Simply look at the power flow 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. Water supply valve (main, with the boiler feed valve, composite feed water control valve) Control requirements: control the amount of water into the boiler to ensure the evaporation of steam to maintain the boiler water level (main and auxiliary boiler feed valve system contains two control valves, one with Used at boiler startup, one for normal water usage). Working conditions: When the boiler is started, the pressure drop of the valve can reach 100-300 kg, the flow rate is small, and the pressure drop is small during normal operation. The flow rate is large, and the flow rate adjustable ratio is 75 / 1-100 / 1. Valve Requirements: WCB / WC9, Cavitation-Resistant, V-Closure Rating for Startup Valves in Dual-Valve Systems, Feature Valve Trim for Complex Feedwater Valves to Meet Both Boiler Startup and Normal Runtime Needs. General valve selection for the fault off. Boiler feed pump minimum flow control valve requirements: the boiler feed pump start and stop running safely, eliminating the flow is too small, increasing 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 rate of 30% of normal flow. Valve requirements: anti-cavitation, anti-blocking structure, V-level seal, the pump starts and stops running the valve continuous work, the pump is normally closed after the valve is closed, the valve is usually open for failure. High and low heater traps (water heater hydrophobic, condensate water heater hydrophobic) Control requirements: control the position of the condensate heater, the timely discharge of condensate, high water discharge, the normal water level hydrophobic conditions conditions: saturated water, heating Between the control valve pressure drop 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. 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: the flow of small start-up phase, the pressure of large temperature, the flow of normal circumstances, the pressure is small, the working conditions similar to the water valve. Valve requirements: effective anti-cavitation at lower flow rates. Temperature control valve (desuperheater) Control requirements: The high-pressure water jet into the steam to make the steam temperature control requirements, conditions conditions: water, the pressure difference is larger, the valve requirements: Type diversity: nozzle type, Self-contained and folder-type. Temperature and pressure 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 boiler can work independently steam turbine. Condition conditions: high temperature and high pressure steam. Valve requirements: thermal shock, noise reduction, rapid response.
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