EP0851173B1 - Procédé de contrôle d'oxyde nitrique dans un générateur de vapeur à lit fluidisé circulant - Google Patents

Procédé de contrôle d'oxyde nitrique dans un générateur de vapeur à lit fluidisé circulant Download PDF

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Publication number
EP0851173B1
EP0851173B1 EP97122925A EP97122925A EP0851173B1 EP 0851173 B1 EP0851173 B1 EP 0851173B1 EP 97122925 A EP97122925 A EP 97122925A EP 97122925 A EP97122925 A EP 97122925A EP 0851173 B1 EP0851173 B1 EP 0851173B1
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EP
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Prior art keywords
fluidized bed
steam generator
circulating fluidized
fuel
emissions
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EP97122925A
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German (de)
English (en)
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EP0851173A3 (fr
EP0851173A2 (fr
Inventor
Peter Schmidt
Michael Chris Tanca
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Alstom Power Inc
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Alstom Power Inc
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C10/00—Fluidised bed combustion apparatus
    • F23C10/02—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed
    • F23C10/04—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone
    • F23C10/08—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone characterised by the arrangement of separation apparatus, e.g. cyclones, for separating particles from the flue gases
    • F23C10/10—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone characterised by the arrangement of separation apparatus, e.g. cyclones, for separating particles from the flue gases the separation apparatus being located outside the combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C6/00—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion
    • F23C6/04—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J2215/00—Preventing emissions
    • F23J2215/10—Nitrogen; Compounds thereof
    • F23J2215/101—Nitrous oxide (N2O)

Definitions

  • This invention relates to fossil fuel-fired circulating fluidized bed steam generators (CFB), and more specifically to a method of controlling nitrous oxides in such fossil fuel-fired circulating fluidized bed steam generators (CFB) while concomitantly maintaining acceptable NO X and SO X emission levels therefrom.
  • fluidized bed steam generators are generally such that for purposes of the combustion process that takes place therewithin, fuel is burned in a bed of hot incombustible particles, the latter particles being suspended by an upwardly flow of fluidizing gas.
  • this fluidizing gas normally is comprised of both air, which is being supplied to the fluidized bed steam generator to support the combustion of fuel therewithin, and the gaseous byproducts, which result from such combustion of fuel and air.
  • Fluidized bed steam generators including but not limited to circulating fluidized bed steam generators (CFB), are normally intended to be operative to produce steam. Moreover, such production of steam results from the combustion of fuel and air within the fluidized bed steam generators. Furthermore, the steam that is so produced within the fluidized bed steam generator (CFB) is designed to be operative to function in accordance with a preselected thermodynamic steam cycle.
  • CFB fluidized bed steam generator
  • a circulating fluidized bed steam generator includes a furnace volume, the walls of which are comprised of vertical waterwall tubes.
  • fuel and sorbent are mixed with and burned in air, producing hot combustion gases in which hot solids become entrained.
  • heat is transferred to the aforementioned waterwall tubes thereby causing saturated steam to be evaporatively produced in conventional fashion from the water rising within the waterwall tubes.
  • This saturated steam is a mix of steam and water. which is thereafter separated in known fashion in a steam drum. From the steam drum, the water is returned to the waterwall tubes in the lower segment of the furnace volume thereby completing an evaporative loop, while the steam is delivered to a superheater.
  • the hot combustion gases and hot solids entrained therewithin are directed to a cyclone where unburned fuel, flyash and sorbent above a predetermined size are mechanically separated from the hot combustion gases.
  • This unburned fuel, flyash and sorbent are collected from the cyclone, then are made to fall under the influence of gravity through a stand pipe and a seal pot, and are thereafter reintroduced into the lower segment of the furnace volume whereupon this unburned fuel, flyash and sorbent are once again subjected to the combustion process.
  • the foregoing describes the circulation path followed by the hot solids, which are above a predetermined size, that become entrained in the hot combustion gases.
