EP0350032B1

EP0350032B1 - Combustion apparatus

Info

Publication number: EP0350032B1
Application number: EP89112363A
Authority: EP
Inventors: Saburo Maruko
Original assignee: Nippon Chemical Plant Consultant Co Ltd
Current assignee: Nippon Chemical Plant Consultant Co Ltd
Priority date: 1988-07-08
Filing date: 1989-07-06
Publication date: 1993-10-13
Anticipated expiration: 2009-07-06
Also published as: EP0350032A3; DE68909851T2; DE68909851D1; DE68924539T2; EP0493376A2; DE68924539D1; EP0350032A2; EP0493376B1; EP0493376A3

Description

The present invention relates to a combustion apparatus according to the preamble of claim 1.
The combustion gas produced in this type of combustion apparatus is preferably produced through a complete combustion so as to be free from any of pollutants such as nitrogen oxides (NO_x), unburned hydrocarbons and carbon monoxide, and to be sufficiently low in its residual oxygen content.
Heretofore, in this type of combustion apparatus, the following three combustion apparatuses have been proposed:

(1) A combustion apparatus in which: fuel is mixed with air to prepare an air/fuel mixture gas an air/fuel ratio of which is within a flammable limit range; an electric spark from an igniter plug of the apparatus initiates combustion of the mixture gas; and thereby the air/fuel mixture gas is continuously burned;
(2) A combustion apparatus disclosed in Japanese Patent Laid-Open No. 62-33213 filed by inventors of the present invention, in which combustion apparatus: fuel is mixed with a preheated air to prepare a preheated air/fuel mixture gas which reacts with catalysts to attain its catalytic combustion; and
(3) A combustion apparatus disclosed in Japanese Patent Laid-Open No. 62-116808 filed by the inventors of the present invention, in which combustion apparatus: an outer peripheral surface of a heating tube of a main combustion unit is constantly heated to temperatures of ignition points of fuels by means of an auxiliary combustion unit; and the fuels are brought into contact with the thus heated heating tube of the main combustion unit so as to be burned continuously.

