U.S. patent application number 13/805922 was filed with the patent office on 2013-04-25 for fluidized bed furnace and waste treatment method.
This patent application is currently assigned to KOBELCO ECO-SOLUTIONS CO., LTD.. The applicant listed for this patent is Hiroyuki Hosoda, Tadashi Ito, Takuya Kawai. Invention is credited to Hiroyuki Hosoda, Tadashi Ito, Takuya Kawai.
Application Number | 20130098277 13/805922 |
Document ID | / |
Family ID | 45371155 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130098277 |
Kind Code |
A1 |
Kawai; Takuya ; et
al. |
April 25, 2013 |
FLUIDIZED BED FURNACE AND WASTE TREATMENT METHOD
Abstract
A waste treatment technique includes: blowing a fluidizing gas
from around a mixture discharge port to form a first fluidization
region having a degree of fluidization of the fluidizable particles
which is set to an extent allowing waste to be accumulated on
fluidizable particles, while blowing a fluidizing gas between the
first fluidization region and an opposite-side wall at a higher
flow velocity to form a second fluid region having a degree of
fluidization of fluidizable particles greater than that in the
first fluidization region, whereby the fluidizable particles are
mixed with the waste to gasify the waste; and supplying waste from
a supply-side sidewall portion onto the fluidized bed to cause the
waste to be accumulated on the first fluidization region while
causing the accumulated waste to be moved into the second
fluidization region step-by-step.
Inventors: |
Kawai; Takuya;
(Nishinomiya-shi, JP) ; Hosoda; Hiroyuki;
(Kobe-city, JP) ; Ito; Tadashi; (Kobe,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kawai; Takuya
Hosoda; Hiroyuki
Ito; Tadashi |
Nishinomiya-shi
Kobe-city
Kobe |
|
JP
JP
JP |
|
|
Assignee: |
KOBELCO ECO-SOLUTIONS CO.,
LTD.
Hyogo
JP
|
Family ID: |
45371155 |
Appl. No.: |
13/805922 |
Filed: |
June 21, 2011 |
PCT Filed: |
June 21, 2011 |
PCT NO: |
PCT/JP2011/003528 |
371 Date: |
December 20, 2012 |
Current U.S.
Class: |
110/230 ;
110/259; 110/346; 431/170; 431/7 |
Current CPC
Class: |
F23G 5/027 20130101;
F23G 5/30 20130101; F23G 2205/101 20130101; F23G 5/0276 20130101;
F23C 10/26 20130101; F23C 10/22 20130101; F23C 10/10 20130101; F23C
10/20 20130101 |
Class at
Publication: |
110/230 ;
431/170; 110/259; 431/7; 110/346 |
International
Class: |
F23G 5/027 20060101
F23G005/027; F23C 10/10 20060101 F23C010/10; F23C 10/20 20060101
F23C010/20; F23G 5/30 20060101 F23G005/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2010 |
JP |
2010-141830 |
Jul 22, 2010 |
JP |
2010-164745 |
Claims
1. A fluidized bed furnace for heating waste to extract a
combustible gas from the waste, comprising: fluidizable particles
making up a fluidized bed to heat the waste; a furnace body having
a bottom wall supporting the fluidizable particles from therebelow,
and a sidewall standing upwardly from the bottom wall, wherein the
bottom wall has a mixture discharge port provided at a position
offset from a center position of the bottom wall in a specific
direction to discharge non-combustible substances in the waste and
carbides produced by heating of the waste, together with a part of
the fluidizable particles, and an upper surface of the bottom wall
is inclined to become lower toward the mixture discharge port so as
to cause the fluidizable particles to fall on the upper surface of
the bottom wall toward the mixture discharge port; a gas supply
section for blowing a fluidizing gas from the bottom wall of the
furnace body toward the fluidizable particles to fluidize the
fluidizable particles; a waste supply section for supplying waste
from a supply-side portion of the sidewall located on the same side
as the mixture discharge port with respect to the center position
of the bottom wall, to a region on the fluidized bed adjacent to
the supply-side sidewall portion, thereby causing the waste on the
fluidized bed to be moved toward an opposite-side portion of the
sidewall on a side opposite to the mixture discharge port across
the center position of the bottom wall, wherein: the gas supply
section is adapted to blow the fluidizing gas from around the
mixture discharge port to form a first fluidization region having a
degree of fluidization of the fluidizable particles which is set to
an extent allowing waste to be accumulated on the fluidizable
particles, while blowing the fluidizing gas between the first
fluidization region and the opposite-side sidewall portion at a
flow velocity greater than that of the fluidizing gas to be blown
in the first fluidization region, to form a second fluidization
region having a degree of fluidization of the fluidizable particles
greater than that in the first fluidization region, whereby the
fluidizable particles are moved in a convection-like pattern and
mixed with the waste to gasify the waste; and the waste supply
section is adapted to supply waste from the supply-side sidewall
portion to the fluidized bed to cause the waste to be accumulated
on the first fluidization region while causing the accumulated
waste to be moved into the second fluidization region
step-by-step.
2. The fluidized bed furnace as defined in claim 1, wherein the
waste supply section is adapted to push new waste generally
horizontally from the supply-side sidewall portion toward the waste
accumulated on the first fluidization region, thereby causing the
waste accumulated on the first fluidization region to be moved into
the second fluidization region step-by-step.
3. The fluidized bed furnace as defined in claim 1, which comprises
a carbide introduction device for separating the carbides from a
mixture of the non-combustible substances, the carbides and the
fluidizable particles discharged from the mixture discharge port,
and returning the separated carbides to the fluidized bed from the
side of the opposite-side sidewall portion.
4. The fluidized bed furnace as defined in claim 1, wherein the gas
supply section is adapted to blow the fluidizing gas in the first
fluidization region at a flow velocity satisfying a condition that
U.sub.o/U.sub.mf ranges from 1 to less than 2, and blow the
fluidizing gas in the second fluidization region at a flow velocity
satisfying a condition that U.sub.o/U.sub.mf ranges from 2 to less
than 5, where U.sub.mf is a minimum fluidization velocity which is
a minimum flow velocity of the fluidizing gas to be blown enough to
fluidize the fluidizable particles, and U.sub.o is a
cross-sectional average flow velocity of the fluidizing gas.
5. The fluidized bed furnace as defined in claim 1, which comprises
a sand circulation device for separating the fluidizable particles
from a mixture of the non-combustible substances, the carbides and
the fluidizable particles, the mixture discharged from the mixture
discharge port, and returning the separated fluidizable particles
to the furnace body.
6. The fluidized bed furnace as defined in claim 5, wherein the
sand circulation device is adapted to return the fluidizable
particles separated from the mixture onto the waste accumulated on
the first fluidization region.
7. The fluidized bed furnace as defined in claim 1, wherein the
furnace body has a shape in plan view, in which a dimension in a
width direction perpendicular to a pushing direction along which
waste is pushed by the waste supply section is equalized in the
pushing direction.
8. The fluidized bed furnace as defined in claim 7, wherein the
waste supply section comprises a pusher having a pushing surface
extending in the width direction, and a drive unit for
reciprocatingly moving the pusher in a direction parallel to the
pushing direction to allow the pushing surface of the pusher to
push waste onto the fluidized bed simultaneously by the entire
widthwise region of the pushing surface.
9. A waste treatment method for heating waste to extract a
combustible gas from the waste, comprising: a preparation step of
preparing a fluidized bed furnace comprising fluidizable particles
making up a fluidized bed to heat the waste, a furnace body having
a bottom wall supporting the fluidizable particles from therebelow
and a sidewall standing upwardly from the bottom wall, wherein the
bottom wall has a mixture discharge port provided at a position
offset from a center position of the bottom wall in a specific
direction to discharge non-combustible substances in the waste and
carbides produced by heating of the waste, together with a part of
the fluidizable particles, and an upper surface of the bottom wall
is inclined to become lower toward the mixture discharge port so as
to cause the fluidizable particles to fall on the upper surface of
the bottom wall toward the mixture discharge port; a
fluidization-region formation step of blowing a fluidizing gas from
a region of the bottom wall of the furnace body around the mixture
discharge port toward the fluidizable particles to form a first
fluidization region having a degree of fluidization of the
fluidizable particles which is set to an extent allowing waste to
be accumulated on the fluidizable particles, while blowing the
fluidizing gas between the first fluidization region and an
opposite-side portion of the sidewall on a side opposite to the
mixture discharge port across the center position of the bottom
wall, at a flow velocity greater than that of the fluidizing gas to
be blown in the first fluidization region, to form a second
fluidization region having a degree of fluidization of the
fluidizable particles greater than that in the first fluidization
region; and a gasification step of supplying waste from a
supply-side portion of the sidewall located on the same side as the
mixture discharge port with respect to the center position of the
bottom wall, to a region on the fluidized bed adjacent to the
supply-side sidewall portion, thereby causing the waste to be
accumulated on the first fluidization region, while causing the
accumulated waste to be moved into the second fluidization region
step-by-step and gasified.
10. The waste treatment method as defined in claim 9, wherein the
gasification step includes pushing new waste generally horizontally
from the supply-side sidewall portion toward the waste accumulated
on the first fluidization region, thereby causing the waste
accumulated on the first fluidization region to be moved into the
second fluidization region step-by-step and gasified.
11. The waste treatment method as defined in claim 9, which
comprises a step of separating the carbides from a mixture of the
non-combustible substances, the carbides and the fluidizable
particles, the mixture discharged from the mixture discharge port,
and returning the separated carbides to the fluidized bed from the
side of the opposite-side sidewall portion.
