Questions regarding the installation of pressure regulating valves

In the scenario you described, the pressure range for the feed gas hydrogen is quite wide (adjusting it from 62 to 200 bar down to 60 bar), and there are also specific requirements regarding the flow rate. Taking these two factors into account, whether to use one valve or two valves to achieve this goal depends mainly on your specific application requirements, cost considerations, and the complexity of the system. **Single-valve solution**: Using one valve with cascade control (that is, controlling both pressure and flow simultaneously) is a simpler approach, as it helps to reduce the complexity and cost of the system. The challenge with this approach is that it requires a highly precise and sensitive control system to meet the control requirements for both pressure and flow, especially when the pressure regulation range is large. Furthermore, the valves and control systems need to be able to respond quickly to changes in flow rate and pressure in order to ensure a stable output. **Dual-valve solution**: A scheme that uses two valves to control pressure and flow separately offers higher flexibility and precision. One valve is responsible for maintaining a stable output pressure, while another valve adjusts the flow rate as needed. The advantage of this approach is that pressure and flow can be controlled more precisely, as each control target has a dedicated valve for managing it. The downside is that it increases the complexity, cost, and space requirements of the system. **Summary**: If the system requires high precision in control, and budget and space allow, using two valves may be a better option, as it provides higher control accuracy and flexibility. If the goal is to simplify the system and reduce costs, while accepting a certain degree of loss in control accuracy, then a cascade control scheme using a single valve is also a viable option. The final choice of approach depends on your specific requirements, budget, and system design. .

It wasn’t decided by the design institute; it’s you who decides what to do

Under a simple process, pressure and flow are related

Series control of a single control valve: It is feasible to use one control valve for series control. In this configuration, the main controller (usually a pressure controller) will output a signal to the flow controller based on the pressure setpoint (60 bar) and the measured value. Operating as a slave controller, the flow controller adjusts the opening degree of the control valve based on the output from the main controller and the set flow value, thereby meeting both the pressure and flow requirements. The advantage of cascade control is its ability to respond quickly to changes in pressure, and to fine-tune the flow rate using a flow controller in order to maintain system stability. However, this configuration may require more complex control systems and algorithms to ensure coordination between the master and slave controllers. Two control valves are used separately for control: Using two control valves to regulate pressure and flow respectively is also a viable option. In this case, one control valve is used to regulate pressure, while another control valve is used to regulate flow. The advantage of this configuration is that each control valve can focus on one control objective, thereby simplifying the design and implementation of the control system. However, this can also lead to interactions between the two control loops, especially when there is a coupling relationship between flow rate and pressure. Therefore, it is necessary to carefully design and adjust the two control loops to ensure they can work together to achieve stable control. Recommendation: If your system requires very high stability in terms of pressure and flow, or if there is a strong coupling between these two variables, then using a single control valve for cascade control might be a better option. This ensures that the system can respond quickly to changes in pressure, and fine-tune the flow rate through a flow controller, thereby maintaining system stability. If your system does not require very high stability in terms of pressure and flow, or if the coupling between the two variables is relatively weak, then using two control valves to regulate them separately may be a simpler and more cost-effective option. However, please make sure to carefully design and adjust the two control loops to ensure they can work together.

This post was last edited by Xin Chang Xiao Xu on 2024-5-31 08:53. It is controlled by a single control valve; this is not called cascade control. The output pressure is determined by the operating conditions downstream; what you need is a stable flow rate. Our workshop uses low-pressure steam to heat a hydrolysis reaction distillation tower; whenever steam is used in other parts of the workshop, it affects the flow rate of the distillation tower. The distillation tower itself uses a control valve and a flow meter to form a PID control system, and the command cycle of Zhejiang University’s control system is 0.5 seconds. Wherever steam is used, the pressure in the steam pipes decreases, which prevents the control system from responding quickly and from adjusting the flow rate promptly. Of course, it’s possible to adjust the derivative parameter in the PID, but the 0.5S sampling period of the PID also doesn’t allow for a rapid response. If a pressure gauge is installed on the steam pipe, and by taking into account changes in pressure as well as the valve opening required to achieve the same flow rate at different pressures, the valve opening can be adjusted quickly to the appropriate value based on experience, which effectively solves this problem. Of course, unstable pressure in the steam supply pipes can be resolved by making the pipes larger or by installing pressure-reducing and stabilizing valves. I say this to give everyone a starting point. A single PID and a single control valve are sufficient; by utilizing the empirical values regarding the valve opening required to achieve a constant flow rate at different pressures, pressure changes can be adjusted rapidly.

A single valve is sufficient. Do not use cascade control; instead, let pressure take effect in a certain proportion. Pressure responds faster than flow, which is advantageous for rapid tracking. I did exactly that in the PVC polymerization reaction.

Our company also deals with polymerization reactions; heat is generated rapidly, and there’s not enough time for the reaction to take place. We asked the experienced engineers in our company who specialize in microcontrollers to handle this issue, as experts from Zhejiang University were unable to solve it. Later, it was controlled by the rate of change of pressure inside the furnace. Temperature changes are far less rapid than pressure changes.

Yes, but first, the heat transfer capacity of the process must be sufficient for polymerization. Additionally, intervention at the i inflection point is necessary in advance