WO2004070271A1

WO2004070271A1 - Gasification and slagging combustion system and method

Info

Publication number: WO2004070271A1
Application number: PCT/JP2004/001142
Authority: WO
Inventors: Ryuichi Ishikawa; Chikao Goke
Original assignee: Ebara Corporation
Priority date: 2003-02-07
Filing date: 2004-02-04
Publication date: 2004-08-19
Also published as: KR101044421B1; TW200424480A; KR20050097991A; JP3913684B2; EP1590604A1; JP2004263886A

Abstract

A gasification and slagging combustion system has a fluidized-bed gasification furnace (11) for gasifying wastes (A) and a slagging combustion furnace (31) for combusting and melting a product produced by the gasification furnace (11). The gasification and slagging combustion system includes an incombustible discharging device (21) for delivering an incombustible contained in the wastes (A) from the gasification furnace (11), and a blower (1a) for drawing air and a combustible gas which has leaked from the gasification furnace (11) through the incombustible discharging device (21) so as to form a mixed gas of the leaked combustible gas and the air. The gasification and slagging combustion system also includes blowers (41, 42) for supplying air and the mixed gas to the gasification furnace (11) and the slagging combustion furnace (31), respectively, and a mixed gas delivery passage (65) for supplying the mixed gas from the blower (1a) to the blowers (41, 42).

Description

DESCRIPTION

GASIFICATION AND SLAGGING COMBUSTION SYSTEM AND METHOD

Technical Field The present invention relates to a gasification and slagging combustion system for treating wastes such as municipal wastes, refuse-derived fuel (RDF), waste plastics, waste fiber-reinforced plastics (waste FRP), biomass wastes, automobile wastes, and waste oil. More particularly, the present invention relates to a gas treatment apparatus and method for treating a combustible gas which leaks through an incombustible discharge line provided at a furnace bottom of a fluidized-bed gasification furnace as a first stage of a gasification and slagging combustion system.

Background Art FIG. 1 shows a conventional fluidized-bed gasification furnace 11. As shown in FIG. 1, the fluidized-bed gasification furnace 11 has an air diffuser plate disposed on a bottom 11a of the furnace. Combustion air B for partial combustion is supplied from the furnace bottom 11a to form a fluidized bed of a fluidized medium P above the air diffuser plate. Wastes A are supplied into the fluidized-bed gasification furnace 11 and fall into the fluidized bed. The wastes A are brought into contact with a fluidized medium P heated to 450 to 750°C and combustion air B, and immediately pyrolyzed to produce a combustible gas (containing combustible components), tar, and char.

The gas and gaseous tar produced by the pyrolysis are accompanied with fine particles of char and discharged from a discharge duct 1 lb provided at an upper portion of the fluidized-bed gasification furnace 11. Char having a large particle diameter, which is produced by the pyrolysis, is pulverized by active turbulent movement of a fluidized medium in the fluidized bed and partial combustion, and discharged from the discharge duct l ib together with the gas and tar. Incombustibles contained in the wastes, such as iron, aluminum, copper, and debris, are discharged together with the fluidized medium P from the furnace bottom 11a through a chute 12 and delivered to an incombustible treatment facility.

As shown in FIG. 1, a conventional incombustible treatment facility has an incombustible discharging device 21, a vibrating screen 23, a sand elevator 24, and a sand feed valve 25. A mixture of the incombustibles and the fluidized medium, which has been discharged from the bottom 11a of the fluidized-bed gasification furnace 11, is delivered through the chute 12 into the incombustible discharging device 21 and further delivered to the vibrating screen 23 by the incombustible discharging device 21. The vibrating screen 23 separates the mixture into incombustibles having a large particle diameter and a fluidized medium having a small particle diameter. The separated fluidized medium is delivered in a vertical direction by the sand elevator 24 and returned through the sand feed valve 25 to the fluidized-bed gasification furnace 11. The separated incombustibles having a large size, such as iron, aluminum, copper, and debris, are discharged from the vibrating screen 23. Valuable materials such as metal are recovered from the discharged incombustibles, and the rest of the incombustibles are landfilled.

