STUDY GUIDE · GKU 7
Process control study guide (Chemical Engineering)
A plant designed at steady state never stays there: feeds change, catalysts age, cooling water warms up in summer. Process control keeps temperatures, levels, pressures and compositions where they should be despite this. The first part of the guide builds dynamic models of tanks, heaters and reactors from balances, classifies the variables, counts degrees of freedom, and turns the models into transfer functions with the Laplace transform. The second part puts the loop together: sensors, transmitters and valves; block diagrams for set-point and disturbance changes; stability by the Routh array and Bode diagrams; and tuning by Ziegler–Nichols and IMC rules.
Structured by the official ETEC subject standard for this topic: every listed topic and learning outcome, with formulas, figures and worked examples. The full sections are available to members in the app.
SKU 7.1 · Dynamic modeling
Dynamic models of tanks, heaters and reactors
Unsteady mass, component and energy balances for a liquid tank, a stirred heater and a continuous stirred-tank reactor, and what the resulting time constants mean.
Variables, set points, disturbances and degrees of freedom
How to classify the inputs and outputs of a unit (controlled, manipulated and disturbance variables, set points), and how a degrees-of-freedom count tells you how many variables can be controlled.
Laplace transforms and transfer functions
Deviation variables, linearization, the Laplace transform and the standard transfer functions of process control: first order, second order, dead time and integrating, with the final-value theorem.
SKU 7.2 · Control of dynamic systems
Instrumentation: sensors, transmitters, valves and data acquisition
The hardware of a loop and its transfer functions: common sensors for temperature, pressure, flow, level and composition, transmitters and the – signal, control valves (fail-safe action, characteristics, sizing), sampling and resolution, and instrument tags on a P&ID.
Block diagrams, servo and regulatory problems
The feedback loop as a block diagram, block-diagram algebra, closed-loop transfer functions for set-point and disturbance changes, P, PI and PID action and offset, and the feedforward, cascade and ratio structures used in plants.
Closed-loop stability: Routh array and frequency response
The characteristic equation and its roots, the Routh array, frequency response (amplitude ratio and phase), Bode diagrams, the Bode stability criterion, and gain and phase margins.
Controller tuning
What a well-tuned loop looks like, the criteria used to judge it, fitting a first-order-plus-dead-time model from a step test, and tuning by Ziegler–Nichols closed-loop rules and by IMC.
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