TWI837404B - A method for reducing the emission of contaminants by a furnace, a furnace and a non-transitory computer readable medium - Google Patents

Abstract

A method for reducing the emission of contaminants 700 by a fumace 250 is provided. The method includes forming a bed 440 from a stream of fuel 122 within the furnace 250; fluidizing the bed 440 with flue gas 272 from the furnace 250; and heating the fuel 122 within the bed 440 so as to generate char 702, ash 704 and contaminants 700. The method further includes capturing the contaminants 700 via the ash 704.

Description

Method for reducing pollutant emissions from a furnace, furnace and non-transitory computer-readable medium

Embodiments of the present invention generally relate to solid fuel boilers, and more particularly to a hybrid boiler-fuel dryer and method.

In known boilers, such as solid fuel boilers, organic materials are often used in industry and utilities to generate steam for operating equipment and generating electricity. For example, electric utility power plants typically generate electricity by using steam to turn the shaft of a turbine, thereby driving a generator. Many power plants generate this steam by burning solid fuels, such as coal or biomass. The fuel is burned in a furnace's combustion chamber to generate heat, which is then used to convert water into steam in the boiler. The steam is then superheated and directed to drive or rotate a steam turbine. These rotating turbines are coupled to an alternator by a shaft or rotor to generate AC power therewith. After the steam passes through the turbine, it is supplied to a condenser and cooled by passing a pipe with cooling water around it, which absorbs heat from the steam. As the steam cools, it condenses into water, which is then pumped back to the boiler to repeat the process of heating it to steam.

Known boilers often burn pulverized coal or biomass fuels, which may have a high moisture content, such as from being stored outdoors and exposed to high humidity conditions. The moisture content of this high moisture content fuel can vary greatly, causing subsequent variability in the combustion process and making it more difficult to operate the boiler efficiently. (As used herein, the term "high moisture content fuel" means and includes any type of solid fuel suitable for combustion in a furnace). The moisture content of solid fuels is known to have an impact on many aspects of boiler operation, including efficiency and emissions. A boiler burning high moisture content fuels (such as coal) will exhibit relatively low thermal efficiency due to the higher moisture content of the fuel. High moisture content in solid fuels can also cause problems with fuel handling, fuel grinding, fan capacity, and flue gas flow rates.

Furthermore, efficient suspended or tangential combustion in boilers firing high moisture content fuels is also affected by the relative moisture content and particle size distribution of the fuel. If the moisture content of the fuel is high enough, the combustion of the fuel in the combustion chamber may be slowed or delayed, causing unburned combustible material to be entrained with the flue gases. Furthermore, if the particle size of the pulverized solid fuel is large enough, the larger fuel particle size will make it difficult to maintain such fuel particles suspended in the combustion chamber, thereby reducing the residence time of the particles at high temperatures for complete combustion of the entire particle. Accordingly, in order to achieve the desired combustion efficiency in a tangentially fired boiler, the high moisture content fuel must be adequately dried and sized. Specifically, in order to achieve efficient combustion in a conventional boiler, both the particle size and moisture content of the fuel must be addressed (i.e., minimized) in a fuel pre-treatment system. Typically, a dryer device is used to pre-treat (i.e., by heating) high moisture content fuels prior to combustion to reduce the moisture content and increase the BTU production of the fuel.

Some known boilers attempt to circumvent the challenges of burning fuels with relatively large and moist particles by employing a semi-suspension system. In such systems, relatively large fuel particles (e.g., greater than 25 mm in diameter) are fed to a grate at the bottom of the boiler, while relatively smaller particles (referred to as "fines") are screened during pre-treatment and partially dried in a separate mill dryer prior to suspension combustion. Generally, for known semi-suspension systems, a particle moisture content of 55% and a maximum particle size of less than 40 mm (90% at <25 mm) is desired. The use of these larger particle size fuels with higher moisture contents generally requires the boiler to achieve heat input greater than 50% of the maximum continuous rating (MCR). As used herein, "MCR" refers to the ability of a steam boiler to continuously and easily generate and deliver a predetermined amount of steam without inadequacy or undesirable effects (such as overloading, slagging, or overheating).

However, using fuel pretreatment of the water-containing fuel (e.g., to achieve a moisture content of less than 40% (i.e., essentially free of surface water) at 96% particle size less than 10 mm and 99% less than 20 mm), suspension combustion with heat inputs of more than 10% MCR is feasible, thus making efficient operation at low loads achievable. Furthermore, suspension combustion is achievable using pulverized and dried fuels in fuels having particles sized 85% less than 1 mm without the loading limitation of up to 25% moisture content. However, such known fuel pretreatments result in undesirable and considerable parasitic loads on the boiler. For example, even for relatively small particle sizes (generally less than 2 mm), a residence time of a few seconds may be sufficient for drying to 20% moisture, while larger particle sizes may require a residence time of several minutes for effective drying. However, in order to make the use of known dryers for drying fuels prior to pulverization economically feasible, residence times of a few seconds or less should preferably be given, so that this can be done while the particles are pneumatically conveyed to the furnace. However, in such dryers, corresponding heat and mass transfer rates are generally only achievable using a fluidizing or atomizing reactor with fuel particle sizes of 1 mm or less. Achieving such particle sizes with known coal mills is already cost-prohibitive in terms of grinding capacity. In addition, the energy consumption required to grind the fuel increases significantly as the moisture content of the fuel rises from 20% to 40% and above.

