Issue with automatic temperature control in the reaction kettle; seeking help from everyone
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I currently have an automatic control system for a reaction kettle, but the temperature control via programming is not satisfactory – the temperature fluctuates quite a lot. Please help and offer some suggestions. After automatic feeding, steam is turned on to raise the temperature to 57 degrees; then the steam valve is closed. The reaction begins when the temperature inside the reactor slowly rises to 63 degrees. It is a slow, continuous exothermic reaction, so steam is no longer used thereafter. Cooling is achieved using jacket cooling water; currently, the flow rate of this cooling water is controlled by adjusting the opening degree of the outlet valve – 40% when the temperature is above 64 degrees, and 80% when it’s above 65 degrees. The circulation of cooling water is stopped once the temperature starts to drop, with the target range being 63–66 degrees. However, the fluctuations in this system are quite large, with temperatures generally ranging between 58–70 degrees, which is far from the required range specified for the process. The current control program is too simple and fails to achieve the desired effect. Does anyone have any good ways to keep the program temperature between 63 and 66 degrees? Please help!
This is really hard to implement; it requires fine-tuning
Find a better automation company and have them rewrite the program for you; it’s likely that PID control will be used, or the S7-1200 series could be employed, as it comes with a PID module that can be utilized
You can first put forward the requirements for the process engineers to review, and then consider how to implement control
It needs to be adjusted; the opening cannot be fixed. We can discuss it in detail
Taking multiple temperature measurement points inside the kettle and using average control based on those points might work better.
Adjust the PID parameters by increasing the derivative term appropriately; it is also possible to tweak the upper and lower limits for valve position output. Additionally, select a control valve with better linearity
The last edit to this post was made by huio1983 on 2017-6-8 at 09:56. According to the original poster, the control of the heating and cooling valves in the reactor can be implemented as a proportional control circuit, with the steam valve switching from open to closed before 63 degrees. After 63 degrees, the cold water valve switches from closed to open. Alternatively, by feeding in 63-degree water, control with a single circuit will be simpler. But it does consume steam.
What is a reaction kettle used for? I think we might be in the same industry. This problem can be solved; your program can still be further optimized – the way it’s written is too rough! Write it in more detail, and add insights gained from experience.
Should you consider increasing the number of adjustment points? Instead of just adjusting the temperature at two levels, make the adjustments more frequent; this way, the fluctuations will occur around the temperature you set. For example, if you set the desired temperature to 50 degrees, making large adjustments within the range of 1 to 100 degrees will have a different effect than making multiple small adjustments around 45/55 degrees. Making one adjustment versus making many adjustments also makes a difference. In theory, the more frequently you make adjustments around the desired value, the smaller the amount of adjustment each time, and thus the greater the precision