JPH0759978B2 - Gas turbine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas turbine, and more particularly to a gas turbine having a two-stage combustion system or a multi-stage combustion system combustor capable of reducing NOx.

[Background of the Invention]

As a gas turbine combustor, recently, a two-stage combustion system or a multi-stage combustor is being adopted for the purpose of achieving low NOx. All of these require that the amount of combustion air be adjusted by the gas turbine load. For example, Japanese Patent Publication Sho 53-43
In the publication, a baffle is provided in the air passage between the primary combustion zone and the secondary combustion zone. During low load operation, the primary combustion zone is reduced and the secondary combustion air is increased to prevent the primary combustion zone from becoming excessive or lean. Further, there is disclosed a combustor that adjusts baffles and suppresses NOx generation so that each air flows in without resistance during high load operation. However, there are problems of combustion performance and emission characteristics when shifting from first-stage combustion to second-stage combustion, and it is difficult to maintain good combustion performance before and after combustion switching by known air control.

[Object of the Invention]

An object of the present invention is to provide a gas turbine that can maintain good combustion performance during transfer from first-stage combustion to second-stage combustion, and can also maintain good emission characteristics.

[Outline of Invention]

The gas turbine of the present invention has a combustor having a primary fuel nozzle for diffusively burning primary fuel and air, and a secondary fuel nozzle disposed around the primary fuel nozzle for premixing and burning secondary fuel and air. A compressor for supplying air to the combustor, and a turbine driven by combustion gas from the combustor. Then, at the time of transition from the diffusion combustion to the premixed combustion, with the air to be used for the premixed combustion reduced, a part of the air supplied from the compressor to the combustor is discharged. Has a bypass means to
The bypass means has a flow rate adjusting valve for adjusting the air flow rate.

In a two-stage combustion type gas turbine combustor, the amount of air that flows into the second-stage combustion section is reduced by a variable device during the transition from first-stage combustion to second-stage combustion, and the second-stage combustion section has combustion performance and emission characteristics. And a good fuel-air ratio (fuel flow rate / air flow rate). Furthermore, the amount of air flowing into the second-stage combustion section was reduced in order to keep the fuel-air ratio within a favorable range due to the increase or decrease of the first-stage and second-stage fuels after the transition from first-stage combustion to second-stage combustion. In this state, the air flowing into the combustor is extracted, so that the combustion air amount is locally and globally adjusted.

Example of Invention

FIG. 1 shows an embodiment of the present invention. In the figure, the gas turbine is composed of a compressor 1, a turbine 2, a combustor 3, and the like. The air 1a compressed by the compressor 1 is guided to the combustor 3 through the inside of the casing 4. Combustor 3
An end cover 10 equipped with a primary fuel nozzle 9 for supplying a primary fuel 8 is attached to the outer cylinders 5a, 5b, the inner cylinder 6 and the front combustion chamber 7. The inner cylinder 6 is formed by a front combustion chamber 7 and a rear combustion chamber 11 having a diameter larger than that of the front combustion chamber 7, and an air supply hole 13 is provided in a connecting portion 12 between the front combustion chamber 7 and the rear combustion chamber 11. .
The secondary fuel 14 is ejected here, and the secondary combustion chamber together with the secondary air
Is fed to 11 to form a secondary combustion flame 15. Ignition of the primary fuel 8 ejected from the primary fuel nozzle 9 is performed by a spark plug (not shown) to form a primary combustion flame 16. On the other hand, the ignition of the secondary fuel 14 is achieved by the transfer from the primary combustion flame 16.

