Safe and reliable power station control valve selection
The power station control valve plays a vital role in the system, so we must be cautious when selecting a safe and reliable power station control valve.
In the thermoelectric industry, the operating conditions of the control valve are special. The power process is just the circulation process of water and steam, but the selection of control valves in this process is both simple and complex. Simple means that the process medium is simple, only water and steam. Complex means that the temperature and pressure of water and steam fluctuate in a large range, which brings a series of problems, such as: flashing, 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 and attached boiler water supply valve, compound water supply control valve)
Control requirements: control the water inflow of the boiler, ensure the evaporation of steam, and maintain the water level of the boiler (the main and auxiliary boiler feedwater valve systems include two control valves, one is used when the boiler is started, and the other is used for normal water supply.
Working conditions: 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 can be adjusted from 75:1 to 100:1.
Valve requirements: WCB/WC9, anti-cavitation is required for the start-up valve in the double-valve system, and the V-level closing level is required. For the composite feedwater valve, the characteristic valve trim is required, and it can meet the needs of boiler startup and normal operation at the same time. Generally, the valve is selected as fault closed.
2. Small flow circulation valve for boiler feed pump
Control requirements: Make the boiler feed pump start and stop safely, and eliminate the damage to the pump due to too small flow, increased temperature rise, and strong water cavitation. Older power stations have smaller flow control valves that use an on-off type, as well as a mechanical pump automatic circulation valve.
Working conditions: The pressure drop is 160-350 kg, which is the valve with a large pressure difference in the power station system, and the flow rate is 30% of the normal flow rate.
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 normally started, and the valve is usually open for failure.
3. High and low heater traps (feed water heater drain, condensate heater drain)
Control requirements: control the position of condensed water in the heater, discharge the condensed water in time, discharge at high water level, and drain the water at normal water level.
Working conditions: saturated water, the pressure difference of the control valve between the heaters is generally 6-30 kg, and the latter is directly connected to the condenser or deaerator.
Valve Requirements: Anti-flash washout, Class V or VI seal rating, valve is normally fail open.
4. Deaerator water level control valve
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.
Working conditions: the flow rate is small in the start-up stage, the pressure difference is large and the temperature is large, and the flow rate is large under normal conditions, the pressure difference is small, and the working conditions are similar to the water supply valve.
Valve Requirements: Effective against cavitation at lower flow rates.
5. Desuperheating valve (desuperheater)
Control requirements: inject high-pressure water into the steam to make the steam temperature meet the control requirements.
Working conditions: water, the pressure difference is large.
Valve requirements: Various types: nozzle type, auxiliary atomization type, self-contained type and wafer type.
6. Temperature and pressure reducing valve (high and low pressure bypass valve)
Control requirements: adjust the high temperature and high pressure steam to steam with a certain temperature and pressure, provide a bypass channel for the turbine, and the boiler can work independently of the turbine.
Working conditions: high temperature and high pressure steam.
Valve requirements: thermal shock resistance, noise reduction, quick response.
The above six points are the whole content of the safe and reliable power station control valve selection shared with you today. I wonder if you have learned it, get it~