Types and selection of control valves in the power industry

1. Feedwater valves Main and auxiliary boiler feedwater valves, composite feedwater regulating valves:
Control requirements: Control boiler water inlet, maintain boiler liquid level and steam flow.
Valve requirements: Valve body material is WCB/WC9, the start valve in the double valve system requires anti-cavitation, V-level closing level, and the composite feedwater valve needs to use characteristic valve trims to meet the needs of boiler startup and normal operation. Generally, the valve is selected as a fault-off valve (it should be noted that hydrazine is added to the feedwater to eliminate dissolved oxygen, which will have an adverse reaction to SATELLITE 6 alloy or other similar alloys, so it is best not to use 316 STELLITE cladding method to treat valve trims, and 416 stainless steel can be directly selected).
2. Boiler feedwater pump minimum flow circulation valve:
Control requirements: Make the boiler feedwater pump start and run safely, and eliminate pump damage caused by too small flow, increased temperature rise, and strong water cavitation. (Old power stations use switch-type minimum flow control valves, and mechanical pump automatic circulation valves).
Valve requirements: anti-cavitation, anti-blocking structure, V-level sealing grade, the valve works continuously when the pump starts and stops, the secondary valve closes after the pump starts normally, and the valve is usually open for failure.
3. High/low heater feedwater heater drain, condensate heater drain:
Control requirements: control the position of condensate in the heater and discharge the condensate in time, that is, high water level discharge and normal water level drain.
Valve requirements: anti-flash erosion, V or VI level sealing grade, the valve is usually open for failure.
4. 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.
Valve requirements: effective anti-cavitation at low flow.
5. Desuperheater valve (desuperheater):
Control requirements: spray high-pressure water into the steam to make the steam temperature reach the control requirements.
6. Temperature and pressure reducing valve (high and low pressure bypass valve):
Control requirements: adjust high temperature and high pressure steam to steam of a certain temperature and pressure; provide a bypass channel for the steam turbine so that the boiler can work independently of the steam turbine.
Valve requirements: resistance to thermal shock, noise reduction, and rapid response.