JPH073154Y2 - Backflow can combustor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a backflow can combustor for a gas turbine.

[Prior Art] Conventionally, in a gas turbine, an air passage is formed between an inner cylinder and an outer cylinder that form a combustor, and air flows from a base end side to a tip end side of the air passage. There is a combustor (for example, see Japanese Utility Model Publication No. 55-142635). An example of this type of backflow can combustor is shown in FIG.

In FIG. 7, 1 is a fuel injection valve, 2 is an inner cylinder of a combustor,
3 is an outer cylinder of the combustor, 4 is an air passage, and the inner and outer cylinders 2,
It is formed in an annular shape between 3 and from the base end side B to the front end side A.
Air, and thus the combustor is a backflow can combustor. This air passage 4 is located upstream of the combustion chamber 6 via the first combustion air hole 5A on the tip side A of the combustor.
6a and also communicates with the downstream portion 6b of the combustion chamber 6 via the second combustion air hole 5B and the dilution air hole (third air hole) 7 on the proximal side B of the combustor. . This combustor is also a two-stage combustor in which a throttle is provided in the intermediate portion 2a of the inner cylinder 2 and the combustion chamber 6 is divided into a rich combustion region in the upstream portion 6a and a lean combustion region in the downstream portion 6b. .

As is well known, in this two-stage combustor, the production of NOx is suppressed. That is, in the rich combustion region of the upstream portion 6a, the fuel supplied from the fuel injection valve 1 is supplied by the air from the first fuel air hole 5A in a state where the fuel is richer than the theoretical air-fuel ratio. The amount of NOx generated is suppressed by burning the fuel to produce an incomplete combustion state in which oxygen is insufficient. On the other hand, the downstream part 6
In the lean burn region of b, air is further taken in from the second combustion air hole and burned in a state where the fuel is leaner than the stoichiometric air-fuel ratio.
You can suppress the generation of x.

[Problems to be Solved by the Invention] However, as shown in FIG. 8, the conventional two-stage combustor can reduce NOx during rated operation with a smaller air-fuel ratio than a general stage combustor. However, NOx increases during partial load operation with a large air-fuel ratio. In other words, in partial load operation, the fuel amount is generally throttled, but the air amount is not so throttled, so the air-fuel ratio in the rich combustion region of the upstream portion 6a in FIG. As a result of not obtaining the state, NOx is easily generated.

Therefore, the number of dilution air holes 7 is increased, and a flow rate adjusting valve is provided in the dilution air holes 7 to throttle the dilution air holes 7 during the rated operation to send a relatively large amount of air to the first combustion air holes 5A. On the other hand, a method may be considered in which NOx generation is reduced even during partial load operation by greatly opening the dilution air hole 7 during partial load operation and restricting the air sent to the first combustion air hole 5A. However, in this way, during the partial load operation in which the flow rate adjusting valve is opened, the amount of air flowing through the air passage 4 on the tip side A with respect to the dilution air hole 7 decreases, so that the wall temperature of the upstream portion 2b of the inner cylinder 2 decreases. As it rises, durability and the like decrease.

The present invention has been made in view of the above-mentioned conventional problems, and provides a backflow can combustor capable of reducing NOx even at a partial load operation and preventing an increase in wall temperature of the inner cylinder. It is an object.

[Means for Solving the Problems] In order to achieve the above object, the present invention allows a part of the air in the air passage communicating with the first combustion air hole to pass from the tip of the air passage to the outside of the outer cylinder. Then, a return passage introduced into the third air hole and a valve for controlling the amount of air passing through the return passage are provided.

In this case, the outlet end forming the downstream end of the return passage is fitted into the third air hole, and a gap is formed in the radial direction between the outlet end and the third air hole. Preferably.

[Operation] According to the present invention, the amount of air introduced from the return passage to the third air hole is controlled by the valve, so that the amount of air supplied from the air passage to the first combustion air hole is controlled. You can control. Moreover, since the return passage introduces a part of the air in the air passage from the tip of the air passage into the third air hole, the air introduced from the third air hole into the inner cylinder through the return passage. Also flows outside the upstream portion of the inner cylinder.

Also, an outlet end forming a downstream end of the return passage,
When a gap is provided between the third air hole and the third cylinder, the inner cylinder expands and contracts due to the temperature change, so that even if the position of the third air hole is displaced, the outlet end portion has the third hole. Since it is not restricted by air holes, there is no risk of thermal stress.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 8 denotes a return passage, which is formed from a pipe 8A which is led out from the tip of the air passage 4 and passes through the outer cylinder 3 and is fitted into the dilution air hole 7A. A part of this is introduced into the dilution air hole 7A.
The return passage 8, that is, a plurality of pipes 8A are provided, but are provided only for some of the dilution air holes 7A, and the other dilution air holes 7 face the air passage 4 and open. ing. An auxiliary dilution air hole 7B that supplements the amount of air is provided upstream of the other dilution air holes 7 and 7A.