Generally, a freeboard l ie of the fluidized-bed gasification furnace 11 is maintained under a negative pressure of about several tens of mm H₂0. When the fluidized medium P is fluidized in the fluidized bed, pressure loss is produced in a vertical direction of the fluidized bed, so that the pressure of the furnace bottom 11a becomes a positive pressure. Therefore, in order to prevent the combustible gas from leaking out of the system, it has been practiced to fill the chute 12 and the incombustible discharging device 21 with a mixture of a fluidized medium and incombustibles so as to provide material sealing effects. Further, a mechanical sealing device such as a double damper may additionally be provided between the incombustible discharging device 21 and the vibrating screen 23 to prevent leakage of the combustible gas more reliably. However, it is practically difficult to obtain complete sealing effects by such material sealing that the chute 11 and the incombustible discharging device 21 are filled with a mixture of a fluidized medium and incombustibles. Specifically, a gas flow is produced due to a pressure difference in a material sealing portion, thereby causing leakage of the combustible gas. Even if a double damper as a mechanical sealing device is provided, leakage of the combustible gas is caused by a differential pressure produced between upstream and downstream portions of the double damper during switching operations of the double damper. Furthermore, under operating conditions for high-temperature particles, it is technically difficult to obtain complete sealing effects by a double damper. Sealing effects of the double damper may become incomplete by engagement or the like to cause leakage of the combustible gas. Such a leaked combustible gas may contain a trace of toxic components. However, such a leaked combustible gas has heretofore been released to an atmosphere without any treatment or only with dust removal treatment. Thus, the leaked combustible gas remaining around the incombustible treatment facility may cause a working environment to be considerably deteriorated.

Disclosure of Invention The present invention has been made in view of the above drawbacks. It is, therefore, an object of the present invention to provide a gasification and slagging combustion system and method which can prevent a combustible gas discharged from a furnace bottom of a fluidized-bed gasification furnace through an incombustible discharging device from being released to an atmosphere and properly treat the combustible gas.

According to a first aspect of the present invention, there is provided a gasification and slagging combustion system having a fluidized-bed gasification furnace for gasifying wastes and a slagging combustion furnace for combusting and melting a product produced by the fluidized-bed gasification furnace. The gasification and slagging combustion system includes an incombustible discharging device for delivering an incombustible contained in the wastes from the fluidized-bed gasification furnace together with a fluidized medium, and a mixed gas drawing device for drawing air from an atmosphere and a combustible gas which has leaked from the fluidized-bed gasification furnace through the incombustible discharging device so as to form a mixed gas of the combustible gas and the air. The gasification and slagging combustion system also includes a combustion air supply device for supplying combustion air of wastes to the fluidized-bed gasification furnace and the slagging combustion furnace, and a mixed gas delivery passage for supplying the mixed gas from the mixed gas drawing device through the combustion air supply device to at least one of the fluidized-bed gasification furnace and the slagging combustion furnace.

Thus, the gasification and slagging combustion system has a combustion air supply device for supplying a mixed gas containing a combustible gas to at least one of a fluidized-bed gasification furnace and a slagging combustion furnace, and a mixed gas delivery passage for supplying the mixed gas to the combustion air supply device. Accordingly, the amount of combustible gas to be released to an atmosphere can be minimized, and thus the combustible gas can properly be treated. According to a second aspect of the present invention, there is provided a gasification and slagging combustion system having a fluidized-bed gasification furnace for gasifying wastes and a slagging combustion furnace for combusting and melting a product produced by the fluidized-bed gasification furnace. The gasification and slagging combustion system includes an incombustible discharging device for delivering an incombustible contained in the wastes from the fluidized-bed gasification furnace together with a fluidized medium, and a mixed gas drawing device for drawing air from an atmosphere and a combustible gas which has leaked from the fluidized-bed gasification furnace through the incombustible discharging device so as to form a mixed gas of the combustible gas and the air. The gasification and slagging combustion system also includes a mixed gas supply passage for supplying the mixed gas from the mixed gas drawing device to at least one of the fluidized-bed gasification furnace and the slagging combustion furnace.

With the above arrangement, a mixed gas containing a combustible gas can be introduced into at least one of a fluidized-bed gasification furnace and a slagging combustion furnace. Accordingly, the amount of combustible gas to be released to an atmosphere can be minimized, and thus the combustible gas can properly be treated.

