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. 11, 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]
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 non-combustible substance 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 together with a part of the fluidizable particles, and an
upper surface of the bottom wall is inclined to become lower toward the non-combustible
substance discharge port so as to cause the non-combustible substances to fall on
the upper surface of the bottom wall toward the non-combustible substance 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 a side opposite to the non-combustible substance discharge port across
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 the non-combustible substance discharge port; and a sand circulation
device for returning the fluidizable particles discharged from the non-combustible
substance discharge port, to the fluidized bed from the side of the waste supply section
to circulate the fluidizable particles, thereby forming a flow of the fluidizable
particles directed from the supply-side sidewall portion located on the side opposite
to the non-combustible substance discharge port, to the non-combustible substance
discharge port. The gas supply section is adapted to blow the fluidizing gas from
around the non-combustible substance discharge port to form a first fluidization region
where the fluidizable particles are moved in a convection-like pattern and mixed with
the waste to gasify the waste, while blowing the fluidizing gas between the first
fluidization region and the waste supply section at a flow velocity less 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 lower
than that in the first fluidization region, 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 second fluidization region while causing the accumulated
waste to be moved into the first 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.
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.
FIG. 3 is a diagram for explaining a nozzle arrangement in a bottom wall of the furnace
body.
FIG. 4 is a diagram for explaining a configuration for pushing fluidizable particles
directly onto a fluidized bed in the furnace body.
FIG. 5 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.
FIG. 6 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.
FIG. 7 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.
FIG. 8 is a diagram for explaining a furnace body having a bent bottom wall thereof,
in a fluidized bed furnace according to yet still another embodiment of the present
invention.
FIG. 9 is a diagram for explaining a furnace body comprising a thermometer and an
air supply section, in a fluidized bed furnace according to another further embodiment
of the present invention.
FIG. 10 is a diagram for explaining a waste supply section, in a fluidized bed furnace
according to still a further embodiment of the present invention.
FIG. 11 is a schematic configuration diagram of a conventional fluidized bed furnace.
DESCRIPTION OF EMBODIMENTS
[0011] With reference to the accompanying drawings, the present invention will now be described
based on one embodiment thereof.
[0012] 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 and a sand
circulation device 50.
[0013] The fluidizable particles 12 are particles 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.
[0014] 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.
[0015] 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 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.
[0016] A portion (front wall) 24 of the sidewall 22 located on a side opposite to an aftermentioned
non-combustible substance discharge port 29 across 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 adapted to introduce fluidizable particles 12 into the
furnace body 20, and the waste introduction port 28 is adapted to introduce waste
18 into the furnace body 20.
[0017] Specifically, the sand introduction section 27 is provided at each of widthwise opposite
ends of a lower portion of the front wall 24 to allow fluidizable particles to be
introduced to widthwise opposite end areas of an inside of the furnace body 20 (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 (fluidized bed 14), toward the fluidized bed 14. It is to be noted
that an input area of fluidizable particles 12 is not limited to the widthwise opposite
end areas. For example, the input area of fluidizable particles 12 may be one of the
widthwise opposite end areas. Alternatively, the input area of fluidizable particles
12 may be an upper surface of the introduced waste 18 (a central area adjacent to
the front wall 24 in FIG. 2). In the case where fluidizable particles 12 are input
onto waste 18, the fluidizable particles 12 serve as an ignition source to allow only
easily combustible trash to be stably combusted (gasified) initially.
[0018] 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. 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.
[0019] 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.
[0020] The bottom wall 21 has a non-combustible substance 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 together with a part of the fluidizable particles
12. The non-combustible substance 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 21 a is inclined to become lower toward the non-combustible substance discharge
port 29 so as to cause the non-combustible substances to fall on the upper surface
21 a. The bottom wall 21 in this embodiment has a non-combustible substance discharge
port 29 at a position offset rearwardly, and an upper surface 21a of the bottom wall
21 extends rearwardly (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.
[0021] 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.
[0022] 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 front region 21 b and a rear region 21 c. Then, the
plurality of nozzles 31 are installed to the front and rear regions 21b, 21c in such
a manner that the number of nozzles 31 provided in the front region 21b becomes greater
than the number of nozzles 31 provided in the rear region 21 c. It is to be noted
that a relationship between the respective numbers of nozzles 31 in the front and
rear regions 21 b, 21c is not particularly limited. For example, the number of nozzles
31 in the front region 21 b may be equal to the number of nozzles 31 in the rear region
21 c. Alternatively, the number of nozzles 31 in the rear region 21 c may be greater
than the number of nozzles 31 in the front region 21b.
