U.S. patent number RE37,300 [Application Number 09/073,062] was granted by the patent office on 2001-07-31 for pressurized internal circulating fluidized-bed boiler.
This patent grant is currently assigned to Ebara Corporation. Invention is credited to Masayuki Horio, Shugo Hosoda, Norihisa Miyoshi, Shuichi Nagato, Takahiro Oshita, Akira Shimokura, Tomoyuki Shinano, Seiichiro Toyoda.
United States Patent |
RE37,300 |
Nagato , et al. |
July 31, 2001 |
Pressurized internal circulating fluidized-bed boiler
Abstract
A pressurized internal circulating fluidized-bed boiler is
incorporated in a combined-cycle electric generating system in
which a fuel such as coal, petro coke or the like is combusted in a
pressurized fluidized bed and an exhaust gas produced by the
combusted fuel is introduced into a gas turbine. The pressurized
internal circulating fluidized-bed boiler includes a pressure
vessel, a combustor disposed in the pressure vessel and a main
fluidized bed combustion chamber provided with an air diffusion
device. A thermal energy recovery chamber is partitioned from the
main combustion chamber by an inclined partition wall. A fluidized
medium flows into and out of the main combustion chamber and the
thermal energy recovery chamber. A free board is provided
integrally above the main combustion chamber and the thermal energy
recovery chamber so that combustion gas from the main combustion
chamber and the thermal energy recovery chamber is mixed in the
free board.
Inventors: |
Nagato; Shuichi (Yokohama,
JP), Horio; Masayuki (Chofu, JP), Oshita;
Takahiro (Yokohama, JP), Miyoshi; Norihisa
(Sodegaura, JP), Toyoda; Seiichiro (Tokyo,
JP), Shimokura; Akira (Yokohama, JP),
Shinano; Tomoyuki (Yokohama, JP), Hosoda; Shugo
(Yokohama, JP) |
Assignee: |
Ebara Corporation (Tokyo,
JP)
|
Family
ID: |
13302820 |
Appl.
No.: |
09/073,062 |
Filed: |
May 6, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
204096 |
Mar 2, 1994 |
05513599 |
May 7, 1996 |
|
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Foreign Application Priority Data
|
|
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|
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Mar 3, 1993 [JP] |
|
|
5-065985 |
|
Current U.S.
Class: |
122/4D; 422/146;
60/39.464 |
Current CPC
Class: |
F23C
10/20 (20130101); F01K 23/062 (20130101); F23L
7/00 (20130101); C10J 3/723 (20130101); F23C
10/06 (20130101); C10J 3/86 (20130101); F23C
10/16 (20130101); F23C 10/28 (20130101); F22B
31/0092 (20130101); C10J 3/56 (20130101); F01K
23/067 (20130101); F23L 9/04 (20130101); C10J
3/76 (20130101); C10J 3/463 (20130101); F23C
10/10 (20130101); C10J 2300/1675 (20130101); C10J
2200/09 (20130101); F23L 2900/07009 (20130101); C10J
2300/0956 (20130101); Y02E 20/18 (20130101); Y02P
20/129 (20151101); Y02P 20/10 (20151101); Y02E
20/16 (20130101); Y02E 20/34 (20130101); C10J
2200/15 (20130101); C10J 2300/1687 (20130101); F23L
2900/07005 (20130101) |
Current International
Class: |
F01K
23/06 (20060101); F23C 10/06 (20060101); F23C
10/28 (20060101); F23C 10/20 (20060101); F23C
10/16 (20060101); F23C 10/00 (20060101); F22B
31/00 (20060101); F23C 10/10 (20060101); F23L
9/00 (20060101); F23L 9/04 (20060101); C10J
3/46 (20060101); C10J 3/76 (20060101); C10J
3/00 (20060101); F23L 7/00 (20060101); B09B
003/00 (); F22B 001/00 () |
Field of
Search: |
;122/4D ;60/39.464
;110/245 ;422/146 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Miller et al., "Technical Evaluation: Pressurized Fluidized-Bed
Combustion Technology", no date Fossil Energy Program, Argonne
Natiounal Laboratory, ANL/FE 81-65, pp. 107-108, no date.* .
"PFBC and a new eral for coal arise from mothballed plant", Journal
of Power, Apr. 1991, pp. 102-108.* .
Kinsinger, "PFBC System Modularity", Journal of Proceedings of the
American Power Conference, pp. 646-650, no date.* .
Ishimoto et al., "Practical Use of IHI's Pressurized
Fluidized-Bed-Boiler", Technical News published by Ishikawajima
Harima Industry Co., vol. 31-5, pp. 301-308, Sep. 1991.* .
Ishigaki et al., "The present technique of Pressurized Fluidized
Bed", Journal of Chemical Device, pp. 51-58, Feb. 1991.* .
Keairns et al., "Circulating-Bed Boiler Concepts for STeam and
Power Generation", Proc. 13th Intersoc. Energy Conversion Eng.
Conf. (Paper No. 789336), vol. 1, pp. 540-547, no date..
|
Primary Examiner: Tanner; Harry B.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Claims
What is claimed is:
1. A pressurized internal circulating fluidized-bed boiler for use
in a combined-cycle electric generating system, comprising:
a pressure vessel;
a combustor disposed in said pressure vessel;
a main fluidized bed combustion chamber having an air diffusion
device provided at the bottom of said combustor and adapted to
inject fluidizing air upwardly under a mass flow that is at least
greater at one side than that at another side;
an inclined partition wall provided above a portion of said air
diffusion device where the mass flow is greater so as to interfere
with the upward flow of the fluidizing air and thereby to deflect
the air towards a portion above said another side of said air
diffusion device where the mass flow is smaller;
a thermal energy recovery chamber partitioned from said main
combustion chamber by said inclined partition wall;
a heat transfer surface means provided in said thermal energy
recovery chamber for a passage of a heat receiving fluid
therethrough;
an air diffuser provided at a lower portion of said thermal energy
recovery chamber; and
a free board provided integrally above said main combustion chamber
and said thermal energy recovery chamber;
wherein said thermal energy recovery chamber is communicated at
upper and lower portions thereof with said main fluidized bed
combustion chamber, a moving bed is formed above the portion of
said air diffusion device where the injected mass flow is smaller
so that a fluidized medium descends and diffuses within the moving
bed, and a circulating fluidized bed is formed above the portion of
said air diffusion device where the mass flow of the fluidizing air
is greater so that said fluidized medium is intensely fluidized and
whirled towards a position above said moving bed and a part of said
fluidized medium is introduced into said thermal energy recovery
chamber beyond an upper portion of said inclined partition wall,
the formation of said moving bed and said circulating fluidized bed
is effected by regulation of the amount of air injected upwardly
from said air diffusion device in said main combustion chamber and
regulating of the fluidizing air injected from said air diffuser in
said thermal energy recovery chamber causes the fluidized medium
within said thermal energy recovery chamber to descend in a state
of a moving bed for circulation to said main combustion chamber,
and combustion gas from said main combustion chamber and said
thermal energy recovery chamber is mixed in said free board.
2. The pressurized internal circulating fluidized-bed boiler
according to claim 1, further comprising at least one secondary air
supplying nozzle for supplying a secondary air into said free board
so that combustion gas from said main combustion chamber and said
thermal energy recovery chamber is mixed and unburned combustible
materials in said combustion gas .[.is.]. .Iadd.are
.Iaddend.combusted.
3. The pressurized internal circulating fluidized-bed boiler
according to claim 1, further comprising screening means provided
between said main combustion chamber and said thermal energy
recovery chamber for preventing combustible materials having a
large grain size from entering said thermal energy recovery
chamber, and for allowing combustion gas from said thermal energy
recovery chamber to pass therethrough while regulating .Iadd.a
.Iaddend.stream of .[.said.]. .Iadd.the .Iaddend.combustion gas and
mixing with combustion gas from said main combustion chamber.
4. The pressurized internal circulating fluidized-bed boiler
according to claim 2, further comprising an air supplying system
for controlling .Iadd.an .Iaddend.amount of combustion air to
combust fuel at a predetermined air ratio in accordance with
.Iadd.an .Iaddend.amount of .[.said.]. .Iadd.the .Iaddend.fuel to
be supplied while maintaining oxygen concentration at a
predetermined rate in exhaust gas discharged from said combustor,
wherein by said air supplying system, the remaining amount of air
is determined by subtracting .Iadd.an .Iaddend.amount of air to be
supplied to said air diffuser in said thermal energy recovery
chamber from .[.said.]. .Iadd.the .Iaddend.amount of combustion air
and .[.said.]. .Iadd.the .Iaddend.remaining amount of air is
divided into .Iadd.an .Iaddend.amount of air to be supplied to said
air diffusion device in said main combustion chamber and .Iadd.an
.Iaddend.amount of air to be supplied to said free board as .[.a.].
secondary air.
5. The pressurized internal circulating fluidized-bed boiler
according to claim 4, wherein .[.said.]. .Iadd.the .Iaddend.amount
of air to be supplied to said main combustion chamber is controlled
so as to be less than a stoichiometric air flow rate.
6. The pressurized internal circulating fluidized-bed boiler
according to claim 1, further comprising a baffle provided in said
free board, wherein said baffle is positioned .[.at an.]. upstream
of a combustion gas outlet of said combustor to prevent .Iadd.a
.Iaddend.short-pass of combustion gas.
7. The pressurized internal circulating fluidized-bed boiler
according to claim 1, further comprising a gas turbine driven by
combustion gas of said combustor, wherein exhaust gas discharged
from said gas turbine is mixed with combustion air to be supplied
to said combustor.
8. The pressurized internal circulating fluidized-bed boiler
according to claim 1, further comprising an equalizing nozzle for
supplying a pressurized gas to a space between said pressure vessel
and said combustor to balance .[.the inner and the outer.].
.Iadd.pressures inwardly and outwardly .Iaddend.of said
combustor.
9. The pressurized internal circulating fluidized-bed boiler
according to claim 1, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector .[.is.].
.Iadd.are .Iaddend.classified into three groups of larger, medium
and smaller particle diameters, and only flying ashes of medium
particle diameter .[.is.]. .Iadd.are .Iaddend.returned to at least
one of said main combustion chamber, said free board and a fuel
supplying system for supplying fuel.
10. The pressurized internal circulating fluidized-bed boiler
according to claim 1, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector .[.is.].
.Iadd.are .Iaddend.returned to said thermal energy recovery chamber
through an opening formed in said pressure vessel.
11. The pressurized internal circulating fluidized-bed boiler
according to claim 1, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector .[.is.].
.Iadd.are .Iaddend.returned to at least one of said main combustion
chamber and said free board through an opening formed in said
pressure vessel.
12. A pressurized internal circulating fluidized-bed boiler for use
in a combined-cycle electric generating system, comprising:
a pressure vessel;
a combustor disposed in said pressure vessel and having a
cylindrical outer wall;
a main fluidized bed combustion chamber having an air diffusion
device provided at the bottom of said combustor and adapted to
inject fluidizing air upwardly under a mass flow that is at least
greater at an outer side than that at a central side;
a partition having a cylindrical partition and a conical partition
formed at an upper portion of said cylindrical partition, said
conical partition being provided above a portion of said air
diffusion device where the mass flow is greater so as to interfere
with the upward flow of the fluidizing air and thereby to deflect
the air towards a portion above said central side of said air
diffusion device where the mass flow is smaller;
an annular thermal energy recovery chamber partitioned from said
main combustion chamber by said partition;
a heat transfer surface means provided in said thermal energy
recovery chamber for a passage of a heat receiving fluid
therethrough; and
an air diffuser provided at a lower portion of said thermal energy
recovery chamber;
wherein said thermal energy recovery chamber is communicated at
upper and lower portions thereof with said main fluidized bed
combustion chamber, a moving bed is formed above the portion of
said air diffusion device where the injected mass flow is smaller
so that a fluidized medium descends and diffuses within the moving
bed, and a circulating fluidized bed is formed above the portion of
said air diffusion device where the mass flow of the fluidizing air
is greater so that said fluidized medium is intensely fluidized and
whirled towards a position above said moving bed and a part of said
fluidized medium is introduced into said thermal energy recovery
chamber beyond an upper portion of said conical partition, the
formation of said moving bed and said circulating fluidized bed is
effected by regulation of the amount of air injected upwardly from
said air diffusion device in said main combustion chamber and
regulating of the fluidizing air injected from said air diffuser in
said thermal energy recovery chamber causes the fluidized medium
within said thermal energy recovery chamber to descend in a state
of a moving bed for circulation to said main combustion
chamber.
13. The pressurized internal circulating fluidized-bed boiler
according to claim 12, wherein said air diffusion device is
provided on a bottom face of said main combustion chamber, and said
bottom face is conical in shape.
14. The pressurized internal circulating fluidized-bed boiler
according to claim 12, further comprising a free board provided
integrally above said main combustion chamber and said thermal
energy recovery chamber, wherein combustion gas from said main
combustion chamber and said thermal energy recovery chamber is
mixed in said free board.
15. The pressurized internal circulating fluidized-bed boiler
according to claim 14, further comprising at least one secondary
air supplying nozzle for supplying a secondary air into said free
board so that combustion gas from said main combustion chamber and
said thermal energy recovery chamber is mixed and unburned
combustible materials in said combustion gas .[.is.]. .Iadd.are
.Iaddend.combusted.
16. The pressurized internal circulating fluidized-bed boiler
according to claim 14, further comprising screening means provided
between said main combustion chamber and said thermal energy
recovery chamber for preventing combustible materials having a
large grain size from entering said thermal energy recovery
chamber, and for allowing combustion gas from said thermal energy
recovery chamber to pass therethrough while regulating .Iadd.a
.Iaddend.stream of .[.said.]. .Iadd.the .Iaddend.combustion gas and
mixing with combustion gas from said main combustion chamber.
17. The pressurized internal circulating fluidized-bed boiler
according to claim 15, further comprising an air supplying system
for controlling .Iadd.an .Iaddend.amount of combustion air to
combust fuel at a predetermined air ratio in accordance with
.Iadd.an .Iaddend.amount of .[.said.]. .Iadd.the .Iaddend.fuel to
be supplied while maintaining oxygen concentration at a
predetermined rate in exhaust gas discharged from said combustor,
wherein by said air supplying system, the remaining amount of air
is determined by subtracting .Iadd.an .Iaddend.amount of air to be
supplied to said air diffuser in said thermal energy recovery
chamber from .[.said.]. .Iadd.the .Iaddend.amount of combustion and
.[.said.]. .Iadd.the .Iaddend.remaining amount of air is divided
into .Iadd.an .Iaddend.amount of air to be supplied to said air
diffusion device in said main combustion chamber and .Iadd.an
.Iaddend.amount of air to be supplied to said free board as .[.a.].
secondary air.
18. The pressurized internal circulating fluidized-bed boiler
according to claim 17, wherein .[.said.]. .Iadd.the .Iaddend.amount
of air to be supplied to said main combustion chamber is controlled
so as to be less than a stoichiometric air flow rate.
19. The pressurized internal circulating fluidized-bed boiler
according to claim 14, further comprising a baffle provided in said
free board, wherein said baffle is positioned .[.at an.]. upstream
of a combustion gas outlet of said combustor to prevent .Iadd.a
.Iaddend.short-pass of combustion gas.
20. The pressurized internal circulating fluidized-bed boiler
according to claim 12, further comprising an equalizing nozzle for
supplying a pressurized gas to a space between said pressure vessel
and said combustor to balance .[.the inner and an outer.].
.Iadd.pressures inwardly and outwardly .Iaddend.of said
combustor.
21. The pressurized internal circulating fluidized-bed boiler
according to claim 12, wherein said air diffuser is provided on a
bottom face of said thermal energy recovery chamber, said bottom
face is inclined inwardly toward said main combustion chamber, and
a lowermost bottom face of said thermal energy recovery chamber
faces a connection opening for returning fluidized medium from said
thermal energy recovery chamber to said main combustion
chamber.
