U.S. patent application number 10/286755 was filed with the patent office on 2003-03-20 for waste gas treatment system.
Invention is credited to Kawamura, Kotaro, Nakamura, Rikiya, Okuda, Kazutaka, Shirao, Yuji, Takemura, Yoshiro, Tsuji, Takeshi.
Application Number | 20030054299 10/286755 |
Document ID | / |
Family ID | 27334472 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030054299 |
Kind Code |
A1 |
Kawamura, Kotaro ; et
al. |
March 20, 2003 |
Waste gas treatment system
Abstract
A waste gas treatment system having a burner part and a
combustion chamber provided at the downstream side of the burner
part, wherein combustion flames are formed from the burner part
toward the combustion chamber, and a waste gas is introduced into
the combustion flames, thereby oxidatively decomposing the waste
gas. The combustion chamber is formed from an inner wall made of a
fiber-reinforced ceramic material. Therefore, the wear of the inner
wall due to heat and corrosion is minimized, and thermal stress
cracking is also reduced. Consequently, the lifetime of the system
increases, and the cost of equipment and the availability factor
can be improved. In addition, because the inner wall exhibits no
catalytic effect, the formation of thermal NOx is suppressed, and
it is possible to achieve environmental preservation and to
simplify the treatment equipment.
Inventors: |
Kawamura, Kotaro; (Tokyo,
JP) ; Nakamura, Rikiya; (Tokyo, JP) ; Shirao,
Yuji; (Tokyo, JP) ; Takemura, Yoshiro;
(Kanagawa, JP) ; Okuda, Kazutaka; (Tokyo, JP)
; Tsuji, Takeshi; (Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27334472 |
Appl. No.: |
10/286755 |
Filed: |
November 4, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10286755 |
Nov 4, 2002 |
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09857025 |
May 31, 2001 |
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09857025 |
May 31, 2001 |
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PCT/JP99/06632 |
Nov 29, 1999 |
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Current U.S.
Class: |
431/5 |
Current CPC
Class: |
B01D 53/68 20130101;
B01D 2257/2064 20130101; B01D 53/70 20130101; B01D 2257/204
20130101; F23G 7/065 20130101; B01D 2257/206 20130101; F23G 5/32
20130101; B01D 2257/20 20130101; B01D 2257/00 20130101; B01D
2257/2066 20130101; F23J 3/02 20130101; F23J 2219/70 20130101; F23G
7/06 20130101; B01D 53/46 20130101; F23M 5/085 20130101; F23M
2900/05004 20130101 |
Class at
Publication: |
431/5 |
International
Class: |
F23D 014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 1998 |
JP |
342243/1998 |
Sep 9, 1999 |
JP |
255855/1999 |
Nov 5, 1999 |
JP |
315271/1999 |
Claims
1. A waste gas treatment system having a burner part and a
combustion chamber provided at a downstream side of said burner
part, wherein combustion flames are formed from said burner part
toward said combustion chamber, and a waste gas is introduced into
said combustion flames, thereby oxidatively decomposing said waste
gas, wherein said combustion chamber is formed from an inner wall
made of a fiber-reinforced ceramic material.
2. A waste gas treatment system according to claim 1, wherein a
thermal insulator made of a porous ceramic material is placed
between said inner wall and an outer wall.
3. A waste gas treatment system according to claim 2, wherein purge
gas supply means is provided to maintain a space between said inner
wall and said outer vessel under a purge gas atmosphere of higher
pressure than a pressure in said combustion chamber.
4. A waste gas treatment system having a burner part and a
combustion chamber provided at a downstream side of said burner
part, wherein combustion flames are formed from said burner part
toward said combustion chamber, and a waste gas is introduced into
said combustion flames, thereby oxidatively decomposing said waste
gas, wherein said burner part has a cylindrical member which is
closed at a top thereof and has an opening at a bottom thereof,
said cylindrical member having a waste gas inlet in the top thereof
and an air nozzle at a predetermined position on a side wall
thereof, said cylindrical member further having an auxiliary
burning gas nozzle in the side wall in the vicinity of said
opening, wherein the waste gas introduced from said waste gas inlet
and air blown off from said air nozzle are mixed together, and an
auxiliary burning gas blown off from said auxiliary burning gas
nozzle is ignited to form combustion flames downward below said
opening, and wherein cooling means is provided to cool an auxiliary
burning gas inlet part for introducing a fuel gas into said
auxiliary burning gas nozzle.
5. A waste gas treatment system according to claim 4, wherein said
auxiliary burning gas inlet part is an auxiliary burning gas
chamber provided at an outer periphery of said cylindrical member,
said auxiliary burning gas nozzle being provided in an inner side
portion of said auxiliary burning gas chamber so as to blow off the
auxiliary burning gas toward a central portion of said combustion
chamber, and said cooling means is arranged to cool said auxiliary
burning gas chamber by supplying a cooling medium to a cooling
jacket provided at a boundary between said auxiliary burning gas
chamber and said combustion chamber.
6. A waste gas treatment system according to claim 4, wherein said
auxiliary burning gas inlet part is a auxiliary burning gas chamber
provided at an outer periphery of said cylindrical member, said
auxiliary burning gas nozzle being provided at a bottom of said
auxiliary burning gas chamber so as to blow off the auxiliary
burning gas toward a central portion of said combustion chamber,
and said cooling means is arranged to cool said auxiliary burning
gas chamber by supplying a cooling medium to a cooling jacket
provided adjacently to said auxiliary burning gas chamber or
provided on an outer periphery of said auxiliary burning gas
chamber.
7. A waste gas treatment system according to claim 4, wherein said
auxiliary burning gas inlet part is an auxiliary burning gas inlet
pipe having said auxiliary burning gas nozzle provided at a distal
end thereof, said auxiliary burning gas inlet pipe being disposed
to extend through a cooling jacket provided at an outer peripheral
portion at a lower end of said cylindrical member so that the
auxiliary burning gas blows off from said auxiliary burning gas
nozzle toward a central portion of said combustion chamber, and
said cooling means is arranged to cool said auxiliary burning gas
inlet pipe by supplying a cooling medium into said cooling
jacket.
8. A waste gas treatment system according to claim 4, wherein said
auxiliary burning gas inlet part is an auxiliary burning gas inlet
pipe having said auxiliary burning gas nozzle provided at a distal
end thereof, said auxiliary burning gas inlet pipe being installed
at an outer peripheral portion at a lower end of said cylindrical
member so that the auxiliary burning gas blows off from said
auxiliary burning gas nozzle toward a central portion of said
combustion chamber, and said cooling means is disposed to extend
through a cooling jacket provided at an outer periphery of said
auxiliary burning gas inlet pipe so as to cool said auxiliary
burning gas inlet pipe by supplying a cooling medium into said
cooling jacket.
9. A waste gas treatment system according to any one of claims 4 to
8, wherein said cooling medium is one of water, air, other liquids
and gases.
10. A waste gas treatment system having a burner part and a
combustion chamber provided at a downstream side of said burner
part, wherein combustion flames are formed from said burner part
toward said combustion chamber, and a waste gas is introduced into
said combustion flames, thereby oxidatively decomposing said waste
gas, wherein dust removing means is provided to remove dust from an
inner wall of said burner part and/or an inner wall of said
combustion chamber or to prevent adhesion of dust thereto.
11. A waste gas treatment system according to claim 10, wherein
said dust removing means comprises a dust scraping plate secured to
a distal end of a shaft vertically moving in said burner part
and/or combustion chamber.
12. A waste gas treatment system according to claim 10, wherein
said dust removing means forms a layer of air stream along an inner
wall surface of said burner part and/or an inner wall surface of
said combustion chamber so that said layer of air stream prevents
dust from adhering to the inner wall surface of said burner part
and/or the inner wall surface of said combustion chamber.
13. A method of operating the waste gas treatment system according
to claim 12, wherein said dust removing means has an air injection
nozzle for forming a layer of air stream along the inner wall
surface of said burner part and/or the inner wall surface of said
combustion chamber, said layer of air stream being formed by
continuously or intermittently injecting air from said air
injection nozzle.
14. A dust remover for removing dust from an inner wall of piping
through which a gas containing a large amount of dust flows, said
dust remover comprising: a scraping mechanism installed in said
piping, said scraping mechanism having a rod-shaped scraping member
secured to a main shaft to extend in a longitudinal direction of
said piping; a support mechanism for supporting the main shaft of
said scraping mechanism so that the scraping member moves in an
inner peripheral direction in contact with an inner surface of the
piping or with a slight gap therebetween; and a driving mechanism
for continuously or periodically oscillating or rotating said
scraping mechanism about the main shaft.
15. A dust remover according to claim 14, wherein said scraping
member and main shaft are formed from hollow pipes, respectively,
and respective hollow portions of said scraping member and main
shaft communicate with each other, and wherein an opening is
provided at a distal end of said scraping member so as to
communicate with the hollow portion, and a cleaning gas is supplied
from an outside of said piping through the hollow portions of said
main shaft and scraping member and blown off from said opening.
16. A dust remover according to claim 14 or 15, wherein said
scraping member and main shaft are formed from hollow pipes,
respectively, and respective hollow portions of said scraping
member and main shaft communicate with each other, and wherein a
multiplicity of holes or slits are provided in surfaces of both
said scraping member and main shaft or in the surface of said
scraping member so as to communicate with the hollow portions, and
a cleaning gas is supplied from an outside of said piping through
the hollow portions of said main shaft and scraping member and
blown off from said multiplicity of holes or slits.
17. A method of operating the dust remover according to claim 15 or
16, wherein said cleaning gas is a neutralizing gas for
neutralizing the gas flowing through said piping.
18. A method of operating the dust remover according to claim 15,
16 or 17, wherein said cleaning gas is blown off continuously or
intermittently.
19. A waste gas treatment system having a burner part and a
combustion chamber provided at a downstream side of said burner
part, wherein combustion flames are formed from said burner part
toward said combustion chamber, and a waste gas is introduced into
said combustion flames, thereby oxidatively decomposing said waste
gas, wherein said burner part has a cylindrical member which is
closed at a top thereof and has an opening at a bottom thereof,
said cylindrical member having a waste gas inlet in the top thereof
and an air nozzle at a predetermined position on a side wall
thereof, said cylindrical member further having an auxiliary
burning gas nozzle in the side wall in vicinity of said opening,
said air nozzle being arranged to blow a swirling air flow downward
against combustion flames formed downward below said opening as a
result of igniting an auxiliary burning gas injected from said
auxiliary burning gas nozzle.
20. A waste gas treatment system according to claim 19, wherein
said air nozzle is provided in such a manner that a center line of
said air nozzle is close to a tangent to an inner wall surface that
is parallel to said center line so that air will not stagnate at
the inner wall surface.