In addition, coal and/or biomass fuels often contain pollutants (i.e., gaseous elements and/or chemicals that cause corrosion, scaling, slagging and/or other undesirable formations in the furnace and/or surrounding environment) that are emitted when the fuel is burned in the furnace.

Therefore, what is needed is a hybrid boiler-dryer method for reducing pollutant emissions from a furnace.

In one embodiment, a method for reducing pollutant emissions from a furnace is provided. The method includes: forming a bed from a fuel stream in the furnace; fluidizing the bed with flue gas from the furnace; and heating the fuel in the bed to produce char, ash, and pollutants. The method further includes capturing the pollutants via the ash.

In another embodiment, a furnace is provided. The furnace includes: a grate operable to form a bed from a fuel stream; and a conduit operable to fluidize the bed with flue gas produced by the furnace. The bed promotes: the production of coke, ash, and pollutants from the fuel; and the capture of the pollutants by the ash.

In yet another embodiment, a non-transitory computer-readable medium is provided that includes instructions. The instructions adjust at least one processor to: adjust at least one property of a bed formed by a fuel stream in a furnace to promote: the production of coke, ash, and contaminants from the fuel; and the capture of the contaminants by the ash.

90: Power plant

100: boiler

102: Combustion system

111: First air fan

112: Valve

114:Conveyor device

116: sieve

120: Fuel

121:Part 1; Arrow

122: Part 2; Arrow; Fuel

140: Storage area

222: First conveyor

250: furnace; boiler

251: Lower part

252: Rear access section

255: Second conveyor

256: The third transmitter

257: Flue gas

259: Exhaust chimney

268: Degassing Device

270: Smoke

271: Part 1

272: Part II; Exhaust flow; Flue gas; First tube

275: Gas

284: Dryer device

330: Steam

340: Turbine

360: Turbine

371: First channel; tube

372: second channel; tube; conduit

373: channel; conveyor; tube

380: Turbine

400:Grate

401: Steps

402: Steps

403: Steps

405:Ash cooler

410:Exit

414: Steps

415: Steps

416: Steps

417: Steps

418: Steps

421: Steps

422: Steps

423: Steps

424: Steps

425: Steps

427: Steps

410:Exit

430: Generator

440:Bed area; bed

444:Ash separator

450: Air chamber

475: ash collection container; collection container

480: Turbine

500: Electricity

700: Dashed line; pollutants

702: Coke

704: ash content

706: Carbon separator

708:Syringe; delivery device

710: Controller

712:Sensor

800: grinder; crusher

900: Hybrid boiler-dryer

901:First fuel dryer

902: Second fuel dryer

The present invention will be better understood by reading the following non-limiting embodiments and referring to the following accompanying figures herein: [FIG. 1] is a schematic diagram of an embodiment; [FIG. 2] is a schematic diagram of an alternative embodiment; [FIG. 3] is a flow chart of an embodiment according to a method; [FIG. 4] is a schematic diagram according to an embodiment; [FIG. 5] is a schematic diagram of another alternative embodiment; [FIG. 6] is a schematic diagram of another embodiment; and [FIG. 7] is another schematic diagram of the embodiment of FIG. 6.

The following is a detailed description of exemplary embodiments of the present invention, which are illustrated in the accompanying drawings. Whenever possible, the same reference characters used throughout the drawings refer to the same or similar components and will not be described repeatedly.

As used herein, the terms "substantially," "generally," and "about" indicate conditions that are within reasonably achievable manufacturing and assembly tolerances relative to ideally desired conditions applicable to achieving the functional purpose of a component or assembly. As used herein, the term "real-time" means a level of processing responsiveness that is perceived by a user as sufficiently immediate or to enable a processor to keep up with external programs. As used herein, "electrically coupled," "electrically connected," and "electrical communication" mean that reference elements are connected directly or indirectly so that an electric current or other propagation medium can flow from one to another. The connection may include a direct conductive connection (i.e., without the use of an intervening capacitor, inductor, or active element), an inductive connection, a capacitive connection, and/or any other suitable electrical connection. Intermediary components may be present. As also used herein, the term "fluid connected" means that the referenced elements are connected so that a fluid (including liquid, gas, and/or plasma) can flow from one element to another. Accordingly, as used herein, the terms "upstream" and "downstream" describe the position of the referenced elements relative to the flow path of the fluid and/or the gas flowing between and/or near the referenced elements. Further, the term "stream" as used herein with respect to particles means a continuous or nearly continuous flow of particles. As also used herein, the term "heating contact" means that the referenced objects are in close proximity to each other so that heat/thermal energy can be transferred therebetween.

Although the embodiments disclosed herein are primarily described with respect to solid fuel boilers, it should be understood that embodiments of the present invention may be applied to other apparatus and/or methods that benefit from the teachings herein. Although coal as a fuel burned in a boiler at a power plant is generally referred to herein as an exemplary particulate material for the purposes of this application, it should be understood that any other solid material that constitutes a useful or beneficial input to an industrial operation may also be used.