The gasification and slagging combustion system may have a dust collector for removing dust from the mixed gas. In such a case, since dust can be removed from the mixed gas, the gasification and slagging combustion system can be operated stably for a long term. It is desirable that the dust collector be located upstream of the mixed gas drawing device. In this case, it is possible to prevent troubles regarding dust in the mixed gas drawing device such as a blower. The mixed gas drawing device may comprise a blower. In this case, the mixed gas containing the combustible gas can safely be treated in the gasification and slagging combustion system. This arrangement is suitable for a case in which a combustible gas to be treated contains a trace of toxic components. According to a third aspect of the present invention, there is provided a gasification and slagging combustion method. Wastes are gasified in a fluidized-bed gasification furnace. A product, which is produced in the fluidized-bed gasification furnace, is combusted and melted in a slagging combustion furnace. An incombustible contained in the wastes is discharged from the fluidized-bed gasification furnace together with a fluidized medium. A combustible gas which leaks from the fluidized-bed gasification furnace is drawn together with air from an atmosphere so as to form a mixed gas of the combustible gas and the air. The mixed gas is supplied together with combustion air of wastes to at least one of the fluidized-bed gasification furnace and the slagging combustion furnace.

Thus, the mixed gas containing the combustible gas, which has been treated, is supplied to at least one of the fluidized-bed gasification furnace and the slagging combustion furnace. Accordingly, the amount of combustible gas to be released to an atmosphere can be minimized, and thus the combustible gas can properly be treated. This method is suitable for a case in which a combustible gas to be treated contains a trace of toxic components.

According to a fourth aspect of the present invention, there is provided a gasification and slagging combustion method. Wastes are gasified in a fluidized-bed gasification furnace. A product, which is produced in the fluidized-bed gasification furnace, is combusted and melted in a slagging combustion furnace. An incombustible contained in the wastes is discharged from the fluidized-bed gasification furnace together with a fluidized medium. A combustible gas which leaks from the fluidized-bed gasification furnace is drawn together with air from an atmosphere so as to form a mixed gas of the combustible gas and the air. The mixed gas is supplied to at least one of the fluidized-bed gasification furnace and the slagging combustion furnace.

Thus, the mixed gas containing the combustible gas, which has been treated, is supplied to at least one of the fluidized-bed gasification furnace and the slagging combustion furnace. Accordingly, the amount of combustible gas to be released to an atmosphere can be minimized, and thus the combustible gas can properly be treated. This method is suitable for a case in which a combustible gas to be treated contains a trace of toxic components. Dust may be removed from the mixed gas. In this case, since dust can be removed from the mixed gas by a dust collector or the like, it is possible to prevent troubles regarding dust in the mixed gas drawing device such as a blower and perform gasification and slagging combustion stably for a long term. The above and other objects,- features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

Brief Description of Drawings

FIG. 1 is a block diagram showing a conventional fluidized-bed gasification furnace having an incombustible treatment facility;

FIG. 2 is a block diagram showing a gasification and slagging combustion system according to a first embodiment of the present invention; and FIG. 3 is a block diagram showing a gasification and slagging combustion system according to a second embodiment of the present invention.

Best Mode for Carrying Out the Invention

A gasification and slagging combustion system according to embodiments of the present invention will be described below with reference to FIGS. 2 and 3. Like or corresponding parts are designated by the same reference numerals throughout the drawings and will not be described repetitively.

FIG. 2 is a block diagram showing a gasification and slagging combustion system according to a first embodiment of the present invention. As shown in FIG. 2, the gasification and slagging combustion system has a fluidized-bed gasification furnace 11 for gasifying wastes A to produce a combustible gas, tar, and char, and a swirling-type slagging combustion furnace 31 for combusting and melting the combustible gas and tar produced by the fluidized-bed gasification furnace 11. The fluidized-bed gasification furnace 11 has a discharge duct l ib provided at an upper portion thereof, and the discharge duct is connected to the slagging combustion furnace 31. In the present embodiment, the slagging combustion furnace 31 has a primary combustion chamber 31a, a secondary combustion chamber 31b, and a tertiary combustion chamber 31c. The gasification and slagging combustion system also has an incombustible treatment facility including an incombustible discharging device 21, a vibrating screen 23, a sand elevator 24, a • sand feed valve 25, and an air supply passage 26 for drawing air from an atmosphere. Wastes A to be treated are supplied into the fluidized-bed gasification furnace 11 and pyrolyzed into a combustible gas, tar, and char in the fluidized bed maintained at 450 to 750°C. Most part of the combustible gas and tar produced by the pyrolysis is discharged from the discharge duct 1 lb together with char in the form of fine particles and introduced into the swirling-type slagging combustion furnace 31. Bulky incombustibles such as iron, aluminum, copper, and debris are withdrawn from a bottom 11a of the fluidized-bed gasification furnace 11 together with a fluidized medium and delivered through a chute 12 to the incombustible discharging device 21. A mixture of the incombustibles and the fluidized medium, which is delivered to the vibrating screen 23 by the incombustible discharging device 21, is separated into incombustibles having a large particle diameter and a fluidized medium having a small particle diameter by the vibrating screen 23. Valuable materials such as iron and aluminum are separated and recovered from the incombustibles having a large particle diameter by a recovery device. The rest of the incombustibles are landfilled. The fluidized medium having a small particle diameter is delivered upward in a vertical direction by the sand elevator 24 and returned through the sand feed valve 25 to the fluidized-bed gasification furnace 11. Thus, the separated fluidized medium is reused as a fluidized medium.