21. A waste gas treatment system according to claim 19 or 20,
wherein said air nozzle and auxiliary burning gas nozzle are
provided close to each other so that dust present between said air
nozzle and auxiliary burning gas nozzle can be blown away with air
blown off from said air nozzle.
22. A waste gas treatment system having a burner part and a
combustion chamber provided at a downstream side of said burner
part, wherein combustion flames are formed from said burner part
toward said combustion chamber, and a waste gas is introduced into
said combustion flames, thereby oxidatively decomposing said waste
gas, wherein said burner part has a cylindrical member which is
closed at a top thereof and has an opening at a bottom thereof,
said cylindrical member having a waste gas inlet in the top thereof
and an air nozzle at a predetermined position on a side wall
thereof, said cylindrical member further having an auxiliary
burning gas nozzle in the side wall in vicinity of said opening,
wherein an inner diameter of said waste gas inlet and/or an inner
diameter of said cylindrical member gradually increases toward said
combustion chamber.
23. A waste gas treatment system comprising: a burner part; a
combustion chamber provided at a downstream side of said burner
part; and a combustion gas cooling section provided at a downstream
side of said combustion chamber; said burner part, combustion
chamber and combustion gas cooling section being provided
integrally, said burner part being provided with a waste gas inlet
for introducing a waste gas, an air nozzle for injecting air to
generate a swirling air flow, and an auxiliary burning gas nozzle
for injecting an auxiliary burning gas; and said combustion gas
cooling section being provided with a liquid spray nozzle for
spraying a liquid for cooling the waste gas flowing in from the
combustion chamber and for capturing dust contained in said waste
gas, an exhaust pipe for discharging said waste gas, and a drain
pipe for draining the liquid sprayed from said liquid spray nozzle.
Description
TECHNICAL FIELD
[0001] The present invention relates to a waste gas treatment
system for treating a waste gas likely to generate dust when it is
treated by combustion. For example, the present invention relates
to a combustion type waste gas treatment system for
combustion-treating hazardous and combustible waste gases
containing silane gas (SiH.sub.4) or a halogen-containing gas
(NF.sub.3, ClF.sub.3, SF.sub.6, CHF.sub.3, C.sub.2F.sub.6,
CF.sub.4, etc.) or hardly decomposable waste gases.
BACKGROUND ART
[0002] Waste gases that are likely to generate dust when treated by
combustion include those which contain hazardous and combustible
gases, e.g. silane (SiH.sub.4) and disilane (Si.sub.2H.sub.6)
discharged from semiconductor manufacturing systems or liquid
crystal panel manufacturing systems. Further, waste gases
containing scarcely decomposable, global warming gases (PFCs) are
also likely to generate dust when treated by combustion. Such waste
gases can not be emitted into the atmosphere as they are because
they would have adverse effects upon the human body and change the
global environment. Therefore, the common practice is to introduce
such waste gases into a pretreatment system where the waste gas is
made harmless by oxidation through combustion. For this treatment,
a method is widely employed in which flames are formed in a furnace
by using an auxiliary burning gas and the waste gas is burned in
the flames.
[0003] In such a combustion type waste gas treatment system, the
auxiliary burning gas uses hydrogen, city gas, LPG or the like as a
fuel gas, and oxygen or air is usually used as an oxidizing agent.
The greater part of the running cost of the system is the cost for
consumption of the fuel gas and the oxidizing agent. Accordingly,
how much hazardous waste gas is decomposed at high efficiency with
a minimum amount of auxiliary burning gas is a measure for
evaluating the performance of this type of system.
[0004] A general arrangement of a combustor used in a conventional
waste gas treatment system of the above-described combustion type
is shown in FIGS. 27 and 28. The illustrated combustor has a burner
part 101 and a combustion reaction part (combustion chamber) 102
for oxidatively decomposing waste gas under heating at a stage
subsequent to the burner part 101. The burner part 101 has a waste
gas nozzle 103 opened in the center of the ceiling of the
combustion reaction part 102 to introduce a waste gas G1 to be
treated into the combustion reaction part 102. The burner part 101
further has a plurality of auxiliary burning gas nozzles 104 opened
in the outer periphery of the waste gas nozzle 103 to introduce an
auxiliary burning gas G2 into the combustion reaction part 102. A
combustion gas outlet 105 is integrally connected to the lower end
of the combustion reaction part 102. Thus, the waste gas G1 is
passed through the center of flames annularly formed by the
auxiliary burning gas G2 blown off from the auxiliary burning gas
nozzles 104. While passing through the center of the flames, the
waste gas G1 is mixed with the flames and thus burned. Combustion
gas resulting from the burning of the waste gas G1 is discharged to
the outside from the combustion gas outlet 105.
[0005] In general, the combustion reaction part 102 is defined and
formed by an inner wall surface 106a of a cylindrical furnace body
106 made of a metal, e.g. a stainless steel. According to need, a
thermal insulator for heat insulation is installed on the outer
peripheral surface of the furnace body 106. Alternatively, a
water-cooling structure is employed.
[0006] Meanwhile, the mainstream method of decomposition-treating
gases containing fluorocarbons, which are considered to be causes
of global warming, is heat decomposition in a high-temperature
environment or decomposition in a plasma for the time being. To use
these techniques, decomposition treatment of
fluorocarbon-containing gases is carried out under application of
an enormous amount of energy for heating and plasma generation in
decomposition treatment equipment having a complicated control
mechanism for controlling a heating device, e.g. a heater, a plasma
generator, a safety device, etc.
[0007] However, in the conventional example as shown in FIGS. 27
and 28, the combustion reaction part 102 is formed by the metallic
furnace body 106, and the furnace body 106 is exposed to a
high-temperature atmosphere of 1300.degree. C. or more when
combustion flames are formed (during operation). Therefore, the
furnace body 106 wears out rapidly and cannot withstand long-term
operation. In particular, when a halogen-containing gas is
decomposition-treated by this system, the furnace body is etched or
corroded under high temperature by a halogen gas (HCl, HF, etc.)
produced after the treatment reaction and hence wears out
rapidly.
[0008] When the furnace body 106 wears out in a short period of
time as stated above, it is necessary to replace the furnace body
106 frequently. This causes the cost of equipment to increase.
Further, when the metallic furnace body wears out, there is a
danger that wear may develop in the surrounding structures (the
thermal insulator, the water-cooled vessel, etc.). Therefore, it is
necessary to inspect the furnace body for the degree of wear by
disassembling it frequently. This causes the availability for use
of the equipment to be reduced markedly and gives rise to an
increase in the running cost.
[0009] Further, because the inner wall surface of the metallic
furnace body 106 is heated to a high temperature by combustion
flames in the combustion reaction part 102, the formation of
thermal NOx is undesirably promoted by the catalytic effect of the
metal. For example, this type of waste gas combustion equipment in
semiconductor industry facilities is generally designed on the
assumption that it will be installed in a clean room. Therefore,
the equipment needs to be made compact in size. However, if a large
amount of NOx is produced, it becomes necessary to provide
separately a special-purpose treatment mechanism for treating the
NOx. Consequently, the equipment cannot be made compact in
size.
[0010] Further, in a combustor that forms combustion flames as
stated above, flames are formed at the lower end of the burner part
101, resulting in a rise in temperature in the vicinity of the
opening portion of the burner part 101, which is made of a
stainless steel or the like. Therefore, there is a danger that the
auxiliary burning gas G2 supplied to the burner part 101 may ignite
and explode.
[0011] Further, when gases such as SiH.sub.4 used in semiconductor
device manufacturing processes, particularly CVD processes or the
like, are made harmless by a heat decomposition type waste gas
treatment system, dust, e.g. SiO.sub.2, is generated. Such dust
flows, together with waste gas, and adheres to the inner wall
surfaces of piping and so forth, causing the exhaust pressure loss
to increase. As methods of preventing the adhesion of dust to the
inner wall surfaces of piping and so forth, the following methods
have heretofore been available: a method wherein dust is blown off
with a cleaning gas; a method wherein dust is scraped off with an
intermittent manual scraper; and a method wherein a cleaning gas is
always supplied through a porous inner wall to prevent adhesion of
dust.
[0012] With the blow-off method using a cleaning gas, a fixed
nozzle is provided over the circumferential area of piping to blow
off a cleaning gas constantly or intermittently to remove dust.
This method involves the problem that if the position of the nozzle
is away from where dust may adhere, the dust removal effect
weakens. If a large amount of cleaning gas is supplied to maintain
the dust removal effect, the cost of cleaning gas increases. In
addition, because a large amount of gas flows, it is necessary to
increase the diameter of piping in order to minimize the pressure
loss.
[0013] With the method using an intermittent manual scraper,
scraping is performed after dust has grown large. Therefore, the
method requires a tank for storing large lumps of scraped dust.
[0014] With the prevention of adhesion of dust by constantly
supplying a cleaning gas through a porous inner wall, it is
necessary to supply a large amount of cleaning gas in order to
maintain the flow velocity of cleaning gas through the inner wall
throughout the piping so as to prevent adhesion of dust.
Accordingly, it is necessary to increase the diameter of the piping
in order to minimize the pressure loss due to the flow of a large
amount of gas.
[0015] Further, the cost of cleaning gas increases, and it is
necessary to increase the size of equipment such as duct for
exhausting the gas discharged from the pretreatment system in a
building to the outside of the building.
[0016] The present invention was made in view of the
above-described circumstances, and an object of the present
invention is to provide a waste gas treatment system designed so
that the wear of an inner wall constituting a combustion reaction
part exposed to a high temperature is minimized to increase the
working life, reduce the cost of equipment and improve the work
availability, and the formation of NOx can be suppressed.
[0017] Another object of the present invention is to provide a
waste gas treatment system designed to suppress a rise in
temperature due to flames in the vicinity of the opening of a
combustion burner so as to be free from the danger of explosion of
an auxiliary burning gas or the like.
[0018] A further object of the present invention is to provide a
waste gas treatment system capable of reliably removing dust from
the inner wall surface of piping and requiring a minimum amount of
cleaning gas when it is injected.
DISCLOSURE OF INVENTION
[0019] The present invention provides a waste gas treatment system
having a burner part and a combustion chamber provided at the
downstream side of the burner part, wherein combustion flames are
formed from the burner part toward the combustion chamber, and a
waste gas is introduced into the combustion flames, thereby
oxidatively decomposing the waste gas. In the waste gas treatment
system, the combustion chamber is formed from an inner wall made of
a fiber-reinforced ceramic material. Therefore, the wear of the
inner wall due to heat and corrosion is minimized, and thermal
stress cracking is also reduced. Consequently, the lifetime of the
system increases, and the cost of equipment and the availability
factor can be improved. In addition, because the inner wall
exhibits no catalytic effect, the formation of thermal NOx is
suppressed, and it is possible to achieve environmental
preservation and to simplify the treatment equipment. In addition,
because the space between the inner wall and the outer vessel is
maintained under a purge gas atmosphere of higher pressure than the
pressure in the combustion chamber, it is possible to prevent
hazardous gases in the combustion chamber from leaking to the
outside.
