In the thermal power industry, the use of power station control valve is more special. Power flow is only water, steam cycle process, but in this process the selection of control valve is simple and complex. Simple means the process medium is simple, only water and steam two kinds, complex means water and steam temperature and pressure fluctuation range is large, bring a series of problems, such as flash, cavitation, erosion, noise, corrosion, etc. But the first thing to consider is the safety and reliability of the control valve.
1. Water Supply Valve (Main, boiler water supply valve, compound water supply control valve)
Control requirements: Control boiler water intake, ensure steam evaporation, maintain boiler water level (main and attached type boiler feed valve system contains two control valves, one for boiler start-up and one for normal feedwater use.
Operating conditions: When the boiler starts, the valve pressure difference can reach 100-300 kg, the flow rate is small, the normal operation pressure difference is small, the flow rate is big, the flow rate adjustable ratio is 75:1 ~ 100:1.
Valve requirements: WCB / WC9, for a dual valve system to start the valve requirements of cavitation, class V closed class, for the composite water valve to use the characteristics of valve internals, and to meet the start-up and normal operation of the boiler needs. General Valve selection for the fault off.
2. Boiler Feed Pump Minimum Flow Circulation Valve
Control requirements: make the boiler feed water pump safe start and stop operation, to eliminate the small flow, temperature increase, water cavitation caused by the pump damage. Old-fashioned power stations have on-off type minimum flow control valves, as well as the use of mechanical pump automatic circulation valves.
Operating conditions: pressure drop of 160-350 kg, is the power station system to withstand the pressure difference of the largest valve, flow for the normal flow of 30% .
Valve requirements: anti-cavitation, anti-blocking structure, v Seal class, pump start and stop the operation of the valve continuous work, pump normal start after the valve closed, the valve is usually open for failure.
3. High And Low Heater Traps (Feedwater heater traps, condensate heater traps)
Control requirements: control the location of condensate in the heater, timely discharge of condensate, high water level discharge, normal water level drainage.
Operating conditions: Saturated Water, the control valve pressure difference between the heaters is generally 6-30 kg, the last level of steam trap directly connected to the condenser or deaerator.
Valve requirements: Flash Resistance, V or VI seal class, valve is usually open for failure.
4. Deaerator Level Control Valve
Control requirements: to provide flow to maintain the normal water level deaerator, by adding steam to raise the water temperature to eliminate dissolved gases in the water.
Operating conditions: start-up phase flow is small, large temperature pressure difference, the normal flow of large, small pressure difference, operating conditions similar to water valve.
Valve requirements: effective cavitation resistance at low flow rates.
5. Temperature Reducing Valve (Temperature reducer)
Control requirements: high-pressure water injection into the steam so that the steam temperature to meet the control requirements.
Working condition: water, big pressure difference.
Valve requirements: Various Types: nozzle type, auxiliary atomization Type, self-contained type and clamp type.
6. Temperature And Pressure Reducing Valves (High and low pressure bypass Valves)
Control requirements: high-temperature and high-pressure steam adjusted to a certain temperature and pressure of the steam engine to provide a bypass channel, the boiler can work independently of the turbine.
Working condition: High temperature and high pressure steam.
Valve requirements: Thermal Shock Resistance, noise reduction, rapid response.
Post time: Jul-28-2021