EP1712839B1

EP1712839B1 - Method of heat recovery and heat recovery apparatus

Info

Publication number: EP1712839B1
Application number: EP04770831.8A
Authority: EP
Inventors: Norihisa Miyoshi
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 2004-01-20
Filing date: 2004-07-20
Publication date: 2018-11-21
Anticipated expiration: 2024-07-20
Also published as: EP1712839A1; EP1712839A4; WO2005068909A1

Description

TECHNICAL FIELD

The present invention relates to a heat recovery method and an apparatus for processing a combustible material, which use the generated heat to melt ash and which can recover the heat effectively, when a combustible material such as municipal waste, waste plastic, shredder dust, construction waste, waste tires or biomass is processed.

BACKGROUND ART

In recent years, a gasification melting method attracts attention as a method for incinerating waste such as municipal waste. The gasification melting method is a method in which waste is partially combusted at approximately 500°C to obtain pyrolysis gas and the pyrolysis gas is combusted at a high temperature in a melting furnace to melt ash content entrained in the gas. Since the pyrolysis gas which can be obtained in this method is gas produced by partial combustion of waste, it contains combustion product gas and has a low calorific value. Therefore, to achieve a sufficiently high temperature to melt ash in a melting furnace, that is, a temperature of approximately 1200°C, the waste to be dumped needs to have a calorific value of approximately 7 to 8 MJ/kg.
However, when waste, especially municipal waste, is supplied, the calorific value varies largely. When the calorific value is insufficient, the actual situation is that auxiliary fuel must be supplied to the melting furnace or the like or oxygen must be used, instead of air, as a supply source of oxygen for combustion in the melting furnace. Therefore, there is a problem of an increase in the running cost, or an increase in the initial cost caused by installation of an oxygen generator.
Also, although the ash content entrained in the pyrolysis gas flowing into the melting furnace contains low-melting point metals, low-boiling point metal salts and so on in addition to silica-, alumina- and calcia-based substances, the components which are melt in the melting furnace are mainly the silica-, alumina- and calcia-based substances and the low-boiling point metal salts and so on flow downstream out of the melting furnace together with the combustion product gas.
Also, the melting furnace has such a structure that a swirling gas flow can be formed inside thereof and, in many cases, a means for suddenly inverting the flow direction of the gas causes the ash content in the gas to collide with the wall surfaces of the melting furnace by inertia force to form a slag flow in order to increase the melting rate of the ash content contained in the substances to be melted. Therefore, particles with large particle sizes are captured by the slag flow, and, consequently, the ash content in the exhaust gas flowing downstream out of the melting furnace has particle sizes of mainly 10 µm or smaller.
The ash content in the gas flowing downstream out of the melting furnace is characterized by a high content of salts and very small particle sizes as described above, which causes various problems. Fine particles are melted at every temperature in various temperature ranges from a high-temperature range of 1200°C or higher immediately after the melting to a temperature range around 400°C. The melted fine particles adhere to the heat transfer surface of a device installed for heat recovery and significantly lower the heat transfer coefficient of the heat transfer surface.
When the heat transfer coefficient decreases, the function of the heat recovery device decreases and it becomes unable to lower the gas temperature, for example. Then, the gas temperature at the exit of the heat recovery step may increase and exceed an allowable temperature of a dust collection step such as a bag filter provided downstream of the heat recovery step. Especially, since the filter cloth of the bag filter is easily affected by heat, the temperature at the entrance of the dust collection step must be not higher than the permissible temperature. Therefore, it is necessary to provide a water spraying gas cooling step in advance or to provide a sufficiently large allowance to the heat transfer area at the heat transfer surface of the heat recovery device to maintain the function of the heat recovery device sufficiently so that the gas temperature at the entrance of the dust collection step cannot be higher than the allowable temperature. This causes an increase in cost due to increase in equipment.
FIG. 1 is a view illustrating the process flow of an apparatus for processing a combustible material employing a conventional gasification melting method (see JP-B-3153091 ). The apparatus for processing a combustible material has a gasification furnace 101, a melting furnace 102, a boiler 103, an economizer or an air preheater 104, a gas cooling tower 105, a bag filter 106, an inducing blower 107, a catalyst denitration tower 108 and a stack 109. The combustible material is supplied to the gasification furnace 101, and is combusted partially and pyrolyzed to generate pyrolysis gas, tar, char, fly ash and so on. The pyrolysis gas entraining the tar, char, fly ash and so on is all supplied to the melting furnace 102.
The pyrolysis gas is combusted at a high temperature of 1200°C or higher in the melting furnace 102, and ash content is melted and discharged out of the furnace as molten slag. High-temperature combustion product gas discharged from the melting furnace is directed to the boiler 103. The combustion product gas is cooled to approximately 450°C in the boiler 103 and further cooled down to approximately 200°C in the economizer or air preheater 104.
The ash content entrained in the high-temperature combustion product gas flowing out of the melting furnace 102 has high adhesivity since it has small particle sizes and contains a large proportion of metal salts with relatively low melting points. Thus, it easily adheres to the heat transfer surfaces of the boiler 103 and the economizer or air preheater 104. Therefore, since it gradually adheres to the heat transfer surfaces of the boiler 103 and the economizer or air preheater 104 and decreases the heat transfer coefficients thereof during operation, the combustion product gas, which can be sufficiently cooled immediately after the start of operation, becomes gradually less able to be cooled with elapse of operation time and the entrance temperature of the bag filter 106 increases correspondingly.
In general, the maximum allowable temperature of a bag filter is approximately 220°C. Thus, there is nothing to do but spray water into the combustion product gas in the gas cooling tower 105 so that the gas temperature cannot exceed it. However, even if the operation is continued in this way, the adhesion of ash to the heat transfer surfaces is not stopped. Thus, the combustion product gas temperature at the entrance of the air preheater gradually increases and the adhesion of ash further increases. In the temperature range exceeding 450°C, the ash is in a semi-molten state and difficult to be scraped or to be brushed off mechanically, and it is difficult to stop adhesion of ash without lowering the temperature. In other words, once the function of the heat transfer surfaces is lowered, it is difficult to suppress adhesion of ash in that state.
Therefore, in a conventional apparatus for processing a combustible material, there is no way to continue stable operation but to provide a sufficiently large safety factor to the heat transfer areas of the boiler 103 and the economizer or air preheater 104 for a heat recovery step and to provide a means for forcibly scraping off the ash having adhered to the heat transfer surfaces. However, when the ash having adhered to the heat transfer surfaces is forcibly scraped off, the surface temperatures of the heat transfer surfaces are varied significantly. Then, protective films valuably formed may be flaked off by thermal shock, and corrosion and wear of the heat transfer surfaces may be promoted.
Also, when ash-returning for returning the ash trapped by the bag filter 106 to the melting furnace 102 is attempted to be conducted in order to increase the melting rate of ash, the following problem and the like occur; since a large amount of low-melting point substances and metal salts, which are not converted into molten slag in the melting furnace and transferred into exhaust gas as they are, may be circulated through the circulation route including a heat exchanger and may promote adhesion of ash to the heat transfer surface of the heat exchanger at an accelerating pace, the ash-returning rate cannot be increased and the slag conversion rate cannot be increased only to a certain limit or lower.
In recent years, on the other hand, as a method not to use auxiliary fuel for melting ash, a method is proposed in which not all the pyrolysis gas from partial combustion is directed to a melting furnace but a pyrolysis furnace of the type, which uses as little oxygen as possible and is close to a dry distillation system, is used in order to increase the calorific value of the pyrolysis gas as much as possible so that the temperature in the melting furnace can be easily maintained. FIG. 2 is a view illustrating the process flow of another apparatus for processing a combustible material.
In FIG. 2, parts that are the same or equivalent to those of FIG. 1 are identified with the same reference numerals. Although this apparatus for processing a combustible material has, like the conventional apparatus, a gasification furnace and a melting furnace, an integrated fluidized bed gasification furnace 110 having a pyrolysis chamber 110-1 and a combustion chamber 110-2 is employed as the gasification furnace. The combustible material is mainly supplied to the pyrolysis chamber 110-1 side of the fluidized bed gasification furnace 110 where pyrolysis gas, tar, char, fly ash and so on are generated. Among them, all that do not remain in the fluidized bed are supplied to the melting furnace 102 and combusted therein at a high temperature of 1200°C or higher. The ash is melted in the melting furnace 102.
The pyrolysis residue left in the fluidized bed flows into the combustion chamber 110-2 together with a fluidized medium. Fluidizing air and secondary air are supplied so as to maintain the fluidized bed of the combustion chamber 110-2 at approximately 550°C to 700°C and a free board part above the fluidized bed at 850°C to 950°C, and the air ratio is maintained at one or higher as a whole to ensure complete combustion. Although only the pyrolysis residue flowing into the combustion chamber 110-2 through the pyrolysis chamber 110-1 may be combusted therein, waste may be directly supplied to the combustion chamber 110-2 depending on the pyrolysis characteristics and combustion characteristics of the waste.
Combustion product gas discharged from the combustion chamber 110-2 is introduced into a dust collector 112 such as a cyclone at a temperature of 850°C to 950°C and subjected to dust removal, and then is introduced into the boiler 103. The ash content particles trapped by the dust collector 112 are directed into the melting furnace 102 and melted therein.
The apparatus for processing a combustible material constituted as described above has an excellent advantage that it can melt ash without using auxiliary fuel when processing a combustible material with a low calorific value. However, the particles entrained in the gas flowing into the boiler 103 are very fine particles (particles with small particle sizes) since the dust on the pyrolysis chamber 110-1 side is trapped in the melting furnace 102 and the dust on the combustion chamber 110-2 side is trapped by the dust collector 112 such as a cyclone. This is not preferred in view of prevention of adhesion of ash particles to the heat transfer surfaces of the boiler 103 and the economizer or air preheater 104 as described before.
JP 09-079545 A discloses superheated steam making apparatus which has a thermal decomposition means (for thermal decomposition reaction within a space at a temperature of at least 300 °C), a char combustion means, a first steam making means (for obtaining steam at a temperature of at most 400 °C) and a second steam making means. At least a lower area of a fluid medium housing part in the char combustion means is expanded in area to lower the fluidization rate of the fluid medium as compared to the upper area thereof. To be more specific, the fluidization rate of the fluid medium should be 0.3 to 2m/sec, preferably 0.3 to 1m/sec., further preferably 0.3-0.6m/sec.