12. The waste treatment method as defined in claim 9, wherein the
fluidizing gas is blown in the first fluidization region at a flow
velocity satisfying a condition that U.sub.o/U.sub.mf ranges from 1
to less than 2, and blown in the second fluidization region at a
flow velocity satisfying a condition that U.sub.o/U.sub.mf ranges
from 2 to less than 5, where U.sub.mf is a minimum fluidization
velocity which is a minimum flow velocity of the fluidizing gas to
be blown so as to fluidize the fluidizable particles, and U.sub.o
is a cross-sectional average flow velocity of the fluidizing gas.
Description
TECHNICAL FIELD
[0001] The present invention relates to a fluidized bed furnace
designed to heat waste in a fluidized bed formed by fluidizing
fluidizable particles to thereby extract a combustible gas from the
waste, and a waste treatment method.
BACKGROUND ART
[0002] Heretofore, as a fluidized bed furnace, there has been known
one type described in the following Patent Document 1. As
illustrated in FIG. 9, this fluidized bed furnace comprises a
furnace body 104 having fluidizable sand (fluidizable particles)
102 in a furnace bottom section, and an air supply section 106 for
supplying air into the fluidizable sand 102 in the furnace bottom
section so as to fluidize the fluidizable sand 102 to form a
fluidized bed. The furnace body 104 has a sidewall. The sidewall is
provided with an input section 108 for inputting waste onto the
fluidized bed therefrom.
[0003] In this fluidized bed furnace 100, the air supply section
106 is adapted to supply air into high-temperature fluidizable sand
102. Consequently, the fluidizable sand 102 is fluidized in a
levitated or suspended state to form a fluidized bed. In this
process, the air supply section 106 is adapted to supply air in
such a manner that a fluidized state of the fluidizable sand 102
becomes approximately equalized in the entire region of the
fluidized bed so as to allow waste input from the input section 108
onto the fluidized bed to be entrapped inside the fluidized bed and
efficiently combusted.
[0004] Every time waste is input from the input section 108 onto
the high-temperature fluidizable sand 102, the input waste is mixed
with the high-temperature fluidizable sand 102 of the fluidized
bed, and thermally decomposed (gasified). Consequently, a
combustible gas is generated. For example, this combustible gas
will be combusted at high temperatures in a melting furnace in a
subsequent stage.
[0005] Waste input into the fluidized bed furnace 100 is entrapped
in the active fluidized bed and combusted or gasified. In this
process, every time waste is intermittently input, combustible
substances in the waste are rapidly combusted, so that a rapid
fluctuation in amount, concentration, etc., of a generated
combustible gas will repeatedly occur. A change in the gasification
reaction is largely dependent on a quantitative characteristic in
supply of waste. Thus, in the case where there is a fluctuation in
supply of waste or a qualitative change in components of waste, it
is impossible to stably generate a combustible gas. Particularly,
when a large amount of easily combustible trash such as paper or
sheet-shaped plastic is comprised in waste, a fluctuation of
generation of a combustible gas becomes larger, and therefore there
is a need for stabilizing the gas generation.
[0006] For example, in the case where generated combustible gas is
used for a gas engine to generate electric power, if a combustible
gas is generated with large fluctuations, it is impossible to
obtain stable energy. Therefore, there is a need for further
stabilizing a combustible gas to be obtained in a fluidized bed
furnace.
LIST OF PRIOR ART DOCUMENTS
Patent Documents
[0007] Patent Document 1: JP 2006-242454A
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide a
fluidized bed furnace capable of stably obtaining a combustible gas
even from waste comprising easily combustible trash, and a waste
treatment method.
[0009] According to one aspect of the present invention, there is
provided a fluidized bed furnace for heating waste to extract a
combustible gas from the waste. The fluidized bed furnace
comprises: fluidizable particles making up a fluidized bed to heat
the waste; a furnace body having a bottom wall supporting the
fluidizable particles from therebelow, and a sidewall standing
upwardly from the bottom wall, wherein the bottom wall has a
mixture discharge port provided at a position offset from a center
position of the bottom wall in a specific direction to discharge
non-combustible substances in the waste and carbides produced by
heating of the waste, together with a part of the fluidizable
particles, and an upper surface of the bottom wall is inclined to
become lower toward the mixture discharge port so as to cause the
fluidizable particles to fall on the upper surface of the bottom
wall toward the mixture discharge port; a gas supply section for
blowing a fluidizing gas from the bottom wall of the furnace body
toward the fluidizable particles to fluidize the fluidizable
particles; a waste supply section for supplying waste from a
supply-side portion of the sidewall located on the same side as the
mixture discharge port with respect to the center position of the
bottom wall, to a region on the fluidized bed adjacent to the
supply-side sidewall portion, thereby causing the waste on the
fluidized bed to be moved toward an opposite-side portion of the
sidewall on a side opposite to the mixture discharge port across
the center position of the bottom wall. The gas supply section is
adapted to blow the fluidizing gas from around the mixture
discharge port to form a first fluidization region having a degree
of fluidization of the fluidizable particles which is set to an
extent allowing waste to be accumulated on the fluidizable
particles, while blowing the fluidizing gas between the first
fluidization region and the opposite-side sidewall portion at a
flow velocity greater than that of the fluidizing gas to be blown
in the first fluidization region, to form a second fluidization
region having a degree of fluidization of the fluidizable particles
greater than that in the first fluidization region, whereby the
fluidizable particles is moved in a convection-like pattern and
mixed with the waste to gasify the waste, and the waste supply
section is adapted to supply waste from the supply-side sidewall
portion to the fluidized bed to cause the waste to be accumulated
on the first fluidization region while causing the accumulated
waste to be moved into the second fluidization region
step-by-step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic configuration diagram of a fluidized
bed furnace according to one embodiment of the present
invention.
[0011] FIG. 2 is a horizontal sectional view of a furnace body, for
explaining an introduction position of waste and an introduction
position of fluidizable particles in the fluidized bed furnace.
[0012] FIG. 3 is a diagram for explaining a nozzle arrangement in a
bottom wall of the furnace body.
[0013] FIG. 4 is a diagram for explaining a furnace body having a
reflecting portion in a front wall thereof, in a fluidized bed
furnace according to another embodiment of the present
invention.
[0014] FIG. 5 is a diagram for explaining a furnace body having a
guide portion in a rear wall thereof, in a fluidized bed furnace
according to yet another embodiment of the present invention.
[0015] FIG. 6 is a diagram for explaining a furnace body having a
roof portion in each of front and rear walls thereof, in a
fluidized bed furnace according to still another embodiment of the
present invention.
[0016] FIG. 7 is a diagram for explaining a furnace body comprising
a thermometer and an air supply section, in a fluidized bed furnace
according to yet still another embodiment of the present
invention.
[0017] FIG. 8 is a diagram for explaining a waste supply section,
in a fluidized bed furnace according to another further embodiment
of the present invention.
[0018] FIG. 9 is a schematic configuration diagram of a
conventional fluidized bed furnace.
DESCRIPTION OF EMBODIMENTS
[0019] With reference to the accompanying drawings, the present
invention will now be described based on one embodiment
thereof.
[0020] A fluidized bed furnace according to this embodiment is
designed to heat waste by high-temperature fluidizable particles,
to extract a combustible gas from the waste. As illustrated in FIG.
1, the fluidized bed furnace comprises fluidizable particles 12, a
furnace body 20, a gas supply section 30, a waste supply section
40, a sand circulation device 50 and a carbide introduction device
60.
[0021] The fluidizable particles 12 make up a fluidized bed 14 to
heat waste 18, inside the furnace body 20. More specifically, the
fluidizable particles 12 are mixed with waste 18 while being heated
up to a high temperature by combustion of a part of waste
components, so that the waste 18 is gasified to generate a
combustible gas. For example, the fluidizable particles 12 may be
silica sand.
[0022] The furnace body 20 is configured to internally have the
fluidizable particles 12 and extract a combustible gas from waste
18 by means of the fluidizable particles 12 in a high temperature
state. The furnace body 20 has a bottom wall 21 supporting the
fluidizable particles 12 from therebelow, a sidewall 22 standing
upwardly from the bottom wall 21, and a combustible gas outlet
portion 23 provided at an upper end of the sidewall 22.
[0023] The sidewall 22 has a rectangular tubular shape extending in
an up-down (vertical) direction. Specifically, as also illustrated
in FIG. 2, the sidewall 22 has a front wall (supply-side sidewall
portion) 24 and a rear wall (opposite-side sidewall portion) 25
which are disposed in opposed and spaced-apart relation to each
other in a front-rear direction (in FIG. 2, in a right-left
direction), and a pair of lateral walls 26, 26 each connecting
corresponding ends of the front wall 24 and the rear wall 25. The
lateral walls 26, 26 are disposed parallel to each other. In other
words, the furnace body 20 has a shape in plan view, in which a
dimension in a width direction (widthwise dimension) as a distance
between the lateral walls 26, 26 is equalized in the front-rear
direction.
[0024] A portion (front wall) 24 of the sidewall 22 located on the
same side as an aftermentioned mixture discharge port 29 with
respect to a center position of the bottom wall 21 has a sand
introduction section 27 and a waste introduction port 28. The sand
introduction section 27 is designed to introduce fluidizable
particles 12 into the furnace body 20, and the waste introduction
port 28 is designed to introduce waste 18 into the furnace body 20.