The configuration of the combustor 3 will be further described with reference to FIG. The primary fuel 8 is ejected into the front combustion chamber 7 by the primary fuel nozzle 9, and the ejection portions 9a are plural so that the fuel is dispersed and ejected. Similarly, the secondary fuel 14 passes through the inside of the secondary fuel nozzle 17 that is sandwiched and fixed by the outer cylinders 5a and 5b, and is further ejected from the tip of a plurality of protruding ejection portions 18. . The primary fuel 8 is jetted into the front combustion chamber 7, mixed with a large amount of combustion air 19 flowing through the casing 4, diffused, and burned to produce the primary combustion flame 16
To form. The secondary combustion unit ejects the secondary fuel ejected from the ejection unit 18 and the combustion air 21 flowing in from the opening 20.
The mixture is mixed downstream of 18 and the mixture is supplied into the rear combustion chamber 11. A movable piece 22 is provided in this opening 20 so as to cover it.
Is provided, and the amount of the combustion air 21 flowing through the opening 20 can be adjusted by moving around the opening 20 by means of a link mechanism or the like. The amount of the combustion air 21 is adjusted according to the amount of secondary fuel so that the above-described fuel-air ratio (fuel amount / air amount) of the air-fuel mixture falls within an appropriate range. Further, in the low load operation range where the secondary fuel is not ejected, the amount of the combustion air 19 flowing into the front combustion chamber 7 is
The movable piece 22 is moved, the opening 20 is opened, and a large amount of the combustion air 21 is caused to flow in and bypassed to reduce the amount. As a result, the fuel-air ratio of the primary combustion section is adjusted to fall within an appropriate range. The primary combustion is used in the range from the start of the gas turbine to the low load operation, and both the primary and secondary combustion are performed in the range from the low load to the rated load operation.
Combustion transition from primary combustion only to both primary and secondary combustion requires ignition from the primary combustion flame to the secondary combustion mixture.
This ignition is performed during low-load operation of the gas turbine, but since the gas turbine is operated at a constant rotation speed, the rotation speed of the compressor is also constant and the compressed air, that is, the combustion air amount is It is constant. For this reason, the fuel-air ratio depends only on the amount of fuel, and in order to maintain good combustion characteristics and exhaust gas characteristics, it is essential to adjust the combustion air. Therefore, when igniting the air-fuel mixture for secondary combustion, the flow passage area of the opening 20 is adjusted to be smaller by moving the movable piece 22 so that the air-fuel ratio can ignite the air-fuel mixture. However, the inflow amount of the combustion air 21 becomes extremely small when the fuel-air ratio becomes appropriate, and the inflow velocity of the air-fuel mixture into the rear combustion chamber becomes very small although the air-fuel mixture is ignited. As a result, the combustion flame flows back to the ejection portion 18 and burns the vicinity of the ejection portion 18, or the combustion flame fluctuates and causes an abnormal state such as combustion vibration. Therefore, the movement of the movable piece 22 is limited to the range where the combustion flame does not flow back. To prevent flashback, the fuel-air ratio of the secondary combustion air-fuel mixture has a smaller value because the air amount is larger than a predetermined amount.

Here, the control of the fuel amount when only the primary combustion is performed and both the primary combustion and the secondary combustion are performed will be described. The output of the gas turbine is proportional to the amount of fuel for power generation, which is operated at a constant rotation speed, and the output is maintained with only the primary fuel during the low load operation of the primary combustion only. However, during the primary and secondary combustion, the output is maintained at the total fuel amount of the primary fuel amount and the secondary fuel amount. As far as the primary fuel is concerned, the case of the primary combustion and the primary and secondary combustion is In the case of transition, the amount of fuel is much smaller in the case of transition to primary and secondary combustion, and the fuel-air ratio becomes smaller, which may adversely affect the combustion performance. In the secondary combustion section, the amount of combustion air is large and the fuel-air ratio is small. In order to solve these problems, as shown in FIG. 1, the combustion air compressed by the compressor is extracted from the holes provided in the casing 4 before flowing into the combustor, and is discharged into the exhaust gas 23 having a low pressure. Discharge. The flow rate adjusting valve 24 controls the amount of bleed air to reduce the combustion air as a whole so that the fuel-air ratio falls within an appropriate range. Here, the high temperature obtained by the work of the compressor,
By extracting a part of high-pressure compressed air, that is, combustion air without passing through the combustor as well as the turbine 2, the amount of combustion gas passing through the turbine 2 tends to decrease and the output tends to decrease. The output lowering portion is compensated by an increase in the fuel amount, and substantially, the bleed air causes an increase in the fuel amount and a decrease in the air amount, leading to an increase in the fuel-air ratio. Moreover, this increase in the fuel-air ratio is very effective at the start of the primary and secondary combustion. FIG. 3 is a control diagram. The gas turbine load is plotted on the abscissa, and the allowable opening, bleed air amount, and fuel-air ratio are shown. The abscissa is the same scale for all three. Generally, in a combustor, a lean low-temperature combustion method with a low combustion flame temperature is said to be effective for achieving low NOx.
Performance will be decided. In FIG. 3, the fuel-air ratio shows that the lower range shows an appropriate range when the primary combustion section is a diffusion combustion system, and the upper range is an appropriate range when the secondary combustion section is a premixed combustion system. Indicates the range. In both ranges, the upper limit is determined by the limit value of NOx value resulting from the flame temperature rise due to the increase of the fuel-air ratio, and the lower limit is determined by the limit value of CO value caused by incomplete combustion resulting from the combustible limit. However, in any case, unless the fuel-air ratio can be controlled within this range, a combustor having satisfactory combustion performance and exhaust gas characteristics cannot be obtained.