DISCLOSURE OF INVENTION

PROBLEM TO BE SOLVED BY INVENTION

The present invention has been made in view of the above point. It is, therefore, an object of the present invention to provide a heat recovery method and an apparatus for processing a combustible material in which ash content can be melted with a combustible material with a low calorific value of 6 to 7 MJ/kg without using auxiliary fuel, in which adhesion of ash to the heat transfer surfaces of heat recovery apparatuses (boiler and economizer or air preheater) can be prevented when heat is recovered from combustion product gas after the melting of the ash content, and which can minimize the allowance of the heat transfer surfaces and eliminate the necessity of equipment such as a water spray type gas cooling system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating the process flow of a conventional apparatus for processing a combustible material.
FIG. 2 is a view illustrating the process flow of a conventional apparatus for processing a combustible material.
FIG. 3 is a view illustrating the process flow of an apparatus for processing a combustible material according to the present invention.
FIG. 4 is a view illustrating the process flow of an apparatus for processing a combustible material according to the present invention.
FIG. 5 is a view illustrating an example of the constitution of an integrated fluidized bed gasification furnace for use in the apparatus for processing a combustible material according to the present invention.
FIG. 6 is a view illustrating an example of the constitution of a twin-tower type fluidized bed gasification furnace for use in the apparatus for processing a combustible material according to the present invention.
FIG. 7 is a view illustrating an example of the constitution of a melting furnace for use in the apparatus for processing a combustible material according to the present invention.
FIG. 8 is a view illustrating the process flow of an apparatus for processing a combustible material according to the present invention.

