EP0308300A1 - Combustion process in a fluidised bed and installation for carrying out the process - Google Patents

Combustion process in a fluidised bed and installation for carrying out the process Download PDF

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Publication number
EP0308300A1
EP0308300A1 EP88402256A EP88402256A EP0308300A1 EP 0308300 A1 EP0308300 A1 EP 0308300A1 EP 88402256 A EP88402256 A EP 88402256A EP 88402256 A EP88402256 A EP 88402256A EP 0308300 A1 EP0308300 A1 EP 0308300A1
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EP
European Patent Office
Prior art keywords
stage
combustion
gases
fuel
fluidized bed
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Granted
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EP88402256A
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German (de)
French (fr)
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EP0308300B1 (en
Inventor
Jean-Louis Bouju
Paul Cosar
Pascal Georges
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Babcock Entreprise
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Fives Cail Babcock SA
Babcock Entreprise
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Publication of EP0308300A1 publication Critical patent/EP0308300A1/en
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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
    • 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

Definitions

  • the present invention relates to solid fuel fireplaces in which combustion is carried out in two stages: a first stage where the fuel is burned in a fludized bed with a quantity of substoichiometric air and a second stage where the gases emerging from the fluidized bed and the fine particles of fuel which they entrain burn with secondary air admitted into the combustion chamber, at a certain height above the fluidized bed.
  • the invention relates to fluidized bed fireplaces, the bottom of which consists of a grid, at least part of which is inclined and in which the major part of the ash is removed at the upper end of the grid, either by mechanical means. in the form of bottom ash, if the temperature within the bed is sufficient to allow agglomeration of the ashes, either by overflow (French patent N ° 83.16290) or defluidization (French patent N ° 82.10385), in the opposite case.
  • the ashes and soot which are entrained by the gases emerging from the bed are separated in one or more dust collectors and reinjected into the fluidized bed.
  • the soot hardly burns in the fluidized bed, which is reducing, and can be trapped by the ashes and evacuated with them, which decreases the combustion efficiency.
  • the present invention improves the combustion efficiency of fireplaces of this type. It consists of recycle in the second stage of combustion the soot and fly ash separated from the smoke, with the exception of a purge flow which makes it possible to eliminate the fly ash. It thus establishes a closed circuit circulation with several passages of soot in the area where the second stage of combustion takes place which allows to obtain an almost complete combustion.
  • the particles separated from the fumes can be reinjected pneumatically, either by means of secondary air, or by an independent circuit.
  • the invention also relates to an installation comprising a fluidized bed hearth of the type concerned and at least one dust collector traversed by the fumes, characterized in that it further comprises means for re-injecting into the combustion chamber, at level of the secondary air intake nozzles or above them, the solid particles separated from the fumes in said dust collector, and a purge circuit making it possible to eliminate a part of said particles.
  • the reference numbers 1 and 2 represent reactors, 3 and 4 are convection heat exchangers, 5 is a primary dust collector and 6 is a final dust collector.
  • the fuel introduced in 7 is fluidized by the air admitted in 8, under an inclined and gas-permeable floor.
  • the ash produced by combustion in a fluidized bed is removed at 9 by overflow or defluidization above the upper end of the hearth, or extracted from the bed, in the form of bottom ash, by a conveyor if the temperature of the bed is sufficient for cause agglomeration of ash.
  • the air flow blown at 8 is less than the stoichiometric flow, so that the gases produced which emerge from the bed are reducing.
  • These gases, which are charged with fly ash and fine fuel particles, are introduced into reactor 2 where secondary air is also introduced, at 11, and if necessary a desulfurizing agent, such as limestone or lime, in finely divided form, at 13.
  • the gases and the fuel particles which they transport burn with the secondary air to produce hot gases which successively pass through the exchanger 3, the dust collector 5, the exchanger 4 and the dust collector 6.
  • the dust separated from the gases in the dust collectors 5 and 6 is returned to the reactor 2, at 15, except for a small fraction which is withdrawn at 17, to remove the ash and the reaction products of desulfurization.
  • This boiler comprises a fluidized bed hearth 10, the bottom of which is formed by the upper strand, inclined with an endless chain 12. This bottom constitutes the bottom of a vertical chamber 18 whose walls and ceiling are formed, so known, of sealed tube panels, which are connected, at their upper end, to a vapor collecting balloon 20.
  • the chamber 18 is connected to a horizontal chamber 22 in which are placed bundles of tubes 24 connected to the balloon 20 and tubes 26 where the vapor collected in the balloon 20 is superheated.
  • the fumes produced in chamber 18 and leaving chamber 22 pass successively through a primary dust collector 28, constituted for example by a multicyclone, an exchanger 30, which could be an economizer, and a final dust collector 32, for example a bag filter.
  • the air necessary for the combustion of the fuel is partly blown through the chain 12 to ensure the fluidization of the solid fuel and its partial combustion, and partly at a certain distance above the bed, by means of nozzles 34.
  • the solid fuel is introduced through a chute 14 into the deepest part of the bed and a desulfurizing agent is injected at 36 into the upper part of the combustion chamber 18.
  • the dust collected in the chamber 22, in the dust collectors 28 and 32 and in the exchanger 30 are reinjected, for example pneumatically, at 37 into the combustion chamber 18, at the level of the nozzles 34 or above the latter; we can, in particular, use secondary air to reinject the dust.
  • Part of the dust is drawn off, continuously or discontinuously, by a purge circuit 38 to remove the products of the desulfurization reaction and the ashes.
  • the circulation rate - ratio of the flow rate of the circulating charge to the purge flow rate - is of the order of 10. Provision may be made for reinjecting the dust at two different levels according to the operating mode of the boiler: a lower level for the walking at low load and a higher level for walking at high load.
  • the combustion in the fluidized bed 10 takes place at a temperature sufficient to allow the ash to agglomerate in the form of bottom ash, these settle on the chain 12 and are discharged through it at its upper end. If the temperature of the fluidized bed is not sufficient to cause agglomeration of the ashes, they are evacuated by overflow or defluidization at the upper end of the hearth. In all cases, most of the ash is thus extracted from the bed, the rest being entrained by the gases emerging from the bed. Combustible gases emerging from the bed and fines fuel particles entrained by them, with the fly ash, burn above the bed 10 with the secondary air introduced by the nozzles 34.
  • the fluidized bed 10 constitutes the first stage of a two-stage reactor, the second of which is similar to a circulating fluidized bed and where the desulphurization and combustion of the soot are carried out entirely.
  • it is distinguished from conventional circulating fluidized beds by the fact that it does not have a fluidization grid and that the circulating charge is much more reduced, for a given rate of circulation of the desulfurizing agent, since the major part of the ashes is extracted from the bed 10 in the form of bottom ash, so that the particles are kept in suspension in the gases in this second stage.
  • the content of desulphurization products in the fraction extracted by the purge circuit 38 is significantly higher, which facilitates the subsequent treatment thereof; the dust concentration of the chambers 18 and 22 is lower and the walls of these chambers as well as the tubes of the bundles 24 and 26 are subjected to less severe erosion.