22. The pressurized internal circulating fluidized-bed boiler
according to claim 21, further comprising an air diffuser provided
at said connection opening for enabling fluidized medium to be
fluidized in said connecting opening.
23. The pressurized internal circulating fluidized-bed boiler
according to claim 12, wherein said heat transfer surface means
comprises heat transfer tubes which are installed in a radial
pattern, said heat transfer tubes are divided into a plurality of
blocks for use as a block of evaporating tubes, a block of steam
superheating tubes and a block of steam reheating tubes.
24. The pressurized internal circulating fluidized-bed boiler
according to claim 13, wherein a fuel inlet for supplying fuel to
said main combustion chamber is provided in the vicinity of said
bottom face of said main combustion chamber.
25. The pressurized internal circulating fluidized-bed boiler
according to claim 12, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector .[.is.].
.Iadd.are .Iaddend.returned to said thermal energy recovery chamber
through an opening formed in said pressure vessel.
26. The pressurized internal circulating fluidized-bed boiler
according to claim 14, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector .[.is.].
.Iadd.are .Iaddend.returned to at least one of said main combustion
chamber and said free board through an opening formed in said
pressure vessel.
27. The pressurized internal circulating fluidized-bed boiler
according to claim 14, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector .[.is.].
.Iadd.are .Iaddend.mixed with a secondary air and .Iadd.a
.Iaddend.mixture of .[.said.]. .Iadd.the .Iaddend.flying ashes and
.[.said.]. secondary air is supplied to said free board through an
opening formed in said pressure vessel.
28. The pressurized internal circulating fluidized-bed boiler
according to claim 12, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor for
collecting flying ashes and a classifier for recovering unreacted
desulfurizing agent and unburned carbon from .[.said.]. .Iadd.the
.Iaddend.ashes.
29. The pressurized internal circulating fluidized-bed boiler
according to claim 28, wherein unreacted desulfurizing agent and
unburned carbon recovered by said classifier are returned to one of
said main combustion chamber and a fuel supplying system for
supplying fuel.
30. The pressurized internal circulating fluidized-bed boiler
according to claim 12, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector .[.is.].
.Iadd.are .Iaddend.classified into three groups of larger, medium
and smaller particle diameters, and only flying ashes of medium
particle diameter .[.is.]. .Iadd.are .Iaddend.returned to at least
one of said main combustion chamber, said free board and a fuel
supplying system for supplying fuel.
31. A topping-cycle combined electric generating system including a
gasifier for generating a gas and char, an oxidizer for combusting
.[.said.]. .Iadd.the .Iaddend.char to produce combustion gas, and a
gas turbine which is driven by a high-temperature gas produced by
combusting .Iadd.a .Iaddend.mixture of .[.said.]. .Iadd.the
.Iaddend.generated gas and .[.said.]. .Iadd.the .Iaddend.combustion
gas, at least one of said gasifier and said oxidizer comprising a
pressurized internal circulating fluidized-bed boiler which
comprises:
a pressure vessel;
a combustor disposed in said pressure vessel and having a
cylindrical outer wall;
a main fluidized bed combustion chamber having an air diffusion
device provided at the bottom of said combustor and adapted to
inject fluidizing air upwardly under a mass flow that is at least
greater at an outer side than that at a central side;
a partition having a cylindrical partition and a conical partition
formed at an upper portion of said cylindrical partition, said
conical partition being provided above a portion of said air
diffusion device where the mass flow is greater so as to interfere
with the upward flow of the fluidizing air and thereby to deflect
the air towards a portion above said central side of said air
diffusion device where the mass flow is smaller;
an annular thermal energy recovery chamber partitioned from said
main combustion chamber by said partition;
a heat transfer surface means provided in said thermal energy
recovery chamber for a passage of a heat receiving fluid
therethrough; and
an air diffuser provided at a lower portion of said thermal energy
recovery chamber;
wherein said thermal energy recovery chamber is communicated at
upper and lower portions thereof with said main fluidized bed
combustion chamber, a moving bed is formed above the portion of
said air diffusion device where the injected mass flow is smaller
so that a fluidized medium descends and diffuses within the moving
bed, and a circulating fluidized bed is formed above the portion of
said air diffusion device where the mass flow of the fluidizing air
is greater so that said fluidized medium is intensely fluidized and
whirled towards a position above said moving bed and a part of said
fluidized medium is introduced into said thermal energy recovery
chamber beyond an upper portion of said conical partition, the
formation of said moving bed and said circulating fluidized bed is
effected by regulation of the amount of air injected upwardly from
said air diffusion device in said main combustion chamber and
regulating of the fluidizing air injected from said air diffuser in
said thermal energy recovery chamber causes the fluidized medium
within said thermal energy recovery chamber to descend in a state
of a moving bed for circulation to said main combustion
chamber.
32. The topping-cycle combined electric generating system according
to claim 31, wherein unburned char .[.discharge.]. .Iadd.discharged
.Iaddend.from said gasifier is entrained, in its entirety, by
.[.said.]. .Iadd.the .Iaddend.generated gas and cooled, and
particles containing char, Na and K are collected by a downstream
dust collector, and .[.said.]. .Iadd.the .Iaddend.particles are
introduced into said oxidizer where they are completely combusted,
and an exhaust gas produced in said oxidizer is discharged
therefrom and cooled, and particles containing at least Na, K
contained in .[.said.]. .Iadd.the .Iaddend.exhaust gas are
collected by and discharged from a downstream dust collector, and
purified exhaust gas and .[.said.]. .Iadd.the .Iaddend.generated
gas which has been discharged from said gasifier and filtered to
remove particles therefrom are mixed and combusted by a
topping-combustor, and then a high-temperature exhaust gas produced
by said combustor is introduced into said gas turbine.
33. An integral type of fluidized-bed furnace for use in a
topping-cycle combined electric generating system, comprising:
a cylindrical outer wall;
a cylindrical partition provided concentrically with said
cylindrical outer wall;
a gasifier formed inside said cylindrical partition;
an oxidizer formed between said cylindrical outer wall and said
cylindrical partition;
an air diffusion device provided at the bottom of said gasifier and
adapted to inject fluidizing air upwardly under a mass flow that is
at least greater at an outer side than that at a central side;
a conical partition formed on said cylindrical partition, said
conical partition being provided above a portion of said air
diffusion device where the mass flow is greater so as to interfere
with the upward flow of the fluidizing air and thereby to deflect
the air towards a portion above said central side of said air
diffusion device where the mass flow is smaller;
an air diffuser provided at a lower portion of said oxidizer;
and
a first free board defined above said gasifier and a second free
board defined above said oxidizer, said first and second free
boards being separated from each other by said cylindrical
partition so that a gas produced by said gasifier and combustion
gas from said oxidizer are separately discharged towards the
outside;
wherein said oxidizer is communicated at intermediate and lower
portions thereof with said gasifier, a moving bed is formed above
the portion of said air diffusion device where the injected mass
flow is smaller so that a fluidized medium descends and diffuses
within the moving bed, and a circulating fluidized bed is formed
above the portion of said air diffusion device where the mass flow
of the fluidizing air is greater so that said fluidized medium is
intensely fluidized and whirled towards a position above said
moving bed and a part of said fluidized medium is introduced into
said oxidizer through an opening formed in an intermediate portion
of said partition, the formation of said moving bed and said
circulating fluidized bed is effected by regulating of the amount
of air injected upwardly from said air diffusion device is said
gasifier and regulating of the fluidizing air injected from said
air diffuser in said oxidizer causes the fluidized medium within
said oxidizer to descend in a state of a moving bed for circulation
to said gasifier.
34. The fluidized-bed furnace according to claim 33, further
comprising a heat transfer surface means provided in said oxidizer
for a passage of a heat receiving fluid therethrough.
35. The fluidized-bed furnace according to claim 33, further
comprising a pressure vessel for accommodating said fluidized-bed
furnace, wherein said pressure vessel has a combustion gas outlet
and a produced gas outlet, said combustion gas outlet is connected
to said oxidizer and said produced gas outlet is connected to said
gasifier.
36. The fluidized-bed furnace according to claim 33, wherein
unburned car discharged from said gasifier is entrained, in its
entirety, by .[.said.]. .Iadd.the .Iaddend.generated gas and
cooled, and particles containing char, Na and K are collected by a
downstream dust collector, and .[.said.]. .Iadd.the
.Iaddend.particles are introduced into said oxidizer where they are
completely combusted, and an exhaust gas produced in said oxidizer
is discharged therefrom and cooled, and particles containing at
least Na, K in .[.said.]. .Iadd.the .Iaddend.exhaust gas are
collected by and discharged from a downstream dust collector, and
purified exhaust gas and .[.said.]. .Iadd.the .Iaddend.generated
gas which has been discharged from said gasifier and filtered to
remove particles therefrom are mixed and combusted by a
topping-combustor, and then a high-temperature exhaust gas produced
by said combustor is introduced into said gas turbine..Iadd.
37. A pressurized cylindrical internal circulating fluidized-bed
boiler for use in a combined cycle electric generating system,
comprising:
a pressure vessel;
a combustor disposed in said pressure vessel;
a main fluidized bed combustion chamber having an air diffusion
device provided at the bottom of said combustor and adapted to
inject fluidizing air upwardly under a mass flow that is at least
greater at one side than that at another side;
a partition wall provided above a portion of said air diffusion
device;
a thermal energy recovery chamber partitioned from said main
combustion chamber by said partition wall;
a heat transfer surface means provided in said thermal energy
recovery chamber for a passage of a heat receiving fluid
therethrough;
an air diffuser provided at a lower portion of said thermal energy
recovery chamber; and
a free board provided above said main combustion chamber and said
thermal energy recovery chamber;
wherein said thermal energy recovery chamber is communicated at
upper and lower portions thereof with said main fluidized bed
combustion chamber, a moving bed is formed above a portion of said
air diffusion device where the injected mass flow is smaller so
that a fluidized medium descends and diffuses within the moving
bed, and a circulating fluidized bed is formed above a portion of
said air diffusion device where the mass flow of the fluidizing air
is greater so that said fluidized medium is intensely fluidized and
whirled towards a position above said moving bed and a part of said
fluidized medium is introduced into said thermal energy recovery
chamber beyond an upper portion of said partition wall, the
formation of said moving bed and said circulating fluidized bed is
effected by regulation of the amount of air injected upwardly from
said air diffusion device in said main combustion chamber and
regulation of the fluidizing air injected from said air diffuser in
said thermal energy recovery chamber causes the fluidized medium
within said thermal energy recovery chamber to descend in a state
of a moving bed for circulation to said main combustion chamber,
and combustion gas from said main combustion chamber and said
thermal energy recovery chamber is mixed in said free
board..Iaddend..Iadd.
38. The pressurized internal circulating fluidized-bed boiler
according to claim 37, further comprising at least one secondary
air supplying nozzle for supplying a secondary air into said free
board so that combustion gas from said main combustion chamber and
said thermal energy recovery chamber is mixed and unburned
combustible materials in said combustion gas are
combusted..Iaddend..Iadd.
39. The pressurized internal circulating fluidized-bed boiler
according to claim 38, further comprising an air supplying system
for controlling an amount of combustion air to combust fuel at a
predetermined air ratio in accordance with an amount of the fuel to
be supplied while maintaining oxygen concentration at a
predetermined rate in exhaust gas discharged from said combustor,
wherein by said air supplying system, the remaining amount of air
is determined by subtracting an amount of air to be supplied to
said air diffuser in said thermal energy recovery chamber from the
amount of combustion air and the remaining amount of air is divided
into an amount of air to be supplied to said air diffusion device
in said main combustion chamber and an amount of air to be supplied
to said free board as secondary air..Iaddend..Iadd.
40. The pressurized internal circulating fluidized-bed boiler
according to claim 39, wherein the amount of air to be supplied to
said main combustion chamber is controlled so as to be less than a
stoichiometric air flow rate..Iaddend..Iadd.
41. The pressurized internal circulating fluidized-bed boiler
according to claim 37, further comprising screening means provided
between said main combustion chamber and said thermal energy
recovery chamber for preventing combustible materials having a
large grain size from entering said thermal energy recovery
chamber, and for allowing combustion gas from said thermal energy
recovery chamber to pass therethrough while regulating a stream of
the combustion gas and mixing with combustion gas from said main
combustion chamber..Iaddend..Iadd.
42. The pressurized internal circulating fluidized-bed boiler
according to claim 37, further comprising a baffle provided in said
free board, wherein said baffle is positioned upstream of a
combustion gas outlet of said combustor to prevent a short-pass of
combustion gas..Iaddend..Iadd.
43. The pressurized internal circulating fluidized-bed boiler
according to claim 37, further comprising a gas turbine driven by
combustion gas of said combustor, wherein exhaust gas discharged
from said gas turbine is mixed with combustion air to be supplied
to said combustor..Iaddend..Iadd.
44. The pressurized internal circulating fluidized-bed boiler
according to claim 37, further comprising an equalizing nozzle for
supplying a pressurized gas to a space between said pressure vessel
and said combustor to balance pressures inwardly and outwardly of
said combustor..Iaddend..Iadd.
45. The pressurized internal circulating fluidized-bed boiler
according to claim 37, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are classified
into three groups of larger, medium and smaller particle diameters,
and only flying ashes of medium particle diameter are returned to
at least one of said main combustion chamber, said free board and a
fuel supplying system for supplying fuel..Iaddend..Iadd.
46. The pressurized internal circulating fluidized-bed boiler
according to claim 37, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are returned to
said thermal energy recovery chamber through an opening formed in
said pressure vessel..Iaddend..Iadd.
47. The pressurized internal circulating fluidized-bed boiler
according to claim 37, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are returned to
at least one of said main combustion chamber and said free board
through an opening formed in said pressure
vessel..Iaddend..Iadd.
48. A pressurized internal circulating fluidized-bed boiler
according to claim 37, wherein said partition has a cylindrical
partition and a conical partition formed at an upper portion of
said cylindrical partition, said conical partition being provided
above a portion of said air diffusion device where the mass flow is
greater so as to interfere with the upward flow of the fluidizing
air and thereby to deflect the air towards a portion above a
central part of said air diffusion device where the mass flow is
smaller, and wherein said thermal energy recovery chamber
partitioned from said main combustion chamber by said partition is
annular..Iaddend..Iadd.
49. The pressurized internal circulating fluidized-bed boiler
according to claim 48, wherein said air diffusion device is
provided on a bottom face of said main combustion chamber, and said
bottom face is conical in shape..Iaddend..Iadd.
50. The pressurized internal circulating fluidized-bed boiler
according to claim 49, wherein a fuel inlet for supplying fuel to
said main combustion chamber is provided in the vicinity of said
bottom face of said main combustion chamber..Iaddend..Iadd.
51. The pressurized internal circulating fluidized-bed boiler
according to claim 48, wherein said free board is provided
integrally above said main combustion chamber and said thermal
energy recovery chamber..Iaddend..Iadd.
52. The pressurized internal circulating fluidized-bed boiler
according to claim 51, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are mixed with
secondary air, and a mixture of said flying ashes and said
secondary air is supplied to said free board through an opening
formed in said pressure vessel..Iaddend..Iadd.
53. The pressurized internal circulating fluidized-bed boiler
according to claim 48, wherein said air diffuser is provided on a
bottom face of said thermal energy recovery chamber, said bottom
face is inclined inwardly toward said main combustion chamber, and
a lowermost bottom face of said thermal energy recovery chamber
faces a connection opening for returning fluidized medium from said
thermal energy recovery chamber to said main combustion
chamber..Iaddend..Iadd.
54. The pressurized internal circulating fluidized-bed boiler
according to claim 53, further comprising an air diffuser provided
at said connection opening for enabling fluidized medium to be
fluidized in said connecting opening..Iaddend..Iadd.