MEANS FOR SOLVING THE PROBLEM

In order to solve the above problem, a heat recovery method according to the invention is provided as recited in Claim 1. Moreover, an apparatus for processing a combustible material is provided as recited in claim 5. Preferred embodiments of the present invention may be gathered from the dependent claims.
As shown in FIG. 3 for example, the following steps are disclosed: recovering heat from first gas G2 entraining particles mostly with large particle sizes; and recovering heat by mixing second gas G3 entraining particles mostly with small particle sizes with the first gas G2 from which heat has been recovered.
Since heat is recovered from the first gas entraining particles mostly with large particle sizes and then the first gas is mixed with the second gas entraining particles mostly with small particle sizes as described above, adhesion of particles, especially the particles with small particle sizes in the second gas, which tend to adhere to a heat transfer surface, to the heat transfer surface can be prevented by the grinding function of grinding the heat transfer surface which the particles with large particle sizes in the first gas exhibit when colliding with the heat transfer surface.
As shown in FIG. 3 for example, the first gas G2 is gas entraining particles generated in a fluidized bed furnace 1 by supplying a combustible material to the fluidized bed furnace 1, and the second gas G3 is gas entraining particles obtained by introducing gas G1 generated in the fluidized bed furnace 1 into a melting furnace 2 and melting ash content therein.
Since the gas generated in the fluidized bed furnace by supplying a combustible material to the fluidized bed furnace is gas entraining particles mostly with large particle sizes and the gas obtained by introducing gas generated in the fluidized bed furnace into the melting furnace and melting ash content therein is gas entraining particles mostly with small particle sizes, the same effect can be achieved by using the gas generated in the fluidized bed furnace as the first gas and the gas obtained in the melting furnace as the second gas.
As shown in FIG. 5 for example, the heat recovery method preferably further comprises the steps of: pyrolyzing the combustible material 34 in the fluidized bed furnace 1 (21) to obtain char and gas G1; and combusting the char in the furnace 1(21). In this configuration, fine particles and combustible gas can be effectively generated from a combustible material with little fluctuation in gas composition.
As shown in FIG. 5 for example, the heat recovery method preferably further comprises the steps of: combusting the char in a combustion chamber 22, and introducing a fluidized medium from the combustion chamber 22 to a pyrolysis chamber 21 for pyrolyzing the combustible material 34 (D, E). In this configuration, the heat generated by combusting the char in the combustion chamber can be transferred to the fluidized medium and the heat can be used for the pyrolysis reaction of the combustible material in the pyrolysis chamber effectively.
As shown in FIG. 3 for example, the heat recovery method preferably further comprises the steps of: mixing the first gas G2 and the second gas G3; cooling the mixed gas to 450°C or lower; separating solid matter from the cooled gas with a dust collector 5; and introducing the separated solid matter into the melting furnace 2 and melting the solid matter therein. Although the gas temperature after the cooling is 450°C or lower, it is preferably 350°C or lower, more preferably 300°C or lower, most preferably 250°C or lower.
Another method for processing a combustible material comprises the steps of, as shown in FIG. 3 for example, generating first gas G2 and second gas G1 both entraining particles in a fluidized bed gasification furnace 1; introducing the first gas G2 from the fluidized bed gasification furnace 1 into a heat recovery apparatus 3; recovering heat by heat exchange between the introduced gas G2 and a heat receiving fluid; introducing the second gas G1 from the fluidized bed gasification furnace 1 into a melting furnace 2 to melt ash content in the particles; and introducing the gas G3 in which the ash content has been melted into the heat recovery apparatus 3.
Since the first gas from the fluidized bed gasification furnace is introduced into the heat recovery apparatus to recover heat therefrom and the second gas from the fluidized bed gasification furnace is introduced into the melting furnace and the gas discharged from the melting furnace is introduced into the same heat recovery apparatus as described above, the first gas is gas entraining particles mostly with large particle sizes. Adhesion of particles to the heat transfer surface can be therefore prevented by the grinding function which the particles exhibit when colliding with the heat transfer surface.
Another method for processing a combustible material comprises the steps of, as shown in FIG. 3 for example, generating first gas G2 and second gas G1 both entraining particles in a fluidized bed gasification furnace 1; introducing the first gas G2 from the fluidized bed gasification furnace 1 into a heat recovery apparatus 3; recovering heat by heat exchange between the introduced gas G2 and a heat receiving fluid; introducing the second gas G1 from the fluidized bed gasification furnace 1 into a melting furnace 2 to melt ash content in the particles; and introducing the gas G3 in which the ash content has been melted into the heat recovery apparatus 3 into which the first gas G2 has been introduced. The heat recovery apparatus for heat exchange with the first gas and the heat recovery apparatus for heat exchange with the mixed gas of the first gas and the second gas maybe the same apparatus or the different apparatuses .
Since the first gas entraining particles mostly with large particle sizes from the fluidized bed gasification furnace is introduced into the heat recovery apparatus to recover heat and then the gas from which heat has been recovered is mixed with the second gas entraining particles mostly with small particle sizes and discharged from the melting furnace to recover heat as described above, adhesion of particles to a heat transfer surface can be prevented by the grinding function which the particles with large particle sizes in the first gas exhibit when colliding with the heat transfer surface.
The method for processing a combustible material preferably further comprises the steps of, as shown in FIG. 3 for example, recovering heat from the first gas G2 and the second gas G3 with a heat recovery apparatus 3, 4 to cool the first gas G2 and the second gas G3 to 450°C or lower; separating solid matter from the first gas G2 and the second gas G3 with a dust collector 5; and introducing the separated solid matter into the melting furnace 2 and melting the solid matter therein. Although the gas temperature after the cooling is 450°C or lower, it is preferably 350°C or lower, more preferably 300°C or lower, most preferably 250°C or lower.
A heat recovery apparatus comprises, as shown in FIG. 3 for example, a first introduction port for introducing first gas G2 entraining particles mostly with large particle sizes; a second introduction port located downstream of the first introduction port along the flowing direction of the gas G2 introduced through the first introduction port for introducing second gas G3 entraining particles mostly with small particle, wherein first gas G2 and second gase G3 flow in the heat recovery apparatus first in a downward direction with respect to gravity as they mix and then in an upward direction with respect to gravity after a change of direction at the bottom of the heat recovery apparatus; a discharge port for discharging gas G4 from which heat has been recovered; and a heat transfer surface for allowing heat exchange between the gases G2,G3 introduced through the first and second introduction ports and a heat receiving fluid to recover heat from the gases G2,G3.
Since the second introduction port for receiving the second gas entraining particles mostly with small particle sizes is located downstream of the first introduction port for receiving the first gas entraining particles mostly with large particle sizes as described above, adhesion of particles, especially the particles with small particle sizes in the second gas introduced through the second introduction port, which tend to adhere can be prevented by the grinding function which the particles with large particle sizes in the first gas introduced through the first introduction port exhibit when colliding with the heat transfer surface. Also, since the first introduction port is located upstream of the second introduction port, the second gas entraining particles mostly with small particle sizes is introduced after the first gas entraining particles mostly with large particle sizes has been cooled. Therefore, the formation of a region with high-temperature gas entraining particles with small particle sizes which tend to adhere to the heat transfer surface can be prevented as much as possible.
In the heat recovery apparatus, the first gas G2 is gas generated in a fluidized bed furnace 1 by supplying a combustible material to the fluidized bed furnace 1, and the second gas G3 is gas obtained by introducing the gas G2 generated in the fluidized bed furnace 1 into a melting furnace 2 and melting ash content entrained in the gas.
Since the gas generated in the fluidized bed furnace by supplying a combustible material to the fluidized bed furnace is gas entraining particles mostly with large particle sizes and the gas obtained by introducing the gas generated in the fluidized bed furnace into the melting furnace and melting ash content therein is gas entraining particles mostly with small particle sizes, the same effect can be achieved by introducing the gas generated in the fluidized bed furnace into the heat recovery apparatus through the first introduction port as the first gas and the gas obtained in the melting furnace into the heat recovery apparatus through the second introduction port as the second gas.
As shown in FIG. 3 for example, after the first gas G2 and the second gas G3 have been mixed and cooled to 450°C or lower, solid matter in the mixed gas G2,G3 is separated with a dust collector 5 and the separated solid matter is introduced into the melting furnace 2 and melted therein. Although the gas temperature after the cooling is 450°C or lower, it is preferably 350°C or lower, more preferably 300°C or lower, most preferably 250°C or lower.
Another apparatus for processing a combustible material comprises, as shown in FIG. 3 for example, a fluidized bed gasification furnace 1 for gasifying a combustible material to generate first gas G2 and second gas G1 both entraining particles; a heat recovery apparatus 3 for receiving the first gas G2 generated in the fluidized bed gasification furnace 1 and allowing heat exchange between the first gas G2 and a heat receiving fluid to recover heat from the first gas G2; a melting furnace 2 for receiving the second gas G1 generated in the fluidized bed gasification furnace 1 and melting ash content therein; and a gas introduction passage for introducing gas G3 discharged from the melting furnace 2, together with particles also generated in the melting furnace 2, into the heat recovery apparatus 3.
Since the second gas generated in the fluidized bed gasification furnace is introduced into the melting furnace and gas discharged from the melting furnace is introduced into the heat recovery apparatus, which receives the first gas generated in the fluidized bed gasification furnace and entraining particles and recovers heat therefrom, as described above, adhesion of particles, especially the particles with small particle sizes in the gas discharged from the melting furnace, which tend to adhere, can be prevented by the grinding function which the particles in the first gas exhibit when colliding with the heat transfer surface.
Another apparatus for processing a combustible material comprises, as shown in FIG. 3 for example, a fluidized bed gasification furnace 1 for gasifying a combustible material to generate first gas G2 and second gas G1 both entraining particles; an heat recovery apparatus 3 for receiving the first gas G2 generated in the fluidized bed gasification furnace 1 and allowing heat exchange between the first gas G2 and a heat receiving fluid to recover heat from the first gas G2; a melting furnace 2 for receiving the second gas G1 generated in the fluidized bed gasification furnace 1 and melting ash content therein; and a gas introduction passage for introducing gas G3 discharged from the melting furnace 2, together with particles also generated in the melting furnace 2, into the heat recovery apparatus 3 into which the first gas g2 has been introduced. The heat recovery apparatus for heat exchange with the first gas and the heat recovery apparatus for heat exchange with the mixed gas of the first gas and the second gas may be the same apparatus or different apparatuses.
In the apparatus for processing a combustible material, as shown in FIG. 5 for example, the fluidized bed gasification furnace 1 preferably comprises a pyrolysis chamber 21 for pyrolyzing the combustible material 34 to generate the second gas G1, a combustion chamber 22 for combusting char to generate the first gas G2, and a passage D,E for directing a fluidized medium from the combustion chamber 22 to the pyrolysis chamber 21.
The apparatus for processing a combustible material preferably further comprises, as shown in FIG. 3 for example, a passage for introducing the second gas G1 from the pyrolysis chamber 1-1 to the melting furnace 2; and a passage for introducing the first gas G2 from the combustion chamber 1-2 to the heat recovery apparatus 3.
In the apparatus for processing a combustible material, the heat recovery apparatus 3 preferably is a waste heat boiler.
In the apparatus for processing a combustible material, as shown in FIG. 3 for example, after the first gas G2 and the second gas G1 have been mixed and cooled to 450°C or lower, solid matter in the mixed gas is separated with a dust collector 5 and the separated solid matter is introduced into the melting furnace 2 and melted therein in the apparatus for processing a combustible material as recited in any one of Claims 12 to 16. Although the gas temperature after the cooling is 450°C or lower, it is preferably 350°C or lower, more preferably 300°C or lower, most preferably 250°C or lower.
Another apparatus for processing a combustible material comprises, as shown in FIG. 8 for example, a fluidized bed gasification furnace 1 for gasifying a combustible material to generate first gas G2 and second gas G1 both entraining particles; a solid separator 12 for trapping the particles in the first gas G2 generated in the fluidized bed gasification furnace 1; and a melting furnace 2 for combusting the second gas G1 generated in the fluidized bed gasification furnace 1 to melt the particles trapped by the solid separator 12 and to generate combustible gas G5. The solid separator for trapping the particles includes a device which separates solid matter from gas by the difference in density such as a cyclone and so on as well as a filter for filtering the first gas to tap the particles therein when the first gas entraining the particles passes through. In this configuration, no combustion product gas is introduced into the melting furnace and only large particles containing ash content are introduced into the melting furnace. Therefore, a combustible material having a low calorific value of, for example, 6 to 7 MJ/kg can be combusted at a high temperature of 1200°C or higher and the ash content can be melted without using auxiliary fuel.
The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed.