Abstract

Combustion process comprising a first stage (1) in which the fuel is burned in a fluidised bed with a sub-stoichiometric quantity of air and a second stage (2) in which the gases being freed from the fluidised bed and the fine particles of fuel drawn along by these gases burn with the secondary air, the majority of the ashes produced in the first stage of the combustion being removed at this stage (at 9). In order to improve the combustion efficiency, the solid particles separated (at 5 and 6) from the smoke resulting from the combustion in the second stage (2), with the exception of a purging flow (17) which makes it possible to eliminate the flying ashes drawn along by the gases, are recycled in this second stage (at 15) so as to obtain, at this stage, a closed-circuit circulation of the fine particles of fuel and of the flying ashes, the flow of which is clearly greater than the purging flow. <IMAGE>

Description

La présente invention concerne les foyers à combustible solide dans lesquels la combustion est effectuée en deux stades : un premier stade où le combustible est brûlé en lit fludisé avec une quantité d'air substoechiomé­trique et un second stade où les gaz se dégageant du lit fluidisé et les fines particules de combustible qu'ils entraînent brûlent avec de l'air secondaire admis dans la chambre de combustion, à une certaine hauteur au-dessus du lit fluidisé.The present invention relates to solid fuel fireplaces in which combustion is carried out in two stages: a first stage where the fuel is burned in a fludized bed with a quantity of substoichiometric air and a second stage where the gases emerging from the fluidized bed and the fine particles of fuel which they entrain burn with secondary air admitted into the combustion chamber, at a certain height above the fluidized bed.