55. The pressurized internal circulating fluidized-bed boiler
according to claim 48, wherein said heat transfer surface means
comprises heat transfer tubes which are installed in a radial
pattern, said heat transfer tubes are divided into a plurality of
blocks for use as a block of evaporating tubes, a block of steam
superheating tubes and a block of steam reheating
tubes..Iaddend..Iadd.
56. The pressurized internal circulating fluidized-bed boiler
according to claim 48, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor for
collecting flying ashes, and a classifier for recovering unreacted
desulfurizing agent and unburned carbon from said
ashes..Iaddend..Iadd.
57. The pressurized internal circulating fluidized-bed boiler
according to claim 56, wherein unreacted desulfurizing agent and
unburned carbon recovered by said classifier are returned to one of
said main combustion chamber and a fuel supplying system for
supplying fuel..Iaddend..Iadd.
58. The pressurized internal circulating fluidized-bed boiler
according to claim 48, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are classified
into three groups of larger, medium and smaller particle diameters,
and only flying ashes of medium particle diameter are returned to
at least one of said main combustion chamber, said free board and a
fuel supplying system..Iaddend..Iadd.
59. The pressurized internal circulating fluidized-bed boiler
according to claim 37, wherein said thermal energy recovery chamber
substantially surrounds said main fluidized bed combustion
chamber..Iaddend..Iadd.
60. The pressurized internal circulating fluidized-bed boiler
according to claim 37, wherein the heat transfer surface means
comprise heat transfer tubes immersed in the fluidized bed in said
thermal energy recovery chamber and divided by function into
blocks..Iaddend..Iadd.
61. The pressurized internal circulating fluidized-bed boiler
according to claim 60, wherein the amount of air from said air
diffuser in said thermal energy recovery chamber can be adjusted in
each of said blocks..Iaddend..Iadd.
62. The pressurized internal circulating fluidized-bed boiler
according to claim 37, wherein said heat transfer surface means
comprise immersed heat transfer tubes installed in a radial pattern
in plan view in said thermal energy recovery
chamber..Iaddend..Iadd.
63. The pressurized internal circulating fluidized-bed boiler
according to claim 37, wherein said partition wall is an inclined
partition wall..Iaddend..Iadd.
64. The pressurized internal circulating fluidized-bed boiler
according to claim 37, wherein said free board is provided
integrally above said main combustion chamber and said thermal
energy recovery chamber..Iaddend..Iadd.
65. A pressurized cylindrical internal circulating fluidized-bed
boiler comprising:
a pressure vessel;
a combustor disposed in said pressure vessel;
a main fluidized bed combustion chamber having an air diffusion
device provided at the bottom of said combustor and adapted to
inject fluidizing air upwardly under a mass flow that is at least
greater at one side than that at another side;
a partition wall provided above a portion of said air diffusion
device;
a thermal energy recovery chamber partitioned from said main
combustion chamber by said partition wall;
a heat transfer surface means provided in said thermal energy
recovery chamber for a passage of a heat receiving fluid
therethrough;
an air diffuser provided at a lower portion of said thermal energy
recovery chamber; and
a free board provided above said main combustion chamber and said
thermal energy recovery chamber;
wherein said thermal energy recovery chamber is communicated at
upper and lower portions thereof with said main fluidized bed
combustion chamber, a moving bed is formed above a portion of said
air diffusion device where the injected mass flow is smaller so
that a fluidized medium descends and diffuses within the moving
bed, and a circulating fluidized bed is formed above the portion of
said air diffusion device where the mass flow of the fluidizing air
is greater so that said fluidized medium is intensely fluidized and
whirled towards a position above said moving bed and a part of said
fluidized medium is introduced into said thermal energy recovery
chamber beyond an upper portion of said partition wall, the
formation of said moving bed and said circulating fluidized bed is
effected by regulation of the amount of air injected upwardly from
said air diffusion device in said main combustion chamber and
regulation of the fluidizing air injected from said air diffuser in
said thermal energy recovery chamber causes the fluidized medium
within said thermal energy recovery chamber to descend in a state
of a moving bed for circulation to said main combustion chamber,
and combustion gas from said main combustion chamber and said
thermal energy recovery chamber is mixed in said free
board..Iaddend..Iadd.
66. The pressurized internal circulating fluidized-bed boiler
according to claim 65, further comprising at least one secondary
air supplying nozzle for supplying a secondary air into said free
board so that combustion gas from said main combustion chamber and
said thermal energy recovery chamber is mixed and unburned
combustible materials in said combustion gas are
combusted..Iaddend..Iadd.
67. The pressurized internal circulating fluidized-bed boiler
according to claim 66, further comprising an air supplying system
for controlling an amount of combustion air to combust fuel at a
predetermined air ratio in accordance with an amount of the fuel to
be supplied while maintaining oxygen concentration at a
predetermined rate in exhaust gas discharged from said combustor,
wherein by said air supplying system, the remaining amount of air
is determined by subtracting an amount of air to be supplied to
said air diffuser in said thermal energy recovery chamber from the
amount of combustion air and the remaining amount of air is divided
into an amount of air to be supplied to said air diffusion device
in said main combustion chamber and an amount of air to be supplied
to said free board as secondary air..Iaddend..Iadd.
68. The pressurized internal circulating fluidized-bed boiler
according to claim 67, wherein the amount of air to be supplied to
said main combustion chamber is controlled so as to be less than a
stoichiometric air flow rate..Iaddend..Iadd.
69. The pressurized internal circulating fluidized-bed boiler
according to claim 65, further comprising screening means provided
between said main combustion chamber and said thermal energy
recovery chamber for preventing combustible materials having a
large grain size from entering said thermal energy recovery
chamber, and for allowing combustion gas from said thermal energy
recovery chamber to pass therethrough while regulating a stream of
the combustion gas and mixing with combustion gas from said main
combustion chamber..Iaddend..Iadd.
70. The pressurized internal circulating fluidized-bed boiler
according to claim 65, further comprising a baffle provided in said
free board, wherein said baffle is positioned upstream of a
combustion gas outlet of said combustor to prevent a short-pass of
combustion gas..Iaddend..Iadd.
71. The pressurized internal circulating fluidized-bed boiler
according to claim 65, further comprising a gas turbine driven by
combustion gas of said combustor, wherein exhaust gas discharged
from said gas turbine is mixed with combustion air to be supplied
to said combustor..Iaddend..Iadd.
72. The pressurized internal circulating fluidized-bed boiler
according to claim 65, further comprising an equalizing nozzle for
supplying a pressurized gas to a space between said pressure vessel
and said combustor to balance inwardly and outwardly of said
combustor..Iaddend..Iadd.
73. The pressurized internal circulating fluidized-bed boiler
according to claim 65, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are classified
into three groups of larger, medium and smaller particle diameters,
and only flying ashes of medium particle diameter are returned to
at least one of said main combustion chamber, said free board and a
fuel supplying system for supplying fuel..Iaddend..Iadd.
74. The pressurized internal circulating fluidized-bed boiler
according to claim 65, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are returned to
said thermal energy recovery chamber through an opening formed in
said pressure vessel..Iaddend..Iadd.
75. The pressurized internal circulating fluidized-bed boiler
according to claim 65, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are returned to
at least one of said main combustion chamber and said free board
through an opening formed in said pressure
vessel..Iaddend..Iadd.
76. A pressurized internal circulating fluidized-bed boiler
according to claim 65, wherein said partition has a cylindrical
partition and a conical partition formed at an upper portion of
said cylindrical partition, said conical partition being provided
above a portion of said air diffusion device where the mass flow is
greater so as to interfere with the upward flow of the fluidizing
air and thereby to deflect the air towards a portion above a
central part of said air diffusion device where the mass flow is
smaller, and wherein said thermal energy recovery chamber
partitioned from said main combustion chamber by said partition is
annular..Iaddend..Iadd.
77. The pressurized internal circulating fluidized-bed boiler
according to claim 76, wherein said air diffusion device is
provided on a bottom face of said main combustion chamber, and said
bottom face is conical in shape..Iaddend..Iadd.
78. The pressurized internal circulating fluidized-bed boiler
according to claim 77, wherein a fuel inlet for supplying fuel to
said main combustion chamber is provided in the vicinity of said
bottom face of said main combustion chamber..Iaddend..Iadd.
79. The pressurized internal circulating fluidized-bed boiler
according to claim 76, wherein said free board is provided
integrally above said main combustion chamber and said thermal
energy recovery chamber..Iaddend..Iadd.
80. The pressurized internal circulating fluidized-bed boiler
according to claim 79, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are mixed with
secondary air, and a mixture of said flying ashes and said
secondary air is supplied to said free board through an opening
formed in said pressure vessel..Iaddend..Iadd.
81. The pressurized internal circulating fluidized-bed boiler
according to claim 76, wherein said air diffuser is provided on a
bottom face of said thermal energy recovery chamber, said bottom
face is inclined inwardly toward said main combustion chamber, and
a lowermost bottom face of said thermal energy recovery chamber
faces a connection opening for returning fluidized medium from said
thermal energy recovery chamber to said main combustion
chamber..Iaddend..Iadd.
82. The pressurized internal circulating fluidized-bed boiler
according to claim 81, further comprising an air diffuser provided
at said connection opening for enabling fluidized medium to be
fluidized in said connecting opening..Iaddend..Iadd.
83. The pressurized internal circulating fluidized-bed boiler
according to claim 76, wherein said heat transfer surface means
comprises heat transfer tubes which are installed in a radial
pattern, said heat transfer tubes are divided into a plurality of
blocks for use as a block of evaporating tubes, a block of steam
superheating tubes and a block of steam reheating
tubes..Iaddend..Iadd.
84. The pressurized internal circulating fluidized-bed boiler
according to claim 76, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor for
collecting flying ashes, and a classifier for recovering unreacted
desulfurizing agent and unburned carbon from said
ashes..Iaddend..Iadd.
85. The pressurized internal circulating fluidized-bed boiler
according to claim 84, wherein unreacted desulfurizing agent and
unburned carbon recovered by said classifier are returned to one of
said main combustion chamber and a fuel supplying system for
supplying fuel..Iaddend..Iadd.
86. The pressurized internal circulating fluidized-bed boiler
according to claim 76, further comprising a dust collector provided
in a passage of combustion gas discharged from said combustor,
wherein flying ashes caught by said dust collector are classified
into three groups of larger, medium and smaller particle diameters,
and only flying ashes of medium particle diameter are returned to
at least one of said main combustion chamber, said free board and a
fuel supplying system for supplying fuel..Iaddend..Iadd.
87. The pressurized internal circulating fluidized-bed boiler
according to claim 65, wherein said thermal energy recovery chamber
substantially surrounds said main fluidized bed combustion
chamber..Iaddend..Iadd.
88. The pressurized internal circulating fluidized-bed boiler
according to claim 65, wherein the heat transfer surface means
comprise heat transfer tubes immersed in the fluidized bed in said
thermal energy recovery chamber and divided by function into
blocks..Iaddend..Iadd.
89. The pressurized internal circulating fluidized-bed boiler
according to claim 88, wherein the amount of air from said air
diffuser in said thermal energy recovery chamber can be adjusted in
each of said blocks..Iaddend..Iadd.
90. The pressurized internal circulating fluidized-bed boiler
according to claim 65, wherein said heat transfer surface means
comprise immersed heat transfer tubes installed in a radial pattern
in plan view in said thermal energy recovery
chamber..Iaddend..Iadd.
91. The pressurized internal circulating fluidized-bed boiler
according to claim 65, wherein said partition wall is an inclined
partition wall..Iaddend..Iadd.
92. The pressurized internal circulating fluidized-bed boiler
according to claim 65, wherein said free board is provided
integrally above said main combustion chamber and said thermal
energy recovery chamber..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressurized internal circulating
fluidized-bed boiler, and more particularly to a pressurized
internal circulating fluidized-bed boiler for use in a pressurized
fluidized-bed combined-cycle electric generating system in which a
fuel such as coal, petro coke, or the like is combusted in a
pressurized fluidized bed and an exhaust gas produced by the
combusted fuel is introduced into a gas turbine.
2. Description of the Prior Art
Efforts to reduce the emission of carbon dioxide from various
sources are important in view of environmental damages that are
being caused by air pollution which appears to be more and more
serious on the earth. It is conjectured that coal will have to be
relied upon as a major energy resource because greater dependency
on nuclear and oil energies is not favorable at present. To
suppress carbon dioxide emission and provide a substitute for oil
and nuclear power, there has been a demand for a highly efficient,
compact electric generating system which is capable of utilizing
coal combustion to generate a clean energy.
To meet such a demand, atmospheric fluidized-bed boilers (AFBC)
capable of burning coals of different kinds for electric generation
have been developed because a stable energy supply cannot be
achieved by pulverized coal boilers which pose a limitation on
available coal types.
However, the atmospheric fluidized-bed boilers (AFBC) fail to
perform the functions that have been expected. In addition, since
only steam turbines can be combined with the atmospheric
fluidized-bed boilers, there are certain limitations on attempts to
increase the efficiency and energy output of the atmospheric
fluidized-bed boilers. These disadvantages of the atmospheric
fluidized-bed boilers have directed research and development trends
toward pressurized fluidized-bed boilers (PFBC) that make it
possible to construct combined-cycle electric generating systems
with gas turbines.
Further, there has been researched a coal gasification
combined-cycle electric generating system in which coal is
converted into gas and a refined gas purified by removing dust
particles is supplied to a gas turbine. The coal gasification
combined-cycle electric generating system, incorporating an
air-cooled gas turbine which uses exhaust gas of 1300.degree. C.,
has a target efficiency of 47.1% at a generating end.
On the other hand, the pressurized bubbling type fluidized-bed
boilers with a capacity over 80 MWe are already in operation
overseas as demonstration or commercial models and, in addition,
has an advantage that a desulfurization equipment is not required.
However, the coal gasification electric generating system is
superior to the pressurized fluidized-bed combined-cycle electric
generating system in efficiency. Thus, a topping-cycle combined
electric generating system which has advantages of both systems and
higher efficiency has been researched.
The topping-cycle combined electric generating system, comprises a
gasifier in which coal is decomposed into coal gas and char, and an
oxidizer comprising a fluidized-bed boiler in which char produced
in the gasifier is combusted. The coal gas produced in the gasifier
and the exhausted gas produced by combustion of char in the
oxidizer are mixed and combusted at the inlet of a gas turbine to
thereby produce high-temperature gas. The produced high-temperature
gas is then supplied to the gas turbine which drives an electric
generator coupled thereto.
Conventionally, the pressurized fluidized-bed boilers with a
capacity over 80 MWe which are in operation as demonstration or
commercial models are made up of pressurized bubbling type
fluidized-bed boilers.
However, the pressurized bubbling type fluidized-bed boiler has the
following disadvantages.
(A) Disadvantage in load control
The pressurized bubbling type fluidized-bed electric generating
system is controlled to meet a load imposed thereon by varying the
height of the fluidized bed in the combustor. More specifically,
the fluidized medium is drawn from the combustor into the storage
container to change heat transfer area of the heat transfer tube,
thereby controlling the steam generation to meet the load. When the
heat transfer surfaces of the heat transfer tube are exposed to the
gas, the heat transfer coefficient thereof is lowered, and hence
the amount of heat recovered is lowered. Since the exhaust gas
emitted from the fluidized bed is cooled by the exposed heat
transfer surfaces, the temperature of the exhaust gas supplied to
the gas turbine is lowered, thus reducing the output energy of the
gas turbine.
However, the above control process is disadvantageous in that the
bed material storage container is necessary to withdraw and return
the high-temperature fluidized medium from and into the combustor,
it is not easy to withdraw and return the fluidized medium at high
temperature and pressure, and agglomeration tends to occur when the
fluidized medium of high heat capacity are taken into and out of
the bed material storage container.
