Combustion apparatus

Abstract: A combustion apparatus provided with a burner (1) includes a fuel injection nozzle (4) disposed rearward of a gas passable solid (3) and a pre-mixture region (8) between a downstream end of the solid (3) and the fuel injection nozzle (4). The gas passable solid (3) may be of a straightener type. Air for combustion includes main air and pilot air separated from each other. The apparatus may be coupled to each end of a radiant tube (32). The apparatus may be provided to a direct and indirect combustion type thermal facilities (200, 201).

Description: The present invention relates to a combustion apparatus wherein a fuel injection portion is located rearward of a gas passable solid (upstream of the solid as viewed in an air flow direction), and a thermal facility provided with the combustion apparatus. In a conventional burner, a fuel injection portion is located so as to face a combustion chamber. As a result, combustion is conducted near the fuel injection portion of the burner, so that a temperature of the fuel injection portion is high. Particularly, in a regenerative combustion type burner, since the fuel injection portion is located frontward of a heat storage member (on a combustion chamber side), the fuel injection portion is at a very high temperature. Further, as a special case, Japanese Utility Model Publication SHO 62-118925 discloses a radiant tube wherein a fuel injection nozzle is located rearward of a heat storage member such that a tip of the nozzle contacts the heat storage member. However, the above-described conventional apparatuses have the following problems: With the burner where the fuel injection portion faces the combustion chamber, since the fuel injection portion is at a high temperature, the life of the burner is shortened. If the fuel injection portion is made from heat proof material, cost will be increased and machining will be difficult. Further, since a complicated mechanism cannot be provided to a high temperature portion, the burner structure will have various limitations. With the burner in which the fuel injection portion is located rearward of the heat storage member like Japanese Utility Model Publication SHO 62-118925, according to tests conducted, it was seen that no flame was formed due to insufficient mixture of fuel and air. If the fuel injection portion was spaced apart from the heat storage member in order to pre-mix fuel and air, when exhaust gas flows through the heat storage member to heat the heat storage member to a high temperature, the mixture of fuel and air self-ignited and burned within the heat storage member to melt the heat storage member. Therefore, the burner having the fuel injection portion rearward of the heat storage member could not be actually used. EP-A-0 593 121 discloses a burner comprising a gas passage, gas passable solids, a fuel injection nozzle disposed within the gas passage and a mixing region formed between the gas passable solid and the fuel injection nozzle. In this burner, gas introduction holes are located completely upstream the gas passable solids and fuel burnt gas is mixed with the combustion.air prior to its introduction into the plenum. EP-A-0 333 239 discloses a regenerative burner wherein fuel burnt gas is recirculated into a casing due to the negative pressure generated inside the casing by the expelled combustion air. In this burner, gas introduction holes are located completely downstream a gas passable solid. An object of the present invention is to provide a combustion apparatus wherein a fuel injection portion can be located in a relatively low temperature portion of the apparatus. The combustion apparatus or heat facility according to the present invention is provided with at least one burner and comprises a gas passage; a gas passable solid disposed in said gas passage, said gas passable solid having a first end, a second opposed end, a first side and a second opposed side, said first end and said second end, respectively, corresponding to said first side and said second side wherein air for combustion enters said gas passable solid from said first side and a flame is formed on said second side; a fuel injection nozzle disposed on said first side of said gas passable solid; and a pre-mixture region for pre-mixing fuel and air for combustion, formed between said second end of said solid and said fuel injection nozzle. Said apparatus according to the present invention is characterised in that it further comprises a casing for supporting said gas passable solid therein, said casing defining a fuel burnt gas introduction hole for passing fuel burnt gas to air for combustion into the casing, said fuel burnt gas introduction hole being located upstream the second end of the gas passable solid