Plus particulièrement l'invention concerne les foyers à lit fluidisé dont le fond est constitué par une grille dont une partie au moins est inclinée et dans lesquels la majeure partie des cendres est évacuée à l'extrémité supérieure de la grille, soit par des moyens mécaniques sous forme de mâchefers, si la température au sein du lit est suffisante pour permettre l'agglomération des cendres, soit par débordement (brevet français N° 83.16290) ou défluidisa­tion (brevet français N° 82.10385), dans le cas contraire.More particularly, the invention relates to fluidized bed fireplaces, the bottom of which consists of a grid, at least part of which is inclined and in which the major part of the ash is removed at the upper end of the grid, either by mechanical means. in the form of bottom ash, if the temperature within the bed is sufficient to allow agglomeration of the ashes, either by overflow (French patent N ° 83.16290) or defluidization (French patent N ° 82.10385), in the opposite case.

Dans les foyers connus de ce type, les cendres et les suies qui sont entrainées par les gaz se dégageant du lit sont séparées dans un ou plusieurs dépoussiéreurs et réinjectées dans le lit fluidisé. Les suies brûlent difficilement dans le lit fluidisé, qui est réducteur, et peuvent être piégées par les cendres et évacuées avec celles-ci, ce qui diminue le rendement de combustion.In known fireplaces of this type, the ashes and soot which are entrained by the gases emerging from the bed are separated in one or more dust collectors and reinjected into the fluidized bed. The soot hardly burns in the fluidized bed, which is reducing, and can be trapped by the ashes and evacuated with them, which decreases the combustion efficiency.

La présente invention permet d'améliorer le rendement de combustion des foyers de ce type. Elle consiste à recycler au seconde stade de la combustion les suies et cendres volantes séparées des fumées, à l'exception d'un débit de purge qui permet d'éliminer les cendres volantes. Il s'établit ainsi une circulation en circuit fermé avec plusieurs passages des suies dans la zone où se déroule le second stade de la combustion qui permet d'obtenir une com­bustion quasi complète. Les particules séparées des fumées peuvent être réinjectées pneumatiquement, soit au moyen d'air secondaire, soit par un circuit indépendant.The present invention improves the combustion efficiency of fireplaces of this type. It consists of recycle in the second stage of combustion the soot and fly ash separated from the smoke, with the exception of a purge flow which makes it possible to eliminate the fly ash. It thus establishes a closed circuit circulation with several passages of soot in the area where the second stage of combustion takes place which allows to obtain an almost complete combustion. The particles separated from the fumes can be reinjected pneumatically, either by means of secondary air, or by an independent circuit.

Dans le cas où le combustible contient du soufre et où il est nécessaire de désulfurer les fumées avant de les rejeter à l'atmosphère, il faut aussi, dans les foyers connus, séparer des fumées les produits de la réaction de désulfuration, qui doivent être éliminés, et l'agent désulfurant n'ayant pas réagi, qui est recyclé dans une zone de la chambre de combustion où règne une température inférieurs à celle du lit fluidisé. Cela nécessite des moyens plus ou moins complexes et efficaces. Grâce à l'invention, il est possible de réinjecter l'agent désulfurant avec les suies et, par conséquent, de se dispenser de moyens pour les récupérer séparément. Dans ce cas, l'ensemble des solides séparés des fumées, à l'exception d'un débit de purge permettant d'éliminer les cendres volantes et les produits de la réaction de désulfuration, sera recyclé au second stade de la com­bustion, dans une zone favorable à la réaction de désulfura­tion. Si le foyer doit fonctionner à des régimes très diffé­ rents, on pourra prévoir de réinjecter les particules solides séparées des fumées à un premier niveau, proche de l'admission d'air secondaire, pour la marche à faible charge et à un niveau supérieur pour la marche à pleine charge.In the case where the fuel contains sulfur and it is necessary to desulfurize the fumes before discharging them into the atmosphere, it is also necessary, in known foci, to separate from the fumes the products of the desulfurization reaction, which must be removed, and the unreacted desulfurizing agent, which is recycled to an area of the combustion chamber where a temperature prevails below that of the fluidized bed. This requires more or less complex and effective means. Thanks to the invention, it is possible to reinject the desulphurizing agent with the soot and, consequently, to dispense with means for recovering it separately. In this case, all of the solids separated from the flue gases, with the exception of a purge flow making it possible to remove the fly ash and the products of the desulfurization reaction, will be recycled in the second stage of combustion, in a zone favorable to the desulfurization reaction. If the fireplace is to operate at very different regimes rents, provision may be made to reinject the solid particles separated from the smoke at a first level, close to the secondary air intake, for walking at low load and at a higher level for walking at full load.