  • the hot combustion gases entering the cyclone which hereinafter will be referred to as flue gases, still contain useful energy, and after separation therefrom of the unburned fuel, flyash and sorbent above a predetermined size, are directed to a backpass, with which the circulating fluidized bed steam generator (CFB) is suitably provided, wherein additional heat exchange surfaces are located.
  • additional heat exchange surfaces commonly comprise superheat surface followed by possibly reheat surface and thereafter economizer surface.
  • the superheat surface in known fashion is operative to heat, i.e., superheat, the steam, which as described hereinbefore has been separated from the water in the steam drum of the circulating fluidized bed steam generator (CFB).
  • this steam, which has been subjected to superheating, is made to flow to a high pressure turbine (HPT).
  • HPT high pressure turbine
  • the aforementioned steam, which has been subjected to superheating is made to flow to the reheat surface, if such reheat surface has been provided in the backpass of the circulating fluidized bed steam generator (CFB).
  • the reheat surface is operative in known fashion to once again heat, i.e., reheat, the steam, which as described hereinbefore has been separated from the water in the steam drum of the circulating fluidized bed steam generator (CFB), whereupon this steam, which has been subjected to reheating, is made to flow to a low pressure turbine (LPT).
  • LPT low pressure turbine
  • the aforereferenced steam which has been subjected to reheating, is condensed to water, whereupon the water that results from condensing of the reheated steam is made to flow to the economizer surface, which is located in the backpass of the circulating fluidized bed steam generator (CFB), where this water is heated before being returned to the steam drum of the circulating fluidized bed steam generator (CFB).
  • CFRB circulating fluidized bed steam generator
  • the water, which is employed in these water spray stations is extracted from the water, which is produced from the condensing of the reheat steam, that is made to flow to the economizer surface located in the backpass of the circulating fluidized bed steam generator (CFB), and as such the water, which is employed in these water spray stations, is, therefore, not available for use in generating steam.
  • CFB circulating fluidized bed steam generator
  • the flue gases during the passage thereof through the backpass of the circulating fluidized bed steam generator (CFB) are cooled as a consequence of the heat exchange that occurs between the flue gases and the superheat surface, the reheat surface (if present), and the economizer surface, which are located in the backpass of the circulating fluidized bed steam generator (CFB).
  • the now cooler flue gases are then preferably utilized in known fashion to effect therewith a preheating of the air, which is supplied to the circulating fluidized bed steam generator (CFB) for the purpose of accomplishing therewith the combustion of the fuel within the circulating fluidized bed steam generator (CFB).
  • the flue gases also in known fashion are generally made to flow to and through a particulate removal system for purposes of effecting the removal of particulates from the flue gases after which the flue gases are emitted to the atmosphere from a stack, which is cooperatively associated with the circulating fluidized bed steam generator (CFB).
  • CFRB circulating fluidized bed steam generator
  • a hydrocarbon fuel is combusted in the presence of air in the lower segment of the furnace volume of the circulating fluidized bed steam generator (CFB).
  • a byproduct of such combustion of hydrocarbon fuel e.g., coal in air, is oxides of nitrogen, i.e., NO X .
  • NO X oxides of nitrogen
  • thermal NO X is produced from the nitrogen, which originates from the air that is employed in the aforereferenced combustion process. Because of the relatively low temperatures at which combustion takes place in circulating fluidized bed steam generators (CFB), thermal NO X is essentially zero in circulating fluidized bed steam generators (CFB).
  • the second main form of NO X is that referred to as "fuel NO X ".
  • Fuel NO X is produced from the nitrogen, which originates as organically bound nitrogen within the hydrocarbon fuel. Insofar as coal as a hydrocarbon fuel is concerned, the nitrogen content thereof is comparatively small. However, although only a fraction of the nitrogen content of a hydrocarbon fuel such as coal is converted to NO X , fuel NO X nevertheless comprises the primary source of the total amount of NO X emissions from a fossil fuel-fired steam generating power plant.
  • organic sulfur is also oxidized during the combustion of hydrocarbon fuel and air within the furnace volume of the circulating fluidized bed steam generator (CFB), and is emitted from the furnace volume as gaseous oxides of sulfur, i.e., SO X .
