Multi-stage control automatic control scheme for reactor temperature
Thread Content
This post was last edited by shijia on 2024-6-20 09:21. For fine chemical reaction kettles, some reactions require heating first; after the reaction starts, the temperature is lowered to maintain it during the reaction, and then the material’s temperature is reduced for use in the next process. For example, first heat the reaction vessel to 80 degrees Celsius; after starting the reaction, continue it at 130°C (with circulating cooling water for cooling). Is it possible to implement a proportional control system using heating and cooling control valves, and what is the reliability of such control? I consulted some instrument experts, who said it should be implemented through programming using a sequential control system. Or if there are other more effective control methods, please give some guidance. Thank you. Relevant discussion threads are: https://bbs.hcbbs.com/forum.php? ... 6%B8%AA%CE%C2%B6%C8
For the multi-stage temperature control issue in fine chemical reactors, it is feasible to use heating and cooling automatic control valves for a split-range control system. By setting up PID controllers to control the heating and cooling processes separately, it is ensured that the temperature can be automatically adjusted as needed to reach the preset multiple temperature points. The reliability of control usually depends on the design of the control system and the quality of the components. It is recommended to use instruments and controllers with a good reputation and proven performance. In addition, a sequential control system is also a good option; it enables precise control of time and temperature through programming, and it is particularly effective in chemical reaction processes that require complex temperature variations and accurate timing control. If conditions permit, a control system that combines a PLC (Programmable Logic Controller) with a PID module can be considered; this allows for more flexible control logic and more precise adjustments, while also facilitating remote monitoring and operation. .
Thank you for your reply; I’ve learned something from it. Could you give an example for everyone to learn from? Thank you.
The problem description is unclear. The following questions need to be provided before advice can be given. 1. What is the initial temperature? 2. Are there any requirements regarding the rate of temperature increase? What is the heating rate? Is there a time requirement for raising the temperature? 3. What is the insulation duration? Are there any requirements for thermal insulation accuracy? 4. Are there any requirements regarding the cooling rate? What is the cooling rate? Is there a time requirement for cooling down? 5. Is there a maximum deviation limit in the control process?
These are two different control loops; where does this division into stages come from?
Sequential control is not feasible, as the reaction processes in fine chemical manufacturing are quite complex; there are various variables such as the feeding rate, reaction speed, and amount of initiator used. It is better to employ DCS control, adjusting the opening degree of control valves and using different heat sources to regulate temperature.
Similar temperature control requirements are common in the fine chemical industry, and there is a need to figure out how to achieve full process automation. Which teacher can give an example? Thank you.
A highly challenging self-control improvement project; it is very difficult to put it into practice. Some ideas are provided for reference. 1. Organize the detailed process of manual control, including the action time for each step, valve opening degree, flow rate (range), temperature, liquid level, and other relevant parameters. Steam, heating elements, circulating water – all of it is needed; the more detailed, the better. Control criteria for each step (parameters used for judgment). Leave it to the automatic control design team (they will decide whether it can be done). PS: Logical control and automatic control are required, with each step corresponding to a different type of automatic control. 2. Jacket heating has a significant lag; fluctuations in steam and cooling water can introduce uncertainty into the operation process. If relative stability cannot be achieved even through manual operation, it is difficult to achieve it through automatic control as well. Controlled by multiple parameters; a regular PID may encounter problems. (I have seen papers on the automatic control of coal-fired boilers, which used self-developed mathematical models.) 3. The sensing elements need to be accurate ； Clarify the cascading and protective requirements that affect safety and quality. 4. Close coordination between process and automatic control is required. We have an automated control upgrade for heating materials with steam; it is required to raise the temperature of the materials to a certain level within a specified time, stop heating once the materials turn gray, and then proceed with discharging them. The research institute has been working on this for a long time, and visual monitoring has been used for individual components. There will still be problems in practical applications.
The batch process for reaction vessels is not difficult; what’s challenging is the continuous process. The difficulty in designing logical control lies in maintaining a stable reaction temperature, as there are various factors that can affect the temperature – which one should be used? First, consider the material balance for continuous production, and then consider the physical adjustment methods.
For heating and cooling the reactor, it’s better to rely on manual operation; even if full automation is achieved in this regard, human monitoring is still required. So why go to the extra effort?