[0023] The gas box 32 has a box shape extending in the width direction. The gas box 32 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 front wall 24 with respect
to the non-combustible substance discharge port 29, and one gas box 32e is disposed
on the side of the rear wall 25 with respect to the non-combustible substance discharge
port 29.
[0024] 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.
[0025] 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 non-combustible substance discharge port 29. In this
process, the gas feeding unit 33 is operable to form a first fluidization region 15
where the fluidizable particles 12 are moved in a convection-like pattern and mixed
with the introduced waste 18 to gasify the waste 18. Concurrently, the gas feeding
unit 33 is operable to blow the fluidizing gas between the first fluidization region
15 and the front wall 24 at a flow velocity less 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 lower 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 32c) 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 32b) of the adjacent gas boxes 32. In
this case, the gas feeding unit 33 is operable to, in the fluidized bed 14, form a
first fluidization region 15 actively fluidized, around the non-combustible substance
discharge port 29, while forming a second fluidization region 16 restrained in fluidization,
between the first fluidization region 15 and the front wall 24. Alternatively, the
gas feeding unit 33 may be configured such that a flow volume of the fluidizing gas
to be fed to each of the gas boxes 32c, 32d, 32e on the side of the rear wall 25 becomes
greater than a flow volume of the fluidizing gas to be fed to each of the gas boxes
32a, 32b on the side of the front wall 24. In this case, the gas feeding unit 33 is
operable to, in the fluidized bed 14, form a second fluidization region 16 restrained
in fluidization, in a region corresponding to the gas boxes 32a, 32b on the side of
the front wall 24, while forming a first fluidization region 15 actively fluidized,
in a region corresponding to the gas boxes 32c, 32d, 32e on the side of the rear wall
25.
[0026] Specifically, the gas feeding unit 33 is adapted to cause the fluidizing gas to be
blown in the second fluidization region 16 at the flow velocity satisfying a condition
that U
o/U
mf ranges from I to less than 2, and blown in the first fluidization region 15 at the
flow velocity satisfying a condition that U
o/U
mf ranges from 2 to less than 5. In this formula, U
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
o is a cross-sectional average flow velocity of the fluidizing gas.
[0027] 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.
[0028] 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.
[0029] 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 around the non-combustible substance discharge
port 29 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.
[0030] 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 non-combustible substance discharge port 29. In other words, the waste supply
section 40 is adapted to push waste 18 to cause the waste 18 to be accumulated on
the second fluidization region 16 while causing the accumulated waste 18 to be moved
into the first fluidization region 15 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. 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.
[0031] The sand circulation device 50 is designed to return the fluidizable particles 12
discharged from the non-combustible substance discharge port 29, to the fluidized
bed 14 at a position on the side of the waste supply section 40 to circulate the fluidizable
particles 12. When the sand circulation device 50 operates to return the fluidizable
particles 12 discharged from the non-combustible substance discharge port 29, to the
fluidized bed 14 at a position on the side of the front wall 24, in the above manner,
a flow of the fluidizable particles 12 directed from the front wall 24 to the non-combustible
substance discharge port 29 is formed inside the fluidized bed 14. In addition, the
second fluidization region 16 is maintained at a high temperature to some extent.
The sand circulation device 50 comprises a non-combustible substance discharge section
51, a separation section 52, and a conveyance section 53.
[0032] The non-combustible substance discharge section 51 is provided just below the non-combustible
substance discharge port 29 of the bottom wall 21, and adapted to move a mixture of
non-combustible substances and a part of the fluidizable particles 12 dropping from
the non-combustible substance discharge port 29, to the separation section 52. The
non-combustible substance discharge section 51 in this embodiment is configured to
move the mixture dropping from the non-combustible substance discharge port 29, to
the separation section 52 by using a screw extruder. The separation section 52 is
adapted to separate the fluidizable particles 12 from the mixture sent from the non-combustible
substance discharge section 51. The separation section 52 in this embodiment is configured
to separate the fluidizable particles 12 from the mixture by using a sieve. The conveyance
section 53 is adapted to convey the fluidizable particles 12 separated in the 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.
