U.S. patent application number 10/563434 was filed with the patent office on 2006-06-29 for gasification system.
Invention is credited to Hiroyuki Fujimura, Tatsuya Hasegawa, Kei Matsuoka, Norihisa Miyoshi, Takahiro Oshita, Seiichiro Toyoda.
Application Number | 20060137579 10/563434 |
Document ID | / |
Family ID | 34100869 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060137579 |
Kind Code |
A1 |
Fujimura; Hiroyuki ; et
al. |
June 29, 2006 |
Gasification system
Abstract
A gasification system has a gasification furnace (1) for
gasifying wastes to produce a combustible gas and a combustion
furnace (2) for combusting char and/or tar produced by gasification
in the gasification furnace (1). The gasification system also has a
return line for returning a combustion gas discharged from the
combustion furnace (2) to the gasification furnace (1) and the
combustion furnace (2).
Inventors: |
Fujimura; Hiroyuki; (Tokyo,
JP) ; Oshita; Takahiro; (Tokyo, JP) ; Miyoshi;
Norihisa; (Tokyo, JP) ; Toyoda; Seiichiro;
(Tokyo, JP) ; Matsuoka; Kei; (Tokyo, JP) ;
Hasegawa; Tatsuya; (Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
34100869 |
Appl. No.: |
10/563434 |
Filed: |
July 23, 2004 |
PCT Filed: |
July 23, 2004 |
PCT NO: |
PCT/JP04/10870 |
371 Date: |
January 5, 2006 |
Current U.S.
Class: |
110/245 ;
110/233 |
Current CPC
Class: |
F23J 15/006 20130101;
F23G 2203/502 20130101; Y02E 20/344 20130101; F23C 13/08 20130101;
F23G 2201/304 20130101; F23J 15/06 20130101; F23G 5/16 20130101;
F23G 5/0276 20130101; F23J 2217/50 20130101; F23G 5/006 20130101;
F23G 5/46 20130101; F23L 2900/07005 20130101; F23G 2202/101
20130101; F23G 5/027 20130101; Y02E 20/30 20130101; Y02E 20/34
20130101; F23G 2209/262 20130101; F23L 2900/07002 20130101; F23G
5/30 20130101; F23G 2201/303 20130101; F23G 2202/104 20130101; Y02E
20/363 20130101 |
Class at
Publication: |
110/245 ;
110/233 |
International
Class: |
F23G 5/00 20060101
F23G005/00; F23B 30/00 20060101 F23B030/00 |
Claims
1. A gasification system comprising: a gasification furnace for
gasifying a combustible to produce a combustible gas; a combustion
furnace for combusting char and/or tar produced by gasification in
said gasification furnace; and a return line for returning a
combustion gas discharged from said combustion furnace to said
gasification furnace and said combustion furnace.
2. The gasification system as recited in claim 1, wherein oxygen is
added to the combustion gas to be returned to said combustion
furnace.
3. The gasification system as recited in claim 1, wherein steam or
inert gas is supplied to said gasification furnace.
4. The gasification system as recited in claim 1, wherein the
combustion gas is supplied to a portion downstream of said
gasification furnace.
5. The gasification system as recited in claim 1, wherein the
combustion gas to be returned to said gasification furnace has an
oxygen concentration of 5% or less.
6. The gasification system as recited in claim 1, wherein said
gasification furnace has a temperature of 350 to 950.degree. C.
7. The gasification system as recited in claim 1, wherein said
combustion furnace has a temperature of 600 to 1000.degree. C.
8. The gasification system as recited in claim 1, further
comprising a slagging combustion furnace for melting ash by using a
portion of the combustible gas produced by gasification in said
gasification furnace.
9. The gasification system as recited in claim 8, wherein a
combustion gas discharged from said slagging combustion furnace is
returned to said combustion furnace.
10. The gasification system as recited in claim 1, further
comprising a water spray gas cooler for spraying water on the
combustion gas discharged from said combustion furnace.
11. The gasification system as recited in claim 1, further
comprising: a scrubber disposed in a line of the combustible gas
discharged from said gasification furnace; and a water spray gas
cooler for spraying water discharged from said scrubber on the
combustion gas discharged from said combustion furnace.
12. The gasification system as recited in claim 1, further
comprising a fluidizing gas heater for exchanging heat between the
combustion gas discharged from said combustion furnace and the
combustion gas to be returned to said gasification furnace and said
combustion furnace.
13. The gasification system as recited in claim 1, further
comprising a high-temperature furnace for pyrolyzing tar in the
combustible gas discharged from said gasification furnace.
14. The gasification system as recited in claim 1, wherein said
gasification furnace comprises a fluidized-bed furnace having a bed
material including at least one of silica sand and catalyst
particles.
15. The gasification system as recited in claim 1, wherein said
combustion furnace comprises a fluidized-bed furnace having a bed
material including at least one of silica sand and catalyst
particles.
16. The gasification system as recited in claim 1, further
comprising a gas cooling apparatus for cooling the combustible gas
discharged from said gasification furnace to remove moisture from
the combustible gas.
17. The gasification system as recited in claim 1, further
comprising a gas cooling apparatus for cooling the combustion gas
discharged from said combustion furnace to remove moisture from the
combustion gas.
18. A gasification system comprising: an integrated gasification
furnace including: a gasification chamber for gasifying a
combustible to produce a combustible gas; and a combustion chamber
for combusting char and/or tar produced by gasification in said
gasification chamber; and a return line for returning a combustion
gas discharged from said combustion chamber to said gasification
chamber and said combustion chamber.
19. The gasification system as recited in claim 18, wherein oxygen
is added to the combustion gas to be returned to said combustion
chamber.
20. The gasification system as recited in claim 18, wherein steam
or inert gas is supplied to said gasification chamber.
21. The gasification system as recited in claim 18, wherein the
combustion gas is supplied to a portion downstream of said
gasification chamber.
22. The gasification system as recited in claim 18, wherein the
combustion gas to be returned to said gasification chamber has an
oxygen concentration of 5% or less.
23. The gasification system as recited in claim 18, wherein said
gasification chamber has a temperature of 350 to 950.degree. C.
24. The gasification system as recited in claim 18, wherein said
combustion chamber has a temperature of 600 to 1000.degree. C.
25. The gasification system as recited in claim 18, further
comprising a slagging combustion furnace for melting ash by using a
portion of the combustible gas produced by gasification in said
gasification chamber.
26. The gasification system as recited in claim 25, wherein a
combustion gas discharged from said slagging combustion chamber is
returned to said combustion chamber.
27. The gasification system as recited in claim 18, further
comprising a water spray gas cooler for spraying water on the
combustion gas discharged from said combustion chamber.
28. The gasification system as recited in claim 18, further
comprising: a scrubber disposed in a line of the combustible gas
discharged from said gasification chamber; and a water spray gas
cooler for spraying water discharged from said scrubber on the
combustion gas discharged from said combustion chamber.
29. The gasification system as recited in claim 18, further
comprising a fluidizing gas heater for exchanging heat between the
combustion gas discharged from said combustion chamber and the
combustion gas to be returned to said gasification chamber and said
combustion chamber.
30. The gasification system as recited in claim 18, further
comprising a high-temperature furnace for pyrolyzing tar in the
combustible gas discharged from said gasification chamber.
31. The gasification system as recited in claim 18, wherein said
gasification chamber comprises a fluidized-bed furnace having a bed
material including at least one of silica sand and catalyst
particles.
32. The gasification system as recited in claim 18, wherein said
combustion chamber comprises a fluidized-bed furnace having a bed
material including at least one of silica sand and catalyst
particles.
33. The gasification system as recited in claim 18, further
comprising a gas cooling apparatus for cooling the combustible gas
discharged from said gasification chamber to remove moisture from
the combustible gas.
34. The gasification system as recited in claim 18, further
comprising a gas cooling apparatus for cooling the combustion gas
discharged from said combustion chamber to remove moisture from the
combustion gas.