Furthermore, since the pressurized fluidized-bed boiler is under
pressure, the heat transfer tube in a splash zone of the fluidized
bed is more subject to erode than that in the atmospheric
fluidized-bed boilers (AFBC). Another problem is that an large
amount of carbon monoxide is produced because an exhaust gas
emitted from the fluidized bed is cooled by the heat transfer tube
and the exhaust gas remains in the fluidized bed for a short period
of time as the height of the fluidized bed is reduced in the time
of low load.
(B) Large-sized pressure vessel
conventionally, the pressurized bubbling type fluidizedbed boiler
comprises square combustors 146 accommodated in a circular pressure
vessel 145 in a plan view as shown in FIG. 14. Therefore, a useless
space is defined between the combustors 146 and the pressure vessel
145, resulting in a large-sized pressure vessel and increasing the
construction cost of the boiler.
In other to solve the above problems, Mr. Jim Anderson of A.B.B
Carbon, A.B. proposed a certain pressurized bubbling type
fluidized-bed boiler in principles and design philosophy for a 350
MWe PFBC module. The pressurized bubbling type fluidized-bed boiler
is constructed by combining diamond-shaped three combustors 147 to
form a hexagonal profile in a plan view as shown in FIG. 15.
Assemblage of the combustors 147 which is brought close to a
circular shape is accommodated in a circular pressure vessel 145. A
useless space between the combustors 147 and the pressure vessel
145 is reduced and the pressure vessel is downsized. The reason for
the above structure is that arrangement of heat transfer tubes is
complicated in the pressurized bubbling type fluidized-bed boiler
having a cylindrical combustor.
Further, since the bed material storage container and pipes are
necessary to withdraw and return the high-temperature fluidized
medium from and into the combustor, housing of bed material storage
container and the pipes inside the pressure vessel makes the
pressure vessel large.
(C) Erosion of the heat transfer tube
In the conventional pressurized bubbling type fluidized-bed boiler,
the heat transfer tube is more subject to erode, because the heat
transfer tube is disposed in the fluidized bed where the fluidized
medium is intensely fluidized. Therefore, the heat transfer tube is
required to have surface treatment like thermal spraying.
(D) Complicated fuel supplying system
In the conventional pressurized bubbling type fluidized-bed boiler,
fuel such as coal is insufficiently dispersed horizontally in the
fluidized bed. In order to avoid nonuniform combustion, many fuel
feeding pipes must be installed in the boiler, resulting in a
complicated fuel supplying system. Further, it is difficult to
supply fuel such as coal to each of the fuel feeding pipes
uniformly. Unbalanced supply of fuel causes nonuniform combustion
and generates agglomeration, resulting in shutdown of the
boiler.
(E) Wear of limestone
In the conventional pressurized fluidized-bed electric generating
system, limestone is mixed with the fluidized medium for
desulfurization. However, the limestone wears rapidly, and is
scattered as ash from the dust collector without sufficiently
contributing to the desulfurizing action. The conventional
pressurized fluidized-bed electric generating system fails to
achieve a high desulfurization rate that are required by power
plants. The conventional pressurized bubbling type fluidized-bed
requires plenty of desulfurizing agent in order to obtain high
desulfurization rate, and then produces a vast amount of ashes.
On the other hand, in the topping-cycle combined electric
generating system, the fluidized-bed boiler which is used as an
oxidizer has the same disadvantages as mentioned above.
Further, a fixed-bed gasifier is disadvantageous in that coal tar
remains in the fixed bed, and an entrained flow gasifier is
disadvantageous in that ash-sticks occurs because of high
temperature reaction. On the contrary, a fluidized-bed gasifier has
advantages that coal tar does not remain, ash-sticks does not occur
and desulfurization is performed in the fluidized bed, because it
is in operation at the intermediate temperature of the above two
types of gasifier. However, the bubbling type fluidized-bed
gasifier has the same disadvantages as enumerated in (A)-(D).
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
pressurized internal circulating fluidized-bed boiler for a
combined-cycle electric generating system, which can be controlled
to meet a load without varying the height of a fluidized bed,
prevents agglomeration, minimize the emission of carbon monoxide
and nitrogen oxide, and can increase a limestone utilization ratio
and a desulfurization rate.
According to one aspect of the present invention, there is provided
a pressurized internal circulating fluidized-bed boiler for use in
a combined-cycle electric generating system, comprising: a pressure
vessel; a combustor disposed in the pressure vessel; a main
fluidized bed combustion chamber having an air diffusion device
provided at the bottom of the combustor and adapted to inject
fluidizing air upwardly under a mass flow that is at least greater
at one side than that at another side; an inclined partition wall
provided above a portion of the air diffusion device where the mass
flow is greater so as to interfere with the upward flow of the
fluidizing air and thereby to deflect the air towards a portion
above the another side of the air diffusion device where the mass
flow is smaller; a thermal energy recovery chamber partitioned from
the main combustion chamber by the inclined partition wall; a heat
transfer surface means provided in the thermal energy recovery
chamber for a passage of a heat receiving fluid therethrough; an
air diffuser provided at a lower portion of the thermal energy
recovery chamber; and a free board provided integrally above the
main combustion chamber and the thermal energy recovery chamber;
wherein the thermal energy recovery chamber is communicated at
upper and lower portions thereof with the main fluidized bed
combustion chamber, a moving bed is formed above the portion of the
air diffusion device where the injected mass flow is smaller so
that a fluidized medium descends and diffuses within the moving
bed, and a circulating fluidized bed is formed above the portion of
the air diffusion device where the mass flow of the fluidizing air
is greater so that the fluidized medium is intensely fluidized and
whirled towards a position above the moving bed and a part of the
fluidized medium is introduced into the thermal energy recovery
chamber beyond an upper portion of the inclined partition wall, the
formation of the moving bed and the circulating fluidized bed is
effected by regulation of the amount of air injected upwardly from
the air diffusion device, and regulation of the fluidizing air
injected from the air diffuser in the thermal energy recovery
chamber causes the fluidized medium within the recovery chamber to
descend in a state of a moving bed for circulation to the main
combustion chamber, and combustion gas from the main combustion
chamber and the thermal energy recovery chamber is mixed in the
free board.
According to a preferred embodiment, the boiler comprises at least
one secondary air supplying nozzle for supplying a secondary air
into the free board so that combustion gas from the main combustion
chamber and the thermal energy recovery chamber is mixed and
unburned combustible materials in the combustion gas is combusted.
Further, the boiler comprises screening means provided between the
main combustion chamber and the thermal energy recovery chamber for
preventing combustible materials having a large grain size from
entering the thermal energy recovery chamber, and for allowing
combustion gas from the thermal energy recovery chamber to pass
therethrough while regulating stream of the combustion gas.
According to another aspect of the present invention, there is
provided a pressurized internal circulating fluidized-bed boiler
for use in a combined-cycle electric generating system, comprising:
a pressure vessel; a combustor disposed in the pressure vessel and
having a cylindrical outer wall; a main combustion chamber having
an air diffusion device provided at the bottom of the combustor and
adapted to inject fluidizing air upwardly under a mass flow that is
at least greater at an outer side than that at a central side; a
partition having a cylindrical partition and a conical partition
formed at an upper portion of the cylindrical partition, the
conical partition being provided above a portion of the air
diffusion device where the mass flow is greater so as to interfere
with the upward flow of the fluidizing air and thereby to deflect
the air towards a portion above the central side of the air
diffusion device where the mass flow is smaller; an annular thermal
energy recovery chamber partitioned from the main combustion
chamber by the partition; a heat transfer surface means provided in
the thermal energy recovery chamber for a passage of a heat
receiving fluid therethrough; and an air diffuser provided at a
lower portion of the thermal energy recovery chamber; wherein the
thermal energy recovery chamber is communicated at upper and lower
portions thereof with the main fluidized bed combustion chamber, a
moving bed is formed above the portion of the air diffusion device
where the injected mass flow is smaller so that a fluidized medium
descends and diffuses within the moving bed, and a circulating
fluidized bed is formed above the portion of the air diffusion
device where the mass flow of the fluidizing air is greater so that
the fluidized medium is actively fluidized and whirled towards a
position above the moving bed and a part of the fluidized medium is
introduced into the thermal energy recovery chamber beyond an upper
portion of the inclined partition wall, the formation of the moving
bed and the circulating fluidized bed is effected by regulation of
the amount of air injected upwardly from the air diffusion device
and regulation of the fluidizing air injected from the air diffuser
in the thermal energy recovery chamber causes the fluidized medium
within the recovery chamber to descend in a state of a moving bed
for circulation.
According to a preferred embodiment, the boiler comprises a free
board provided integrally above the main combustion chamber and the
thermal energy recovery chamber, wherein combustion gas from the
main combustion chamber and the thermal energy recovery chamber is
mixed in the free board. Further, the boiler comprises at least one
secondary air supplying nozzle for supplying a secondary air into
the free board so that combustion gas from the main combustion
chamber and the thermal energy recovery chamber is mixed and
unburned combustible materials in the combustion gas is
combusted.
According to a preferred embodiment, the boiler comprises screening
means provided between the main combustion chamber and the thermal
energy recovery chamber for preventing combustible materials having
a large grain size from entering the thermal energy recovery
chamber, and for allowing combustion gas from the thermal energy
recovery chamber to pass therethrough while regulating stream of
the combustion gas. Further, the boiler comprises a second air
diffuser provided at the connection opening for enabling fluidized
medium to be actively fluidized in the connecting opening.
According to a preferred embodiment, the heat transfer surface
means comprises heat transfer tubes which are installed in a radial
pattern, the heat transfer tubes are divided into a plurality of
blocks for use as a block of evaporating tubes, a block of steam
superheating tubes and a block of steam reheating tubes. Further,
the boiler comprises a dust collector provided in a passage of
combustion gas, wherein flying ashes caught by the dust collector
is returned to the thermal energy recovery chamber through an
opening formed in the pressure vessel.
According to another aspect of the present invention, there is
provided a topping-cycle compound electric generating system
including a gasifier for generating a gas and char, an oxidizer for
combusting the char to produce combustion gas, and a gas turbine
which is driven by a high-temperature gas produced by combusting
mixture of the generated gas and the combustion gas, at least one
of the gasifier and the oxidizer comprising a pressurized internal
circulating fluidized-bed boiler which comprises: a pressure
vessel; a combustor disposed in the pressure vessel and having a
cylindrical outer wall; a main combustion chamber having an air
diffusion device provided at the bottom of the combustor and
adapted to inject fluidizing air upwardly under a mass flow that is
at least greater at an outer side than that at a central side; a
partition having a cylindrical partition and a conical partition
formed at an upper portion of the cylindrical partition, the
conical partition being provided above a portion of the air
diffusion device where the mass flow is greater so as to interfere
with the upward flow of the fluidizing air and thereby to deflect
the air towards a portion above the central portion of the air
diffusion device where the mass flow is smaller; an annular thermal
energy recovery chamber partitioned from the main combustion
chamber by the partition; a heat transfer surface means provided in
the thermal energy recovery chamber for a passage of a heat
receiving fluid therethrough; and an air diffuser provided at a
lower portion of the thermal energy recovery chamber; wherein the
thermal energy recovery chamber is communicated at upper and lower
portions thereof with the main fluidized bed combustion chamber, a
moving bed is formed above the portion of the air diffusion device
where the injected mass flow is smaller so that a fluidized medium
descends and diffuses within the moving bed, and a circulating
fluidized bed is formed above the portion of the air diffusion
device where the mass flow of the fluidizing air is greater so that
the fluidized medium is actively fluidized and whirled towards a
position above the moving bed and a part of the fluidized medium is
introduced into the thermal energy recovery chamber beyond an upper
portion of the inclined partition wall, the formation of the moving
bed and the circulating fluidized bed is effected by regulation of
the amount of air injected upwardly from the air diffusion device
and regulation of the fluidizing air injected from the air diffuser
in the thermal energy recovery chamber causes the fluidized medium
within the recovery chamber to descend in a state of a moving bed
for circulation.
According to another aspect of the present invention, there is
provided an integral type of influidized-bed boiler for use in a
topping-cycle compound electric generating system, comprising: a
cylindrical outer wall; a cylindrical partition provided
concentrically with the cylindrical outer wall; a gasifier formed
inside the cylindrical partition; an oxidizer formed between the
cylindrical outer wall and the cylindrical partition; an air
diffusion device provided at the bottom of the gasifier and adapted
to inject fluidizing air upwardly under a mass flow that is at
least greater at an outer side than that at a central side; a
conical partition formed on the cylindrical partition, the conical
partition being provided above a portion of the air diffusion
device where the mass flow is greater so as to interfere with the
upward flow of the fluidizing air and thereby to deflect the air
towards a portion above the central portion of the air diffusion
device where the mass flow is smaller; an air diffuser provided at
a lower portion of the oxidizer; and a first free board defined
above the gasifier and a second free board defined above the
oxidizer, the first and second free boards are separated from each
other by the cylindrical partition so that a gas produced by the
gasifier and combustion gas from the oxidizer are separately
discharged towards the outside; wherein the oxidizer is
communicated at intermediate and lower portions thereof with the
gasifier, a moving bed is formed above the portion of the air
diffusion device where the injected mass flow is smaller so that a
fluidized medium descends and diffuses within the moving bed, and a
circulating fluidized bed is formed above the portion of the air
diffusion device where the mass flow of the fluidizing air is
greater so that the fluidized medium is actively fluidized and
whirled towards a position above the moving bed and a part of the
fluidized medium is introduced into the oxidizer beyond an
intermediate portion of the partition wall, the formation of the
moving bed and the circulating fluidized bed is effected by
regulation of the amount of air injected upwardly from the air
diffusion device and regulation of the fluidizing air injected from
the air diffuser in the oxidizer causes the fluidized medium within
the oxidizer to descend in a state of a moving bed for
circulation.
With the above arrangements, the present invention offers the
following operations or advantages:
(1) Since the main combustion chamber and the thermal energy
recovery chamber are functionally separated from each other within
the combustor, the boiler can be controlled to meet a load simply
by varying the overall heat transfer coefficient of the heat
transfer tubes through adjustment of the amount of air introduced
into the thermal energy recovery chamber, rather than by varying
the height of the fluidized bed in the combustion chamber.
Therefore, no complex process and equipment is necessary to take
the fluidized medium into and out of the combustion chamber and the
thermal energy recovery chamber, and no agglomeration is generated
as the fluidized medium flows into and out of the main combustion
chamber and the thermal energy recovery chamber. Since the
temperature of the fluidized bed is kept at a constant level even
when the load on the boiler varies, the boiler can be operated
under a temperature condition optimum for the suppression of NOx,
SOx, and other undesirable emissions. Inasmuch as the heat transfer
tubes are positioned only in the thermal energy recovery chamber
which is exposed to a gradual flow of the fluidized medium, the
heat transfer tubes are less subject to erode than would be if they
were placed in the fluidized bed which is in an intense flow
condition.
As swirling flows are developed in the fluidized bed, the fluidized
medium does not stay stagnant in the fluidized bed, and the fuel
such as coal or petro coke is uniformly dispersed and combusted,
with no agglomeration produced. Thus, efficiency of gas turbine is
not lowered. The amount of carbon monoxide and nitrogen oxide (NOx)
produced is kept low because the exhaust gas emitted from the
fluidized bed is not cooled by the heat transfer tubes.
Further, a free board having a wide space is defined above he
thermal energy recovery chamber and the main combustion chamber,
combustion gas from the thermal recovery chamber and the main
combustion chamber is sufficiently mixed in the free board.
Therefore, combustion gas remains in the free board for a long
period of time, combustible materials are sufficiently combusted in
the free board. Furthermore, since secondary air is supplied to the
free board, combustion gas from the thermal recovery chamber and
the main combustion chamber is fully mixed and unburned combustible
materials entrained in combustion gas are sufficiently combusted in
the free board.