[0020] In addition, there is provided a waste gas treatment system
wherein a burner part has a cylindrical member which is closed at
the top thereof and has an opening at the bottom thereof. The
cylindrical member has a waste gas inlet in the top thereof and an
air nozzle at a predetermined position on the side wall thereof.
The cylindrical member further has an auxiliary burning gas nozzle
in the side wall in the vicinity of the opening. A waste gas
introduced from the waste gas inlet and air blown off from the air
nozzle are mixed together, and an auxiliary burning gas blown off
from the auxiliary burning gas nozzle is ignited to form combustion
flames downward below the opening. In addition, a cooling means is
provided to cool an auxiliary burning gas inlet part for
introducing a fuel gas into the auxiliary burning gas nozzle.
Accordingly, even when the auxiliary burning gas inlet part is
heated by flames, the rise in temperature is suppressed below the
ignition point of the auxiliary burning gas. Therefore, there is no
danger that the auxiliary burning gas may explode.
[0021] In addition, there is provided a waste gas treatment system
that is provided with a dust removing means for removing dust from
the inner wall of the burner part and/or the inner wall of the
combustion chamber or for preventing adhesion of dust thereto,
thereby allowing the waste gas treatment system to be operated for
a long period of time.
[0022] In addition, there is provided a dust remover for removing
dust from the inner wall of piping through which a gas containing a
large amount of dust flows. The dust remover includes a scraping
mechanism placed in the piping. The scraping mechanism has a
rod-shaped scraping member secured to a main shaft to extend in the
longitudinal direction of the piping. The dust remover further
includes a support mechanism for supporting the main shaft of the
scraping mechanism so that the scraping member moves in the inner
peripheral direction in contact with the inner surface of the
piping or with a slight gap therebetween, and a driving mechanism
for continuously or periodically oscillating or rotating the
scraping mechanism about the main shaft. Thus, a cleaning gas is
supplied from the outside of the piping through the hollow portions
of the main shaft and the scraping member and blown off from the
distal end of the scraping member or from a multiplicity of holes
or slits in the surface thereof. Consequently, it is possible to
remove dust from an area in the piping that cannot be reached by
the scraping member. In addition, it becomes possible to remove
dust attached to the scraping mechanism itself.
[0023] In addition, there is provided a waste gas treatment system
wherein a burner part has a cylindrical member which is closed at
the top thereof and has an opening at the bottom thereof. The
cylindrical member has a waste gas inlet in the top thereof and an
air nozzle at a predetermined position on the side wall thereof.
The cylindrical member further has an auxiliary burning gas nozzle
in the side wall in the vicinity of the opening. The air nozzle is
arranged to promote ignition of an auxiliary burning gas injected
from the auxiliary burning gas nozzle and to blow a swirling air
flow downward against combustion flames formed downward below the
opening. Accordingly, it becomes unlikely that dust will adhere to
the inner wall of the burner part.
[0024] In addition, there is provided a waste gas treatment system
wherein a burner part has a cylindrical member which is closed at
the top thereof and has an opening at the bottom thereof. The
cylindrical member has a waste gas inlet in the top thereof and an
air nozzle at a predetermined position on the side wall thereof.
The cylindrical member further has an auxiliary burning gas nozzle
in the side wall in the vicinity of the opening. The inner
diameters of the waste gas inlet and the cylindrical member
gradually increase toward the combustion chamber. Consequently,
there is no angular portion such as a right-angled portion in the
burner part, and it becomes unlikely that dust will adhere to the
inner wall of the nozzle part.
[0025] In addition, there is provided a waste gas treatment system
having a burner part, a combustion chamber provided at the
downstream side of the burner part, and a combustion gas cooling
section provided at the downstream side of the combustion chamber.
The burner part, the combustion chamber and the combustion gas
cooling section are provided integrally. The burner part is
provided with a waste gas inlet for introducing a waste gas and an
air nozzle for injecting air to generate a swirling flow. The
combustion gas cooling section is provided with a liquid spray
nozzle for spraying a liquid for cooling the waste gas flowing in
from the combustion chamber and for capturing dust contained in the
waste gas, an exhaust pipe for discharging the waste gas, and a
drain pipe for draining the liquid sprayed from the liquid spray
nozzle. With the waste gas treatment system thus arranged, the
waste gas can be decomposition-treated, and dust, HCl and HF in the
waste gas introduced from the waste gas inlet can be efficiently
captured and absorbed in the liquid sprayed from the spray
nozzle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a diagram showing the arrangement of a waste gas
combustor in the waste gas treatment system according to the
present invention.
[0027] FIG. 2 is a sectional view taken along the line I-I in FIG.
1.
[0028] FIG. 3 is a diagram showing a structural example of a burner
part in the waste gas treatment system according to the present
invention.
[0029] FIG. 4 is a diagram as seen in the direction of the arrow A
in FIG. 3.
[0030] FIG. 5 is a diagram showing a structural example of a burner
part in the waste gas treatment system according to the present
invention.
[0031] FIG. 6 is a diagram as seen in the direction of the arrow D
in FIG. 5.
[0032] FIG. 7 is a diagram showing a structural example of a burner
part in the waste gas treatment system according to the present
invention.
[0033] FIG. 8 is a diagram as seen in the direction of the arrow E
in FIG. 7.
[0034] FIG. 9 is a diagram showing a structural example of a burner
part in the waste gas treatment system according to the present
invention.
[0035] FIG. 10 is a diagram as seen in the direction of the arrow F
in FIG. 9.
[0036] FIG. 11 is a diagram showing a structural example of a
burner part in the waste gas treatment system according to the
present invention.
[0037] FIG. 12 is a diagram showing the external appearance of a
cooling jacket in FIG. 11.
[0038] FIG. 13 is a diagram showing a structural example of a dust
remover in the waste gas treatment system according to the present
invention.
[0039] FIG. 14 is a plan view of a scraping plate in FIG. 13.
[0040] FIG. 15 is a diagram showing a structural example of a dust
remover in the waste gas treatment system according to the present
invention.
[0041] FIG. 16 is a sectional view as seen in the direction of the
arrow II-II in FIG. 15.
[0042] FIG. 17 is a diagram showing a structural example of a dust
remover in the waste gas treatment system according to the present
invention.
[0043] FIG. 18 is a sectional view as seen in the direction of the
arrow III-III in FIG. 17.
[0044] FIG. 19 is a diagram showing a structural example of a dust
remover in piping according to the present invention.
[0045] FIG. 20 is a diagram showing a structural example of a dust
remover in the waste gas treatment system according to the present
invention.
[0046] FIG. 21 is a diagram showing a structural example of a dust
remover in piping according to the present invention.
[0047] FIG. 22 is a diagram showing a structural example of a dust
remover in piping according to the present invention.
[0048] FIG. 23 is a diagram showing a structural example of a dust
remover in piping according to the present invention.
[0049] FIG. 24 is a diagram showing a structural example of a
burner part in the waste gas treatment system according to the
present invention.
[0050] FIG. 25 is a diagram as seen in the direction of the arrow L
in FIG. 24.
[0051] FIG. 26 is a diagram showing a structural example of a
burner part in the waste gas treatment system according to the
present invention.
[0052] FIG. 27 is a diagram showing a structural example of a
conventional waste gas treatment system.
[0053] FIG. 28 is a sectional view as seen in the direction of the
arrow IV-IV in FIG. 27.
BEST MODE FOR CARRYING OUT THE INVENTION
[0054] FIGS. 1 and 2 are diagrams showing the arrangement of a
waste gas combustor in the waste gas treatment system according to
the present invention. FIG. 1 is a vertical sectional view, and
FIG. 2 is a sectional view taken along the line I-I in FIG. 1. The
waste gas combustor is formed in the shape of a cylindrical closed
vessel as a whole. The waste gas combustor has a burner part 10 in
an upper stage and a combustion chamber (combustion reaction part)
30 in an intermediate stage. The waste gas combustor has a cooling
part 51 and a discharge part 52 in a lower stage. As a cooling
medium in the cooling part 51, for example, a liquid, e.g. water,
or a gas, e.g. air, is used.
[0055] The burner part 10 has a cylindrical member 11 forming a
flame stabilizing portion 18 opening toward the combustion chamber
30. The burner part 10 further has an outer cylinder 12 surrounding
the cylindrical member 11 with a predetermined space therebetween.
Between the cylindrical member 11 and the outer cylinder 12, an air
chamber 19 for holding air for combustion is formed, together with
an auxiliary burning gas chamber 20 for holding an auxiliary
burning gas, e.g. a premixed gas of hydrogen and oxygen. The air
chamber 19 and the auxiliary burning gas chamber 20 are
communicated with an air source and a gas source (not shown),
respectively. As the auxiliary burning gas, hydrogen, propane gas,
city gas, etc. is used.
[0056] Waste gas inlet pipes 14 are connected to the top of the
cylindrical member 11 covering the upper side of the flame
stabilizing portion 18 to introduce into the flame stabilizing
portion 18 a waste gas G1 containing silane (SiH.sub.4) or the like
discharged, for example, from a semiconductor manufacturing
system.
[0057] The cylindrical member 11 is provided with a plurality of
air nozzles 15 for providing communication between the air chamber
19 and the flame stabilizing portion 18 and a plurality of
auxiliary burning gas nozzles 16 for providing communication
between the auxiliary burning gas chamber 20 and the flame
stabilizing portion 18. As shown in FIG. 2, the air nozzles 15
extend at a predetermined angle to the tangential direction to the
cylindrical member 11 to blow off air so as to produce swirling
flows in the flame stabilizing portion 18. Similarly, the auxiliary
burning gas nozzles 16 extend at a predetermined angle to the
tangential direction to the cylindrical member 11 to blow off an
auxiliary burning gas so as to form swirling flows in the flame
stabilizing portion 18. The air nozzles 15 and the auxiliary
burning gas nozzles 16 are disposed equally in the circumferential
direction of the cylindrical member 11.
[0058] A secondary air chamber 31 is formed around the boundary
between the flame stabilizing portion 18 and the combustion chamber
30 so as to surround the opening of the flame stabilizing portion
18. The secondary air chamber communicates with an air source (not
shown) for supplying secondary air. A partition plate 32 dividing
the secondary air chamber 31 from the combustion chamber 30 is
provided with secondary air nozzles 33 equally disposed in the
circumferential direction to blow off secondary air into the
combustion chamber 30 to oxidize waste gas.
[0059] The combustion chamber 30 is a space for oxidatively
decomposing waste gas at a stage subsequent to the burner part 10.
