4 replies to this topic

[winstona]

Hi Good day.I'm currently having trouble with temperature spikes during cooking/heating and cooling on our product. We using halve pipe coil jacket to heat product.We use a automamative system to close the main steam supply when the product reach a temperature which the system calculate at a slope during the time of cooking.Even when main steam valve are close the temperature spike. We use 4.5 bar steam pressure to heat the product. This problem happens when we do heating and cooling also,the spike or drop in temperature are between 2 and 5 degrees celcuis. Can someone please assist.

[Pilesar]

Perhaps your temperature measurement is not reading the bulk temperature of the product. Unless the product is continually mixed there may be temperature gradients in the product that eventually equalize. Or there may be a time delay in the measurement itself. If the amount of process delay is repeatable, a proper control scheme can be devised to avoid overshooting the target temperature. I am not familiar with your automamative system, but I suspect better tuning of the control response could eliminate the problem.

[winstona]

Hi pilesar
Thanks for your reply, will definitely look in depth with your reply. If you talk about measurement you sertunly talking about the temperature probes if I'm correct? Can you maybe just explain what you mean with a proper control scheme. We using Schneider automative system. Yet again thank you for replying.

[Pilesar]

If you wait until the measured temperature reaches the target temperature to adjust the heating or cooling, this might explain the reason the target temperature is exceeded. Instead you might begin to reduce the heating and cooling as the temperature approaches the target to avoid excessive overshoot. If the process response is repeatable and predictable, then you must learn how to control the heating and cooling and then teach (tune) the control system to behave as if it had the eyes and hands of a good process operator. You are measuring the temperature of the process at one location and trying to adjust that temperature by putting steam to the outside of a thick metal wall. There will have to be some delay in the process response. Even if you close the main steam supply, there will be heat transfer as the steam continues to condense. Is your process mixed well so that the temperature you measure is close to the bulk temperature? You may not have to find all the sources of error that affect the process response if you tune the controller and do not expect too much precision since you are using a jacket. Note that the jacket will transfer heat to liquid contents much more than to vapor contents.

[latexman]

Try turning the heating and cooling off 2-5 ^oC BEFORE the set temperature is reached.