Here, FIG. 3 will be described in detail. Control from startup to the rated speed is not shown here,
Only in the primary combustion, the fuel amount is increased to reach the predetermined fuel-air ratio in proportion to the increase in the air amount due to the increase in the rotation speed, the rated rotation speed is reached, and the fuel at the position of gas turbine load 0 (zero) shown in this figure It becomes an empty ratio. After reaching the rated speed, the gas turbine load operation starts, but during this period, the speed is constant and the compressed air from the compressor, that is, the combustion air flowing into the combustor, is constant. . Therefore, unless the amount of combustion air is specially adjusted, the load on the gas turbine is controlled by controlling the amount of fuel. In low-load operation with only primary combustion, when the movable piece that adjusts the air flowing into the secondary combustion section is fully opened without changing the opening, the amount of fuel changes from load 0 (zero) to increase in load. As it increases, it rises within the proper fuel-air ratio range.
Further, the fuel-air ratio rises due to the increase in the fuel amount due to the load increase, but the NOx amount tends to increase near the upper limit of the fuel-air ratio, so here, as described above, it flows into the secondary combustion section. The amount of air is gradually reduced by moving the opening of the movable piece in the closing direction. By this operation, the amount of air flowing into the head combustion chamber is increased, and as the fuel amount is increased due to the increased load, the fuel-air ratio is kept substantially constant, and the increase in the NOx amount is suppressed. The opening of the movable piece further moves in the closing direction as the load increases, and the movement is completed in a state where it is open to some extent before being fully closed. Incidentally, the reason why the movable piece is not fully closed is that, as described above, the amount of air becomes extremely small, which may cause backflow of combustion flame or abnormal combustion. After that, the load of the secondary fuel is increased without changing the air amount by increasing the primary fuel to increase the load. The amount of fuel in the case of shifting from only the primary combustion to the primary and secondary combustion is only the primary fuel amount before the shifting and becomes the total fuel amount of the primary fuel and the secondary fuel after the shifting. If the gas turbine load does not change before and after the transition, the total fuel amount must also be constant, and the fuel-air ratio of the primary combustion part and the primary combustion part, The fuel-air ratio of each secondary combustion unit must be within an appropriate fuel-air ratio range that can maintain good combustion performance and exhaust gas characteristics. However, when an attempt is made to shift from the primary combustion to the primary combustion and the secondary combustion with the air amount kept constant after the movement of the movable piece is completed, the fuel-air ratio changes as shown by the broken line in FIG. The result will be below the lower limit of the fuel-air ratio. As shown in FIG. 4, CO due to incomplete combustion is generated as shown by the broken line in the exhaust gas characteristics, and although NOx is low, combustion performance is extremely low and unstable combustion results in various problems. Therefore, according to the present invention, in a state where the movement of the movable piece is completed, the combustion air flowing into the combustor is extracted and reduced so that the fuel-air ratio becomes appropriate. Specifically, the compressed air from the compressor is gradually extracted as the load increases, and is controlled by the flow rate adjustment valve so that it becomes maximum at the point where the primary combustion changes to the primary and secondary combustion. There is. In the gas turbine, the amount of combustion air decreases and the amount of combustion gas decreases due to the extraction of air.
The output will decrease. However, since the control is performed so as to perform the constant load operation, an amount of fuel that compensates for the output reduction is further supplied in proportion to the extraction amount, and as a result, the fuel-air ratio shown in FIG. 3 is obtained. The fuel-air ratio will increase as seen in the change of. Due to the bleed air, the fuel-air ratio is increased, so that the combustion temperature is increased and the NOx value is slightly increased as shown in FIG. Regarding CO, there is not much change at the time of primary combustion, but the primary after the transition to primary and secondary combustion,
The fuel-air ratio of the secondary combustion section becomes higher due to the increase in the amount of fuel to compensate for the output reduced by the bleed air, and falls within the appropriate fuel-air ratio range, so it is extremely reduced compared to the past and the combustion performance is improved. be able to. In the primary / secondary combustion transition, the fuel-air ratio tends to increase due to an increase in the fuel amount as the load increases. The amount of bleed air is gradually reduced by closing the flow rate adjusting valve, and the fuel-air ratio is kept substantially constant within the proper fuel-air ratio range, while the amount of bleed air is zero. further,
As the load increases, the amount of air flowing into the secondary combustion section is moved to the fully open direction by moving the movable piece so that it is within the proper fuel-air ratio range, while moving the movable piece to full open. Let After that, the air amount is not adjusted, the load increases due to the increase in the fuel amount, and the fuel-air ratio increases with the increase in the fuel amount. In this high load range, the fuel-air ratio when the air amount adjustment is completed is adjusted to be near the lower limit of the proper fuel-air ratio range. The fuel-air ratio only rises within the ratio range, and the combustion performance and exhaust gas characteristics are not affected. Thus, the present invention can be applied to a two-stage combustor or a multi-stage combustor, but within a proper fuel-air ratio range in all load zones in order to maintain good combustion characteristics and exhaust gas characteristics of the combustor. Therefore, it is characterized in that it has both a local adjustment of the combustion air and an adjustment of the total amount.