Description
TECHNICAL FIELD
[0001] The present invention relates to a gasification system for
gasifying various wastes such as municipal solid wastes, industrial
wastes, and waste plastics, biomass, and combustible materials such
as coal and refuse-derived fuel (RDF) in a gasification furnace or
chamber and recovering a valuable combustible gas produced by
gasification.
BACKGROUND ART
[0002] A gasification and slagging combustion furnace has been
developed as incineration technology for wastes. The gasification
and slagging combustion furnace has a gasification apparatus for
gasifying wastes into a combustible gas and combusting the
combustible gas at a high temperature immediately after
gasification. Combustion at a high temperature has the following
advantages. The volume of ash can be reduced by melting ash from
the wastes. The ash can be made harmless by melting ash. The
combustion efficiency can be improved, i.e., the amount of unburned
combustibles can be reduced in incinerated ash, and the amount of
exhaust gas is reduced by operation at a low air ratio.
[0003] However, from the viewpoint of energy use, the conventional
gasification and slagging combustion furnace converts the whole
energy into heat as with a conventional incineration furnace. Thus,
the conventional gasification and slagging combustion furnace has a
limited efficiency of energy use. Further, the conventional
gasification and slagging combustion furnace cannot produce
storable energy.
[0004] In recent years, there has been developed technology which
produces a gas (hereinafter referred to as a produced gas) in a
gasification apparatus and does not combust the produced gas but
utilizes the produced gas as a product gas. The product gas is
utilized as fuel in an electric power generator such as a gas
turbine, a gas engine, or a fuel cell, or as a raw material for
synthesis of liquid fuel.
[0005] There has been used a cogeneration system combining electric
power generation utilizing a product gas and electric power
generation utilizing heat recovery. Such a cogeneration system has
an improved efficiency of energy use. Accordingly, this type of
cogeneration system has been developed not only in a field of waste
treatment, but also in a field of thermal power generation. For
example, a cogeneration system has been utilized in a
high-efficiency thermal power generating system using coal. The
technology that utilizes a product gas as a raw material for
synthesis of liquid fuel can produce storable energy from energy
resources that have heretofore been discarded and is thus
advantageous in future energy security including stable supply of
energy and total crisis management.
[0006] When a raw material having a large amount of fixed carbon,
such as coal or ligneous biomass, is gasified in a gasification
apparatus, char containing a large amount of fixed carbon is
produced in the gasification apparatus. Because such char has an
extremely low combustion rate as compared to that of a volatile
gas, char is accumulated in the gasification apparatus. Thus,
produced char is problematic in operation of the gasification
apparatus in many cases. For example, when the gasification
apparatus comprises a fluidized-bed furnace, char is accumulated on
a surface of a fluidized bed because char has a specific gravity
smaller than a bed material in the fluidized bed. Therefore, even
if incombustibles are to be withdrawn together with a bed material
from a furnace bottom, char cannot be withdrawn from the
fluidized-bed furnace, but only a bed material is withdrawn from
the fluidized-bed furnace. Thus, a char bed is formed in the
fluidized-bed furnace. Specifically, a fluidized bed having a large
amount of char accumulated is formed in the fluidized-bed furnace.
Since char has a large particle diameter, a char bed inhibits
fluidization of the fluidized-bed furnace and thus may cause a
shutdown of the system.
[0007] Since a combustion rate of char is not more than a
combustion rate of a combustible gas, oxygen is usually consumed by
combustion of a combustible gas prior to combustion of char.
Therefore, even if oxygen is supplied into the fluidized-bed
furnace in order to increase the amount of combustion of char so as
to reduce the amount of char accumulated in the fluidized-bed
furnace, oxygen is consumed to combust a combustible gas.
Specifically, energy of the combustible gas is excessively
converted into heat. Since the temperature of the furnace is
increased by supplied oxygen, an efficiency of combustion of char
is improved to a certain extent. However, a combustion rate of char
is not sufficiently improved.
[0008] When a char combustion apparatus is provided separately from
a gasification apparatus so that char is withdrawn from the
gasification apparatus and combusted in the char combustion
apparatus, the following advantages can be obtained.
[0009] (1) Char can be combusted under proper conditions (e.g.
combustion temperature and residence time) that are independent of
conditions in the gasification apparatus.
[0010] (2) Oxygen supplied to combust char does not combust a
product gas.
[0011] (3) The combustible gas is not diluted by a char combustion
gas. Thus, a gas having a high heating value can be obtained.
[0012] (4) It is possible to utilize a valuable combustible gas and
a low-value combustion gas separately for respective purposes of
use.
[0013] (5) In a case where a raw material has a large amount of
fixed carbon, such as coal or ligneous biomass, a ratio of energy
utilization at the time when a large amount of char discharged is
withdrawn and discarded is lowered below a ratio of energy
utilization at the time when the raw material is completely
combusted as it is. By combusting char in the char combustion
apparatus and utilizing heat of combustion of char as a heat source
for the gasification apparatus or a deteriorated catalyst
regeneration device, a ratio of energy utilization of the raw
material can be improved.
[0014] If the amount of char to be gasified per time is to be
increased, then a furnace is required to have an extremely large
volume of a bed because char has a low pyrolysis rate. Thus, it is
difficult to gasify an entire amount of char into a product gas. In
the gasification process of a raw material containing a large
amount of fixed carbon, carbon conversion, which is a ratio of
carbon in fuel converted into a gas, is frequently used as a
criterion for evaluation. However, even if fixed carbon which is
unlikely to be gasified or converted into a gas cannot be gasified,
energy of fixed carbon can be utilized as heat by combusting fixed
carbon in the char combustion apparatus as described above.
[0015] In a conventional cogeneration system using gasification,
sensible heat of a combustion exhaust gas produced by combustion of
char can be recovered through steam and utilized for electric power
generation. However, when a pyrolyzed gas is produced at a
relatively low temperature, a ratio of energy utilization is higher
in a case where heat of the combustion exhaust gas produced by
combustion of char is used as a heat source for regeneration of the
catalyst for gasification or cracking of a produced gas so as to
maintain the gasification chamber at a lower temperature than that
in a case where heat of the combustion exhaust gas is recovered by
a boiler or the like.
[0016] A conventional gasification system having a gasification
apparatus for gasifying various wastes or biomass to recover a
valuable combustible gas and a combustion apparatus for combusting
char and tar, which are produced as residues in the gasification
apparatus, releases a combustion gas from the combustion apparatus
to an atmosphere.
DISCLOSURE OF INVENTION
[0017] 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 system having a gasification furnace or
chamber for gasifying various wastes such as municipal solid
wastes, industrial wastes, and waste plastics, biomass, and
combustible materials such as coal and refuse-derived fuel (RDF) to
recover a valuable combustible gas, and a combustion furnace or
chamber for combusting char and tar produced as a residue in the
gasification furnace or chamber. The gasification system returns a
combustion gas discharged from a combustion furnace or chamber to
the combustion furnace or chamber and to a gasification furnace or
chamber so as not to release an exhaust gas to an atmosphere and
can eliminate any chimneys.
[0018] According to a first aspect of the present invention, there
is provided a gasification system having a gasification furnace for
gasifying a combustible to produce a combustible gas, and a
combustion furnace for combusting char and/or tar produced by
gasification in the gasification furnace. The gasification system
also has a return line for returning a combustion gas discharged
from the combustion furnace to the gasification furnace and the
combustion furnace.
[0019] According to a second aspect of the present invention, there
is provided a gasification system having an integrated gasification
furnace. The integrated gasification furnace has a gasification
chamber for gasifying a combustible to produce a combustible gas,
and a combustion chamber for combusting char and/or tar produced by
gasification in the gasification chamber. The gasification system
also has a return line for returning a combustion gas discharged
from the combustion chamber to the gasification chamber and the
combustion chamber.
[0020] According to the present invention, no exhaust gas is
released to an atmosphere from the gasification system.
Accordingly, the gasification system does not contaminate the
atmosphere. Further, it is possible to simplify an exhaust gas
treatment facility. Furthermore, the gasification system does not
need any chimneys and can achieve a clean system.