in the flow direction of the air for combustion and downstream the first end of the gas passable solid. In this combustion apparatus, since the fuel injection nozzle is located on a rear side of the gas passable solid, that is, at a relatively low temperature portion of the apparatus, durability of a mechanism including the fuel injection nozzle is improved. Further, the mechanical portion can be machined because the portion does not need to be made from refractory. Further, by using a gas passable solid of a straightener type, it is possible to form a stable flame of a laminar boundary diffusion whereby a stable slack combustion is obtained. Due to the slack combustion, suppression of NOx generation, prolongation of the flame, flattening of a heat flux, prevention of local overheat of the furnace, improvement of durability of the furnace, formation of a bright flame, and improvement of a radiation heat transfer characteristic can be achieved. Further, since the pre-mixture region is provided, it is possible to ignite a mixture of fuel and air at an exit of the gas passable solid and to form a flame. The above and other objects, features, and advantages of the present invention will become more apparent and will be more readily appreciated from the following detailed description including the description of combustion apparatuses not forming part of the present invention and the description of one embodiment of a combustion apparatus according to the present invention in conjunction with the accompanying drawing, in which : FIG. 1 is a cross-sectional view of a first combustion apparatus not forming part of the present invention; FIG. 2 is a cross-sectional view of a second combustion apparatus not forming part of the present invention; FIG. 3 is a cross-sectional view of a third combustion apparatus not forming part of the present invention; FIG. 4 is a cross-sectional view of a fourth combustion apparatus not forming part of the present invention; FIG. 5 is a cross-sectional view of a fifth combustion apparatus not forming part of the present invention; FIG. 6 is a cross-sectional view of a sixth combustion apparatus not forming part of the present invention; FIG. 7 is an elevational view of the sixth combustion apparatus not forming part of the present invention; FIG. 8 is a cross-sectional view of a seventh combustion apparatus not forming part of the present invention; FIG. 9 is a cross-sectional view of a eighth combustion apparatus not forming part of the present invention in a case where the apparatus has a high velocity port; FIG. 10 is a cross-sectional view of the eighth combustion apparatus not forming part of the present invention in a case where the apparatus has a swirl generation port; FIG. 11 is a cross-sectional view of the eighth combustion apparatus not forming part of the present invention in a case where the apparatus has a low pressure loss port; FIG. 12 is a cross-sectional view of a ninth combustion apparatus not forming part of the present invention; FIG. 13 is a cross-sectional view of a combustion apparatus according to one embodiment of the present invention; Portions common or similar to all combustion apparatuses are denoted with the same reference numerals throughout all of the apparatuses including apparatuses not forming part of the present invention and apparatus according to the present invention. First, portions common or similar to all apparatuses including apparatuses not forming part of the present invention and apparatus according to the present invention will be explained with reference to, for example, FIG. 1. As illustrated in FIG. 1, a first combustion apparatus not forming part embodiment of the present invention is provided with at least one burner 1. The apparatus including the burner 1 includes a gas passage 2, a gas passable solid 3 disposed in the gas passage 2, and a fuel injection nozzle (fuel supply nozzle) 4. The gas passable solid 3 has a first end and a second, opposite, end and a first side and a second, opposite, side which correspond to the first end and the second end, respectively. From the first side, air for combustion 5 enters the solid 3 and on the second side flame 7 is formed. The fuel injection nozzle 4 is disposed on the first side of the solid 3. A pre-mixture region 8 for pre-mixing fuel 6 and air for combustion 5 is formed between the first end of the solid 3 and the fuel injection nozzle 4. The fuel injection nozzle 4 penetrates a casing 9 and supplies fuel 6 to the solid 3 from the first side of the solid. A mixture of fuel and air for combustion is ignited by an ignition apparatus (not shown in FIG. 1, and made from a heat-proof metal or electrically conductive ceramic), so that a flame 7 is formed on the second, front side of the solid 3. In