In simple terms, the power process is actually a cycle of water and steam. The selection of control valves in this process is simple and complicated. The simple process medium is simple, only water and steam. The complicated temperature and pressure fluctuation range of water and steam brings a series of problems such as flashing, cavitation, erosion, noise and corrosion. But the first thing to consider is the safety and reliability of the control valve.
Water supply valve (main, with boiler feed water valve, composite feed water regulating valve)
Control requirements: control boiler water intake, ensure steam evaporation, maintain boiler water level (main, attached boiler feed valve system contains two control valves, one for boiler start-up, one for normal water supply).
Working condition: When the boiler starts, the valve pressure difference can reach 100-300 kg, the flow rate is small, the pressure difference 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, for the starter valve in the double valve system requires anti-cavitation, V-level shutdown level, for the composite type water supply valve to use the characteristic valve internals to meet the needs of boiler start-up and normal operation. The general valve selection is fault off.
Boiler feed pump minimum flow circulation valve
Control requirements: to make the boiler feed pump safely start and stop running, to eliminate the damage caused by excessive flow, increased temperature rise, and strong cavitation of water. (Old-fashioned power plants have a switch-type minimum flow control valve, as well as a mechanical pump automatic circulation valve).
Working condition: The pressure drop reaches 160-350 kg, which is the valve with the largest pressure difference in the power station system, and the flow rate is 30% of the normal flow.
Valve requirements: anti-cavitation, anti-blocking structure, V-class sealing level, the valve works continuously when the pump starts and stops running, the valve is closed after the pump is started normally, and the valve is usually fault open.
High and low heater traps (water supply heater hydrophobic, condensate heater hydrophobic)
Control requirements: control the position of the condensate in the heater, discharge the condensed water in time, discharge at a high water level, and drain the normal water level.
Working condition: saturated water, the control valve pressure difference between the heaters is generally 6-30 kg, and the last stage steam trap is directly connected to the condenser or deaerator.
Valve requirements: anti-flash scouring, V or VI seal rating, the valve is usually fault open.
Deaerator water level control valve (DALC)
Control requirements: Provide flow to maintain the normal water level of the deaerator, increase the water temperature by adding steam to eliminate the gas dissolved in the water.
Working condition: The flow in the starting stage is small, the pressure difference is large, the normal flow is large, the pressure difference is small, and the working condition is similar to the water supply valve.
Valve requirements: Effective against cavitation at lower flow rates.
Desuperheater (desuperheater)
Control requirements: Inject high-pressure water into the steam to make the steam temperature meet the control requirements. The working condition: water, pressure difference is large.
Valve requirements: Various types: nozzle type, auxiliary atomization type, self-contained type and clip type.
Desuperheating pressure reducing valve (high and low pressure bypass valve)
Control requirements: The high temperature and high pressure steam is adjusted to a certain temperature and pressure steam to provide a bypass passage for the steam turbine to work independently.
Working condition: high temperature and high pressure steam.
Valve requirements: resistance to thermal shock, noise reduction, and rapid response.
Water supply valve (main, with boiler feed water valve, composite feed water regulating valve)
Control requirements: control boiler water intake, ensure steam evaporation, maintain boiler water level (main, attached boiler feed valve system contains two control valves, one for boiler start-up, one for normal water supply).
Working condition: When the boiler starts, the valve pressure difference can reach 100-300 kg, the flow rate is small, the pressure difference 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, for the starter valve in the double valve system requires anti-cavitation, V-level shutdown level, for the composite type water supply valve to use the characteristic valve internals to meet the needs of boiler start-up and normal operation. The general valve selection is fault off.
Boiler feed pump minimum flow circulation valve
Control requirements: to make the boiler feed pump safely start and stop running, to eliminate the damage caused by excessive flow, increased temperature rise, and strong cavitation of water. (Old-fashioned power plants have a switch-type minimum flow control valve, as well as a mechanical pump automatic circulation valve).
Working condition: The pressure drop reaches 160-350 kg, which is the valve with the largest pressure difference in the power station system, and the flow rate is 30% of the normal flow.
Valve requirements: anti-cavitation, anti-blocking structure, V-class sealing level, the valve works continuously when the pump starts and stops running, the valve is closed after the pump is started normally, and the valve is usually fault open.
High and low heater traps (water supply heater hydrophobic, condensate heater hydrophobic)
Control requirements: control the position of the condensate in the heater, discharge the condensed water in time, discharge at a high water level, and drain the normal water level.
Working condition: saturated water, the control valve pressure difference between the heaters is generally 6-30 kg, and the last stage steam trap is directly connected to the condenser or deaerator.
Valve requirements: anti-flash scouring, V or VI seal rating, the valve is usually fault open.
Deaerator water level control valve (DALC)
Control requirements: Provide flow to maintain the normal water level of the deaerator, increase the water temperature by adding steam to eliminate the gas dissolved in the water.
Working condition: The flow in the starting stage is small, the pressure difference is large, the normal flow is large, the pressure difference is small, and the working condition is similar to the water supply valve.
Valve requirements: Effective against cavitation at lower flow rates.
Desuperheater (desuperheater)
Control requirements: Inject high-pressure water into the steam to make the steam temperature meet the control requirements. The working condition: water, pressure difference is large.
Valve requirements: Various types: nozzle type, auxiliary atomization type, self-contained type and clip type.
Desuperheating pressure reducing valve (high and low pressure bypass valve)
Control requirements: The high temperature and high pressure steam is adjusted to a certain temperature and pressure steam to provide a bypass passage for the steam turbine to work independently.
Working condition: high temperature and high pressure steam.
Valve requirements: resistance to thermal shock, noise reduction, and rapid response.
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