  • Sorbent to which reference has been had herein previously, is introduced into the furnace volume of the circulating fluidized bed steam generator (CFB) in order to effect therewith control over the extent to which SO X formation occurs within the furnace volume of the circulating fluidized bed steam generator (CFB) during the combustion process, which takes place therewithin.
  • the air is staged in two or more vertical levels of the furnace volume of the circulating fluidized bed steam generator (CFB) and may also be equally divided amongst these various levels.
  • this temperature is also essentially uniform throughout the circulation path, which the hot solids, to which reference has been had herein previously, follow during the course of their passage through the circulating fluidized bed steam generator (CFB) and through the components cooperatively associated therewith.
  • a principal advantage of a circulating fluidized bed steam generator resides in the fact that NO X and SO X emissions therefrom are lower than, for example, a pulverized coal-fired steam generator. This is attributable to the lower temperatures at which combustion takes place within the circulating fluidized bed steam generator (CFB).
  • combustion temperatures on the one hand produce lower NO X and SO X emissions
  • combustion temperatures on the other hand permit the formation of nitrous oxide, i.e., N 2 O.
  • N 2 O is a gas, which allegedly contributes to the greenhouse effect and to ozone depletion.
  • the formation of N 2 O from the combustion of hydrocarbon fuel and air is perhaps best understood from those chemical reactions, which have been suggested by L. E. Amand and B.
  • the levels of N 2 O produced in a circulating fluidized bed steam generator may possibly range up to about 200 ppm.
  • N 2 O has been found to be very much dependent upon combustion temperature in that as the combustion temperature rises N 2 O levels decrease linearly. However, as mentioned herein previously this rise in combustion temperature leads to an increase in NO X and SO X formation. Thus, it is important that any reduction in the level of N 2 O formation be attainable while at the same time ensuring that the levels of NO X emissions and SO X emissions do not increase.
  • N 2 O emissions be such N 2 O emissions from circulating fluidized bed steam generators (CFB) or from some other type of equipment, are known to have been provided heretofore in the prior art.
  • CFB fluidized bed steam generators
  • one such method and/or means for reducing N 2 O emissions is that to which U.S. Patent No. 5,171,553 entitled "Catalytic Decomposition Of N 2 O". which issued on December 15, 1992 and which is assigned to Air Products and Chemicals, Inc., is directed. More specifically, the teachings of U.S. Patent No. 5,171,553 are directed to a catalytic pollution control process for removing N 2 O from gaseous mixtures.
  • an N 2 O-containing gaseous mixture is contacted with a catalyst comprising a crystalline zeolite which, at least in part, is composed of five membered rings having a structure type selected from the group consisting of BETA, MOR, MFI, MEL and FER and wherein the crystalline zeolite has been at least partially ion-exchanged with a metal selected from the group consisting of copper, cobalt, rhodium, iridium, ruthenium and palladium under conditions sufficient to convert the N 2 O into gaseous nitrogen and gaseous oxygen.
  • a lower region of the furnace section of the fluidized bed reactor is operated under substoichiometric conditions so that combustion in the lower region is incomplete, thereby inhibiting formation of N 2 O and nitrogen oxides (NO X ).
  • an upper region of the furnace section of the fluidized bed reactor is operated under oxidizing conditions to promote further combustion. Furthermore, an amount of particulate material is present in this upper region, and this amount of particulate material in the upper region is controlled to maintain a temperature in the upper region for destroying N 2 O formed during combustion.
  • the amount of N 2 O in flue gases discharged from a fluidized bed combustion system is minimized by effecting vigorous and intimate mixing of the flue gases (with entrained particles) from a fluidized bed by increasing the velocity of the flue gases and then decreasing the velocity from the increased level, introducing a N 2 O decomposing catalyst such as CaO or limestone into the flue gases and particles immediately after increasing and decreasing of the velocity, and mixing the N 2 O catalyst with the flue gases and particles, to effect decomposition of the N 2 O.