EFFECT OF THE INVENTION

As described above, according to the invention recited in the claims, the following excellent effects can be achieved.
Heat is recovered from the first gas entraining particles mostly with large particle sizes and then the first gas is mixed with the second gas entraining particles mostly with small particle sizes. Therefore, there can be provided a heat recovery method in which adhesion of particles, especially adhesion of the particles with small particle sizes which tend to adhere to a heat transfer surface, in the second gas to the heat transfer surface can be prevented by the grinding function to grind the heat transfer surface which the particles with large particle sizes in the first gas exhibit when colliding with the heat transfer surface.
The first gas from the fluidized bed gasification furnace is introduced into the heat recovery apparatus to recover heat therefrom, and the second gas from the fluidized bed gasification furnace is introduced into the melting furnace and gas discharged from the melting furnace is introduced into the heat recovery apparatus. Since the first gas is gas entraining particles mostly with large particle sizes, there can be provided a method for processing a combustible material in which adhesion of particles to a heat transfer surface can be prevented by the grinding function which the particles exhibit when colliding with the heat transfer surface.
The first gas entraining particles mostly with large particle sizes from the fluidized bed gasification furnace is introduced into the heat recovery apparatus to recover heat therefrom. Then the gas from which heat has been recovered is mixed with the second gas discharged from the melting furnace and entraining particles mostly with small particle sizes and heat is recovered from the mixture. Therefore, there can be provided a method for processing a combustible material in which adhesion of particles to a heat transfer surface can be further prevented by the grinding function which the particles with large particle sizes in the first gas exhibit when colliding with the heat transfer surface.
The second introduction port for receiving the second gas entraining particles mostly with small particle sizes is located downstream of the first introduction port for receiving the first gas entraining particles mostly with large particle sizes. Therefore, there can be provided a heat recovery apparatus in which adhesion of particles, especially the particles with small particle sizes in the second gas introduced through the second introduction port, which tend to adhere to a heat transfer surface can be prevented by the grinding function which the particles with large particle sizes in the first gas introduced through the first introduction port exhibit when colliding with the heat transfer surface. Also, since the first introduction port is located upstream of the second introduction port, the second gas entraining particles mostly with small particle sizes is introduced after the first gas entraining particles mostly with large particle sizes has been cooled, resulting in the prevention of formation of a region with high-temperature gas entraining particles with small particle sizes, which tend to adhere to the heat transfer surface.
The second gas generated in the fluidized bed gasification furnace is introduced into the melting furnace and gas discharged from the melting furnace is introduced into the heat recovery apparatus, which receives the first gas generated in the fluidized bed gasification furnace and entraining fine particles and recovers heat therefrom. Therefore, there can be provided an apparatus for processing a combustible material in which adhesion of particles, especially the fine particles with small particle sizes in the gas discharged from the melting furnace, which tend to adhere to a heat transfer surface, to the heat transfer surface can be prevented by the grinding function which the particles in the first gas exhibit when colliding with the heat transfer surface.
The second gas generated in the fluidized bed gasification furnace and entraining fine particles and particles with large particle sizes entrained in the first gas generated in the fluidized bed gasification furnace are introduced into the melting furnace and ash content is melted therein. Therefore, the ash content can be melted with a combustible material with a low calorific value without using auxiliary fuel.