Of the conventional combustion apparatuses described in the above items (1) to (3):
The combustion apparatus described in the item (1) suffers from the fact that the combustion gas is partially kept at a high temperature in order to keep the flame alight, which high temperature makes it impossible to prevent nitrogen oxides (NO_x) from occurring in the combustion gas. In this combustion apparatus, since the time taken for fuel to mix with air is very short and the time taken for the thus prepared air/fuel mixture gas to be burned is also very short, the combustion gas produced in the combustion apparatus of the item (1) suffers from pollutants such as unburned hydrocarbons and the like together with a considerable amount of residual oxygen therein;
The combustion apparatus described in the item (2) enables the air/fuel mixture gas to burst into flame at a relatively low temperature. However, when the mixture gas is burned at a temperature of more than 1300 °C, such high-temperature combustion of the mixture gas shortens the service life of the catalysts employed in the combustion apparatus, which makes it impossible to operate the combustion apparatus over an extended period of time. In addition, in this combustion apparatus, it is impossible to use sulfur-containing fuels because the sulfur has poisoning effects on the catalysts; and
The combustion apparatus described in the item (3) suffers from the fact that the auxiliary combustion unit is also constantly kept in operation together with the main combustion unit, which disturbs the operator of the apparatus in control of both units. In addition, in this combustion apparatus, it is not possible to substantially completely prevent nitrogen oxides (NO_x) from occurring in the combustion gas.
In an air/fuel mixing unit employed in this type of combustion apparatus, an oxygen-containing gas such as air is mixed with fuel at a predetermined ratio to prepare an air/fuel mixture gas which is supplied under a predetermined pressure to the combustion unit of the apparatus. The air/fuel mixing unit is provided with a venturi tube having a venturi throat portion in which a fuel discharge nozzle is provided. As a preheated air flows through the throat portion of the venturi tube of the air/fuel mixing unit, a partial vacuum is produced at the venturi throat portion. This vacuum then causes the fuel discharge nozzle to deliver a spray of fuel into the passing preheated air stream in the venturi throat portion.
In the above combustion apparatus, in case that the combustion is conducted at a temperature of from 1200 to 1400 °C, the fuel is mixed with the oxygen-containing preheated gas or air in the air/fuel mixing unit, which air has been preheated to a temperature of from 500 to 900 °C. In this case, the fuel discharge nozzle provided in the throat portion of the venturi tube is also heated to a temperature of from 500 to 900 °C together with a fuel feed pipe connected with the fuel discharge nozzle. As a result, the fuel is often pyrolyzed or thermally decomposed to precipitate carbon particles in the fuel discharge nozzle and the fuel feed pipe. The thus precipitated carbon particles often clog these nozzle and pipe.
Particularly, in case that the combustion apparatus for supplying a high-temperature combustion gas (the temperature of which is about 1400 °C) to each of a plurality of boilers connected to each other in series is provided in a front portion of each of the boilers: the combustion gas discharged from the first one of the combustion apparatuses is supplied to the first one of the boilers; the combustion gas having passed through such first boiler is then supplied to the second one of the combustion apparatuses; the combustion gas having passed through such second combustion apparatus is supplied to the second one of the boilers; and operations similar to the above are sequentially conducted through the remaining boilers and combustion apparatuses until the combustion gas passes through the last one of the boilers; whereby multistage utilization of the combustion gas is realized. In this case, the combustion gas is supplied at a temperature of about 1400 °C to each of the boilers, while discharged at a temperature of about 700 °C from each of the boilers after it passes through each of the boilers. The thus discharged combustion gas is supplied to an air/fuel mixing unit of a subsequent combustion apparatus so as to be mixed with fuel and burned to be heated again to a temperature of about 1400 °C. At this time, since the venturi tube of the air/fuel mixing unit has been heated to a considerably high temperature in a portion in the vicinity of the fuel discharge nozzle, the fuel in the nozzle is often pyrolyzed or thermally decomposed to precipitate carbon particles which disadvantageously clog the fuel discharge nozzle in the venturi tube of the air/fuel mixing unit.

SUMMARY OF THE INVENTION

The present invention is made under such circumstances.
Consequently, it is an object of the present invention to provide a combustion apparatus which may produce a combustion gas substantially completely free from any of pollutants such as nitrogen oxides (NO_x), unburned hydrocarbons, carbon monoxide and the like.
It is another object of the present invention to provide a combustion apparatus which may attain a complete combustion of a mixture gas consisting of an oxygen-containing gas or air and fuel, the mixture gas being brought into contact with a large number of high-temperature surfaces, and the combustion apparatus being provided in multistage combustion-gas utilization systems connected to each other in series so as to effectively use the combustion gas, whereby a considerable energy saving is accomplished.
It is further another object of the present invention to provide an air/fuel mixing unit for the combustion apparatus, which mixing unit is substantially free from a fear that a fuel discharge nozzle and a fuel feed pipe connected to the fuel discharge nozzle of the mixing unit are clogged with carbon particles produced through pyrolysis or thermal decomposition of the fuel supplied to the nozzle and the pipe.
According to a first embodiment of the present invention, the above objects of the present invention are accomplished by providing:
A combustion apparatus comprising:

(a) an incoming passage for flowing a combustion gas in a predetermined direction, said incoming passage being defined by heat insulating material (10) disposed in a substantially central portion of an outer casing (10a) and closed at its upstream end;
(b) an outgoing passage for flowing, in a direction counter to said predetermined direction, said combustion gas having passed through said incoming passage, said outgoing passage being open at its opposite end portions and disposed in said incoming passage so as to communicate with said incoming passage at the downstream end thereof through a space defined in the downstream end portion of the incoming passage;
(c) a mixture gas main incoming duct for supplying a mixture gas consisting of an oxygen-containing gas and fuel, said mixture gas main incoming duct being directly connected to the upstream end portion of said incoming passage through a peripheral wall thereof;
(d) an oxygen-containing gas/fuel mixing unit for mixing a preheated oxygen-containing gas with fuel at a predetermined ratio to prepare said mixture gas, said oxygen-containing gas/fuel mixing unit being connected to said mixture gas main incoming duct to supply said mixture gas to said mixture gas main incoming duct at a predetermined pressure;
(e) a combustion-gas auxiliary incoming duct for supplying another combustion gas to said incoming passage, said another combustion gas being produced by burning fuel with an oxygen-containing gas through a pilot burner, said combustion-gas auxiliary incoming duct being connected to an end portion of said incoming passage diametrically opposite from said mixture gas main incoming duct; and
(f) a combustion-gas outlet duct defined in side portions of aid outer casing (10a) and said heat-insulating material so as to be connected to a downstream side outlet portion of said outgoing passage.

According to a second embodiment of the present invention, the above objects of the present invention are accomplished by providing:
The combustion apparatus having the above construction of the first embodiment of the present invention, wherein:
a honeycomb passage member is provided in each of the outlet portions of the incoming passage and the outgoing passage.
According to a third embodiment of the present invention, the above objects of the present invention are accomplished by providing:
The combustion apparatus having the above construction of the first embodiment of the present invention, wherein:
both of the incoming passage and the outgoing passage are constructed of sleeve elements, provided that the sleeve element constituting the outgoing passage is smaller in diameter than the sleeve element constituting the incoming passage while concentrically disposed in the incoming passage.
According to a fourth embodiment of the present invention, the above objects of the present invention are accomplished by providing: The combustion apparatus having the above construction of the first embodiment of the present invention, wherein:
both of the incoming passage and the outgoing passage are constructed of sleeve elements, provided that a plurality of the sleeve elements constitute the outgoing passage, each of which sleeve elements constituting the outgoing passage is smaller in diameter than the sleeve element constituting the incoming passage while disposed in the incoming passage.
According to a fifth embodiment of the present invention, the above objects of the present invention are accomplished by providing:
The combustion apparatus having the above construction of the fourth embodiment of the present invention, wherein:
at least one baffle plate member is so disposed in the incoming passage as to extend in a direction perpendicular to a longitudinal direction of the incoming passage.
According to a sixth embodiment of the present invention, the above objects of the present invention are accomplished by providing:
The combustion apparatus having the above construction of the first embodiment of the present invention, wherein:
the oxygen-containing gas/fuel mixing unit comprises:
a venturi tube, provided with a venturi throat portion and surrounded by a heat-insulating material;
a fuel feed pipe having its fuel discharge nozzle opened into the venturi throat portion of the venturi pipe, the fuel discharge nozzle being provided in a front-end portion of the fuel feed pipe; and
a cooling unit for cooling suitable portions of the fuel discharge nozzle and the fuel feed pipe communicating with the fuel discharge nozzle.
Additional objects, embodiments and advantages of the present invention will become apparent to anyone skilled in the art from the following detailed description of the preferred embodiments of the present invention, which will be made with reference to the accompanying drawings.