Reference numeral 9 denotes a valve, which is, for example, a butterfly valve provided in the middle of each return passage 8 and controls the amount of air passing through the return passage 8. In addition, this valve 9
For example, it is set to be fully closed during rated operation, and is opened / closed by an actuator (not shown) connected to each valve 9.

Other configurations are similar to those of the conventional example of FIG. 7, and the same portions or corresponding portions will be denoted by the same reference numerals and detailed description thereof will be omitted.

Next, the operation of the combustor will be described.

First, during the rated operation, the valve 9 is in the fully closed state as shown by the solid line. Therefore, a part of the air flowing from the base end side B to the tip end side A in the air passage 4 is introduced into the combustion chamber 6 from the diluted air hole 7, and the remaining air is left in the first combustion air hole 5A.
And it is introduced into the combustion chamber 6 through the second combustion air hole 5B. As a result, as is well known, two-stage combustion is performed and NOx generation is suppressed.

Next, during the partial load operation, the valve 9 is opened as shown by the alternate long and short dash line and the return passage 8 is opened. Therefore, the air also flows from the front end side A of the air passage 4 to the return passage 8 as shown by the alternate long and short dash line, and this air is also introduced into the combustion chamber 6 from the diluted air hole 7A. Therefore, the first air hole
The amount of air introduced from 5A to the upstream portion 6a of the combustion chamber 6 decreases, and the amount becomes appropriate during the partial load operation with a small amount of fuel. As a result, in the rich combustion region of the upstream portion 6a, the fuel is burned while being kept richer than the stoichiometric air-fuel ratio, so that the generation of NOx is suppressed as shown in FIG.

On the other hand, since the return passage 8 in FIG. 1 is led out from the tip side A of the air passage 4, not only the first combustion air hole 5A but also the dilution air hole 7A from the combustion chamber through the return passage 8 The air introduced into 6 also flows outside the upstream portion 2b of the inner cylinder 2. Therefore, even during partial load operation, the upstream portion 2b
Since the flow velocity of the air flowing through the air passage 4 on the outer side of the inner cylinder 2 does not decrease, the wall of the upstream portion 2b of the inner cylinder 2 can be sufficiently cooled, so that the temperature rise of this wall can be prevented and, for example, the durability of the inner cylinder 2 can be improved. Does not decrease.

FIG. 2 shows a second embodiment of this invention.

In FIG. 2, the outlet end 8B forming the downstream end 8b of the return passage 8 is fitted into the dilution air hole 7A and is formed to have a smaller diameter than the dilution air hole 7A.
A gap 10 is set between it and 7A. The dilution air hole 7A into which the outlet end 8B is fitted is the inner cylinder 2 made of ceramic.
A plurality of equiangular pitches are provided all around. A return passage 8 is provided for all of the dilution air holes 7A. The rest of the configuration is the same as that of the first embodiment, and the same parts or corresponding parts are designated by the same reference numerals,
The detailed description is omitted.

In the above configuration, since the pipe 8A and the outer cylinder 3 and the inner cylinder 2 forming the combustion chamber 6 have a large temperature difference, the expansion and contraction amounts due to the temperature change are different from each other. Therefore, the exit end 8B
And the position of the dilution air hole 7A are relatively displaced.
Here, in this embodiment, since the gap 10 is provided between the outlet end 8B and the dilution air hole 7A, thermal stress does not occur even if the positions of both 8B and 7A are relatively displaced. Especially the inner cylinder 2
When the product is made of ceramic, there is a large difference in the amount of expansion and contraction of both 8B and 7A, so the effect of not generating the thermal stress is large.

By the way, in the first embodiment of FIG. 1, since air is not introduced from some of the dilution air holes 7A during the rated operation, the air supply may become uneven in the circumferential direction. On the other hand, in the embodiment of FIG. 2, since air is introduced from all the dilution air holes 7A in which the outlet end portions 8B are fitted, the dilution air holes 7A are arranged in the circumferential direction of the inner cylinder 2, for example. By providing the pitches at equal angles, the air can be uniformly supplied in the circumferential direction. Moreover, since the air can be uniformly supplied in this manner, it is not necessary to provide the auxiliary dilution air holes 7B shown in FIG. 1, so that the number of the dilution air holes can be reduced.

3 to 5 show a third embodiment of the present invention.

In FIG. 3, reference numeral 18 denotes an annular return passage, which is an outer cylinder 3
And a cylindrical passage wall 18A provided further outside the outer cylinder 3 to form a gap. Reference numeral 18B is a communication pipe, which is fixed to the passage wall 18A by a bolt (not shown), forms the downstream end portion 18b of the return passage 18, is inserted into the outer cylinder 3, and is diluted from the opening portion to the dilution air hole 7A. Introduce air. A gap is similarly provided between the communication pipe 18B and the dilution air hole 7A in the embodiment of FIG.

