EP0493376B1

EP0493376B1 - Combustion apparatus

Info

Publication number: EP0493376B1
Application number: EP92105621A
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: 1995-10-11
Anticipated expiration: 2009-07-06
Also published as: DE68924539D1; DE68924539T2; EP0350032A2; EP0350032A3; EP0350032B1; EP0493376A2; EP0493376A3; DE68909851T2; DE68909851D1

Description

The present invention refers to a combustion apparatus according to the preamble of claim 1.
An apparatus of this kind is disclosed by the US-A-4 089 088.
The present invention relates to a combustion apparatus for supplying a high-temperature combustion gas to a suitable machine or plant, for example such as gas turbines, heating furnaces, boilers and the like, and more particularly to a combustion apparatus for supplying a high-temperature combustion gas to multistage combustion-gas utilization systems connected to each other in series, in which combustion apparatus an air/fuel mixture gas is brought into contact with a number of high-temperature heating surfaces to attain a complete combustion thereof so as to produce the high-temperature combustion gas which is substantially free from oxygen.
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 published patent application 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 published patent application 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.
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.
The present invention provides 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.
Furthermore the present invention provides 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 the present invention, the above objects of the present invention are accomplished by the features of claim 1.
The following detailed description of the preferred embodiments of the present invention, will be made with reference to the accompanying drawings.

Fig. 1 is a longitudinal sectional view of the combustion apparatus of the present invention;
Fig. 2 is a cross-sectional view of the combustion apparatus of the present invention, take along the line V11-V11 of Fig. 1;
Fig. 3 is a longitudinal sectional view of a first embodiment of an oxygen-containing gas/fuel mixing unit employing in the combustion apparatus of the present invention; and
Fig. 4 is a longitudinal sectional view of a second embodiment of an oxygen-containing gas/fuel mixing unit employing in the combustion apparatus of the present invention.

