Automatic control scheme for batch reactors with gaps
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The reaction vessel is an 5M3 enamel-jacketed tank. Steam is used only in winter, as the temperature is too low for the reaction to take place. The production cycle is 3 batches per 24 hours; circulating water is used for most of the production time, while cold water is used only during the cooling phase after product discharge. What I would like to ask is: in my control scheme, when no further feeding occurs and there is no reaction taking place, the temperature might rise above 25 degrees. In such a case, will the cold water system be activated? I haven’t fully understood this point; I’ve asked several people, but their answers vary. So please provide some guidance. Thank you. The process is as follows: The reaction takes place at a temperature of 40–60 degrees, and it’s an exothermic reaction, so cooling is necessary during the reaction. At the beginning, the temperature needs to be raised to the reaction temperature, and once the reaction stops, cooling begins. Circulating water is used between 60–40 degrees, while 7-degree water is used between 40–25 degrees. Then, product discharge occurs. My designed control scheme is as follows: Feeding → Temperature monitoring → DCS-controlled steam activation; steam is turned off at 45 degrees. If the temperature exceeds 55 degrees, circulating water is activated, and the flow rate is adjusted to keep the temperature at 50 degrees. After the reaction is complete, no more heat is generated and the temperature starts to drop. If the temperature falls below 40 degrees, circulating water is turned off and cold water is activated. If the temperature drops below 25 degrees, the cold water system is turned off and product discharge begins. However, there’s one problem: when no further feeding occurs and there is no reaction taking place, the temperature might rise above 25 degrees. In such a case, will the cold water system be activated?
In my opinion, there is no need to do this; it’s sufficient to control the preheating temperature of the feed material in accordance with climate changes!
According to your control scheme, the low-temperature water control valve will open when there is no reaction.
According to the control method you described, when there is no response and the temperature is above 25 degrees, the low-temperature water supply must be turned on. Since this is a batch-controlled system, you can set it so that the batch process stops once the discharge is complete; in that case, the valve for low-temperature water will not open.
If you want to figure this issue out, you need to address another question: is your unit controlled by a PLC? Or more advanced controls such as some kind of automated control. At present, your descriptions are all at the process operation level. This post was last edited by weiqj on 2008-1-30 10:55.]
In your program, just add one line to set the output of the control valve to 0; this way, the valve will not open.
The poster is using DCS, which is very convenient; during configuration, a condition is added to the low-temperature water control circuit – namely, the low-temperature water valve closes once discharge is complete, and it can be opened only when feeding resumes. For example: The low-temperature water valve is of the air-open type; when the material has been completely discharged and the conditions are met, the DCS sends out a digital signal to shut off the solenoid valve that supplies air to the low-temperature water valve, causing the valve to close. When feeding again, the solenoid valve resumes air supply, and the valve operates normally.
As long as the controller is set to manual shutdown, there will be no problem