Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
  • F23G5/02—Incineration of waste; Incinerator constructions; Details, accessories or control therefor with pretreatment
  • F23G5/027—Incineration of waste; Incinerator constructions; Details, accessories or control therefor with pretreatment pyrolising or gasifying stage
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
  • F23G5/32—Incineration of waste; Incinerator constructions; Details, accessories or control therefor the waste being subjected to a whirling movement, e.g. cyclonic incinerators
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
  • F23G5/50—Control or safety arrangements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23N—REGULATING OR CONTROLLING COMBUSTION
  • F23N3/00—Regulating air supply or draught
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23N—REGULATING OR CONTROLLING COMBUSTION
  • F23N5/00—Systems for controlling combustion
  • F23N5/02—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G2203/00—Furnace arrangements
  • F23G2203/30—Cyclonic combustion furnace
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G2900/00—Special features of, or arrangements for incinerators
  • F23G2900/00001—Exhaust gas recirculation
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23N—REGULATING OR CONTROLLING COMBUSTION
  • F23N2225/00—Measuring
  • F23N2225/26—Measuring humidity
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23N—REGULATING OR CONTROLLING COMBUSTION
  • F23N5/00—Systems for controlling combustion
  • F23N5/003—Systems for controlling combustion using detectors sensitive to combustion gas properties

Definitions

• the present invention relates to a system and method for implementing a gasification-combustion process that converts waste or solid fuel into energy, while producing a minimal amount of undesirable emissions.
• MSW Municipal solid waste
• MSW includes durable and non-durable goods, containers and packaging, food and yard wastes, as well as miscellaneous inorganic wastes from residential, commercial, and industrial sources. Examples include newsprint, appliances, clothing, scrap food, containers and packaging, disposable diapers, plastics of all sort including disposable tableware and foamed packaging materials, rubber and wood products, potting soil, yard trimmings and consumer electronics, as part of an open-ended list of disposable or throw-away products.
• a traditional method of waste disposal is a landfill, which is still a common practice in some areas. Many local authorities, however, have found it difficult to establish new landfills. In those areas, the solid waste must be transported for disposal, making it more expensive.
• MSW Municipal solid waste combustor
• WTE waste-to-energy plant
• the typical MWC has a moving grate that enables the movement of waste through the combustion chamber and thus allows complete combustion of the waste.
• the MWC usually includes a primary air source and a secondary air source. Primary air is supplied from under the grate and is forced through the grate to sequentially dry (evolve water), de- volatilize (evolve volatile hydrocarbons), and burn out (oxidize nonvolatile hydrocarbons) the waste bed.
• the quantity of primary air is typically adjusted to maximize burn out of the carbonaceous materials in the waste bed, without having any excess air.
• Secondary air is supplied through nozzles located above the grate and is used to create turbulent mixing that destroys the hydrocarbons that evolved from the waste bed.
• the total amount of air (primary and secondary) used in a typical MWC is approximately 60% to 100% more than the amount of air required to achieve stoichiometric conditions (i.e., the theoretical conditions under which a fuel is completely burned).
• NOx is formed during combustion through two primary mechanisms.
• fuel NOx is formed by the oxidation of organically bound nitrogen (N) found in MSW and other fuels.
• N 2 organically bound nitrogen
• thermal NOx is formed by the oxidation of atmospheric N 2 at high temperatures. Because of the high activation energy required, thermal NOx formation does not become significant until flame temperatures reach 1,100 0 C (2,000 0 F).
• combustion controls limit the formation of NOx during the combustion process by reducing the availability of O 2 within the flame and by lowering combustion zone temperatures.
• post-combustion controls involve the removal of the NOx emissions produced during the combustion process (e.g., selective non-catalytic reduction (SNCR) systems and selective catalytic reduction (SCR) systems).
• SNCR selective non-catalytic reduction
• SCR selective catalytic reduction
• the present invention relates to a gasification-combustion system and method that converts waste or other solid fuels to energy while producing significantly lower quantities of NOx, carbon monoxide, dioxins, and other undesirable emissions than conventional mass combustion.
• Gasification is the partial combustion of a solid fuel that produces a gas mixture.
• the gasifier of the present invention operates at lower temperatures and introduces less air than conventional combustion systems, and thus it produces a lower amount of undesirable emissions.
• a post combustor uses the gas mixture produced by the gasifier to generate thermal energy. The post combustor controls combustion of the gas mixture using adjustable injection nozzles.