the combustion apparatus having the above-described structures, since the mechanism portion including the fuel injection nozzle 4 is disposed in a relatively low temperature portion of the apparatus, durability of the apparatus including the burner 1 is improved, and a freedom of design in a high temperature environment also is improved. Next, portions unique to each combustion apparatuses will be explained. With said first apparatus not forming part of the present invention, as illustrated in FIG. 1, the solid 3 of the combustion apparatus including the burner 1 may be of a straightener type or of a diffusion type. FIG. 1 shows that the solid 3 is made from diffusion type material. In a case where the solid 3 is of a diffusion type, the pre-mixture region 8 includes a space defined between the solid 3 and the fuel injection nozzle 4. In the case where the solid 3 is of the diffusion type, while the fuel 6 is flowing within the solid 3, the fuel 6 is mixing with air and is diffusing in an entire transverse cross-section of the solid 3. As a result, the flame 7 is formed in the front of the entire surface of a downstream end of the solid 3. Since the fuel and air for combustion which are at a low temperature flow within the solid 3, the solid 3 is maintained at a relatively low temperature except at a most downstream portion of the solid 3 which is heated by radiation, so that it is possible to freely select a material for the solid 3. With a second combustion apparatus not forming part of the present invention, as illustrated in FIG. 2, the gas passable solid 3 of the apparatus including the burner 1 is of a straightener type. In this instance, a solid of the straightener type is defined as a solid which includes a lot of passages substantially independent of each other and extending axially and straightens a flow of air for combustion while the air for combustion is flowing within the solid 3. The solid of the straightener type may be of any structure provided that it has a lot of axially extending passages. For example, the solid of the straightener type may be of a honeycomb structure, of a bundle of solid rods having a number of passages between the rods, of a bundle of pipes each having a small diameter, of a structure made by piling wave plates and flat plates alternatively, and of a structure made by piling a wave plate and a flat plate and then winding the piled plates to the form of a roll. The solid is made from any material provided that it has a required heat-proof characteristic, a required shock-proof characteristic and a required chemical stability. For example, the solid is made from ceramic or metal. In order to form the solid 3 easily and to reduce thermal stresses generated in the solid, the solid 3 may be divided into a plurality of sections in an axial direction as well as in a circumferential direction of the solid. In the case where the solid 3 is of the straightener type, when fuel flows in the pre-mixture region 8, fuel mixes with air for combustion at a peripheral portion of the fuel flow, and then enters the gas passable solid 3. In the solid 3, the fuel flow, the mixture flow around the fuel flow, and the air flow around the mixture flow flow independently of each other without mixing with each other, and then flow out from the downstream end of the solid in the form of a cylindrical laminar flow. Immediately after flowing from the solid 3, the mixture of fuel and air for combustion is ignited by an ignition device (not shown in FIG. 2). Fuel gas flow slackly diffuses to the cylindrical burning mixture gas layer to mix with it so that a slack self-combustion is conducted to form a gradually spread flame. Since the combustion is conducted slackly, the flame is elongated in the axial direction so that the fuel is burned more completely in the prolonged combustion. In the combustion in the form of a cylindrical laminar flow, hydrogen generated through decomposition of the fuel is selectively burned prior to combustion of carbon, and the remaining carbon forms an elongated brilliant flame (having yellow color) when slackly burned. Due to the slack combustion, generation of NOx (nitrogen oxides) is suppressed, so that the amount of NOx contained in the fuel-burnt gas exhausted from the combustion apparatus to the atmosphere is decreased. This means that the combustion is clean and friendly to the environment. Further, due to the slack combustion and provision of a cylindrical air layer of a low temperature surrounding the burning cylindrical mixture layer, a portion of the apparatus (furnace or tube) adjacent to the downstream end of the solid is prevented from locally overheating, thereby the durability of the apparatus is improved. Further, due to the slack combustion and the elongated