JPH08296405A - Thermal stress decreasing operation method for steam turbine in uniaxial combined cycle - Google Patents

Abstract

PURPOSE: To minimize the temperature change width around a steam turbine rotor by quickly closing a high pressure steam governor and decreasing a low pressure steam governor in case of emergency shutdown of a generator, holding the low pressure steam governor in its slightly opened state so as to introduce a cooling air, and cooling an area in the vicinity of a steam turbine low pressure last stage. CONSTITUTION: When the load of a generator 1 is abruptly decreased or shut down in an emergency and a signal of load decrease caused by failure of an auxiliary machine, etc., is input, opening of a high pressure steam governor 8 is quickly closed. A low pressure steam governor 10 is also closed simultaneously with the input of the load decrease signal. After that, the opening of the low pressure steam governor 10 is held in its slightly opened position and the cooling steam is introduced into a steam turbine 2 so as to cool an area in the vicinity of the low pressure last stage of the steam turbine 2. The temperature change width around the rotor of the steam turbine 2 can be thus minimized so that generation of the thermal stress can be decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating a generator of a single-shaft combined cycle when the load is suddenly reduced or when an emergency stop occurs.

[0002]

2. Description of the Related Art FIG. 2 shows a schematic system of a uniaxial combined cycle. The uniaxial combined cycle is a system in which a gas turbine 3, a steam turbine 2, and a generator 1 are uniaxially connected. The gas turbine exhaust gas that has worked in the gas turbine 3 undergoes heat exchange in the exhaust heat recovery boiler 4 to generate high pressure steam and low pressure steam. The high-pressure steam generated in the exhaust heat recovery boiler 4 passes through the high-pressure steam pipe 5, the high-pressure steam stop valve 7 and the high-pressure steam control valve 8, and the low-pressure steam similarly has the low-pressure steam pipe 6,
It is introduced into the steam turbine 2 through the low-pressure steam stop valve 9 and the low-pressure steam control valve 10.

The load control of the steam turbine 2 is performed by the generator output,
A valve opening signal is output by fetching the shaft rotation speed and the like into the control device 11 and comparing the calculated value with a set value. The valve opening signal is converted into a hydraulic pressure signal by the electric oil exchanging devices 12 and 13, and the control valves 8 and 10 are opened and closed via the control valve drive device.

In the single-shaft combined cycle, there is an operating state in which the power output from the generator is not entirely covered by the gas turbine 3 and the steam turbine 2 rotates while being driven by the gas turbine 3. At this time, in order to prevent the vicinity of the low-pressure final stage moving blade of the steam turbine 2 from overheating due to windage of the moving blade, a low-pressure steam control valve 10 is output with a slight opening signal.
The cooling steam is introduced through 0 to control so as to prevent overheating in the vicinity of the low pressure final stage moving blade.

[0005]

As described above, in the conventional single-shaft combined cycle, the steam turbine 2 is used.
Although the steam flowing into the exhaust heat recovery boiler 4 is generated, the high temperature steam temperature flowing into the steam turbine 2 also decreases because the gas turbine exhaust gas temperature decreases as the load decreases.

Generally, when the steam temperature around the steam turbine rotor changes, thermal stress is generated in the steam turbine rotor. The load change rate is set so that the thermal stress generated during normal load changes is kept small. However, when it is necessary to reduce the load abruptly due to an accessory failure or the like, the high-pressure steam temperature also drops in a short time as the load suddenly decreases. When this high-pressure steam flows into the steam turbine 2, excessive thermal stress is generated in the steam turbine rotor, and in the worst case, cracks may occur in the steam turbine rotor.

In order to prevent the occurrence of this excessive thermal stress, it is necessary to reduce the temperature change width or the temperature change rate around the steam turbine rotor.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of conventional apparatuses, and in a combined cycle in which a generator, a steam turbine and a gas turbine are uniaxially connected, power generation is performed. In the event of sudden load reduction or emergency stop of the machine, by rapidly closing the high pressure steam control valve and by rapidly reducing the low pressure steam control valve, by holding the low pressure steam control valve slightly open and introducing cooling air. A method for reducing the thermal stress of a steam turbine in a single-shaft combined cycle, which is characterized in that the vicinity of the low-pressure final stage of the steam turbine is cooled.

