Selection of large-diameter control valves
Thread Content
A problem encountered in recent engineering work is related to the blast furnace gas vent tower. To stabilize the pressure in the main gas pipeline, an electric control valve is installed on the vent pipe; when the pressure is high, the valve opening is increased, and when the pressure is low, it is decreased. A PID control algorithm is used, which outputs a 4–20mA signal to the control valve based on the difference between the actual pressure value and the set value. Problems identified during actual operation: The diameter of the vent pipe is 1.4 meters, and the electric control valve actuator used is a 3-phase motor; both the accuracy and sensitivity of this actuator are insufficient. The valve will only act when the input valve position signal changes by at least 3%, and after it stops, the deviation between the valve position feedback signal and the set signal is also around 3%. This causes the valve to operate frequently, resulting in severe overheating of the motor. At the same time, the pipeline pressure is also not well controlled, with significant fluctuations. I asked the valve manufacturer, and they replied that this is the case for all large-diameter control valves. That expert knew what the standard precision and sensitivity of actuators should be for such large valves. If an electric actuator must be chosen, which one should be selected?
It is recommended to use stepwise regulation, adopting a control scheme with 1 small valve (bypass) and 1 large valve (main pipeline), which helps to ensure the stability of the system!
Hehe, it’s normal – whether it’s domestic or imported products, this issue exists to some extent. In fact, the main reason for this is inaccurate feedback. For pipes with a diameter of 700 mm or less here, we use pneumatic valves. Similarly, we also have control valves with diameters of 1200 mm and 1600 mm, but the effect of these valves is not very significant. However, LZ is inquiring about pressure and flow regulation valves; such valves are quite expensive, costing over 100,000 yuan. It was precisely because of the high cost that we gave up using such valves!