Referring to FIG. 1 , there is shown a schematic diagram of one embodiment of a solid fuel type power plant 90 for generating electricity. The power plant 90 operates to increase the temperature and pressure of a gas to drive one or more turbines. The rotating turbines are coupled to an AC generator via a shaft or rotor to generate AC power therewith.

The power plant 90 includes a boiler 100 including a furnace 250 configured to combust a solid fuel 120 therein. As will be described in more detail herein, the solid fuel 120 in the form of particles is fed from a storage area 140 (such as a coal silo) to the boiler 100 and combusted therein to generate heat.

The furnace 250 operates to ignite and burn the solid fuel 120 in a known manner. For example, in one embodiment, the furnace 100 may employ a known combustion system 102 (such as a suspended combustion system) to burn the fuel 120. Other embodiments may include other types of known furnace combustion systems 102 without departing from the scope of the invention. In some embodiments, the furnace 250 may include a known back-pass portion 252 (FIG. 2).

As depicted in FIG. 2 , during operation, relatively hot flue gas 270 is generated by burning fuel 120 ( FIG. 1 ) in furnace 250 and is provided to and exhausted from flue 257 , such as via exhaust chimney 259 . In various embodiments, flue 257 may be defined by one or more tubes configured to receive hot flue gas 270 generated in furnace 250 . As described in greater detail herein, at least a first portion 271 ( FIG. 4 ) and a second portion 272 ( FIG. 4 ) of hot flue gas 270 may be extracted from flue 257 and recovered to enable operation of various embodiments described herein.

Additionally, as depicted in FIG. 4 , in some embodiments, one or more pollution control devices may be configured to receive hot flue gas 270 from flue 257. For example, a degasser 268 (such as a known wet degasser) may be configured to be in fluid communication with flue 257 to receive flue gas 270 therefrom to extract pollutants, such as sulfur compounds, sulfur oxides (e.g., sulfur dioxide), and ash particles from flue gas 270 before extracting and recovering first and second portions 271, 272 of flue gas 270.

The boiler 100 further includes a hybrid boiler-dryer 900. As shown, an embodiment of the hybrid boiler-dryer 900 includes a first fuel dryer 901 and a second fuel dryer 902. In one embodiment, the first fuel dryer 901 may include an in-suspension fuel dryer, and the second fuel dryer 902 may include an on-grate fuel dryer. As used herein, the term "fuel dryer" means any equipment that can be used to reduce the moisture content of a particulate material by the direct or indirect application of heat, including but not limited to a fluidized bed dryer, a vibrating fluidized bed dryer, a fixed bed dryer, a moving bed dryer, a cascaded whirling bed dryer, or an elongated slot dryer.

During operation, as shown in FIG1 , water in the tubes (not shown) is heated and converted into steam 330 by heat generated by the normal combustion reaction of the fuel 120 burning in the furnace 250, which is delivered to the steam turbine 340. In some embodiments, the steam turbine 340 may include a plurality of turbines, such as a high pressure steam turbine 360, an intermediate pressure steam turbine 380, and a low pressure steam turbine 480 operatively connected in series. The steam 330 performs work by being pushed against fan-shaped blades (not shown) that are connected to a series of wheels (not shown) contained in each turbine 340, 360, 380, which are mounted on a shaft (not shown). As the steam 330 pushes against the blades (not shown), it causes both the wheels and the turbine shaft to rotate. The rotating shaft rotates the rotor of the generator 430, thereby generating electricity 500. The steam 330 leaving the steam turbine 360 is delivered to a condenser (not shown) where it is cooled by cooling water to convert the steam back into water.

In the embodiment depicted in FIGS. 2 and 4 , solid fuel 120 ( FIG. 1 ; such as relatively high moisture content raw coal) may be collected in a storage area 140 (such as a coal silo) until needed. The high moisture content fuel 120 may include a first portion 121 of fuel (as indicated by arrow 121 in FIG. 4 ) and a second portion 122 of fuel (as indicated by arrow 122 in FIG. 4 ), the first portion of fuel defining relatively small particle sizes or “fines” (e.g., less than 25 mm in diameter) and the second portion of fuel defining relatively large particle sizes that are coarser or larger (e.g., at least 25 mm in diameter) than the relatively fine or small particle sizes defined by the first portion 121. In one embodiment, the first portion 121 of the fuel further defines predetermined particle sizes that are suitable for combustion by the combustion system 102 without requiring grinding or other steps to reduce the particle size within the first portion 121 of the fuel; and the second portion 122 of the fuel defines predetermined particle sizes that require grinding or other steps to reduce the particle size within the second portion 122 of the fuel to enable combustion by the combustion system 102.

During operation, raw fuel 120 is provided or conveyed by a known conveyor device 114 to a filter or screen 116 for screening. Screen 116 operates to separate the first portion 121 of fuel from the second portion 122 of fuel based on the relative particle sizes of the first portion 121 of fuel and the second portion 122 of fuel. In various embodiments, screen 116 may include a roller screen. In other embodiments, screen 116 may include one or more of a centrifuge, a trommel screener, a vibrating screen, a screw feeder, and a rotating drum feeder. In other embodiments, any desired screen 116 device may be used to separate the first portion 121 of the fuel from the second portion 122 of the fuel which enables the furnace to be operated as described herein without departing from the scope of the claimed subject matter.