Further, a portion (rear wall) 25 of the sidewall 22 located on a
side opposite to the aftermentioned mixture discharge port 29
across the center position of the bottom wall 21 has a carbide
introduction section 63. The carbide introduction section 63 is
designed to introduce carbides (e.g., char) produced by heating of
the waste 18, into the furnace body 20.
[0025] Specifically, the sand introduction section 27 is provided
at a widthwise central region of a lower portion of the front wall
24 to allow fluidizable particles to be introduced into the furnace
body 20 in a widthwise central area adjacent to the front wall 24
(see FIG. 2). The sand introduction section 27 is provided at a
height position where fluidizable particles 12 can be input from
above the fluidizable particles 12 supported by the bottom wall 21
of the furnace body 20 (fluidized bed 14), toward the fluidized bed
14 (more specifically, the waste 18 supplied onto and accumulated
on the fluidized bed 14). Based on providing the sand introduction
section 27 at the above specific position, it becomes possible to
input fluidizable particles 12 onto the waste 18 accumulated on the
fluidized bed 14. In this case, the fluidizable particles 12 serve
as an ignition source to allow easily-combustible trash in the
waste 18 to be stably combusted (gasified) initially. It is to be
noted that a section for inputting fluidizable particles 12 is not
limited to the front wall, but may be provided in the rear wall 25
or the lateral wall 26.
[0026] The carbide introduction section 63 is provided at a
widthwise central region of a lower portion of the rear wall 25 to
allow carbides to be introduced into the furnace body 20 in a
widthwise central area adjacent to the rear wall 25 (see FIG. 2).
The carbide introduction section 63 is provided at a height
position where carbides can be input from above the fluidized bed
14 in the furnace body 20, toward the fluidized bed 14.
Alternatively, the carbide introduction section 63 may be provided
at a vertically intermediate height position of the fluidized bed
14. When the carbide introduction section 63 is provided at the
above position, the carbides are directly introduced into the
fluidized bed 14. This allows carbides to be reliably introduced
into the fluidized bed 14 and reliably gasified, although carbide
is light in weight, so that, when the carbides are input from above
the fluidized bed 14, they are apt to be accumulated on the
fluidized bed 14 and hard to be sufficiently mixed with the
fluidizable particles 12.
[0027] The waste introduction port 28 is provided in approximately
the entire region of the lower portion of the front wall 24 in the
width direction. The waste introduction port 28 is provided at a
height position where waste 18 can be pushed generally horizontally
onto an upper surface of the fluidized bed 14 made up of the
fluidizable particles 12 supported by the bottom end 21 of the
furnace body 20. In other words, the waste introduction port 28 is
provided in such a manner that a lower end thereof is located at a
position slightly higher than the upper surface of the fluidized
bed 14.
[0028] The combustible gas outlet portion 23 is designed to
discharge a combustible gas generated inside the furnace body 20.
The combustible gas outlet portion 23 has an outer diameter
squeezed more than the sidewall 22, so that a duct or the like for
supplying the combustible gas obtained in the furnace body 20 to a
subsequent stage, for example, a gas engine for electric power
generation processes, can be connected thereto.
[0029] The bottom wall 21 has a mixture discharge port 29 provided
at a position offset from the center position thereof in a specific
direction to discharge non-combustible substances in waste 18 and
carbides produced by heating of the waste 18, together with a part
of the fluidizable particles 12. The mixture discharge port 29 has
an opening extending over the widthwise entire region of the bottom
wall 21. The bottom wall 21 has an upper surface 21a inclined to
become lower toward the mixture discharge port 29 so as to cause
the fluidizable particles 12 to fall on the upper surface 21a. The
bottom wall 21 in this embodiment has a mixture discharge port 29
at a position offset frontwardly, and the upper surface 21a of the
bottom wall 21 extends frontwardly (in FIG. 1, in a left-to-right
direction) at a constant downward inclination. Specifically, the
upper surface 21a of the bottom wall 21 has an inclination angle of
15 degrees to 25 degrees with respect to a horizontal plane. Based
on providing the mixture discharge port 29 at the above position,
non-combustible substances and carbides sinking down from the waste
18 introduced from the waste introduction port 28 provided in the
front wall 24, to a region on the fluidized bed 14 adjacent to the
front wall 24, are efficiently discharged to an outside of the
furnace body 20 therethrough. Further, non-combustible substances
and carbides sinking down from the waste 18 spread on the fluidized
bed 14 toward the rear wall 25 while passing through the fluidized
bed 14, and fall to the mixture discharge port 29 along the
inclination of the upper surface 21a of the bottom wall 21 and will
reach. Thus, the non-combustible substances and carbides which have
sunk down on the side of the rear wall 25 are also discharged to
the outside of the furnace body 20 in an easy manner.
[0030] The upper surface 21a of the bottom wall 21 is inclined to
become lower toward the mixture discharge port 29. Thus, during
operation of the fluidized bed furnace 10, the fluidizable
particles 12 in a region of the fluidized bed 14 adjacent to the
upper surface 21a are moved from the side of the rear wall 25
toward the front wall 24.
[0031] The gas supply section 30 is designed to blow a fluidizing
gas from the bottom wall 21 toward the fluidizable particles 12 to
fluidize the fluidizable particles 12. The gas supply section 30
comprises a plurality of nozzles 31 for blowing the fluidizing gas,
a gas box 32 for supplying the fluidizing gas to the nozzles 31,
and a gas feeding unit 33 for feeding the fluidizing gas to the gas
box 32.
[0032] The plurality of nozzles 31 are installed to the bottom wall
21 in spaced-apart relation to each other in the width direction
and the front-rear direction, i.e., in a lattice arrangement. Each
of the nozzles 31 is attached to the bottom wall 21 to penetrate
through the bottom wall 21. In this embodiment, as also illustrated
in FIG. 3, the bottom wall 21 is divided into a rear region 21b and
a front region 21c. Then, the plurality of nozzles 31 are installed
to the rear and front regions 21b, 21c in such a manner that the
number of nozzles 31 provided in the rear region 21b becomes
greater than the number of nozzles 31 provided in the front region
21c. It is to be noted that a relationship between the respective
numbers of nozzles 31 in the rear and front regions 21b, 21c is not
particularly limited. For example, the number of nozzles 31 in the
front region 21c may be equal to the number of nozzles 31 in the
rear region 21b. Alternatively, the number of nozzles 31 in the
front region 21c may be greater than the number of nozzles 31 in
the rear region 21b.
[0033] The gas box 32 has a box shape extending in the width
direction, and serves as a header for distributing the fluidizing
gas to an array of the nozzles 31 arranged side-by-side in the
width direction in the bottom wall 21. The gas box 32 has a
function of equalizing respective flow volumes of the fluidizing
gas to be blown from the array of nozzles 31 arranged in the width
direction. In this embodiment, a plurality of the gas boxes 32 are
provided on the side of a lower surface of the bottom wall 21 and
arranged side-by-side in the front-rear direction. Thus, with
respect to each of a plurality of the arrays of nozzles 31
corresponding to respective ones of the gas boxes 32, the flow
volume of the fluidizing gas to be blown from the array of nozzles
31 can be changed. In this embodiment, five gas boxes 32a, 32b,
32c, 32d, 32e are arranged side-by-side in the front-rear
direction. Specifically, four gas boxes 32a, 32b, 32c, 32d are
disposed on the side of the rear wall 25 with respect to the
mixture discharge port 29, and one gas box 32e is disposed on the
side of the front wall 24 with respect to the mixture discharge
port 29.
[0034] The gas feeding unit 33 is designed to feed (supply) the
fluidizing gas to the respective gas boxes 32. The gas feeding unit
33 is capable of feeding the fluidizing gas to each of the gas
boxes 32 in a different flow volume. The gas feeding unit 33 in
this embodiment is configured to feed the fluidizing gas to two of
the gas boxes 32 adjacent to each other in the front-rear
direction, in such a manner that a flow volume of the fluidizing
gas to be fed to a rear one of the adjacent gas boxes 32 becomes
greater than a flow volume of the fluidizing gas to be fed to a
front one of the adjacent gas boxes 32. The gas feeding unit 33 is
adapted to feed only air to the respective gas boxes 32 to serve as
the fluidizing gas. Alternatively, an inert gas such as nitrogen
may be fed in combination with the air.
[0035] Specifically, during a normal operation of the fluidized bed
furnace 10, i.e., when waste 18 is introduced into the furnace body
20 to generate a combustible gas from the introduced waste 18, the
gas feeding unit 33 is operable to cause the fluidizing gas to be
blown from around the mixture discharge port 29. In this process,
the gas feeding unit 33 is operable to form a first fluidization
region 15 having a degree of fluidization of the fluidizable
particles 12 which is set to an extent allowing the waste 18 to be
accumulated on the fluidizable particles 12. Concurrently, the gas
feeding unit 33 is operable to blow the fluidizing gas between the
first fluidization region 15 and the rear wall 25 at a flow
velocity greater than that of the fluidizing gas to be blown in the
first fluidization region 15, to form a second fluidization region
16 having a degree of fluidization of the fluidizable particles 12
higher than that in the first fluidization region 15. More
specifically, as mentioned above, the gas feeding unit 33 is
configured such that a flow volume of the fluidizing gas to be fed
to a rear one (e.g., the gas box 32b) of the gas boxes 32 adjacent
to each other in the front-rear direction becomes greater than a
flow volume of the fluidizing gas to be fed to a front one (e.g.,
the gas box 32c) of the adjacent gas boxes 32. In this case, the
gas feeding unit 33 is operable to, in the fluidized bed 14, form
the first fluidization region 15 restrained in fluidization, around
the mixture discharge port 29, while forming the second
fluidization region 16 actively fluidized, between the first
fluidization region 15 and the rear wall 25. Alternatively, the gas
feeding unit 33 may be configured to feed the fluidizing gas to
each of the gas boxes 32c, 32d, 32e on the side of the front wall
24, in a constant flow volume, and feed the fluidizing gas to each
of the gas boxes 32a, 32b on the side of the rear wall 25, in a
flow volume greater than the constant flow volume. In this case,
the gas feeding unit 33 is operable to, in the fluidized bed 14,
form the first fluidization region 15 restrained in fluidization,
in a region corresponding to the gas boxes 32c, 32d, 32e on the
side of the front wall 24, while forming the second fluidization
region 16 actively fluidized, in a region corresponding to the gas
boxes 32a, 32b on the side of the rear wall 25.