  • a N 2 O decomposing catalyst such as CaO or limestone
  • yet still another such method and/or means for reducing N 2 O emissions is that to which U.S. Patent No. 5,378,443 entitled “Method For Reducing Emissions When Burning Nitrogen Containing Fuels", which issued on January 3, 1995 and which is assigned to A. Ahlstrom Corporation, is directed.
  • U.S. Patent No. 5,378,443 entitled "Method For Reducing Emissions When Burning Nitrogen Containing Fuels", which issued on January 3, 1995 and which is assigned to A. Ahlstrom Corporation, is directed.
  • a method for reducing the emissions of N 2 O in flue gases from the combustion of nitrogen containing fuel in a fluidized bed combustor is provided.
  • the subject method for reducing the emissions of N 2 O in flue gases comprises the steps of (a) supplying nitrogen containing fuel and an oxygen containing gas for combustion of the fuel in the combustion stage of the combustor; (b) maintaining a temperature of about 700 degrees C. to 1000 degrees C.
  • WO 96 35080 A discloses a method for controlling NO x emissions from a circulating fluidized bed steam generator which has a furnace volume.
  • the method includes injecting fuel of a predetermined size via fuel chutes 30 into the interior of the furnace 16 of a circulating fluid bed steam generator 12 and injecting air into the furnace volume from a first source in the form of a fluidizing grate means 24.
  • the method further includes injecting air into the furnace volume below the point of injection of the fuel, this air being injected from a second source in the form of a downwardly extending duct 50b.
  • the method disclosed in WO 96 35080 A includes injecting air into the furnace volume above the point of injection of the fuel, this air being injected from a third source in the form of a downwardly extending duct 50A.
  • CFB fluidized bed steam generator
  • CFB circulating fluidized bed steam generator
  • Another object of the present invention is to provide such a new and improved method for reducing N 2 O emissions from a circulating fluidized bed steam generator (CFB), which is characterized in that such reduction of N 2 O emissions is achievable therewith while at the same time the overall operating efficiency of the circulating fluidized bed steam generator (CFB) is still maintained and while at the same time the stoichiometric ratio of the combustion process of the circulating fluidized bed steam generator (CFB) is also still maintained.
  • a circulating fluidized bed steam generator CFB
  • a still another object of the present invention is to provide such a new and improved method for reducing N 2 O emissions from a circulating fluidized bed steam generator (CFB), which is characterized in that such reduction of N 2 O emissions is achievable therewith while concomitantly it is possible to reduce the required surface area of the superheater and/or reheater and/or the economizer that are located in the backpass volume of the circulating fluidized bed steam generator (CFB).
  • CFB circulating fluidized bed steam generator
  • a further object of the present invention is to provide such a new and improved method for reducing N 2 O emissions from a circulating fluidized bed steam generator (CFB), which is characterized in that such reduction of N 2 O emissions is achievable therewith while concomitantly it is possible to reduce the volume required by the backpass volume of the circulating fluidized bed steam generator (CFB).
  • CFB circulating fluidized bed steam generator
  • Yet another object of the present invention is to provide such a new and improved method for reducing N 2 O emissions from a circulating fluidized bed steam generator (CFB), which is characterized in that such reduction of N 2 O emissions is achievable therewith in such a manner that the operational versatility of the circulating fluidized bed steam generator (CFB) is enhanced in that the cyclone cooperatively associated therewith is operative as a separator for effecting therewithin separation of entrained solids from flue gases and as a combustor within which combustion can take place.
  • a circulating fluidized bed steam generator COB
  • Yet still another object of the present invention is to provide such a new and improved method for reducing N 2 O emissions from a circulating fluidized bed steam generator (CFB), which is characterized in that the reduction of N 2 O emissions is achievable therewith without requiring either the added expense or the added complexity that is inherently associated with the use of catalytic agents for purposes of effecting the reduction of N 2 O emissions.
