What are good methods for tuning PID parameters for the cascade control system that regulates the liquid level in the stabilizer reflux tank and the flow rate of liquefied gas exiting the unit?
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Our main level gauge experiences large fluctuations in flow rate, and the tuning done did not yield good results. May I ask, what value do experts usually set for the pID parameter to achieve stability?
PID parameter tuning should be determined based on actual conditions; there are no fixed values.
The DCS systems of different manufacturers vary, so the PID parameters differ as well. However, if there are large fluctuations in flow rate, then the control valve used for flow regulation needs to be able to keep up with these changes, which means it will have to be adjusted frequently.
PID tuning requires continuous experimentation based on the characteristics of the device itself and the operation of the valve; it is recommended to involve individuals with extensive experience in carrying out PID tuning. It is beneficial for your company’s PID tuning. 、
Today, a expert was found to make adjustments again, and the situation has improved compared to before; it still needs to be observed. For both the liquid level (main gauge) and flow rate (secondary gauge), only the proportional gain and integral time need to be adjusted; there is no need to set a derivative time.
This needs to be fine-tuned according to the changing conditions. Currently, many companies under Sinopec have given the authority to adjust the PID to the operators. Are there any issues with the positioners of your control valves?
Actually, PID control isn’t as complicated as people say; it’s sufficient to master the principles. For loops like the one you mentioned, generally, the secondary loop is first adjusted to stability, and then the primary loop is regulated in a cascade manner! For liquid levels, a certain differential value generally needs to be set, but it is usually quite small! For traffic parameters, PI settings are generally sufficient! I also strongly agree with the opinions of the fellow sailors mentioned above; there is no fixed value for this parameter. Even for a single valve, after maintenance, these parameters may no longer be appropriate! But the general direction should be good!