[0036] Specifically, the gas feeding unit 33 is adapted to cause
the fluidizing gas to be blown in the first fluidization region 15
at the flow velocity satisfying a condition that U.sub.o/U.sub.mf
ranges from 1 to less than 2, and blown in the second fluidization
region 16 at the flow velocity satisfying a condition that
U.sub.o/U.sub.mf ranges from 2 to less than 5. In this formula,
U.sub.mf is a minimum fluidization velocity which is a minimum flow
velocity of the fluidizing gas to be blown so as to fluidize the
fluidizable particles 12. Further, U.sub.o is a cross-sectional
average flow velocity of the fluidizing gas.
[0037] On the other hand, during stop of the fluidized bed furnace
10, i.e., when the introduction of waste 18 into the furnace body
20 is stopped, the gas feeding unit 33 is operable to feed a
mixture formed by mixing an inert gas with air, as the fluidizing
gas to be supplied to the respective gas boxes 32. Then, the gas
feeding unit 33 is operable to gradually increase the inert gas in
a ratio between air and the inert gas in the fluidizing gas.
Consequently, the gas feeding unit 33 can suppress violent or rapid
combustion of the waste 18 remaining in the furnace body 20,
thereby restraining a rise in internal temperature of the furnace
body 20.
[0038] More specifically, during the normal operation, in the
furnace body 20, combustion, gasification, etc., of the waste 18
are performed under a condition that an oxygen concentration is set
to a value less than that suitable for combustion of the waste 18.
In this state, when the introduction of waste 18 into the furnace
body 20 is stopped, an amount of combustible substances in the
furnace body 20 will be reduced. In this process, the fluidizing
gas (air) is continuously supplied into the furnace body 20 in a
predetermined flow volume to maintain the fluidized bed 14, so that
the oxygen concentration in the furnace body 20 will be increased.
When the oxygen concentration in the furnace body 20 reaches a
value suitable for combustion of the waste 18 remaining in the
furnace body 20, the waste 18 is violently or rapidly combusted, so
that the internal temperature of the furnace body 20 becomes higher
than that during the normal operation. In such a high-temperature
state of the inside of the furnace body 20, the fluidizable
particles 12 forming the fluidized bed 14 are agglomerated due to
the heat. Once the fluidizable particles 12 are agglomerated, even
if the fluidizing gas is subsequently blown into the agglomerated
fluidizable particles 12 in order to form the fluidized bed 14, the
agglomerated fluidizable particles 12 will never be fluidized.
Therefore, the gas feeding unit 33 is operable, when the
introduction of waste 18 into the furnace body 20 is stopped, to
mix an inert gas with air to be blown into the furnace body 20, and
gradually increase the ratio of the inert gas. This allows the
oxygen concentration in the furnace body 20 to be kept at a value
less than that suitable for combustion of the waste 18.
Consequently, it becomes possible to suppress violent or rapid
combustion of the waste 18 remaining in the furnace body 20.
[0039] Further, the gas feeding unit 33 is adapted to be capable of
adjusting a temperature of the fluidizing gas to be fed to the gas
boxes 32. The gas feeding unit 33 is operable, upon start of the
operation of the fluidized bed furnace 10, to blow the fluidizing
gas in a high temperature state from a region corresponding to the
second fluidization region 16, toward the fluidizable particles 12.
In this way, the gas feeding unit 33 is operable to heat the
fluidizable particles 12 until the fluidizable particles 12 reach a
temperature capable of performing combustion and gasification of
the waste 18. In this case, when the fluidizable particles 12 is
heated up to a high temperature and combustion of the waste 18 is
started, the temperature of the fluidizable particles 12 will be
maintained by the combustion. Thus, the gas feeding unit 33 may be
configured to lower the temperature of the fluidizing gas to be fed
to the gas boxes 32 just after start of the combustion.
[0040] The waste supply section 40 is designed to supply waste 18
from the front wall 24 to a region on the fluidized bed 14 adjacent
to the front wall 24. The waste supply section 40 in this
embodiment is configured to push waste 18 generally horizontally
from the front wall 24 (specifically, the waste introduction port
28 of the front wall 24) onto the fluidized bed 14, thereby causing
the waste 18 to be moved toward the second fluidization region 16.
In other words, the waste supply section 40 is adapted to push
waste 18 to cause the waste 18 to be accumulated on the first
fluidization region 15 while causing the accumulated waste 18 to be
moved into the second fluidization region 16 step-by-step. The
waste supply section 40 comprises a pusher 41 and a drive unit
(illustration is omitted) for driving the pusher 41. The pusher 41
has a pushing surface 42 extending in the width direction. In this
embodiment, the pushing surface 42 has a widthwise length equal to
a width of the waste introduction port 28 of the front wall 24.
Further, the pushing surface 42 has a vertical length which is
approximately a half of a height dimension of an opening of the
waste introduction port 28. The pusher 41 is installed to be
movable in the front-rear direction, at the same height position as
that of the waste introduction port 28. The drive unit comprises a
driving power source such as a motor or a cylinder, and is adapted
to reciprocatingly move the pusher 41 in the front-rear direction
by the driving power. It is to be noted that the waste supply
section 40 is not limited to a specific configuration. For example,
the waste supply section 40 in this embodiment is configured such
that the pusher 41 is employed to push waste 18 into the furnace
body. However, the waste supply section may be configured such that
a screw extruder or the like is employed to push waste 18 into the
furnace body (see FIG. 8A). Based on employing the pusher 41 or the
screw extruder, it becomes possible to supply trash which is likely
to be scattered due to its small bulk specific gravity, such as
paper or plastic sheet, into the furnace body 20 while keeping a
massive form. This makes it possible to suppress scattering of
trash inside the furnace body 20, as compared to a conventional
furnace in which trash is input from an upper portion thereof.
[0041] The sand circulation device 50 is designed to separate the
fluidizable particles 12 from a mixture of the non-combustible
substances, the carbides and the fluidizable particles 12
discharged from the mixture discharge port 29, and return the
separated fluidizable particles 12 to the inside of the furnace
body 20, thereby circulating the fluidizable particles 12. As
above, according to the sand circulation device 50, the
high-temperature fluidizable particles 12 are separated from the
mixture and returned to the inside of the furnace body 20, which
makes it possible to maintain an amount of the fluidizable
particles 12 making up the fluidized bed 14 inside the furnace body
20, and makes it easy to maintain a temperature of the fluidized
bed 14. The sand circulation device 50 comprises a mixture
discharge section 51, a fluidizable-particle separation section 52,
and a fluidizable-particle conveyance section 53.
[0042] The mixture discharge section 51 is provided just below the
mixture discharge port 29 of the bottom wall 21, and adapted to
move the mixture of the non-combustible substances, the carbides
and the fluidizable particles 12 dropping from the mixture
discharge port 29, to the fluidizable-particle separation section
52. The mixture discharge section 51 in this embodiment is
configured to move the mixture dropping from the mixture discharge
port 29, to the fluidizable-particle separation section 52 by using
a screw extruder. The fluidizable-particle separation section 52 is
adapted to separate the fluidizable particles 12 from the mixture
sent from the mixture discharge section 51. The
fluidizable-particle separation section 52 in this embodiment is
configured to separate the fluidizable particles 12 from the
mixture by using a sieve. The fluidizable-particle separation
section 52 is operable to send the mixture after subjected to the
separation of the fluidizable particles 12, to a carbide separation
section 61. The fluidizable-particle conveyance section 53 is
adapted to convey the fluidizable particles 12 separated in the
fluidizable-particle separation section 52, to the sand
introduction section 27, and introduce the conveyed fluidizable
particles 12 into the furnace body 20 via the sand introduction
section 27.
[0043] In this embodiment, the sand circulation device 50 is
configured to input the fluidizable particles 12 from above the
fluidized bed 14 toward the upper surface of the fluidized bed 14.
Alternatively, the sand circulation device may be configured to
return the fluidizable particles 12 to the fluidized bed 14 in such
a manner as to push the fluidizable particles 12 directly into the
fluidized bed 14.
[0044] The carbide introduction device 60 is designed to separate
the carbides from the mixture discharged from the mixture discharge
port 29, and return the separated carbides to the inside of the
furnace body 20 from the side of the rear wall 25. As above,
according to the carbide introduction device 60, the carbides
discharged from the mixture discharge port 29 are returned to the
second fluidization region 16, which makes it possible to obtain a
combustible gas from the carbides discharged to outside of the
furnace body 20 together with the non-combustible substances.