After the first portion 121 of the fuel is filtered or separated from the second portion 122 of the fuel by the screen 116, the first portion 121 of the fuel can then be provided to the combustion system 102 of the furnace 250 for combustion via the first fuel dryer 901. In one embodiment, the first fuel dryer 901 includes a first passage or tube 371 through which the first portion 121 of the fuel is conveyed by a stream of the first portion 271 of flue gas. For example, in one embodiment, the first tube 371 is configured to receive the first portion 121 of the coal directly from the screen 116. In other embodiments, the first tube 371 is configured to receive the first portion 121 of the coal from a first conveyor 222 (such as a pressurized tube coupled in fluid communication between the first tube 371 and the screen 116). In other embodiments, the first conveyor 222 can be a mechanical first conveyor 222, such as a belt conveyor or chute, or any other known conveyor that enables the first portion 121 of coal to be received from the screen 116 by the first tube 371. In addition, the first tube 371 is configured to be in fluid communication with the flue 257 to receive the first portion 271 of flue gas therefrom. The first portion 271 of flue gas flows through the first tube 371 to thereby convey the first portion 121 of fuel therethrough to the furnace 250 for combustion by the combustion system 102. The first portion 271 of flue gas can be provided using a first air blower 111 (such as a primary air blower) that is in fluid communication with the first tube 371. In some embodiments, the first air blower 111 may include a flue gas recirculation blower.

In this way, in the first fuel dryer 901 including the first tube 371, heat from the first portion 271 of the recovered flue gas is advantageously used to further dry the first portion 121 of the fuel in suspension in the first tube 371 before combustion in the furnace 250 (e.g., by suspended combustion or tangential combustion).

After filtering or separating the second portion 122 of the fuel from the first portion 121 of the fuel, the second portion 122 of the fuel may be further dried and sized before being provided to the combustion system 102 for combustion in the furnace 250. The second portion 122 of the fuel is dried by a second fuel dryer 902. For example, the second fuel dryer 902 may include a grate 400 having an opening (not shown) defined therethrough, configured to receive the second portion 122 of the fuel thereon, and disposed within a lower portion 251 of the furnace 250 adjacent the combustion system 102. The second portion 122 of the fuel is conveyed from the screen 116 to the furnace 250 by a second conveyor 255 (such as a known mechanical belt-type conveyor) and disposed on the grate 400. In other embodiments, the second conveyor 255 may include a pressurized pipe. During an operation of the furnace 250, while the second portion 122 of the fuel is on the grate 400, the second portion 122 of the fuel is exposed to heat and a reducing environment due to combustion occurring in the furnace 250, and is fluidized by the oxygen-deficient exhaust gas stream 272, whereby the second portion 122 of the fuel is at least partially devolatilized and dried in a known manner. It should be understood that the second portion 122 of the fuel disposed on the grate 400 defines a bed region 440 (also referred to herein as a "bed") in which fluidization occurs. For example, the bed region 440 may include one of a fixed bed, a fluidized bed, a bubbling fluidized bed, or a sluggish fluidized bed.

In addition, ash particles generated by combustion in the furnace 250 and present in the bed region 440 can be separated from the second portion 122 of the fuel. For example, in some embodiments, such as depicted in FIG. 5 , the fixed bed region 440 is fluidly coupled to an ash separator 444 whereby relatively heavier ash particles in the second portion 122 of the fuel migrate to the bottom of the bed region 440 and are captured to be placed in an ash container 475 that is fluidly coupled to the bottom of the bed region 440 via an outlet 410. Conversely, the relatively lighter ash and fuel particles within the second portion 122 of the fuel may be retained toward an upper portion or top of the bed region 440 and provided therefrom to an ash cooler 405, such as a rotary ash cooler, prior to being delivered to the grinder 800. In one embodiment, the residence time of the bed region 440 (i.e., the period of time that the second portion 122 of the fuel remains in the bed region 440 in the furnace 250) may be based on a predetermined period of time. In other embodiments, the residence time of the second portion 122 of the fuel in the bed 440 may be determined based on a desired property of the second portion 122 of the fuel, such as a predetermined moisture content. When the desired properties of the second portion of the fuel 122 are met, and/or when the predetermined residence time of the second portion of the fuel 122 on the grate 400 is met, the second portion of the fuel 122 is then removed or extracted from the bed 440.

In one embodiment, a second passage or tube 372 is configured to be in fluid communication with the flue 257 and is configured to receive a second portion 272 of flue gases exiting the furnace 250 therethrough. The second portion 272 of flue gases is directed to the second fuel dryer 902 via the second tube 372 to fluidize the second portion 122 of fuel disposed in the bed 440. Some embodiments may include any number of second tubes 372 to deliver the second portion 272 of flue gases to the second fuel dryer 902.

In one embodiment, the second portion 272 of flue gas may be provided to an air chamber 450 disposed below and adjacent to the grate 400. The second portion 272 of flue gas may be provided through the second tube 372 using a blower such as the first air blower 111. In other embodiments, a second air blower (not shown) may be used in place of or in conjunction with the first air blower 111.

In one embodiment, additional gas 275 (such as ambient air) may be drawn in through a valve 112 or regulator in conjunction with the first air blower 111 and added to the second portion 272 of flue gas to adjust or control the flow rate and oxygen content of the second portion 272 of flue gas delivered to the second portion 122 of fuel fluidized on the bed 440. In this manner, the temperature, gas velocity, and chemical composition of the fluidizing gas (i.e., the second portion 272 of flue gas) for the fuel (i.e., the second portion 122 of fuel) above the grate 400 may be controlled.

