Patent Application
20110094233
This application claims priority to and the benefit of Japanese Patent Application No. 2008-136068, filed in Japan Patent Office on May 23, 2008, the entire disclosure of which is incorporated herein by reference.
The present invention relates to a combustion device used for a device, such as a gas turbine engine or a boiler, which requires supply of a high-temperature gas and a method for controlling a radial fuel concentration of especially a pre-mixed gas in the combustion device.
Out of consideration for environmental preservation, strict environmental standards for the composition of an exhaust gas discharged by combustion in the gas turbine engine are set up, and toxic substances, such as nitrogen oxide (hereinafter referred to as “NOx”), need to be reduced. In contrast, in the gas turbine engines for large-scale ground equipment and aircraft, a pressure ratio tends to be set high in order to reduce fuel consumption and increase an output, and this increases the temperature and pressure at an entrance of the combustion device. Since the temperature of the combustion easily increases by the increase in the temperature at the entrance of the combustion device, it is anticipated that NOx may rather increase.
Here, a combustion system adopting a lean premix combustion system which effectively reduces a NOx generation amount has been proposed in recent years. For example, a combined combustion system obtained by combining the lean premix combustion system and a diffusion combustion system has been proposed (see Japanese Laid-Open Patent Application Publication No. 8-28871 and Japanese Laid-Open Patent Application Publication No. 8-210641). In the lean premix combustion system, the air and the fuel are premixed and combusted as an air-fuel mixture whose fuel concentration is uniformized. Therefore, a combustion region where a flame temperature is locally high does not exist. In addition, the flame temperature can be wholly lowered by the dilution of the fuel. On this account, the NOx generation amount can be effectively reduced. In contrast, blow-off tends to occur at the time of low-load combustion. Moreover, since the diffusion combustion system combusts the fuel and the air while diffusing and mixing the fuel and the air, the blow-off is unlikely to occur even at the time of the low load, and a flame holding performance is excellent. In contrast, the diffusion combustion system has a problem with the reduction in the NOx generation amount. Therefore, in accordance with the combined combustion system, the reduction in the NOx generation amount can be achieved by the premix combustion at the time of high load while securing the combustion stability by the diffusion combustion at the time of start-up and low load.
For example, as shown in
In order to enhance the flame holding in the conventional combustion device 80 using the swirl-type main burner 84 including the radial swirler 83, the conventional combustion device 80 is set such that the swirling of the pre-mixed gas is enhanced to enhance a reverse flow R of the pre-mixed gas. In order to do this, a vane angle of the fixed swirl vane of the radial swirler 83 needs to be increased. However, in this case, an axial vane height needs to be increased at the same time in order to secure a passage area of the pre-mixed gas P, and an entrance height of the radial swirler 83 also increases. With this, an axial size of an entrance portion to which the air and the fuel are introduced also increases.
In the conventional combustion device 80, in order to reduce the device size, an air passage 86 extending from a gas turbine compressor is formed between the combustion liner 81 and a housing H covering the outer side of the combustion liner 81, and the air A is introduced in a direction from a downstream end of the combustion liner 81 toward the top portion 81a that is an upstream end of the combustion liner 81, that is, in a direction opposite to the flow of the combustion gas. In this case, the air A having flowed through the air passage 86 is introduced to a premix passage through an entrance of the radial swirler 83 which opens in a radially outward direction, mixed with the fuel, and injected as the pre-mixed gas into the combustion liner in a direction opposite to the flow of compressed air.
To be specific, the flow direction of the air A introduced through the air passage 86 to the radial swirler 83 is changed by substantially 90°. Therefore, by a centrifugal force generated by the above direction change, an axial flow rate distribution of the air at an upstream portion of the premix passage is biased. Moreover, in the case of stabilizing the flame holding by increasing the vane angle of the swirl vane of the radial swirler as described above, the axial size of the entrance portion increases, so that the flow rate distribution is biased further significantly. As a result, a radial fuel concentration distribution of the pre-mixed gas injected through the premix passage into the combustion chamber is also biased. Therefore, the problem is that it is difficult to perform control operations, such as uniformizing the radial fuel concentration distribution and realizing the intended fuel concentration distribution.
