of the one embodiment of the sorbent conditioning and
direct feed apparatus includes all of the features of the one roll crusher
embodiment variation shown in Figure 5A with the addition, in this other
variation, of a drying arrangement 438 for effecting at least some reduction in the
moisture content of the raw limestone prior to its feed into the roll crusher. The
drying arrangement 438 may be configured, for example, as a conventional
tempered air drying arrangement which diverts a portion of the air heated in the
circulating fluidized bed steam generator and, by means of a conventional rotary
dryer, passes the heated air into contact with the raw limestone with the now
cooler heated air being returned via a return loop to the steam generator.
A further preferred embodiment of the sorbent conditioning and direct feed
apparatus of the present invention is illustrated in the schematic arrangement of
Figure 6 in which limestone, which has not yet been subjected to a particle size
reduction treatment, is conditioned into a final particle size distribution in which
the conditioned limestone can be fed into a direct fired steam generator such as a
pulverized coal combustor having comer mounted or wall mounted burners for
directly injecting pulverized coal and conditioned limestone into the combustor.
The steam generator shown in Figure 6 is exemplarily illustrated as a conventional
pulverized coal direct fired boiler 500.
Limestone is supplied from a conventional limestone storage facility 502
to a feed hopper 504. Limestone is then fed by the feed hopper 504 onto a weigh
scale belt 506 which is part of a gravimetric feeder device 508 and is moved
thereby to fall through a chute 510 into the selected limestone size conditioning
apparatus such as, for example, a roller mill 512. The roller mill 512 is driven by
a conventional prime mover (not shown) which is controllable as will be presently
described.
The roller mill 512 may optionally include a dynamic classifier or a static
classifier for classifying the limestone particles conditioned by the roller mill.
Merely for the purpose of illustrating such an option, the sorbent conditioning and
direct feed apparatus shown in Figure 6 is provided with a dynamic classifier 514,
whose rate of rotation is controllable as will be presently described, which
classifies the limestone in the roller mill 512 such that a portion of the conditioned
limestone having a size below a predetermined size are permitted to exit the roller
mill 512 via an outlet 516 while another portion of the limestone having a size
above the predetermined size are returned to the grinding area of the roller mill
512 for further size reduction. The outlet 516 communicates with a conventional
pneumatic transport assembly 518 operable to pneumatically transport conditioned
limestone from the roller mill 512 to the plurality of burners at which the
conditioned limestone is mixed with pulverized coal during direct firing thereof
into the pulverized coal direct fired boiler 500. The conditioned limestone travels
from the outlet 516 via the pneumatic transport assembly 518 to the pulverized
coal direct fired boiler 500 at which it is combined with the pulverized solid fuel
such as, for example, pulverized coal, which is supplied from a solid fuel feed
supply 520. The pulverized coal is itself supplied to the solid fuel feed supply 520
in a separate solid fossil fuel preparation process which may include, for example,
size reduction of raw untrammeled coal in a conventional pulverizer 521. The
conventional pulverizer 521 uses some combination of impact, attrition and
crushing to reduce a solid fuel to a particular particle size. Several types of
pulverizer mills can be employed for the pulverization of the solid fuel, which
may be, for example, coal, to a particulate size appropriate for firing in a furnace.
These can comprise, for example, ball-tube mills, impact mills, attrition mills, ball
race mills, and ring roll or bowl mills. Most typically, however, bowl mills are
employed for the pulverization of the solid fuel to allow for direct firing of the
pulverized fuel entrained in an air stream.
A limestone feed system control unit 522 controls the limestone feed
operation through the various assemblies just noted to ultimately feed conditioned
limestone to the pulverized coal direct fired boiler 500. The limestone feed
system control unit is connected via a connector 524 to the drive motor which
drives the belt of the weight scale belt 506 of the gravimetric feeder device 508
and is connected via a connector 526 to the weight assessment sub-assembly of
the gravimetric feeder device 508 for receiving from the connectors 524 and 526
signals relating to the output rate and the quantity (i.e., volume by weight) of the
limestone being fed by the gravimetric feeder device 508 to the roller mill 512.
A connector 528 connects the limestone feed system control unit 522 to
the grinding bowl drive motor of the roller mill 512 and a connector 530 connects
the limestone feed system control unit to the dynamic classifier 514. The
limestone feed system control unit thus controls the speed of the roller mill 512
and the speed of the dynamic classifier 514. In accordance, for example, with one
typical control regime, as the limestone feed system control unit controls the
speed of the roller mill 512 to thereby increase the grinding capacity of the
limestone, the speed of the dynamic classifier 514 is reduced.
In lieu of the sulfur level sensing performed by the sulfur level sensing
device 132 described with respect to the one embodiment of the sorbent
conditioning and direct feed apparatus shown in Figure 2, the further embodiment
of the sorbent conditioning and direct feed apparatus shown in Figure 6 does not
perform any real time sulfur sensing but. instead, operates to control the feed of
conditioned limestone to the pulverized coal direct fired boiler 500 in accordance
with a pre-programmed limestone feed regime. The limestone feed system control
522 is configured to increase, decrease, or maintain the feed rate of the
conditioned limestone to the pulverized coal direct fired boiler 500 in accordance
with a limestone feed program stored in the limestone feed system control. The
stored limestone feed program is configured based upon empirical data concerning
suitable limestone feed rates.
The operation of the roller mill 512 for grinding limestone is subjected to
certain signals received by the limestone feed system control unit 522 from the
various components connected thereto. Thus, for example, in accordance with
one exemplary limestone feed control regime, the limestone feed system control
unit 122, in accordance with the stored limestone feed program, controls the feed
hopper 104 to feed raw untrammeled limestone onto the gravimetric feed device
108 at a predetermined feed rate. The operation of the gravimetric feed device
108 is also controlled by the limestone feed system control unit 122 to effect the
supply of a predetermined volume (by weight) of raw untrammeled limestone to
the roller mill 512. The roller mill 512 then performs a size reduction operation
on the limestone supplied thereto while the limestone feed system control unit 122
controls the operation of the classifier 514 to ensure that the limestone particles
exiting the roller mill 512 onto the pneumatic transport assembly 518 conform to
the desired particle size distribution. The thus supplied limestone particles are
then transported by the pneumatic transport assembly 518 to the pulverized coal
direct fired boiler 500. In connection with outputs from the stored limestone feed
program, the limestone feed system control unit 522 controls the system to reduce
or cease the supply of prepared limestone.
While an embodiment and variations of the present invention have been
shown, it will be appreciated that modifications thereof, some of which have been
alluded to hereinabove, may still be readily made thereto by those skilled in the
art. It is, therefore, intended that the appended claims shall cover the
modifications alluded to herein as well as all the other modifications which fall
within the true spirit and scope of the present invention.
WE CLAIM:
1. A sorbent conditioning and direct feed apparatus for direct feeding of a
conditioned solid sorbent to a fluidized bed combustor (12) comprising:
raw solid sorbent storage means (102);
particle size reducing means (112) for reducing the particle size of solid
sorbent supplied thereto from the raw solid sorbent storage means from a
relatively coarse particle size to a relatively smaller fine particle size;
transport means (118) for transporting to the combustor (12) solid
sorbent that has been conditioned by the particle size reducing means in a
separate particle size reduction operation prior to the supply thereof to the
transport means in a manner in which most of the conditioned solid sorbent are
delivered from the particle size reducing means (112) to the combustor (12)
within a predetermined time period following their size reduction whereby
conditioned solid sorbent is fed to the combustor with substantially no
intermediate storage of the solid sorbent between the raw solid sorbent storage
means (102) and the transport means (118);
characterized in the control means (122) being operatively connected to
the raw solid sorbent storage means (102) and the particle size reducing means
(112) for controlling the feed of conditioned solid sorbent in the fluidized bed
combustor; and in the
means for sensing a sulfur concentration (132) in the fluidized bed
combustor being operatively connected to the control means (122), the control
means being operable to control the feed of conditioned solid sorbent to the
fluidized bed combustor (12) in response to a sensed sulfur concentration
condition of the fluidized bed combustor.
2. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein the predetermined time period is less than thirty (30) minutes.
3. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein, on average, at least ninety percent (90%) of the conditioned solid
sorbent are delivered from the particle size reducing means (112) to the
combustor (12) in less than thirty (30) minutes following their size reduction.
4. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein the transport means (118) is a fuel feed transport means operable to
transport as well conditioned solid fossil fuel to the fluidized bed combustor (12)
whereby the conditioned solid sorbent and the conditioned solid fossil fuel are
fed as a mixture to the fluidized bed combustor.
5. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein the control means is operatively connected to the transport means for
controlling the feed of conditioned solid sorbent to the fluidized bed combustor.
6. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein the particle size reducing means (112) is a roller mill.
7. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein the particle size reducing means (112) is a roll crusher.
8. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein the particle size reducing means (112) is an impact mill.
9. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein the particle size reducing means (112) is a rod mill.
10. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein the particle size reducing means (112) is a hammer crusher.
11. The sorbent conditioning and direct feed apparatus as claimed in claim 1
wherein the transport means has a mechanical transport assembly and the
conditioned solid sorbent is transported solely by mechanical transport to the
fluidized bed combustor.