(2) A cylindrical combustor is accommodated in a pressure vessel
which can retain higher inner pressure than atmospheric pressure.
The pressure vessel may be of a cylindrical shape or a spherical
shape. Inside the fluidized bed of the cylindrical combustor, there
is provided a cylindrical partition, with a tapered upper section
constituting a conical partition, which separates the main
combustion chamber from the thermal energy recovery chamber. The
conical partition serves to interfere with the upward flow of the
fluidizing air and to thereby deflect the air towards the central
part of the main combustion chamber. In the thermal energy recovery
chamber, immersed heat transfer tubes are installed in a radial
pattern in the plan view. A bottom face of the main combustion
chamber is conical in shape and is provided with air diffusion
nozzles which fluidize the bed material in the main combustion
chamber. The volume of air to be injected from these air diffusion
nozzles is controlled in such a manner that the fluidizing gas
velocity within the range of a concentric circle which has about
half the diameter of the main combustion chamber slows to a
velocity of approximately 1 to 2.5 times the minimum fluidizing gas
velocity (Umf). The fluidizing gas velocity in the annular area
surrounding the concentric circle achieves a high velocity of
approximately 4 to 12 times the minimum fluidizing gas velocity
(Umf).
Because of this arrangements, the bed material (fluidized medium)
in the fluidized bed of the main combustion chamber starts to
descend in the central part of the main combustion chamber and then
slowly disperses in all directions along the conically shaped
bottom face to reach the surrounding annular area, where due to the
existing intense fluidization, the fluidized medium is forced to
blow upward and moves along the inner face of the cylindrical
partition. At this time, since the conical partition is formed at
the upper section of the cylindrical partition, the blowing force
is concentrated to finally achieve its maximum level when reaching
the surface of the fluidized bed where the fluidized medium
forcibly reverses its course by reactive force to thus disperse
horizontally in all directions as well as partly upward
direction.
As a result of this action, a large quantity of fluidized medium
(bed material) flows into the thermal energy recovery chamber
beyond the top of the partition, while the residual medium
remaining on the surface of the fluidized bed settles as a
cylindrical flow in the vicinity of the central part while
entraining the surrounding fluidized medium. When the fluidized
medium reaches the area near the central part of the conical bottom
face of the main combustion chamber, it develops a circulating flow
moving in a horizontal direction toward a circumferential area. The
circulating flow causes the fluidized medium to flow as a dispersed
flow from the central part along the conical bottom face gradually
in all directions, thereby uniformly dispersing fuel and
desulfurizing agent. Therefore, the combustion becomes uniform
without developing an agglomeration. The number of fuel feeding
ports may be minimized, resulting in a highly simplified fuel
supply system. Since the fluidized medium remaining on the surface
of the fluidized bed settles as a cylindrical flow in the vicinity
of the central part while entraining the surrounding fluidized
medium, the fuel and the desulfurizing agent remain in the
fluidized bed for a long period of time for increased combustion
efficiency and desulfurization efficiency.
A large amount of fluidized medium flows over the partition and
enters the thermal energy recovery chamber. A comb-toothed screen
is disposed in the free board above an upper portion of the main
combustion chamber and the thermal energy recovery chamber in
surrounding relation to the thermal energy recovery chamber. The
comb-toothed screen is effective to prevent a solid fuel such as
coal particles of large diameter from entering the thermal energy
recovery chamber. Accordingly, the development of an agglomeration
can be avoided in the fluidized bed in the thermal energy recovery
chamber though the fluidized bed is slowly flowing at a speed that
is less than twice the minimum fluidizing gas velocity. The screen
serves as a baffle against combustion gas generated in the thermal
energy recovery chamber, thus permitting the combustion gas to be
mixed and agitated sufficiently with combustion gas generated in
the main combustion chamber. In the pressurized fluidized-bed
boiler, when the combustion gas entrains a large amount of unburned
materials, the combustion efficiency is lowered, the unburned
materials are combusted in a downstream dust collector such as a
cyclone, developing a agglomeration, and, if the dust collector
comprises ceramic filters, the unburned materials are combusted on
the surface of the ceramic filters, damaging the ceramic filters.
These troubles are responsible for the failure of the pressurized
fluidized-bed boiler to operate. Therefore, it is desirable to
completely combust combustible materials in the combustor. The
mixing and agitating action achieved by the screen as it functions
as a baffle is highly effective, in combination with the manner in
which secondary air is charged, the height of the free board, and
the period of time for which the combustion gas remains in the free
board, to completely combust combustible materials in the free
board.
(3) Since no heat transfer surface is disposed in the main
combustion chamber of the internal circulating fluidized-bed boiler
according to the present invention, it is possible to combust the
fuel in a reducing atmosphere in the main combustion chamber.
Therefore, by setting a distribution ratio for combustion air, the
main combustion chamber is supplied with air at a rate equal to or
lower than a stoichiometric air flow rate required for combustion,
and the thermal energy recovery chamber is charged with air at a
flow rate required for thermal energy recovery control, and the
remaining air required for complete combustion is supplied as
secondary air through a plurality of secondary air nozzles mounted
in the free board to perform two-stage combustion. As a result, the
fuel is combusted in a reducing atmosphere in the main combustion
chamber to actively discharge volatile matter of coal. Hydrocarbons
such as CH.sub.4, CO or gaseous N chemical species including NHi,
HCN, etc. reduce nitrogen oxides generated by combustion in gas
phase reaction, and selectivity or probability for N chemical
species to convert into nitrogen oxides is lowered. Therefore, it
is possible to effect a lowNOx combustion in the main combustion
chamber.
(4) The air chamber and the air diffuser which are disposed in the
furnace bed beneath the connecting opening below the partition are
effective to fluidize the fluidized medium in the entire connecting
opening for thereby increasing the amount of fluidized medium that
is circulated through the thermal energy recovery chamber into the
main combustion chamber. The air chamber may communicate with an
air chamber for thermal energy recovery control, or may be
controlled independently of such an air chamber. If the air chamber
is controlled independently of the air chamber for thermal energy
recovery control, then it is possible to control the circulated
amount of fluidized medium independently of the amount of diffused
air in the thermal energy recovery chamber. In this case, the air
chamber functions as a regular valve. As a result, it is possible
for the cylindrical combustor to circulate a greater amount of
fluidized medium than that of a rectangular combustor, and the
thermal energy recovery chamber of the cylindrical combustor can be
larger in size than that of the rectangular combustor, allowing the
cylindrical combustor to manifest its advantages.
(5) The immersed heat transfer tubes in the fluidized bed in the
thermal energy recovery chamber are arranged radially and divided
by function into a block of evaporation tubes, a block of steam
superheating tubes, and a block of steam reheating tubes. The
amount of diffused air from the furnace bed in the thermal energy
recovery chamber can thus be adjusted in each of the blocks so that
the amount of recovered thermal energy can be controlled
independently in each block. Maintenance spaces are provided
between the blocks for inspecting the immersed heat transfer tubes.
Since the maintenance spaces may not necessarily be required, the
boiler may be made more compact if the maintenance spaces are
dispensed with.
(6) Where flying ashes collected by a particle separator disposed
in the downstream end of exhaust gas flow path are returned to the
thermal energy recovery chamber, the average diameter and specific
gravity of particles in the thermal energy recovery chamber are
reduced. While the average diameter of particles in the main
combustion chamber is about 0.6 mm, the diameter of particles
accompanying the combustion gas and collected by the particle
separator for recycling is much smaller, and their specific gravity
is also small as they contain char. In the thermal energy recovery
chamber, the fluidizing gas velocity is small, about twice the
minimum fluidizing gas velocity. Therefore, the recycled particles
are prevented from being entrained again, so that the average
diameter and specific gravity of particles in the thermal energy
recovery chamber are smaller than those in the main combustion
chamber.
The minimum fluidizing gas velocity (Umf) is proportional to the
square of the particle diameter of the fluidized medium and also to
the specific gravity thereof, so that the fluidizing gas velocity
in the thermal energy recovery chamber is considerably smaller than
that in the main combustion chamber. Consequently, the air flow
rate for thermal energy recovery control may be considerably lower
than if the flying ashes were not recycled into the thermal energy
recovery chamber. As a result, the fluidizing gas velocity (U0) in
the thermal energy recovery chamber is lowered. Inasmuch as the
erosion rate of the immersed heat transfer tubes disposed in the
thermal energy recovery chamber is proportional to the cube of the
fluidizing gas velocity (U0), the erosion rate of the immersed heat
transfer tubes is greatly reduced when the fluidizing gas velocity
(U0) is lowered. The reduction in the thermal-energy-recovery air
flow rate can minimize effects on the combustion when any change of
the air flow rate occurs, and is highly effective to achieve a
stable combustion.
(7) A dust collector is disposed in the passage of the exhaust gas
delivered from the cylindrical internal circulating fluidized-bed
boiler, and a classifying device is provided for collecting an
unreacted desulfurizing agent and unburned carbon from collected
flying ashes and classifying the flying ashes into three groups of
larger, medium, and smaller particle diameters, with only those
flying ashes of medium particle diameter also returned to the main
combustion chamber and/or the free board and/or the fuel supply
system. Since only particles having a diameter ranging from 10 to
60 .mu.m with a highest char concentration are returned to the
cylindrical combustor, it is possible to lower NOx, reduce erosion
of the exhaust gas flow path, and increase the combustion
efficiency with a minimum amount of circulating ashes.
(8) In the topping-cycle combined electric generating system, a
cylindrical internal circulating fluidized-bed boiler is used as a
gasifier and/or an oxidizer. Unburned char discharged from the
gasifier is entrained, in its entirety, by the generated gas and
cooled to 600.degree. C. or below, and then collected by a
downstream dust collector. Thereafter, the particles containing
unburned char are introduced into the oxidizer where they are
completely combusted. An exhaust gas produced in the oxidizer is
discharged therefrom, and cooled to 600.degree. C. or below.
Particles containing Na, K, etc. entrained in the exhaust gas are
collected by and discharged from a downstream dust collector. The
purified exhaust gas and the generated gas which has been
discharged from the gasifier and filtered to remove particles
containing Na, K, etc. therefrom are mixed and burned in a
topping-cycle combustor. A high-temperature exhaust gas produced by
the topping-cycle combustor is introduced into a gas turbine.
Inasmuch as the exhaust gas does not entrain particles containing
alkaline metal such as Na, K, etc., which would otherwise be
responsible to high-temperature corrosion of the turbine blades,
the gas turbine may be made of conventional materials and designed
in a conventional manner.
The above and other objects, features, and advantages of the
present invention will become apparent from the following
description when taken in conjunction with the accompanying
drawings which illustrate preferred embodiments of the present
invention by way of examples.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a pressurized internal
circulating fluidized-bed boiler according to a first embodiment of
the present invention;
FIG. 2A is a cross-sectional view taken along lines IIA--IIA of
FIG. 1;
FIG. 2B is a cross-sectional view corresponding to FIG. 2A, showing
a modified arrangement of heat transfer tubes;
FIG. 3 is a system diagram of a combined-cycle electric generating
system which incorporates a pressurized internal circulating
fluidized-bed boiler according to a first embodiment of the present
invention;
FIG. 4 is a graph showing the relationship between overall heat
transfer coefficient of immersed heating surface and fluidizing gas
velocity;
FIG. 5 is a cross-sectional view showing a detailed structure of
the cylindrical combustion of FIG. 1;
FIG. 6 is a system diagram of a combined-cycle electric generating
system which incorporates a pressurized internal circulating
fluidized-bed boiler according to a second embodiment of the
present invention;
FIG. 7 is a system diagram of a combined-cycle electric generating
system which incorporates a pressurized internal circulating
fluidized-bed boiler according to a third embodiment of the present
invention;
FIG. 8 is a modified system diagram of a combined-cycle electric
generating system which incorporates a pressurized internal
circulating fluidized-bed boiler according to a third embodiment of
the present invention;
FIG. 9 is a system diagram of a combined-cycle electric generating
system which incorporates a pressurized internal circulating
fluidized-bed boiler according to a fourth embodiment of the
present invention;
FIG. 10 is a system diagram of a topping-cycle combined electric
generating system which incorporates a pressurized internal
circulating fluidized-bed boiler as an oxidizer according to a
fifth embodiment of the present invention;
FIG. 11 is a system diagram of a topping-cycle combined electric
generating system which incorporates a pressurized internal
circulating fluidized-bed boiler as an oxidizer and an gasifier
according to a sixth embodiment of the present invention;
FIG. 12 is a cross-sectional view showing an integral furnace
including an oxidizer and a gasifier for use in a topping-cycle
combined electric generating system according to a seventh
embodiment of the present invention;
FIG. 13 is a system diagram of a topping-cycle combined electric
generating system which incorporates the integral furnace including
the oxidizer and the gasifier shown in FIG. 12 according to an
eighth embodiment of the present invention;
FIG. 14 is a plan view showing a conventional pressurized bubbling
type fluidized-bed boiler; and
FIG. 15 is a plan view showing another conventional pressurized
bubbling type fluidized-bed boiler.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A pressurized internal circulating fluidized-bed boiler according
to the present invention will be described below with reference to
FIGS. 1 through 13.
(First embodiment)
As shown in FIG. 1, the combined-cycle electric generating system
includes a pressure vessel 1 which is of a cylindrical
receptacle-like structure. The pressure vessel 1 is provided with a
combustion gas outlet 4 at the top, a fluidizing air inlet 3 and
thermal energy recovery chamber control air inlets 5 at the bottom.
The pressure vessel 1 is constructed in such a way that it can
retain higher inner pressure than atmospheric pressure. The
pressure vessel 1 may be of a spherical body.
Inside the pressure vessel 1, there is provided a cylindrical
combustor 2 which is an air tight vessel having a cylindrical
membrane wall 11 consisting of water tubes. A main fluidized bed
combustion chamber 9 is formed inside the cylindrical combustor 2.
On the top of the cylindrical combustor 2, there is provided a
combustion gas outlet 2a which is connected to the combustion gas
outlet 4 of the pressure vessel 1. The cylindrical combustor 2 is
firmly held to the bottom by a cylindrical support 7 installed on
the end plate of the pressure vessel 1. Inside the fluidized-bed of
the cylindrical combustor 2, there is provided a partition 8 which
separates a thermal energy recovery chamber 10 from the main
combustion chamber 9. The partition 8 is composed of water tubes
extending radially inwardly from the cylindrical membrane wall 11
and refractories lined on the membrane wall. The partition 8
comprise a cylindrical partition 8a and a conical partition 8b,
having a radially inwardly inclined inner surface, formed at the
upper portion of the cylindrical partition 8a. The conical
partition 8b serves as a reflective wall for reflecting the
fluidizing air injected from air nozzles towards the center of the
main combustion chamber 9 so that swirling flows of the fluidized
medium are developed in the main combustion chamber 9 as indicated
by the arrows in FIG. 1. A free board 31 is defined above the main
combustion chamber 9 and the thermal recovery chamber 10. There is
no wall such as a partition wall between a free board above the
thermal energy recovery chamber 10 and a free board above the main
combustion chamber 9 to thus define a vast integral free board,
thereby allowing combustion gas from both chambers to
intercommunicate freely.
In the thermal energy recovery chamber 10, immersed heat transfer
tubes 15 are installed in a radial pattern in the plan view as
shown in FIG. 2A. These tubes 15 are branched from upper and lower
headers 13, 14 located on the cylindrical membrane wall 11 of the
cylindrical combustor 2. A feed water inlet 16 is provided at the
lower portion of the pressure vessel 1. Boiler water introduced
from the feed water inlet 16 flows through the cylindrical membrane
wall 11 and a connecting pipe 16a and is introduced into the lower
header 14, and then distributed to the heat transfer tubes 15.