[0033] The sand circulation device 50 in this embodiment is configured to return the fluidizable
particles 12 discharged from the non-combustible substance discharge port 29, to the
fluidized bed 14 by inputting the fluidizable particles 12 from above the fluidized
bed 14 toward an upper surface of the fluidized bed 14. However, it is not limited
to this configuration. For example, as illustrated in FIG. 4, the fluidizable particles
12 discharged from the non-combustible substance discharge port 29 may be directly
returned to an inside of the fluidized bed 14. In the example illustrated in FIG.
4, a sand introduction section (sand introduction opening) 27A is provided in the
front wall 24 at an intermediate height position of the fluidized bed 14. A screw
extruder 55 is provided at an end of the conveyance section 53 of the sand circulation
device 50 on the side of the furnace body 20, and the furnace body-side end of the
conveyance section 53 is inserted into the sand introduction section 27. In this manner,
the fluidizable particles 12 discharged from the non-combustible substance discharge
port 29 may be returned to the fluidized bed 14 in such a manner as to be directly
pushed into the fluidized bed 14. In this case, the sand introduction section 27 is
not limited to the intermediate height position of the fluidized bed 14, but may be
located on a relatively upper or lower side in a height direction of the fluidized
bed 14. When the fluidizable particles 12 are pushed into the fluidized bed 14, a
movement of the fluidizable particles 12 in a horizontal direction is more forcibly
performed, so that it becomes possible to suppress non-combustible substances from
being accumulated on a furnace floor.
[0034] In the fluidized bed furnace 10 configured as above, a combustible gas is collected
from waste 18 in the following manner.
[0035] Upon feeding the fluidizing gas from the gas feeding unit 33 to the respective gas
boxes 32, 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 actively fluidized is formed
on the side of the non-combustible substance discharge port 29, and the second fluidization
region 16 restrained in fluidization is formed between the first fluidization region
15 and the front wall 24. 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 32c,
32d, 32e) of the gas boxes 32 corresponding to the first fluidization region 15 to
positively heat the fluidizable particles 12 in the first fluidization region 15.
[0036] Concurrently, the sand circulation device 50 circulates the fluidizable particles
12 to form a flow of the fluidizable particles 12 in the fluidized bed. Specifically,
the non-combustible substance discharge section 51 sends the fluidizable particles
12 dropping from the non-combustible substance discharge port 29 of the furnace body
20, to the separation section 52. Then, the conveyance section 53 conveys the fluidizable
particles 12 passing through the separation section 52, to the sand introduction section
27 of the furnace body 20. The conveyed fluidizable particles 12 are returned to the
fluidized bed 14 at a position on the side of the front wall 24, via the sand introduction
section 27. When the fluidizable particles 12 discharged from the non-combustible
substance discharge port 29 located on the side of the rear wall 25 is returned to
the fluidized bed 14 at a position on the side of the front wall 24, in the above
manner, a flow of the fluidizable particles 12 directed from the front wall 24 to
the non-combustible substance discharge port 29 is formed in the fluidized bed 14.
In this process, the fluidizable particles 12 in the first fluidization region 15
in a higher-temperature state are partially discharged from the non-combustible substance
discharge port 29, and the sand circulation device 50 returns the discharged fluidizable
particles 12 to the fluidized bed 14 at a position on the side of the front wall 24.
This allows a temperature of the second fluidization region 16 to be maintained at
a predetermined value. However, during the period in which the fluidizable particles
12 discharged from the non-combustible substance discharge port 29 are returned to
the fluidized bed 14 by the sand circulation device 50, a temperature of the fluidizable
particles 12 is lowered. Therefore, the second fluidization region 16 has a temperature
less than that of the first fluidization region 15. Preferably, the temperature of
the first fluidization region 15 is kept in the range of 600 to 800°C, whereas the
temperature of the second fluidization region 16 is kept in the range of about 400
to 600°C.
[0037] When the temperatures of the regions 15, 16 in the fluidized bed 14 within the furnace
body 20 reach respective predetermined values, 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 second fluidization
region 16 at a position adjacent to the front wall 24 (see FIG. 2).