An object of the present invention is to provide a combustion device capable of easily controlling the radial concentration distribution of the pre-mixed gas injected from the burner into the combustion chamber while stabilizing the flame holding by maintaining the large vane angle of the swirl vane of the radial swirler to generate the strong reverse flow in the combustion chamber, and a method for controlling the combustion device to easily control the radial fuel concentration distribution of the pre-mixed gas in the combustion device.
To achieve the above object, a combustion device according to the present invention includes: a combustion liner in which a combustion chamber is formed; a main burner provided at a top portion of the combustion liner and including a premix passage configured to annularly inject a pre-mixed gas of a fuel and air into the combustion chamber and a radial swirler configured to introduce the fuel and the air to the premix passage in a radially inward direction; and a fuel injection pipe configured to inject the fuel to the radial swirler from an entrance side of the radial swirler, wherein the radial swirler is divided into a plurality of swirler stages by dividing plates in an axial direction.
In accordance with this configuration, since the radial swirler is divided into a plurality of swirler stages by the dividing plates in the axial direction, the flow rate of the air introduced to the radial swirler can be prevented from being biased in the axial direction.
It is preferable that in the above combustion device, the fuel injection pipe include a plurality of fuel injection openings respectively corresponding to the swirler stages. In accordance with this configuration, since the fuel injection pipe configured to inject the fuel to the radial swirler includes the injection openings respectively corresponding to the swirler stages, the bias of the radial fuel concentration distribution of the pre-mixed gas injected from the premix passage into the combustion chamber can be significantly prevented.
In the above combustion device, a flow rate of the fuel supplied from the fuel injection pipe may be able to be set for each of the swirler stages. In accordance with this configuration, control operations become easy. For example, the radial fuel concentration distribution of the pre-mixed gas injected through the premix passage into the combustion chamber can be further uniformized, or the intended fuel concentration distribution can be realized.
As described above, in order to set the flow rate of the fuel for each of the swirler stages, for example, at least a part of the plurality of fuel injection openings of the fuel injection pipe may be different in inner diameter from one another. To be specific, the plurality of fuel injection openings may be configured to have individually set inner diameters. With this configuration, the radial fuel concentration distribution of the pre-mixed gas injected through the premix passage into the combustion chamber can be effectively controlled with a simple configuration.
In the combustion device according to the present invention, a radial length of the dividing plate may be shorter than that of a radially extending straight portion which forms an upstream portion of the premix passage. When the air having passed through the air passage changes its direction toward the radial swirler, it receives the highest centrifugal force at the entrance portion of the radial swirler. Therefore, the radial length may be a length capable of suppressing the axial bias of the flow rate of the air at this portion. In addition, shorter the radial length of the radial swirler is, longer the premix passage behind the radial swirler becomes. Therefore, the premixing is accelerated.
In the above combustion device, a method for controlling the combustion device according to the present invention includes the step of controlling a flow rate of the fuel supplied for each of the swirler stages to control a radial fuel concentration distribution of the pre-mixed gas injected from the main burner into the combustion chamber.
In the method for controlling the combustion device according to the present invention, since the axial flow rate distribution of the air is uniformized by dividing the radial swirler in the axial direction, the radial fuel concentration distribution of the pre-mixed gas injected into the combustion chamber can be easily controlled only by controlling the flow rates of the fuel supplied to respective swirler stages.
Hereinafter, an embodiment according to the present invention will be explained in detail in reference to the drawings.
The combustion device 2 is a reverse flow type. An air passage 30 is formed between the housing H and a side wall 12b of the combustion liner 12. The air passage 30 introduces the compressed air A, supplied from the compressor 1, in a direction shown by an arrow toward the burner unit 14, that is, in a direction opposite to a flow direction of a fuel gas G in the combustion chamber 10.