Now, the 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.
Figs. 1 and 2 show the combustion apparatus of the present invention, in which: the reference numeral 41 denotes a heat-insulating material; and 31 a sleeve-like casing made of ceramic material, which sleeve-like casing 31 has a circular cross section and extends vertically. In the sleeve-like casing 31 is concentrically and rotatably mounted an annular honeycomb passage member 32 which is made of ceramic materials while rotatably supported on a supporting shaft 31a an axis of which is aligned with that of the sleeve-like casing 31. In an upper portion of the sleeve-like casing 31 are provided a pair of chambers 34a, 34b which are oppositely disposed from an upper-end surface of the honeycomb passage member 32. These chambers 34a, 34b are adjacent to each other through a partition wall 33 which is so integrally formed with the sleeve-like casing 31 as to extend in a diametrical direction of the casing 31. One 34a of the chamber 34a, 34b serves as an air/fuel mixture gas inlet chamber 34a, while the other 34b serves as a combustion-gas outlet chamber 34b. An air/fuel mixture gas inlet port 35 opens into a side portion of the mixture gas inlet chamber 34a. On the other hand, a combustion-gas outlet port 37 opens into the a side portion of the combustion-gas outlet chamber 34b. In a lower portion of the sleeve-like casing 31 is formed a combustion-gas chamber 38 which is oppositely disposed from a lower-end surface of the honeycomb passage member 32.
A lower-end portion of the supporting shaft 31a of the honeycomb passage member 32 is rotatably mounted in a supporting frame 39, while connected to a suitable driving unit 40 for rotatably driving the supporting shaft 31a. In the honeycomb passage member 32, there are provided a plurality of fine passages which extend in parallel with the axis of the honeycomb passage member 32 over the whole axial length of the passage member 32 and are adjacent to each other. An upper-end portion of each of the above fine passages of the honeycomb passage member 32 opens into the mixture gas inlet chamber 34a and the combustion-gas outlet chamber 34b, while a lower-end portion of each of such fine passages opens into the combustion-gas chamber 38, as shown in Fig. 6. Namely, as the honeycomb passage member 32 rotates, the fine passages of the honeycomb passage member 32 alternately serve as the incoming passage and the outgoing passage.
As shown in Fig. 1, the pilot burner 12 provided with the auxiliary incoming port 36 is connected to the mixture gas inlet chamber 34a at a position oppositely disposed diametrically from that of the mixture gas inlet port 35 which also opens into the mixture gas inlet chamber 34a. The sleeve-like casing 31 is surrounded with a heat-insulating material 41, while fixedly mounted in an outer casing 42 through the heat-insulating material 41.
In operation of the combustion apparatus of the present invention having the above construction, the honeycomb passage member 32 is constantly rotated at a predetermined rotational speed. Under such circumstances, first of all, the pilot burner 12 is operated to issue a combustion gas to the mixture gas inlet chamber 34a through the auxiliary incoming port 36, so that both of the mixture gas inlet chamber 34a and the upper-end portion of the honeycomb passage member 32 are heated together by the combustion gas. During such heating, since the honeycomb passage member 32 is rotated constantly, the whole area of the upper-end portion of the honeycomb passage member 32 is sequentially heated to a predetermined temperature of about 900 °C. When the temperature of the upper-end portion of the honeycomb passage member 32 reaches about 900 C, operation of the pilot burner 12 is stopped to stop the heating of the honeycomb passage member 32, while a preheated air/fuel mixture gas is supplied to the mixture gas inlet chamber 34a through the mixture gas inlet port 35. The thus supplied mixture gas is then brought into contact with a preheated wall surface of the chamber 34a to burst into flame, and flows downward through a part of the honeycomb passage member 32 serving as the incoming passage so that the combustion of the mixture gas conducted in the incoming passage is completed when the gas reaches the combustion-gas chamber 38. The combustion gas entered the combustion-gas chamber 38 then flows into the other part of the honeycomb passage member 32 serving as the outgoing passage which is partially constructed of the fine passages of honeycomb passage member 32 located in a position corresponding to that of the combustion-gas outlet chamber 34b. Combustion of the mixture gas continues in the outgoing passage so that the combustion gas reaches the combustion-gas outlet chamber 34b from which the combustion gas is discharged through the combustion-gas outlet port 37. At this time, the outgoing passage 32 oppositely disposed from the combustion-gas outlet chamber 34b is heated by the combustion gas issued from the combustion-gas chamber 38. As the honeycomb passage member 32 rotates, the thus heated outgoing passage or some of the fine passages of the honeycomb passage member 32 is sequentially transferred to a position oppositely disposed from the mixture gas inlet chamber 34a so as to serve as the incoming passage. Consequently, since the thus sequentially transferred outgoing passage has been sufficiently heated by the combustion gas and serves as the incoming passage, the mixture gas entered the thus heated incoming passage is brought into contact with the sufficiently heated wall surfaces of the incoming passage constructed of the honeycomb passage member 32, to enable the mixture gas to continuously burst into flame.
The combustion apparatus of the present invention shown in Figs. 1 and 2 may be modified to form an embodiment of the combustion apparatus of the present invention in which each of the wall surfaces of the fine passages of the honeycomb passage member 32 are coated with catalysts to attain a catalytic combustion of the mixture gas. The catalysts employed in the present invention comprise platinum, palladium and the like. Coating of the wall surfaces of the honeycomb passage member 32 with the catalysts is conducted by dipping the honeycomb passage member 32 in solutions of the catalysts.
The above embodiment of the combustion apparatus of the present invention enables the mixture gas supplied from the mixture gas inlet port 35 to burst into flame to attain a catalytic combustion thereof even when the temperatures of the wall surfaces of the upstream side of the incoming passage are less than 900 °C, which wall surfaces are heated by the combustion gas which is produced by the pilot burner 12 and issued from the auxiliary incoming port 36.
Namely, in the embodiment of the combustion apparatus of the present invention, the fuel is mixed with a preheated air to prepare the mixture gas. In case that a gaseous fuel is employed, it is possible to eliminate the preheating operation of the air. In case that a liquid fuel is employed, it is possible to extremely lower the temperature of the preheated air, provided that the temperature of the fuel in the air is slightly higher than dew point.
Incidentally, in the above embodiment of the combustion apparatus of the present invention, sulfur-containing fuels can not be employed because sulfur has poisoning effects on the catalysts employed in the above embodiment.
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, inner sleeve, sleeve-like casing 31 and the honeycomb passage member 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 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 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. 3 and 4.
In a first embodiment of the air/fuel mixing unit of the present invention shown in Fig. 3: 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. 3, 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. 3, 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. 3, 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. 4 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. 4, 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. 4, 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. 3, 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. 3 and 4, the reference numeral 61 denotes a heat-insulating material.
In the above air/fuel mixing unit shown in Figs. 3 and 4, 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