A sorbent conditioning and direct feed apparatus for direct feeding of a conditioned solid sorbent
to a fluidized bed combustor (12) comprising raw solid sorbent storage means (102); particle size
reducing means (112) for reducing the particle size of solid sorbent supplied thereto from the
raw solid sorbent storage means from a relatively coarse particle size to a relatively smaller fine
particle size; transport means (118) for transporting to the combustor (12) solid sorbent that has
been conditioned by the particle size reducing means in a separate particle size reduction
operation prior to the supply thereof to the transport means in a manner in which most of the
conditioned solid sorbent are delivered from the particle size reducing means (112) to the
combustor (12) within a predetermined time period following their size reduction whereby
conditioned solid sorbent is fed to the combustor with substantially no intermediate storage of
the solid sorbent between the raw solid sorbent storage means (102) and the transport means
(118); characterized in the control means (122) being operatively connected to the raw solid
sorbent storage means (102) and the particle size reducing means (112) for controlling the feed
of conditioned solid sorbent in the fluidized bed combustor; and in the means for sensing a sulfur
concentration (132) in the fluidized bed combustor being operatively connected to the control
means (122), the control means being operable to control the feed of conditioned solid sorbent
to the fluidized bed combustor (12) in response to a sensed sulfur concentration condition of the
fluidized bed combustor.