Thermal energy generated in the main combustion chamber 9 is
recovered by the heat transfer tubes 15 in the thermal recovery
chamber 10 to thus generate steam. Steam generated in the heat
transferred tubes 15 is collected in the upper header 13 and
discharged from a steam outlet 17 to the outside.
An equalizing nozzle 18 is provided on the pressure vessel 1. The
equalizing nozzle 18 is connected to a fluidizing air supply system
19 through an equalizing air supply pipe 19a. The fluidizing air
supply system 19 is connected to the fluidizing air inlet 3. The
fluidizing air supply system 19 provides the same pressure both to
the pressure vessel 1 and the cylindrical combustor 2, thereby
balancing the inner and the outer pressure of the cylindrical
combustor 2 except for a small pressure difference due to pressure
loss of the fluidized bed. With this construction, the cylindrical
combustor 2 does not require a pressure-tight construction. In this
case, in the free board 31 of the cylindrical combustor 2, the
combustor 2 is subject to an exterior pressure. When balancing
pressure of a space 36 between the pressure vessel 1 and the
cylindrical combustor 2 and pressure of the free board 31 by
providing a pressure reducing valve at the upstream of the
equalizing nozzle 18, the lower portion of the fluidized bed is
subject to the internal pressure due to pressure loss of the
fluidized bed. A fuel supplying inlet 6 is provided on the pressure
vessel 1. The fuel supplying inlet 6 is connected to a fuel feeding
port 22. A bottom face 20 of the main combustion chamber 9 is
conical in shape and is provided with air diffusion nozzles 21
which fluidize the fluidized medium in the main combustion chamber
9. The fuel feeding port 22 has an opening end in the vicinity of
the bottom face 20 of the main combustion chamber 9. The volume of
air to be blown out from the air diffusion nozzles 21 is controlled
in such a manner that the fluidizing gas velocity within the range
of a concentric circle which has about half the diameter of the
main combustion chamber 9 slows to a velocity of approximately 1 to
2.5 times the minimum fluidizing gas velocity (Umf). The fluidizing
gas velocity in the annular area surrounding the concentric circle
achieves a high velocity of approximately 4 to 12 times the minimum
fluidizing gas velocity (Umf).
Because of the above arrangement, the fluidized medium to the
fluidized bed of the main combustor chamber 9 starts to descend in
the central part of the main combustion chamber 9 and then slowly
disperses in all directions along the conically shaped bottom face
to reach the surrounding annular area, where due to the existing
intense fluidization, the fluidized medium are forced to blow
upward and moves along the inner face of the partition 8. At this
time, since the conical partition 8b is formed at the upper section
of the cylindrical partition 8a, the blowing force is concentrated
to finally achieve its maximum level when reaching the surface of
the fluidized bed where the fluidized medium forcibly reverses its
course by reactive force to thus disperse horizontally in all
direction as well as partly upward direction.
As a result of this action, a large quantity of fluidized medium
flows into the thermal energy recovery chamber 10 beyond the
partition 8. The fluidized bed in the thermal energy recover
chamber 10 has a velocity of not more than 2 times the minimum
fluidizing gas velocity (Umf). Since the fluidized bed is in a slow
fluidizing state, agglomeration tends to be generated. Therefore, a
solid fuel such as coal particles of large diameter is required not
to enter the thermal energy recovery chamber 10. A comb-toothed
screen 12 is disposed in the free board 31 above an upper portion
of the main combustion chamber 9 and the thermal energy recovery
chamber 10 in surrounding relation to the thermal energy recovery
chamber 10. The comb-toothed screen 12 is effective to prevent a
solid fuel of large diameter from entering the thermal energy
recovery chamber 10. Accordingly, the development of an
agglomeration can be avoided in the fluidized bed in the thermal
energy recovery chamber 10 though the fluidized bed is slowly
flowing at a speed that is less than twice the minimum fluidizing
velocity. The screen 12 serves as a baffle against combustion gas
generated in the thermal energy recovery chamber 10, thus
permitting the combustion gas to be mixed and agitated sufficiently
with combustion gas generated in the main combustion chamber 9. In
the pressurized fluidized-bed boiler, when the combustion gas
entrains a large amount of unburned materials, the combustion
efficiency is lowered, the unburned materials are combusted in a
downstream dust collector such as a cyclone, developing an
agglomeration, and, if the dust collector comprises ceramic
filters, the unburned materials are combusted on the surface of the
ceramic filters, damaging the ceramic filters. These troubles are
responsible for the failure of the pressurized fluidized-bed boiler
to operate. Therefore, it is desirable to completely combust
combustible materials in the combustor. The mixing and agitating
action achieved by the screen 12 as it functions as a baffle is
highly effective, in combination with the manner in which secondary
air is charged, the height of the free board 31, and the period of
time for which the combustion gas remains in the free board 31, to
completely combust combustible materials in the free board 31.
On the other hand, the fluidized medium of the main combustion
chamber 9 starts to descend in the central part in a state of
cylindrical flow. As soon as the descending medium reaches the
central part of the conical bottom face 20 of the main combustion
chamber 9, the medium start to disperse in all directions again. In
this way, the internal circulation is produced as shown in FIG. 1.
By this internal circulation, a fuel such as coal water paste
supplied from the fuel feeding port 22 disperses in all directions
uniformly in the main combustion chamber 9. Therefore, even if the
fuel supplying system has a simple structure, an uneven
distribution of fuel is avoidable to thus prevent
agglomeration.
A bottom face 23 of the thermal energy recovery chamber 10 is
conical in shape and is provided with air diffusion nozzles 24
which fluidize the fluidized medium in the thermal energy recovery
chamber 10. By injecting air from the air diffusion nozzles 24
which are connected to the thermal energy recovery chamber control
air inlets 5, the fluidized medium entering the thermal energy
recovery chamber 10 beyond the partition 8 starts to descend slowly
through the fluidized bed of the thermal energy recovery chamber 10
where it undergoes the heat exchange process through the heat
transfer tubes 15. The medium then passes through a connection
opening 27 provided below the cylindrical partition 8a to return to
the main combustion chamber 9. In this way, thermal energy produced
in the main combustion chamber 9 is efficiently recovered through
the heat transfer tubes 15 provided in the thermal energy recovery
chamber 10.
In addition, supplemental air diffusion nozzles 26 and an air
supplying pipe 25 connected to the nozzles 26 may be installed on
the outer surface of the conical partition 8b. The supplemental air
diffusion nozzles 26 injects air to fluidize the medium and combust
combustible materials partly that has entered the thermal energy
recovery chamber 10. However, in case of the conical partition 8b
with a large inclined angle, such supplemental air diffusion
nozzles 26 are not necessarily provided.
A fluidizing air chamber 28 is defined below the bottom face 20 of
the main combustion chamber 9. The fluidizing air chamber 28 is
enclosed by the membrane wall 29 which supports the partition 8 and
connected to the fluidizing air inlet 3. Thermal energy recovery
control air chamber 30 is defined below the bottom face 23 of the
thermal energy recovery chamber 10. The thermal energy recovery
control air chamber 30 is connected to an air supplying system
through the thermal energy recovery control air inlets 5.
The free board 31 having a wide space is defined above the main
combustion chamber 9 and the thermal energy recovery chamber 10.
That is, there is no throat between the main combustion chamber 9
and the thermal energy recovery chamber 10, and the free board 31.
Therefore, combustion gas from the main combustion chamber 9 and
the thermal energy recovery chamber 10 is sufficiently mixed with
each other in the free board 31 and remain in the free board 31 for
a long period of time, thus combustible materials entrained in the
gas can be sufficiently combusted in the free board 31.
Further, a plurality of secondary air nozzles 33 connected to a
secondary air inlet 34 are provided in the free board 31 to enable
two-stage combination. Since no heat transfer surface is disposed
in the main combustion chamber 9, it is possible to combust the
fuel in a reducing atmosphere in the main combustion chamber 9.
Therefore, by setting a distribution ratio for combustion air, the
main combustion chamber 9 is supplied with air at a rate equal to
or lower than a stoichiometric air flow rate required for
combustion, and the thermal energy recovery chamber 10 is charged
with air at a flow rate required for thermal energy recovery
control, and the remaining air required for complete combustion is
supplied as secondary air through a plurality of secondary air
nozzles 33 mounted in the free board 31 to perform two-stage
combustion. As a result, the fuel is combusted in a reducing
atmosphere in the main combustion chamber 9 to actively discharge
volatile matter of coal. Hydrocarbons such as CH.sub.4, CO or
gaseous N chemical species including NHi, HCN, etc. reduce nitrogen
oxides generated by combustion in gas phase reaction, and
selectivity or probability for N chemical species to convert into
nitrogen oxides is lowered. Therefore, it is possible to effect a
low-NOx combustion in the main combustion chamber 9.
A baffle 32 is provided in the free board 31 to prevent combustion
gas from causing short-pass toward the combustion gas outlet 4 and
to enable combustion gas to be mixed sufficiently in the free board
31. However, in the case where combustion gas is sufficiently mixed
by the secondary air, or superficial gas velocity is low and the
free board has a sufficient height, the baffle 32 is not
necessarily provided, because there is a low possibility of the
short-pass.
FIG. 2B shows a modified arrangement of heat transfer tubes shown
in FIG. 2A. The immersed heat transfer tubes in the fluidized bed
in the thermal energy recovery chamber are arranged radially and
divided by function into a block 40 of evaporation tubes, a No.1
block 41 of steam superheating tubes, a No.2 block 42 of steam
superheating tubes, a No.3 block 43 of steam superheating tubes,
and a block 44 of steam reheating tubes. In case of an once-through
boiler, steam flows through the block 40 of evaporation tubes, the
No.1 block 41 of steam superheating tubes, the No.2 block 42 of
steam superheating tubes, and the No.3 block 43 of steam
superheating tubes in sequence. The generated superheated steam is
introduced into a high-pressure steam turbine, and then returned to
the block 44 of steam reheating tubes again. The steam heated by
the block 44 of steam reheating tubes is introduced into an
intermediate-pressure steam turbine.
With this arrangement of the heat transfer tubes, the amount of air
from the air distribution nozzles 24 in the thermal energy recovery
chamber 10 can thus be adjusted in each of the blocks so that the
amount of recovered thermal energy can be controlled independently
in each block. Maintenance spaces 45 are provided between the
blocks for inspecting the immersed heat transfer tubes. The boiler
may be made more compact if the maintenance spaces are dispensed
with.
FIG. 3 is illustrative of an arrangement for controlling an air
supplying system depending on a change in the load. When the load
changes, the steam flow rate in a steam outlet 17, i.e., a steam
line connected to a turbine inlet, varies, thus varying a steam
flow rate signal generated by a steam flow meter F31. A computing
unit Y0 calculates an output signal based on the steam flow rate
signal from the steam flow meter F31 and a pressure signal from a
steam pressure controller P31, and sends the calculated output
signal to a fuel supplying system for supplying a fuel at a rate
corresponding to the load. The output signal from the computing
unit Y0 is also sent to a computing unit Y0 ' of the air supplying
system.
The computing unit Y0' receives, in addition to the output signal
from the computing unit Y0, output signal from an oxygen content
controller A25 and a thermal-recovery-control air flow controller
F21 of an exhaust gas flow path 50. Based on the received signals,
the computing unit Y0 ' calculates an output signal indicative of a
remaining air flow rate, which is equal to the difference between a
total air flow rate for complete combustion and a
thermal-energy-recovery air flow rate, for thereby regulating the
combustion air flow rate to make constant the oxygen content in the
flue gas. Based on the output signal from the computing unit Y0 ',
computing units Y1, Y2 effect predetermined calculations to produce
respective output signals that are sent to a fluidizing air flow
controller F22 and a secondary air flow controller F24 for
supplying fluidizing air and secondary air at a constant ratio to
the combustor 2.
With the fluidizing air and secondary air being supplied at a
constant ratio, it is possible to effect a two-stage combustion
mode in which the main combustion chamber 9 is supplied with air at
a rate equal to or lower than a stoichiometric air flow rate
required for combustion, and the thermal energy recovery chamber 10
is charged with air at a flow rate required for thermal energy
recovery control, and the remaining air required for complete
combustion is supplied as secondary air to the free board 31.
Since the combustion is effected in a reducing atmosphere in the
main combustion chamber 9, volatile matter of the coal are actively
discharged by the reducing combustion, and hydrocarbons such as
CH.sub.4, CO or gaseous N chemical species including NHi, HCN, etc.
reduce generated nitrogen oxides in gas phase reaction, and
selectively or probability for N chemical species to convert them
into nitrogen oxides is lowered. Therefore, it is possible to
effect a low-NOx combustion in the main combustion chamber 9.
The output signal from the steam pressure controller P31 serves to
control a fluidized bed temperature controller T58 through a
computing unit Y31. More specifically, when the steam pressure is
lowered slightly, an output signal from the computing unit Y31
slightly reduces the bed temperature setting value of the fluidized
bed temperature controller T58. A control signal from the fluidized
bed temperature controller T58 is varied and applied through a
computing unit Y21 to the thermal-recovery-control air flow
controller F21, which then increases the thermal-energy-recovery
air flow rate.
As shown in FIG. 4, the overall heat transfer coefficient of the
immersed heat transfer tubes in the thermal energy recovery chamber
10 is substantially proportional to the fluidizing gas velocity in
the fluidized bed in the thermal energy recovery chamber 10.
Therefore, as the thermal-energy-recovery air flow rate, i.e., the
fluidizing gas velocity, increases, the amount of collected heat
increases to thus recover the steam pressure. When the steam
pressure increases beyond a preset value, the system operates in an
opposite manner to reduce the thermal-energy-recovery air flow rate
for thereby lowering the steam pressure.
In this manner, the fuel feeding rate is regulated in a main
control mode, and the rate of thermal-energy-recovery air flow is
regulated in an auxiliary control mode, so that any adverse effects
caused by load changes are minimized for quick and stable
combustion control.
The gas outlet of the gas turbine 28 and the air inlet of the
compressor 39 may be connected to each other through a valve 49
which is operable to regulate the rate of an exhaust gas mixed into
air to be supplied to the compressor 39 for reducing NOx and
stabilizing fluidization due to an increase in the fluidizing gas
velocity at low loads.
FIG. 5 shows a detailed structure of the cylindrical combustor 2
shown in FIG. 1. Where the combustor 2 is of a cylindrical shape as
shown in FIG. 1, the thermal energy recovery chamber 10 extends as
an annular chamber outside of the partition 8 and thus can have a
larger size than a rectangular combustor, so that it can
accommodate more heat transfer tubes therein. To allow the thermal
energy recovery chamber 10 to manifest its advantages, it is
necessary to circulate a greater amount of fluidized medium than
the rectangular combustor.
Heretofore, since there is no air diffusion nozzles in the
connecting opening 27 below the partition 8, the bed is fluidized
in an auxiliary manner by fluidizing air from the air diffusion
nozzles 24 in the thermal energy recovery chamber 10 and the air
diffusion nozzles 21 in the main combustion chamber 9. Therefore,
there has been heretofore been a region 27a where the fluidization
is not active. According to the present invention, such a problem
can be solved by an air chamber 30' and an air diffuser nozzles 24'
which are disposed in the furnace bed beneath the connecting
opening 27 below the partition 8. The air chamber 30' and the air
diffusion nozzles 24' are effective to fluidize the bed in the
entire connecting opening 27 for thereby increasing the amount of
fluidized medium that is circulated through the thermal energy
recovery chamber 10 into the main combustion chamber 9.
The air chamber 30.varies. may communicate with an air chamber 30
for thermal energy recovery control, or may be controlled
independently of the air chamber 30. If the air chamber 30' is
controlled independently of the air chamber 30, then it is possible
to control the circulated amount of fluidized medium independently
of the amount of diffused air in the thermal energy recovery
chamber 10. In this case, the air chamber 30' functions as a
regulator valve.