Consequently, a combustible gas can be efficiently obtained from
waste 18 supplied to the fluidized bed furnace 10. In addition, a
temperature of the second fluidization region 16 can be kept at a
high value by heat generated when the carbides are gasified. The
carbide introduction device 60 comprises a carbide separation
section 61, and a carbide conveyance section 62.
[0045] The carbide separation section 61 is adapted to separate the
carbides from the mixture sent from the fluidizable-particle
separation section 52. The carbide separation section 61 in this
embodiment is configured to separate the carbides from the mixture
after subjected to the separation of the fluidizable particles 12
in the fluidizable-particle separation section 52. For example, the
carbide separation section 61 may be a gravity (specific gravity)
separator for separating a carbide from a mixture by means of
vibration. The carbide conveyance section 62 is adapted to convey
the carbides separated in the carbide separation section 61, to the
carbide introduction section 63, and introduce the conveyed
carbides into the furnace body 20 via the carbide introduction
section 63.
[0046] In the fluidized bed furnace 10 configured as above, a
combustible gas is collected from waste 18 in the following
manner.
[0047] The gas feeding unit 33 feeds the fluidizing gas to the
respective gas boxes 32. Thus, the fluidizing gas is blown from the
bottom wall 21 into the furnace body 20 toward the fluidizable
particles 12, so that the fluidized bed 14 is formed inside the
furnace body 20. In this process, the gas feeding unit 33 adjusts a
flow volume of the fluidizing gas to be fed to each of the gas
boxes 32. Through this adjustment, in the fluidized bed 14, the
first fluidization region 15 restrained in fluidization is formed
on the side of the mixture discharge port 29, and the second
fluidization region 16 actively fluidized is formed between the
first fluidization region 15 and the rear wall 25. Further, the gas
feeding unit 33 feeds the fluidizing gas in a high-temperature
state to a part (e.g., in this embodiment, the gas boxes 32a, 32b)
of the gas boxes 32 corresponding to the second fluidization region
16 to positively heat the fluidizable particles 12 in the second
fluidization region 16. Concurrently, heat is supplied to the first
fluidization region 15 by a movement of the fluidizable particles
12 from the second fluidization region 16 to the first fluidization
region 15 which occurs in a region of the fluidized bed 14 adjacent
to the upper surface 21a of the bottom wall 21 due to the
inclination of the upper surface 21a.
[0048] Subsequently, when temperatures of the regions 15, 16 in the
fluidized bed 14 formed inside the furnace body 20 reach respective
predetermined values (in this embodiment, the predetermined
temperature of the second fluidization region 16 is in the range of
about 600 to 800.degree. C., and the predetermined temperature of
the first fluidization region 15 is in the range of about 400 to
600.degree. C.), the waste supply section 40 starts to push waste
18 into the furnace body 20 via the waste introduction port 28.
Specifically, the pusher 41 driven by the drive unit pushes waste
18 generally horizontally toward the rear wall 25. Through this
operation, the waste 18 is pushed onto the first fluidization
region 15 at a position adjacent to the front wall 24 (see FIG.
2).
[0049] The fluidization of the fluidizable particles 12 in the
first fluidization region 15 is restrained. Thus, the pushed waste
18 is not positively mixed with the fluidizable particles 12, so
that most of the waste 18 is accumulated on the first fluidization
region 15, and heavy non-combustible substances and a part of
carbides therein sink down. Consequently, in the first fluidization
region 15, rapid combustion of the waste 18 is suppressed, and
easily gasifiable substances in the waste 18 are gasified by heat
radiation within the furnace body 20. In other words, easily
gasifiable waste 18 such as plastic or paper is gasified while
being moved in a surface layer of the first fluidization region 15.
In other words, easily gasifiable waste 18 such as plastic or paper
is gasified while being moved in a surface layer of the second
fluidization region 16. On the other hand, not-easily gasifiable
waste such as a wood piece is partially gasified, but a large part
thereof reaches the second fluidization region 16 without being
gasified. In this manner, the easily gasifiable waste 18 is
gasified under a mild condition in the first fluidization region 15
before it reaches the highly fluidized bed (second fluidization
region 16). This makes it possible to suppress a fluctuation of
generation of the combustible gas. The heavy non-combustible
substances sink down in the first fluidization region 15, and
directly discharged from the mixture discharge port 29. This, the
non-combustible substances are less likely to be accumulated on a
furnace floor. Further, in some cases, a part of the not-easily
gasifiable waste such as a wood piece is also discharged from the
mixture discharge port 29 in a state in which it is carbonized by
passing through the first fluidization region 15. The accumulated
waste 18 is combusted due to the internal temperature of the
furnace body 20 (heat in a free board section), as mentioned above.
However, although the internal temperature of the furnace body 20
is in the range of 800 to 900.degree. C. which is greater than that
of the fluidizable particles 12 forming the fluidized bed 14, a
contact between the waste 18 and air is not satisfactory. Thus,
easily combustible trash, such as paper or sheet-shaped plastic, in
waste 18, is mainly gasified. In this process, the first
fluidization region 15 has a relatively low temperature, and an
amount of air (fluidizing gas) to be supplied to the first
fluidization region 15 is relatively small, so that even the easily
combustible trash will be gradually gasified. Further, according to
fluidization of the fluidizable particles 12 caused by the
fluidizing gas, a part of the accumulated waste 18 is moved or
spread from the first fluidization region 15 to the second
fluidization region 16 (in FIG. 1, in a right-to-left direction)
step-by-step. Therefore, even if waste 18 is input in a massive
form, and easily combustible papers are comprised therein, the
papers will be gasified based on a phenomenon that the papers are
moved toward a surface of the massive waste during the spreading.
As above, in the first fluidization region 15, rapid combustion of
the waste 18 is suppressed to prevent a rapid increase of
combustible gas during introduction of waste 18.
[0050] Subsequently, new waste 18 is pushed into the furnace body
20 via the waste introduction port 28 by the pusher 41. Thus, the
waste 18 accumulated on the first fluidization region 15 is pushed
by the new waste 18, and moved into the second fluidization region
16 step-by-step. The second fluidization region 16 is actively
fluidized and heated up to a high temperature by combustion of the
waste 18, so that the waste 18 moved from a position on the first
fluidization region 15 is mixed with the fluidizable particles 12
and sufficiently gasified. Consequently, a combustible gas is
generated. More specifically, in the fluidized bed 14, a fluidized
state gradually becomes more active in a direction from the front
wall 24 to the rear wall 25. Thus, when the waste 18 is moved from
a position on the first fluidization region 15 adjacent to the
front wall 24 to the second fluidization region 16 step-by-step, it
will be gradually mixed with the fluidizable particles 12. Further,
an amount of air (fluidizing gas) blown toward the fluidized bed 14
is gradually increased in the direction from the front wall 24 to
the rear wall 25. Thus, when the waste 18 is moved from the first
fluidization region 15 to the second fluidization region 16
step-by-step, it will be gradually combusted, causing an increase
in temperature of the fluidizable particles 12. In the
high-temperature second fluidization region 16, the waste 18 is
sufficiently mixed with the fluidizable particles 12. This allows
the uncombusted waste 18 remaining after passing through the first
fluidization region 15 to be sufficiently gasified in the second
fluidization region 16.
[0051] On the other hand, the waste 18 newly pushed onto the first
fluidization region 15 by the pusher 41 is accumulated on the first
fluidization region 15 almost without being mixed with the
fluidizable particles 12 as mentioned above. Then, the accumulated
waste 18 is gradually combusted under the condition that violent or
rapid combustion is suppressed.
[0052] As above, under the condition that the first fluidization
region 15 and the second fluidization region 16 are formed in the
fluidized bed 14, waste 18 is pushed in one after another by the
pusher 41, which makes it possible to suppress intermittent and
rapid generation of a combustible gas, thereby stabilizing the gas
generation.
[0053] The non-combustible substances and carbides which have sunk
down in the first fluidization region 15 are discharged from the
mixture discharge port 29 provided on the underside of the first
fluidization region 15, together with a part of the fluidizable
particles 12. Further, the non-combustible substances and carbides
which have sunk down in the second fluidization region 16 are moved
to the mixture discharge port 29 while falling along the upper
surface 21a of the bottom wall 21, because the upper surface 21a is
inclined with a downward slope toward the mixture discharge port
29. The moved non-combustible substances and carbides are
discharged together with a part of the fluidizable particles 12.
Then, the sand circulation device 50 separates the fluidizable
particles 12 from the mixture discharged from the mixture discharge
port 29, and introduces the separated fluidizable particles 12 into
the furnace body 20. Concurrently, the carbide introduction device
60 separates the carbides from the mixture discharged from the
mixture discharge port 29, and introduces the separated carbides
into the furnace body 20. Specifically, the mixture discharge
section 51 sends the mixture dropping from the mixture discharge
port 29 of the furnace body 20, to the fluidizable-particle
separation section 52. The fluidizable-particle separation section
52 separates the fluidizable particles 12 from the mixture, and the
fluidizable-particle conveyance section 53 conveys the fluidizable
particles 12 separated by the fluidizable-particle separation
section 52, to the sand introduction section 27 of the furnace body
20. In this way, in the furnace body 20, an amount of the
fluidizable particles 12 forming the fluidized bed 14 is
maintained. Further, the fluidizable-particle separation section 52
sends the mixture after subjected to the separation of the
fluidizable particles 12, to the carbide separation section 61, and
then the carbide separation section 61 separates the carbides.