L'invention a également pour objet une installation comportant un foyer à lit fluidisé du type concerné et au moins un dépoussiéreur traversé par les fumées, caractérisée en ce qu'elle comporte, en outre, des moyens pour réinjecter dans la chambre de combustion, au niveau des buses d'admission d'air secondaire ou au-dessus de celles-ci, les particules solides séparées des fumées dans ledit dépoussiéreur, et un circuit de purge permettant d'éliminer une partie desdites particules.The invention also relates to an installation comprising a fluidized bed hearth of the type concerned and at least one dust collector traversed by the fumes, characterized in that it further comprises means for re-injecting into the combustion chamber, at level of the secondary air intake nozzles or above them, the solid particles separated from the fumes in said dust collector, and a purge circuit making it possible to eliminate a part of said particles.

D'autres caractéristiques de l'invention apparaitront à la lecture de la description qui suit et se réfère au dessin l'accompagnant qui montre, à titre d'exemple non limitatif un mode de réalisation de l'invention et sur lequel :

  • La figure 1 est un schéma illustrant le procédé de l'invention ; et
  • La figure 2 est une représentation schématique d'une chaudière équipée d'un foyer conforme à l'invention.
Other characteristics of the invention will appear on reading the description which follows and refers to the accompanying drawing which shows, by way of nonlimiting example an embodiment of the invention and in which:
  • Figure 1 is a diagram illustrating the method of the invention; and
  • Figure 2 is a schematic representation of a boiler equipped with a fireplace according to the invention.

Sur le schéma de la figure 1, les numéros de référence 1 et 2 représentent des réacteurs, 3 et 4 sont des échangeurs de chaleur à convection, 5 est un dépoussiéreur primaire et 6 un dépoussiéreur final.In the diagram of FIG. 1, the reference numbers 1 and 2 represent reactors, 3 and 4 are convection heat exchangers, 5 is a primary dust collector and 6 is a final dust collector.

Dans le réacteur 1, le combustible introduit en 7 est fluidisé par l'air admis en 8, sous une sole inclinée et perméable au gaz. Les cendres produites par la combustion en lit fluidisé sont évacuées en 9 par débordement ou défluidisation au-dessus de l'extrémité supérieure de la sole, ou extraites du lit, sous forme de mâchefers, par un transporteur si la température du lit est suffisante pour provoquer l'agglomération des cendres. Le débit d'air insufflé en 8 est inférieur au débit stoechiométrique, de sorte que les gaz produits qui se dégagent du lit sont réducteurs. Ces gaz, qui sont chargés de cendres volantes et de fines particules de combustible, sont introduits dans le réacteur 2 où on introduit également de l'air secondaire, en 11, et le cas échéant un agent désulfurant, tel que du calcaire ou de la chaux, sous forme finement divisée, en 13. Les gaz et les particules de combustible qu'ils transportent brûlent avec l'air secondaire pour produire des gaz chauds qui traversent successivement l'échangeur 3, le dépoussié­reur 5, l'échangeur 4 et le dépoussiéreur 6. Les poussières séparées des gaz dans les dépoussiéreurs 5 et 6 sont renvoyées dans le réacteur 2, en 15, à l'exception d'une faible fraction qui est soutirée en 17, pour éliminer les cendres et les produits de la réaction de désulfuration. En contrôlant le débit des poussières réinjectées en 15, on maintient la charge circulante égale à plusieurs fois le débit de purge, de sorte que chaque particule d'agent désulfurant et de combustible passe plusieurs fois dans le réacteur 2 ce qui permet d'obtenir de très bons rendements de combustion et de désulfuration.In reactor 1, the fuel introduced in 7 is fluidized by the air admitted in 8, under an inclined and gas-permeable floor. The ash produced by combustion in a fluidized bed is removed at 9 by overflow or defluidization above the upper end of the hearth, or extracted from the bed, in the form of bottom ash, by a conveyor if the temperature of the bed is sufficient for cause agglomeration of ash. The air flow blown at 8 is less than the stoichiometric flow, so that the gases produced which emerge from the bed are reducing. These gases, which are charged with fly ash and fine fuel particles, are introduced into reactor 2 where secondary air is also introduced, at 11, and if necessary a desulfurizing agent, such as limestone or lime, in finely divided form, at 13. The gases and the fuel particles which they transport burn with the secondary air to produce hot gases which successively pass through the exchanger 3, the dust collector 5, the exchanger 4 and the dust collector 6. The dust separated from the gases in the dust collectors 5 and 6 is returned to the reactor 2, at 15, except for a small fraction which is withdrawn at 17, to remove the ash and the reaction products of desulfurization. By controlling the flow rate of the dust reinjected at 15, the circulating charge is maintained equal to several times the purge flow rate, so that each particle of desulphurizing agent and of fuel passes several times through the reactor 2 which makes it possible to obtain very good yields combustion and desulfurization.