The combustion chamber 30 is defined by a cylindrical inner wall 35
provided inside a hermetic cylindrical outer vessel 34 made of a
metal or the like. The inner wall 35 is disposed to be contiguous
with the flame stabilizing portion 18. The inner wall 35 is formed
from a fiber-reinforced ceramic material as described later. A
thermal insulator 37 of a porous ceramic material is inserted into
a space 36 between the inner wall 35 and the outer vessel 34. A
purge air inlet pipe 40 is connected to the outer vessel 34 to
introduce air for purging into the space 36.
[0060] The fiber-reinforced ceramic material constituting the inner
wall 35 is as follows. Fibers formed from a ceramic material are
woven into a cloth. The cloth is coated with a binder-containing
ceramic material. The coated cloth is formed into a cylindrical
shape and solidified. Usually, a plurality of ceramic fiber layers
are stacked on top of each other. By reinforcing the ceramic
material with ceramic fibers in this way, the mechanical strength
and the high-temperature strength can be improved. Thus, even when
the inner wall 35 is exposed to a high temperature owing to
combustion and subjected to thermal stress, cracking can be
minimized. Further, it is also unlikely that the inner wall 35 will
be etched or corroded by a corrosive gas such as a halogen gas
generated as a result of combustion treatment. Accordingly, a long
useful life can be obtained. Meanwhile, the thermal insulator 37 of
a porous ceramic material may be such that fibers are made from a
ceramic material and formed by a forming suction device so as to
conform to the shape of the space 36.
[0061] Examples of ceramic materials usable for the thermal
insulator 37 and the inner wall 35 include alumina having a purity
of 80 to 99.7% and Si-based ceramic materials. To treat a waste gas
containing fluorine, it is desirable to use alumina having high
corrosion resistance to the fluorine-containing waste gas. If
alumina continuous fibers are used as a fiber-reinforced ceramic
material for the inner wall 35, the inner wall 35 is improved in
heat resistance, wind velocity resistance and wear resistance and
capable of withstanding large thermal shock and temperature
gradient.
[0062] The combustion chamber 30 is provided with a UV sensor 38
for detecting flames and a pilot burner 39 for ignition in the
burner part 10. It should be noted that the UV sensor 38 and the
pilot burner 39 may be installed on the top (the top plate of the
burner part 10) of the cylindrical member 11, as shown in FIG. 3.
The UV sensor 38 is disposed at a tilt with respect to the top of
the cylindrical member 11 to detect formed flames from an oblique
direction. The reason for this is that flames form swirling flows
in the combustion chamber 30 and hence become short with respect to
the radial direction. When silane (SiH.sub.4) or the like is
treated, dust of SiO.sub.2 adheres to the inner wall surface of the
combustion chamber 30, and it becomes impossible for the UV sensor
38 to detect flames. However, installing the UV sensor 38 on the
top plate of the burner part 10 as stated above makes it possible
to avoid the problem that the UV sensor 38 becomes unable to detect
flames owing to the adhesion of dust. Further, to treat scarcely
decomposable global warming gases (PFCs), a high temperature of
1300.degree. C. or more is needed, and hence the piping is corroded
by heat. However, high-temperature corrosion can be avoided by
installing the UV sensor 38 and the pilot burner 39 on the top
plate of the burner part 10 as stated above.
[0063] A discharge part 52 is provided at the bottom of the
combustion chamber 30 with a cooled cooling part 51 interposed
between the combustion chamber 30 and the discharge part 52. A
plurality of nozzles 53 are provided on the lower edge of the
cooling part 51 at equal spaces in the circumferential direction.
Water is injected from the nozzles 53 toward the center to form a
curtain of water, thereby cooling the waste gas and capturing
particles contained in the waste gas. The side wall of the
discharge part 52 is provided with an exhaust pipe 54 for
discharging the treated waste gas. The bottom of the discharge part
52 is provided with a drain port 55 for discharging water injected
from the nozzles 53.
[0064] Next, the operation of the waste gas treatment system
according to the above-described embodiment will be described.
First, the auxiliary burning gas is introduced and held in the
auxiliary burning gas chamber 20 and blown off from the auxiliary
burning gas nozzles 16, which are provided in the inner peripheral
surface of the cylindrical member (inner cylinder) 11, toward the
flame stabilizing portion 18 so as to produce swirling flows. When
ignited by the pilot burner 39, the auxiliary burning gas forms
swirling flames along the inner peripheral surface of the
cylindrical member (inner cylinder) 11.
[0065] Hereupon, the auxiliary burning gas forms swirling flames,
and swirling flames have the feature that they can burn stably over
a wide range of equivalence ratios. In other words, because the
flames swirl strongly, they supply heat and radicals to each other.
Therefore, flame stabilizing properties are improved. Accordingly,
even at such a small equivalence ratio that unburned gas may be
generated or quenching may occur in the conventional system, the
auxiliary burning gas can burn stably without generating unburnt
gas and without causing pulsating combustion even in the vicinity
of the equivalence ratio of 1.
[0066] Meanwhile, the waste gas G1 to be treated is blown off
toward the flame stabilizing portion 18 from the waste gas inlet
pipes 14, which open on the lower surface of the top of the
cylindrical member 11. The waste gas G1 blown off mixes with the
swirling flows of the auxiliary burning gas and burns. At this
time, because the auxiliary burning gas is blown off from all the
auxiliary burning gas nozzles provided in the circumferential
direction so as to swirl strongly in one direction downstream the
nozzles, all the auxiliary burning gas mixes satisfactorily with
the flames. Thus, the efficiency of combustion of the waste gas
becomes very high.
[0067] If the auxiliary burning gas is overheated in excess of the
ignition temperature thereof, it may initiate combustion in the
auxiliary burning gas chamber 20 when an oxidizing agent is
contained in the auxiliary burning gas. Therefore, it is necessary
to effect cooling so that the temperature will not exceed the
ignition temperature of the auxiliary burning gas. Further,
research carried out by the present inventors reveals that swirling
flames heat the cylindrical member 11 and the auxiliary burning gas
in the auxiliary burning gas chamber 20. Accordingly, it is
necessary in order to continue stable combustion to effect cooling
so that the temperature will not exceed the heat resistance of the
constituent material of the cylindrical member 11. The swirling air
flows injected into the flame stabilizing portion 18 from the air
nozzles 15 act to cool the auxiliary burning gas chamber 20.
[0068] Furthermore, flames from the auxiliary burning gas nozzles
16 are swirling, and the air injected from the air nozzles 15 is
also swirling. Therefore, as they mix with the flames, the air
flows further accelerate the swirling flows of the flames to form
strong swirling flows. When swirling flames are formed, the
pressure of the gas flow in the center of the swirl reduces.
Consequently, self-circulating flows that flow backward from the
forward ends of the flames toward the waste gas inlet pipes 14 and
the auxiliary burning gas nozzles 16 occur in the center of the
swirl. The circulating flows mix with the flames from the auxiliary
burning gas nozzles 16 and the combustion gas, thereby suppressing
the formation of NOx. Alternatively, it is possible to perform
low-NOx combustion even if a premixed gas is used as an auxiliary
burning gas and the equivalence ratio of the auxiliary burning gas
is reduced.
[0069] Further, because the flames from the auxiliary burning gas
nozzles 16 are swirling strongly, when the system is used to treat
a gas that generates dust when burns, such as silane gas, the
swirling flows of the flames prevent silica (SiO.sub.2), which
results from the combustion of silane gas, from adhering to the
waste gas inlet pipes 14 or the auxiliary burning gas nozzles 16.
More specifically, when silane (SiH.sub.4) or the like burns,
powdery silica (SiO.sub.2) is formed. If the silica (SiO.sub.2)
adheres to the vicinities of the waste gas inlet pipes 14 or the
auxiliary burning gas nozzles 16, it may reduce the amount of
auxiliary burning gas blown off or change the gas blowing
direction, causing the blowing off of the gas to be unstable. Under
such circumstances, the blowing off of the gas cannot be
stabilized, and it becomes impossible to perform stable
combustion.
[0070] In this embodiment, because there are swirling flames from
the auxiliary burning gas nozzles 16, the swirling flames cause
fast flows to occur at the distal ends of the waste gas inlet pipes
14 and the auxiliary burning gas nozzles 16. The fast flows act to
clean the distal end portions of the waste gas inlet pipes 14 and
the auxiliary burning gas nozzles 16, thereby preventing the
resulting powdery silica (SiO.sub.2) from adhering to the distal
end portions of the waste gas inlet pipes 14 and the auxiliary
burning gas nozzles 16. This effect becomes even more remarkable in
the presence of the swirling air flows from the air injection
nozzles 15.
[0071] Further, the above-described effect does not confine itself
to the distal end portions of the waste gas inlet pipes 14 and the
auxiliary burning gas nozzles 16. That is, because the flames swirl
in the combustion chamber 30, fast flows also occur along the wall
surface of the combustion chamber 30. The fast flows clean the wall
surface of the combustion chamber 30, thereby removing silica
(SiO.sub.2) from the wall surface. Thus, silica (SiO.sub.2)
attached to the distal end portions of the waste gas inlet pipes 14
and the auxiliary burning gas nozzles 16 and the wall surface of
the combustion chamber 30 is removed in self-cleaning manner by the
swirling flows.
[0072] As an example, a premixed gas containing an oxidizing agent
is used as an auxiliary burning gas to be supplied, and the mixture
ratio of the oxidizing agent to the fuel gas in the premixed gas is
made lower than the stoichiometric oxidizing agent mixture ratio to
form an over-rich premixed gas that is over-rich in fuel. The
premixed gas is injected to swirl from the auxiliary burning gas
nozzles 16, thereby forming primary swirling reducing flames in the
flame stabilizing portion 18. The reducing flames and the waste gas
from the waste gas inlet pipes 14 are brought into contact with
each other to reductively decompose the waste gas, particularly a
waste gas containing PFCs.
[0073] Next, oxygen is sufficiently given to the reducing flames in
excess of the stoichiometric amount from the air injected from the
air nozzles 15 and the secondary air nozzles 33 to create an excess
oxygen condition, thereby forming secondary oxidizing flames.
Oxidative decomposition of the waste gas is effected by the
oxidizing flames. The waste gas is exposed to flames in two stages,
i.e. reducing flames and oxidizing flames. Thus, the length of time
that the waste gas is in contact with the flames is increased.
Consequently, the high-temperature resident time can be lengthened.
A waste gas containing PFCs has the property that it can be
decomposed if the atmosphere temperature is raised and the
high-temperature state is maintained for a long period of time.
Thus, the waste gas is exposed to different flames in two stages,
i.e. oxidizing and reducing flames, and the high-temperature state
created by the flames is maintained for an extended period of time.
By doing so, waste gas, particularly a gas containing PFCs, can be
decomposed completely.