When extracted from the grate 400, the second portion 122 of the fuel is then conveyed to a grinder or pulverizer 800 for grinding (i.e., to mechanically reduce the particle size of the fuel 122) and thereafter reintroduced into the furnace 250 for combustion therein. The second portion 122 of the fuel is conveyed away from the furnace 250 to the pulverizer by a third conveyor 256 (which may be a pressurized pipe). In other embodiments, the third conveyor 256 may alternatively include a known mechanical belt-type conveyor or a chute. In some embodiments, the second portion 122 of the fuel may be conveyed to a dryer device 284 (FIG. 4) (such as a known carbon separator and/or heat exchanger) via a third conveyor 256 prior to conveying from the furnace 250 to the pulverizer 800 for further optimizing (i.e., reducing) moisture content and ash removal prior to conveying to the pulverizer 800 and particle classification by the pulverizer. Still other embodiments may omit the dryer device 284 and convey the second portion 122 of the fuel directly from the furnace 250 to the pulverizer 800 via the third conveyor 256 for grinding. After grinding in the pulverizer 800, the second portion 122 of the fuel is then conveyed to the furnace's suspended combustion system 102 for combustion.

In one embodiment, the second portion 122 of the fuel may be transported from the pulverizer 800 and provided to the first tube 272 for transport to the combustion system 102 along with the first portion 121 of the fuel. In other embodiments, the second portion 122 of the fuel may be transported from the pulverizer 800 (i.e., outside the furnace 250) to the combustion system 102 (i.e., inside the furnace) via a fourth conveyor 373 separately from the first portion 121 of the fuel in the first tube 371. For example, in an embodiment where the grinder 800 may be a beater wheel type grinder, the fourth conveyor 373 may include a pressurized passage or tube 373 configured to be in fluid communication with the grinder 800 to receive the second portion 122 of the fuel therefrom using pressurized air blown out of the grinder 800. In other embodiments, the fourth conveyor 373 may include a fourth tube 373 in fluid communication with a blower (not shown; such as a known secondary air blower) to pressurize air in the fourth tube 373 to coordinately convey the second portion 122 of the fuel from the grinder 800 through the fourth tube 373 to the combustion system 102 in the furnace 250. Still other embodiments may use any number of mechanical conveyors configured to define the fourth conveyor 373 to convey the second portion 122 of the fuel to the combustion system 102 in the furnace 250. As depicted in FIG. 2, some embodiments may include a fourth conveyor 373 that includes any number of fourth tubes to convey the second portion 122 of the fuel from the grinder 800 to the combustion system 102.

Referring back to the system described in Figure 1, the boiler 100 may be started as a known semi-suspension system. However, when the temperature of the furnace has reached a predetermined or desired level (e.g., when the heat input on the grate 400 can be reduced without adversely affecting boiler performance), the second portion 272 of the flue gases is recirculated and devolatization and drying of the second portion 122 of the fuel on the grate 400 is initiated. A second portion 122 of the fuel is then extracted from the furnace 250 at a preferred moisture content for particle classification in the pulverizer 800 (having a relatively low parasitic load due to the lower moisture content) and then reinjected into the furnace 250 via the suspended combustion system 102. In this way, the heat input is offset to the suspended combustion system 102, thereby giving more flexibility to quickly adjust to any changes in load demand.

Referring now to FIG. 3 , in one embodiment, a method of operating a furnace is provided, the furnace having a combustion system configured to burn particles of a solid fuel received therein. The method includes: providing particles of the solid fuel to a screen at step 401; dividing the solid fuel into a first portion of fuel and a second portion of fuel based on the particle size of the solid fuel at step 402, wherein the particle size in the first portion of the fuel is less than a predetermined size, and the particle size of the fuel in the second portion of the fuel is greater than a predetermined size; directing a flue gas through a flue at step 403; providing at step 414 a first portion of the flue gas to a first fuel dryer, the first fuel dryer including a first tube in fluid communication with the flue; at step 415, delivering the first portion of the fuel to the first tube; at step 416, drying the first portion of the fuel in the first tube; at step 417, delivering the first portion of the fuel through the first tube to the furnace; and at step 418, combusting the first portion of the fuel with a combustion system. The method further includes: at step 421, conveying the second portion of the fuel to a second fuel dryer disposed in a lower portion of the furnace, and conveying a second portion of the flue gas to the second fuel dryer portion; at step 422, drying the second portion of the fuel with the second fuel dryer portion; at step 423, conveying the second portion of the fuel from the second fuel dryer portion in the furnace to a grinder disposed outside the furnace; at step 424, reducing the particle size of the second portion of the fuel with the grinder; at step 425, conveying the second portion of the fuel from the grinder to the furnace; and at step 427, burning the second portion of the fuel with a combustion system.

In the above-mentioned embodiments, the second portion 122 of the fuel is fed to the boiler 250 on the grate 400 and exposed to the reducing atmosphere, and the low gas velocity is used for a predetermined retention time to release the pollutants from the fuel 122. The technical effect of these embodiments is that the biomass ash mist away from the grate 400 is limited by the low gas velocity, thereby reducing the tendency of downstream clogging or fouling of the furnace 250.