[0038] The fluidization of the fluidizable particles 12 in the second fluidization region
16 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 second fluidization
region 16, and heavy non-combustible substances therein sink down. Consequently, in
the second fluidization region 16, rapid combustion of the waste 18 is suppressed,
and easily-gasifiable substances in the waste 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 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 first fluidization region
15 without being gasified. In this manner, the easily gasifiable waste 18 is gasified
under a mild condition in the second fluidization region 16 before it reaches the
highly fluidized bed (first fluidization region 15). This makes it possible to suppress
a fluctuation of generation of a combustible gas. The accumulated waste 18 is combusted
by radiation heat within the furnace body 20, as mentioned above. However, although
the radiation heat has a temperature of 800 to 900°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 second fluidization
region 16 has a relatively low temperature, and an amount of air (fluidizing gas)
to be supplied to the second fluidization region 16 is relatively small, so that even
the easily combustible trash will be gradually gasified. Further, the fluidizable
particles 12 are gradually discharged through the non-combustible substance discharge
port 29, so that, according to the discharge of the fluidizable particles 12 and the
fluidization of the fluidizable particles 12 by the fluidizing gas, a part of the
accumulated waste 18 is moved or spread step-by-step in a left-to-right direction
in FIG. 1. Therefore, even if waste 18 is input in a massive form, and easily combustible
papers are comprised therein, it can be expected to promote gasification of the papers
based on a phenomenon that the papers are moved toward a surface of the massive waste
during the spreading. As above, in the second fluidization region 16, rapid combustion
of the waste 18 is suppressed to prevent a rapid increase of combustible gas during
introduction of waste 18.
[0039] 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 second fluidization
region 16 is pushed by the new waste 18, and moved into the first fluidization region
15 step-by-step. The first fluidization region 15 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 second fluidization region 16 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 non-combustible substance discharge
port 29. Thus, when the waste 18 is moved from a position on the second fluidization
region 16 adjacent to the front wall 24 to the first fluidization region 15 step-by-step,
it will be gradually mixed with the fluidizable particles 12. Further, an amount of
blowing air (fluidizing gas) is gradually increased in the direction from the front
wall 24 to the non-combustible substance discharge port 29. Thus, when the waste 18
is moved from the second fluidization region 16 to the first fluidization region 15
step-by-step, it will be gradually combusted, causing an increase in temperature of
the fluidizable particles 12. In a region of this high-temperature fluidized bed 14
just above the non-combustible substance discharge port 29 and the vicinity thereof,
the waste 18 is sufficiently mixed with the fluidizable particles 12. This allows
the uncombusted waste 18 remaining after passing through the second fluidization region
16 to be sufficiently gasified in the first fluidization region 15.
[0040] On the other hand, the waste 18 newly pushed onto the second fluidization region
16 by the pusher 41 is accumulated on the second fluidization region 16 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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. Specifically, in the fluidized bed 14, the first fluidization
region 15 around the non-combustible substance discharge port 29 and the second fluidization
region 16 having a fluidization degree lower than that in the first fluidization region
15 are formed. In this state, new waste 18 is pushed onto the second fluidization
region 16. The input of the new waste 18 causes the waste 18 accumulated on the second
fluidization region 16 to be moved toward the first fluidization region 15 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 first fluidization region 15), 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.
[0045] In the furnace body 20, the upper surface 21a of the bottom wall 21 is inclined to
become lower toward the non-combustible substance discharge port 29. Thus, when non-combustible
substances in the waste 18 sinks down to the bottom wall 21 in the fluidized bed 14,
they fall on the upper surface 21a of the bottom wall 21 toward the non-combustible
substance discharge port 29. In this manner, the non-combustible substances are discharged
from the non-combustible substance discharge port 29 together with a part of the fluidizable
particles 12, so that it becomes possible to easily discharge non-combustible substances
from the furnace body 20. The non-combustible substances discharged from the non-combustible
substance discharge port 29 together with a part of the fluidizable particles 12 are
separated from the fluidizable particles 12 in the separation section 52 of the sand
circulation device 50.
[0046] 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 second fluidization region 16 is pushed by waste 18 newly pushed by the waste
supply section 40, and moved toward the first fluidization region 15, the movement
of the waste 18 is stabilized. In addition, a flow of the fluidizable particles 12
formed in a direction from the second fluidization region 16 to the first fluidization
region 15 by the sand circulation device 50 is directionally the same as the movement
of the waste 18, so that the flow of the fluidizable particles 12 is also stabilized.
