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1. Feed valve main and auxiliary boiler feed valve, composite feed water control valve:
Control requirements: control the boiler inlet water, maintain the liquid level and steam flow of the steam boiler.
Working condition requirements: the valve pressure difference can reach 100-300 kg when the boiler is started, the flow rate is small, the pressure difference is small during normal operation, the flow rate is large, and the flow adjustable ratio is 75:1-100:1.
Valve requirements: The valve body is made of WCB/WC9, the starting valve in the double valve system is required to be anti-cavitation, V-level closing level, and the composite feed valve needs to use characteristic valve trim to meet the needs of boiler start-up and normal operation at the same time. Generally, the valve is selected as fault shut-off, (it should be noted that hydrazide will be added to the general feed water to eliminate the oxygen dissolved in it, and it will have adverse reactions to alloy SATELLITE6 or other similar alloys, so it is best not to use 316 STELLITE surfacing method to deal with the valve trim, and 416 stainless steel material can be directly selected).
2. Minimum flow rate circulation valve of boiler feed pump:
Control requirements: make the boiler feed pump start and run safely, and eliminate the damage to the pump due to too small flow, increased temperature rise, and strong cavitation of water. (Older power stations have a minimum flow control valve that uses a switch-type type, and there are also automatic circulation valves that use a mechanical pump.)
Working conditions: The pressure drop is 160-350 kg, which is the valve with the largest pressure difference in the power station system, and the flow rate is generally 30% of the normal flow.
Valve requirements: anti-cavitation, anti-blocking structure, V-level sealing level, the valve works continuously when the pump starts and stops running, and the secondary valve closes after the pump starts normally, and the valve is usually opened by fault.
3. High/low heater feed water heater hydrophobic, condensate heater hydrophobic:
Control requirements: control the position of the condensate in the heater, and discharge the condensate in time, that is, discharge at high water level, and drain water at normal water level.
Working conditions: the medium is saturated water, the pressure difference between the control valves between the heaters is generally 6-30 kg, and the last stage of the trap is directly connected to the condenser or deaerator.
Valve requirements: flash washout resistance, V or VI sealing level, the valve is usually faulty open.
4. Deaerator water level control valve (DALC):
Control requirements: provide flow to maintain the normal water level of the deaerator, and eliminate the gas dissolved in the water by adding steam to increase the water temperature.
Working conditions: the flow rate is small and the pressure difference is large in the starting stage, and the flow rate is large and the pressure difference is small under normal conditions, and the working conditions are similar to those of the water supply valve.
Valve requirements: Effective cavitation resistance at lower flow rates.
5. Thermoceleration valve (desuperheater):
Control requirements: high-pressure water is injected into the steam to make the steam temperature meet the control requirements.
Working conditions: the medium is water, the pressure difference is large, and the valve requirements: various types: nozzle type, auxiliary atomization type, self-contained type and clamp type.
6. Temperature and pressure reduction valve (high and low pressure bypass valve):
Control requirements: steam that adjusts the high temperature and high pressure steam to a certain temperature and pressure; Provide a bypass channel for the steam turbine, and the boiler can work independently of the steam engine.
Working conditions: high temperature and high pressure steam deheating and decompression.
Valve requirements: thermal shock resistance, noise reduction, rapid response.
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