  • CFB circulating fluidized bed steam generator
  • the subject method for reducing N 2 O emissions from a circulating fluidized bed steam generator (CFB) is operative wherein through the appropriate distribution of air with which the combustion of hydrocarbon fuel is effected and/or through the selective sizing of the particles of hydrocarbon fuel, which is subjected to combustion, it is possible with the subject method to have afterburning occur under controlled conditions within the cyclone, which is cooperatively associated with the furnace volume of the circulating fluidized bed steam generator (CFB) whereby as a consequence of such afterburning a reduction is realized in the level of N 2 O emissions while concomitantly therewith NO X emissions and SO X emissions are maintained at acceptable levels.
  • the combustion of the hydrocarbon fuel is delayed as the hydrocarbon fuel traverses the furnace volume of the circulating fluidized bed steam generator (CFB).
  • the lower segment of the furnace volume of the circulating fluidized bed steam generator (CFB) is operated under substoichiometric or fuel rich conditions while the upper segment of the furnace volume of the circulating fluidized bed steam generator (CFB) is operated under oxidizing or fuel lean conditions.
  • the N2O that is formed within the circulating fluidized bed steam generator (CFB) is reduced. Furthermore, this reduction in N 2 O emissions is accomplished while NO X emissions and SO X emissions are maintained at acceptable levels due to the lower temperature within the furnace volume of the circulating fluidized bed steam generator (CFB).
  • combustion of the particle of hydrocarbon fuel is more likely to take place between the exit of the furnace volume of the circulating fluidized bed steam generator (CFB) and the exit of the cyclone cooperatively associated with the furnace volume of the circulating fluidized bed steam generator (CFB) thereby raising the temperature between the aforesaid exit of the furnace volume and the aforesaid exit of the cyclone with a concomitant reduction being had in the level of N 2 O emissions from the circulating fluidized bed steam generator (CFB).
  • the subject method for reducing N 2 O emissions from a circulating fluidized bed steam generator is also advantageously characterized in that such reduction of N 2 O emissions is achievable therewith while at the same time the overall operating efficiency of the circulating fluidized bed steam generator (CFB) is still maintained and while at the same time the stoichiometric ratio of the combustion process of the circulating fluidized bed steam generator (CFB) is also still maintained.
  • the subject method for reducing N 2 O emissions from a circulating fluidized bed steam generator (CFB) is additionally characterized in that due to the higher flue gas temperature at the exit of the cyclone cooperatively associated with the furnace volume of the circulating fluidized bed steam generator (CFB), it is possible with the subject method of the present invention both to effect reduction of N 2 O emissions therewith while concomitantly effecting a reduction in the required surface area of the superheater and/or the reheater and/or the economizer that are provided in the backpass volume of the circulating fluidized bed steam generator (CFB) as well as in the volume required for the backpass volume itself.
  • the drawing is a schematic representation in the nature of a side elevational view of a circulating fluidized bed steam generator (CFB) including a furnace volume, a cyclone section cooperatively associated with the furnace volume, and a backpass volume cooperatively associated with the cyclone section, along with interconnecting ductwork and pipework, constructed in accordance with the present invention.
  • CFB circulating fluidized bed steam generator
  • the circulating fluidized bed steam generator 2 includes a furnace volume, denoted therein by the reference numeral 4, the latter being defined by waterwall tubes, denoted therein by the reference numeral 4a; a first section of ductwork, denoted therein by the reference numeral 6; a cyclone section, denoted therein by the reference numeral 8; a second section of ductwork, denoted therein by the reference numeral 10; a backpass volume, denoted therein by the reference numeral 12, from which ductwork, denoted therein by the reference numeral 12a, extends.
  • a furnace volume denoted therein by the reference numeral 4
  • the latter being defined by waterwall tubes, denoted therein by the reference numeral 4a
  • a first section of ductwork denoted therein by the reference numeral 6
  • a cyclone section denoted therein by the reference numeral 8
  • a second section of ductwork denoted therein by the reference numeral 10
  • the upper segment, denoted therein by the reference numeral 8b. of the cyclone 8 is connected in fluid flow relation with the upper segment of the furnace volume 4 by means of the first section of ductwork 6.