In the gasification and slagging combustion system according to the present embodiment, a freeboard l ie of the fluidized-bed gasification furnace 11 is normally maintained under a negative pressure of about several tens of mm H₂0. When a fluidized medium is fluidized in the fluidized-bed gasification furnace 11, pressure loss is produced in a vertical direction of the fluidized bed. Accordingly, the fluidized-bed gasification furnace 11 is operated so as to have a positive pressure of about 1500 mm H₂O at the furnace bottom 1 la. In order to prevent the combustible gas in the gasification furnace 11 from leaking out of the system, the chute 12 and/or the incombustible discharging device 21 are filled with a mixture of a fluidized medium and incombustibles so as to provide material sealing effects. However, complete sealing effects cannot be obtained by such material sealing, and thus a small amount of combustible gas would unavoidably leak to an atmosphere.

From this point of view, the gasification and slagging combustion system has a gas treatment apparatus 1 for treating the leaked combustible gas, which has a trace of toxic components, mixed with a large amount of air drawn from an atmosphere. Specifically, the gas treatment apparatus 1 treats a mixed gas of a combustible gas discharged from the bottom 11a of the fluidized-bed gasification furnace 11 through the chute 12 and the incombustible discharging device 21, and a large amount of air. The gasification and slagging combustion system also has a mixed gas delivery passage 65 for introducing the mixed gas, which contains a combustible gas, treated by the gas treatment apparatus 1.

The gas treatment apparatus 1 has a bag filter lb as a dust collector for removing dust from the mixed gas and a blower la as a mixed gas drawing device for drawing a combustible gas from the incombustible discharging device 21 and air from an atmosphere. The bag filter lb is provided upstream of the blower la. In order to prevent a combustible gas discharged from fluidized-bed gasification furnace 11 from leaking out of the system, as shown in FIG. 2, a line 61 is connected to an upper portion of the incombustible discharging device 21, and a line 62 is connected to a chute upstream of the vibrating screen 23. The sand elevator 24 has a suction port 24a provided at an upper portion thereof, and the suction port 24a is connected to a line 63. The lines 61, 62, and 63 are joined to a line 64, which is connected to the bag filter lb of the gas treatment apparatus 1. With these lines, a mixed gas of a combustible gas discharged from the fluidized-bed gasification furnace 11 and air is introduced into the gas treatment apparatus 1. With the above arrangement, it is possible to concentrate the combustible gas without leaking out of the system. Points from which the combustible gas is drawn are not limited to the illustrate example, and the combustible gas can be drawn from any points in the system as long as the combustible gas can be prevented from leaking out of the system. It is desirable and effective to draw the combustible gas near the incombustible discharging device 21 because the vicinity of the incombustible discharging device 21 has a high concentration of the combustible gas.

Air is introduced from an atmosphere through the air supply passage 26 and the vibrating screen 23 into the line 62 to dilute a combustible gas to be drawn. Thus, a drawn combustible gas is diluted by a large amount of air so as to maintain the mixed gas within an explosion limit. The mixed gas of the diluted combustible gas and air is supplied into the bag filter lb. After removal of dust by the bag filter lb, the mixed gas is introduced into the blower la.