One of the technical effects of the above embodiment is that by recirculating flue gas, the reducing environment in the lower section of the furnace is controlled, and the suspended combustion of dried fuel allows better NOx emission control.

Thus, according to the claimed subject matter, the boiler comprises a hybrid dryer in which the residence time is adapted for larger size, high moisture, wet fuel particles. Pre-drying the fuel using hot flue gases prior to comminution enables the moisture to be removed without the need for expensive heat transfer equipment such as known rotary and fluidized bed dryers.

Moving now to FIG. 6 , it should be appreciated that in embodiments, the bed 440 formed on the grate 400 by the flow of the second fuel 122 is operable to reduce emissions from the furnace 250 by facilitating the capture of pollutants (represented by dashed line 700; e.g., NOx, SOx, one or more alkalis, one or more alkaline earth elements, other contaminant metals, and/or other elements and/or chemicals that may cause corrosion, scaling, slagging, greenhouse effects, acid rain, or that are desired to be prevented from being emitted to the atmosphere/environment). In such embodiments, the bed 440 may be fluidized by recycled flue gas (e.g., a second portion of the flue gas 272 passing through the tube 372). As will be appreciated, heat and/or flue gases 272 from furnace 250 cause fuel 122 to produce coke 702, ash 704, and pollutants 700 as fuel 122 travels across bed 440. In other words, fuel 122 is partially gasified and combusted within bed 440. By adjusting and/or controlling one or more properties of bed 440, embodiments of the present invention facilitate capture of pollutants 700 by ash 704, and subsequently coke 702 (i.e., the portion of fuel 122 that is ultimately combusted in furnace 250) has significantly fewer pollutants than fuel 122 before entering bed 440, or, in some embodiments, no pollutants.

For example, in embodiments, one or more properties of the bed 440 may include: a flow rate of the flue gas 272 across the bed 440, which may range from about 0.05 ft/s to about 5.0 ft/s; an oxygen concentration of the flue gas 272 within the bed 440, which may range from about 0% by volume to about 21% by volume; a temperature of the flue gas 272 within the bed 440, which may range from about an ambient temperature (e.g., 70-80°F) to about 600°F; a height H of the bed 440, which may range from about 3 ft to about 100 ft; and a relative humidity of the flue gas 272. about 60ft; the length L of bed 440, which may range from about 1ft to about 500ft; the width W of bed 440 (not shown because it is normal to the diagram of FIG. 6 ), which may range from about 10ft to about 250ft; the residence time (i.e., the amount of time fuel 122 spends in bed 440), which may range from about 1s to about 2hrs (depending on the moisture content and temperature of the fuel); and/or other properties of bed 440 that affect the chemical and/or stoichiometric conditions within bed 440.

In some embodiments, the composition (i.e., the material that makes up the bed 440) can be varied. For example, in embodiments, the furnace 250 can further include an injector/delivery device 708 that delivers/feeds additives to the bed 440 to change the chemical composition of the bed 440. Such additives can include limestone (to control sulfur emissions), clay (to capture alkali), recycled fuel ash, lime, and/or any other sorbent capable of capturing pollutants.

Referring to FIG. 7 , in an embodiment, the furnace 250 and/or a facility housing it (e.g., power plant 90 ( FIG. 1 )) may further include a carbon separator 706 disposed downstream of the bed 440 and operable to separate the coke 702 from the ash 704 so that the coke 702 may be combusted in the furnace 250 and the ash 704 containing the contaminants may be disposed of and/or further processed.

In some embodiments, the grate 400 can function as a carbon separator by allowing ash 704 to fall from the bed 440 while retaining the coke 702 in the bed 440, wherein the ash 704 moves through the outlet 410 to the receiver 475 (Figure 5).

As described above, after the coke 702 has been dried by the furnace 250, it can be transferred to the grinder 800 (Figure 5) for processing before being burned in the furnace 250.

In an embodiment, controller 710 may monitor the chemical conditions of bed 440 via one or more sensors 712 and adjust the properties of bed 440 as discussed above to optimize capture of contaminants 700 (FIG. 6).

Finally, it should also be understood that furnace 250, boiler 100, and/or power plant 90 housing the same may include necessary electronics, software, memory, storage, databases, firmware, logic/state machines, microprocessors, communication links, displays or other visual or audio user interfaces, printing devices, and any other input/output interfaces to perform the functions described herein, and/or to achieve the results described herein, which may be performed in real time. For example, controller 710 may include at least one processor and system memory/data storage structures, which may include random access memory (RAM) and read-only memory (ROM). At least one processor of the controller 710 may include one or more conventional microprocessors and one or more additional co-processors, such as a mathematical co-processor or the like. The data storage structures discussed herein may include an appropriate combination of magnetic, optical and/or semiconductor memory and may include, for example, RAM, ROM, flash drives, optical disks (such as optical disks and/or hard disks or drives).