Fig. 1 is a longitudinal sectional view of a first embodiment of the combustion apparatus of the present invention;
Fig. 2 is a cross-sectional view of the first embodiment of the combustion apparatus of the present invention, taken along the line 11-11 of Fig. 1;
Fig. 3 is a longitudinal sectional view of a second embodiment of the combustion apparatus of the present invention;
Fig. 4 is a cross-sectional view of the second embodiment of the combustion apparatus of the present invention, take along the line 1V-1V of Fig. 3;
Fig. 5 is a cross-sectional view of the second embodiment of the combustion apparatus of the present invention, take along the line V-V of Fig. 3;
Fig. 6 is a longitudinal sectional view of a first embodiment of the oxygen-containing gas/fuel mixing unit employing in the combustion apparatus of the present invention; and
Fig. 7 is a longitudinal sectional view of a second embodiment of the oxygen-containing gas/fuel mixing unit employing in the combustion apparatus of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of a combustion apparatus of the present invention and those of an oxygen-containing gas/fuel mixing unit employed in the combustion apparatus will be described in detail with reference to the accompanying drawings.
First of all, Figs. 1 and 2 show a first embodiment of the combustion apparatus of the present invention, in which: the reference numeral 1 denotes an outer sleeve; and 2 an inner sleeve concentrically disposed in the outer sleeve 1. Both of the outer sleeve 1 and the inner sleeve 2 are made of ceramic materials. As shown in Fig. 1, an annular incoming passage 3 of an oxygen-containing gas/fuel mixture gas is defined between an inner peripheral surface of the outer sleeve 1 and an outer peripheral surface of the inner sleeve 2, while the interior portion of the inner sleeve 2 forms an outgoing passage 4 of a combustion gas. The incoming passage 3 is closed at its end portion located in an upstream side of a stream of the mixture gas, while opened at its the other end portion into a space located in a downstream side of the stream of the mixture gas, the space being formed in an end portion of the outer sleeve 1 so as to communicate with an inlet opening of the outgoing passage 4. Consequently, the incoming passage 3 communicates with the outgoing passage 4 through such space. A main incoming port 5 opens into a peripheral wall of the incoming passage 3 at a position in the vicinity of its end portion located in the upstream side of the mixture gas. On the other hand, an auxiliary incoming port 6 also opens into the peripheral wall of the incoming passage 3 at a position circumferentially spaced apart from that of the main incoming opening 5. An outlet opening of the outgoing passage 4 opens into a combustion-gas output port 7. In the downstream side end portion of the incoming passage 3 is fixedly mounted an annular honeycomb passage member 8 made of ceramic materials. On the other hand, in the outlet opening of the outgoing passage 4 is fixedly mounted a plug-shaped honeycomb passage member 9 made of ceramic materials. These honeycomb passage members 8, 9 increase the number of passage surfaces brought into contact with the combustion gas.
As shown in Fig. 1, the outer sleeve 1 is fixedly mounted in an outer casing 10a through a heat-insulating material 10.
An oxygen-containing gas/fuel mixing unit 11 is connected to the main incoming port 5 in an upstream side of the incoming passage 3. On the other hand, a pilot burner 12 is connected to the auxiliary incoming port 6 in the upstream side of the incoming passage 3. To the mixing unit 11 are connected: a preheated oxygen-containing gas inlet pipe or preheated air inlet pipe 13; and a fuel feed pipe 14. Fuel supplied from the fuel feed pipe 14 is mixed with a preheated oxygen-containing gas (hereinafter simply referred as the preheated air) supplied from the preheated air inlet pipe 13 at a predetermined ratio in an air/fuel mixing portion 15 of the mixing unit 11 to prepare an air/fuel mixture gas which is supplied to an upstream side of the incoming passage 3. To the pilot burner 12 are connected: an air inlet pipe 16; and a fuel feed pipe 17. A combustion gas issued from the pilot burner 12 is supplied to an upstream side of the incoming passage 3 through the auxiliary incoming port 6.