The amount of air to be supplied into the line 62 should preferably be at least two times the amount of the leaked combustible gas, more preferably at least five times the amount of the leaked combustible gas. When the amount of air to be supplied is at least two times the amount of the leaked combustible gas, the combustible gas can substantially reliably be prevented from leaking out of the system. If the amount of air to be supplied is excessively small, then the temperature of the mixed gas is increased. Thus, the temperature of the combustible gas may be increased beyond an explosion limit to thereby cause explosion of the combustible gas by an ignition source. Therefore, a sufficient amount of air having a low temperature is required to be supplied so as to dilute the combustible gas sufficiently. When the amount of air to be supplied is at least five times the amount of the leaked combustible gas, leakage of the combustible gas can further reliably be prevented.

The mixed gas of the combustible gas and a large amount of air, which is drawn by the blower la, is supplied through the mixed gas delivery passage (pipe) 65 to a first suction line 51 and a second suction line 53, respectively. The first suction line 51 is connected to a fluidizing blower 41 (combustion air supply device) for supplying air to the fluidized-bed gasification furnace 11. The second suction line 53 is connected to a secondary fan 42 (combustion air supply device) for supplying air to the slagging combustion furnace 31. The fluidizing blower 41 and the secondary fan 42 draw air from waste pits. Thus, air having an unpleasant odor in the waste pits is prevented from leaking out of the system.

The mixed gas is mixed with air from the waste pits and then introduced through the first suction line 51 and the second suction line 53 into the fluidized-bed gasification furnace 11 and the slagging combustion furnace 31, respectively. Thus, the combustible gas which has leaked from the gasification furnace 11 is combusted at high temperatures in the fluidized-bed gasification furnace 11 and the slagging combustion furnace 31. Therefore, even if the combustible gas contains organic toxic components, the organic toxic components can completely be oxidized and decomposed in the fluidized-bed gasification furnace 11 and the slagging combustion furnace 31.

In FIG. 2, the mixed gas delivery passage 65 is connected to both of the first suction line 51 for the fluidizing blower 41 and the second suction line 53 for the secondary fan 42. However, the mixed gas delivery passage 65 may be connected to either one of the first suction line 51 for the fluidizing blower 41 and the second suction line 53 for the secondary fan 42. Alternatively, the mixed gas delivery passage 65 may bypass the blower 41 and fan 42 and may be connected directly to the fluidized-bed gasification furnace 11 and/or the slagging combustion furnace 31 to supply the mixed gas directly into the fluidized-bed gasification furnace 11 and/or the slagging combustion furnace 31. When the mixed gas is supplied to the slagging combustion furnace 31, equivalent effects can be expected whichever one of the primary combustion chamber 31a, the secondary combustion chamber 31b, and the tertiary combustion chamber 31c in the slagging combustion furnace 31 the mixed gas is supplied to.

FIG. 3 is a block diagram showing a gasification and slagging combustion system according to a second embodiment of the present invention. As shown in FIG. 3, the gasification and slagging combustion system has a double damper 22 as a mechanical sealing device located between an incombustible discharging device 21 and a vibrating screen 23. A line 62 is connected to a location downstream of the double damper 22 and upstream of the vibrating screen 23. A combustible gas and air are drawn through the line 62 to a bag filter lb. In this case, it is not necessary to draw from the incombustible discharging device 21. With a double damper 22 having a high sealing capability, a suction line from the incombustible discharging device 21, which is shown by the line 61 in FIG. 2, adversely forces a combustible gas to be drawn from the fluidized-bed gasification furnace 11. Other structures are the same as those shown in FG. 2.

When a mechanical sealing device such as a double damper is provided, the amount of leaked combustible gas can be reduced. When wastes having high heating values are treated, the produced combustible gas has a high concentration of combustible components. Therefore, such a mechanical sealing device is suitable in cases where wastes having high heating values are treated. Instead of a double damper, a triple damper or a sealing device having a plurality of gate valves may be employed as a mechanical sealing device.

As described above, according to embodiments of the present invention, the gasification and slagging combustion system has a gas treatment apparatus for treating a mixed gas containing a combustible gas, which leaks from a fluidized-bed gasification furnace through an incombustible discharging device, and air drawn from an atmosphere. The mixed gas drawn by a blower of the gas treatment apparatus is mixed with combustion air to be supplied to the fluidized-bed gasification furnace, or with combustion air to be supplied to a slagging combustion furnace. Alternatively, the mixed gas is introduced directly into at least one of the fluidized-bed gasification furnace and the slagging combustion furnace. Thus, the leaked combustible gas can effectively be treated in a proper manner. Further, since the mixed gas is allowed to pass through a high-temperature combustion region in the slagging combustion furnace, a trace of toxic components can be oxidized and decomposed.

