Control of polymerization temperature in reaction vessels
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For temperature control in the resin reaction vessel, steam is supplied to the jacket for heating after the materials are added. Once the reaction begins to release heat, the steam supply is stopped, and cooling water is used to lower the temperature. Due to the high viscosity of the materials, there is a significant delay in temperature changes; it takes about three to four minutes before any change occurs. Steam and cooling water cannot be used simultaneously, as it is a single jacket. It is now required to control the heating rate; for example, it should take 30 minutes to raise the temperature from 50°C to another 50°C, and 90 minutes to raise it from 50°C to 80°C. A stable DCS is being used, with both steam and cooling water being controlled by control valves. Currently, the programs are adjusted based on experience; either the steam supply stops too late, resulting in a too rapid increase in temperature, or the water supply duration is too long, which slows down the material’s reaction and heating rate, failing to meet the process requirements. I would like to ask those with experience in this field whether they could share successful cases of temperature control in reaction vessels, as well as their experiences in such control tasks. Those who have worked on similar projects are also welcome to get in touch with me.
Above 50°C, steam is no longer used; the heating rate is controlled solely by cooling water.
This post was last edited by Dariga on 2020-5-27 07:04. Generally, for temperatures below 80, hot water (with temperature control) is used for heating to maintain the desired temperature. The thermometer is installed in the correct position. Thermal resistors have a fast response time.
Above 50°C, I no longer need steam; it cools down quickly on its own, and I use cooling water to slow down its rate of temperature increase
Does the steam go directly into the jacket? That would definitely result in drastic changes, and there’s also a delay in temperature measurement. It is recommended to add a heat exchanger; steam is used to heat the cooling water through this heat exchanger, while the cooling water flows inside the jacket, and additional cooling water can be added to lower the temperature. We use Yokogawa’s DCS, and the rate control is excellent
Steam enters the jacket directly; the jacket is equipped with a thermistor temperature sensor that can reach 140°C, while the cooling water temperature is around 20°C. Could you tell me about the control schemes? As far as I know, there are single PID control and cascade control. Thank you
The possible reason is that the dynamic effects of steam heating and cooling water on temperature differ significantly, and since there is only one temperature controller, if the PID parameters of this controller are tuned for heating purposes, it cannot effectively control the temperature during cooling, and vice versa. In this case, it is possible to consider adding a temperature PID controller on the DCS side; different controllers can be used for heating and cooling, with the PID parameters being tuned separately for each process.
It’s difficult to achieve this using the programming features built into the system. To be honest, the process I was familiar with before is basically the same as what you described, with the only difference being the hydrogenation reaction. To achieve automatic stabilization, one has to spend money on a small program developed by someone else
In other words, there are technical personnel who specialize in development; they have written their own set of programs, not using the language available in DCS. These programs can be integrated into the system, and they offer greater intelligence as well as memory functions that help to make the control loops more stable.