Process Control

Automatic control of process variables (pressure, flow rate, temperature, etc.) of each device that makes up a process. There are two control methods: feedback control and feedforward control. The former detects the output signal of the process and adjusts it according to the deviation between it and the target value, and is particularly effective for processes with a fast response. However, in a reactor with a long reaction time, for example, if there is a change in the composition of the raw materials, if the quality of the finished product is detected and then a control variable such as the reaction temperature is adjusted, the composition of the raw materials will have already changed again, making sufficient control impossible. There are many chemical processes in which the response is slow like this, and in such cases, a method is used in which the relationship between the composition of the raw materials, the reaction temperature, and the quality of the product is expressed in a mathematical formula (process model), and the change in the composition of the raw materials is detected and the reaction temperature is adjusted accordingly (feedforward control), or a method that combines this with feedback control, is used. In process control, while it is important to increase the efficiency of each device, the ultimate goal is to increase the efficiency of the entire process, and it is common for the operating conditions of each device to not match the optimal conditions for operating each device alone.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

一つのプロセスを形成している各装置のプロセス変数(圧力，流量，温度など)を自動制御すること．制御方法としては，フィードバック制御とフィードフォワード制御がある．前者は，プロセスの出力信号を検出し，それと目標値との偏差に応じた調節をする方法で，とくに応答の速いプロセスに有効である．しかし，反応時間の長い反応装置などでは，たとえば原料の組成に変動があると，できあがった製品の品質を検出してから反応温度などの制御量を調節したのでは，すでに原料の組成がふたたび変動してしまい，十分な制御ができない．化学プロセスには，このように応答の遅い装置が多くあり，この場合，原料の組成と反応温度と製品の品質との間の関係を数式(プロセスモデル)に表しておいて，原料組成の変動を検出し，それに応じて反応温度を調節するフィードフォワード制御，あるいはそれとフィードバック制御とを組み合わせた方式がとられる．なお，プロセス制御の場合，各装置の効率を上げることも大切であるが，最終的な目標はプロセス全体の効率を上げることであり，各装置の運転条件がそれぞれの装置を単独で運転する場合の最適条件に一致しないのが一般的である．

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