Thus, according to the present invention, a gasification and slagging combustion system has a combustion air supply device for supplying a mixed gas containing a combustible gas to at least one of a fluidized-bed gasification furnace and a slagging combustion furnace, and a mixed gas delivery passage for supplying the mixed gas to the combustion air supply device. Accordingly, the amount of combustible gas to be released to an atmosphere can be minimized, and thus the combustible gas can properly be treated.

Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.

Industrial Applicability The present invention is suitable for use in a gasification and slagging combustion system for treating wastes such as municipal wastes, refuse-derived fuel (RDF), waste plastics, waste fiber-reinforced plastics (waste FRP), biomass wastes, automobile wastes, and waste oil.

Claims

1. A gasification and slagging combustion system comprising: a fluidized-bed gasification furnace for gasifying wastes; a slagging combustion furnace for combusting and melting a product produced by said fluidized-bed gasification furnace; an incombustible discharging device for delivering an incombustible contained in the wastes from said fluidized-bed gasification furnace together with a fluidized medium; a mixed gas drawing device for drawing air from an atmosphere and a combustible gas which has leaked from said fluidized-bed gasification furnace through said incombustible discharging device so as to form a mixed gas of the combustible gas and the air; a combustion air supply device for supplying combustion air of the wastes to said fluidized-bed gasification furnace and said slagging combustion furnace; and a mixed gas delivery passage for supplying the mixed gas from said mixed gas drawing device through said combustion air supply device to at least one of said fluidized-bed gasification furnace and said slagging combustion furnace.

2. The gasification and slagging combustion system as recited in claim 1, further comprising a dust collector for removing dust from the mixed gas.

3. The gasification and slagging combustion system as recited in claim 2, wherein said dust collector is disposed upstream of said mixed gas drawing device.

4. The gasification and slagging combustion system as recited in claim 1, wherein said mixed gas drawing device comprises a blower.

5. A gasification and slagging combustion system comprising: a fluidized-bed gasification furnace for gasifying wastes; a slagging combustion furnace for combusting and melting a product produced by said fluidized-bed gasification furnace; an incombustible discharging device for delivering an incombustible contained in the wastes from said fluidized-bed gasification furnace together with a fluidized medium; a mixed gas drawing device for drawing air from an atmosphere and a combustible gas which has leaked from said fluidized-bed gasification furnace through said incombustible discharging device so as to form a mixed gas of the combustible gas and the air; and a mixed gas supply passage for supplying the mixed gas from said mixed gas drawing device to at least one of said fluidized-bed gasification furnace and said slagging combustion furnace.

6. The gasification and slagging combustion system as recited in claim 5, further comprising a dust collector for removing dust from the mixed gas.

7. The gasification and slagging combustion system as recited in claim 6, wherein said dust collector is disposed upstream of said mixed gas drawing device.

8. The gasification and slagging combustion system as recited in claim 5, wherein said mixed gas drawing device comprises a blower.

9. A gasification and slagging combustion method comprising: gasifying wastes in a fluidized-bed gasification furnace; combusting and melting a product, which is produced by said gasifying, in a slagging combustion furnace; discharging an incombustible contained in the wastes from the fluidized-bed gasification furnace together with a fluidized medium; drawing air from an atmosphere and a combustible gas which leaks during said discharging so as to form a mixed gas of the combustible gas and the air; and supplying combustion air of the wastes and the mixed gas to at least one of the fluidized-bed gasification furnace and the slagging combustion furnace.

10. The method as recited in claim 9, further comprising removing dust from the mixed gas.

11. A gasification and slagging combustion method comprising: gasifying wastes in a fluidized-bed gasification furnace; combusting and melting a product, which is produced by said gasifying, in a slagging combustion furnace; discharging an incombustible contained in the wastes from the fluidized-bed gasification furnace together with a fluidized medium; drawing air from an atmosphere and a combustible gas which leaks during said discharging so as to form a mixed gas of the combustible gas and the air; and supplying the mixed gas to at least one of the fluidized-bed gasification furnace and the slagging combustion furnace.

12. The method as recited in claim 11, further comprising removing dust from the mixed gas.