[0021] Oxygen may be added to the combustion gas to be returned to
the combustion furnace or chamber. Steam or inert gas such as
nitrogen or carbon dioxide is supplied to the gasification furnace
or chamber. The combustion gas may be supplied to a portion
downstream of the gasification furnace or chamber. The combustion
gas to be returned to the gasification furnace or chamber may have
an oxygen concentration of 5% or less. The gasification furnace or
chamber may have a temperature of 350 to 950.degree. C. The
combustion furnace or chamber may have a temperature of 600 to
1000.degree. C.
[0022] The gasification system may also include a slagging
combustion furnace for melting ash by using a portion of the
combustible gas produced by gasification in the gasification
furnace or chamber. In this case, a combustion gas discharged from
the slagging combustion chamber may be returned to the combustion
furnace or chamber.
[0023] The gasification system may also include a water spray gas
cooler for spraying water on the combustion gas discharged from the
combustion furnace or chamber. The gasification system may also
include a scrubber disposed in a line of the combustible gas
discharged from the gasification furnace or chamber, and a water
spray gas cooler for spraying water discharged from the scrubber on
the combustion gas discharged from the combustion furnace or
chamber.
[0024] The gasification system may also include a fluidizing gas
heater for exchanging heat between the combustion gas discharged
from the combustion furnace or chamber and the combustion gas to be
returned to the gasification furnace or chamber and the combustion
furnace or chamber. The gasification system may also include a
high-temperature furnace for pyrolyzing tar in the combustible gas
discharged from the gasification furnace or chamber.
[0025] The gasification furnace or chamber may comprise a
fluidized-bed furnace having a bed material including at least one
of silica sand and catalyst particles. The combustion furnace or
chamber may comprise a fluidized-bed furnace having a bed material
including at least one of silica sand and catalyst particles.
[0026] The gasification system may also include a gas cooling
apparatus for cooling the combustible gas discharged from the
gasification furnace or chamber to remove moisture from the
combustible gas. The gasification system may also include a gas
cooling apparatus for cooling the combustion gas discharged from
the combustion furnace or chamber to remove moisture from the
combustion gas.
[0027] 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
[0028] FIG. 1 is a schematic diagram explanatory of principles of a
gasification system according to the present invention;
[0029] FIG. 2 is a schematic diagram explanatory of principles of a
variation of a gasification system according to the present
invention;
[0030] FIG. 3 is a schematic diagram showing a gasification system
according to a first embodiment of the present invention;
[0031] FIG. 4 is a schematic diagram showing a gasification system
according to a second embodiment of the present invention;
[0032] FIG. 5 is a schematic diagram showing a gasification system
according to a third embodiment of the present invention;
[0033] FIG. 6 is a schematic diagram showing a gasification system
according to a fourth embodiment of the present invention;
[0034] FIG. 7 is a schematic diagram showing a gasification furnace
in a gasification system according to a fifth embodiment of the
present invention;
[0035] FIG. 8 is a schematic diagram showing a gasification system
according to a sixth embodiment of the present invention;
[0036] FIG. 9 is a schematic diagram showing a gasification system
according to a seventh embodiment of the present invention; and
[0037] FIG. 10 is a schematic diagram showing a gasification system
according to an eighth embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0038] A gasification system according to embodiments of the
present invention will be described below with reference to FIGS. 1
through 10.
[0039] FIG. 1 is a schematic diagram explanatory of principles of a
gasification system according to the present invention. The
gasification system shown in FIG. 1 has a gasification furnace 1
with a fluidized bed and a combustion furnace 2. In FIG. 1, various
wastes and combustibles such as biomass are supplied into the
gasification furnace 1, where the wastes and biomass are gasified
(or pyrolyzed) to produce a combustible gas and char. The valuable
combustible gas produced by gasification (or pyrolysis) in the
gasification furnace 1 is utilized for power recovery or energy
recovery, or used as a raw material for chemosynthesis. Char and
tar as residues produced by gasification (or pyrolysis) in the
gasification furnace 1 are introduced into the combustion furnace
2, where the char and tar are combusted by oxygen supplied into the
combustion furnace 2. Sensible heat produced by combustion in the
combustion furnace 2 is utilized as a heat source for gasification
in the gasification furnace 1. Because the char and tar introduced
into the combustion furnace 2 mainly contain carbon, combustion in
the combustion furnace 2 produces a combustion gas containing
CO.sub.2 as a principal component.
[0040] A portion of the combustion gas produced in the combustion
furnace 2 is returned as a fluidizing gas to the combustion furnace
2. The rest of the combustion gas is returned as a fluidizing gas
to the gasification furnace 1. A booster 3 is provided to return
the combustion gas produced in the combustion furnace 2 to the
combustion furnace 2 and the gasification furnace 1. Since the
booster 3 is thus employed in the gasification system, a heat
exchanger 4 for cooling the combustion gas and a dust collector 5
for removing dust from the combustion gas are provided downstream
of the combustion furnace 2. The combustion gas returned to the
combustion furnace 2 serves to fluidize a bed material in the
combustion furnace 2 and to dilute oxygen so as to prevent local
combustion in the combustion furnace 2. The amount of combustion
gas to be returned to the combustion furnace 2 is adjusted so that
the combustion furnace 2 maintains a fluidized state proper to
combust char and tar in a fluidized bed of the combustion furnace
2.
[0041] The amount of oxygen supplied to the combustion furnace 2 is
slightly larger than a theoretical amount of oxygen required for
stable combustion of char and tar. If oxygen is excessively
supplied to the combustion furnace 2, the concentration of oxygen
in the combustion gas is increased so that the combustion gas
partly returned to the gasification furnace 1 combusts the
combustible gas in the gasification furnace 1. Thus, the quality
(or calorie) of the combustible gas is adversely lowered. It is
desirable that the concentration of oxygen in the combustion gas
should be 5% or less, preferably 1% or less. As described above, a
portion of the combustion gas discharged from the combustion
furnace 2 is returned to the combustion furnace 2. The amount of
combustion gas to be returned to the combustion furnace 2 is
adjusted so as to be proper for fluidization in the combustion
furnace 2 and dilution of oxygen in the combustion furnace 2. The
rest of the combustion gas is supplied to the gasification furnace
1. Specifically, no combustion gas is released to an atmosphere
from the combustion furnace 2. Since no combustion gas is released
to an atmosphere through a chimney, it does not matter whether the
combustion gas contains CO. For example, CO may be produced by
local incomplete combustion due to low combustion temperatures. The
combustion gas supplied to the gasification furnace 1 serves to
fluidize a bed material in the gasification furnace 1. The bed
material may include at least one of silica sand and catalyst
particles.
[0042] When the amount of combustion gas to be supplied to the
gasification furnace 1 is larger than an amount proper to be
supplied as a fluidizing gas to the gasification furnace 1, i.e.,
when wastes have low heating values and the amount of combustion is
large, an excessive combustion gas may be supplied downstream of
the fluidized bed in the gasification furnace 1. For example, an
excessive combustion gas may be returned to a freeboard of the
gasification furnace 1.
[0043] However, when a combustion gas is to be returned to the
freeboard 6, because the combustion gas has been cooled below the
temperature of the freeboard, the combustion gas lowers the
temperature of the freeboard to lower a pyrolysis rate of tar.
Therefore, the concentration of tar in the valuable combustible gas
may be increased so as to cause troubles such as attachment of tar.
In such a case, it is desirable that the combustion gas bypasses
the gasification furnace 1 so as to be supplied to a stage
downstream of the gasification furnace 1, at which the produced gas
has been cooled. When the amount of combustion gas to be supplied
to the gasification furnace 1 is larger than an amount proper to be
supplied as a fluidizing gas to the gasification furnace 1, i.e.,
when wastes have low heating values and the amount of combustion is
large, an excessive combustion gas may be adsorbed and fixed so
that CO.sub.2 is fixed. The combustion gas in the gasification
system according to the present invention has a higher
concentration of CO.sub.2 as compared to an exhaust gas discharged
from conventional combustion furnaces, incineration furnaces,
boilers, or gasification and slagging combustion furnaces.