Dans la chaudière de la figure 2, les deux zones de combustion sont superposées, sans séparation, dans une même enceinte. Cette chaudière comporte un foyer à lit fluidisé 10 dont la sole est constituée par le brin supérieur, incliné d'une chaîne sans fin 12. Cette sole constitue le fond d'une chambre verticale 18 dont les parois et le pla­fond sont formés, de manière connue, de panneaux de tubes étanches, qui sont raccordés, par leur extrémité supérieure, à un ballon collecteur de vapeur 20. La chambre 18 est raccordée à une chambre horizontale 22 dans laquelle sont placés des faisceaux de tubes 24 raccordés au ballon 20 et de tubes 26 où la vapeur collectée dans le ballon 20 est surchauffeé. Les fumées produites dans la chambre 18 et sortant de la chambre 22 traversent successivement un dépoussiéreur primaire 28, constitué par exemple par un multicyclone, un échangeur 30, qui pourra être un économi­seur, et un dépoussiéreur final 32, par exemple un filtre à manches.In the boiler of FIG. 2, the two combustion zones are superimposed, without separation, in the same enclosure. This boiler comprises a fluidized bed hearth 10, the bottom of which is formed by the upper strand, inclined with an endless chain 12. This bottom constitutes the bottom of a vertical chamber 18 whose walls and ceiling are formed, so known, of sealed tube panels, which are connected, at their upper end, to a vapor collecting balloon 20. The chamber 18 is connected to a horizontal chamber 22 in which are placed bundles of tubes 24 connected to the balloon 20 and tubes 26 where the vapor collected in the balloon 20 is superheated. The fumes produced in chamber 18 and leaving chamber 22 pass successively through a primary dust collector 28, constituted for example by a multicyclone, an exchanger 30, which could be an economizer, and a final dust collector 32, for example a bag filter.

L'air nécessaire à la combustion du combustible est en partie insufflé à travers la chaîne 12 pour assurer la fluidisation du combustible solide et sa combustion partielle, et en partie à une certaine distance au-dessus du lit, au moyen de buses 34.The air necessary for the combustion of the fuel is partly blown through the chain 12 to ensure the fluidization of the solid fuel and its partial combustion, and partly at a certain distance above the bed, by means of nozzles 34.

Le combustible solide est introduit par une goulotte 14 dans la partie la plus profonde du lit et un agent désulfurant est injecté en 36 dans la partie supérieure de la chambre de combustion 18.The solid fuel is introduced through a chute 14 into the deepest part of the bed and a desulfurizing agent is injected at 36 into the upper part of the combustion chamber 18.