• nozzles can be adjusted based on the composition of the specific gas mixture entering the post combustor, so as to achieve optimal combustion conditions with minimal emissions.
• the gasification-combustion process using the post combustor of the present invention significantly reduces the amount of undesirable emissions produced when converting waste or solid fuel to energy.
• the above-described method and system is just one example of the present invention, which can vary in other embodiments.
• a system for gasifying and combusting waste is provided.
• the system may contain a gasifier for mixing syngas with air or recirculated flue gas; said gasifier may contain an entrance duct and a premixing nozzle designed to inject the air or recirculated flue gas into the gasifier.
• the system may also contain a post combustor.
• the post combustor may contain an entrance duct for receiving syngas from the gasifier; a cyclone-shaped chamber positioned near the end of the entrance duct designed to collect fly ash or heavy weight particles; a top injection nozzle for directing air to flow through the post combustor into the cyclone shaped chamber; tangential nozzles for directing air or recirculated flue gas into the post combustor; sensors for measuring temperature, moisture, and carbon dioxide; a controller for positioning and controlling the nozzles to make air flow and temperature more uniform in the post combustor; and an exit duct for allowing gas to leave the post combustor.
• the top injection nozzle may be positioned so that the air flowing through the nozzle forces fly ash or heavy weight particles into the cyclone-shaped chamber; the tangential nozzles may have a direction and a position; and/or the controller may rely upon information from the sensors to determine the direction and position of the tangential nozzles.
• Another configuration of the present invention sets forth a method for gasifying and combusting waste.
• the method may comprise one or more of the following steps: mixing syngas with air or recirculated flue gas in a gasifier; receiving the syngas from the gasifier at a post combustor; collecting fly ash or heavy particles with a cyclone- shaped chamber; directing air to flow through the post combustor into the cyclone shaped chamber; directing air or recirculated flue gas into the post combustor; using a sensor to gather measurements relating to temperature, moisture, and carbon dioxide of gas inside the post combustor; analyzing these measurements for determining which direction and position tangential nozzles connected to the post combustor should face; adjusting the tangential nozzles so that they face the determined direction and position; and/or allowing gas to leave the post combustor.
• FIG. l(a) is a side schematic view of an embodiment of the post combustor used in the gasification-combustion process of the present invention.
• FIG. l(b) is a top schematic view of an embodiment of the post combustor used in the gasification-combustion process of the present invention.
• the present invention relates to a system and method that converts MSW or other solid fuels into energy while producing a reduced amount of undesirable emissions.
• the first step of the present invention gasification, involves the partial combustion of a solid fuel.
• the second step, combustion involves using the gas mixture produced during gasification to generate thermal energy. Both steps of the gasification-combustion process, and the apparatuses used to perform them, will be described in detail below.
• Gasification is the partial combustion of MSW or other solid fuels.
• gasification of solid fuel has several advantages over the conventional process of complete combustion.
• complete combustion generally requires mixing the fuel with air in excess of the amount needed to achieve stoichiometric conditions (i.e., the ideal conditions in which fuel is completely burned).
• the high amount of oxygen present during complete combustion facilitates the production of harmful gases, such as NOx and dioxins.
• gasification involves only partial combustion, and, as a result, it requires significantly less air than complete combustion.
• the gasifier of the present invention can perform gasification of a solid fuel using a sub- stoichiometric amount of air.
• the gasifier of the present invention is designed to operate at significantly lower temperatures than a conventional combustion system.
• the gasifier operates at temperatures below the melting temperature of ash. This is significant because the combustion of solid fuel produces both bottom ash and fly ash. When a combustion system operates at high temperatures, the ash can melt and cause slag formation on the moving grate components, which may require substantial maintenance. Thus, by sustaining an operating temperature below the melting point of ash, the gasifier of the present invention limits the potential for slagging. This reduces the overall maintenance costs associated with converting waste or solid fuel to energy and makes its more practical to use conventional moving grate technology.
• the low temperature gasification of solid fuel is also advantageous because it produces less particulate emissions and noxious gases, such as NOx, than conventional high temperature combustion.
• the syngas produced during gasification flows out of the gasifier and into a post combuster, where the syngas undergoes combustion.
• the post combustor subjects the syngas to turbulent air flow that is only slightly in excess of stoichiometric conditions (and thus still less than the amount of air used in conventional combustion systems).
• the post combustor operates at higher temperatures than the gasifier, which has the effect of reducing carbon monoxide emissions and destroying most of the dioxins formed during gasification.