flame, the heat flux becomes flat in the axial direction of the apparatus so that the heating is uniform and the temperature of the interior of the furnace or the tube can be raised to an allowable limit throughout all portions of the furnace or the tube resulting in improvement of the heat transmittance efficiency. With a third combustion apparatus not forming part of the present invention, as illustrated in FIG. 3, the gas passable solid 3 is of the straightener type, and the pre-mixture region 8 is formed within the gas passable solid 3. In the apparatus of FIG. 3, another pre-mixture region 8A is formed between the upstream end of the solid 3 and the fuel injection nozzle 4. Due to this structure, a portion of the fuel gas 6 and a portion of the air for combustion 5 pre-mixes with each other in the pre-mixture region 8 to form a mixture. As a result, a cylindrical laminar flow having the fuel gas layer 10, the pre-mixture layer 11 outside the layer 10 and the air layer 12 outside the layer 11 is formed downstream of the solid 3. When the pre-mixture layer 11 is ignited, the combustion explained in the second embodiment of the present invention is conducted. With a fourth combustion apparatus not forming part of the present invention, as illustrated in FIG. 4, the gas passable solid 3 is of the straightener type, and the pre-mixture region 8' is of a gas passable type that is made from a gas passable solid (having thickness t) of the diffusion type disposed between the upstream end of the gas passable solid 3 and the tip of the fuel injection nozzle 4. The tip of the fuel injection nozzle 4 may contact the gas passable solid of the diffusion type. Due to this structure, a portion of the fuel gas 6 and a portion of the air for combustion 5 pre-mixes with each other in the pre-mixture region to form a mixture. As a result, a cylindrical laminar flow having the fuel gas layer 10, the pre-mixture layer 11 outside the layer 10 and the air layer 12 outside the layer 11 is formed downstream of the solid 3. When the pre-mixture layer 11 is ignited, the combustion explained with reference to the second apparatus is conducted. With a fifth combustion apparatus not forming part of the present invention, as illustrated in FIG. 5, the gas passable solid 3 is of the straightener type, and the pre-mixture region 8 includes a space (having thickness t) defined between the upstream end of the gas passable solid 3 and the tip of the fuel injection nozzle 4. Though FIG. 5 illustrates the fuel injection nozzle in the form of a pipe, the shape of the nozzle may vary. In this instance, a thickness of a wall of a pipe end, a diameter thereof, and a configuration are factors for controlling the pre-mixture characteristic. When the pipe wall thickness is thick, a turbulence is generated in the vicinity of the pipe end so that pre-mixture is promoted. When the difference between an air speed and a fuel speed is increased by changing the diameter of the pipe, turbulence generated at the boundary of the air layer and the fuel layer becomes strong so that pre-mixture is promoted. Further, by providing an end plate at the pipe end and forming a plurality of holes in the end plate or by forming a hold of a side of the pipe, pre-mixture is further promoted. Due to this structure, a portion of the fuel gas 6 and a portion of the air for combustion 5 pre-mixes with each other in the pre-mixture region 8 to form a mixture. As a result, a cylindrical laminar flow having the fuel gas layer 10, the pre-mixture layer 11 outside the layer 10 and the air layer 12 outside the layer 11 is formed downstream of the solid 3. When the pre-mixture layer 11 is ignited, the combustion explained with respect to the second apparatus is conducted. With a sixth combustion apparatus not forming part of the present invention, as illustrated in FIGS. 6 and 7, the combustion apparatus including the burner 1 further includes a casing 9 supporting the gas passable solid 3 therein, an air header 13 coupled to the casing 9 and defining a portion of the gas passage 2 therein, an ignition device 14, and a detection device 15 for detecting a flame. The gas passable solid 3, the fuel injection nozzle 4, the casing 9, the ignition device 14, and the flame detecting device 15 are assembled to form a package. This package is detachably coupled to the furnace (or the tube). With respect to the ignition device 14, it is possible to ignite the mixture by forming an electric discharge between the casing 9 which is electrically conductive and a spark rod 16 which penetrates the gas passable solid 3. Further, with respect to the flame detecting device 15, it is possible to detect a flame by using a flame rod which penetrates the gas passable solid 3 or by using an optical flame detecting