[0047] 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 second fluidization region 16 to the first
fluidization region 15 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.
[0048] 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.
[0049] 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. 5, 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 second fluidization
region 16 at a predetermined height position. The front wall 24A allows the waste
18 accumulated on the second fluidization region 16 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 second fluidization region 16. In other words,
gasification of the waste 18 accumulated on the second fluidization region 16 is promoted.
[0050] Alternatively, as illustrated in FIG. 6, 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 first fluidization region 15 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 first fluidization region 15 to allow the combustible gas to be
brought into contact with the waste 18 accumulated on the second fluidization region
16. In this way, the guide portion 225 allows the combustible gas to contribute to
heating of the waste 18 accumulated on the second fluidization region 16. Consequently,
it becomes possible to promote gasification of the waste 18 accumulated on the second
fluidization region 16 without adding special heating means to the furnace body 20.
[0051] Alternatively, as illustrated in FIG. 7, 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 second
fluidization region 16 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.
[0052] In the above embodiment, the upper surface 21a of the bottom wall 21 has an inclination
angle which is constant in the range from the front wall 24 to the non-combustible
substance discharge port 29, the present invention is not limited thereto. Alternatively,
for example, as illustrated in FIG. 8, an inclination angle α of an upper surface
21d of a bottom wall 21 A on the side of the second fluidization region 16 with respect
to a horizontal surface may be greater than an inclination angle β of an upper surface
21e of the bottom wall 21A on the side of the first fluidization region 15 with respect
to the horizontal surface. When the upper surface 21d supporting the second fluidization
region 16 restrained in fluidization, from therebelow, has a relatively large inclination
angle in the above manner, non-combustible substances sinking down to the bottom wall
21 A more reliably falls to the non-combustible substance discharge port 29. Specifically,
the inclination angle β of the upper surface 21e on the side of the first fluidization
region 15 with respect to the horizontal surface is in the range of 15 degrees to
25 degrees, and the inclination angle α of the upper surface 21d on the side of the
second fluidization region 16 with respect to the horizontal surface is in the range
of 20 degrees to 75 degrees, preferably, in the range of 20 degrees to 30 degrees.
[0053] Alternatively, the upper surface 21a of the bottom wall 21 may be curved from the
front wall 24 to the non-combustible substance discharge port 29, instead of being
inclined straight.
[0054] As illustrated in FIG. 9, a plurality of thermometers T may be disposed just above
the second fluidization region 16, and an air supply section 60 capable of supplying
air onto the second fluidization region 16 may be provided. In this fluidized bed
furnace, an accumulated amount of the waste 18 accumulated on the second fluidization
region 16 can be estimated, so that it becomes possible to control the accumulated
amount. Specifically, the accumulated amount of the waste 18 on the second fluidization
region 16 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 60 is operable to supply air to increase an internal temperature
of the furnace body 20. Accordingly, gasification of the waste 18 accumulated on the
second fluidization region 16 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.
[0055] 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.
[0056] The fluidizing gas to be supplied to the second fluidization region 16 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 second
fluidization region 16 only by the circulation of the fluidizable particles 12, the
temperature of the second fluidization region 16 can be maintained at a high value
without increasing an amount of the fluidizing gas to be supplied.
[0057] 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. 10A and FIG. 10B, 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 free of contact with waste 18 when it is newly
supplied onto the waste 18 accumulated (on the second fluidization region 16) in a
region of the upper surface of the fluidized bed 14 adjacent to the front wall 24.
In this case, as illustrated, for example, in FIG. 10A, 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. 10B, 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
first fluidization region 15. Further, according to the flow of the fluidizable particles
12 formed in the fluidized bed 14 in the direction from the front wall 24 to the non-combustible
substance discharge port 29, the waste 18 accumulated on the fluidized bed 14 is also
moved toward the first fluidization region 15. 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.