  • the lower segment, denoted by the reference numeral 8c, of the cyclone 8 is connected in fluid flow relation with the lower segment of the furnace volume 4 by means of pipework, which in accordance with the illustration thereof in the drawing consists of a seal pot, denoted therein by the reference numeral 14 and a hot solids inlet, denoted therein by the reference numeral 16.
  • the flow path which extends from the furnace volume 4 through the first section of ductwork 6 and through the cyclone 8 and the pipework 14,16, and returning to the lower segment of the furnace volume 4, will be referred to hereinafter as the hot solids circulation path 4, 6, 8, 14, 16, 4.
  • the flow path which begins at the furnace exit, denoted in the drawing by the reference numeral 4c, and which continues through the first section of ductwork 6 and through the upper segment 8b of the cyclone 8, and which terminates at the cyclone exit, denoted in the drawing by the reference numeral 8a, will be referred to hereinafter as the afterburning volume 4c, 6, 8b, 8a.
  • the furnace volume 4 is supplied with a mixture of fuel and sorbent, denoted in the drawing by the reference numeral 28, and a first source of air, denoted in the drawing by the reference numeral 24.
  • the furnace volume 4 is also supplied with a second source of air, denoted in the drawing by the reference numeral 26, and a third source of air, denoted in the drawing by the reference numeral 30.
  • the first source of air is fed through an air distributor, denoted in the drawing by the reference numeral 4b, to the lower segment of the furnace from therebeneath.
  • the hot combustion gases 32 with the hot solids 34 entrained therewith are made to flow through the first section of ductwork 6 to the cyclone 8.
  • the hot solids 34 that are made to flow thereto which are above a predetermined size, are separated from the hot combustion gases 32 in which the hot solids 34 are entrained.
  • the separated hot solids 34 which contain unburned fuel, flyash and sorbent flow through the cyclone. From the cyclone 8 the hot solids 34 are discharged under the influence of gravity into the seal pot 14.
  • the hot solids 34 are reintroduced into the lower segment of the furnace volume 4 by means of the hot solids inlet 16 whereupon the hot solids 34 are once again subjected to the combustion process that takes place in the circulating fluidized bed steam generator 2.
  • the hot combustion gases 32 leaving the cyclone 8, hereinafter referred to as flue gases are directed by means of the second section of ductwork 10 from the cyclone 8 to the backpass volume 12 of the circulating fluidized bed steam generator 2.
  • flue gases 32 traverse the backpass volume 12 additional heat transfer duty is performed therewith in accordance with a predetermined thermodynamic steam cycle relative to the heat transfer surfaces, e.g., the superheater, the reheater and the economizer, denoted by the reference numerals 18, 20, 22, respectively, which are suitably located for this purpose in the backpass volume 12.
  • the flue gases 32 exit through the ductwork 12a to a particulate removal system (not shown in the interest of maintaining clarity of illustration in the drawing) whereupon the flue gases 32 are discharged to the atmosphere through a stack (not shown in the interest of maintaining clarity of illustration in the drawing).
  • the total amount of air supplied to the furnace volume 4 by the second source of air 26 and the third source of air 30 is ordinarily evenly distributed therebetween such that the furnace volume 4 is subjected to certain prescribed stoichiometric conditions.
  • such prescribed stoichiometric conditions are designed to produce an essentially constant temperature of between approximately 843.33 degrees C and 871.11 degrees C (1550 degrees F. and 1600 degrees F.) throughout the furnace volume 4. It is also the desired intent that this temperature be essentially constant throughout the hot solids circulation path 4, 6, 8, 14, 16, 4, to which reference previously has been had herein.
  • afterburning may occur to a very slight extent between the furnace exit 4c and the cyclone exit 8a.
  • the term afterburning as employed herein is meant to refer to the combustion of unburned fuel, which occurs within the afterburning volume 4c, 6, 8b, 8a, to which reference previously has been had herein.