[0009]

In general, it is difficult to reduce the temperature change rate of the high-pressure steam generated in the exhaust gas boiler at the time of an abnormality such as an auxiliary machine failure. If a high-pressure steam control valve is issued, a quick close command is issued to prevent the high-temperature steam whose temperature has dropped from flowing into the steam turbine. However, if this is fully closed, another problem will occur in that the temperature near the low-pressure final stage of the steam turbine will rise due to the windage of the long blades. Is introduced to cool the vicinity of the low-pressure final stage of the steam turbine.

Thus, in the present invention, the generation of excessive thermal stress due to rapid cooling of the surface of the steam turbine rotor due to the inflow of high-pressure steam whose temperature has decreased as the generator output decreases. On the other hand, by keeping the low-pressure steam control valve slightly open and introducing the cooling steam into the steam turbine, overheating in the vicinity of the low-pressure final stage moving blades of the steam turbine is prevented.

[0011]

Embodiments of the present invention will be described with reference to FIG. Since the arrangement of the apparatus for carrying out the present invention is as shown in FIG. 2 described above, the overlapping portions are omitted and the necessary portions are referred to by the numbering in FIG. The operating status will be described.

The load reduction signal S becomes a line segment 1 due to an accessory failure or the like.
When the gas turbine load P _GT is input to the control device 11 as shown by 4, the gas turbine load P _GT starts to decrease sharply as shown by the line segment 15. When the gas turbine load P _GT drops below a certain load value, the high pressure steam temperature T _HP generated in the exhaust heat recovery boiler 4 drops as shown by the line segment 16, and the rated temperature cannot be maintained.

In normal operation, the high-pressure steam control valve 8 is operated at a normal load reduction, when the gas turbine load P _GT reaches a certain value P, as shown by the line segment 17, the high-pressure control valve opening L' _HP.
Is gradually closed, but in this operation, when the high-pressure steam control valve 8 is fully closed, the high-pressure steam temperature 16 is greatly reduced from the rated temperature as in the part Z, and the normal temperature is high. Since the rate of change in load is very large compared to the decrease in load, the temperature around the rotor of the steam turbine 2 changes within a short time and excessive thermal stress occurs.

In contrast to this general operation method, in the present embodiment, the valve opening L _HP of the high pressure control valve is input with a load reduction signal 14 due to an auxiliary machine failure or the like as shown by a line segment 18. Immediately, the high pressure regulator valve 8 begins to close. By performing such an operation, the amount of decrease in the high pressure steam temperature 16 at R from the rated temperature when the high pressure control valve 8 is fully closed can be made small as indicated by the line segment X, and as a result, the steam turbine rotor It is possible to reduce the thermal stress generated in the.

On the other hand, the low-pressure steam control valve 10 also starts to close at the same time when the load reduction signal 14 is input, and the valve opening L _LP of the low-pressure steam control valve 10 is held at the slightly open position T as indicated by the line segment 19. The cooling steam is introduced into the steam turbine 8 to suppress the temperature rise near the steam turbine low-pressure stage moving blades.

[0016]

As described above in detail, according to the present invention, the thermal stress caused by the sudden load reduction or the emergency stop of the generator due to the constant operation of the high pressure steam control valve and the low pressure steam control valve. Can be reduced.

As a result, the reliability of the steam turbine alone can be improved, and the reliability of the entire power generation facility can be greatly improved to contribute to the stable supply of electric power.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a driving situation according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a combined unit in which a generator, a steam turbine, and a gas turbine are uniaxially connected.

[Explanation of symbols]

1 generator 2 steam turbine 3 gas turbine 4 exhaust heat recovery boiler 5 high pressure steam pipe 6 low pressure steam pipe 7 high pressure steam stop valve 8 high pressure steam control valve 9 low pressure steam stop valve 10 low pressure steam control valve 11 controller P _GT gas turbine load T _HP High-pressure steam temperature L' _HP High-pressure steam control valve opening (normal operation) L _HP High-pressure steam control valve opening (during sudden load decrease) L _LP Low-pressure steam control valve opening

Claims (1)

[Claims] 1. In a combined cycle in which a generator, a steam turbine, and a gas turbine are uniaxially connected, the high-pressure steam control valve is rapidly closed and the low-pressure steam control is performed at the time of sudden load reduction or emergency stop of the generator. In the single-shaft combined cycle, the number of valves is suddenly reduced, and then the low-pressure steam control valve is kept slightly opened to introduce cooling air to cool the vicinity of the steam turbine low-pressure final stage. Operation method for reducing thermal stress of steam turbine.