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PROCESS DYNAMIC MODELS

ChE 182 June 19/20/21, 2012

1

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Continuously-stirred tank heater2

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Why develop models?4

Important in:

Understanding the process

Process simulationsControl strategy development

Optimization

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Types of models5

Types:

Theoretical

Empirical and Semi-empirical

Treatment of systemsLumped parameter system

Distributed parameter system

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Conservation principles6

accumulation = in out + internal production

Mass balanceOverall/total mass balance

Component mass balance

Energy balance Momentum balance

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Conservation principles7

Overall material balance:

Material balance of component i

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Conservation principles8

Energy balance

Kinetic energy and potential energy terms are negligible

For liquids: U H

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Consitutive equations9

Equations of properties of matter

Definitions of mass, heat, and momentum using

measurable properties

Transport rate equations

Chemical kinetic rate expressions

Law of mass action

Arrhenius expression

Thermodynamic relations

EOS

Chemical and phase equilibria

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Liquid storage system

Some chemical processes

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Stirred-Tank Heating Process (instantaneous heating)

Constant hold-up

T1

w1

x1

T2w2

x2

T

w

x

Some chemical processes

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Stirred-Tank Heating Process (instantaneous heating)

Variable hold-up

T1

w1

x1

T2w2

x2

T

w

x

Some chemical processes

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Electrically Heated Stirred Tank (non-instantaneous)

Constant hold-up

Ti

wi

T

w

Te

Some chemical processes

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Non-isothermal continuously-stirred tank reactor

(CSTR)

A B

rA = -kCA

Some chemical processes

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Objectives15

Have you been able to:

understand the importance of process

modelling?

derive unsteady-state models of chemical

processes?

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HW: Seborg 2nd ed, Problem 2.6

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cAi

cA1

cA2

HW: Seborg 2nd ed, Problem 2.6

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Reminders

Homework is not to be submitted but

please do it for practice.

For appreciation of dynamic models inother processes you encountered in

previous ChE courses, read on dynamic

models of flash drums, distillation systems,bioreactors, series of reactors in our

textbook and other references.

(cont. on next slide)

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Reminders

Review Laplace Transforms (Laplace transform

of functions, inverse Laplace transform,

properties / theorems, partial fraction

expansion, solution to ODE); this will not bediscussed anymore in class.

Suggested references:

ChE 106 materials/references Ch 3 of Seborg 2nd ed

Prepare for a QUIZ next meeting (June 26-28)

on Laplace transforms, including solution to

ODE