Specifically, the combustion gas in the gasification system
according to the present invention contains no nitrogen and has a
low moisture concentration. Therefore, the combustion gas in the
gasification system according to the present invention is effective
in fixing CO.sub.2. If the amount of excessive combustion gas is so
large that the produced gas is excessively diluted by the excessive
combustion gas, then a catalyst packed tower having a catalyst such
as CaO, MgO, or K.sub.2O for absorbing carbon dioxide or a wet gas
absorber for absorbing carbon dioxide may be provided in a produced
gas line to absorb carbon dioxide so as to increase the
concentration of the combustible gas in the produced gas.
[0044] When the amount of combustion gas to be supplied to the
gasification furnace 1 is larger than an amount proper to be
supplied as a fluidizing gas to the gasification furnace 1, i.e.,
when wastes have low heating values and the amount of combustion is
large, the combustion gas may be cooled to condense moisture in the
combustion gas and thus reduce the volume of the gas so as to
increase the concentration of the combustible gas in the produced
gas. Specifically, when wastes have low heating values, a large
amount of combustible components in the wastes is required to be
combusted in the combustion furnace in order to compensate heat
required for evaporation of moisture in the wastes and gasification
and pyrolysis of the wastes with heat of combustion in the
combustion furnace. Accordingly, the amount of combustion gas
produced becomes large. For example, as shown in FIG. 2, a gas
cooling apparatus 7 may be provided upstream of the booster 3 to
cool the combustion gas. With the gas cooling apparatus 7, moisture
in the combustion gas is condensed and removed to an exterior of
the system. Accordingly, the volume of the gas is reduced so as to
increase the concentration of the combustible gas in the produced
gas. Thus, the gasification system according to the present
invention can be applied to wastes having much moisture and low
heating values.
[0045] Further, as shown in FIG. 2, a scrubber (gas cooling
apparatus) 8 may be provided to cool the combustible gas. With the
scrubber 8, moisture in the combustible gas is condensed and
removed to an exterior of the system. Accordingly, the volume of
the gas is reduced so as to increase the concentration of the
combustible gas in the produced gas. Thus, the gasification system
according to the present invention can be applied to wastes having
low heating values.
[0046] When the amount of combustion gas to be supplied to the
gasification furnace 1 is smaller than an amount proper to be
supplied as a fluidizing gas to the gasification furnace 1, i.e.,
when wastes have high heating values and the amount of combustion
is small, a fluidizing gas tends to be insufficient in the
gasification furnace 1. In such a case, steam (water vapor) or
inert gas such as nitrogen or CO.sub.2 may be supplied to the
gasification furnace 1 to compensate an insufficient fluidizing
gas. Specifically, when wastes have high heating values, only a
small amount of combustible components in the wastes is required to
be combusted in the combustion furnace in order to compensate heat
required for evaporation of moisture in the wastes and gasification
and pyrolysis of the wastes with heat of combustion in the
combustion furnace. Accordingly, the amount of combustion gas
produced becomes small. When a fluidizing gas is compensated with
steam in the gasification furnace 1, the steam is not required to
have high quality. Specifically, water may be sprayed on the
combustion gas, which is circulated, to produce steam. In this
case, the amount of heat to be recovered from the combustion gas
line can reduced, and hence it is possible to make the heat
exchanger 4 compact in size. Alternatively, water discharged from a
scrubber may be sprayed on a gas discharged from the combustion
furnace 2 to produce steam for a fluidizing gas. In this case,
contaminants in the water become dry ash, which is trapped by the
dust collector 5 such as a bag filter. Waste water discharged from
various processes, e.g., waste water from a waste supply device
with squeezing wastes to remove water content from the wastes or
waste water from a waste pit, may be sprayed on a gas discharged
from the combustion furnace 2 for cooling the gas.
[0047] When the fluidizing gas of the gasification furnace 1 is
heated, the amount of combustion in the combustion furnace 2 can be
reduced. Thus, it is possible to obtain the same advantages as in a
case where a raw material has a high heating value. Depending upon
conditions, the heat exchanger 4 can be eliminated. Catalyst
particles may be mixed into the fluidized beds in the gasification
furnace 1 and the combustion furnace 2. The catalyst particles
serve to decompose tar and remove toxic substances under a reducing
atmosphere having a low temperature in the gasification furnace 1.
The catalyst particle may include MgO, iron oxide, Al.sub.2O.sub.3,
zeolite, CaO, or a catalyst having a noble metal, such as Ni or Co.
The catalyst particles are regenerated under an oxidizing
atmosphere having a high temperature in the combustion furnace 2 so
as to recover deteriorated functions of the catalyst particles.
[0048] FIG. 3 is a schematic diagram showing a gasification system
according to a first embodiment of the present invention. As shown
in FIG. 3, the gasification system has an integrated gasification
furnace 11 including a gasification chamber 12 and a combustion
chamber 13. Wastes (combustibles) are supplied into the
gasification chamber 12, where the wastes are gasified (or
pyrolyzed) to produce a combustible gas and char. Char and tar as
residues produced by gasification (or pyrolysis) are introduced
into the combustion chamber 13, where the char and tar are
combusted by oxygen supplied into the combustion chamber 13. The
gasification chamber 12 includes a fluidized bed having a
temperature of 350 to 950.degree. C. A combustion gas produced in
the combustion chamber 13 is supplied as a fluidizing gas into the
gasification chamber 12. The amount of combustion gas to be
supplied to the gasification chamber 12 is adjusted so that the
gasification chamber 12 maintains a proper fluidized state. The
proper fluidized state is defined as a state in which the following
conditions are met: The raw material is mixed with the bed material
in the fluidized bed and dispersed uniformly. The temperature of
the fluidized bed is uniform. A sufficient amount of bed material
is circulated.
[0049] When wastes have high heating values and the amount of
combustion is small, steam or inert gas such as nitrogen or
CO.sub.2 may be supplied as a fluidizing gas to the gasification
chamber 12 in addition to the combustion gas. The amount of steam
or inert gas to be supplied to the gasification chamber 12 is
adjusted so that the gasification chamber 12 maintains a proper
fluidized state. When wastes have low heating values and the amount
of combustion is large, the combustion gas from the combustion
chamber 13 may be supplied to a freeboard of the gasification
chamber 12. A produced gas is discharged from the gasification
chamber 12 into a dust collector 14 such as a cyclone, where dust
is removed from the produced gas. The produced gas is discharged
from the dust collector 14 into a scrubber 15. In the scrubber 15,
the produced gas is cooled, and toxic substances such as acid gas
and tar are removed from the produced gas. The produced gas
discharged from the scrubber 15 is utilized as a fuel gas or the
like. Waste water from the scrubber 15 is treated in a waste water
treatment facility 16.
[0050] Char and tar as residues produced by gasification (or
pyrolysis) in the gasification chamber 12 are introduced into the
combustion chamber 13, which includes a fluidized bed having a
temperature of 600 to 1000.degree. C. The combustion gas is
discharged from the combustion chamber 13 into a boiler 17. In the
boiler 17, the combustion gas is cooled, and a portion of dust in
the combustion gas is removed. Steam is produced in the boiler 17
by heat recovery and supplied to a steam turbine power generator 18
to generate electric power. The combustion gas is discharged from
the boiler 17 into a bag filter 19, where dust in the combustion
gas is collected. The combustion gas discharged from the bag filter
19 is returned through a booster 20 to the gasification chamber 12
and the combustion chamber 13.
[0051] The combustion chamber 13 is supplied with oxygen-containing
gas such as oxygen, oxygen-enriched air, air, or mixed gas of
oxygen and steam. The combustion chamber 13 is also supplied with
the combustion gas as a fluidizing gas from the booster 20. The
amounts of oxygen and combustion gas to be supplied to the
combustion chamber 13 are adjusted so that the combustion chamber
13 maintains a proper fluidized state, and that the combustion gas
has an oxygen concentration of 5% or less, preferably 1% or
less.