  • the temperature of the flue gases 32 at the cyclone exit 8a will as a consequence of such afterburning slightly exceed the temperature of the hot combustion gases 32 at the furnace exit 4c.
  • the distribution of the air 26, 30 is such that the amount of the third source of air 30, which is injected into the furnace volume 4, is greater than the amount of the second source of air 26, which is injected into the furnace volume 4, completion of the combustion of the fuel 28 will be delayed as the fuel 28 traverses the furnace volume 4.
  • the lower segment of the furnace volume 4 will be operated under substoichiometric conditions and the upper segment of the furnace volume 4 will be operated under oxidizing conditions.
  • this will result in a lowering of the overall furnace temperature as well as a lowering of the temperature gradient within the furnace volume 4 such that the temperature within the upper segment of the furnace volume 4 is greater than within the lower segment of the furnace volume 4.
  • N 2 O emissions may in addition be reduced in accordance with the present invention by manipulating together in combination both the distribution of the air 26, 30 and the particle size of the fuel.
  • the backpass volume 12 may also be reduced with attendant cost savings being realizable from the reduction in the superheat, reheat and economizer surfaces 18, 20, 22, respectively, and/or from the reduction in the backpass volume 12.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Fluidized-Bed Combustion And Resonant Combustion (AREA)
  • Treating Waste Gases (AREA)
  • Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)

Claims (9)

  1. Procédé de contrôle des émissions de N2O provenant d'un générateur de vapeur à lit fluidisé à circulation (2), ledit générateur de vapeur (2) comprenant un volume de four (4) ayant une sortie (4c), un cyclone (8) fonctionnant tout à la fois en tant que séparateur et en tant que dispositif de combustion et ayant une sortie (8a) partant de ce dernier, prévue à au moins une extrémité de ce dernier sous la forme d'un segment inférieur (8c) communiquant avec, et disposé en relation d'écoulement entre le volume de four (4), un volume de passage arrière (12), contenant en son sein des surfaces de transfert thermique (18, 20, 22), un premier moyen de conduits (6) reliant le volume de four (4) en relation d'écoulement fluide avec le cyclone (8), et un second moyen de conduits (10) reliant le cyclone (8) en relation d'écoulement fluide avec le volume de passage arrière (12), ledit procédé comprenant les étapes d'injection de combustible (28) d'une grandeur prédéterminée dans le volume de four (4), d'injection, d'en dessous du volume de four (4), d'air provenant d'une première source (24) dans un segment inférieur du volume de four (4), d'injection d'air provenant d'une deuxième source (26) dans un segment supérieur du volume de four (4) en dessous du point d'injection de combustible (28) dans le volume de four (4) et d'injection d'air provenant d'une troisième source (30) dans le volume de four (4) au-dessus du point d'injection de combustible (28) dans le volume de four (4), caractérisé en ce que ledit procédé comprend en outre les étapes :
    d'exécution d'une combustion partielle du combustible (28) au sein du volume de four (4), provoquant la génération de gaz de fumées (32) et de matières solides chaudes (34) cette combustion partielle du combustible (28) ;
    de retardement du restant de la combustion du combustible (28) jusqu'à ce que le combustible (28) ait passé au delà de la sortie (4c) du volume de four (4) ; et
    d'exécution de l'achèvement du restant de la combustion du combustible (28) entre la sortie (4c) du volume de four (4) et le segment inférieur (8c) du cyclone (8), de manière à produire une température de ce dernier apte à effectuer une réduction des émissions de N2O.
  2. Procédé de contrôle des émissions de N2O provenant du générateur de vapeur à lit fluidisé à circulation selon la revendication 1, caractérisé en ce que l'étape d'exécution de l'achèvement du restant de la combustion du combustible (28) entre la sortie (4c) du volume de four (4) et le segment inférieur (8c) du cyclone (8) comprend l'exécution de la combustion de la portion imbrûlée du combustible (28) dans le cyclone (8).