Les poussières recueillies dans la chambre 22, dans les dépoussiéreurs 28 et 32 et dans l'échangeur 30 sont réinjectées, par exemple pneumatiquement, en 37 dans la chambre de combustion 18, au niveau des buses 34 ou au­dessus de celle-ci ; on pourra, en particulier, utiliser l'air secondaire pour réinjecter les poussières. Une partie des poussières est soutirée, en continu ou en discontinu, par un circuit de purge 38 pour éliminer les produits de la réaction de désulfuration et les cendres. Le taux de circulation - rapport du débit de la charge circulante au débit de purge - est de l'ordre de 10. On pourra prévoir de réinjecter les poussières à deux niveaux différents suivant le régime de marche de la chaudière : un niveau inférieur pour la marche à faible charge et un niveau supérieur pour la marche à forte charge.The dust collected in the chamber 22, in the dust collectors 28 and 32 and in the exchanger 30 are reinjected, for example pneumatically, at 37 into the combustion chamber 18, at the level of the nozzles 34 or above the latter; we can, in particular, use secondary air to reinject the dust. Part of the dust is drawn off, continuously or discontinuously, by a purge circuit 38 to remove the products of the desulfurization reaction and the ashes. The circulation rate - ratio of the flow rate of the circulating charge to the purge flow rate - is of the order of 10. Provision may be made for reinjecting the dust at two different levels according to the operating mode of the boiler: a lower level for the walking at low load and a higher level for walking at high load.

Si la combustion dans le lit fluidisé 10 s'effectue à une température suffisante pour permettre l'agglomération des cendres sous forme de mâchefers, ceux-ci se déposent sur la chaîne 12 et sont évacués par celle-ci à son extrémité supérieure. Si la température du lit fluidisé n'est pas suffisante pour provoquer l'agglomération des cendres, celles-ci sont évacuées par débordement ou défluidisation à l'extrémité supérieure de la sole. Dans tous les cas, c'est la majeure partie des cendres est ainsi extraite du lit, le reste étant entrainée par les gaz se dégageant du lit. Les gaz combustibles se dégageant du lit et les fines particules de combustible entraînées par ceux-ci, avec les cendres volantes, brûlent au-dessus du lit 10 avec l'air secondaire introduit par les buses 34.If the combustion in the fluidized bed 10 takes place at a temperature sufficient to allow the ash to agglomerate in the form of bottom ash, these settle on the chain 12 and are discharged through it at its upper end. If the temperature of the fluidized bed is not sufficient to cause agglomeration of the ashes, they are evacuated by overflow or defluidization at the upper end of the hearth. In all cases, most of the ash is thus extracted from the bed, the rest being entrained by the gases emerging from the bed. Combustible gases emerging from the bed and fines fuel particles entrained by them, with the fly ash, burn above the bed 10 with the secondary air introduced by the nozzles 34.

On peut considérer que le lit fluidisé 10 constitue le premier étage d'un réacteur à deux étages dont le second s'apparente à un lit fluidisé circulant et où s'effectue en totalité la désulfuration et la combustion des suies. Il se distingue cependant des lits fluidisés circulants classiques par le fait qu'il ne comporte pas de grille de fluidisation et que la charge circulante est beaucoup plus réduite, pour un taux de circulation donné de l'agent désulfurant, puisque la majeure partie des cendres est extraite du lit 10 sous forme de mâchefers, de sorte que les particules sont maintenues en suspension dans les gaz dans ce second étage. En conséquence, la teneur en produits de la désulfuration de la fraction extraite par le circuit de purge 38 est nettement plus élevée, ce qui facilite le traitement ultérieur de celle-ci; la concentration en poussières des chambres 18 et 22 est inférieure et les parois de ces chambres ainsi que les tubes des faisceaux 24 et 26 sont soumis à une érosion moins sévère.It can be considered that the fluidized bed 10 constitutes the first stage of a two-stage reactor, the second of which is similar to a circulating fluidized bed and where the desulphurization and combustion of the soot are carried out entirely. However, it is distinguished from conventional circulating fluidized beds by the fact that it does not have a fluidization grid and that the circulating charge is much more reduced, for a given rate of circulation of the desulfurizing agent, since the major part of the ashes is extracted from the bed 10 in the form of bottom ash, so that the particles are kept in suspension in the gases in this second stage. Consequently, the content of desulphurization products in the fraction extracted by the purge circuit 38 is significantly higher, which facilitates the subsequent treatment thereof; the dust concentration of the chambers 18 and 22 is lower and the walls of these chambers as well as the tubes of the bundles 24 and 26 are subjected to less severe erosion.

Il est bien entendu que toutes les modifications qui peuvent être apportées aux modes de réalisation décrits par la substitution de moyens équivalents entrent dans le cadre de l'invention.It is understood that all the modifications which can be made to the embodiments described by the substitution of equivalent means are within the scope of the invention.