[0074] Because the auxiliary burning gas nozzles 16 face obliquely
downward toward the downstream side of the flame stabilizing
portion 18 to blow off the auxiliary burning gas so as to form
swirling flows, flames blowing off from the auxiliary burning gas
nozzles 16 form spiral swirling flows toward the downstream side of
the flame stabilizing portion 18. Accordingly, the length of swirl
when the swirling flames flow inside the cylindrical member 11 is
shorter than in a case where the auxiliary burning gas is blown off
horizontally. Consequently, an area where the flames heat the inner
wall surface of the cylindrical member 11 narrows. Thus, heating of
the inner peripheral wall of the cylindrical member 11 by the
swirling flows and the rise in temperature are suppressed.
[0075] Thus, it is possible to extend the heat life of the
constituent material of the cylindrical member 11. In addition, it
is possible to reduce the amount of cooling air supplied from the
air nozzles 15 and hence possible to suppress the reduction in
flame temperature due to cooling and to maintain the
high-temperature state. Accordingly, it is possible to increase the
efficiency of decomposition of a halogen-containing waste gas,
particularly a fluorocarbon-containing waste gas. Further, a
plurality of auxiliary burning gas nozzles 16 may be provided so as
to open in the tangential direction to the cylindrical member 11 as
seen from above and open obliquely downward in a vertical plane.
This arrangement also allows flames to form spiral swirling flows
toward the downstream side of the flame stabilizing portion 18.
[0076] Although in this embodiment the secondary air nozzles 33 are
directed downward, they may be arranged to inject secondary air
toward the center of the cylindrical member 11. It is also possible
to provide the secondary air nozzles 33 so that air injected from
the nozzles forms swirling flows in the combustion chamber. With
this arrangement, it is possible to cool the combustion-treated
gas, discharge the treated gas to the outside of the combustion
chamber 30, and remove silica (SiO.sub.2) adhering to the wall
surface of the combustion chamber 30, even more effectively. The
way in which the nozzles are provided is the same as in the case of
the above-described auxiliary burning gas nozzles 16.
[0077] It is also possible to provide an air injection nozzle in
the top of the cylindrical member 11 so that air is supplied into
the flame stabilizing portion 18 from this air injection nozzle to
increase the oxygen density according to need, thereby allowing
combustibility to be improved.
[0078] It is also possible to provide secondary combustion air
holes in an extended peripheral wall of the flame stabilizing
portion 18 downstream from the auxiliary burning gas nozzles 16 so
as to form reducing flames for primary combustion and oxidizing
flames for secondary combustion by the air in the flame stabilizing
portion 18, thereby improving the decomposition rate of the waste
gas G1, especially a halogen-containing waste gas, particularly a
fluorocarbon-containing waste gas. In this case, it is preferable
for the air holes to inject air toward the flame stabilizing
portion 18 so as to form swirling flows for the reasons stated
above. The air holes may be arranged to inject air toward the
center of the cylindrical member 11 so that the air mixes
turbulently with the waste gas after the primary combustion by the
reducing flames.
[0079] Although an example in which flames blow off downward is
shown, the present invention may also be applied to an arrangement
in which flames blow off horizontally. The auxiliary burning gas is
not necessarily limited to a premixed gas of hydrogen and oxygen
but may be a fuel gas, e.g. hydrogen, city gas or LPG, or a
premixed gas prepared by mixing together city gas or LPG and
oxygen, air or oxygen enrichment air, as a matter of course.
[0080] An example of the process is as follows:
[0081] Gas to be treated: CF.sub.4
[0082] Reductive decomposition reaction in reducing flames:
[0083] CF.sub.4+H.sub.2.fwdarw.CHmFn+HF+F.sub.2 (m, n is from 0 to
4)
[0084] Oxidative decomposition reaction:
[0085] CHmFn+O.sub.2.fwdarw.CO.sub.2+H.sub.2O
[0086] In the combustion chamber 30, the ceramic material
constituting the inner wall has excellent heat resistance and
corrosion resistance. Therefore, wear due to heat and corrosion is
minimized. In addition, because the ceramic material is reinforced
with fibers, thermal stress cracking is prevented. Accordingly, the
combustion chamber 30 can be used for a long period of time.
Moreover, because there is no catalytic effect as occurs in the
case of a metal, the formation of thermal NOx is suppressed even
when the temperature in the combustion chamber 30 becomes high.
Even when a halogen-containing gas is subjected to decomposition
treatment, it is possible to suppress corrosion and etching of the
inner wall 35 under high temperature by a halogen gas (HCl, HF,
etc.) resulting from the decomposition treatment.
[0087] In particular, when a fiber-reinforced ceramic material
having alumina as a raw material is used, the thermal conductivity
under normal running conditions (600 to 1300.degree. C.) is of the
order of 0.65 to 0.88 (W/m.K), which is several hundred times
higher than the average thermal conductivity of stainless steels or
other similar metals, which is of the order of 0.0017 (W/m.K).
Accordingly, thermal stress cracking is further reduced. Further,
because the thermal insulator 37 made of a porous ceramic material
is disposed on the outer periphery of the inner wall 35, the amount
of heat loss can be reduced more than in the case of using the
conventional inner wall made of a stainless steel or other similar
metal. The same is the case with the use of other ceramic
materials, e.g. an Si-based ceramic material.
[0088] From the purge air inlet pipe 40, air for purging is
introduced into the space 36 between the outer vessel 34 and the
inner wall 35 at a pressure slightly higher than the pressure in
the combustion chamber 30. The air blows off into the combustion
chamber 30 through the inner wall 35 and also through minute gaps
at the ends of the inner wall 35 and mixes with the combustion gas
and the waste gas before being discharged to the outside from the
discharge part 52. Thus, hazardous and corrosive gases in the
combustion chamber 30 can be prevented from leaking to the outside
from the outer vessel 34.
[0089] Further, by forming the inner wall 35 of the combustion
chamber 30 from a ceramic material as stated above, the occurrence
of a catalytic action is prevented to accomplish low-NOx
combustion. If the equivalence ratio of the auxiliary burning gas
is reduced, even lower NOx combustion can be realized.
[0090] The following is a result of comparison between the amount
of NOx generated in a combustor using an inner wall made of a
ceramic material and that generated in a combustor using an inner
wall made of a stainless steel. The two combustors were under the
same conditions in terms of the type and so forth.
[0091] Combustion temperature: 1300.degree. C. or more
[0092] Gas to be treated: N.sub.2 gas
[0093] Concentration of NOx in exhaust gas
[0094] Inner wall made of ceramic material:
[0095] 25 ppm
[0096] Inner wall made of stainless steel:
[0097] several 100 to several 1000 ppm
[0098] FIGS. 3 and 4 are diagrams showing another structural
example of the burner part of the waste gas treatment system
according to the present invention. FIG. 3 is a vertical sectional
view, and FIG. 4 is a diagram as seen in the direction of the arrow
A in FIG. 3. In the figures, portions denoted by the same reference
symbols as those in FIGS. 1 and 2 are the same or corresponding
portions. The same shall apply to other drawings. The burner part
10 in this example has a cooling jacket 21 provided at an outer
peripheral portion of the cylindrical member 11 adjacent to the
auxiliary burning gas chamber 20. The cooling jacket 21 is supplied
with a cooling medium. Supplying a cooling medium to the cooling
jacket 21 allows the cooling jacket 21 to cool the cylindrical
member 11 heated by flames formed at the opening. As the cooling
medium, any medium having a temperature difference may be used.
That is, a liquid, e.g. water, or a gas, e.g. air, is used.
[0099] Pilot burners 39 are provided on the top (the top plate of
the burner part 10) of the cylindrical member 11 at a predetermined
angle of tilt. The reason for this is that an auxiliary burning gas
(flames) injected from the auxiliary burning gas nozzles 16 becomes
short with respect to the radial direction. Therefore, it is
preferable to provide the pilot burners at a predetermined angle of
tilt.
[0100] In the burner part 10 of the combustor shown in FIG. 1, the
temperature in the cylindrical member 11 rises to 400.degree. C.
However, in the case of a water-cooled system in particular, the
temperature in the burner part 10 is reduced to 70.degree. C.
Accordingly, there is no danger that the auxiliary burning gas held
in the auxiliary burning gas chamber 20 may ignite and explode.
However, because the above-described secondary air nozzles are not
provided, the lack of air is compensated for by increasing the
amount of primary air from the air nozzles 15 or by increasing the
amount of O.sub.2 to be premixed. It should be noted that in this
example the air nozzles 15 are provided to face obliquely downward
to form swirling air flows in an obliquely downward direction.
However, the air nozzles 15 may be provided horizontally, as shown
in FIG. 1, so as to form swirling air flows horizontally, as a
matter of course.
[0101] By forming the burner part 10 in a cooling structure as
stated above, the temperature of the cylindrical member 11 is
reduced, but the capacity of treating C.sub.2F.sub.6, which is a
hardly decomposable gas, is reduced from 80% to 41% (the global
warming coefficient of this gas is said to be 10,000 times as large
as that of CO.sub.2; it is demanded from the viewpoint of global
warming control that C.sub.2F.sub.6 be decomposed 100%). This is
considered due to the fact that the temperature of the burner part
10 is reduced, and this causes a reduction in the temperature of
flames. The following is a description of the arrangement of a
burner part capable of effectively cooling a fuel gas inlet for
introducing an auxiliary burning gas to the auxiliary burning gas
nozzles 16, which may explode when heated to high temperature.
[0102] FIGS. 5 and 6 are diagrams showing another structural
example of the burner part of the waste gas treatment system
according to the present invention. FIG. 5 is a vertical sectional
view, and FIG. 6 is a diagram as seen in the direction of the arrow
D in FIG. 5. This burner part 10 has a cylindrical member 11. An
air chamber 22 is provided around the outer periphery of an upper
part of the cylindrical member 11. Further, a cooling jacket 24, an
auxiliary burning gas chamber 23 and another cooling jacket 24 are
concentrically provided around the outer periphery of a lower part
of the cylindrical member 11. The inner peripheral wall of the
cylindrical member 11 is provided with air nozzles 15 communicating
with the air chamber 22. The bottom of the auxiliary burning gas
chamber 23 is provided with auxiliary burning gas nozzles 16
communicating with the auxiliary burning gas chamber 23.
[0103] The auxiliary burning gas from the auxiliary burning gas
nozzles 16 is injected toward the center below the opening of the
cylindrical member 11 or obliquely downward so as to form swirling
flows as shown by the arrows B. The air injected from the air
nozzles 15 forms swirling flows swirling within the cylindrical
member 11 as shown by the arrows C.