  3. Procédé de contrôle des émissions de N2O en provenant du générateur de vapeur à lit fluidisé à circulation selon la revendication 1, caractérisé en ce que l'étape d'exécution de l'achèvement du restant de la combustion du combustible (28) entre la sortie (4c) du volume de four (4) et le segment inférieur (8c) du cyclone (8) comprend la manipulation d'au moins la grandeur des particules du combustible (28).
  4. Procédé de contrôle des émissions de N2O provenant du générateur de vapeur à lit fluidisé à circulation selon la revendication 3, caractérisé en ce que la quantité d'air injectée dans le volume de four (4) à partir de la troisième source d'air (30) est supérieure à la quantité d'air injectée dans le volume de four (4) à partir de la deuxième source d'air (26).
  5. Procédé de contrôle des émissions de N2O provenant du générateur de vapeur à lit fluidisé à circulation selon la revendication 2, caractérise en ce que le retard dans l'exécution de la combustion du restant du combustible (28) est causé par la manipulation de la grandeur des particules du combustible (28).
  6. Procédé de contrôle des émissions de N2O provenant du générateur de vapeur à lit fluidisé à circulation selon la revendication 2, caractérisé en ce que le retard dans l'exécution de la combustion du restant du combustible (28) est causé tout à la fois par la manipulation de la distribution de l'air injecté dans le volume de four (4) à partir de la deuxième source d'air (26) et de la troisième source d'air (30), et par la manipulation de la grandeur des particules du combustible (28).
  7. Procédé de contrôle des émissions de N2O provenant du générateur de vapeur à lit fluidisé à circulation selon la revendication 2, caractérisé en ce que l'air injecté dans le volume de four (4) à partir de la première source d'air (24) est injecté dans le volume de four (4) à travers un moyen de distribution d'air.
  8. Procédé de contrôle des émissions de N2O provenant du générateur de vapeur à lit fluidisé à circulation selon la revendication 2, comprenant en outre l'étape de maintien de l'efficacité globale désirée du générateur de vapeur à lit fluidisé à circulation.
  9. Procédé de contrôle des émissions de N2O provenant du générateur de vapeur à lit fluidisé à circulation selon la revendication 2, comprenant en outre l'étape de maintien du rapport stoechiométrique désiré du processus de combustion qui se produit au sein du générateur de vapeur à lit fluidisé à circulation.
EP97122925A 1996-12-30 1997-12-29 Procédé de contrôle d'oxyde nitrique dans un générateur de vapeur à lit fluidisé circulant Expired - Lifetime EP0851173B1 (fr)

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US774763 1996-12-30

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FI20055063A (fi) * 2005-02-11 2006-08-12 Kvaerner Power Oy Menetelmä kerrosleijukattilan typenoksidipäästöjen vähentämiseksi ja kerrosleijukattilan ilmanjakojärjestelmä
JP5435973B2 (ja) * 2009-01-30 2014-03-05 メタウォーター株式会社 流動焼却炉
JP5916470B2 (ja) * 2011-08-04 2016-05-11 三菱重工業株式会社 流動層処理システム及び流動層燃焼排ガスのｎ２ｏ除去方法
CN102278743A (zh) * 2011-08-16 2011-12-14 江苏太湖锅炉股份有限公司 循环流化床锅炉
CN102721046B (zh) * 2012-07-06 2015-01-14 无锡华光锅炉股份有限公司 燃用造纸废渣和污泥的循环流化床锅炉
CN104748108B (zh) * 2015-04-10 2017-05-31 东方电气集团东方锅炉股份有限公司 协同控制cfb锅炉炉内脱硫脱硝的燃烧系统及方法
CN105465771B (zh) * 2015-11-06 2017-10-13 广东工业大学 一种旋风粗煤粉气化燃烧装置
CN112413573B (zh) * 2019-08-21 2022-12-27 中国科学院工程热物理研究所 一种循环流化床富氧燃烧系统及富氧燃烧方法

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DE69717240D1 (de) 2003-01-02
EP0851173A2 (fr) 1998-07-01
ATE228225T1 (de) 2002-12-15

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