5 to 7 show a modification of the present invention. Each of them shows a method of extracting air when a movable piece for adjusting the amount of air flowing into the secondary combustion section is provided.

FIG. 5 shows the casing 1 for the air 1a compressed by the compressor 1.
It shows that the air is extracted from the section and communicates with the intermediate stage of the turbine 2 section through the flow rate adjusting valve 24 by the pipe 25. By communicating the extracted air with the turbine section intermediate stage 2a,
Unlike the case of communicating with the exhaust gas 23, energy can be recovered by joining the compressed air with high pressure with the combustion gas of the turbine section, so that the efficiency decrease due to extraction can be mitigated.

FIG. 6 shows that the extracted air is communicated with the intermediate stage 1b of the compressor 1. This is to reduce the inlet air amount of the compressor and the amount of air flowing into the combustor by extracting and returning the compressed air upstream of the compressor.

In FIG. 7, the head 3a of the combustor 3 is located at the location where the air is extracted, and the compressed air 1a is used to sufficiently cool the surface of the inner cylinder 6 of the combustor 3 before the air is extracted. Is effective in reducing the metal temperature. As shown in FIG. 7, the air extracted from the head 3a of the combustor 3 is introduced into the exhaust gas 23 through the flow rate adjusting valve 24 through the pipe 25 or the turbine 2
The intermediate stage 2a, the intermediate stage 1b of the compressor 1, or a combination thereof can be connected.

〔The invention's effect〕

According to the present invention, the amount of air for combustion of the combustor can be adjusted locally or entirely, so that it can be accurately controlled under all conditions so that it is within an appropriate fuel-air ratio range,
Especially in the full load zone of the gas turbine, the combustion performance and the exhaust gas characteristics of the combustor can be kept good especially during the transition from primary combustion to primary and secondary combustion.

[Brief description of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention, FIG. 2 is a sectional view of a combustor of the present invention, FIG. 3 is an explanatory diagram of a control method, FIG. 4 is an exhaust gas characteristic diagram, and FIGS. FIG. 7 is a system diagram of a modified example of the present invention. 1 ... Compressor, 2 ... Turbine, 3 ... Combustor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsukuni Kuno 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Kenji Tokunaga 3-chome, Hitachi-shi, Ibaraki No. 1 No. 1 Hitachi Ltd., Hitachi Factory (72) Inventor Tomio Kuroda, 502 Kintatemachi, Tsuchiura City, Ibaraki Prefecture 502, Inst. In the Institute of Mechanical Research, Hitate Manufacturing Co., Ltd. (72) Yoji Ishibashi, 502, Kandamachi, Tsuchiura City, Ibaraki Prefecture In the Mechanical Research Laboratory, Hitachi, Ltd. (72) Isao Sato, 502, Kandachimachi, Tsuchiura City, Ibaraki Prefecture Machinery Research Laboratory (72) Inventor Tsuneyuki Hata 3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Factory (56) Reference Document JP Akira 60-66020 (JP, A)

Claims (1)

[Claims] 1. A combustor having a primary fuel nozzle for diffusively burning primary fuel and air, and a secondary fuel nozzle arranged around the primary fuel nozzle for premixing and burning secondary fuel and air, A compressor that supplies air to the combustor,
In a gas turbine having a turbine driven by combustion gas from the combustor, at the time of transition from the diffusion combustion to the premixed combustion,
With reduced air to be used for the premixed combustion,
A gas turbine comprising: bypass means for discharging a part of the air supplied from the compressor to the combustor; and the bypass means having a flow rate adjusting valve for adjusting an air flow rate.