[0104] In the burner part 10 having the above-described
arrangement, gas G1 to be treated, which is introduced into the
cylindrical member 11, is mixed with the swirling air flows from
the air nozzles 15 and further mixed with the auxiliary burning gas
injected from the auxiliary burning gas nozzles 16 toward the lower
side of the burner part 10. Upon ignition, flames are formed to
extend toward the lower side of the opening of the cylindrical
member 11. At this time, the auxiliary burning gas chamber 23 is
cooled from both sides thereof by the cooling jackets 24.
Accordingly, the temperature is held at a low level. In addition,
because flames are formed below the cylindrical member 11, the
reduction in temperature of the cylindrical member 11 does not
exert a significant influence upon the flames.
[0105] FIGS. 7 and 8 are diagrams showing another structural
example of the burner part of the waste gas treatment system
according to the present invention. FIG. 7 is a vertical sectional
view, and FIG. 8 is a diagram as seen in the direction of the arrow
E. This burner part 10 differs from the burner part 10 shown in
FIGS. 5 and 6 in that auxiliary burning gas chambers 23 are
provided in a cooling jacket 24 provided around the outer periphery
of a cylindrical member 11, and the auxiliary burning gas chambers
23 are surrounded with a cooling medium. In addition, the bottom of
each auxiliary burning gas chamber 23 is provided with auxiliary
burning gas nozzles 16 communicating with the auxiliary burning gas
chamber 23.
[0106] This burner part 10 is the same as the burner part 10 shown
in FIGS. 5 and 6 in that the auxiliary burning gas from the
auxiliary burning gas nozzles 16 is injected toward the center
below the opening of the cylindrical member 11 or obliquely
downward so as to form swirling flows as shown by the arrows B, and
that the air injected from the air nozzles 15 forms swirling flows
swirling within the cylindrical member 11 as shown by the arrows
C.
[0107] In the burner part 10 having the above-described
arrangement, waste gas G1 to be treated, which is introduced into
the cylindrical member 11, is mixed with the swirling air flows
from the air nozzles and further mixed with the auxiliary burning
gas injected from the auxiliary burning gas nozzles 16 toward the
lower side of the burner part 10. Upon ignition, flames are formed
to extend toward the lower side of the opening of the cylindrical
member 11. At this time, because the auxiliary burning gas chambers
23 are surrounded with the cooling medium in the cooling jacket 24,
the auxiliary burning gas chambers 23 are cooled, and the
temperature is held at a low level. In addition, because flames are
formed below the cylindrical member 11, the reduction in
temperature of the cylindrical member 11 does not exert a
significant influence upon the flames as in the case of the burner
part 10 shown in FIGS. 5 and 6.
[0108] FIGS. 9 and 10 are diagrams showing another structural
example of the burner part of the waste gas treatment system
according to the present invention. FIG. 9 is a vertical sectional
view, and FIG. 10 is a diagram as seen in the direction of the
arrow F. This burner part 10 differs from the burner part 10 shown
in FIGS. 5 and 6 in that cylindrical auxiliary burning gas chambers
25 are disposed in a cooling jacket 24 formed around the outer
periphery of a cylindrical member 11. Auxiliary burning gas nozzles
16 are provided at the distal end of each cylindrical auxiliary
burning gas chamber 25. The cylindrical auxiliary burning gas
chambers 25 are disposed to extend through the cooling jacket 24
obliquely so that the auxiliary burning gas nozzles 16 are at the
lower end of each auxiliary burning gas chamber 25.
[0109] This burner part 10 is approximately the same as the burner
part 10 shown in FIGS. 5 and 6 in that the auxiliary burning gas
from the auxiliary burning gas nozzles 16 is injected toward the
center below the opening of the cylindrical member 11 or obliquely
downward so as to form swirling flows as shown by the arrows B, and
that the air injected from the air nozzles 15 forms swirling flows
swirling within the cylindrical member 11 as shown by the arrows
C.
[0110] In the burner part having the above-described arrangement,
waste gas G1 to be treated, which is introduced into the
cylindrical member 11, is mixed with the swirling air flows from
the air nozzles 15 and further mixed with the fuel gas injected
from the auxiliary burning gas nozzles 16 toward the lower side of
the burner part 10. Upon ignition, flames are formed to extend
toward the lower side of the opening of the cylindrical member 11.
At this time, because the auxiliary burning gas chambers 25 are
surrounded with the cooling medium in the cooling jacket 24, the
auxiliary burning gas chambers 25 are cooled, and the temperature
is held at a low level. In addition, because flames are formed
below the cylindrical member 11, the reduction in temperature of
the cylindrical member 11 does not exert a significant influence
upon the flames as in the case of the burner part 10 shown in FIGS.
5 and 6.
[0111] FIGS. 11 and 12 are diagrams showing another structural
example of the burner part of the waste gas treatment system
according to the present invention. FIG. 11 is a vertical sectional
view, and FIG. 12 is a diagram showing the external appearance of a
cooling jacket 26. This burner part 10 differs from the burner part
10 shown in FIGS. 5 and 6 in that cooling jackets 26 are provided
on the outer periphery of a lower part of the cylindrical member
11, and a cylindrical auxiliary burning gas chamber 27 is disposed
in each cooling jacket 26. Auxiliary burning gas nozzles 16 are
provided at the distal end of the cylindrical auxiliary burning gas
chamber 27 so as to extend obliquely toward the lower side of the
opening of the cylindrical member 11 and at a predetermined angle
to the tangential direction to the inner peripheral surface.
[0112] The auxiliary burning gas from the auxiliary burning gas
nozzles 16 is injected toward the center below the opening of the
cylindrical member 11 or obliquely downward so as to form swirling
flows as shown by the arrows B. The air injected from the air
nozzles 15 swirls within the cylindrical member 11, as shown by the
arrows C, as in the case of the burner part 10 shown in FIGS. 5 and
6.
[0113] In the burner part 10 having the above-described
arrangement, the gas to be treated, which is introduced into the
cylindrical member 11, is mixed with the swirling air flows from
the air nozzles 15 and further mixed with the auxiliary burning gas
injected from the auxiliary burning gas nozzles 16 toward the lower
side of the burner part 10. Upon ignition, flames are formed to
extend toward the lower side of the opening of the cylindrical
member 11. At this time, because the auxiliary burning gas chambers
27 are surrounded with the cooling medium in the cooling jackets
26, the auxiliary burning gas chambers 27 are cooled, and the
temperature is held at a low level. In addition, because flames are
formed below the cylindrical member 11, the reduction in
temperature of the cylindrical member 11 does not exert a
significant influence upon the flames as in the case of the burner
part 10 shown in FIGS. 5 and 6.
[0114] There are gases that give rise to a problem when made
harmless by heat decomposition in a combustor, such as waste gases
containing SiH.sub.4 and so forth. That is, when such a waste gas
is subjected to heat decomposition in a combustor to make it
harmless, dust such as SiO.sub.2 is generated and adheres to the
inner wall of the cylindrical member 11 in the burner part 10 and
the inner wall of the combustion chamber 30 and also to the inner
wall of piping subsequent to the combustion chamber, causing the
exhaust pressure loss to increase. Therefore, the waste gas
combustor of the waste gas treatment system according to the
present invention is provided with a dust remover for removing dust
from the inner wall thereof.
[0115] FIG. 13 is a diagram showing a structural example of a dust
remover. As illustrated in the figure, the dust remover has a
scraping plate 56 secured to the distal end of a shaft 57
vertically moving between the burner part 10 and the combustion
chamber 30. By vertically moving the scraping plate 56, dust
attached to the inner wall surfaces of the burner part 10 and the
combustion chamber 30 is scraped off. As shown in FIGS. 14(A) and
(B), the scraping plate 56 is formed with circular holes 56a or
sectorial holes 56b, which are larger than the opening of each
waste gas inlet pipe 14. Thus, when the scraping plate 56 is raised
to the uppermost, withdrawn position (the solid-line position in
FIG. 13), the holes 56a correspond to the respective openings of
the waste gas inlet pipes 14 so that the scraping plate 56 will not
interfere with the flow of waste gas flowing into the burner part
10 (into the cylindrical member 11) from the waste gas inlet pipes
14. In addition, when the scraping plate 56 is raised to the
withdrawn position, it will not interfere with the swirling flows
of air and auxiliary burning gas blowing off from the air nozzles
15 and the auxiliary burning gas nozzles 16.
[0116] A cooling receiver 44 is provided at the lower end of the
combustion chamber 30 to cool the waste gas burned in the
combustion chamber 30 and to receive dust scraped off with the
scraping plate 56. A shut-off valve 45 is installed at the lower
end of the cooling receiver 44, and a dust tank 47 is secured to
the lower end of the shut-off valve 45 through a clamp 46. The
cooling receiver 44 is provided with an exhaust pipe 54 and a drain
port 52. Further, a U trap 58 is connected to the dust tank 47
through a valve V1, and a drain pipe 59 is connected to the U trap
through a valve V2.
[0117] In the dust remover having the above-described arrangement,
when it is detected that a predetermined amount of dust is attached
to the inner wall surfaces of the burner part 10 and the combustion
chamber 30, the shaft 57 is moved vertically by a manual or
automatic operation, whereby the attached dust is scraped off and
dropped into the cooling receiver 44 with the scraping plate 56.
Dust is stored in the cooling receiver 44 while water is being
drained through the drain port 52 by opening a valve V3. When the
amount of dust stored reaches a predetermined value, the shut-off
valve 45 is opened to put the dust into the dust tank 47. Then, the
shut-off valve 45 is closed, and the valves V1 and V2 are opened to
drain waste water from the dust tank 47 through the drain pipe 59
via the U trap 58. The reason for providing the U trap 58 is that
if waste water is drained directly through the drain pipe 59,
hazardous gases are undesirably discharged simultaneously.
[0118] It should be noted that the dust scraping operation may be
performed as follows. The amount of dust attached is detected with
a detecting means (e.g. a pressure sensor for detecting the
pressure in the combustion chamber 30, a temperature sensor for
detecting the wall surface temperature of the combustion chamber
30, or a monitor for monitoring the amount of dust attached to the
inner wall surface), and when the amount of dust attached reaches a
predetermined value, the shaft 57 is automatically moved vertically
to scrape off the dust. The arrangement may also be such that a
timer is provided, and when a predetermined period of operating
time has elapsed, the shaft 57 is moved vertically to scrape off
the dust. The scraping plate 56 and so forth are made of a
corrosion-resistant and heat-resistant material, e.g. a ceramic
material.
[0119] The arrangement may be such that, although illustration
thereof is omitted, the dust tank 47 is provided with a transparent
observation port for checking the amount of dust collected in the
dust tank 47 and a dust detecting sensor, e.g. a photoelectric
sensor, for detecting that a predetermined amount of dust has been
collected, together with a water supply pipe for supplying water
into the dust tank 47. When a predetermined amount of dust has been
collected in the dust tank 47, the shut-off valve 45 is closed, and
the valves V1 and V2 are opened to supply water into the dust tank
47 from the above-described water supply pipe so as to wash away
the dust, thereby carrying away the dust from the dust tank 47
through the U trap 58.