[0052] Catalyst particles may be mixed into the fluidized beds in
the gasification chamber 12 and the combustion chamber 13. The
catalyst particles serve to decompose tar and remove toxic
substances under a reducing atmosphere having a low temperature in
the gasification chamber 12. The catalyst particle may include MgO,
iron oxide, Al.sub.2O.sub.3, zeolite, CaO, or a catalyst having a
noble metal, such as Ni or Co. The catalyst particles are
regenerated under an oxidizing atmosphere having a high temperature
in the combustion chamber 13 so as to recover deteriorated
functions of the catalyst particles.
[0053] Ash is collected by the dust collector 14 such as a cyclone
in a produced gas line and by the boiler 17 and the bag filter 19
in a combustion gas line and then stored in an ash reservoir tank
21. In order to melt ash stored in the ash reservoir tank 21 into
slag, a slagging combustion furnace 22 may additionally be provided
as optional equipment. The slagging combustion furnace 22 is
supplied with ash stored in the ash reservoir tank 21, a portion of
the fuel gas in the produced gas line, and a portion of the
combustion gas which has been discharged from the booster 20 in the
combustion gas line (if the produced gas is required to be diluted)
and also with oxygen. In the slagging combustion furnace 22, the
fuel gas is combusted and heated above an ash melting temperature
to melt ash into slag. The slagging combustion furnace 22 may have
a temperature of 1000 to 1400.degree. C., preferably at least
1200.degree. C. The ash melted into slag is discharged to the
exterior of the system. The combustion gas discharged from the
slagging combustion furnace 22 is returned to the combustion
chamber 13. Alternatively, the combustion gas discharged from the
slagging combustion furnace 22 may be treated in a conventional gas
treatment facility (not shown) which is separately provided. For
example, such a conventional gas treatment facility has a heat
recovery device such as a boiler to lower the temperature of a
combustion gas, an adsorbent spraying device for spraying an
adsorbent such as hydrated lime or activated carbon on the
combustion gas to remove hydrogen chloride and dioxin from the
combustion gas, a bag filter for collecting particles in the gas, a
denitrogenation catalyst tower for removing nitrogenous compounds
from the combustion gas, and a chimney.
[0054] The amount of gas introduced into the slagging combustion
furnace 22 is smaller than the amount of gas introduced into a
conventional gasification and slagging combustion furnace.
Therefore, the slagging combustion furnace 22 can be made compact
in size. Since ash discharged from the integrated gasification
furnace 11 can be stored in the ash reservoir tank 21, the
gasification system according to the present embodiment can be
operated even if operation of the slagging combustion furnace 22 is
stopped. Thus, the gasification system according to the present
embodiment is effective in achieving a high operating ratio.
[0055] Further, chlorine compounds and sulfur compounds contained
in a gas produced in the gasification chamber 12 are absorbed and
removed, and absorption catalysts such as calcium compounds are
used as at least a portion of medium particles to purify the
produced gas. Thus, it is possible to reduce the concentration of
toxic components in the produced gas to be discharged.
[0056] FIG. 4 is a schematic diagram showing a gasification system
according to a second embodiment of the present invention. As shown
in FIG. 4, the gasification system has an integrated gasification
furnace 11 including a gasification chamber 12 and a combustion
chamber 13. Wastes (combustibles) are supplied into the
gasification chamber 12, where the wastes are gasified (or
pyrolyzed) to produce a combustible gas and char. Char and tar as
residues produced by gasification (or pyrolysis) are introduced
into the combustion chamber 13, where the char and tar are
combusted by oxygen supplied into the combustion chamber 13. The
gasification chamber 12 includes a fluidized bed having a
temperature of 350 to 950.degree. C. A combustion gas produced in
the combustion chamber 13 is supplied as a fluidizing gas into the
gasification chamber 12. The amount of combustion gas to be
supplied to the gasification chamber 12 is adjusted so that the
gasification chamber 12 maintains a proper fluidized state.
[0057] When wastes have high heating values and the amount of
combustion is small, steam or inert gas such as nitrogen or
CO.sub.2 may be supplied as a fluidizing gas to the gasification
chamber 12 in addition to the combustion gas. The amount of steam
or inert gas to be supplied to the gasification chamber 12 is
adjusted so that the gasification chamber 12 maintains a proper
fluidized state. When wastes have low heating values and the amount
of combustion is large, the combustion gas from the combustion
chamber 13 may be supplied to a freeboard of the gasification
chamber 12. A produced gas is discharged from the gasification
chamber 12 into a dust collector 14 such as a cyclone, where dust
is removed from the produced gas. The produced gas is discharged
from the dust collector 14 into a scrubber 15. In the scrubber 15,
the produced gas is cooled, and toxic substances such as acid gas
and tar are removed from the produced gas. The produced gas
discharged from the scrubber 15 is utilized as a fuel gas or the
like.
[0058] Char and tar as residues produced by gasification (or
pyrolysis) in the gasification chamber 12 are introduced into the
combustion chamber 13, which includes a fluidized bed having a
temperature of 600 to 1000.degree. C. The combustion gas is
discharged from the combustion chamber 13 into a gas cooler 23. In
the gas cooler 23, the combustion gas is cooled, and a portion of
dust in the combustion gas is removed. In the gas cooler 23, water
discharged from the scrubber 15 is sprayed on the combustion gas to
cool the combustion gas and produce steam. Waste water discharged
from various processes, e.g., waste water from a waste supply
device with squeezing wastes to remove water content from the
wastes or waste water from a waste pit, may be sprayed on a gas
discharged from the combustion chamber 13 for cooling the gas. A
required amount of make-up water is supplied to the scrubber 15.
The combustion gas and the steam are discharged from the gas cooler
23 into a bag filter 19, where dust in the combustion gas is
collected. The combustion gas discharged from the bag filter 19 is
returned through a booster 20 to the gasification chamber 12 and
the combustion chamber 13.
[0059] The combustion chamber 13 is supplied with oxygen-containing
gas such as oxygen, oxygen-enriched air, air, or mixed gas of
oxygen and steam. The combustion chamber 13 is also supplied with
the combustion gas as a fluidizing gas from the booster 20. The
amounts of oxygen and combustion gas to be supplied to the
combustion chamber 13 are adjusted so that the combustion chamber
13 maintains a proper fluidized state, and that the combustion gas
has an oxygen concentration of 5% or less, preferably 1% or
less.
[0060] Catalyst particles may be mixed into the fluidized beds in
the gasification chamber 12 and the combustion chamber 13. The
catalyst particles serve to decompose tar and remove toxic
substances under a reducing atmosphere having a low temperature in
the gasification chamber 12. The catalyst particle may include MgO,
iron oxide, Al.sub.2O.sub.3, zeolite, CaO, or a catalyst having a
noble metal, such as Ni or Co. The catalyst particles are
regenerated under an oxidizing atmosphere having a high temperature
in the combustion chamber 13 so as to recover deteriorated
functions of the catalyst particles.
[0061] Ash is collected by the dust collector 14 such as a cyclone
in a produced gas line and by the gas cooler 23 and the bag filter
19 in a combustion gas line and then stored in an ash reservoir
tank 21. In order to melt ash stored in the ash reservoir tank 21
into slag, a slagging combustion furnace 22 may additionally be
provided as optional equipment. The slagging combustion furnace 22
is supplied with ash stored in the ash reservoir tank 21, a portion
of the fuel gas in the produced gas line, and a portion of the
combustion gas which has been discharged from the booster 20 in the
combustion gas line (if the produced gas is required to be diluted)
and also with oxygen. In the slagging combustion furnace 22, the
fuel gas is combusted and heated above an ash melting temperature
to melt ash into slag. The slagging combustion furnace 22 may have
a temperature of 1000 to 1400.degree. C., preferably at least
1200.degree. C. The ash melted into slag is discharged to the
exterior of the system. The combustion gas discharged from the
slagging combustion furnace 22 is returned to the combustion
chamber 13. Alternatively, the combustion gas discharged from the
slagging combustion furnace 22 may be treated in a conventional gas
treatment facility (not shown) which is separately provided.