(Second embodiment)
FIG. 6 shows a system diagram of a combined-cycle electric
generating system which incorporates a pressurized internal
circulating fluidized-bed boiler according to a second embodiment
of the present invention.
As shown in FIG. 6, an exhaust gas discharged from a pressure
vessel 1 is introduced through an exhaust gas flow path 50 into a
cyclone 51. Flying ashes collected by the cyclone 51 fall by
gravity and are stored in a seal mechanism 52, from which they are
carried by ash recycling 53 and returned to a thermal energy
recovery chamber 10 through a recycled ash inlet pipe 54 that
extends through side walls of a pressure vessel 1 and a cylindrical
combustor 2.
Since flying ashes are recycled into the thermal energy recovery
chamber 10, the average diameter and specific gravity of particles
in the thermal energy recovery chamber 10 are reduced. While the
average diameter of particles in the main combustion chamber 9 is
about 0.6 mm, the diameter of particles which are entrained by the
exhaust gas, trapped by the cyclone, and recycled into the thermal
energy recovery chamber 10 is much smaller. The specific gravity of
those particles is small as they contain char.
Because the fluidizing gas velocity in the thermal energy recovery
chamber 10 is low, about twice the minimum fluidizing gas velocity,
the recycled particles are not entrained again, and hence the
average diameter of particles in the thermal energy recovery
chamber 10 are smaller than those in the main combustion chamber
9.
The minimum fluidizing gas velocity (Umf) is proportional to the
square of the particle diameter of the fluidized medium and also
the specific gravity thereof, so that the minimum fluidizing gas
velocity in the thermal energy recovery chamber 10 is considerably
smaller than that in the main combustion chamber 9. Consequently,
the air flow rate for thermal energy recovery control may be
considerably lower than if the flying ashes were not recycled into
the thermal energy recovery chamber 10. As a result, the fluidizing
gas velocity (U0) in the thermal energy recovery chamber 10 is
lowered.
Inasmuch as the erosion rate of the immersed heat transfer tubes
disposed in the thermal energy recovery chamber 10 is proportional
to the cube of the fluidizing gas velocity (U0), the erosion rate
of the immersed heat transfer tubes is greatly reduced when the
fluidized gas velocity (U0) is lowered.
As shown in FIG. 3, the air flow rate for thermal energy recovery
control, i.e., the thermal-energy-recovery air flow rate,
fluctuates at all times as it controls the temperature of the
fluidized bed in the main combustion chamber 9. The reduction in
the thermal-energy-recovery air flow rate can minimize effects on
the combustion energy when any change of the air flow rate occurs,
and is highly effective to achieve a stable combustion.
As shown in FIG. 6, the exhaust gas is introduced through the
cyclone 51 into a dust collector 55 which may comprise ceramic
filters or high-temperature bag filters. Flying ashes collected by
the dust collector 55 are cooled by an ash cooler 56 and discharged
through a lock hopper 57 into the atmosphere. The high-temperature
exhaust gas which has been filtered and made clean is introduced
from the dust collector 55 into a gas turbine 58.
Coal stored as a fuel in a coal bunker 59 is crushed by a crusher
60 and sent to an agitating tank 61 in which it is mixed with a
desulfurizer charged from a desulfurizer bunker 62 and water from a
water tank 64, and the mixture is agitated into a slurry fuel. The
slurry fuel is then delivered by a slurry pump 65 to the
cylindrical combustor 2 where it is supplied from a fuel feeding
port 22 into the fluidized bed in the main combustion chamber
9.
Further, it is possible to return flying ashes to the free board 31
by a recycled ash inlet pipe 54a. By this recycling, concentration
of particles increases, agitation effect of the combustion gas is
improved and the contacting chances of unburned char and unreacted
desulfurizing agent increases, resulting in improving the
combustion efficiency and performance of desulfurization and NOx
reduction.
By making the recycled ash inlet pipe 54a to extend in the vicinity
of the central part of the main combustion chamber 9, flying ashes
can be supplied to a surface of moving bed or the inside of the
moving bed. By allowing the fluidized medium to accompany flying
ashes, it is possible for ashes to remain in the fluidized bed for
a long period of time, thereby improving combustion of unburned
materials and performance of desulfurization and NOx reduction.
The pressurized internal circulating fluidized-bed boilers shown in
FIGS. 6 through 8 are of the forced circulation type whereas the
pressurized internal circulating fluidized-bed boiler shown in FIG.
1 is of the once-through type. In the forced-circulation boilers,
there is a steam drum 71 supplied with water from a boiler water
supply system 70, and water from the steam drum 71 is circulated
through a forced-circulation pipe 73 into water walls and
evaporation tubes in the thermal energy recovery chamber 10 by a
forced-circulation pump 72.
Steam 74 generated in the steam drum 71 is delivered through a
connecting pipe (not shown) to superheating tubes in the thermal
energy recovery chamber 10 where superheated steam 74' is
generated. The generated superheated steam 74' is then supplied to
a high-pressure steam turbine.
(Third embodiment)
FIG. 7 illustrates a pressurized internal circulating fluidized-bed
boiler according to a third embodiment of the present invention,
the boiler including a system for processing an exhaust gas.
As shown in FIG. 7, flying ashes collected by a cyclone 51 in an
exhaust gas flow path 50 are cooled by an ash cooler 77. A coolant
used in the ash cooler 77 may be water supplied to the boiler or
fluidizing air for effective recovery of the thermal energy from
the ashes.
The cooled ashes are introduced through a lock hopper 78 into a
classifying tank 79 in which they are mixed with flying ashes
supplied from a dust collector 55 through an ash cooler 56 and a
lock hopper 57, and the mixture is classified. In the illustrated
embodiment, classifying air 80 is charged into the classifying tank
79 through an air diffuser pipe 81 for fluidized bed
classification. However, this embodiment may not necessarily be
limited to such type of classification.
Particles of unreacted desulfurizer and unburned carbon which have
been selectively separated in the classifying tank 79 and have a
diameter of 60 .mu.m or smaller are carried to a cyclone 83 by air.
The particles are further classified by the cyclone 83. Classified
particles separated by the cyclone 83 which have a diameter of
about 10 .mu.m or smaller are introduced into a dust collector 84,
separated from the air by the dust collector 84, and then
discharged out of the dust collector 84. Flying ashes discharged
from the cyclone 83 which have a diameter ranging from 10 to 60
.mu.m are charged through a seal valve 85, a lock hopper 86, and a
rotary valve 87 into a cylindrical combustor 2 by recycled ash
delivery air 88. In the case where flying ashes is returned to the
thermal energy recovery chamber 10 by the recycled ash inlet pipe
54, the same advantages stated in the embodiment in FIG. 6 can be
obtained. By recycling of flying ashes to the free board 31 through
recycled ash inlet pipe 54a, concentration of particles increases,
agitation effect of the combustion gas is improved and the
contacting chances of unburned char and unreacted desulfurizing
agent increase, resulting in improving the combustion efficiency
and performance of desulfurization and NOx reduction.
By making the recycled ash inlet pipe 54a to extend in the vicinity
of the central part of the main combustion chamber 9, flying ashes
can be supplied to a surface of moving bed or the inside of the
moving bed. By allowing the fluidized medium to accompany flying
ashes, it is possible for ashes to remain in the fluidized bed for
a long period of time, thereby improving combustion of unburned
materials and performance of desulfurization and NOx reduction.
In this manner, particles are classified into three groups by
diameter. Since only those particles of highest char concentration
which have a diameter ranging from 10 to 60 .mu.m are returned to
the cylindrical combustor 2, it is possible to reduce NOx and SOx
emissions, lower erosion rate of the exhaust gas flow path, and
increase the combustion efficiency with a minimum amount of
circulating ashes.
While dust particles are collected in two steps by the cyclone 51
and the dust collector 55, the cyclone 51, the ash cooler 77, and
the lock hopper 78 may be dispersed with, and only the dust
collector 55 may be used to collect dust particles. In such a
modification, the dust particles may be classified under pressure
without being passed through the ash cooler 56 and the lock hopper
57. The dust collector 55 usually comprises ceramic filters.
FIG. 8 shows an other arrangement for processing classified flying
ashes.
As shown in FIG. 8, particles of unreacted desulfurizer and
unburned carbon which have been selectively separated in a
classifying tank 79 and have a diameter of 60 .mu.m or smaller are
carried to a cyclone 83 by air. The particles are further
classified by the cyclone 83. Classified particles separated by the
cyclone 83 which have a diameter of about 10 .mu.m or smaller are
introduced into a dust collector 84, separated from the air by the
dust collector 84, and then discharged out of the dust collector
84.
Flying ashes discharged from the cyclone 83 which have a diameter
ranging from 10 to 60 .mu.m are supplied through a seal valve 85, a
lock hopper 86, and a rotary valve 87 into a hopper 89. Thereafter,
the ashes discharged from the hopper 89 are mixed with coal and a
desulfurizer into a fuel in the form of particles by a mixer 90.
The fuel thus produced is then supplied to a cylindrical combustor
2 by fuel delivery air from an air tank 92.
Flying ashes discharged from the rotary valve 87 which have a
diameter ranging from 10 to 60 .mu.m may be supplied into the free
board 31 by pneumatic transportation utilizing the secondary air
34.
(Fourth embodiment)
FIG. 9 shows an overall system of pressurized fluidized-bed boiler
according to a fourth embodiment of the present invention.
As shown in FIG. 9, the pressurized fluidized-bed boiler is
constructed as a once-through pressurized fluidized-bed boiler.
During operation of the pressurized fluidized-bed boiler, a slurry
fuel is fed by a slurry pump 65 to a combustor 2 where it is
supplied to and combusted in a fluidized bed in a main combustion
chamber 9. An exhaust gas produced when the fuel is combusted flows
through an exhaust gas flow path 50, and is then filtered by a dust
collector 55 which removes dust particles from the exhaust gas.
Then, the exhaust gas drives a high-pressure gas turbine 100 and a
low-pressure gas turbine 101, after which it heats water to be
supplied to the boiler in an exhaust gas cooler 102. Thereafter,
the exhaust gas is discharged into the atmosphere from a stack
103.
Fluidized bed combustion air is pressurized by low- and
high-pressure compressors 104, 106 which are driven by the
respective gas turbines 101, 100. Part of the air is branched as
air for thermal energy recovery control and introduced into an air
chamber 30 for thermal energy recovery control. The remaining air
is introduced into an air chamber 28, combusting the fuel while
causing a fluidized medium to swirl in the main combustion chamber
9.
In a steam generation system, water is supplied by a boiler water
feed pump 107 to the exhaust gas cooler 102, and then heated there.
The heated water is sent to the boiler in which it flows through
water tubes that constitute a cylindrical wall, after which the
water passes through evaporation tubes 108 and steam superheating
tubes 109 during which time it becomes a superheated steam.
The produced superheated steam drives a high-pressure steam turbine
110, and then flows back to the combustor 2 where it is reheated by
immersed heat transfer tubes 111. Thereafter, the steam drives a
medium-pressure turbine 112 and a low-pressure turbine 113 to cause
an electric generator 114 to generate electric energy. Then, the
steam is condensed by a condenser 115 into water which is supplied
again to the boiler.
(Fifth embodiment)
FIG. 10 shows an internal circulating fluidized-bed boiler
according to a fifth embodiment of the present invention, the
boiler being incorporated as an oxidizer in a topping-cycle
combined electric generating system.
Although not shown, a pressurized cylindrical fluidized-bed boiler
according to the present invention may also be employed as a
gasifier in the topping-cycle combined electric generating system
shown in FIG. 10. Application to the gasifier will be described
below. As described in detail above with reference to FIGS. 1 and
3, no heat transfer surface is disposed in the main combustion
chamber 9 of the pressurized internal circulating fluidized-bed
boiler according to the present invention. Therefore, the two-stage
combustion is carried out for the purpose of reducing NOx, with the
result that the fuel is combusted in the main combustion chamber 9
in a reducing atmosphere with an air ratio of about 0.8. Since
different fluidized gas velocities are developed in the main
combustion chamber 9, the substantial air ratio in the moving bed
in the main combustion chamber 9 is about 0.5, a value close to
that in the gasifier. Therefore, it is quite easy to convert the
boiler into a topping-cycle gasifier. If no thermal energy recovery
in the bed is required in view of a desired thermal balance, the
supply of air for thermal energy recovery control may be stopped,
or the immersed heat transfer tubes may be removed.
The internal circulating fluidized-bed boiler shown in FIG. 10 will
be described below.
Coal from a coal bunker 121 and a desulfurizing agent from a
desulfurizer bunk 122 are supplied to a gasifier 120, in which they
are decomposed into a coal gas, char, and CaS by air 124.
The char and CaS are discharged from the gasifier 120, and a dust
collector 123 connected to a coal gas passage, and introduced
through a passage 125 into an oxidizer 126 in the form of the
internal circulating fluidized-bed boiler where it is supplied in
the vicinity of the furnace bed of a cylindrical combustor 2. The
char and CaS may be supplied onto a fluidized bed, rather than in
the vicinity of the furnace bed.
The oxidizer 126 may be supplied with coal from the coal bunker 121
and the desulfurizing agent from the desulfurizer bunk 122, which
are charged through a fuel feeding port 22 into the main combustion
chamber 9 where they are combusted with the char.
An exhaust gas produced in the oxidizer 126 is filtered by a dust
collector 127, and thereafter introduced into a combustor 129
connected to the inlet of a gas turbine 128. In the combustor 129,
the exhaust gas is mixed with the coal gas that has been discharged
from the gasifier 120 and filtered by dust collectors 123, 130. The
mixture is combusted, producing a high-temperature gas that drives
the gas turbine 128 highly efficiently.
The gas turbine 128 in turn drives a compressor 131 and an electric
generator 132. The exhaust gas discharged from the gas turbine 128
is cooled by a heat recovery unit 133, and then discharged into the
atmosphere.
A superheated steam 74' generated in the boiler drives a steam
turbine 134 and an electric generator 135 coupled thereto, after
which it is condensed into water by a condenser 136. The water is
then supplied again to the boiler by a boiler water feed pump 137.
Operation of the pressurized cylindrical fluidized-bed boiler in
the oxidizer 126 is the same as that of the boilers according to
the first through fourth embodiments of the present invention.
(Sixth embodiment)
FIG. 11 shows a pressurized cylindrical fluidized-bed boiler
according to a sixth embodiment of the present invention, which is
incorporated as a gasifier 120 and an oxidizer 126 in a
topping-cycle combined electric generating system.
In FIG. 11, the gasifier 120 is supplied with coal from a coal
burner 121 and a desulfurizer from a desulfurizer bunk 122. Air is
also supplied to the gasifier 120 to partially combust the coal
into a gas. Oxygen from an oxygen tank 150 or steam from a steam
tank 151 may be charged as an oxidizing agent instead of air.
Unburned char, etc. generated in the gasifier 120 is entrained, in
its entirety, by the generated gas and cooled to 600.degree. C. or
below by a gas cooling unit 140 that is connected downstream of the
gasifier 120 for solidifying alkaline metal particles of Na, K,
etc., which would be responsible to high-temperature corrosion of
turbine blades, or fixing those alkaline metals to the surface of
particles. Those particles are then collected by a dust collector
141 and introduced into the oxidizer 126 where they are completely
combusted. An exhaust gas produced in the oxidizer 126 is
discharged therefrom, and cooled to 600.degree. C. or below by a
gas cooling unit 142 that is connected downstream of the oxidizer
126. Alkaline metal particles of Na, K, etc. which are solidified
when the exhaust gas is cooled by the gas cooling unit 142 are
collected by and discharged from a particle dust collector 143. The
dust collectors 141, 143 normally comprise ceramic filters.
