On the main steam pipe, there is a control valve that is meant to regulate both the steam flow rate and the steam pressure. How is this control achieved?

To control both steam flow rate and pressure simultaneously, a dual flow-pressure control method can be employed. Specifically, a flow meter can be connected in front of the control valve; by using the feedback from the flow signal, the opening degree of the control valve can be adjusted, thereby achieving precise control over the steam flow rate ； At the same time, a pressure sensor can also be installed behind the control valve; by using the feedback pressure signal, the opening degree of the control valve can be adjusted, thereby achieving precise control over the steam pressure. Whether cascade control can achieve stable regulation depends on the specific application scenario. The advantage of cascade control is that it can improve the system’s response speed and accuracy, but instability may occur if the control parameters are not set properly or if there are disturbances in the system. Therefore, before implementing cascade control, it is necessary to conduct a thorough analysis and simulation of the system to ensure its stable operation. .

The two factors that determine flow rate are flow resistance and pressure difference. Flow rate and pressure difference are interrelated and not independent; therefore, on a pipeline without branches, a control valve cannot simultaneously regulate both the flow rate and the pressure difference.

I still think the idea for the 3rd floor is more reliable; if the control requirements aren’t high, a simple control system will suffice； In most cases, simple control systems can meet over 80% of the requirements ；

In the case of the main pipeline, considering the need to balance the flow demand at various steam usage points downstream, we generally do not control the flow rate in the main pipeline; instead, the pressure in the main pipeline is used as the primary parameter for controlling the regulating valves, thereby maintaining stable pressure and ensuring the appropriate pressure difference at each steam usage point.

This post was last edited by pzhmotor on 2023-4-19 at 10:15. On the 5th floor, it is stated that \"if it’s the main pipe, considering the need to balance the flow rate at various points where steam is used, we generally do not control the flow rate of the main pipe.\" When pressure or temperature adjustment is needed on the steam main, a pressure and temperature reducing valve is usually used. (In large systems, turbines, steam turbines, and other devices that utilize the thermal energy of steam are used to save energy. ) Reducing only the pressure without lowering the temperature may lead to excessively high steam superheat, which can affect equipment at the user end that uses saturated steam. Adjustment is made directly on the main pipe based on flow rate; when the valves are adjusted significantly, it is very likely to cause the safety valve of the boiler’s drum to activate and discharge steam! It is neither economical nor safe. The conventional approach is to connect the inlet pressure signal of the temperature-reducing pressure regulator to the boiler room control room; by controlling the inlet pressure, a stable steam supply can be ensured (the inlet control valve of the temperature-reducing pressure regulator and the amount of water used for temperature reduction are automatically adjusted by PID regulators, resulting in relatively stable outlet pressure and temperature). The regulation of steam flow is achieved by installing steam control valves on the steam inlet pipes after the steam is distributed to various user units. Based on the parameters that need to be controlled (such as flow rate, pressure, and material temperature), PID control is used for automatic regulation (either through DCS or PLC, or a separate PID controller can be used). In this way, the system remains relatively stable, and the control accuracy is high as well.