Claims (5)

1. Procédé de combustion comportant un premier stade où le combustible est brûlé en lit fluidisé avec une quantité d'air substoechiométrique et un second stade où les gaz se dégageant du lit fluidisé et les fines particules de combustible entrainées par ces gaz brûlent avec de l'air secondaire, la majeure partie des cendres produites au premier stade de la combustion étant évacuées à ce stade, caractérisé en ce que les particules solides séparées des fumées résultant de la combustion au second stade, à l'exception d'un débit de purge qui permet d'éliminer les cendres volantes entrainées par les gaz, sont recyclées à ce second stade de la combustion, de façon à obtenir à ce stade une circulation en circuit fermé des fines particules de combustible et des cendres volantes dont le débit est nettement supérieur audit débit de purge.1. Combustion process comprising a first stage where the fuel is burned in a fluidized bed with a quantity of substoichiometric air and a second stage where the gases emerging from the fluidized bed and the fine particles of fuel entrained by these gases burn with l secondary air, most of the ash produced in the first stage of combustion being exhausted at this stage, characterized in that the solid particles separated from the fumes resulting from the combustion in the second stage, with the exception of a purge flow which eliminates the fly ash entrained by the gases, are recycled at this second stage of combustion, so as to obtain at this stage a closed circuit circulation of the fine particles of fuel and the fly ash whose flow rate is much higher said purge flow. 2. Procédé de combustion d'un combustible contenant du soufre avec désulfuration des gaz produits comportant un premier stade où le combustible est brûle en lit fluidisé avec une quantité d'air substoechiométrique et un second stade où les gaz se dégageant du lit fluidisé et les fines particules du combustible entrainées par ces gaz brûlent avec de l'air secondaire, la majeure partie des cendres produites au premier stade étant évacuées à ce stade et un agent désulfurant étant injecté dans la zone où se produit le second stade de la combustion, caractérisé en ce que les particules solides séparées des gaz résultant de la combustion au second stade, à l'exception d'un débit de purge qui permet d'éliminer les cendres volantes entrainées par les gaz et les produits de la réaction de désulfuration, sont recyclées à ce second stade de la combustion, de façon à obtenir à ce stade une circulation en circuit fermé des fines particules de combustible, des cendres volantes, de l'agent désulfurant et des produits de la réaction de désulfuration dont le débit est nettement supérieur audit débit de purge.2. Method of combustion of a fuel containing sulfur with desulphurization of the gases produced comprising a first stage where the fuel is burned in a fluidized bed with a quantity of substoichiometric air and a second stage where the gases emerging from the fluidized bed and the fine particles of fuel entrained by these gases burn with secondary air, the major part of the ash produced in the first stage being removed at this stage and a desulphurizing agent being injected into the area where it occurs the second stage of combustion, characterized in that the solid particles separated from the gases resulting from the combustion in the second stage, with the exception of a purge flow which makes it possible to remove the fly ash entrained by the gases and the products from the desulfurization reaction, are recycled at this second stage of combustion, so as to obtain at this stage a closed circuit circulation of the fine fuel particles, fly ash, the desulfurizing agent and the products of the reaction desulfurization, the flow rate of which is significantly higher than the said purge flow rate. 3. Procédé selon la revendication 2, caractérisé en ce que lesdites particules recyclées au second stade sont injectées à deux niveaux différents en fonction du régime de la combustion : un premier niveau, proche du niveau d'admission de l'air secondaire, pour la marche à faible charge et un niveau supérieur pour la marche de forte charge.3. Method according to claim 2, characterized in that said particles recycled in the second stage are injected at two different levels depending on the combustion regime: a first level, close to the intake level of secondary air, for the low load walking and a higher level for high load walking. 4. Procédé selon la revendication 1, 2 ou 3, caractérisé en ce que lesdites particules sont réinjectées pneumatiquement au moyen d'air secondaire.4. Method according to claim 1, 2 or 3, characterized in that said particles are reinjected pneumatically by means of secondary air. 5. Installation pour la mise en oeuvre du procédé selon la revendication 1, 2, 3, ou 4, comprenant une chambre de combustion (18) dont la partie inférieure constitue un réacteur à lit fluidisé (10), à sole inclinée (12) et conçu pour permettre l'évacuation des cendres à l'extrémité supérieure de la sole et qui comporte des buses d'admission d'air secondaire (34) et éventuellement des moyens d'injection d'un agent désulfurant (36) à une certaine hauteur au-dessus du lit fluidisé, et au moins un dépous­siéreur (28, 32) placé à la sortie de ladite chambre, carac­térisée en ce qu'elle comporte, en outre, des moyens (37) pour réinjecter dans la chambre de combustion, au niveau desdites buses (34) ou au-dessus, les particules solides séparées des gaz de combustion dans ledit dépoussiéreur (28, 32), et un circuit de purge (32) permettant d'éliminer une fraction de ces particules.5. Installation for implementing the method according to claim 1, 2, 3, or 4, comprising a combustion chamber (18), the lower part of which constitutes a fluidized bed reactor (10), with inclined bottom (12) and designed to allow the evacuation of the ashes at the upper end of the hearth and which comprises secondary air intake nozzles (34) and possibly means for injecting a desulfurizing agent (36) at a certain height at the above the fluidized bed, and at least one dust collector (28, 32) placed at the outlet of said chamber, characterized in that it further comprises means (37) for re-injecting into the combustion chamber, at the level from said nozzles (34) or above, the solid particles separated from the combustion gases in said dust collector (28, 32), and a purge circuit (32) making it possible to remove a fraction of these particles.
EP88402256A 1987-09-14 1988-09-08 Combustion process in a fluidised bed and installation for carrying out the process Expired - Lifetime EP0308300B1 (en)