The exhaust gas that has been purified by the removal of Na, K,
etc. and the generated gas that has been filtered and cleaned after
being discharged from the gasifier 120 are mixed and combusted by a
combustor 129. Since these gases have been cooled, the combustion
temperature at which they are combusted by the combustor 129 is
slightly lowered. To prevent the combustion temperature from being
unduly reduced, the oxidizer 126 is operated at as low excess air
as possible to reduce the amount of an exhaust gas produced
therein. Oxygen that is required by the combustor 129 is supplied
from an oxygen tank 150 to the combustor 129.
A high-temperature exhaust gas produced by the combustor 129 drives
a gas turbine 128 highly efficiently. The gas turbine 128 then
drives a compressor 131 and an electric generator 132. The exhaust
gas discharged from the gas turbine 128 is cooled by a thermal
energy recovery unit 133, and then discharged into the atmosphere.
If the turbine blades of the gas turbine 128 are of improved
corrosion-resistant materials, then the gas cooling units 140, 142
may be dispensed with.
(Seventh embodiment)
FIG. 12 shows an integral furnace 201 which incorporates a gasifier
and an oxidizer integrally and is used as a pressurized internal
circulating fluidized-bed boiler for use in a topping-cycle
combined electric generating system.
As shown in FIG. 12, a cylindrical fluidized-bed boiler 201 for use
in a topping-cycle combined electric generating system has a
cylindrical outer wall 202 and a partition 203 provided
concentrically with the cylindrical outer wall 202. The partition
203 comprises a cylindrical partition 203a, a conical partition
203b, a conical partition 203b' and a cylindrical partition 203a'.
A connection opening 204 is formed between the conical partition
203b and the conical partition 203b', and a connection opening 205
is formed underneath the cylindrical partition 203a. The upper end
of the cylindrical partition 203a' is connected to the top of the
cylindrical outer wall 202 and defines a gas outlet 206
therein.
The partition 203 separates an inner space serving as a gasifier
207 from an annular outer space serving as an oxidizer 208. A
bottom face 209 of the gasifier 207 is conical in shape and a
bottom face 212 of the oxidizer 208 is conical in shape. That is,
the bottom face of overall furnace is of W-shaped profile in cross
section.
Further, air supplying chambers 214-217 which are separately formed
with one another are provided below the bottom faces 209 and 212 of
the gasifier 207 and the oxidizer 208.
The volume of air to be blown out from air diffusion nozzles 210 is
controlled in such a manner that the fluidizing gas velocity within
the range of a concentric circle which has about half the diameter
of the gasifier 207 slows to a velocity of approximately 1 to 2.5
times the minimum fluidizing gas velocity (Umf). The fluidizing gas
velocity in the annular area surrounding the concentric circle
achieves a high velocity of approximately 4 to 12 times the minimum
fluidizing gas velocity (Umf).
Because of the above arrangement, the fluidized medium in the
fluidized bed of the gasifier 207 starts to descend in the central
part, and then slowly dispenses in all directions along the
conically shaped bottom face of the gasifier 207 to reach the
surrounding annular area, where due to the existing intense
fluidization, the fluidized medium are forced to blow upward and
moves along the inner face of the partition 203. At this time,
since the conical partition 203b is formed at the upper section of
the cylindrical partition 203a, the blowing force is concentrated
to finally achieve its maximum level when reaching the surface of
the fluidized bed where the fluidized medium forcibly reverses its
course by reactive force to thus disperse horizontally in all
directions as well as partly upward direction. As a result of this
action, a large quantity of fluidized medium flows into the
oxidizer 208 through the connection opening 204.
On the other hand, the fluidized medium of the gasifier 207 starts
to descend in the central part in a state of cylindrical flow. As
soon as the descending medium reaches the central part of the
conical bottom face 209 of the gasifier 207, the medium start to
disperse in all direction again. In this way, the internal
circulation is formed as shown in FIG. 12. By this internal
circulation, a fuel such as coal water paste supplied from a fuel
feeding port 211 disperses in all directions uniformly in the
gasifier 207. Therefore, even if the fuel supplying system has a
simple structure, an uneven distribution of fuel is avoidable to
thus prevent agglomeration.
A bottom face 212 of the oxidizer 208 is conical in shape and is
provided with air diffusion nozzles 213 which fluidize the
fluidized medium in the oxidizer 208. By injecting air from the air
diffusion nozzles 213, the fluidized medium entering the oxidizer
208 through the connecting opening 204 starts to descend slowly
through the fluidized bed of the oxidizer 208. The medium then
passes through the connection opening 205 provided below the
cylindrical partition 203a to return to the gasifier 207. In
addition, supplemental air diffusion nozzles and an air supplying
pipe connected to the nozzles may be installed on the outer surface
of the conical partition 203b. In case of the conical partition
203b with a large inclined angle, such supplemental air diffusion
nozzles are not necessarily provided.
By adjusting volume of air from air diffusion nozzles 213 provided
on the bottom face 212 of the oxidizer 208 so that the fluidizing
gas velocity within the range of an annular portion along the
cylindrical outer wall 202 is larger than the fluidizing gas
velocity within the range of an annular portion along the partition
203, the fluidized medium starts to descending along the partition
203 and is forced to blow upward and moves along the cylindrical
outer wall 202, thereby forming a swirling flow. By this swirling
flow, unburned char is completely combusted because of its long
residence time.
In order to form the swirling flow, an air chamber 214 for forming
a moving bed is provided below a central portion of the bottom face
209 of the gasifier 207 to supply a small volume of air, and an air
chamber 215 for forming a fluidized bed is provided below the outer
portion of the bottom face 209 of the gasifier 207. The air
chambers 214 and 215 are communicated with each air inlet.
Further, an air chamber 216 is provided at the side of the
partition 202 and an air chamber 217 is provided at the side of the
cylindrical outer wall. The air chambers 216 and 217 serve to
control fluidizing air flow rate. The cylindrical outer wall 202
has combustion gas outlets 218 connected to the oxidizer 208.
With the above arrangement, coal and desulfurizing agent are
supplied to the gasifier 207 and circulated in the fluidized bed to
thus produce coal gas and char. The coal gas is discharged from the
gas outlet 206, and the bed material including the char is
introduced through the connection opening 204 into the oxidizer
208. The char is completely combusted in the oxidizer 208 where it
is circulated. Combustion gas is discharged from the combustion gas
outlet 218. Secondary air nozzles 219 may be provided in a free
board of the oxidizer 208 to perform two-stage combustion.
(Eighth embodiment)
FIG. 13 shows a system diagram of a topping-cycle combined electric
generating system which incorporates the internal furnace shown in
FIG. 12.
Coal 251 and desulfurizing agent 252 are supplied to the gasifier
207 and combusted partly and gasified by air 253 in the gasifier
207. Oxygen 150 or steam 151 may be supplied to the gasifier 207 as
oxidizing agent or gasification agent.
Unburned char, etc. generated in the gasifier 207 is entrained, in
its entirety, by the generated gas and cooled to 600.degree. C. or
below by a gas cooling unit 254 that is connected downstream of the
gasifier 207 for solidifying alkaline metal particles of Na, K,
etc., which would be responsible to high-temperature corrosion of
turbine blades, or fixing those alkaline metals to the surface of
particles. Those particles are then collected by a dust collector
255 and introduced by fluidizing air 260 into the oxidizer 208
where they are completely combusted. An exhaust gas produced in the
oxidizer 208 is discharged therefrom, and cooled to 600.degree. C.
or below by a gas cooling unit 256 that is connected downstream of
the oxidizer 208. Alkaline metal particles of Na, K, etc. which are
solidified when the exhaust gas is cooled by the gas cooling unit
256 are collected by and discharged from a particle dust collector
257.
Particles caught by the dust collector 255 are supplied to the
oxidizer 208 by pneumatic transportation. The dust collectors 255,
256 normally comprises a ceramic filter. The purified gas produced
by removing Na, K which causes high temperature corrosion and
combustion gas are mixed and combusted in a combustor 258, and
high-temperature combustion gas is introduced into a gas turbine
261 driven in high efficiency. The gas turbine 261 drives in turn a
compressor 262 and an electric generator 263. The exhaust gas from
the gas turbine 261 is cooled by a heat recovery device 264 and
discharged toward atmosphere. Gas cooling units 254 and 256 may be
omitted if the turbine blades of the gas turbine 261 are of
improved corrosion-resistant material.
Further, immersed heat transfer tubes man be disposed in the
oxidizer 208. A pressure vessel 266 may be provided to accommodate
the integral furnace 201 so that the integral furnace 201 does not
require pressure-tight construction.
As is apparent from the above description, the present invention
offers the following advantages:
(1) Since the main combustion chamber and the thermal energy
recovery chamber are functionally separated from each other in the
same combustor, the load can easily be controlled not by varying
the height of the fluidized bed, but by varying the overall heat
transfer coefficient of the immersed heat transfer tubes through
the adjustment of an air fluidizing air flow rate into the thermal
energy recovery chamber. Therefore, complex control processes and
devices such as a bed material storage container for taking the
fluidized medium into and out of the combustor are not required,
and any agglomeration is prevented from being developed which would
otherwise occur. When the fluidized medium is taken into and out of
the combustor. As any change of the temperature of the fluidized
bed is small even when the load varies, it is possible to operate
the boiler under temperature conditions optimum for the suppression
of NOx, SOx, and other undesirable emissions. Because the immersed
heat transfer tubes are positioned only in the thermal energy
recovery chamber where the fluidized bed is in a gradually flowing
condition, the immersed heat transfer tubes are subject to less
erode than would if they were placed in an intense
fluidization.
(2) The fluidized medium flows as a dispersed flow from the center
along the conical bottom face gradually in all directions, for
thereby uniformly dispersing a fuel and a desulfurizing agent.
Therefore, the combustion becomes uniform without developing an
agglomeration. The number of coal feeding ports may be minimized,
resulting in a highly simplified coal supply system.
(3) The fluidized medium on the surface of the fluidized bed of the
main combustion chamber descend as a cylindrical flow in the
vicinity of the center while entraining the surrounding fluidized
medium. Therefore, the fuel and the desulfurizer remain in the
fluidized bed for a long period of time for increased combustion
efficiency and desulfurization efficiency.
(4) In the conventional rectangular internal circulating
fluidized-bed boilers, the immersed heat transfer tubes are
arranged on two confronting sides of a rectangular shape. According
to the present invention, however, since the entire circumference
is available for the placement of the heat transfer tubes, more
heat transfer tubes can be installed, resulting in a more compact
structure.
(5) In the conventional pressurized fluidized-bed boilers, the
rectangular combustor having a water wall structure is housed in
the pressure vessel, and sufficient reinforcements are necessary to
protect the combustor against pressure differential between the
inner and the outer of the combustor. According to the present
invention, since the combustor is cylindrical in shape, it has a
sufficient mechanical strength and may be reinforced with simple
reinforcements. As the vessel container and the combustor are of a
combination of circular shape, they do not create wasteful spaces,
and may be arranged in a compact configuration.
(6) The comb-toothed screen, which is disposed in the free board in
surrounding relation to the thermal energy recovery chamber, is
effective to prevent a solid fuel such as coal particles of large
diameter from entering the thermal energy recovery chamber.
Accordingly, the development of an agglomeration can be avoided in
the thermal energy recovery chamber. The screen serves as a baffle
against an exhaust gas generated in the thermal energy recovery
chamber, thus permitting the exhaust gas to be mixed and agitated
sufficiently with an exhaust gas generated in the main combustion
chamber.
(7) Since the internal circulating fluidized-bed boiler has no heat
transfer surface in the main combustion chamber, it is possible to
combust the fuel in a reducing atmosphere in the main combustion
chamber. Therefore, volatile matter can actively be discharged in
the main combustion chamber. Hydrocarbons such as CH.sub.4, CO or
gaseous N chemical species including NHi, HCN, etc. reduce Nitrogen
oxides in gas phase reaction, and selectivity or probability for N
chemical species to convert into oxides. Therefore, it is possible
to effect a low-NOx combustion in the main combustion chamber.
(8) The immersed heat transfer tubes in the fluidized bed in the
thermal energy recovery chamber are arranged radially and divided
by function into a block of evaporating tubes, a block of steam
superheating tubes, and a block of stream reheating tubes. With the
tube groups being functionally divided as viewed in plan view, the
amount of fluidizing air for thermal energy recovery can be
adjusted in each of the blocks so that the amount of recovered heat
can be controlled independently in each of the blocks.
(9) Where flying ashes collected by a particle separator disposed
in the downstream end of the exhaust gas flow path are recycled to
the thermal energy recovery chamber, the average diameter and
specific gravity of particles in the thermal energy recovery
chamber are reduced. As a result, the minimum fluidizing gas
velocity is lowered, and the amount of fluidizing air for thermal
energy recovery may be reduced. Erosion rate of the immersed heat
transfer tubes is greatly reduced, and effects which any change in
the amount of fluidizing air for thermal energy recovery may have
on the combustion are reduced, which is highly effective to achieve
a stable combustion.
(10) Flying ashes containing unburned carbon and an unreacted
desulfurizing agent collected from the exhaust gas discharged from
the combustor are classified. Only those flying ashes having a
particle diameter ranging from 10 to 60 .mu.m are returned to the
combustor. Thus, it is possible to lower NOx, reduce erosion rate
of the exhaust gas flow path, and increase the combustion
efficiency with a minimum amount of circulating ashes.
Consequently, any desulfurizing device may possibly be dispensed
with, and the utilization efficiency of the desulfurizer for
desulfurization in the furnace may be increased for an increased
desulfurization rate.
(11) Flying ashes collected by the dust collector are cooled and
thereafter classified under atmospheric pressure, and unburned
carbon and an unreacted desulfurizing agent are selectively
returned to the combustor. Accordingly, problems such as slugging
which may occur when high-temperature particles are treated under
high pressure can be avoided, and the amount of substances that are
treated is reduced as only useful substances are recycled by
classification. cation. Since those useful substances are recycled
into the fuel supply system to the combustor, an other recycling
system to the combustor is dispensed with, and the unreacted
desulfurizing agent and the fuel are brought into good contact with
each other for an increased desulfurization rate.
(12) In the topping-cycle combined electric generating system, the
cylindrical internal circulating fluidized-bed boiler according to
the present invention is used as a gasifier and/or an oxidizer.
Unburned char discharged from the gasifier is entrained, in its
entirety, by the generated gas and cooled to 600.degree. C. or
below, and collected by a downstream dust collector. Thereafter,
the particles containing unburned char are introduced into the
oxidizer where they are completely combusted. An exhaust gas
produced in the oxidizer is discharged therefrom, and cooled to
600.degree. C. or below. Particles containing Na, K, etc. entrained
in the exhaust gas are collected by and discharged from a
downstream dust collector. The purified exhaust gas and the
generated gas which has been discharged from the gasifier and
filtered to remove particles containing Na, K, etc. therefrom are
mixed and burned in a topping-cycle combustor. A high-temperature
exhaust gas produced by the topping-cycle combustor is introduced
into a gas turbine. Inasmuch as the exhaust gas does not entrain
particles containing alkaline metal such as Na, K, etc., which
would otherwise be responsible to high-temperature corrosion of the
turbine blades, the gas turbine may be made of conventional
materials and designed in a conventional manner.
(13) In the cylindrical fluidized-bed frame in the pressurized
fluidized-bed combined electric generating system, a partition wall
concentric with the cylindrical outer wall is disposed in the
fluidized bed, and connection openings are formed in intermediate
and lower portions of the partition wall. The partition wall has an
upper end held in contact with the ceiling of the cylindrical outer
wall, defining a gas outlet. The space inward of the partition wall
serves as a gasifier, and an annular space outward of the partition
wall serves as an oxidizer. Therefore, while the cylindrical
fluidized-bed furnace is a single furnace, it serves as a compound
furnace which has two functions as the gasifier and the oxidizer
and can operate highly efficiently.
* * * * *