At an upstream peripheral wall of the combustion liner 12, one or a plurality of spark plugs 36 are fixed to the housing H so as to penetrate the housing H and the combustion liner 12. The spark plug 36 ignites the pre-mixed gas injected from a below-described pilot burner 44 of the burner unit 14 to form a combustion region S at an upstream portion of the combustion liner 12. Moreover, a plurality of dilution air holes (not shown) are formed downstream of the combustion region S in the combustion liner 12 by causing short pipes to penetrate the housing H and the combustion liner 12.
The first premix passage 42a of the main burner 42 is formed to have an L shape in a vertical cross section passing through the axis line O (that is, a cross section that is a surface containing the axis line O). A radial swirler 50 is attached to an upstream portion of the first premix passage 42a which portion faces in a radially outward direction, that is, the radial swirler 50 is attached to between outermost peripheral portions of two disc portions 46b and 48b. A downstream portion of the first premix passage 42a faces in an axial direction. A radially outer end of the radial swirler 50 is formed as an entrance portion 50a through which the air A and a fuel F1 is introduced to the first premix passage 42a in a radially inward direction. A first fuel injection pipe 52 which forms a fuel passage through which the fuel F1 is supplied is provided on a further radially outward side of the entrance portion 50a so as to penetrate the end cover 18. A plurality of first fuel injection pipes 52 are arranged at regular intervals in a circumferential direction.
The radial swirler 50 is fixed to the main burner 42 by fitting in a fitting portion 42b formed between the outermost peripheral portions of two disc portions 46b and 48b. As shown in
As shown in
The dividing plate 56 may have such an adequate radial length that the compressed air A having flowed through the air passage 30 changes its direction to the radially inward direction to be introduced to the first premix passage 42a. A radial length L1 of the dividing plate 56, that is, a radial length of the radial swirler 50 is preferably in a range from ⅙ to ⅔ of a length L2 of an upstream radially straight portion of the first premix passage 42a, and more preferably ¼ to ½ of the length L2. In the present embodiment, the radial length L1 of the dividing plate 56 is set to ⅓ of the length L2 of the radially straight portion of the first premix passage 42a.
A ratio L1/D of the radial length L1 of the dividing plate 56 and an interval (that is an axial width of each swirler stage 50b) D between the adjacent dividing plates 56 along the axis line O is 2.0 in the present embodiment but is preferably 1.0 to 3.0, and more preferably 1.5 to 2.5. In a case where the ratio L1/D is lower than 1.0, the length L1 of the fixed swirl vane 54 is relatively short with respect to a large passage area (Circumferential Length of Entrance of Swirler×D). As a result, the effect of suppressing the bias of the axial air flow rate at each swirler stage 50b becomes small. In contrast, in a case where the ratio L1/D exceeds 3.0, an area (Circumferential Length of Dividing Plate 56×L1) of the dividing plate 56 is relatively large with respect to the large passage area of the swirler stage 50b. As a result, the frictional resistance of the air A by the dividing plate 56 increases.
The first fuel injection pipe 52 is provided with fuel injection openings 52a arranged in the axial direction. The number of fuel injection openings 52a is the same as that of the plurality of swirler stages 50b. The fuel injection openings 52a are provided so as to be respectively opposed to the swirler stages 50b on the entrance side. The fuel F1 is injected to the swirler stages 50b through the plurality of fuel injection openings 52a. In the present embodiment, inner diameters of the fuel injection opening 52a are the same as one another, and the flow rates of the fuel F1 injected to respective swirler stages 50b are set to be the same as one another.
An upstream portion of the second pre-mixed gas passage 44a is formed between an annular first passage plate 63 supported by the pilot burner 44 and a disc-shaped second passage plate 66 attached to the first passage plate 63 via a spacer 64 by a bolt 65 so as to be opposed to the first passage plate 63 in the axial direction. A second fuel injection pipe 67 configured to supply a fuel F2 is provided on a radially outward side of the upstream end of the second pre-mixed gas passage 44a so as to penetrate the end cover 18. The first fuel injection pipe 52 configured to supply the fuel F1 to the main burner 42 and the second fuel supplying passage 67 configured to supply the fuel F2 to the pilot burner 44 are provided as separate fuel supply systems. By individually controlling the fuel flow rate, the fuel concentration (air-fuel ratio) of the air-fuel mixture can be independently adjusted.
