Medium-pressure bypass system of fuel gas-steam combined cycle unit

Abstract

The invention discloses a medium-pressure bypass system of a fuel gas-steam combined cycle unit. The medium-pressure bypass system at least comprises a preheating steam pipeline, a medium-pressure bypass pipeline, a medium-pressure bypass control valve and a medium-pressure bypass water spray adjusting valve, medium-pressure bypass cooling water in the medium-pressure bypass pipeline is led to the outside through the preheating steam pipeline, subjected to pressure reduction through the medium-pressure bypass control valve, then cooled by the medium-pressure bypass water spray adjusting valve and finally discharged into a condenser; the medium-pressure bypass control valve controls the cooling water through an enthalpy value; the medium-pressure bypass control valve has four pressure reduction grades; the outlet pipe of the medium-pressure bypass pipeline is provided with a horizontal straight pipe section; enthalpy value computation is adopted for control the amount of the cooling water in the cooling water control of the medium-pressure bypass control valve. Through the adoption of such a structure and control strategy, the bypasses and the pipelines operate stably in the starting process of the unit, the problems of high frequency vibration and noise standard violation of the medium-pressure bypass control valve and the outlet pipe in the similar power plant at present can be prevented, and the remarkable technical effect is achieved.

Description

technical field [0001] The invention relates to the technical field of gas-fired power generation, in particular to a medium-pressure bypass system of a gas-steam combined cycle unit. Background technique [0002] In the same type of Siemens gas turbine power plants in China, there are problems of high frequency vibration and noise exceeding the standard of the medium pressure bypass valve and its outlet pipeline. During the start-up process of the gas turbine unit, there was serious high-frequency vibration in the outlet pipeline of the medium-pressure bypass valve, and the noise was as high as 110 decibels. There are also cracks due to high-frequency vibration, and sometimes serious water hammer occurs. [0003] To analyze the causes of high-frequency vibration at the outlet of the medium pressure bypass, there are mainly the following: [0004] 1. The flow velocity at the outlet of the medium pressure bypass is too high [0005] According to the design requirements of ...

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Problems solved by technology

[0008] 2. The number of decompression stages of the medium pressure bypass valve is not enough

The design of the valve with only two stages of decompression is not only difficult to achieve such a large decompression effect, but also brings a great impact to the shrouded orifice of the bypass valve itself, which also increases the vibration of the bypass valve itself

If the decompression is not carried out according to the design requirements of the inlet of the condenser into the device, it will also cause the inlet pressure of the condenser to be too high, which will have an impact on the condenser and cause vibration

This is another major cause of high-frequency vibration and noise in the side valve outlet pipeline in other similar power plants

[0010] 3. The layout of the medium pressure bypass valve outlet pipeline is unreasonable

However, according to the above analysis of vibration causes, this improvement cannot fundamentally solve the vibration problem

Because the throttling orifice only compensates for the problem caused by the insufficient number of decompression stages of the bypass valve, it cannot reduce the flow rate entering the inlet of the condenser

And in the case of such a high flow rate, the flow orifice is easily damaged by washing

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