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(11) | EP 0 438 171 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Circulating fluid-bed combustion apparatus |
| (57) A circulating fluid-bed combustion apparatus comprises a fluid-bed combustion chamber
(1) for combusting solid fuels, a separator (2) for separating particles accompanying
combustion gases, a conduit (5) for taking out particles, which is arranged at the
bottom of the fluid-bed combustion apparatus, a pulverizer (6) for pulverizing particles
introduced from the conduit for taking out particles and a conduit (8) for returning
particles to the fluid-bed combustion chamber. The conbustion apparatus can have a classifier (7) before the pulverizer. |
[0001] The present invention relates to a circulating fluid-bed combustion apparatus which effectively combusts solid fuels such as coal and the like.
[0002] Japanese Examined Patent Publication No.28046/82 discloses a circulating fluid-bed combustion apparatus as shown in Fig.5. Said apparatus is composed of a fluid-bed combustion chamber 1, a separator 2 behind said combustion chamber 1 and a particle recycling conduit 3 leading separated particles to said combustion chamber. An ash discharging nozzle 4 is positioned at the bottom of said combustion chamber or in the middle of the particle recycling conduit 3.
[0003] A superficial velocity of fluidizing gases in the fluid-bed combustion chamber 1 is determined to be a terminal velocity of fluidized particles or more. The fluidized particles accompanied by gases are separated by means of the separator 2. The separated particles are returned to the fluid-bed combustion chamber 1 thorugh the particle recycling conduit 3. A long retention time of particles is secured, which decreases a combustible loss.
[0004] Another circulating fluid-bed combustion apparatus is shown in Fig.6. This apparatus is composed of a fluid-bed combustion chamber 1, a separator 2 arranged in an upper portion of said combustion chamber 1 and an ash discharging nozzle 4 arranged at the bottom of the fluid-bed combustion chamber.
[0005] Solid fuels such as coal and the like are crushed into coarse particles and charged into a lower portion of the combustion chamber 1. The solid fuels are fluidized by combustion air blown from the bottom of the combustion chamber into the combustion chamber and begin to be combusted.
[0006] Coarse particles not reaching the terminal velocity are present in the particles inside the combustion chamber 1. A fluidized bed is formed by combustion air at the bottom of the combustion chamber, the coarse particles being blown upward together with fine particles. The higher said coarse particles ascend in the combustion chamber, the more the coarse particles are liable to fall to the bottom of the combustion chamber. Since the particles are recycled in the combustion chamber in this way, a suspension concentration of the particles in the combustion chamber is high in the lower portion of the combustion chamber and low in the upper portion of the combustion chamber. The particles become finer as the combustion proceeds. The particles are repeatedly recycled through the separator until the combustion of the particles are terminated.
[0007] On the other hand, ash converts to fly ash which passes through the separator 2 and is discharged together with combustion gas out of the circulating fluid-bed combustion chamber. Discharged fly ash is recovered by a dust catcher.
[0008] Foreign matters are included in fuels which do not contain combustible components such as pebbles. There is a case where ash of the fuels does not become fine depending on the properties of the fuels. Those foreign matters and the ash which does not become fine convert to the incombustible particles which are not discharged out of the circulating fluid-bed combustion apparatus. Accordingly, since the incombustible particles which are not discharged out of the system are increased with the lapse of time, it is necessary to limit the total amount of fluidized particles in the circulating fluid-bed combustion apparatus by discharging a part of the fuidized particles by the use of the ash discharging nozzle 4. A great amount of combustible components is included, however, in the fluidized particles discharged out of the system. The combustible components in the fluidized particles are uselessly discharged without being combusted out of the system. In consequence, combustible loss is increased
[0009] It is an object of the present invention to provide a circulating fluid-bed combustion apparatus which effectively combusts solid fuels such as coal and the like.
[0010] To attain the aforementioned object, the present invention provides a circulating fluid-bed combustion apparatus, comprising:
a fluid-bed combustion chamber for combusting solid fuels;
a separator for separating particles accompanying combustion gases;
a conduit for taking out particles, which is arranged at the bottom of the fluid-bed combustion chamber;
a pulverizer for pulverizing particles introduced from the conduit for taking out particles; and
a conduit for returning pulverized particles to the fluid-bed combustion chamber.
[0011] Further, the present invention provides another circulating fluid-bed combustion apparatus, comprising:
a fluid-bed combustion for combusting solid fuels;
a separator for separating particles accompanying combustion gases behind the fluid-bed combustion chamber;
a conduit for taking out particles which is arranged at the bottom of the combustion chamber;
a classifier for classifying particles introduced from the conduit for taking out particles;
a conduit for returning particles fine particles after classification to the combustion chamber;
a pulverizer for pulverizing coarse particles after classification; and
a conduit for returning pulverized particles to the fluid-bed combustion chamber.
[0012] The above objects and other objects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the appended drawinngs.
Figs.1 to 4 are schematic illustrations showing a circulating fluid-bed combustion apparatus of the present invention; and
Figs.5 and 6 are schematic illustrations showing the prior art circulating fluid-bed combustion apparatus.
