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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
Dynamics Are Important for the Analysis of ProcessSafety
L
F
T
A
Cooling
water
feed
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time
Temperature Dangerous
Dynamics Are Important for the Analysis of ProcessSafety
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
Dynamics Are Important for the Analysis of ProcessSafety
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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?
Dynamics Are Important for the Analysis of ProcessSafety
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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