[0058] In the above embodiment, the fluidizing gas to be supplied to the fluidized bed 14
is supplied in the second fluidization region 16 at a flow velocity satisfying the
condition that U
o/U
mf ranges from 1 to less than 2, and supplied in the first fluidization region 15 at
a flow velocity satisfying a condition that U
o/U
mf ranges from 2 to less than 5, as mentioned above. Alternatively, for example, in
a situation where non-combustible substances are accumulated on a furnace floor (the
upper surface 21a of the bottom wall 21) without being discharged to the outside,
the fluidizing gas may also be supplied in the second fluidization region 16 at a
flow velocity satisfying the condition that U
o/U
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
step-by-step in a direction from the front wall 24 (left side in FIG. 1) to the rear
wall 25 (right side in FIG. 1) of the furnace body 20, instead of blowing the fluidizing
gas evenly in the entire second fluidization region 16. Specifically, at a certain
time t0, a flow volume of the fluidizing gas to be supplied to the gas box 32a becomes
greater than that of the fluidizing gas to be supplied to each of the remaining gas
boxes. Then, at a time t1 after an elapse of several seconds, the flow volume of the
fluidizing gas to be supplied to the gas box 32a is returned to a value during a normal
operation, and a flow volume of the fluidizing gas to be supplied to the adjacent
gas box 32b becomes greater than that of the fluidizing gas to be supplied to each
of the remaining gas boxes. Then, at a time t2 after a further elapse of several seconds,
the flow volume of the fluidizing gas to be supplied to the gas box 32b is returned
to an original value, and a flow volume of the fluidizing gas to be supplied to the
adjacent gas box 32c becomes greater than that of the fluidizing gas to be supplied
to each of the remaining gas boxes. Based on the above operation, even if non-combustible
substances are accumulated on 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]
[0059] The outline of the above embodiment is as follows.
[0060] 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 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 non-combustible
substance 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 together with a part of the fluidizable particles, and an upper surface of the
bottom wall is inclined to become lower toward the non-combustible substance discharge
port so as to cause the non-combustible substances to fall on the upper surface of
the bottom wall toward the non-combustible substance 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 the waste from a supply-side portion of the sidewall located on a side
opposite to the non-combustible substance discharge port across 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 the non-combustible
substance discharge port; and a sand circulation device for returning the fluidizable
particles discharged from the non-combustible substance discharge port, to the fluidized
bed from the side of the waste supply section to circulate the fluidizable particles,
thereby forming a flow of the fluidizable particles directed from the supply-side
sidewall portion located on the side opposite to the non-combustible substance discharge
port, to the non-combustible substance discharge port, wherein: the gas supply section
is adapted to blow the fluidizing gas from around the non-combustible substance discharge
port to form a first fluidization region where the fluidizable particles are moved
in a convection-like pattern and mixed with the waste to gasify the waste, while blowing
the fluidizing gas between the first fluidization region and the waste supply section
at a flow velocity less 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 lower than that in the first fluidization region; 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 second fluidization
region while causing the accumulated waste to be moved into the first fluidization
region step-by-step.
[0061] In this fluidized bed furnace, the first fluidization region around the non-combustible
substance discharge port and the second fluidization region having a fluidization
degree lower 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 second fluidization region while causing the waste accumulated on the second
fluidization region to be moved into the first 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.
[0062] Specifically, fluidization in the second fluidization region is restrained, so that
the waste is accumulated on the second fluidization region without being mixed with
the fluidizable particles, and easily combustible components of the waste are slowly
gasified. Therefore, in the second 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 second fluidization region is moved into
the first fluidization region step-by-step. In the first 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 second 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. A temperature of the second fluidization region is maintained by the sand
circulation device which returns the high-temperature fluidizable particles discharged
from the non-combustible substance discharge port, to the second fluidization region
of the fluidized bed. However, during the period in which the fluidizable particles
discharged from the non-combustible substance discharge port are returned to the fluidized
bed by the sand circulation device, a temperature of the fluidizable particles is
lowered, so that the second fluidization region has a temperature less than that of
the first fluidization region.
[0063] The upper surface of the bottom wall is inclined to become lower toward the non-combustible
substance discharge port, so that, when non-combustible substances in the waste sinks
down to the bottom wall in the fluidized bed, they fall on the upper surface of the
bottom wall toward the non-combustible substance discharge port. In this manner, the
non-combustible substances are discharged from the non-combustible substance discharge
port together with a part of the fluidizable particles, so that it becomes possible
to easily discharge non-combustible substances from the furnace body.
[0064] 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 second fluidization
region, thereby causing the waste accumulated on the second fluidization region to
be moved into the first fluidization region step-by-step.