[0062] According to the second embodiment, steam can be supplied to
the fluidizing gas by the gas cooler 23 provided on the combustion
gas line. Therefore, it becomes unnecessary to provide a boiler as
shown in FIG. 3. The gas cooler 23 does not require tap water, and
thus water discharged from the scrubber 15 can be used in the gas
cooler 23.
[0063] Further, chlorine compounds and sulfur compounds contained
in a gas produced in the gasification chamber 12 are absorbed and
removed, and absorption catalysts such as calcium compounds are
used as at least a portion of medium particles to purify the
produced gas. Thus, it is possible to reduce the concentration of
toxic components in the produced gas to be discharged.
[0064] FIG. 5 is a schematic diagram showing a gasification system
according to a third embodiment of the present invention. As shown
in FIG. 5, the gasification system has an integrated gasification
furnace 11 including a gasification chamber 12 and a combustion
chamber 13. Wastes (combustibles) are supplied into the
gasification chamber 12, where the wastes are gasified (or
pyrolyzed) to produce a combustible gas and char. Char and tar as
residues produced by gasification (or pyrolysis) are introduced
into the combustion chamber 13, where the char and tar are
combusted by oxygen supplied into the combustion chamber 13. The
gasification chamber 12 includes a fluidized bed having a
temperature of 350 to 950.degree. C. A combustion gas produced in
the combustion chamber 13 is supplied as a fluidizing gas into the
gasification chamber 12. The amount of combustion gas to be
supplied to the gasification chamber 12 is adjusted so that the
gasification chamber 12 maintains a proper fluidized state.
[0065] When wastes have high heating values and the amount of
combustion is small, steam or inert gas such as nitrogen or
CO.sub.2 may be supplied as a fluidizing gas to the gasification
chamber 12 in addition to the combustion gas. The amount of steam
or inert gas to be supplied to the gasification chamber 12 is
adjusted so that the gasification chamber 12 maintains a proper
fluidized state. When wastes have low heating values and the amount
of combustion is large, the combustion gas from the combustion
chamber 13 may be supplied to a freeboard of the gasification
chamber 12. A produced gas is discharged from the gasification
chamber 12 into a dust collector 14 such as a cyclone, where dust
is removed from the produced gas. The produced gas is discharged
from the dust collector 14 into a scrubber 15. In the scrubber 15,
the produced gas is cooled, and toxic substances such as acid gas
and tar are removed from the produced gas. The produced gas
discharged from the scrubber 15 is utilized as a fuel gas or the
like.
[0066] Char and tar as residues produced by gasification (or
pyrolysis) in the gasification chamber 12 are introduced into the
combustion chamber 13, which includes a fluidized bed having a
temperature of 600 to 1000.degree. C. The combustion gas is
discharged from the combustion chamber 13 through a fluidizing gas
heater 24 into a gas cooler 23. In the fluidizing gas heater 24 and
the gas cooler 23, the combustion gas is cooled. In the gas cooler
23, water discharged from the scrubber 15 is sprayed on the
combustion gas to cool the combustion gas and produce steam. The
combustion gas and the steam are discharged from the gas cooler 23
into a bag filter 19, where dust in the combustion gas is
collected. The combustion gas and the steam discharged from the bag
filter 19 are supplied through a booster 20 to the fluidizing gas
heater 24, where the combustion gas and the steam are heated by
heat exchange with the combustion gas discharged from the
combustion chamber 13. Then, the combustion gas and the steam are
returned to the gasification chamber 12 and the combustion chamber
13.
[0067] The combustion chamber 13 is supplied with oxygen-containing
gas such as oxygen, oxygen-enriched air, air, or mixed gas of
oxygen and steam. The combustion chamber 13 is also supplied with
the combustion gas as a fluidizing gas from the booster 20. The
amounts of oxygen and combustion gas to be supplied to the
combustion chamber 13 are adjusted so that the combustion chamber
13 maintains a proper fluidized state, and that the combustion gas
has an oxygen concentration of 5% or less, preferably 1% or
less.
[0068] Catalyst particles may be mixed into the fluidized beds in
the gasification chamber 12 and the combustion chamber 13. The
catalyst particles serve to decompose tar and remove toxic
substances under a reducing atmosphere having a low temperature in
the gasification chamber 12. The catalyst particle may include MgO,
iron oxide, Al.sub.2O.sub.3, zeolite, CaO, or a catalyst having a
noble metal, such as Ni or Co. The catalyst particles are
regenerated under an oxidizing atmosphere having a high temperature
in the combustion chamber 13 so as to recover deteriorated
functions of the catalyst particles.
[0069] Ash is collected by the dust collector 14 such as a cyclone
in a produced gas line and by the gas cooler 23 and the bag filter
19 in a combustion gas line and then stored in an ash reservoir
tank 21. In order to melt ash stored in the ash reservoir tank 21
into slag, a slagging combustion furnace 22 may additionally be
provided as optional equipment. The slagging combustion furnace 22
is supplied with ash stored in the ash reservoir tank 21, a portion
of the fuel gas in the produced gas line, and a portion of the
combustion gas which has been discharged from the booster 20 in the
combustion gas line (if the produced gas is required to be diluted)
and also with oxygen. In the slagging combustion furnace 22, the
fuel gas is combusted and heated above an ash melting temperature
to melt ash into slag. The slagging combustion furnace 22 may have
a temperature of 1000 to 1400.degree. C., preferably at least
1200.degree. C. The ash melted into slag is discharged to the
exterior of the system. The combustion gas discharged from the
slagging combustion furnace 22 is returned to the combustion
chamber 13. Alternatively, the combustion gas discharged from the
slagging combustion furnace 22 may be treated in a conventional gas
treatment facility (not shown) which is separately provided.
[0070] According to the third embodiment, since the fluidizing gas
can be heated in the fluidizing gas heater 24, it is possible to
reduce the amount of combustion of a raw material (wastes), which
are combusted in the gasification furnace 11, and also reduce the
amount of oxygen to be supplied. This embodiment is particularly
effective in a case where a raw material has a low heating value.
Similar effects can be obtained when the concentration of oxygen in
the fluidizing gas to be supplied to the combustion chamber 13 is
increased.
[0071] Further, chlorine compounds and sulfur compounds contained
in a gas produced in the gasification chamber 12 are absorbed and
removed, and absorption catalysts such as calcium compounds are
used as at least a portion of medium particles to purify the
produced gas. Thus, it is possible to reduce the concentration of
toxic components in the produced gas to be discharged.
[0072] FIG. 6 is a schematic diagram showing a gasification system
according to a fourth embodiment of the present invention. The
gasification system shown in FIG. 6 has a high-temperature furnace
25 disposed between the dust collector 14 and the scrubber 15 in
the gasification system shown in FIG. 5. A produced gas is
discharged from the dust collector 14 and introduced into the
high-temperature furnace 25. The high-temperature furnace 25 is
supplied with oxygen-containing gas such as oxygen, oxygen-enriched
air, air, or mixed gas of oxygen and steam, and the produced gas
supplied into the high-temperature furnace 25 is partly combusted.
In this case, the temperature of the interior of the
high-temperature furnace 25 is increased to 900 to 1400.degree. C.,
preferably about 1200.degree. C. Accordingly, tar in the produced
gas is pyrolyzed into hydrogen, carbon monoxide, and low molecular
hydrocarbon. In the high-temperature furnace 25, carbon monoxide or
hydrocarbon such as methane in the produced gas reacts with steam
(for example, shift reaction) so as to change the composition of
the produced gas. Accordingly, the produced gas can contain a large
amount of hydrogen. In order to promote such reaction, steam may be
supplied to the high-temperature furnace 25. Thus, the
high-temperature furnace 25 has a function to adjust the
composition of the produced gas. Accordingly, a fuel gas having
desired composition can be obtained by adjusting conditions of the
high-temperature furnace 25. A portion of ash in the produced gas
is removed in the high-temperature furnace 25. Particularly, when
the high-temperature furnace 25 has a temperature higher than about
1200.degree. C., ash contained in the produced gas is melted into
slag in the high-temperature furnace 25. The molten slag falls down
into a tank located at a lower portion of the high-temperature
furnace 25 to form granulated slag. The granulated slag is
discharged from the high-temperature furnace 25 by a conveyer. When
the high-temperature furnace 25 has a temperature lower than about
1200.degree. C., ash is not melted in the high-temperature furnace
25. In such a case, the ash is recovered by an inertial dust
collector in the high-temperature furnace 25 and discharged from
the bottom of the high-temperature furnace 25. The discharged ash
is delivered to the ash reservoir tank 21 and stored therein.
