a | Lecture Chemical process control - Chapter 1 Introduction to Process Control Chapter 1 a) prototype system-blending tank b) feedback control c) implementation of control d) justification of control 1 Chapter 1 2 Chapter 1 3 Control Terminology controlled variables - these are the variables which quantify the performance or quality of the final product, which are also called output variables. Chapter 1 manipulated variables - these input variables are adjusted dynamically to keep the controlled variables at their set-points. disturbance variables - these are also called "load" variables and represent input variables that can cause the controlled variables to deviate from their respective set points. 4 Chapter 1 5 Chapter Chapter11 6 Control Terminology(2) set-point change - implementing a change in the operating conditions. The set-point signal is changed and the manipulated variable is adjusted Chapter 1 appropriately to achieve the new operating conditions. Also called servomechanism (or "servo") control. disturbance change - the process transient behavior when a disturbance enters, also called regulatory control or load change. A control system should be able to return each controlled variable back to its set-point. 7 Chapter 1 Illustrative Example: Blending system Notation: • w1, w2 and w are mass flow rates • x1, x2 and x are mass fractions of component A 8 Assumptions: 1. w1 is constant 2. x2 = constant = 1 (stream 2 is pure A) 3. Perfect mixing in the tank Chapter 1 Control Objective: Keep x at a desired value (or “set point”) xsp, despite variations in x1(t). Flow rate w2 can be adjusted for this purpose. Terminology: • Controlled variable (or “output variable”): x • Manipulated variable (or “input variable”): w2 9 • Disturbance variable (or “load variable”): x1 .