[0065] According to this feature, new waste is pushed generally horizontally toward the
waste accumulated on the second fluidization region. Thus, the waste accumulated on
the second fluidization region is pushed by the new waste and reliably moved into
the first fluidization region.
[0066] Preferably, in the fluidized bed furnace of the present invention, the gas supply
section is adapted to blow the fluidizing gas in the second fluidization region at
a flow velocity satisfying a condition that U
o/U
mf ranges from 1 to less than 2, and blow the fluidizing gas in the first fluidization
region at a flow velocity satisfying a condition that U
o/U
mf ranges from 2 to less than 5, where U
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
o is a cross-sectional average flow velocity of the fluidizing gas.
[0067] The first fluidization region and the second fluidization region can be desirably
formed 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.
[0068] 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.
[0069] According to this feature, when the waste on the second fluidization region is pushed
by waste newly pushed by the waste supply section, and moved toward the first 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. In addition, the flow of the fluidizable particles formed in a direction
from the second fluidization region to the first fluidization region by the sand circulation
device is directionally the same as the movement of the waste, so that the flow of
the fluidizable particles is also stabilized.
[0070] 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.
[0071] According to this feature, waste is pushed onto the fluidized bed with an even force
in the width direction, so that the movement of the waste from the second fluidization
region to the first 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.
[0072] The waste treatment method according to the above embodiment is designed to heat
waste to extract a combustible gas from the waste. The 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 non-combustible substance 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 together with a part
of the fluidizable particles, and an upper surface of the bottom wall is inclined
to become lower toward the non-combustible substance discharge port so as to cause
the non-combustible substances to fall on the upper surface of the bottom wall toward
the non-combustible substance 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 non-combustible substance discharge port toward the fluidizable particles to form
a first fluidization region where the fluidizable particles are moved in a convection-like
pattern, while blowing a fluidizing gas between the first fluidization region and
a supply-side portion of the sidewall located on a side opposite to the non-combustible
substance discharge port across the center position of the bottom wall, at a flow
velocity less 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 lower than that in the first fluidization region; a fluidizable-particle-flow
formation step of returning the fluidizable particles discharged from the non-combustible
substance discharge port, to the fluidized bed from the side of the supply-side sidewall
portion to circulate the fluidizable particles, thereby forming a flow of the fluidizable
particles directed from the supply-side sidewall portion to the non-combustible substance
discharge port; and a gasification step of supplying waste from the supply-side sidewall
portion to a region on the fluidized bed adjacent to the supply-side sidewall portion,
thereby causing the waste to be accumulated on the second fluidization region, while
causing the accumulated waste to be moved into the first fluidization region step-by-step
and gasified.
[0073] In this waste treatment method, the first fluidization region around the non-combustible
substance discharge port and the second fluidization region having a fluidization
degree lower than that in the first fluidization region are formed in the fluidized
bed. Then, the waste is accumulated on the second fluidization region, and the waste
accumulated on the second fluidization region is moved into the first 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.
[0074] The upper surface of the bottom wall is inclined to become lower toward the non-combustible
substance discharge port, so that non-combustible substances in the waste fall on
the upper surface of the bottom wall toward the non-combustible substance discharge
port. In this manner, the non-combustible substances are discharged from the non-combustible
substance discharge port together with a part of the fluidizable particles, so that
it becomes possible to easily discharge non-combustible substances from the furnace
body.
[0075] Preferably, the gasification step includes pushing new waste generally horizontally
from the supply-side sidewall portion toward the waste accumulated on the second fluidization
region, thereby causing the waste accumulated on the second fluidization region to
be moved into the first fluidization region step-by-step and gasified.
[0076] According to this feature, new waste is pushed generally horizontally toward the
waste accumulated on the second fluidization region. Thus, the waste accumulated on
the second fluidization region is pushed by the new waste and reliably moved into
the first fluidization region, and gasified.
[0077] Preferably, in the waste treatment method, the fluidizing gas is blown in the second
fluidization region at a flow velocity satisfying a condition that U
o/U
mf ranges from 1 to less than 2, and blown in the first fluidization region at a flow
velocity satisfying a condition that U
o/U
mf ranges from 2 to less than 5, where U
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
o is a cross-sectional average flow velocity of the fluidizing gas.
[0078] The first fluidization region and the second fluidization region can be desirably
formed 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
[0079] 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.