BEST MODE FOR CARRYING OUT THE INVENTION

Description is hereinafter made of the embodiment of the present invention with reference to the drawings. FIG. 3 is a view illustrating the process flow of an apparatus for processing a combustible material according to the present invention. As shown in the drawing, the apparatus for processing a combustible material has a gasification furnace 1, a melting furnace 2, a boiler 3, a heat recovery device 4 such as an economizer or air preheater, a dust collector 5 such as a cyclone, a gas cooling tower 6, a bag filter 7, an inducing blower 8, a catalyst denitration tower 9 and a stack 10. As the gasification furnace 1, an integrated fluidized bed gasification furnace having a pyrolysis chamber 1-1 and a combustion chamber 1-2 is employed. To the gasification furnace 1 is connected a combustible material supplying device for supplying a combustible material from outside. The combustible material supplying device 36 has, for example, a hopper for receiving the combustible material, a screw for crushing the combustible material received by the hopper while transferring it to the gasification furnace 1, and a combustible material passage.
The combustible material is mainly supplied from the combustible material supplying means 36 to the pyrolysis chamber 1-1 side in the gasification furnace 1 and is pyrolyzed therein to generate pyrolysis gas, tar, char, fly ash and so on. Pyrolysis gas G1 entraining the tar, char, fly ash and so on among those generated, which do not remain in the fluidized bed, is all supplied to the melting furnace 2 and combusted at a high temperature of 1200°C or higher in the melting furnace 2. The ash content is melted and discharged out of the melting furnace 2 as molten slag.
The pyrolysis residue left in the fluidized bed of the pyrolysis chamber 1-1 of the gasification furnace 1 flows into the combustion chamber 1-2 together with a fluidized medium. In order to maintain the fluidized bed of the combustion chamber 1-2 at approximately 550°C to 700°C and a free board part above the fluidized bed at 850°C to 950°C, fluidizing air is supplied from under the furnace and secondary air is supplied to the part above the free board. The air ratio is maintained at one or higher as a whole to ensure complete combustion. Although only the pyrolysis residue flowing into the combustion chamber 1-2 through the pyrolysis chamber 1-1 may be combusted therein, the combustible material may be directly supplied to the combustion chamber 1-2 depending on the pyrolysis characteristics and combustion characteristics of the combustible material.
Combustion product gas G2 discharged from the combustion chamber 1-2 of the gasification furnace 1 flows into the boiler 3 at a temperature of 850°C to 950°C through a passage constituted of a pipe and so on, is cooled to approximately 700°C, and is mixed with combustion product gas G3 at a high temperature discharged from the melting furnace 2. At this time, the mixing is conducted at such a point that the temperature of the mixed gas at the mixing point does not exceed 1100°C, preferably 1050°C, more preferably 1000°C. The temperature of the mixed gas must be the above-mentioned temperature or lower since some of the ash content entrained in the mixed gas may be melted to cause a trouble of adhesion to a boiler pipe or inner surfaces of the boiler 3 when the temperature of the mixed gas is too high. The temperature of the mixed gas must be 400°C or higher, preferably 500°C or higher since some of the tar in the mixed gas may condense to cause a trouble of adhesion to a boiler pipe or inner surfaces of the boiler 3 when the temperature of the mixed gas is too low.
The mixed combustion product gas G4 is cooled to approximately 450°C in the boiler 3 and further cooled to approximately 200°C in the heat recovery device 4 such as an economizer or air preheater, and then is subjected to dust removal in the dust collector 5 such as a cyclone. The above devices are connected by passages for the combustion product gas constituted of pipes and so on. Ash 11 collected by the dust collector 5 is returned to the melting furnace 2 through a passage constituted of a pipe and so on and melted in the melting furnace 2. The heat exchanger such as an economizer or air preheater may be omitted. In this case, the dust collection is performed at a temperature of 450°C or lower. The dust correction is preferably performed at a temperature of 350°C or lower, more preferably at 300°C or lower, most preferably at 250°C or lower. It is because inexpensive carbon steel can be used as the material for the dust collector and because the corrosion condition can be much less strict that a condition of 350°Cor lower is preferred. As the temperature is lowered to 300°C or lower and further lowered to 250°C or lower, the possibility that low-melting point metals exist in a solid state becomes higher. Therefore, troubles in the dust collector caused by low-melting point metals is less likely to occur. Although the combustion product gas G4 after the dust collection passes through the gas cooling tower 6 and is subjected to final dust collection in the bag filter 7 in this apparatus for processing a combustible material, the gas cooling tower 6 can be omitted in many cases in the present invention.
Combustion product gas generated by combusting a combustible material such as municipal waste, waste plastic, shredder dust, construction waste, waste tires entrains particles of ash content. The size of the particles is determined by various factors such as physical nature of the material to be combusted, chemical reactions induced by combustion reactions, and a rise of combustion product gas. In general, the ash generated by combusting municipal waste is particles with particle sizes ranging from a few dozens of microns to approximately 100 microns although it depends on the type of the incinerator. However, most of the ash particles entrained in the combustion product gas having passed through the melting furnace 2 are fine particles with particle sizes of 10 micron or less.
Fluidized bed incinerators, which had been employed in a large number of incineration facilities for municipal waste before gasification melting furnaces were commercialized, utilized highly reliable incineration technologies. Since no melting furnace was used, the ash particles in the exhaust gas to be introduced into an exhaust gas processing step included a large amount of silica, alumina and calcia components and had relatively large particle sizes. Therefore, only a small amount of ash adhered to the heat transfer surfaces of the devices for use in a heat recovery step such as a boiler, economizer and air preheater and no serious problem occurred.
Since the combustion product gas G2 discharged from the combustion chamber 1-2 of the gasification furnace 1 in the apparatus for processing a combustible material of this embodiment does not pass through the melting furnace 2, the ash particles in the combustion product gas G2 have generally the same properties, shape and size as the ash particles in combustion product gas discharged from a conventional fluidized bed incinerator and have large particle sizes. Therefore, the ash particles have little possibility of causing a trouble by adhering to the heat transfer surfaces of the devices for use in a heat recovery step such as the boiler 3 and the heat recovery device 4 such as an economizer or air preheater.
The pyrolysis gas G1 from the pyrolysis chamber 1-1 of the gasification furnace 1 is introduced into the melting furnace 2 through a passage constituted of a pipe and so on and is combusted therein. Since the combustion product gas G3 discharged from the melting furnace 2 has passed through the melting furnace 2, the combustion product gas entrains fine ash particles as in the case with combustion product gas discharged from a conventional gasification melting furnace. According to the result of an experiment conducted by the present inventors and so on, when municipal waste is processed in the gasification furnace 1 as an integrated fluidized bed gasification furnace, the ratio between the amount of the pyrolysis gas G1 from the pyrolysis chamber 1-1 and the amount of combustion product gas G2 from the combustion chamber 1-2 is approximately 1:3, that is, the amount of the combustion product gas G2 from the combustion chamber 1-2 is greater. Therefore, the ash particles in the gas mixed in the boiler 3 has a particle size distribution which is relatively close to that of gas from a conventional fluidized bed incinerator and has little possibility of causing a trouble by adhering to the heat transfer surfaces of the devices for use in the heat recovery step such as the boiler 3 and the heat recovery device 4 such as an economizer or air preheater.
As described before, the combustion product gas G3 discharged from the melting furnace 2 entrains ash particles mostly with small particle sizes. Since the small-size ash particles in the combustion product gas G3 tend to adhere to the heat transfer surface of the boiler 3, the adhesion of ash to the heat transfer surface is promoted in the case the combustion product gas G3 is solely introduced into the boiler 3. In this apparatus, however, the combustion product gas G2 discharged from the combustion chamber 1-2 of the gasification furnace 1 is also introduced into the boiler 3. Since the combustion product gas G2 entrains mostly large-size ash particles, the large-size ash particles exhibit a function of grinding the part of the heat transfer surface when the large-size ash particles collide with the heat transfer surface, and the large-size ash particles have an effect of preventing adhesion of ash particles. Therefore, when the combustion product gas G2 from the combustion chamber 1-2 and the combustion product gas G3 from the melting furnace 2 are introduced into the boiler 3, the combustion product gas G2 must be mixed with the combustion product gas G3 before introduction into the boiler 3 or the introduction port for the combustion product gas G2 must be located upstream of the introduction port for the combustion product gas G3 so that the combustion product gas G2 can be introduced at a point upstream of the point at which the combustion product gas G3 is introduced in order to prevent the formation of a region in which the combustion product gas G3 entraining small-size ash particles exists solely.