Figs.1 and 2 show a case where the separator 2 is arranged outside a fluid-bed combustion chamber 1. In this case, separated particles are returned to the fluid-bed combustion chamber 1 through a conduit 3 for recycling particles. A conduit 5 for taking out particles is arranged at the bottom of the fluid-bed combustion chamber. The particles taken out are pulverized by a pulverizer 6. Pulverized particles are returned to the fluid-bed combustion chamber 1 through a conduit 8 for returning particles.
[0013] In a combustion apparatus in Fig.2, a classifier 7 is arranged in the middle of a conduit 5 for taking out particles. Classified particles are returned to a combustion chamber 1 through a conduit 9. Coarse particles after having been classified are pulverized by a pulverizer 6. Pulverized particles are returned to the fluid-bed combustion chamber 1 through a conduit 8 for returning particles.
[0014] Figs.3 and 4 are a case where a separator 2 is arranged in an upper portion of the fluid-bed combustion chamber 1. The arrangement of the pulverizer 6 and classifier 7 is the same with that in Figs.1 and 2. As the pulverizer, a roller mill, ball mill or hammer mill is used. As the classifier, a wind power classifier is desired because the particle size of the particles is minute. An ordinary sieving machine can be used. The work of the circulating fluid-bed combustion apparatus having the pulverizer of the above-mentioned structure will now be described.
[0015] Solid fuels are crushed into particles of 0.5 to 10 mm in particle size and charged into the lower portion of the fluid-bed combustion chamber 1.
[0016] Since coarse particles which do not reach a terminal velocity are in a fluidized state in the lower portion of the fluid-bed combustion chamber 1, the suspension concentration of particles is high in the lower portion of the fluid-bed combustion chamber and low in the upper portion of the fluid-bell combustion chamber.
[0017] When incombustible particles such as foreign matters contained in fuels and ash which does not convert to fine particles are accumulated in the lower portion of the combustible chamber, the incombustible particles are introduced into pulverizer 6 through the conduit 5 located in the lower fluid-bed combustion chamber 1. Incombustible particles pulverized by the pulverizer 6 are returned to the combustion chamber 1 through the conduit 8.
[0018] This pulverizing treatment is applied to both the incombustible particles such as the foreign matters and ash not pulverized into fine particles and the combustible particles being combusted. The incombustible components having become fine are discharged together with combustion gases as fly ash out of the combustion apparatus and recovered by the dust catcher. The combustible components having become fine completes their combustion in the fluid-bed combustion chamber 1. Accordingly, incombustible components accumulated in the fluid-bed combustion chamber 1 can be discharged without uselessly discharging the particles not combusted.
[0019] When the classifier 7 is arranged in the middle of the conduit 5 for taking out particles, particles which do not require the pulverizing treatment are separated by the classifier 7 and returned to the combustion chamber 1 through the conduit 9. Only coarse particles having undergone the classification are pulverized by the pulverizer 6 and returned to the combustion chamber 1.
[0020] The circulating fluid-bed combustion apparatus having a pulverizer of the present invention produces the following effect:
[0021] The foreign matters contained in fuels retained in the lower portion of the fluid-bed combustion chamber and coarse particles containing ash which does not become fine during operation of the combustion apparatus are not directly discharged from the ash discharging nozzle as prior art. Said coarse particles are introduced into the pulverizer to be pulverized and returned to the combustion chamber. The incombustible components having become fine are discharged as fly ash out of the fluid-bed combustion apparatus, accompanying combustion gases. The incombustible components discharged are recovered by the dust catcher. The combustible components having become fine complete their combustion during their passing through the fluid-bed combustion chamber 1. Accordingly, the incombustible components are not discharged from the ash discharging nozzle as in the prior art apparatus, which decreases the combustible loss.
[0022] For the reason that the particles to be applied to the pulverizing treatment are in combustion reaction in the fluid-bed combustion chamber or that the particles receive a rapid thermal shock during charging thereof, the strength of the particles is lowered before charging thereof. A motive power necessary for pulverizing the particles can be decreased compared with that in the case of pulverizing the particles before charging thereof.
[0023] Further, when the classifier is arranged before the pulverizer,fine particles are removed beforehand by the classifier.
a fluid-bed combustion chamber (1) for combusting solid fuels; and
a separator (2) for separating particles accompanying combustion gases;
characterized by comprising:
a conduit (5) for taking out particles, which is arranged at the bottom of the fluid-bed combustion apparatus;
a pulverizer (6) for pulverizing particles introduced from the conduit for taking out particles; and
a conduit (8) for returning pulverized particles to the fluid-bed combustion chamber.
a fluid-bed combustion chamber (1) for combusting solid fuels; and
a separator (2) for separating particles accompanying combustion gases behind the fluid-bed combustion chamber;
characterized by comprising:
a conduit (5) for taking out particles which is arranged at the bottom of the combustion chamber;
a classifier (7) for classifying particles introduced from the conduit for taking out particles;
a conduit (9) for returning fine particles after classification to the combustion chamber;
a pulverizer (6) for pulverizing coarse particles after classification; and
a conduit (8) for returning pulverized particles to the fluid-bed combustion chamber.