Precise pressure control method behind the buffer tank

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Under your operating conditions, achieving precise control of the pressure in the buffer tank presents significant challenges, especially when there are large fluctuations in inlet air pressure and changes in the backpressure at the points where air is used. You have already tried using conventional PID control and a speed increaser, but with little success. In this case, the following strategies can be considered: 1. **Cascade PID control**: The main PID controller is responsible for regulating the pressure behind the valve, while the secondary PID controller controls the opening degree of the butterfly valve. By separating pressure control from flow or valve position control, it is possible to compensate for fluctuations more accurately and improve control performance. 2. **Fuzzy control systems**: Fuzzy control can handle uncertainty and non-linear problems, making it suitable for process control under changing conditions. It does not rely on precise mathematical models, but operates based on empirical rules. This can be a solution, especially when PID control is difficult to adjust to an ideal state. 3. **Combination of feedforward + feedback control**: In systems with significant disturbances, combining feedforward control with PID feedback control can effectively improve control performance. You can reduce the impact of intake pressure fluctuations on the system by measuring the intake pressure and using it as a feedforward signal to adjust the opening degree of the butterfly valve. 4. **Adaptive control**: Due to the significant variations in operating conditions, an adaptive control system is considered to adjust control parameters in real time in order to cope with different working environments. An adaptive control system can dynamically adjust PID parameters based on the data collected during the control process. 5. **High-speed electric actuator**: Given that you mentioned the response speed of pneumatic butterfly valves might be insufficient, considering using a high-speed electric actuator as a replacement is an option. Electric actuators have a short response time and high control precision, making them more suitable for applications that require fast and accurate control. By combining the above methods, an appropriate control strategy can be selected based on actual operating conditions and feasibility. In practical applications, a combination of multiple control strategies may be necessary to achieve the best control results. .

Is the pressure signal of the control valve taken from the valve outlet, and what is the user’s gas usage situation?

Fuzzy control can be used; automatic control is already very advanced nowadays. You can implement it yourself using DCS

1. Based on the pressure fluctuations, it is necessary to determine whether the size of this buffer tank is appropriate; if it is too small, pressure fluctuations will be significant, and the buffering effect will not be sufficient, making it difficult to maintain control. 2. The large pipe diameter results in poor regulation capability of gas butterfly valves. It is better to use a straight-stroke single-seat control valve (considering cost, it allows for necking). Considering adding a self-acting control valve is also an option. 3. Is control usually based on flow rate or pressure? For control purposes, set output limits for the valve based on the actual conditions; since the stroke is only 1 second, using a PID controller should work well, though the operating conditions are unstable. My personal understanding. For reference!

If the first range of fluctuations is between 20 and 50 kPa, it is necessary to know what your operating pressure is and what proportion of these fluctuations correspond to that pressure, in order to determine more accurately whether it is a design issue or whether more precise control is required. There are two reasons for slow valve operation: one is a slow response time, in which case it is necessary to adjust the PID parameters of the valve or add differential control for advanced regulation; the other reason is an excessive amount of air entering the cylinder, which slows down the valve’s operation. The air supply pipes used by the company in the past were not of such large capacity, and self-acting control valves were used, which proved to provide stable control. We have also encountered situations where unstable air supply from RTO units caused the system to stop operating; in those cases, we replaced the control valves connected to the DCS with self-acting control valves. If the control system is centralized, you can try using their PID adjustment tool to take pictures and automatically modify the parameters

PT1001 controls the inlet control valve, while PT1002 controls the outlet control valve; it is essential to have stable and good regulation in either case. Depending on the situation, it’s possible to introduce the load parameters to determine a certain proportion of the adjustment output; stabilizing such a system isn’t difficult.

The last edit to this post was made by leefloyd0627 on 2024-8-2 at 08:49. There is a pressure transmitter on the buffer tank, and another pressure transmitter behind the control valve; these transmitters are used to regulate the pressure behind the control valve