When the introduction port for the combustion product gas G2 is located upstream of the introduction port for the combustion product gas G3, the combustion product gas G3 at a high temperature from the melting furnace 2 is mixed after the combustion product gas G2 from the combustion chamber 1-2 has been cooled in the boiler 3. Consequently, the formation of a region with high-temperature gas entraining molten slag particles which easily adhere to the heat transfer surface can be prevented as much as possible.
FIG. 4 is a view illustrating the process flow of another apparatus for processing a combustible material according to the present invention. As shown in the drawing, in this apparatus, ash 13 trapped by a bag filter 12 as a solid separator located downstream of the gas cooling tower 6 is supplied to the melting furnace 2 and melted therein. A solid separator such as a cyclone may be provided instead of the bag filter 12. In this case, when all the trapped ash 13 is supplied to the melting furnace 2, there is a possibility that fine particles of ash may be confined and circulated within the system. Thus, some ash 13a is taken out of the ash 13 by operation of control valves V1 and V2. Activated carbon 14 is added to the combustion product gas G4 discharged from the bag filter 12 to cause the activated carbon 14 to adsorb harmful substances, and the activated carbon 14 having adsorbed the harmful substances is trapped and removed by a bag filter 7.
FIG. 5 is a view illustrating an example of the constitution of an integrated fluidized bed gasification furnace as an example of the gasification furnace 1. The gasification furnace 1 has a pyrolysis chamber 21 (corresponding to the pyrolysis chamber 1-1), a combustion chamber 22 (corresponding to the combustion chamber 1-2), and a heat recovery chamber 23. A combustible material 34 supplied to the pyrolysis chamber 21 is pyrolyzed while being agitated by a fluidized medium revolving in the pyrolysis chamber 21 as indicated by arrows F in the drawing to generate pyrolysis gas, tar, char, fly ash and so on. Pyrolysis gas G1 entraining the tar , char, fly ash and so on flows into the melting furnace 2 as shown in FIG. 3 and FIG. 4. Unpyrolyzed residues such as tar, char, and so on left in the fluidized bed of the pyrolysis chamber 21 flow into a combustion chamber 22 through an opening 26 of a partition wall 25 together with a fluidized medium as indicated by an arrow A. The unpyrolyzed residues such as char having flown from the pyrolysis chamber 21 into the combustion chamber 22 are combusted in the combustion chamber 22 to generate combustion product gas G2, and the fluidized medium is heated by the combustion heat. The combustion product gas G2 flows into the boiler 3 as shown in FIG. 3 and FIG. 4.
The fluidized medium heated by the combustion of the unpyrolyzed residues such as tar and char in the combustion chamber 22 flows into the heat recovery chamber 23 over the upper end of a partition wall 24 as indicated by an arrow B and has its heat absorbed by an immersed heat-transfer pipe 27 placed below an interface in the heat recovery chamber 23. After having been cooled, the fluidized medium flows again into the combustion chamber 22 through a lower opening 28 of the partition wall 24 as indicated by an arrow C. The fluidized medium heated in the combustion chamber 22 flows into a settling chamber between a partition wall 29 and a partition wall 30 over an upper end of the partition wall 29 as indicated by an arrow D and then flows into the pyrolysis chamber 21 through a lower opening 31 of the partition wall 30 as indicated by an arrow E. As described above, a fluidized medium passage is formed in the gasification furnace 1. The flow of the fluidized medium is controlled by fluidizing gases 32 and 33.
FIG. 6 is a view illustrating an example of the constitution of a twin-tower fluidized bed type fluidized bed gasification furnace as an example of the gasification furnace 1. As shown in the drawing, this gasification furnace 1 has a pyrolysis fluidized bed furnace 41 (corresponding to the pyrolysis chamber 1-1) and a combustion fluidized bed furnace 42 (corresponding to the combustion chamber 1-2) arranged side by side. Both the fluidized bed furnaces are communicated by two sloped pipes 43 and 44, and a fluidized medium is circulated between the beds through the sloped pipes 43 and 44 so that the amount of heat necessary for pyrolysis can be made up for.
That is, when a combustible material is supplied to the pyrolysis fluidized bed furnace 41, the combustible material is pyrolyzed to generate pyrolysis gas, tar, char, fly ash and so on. Pyrolysis gas G1 entraining the char, fly ash and so on flows into the melting furnace 2 as shown in FIG. 3 and FIG. 4. Unpyrolyzed residues such as char left in the fluidized bed of the pyrolysis fluidized bed furnace 41 flow into the combustion fluidized bed furnace 42 through the sloped pipe 43 together with a fluidized medium and are combusted therein to generate combustion product gas G2, and the fluidized medium is heated by the combustion heat. The heated fluidized medium flows into the pyrolysis fluidized bed furnace 41 through the sloped pipe 44 and is used as a source of heat for pyrolysis of the combustible material.
The combustion product gas G2 is supplied to the boiler 3 as shown in FIG. 3 and FIG. 4. In this twin-tower fluidized bed type fluidized bed gasification furnace, since no combustion product gas is entrained in the pyrolysis gas G1, pyrolysis gas G1 with a high calorific value can be obtained and the gas is supplied to the melting furnace. Therefore, even a combustible material with a low calorific value of, for example, 6 to 7 MJ/kg can be combusted at a high temperature of 1200°C or higher in the melting furnace without using auxiliary fuel and ash content can be melted. Gas free of oxygen such as water vapor, carbon dioxide gas, or nitrogen gas is used as fluidizing gas 45 for the fluidized bed of the pyrolysis fluidized bed furnace 41, and gas containing oxygen such as air is used as fluidizing gas 46 for the fluidized bed of the combustion fluidized bed furnace 42.
FIG. 7 is a view illustrating an example of the constitution of the melting furnace 2. The melting furnace 2 has a primary combustion chamber 51, a secondary combustion chamber 52, and a tertiary combustion chamber 53. As shown in FIG. 3 and FIG. 4, the pyrolysis gas G1 flows into the primary combustion chamber 51 of the melting furnace 2 from a gasification furnace 1, and gas for combustion 55 (air, oxygen-enriched air, or oxygen) flows into the primary combustion chamber 51 as well. The pyrolysis gas G1 and the gas for combustion 55 are mixed with each other and form a swirling flow. The mixture is combusted and subjected to high-temperature combustion (1200°C to 1400°C, preferably 1350 °C) while it is flowing into the secondary combustion chamber 52. Combustion product gas G3 is mixed with gas 55 for combustion in the tertiary combustion chamber 53, and uncombusted matter in the gas are combusted completely therein and discharged as combustion product gas G3. By the high-temperature combustion, the ash content entrained in the pyrolysis gas G1 and the ash 13 trapped from the combustion product gas G2 and supplied to the melting furnace 2 are melted and discharged out of the furnace through a slag discharge port 57 as molten slag 56. The discharge of the molten slag 56 out of the system can be made by dropping the molten slag 56 into a water tank placed under the slag discharge port 57. The molten slag 56 is cooled and pulverized in the water tank into granular slag. The granular slag having sunk in the water tank is transported out of the system on a conveyor installed in the water tank. The gas G3 in the melting furnace is water-sealed by water in the water tank and cannot leak out of the system.
FIG. 8 is a view illustrating the process flow of another apparatus for processing a combustible material according to the present invention. As shown in the drawing, in this apparatus, ash 13 trapped by a bag filter 12 as a solid separator located downstream of the gas cooling tower 6 is supplied to the melting furnace 2 and melted therein as in the case with FIG. 4. A solid separator such as a cyclone may be provided instead of the bag filter 12. In this case, when all the trapped ash 13 is supplied to the melting furnace 2, fine particles of ash may be confined and circulated within the system. Thus, some ash 13a is taken out of the ash 13 by operation of control valves V1 and V2.
The melting furnace 2 is a melting furnace for obtaining low-calorie (4 to 6 kJ/Nm³ (dry)) or intermediate-calorie (10 to 19 kJ/Nm³ (dry)) gas from the pyrolysis gas G1 introduced from the pyrolysis chamber 1-1 of the gasification furnace 1. When the pyrolysis gas G1 from the pyrolysis chamber 1-1 flows into the melting furnace 2 and is converted to high-temperature gas at 1300°C or higher, the char and tar entrained therein are completely gasified and the ash content is discharged out of the system as molten slag. Here, gases selected from oxygen-enriched air, steam, oxygen and a mixed gas thereof are supplied to the melting furnace 2 individually or mixedly as gasifying gases . When the total amount of oxygen in the gasifying gases is limited, in conformity with that of the pyrolysis gas G1, within the range of 0.1 to 0.6 (the ratio of oxygen in the melting furnace) of the theoretical amount of oxygen required to combust the material to be processed completely specified as 1, low-calorie or intermediate-calorie combustible gas G5 as described above can be obtained at the melting furnace 2.
