CHE3162 Process Control
Week 6 Workshop
30 August 2023
Week 6 Announcements
• Labs
o Going well
o Please continue to arrive PREPARED and EARLY!
• Mid-sem. test
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o
o
o
o
Tuesday 2pm Week 7
Content week 1-4 inclusive
Short answer x3 (5 marks each) + hand calc x1 (15 marks)
30 marks in 60 min - use the time wisely!
Online, Invigilated, Open access
• No GenAI, No Simulink, No collab tools (e.g. Google Docs /
Sheets, even if not shared)
• Answer in your own words
• Marks allocated for hand calculation working!
CHE3162 S2 2023 - Week 6
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GroupUp
Mock test provided.
NOTE: Make sure you revise ALL the concepts and methods we have covered, not only those given here as
examples. This mock test indicates only the type and length of questions you can expect, it is not a
comprehensive review of the examinable content.
Date: 31/08/2023 (Thursday)
Time: 2.00 p.m to 4.00 p.m
Location: CL_19 Ancora Imparo Way, Room 321 - LTB (Bldg 92)
Be sure to attend the whole session and make the most of it !!
CHE3162 S2 2023 - Week 6
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Week 6 - Safety Moment
Dust explosions
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•
Estimated 2000 incidents annually in Europe,
24% in the food industry, 15% in wood products industry
Any organic and some inorganic materials can cause a dust explosion:
• Sugar, powdered milk, coffee, cocoa, potato, soup, flour, cornflour, cheese
• Grain, pollen, sawdust, cellulose (paper)
• Coal
• Plastics, polymers
• Metal powder, ink
Similar to the incompatible chemicals and runaway reaction examples, it is critical
to understand the chemistry and reactivity of the materials in our process. Most
incidents occur in well-established facilities.
https://ameml.co.uk/dust-explosions/
https://www.hazardexonthenet.net/article/40288/Dust-to-Dust.aspx
CHE3162 S2 2023 - Week 6
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Week 6 - Safety Moment
Dust explosions
On February 7, 2008, a huge explosion and
fire occurred at the Imperial Sugar refinery
northwest of Savannah, Georgia, causing
14 deaths and injuring 38 others, including
14 with serious and life-threatening burns.
The explosion was fueled by massive
accumulations of combustible sugar dust
throughout the packaging building.
https://www.youtube.com/watch?v=
Jg7mLSG-Yws&t=199s
Recommendations?
https://www.csb.gov/imperial-sugarcompany-dust-explosion-and-fire/
CHE3162 S2 2023 - Week 6
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Learning objectives: Week 5&6
Advanced classical control, multi-loop control
Week 5
• Understand the limitation of simple feedback PID
control loops
• Understand when and why to use advanced single
control loops
• Design and implement advanced single control loops
to mitigate system disturbances and other
complexities
CHE3162 S2 2023 - Week 6
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Week 5 recap
Advanced classical control
Cascade, feedforward, ratio, split range, override
● All build on SISO feedback loop
● They are (more or less) the most complex regulatory
control loops
● Each mitigates one or more limitation of SISO feedback
Feedback loops are:
● Reactive
● Don’t mitigate MV disturbances
● Don’t prevent predictable CV disturbances in advance
● Advanced SISO loops give us additional functionality as well: e.g. ratio,
split range, override select
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Cascade
Mitigates MV disturbances
Features
• Inner loop must be faster (rule of
thumb, at least 3x faster, 5x is
better)
• Usually P-only to minimise
instability (offset managed by FB
loop)
• Adds hardware and software
complexity (implications for design,
capex and opex)
S
S1
S2
CHE3162 S2 2023 - Week 6
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Feedforward
Mitigates PROCESS disturbances
Features
• Proactive control (cancellation) of known
process disturbances
• FF TF must be realisable, i.e. make
physical sense
o
o
o
S
Equal or lower order of numerator than
denominator (must be physically possible,
causal and stable)
Negative (or no) deadtime (must be
physically possible and causal)
Non-infinite, non-zero gain
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Ratio, split range, override select
Additional functionality with (relatively) low additional cost
https://instrumentationtools.com/ratio-control/
https://enggcyclopedia.com/2012/06/split-range-control-loop/
http://instrumentationinnutshell.blogspot.com/20
18/01/override-control.html
CHE3162 S2 2023 - Week 6
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Active learning - Week 5
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Simulink Week 6
Follow-Along Demonstration
Topics from Week 4+5
• PID control - frequency response & Bode Stability
Criterion
• Feedback control
Next week: DIY Simulink!!
CHE3162 S2 2023 - Week 6
https://au.mathwor
ks.com/products/m
atlab-online.html
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PID tuning
Ultimate sensitivity frequency response
Key steps
-
Explore the Bode function and Bode plots in MATLAB
Derive the ultimate frequency and AR at this frequency from the Bode plot
Calculate Ku, the ultimate gain
Calculate P-only controller using Ku and ZN tuning rules
Compare with the step response tuning from last week
Plot the tuned response in the model from last week (see below)
CHE3162 S2 2023 - Week 6
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