Documents:

1271-KOLNP-2004-FORM-27.pdf

1271-kolnp-2004-granted-abstract.pdf

1271-kolnp-2004-granted-assignment.pdf

1271-kolnp-2004-granted-claims.pdf

1271-kolnp-2004-granted-correspondence.pdf

1271-kolnp-2004-granted-description (complete).pdf

1271-kolnp-2004-granted-drawings.pdf

1271-kolnp-2004-granted-examination report.pdf

1271-kolnp-2004-granted-form 1.pdf

1271-kolnp-2004-granted-form 18.pdf

1271-kolnp-2004-granted-form 2.pdf

1271-kolnp-2004-granted-form 26.pdf

1271-kolnp-2004-granted-form 3.pdf

1271-kolnp-2004-granted-form 5.pdf

1271-kolnp-2004-granted-reply to examination report.pdf

1271-kolnp-2004-granted-specification.pdf

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Patent Number

233861

Indian Patent Application Number

1271/KOLNP/2004

PG Journal Number

16/2009

Publication Date

17-Apr-2009

Grant Date

16-Apr-2009

Date of Filing

31-Aug-2004

Name of Patentee

ALSTOM TECHNOLOGY LTD.

Applicant Address

BROWN BOVERI STRASSE 7 CH-5400 BADEN

Inventors:

#	Inventor's Name	Inventor's Address
1	DURANT, JAMES F.	166 SUNNYFIELD DRIVE, WINDSOR, CONNECTICUT 06095
2	FERGUSON, JOHN E.	60 BLACK BRIDGE ROAD, NEW HARTFORD CONNECTICUT 06057
3	JUKKOLA, GLEN D.	55 SHAGBARK ROAD, GLASTONBURY CONNECTICUT 06033
4	ROGERS, REED S. C.	4 COACHMENS RUN AVON, CONNECTICUT 06001

PCT International Classification Number

F23J 7/00

PCT International Application Number

PCT/US2003/00984

PCT International Filing date

2003-01-14

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10/073,615	2002-02-11	U.S.A.