Then, the carbide conveyance section 62 conveys the carbides
separated by the carbide separation section 61, to the carbide
introduction section 63 of the furnace body 20. This allows the
carbides discharged from the furnace body 20 together with the
non-combustible substances to be returned to the inside of the
furnace body 20, and gasified. Consequently, the fluidized bed
furnace 10 becomes capable of efficiently obtaining a combustible
gas from waste 18.
[0054] In advance of stopping the fluidized bed furnace 10, the
pushing of waste 18 into the furnace body 20 by the pusher 41 is
firstly stopped. Upon stopping the pushing of waste 18, the gas
feeding unit 33 feeds a mixture formed by mixing an inert gas with
air, as the fluidizing gas to be supplied to the respective gas
boxes 32. In this process, the gas feeding unit 33 operates to
gradually increase the inert gas in a ratio between air and the
inert gas in the fluidizing gas, with time. In this manner, the gas
feeding unit 33 restrains an oxygen concentration within the
furnace body 20 to suppress violent or rapid combustion of the
waste 18 remaining in the fluidized bed 14.
[0055] In this embodiment, during stop of the fluidized bed furnace
10, violent or rapid combustion of the waste 18 remaining in the
fluidized bed 14 is suppressed by gradually increasing the ratio of
the inert gas occupied in the fluidizing gas. Alternatively, during
stop of the fluidized bed furnace 10, combustion of the remaining
waste 18 may be prevented by spraying water onto the fluidized bed
14.
[0056] As mentioned above, the fluidized bed furnace 10 according
to the above embodiment is capable of suppressing intermittent and
rapid generation of a combustible gas to stabilize the gas
generation, even in a situation where a large amount of easily
combustible trash is comprised in waste 18. Specifically, in the
fluidized bed 14, the first fluidization region 15 around the
mixture discharge port 29 and the second fluidization region 16
having a fluidization degree higher than that in the first
fluidization region 15 are formed. In this state, new waste 18 is
pushed onto the first fluidization region 15. The input of the new
waste 18 causes the waste 18 accumulated on the first fluidization
region 15 to be moved toward the second fluidization region 16
step-by-step. The above operation will be repeated. Thus, the
fluidized bed furnace 10 can sufficiently gasify the waste 18,
while suppressing rapid fluctuation of generation of a combustible
gas. Consequently, it becomes possible to stably generate a
combustible gas from the waste 18. In addition, just after input
into the furnace body 20, the waste 18 is not exposed to the highly
fluidized bed (the second fluidization region 16), so that it
becomes possible to suppress a situation where a large amount of
lightweight trash flies up inside the furnace body 20 and undergoes
rapid combustion in a free board section.
[0057] In addition, the first fluidization region 15 is formed just
above the mixture discharge port 29, and waste 18 is supplied onto
the first fluidization region 15. Thus, even if the waste 18 is
accumulated on the first fluidization region 15, and, during a
period where easily combustible trash in the waste 18 is slowly
gasified, non-combustible substances and carbides sink down to a
furnace bottom, such non-combustible substances and carbides can be
easily discharged from the furnace body 20. Further, even when
non-combustible substances and carbides sink down to the bottom
wall 21 after the waste 18 is moved from the first fluidization
region 15 into the second fluidization region 16, the
non-combustible substances and carbides will fall along the upper
surface 21a of the bottom wall 21 which is inclined to become lower
toward the mixture discharge port 29. Thus, such non-combustible
substances and carbides can also be easily discharged. In the
second fluidization region 16, the fluidizing gas is actively
supplied. This also accelerates the falling of the non-combustible
substances and carbides toward the mixture discharge port 29.
[0058] The furnace body 20 has a shape in plan view, in which a
dimension in the width direction thereof is equalized in a pushing
direction of waste 18. Thus, when the waste 18 on the first
fluidization region 15 is pushed by waste 18 newly pushed by the
waste supply section 40, and moved toward the second fluidization
region 16, the movement of the waste 18 is stabilized.
[0059] In the waste supply section 40, the pusher 41 is adapted to
be reciprocatingly moved in a direction parallel to the pushing
direction (front-rear direction) to allow the pushing surface 42 to
push waste 18 onto the fluidized bed 14 simultaneously by the
entire widthwise region of the pushing surface 42. This allows the
pushing surface 42 to push waste 18 onto the fluidized bed 14 with
an even force in the width direction. Thus, the movement of the
waste 18 from the first fluidization region 15 to the second
fluidization region 16 is approximately equalized in the width
direction, so that it becomes possible to prevent the waste 18 from
concentrating on a certain portion inside the furnace.
[0060] It is to be understood that a fluidized bed furnace and a
waste treatment method of the present invention are not limited to
the above embodiment, but various changes and modifications may be
made therein without departing from the spirit and scope of the
present invention hereinafter defined.
[0061] In the above embodiment, the sidewall 22 stands upwardly and
straight from the bottom wall 21 to the combustible gas outlet
portion 23. Alternatively, for example, as illustrated in FIG. 4,
the sidewall may comprise a front wall 24A having a reflecting
portion 224 extending toward the rear wall 25 to cover an upper
side of the first fluidization region 15 at a predetermined height
position. The front wall 24A allows the waste 18 accumulated on the
first fluidization region 15 to be heated by radiation heat from
the reflecting portion 224. Consequently, it becomes possible to
generate a combustible gas from the waste 18 accumulated on the
first fluidization region 15. In other words, gasification of the
waste 18 accumulated on the first fluidization region 15 is
promoted. In this case, the sand introduction section 27 may be
provided in the portion of the front wall 24A standing vertically
from the bottom wall 21, or may be provided in the reflecting
portion 224.
[0062] Alternatively, as illustrated in FIG. 5, the sidewall may
comprise a rear wall 25A having a guide portion 225 extending
toward the front wall 24 to cover an upper side of the second
fluidization region 16 at a predetermined height position. The
guide portion 225 is adapted to guide a high-temperature
combustible gas generated from the waste 18 in the second
fluidization region 16 to allow the combustible gas to be brought
into contact with the waste 18 accumulated on the first
fluidization region 15. In this way, the guide portion 225 allows
the combustible gas to contribute to heating of the waste 18
accumulated on the first fluidization region 15. Consequently, it
becomes possible to promote gasification of the waste 18
accumulated on the first fluidization region 15 without adding
special heating means to the furnace body 20. In this case, the
carbide introduction section 63 may be provided in the portion of
the rear wall 25 standing vertically from the bottom wall 21, or
may be provided in the guide portion 225.
[0063] Alternatively, as illustrated in FIG. 6, the sidewall may
comprise a front wall 24B and a rear wall 25B having, respectively,
two roof portions 324, 325 extending in a direction causing them to
come closer to each other at the same height position. The front
wall 24B and the rear wall 25B allow the waste 18 accumulated on
the first fluidization region 15 to be heated by radiation heat
from the roof portion 324 of the front wall 24B, so as to promote
gasification thereof. In addition, a dimension of a furnace body
20B in the front-rear direction is reduced at a position lower than
the combustible gas outlet portion 23 at the upper end of the
furnace body 20B, so that it becomes possible to facilitate a
reduction in size of the furnace body 20B. In this case, the sand
introduction section 27 may be provided in a portion of the front
wall 24B standing vertically from the bottom wall 21, or may be
provided in the roof portion 324. Further, the carbide introduction
section 63 may be provided in a portion of the rear wall 25B
standing vertically from the bottom wall 21, or may be provided in
the roof portion 325.
[0064] In the above embodiment, only carbides are introduced into
the furnace body 20 from the carbide introduction section 63.
Alternatively, the carbides may be introduced into the furnace body
20 from the carbide introduction section 63, together with
fluidizable particles 12.
[0065] In the above embodiment, the carbide introduction device 60
is adapted to introduce the carbides separated from the mixture
directly into the furnace body 20 from the carbide introduction
section 63. Alternatively, the carbides separated from the mixture
may be pulverized and then introduced into the furnace body 20. In
this case, even if carbides discharged from the mixture discharge
port 29 are agglomerated into a large block, the block can be
pulverized into a size suitable for facilitating gasification by
heating, and returned to the furnace body 20.
[0066] The upper surface 21a of the bottom wall 21 may be curved
from the rear wall 25 to the mixture discharge port 29, instead of
being inclined straight.
[0067] As illustrated in FIG. 7, a plurality of thermometers T may
be disposed just above the first fluidization region 15, and an air
supply section 65 capable of supplying air onto the first
fluidization region 15 may be provided. In this fluidized bed
furnace, an accumulated amount of the waste 18 accumulated on the
first fluidization region 15 can be estimated, so that it becomes
possible to control the accumulated amount. Specifically, the
accumulated amount of the waste 18 on the first fluidization region
15 is estimated by utilizing a phenomenon that an indication value
of the thermometer T embedded in the waste 18 is lowered. When the
accumulated amount is relatively large, i.e., the number of the
thermometers T embedded in the waste 18 is relatively large, the
air supply section 65 is operable to supply air to increase an
internal temperature of the furnace body 20. Accordingly,
gasification of the waste 18 accumulated on the first fluidization
region 15 is prompted, so that the accumulated amount of the waste
18 is reduced. As another method, an amount of the air may be
controlled based on determinations made as follows: when a
temperature of a designated one of the thermometers T is equal to
or greater than a threshold value, it is determined that there is
no waste at a position of the designated thermometer T, and, when
the temperature is less than the threshold value, it is determined
that there is waste at the position of the designated thermometer T
(the designated thermometer T is embedded in waste). Alternatively,
instead of control of the amount of the air, an amount of waste to
be input may be controlled.