In operation of the first embodiment of the combustion apparatus of the present invention having the above construction, first of all, the pilot burner 12 is operated to issue the combustion gas to the upstream side of the incoming passage 3 so that the combustion gas heats both the outer sleeve 1 and the inner sleeve 2 in the upstream side of the incoming passage 3. After both the outer sleeve 1 and the inner sleeve 1 are heated to predetermined temperatures of more than about 900 °C in the upstream side of the incoming passage 3, the mixing unit 11 is operated to issue an oxygen-containing gas/fuel mixture gas, i.e., an air/fuel mixture gas to the upstream side of the incoming passage 3 through the main incoming port 5. At this time, operation of the pilot burner 12 is immediately, or gradually stopped so as to cooperate with that of the mixing unit 12 for a while.
Under such circumstances, the thus issued air/fuel mixture gas enters the incoming passage 3 through the main incoming port 5, and is brought into contact with both of the inner peripheral surface of the outer sleeve 1 and the outer peripheral surface of the inner sleeve 2, which peripheral surfaces have been heated to sufficiently high temperatures, so that the mixture gas bursts into flame to produce a combustion gas. The thus produce combustion gas passes through the incoming passage 3 to enter the outgoing passage 4, and is then discharged from the combustion-gas outlet port 7. Consequently, the combustion gas heats the outer and inner peripheral surface of the incoming passage 3 and the inner peripheral surface of the outgoing passage 4 sequentially, to make it possible to attain a complete combustion of the mixture gas which is issued from the mixing unit 11 to the incoming passage 3. As described above, the fuel supplied to the mixing unit 11 is so mixed with the preheated air in the mixing unit 11 as to constantly keep the combustion gas at a predetermined temperature of from 1200 to 1400 °C.
In the above operation, the combustion initiated at the upstream side of the incoming passage 3 propagates to the downstream side of the incoming passage 3, and further propagates to the outlet opening of the outgoing passage 4 therethrough. Consequently, the inner sleeve 2 interposed between the incoming passage 3 and the outgoing passage 4 is heated by the combustion gas in its inner and outer peripheral surface. The honeycomb passage members 8 and 9, which are mounted in the downstream side end portion of the incoming passage 3 and the outlet opening of the outgoing passage 9 respectively, further ensure the mixture gas a complete combustion. In addition, in case that the inner peripheral surface of the outer sleeve 1 is coated with a suitable material excellent in infrared-absorption properties, it is possible to further increase the temperature of the inner peripheral surface of the outer sleeve 1 because infrared radiation from the outer peripheral surface of the inner sleeve 2 is effectively received by the inner peripheral surface of the outer sleeve 1 so as to increase the temperature of the inner peripheral surface of the outer sleeve 1. The thus coated inner surface of the outer sleeve 1 may serve as an effective heating surface for enhancing the combustion of the mixture gas.
Figs. 3 to 5 show a second embodiment of the combustion apparatus of the present invention. In the second embodiment of the present invention, the components which are the same as ones in the first embodiment of the present invention shown in Figs. 1 and 2 have been given the same reference numerals, and therefore are not further explained hereinbelow.
As shown in Fig. 3, in the second embodiment of the combustion apparatus of the present invention, a plurality of inner sleeves 22 made of ceramic materials are fixedly mounted in the outer sleeve 21 made of ceramic materials so that the incoming passage 23 is defined between the inner peripheral surface of the outer sleeve 21 and the outer peripheral surfaces of the inner sleeves 22. On the other hand, the interior portion of each of the inner sleeves 22 forms the outgoing passage 24. An upstream side end of the incoming passage 23 is closed with a supporting wall member 25 which supports each of the outlet opening portions of the inner sleeves 22. Honeycomb passage members 26 and 27 are fixedly mounted in the downstream side portion of the incoming passage 23 and the outlet opening portions of the outgoing passages 24, respectively. In addition, in the incoming passage 23, there are also fixedly mounted at least one baffle plate member 28 the number of which is three in the second embodiment of the combustion apparatus of the present invention, as shown in Fig. 3.
