Selection of control valves
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This post was last edited by zhoudingshengs on 2023-12-4 at 10:46. Everyone is encouraged to participate: 1. The diagram below shows a heater that uses the waste heat from the main medium in a process to heat a certain fluid; the outlet temperature of this fluid needs to remain constant. To this end, a temperature control system is designed to control the outlet temperature of the fluid stream by adjusting the flow rate of the heat carrier entering the heater. However, since the heat carrier is the main medium in this process, its total flow rate cannot be changed, and there is sufficient excess of its waste heat to heat the material stream. Based on the above process conditions, which type of control valve should be selected? Which pipeline is the control valve installed on?
Based on the situation you described, we need to select a control valve to regulate the flow rate of the heat carrier entering the heater, thereby controlling the outlet temperature of the fluid stream. Given that the total flow rate of the heat carrier remains constant, what we need is a control valve that can distribute the flow rate without changing the total flow rate. Here are some common types of control valves, along with a brief analysis of whether they are suitable for this application: 1. **Throttling Valve** – This type of valve regulates flow by changing the position of its valve element. Reducing the valve orifice of a throttle valve increases the velocity and pressure drop of the fluid flowing through the valve, but this may not be applicable in this case, as they are generally used to regulate flow rate rather than distribute it. 2. **Bypass Control Valve** – In this system, a portion of the heat carrier passes around the heater through the bypass control valve, while the rest passes through the heater. By adjusting the opening degree of the bypass control valve, the amount of heat carrier passing through the heater can be changed, thereby regulating the outlet temperature of the fluid stream. Since the total flow rate of the heat carrier remains constant, this type of valve is suitable for distributing flow to different paths. 3. **Three-Way Control Valve** – This type of valve has two inlets and one outlet, or one inlet and two outlets. In your application, a three-way valve with one inlet and two outlets can be used, one of the outlets being connected to the heater, while the other is used for reflux or connection to other processes. By changing the position of the internal spool/ball, the three-way valve can distribute flow without altering the total flow rate. 4. **Split-Range Control Valve** – Uses two or more valves to control a flow process, with each valve covering a different range of flow rates. This configuration may not be necessary in your application, as what you need is to allocate traffic rather than control it across different traffic ranges. In your case, selecting a **three-way control valve** may be the most suitable option, as it can maintain a constant total flow rate of the heat carrier while also allowing control of the outlet temperature of the fluid by distributing the flow between the heater and the bypass path. You can select the appropriate model and specifications for the three-way control valve based on the actual process requirements and system design parameters (such as pressure, temperature, flow rate, etc.). At the same time, you also need to ensure that the material, connection method, and control type of the selected control valve are compatible with your system. .
Choosing regulators with equal percentages will suffice. By adjusting the level of the outlet temperature (temperature transmitter), the opening degree of the control valve actuator is controlled, thereby determining the flow rate of the heat medium.
Very professional! May I ask, is it feasible to install a three-way valve on the outlet pipeline of the heater?
A three-way valve can be used, installed on the inlet pipeline of the heat carrier, utilizing a three-way diverter valve.
There’s a problem with this question! 1. Control the outlet temperature of the fluid stream by adjusting the flow rate of the heat carrier entering the heater. 2. However, since the heat carrier is the main medium in this process, its total flow rate cannot be changed! 3. Moreover, there is sufficient surplus of its waste heat to heat the material stream. 4. The outlet temperature of the logistics system needs to be kept constant. Of the above four points, the first and second are contradictory to each other! Then the third one can barely be used as a supplement. However, taking all four points above into consideration, as can be seen from the diagram, there are only four pipes in the heat exchanger; installing a flow-dividing valve on the pipe carrying the heat transfer medium to control the temperature of the fluid is not a good approach. The best approach is to control the temperature of the material at the outlet of the heat exchanger by adjusting the flow rate of the material being heated; this method is both reliable and simple.