Additionally, a software application that adapts the controller to execute the methods disclosed herein may be read from a computer-readable medium into a main memory of the at least one processor. As used herein, the term "computer-readable medium" refers to any medium that provides or participates in providing instructions to at least one processor of the controller 710 (or any other processor of the device described herein) for execution. Such a medium may take many forms, including but not limited to non-volatile media and volatile media. Non-volatile media include, for example, optical, magnetic, or magneto-optical disks, such as memory. Volatile media include dynamic random-access memory (DRAM), which generally constitutes main memory. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, RAM, PROMs, EPROMs or EEPROMs (electronically erasable programmable read-only memory), FLASH-EEPROMs, any other memory chips or memory cartridges, or any other media from which a computer can read.

Although in the embodiments, executing a sequence of instructions in the software application causes at least one processor to perform the method/procedure described herein, hard-wired circuitry may be used in place of or in combination with software instructions to perform the method/procedure of the present invention. Therefore, embodiments of the present invention are not limited to any specific combination of hardware and/or software.

It is further understood that the above description is intended to be illustrative rather than restrictive. For example, the above embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to the teachings of the present invention to adapt to particular circumstances or materials without departing from the scope of the present invention.

For example, in one embodiment, a method for reducing pollutant emissions from a furnace is provided. The method includes: forming a bed from a fuel flow within the furnace; fluidizing the bed with flue gas from the furnace; and heating the fuel in the bed to produce char, ash, and pollutants. The method further includes capturing the pollutants via the ash. In certain embodiments, the pollutants are NOx, SOx, one or more alkalis, and/or one or more alkaline earth elements. In certain embodiments, the method further includes adjusting at least one property of the bed. In certain embodiments, the at least one property is: the flow rate of the flue gas across the bed; the oxygen concentration of the flue gas within the bed; the temperature of the flue gas within the bed; the height of the bed; and/or the residence time of the bed. In some embodiments, the at least one property is the flow rate of the flue gas across the bed and is adjusted to be within the range of about 0.05 ft/s to about 5.0 ft/s. In some embodiments, the at least one property is the temperature of the flue gas within the bed and is adjusted to be within the range of about 70°F to about 600°F. In some embodiments, the at least one property is the height of the bed and is adjusted to be between about 3 ft to about 60 ft. In some embodiments, the at least one property is the residence time of the bed and is adjusted to be between about 1 s to about 2 hrs. In some embodiments, the method further comprises separating the char from the ash via a carbon separator.

Other embodiments provide a furnace. The furnace includes: a grate operable to form a bed from a fuel stream; and a conduit operable to fluidize the bed with flue gas produced by the furnace. The bed promotes: the production of coke, ash, and pollutants from the fuel; and the capture of the pollutants by the ash. In certain embodiments, the pollutants include NOx, SOx, one or more alkalis, and/or one or more alkaline earth elements. In certain embodiments, one or more properties of the bed are operable to maximize the pollutants captured by the ash. In certain embodiments, the flue gas has a flow rate across the bed of about 0.05 ft/s to about 5 ft/s. In certain embodiments, the temperature of the flue gas within the bed is between about 70°F and about 600°F. In certain embodiments, the bed has a height between about 3 ft and about 5 ft. In certain embodiments, the bed has a residence time between about 1 s and about 2 hrs. In certain embodiments, the furnace includes a delivery device that feeds an additive to the bed. In certain embodiments, the furnace further includes a carbon separator that is operable to separate the coke from the ash. In certain embodiments, the furnace further includes a grinder that is operable to process the coke.

Still other embodiments provide a non-transitory computer-readable medium comprising instructions. The instructions adjust at least one processor to: adjust at least one property of a bed formed by a fuel stream in a furnace to promote: the production of coke, ash, and contaminants from the fuel; and the capture of the contaminants by the ash.

It should therefore be appreciated that by adjusting one or more properties of the fluidized bed of fuel disposed within the furnace as described above, some embodiments of the present invention may provide improved emissions reductions over conventional pollutant capture systems and methods.

Although the dimensions and material types described herein are intended to define parameters of various embodiments, they are not intended to be limiting and are merely exemplary embodiments. Many other embodiments will be apparent to those of ordinary skill in the art upon reviewing the above description. Therefore, the scope of the present invention should be determined by reference to the appended claims, along with the full range of equivalents to such claims. In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the terms "comprising" and "comprise." In addition, in the following claims, terms such as "first," "second," "third," "upper," "lower," "above," and "below" are used merely as labels and are not intended to impose numerical or positional requirements on such subject matter. Furthermore, the following claims limitations are not written in means-plus-function form and are not intended to be so construed unless and until such claims limitations expressly use the term "means for" followed by a description of the function without further structure.

This written description uses examples to disclose several embodiments of the invention (including the best mode) and enables a person of ordinary skill in the art to practice the embodiments of the invention, including making and using any device or system and performing any incorporated method. The patentable scope of the invention is defined by the claims and may include other examples that occur to a person of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they do not have structural elements that differ from the literal language of the claims, or if they include equivalent structural elements that do not differ substantially from the literal language of the claims.

As used herein, an element or step cited in the singular and followed by the word "a/an" should be understood as not excluding the plural of the element or step, unless such exclusion is explicitly stated. Furthermore, reference to "an embodiment" of the present invention is not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the cited features. In addition, unless explicitly stated to the contrary, an embodiment that "comprising," "including," or "having" an element or multiple elements having a particular property may include additional such elements that do not have that property.

