Steam two-way regulating valve should be how to choose?

Steam-driven two-way control valve because of its use of high temperature and pressure medium, so the selection is quite exquisite, if improper selection, it will frequently occur in the course of failure, seriously affecting the normal operation of equipment and systems. Below we use an example to talk about the steam control valve selection and use in the need to pay attention to some of the problems.

A large chemical company needs steam to control the temperature of the reaction tank. The steam comes from the waste heat of the thermal power plant. The temperature is about 200°C, and the pressure is about 1.2MPa. Steam regulators are required to control the constant steam pressure. The valve inlet pressure is 0.8~1.0. MPa, outlet pressure 0.4~0.5MPa. At the beginning of model selection, because the on-site parameters were not clearly identified, the steam electric single-seat control valve was selected. Faults frequently occurred in the near future, the motor of the actuator was burned out, the control module was damaged, and the reduction gear was broken.

After sending people to the scene to observe and analyze, only to find out the cause of the failure. It turned out that the pressure difference between the inlet and outlet of the control valve is relatively large, and the actuator is overloaded during operation. It can also be said to be overloaded. Therefore, the reduction gear is overwhelmed, and several times the damage is caused and the motor and module are damaged. In the system design, the user chooses the wrong pressure point (if the pressure change is extremely fast), the PID parameter setting of the pressure control module in the control system is also problematic, resulting in the entire system being too sensitive and the pressure slightly changing. The controller will output the control signal to drive the regulating valve, causing the regulator valve to frequently operate and oscillating, which will cause the entire system to oscillate. Not only will the controlled variable not be stable, but also the regulating valve will be overwhelmed and unable to complete the adjustment task.

After consultation with the user, it was decided decisively to use a steam electric sleeve control valve instead of a steam single seat control valve. Because the sleeve valve balance structure of the valve core, can greatly offset the unbalanced force generated by the passage of steam, reduce the electric actuator The load is conducive to long-term stable operation of the regulating valve. The reason why the balanced single-seat control valve was not selected is that the single-seat valve's guide ring is not resistant to long-term wear under steam conditions, and the system does not require high standards for leakage of the control valve. The steam sleeve valve is fully capable of performing the task. This condition. At the same time, to re-determine the pressure point, when the steam sleeve valve is replaced, when the system is commissioned, the PID parameters are reset, the proportional band is reduced, and the integration time is increased, that is, the system response time is slightly adjusted, the steam pressure Changes in volatility are based on the premise that they can be used. After such adjustments, this issue was basically solved.

In fact, if we consider from the plan, according to the site conditions and requirements here, the use of pneumatic two-seat regulating valve is more appropriate, but it is not convenient for the user to lay the gas source pipeline.

It can be seen that for the steam and electric two-way regulating valve, the type selection is important, and the installation, debugging and maintenance are more important. There are a lot of faults caused by the user's unfamiliarity with the performance of the regulating valve and the use and maintenance features. You cannot isolate the control valve from the control system. Instead, consider it together with the entire system. The control valve is a dynamic actuator and is prone to various failures. This cannot be compared to a manual valve. of. Moreover, with the increasing deployment of fieldbus regulators, the task that was originally completed by the system was devolved onto the body of the regulating valve, which puts forward higher requirements for the use and maintenance of the regulating valve.

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