Regarding the automatic operation at high liquid level in the hydrogenation cooling section
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The cold high-level gauge consists of two units, A and B; after high-level selection, these two valves are controlled. Before 50, valve A is open, and after 50, valve B is open. When A is fully open at 100, how can automatic operation be carried out in the most stable manner?
Do both Valve A and Valve B control the liquid level? In series or in parallel. Here, we have just one valve for liquid control.
They are all control valves that open in response to different signals; after the high-level selection, the B valve will open only if the MV output is greater than 50. For example, after the high level selection for fluid level gauge AB, the MV is 60. At this point, valve A is fully open, while valve B is open to 20%.
Step control? In my opinion, when this valve is in normal operation, one unit is sufficient to meet the requirements, while the other should be used as a backup. With the PID tuned properly, it should be quite stable.
The operating procedures should contain relevant descriptions; based on operational experience, for a high-range control like this, it is advisable to use one level gauge at the highest possible setting, and to adjust the PID parameters accordingly. When switching to automatic mode, first set the level gauge MV to half of the value corresponding to the valve opening (keep in mind that the valve position is twice the MV value). Next, put the control valve in cascade mode, and then switch the level gauge to automatic mode. As long as there are no fluctuations in the valve position output before and after switching to automatic mode, everything will be fine. There is definitely some deviation in the readings provided by the two level gauges; try to prevent the selector from switching back and forth. It’s best to rely on one level gauge for accurate readings, using the other as a reference only
Thank you, I now know how to use it