[0120] The arrangement may also be such that water and dust are
cast into the dust tank 47 from the cooling receiver 44 by opening
the shut-off valve 45 and the valves V1 and V2 without providing
the drain port 52, and water is drained through the U trap 58.
[0121] Although in the structural example in FIG. 13 the scraping
plate 56 is moved vertically between the burner part 10 and the
combustion chamber 30, it may be arranged to move vertically only
in the burner part 10 as shown in FIG. 15. Further, the withdrawn
position is not necessarily limited to the top of the burner part
10. For example, the withdrawn position may be set at the bottom of
the combustion chamber 30 by providing a driving mechanism for
vertically moving the shaft 57 at the lower side of the combustion
chamber 30 or the cooling receiver 44.
[0122] FIG. 15 is a diagram showing another structural example of
the dust remover. As illustrated in the figure, the dust remover
has a scraper installed in the burner part 10. The scraper has a
scraping plate 56 provided at the distal end of a shaft 57 as shown
in FIG. 13. By vertically moving the shaft 57, dust attached to the
inner wall is scraped off. A ring-shaped air chamber 41 is provided
on top of the combustion chamber 30. As shown in FIG. 16, the
bottom of the air chamber 41 is provided with a multiplicity of air
injection nozzles 42. Air is blown off from the air injection
nozzles 42 downwardly or obliquely downward along the wall surface
of the combustion chamber 30, thereby blowing off dust from the
inner wall surface of the combustion chamber 30. In addition, a
layer of air stream flowing downward from the upper side is formed
to prevent adhesion of dust to the inner wall surface by the layer
of air stream.
[0123] At the lower end of the combustion chamber 30, a cooling
receiver 44 and so forth are provided as in the case of FIG. 13,
although illustration thereof is omitted. It should be noted that
the vertical movement of the shaft 57 is effected by a manual or
automatic operation or every time a predetermined period of
operating time measured with a timer has elapsed as in the case of
the dust remover shown in FIG. 13.
[0124] In the above-described example, dust attached to the inner
wall of the burner part 10 is scraped off with the scraping plate
56 secured to the shaft 57 and air is blown along the inner wall
surface of the combustion chamber 30 to blow off the attached dust,
or a layer of air stream is formed to prevent adhesion of dust. It
should be noted, however, that a layer of air stream may be formed
over the inner wall surfaces of both the burner part 10 and the
combustion chamber 30 to prevent adhesion of dust.
[0125] If air is intermittently blown off from the air injection
nozzles 42, dust attached to the inner wall surface can be removed
with a minimal amount of air blown.
[0126] FIGS. 17 and 18 are diagrams showing another structural
example of the dust remover. FIG. 17 is a vertical sectional view
of a combustion chamber, and FIG. 18 is a sectional view as seen in
the direction of the arrow III-III in FIG. 17. The inner wall 35 is
formed from a porous material (e.g. a granular filter, a porous
ceramics, or a heat-resistant plate material bored with a
multiplicity of small holes). In addition, a plurality of
independent annular air chambers 36' are provided between the inner
wall 35 made of the porous material and the outer vessel 34. Each
air chamber is connected to an air source so as to be supplied with
compressed air from the air source, whereby air is uniformly blown
into the combustion chamber 30 through the pores of the inner wall
35. The air blown off in this way removes dust from the inner wall
or uniformly prevents adhesion of dust to the inner wall 35.
[0127] In the dust remover having the above-described arrangement,
air may be continuously blown off from the pores of the inner wall
35 during the operation of the waste gas treatment system. However,
depending upon the situation, the arrangement may be such that when
it is detected with the above-described detecting means that a
predetermined amount of dust has attached to the inner wall, air is
blown off to remove the attached dust. Air may be blown off every
time a predetermined period of time has elapsed.
[0128] FIG. 19 is a vertical sectional view showing a structural
example of a dust remover for removing dust from the piping inner
wall when a gas containing dust flows. As shown in the figure, the
dust remover has a scraping mechanism installed in piping 61
through which a dust-containing waste gas G3 flows. The scraping
mechanism has a main shaft 62 and two rod-shaped scraping members
63 secured to the main shaft 62 to extend in the longitudinal
direction of the main shaft 62. The dust remover has a support seal
mechanism 64 for supporting the main shaft 62 of the scraping
mechanism so that the scraping members 63 contact the inner surface
of the piping 61 or lie with a slight gap therebetween. In
addition, the support seal mechanism 64 has a sealing function. The
dust remover further has a driving mechanism 65 for continuously or
periodically oscillating (rotational reciprocating motion through a
predetermined angle) or rotating the scraping mechanism about the
main shaft 62.
[0129] The main shaft 62 and the scraping members 63 are hollow
pipes, respectively, and the hollow portions of these pipes
communicate with each other. A cleaning gas G4 supplied through a
joint 66, e.g. a rotary joint, is passed through the hollow portion
of the main shaft 62 and the hollow portions of the scraping
members 63 and blown into the piping 61 from the distal (upper)
ends of the scraping members 63. A dust receiver 67 is provided at
the lower end of the piping 61, and a water injection nozzle 69 is
provided on the inner wall surface of the dust receiver 67 to
inject water. A drain pipe 70 is provided in the bottom of the dust
receiver 67.
[0130] In the dust remover having the above-described arrangement,
gas G3 containing dust, which flows into the piping 61, is
discharged through an exhaust pipe 68, and dust adheres to the
inside of the piping 61. When the scraping mechanism is
continuously or periodically oscillated or rotated about the main
shaft 62 by the driving mechanism 65, the dust attached to the
inner wall of the piping 61 is scraped off with the scraping
members 63 and drops into the dust receiver 67. At this time, a
cleaning gas G4, e.g. air, is continuously or intermittently
injected from the distal ends of the scraping members 63. Thus, it
is possible to remove dust even in an area that cannot be reached
by the scraping members 63.
[0131] Dust removed by this method drops into the dust receiver 67
in the state of being fine particles. Therefore, injection of water
into the dust receiver 67 from the water injection nozzle 69 allows
the dust to be discharged to the outside from the drain pipe 70
without causing clogging. When the waste gas G1 is a corrosive gas,
the cleaning gas G4 is mixed with ammonia gas, whereby the inner
surface of the piping 61 is neutralized and thus the progress of
corrosion can be prevented.
[0132] FIG. 20 is a diagram showing a structural example of the
dust remover arranged as shown in FIG. 19 in a case where it is
provided in a waste gas combustor of a waste gas treatment system.
As illustrated in the figure, the dust remover includes a scraping
mechanism provided in a combustion chamber 30 into which waste gas
G1 from semiconductor manufacturing equipment flows. The scraping
mechanism has a main shaft 72 and two rod-shaped scraping members
73 secured to the main shaft 72 to extend in the longitudinal
direction of the main shaft 72. A support seal mechanism 74
supports the main shaft 72 of the scraping mechanism so that the
scraping members 73 move in the inner peripheral direction in
contact with the inner surface of the combustion chamber 30 or with
a slight gap therebetween. The support seal mechanism 74 further
has a sealing function. The dust remover further includes a driving
mechanism 75 for continuously or periodically oscillating or
rotating the scraping mechanism about the main shaft 72.
[0133] A cleaning gas G4 supplied through a joint 76, e.g. a rotary
joint, is passed through the hollow portion of the main shaft 72
and the hollow portions of the scraping members 73 and injected
from the upper ends of the scraping members 73 into piping 71
constituting the combustion chamber 30. Burners 81 are provided in
an upper part of the inner wall surface of the combustion chamber
30 that constitutes a burner part 10. A cooling receiver 77 is
provided at the lower end of the combustion chamber 30. An exhaust
port 78 is provided in a side portion of the cooling receiver 77.
The upper surface of the inner wall of the cooling receiver 77 is
provided with water injection nozzles 79 for injecting water. In
addition, a drain port 80 is provided in a lower end portion of the
cooling receiver 77 to communicate with the inside of the cooling
receiver 77.
[0134] Waste gas G1 from semiconductor manufacturing equipment or
the like is heated with flames formed by the burners 81. As a
result, the waste gas G1 is made harmless and becomes a
high-temperature waste gas containing dust at a high density.
Because the temperature of flames 82 formed by the burners 81
reaches about 2000.degree. C., it is considered that most
substances are melted upon contacting the flames 82 directly.
Because the inner wall surface temperature of the combustion
chamber 30 immediately downstream the burners 81 is lower than
2000.degree. C., dust is likely to adhere to the inner wall surface
of the combustion chamber 30. This may cause blockage. The same is
the case with the vicinities of the burners 81.
[0135] By rotating or oscillating the scraping mechanism about the
main shaft 72 by the driving mechanism 75 under the above-described
environmental conditions, dust attached to the inner wall surface
of the combustion chamber 30 can be scraped off directly with the
scraping members 73. Thus, blockage due to adhesion of dust can be
prevented. Even in an area where the scraping members 73 cannot be
inserted because the flames 82 would touch them, dust attached to
the inner wall surface can be removed with the cleaning gas G4
supplied through the joint 76, e.g. a rotary joint, and blown off
from the upper ends of the scraping members.
[0136] The waste gas G1 heated and burned with the flames 82 flows
into the cooling receiver 77, in which it is cooled with water
injected from the water injection nozzles 79 and then discharged
from the exhaust port 78. In addition, water containing dust
scraped off is discharged from the drain port 80.
[0137] FIG. 21 is a diagram showing another structural example of
the main shaft 72 and the scraping members 73 of the
above-described scraping mechanism. In this scraping mechanism, as
illustrated in the figure, a multiplicity of small holes 73a are
provided in the outer peripheral surface of each scraping member 73
so as to communicate with the inner hollow portion. When a cleaning
gas G4 is supplied via the joint 76, e.g. a rotary joint, shown in
FIG. 14, and through the hollow portions of the main shaft 72 and
the scraping members 73, the cleaning gas G4 is blown against the
inner wall of the combustion chamber 30 through the holes 73a. The
cleaning gas G4 is also blown off from the upper ends of the
scraping members 73. Thus, dust adhering to an area of gap d
between each scraping member 73 and the inner wall surface of the
combustion chamber 30 can also be removed by blow-off.
[0138] FIG. 22 is a diagram showing another structural example of
the scraping mechanism comprising the main shaft 72 and the
scraping members 73. In this scraping mechanism, as illustrated in
the figure, a multiplicity of small holes 73a and 72a are provided
over the whole surface of each of the scraping members 73 and the
main shaft 72 so as to communicate with the corresponding hollow
portions. With this arrangement, dust can be removed by blow-off
from the area of gap between each scraping member 73 and the inner
wall surface of the combustion chamber 30 by introducing a cleaning
gas G4 into the hollow portions of the main shaft 72 and the
scraping members 73. In addition, dust attached to the main shaft
72 and the scraping members 73 themselves can be removed by
blow-off.
