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Hi, it’s still the Industrial Control Assistant here. Today I’ll share some knowledge about control valves; let’s take a look together. Types and selection of control valves in the power industry 1. Feedwater valves: main and auxiliary boiler feedwater valves, composite feedwater control valves: Control requirements: Regulate the water supply to the boiler in order to maintain the liquid level in the boiler and the steam flow rate. Operating requirements: During boiler startup, the valve pressure difference can reach 100–300 kilograms, with a low flow rate; during normal operation, the pressure difference is lower while the flow rate is higher. The adjustable flow ratio ranges from 75:1 to 100:1. Valve requirements: The valve body material should be WCB/WC9. Start-up valves in dual-valve systems are required to be resistant to cavitation and have a V-class closing performance. For composite feedwater valves, specialized internal components are necessary to meet the demands during both boiler start-up and normal operation. Generally, valves are selected to operate in a fail-closed mode. (It should be noted that in water supply systems, hydrazine is often added to remove dissolved oxygen; this substance can have adverse effects on SATELLITE6 alloy or other similar alloys. Therefore, it is recommended not to use 316 STELLITE for cladding the valve internals, and instead 416 stainless steel can be used directly.) 2. Boiler feed pump minimum flow control valve: Control requirement: To ensure the safe start-up and operation of the boiler feed pump, and to prevent damage to the pump caused by too low flow rates, increased temperature rise, or severe cavitation. (Old-style power plants use switch-type minimum flow control valves, as well as mechanical pump automatic circulation valves.) Operating conditions: The pressure drop ranges from 160 to 350 kilograms; it is the valve in the power plant system that experiences the greatest pressure difference, with a flow rate typically equal to 30% of the normal flow rate. Valve requirements: cavitation resistance, anti-clogging design, V-class sealing standard; the valve must operate continuously during pump startup and shutdown, and it should close after the pump starts properly; the valve typically operates in the open position in case of a fault. 3. High/Low heater feedwater heaters – drain valves, condensate heater drain valves: Control requirements: Control the location of condensate within the heaters and discharge it promptly; that is, discharge it when the water level is high, and use the drain valves at normal water levels. Operating conditions: The medium is saturated water; the pressure difference across the control valves between the heaters is generally 6–30 kilograms. The final drain valve is connected directly to the condenser or deaerator. Valve requirements: resistant to flashback erosion, with V or VI sealing grade; the valve is typically fail-open. 4. Deaerator level control valve (DALC): Control requirement: It ensures a constant flow rate to maintain the proper level in the deaerator, and increases the water temperature by adding steam in order to remove gases dissolved in the water. Operating conditions: During startup, the flow rate is low while the pressure difference is high; under normal operation, the flow rate is high and the pressure difference is low. The operating conditions are similar to those of a feed water valve. Valve requirements: effective cavitation resistance at low flow rates. 5. Temperature reduction valve (desuperheater): Control requirement: Inject high-pressure water into the steam to bring its temperature to the desired level. Operating conditions: The medium is water, and the pressure difference is high. Valve requirements: Various types are available, including nozzle type, auxiliary atomization type, self-contained type, and wafer type. 6. Temperature and pressure reducing valve (high and low pressure bypass valves): Control requirements: Adjust the high-temperature, high-pressure steam to a certain temperature and pressure; provide a bypass path for the turbine, enabling the boiler to operate independently of the turbine. Operating condition: Temperature and pressure reduction of high-temperature, high-pressure steam. Valve requirements: resistant to thermal shock and fast-acting. That’s it for today. If there’s anything else you’d like to know, feel free to leave a message. I’ll provide you with the most professional insights on automated equipment, and I’ll keep updating the content – so please stay tuned.