device in a case where light can penetrate the solid 3. Due to the package structure, detachability of the burner to the furnace or tube, and maintenance thereof are easy. With seventh combustion apparatus not forming part of the present invention, as illustrated in FIG. 8, the combustion apparatus provided with the burner 1 further includes a main air supply passage 2A for supplying main air for combustion 5A and a pilot air supply passage 2B for supplying pilot air for combustion 5B. The summation of the amount of the main air 5A and the amount of the pilot air 5B is equal to the amount of the air for combustion. The pilot air supply passage 2B and the main air supply passage 2A are independent of each other. The fuel injection nozzle 4 is disposed within the pilot air supply passage 2B therein contacts the gas passable solid 3. A tip of the fuel injection nozzle 4 is spaced apart from the surface of the solid through which the air for combustion enters the solid 3 so that a space defined between the tip of the fuel injection nozzle 4 and that surface of the solid defines the pre-mixture region 8. To stably hold the fuel injection nozzle 4 within the pilot air supply passage 2B, the two pipes (the pipe for defining the pilot air supply passage 2B therein and the fuel injection nozzle 4) are spline-coupled or gear-coupled to each other so as to permit air to pass through the coupling portion, though the holding structure is not limited to that coupling structure. The reason why the tip of the pipe defining the pilot air supply passage therein contacts the solid 3 is to distinctly separate a range where the pilot air flows from a range where the main air flows in the gas passable solid 3. If necessary, a gasket may be inserted between the tip of the pipe and the solid, or the tip of the pipe defining the pilot air supply passage therein may be inserted into an intermediate portion of the gas passable solid of the straightener type. By separating the pilot air flowing range from the main air flowing range, when the apparatus is used for a burner of a regenerative combustion system (wherein when the exhaust gas passes through the gas passable solid 3, the solid stores the heat of the exhaust gas, and when air for combustion passes through the solid, the solid releases the heat which the solid has stored to the air), a cylindrical low temperature region is formed in the solid so as to surround a core region where the fuel and the mixture of fuel and air flow, separating the core region from a peripheral region which is heated to a temperature above about 700 C by the exhaust gas flowing through the peripheral region. As a result, it is possible to prevent the fuel and the mixture of the fuel and air from being burned to melt the solid 3. Due to that structure for separating the pilot air flow region from the main air flow region, it becomes practical to apply the apparatus to the regenerative combustion burner. With an eighth combustion apparatus not forming part of the present invention, as illustrated in FIGS. 9, 10 and 11, the apparatus provided with the burner 1 further includes a port defining member 18A, 18B or 18C disposed on the flame formation side of the gas passable solid 3. The port defining member 18A of FIG. 9 includes an exit reduced in a transverse cross-sectional area thereof for increasing the speed of gas. This port may be called a high speed port. The port defining member 18B of FIG. 10 includes a vane for generating a swirl flow. The port defining member 18C is formed in the form of a venturi and is called a low pressure loss port. By selecting the kind of port, a desirable flow characteristic of the port is obtained. With a ninth combustion apparatus not forming part of the present invention, as illustrated in FIG. 12, the apparatus provided with the burner 1 includes a casing 9 housing the gas passable solid 3 therein. The casing 9 includes a port defining portion 9A for forming a port of a desirable configuration. At least a portion of the casing 9 (the entire portion of the casing in the embodiment shown) is made from refractory. The port defining portion 9A is of a high speed port having an exit reduced in diameter. The refractory is, for example, ceramic. In this instance, a local conductive portion (spark rod) to be disposed on the downstream side of the air passage may be made from heat-resistant metal, or the entire portion of the casing may be made from ceramics by using electrically conductive ceramics so that the casing can endure a higher temperature. In the case where the casing 9 is made form refractory and the casing 9 is disposed in the furnace, the heat-resistance characteristic of the combustion apparatus can be improved. With a combustion apparatus according to the present