Reference numeral 10 denotes a valve seat, which is flange-joined to the lid 11 and the passage wall 18A, and has a large number of first vent holes 10a on the annular plate and the fourth vent hole 10a.
As shown by the solid line in the figure, it is provided with equiangular pitches. Reference numeral 12 in FIG. 3 denotes a valve element, which is arranged so as to face the valve seat 10, and a large number of second vent holes 12a shown by broken lines in FIG. 4 are provided on the annular plate by equiangular pitches. Has been. In addition,
The valve 9 and the valve seat 10 shown in FIG. 3 form a valve 9. The valve body 12 is slidable in the circumferential direction and has an arcuate rack 12b in a part of the circumferential direction as shown in FIG. An actuator 13 is a pinion 15 that engages with the rack 12b at the tip of a drive shaft 14 connected to the motor M.
The valve body 12 is rotated by a half pitch P / 2 from the fully closed position shown in FIG. As a result, during the partial load operation, the first vent hole 10a and the second vent hole 12a face each other, and the air flows through the return passage 18 as shown by the alternate long and short dash line in FIG. It is supplied into the combustion chamber 6 from the dilution air hole 7A. Needless to say, the rotational position of the valve element 12 is adjusted according to the load, and the amount of air flowing through both through holes 10a, 12a (Fig. 5) is controlled. The other structure is the same as that of the first embodiment shown in FIG. 1, and the same portions or corresponding portions are designated by the same reference numerals and detailed description thereof will be omitted.

In the above-mentioned structure, the return passage 18 of FIG. 3 is annular and the annular valve body 12 is provided. Therefore, the embodiment of FIG. 1 is different, and the valve 9 is operated by one actuator 13 of FIG. Can be opened and closed. Moreover, since the seal portion 16 on the drive shaft 14 of the actuator 13 is reduced,
Air leakage is also reduced.

By the way, the valve 9 is provided in the middle of the return passage in each of the above embodiments, but it may be provided at the upstream end of the return passage 18 as in the fourth embodiment of FIG. In the case of this embodiment, the valve 9 is formed in a cylindrical shape, and by sliding on the outer cylinder 3, the return passage 18
Open and close.

Further, although the two-stage combustor has been described in each of the above embodiments, the present invention can be applied to a premix type combustor.
Here, the premixing type combustor includes a premixing device that preliminarily mixes air and combustion at a predetermined ratio to create a homogeneous air-fuel mixture, and supplies the air-fuel mixture to the combustion chamber for combustion. Say. In this case, the holes for supplying air to the premixing device become the first combustion air holes.

[Advantage of the Invention] As described above, according to the present invention, the amount of air supplied from the air passage to the first combustion air hole can be controlled, so that NOx can be reduced even during partial load operation. Since the air introduced into the combustion chamber from the return passage also flows outside the upstream portion of the inner cylinder, it is possible to prevent the wall temperature of the inner cylinder from rising.

Further, when a gap is provided between the outlet end that forms the downstream end of the return passage and the third air hole, there is no risk of thermal stress.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a combustor showing a first embodiment of the present invention, FIG. 2 is a sectional view of a combustor showing a second embodiment, and FIG.
FIG. 4 is a sectional view of a combustor showing a third embodiment, FIG. 4 is a front view of a valve, FIG. 5 is a sectional view showing an actuator, and FIG. 6 is a sectional view of a combustor showing the fourth embodiment. FIG. 7 is a sectional view of a conventional combustor, and FIG. 8 is a characteristic diagram showing a performance comparison between a conventional example and a combustor according to the present invention. 2 ... inner cylinder, 3 ... outer cylinder, 4 ... air passage, 5A ... first
Combustion air holes, 5B ... Second combustion air holes, 7,7A, 7B
...... Second air hole (dilution air hole), 8,18 ...... Return passage, 8b ...... Downstream end, 8B ...... Outlet end, 9 ...... Valve,
10 …… Gap, A …… tip side, B …… base side.

Claims (2)

[Scope of utility model registration request] 1. An annular air passage which is formed between an inner cylinder and an outer cylinder forming a combustor and through which air flows from a base end side to a tip end side, and a first combustion air hole on the tip side. The second combustion air hole and the third air hole on the base end side, and a part of the air in the air passage are introduced into the third air hole from the tip of the air passage through the outside of the outer cylinder. And a valve for controlling the amount of air passing through the return passage. 2. The outlet end forming a downstream end of the return passage is fitted into the third air hole, and the outlet end and the third air hole are connected to each other. A backflow can combustor with a radial gap between them.