Applications Claiming Priority (2)

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FR8712680 1987-09-14
FR8712680A FR2620517B1 (en) 1987-09-14 1987-09-14 FLUIDIZED BED COMBUSTION PROCESS AND INSTALLATION FOR CARRYING OUT SAID METHOD

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EP0308300B1 EP0308300B1 (en) 1993-01-07

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Publication number Priority date Publication date Assignee Title
WO1993018341A1 (en) * 1992-03-05 1993-09-16 Technische Universiteit Delft Method and apparatus for combusting a carbonaceous material

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US10415825B2 (en) * 2016-06-07 2019-09-17 The Babcock & Wilcox Company Methods of generating energy from cellulosic biofuel waste
CN114234178B (en) * 2021-11-02 2022-07-12 平湖弘欣热电有限公司 Fly ash recirculation system of fluidized bed boiler

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FR2323101A1 (en) * 1975-09-05 1977-04-01 Metallgesellschaft Ag PROCESS FOR THE COMBUSTION OF MATERIALS CONTAINING CARBON
EP0033808A1 (en) * 1979-12-26 1981-08-19 Battelle Development Corporation NOx reduction in multisolid fluidized bed combustors
WO1986003986A1 (en) * 1985-01-11 1986-07-17 A. Ahlstrom Corporation Method and apparatus for separating solid particles from flue gases in a circulating fluidized bed reactor
FR2583305A1 (en) * 1985-06-18 1986-12-19 Fives Cail Babcock Process for desulphurising gases originating from the hearth of a boiler and plant for implementing this process.

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DE3688007D1 (en) * 1985-06-12 1993-04-22 Metallgesellschaft Ag COMBUSTION DEVICE WITH CIRCULATING FLUID BED.

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Publication number Priority date Publication date Assignee Title
FR2323101A1 (en) * 1975-09-05 1977-04-01 Metallgesellschaft Ag PROCESS FOR THE COMBUSTION OF MATERIALS CONTAINING CARBON
EP0033808A1 (en) * 1979-12-26 1981-08-19 Battelle Development Corporation NOx reduction in multisolid fluidized bed combustors
WO1986003986A1 (en) * 1985-01-11 1986-07-17 A. Ahlstrom Corporation Method and apparatus for separating solid particles from flue gases in a circulating fluidized bed reactor
FR2583305A1 (en) * 1985-06-18 1986-12-19 Fives Cail Babcock Process for desulphurising gases originating from the hearth of a boiler and plant for implementing this process.

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1993018341A1 (en) * 1992-03-05 1993-09-16 Technische Universiteit Delft Method and apparatus for combusting a carbonaceous material

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DE3877298D1 (en) 1993-02-18
ES2038325T3 (en) 1993-07-16
FR2620517B1 (en) 1989-12-22
FR2620517A1 (en) 1989-03-17
KR960010317B1 (en) 1996-07-30
EP0308300B1 (en) 1993-01-07
KR890005454A (en) 1989-05-15
IN171723B (en) 1992-12-19

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