Next, the operation of the combustion device 2 configured as above will be explained.
As shown in
In this case, in accordance with the conventional radial swirler 50 not including the dividing plates, as shown in
Further, since the fuel injection openings 52a provided to respectively correspond to the swirler stages 50b of
To be specific, in the radial swirler 50 used in the present embodiment, the flow rates of the air A introduced to respective swirler stages 50b formed by dividing the radial swirler 50 by the dividing plates 56 in the axial direction are controlled to be substantially the same as one another, and the flow rates of the fuel F1 introduced to respective swirler stages 50b are controlled to be substantially the same as one another. Therefore, the axial fuel concentration distribution of the pre-mixed gas P1 generated at the upstream portion of the first premix passage 42a is uniformized. As a result, the radial fuel concentration distribution of the pre-mixed gas P1 injected through the first premix passage 42a into the combustion chamber 10 can be uniformized.
Moreover, unlike the present embodiment, the inner diameters of the plurality of fuel injection openings 52a of the first fuel injection pipe 52 may not be the same as one another and may be individually set. To be specific, the inner diameters of the plurality of fuel injection openings 52a of the first fuel injection pipe 52 may be different from one another. The appropriate fuel concentration distribution of the pre-mixed gas P1 injected into the combustion chamber 10 in order to realize low NOx combustion may change depending on various factors, such as the shape of the combustion chamber 10 and the structure of the pilot burner 44 used in combination with the main burner 42. To be specific, there is a case where the fuel concentration of the pre-mixed gas P1 injected into the combustion chamber 10 should be controlled to be not necessarily uniform but intentionally biased.
Even in such case, in accordance with the combustion device 2 according to the present invention, since the axial flow rate distribution of the air A is uniformized by dividing the radial swirler 50 in the axial direction, the radial fuel concentration distribution of the pre-mixed gas P1 injected into the combustion chamber 10 can be easily controlled only by controlling the flow rates of the fuel F1 supplied to respective swirler stages 50b.
As described above, the flow rates of the fuel supplied to respective swirler stages 50b can be easily controlled by, for example, individually setting the inner diameters of the fuel injection openings 52a corresponding to respective swirler stages 50b.
Moreover, the swirler 50 divided into multiple stages in the axial direction can obtain an especially large effect in the case of the present embodiment. To be specific, in the combustion device 2, the air A introduced to the radial swirler 50 receives the high centrifugal force since the flow direction thereof is changed by 90° through the radial swirler 50. However, by providing the dividing plates 56 at the radial swirler 50, the bias of the axial flow rate distribution of the air A introduced to the radial swirler 50 can be suppressed at minimum. Therefore, while realizing a compact configuration of the combustion device 2, the radial fuel concentration distribution of the pre-mixed gas P1 in the combustion chamber 10 can be optimized, and the low NOx combustion can be realized.
In the present embodiment, as one example, the radial swirler 50 is divided into five swirler stages 50b by four dividing plates 56. However, the number of swirler stages 50b is not limited to five and may be suitably set.
Moreover, in the above embodiment, the fixed swirl vane 54 and dividing plate 56 of the radial swirler 50 have substantially the same radial length as each other. However, the fixed swirl vane 54 and the dividing plate 56 may have the different radial lengths from each other. Further, the swirler stages 50b may be different in the radial length and axial length from one another.
The shape of an internal corner portion 42d of the first pre-mixed gas passage 42a may be a circular-arc shape, which is like a part of an oval shape, as shown by a chain double-dashed line in
As above, the preferred embodiments have been explained in reference to the drawings. Various changes and modifications may be easily made by one skilled in the art within the scope of the present description. Therefore, such changes and modifications are within the scope of the present invention claimed in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-136068 | May 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/002274 | 5/22/2009 | WO | 00 | 11/30/2010 |