The second embodiment of the combustion apparatus of the present invention shown in Figs. 3 to 5 is the substantially same in operation as the first embodiment of the combustion apparatus of the present invention shown in Figs. 1 and 2. The second embodiment of the combustion apparatus of the present invention is advantageous in producing a large quantity of the combustion gas.
Namely, in operation of the second embodiment of the combustion apparatus of the present invention shown in Figs. 3 to 5, first of all, walls of the incoming passage 23 are heated to predetermined temperatures of about 900 °C by means of the pilot burner 12 in the upstream side of the incoming passage 23. After that, the air/fuel mixture gas produced in the mixing unit 11 is supplied to the interior of the incoming passage 23 so as to burst into flame therein to produce the combustion gas. The thus produced combustion gas passes through a labyrinth constructed of the baffle plate members 28 within the incoming passage 23, and flows to the downstream side of the incoming passage 23. Consequently, when the mixture gas passes through the incoming passage 23, it is sufficiently agitated so as to attain a complete combustion thereof. Then, the combustion gas reached the downstream side of the incoming passage 23 enters the honeycomb passage members 26. The combustion gas having passed through the honeycomb passage members 26 enters the outgoing passages 24 in which the combustion gas is brought into contact with the inner peripheral walls of the inner sleeves 22 so as to be further heated to ensure the complete combustion of the mixture gas. After that, the combustion gas enters the honeycomb passage members 27, and passes therethrough to flow into the combustion-gas outlet port 7 from which the combustion gas is discharged.
In each of the above embodiments of the combustion apparatus of the present invention, the ceramic materials constituting each of the components such as the outer sleeve 1, inner sleeve 2, 22, sleeve-like casing 31 and the honeycomb passage member 8, 9, 26, 27, 32 may be silicon carbide which is excellent in mechanical strength, heat-resisting properties and thermal shock resistance. However, it is also possible that these components are made of any other suitable ceramic materials such as zirconia-base ceramics and cordierite-base ceramics.
In addition, each of the outer sleeve 1, 21 and the sleeve-like casing 31 may be made of alumina-fiber ceramics. In this case, it is preferable to firmly coat, by a suitable applying process such as spraying and the like, the inner surfaces of the outer sleeve 1, 21 and the sleeve-like casing 31 with a paint a main component of which is a suitable oxide such as SiZrO₄, MnO₂·Cr₂O₃ and the like excellent in infrared-absorption properties.
Now, two different embodiments of the oxygen-containing gas/fuel mixing unit (hereinafter referred to as the air/fuel mixing unit) employed in the combustion apparatus of the present invention having the above construction will be described in detail with reference to Figs. 6 and 7.
In a first embodiment of the air/fuel mixing unit of the present invention shown in Fig. 6: the reference numeral 50 denotes a venturi tube comprising an inlet reducer portion 51, an outlet diffuser portion 52 and a venturi throat portion 53 sandwiched between these portions 50 and 51. A performance-control rod 54 provided with a tapered front portion is threadably engaged with a supporting member 55 so as to be axially displaceable relative to the supporting member 55 which is fixedly mounted in the venturi tube 50. A preheated-air inlet pipe 13 is connected to an air-inlet opening of the venturi tube 50 an air/fuel mixture gas outlet opening of which is connected to the combustion apparatus of the present invention.
A plurality of fuel discharge openings 56 are so provided in an inner peripheral surface of the throat portion 53 of the venturi tube 50 as to be spaced apart from each other in a circumferential direction of the of the inner peripheral surface of the throat portion 53, to which openings 56 a fuel feed pipe 14 is connected. As is clear from Fig. 6, an annular water jacket 57 is placed around the venturi throat portion 53 to keep this portion 53 cool. To the water jacket 57 are connected: a cooling-water inlet pipe 58; and a cooling-water outlet pipe 59.
