I would like to ask everyone about the control of the v1 valve
Thread Content
Dear experts, our unit is equipped with a Hangyang 40000 external compression air separation system, which has two valves of type v1, namely v1a and v1b. During operation, one of these valves remains at a fixed opening level, while the other is controlled by the liquid level in the lower tower. Currently, molecular sieves are used in parallel; during the switching process, v1a experiences significant fluctuations, which has led to several instances of operational disruptions. We have adjusted the PID parameters on multiple occasions, but with little effect. I would like to ask if anyone here has encountered a similar situation and how they resolved it? Are there any better control schemes available? Thank you all! ! !
Have you considered making the V1 valve manually controllable to see if it can be stabilized?
Operating in manual mode helps to maintain stability; currently, all operations are carried out in manual mode at this stage. It’s strange that the pressure in the tower remains very stable during the switching process of the molecular sieves. Throughout the process of equalizing pressure with the molecular sieves, the pressure fluctuation in the tower does not exceed 3 kPa, and during the switching process it does not exceed 1 kPa. The only thing that shows some fluctuation is the air volume, and this cannot be avoided. There is a period of time during which both molecular sieves operate simultaneously, but the fluctuations in air volume are not significant either – the maximum fluctuation is around 1% of the total air volume. Although it’s a packed tower for descending, I don’t think it should be that sensitive, right?
This issue really needs careful consideration; observe more, and perhaps you’ll uncover the secret behind it. I’d like to ask, are the fluctuations usually large?
There are normal fluctuations, but they are not significant and are acceptable. The valve operates properly as well. However, right after the switch to the molecular sieve, V1 starts to experience large fluctuations. Most of the time, it manages to adjust itself after a few such fluctuations, but sometimes the large fluctuations cause V1 to stop receiving liquid, which results in a failure of the system. We are currently trying to find the cause; nothing seems to explain it. The level of the primary cooling liquid has hardly changed either. At the crude argon condenser, V701 is also set to automatic mode, but that valve remains very stable with no changes. The resistance at the lower tower increases slightly during this process. The flow of liquid nitrogen to the upper tower via v3 is controlled manually, and its opening remains constant. The pressure in the upper tower fluctuates very little during this process, remaining below 1 kPa. It’s impossible to explain the reason for the fluctuations in v1; the valve has been checked and there are no issues with it.
Could it be that during the switching of the molecular sieve, the guide vanes of the air compressor are opened or closed wider, which causes large fluctuations in current? What is the voltage at this time? During fluctuations, could the voltage and current cause disturbances in some particularly sensitive valve positioners?
The control program for the pressure equalization process of our molecular sieves, v1207, was developed by me; it is based on a linear table format. Some optimizations have also been applied to the control of the molecular sieves. Now, the control of the air compressor is very stable, with no significant fluctuations in current, which means there is no impact on the columns. For our v1 system, we use valves from Samson, which are of excellent quality. In the past, even when the air separation column was struck by lightning, these valves did not suffer any damage. Therefore, I believe there will be no issues related to interference.
Try changing the v1a to a fixed opening value
It’s still in the parallel phase at the beginning of voltage boosting~~ Is this issue occurring?
I think we should start with parallel operation; here, in order to reduce pressure fluctuations in the lower tower, the parallel operation time for the molecular sieve is 20 seconds, which is basically the valve operation time plus a 5-second buffer. By the time fluctuations occurred in v1, the switch had already been made, as there is always a delay both in level changes and in instrument readings. What’s unclear is that level fluctuations occur regularly, and the valves are able to adjust back to normal. At this stage, it seems as though the effect is amplified, but the data doesn’t reflect this; the fluctuations remain large, and the output starts to oscillate. I’ve been suspecting that there’s an issue with the PID parameters, and I had the most experienced technicians try several different sets of parameters, but nothing worked. It seems that there must be some problem with the process itself.
For the V1207 pressure equalizing valve, has the opening setting been adjusted again? It might be worth trying to set the valve opening at the start of pressure equalization to a lower value – this can help prevent large fluctuations in the amount of air entering the tower~~