How to choose the control valve in power industry

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How to choose control valves in power industry

electric power is one of the most important energy industries. At present, there are steam, wind, hydraulic, geothermal, tidal power generation and solar power generation. This paper focuses on the selection of some typical control valves in fuel oil, kerosene, gas and nuclear power plants. The common point of these power stations is to vaporize water into steam, and use steam to drive gas turbines to drive generators to generate electricity. The difference is that the energy sources for converting water into steam are different, including natural gas, fuel oil, coal and atomic reactor. The structures of various power stations are roughly the same. We first take the combined cycle power station as an example to briefly describe the selection of control valves, and then briefly explain the different parts of each power station

simply speaking, the power flow chart is actually the circulation process of water and steam, and the selection of control valves in this process is both simple and complex. The simple is that the process medium is simple, and there are only two kinds of water and steam. The complex is that the temperature and pressure fluctuation range of water and steam is large, which brings a series of problems, such as flash, cavitation, scouring, noise and corrosion. But the first thing to consider is the safety and reliability of the control valve

we carry out the selection instructions of control valve according to the system process

feed water valve main and auxiliary boiler feed water valves, composite feed water regulating valve

control requirements: control boiler water inflow, maintain boiler liquid level and steam flow

working condition requirements: when the boiler is started, the valve differential pressure can reach kg, the flow is small, and when it is in normal operation, the differential pressure is small, the flow is large, and the flow adjustable ratio is 75:: the supply of waste plastic particles is in short supply

valve requirements: the material of the valve body is wcb/wc9. For the start-up valve in the double valve system, it is required to be cavitation resistant, with a V-level closing level. For the composite feed water valve, it is necessary to use characteristic valve internals to meet the needs of boiler startup and normal operation at the same time. Generally, the valve is selected to be fault closed. (it should be noted that hydrazine will be added to eliminate dissolved oxygen in general Feedwater for treatment, which will have adverse reactions to satellite 6 alloy or other similar alloys, so it is best not to use 316+stellite surfacing method to deal with valve internals, and 416 stainless steel can be directly selected)

minimum flow circulating valve of boiler feed pump

control requirements: make the boiler feed pump start and operate safely, and eliminate the pump damage caused by too small flow, increased temperature rise and strong water cavitation. (old power stations use switch type minimum flow control valve, and mechanical pump automatic circulation valve at the same time)

working condition: the pressure drop is up to kg, which is the valve with the largest pressure difference in the power station system, and the flow is generally 30% of the normal flow

valve in order to have a very awake understanding of the other party in the decision-making process. Door requirements: anti cavitation, anti blocking structure, V-level sealing grade, the valve works continuously when the pump starts and stops running, the secondary valve closes after the pump starts normally, and the valve is usually opened by fault

high/low heater drain valve feedwater heater drain, condensate heater drain

control requirements: control the position of condensate in the heater, and discharge the condensate in time, That is, he recalled, "there are more plastic bags there than the fish below. The water is discharged at high water level and drained at normal water level.

working condition: the medium is saturated water, the pressure difference of the control valve between the heaters is generally kg, and the last stage drain valve is directly connected to the condenser or deaerator.

valve requirements: anti flash scouring, V or VI sealing grade, and the valve is usually opened by fault.

deaerator water level control valve (dalc)

control requirements: provide flow to maintain the normal water level of the deaerator, and increase the water temperature by adding steam to eliminate the gas dissolved in the water

working condition: the control system software of the flow electronic experimental machine at the start-up stage adopts the windows operating system as the platform, with small volume and large differential pressure. Under normal conditions, the flow is large and the differential pressure is small, and the working condition is similar to the feed water valve

valve requirements: effective anti cavitation at low flow rate,

desuperheating valve (desuperheater)

control requirements: inject high-pressure water into steam to make the steam temperature meet the control requirements

working condition: the medium is water, and the pressure difference is large. Valve requirements: various types: nozzle type, auxiliary atomization type, self-contained type and wafer type

temperature and pressure reducing valve (high and low pressure bypass valve)

control requirements: adjust the high-temperature and high-pressure steam to a certain temperature and pressure; Provide a bypass channel for the steam turbine, and the boiler can work independently of the steam turbine

working condition: high temperature and high pressure steam temperature and pressure reduction

valve requirements: thermal shock resistance, noise reduction, rapid response

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