[0073] Then, the produced gas is discharged from the
high-temperature furnace 25 into the scrubber 15. In order to lower
the temperature of the produced gas introduced into the scrubber
15, water may be sprayed in a gas passage at an inlet of the
scrubber 15, or a gas cooler such as a water spray cooler or a
boiler may be provided between the high-temperature furnace 25 and
the scrubber 15. The high-temperature furnace 25 has a water-cooled
pipe disposed in a wall thereof. Water in the water-cooled pipe is
heated so as to produce steam. The produced steam may be utilized
as a fluidizing gas in the gasification chamber 12. Other
arrangements are the same as the gasification system in the third
embodiment shown in FIG. 5. The high-temperature furnace 25 in the
fourth embodiment shown in FIG. 6 may be applied to the first,
second, and third embodiments, respectively.
[0074] According to the fourth embodiment, with the
high-temperature furnace 25, tar can be removed by pyrolysis at a
high temperature even if a catalyst is not used in the gasification
furnace 11. Since reaction is promoted between carbon monoxide or
hydrocarbon such as methane in the produced gas and steam, it is
possible to change the composition of the produced gas so as to
obtain a produced gas containing a large amount of hydrogen.
Further, ash can be collected or recovered as slag. Furthermore,
the high-temperature furnace 25 can reliably pyrolyze tar produced
in the gasification chamber 12 even if catalyst particles used in
the gasification chamber 12 do not have a long-lasting function of
decomposing tar. Thus, the high-temperature furnace 25 serves as a
fail safe when catalyst particles used in the gasification chamber
12 do not have a long-lasting function of decomposing tar.
[0075] Further, chlorine compounds and sulfur compounds contained
in a gas produced in the gasification chamber 12 are absorbed and
removed, and absorption catalysts such as calcium compounds are
used as at least a portion of medium particles to purify the
produced gas. Thus, it is possible to reduce the concentration of
toxic components in the produced gas to be discharged.
[0076] FIG. 7 is a schematic diagram showing a gasification furnace
in a gasification system according to a fifth embodiment of the
present invention. The gasification furnace shown in FIG. 7
comprises a twin tower circulation type gasification furnace. As
shown in FIG. 7, the twin tower circulation type gasification
furnace has two furnaces (towers) including a gasification furnace
31 and a char combustion furnace 32. A bed material and char are
circulated between the gasification furnace 31 and the char
combustion furnace 32 so as to supply sensible heat of the bed
material, which is heated by combustion heat of char in the char
combustion furnace 32, to the gasification furnace 31 to provide an
amount of heat required for gasification. For purposes of
illustration, FIG. 7 shows only gas paths between the gasification
furnace 31 and the char combustion furnace 32. However, the
gasification system practically has other paths as shown in FIGS. 3
through 6.
[0077] In the twin tower circulation type gasification furnace,
wastes (combustibles) are supplied into the gasification furnace
31, where the wastes are gasified (or pyrolyzed) to produce a
combustible gas and char. The gasification furnace 31 includes a
fluidized bed having a temperature of 350 to 950.degree. C. A gas
produced in the gasification furnace 31 is accompanied with char
and a bed material, which are introduced into a cyclone 33. In the
cyclone 33, gas-solid separation is performed, and the char and the
bed material are returned to the char combustion furnace 32. The
produced gas, from which a portion of dust has been removed in the
cyclone 33, is utilized as a fuel gas. On the other hand, char and
tar as residues produced by gasification (or pyrolysis) in the
gasification furnace 31 are introduced into the combustion furnace
32, where the char and tar are combusted by oxygen supplied into
the combustion furnace 32. The combustion furnace 32 includes a
fluidized bed having a temperature of 600 to 1000.degree. C. A
combustion gas discharged from the char combustion furnace 32 is
accompanied with a bed material, which is introduced into a cyclone
34. In the cyclone 34, gas-solid separation is performed, and the
bed material is returned to the gasification furnace 31. The
combustion gas discharged from the cyclone 34 is supplied through a
drier 35 to the gasification furnace 31. In the drier 35, wastes
such as biomass are dried to provide a raw material. Oxygen is
introduced into the char combustion furnace 32. A portion of the
combustion gas discharged from the char combustion furnace 32 is
also introduced into the char combustion furnace 32. On the other
hand, a portion of the combustion gas discharged from the char
combustion furnace 32 is supplied into the gasification furnace 31.
In this case, steam or inert gas such as nitrogen or CO.sub.2 is
supplied into the gasification furnace 31 when the fluidizing gas
is insufficient.
[0078] According to the fifth embodiment, it is not necessary to
combust a gas produced in the gasification furnace 31. Accordingly,
it is possible to maintain a high heating value of the produced
gas. Since no combustion gas is released to an atmosphere from the
gasification system employing the twin tower circulation type
gasification furnace, the gasification system does not need any
chimneys.
[0079] Further, chlorine compounds and sulfur compounds contained
in a gas produced in the gasification furnace 31 are absorbed and
removed, and absorption catalysts such as calcium compounds are
used as at least a portion of medium particles to purify the
produced gas. Thus, it is possible to reduce the concentration of
toxic components in the produced gas to be discharged.
[0080] FIG. 8 is a schematic diagram showing a gasification system
according to a sixth embodiment of the present invention. The
gasification system shown in FIG. 8 employs a catalyst (e.g.
Al.sub.2O.sub.3) to reform a gas (or decompose tar). The
gasification system employs char combustion heat as heat for
regenerating a deteriorated catalyst. The gasification system has a
gasification furnace 71 and a combustion furnace 72 for combusting
char (unburned carbon combustibles) produced by gasification of a
raw material. Heat of a combustion exhaust gas produced by
combustion of the char in the combustion furnace 72 is supplied to
a catalyst regeneration device 73 as heat for regenerating a
deteriorated catalyst. A raw material is supplied into the
gasification furnace 71 having a temperature of 350 to 950.degree.
C., where the raw material is gasified (or pyrolyzed) to produce a
combustible gas and char. The combustible gas produced by
gasification of the raw material in the gasification furnace 71 is
introduced into a gas reforming device 74, where the gas is
reformed (or tar is decomposed). The gas reforming device 74
includes a catalyst bed having a temperature of 600 to 950.degree.
C. Tar and char as residues produced by gasification (or pyrolysis)
in the gasification furnace 71 are introduced into the combustion
furnace 72 having a temperature of 650 to 1000.degree. C., where
the tar and char are combusted by oxygen supplied into the
combustion furnace 72. For purposes of illustration, FIG. 8 shows
only gas paths between the gasification furnace 71 and the
combustion furnace 72. However, the gasification system practically
has other paths as shown in FIGS. 3 through 6.
[0081] When gas reformation (or tar decomposition) is performed on
the produced gas from the gasification furnace 71, a catalyst
function of the catalyst in the gas reforming device 74 is somewhat
deteriorated due to deposition of carbon or the like. The catalyst
in the gas reforming device 74 is supplied to the gasification
furnace 71. When the catalyst supplied into the gasification
furnace 71 performs gas reformation (or tar decomposition) on a gas
produced by gasification (or pyrolysis) in the gasification furnace
71, a catalyst function of the catalyst is considerably
deteriorated due to deposition of carbon or the like. The catalyst
in the gasification furnace 71 is supplied to the catalyst
regeneration device 73. The catalyst regeneration device 73 heats
the deteriorated catalyst with the combustion exhaust gas from the
combustion furnace 72 to 700 to 1000.degree. C. so as to regenerate
the catalyst and introduces the regenerated catalyst into the gas
reforming device 74.