[0139] Although in the embodiments shown in FIGS. 21 and 22 a
multiplicity of 72a and 73a are provided in the surfaces of the
main shaft 72 and the scraping members 73 so as to communicate with
the hollow portions thereof, it should be noted that slits
communicating with the hollow portions may be provided in place of
the holes 72a and 73a. The arrangement of the scraping mechanism
shown in FIGS. 15 and 16 is also applicable to the scraping
mechanism comprising the main shaft 62 and the scraping members 63,
which is shown in FIG. 19, as a matter of course.
[0140] Further, the number of scraping members 73 of the scraping
mechanism is not necessarily limited to two. As shown in FIG. 23,
three scraping members 73 may be provided on the main shaft 72.
Further, the number of scraping members 73 may exceed three. In the
case of FIG. 19 also, three or more scraping members may be
provided on the main shaft 62 to constitute the scraping
mechanism.
[0141] By increasing the number of scraping members 73 to three or
more, the number of times of dust scraping per revolution of the
scraping mechanism is increased. Thus, it is possible to cope with
circumstances when the dust density is high. In a case where the
scraping mechanism performs rotational reciprocating motion through
a predetermined angle, dust in the whole area can be scraped off
even if the oscillating angle of the scraping mechanism is reduced.
However, if the number of scraping members 73 is increased
extremely, dust adhering to the scraping mechanism itself may block
the combustion chamber 30.
[0142] It should be noted that the scraping mechanisms as shown in
FIGS. 20 to 23 may be installed in the waste gas treatment system
shown in FIG. 1 to remove dust from the inner walls of the burner
part 10 and the combustion chamber 30, although illustration of the
arrangement is omitted.
[0143] In the dust removers arranged as shown in FIGS. 19 to 23,
when the gas G1 or G3 flowing into the piping 61, the flame
stabilizing part 10 and the combustion chamber 30 contains not only
dust but also a component that may corrode the inner walls of the
piping 61, the flame stabilizing part 10 and the combustion chamber
30 by a corrosive action or the like, a gas having the property of
neutralizing the corrosive action is introduced into the cleaning
gas G4 (for example, with respect to an acid gas flowing in, an
alkaline gas, e.g. ammonia, is introduced). By doing so, the
corrosion of the piping can be suppressed in an area covered with
the cleaning gas G4.
[0144] FIGS. 24 and 25 are diagrams showing another structural
example of the burner part of the waste gas treatment system
according to the present invention. FIG. 24 is a vertical sectional
view, and FIG. 25 is a diagram as seen in the direction of the
arrow L in FIG. 24. In the burner part 10, the height H of the
flame stabilizing portion 18 is reduced and the spacing I between
the air nozzles 15 and the auxiliary burning gas nozzles 16 is also
reduced in comparison to the burner part 10 shown in FIGS. 3 and 4,
by way of example. In other words, the air outlets of the air
nozzles 15 are brought as close to the auxiliary burning gas
outlets of the auxiliary burning gas nozzles 16 as possible. In
addition, the spacing J between the center line of each air nozzle
15 and the tangent to the inner wall surface of the cylindrical
member 11 is reduced so that air blown off from the air nozzles 15
comes as close to the tangent to the inner wall surface of the
cylindrical member 11 as possible.
[0145] By reducing the height H of the flame stabilizing portion 18
and reducing the spacing I between the air nozzles 15 and the
auxiliary burning gas nozzles 16 as stated above, the stagnation of
flow in the valley between the air outlets and the auxiliary
burning gas outlets is eliminated, and dust attached or going to
adhere to the inner wall surface of the flame stabilizing portion
18 is blown off by the air flow, thereby preventing adhesion of
dust to the inner wall surface as much as possible.
[0146] Further, because the air blown off from the swirling nozzles
15 is close to the tangent to the inner wall surface of the
cylindrical member 11, the stagnation of flow near the inner wall
surface of the cylindrical member 11 is prevented, and it becomes
unlikely that dust will adhere to the inner wall surface.
[0147] Furthermore, the air nozzles 15 are provided so that the
flows of air blown off from the air nozzles 15 are inclined toward
the downstream side from the horizontal. When the angle .theta.1 of
inclination of the air nozzles 15 with respect to a horizontal
plane is set at about 30.degree., the dust adhesion preventing
effect is significant in the vicinities of the auxiliary burning
gas nozzles 16. Further, a multiplicity of air nozzles 15 are
provided so that the nozzle outlets are open equally in the
circumferential direction of the inner wall surface of the
cylindrical member 11, whereby the flows of air immediately after
blow-off and at high flow velocity, which have high blow-off
effect, are allowed to extend over the whole inner wall
surface.
[0148] The horizontal air injection angle .theta.2 of the air
nozzles 15 is set to .theta.2=360.degree./n, where n is the number
of air nozzles 15 disposed in the circumferential direction, which
is an integer of 3 or higher. Regarding the number n of air
nozzles, when it was 4, 8, 12, 16 and 24, favorable results were
obtained.
[0149] The ratio of the height H of the flame stabilizing portion
18 to the inner diameter K (H/K) is set at 15 mm/80 mm, whereas it
has heretofore been 50 mm/80 mm. The spacing I between the lower
air nozzle 15 and the upper auxiliary burning gas nozzle 16 is
herein set at 16 mm, whereas it has heretofore been 26 mm. The
spacing I is constant regardless of variations in the inner
diameter K. The spacing J between the center line of each air
nozzle 15 and the tangent to the inner wall surface, which is
parallel to the center line, is herein set at 5 mm, whereas it has
heretofore been 15 mm.
[0150] FIG. 26 is a vertical sectional view showing another
structural example of the burner part of the waste gas treatment
system according to the present invention. In this burner part 10,
as illustrated in the figure, the inner diameter of the opening 14a
of each waste gas inlet pipe 14 gradually increases downwardly, and
the inner diameter of the cylindrical member 11 also gradually
increases downwardly. Thus, there is no angular portion such as a
right-angled portion at the openings 14a of the waste gas inlet
pipes 14 and inside the cylindrical member 11. In addition, an
inverted frusto-conical projection 11a may be provided between the
openings 14a of the waste gas inlet pipes 14.
[0151] In general, dust in the burner part 10 is likely to adhere
to angular portions and portions where air or waste gas stagnates.
In this example, there is no angular portion such as a right-angled
portion at the openings 14a of the waste gas inlet pipes 14 and
inside the cylindrical member 11 as stated above. In addition,
there is no area where waste gas may stagnate between the waste gas
inlet pipes 14. Therefore, it becomes unlikely that dust will
adhere to the inner wall surface.
[0152] Industrial Applicability
[0153] As has been stated above, according to the invention as set
forth in claims 1 to 3, the combustion chamber is formed from an
inner wall made of a fiber-reinforced ceramic material.
Accordingly, the wear of the inner wall due to heat and corrosion
is minimized, and thermal stress cracking is also reduced.
Consequently, the lifetime of the system increases, and the cost of
equipment and the availability factor can be improved. In addition,
because the inner wall exhibits no catalytic effect, the formation
of thermal NOx is suppressed, and it is possible to achieve
environmental preservation and to simplify the treatment equipment.
Accordingly, it is possible to provide a compact and low-cost waste
gas treatment system as a whole.
[0154] In addition, according to the invention as set forth in
claim 3, the space between the inner wall and the outer vessel is
maintained under a purge gas atmosphere of higher pressure than the
pressure in the combustion chamber. Therefore, hazardous gases in
the combustion chamber can be prevented from leaking to the
outside.
[0155] In addition, according to the invention as set forth in
claims 4 to 9, a cooling means is provided to cool an auxiliary
burning gas inlet part for introducing an auxiliary burning gas
into the auxiliary burning gas nozzle in the burner part.
Accordingly, even when the auxiliary burning gas inlet part is
heated by flames, the rise in temperature is suppressed below the
ignition point of the auxiliary burning gas. Therefore, there is no
danger that the auxiliary burning gas may explode.
[0156] In addition, according to the invention as set forth in
claims 6 to 9, flames cannot come in direct contact with the
cooling jacket. Therefore, the amount of heat of flames that is
carried away by the cooling medium is reduced, and an increased
amount of heat can be used for the waste gas treatment.
[0157] In addition, according to the invention as set forth in
claims 10 to 13, a dust removing means is provided to remove dust
from the inner wall of the burner part and/or the inner wall of the
combustion chamber or to prevent adhesion of dust thereto.
Therefore, it is possible to operate the waste gas treatment system
for a long period of time without blocking the burner part and/or
the combustion chamber with dust.
[0158] In addition, according to the invention as set forth in
claim 14, dust attached to the inside of piping is removed by
continuously or periodically oscillating or rotating a scraping
mechanism installed in the piping. Consequently, the waste gas is
allowed to flow through the piping with a minimal pressure
loss.
[0159] In addition, according to the invention as set forth in
claims 15 to 18, the scraping member and the main shaft are formed
from hollow pipes, respectively, and a cleaning gas is supplied
from the outside of the piping through the hollow portions of the
main shaft and the scraping member and blown off from the distal
end of the scraping member or from a multiplicity of holes or slits
in the surface thereof. Consequently, it is possible to remove dust
from an area in the piping that cannot be reached by the scraping
member. In addition, it becomes possible to remove dust attached to
the scraping mechanism itself. In a case where a high-temperature
gas flows through the piping, the durability of the system itself
is improved by the cooling effect of the cleaning gas.
[0160] In addition, according to the invention as set forth in
claim 17, a neutralizing gas for neutralizing the gas flowing
through the piping is used as a cleaning gas. Therefore, in a case
where a high-temperature, corrosive gas flows through the piping,
it is possible to expect not only the cooling effect but also the
piping corrosion preventing effect.
[0161] In addition, according to the invention as set forth in
claims 19 to 21, the air nozzle is arranged to blow a swirling air
flow downward against combustion flames formed downward below the
opening. Accordingly, it is possible to provide a waste gas
treatment system in which dust is unlikely to adhere to the inner
wall of the nozzle part.
[0162] In addition, according to the invention as set forth in
claim 22, the inner diameter of the waste gas inlet and the inner
diameter of the cylindrical member gradually increase toward the
combustion chamber. Consequently, there is no angular portion such
as a right-angled portion in the burner part. Accordingly, it is
possible to provide a waste gas treatment system in which dust is
unlikely to adhere to the inner wall of the nozzle part.
[0163] In addition, according to the invention as set forth in
claim 23, it is possible to provide a waste gas treatment system
which is compact and capable of efficiently treating waste gases
containing hazardous and combustible gases or scarcely decomposable
gases.
* * * * *