Since certain changes may be made to the above invention without departing from the spirit and scope of the invention as described herein, it is intended that all of the subject matter described above as shown in the accompanying drawings should be interpreted only as examples illustrating the concepts of the invention herein and should not be used as limitations on the invention.

100: boiler

102: Combustion system

111: First air fan

114:Conveyor device

116: sieve

120: Fuel

121:Part 1; Arrow

122: Part 2; Arrow; Fuel

140: Storage area

222: First conveyor

250: furnace; boiler

251: Lower part

255: Second conveyor

256: The third transmitter

257: Flue gas

268: Degassing Device

270: Smoke

271: Part 1

272: Part II; Exhaust flow; Flue gas; First tube

284: Dryer device

371: First channel; tube

372: second channel; tube; conduit

373: channel; conveyor; tube

400:Grate

450: Air chamber

800: grinder; crusher

900: Hybrid boiler-dryer

901:First fuel dryer

902: Second fuel dryer

Claims (20)

A method for reducing pollutant emissions from a furnace having a combustion system for burning fuel, the method comprising: supplying a fuel stream to the furnace, wherein the fuel stream comprises a first portion of fuel having a relatively fine particle size and a second portion of fuel having a relatively coarse particle size; separating the fuel stream into a relatively fine particle size fuel stream and a relatively coarse particle size fuel stream before entering the furnace; providing the relatively fine particle size fuel stream to the combustion system for combustion thereof; forming a bed from only the relatively coarse particle size fuel stream within the furnace, wherein the bed is located within the combustion system; a lower portion of the furnace near the system; fluidizing the bed formed from the relatively coarse particle size fuel stream with flue gases from the combustion of the relatively fine particle size fuel stream in the combustion system of the furnace; heating the relatively coarse particle size fuel stream in the bed to produce coke, ash and pollutants; capturing the pollutants through the ash; conveying the heated relatively coarse particle size fuel stream from the bed outside the furnace to a pulverizer for grinding to form relatively fine particle size pulverized fuel; and providing the relatively fine particle size pulverized fuel to the combustion system for combustion thereof. The method of claim 1, wherein the pollutants are NOx, SOx, one or more alkalis, and/or one or more alkaline earth elements. The method of claim 1 further comprises: adjusting at least one property of the bed. The method of claim 3, wherein the at least one property is: the flow rate of the flue gas across the bed; the oxygen concentration of the flue gas in the bed; the temperature of the flue gas in the bed; the height of the bed; the chemical composition of the bed; and/or the residence time of the bed. The method of claim 3, wherein the at least one property is the flow rate of the flue gas across the bed and is adjusted to be in the range of about 0.05 ft/s to about 5 ft/s. The method of claim 3, wherein the at least one property is the temperature of the flue gas in the bed and is adjusted to be within a range of about 70°F to about 600°F. The method of claim 3, wherein the at least one property is the height of the bed and is adjusted to be between about 3 ft and about 60 ft. The method of claim 3, wherein the at least one property is the bed residence time, which is adjusted to be between about 1 s and about 2 hrs. The method of claim 1 further comprises: separating the coke from the ash via a carbon separator. A furnace comprising: a first inlet operable to receive a relatively fine particle size fuel stream; a second inlet operable to receive a relatively coarse particle size fuel stream; a combustion system to combust the fuel, wherein the combustion system is operable to receive the relatively fine particle size fuel stream for combustion thereof; a grate operable to form a bed from only the relatively coarse particle size fuel stream; a first conduit operable to use the relatively fine particle size fuel in the combustion system to The invention relates to a furnace comprising: a furnace comprising: a furnace comprising: a furnace comprising: a furnace having a plurality of relatively coarse particle size fuel streams and a bed formed from the relatively coarse particle size fuel stream formed on the grate; ... The furnace of claim 10, wherein the pollutants include: NOx, SOx, one or more alkalis, and/or one or more alkaline earth elements. The furnace of claim 10, wherein the bed comprises one or more properties operable to maximize capture of contaminants by the ash. The furnace of claim 10, wherein the flue gas has a flow rate across the bed of about 0.05 ft/s to about 5 ft/s. The furnace of claim 10, wherein the temperature of the flue gas in the bed is between about 70°F and about 600°F. The furnace of claim 10, wherein the bed has a height between about 3 ft and about 60 ft. The furnace of claim 10, wherein the bed has a residence time between about 1 s and about 2 hrs. The furnace of claim 10 further comprises: a delivery device that feeds an additive to the bed. The furnace of claim 10, further comprising: a carbon separator operable to separate the coke from the ash. The furnace of claim 10, further comprising: a grinder operable to process one or more of the coke carried by the second conduit and the heated relatively coarse particle size fuel stream. A non-transitory computer-readable medium comprising instructions that adapt at least one processor to: adjust at least one property of a bed formed solely by a relatively coarse particle size fuel stream within a lower portion of a furnace having a combustion system located proximate the bed, the combustion system being operable to receive a relatively fine particle size fuel stream for combustion thereof, wherein the bed is fluidized by flue gases generated by combustion of the relatively fine particle size fuel stream in the combustion system, the adjustment of the at least one property of the bed formed solely by the relatively coarse particle size fuel stream promoting: the generation of coke, ash, and contaminants from the relatively coarse particle size fuel stream; and the capture of the contaminants by the ash.

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