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Process Dynamics and Control

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Overview

Context and direction Processes and Systems

Process control

Process control is anapplication area of

chemical engineering.

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WHY PROCESS CONTROL?

Advantages of Process Control Enhanced process safety Satisfying environmental constraints Meeting ever-stricter product quality specifications More efficient use of raw materials and energy Increased profitability

QUESTION: As an engineer, whatis the job that youre going to doif you encounter a process?

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Planning a control scheme

liquid level, h controlled variable

Let h r set point

volumetric flow Fi manipulatedvariable

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Put a timer on the valve. Calculatethe time required for filling from(eqn. 3). Close the valve whentime has expired.

QUESTION: What scheme will you propose?Hint: see equation below

A new scheme is proposed:

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Generalized Process Control System

Error = (Set point value) - (Measurement signal of controlled variable)

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Types of Control Systems

closed-loop feedback control system (automaticmode )

Closed-loop refers to the fact that the controller automatically actsto return the controlled variable to its desired value.

open-loop system ( manual mode )In contrast, an open-loop system would have the measurementsignal disconnected from the controller, and the controller outputwould have to be manually adjusted to change the value of thecontrolled variable.

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Hot water tank control system

Block diagram of a hot water heater control system.

Error = Tset point - Tmeasured

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Furthermore, the inputs and outputs of asystem need not be material and energy

streams, as they are for a process. Systeminputs are "things that cause" or stimuli ;outputs are "things that are affected" orresponses .

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FOR NEXT MEETING Be ready for a graded seatwork

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