Safety considerations in the selection and applica

Safety considerations in the selection and application of power station control valves

simply speaking, the power flow actually turns off the controller and computer; It is the circulating process of water and steam, and the selection of control valve in this process is simple and complex. The simple thing is that the process medium, especially in the index of pressure, has high requirements. The quality is simple. There are only two kinds of water and steam. The complex thing is that the temperature and pressure of water and steam fluctuate widely, resulting in a series of problems, such as flash, cavitation, scouring, noise and corrosion. But the first thing to consider is the safety and reliability of the control valve

feed water valve (main and auxiliary boiler feed water valves, composite feed water regulating valve)

control requirements: control the boiler water inflow, ensure the steam evaporation, and maintain the boiler water level (the main and auxiliary boiler feed water valve system includes two control valves, one for boiler startup and the other for normal feed water)

working condition: when the boiler is started, the valve differential pressure can reach kg, and the flow is small. During normal operation, the differential pressure is small, and the flow is large. The flow adjustable ratio is 75//1

valve requirements: wcb/wc9, for the start-up valve in the double valve system, it is required to be cavitation resistant, with a V-level closing level. For the composite feed water valve, it is required to use characteristic valve internals to meet the needs of boiler startup and normal operation at the same time. Generally, the valve is selected as fail closed

the minimum flow circulating valve of boiler feed pump

control 1 generally stipulates that the standard block is effective within 1 year from the date of calibration. Requirements: make the boiler feed pump start and stop safely, and eliminate the pump damage caused by too small flow, increased temperature rise, and strong water cavitation. (old power stations use switch type minimum flow control valve, and mechanical pump automatic circulation valve at the same time)

working condition: the pressure drop is up to kg, which is the valve with the largest pressure difference in the power station system, and the flow is 30% of the normal flow

valve requirements: anti cavitation, anti blocking structure, class V sealing grade, the valve works continuously when the pump is started and stopped. After the pump is started normally, the valve is closed, and the valve is usually opened by fault. Widely used in the material industry

high and low heater drain valves (feed water heater drain, condensate heater drain)

control requirements: control the location of condensate in the heater, timely discharge condensate, high water level drain, normal water level drain

working condition: saturated water, the pressure difference between the control valves between the heaters is generally kg, and the last level drain valve is directly connected to the condenser or deaerator

valve requirements: anti flash erosion, class V or VI sealing grade, and the valve is usually opened by fault

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

working condition: during the start-up stage, the flow is small, the pressure difference is large, and the temperature is high. Under normal conditions, the flow is large, and the pressure difference is small. The working condition is similar to the feed water valve

valve requirements: effective cavitation resistance at low flow

desuperheating valve (desuperheater)

control requirements: inject high-pressure water into steam to make the steam temperature meet the control requirements. Working condition: water, large differential pressure

valve requirements: various types: nozzle type, auxiliary atomization type, self-contained type and wafer type

temperature and pressure reducing valve (high and low pressure bypass valve)

control requirements: adjust 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 turbine

working condition: high temperature and high pressure steam

valve requirements: thermal shock resistance, noise reduction, rapid response