[0068] In the above embodiment, the gas feeding unit 33 is
configured to feed air and/or an inert gas as the fluidizing gas.
Alternatively, for example, the gas feeding unit 33 may be
configured to feed water vapor and/or oxygen as the fluidizing gas,
depending on a combustion state within the furnace body 20. The
fluidized bed furnace 10 may further comprise a second gas supply
section provided in the sidewall 22 in addition to the first gas
supply section 30, wherein the second gas supply section may be
configured to be capable of supplying air, oxygen, water vapor or
the like into the furnace body 20, depending on a combustion state
in the fluidized bed 14 or of the waste 18.
[0069] The fluidizing gas to be supplied to the first fluidization
region 15 may be a high-temperature fluidizing gas. In the case of
supplying the high-temperature fluidizing gas, even in a situation
where it is difficult to sufficiently keep a temperature of the
first fluidization region 15 only by heat transferred from the
second fluidization region 16, the temperature of the first
fluidization region 15 can be maintained at a high value without
increasing an amount of the fluidizing gas to be supplied.
[0070] In the above embodiment, the waste introduction port 28 is
provided at a height position partially overlapping with respect to
the waste 18 accumulated on the fluidized bed 14 in the up-down
direction, so that waste 18 supplied from the waste introduction
port 28 positively moves the waste 18 accumulated on the upper
surface of the fluidized bed 14, generally horizontally (toward the
first fluidization region 15). Alternatively, the fluidized bed
furnace 10 may have any configuration capable of supplying waste 18
to a region on the fluidized bed 14 adjacent to the front wall
(supply-side sidewall portion) 24. For example, as illustrated in
FIG. 8A and FIG. 8B, the waste introduction port 28 may be provided
at a height position which is located adjacent to the upper surface
of the fluidized bed 14, and where new waste can be introduced in
such a manner that it is placed on the waste 18 accumulated on the
fluidized bed 14. In this case, as illustrated, for example, in
FIG. 8A, the waste introduction port 28 may be provided to allow
new waste to be supplied generally horizontally from a height
position above the waste 18 accumulated on the fluidized bed 14.
Alternatively, as illustrated in FIG. 8B, the waste introduction
port 28 may be provided to allow new waste to be supplied
downwardly from a height position above the waste 18 accumulated on
the fluidized bed 14. Even if waste 18 is supplied into the furnace
body 20 in the above manner, when the new waste 18 is supplied onto
the accumulated waste 18, a pile of waste 18 is broken and spread,
and the spread waste 18 is moved toward the second fluidization
region 16. Thus, gasification of the waste 18 is sufficiently
performed while suppressing rapid fluctuation of generation of a
combustible gas to be collected from the fluidized bed furnace 10.
Consequently, it becomes possible to stably generate a combustible
gas from the waste 18.
[0071] In the above embodiment, in a situation where
non-combustible substances are accumulated around the mixture
discharge port 29 of the furnace floor (upper surface 21a of the
bottom wall 21) without being discharged to the outside, the
fluidizing gas may be supplied in the first fluidization region 15
at a flow velocity satisfying the condition that U.sub.o/U.sub.mf
ranges from 2 to less than 5, only for a certain period of time in
order to discharge the accumulated non-combustible substances to
the outside. In this case, preferably, an amount of the fluidizing
gas to be supplied to each of the gas boxes 32 is increased to a
value greater than that during the normal operation, step-by-step
in a direction from the rear wall 25 (left side in FIG. 1) to the
front wall 24 (right side in FIG. 1) of the furnace body 20,
instead of blowing the fluidizing gas evenly in the entire first
fluidization region 15. Based on the above operation, even if
non-combustible substances are accumulated around the mixture
discharge port 29 of the furnace floor during the normal operation,
it becomes possible to reliably discharge the non-combustible
substances to the outside of the furnace body 20. The above
specific operation is performed only for a significantly short
time, so that an influence on facilities in a subsequent stage can
be minimized.
Outline of Embodiment
[0072] The outline of the above embodiment is as follows.
[0073] The fluidized bed furnace according to the above embodiment
is designed to heat waste to extract a combustible gas from the
waste. The fluidized bed furnace comprises: fluidizable particles
making up a fluidized bed to heat the waste; a furnace body having
a bottom wall supporting the fluidizable particles from therebelow,
and a sidewall standing upwardly from the bottom wall, wherein the
bottom wall has a mixture discharge port provided at a position
offset from a center position of the bottom wall in a specific
direction to discharge non-combustible substances in the waste and
carbides produced by heating of the waste, together with a part of
the fluidizable particles, and an upper surface of the bottom wall
is inclined to become lower toward the mixture discharge port so as
to cause the fluidizable particles to fall on the upper surface of
the bottom wall toward the mixture discharge port; a gas supply
section for blowing a fluidizing gas from the bottom wall of the
furnace body toward the fluidizable particles to fluidize the
fluidizable particles; a waste supply section for supplying waste
from a supply-side portion of the sidewall located on the same side
as the mixture discharge port with respect to the center position
of the bottom wall, to a region on the fluidized bed adjacent to
the supply-side sidewall portion, thereby causing the waste on the
fluidized bed to be moved toward an opposite-side portion of the
sidewall on a side opposite to the mixture discharge port across
the center position of the bottom wall, wherein: the gas supply
section is adapted to blow the fluidizing gas from around the
mixture discharge port to form a first fluidization region having a
degree of fluidization of the fluidizable particles which is set to
an extent allowing waste to be accumulated on the fluidizable
particles, while blowing the fluidizing gas between the first
fluidization region and the opposite-side sidewall portion at a
flow velocity greater than that of the fluidizing gas to be blown
in the first fluidization region, to form a second fluidization
region having a degree of fluidization of the fluidizable particles
greater than that in the first fluidization region, whereby the
fluidizable particles are moved in a convection-like pattern and
mixed with the waste to gasify the waste; and the waste supply
section is adapted to supply waste from the supply-side sidewall
portion to the fluidized bed to cause the waste to be accumulated
on the first fluidization region while causing the accumulated
waste to be moved into the second fluidization region
step-by-step.
[0074] In this fluidized bed furnace, the first fluidization region
around the mixture discharge port and the second fluidization
region having a fluidization degree higher than that in the first
fluidization region are formed in the fluidized bed. In this state,
the waste supply section supplies waste to a region on the
fluidized bed adjacent to the supply-side sidewall portion to cause
the waste to be accumulated on the first fluidization region while
causing the waste accumulated on the first fluidization region to
be moved into the second fluidization region step-by-step. Thus,
gasification of the waste is sufficiently performed while
suppressing rapid fluctuation of generation of a combustible gas to
be collected from the fluidized bed furnace, so that it becomes
possible to stably generate a combustible gas from the waste.
[0075] Specifically, in the first fluidization region, fluidization
in restrained to allow the waste to be accumulated on the upper
surface of the first fluidization region, so that the waste is
accumulated on the first fluidization region without being mixed
with the fluidizable particles, and easily combustible trash in the
waste is slowly gasified. Therefore, in the first fluidization
region, rapid combustion of the waste is suppressed, and generation
of a combustible gas caused by rapid gasification of the waste is
minimized. When new waste is supplied into the furnace body by the
waste supply section, the waste accumulated on the first
fluidization region is moved into the second fluidization region
step-by-step. In the second fluidization region, the fluidizable
particles are actively fluidized and heated to a high temperature
by combustion of the waste, so that the waste moved from a position
on the first fluidization region is sufficiently mixed with the
fluidizable particles, and thereby the waste is sufficiently
gasified to generate a combustible gas. Consequently, it becomes
possible to suppress intermittent and rapid generation of a
combustible gas, thereby stabilizing the gas generation.
[0076] The first fluidization region is formed just above the
mixture discharge port, and waste is supplied onto the first
fluidization region. Thus, even if the waste is accumulated on the
first fluidization region, and, during a period where easily
combustible trash in the accumulated waste 18 is slowly gasified,
non-combustible substances in the waste and carbides produced by
heating of the waste sink down to a furnace bottom, such
non-combustible substances and carbides can be easily discharged
from the furnace body. Further, even when non-combustible
substances and carbides sink down to the bottom wall after the
waste is moved from the first fluidization region into the second
fluidization region, the non-combustible substances and carbides
will fall along the upper surface of the bottom wall which is
inclined to become lower toward the mixture discharge port. Thus,
such non-combustible substances and carbides can also be easily
discharged from the furnace body.
[0077] The upper surface of the bottom wall is inclined to become
lower toward the mixture discharge port (i.e., inclined to become
lower in the direction from the second fluidization region to the
first fluidization region), so that the high-temperature
fluidizable particles in the second fluidization region 16 fall on
the upper surface of the bottom wall toward the first fluidization
region. Consequently, heat is supplied to the first fluidization
region.
[0078] Preferably, the waste supply section is adapted to push new
waste generally horizontally from the supply-side sidewall portion
toward the waste accumulated on the first fluidization region,
thereby causing the waste accumulated on the first fluidization
region to be moved into the second fluidization region
step-by-step.
[0079] According to this feature, new waste is pushed generally
horizontally toward the waste accumulated on the first fluidization
region. Thus, the waste accumulated on the first fluidization
region is pushed by the new waste and reliably moved into the
second fluidization region.