• the amount of excess air present in the post combustor is minimal, which, along with the ammonia and hydrogen cyanide formed during gasification, reduces the amount of NOx generated by combustion of the syngas.
• the syngas is resident in the combustion chamber of the post combustor for longer than two seconds and the operating temperature is greater than 800 0 C.
• the thermal energy created by combustion of the syngas can be used in a variety of ways, such as to produce steam and generate electricity.
• the gasification-combustion process of the present invention can convert MSW or other solid fuel into energy while generating significantly lower emissions of carbon monoxide, NOx, and other organics such as dioxins than the conventional process of complete combustion.
• FIGS. l(a) and l(b) show preferred embodiments of the post combustor 10 used in the gasification-combustion process of the present invention.
• the syngas generated by the gasifier flows into the post combustor 10 through an entrance duct 20.
• the syngas Prior to entering the combustion chamber 30 of the post combustor 10, the syngas is premixed with air, flue gas recirculation (FGR), or another oxidant such as plasma that is injected into the entrance duct 20 via premixing nozzle 44.
• FGR flue gas recirculation
• Premixing the syngas with an oxidant allows the combustion of the syngas to occur at a lower temperature than it would without such premixing.
• the post combustor 10 is designed so that there is a cyclone shaped chamber 50 at the end of the entrance duct 20, where the syngas enters the combustion chamber 30.
• the cyclone shaped chamber 50 is used to collect fly ash or heavy weight particles that are created during gasification or combustion.
• the cyclone shaped chamber 50 is aided by the downward flow of air from the top injection nozzle 41. The downward air flow forces fly ash and other heavy weight particles downward into the cyclone shaped chamber 50, while allowing the syngas to enter the combustion chamber 30.
• the fly ash and other particles can either concentrate in the center of cyclone shaped member 50 and flow downward, or form slag on the walls of the cyclone shaped member 50 and flow downward.
• the combustion chamber 30 of post combustor 10 includes multiple nozzles for injecting air or another oxidant into the combustion chamber 30.
• the top injection nozzle 41 is designed to inject air or another oxidant into the combustion chamber 30 in a generally downward direction.
• Tangential injection nozzles 42 and 43 are configured to inject air or another oxidant tangentially into the combustion chamber 30 from desired angles.
• additional nozzles can be provided so as to achieve the desired injection of air into the combustion chamber 30.
• the nozzles 41, 42, and 43 can be positioned and controlled by a controller 51 so that a uniform flow of air, as well as a uniform temperature, is maintained throughout the combustion chamber 30 during combustion of the syngas. This is important because temperature variations, and specifically pockets of higher temperatures, promote the creation of NOx.
• the post combustor 10 of the present invention reduces the amount of NOx generated during combustion.
• the post combustor 10 measures certain characteristics, such as the temperature, moisture, and carbon dioxide content, of the syngas as it enters the post combustor 10 from the gasifier. This information is then used to adjust the nozzles 41-44, so as to obtain optimal air flow and conditions for combustion of the specific type of syngas entering the combustion chamber 30. To obtain optimal conditions, the direction and amount of air flow from each nozzle 41-44 is adjusted individually and independently of one another. Computational fluid dynamics (“CFD”) is used to determine exactly how the nozzles 41-44 should be adjusted in response to the measurements taken as the syngas enters the combustion chamber 30.
• CFD computational fluid dynamics
• the post combustor 10 also includes an exit duct 60 that permits flue gas to leave the combustion chamber 30. As explained above, the flue gas can then be injected back into the combustion chamber 30 via the nozzles 41-44. This is known as flue gas recirculation ("FGR"). FGR lowers the amount of O 2 in the combustion chamber 30 and suppresses the temperature in the combustion chamber 30. As a result, FGR has the effect of reducing the amount of NOx generated by combustion of the syngas. [0024] While exemplary embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Incineration Of Waste (AREA)
• Processing Of Solid Wastes (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 2009
  • 2009-07-15 EP EP09790468A patent/EP2321579A2/de not_active Withdrawn
  • 2009-07-15 WO PCT/US2009/050694 patent/WO2010009231A2/en not_active Ceased
  • 2009-07-15 MX MX2011000665A patent/MX2011000665A/es not_active Application Discontinuation
  • 2009-07-15 CN CN2009801346752A patent/CN102144125A/zh active Pending
  • 2009-07-15 CA CA2730936A patent/CA2730936A1/en not_active Abandoned

Non-Patent Citations (1)

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