3P04 Tutorial 3 Why Model 2008

7/30/2019 3P04 Tutorial 3 Why Model 2008

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Chemical Engineering 3P04

Process Control

Tutorial # 3

Learning goals

1. Discuss what questions we answer usingdynamic models (a few interesting examples)

2. Continue to practice formulating dynamicmodels of processes


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Copyrights by CCPS/American Institute of Chemical Engineers and copied with the permission of AIChE

Dynamics Are Important for the Analysis of ProcessSafety

I suppose that I

should have paid

attention in

Process Control!


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The cooling water pumps have failed. How long do we have

until the exothermic reactor runs away?

time

Temperature Dangerous


L

F

T

A

Cooling

water

feed


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time

Temperature Dangerous


This was in the news

recently for the nuclearreactor at Chalk River.

The cooling system did

not have appropriate

reliability.

McMaster University has

a nuclear reactor oncampus. Are you

concerned?

What can be done to

provide time to repair?


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We must keep

%C4 close to but

below the

combustion limit.

We want tocontrol this

critical variable,

which valve

should we use?

Bartek Maleic Anhydride ProcessVaporizer



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Safety-critical variable

Causal yes, but rather

slow

How about v2?

Causal yes, & fast!

How about v4?

Causal yes & fast

How about v3?



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Feed material is delivered periodically, but the process

requires a continuous feed flow. How large should should

the tank volume be?

Time

Periodic Delivery flow

Continuous

Feed to process

Dynamics Are Important for the Analysis of ProcessInventories (Feed, Products, Intermediates)


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0

100

200

300

400

0 20 40 50 70 80 100

time (h)

Volume(m3)

The tank must be at least this large.

Dynamics Are Important for the Analysis of ProcessInventories (Feed, Products, Intermediates)


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Dynamics Are Important for Product Quality

1

2

3

15

16

17 LC-1

LC-3

dP-1

dP-2

To flare

T5

T6

TC-7

AC-1

LAHLAL

Cooling Water(CW)

PC-1

P3

F3

F4

F7

F8

F9

PV-3

TAL

T10

L4

T20

A

Distillate

product

Bottoms

product

Feed

Weve studied distillation.

I suppose that we should

know what to manipulate

to control the distillate

composition!


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Dynamics Are Important for Product Quality

1

2

3

15

16

17 LC-1

LC-3

dP-1

dP-2

To flare

T5

T6

TC-7

AC-1

LAHLAL

Cooling Water(CW)

PC-1

P3

F3

F4

F7

F8

F9

PV-3

TAL

T10

L4

T20

AC

Distillate

product

Bottoms

product

Feed

Adjusting the reflux has a

strong and fast response on

the top composition


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For all of these practical applications, we need tounderstand and use dynamic analysis.

Formulate models based on fundamental principles

Determine how the key model parameters depend on the

process conditions and equipment design

- Steady-state gain (KP)

- Time constants ()- Dead time (discussed soon)

Determine the transient behavior for specific input

function (e.g., step, impulse, ramp)

- Solve Linear equations analytically

- Solve Non-linear equations using numerical methods (3E04!)

- Solve linearized approximations analytically

- Use qualitative analysis (e.g., step response)

Very important to know how the

process affects the dynamics!


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Modelling exercises: Perform the

following modelling exercises from

Tutorials on the PC-Education WEB:

3.1mixing point

3.2energy balance

3.3isothermal CSTR

1. Define Goals

2. Prepare

information

3. Formulatethe model

4. Determine

the solution

5. AnalyzeResults

6. Validate the

model

Modeling: Practice, Practice, Practice!!!

We apply this procedure

to many physical systems

overall material balance

component material balance

energy balances

3P04 Tutorial 3 Why Model 2008

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