As shown in Fig. 6, in this first embodiment of the air/fuel mixing unit employed in the combustion apparatus of the present invention, an incoming gas comprising the preheated air and the oxygen-containing gas such as the combustion gas is supplied from the preheated-air inlet pipe 13 to the venturi throat portion 53 in which the incoming gas is accelerated to cause the fuel discharge openings 56 to deliver the fuel in spraying manner so that the air/fuel mixture gas is produced. The thus produced air/fuel mixture gas is then supplied to the combustion apparatus of the present invention, while agitated in the subsequent outlet diffuser portion 52 of the venturi tube 50.
In the air/fuel mixing unit described above, when the fuel is sprayed into the heated incoming gas to produce the air/fuel mixture gas, a part of the thus produced mixture gas reaches a flammable limit range. In order to prevent the air/fuel mixture from burning in the venturi tube 50, the thus produced air/fuel mixture gas must be rapidly agitated in the venturi tube 50. Consequently, in the air/fuel mixing unit employed in the present invention, it is necessary to accelerate the incoming gas to a velocity of at least 100 m/second in the venturi throat portion 53 so as to make it possible to rapidly agitate the thus produced air/fuel mixture gas.
Since the performance-control rod 54 is disposed in the axially central portion of the venturi throat portion 53, an axially central passage of the incoming gas in the venturi throat portion 53 is decreased in its cross-sectional area to keep a thickness of a stream of the incoming gas thin in the venturi throat portion 53. Consequently, even when the venturi throat portion 53 is relatively large in its cross-sectional area, it is possible to sufficiently accelerate the incoming gas and cause the resultant air/fuel mixture gas to rapidly agitated in the subsequent outlet diffuser portion 52 of the venturi tube 50.
The cross-sectional area of the venturi throat portion 53 is so controlled by axially displacing the performance-control rod 54 as to keep a flow rate of the incoming gas constant in the venturi throat portion 53 even when a quantity of the incoming gas varies, whereby it is possible to supply the air/fuel mixture gas having a constant mixing ratio to the combustion apparatus of the present invention.
In the above first embodiment of the air/fuel mixing unit shown in Fig. 6, a cooling water is supplied to the water jacket 57 to cool the venturi throat portion 53. Since the venturi throat portion 53 is adequately cooled in the above manner, the fuel discharge openings 56 and a front-end portion of the fuel feed pipe 14 connected thereto are also adequately cooled to prevent the fuel from being thermally decomposed in the fuel discharge openings 56. When the fuel is thermally decomposed to produce carbon particles, the fuel discharge openings 56 are clogged with the thus produced carbon particles. Consequently, it is possible to prevent the fuel discharge openings 56 from being clogged with the carbon particles by adequately cooling the venturi throat portion 53.
Fig. 7 shows a second embodiment of the air/fuel mixing unit employed in the combustion apparatus of the present invention, which second embodiment represents a constant-performance type air/fuel mixing unit. As shown in Fig. 9, the fuel discharge nozzle 56 is so disposed in the throat portion 53 of the venturi tube 50a as to be oriented toward a downstream side of the venturi tube 50a. The fuel discharge nozzle 56 is formed in a front-end portion of the fuel feed pipe 14 around which is placed the water jacket 57 to which are connected the cooling-water inlet pipe 58 and the cooling-water outlet pipe 59.
In this second embodiment of the air/fuel mixing unit shown in Fig. 7, a cooling water is supplied to the water jacket 57 to adequately cool both the fuel discharge nozzle 56 and the fuel feed pipe 14 so that the fuel is prevented from being thermally decomposed and from producing the carbon particles in the fuel discharge nozzle 56 and the fuel feed pipe 14, whereby these components 56, 14 are prevented from being clogged with the resultant carbon particles.
Incidentally, in the first embodiment of the air/fuel mixing unit shown in Fig. 6, it is also possible to control the performance-control rod 54 automatically according to a quantity of the preheated incoming gas or air.
In Figs. 6 and 7, the reference numeral 61 denotes a heat-insulating material.
In the above air/fuel mixing unit shown in Figs. 6 and 7, preferably, the venturi throat portion 53 is made of a suitable heat-resisting alloy such as Inconel alloys and Hastelloy alloys, while each of the inlet reducer portion 51, outlet diffuser portion 52 and other inner components of the venturi tube 50 is made of a suitable ceramic material such as silicon carbide, zirconia, cordierite and the like.