The low-calorie or intermediate-calorie combustible gas G5 contains a large amount of useful gas components such as carbon monoxide CO and hydrogen H₂. When such combustible gas G5 from the melting furnace 2 is passed through a heat recovery device 15 such as a boiler to recover heat therefrom and passed through a scrubber 16, gas 17 as industrial fuel gas or raw materials for chemical industry can be obtained.
Also, a method for processing a combustible material has: a pyrolysis step of pyrolyzing a combustible material at a temperature of 350°C or higher to obtain char and pyrolysis gas; a combustion step of combusting unpyrolyzed residues, tar and char generated in the pyrolysis step at a temperature of 500°C or higher; a melting combustion step of combusting the pyrolysis gas generated in the pyrolysis step at 1200°C or higher and melting ash content entrained in the pyrolysis gas; a heat recovery step of recovering sensible heat from the combustion product gas discharged in the combustion step until the combustion product gas reaches 450 °C or lower; and a dust collection step of trapping ash content entrained in the combustion product gas at a point downstream of the heat recovery step, and the ash content trapped in the dust collection step is supplied to the melting combustion step and melted therein.
In such a method for processing a combustible material, since the combustion product gas discharged in the combustion step does not pass through a melting furnace, the ash particles in the combustion product gas have generally the same properties, shape and size as the ash particles in the combustion product gas discharged from a conventional fluidized bed incinerator and have large particle sizes. Therefore, the ash particles have little possibility of causing a trouble by adhering to the heat transfer surfaces of heat recovery apparatus even when heat is recovered from the combustion product gas in the heat recovery step.
Also, the above method for processing a combustible material is characterized in that the pyrolysis step and the combustion step are both conducted in a fluidized bed furnace, and the amount of heat necessary for the pyrolysis in the pyrolysis step is obtained from the sensible heat of a fluidized medium in the fluidized bed furnace in which the combustion step is conducted.
Since the amount of heat necessary for the pyrolysis in the pyrolysis step is obtained from the sensible heat of a fluidized medium in the fluidized bed furnace in which the combustion step is conducted as described above, there is no need for an oxygen generator or the like as a supplying source of oxygen for combustion or auxiliary combustion, and the running cost and initial cost can be reduced.
Also, the above method for processing a combustible material is characterized in that the pyrolysis step is maintained at 650°C or lower, preferably 600°C or lower, more preferably 550°C or lower, and the temperature in the combustion step is maintained at 900°C or lower, preferably 800°C or lower, more preferably 700°C or lower.
To pyrolyze and gasify a combustible material such as municipal waste stably with little fluctuation, the pyrolysis and gasification are preferably performed at a low temperature of 650°C or lower as described above. When the pyrolysis and gasification are performed at 550°C or lower, they can be performed more stably. It is also preferred to maintain the pyrolysis step at a low temperature to combust a combustible material such as municipal waste stably with little fluctuation. The combustion is preferably performed at a low temperature of 700°C or lower. At a high temperature of 900°C or higher, there arises a problem in the heat resistance and so on of metal parts, especially, of the dispersion nozzle or the like. The lower limit of the temperature in the pyrolysis step depends on the type of the combustible material. For example, when the combustible material is only biomass, the lower limit is 280°C or higher, preferably 300°C or higher, since the decomposition temperature of typical lignin is 280°C. When plastic is contained in the combustible material, the lower limit is 390°C or higher, preferably 400°C or higher, since the decomposition temperature of typical high-density polyethylene HDPE is 390°C.
Also, an apparatus for processing a combustible material has: a pyrolysis chamber for pyrolyzing a combustible material at a temperature of 350°C or higher to obtain char and pyrolysis gas; a combustion chamber for combusting unpyrolyzed residues, tar and char generated in the pyrolysis chamber at a temperature of 500°C or higher; a melting furnace for combusting the pyrolysis gas generated in the pyrolysis chamber at 1200°C or higher and melting ash content entrained in the pyrolysis gas; a heat recovery apparatus for recovering sensible heat from combustion product gas discharged from the combustion chamber until the combustion product gas reaches 450°C or lower; and a dust collector for trapping ash content entrained in the combustion product gas at a point downstream of the heat recovery apparatus, and the ash content trapped by the dust collector is supplied to the melting furnace and melted therein.
Since the combustion product gas discharged from the combustion chamber does not pass through the melting furnace as described above, the ash particles in the combustion product gas have generally the same properties, shape and size as the ash particles in the combustion product gas discharged from a conventional fluidized bed incinerator and have large particle sizes. Therefore, the ash particles have little possibility of causing a trouble by adhering to the heat transfer surfaces even when heat is recovered from the combustion product gas in the heat recovery apparatus. Also, since ash content trapped at a point downstream of the heat recovery apparatus by the dust collector is supplied to the melting furnace, low-boiling point substances and metal salts pulverized into fine particles in, for example, a cyclone used as a dust collector are trapped and cannot be circulated. Therefore, the slag conversion rate can be improved.
The above apparatus for processing a combustible material is characterized in that the pyrolysis chamber and the combustion chamber are both constituted of a fluidized bed furnace.
Since the pyrolysis chamber and the combustion chamber are both constituted of a fluidized bed furnace as described above, the combustible material can be stably pyrolyzed and gasified in the pyrolysis chamber. Also, since the combustion chamber functions as a fluidized bed incinerator, combustion product gas from the combustion chamber has generally the same properties, shape and size as the ash particles in the combustion product gas discharged from a conventional fluidized bed incinerator and has large particle sizes. Therefore, the combustion product gas has little possibility of causing a trouble by adhering to the heat transfer surfaces of the devices for use in the heat recovery step even when heat is recovered from the combustion product gas in the heat recovery step.
The above apparatus for processing a combustible material is characterized in that a fluidized medium is circulating between the fluidized bed furnace constituting the pyrolysis chamber and the fluidized bed furnace constituting the combustion chamber.
Since a fluidized medium is circulating between the fluidized bed furnace constituting the pyrolysis chamber and the fluidized bed furnace constituting the combustion chamber, unpyrolyzed residues, tar and char left in the fluidized bed of the pyrolysis chamber flow into the combustion chamber together with the fluidized medium and the unpyrolyzed residues, tar and char are combusted in the combustion chamber. The fluidized medium in the fluidized bed of the combustion chamber heated by the combustion flows into the pyrolysis chamber and is used as heat source for pyrolysis gasification.
The above apparatus for processing a combustible material is characterized in that water vapor, carbon dioxide gas, nitrogen gas, and combustion exhaust gas are used as fluidizing gases for the fluidized bed of the fluidized bed furnace constituting the pyrolysis chamber.
Since water vapor, carbon dioxide gas, nitrogen gas, or the like are used as fluidizing gases for the fluidized bed of the fluidized bed furnace constituting the pyrolysis chamber, partial combustion of the combustible material supplied to the pyrolysis chamber does not occur and heating of the fluidized medium caused by the combustion does not occur. Therefore, the heat of the fluidized medium from the combustion chamber can be absorbed effectively. Also, partial combustion of the combustible material in the pyrolysis chamber does not occur, no combustion product gas is contained in the pyrolysis gas and gas with a high calorific value can be obtained from the pyrolysis chamber. Since the gas is supplied to the melting furnace, even a combustible material with a low calorific value of, for example, 6 to 7 MJ/kg can be combusted at a high temperature of 1200°C or higher without using auxiliary fuel in the melting furnace and ash content can be melted.
combustible material in the pyrolysis chamber does not occur, no combustion product gas is contained in the pyrolysis gas and gas with a high calorific value can be obtained from the pyrolysis chamber. Since the gas is supplied to the melting furnace, even a combustible material with a low calorific value of, for example, 6 to 7 MJ/kg can be combusted at a high temperature of 1200°C or higher without using auxiliary fuel in the melting furnace and ash content can be melted.
The above example is one embodiment of the present invention, and the inventions recited in the claims are not limited thereto and can be modified within the scope of the same technical ideas as those of the inventions recited in the claims.

