For the control valve of an FC, if the air supply is cut off and then restored suddenly, could this cause the opening degree to become suddenly higher than the normal value?
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For example, after the interlock is triggered, the solenoid valve that controls the air supply for the control valve loses power, causing the control valve to close. Once the interlock is restored and the solenoid valve receives power again, could this cause the opening degree of the control valve to increase sharply at that moment, leading to fluctuations in flow? How can this situation be avoided
When the solenoid valve is powered, air supply is restored, and the opening degree of the control valve is determined by the MV value that controls it. Also, the phrase “The solenoid valve that controls the air supply for the control valve loses power, causing the valve to close...” should be changed to “The solenoid valve that controls the air supply for the control valve loses power, resulting in the closure of the control valve...”, which is more accurate; I almost didn’t realize that.
Under normal circumstances, it will not operate on its own after power is restored
Okay, it has been modified. In this situation, is it normal for the actual opening degree of the control valve to be too large (greater than the MV value) after the solenoid valve is powered on and the air supply to the control valve is restored?
Perhaps my description isn’t accurate enough: when the solenoid valve is powered, the air supply to the control valve is restored, and at that moment the control valve comes under DCS control again. However, in practice, the control valve opened too wide after the air supply was restored, but the reason for this has not been identified
This post was last edited by jlshnlhj on 2022-5-5 23:14. Which one initiates the interlocking action? After an ESD, SIS, or DCS interlock activates, the DCS should receive a signal indicating that the interlock has been activated. Based on this signal, along with other criteria such as the feedback signal from the solenoid valve, the controller (PID) that regulates the control valve is switched to manual mode, and the control valve is moved to a safe and appropriate position. These conditions then serve as the requirements for resetting the interlock, allowing it to be reset. Without the aforementioned configuration, especially if the controller (PID) that regulates the control valve is set to automatic, it’s difficult to determine what value the MV of the control valve will be. As for whether it is a \"normal phenomenon,\" it’s hard to say, because even in the absence of such configurations (such requirements are generally not specified in the design; they arise from years of experience with standard configurations), manual operation is still possible. If the process control requirements are not met, modifications must be made. Either change the configuration or modify the reset procedure. When the solenoid valve is powered and the air supply to the control valve is restored, the actual opening degree is greater than the MV value, which is abnormal; however, it seems unlikely that this would happen, unless there is a problem with the valve positioner or oscillation is occurring.
The interlock action is issued by the LHCS system of the regeneration system; the DCS does not have any configuration for this purpose. Moreover, there is no reset button; once the interlock value is reached, the solenoid valve loses power, and it regains power as soon as the interlock conditions are no longer met. This results in false readings from the instruments, causing the interlock to activate and then deactivate again. With no change in the output of the control valve, the flow rate rises suddenly from 14 standard units to over 300, triggering additional interlocks and leading to the shutdown of the regeneration process
This post was last edited by jlshnlhj on 2022-5-5 22:21; please make the changes according to the process requirements. Based on the description, it should be that PID is in automatic mode, and MV changes as a result of the action of PID.
The control valve’s interlock cuts off the air supply; the output of the positioner remains unchanged, and it returns to its original position once the air supply is restored
Based on the flow trend analysis afterwards, it can be inferred that once the solenoid valve was activated, the control valve may have opened to a relatively large degree (significantly deviating from the MV value at that time) before closing quickly again, thereby restoring normal flow. Will this situation occur?