Electricity is one of the most important energy industries. Currently there are steam, wind, hydro, geothermal, tidal power and solar power generation. This article focuses on the selection of some typical control valves in fuels, kerosene, gas and nuclear power plants. The common ground for such plants is to turn the water into steam and use the steam to drive the turbine to power the generator. The difference is that the energy used to convert the water into steam varies from natural gas to fuel oil to coal to nuclear reactors. The structure of various power plants are roughly the same. Let us take the combined cycle power plant as an example to briefly describe the selection of control valves, and then briefly explain the different parts of each power plant. Simply look at the power flow chart is actually water, steam circulation process, the selection of control valve in this process is simple and complex. Simple is the process medium is simple, only water and steam two kinds of complicated water and steam temperature and pressure fluctuations range, bringing a series of problems such as: flash, cavitation, erosion, noise, corrosion. But the first thing to consider is the safety and reliability of the control valve. We follow the system flow to expand the control valve selection instructions. 1, the main water supply valve, sub boiler feed valve, water supply control valve composite control requirements: control of boiler water to maintain the steam boiler level and steam flow. Working conditions: When the boiler is started, the pressure difference of the valve can reach 100-300 kg, the flow rate is small, the pressure difference is smaller during normal operation, the flow rate is large, the flow rate adjustable ratio is 75: 1-100: 1. Valve requirements: body material WCB / WC9, for the two-valve system requires anti-cavitation valve start, V-level closure level, for the composite valve to be used to the characteristics of the valve parts at the same time meet the boiler startup and normal operation need. General valve selection for the fault off, (Note that the general water to dissolve the oxygen which will join the diamine for processing, it will SATELLITE6 alloy or other similar alloy adverse reactions, it is best not to use 316 + STELLITE surfacing method to deal with the valve trim, direct selection of 416 stainless steel). 2, the minimum flow boiler feed pump valve control requirements: the boiler feed pump start and run safely, eliminating the flow is too small, increasing the temperature, water erosion caused by strong cavitation damage. (The old power station has a minimum flow control valve that uses a switch type, along with an automatic circulation valve using a mechanical pump). Condition conditions: pressure drop of 160-350 kg, is the largest pressure drop in the power plant valve, the flow is generally 30% of normal flow. Valve requirements: anti-cavitation, anti-blocking structure, V-class seal, the pump starts and stops running continuously when the valve is working, the pump normally activated after the next valve off valve, the valve is usually open for failure. 3, high / low heater trap water heater hydrophobic, condensate water heater hydrophobic control requirements: control the position of condensate heater, timely discharge of condensate, the high water discharge, the normal water level hydrophobic. Condition conditions: the medium is saturated water, the pressure between the control valve heater is generally 6-30 kg, the last level of the trap directly connected to the condenser or deaerator. Valve requirements: Anti-flash flushing, V or VI-level seal, the valve is usually open fault. 4, deaerator water level control valve (DALC) control requirements: to provide flow to maintain the normal deaerator water level, by adding steam to increase the water temperature to eliminate dissolved in water gas. Condition conditions: Start phase flow is smaller, the pressure is larger, the normal flow, pressure is small, the condition is similar to the water valve. Valve requirements: effective anti-cavitation at lower flow rates, 5, temperature control valve (desuperheater) control requirements: high-pressure water injection into the steam to make the steam temperature control requirements. Working conditions: medium water, large pressure drop, the valve requirements: various types: nozzle type, auxiliary atomization type, self-contained type and folder type. 6, temperature reducing valve (high and low pressure bypass valve) control requirements: the high temperature and high pressure steam to a certain temperature and pressure steam; to provide a bypass steam turbine, the steam turbine can work independently. Condition conditions: high temperature and pressure steam temperature and pressure reduction. Valve requirements: thermal shock, noise reduction, rapid response.
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