BRIEF DESCRIPTION OF DRAWINGS

DESCRIPTION OF REFERENCE NUMERALS

1:: gasification furnace
2:: melting furnace
3:: boiler
4:: heat recovery device
5:: dust collector
6:: gas cooling tower
7:: bag filter
8:: inducing blower
9:: catalyst denitration tower
10:: stack
11:: ash
12:: bag filter (solid separator)
13:: ash
14:: activated carbon
15:: boiler
16:: scrubber
17:: raw material gas
21:: pyrolysis chamber
22:: combustion chamber
23:: heat recovery chamber
24:: partition wall
25:: partition wall
26:: opening
27:: immersed heat-transfer pipe
28:: lower opening
29:: partition wall
30:: partition wall
31:: lower opening
32:: fluidizing gas
33:: fluidizing gas
36:: combustible material supplying device
41:: pyrolysis fluidized bed furnace
42:: combustion fluidized bed furnace
43:: sloped pipe
44:: sloped pipe
45:: fluidizing gas
46:: fluidizing gas
51:: primary combustion chamber
52:: secondary combustion chamber
53:: tertiary combustion chamber
56:: molten slag
57:: slag discharge port

Claims

A heat recovery method, comprising the steps of:
recovering heat using a heat recovery apparatus (3) from a first gas (G2) entraining particles with large particle sizes; and

recovering heat using the heat recovery apparatus (3) from a mixed gas, wherein a second gas (G3) entraining particles with small particle sizes is mixed with the first gas (G2) from which heat has been recovered to form the mixed gas,

supplying a combustible material (34) to a pyrolysis chamber (1-1, 21) having a fluidized bed in which a fluidized medium is revolving, and pyrolyzing the combustible material (34) in the fluidized bed, to generate char and pyrolysis gas (G1) entraining particles including ash;

combusting the char in a fluidized bed in a combustion chamber (1-2, 22) having the fluidized bed in which a fluidized medium is revolving, to generate the first gas (G2); and

generating the second gas (G3) by introducing the pyrolysis gas (G1) into a melting furnace (2) and melting the ash;

wherein the first gas (G2) is introduced into the heat recovery apparatus (3), so that the first gas (G2) is introduced into the heat recovery apparatus (3) with the particles in the first gas (G2),

wherein the second gas (G3) is introduced into the heat recovery apparatus (3) at a downstream of flow of the first gas (G2) in the heat recovery apparatus (3) so that the second gas (G3) is mixed with the first gas (G2); and

the second gas (G3) is mixed with the first gas (G2) at a downstream of flow of the first gas (G2) in the heat recovery apparatus (3).
The heat recovery method as recited in Claim 1, further comprising the step of:
introducing the fluidized medium from the combustion chamber (1-2, 22) to the pyrolysis chamber (1-1, 21).
The heat recovery method as recited in any one of Claims 1 or 2, further comprising the steps of:
cooling the mixed gas to 450°C or lower;

separating solid matter from the cooled gas with a dust collector (5); and

introducing the separated solid matter into the melting furnace (2) and melting the solid matter therein.
The heat recovery method as recited in any one of Claims 1 to 3, further comprising the step of:
introducing the first gas (G2) and the second gas (G3) in the heat recovery apparatus (3) so that the first gas (G2) and the second gas (G3) are flowing in the heat recovery apparatus (3) first in a downward direction with respect to gravity and then in an upward direction with respect to gravity after a change of direction at the bottom of the heat recovery apparatus (3).
An apparatus for processing a combustible material comprising:
heat recovery apparatus (3) having:
a first introduction port for introducing a first gas (G2) ;

a second introduction port for introducing a second gas (G3) entraining particles, the second introduction port being located downstream of the first introduction port along a flowing direction of the first gas (G2) introduced through the first introduction port;

a discharge port for discharging gas from which heat has been recovered; and

a heat transfer surface for allowing heat exchange between the first and second gases (G2, G3);

a pyrolysis chamber (1-1, 21) having a fluidized bed in which a fluidized medium is revolving, and pyrolyzing a combustible material (34) in the fluidized bed, to generate char and pyrolysis gas (G1) entraining particles including ash;

a combustion chamber (1-2, 22) having a fluidized bed in which a fluidized medium is revolving, to combust the char in the fluidized bed and generate the first gas (G2), the char having been generated in the pyrolysis chamber (1-1, 21);

a melting furnace (2) to generate the second gas (G3) by introducing the pyrolysis gas (G1) thereinto and melt the ash;

a gas introduction passage connected to the second introduction port for introducing the second gas discharged from the melting furnace (2) into the heat recovery apparatus (3);

a passage connected to the first introduction port for introducing the first gas (G2) into the heat recovery apparatus (3), so that the first gas (G2) is introduced into the heat recovery apparatus (3) with the particles in the first gas (G2).
The apparatus for processing a combustible material as recited in Claim 5, further comprising:
a second heat recovery apparatus (4) for cooling a mixed gas of the first gas (G2) and the second gas (G3) to 450°C or lower , after the first gas (G2) and the second gas (G3) have been mixed ,

a dust collector (5) for separating solid matter in the mixed gas; and

a dust passage for introducing the separated solid into the melting furnace (2) to melt the solid matter therein.
The apparatus for processing a combustible material as recited in Claim 5 or 6, further comprising:
a passage for directing the fluidized medium from the combustion chamber (1-2, 22) to the pyrolysis chamber (1-1, 21) .
The apparatus for processing a combustible material as recited in Claim 6 or 7, wherein the heat recovery apparatus (3) is constituted so that the first gas (G2) and the second gas (G3) are introduced in the heat recovery apparatus (3) so that the first gas (G2) and the second gas (G3) flow in the heat recovery apparatus (3) first in a downward direction with respect to gravity and then in an upward direction with respect to gravity after a change of direction at the bottom of the heat recovery apparatus (3).
The apparatus for processing a combustible material as recited in any one of Claims 5 to 8,
wherein the heat recovery apparatus (3) is a waste heat boiler.