[0080] Preferably, the fluidized bed furnace comprises a carbide
introduction device for separating the carbides from a mixture of
the non-combustible substances, the carbides and the fluidizable
particles discharged from the mixture discharge port, and returning
the separated carbides to the fluidized bed from the side of the
opposite-side sidewall portion.
[0081] According to this feature, the carbide introduction device
operates to return the carbides discharged from the mixture
discharge port together with the fluidizable particles and the
non-combustible substances, to the second fluidization region
actively fluidized and highly heated. This makes it possible to
obtain a combustible gas from the carbides. Consequently, the
combustible gas can be efficiently obtained from waste. In
addition, the temperature of the second fluidization region can be
kept at a high value by heat generated when the carbides are
gasified.
[0082] Preferably, in the fluidized bed furnace of the present
invention, the air supply section is adapted to blow the fluidizing
gas in the first fluidization region at a flow velocity satisfying
a condition that U.sub.o/U.sub.mf ranges from 1 to less than 2, and
blow the fluidizing gas in the second fluidization region at a flow
velocity satisfying a condition that U.sub.o/U.sub.mf ranges from 2
to less than 5, where U.sub.mf is a minimum fluidization velocity
which is a minimum flow velocity of the fluidizing gas to be blown
enough to fluidize the fluidizable particles, and U.sub.o is a
cross-sectional average flow velocity of the fluidizing gas. The
first fluidization region and the second fluidization region can be
desirably formed in the fluidized bed by blowing the fluidizing gas
at the above flow velocities. Consequently, it becomes possible to
desirably gasify the waste while suppressing rapid combustion of
the waste, thereby stably obtaining a combustible gas from the
waste.
[0083] Preferably, the fluidized bed furnace comprises a sand
circulation device for separating the fluidizable particles from
the mixture discharged from the mixture discharge port, and
returning the separated fluidizable particles to the furnace
body.
[0084] According to this feature, the sand introduction device
operates to return the high-temperature fluidizable particles
discharged from the mixture discharge port to the inside of the
furnace body. This makes it possible to maintain an amount of the
fluidizable particles making up the fluidized bed, and makes it
easy to maintain a temperature of the fluidized bed.
[0085] More preferably, the sand circulation device is adapted to
return the fluidizable particles separated from the mixture onto
the waste accumulated on the first fluidization region.
[0086] According to this feature, the sand circulation device
operates to return the high-temperature fluidizable particles
discharged from the mixture discharge port onto the waste
accumulated on the first fluidization region. Thus, the
high-temperature fluidizable particles serve as an ignition source
to allow easily-combustible trash in the waste to be stably
combusted (gasified).
[0087] Preferably, the furnace body has a shape in plan view, in
which a dimension in a width direction perpendicular to a pushing
direction along which waste is pushed by the waste supply section
is equalized in the pushing direction.
[0088] According to this feature, when the waste on the first
fluidization region is pushed by waste newly pushed by the waste
supply section, and moved toward the second fluidization region,
the movement of the waste is stabilized, because the dimension of
the furnace body in a direction perpendicular to the waste pushing
direction (width direction) is equalized.
[0089] Preferably, the waste supply section comprises a pusher
having a pushing surface extending in the width direction, and a
drive unit for reciprocatingly moving the pusher in a direction
parallel to the pushing direction to allow the pushing surface of
the pusher to push waste onto the fluidized bed simultaneously by
the entire widthwise region of the pushing surface.
[0090] According to this feature, waste can be pushed with an even
force in the width direction, so that the movement of the waste
from the first fluidization region to the second fluidization
region is approximately equalized in the width direction. Thus, it
becomes possible to prevent the waste from concentrating on a
certain portion inside the furnace.
[0091] The waste treatment method according to the above embodiment
is designed to heat waste to extract a combustible gas from the
waste. The waste treatment method comprises: a preparation step of
preparing a fluidized bed furnace comprising fluidizable particles
making up a fluidized bed to heat the waste, a furnace body having
a bottom wall supporting the fluidizable particles from therebelow
and a sidewall standing upwardly from the bottom wall, wherein the
bottom wall has a mixture discharge port provided at a position
offset from a center position of the bottom wall in a specific
direction to discharge non-combustible substances in the waste and
carbides produced by heating of the waste, together with a part of
the fluidizable particles, and an upper surface of the bottom wall
is inclined to become lower toward the mixture discharge port so as
to cause the fluidizable particles to fall on the upper surface of
the bottom wall toward the mixture discharge port; a
fluidization-region formation step of blowing a fluidizing gas from
a region of the bottom wall of the furnace body around the mixture
discharge port toward the fluidizable particles to form a first
fluidization region having a degree of fluidization of the
fluidizable particles which is set to an extent allowing waste to
be accumulated on the fluidizable particles, while blowing the
fluidizing gas between the first fluidization region and an
opposite-side portion of the sidewall on a side opposite to the
mixture discharge port across the center position of the bottom
wall, at a flow velocity greater than that of the fluidizing gas to
be blown in the first fluidization region, to form a second
fluidization region having a degree of fluidization of the
fluidizable particles greater than that in the first fluidization
region; and a gasification step of supplying waste from a
supply-side portion of the sidewall located on the same side as the
mixture discharge port with respect to the center position of the
bottom wall, to a region on the fluidized bed adjacent to the
supply-side sidewall portion, thereby causing the waste to be
accumulated on the first fluidization region, while causing the
accumulated waste to be moved into the second fluidization region
step-by-step and gasified.
[0092] In this waste treatment method, the first fluidization
region around the mixture discharge port and the second
fluidization region having a fluidization degree higher than that
in the first fluidization region are formed in the fluidized bed.
In this state, the waste is accumulated on the first fluidization
region, and the waste accumulated on the first fluidization region
is moved into the second fluidization region step-by-step. Thus,
gasification of the waste is sufficiently performed while
suppressing rapid fluctuation of generation of a combustible gas to
be collected from the fluidized bed furnace, so that it becomes
possible to stably generate a combustible gas from the waste.
[0093] The first fluidization region is formed just above the
mixture discharge port, and waste is supplied onto the upper
surface of the first fluidization region. Thus, even if the waste
is accumulated on the first fluidization region, and, during a
period where easily combustible trash in the accumulated waste is
slowly gasified, non-combustible substances in the waste and
carbides produced by heating of the waste sink down to a furnace
bottom, such non-combustible substances and carbides can be easily
discharged from the furnace body. Further, even when
non-combustible substances and carbides sink down to the bottom
wall after the waste is moved from the first fluidization region
into the second fluidization region, the non-combustible substances
and carbides will fall along the upper surface of the bottom wall
which is inclined to become lower toward the mixture discharge
port. Thus, such non-combustible substances and carbides can also
be easily discharged from the furnace body.
[0094] The upper surface of the bottom wall is inclined to become
lower toward the mixture discharge port (i.e., inclined to become
lower in the direction from the second fluidization region to the
first fluidization region), so that the high-temperature
fluidizable particles in the second fluidization region fall on the
upper surface of the bottom wall toward the first fluidization
region. Consequently, heat is supplied to the first fluidization
region.
[0095] Preferably, the gasification step includes pushing new waste
generally horizontally from the supply-side sidewall portion toward
the waste accumulated on the first fluidization region, thereby
causing the waste accumulated on the first fluidization region to
be moved into the second fluidization region step-by-step and
gasified.
[0096] According to this feature, new waste is pushed generally
horizontally toward the waste accumulated on the first fluidization
region. Thus, the waste accumulated on the first fluidization
region is pushed by the new waste and reliably moved into the
second fluidization region, and gasified.
[0097] Preferably, the above waste treatment method comprises a
step of separating the carbides from a mixture of the
non-combustible substances, the carbides and the fluidizable
particles discharged from the mixture discharge port, and returning
the separated carbides to the fluidized bed from the side of the
opposite-side sidewall portion.
[0098] According to this feature, the carbides discharged from the
mixture discharge port together with the fluidizable particles and
the non-combustible substances are separated and returned to the
second fluidization region actively fluidized and highly heated.
This makes it possible to reliably gasify the carbides. In
addition, the temperature of the second fluidization region can be
kept at a high value by heat generated when the carbides are
gasified.
[0099] Preferably, in the above waste treatment method, the
fluidizing gas is blown in the first fluidization region at a flow
velocity satisfying a condition that U.sub.o/U.sub.mf ranges from 1
to less than 2, and blown in the second fluidization region at a
flow velocity satisfying a condition that U.sub.o/U.sub.mf ranges
from 2 to less than 5, where U.sub.mf is a minimum fluidization
velocity which is a minimum flow velocity of the fluidizing gas to
be blown so as to fluidize the fluidizable particles, and U.sub.o
is a cross-sectional average flow velocity of the fluidizing
gas.
[0100] The first fluidization region and the second fluidization
region can be desirably formed in the fluidized bed by blowing the
fluidizing gas at the above flow velocities. Consequently, it
becomes possible to desirably gasify the waste while suppressing
rapid combustion of the waste, thereby stably obtaining a
combustible gas from the waste.
INDUSTRIAL APPLICABILITY
[0101] As above, the fluidized bed furnace and the waste treatment
method of the present invention are useful in heating waste in a
fluidized bed formed by fluidizing fluidizable particles, to
extract a combustible gas from the waste, and suitable for stably
obtaining a combustible gas even from waste comprising easily
combustible trash.
* * * * *