KING FAHD UNIVERSITY CHEMICAL ENGINEERING COURSE NOTES (Simulation)-Chapter_10

KING FAHD UNIVERSITY CHEMICAL ENGINEERING COURSE NOTES (Simulation)-Chapter_10

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1 Overview of Control System Design Chapter 10 1. Safety. It is imperative that industrial plants operate safely so as to promote the well-being of people and equipment within the plant and in the nearby communities. Thus, plant safety is always the most important control objective and is the subject of Section 10.5. 2. Environmental Regulations . Industrial plants must comply with environmental regulations concerning the discharge of gases, liquids, and solids beyond the plant boundaries. 3. Product Specifications and Production Rate . In order to be profitable, a plant must make products that meet specifications concerning product quality and production rate. General Requirements
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2 Chapter 10 1. Economic Plant Operation . It is an economic reality that the plant operation over long periods of time must be profitable. Thus, the control objectives must be consistent with the economic objectives. 2. Stable Plant Operation . The control system should facilitate smooth, stable plant operation without excessive oscillation in key process variables. Thus, it is desirable to have smooth, rapid set-point changes and rapid recovery from plant disturbances such as changes in feed composition.
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3 Chapter 10 Steps in Control System Design After the control objectives have been formulated, the control system can be designed. The design procedure consists of three main steps: 1. Select controlled, manipulated, and measured variables. 2. Choose the control strategy (multiloop control vs. multivariable control) and the control structure (e.g., pairing of controlled and manipulated variables). 3. Specify controller settings.
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4 Control Strategies Multiloop Control: Each output variable is controlled using a single input variable. Multivariable Control: Each output variable is controlled using more than one input variable. Chapter 10
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5 10.2 THE INFLUENCE OF PROCESS DESIGN ON PROCESS CONTROL Traditionally, process design and control system design have been separate engineering activities. Thus in the traditional approach, control system design is not initiated until after the plant design is well underway and major pieces of equipment may even have been ordered. This approach has serious limitations because the plant design determines the process dynamic characteristics, as well as the operability of the plant. In extreme situations, the plant may be uncontrollable even though the process design appears satisfactory from a steady-state point of view. Chapter 10
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6 A more desirable approach is to consider process dynamics and control issues early in the plant design. This interaction between design and control has become especially important for modern processing plants, which tend to have a large degree of material and energy integration and tight performance specifications. As Hughart and Kominek (1977) have noted: "The control
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KING FAHD UNIVERSITY CHEMICAL ENGINEERING COURSE NOTES (Simulation)-Chapter_10

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