Combustion apparatus comprising
(a) a sleeve-like casing (31), having a circular cross section and surrounded by a heat-insulating material (41);

(b) a cylindrical combustion-gas passage member (32) provided with a plurality of combustion-gas passages adjacent each other for providing a plurality of honeycomb-like passage wall surfaces so as to assume a honeycomb-like cross section as a whole, through which a combustion gas flows axially, said cylindrical combustion-gas passage member being rotatably mounted in said sleeve-like casing so as to be rotated on a supporting shaft (31a) which is mounted in said sleeve-like casing (31), an axis of said supporting shaft being aligned with an axis of said sleeve-like casing, a driving unit (40) being connected to said supporting shaft (31a).

(c) a mixture-gas inlet means (35) provided with a mixture gas inlet port opened to said cylindrical combustion-gas passage member (32);

(d) an auxiliary incoming means (36) provided with a pilot burner (12), said auxiliary incoming means being provided with an auxiliary incoming port of said mixture gas, which opens into said combustion-gas passage member (32);

(e) combustion-gas outlet means being provided with a combustion-gas outlet port which opens into one side of said combustion-gas passage member,
characterized by

(f) a pair of chambers (34a,34b), one of which (34a) serves as an inlet and outlet chamber of an oxygen-containing gas/fuel mixture gas, the other one (34b) serves as an inlet and an outlet chamber of said combustion gas, said pair of chambers (34a,34b) being formed in one axial end portion of said sleeve-like casing (31) adjacent to each other on opposite sides of a diametrical partition wall (33) being integrally formed with said sleeve-like casing (31), the mixture gas inlet port opening into one side portion of the inlet chamber (34a) the auxiliary incoming port opening into the inlet chamber (34a) spaced apart from said mixture gas inlet port and at right angles to it, a combustion-gas outlet port (37) opening into one side portion of the outlet chamber (34b) of the combustion-gas.

(g) a combustion-gas chamber (38) formed in the axial end portion of the sleeve-like casing (31) opposite to the combustion gas inlet (34a) and outlet chamber (34b) respectively.
The combustion apparatus as set forth in claim 1, characterized in that said combustion apparatus further comprises an oxygen-containing gas/fuel mixing unit which is provided with:
a venturi tube (50), provided with a venturi throat (53) portion and surrounded 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 portion of said fuel discharge nozzle and said fuel feed pipe communicating with said fuel discharge nozzle.
The combustion apparatus as set forth in claim 1 or 2, characterized in that said honeycomb-like passage wall surfaces of said cylindrical combustion-gas passage member (32) are coated with catalysts to attain a catalytic combustion of said mixture gas.
The combustion apparatus as set forth in claim 3, characterized in that said catalysts comprises platinum or palladium.
The combustion apparatus as set forth in one of claims 1 to 4, characterized in that each of said incoming passage means (31) and said outgoing means (31) is made of at least one of ceramic materials selected from the group consisting of silicon carbide, zirconia and cordierite.
The combustion apparatus as set forth in one of claims 1 to 5, characterized in that said honeycomb passage member (32) is made of at least one of ceramic materials selected from the group consisting of silicon carbide, zirconia and cordierite.
The combustion apparatus as set forth in one of claims 1 to 6, characterized in that said venturi tube (50) is made of at least one of ceramic materials selected from the group consisting of silicon carbide, zirconia and cordierite.
The combustion apparatus as set forth in one of claims 1 to 7, characterized in that each of said sleeve-like casing (31) and said cylindrical combustion-gas passage member (32) is made of at least one of ceramic materials selected from the group consisting of silicon carbide, zirconia and cordierite.
The combustion apparatus as set forth in one of claims 2 to 8, characterized in that said venturi tube (50) is made of at least one of ceramic materials selected from the group consisting of silicon carbide, zirconia and cordierite.