Claims

A combustion apparatus, characterized by
(a) an incoming passage (3,23) for flowing a combustion gas in a predetermined direction, said incoming passage being defined by heat insulating material (10) disposed in a substantially central portion of an outer casing (10a) and closed at its upstream end;

(b) an outgoing passage (4,24) for flowing, in a direction counter to said predetermined direction, said combustion gas having passed through said incoming passage (3,23), said outgoing passage (4,24) being open at its opposite end portions and disposed in said incoming passage so as to communicate with said incoming passage at the downstream end thereof through a space defined in the downstream end portion of the incoming passage (3,23);

(c) a mixture gas main incoming duct (5) for supplying a mixture gas consisting of an oxygen-containing gas and fuel, said mixture gas main incoming duct (5) being directly connected to the upstream end portion of said incoming passage (3,23) through a peripheral wall thereof;

(d) an oxygen-containing gas/fuel mixing unit (14) for mixing a preheated oxygen-containing gas with fuel at a predetermined ratio to prepare said mixture gas, said oxygen-containing gas/fuel mixing unit being connected to said mixture gas main incoming duct (5) to supply said mixture gas to said mixture gas main incoming duct at a predetermined pressure;

(e) a combustion-gas auxiliary incoming duct (6) for supplying another combustion gas to said incoming passage (3,23), said another combustion gas being produced by burning fuel with an oxygen-containing gas through a pilot burner, said combustion-gas auxiliary incoming duct (6) being connected to an end portion of said incoming passage (3,23) diametrically opposite from said mixture gas main incoming duct (5); and

(f) a combustion-gas outlet duct (7) defined in a side portions of said outer casing (10a) and said heat-insulating material (10) so as to be connected to a downstream side outlet portion of said outgoing passage (4,24);
The combustion apparatus as set forth in claim 1, characterized in that a honeycomb passage member (8,9,26,27) is provided in each of said outlet portions of said incoming passage (3,23) and said outgoing passage (4,24).
The combustion apparatus as set forth in claims 1 or 2, characterized in that
both of said incoming passage and said outgoing passage are constructed of sleeve elements (1,2,21,22), whereby said sleeve element constituting said outgoing passage is different in diameter from said sleeve element constituting said incoming passage.
The combustion apparatus as set forth in claim 1 or 2, characterized in that
both of said incoming passage (3) and said outgoing passage (4) are constructed of sleeve elements (1,2), whereby said sleeve element constituting said outgoing passage is smaller in diameter than said sleeve element constituting said incoming passage while concentrically disposed in said incoming passage.
The combustion apparatus as set forth in claim 3, characterized in that
both of said incoming passage and said outgoing passage are constructed of sleeve elements (21,22), whereby a plurality of said sleeve elements constitute said outgoing passage, each of which sleeve elements constituting said outgoing passage is smaller in diameter than said sleeve element constituting said incoming passage while disposed in said incoming passage.
The combustion apparatus as set forth in claim 3 or 5 characterized in that
at least one baffle plate member (28) is so disposed in said incoming passage (23) as to extend in a direction perpendicular to a longitudinal direction of said incoming passage.
The combustion apparatus as set forth in anyone of claims 1 to 6, characterized in that
said oxygen-containing gas/fuel mixing unit (15) comprises:
a venturi tube (50), provided with a venturi throat portion (53) and surrouned by a heat-insulating material (61);
a fuel feed pipe having its fuel discharge nozzle (56) opened into said venturi throat portion of said venturi pipe, said fuel discharge nozzle being provided in a front-end portion of said fuel feed pipe; and
a cooling unit (57,58,59) for cooling suitable portions of said fuel discharge nozzle and said fuel feed pipe communicating with said fuel discharge nozzle.