invention, as illustrated in FIG. 13, the burner 1 includes a casing 9 supporting the gas passable solid 3 therein. The casing 9 has a gas introduction hole 20 formed therein for causing fuel burnt gas to pass through the hole 20 to air for combustion inside the casing 9 due to a negative pressure generated inside the casing 9 by the air expelled from the downstream end of the gas passable solid 3. Due to this structure, the air for combustion and the exhaust gas in the furnace mix with each other so that combustion is slack whereby generation of NOx is suppressed. Further, by using both the gas introduction hole 20 and the high speed port, self-recirculation of the exhaust gas in the furnace is strongly conducted even at a flame formation region so that generation of NOx is further suppressed. According to the present invention, the following technical advantages are obtained: First, since the fuel injection nozzle is disposed rearward of the gas passable solid, the mechanism portion including the fuel injection nozzle can be located at a low temperature portion of the apparatus. As a result, durability of the apparatus is improved. Second, in the case where the gas passable solid is of the straightener type, a laminar combustion is conducted. As a result, the combustion is slack and the flame is prolonged. Further, generation of NOx is suppressed, and the temperature distribution is flat so that local over heating of the furnace or tube is prevented and the heat transfer efficiency is improved. Third, in the case with the pre-mixture regions, a cylindrical layer of the mixture is formed in front of the downstream end of the gas passable solid, a laminar boundary combustion is conducted and ignition is smooth. Fourth, in the case where the members are assembled in the form of a package, coupling the apparatus to the furnace or tube and decoupling thereof are easy. Fifth, in the case where the main air passage and the pilot air passage are independent of each other, a cylindrical pilot air flow region at a low temperature is formed around the fuel gas flow region. As a result, the fuel gas flow region is separated by the pilot air flow from the exhaust gas at a high temperature, so that the fuel and the mixture of fuel and air are prevented from self-ignition and the gas passable solid is prevented from melting. Sixth, the configuration of the port can be selected to a desirable one. Seventh, by making the casing from refractory, durability of the apparatus is improved. Eighth, by causing a portion of the exhaust gas to recirculate, generation of NOx is suppressed. Last, by providing the apparatus to each of opposite ends of a tube, the apparatus can be applied to a radiant tube combustion system.

Claims: A combustion apparatus provided with at least one burner (1), said apparatus comprising: a gas passage (2); a gas passable solid (3) disposed in said gas passage (2), said gas passable solid (3) having a first end, a second opposed end, a first side and a second opposed side, said first end and said second end, respectively, corresponding to said first side and said second side wherein air for combustion (5) enters said gas passable solid (3) from said first side and a flame (7) is formed on said second side; a fuel injection nozzle (4) disposed on said first side of said gas passable solid (3); and a pre-mixture region (8) for pre-mixing fuel (6) and air for combustion (5), formed between said second end of said solid (3) and said fuel injection nozzle (4); characterised in that said apparatus further comprises a casing (9) for supporting said gas passable solid (3) therein, said casing (9) defining a fuel burnt gas introduction hole (20) for passing fuel burnt gas to air for combustion into the casing, said fuel burnt gas introduction hole being located upstream the second end of the gas passable solid (3) in the flow direction of the air for combustion and downstream the first end of the gas passable solid (3). An apparatus according to claim 1, further comprising a port defining member (18A, 18B, 18C) disposed on said second side of said gas passable solid (3). An apparatus according to claim 2, wherein said port defining member (18A) includes an entrance end and an exit end, wherein said exit end is reduced in a transverse cross-sectional area relative to said entrance end. An apparatus according to claim 2, wherein said port defining member (18B) includes a vane for generating a swirl flow. An apparatus according to claim 2, wherein said port defining member (18C) is formed in the form of a venturi.

Inventors: FUKUTA YUKIO, MITANI KAZUHISA, FUKUTA, YUKIO, MITANI, KAZUHISA
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1997
Main classification: F23D14
IPC codes: F23D14, F23C9, F23C3, F23L15, F23D23, F23D17