[0082] Oxygen is supplied to the combustion furnace 72 to combust
char. A combustion gas (containing oxygen) produced by combustion
of the char in the combustion furnace 72 is introduced into the
catalyst regeneration device 73, where the catalyst is regenerated
by heat of the combustion gas. An exhaust gas discharged from the
catalyst regeneration device 73 is supplied to the gas reforming
device 74, the gasification furnace 71, and the combustion furnace
72. With the above arrangement, since no exhaust gas is released to
an atmosphere from the gasification system, the gasification system
does not need any chimneys.
[0083] Further, chlorine compounds and sulfur compounds contained
in a gas produced in the gasification furnace 71 are absorbed and
removed, and absorption catalysts such as calcium compounds are
used as at least a portion of medium particles to purify the
produced gas. Thus, it is possible to reduce the concentration of
toxic components in the produced gas to be discharged.
[0084] FIG. 9 is a schematic diagram showing a gasification system
according to a seventh embodiment of the present invention. FIG. 9
shows another arrangement of an integrated gasification furnace.
The integrated gasification furnace has a gasification chamber 81,
a collector 82, and a combustion chamber 83. For purposes of
illustration, FIG. 9 shows only gas paths between the gasification
chamber 81 and the combustion chamber 82. However, the gasification
system practically has other paths as shown in FIGS. 3 through 6.
The gasification chamber 81 comprises a fluidized-bed furnace
having a temperature of 350 to 950.degree. C. The combustion
chamber 83 comprises a fluidized-bed furnace having a temperature
of 600 to 1000.degree. C. Wastes (combustibles) are supplied into a
bed in the gasification chamber 81, where gasification (or
pyrolysis) of the wastes and decomposition and reformation of the
produced gas are performed. Char and tar produced in the
gasification chamber 81 flow into the combustion chamber 83
together with a bed material. The combustion chamber 83 has a dense
fluidized bed or a fast fluidized bed formed at a lower portion
thereof. When the combustion chamber 83 has a dense fluidized bed
at a lower portion thereof, a fluidizing gas is supplied from an
upper portion of the dense fluidized bed to form a fast fluidized
bed at an upper portion of the combustion chamber 83. The
combustion chamber 83 is supplied with a gas containing oxygen
required for combustion. A combustion gas produced in the
combustion chamber 83 flows into the collector 82 together with a
bed material. In the collector 82, scattering particles are
collected, and a combustion gas is separated from the scattering
particles.
[0085] The collector 82 shown in FIG. 9 comprises a cyclone dust
collector utilizing centrifugal forces. A portion of the combustion
gas separated in the collector 82 is returned to the combustion
chamber 83. The amount of combustion gas to be returned to the
combustion chamber 83 is adjusted so as to be proper for
fluidization in the combustion chamber 83 and dilution of oxygen in
combustion chamber 83. The rest of the combustion gas is supplied
to the gasification chamber 81 as a fluidizing gas. If the
combustion gas is excessively supplied to the gasification chamber
81 as a fluidizing gas, then an excessive amount of combustion gas
is supplied to a freeboard of the gasification chamber 81. If the
combustion gas is insufficiently supplied to the gasification
chamber 81 as a fluidizing gas, then steam or inert gas such as
nitrogen or CO.sub.2 is supplied to the gasification chamber 81.
Specifically, no combustion gas is released to an atmosphere from
the integrated gasification furnace shown in FIG. 9. On the other
hand, the scattered particles which have been collected flow
through a loop seal into the gasification chamber 81. Material
sealing effects of the scattered particles in the loop seal prevent
the produced gas and the combustion gas from mixing with each
other. The scattered particles in the loop seal may be fluidized.
In this case, it is desirable to use steam or inert gas such as
nitrogen or CO.sub.2 as a fluidizing gas in the loop seal.
[0086] In a case where the gasification chamber 81 uses catalyst
particles as at least a portion of bed materials, a gas produced by
pyrolysis gasification of a raw material in the fast fluidized bed
of the gasification chamber 81 is decomposed and reformed. During
this process, carbon or the like is deposited on surfaces of
catalyst particles, and combusted and removed in the combustion
chamber 83. Thus, catalyst particles are regenerated. The
combustion chamber 83 may be supplied with an auxiliary fuel such
as oil.
[0087] Further, chlorine compounds and sulfur compounds contained
in a gas produced in the gasification chamber 81 are absorbed and
removed, and absorption catalysts such as calcium compounds are
used as at least a portion of medium particles to purify the
produced gas. Thus, it is possible to reduce the concentration of
toxic components in the produced gas to be discharged.
[0088] FIG. 10 is a schematic diagram showing a gasification system
according to an eighth embodiment of the present invention. The
gasification system shown in FIG. 10 has a gasification furnace 91,
a combustion furnace 92, and a heat recovery furnace 93. For
purposes of illustration, FIG. 10 shows only gas paths between the
gasification furnace 91, the combustion furnace 92, and the heat
recovery furnace 93. However, the gasification system practically
has other paths as shown in FIGS. 3 through 6. The gasification
furnace 91 comprises a fluidized-bed furnace having a temperature
of 350 to 950.degree. C. The combustion furnace 92 comprises a
fluidized-bed furnace having a temperature of 600 to 1000.degree.
C. The heat recovery furnace 93 comprises a fluidized-bed furnace.
Wastes are supplied to the gasification furnace 91, where the
wastes are gasified (or pyrolyzed) to produce a combustible gas and
char as a pyrolysis residue. The combustible gas is utilized as a
fuel gas. Char is supplied into the combustion furnace 92 together
with a bed material. The combustion furnace 92 is supplied with
oxygen. Char supplied from the gasification furnace 91 is combusted
in the combustion furnace 92. The combustion gas discharged from
the combustion furnace 92 is returned to the combustion furnace 92,
the gasification furnace 91, and the heat recovery furnace 93,
respectively. The same amount of bed material as a bed material
supplied from the gasification furnace 91 into the combustion
furnace 92 is supplied to the heat recovery furnace 93. The heat
recovery furnace 93 has a heat transfer pipe disposed in a
fluidized bed of the heat recovery furnace 93. Water in the heat
transfer pipe is heated so as to produce steam. The combustion gas
supplied from the combustion furnace 92 into the heat recovery
furnace 93 as a fluidizing gas is discharged from the heat recovery
furnace 93 and returned to the combustion furnace 92. The same
amount of bed material as a bed material supplied from the
combustion furnace 92 into the heat recovery furnace 93 is supplied
from the heat recovery furnace 93 to the gasification furnace 91.
The combustion gas discharged from the combustion furnace 92 is
returned to the gasification furnace 91 as a fluidizing gas. If the
combustion gas is insufficiently discharged from the combustion
furnace 92 as a fluidizing gas to the gasification furnace 91, then
water vapor (steam) or inert gas such as nitrogen or CO.sub.2 is
supplied to the gasification furnace 91. With the above
arrangement, since no combustion gas is released to an atmosphere
from the gasification system, the gasification system does not need
any chimneys.
[0089] According to the eighth embodiment, since no exhaust gas is
released to an atmosphere from the gasification system, the
gasification system does not contaminate the atmosphere. Further,
it is possible to simplify an exhaust gas treatment facility.
Furthermore, the gasification system does not need any chimneys and
can achieve a clean system.
[0090] Further, chlorine compounds and sulfur compounds contained
in a gas produced in the gasification furnace 91 are absorbed and
removed, and absorption catalysts such as calcium compounds are
used as at least a portion of medium particles to purify the
produced gas. Thus, it is possible to reduce the concentration of
toxic components in the produced gas to be discharged.
[0091] 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
[0092] The present invention is suitable for use in a gasification
system for gasifying various wastes such as municipal solid wastes,
industrial wastes, and waste plastics, biomass, and combustible
materials such as coal and refuse-derived fuel (RDF) in a
gasification furnace or chamber and recovering a valuable
combustible gas produced by gasification.
* * * * *