Chemical and Biological Engineering

Twin-Screw Food Extruder: A Multivariable Case Study for a Process

Control Course

Joel SchlosburgB. Wayne Bequette

• Process Control Course Overview• Case Studies

• Realistic Industrial Problems• Motivating to Students• Integrate Techniques Learned Throughout Course

BES-0411693

Process Control @ RPI

Four credit hours, Spring Junior yearThree 2-hour sessions/weekStudio: Lectures and SimulationsMajor Case Study Project

Selected from multiple options

Teamwork

Written reports & frequent meetings

Final oral presentation

Link between theory and practice“Feels real”

Multivariable

Noise, constraints

Case Study ProjectsFinal 1/3 of CourseChoice of Projects

Reactive Ion Etcher

Lime Kiln

Fluidized Catalytic Cracking (FCCU)

Anaerobic Sludge Digester

Drug Infusion Control (Critical Care)

Different Advisor (Instructor/TA/RA) for Each ProjectWritten Reports & Final Presentation To Main Column

Feed Oil from Crude Unit

T1CTYC

F s

F a

Heat Exchange

Flue Gas

Air

T rg

Crc

Tcy

T 1

Steam

T 1sp

T cysp

Riser

Reactor (actually a separator)

Regenerator

Spent Catalyst

Regenerated Catalyst

Sensors Controller

Drugs Infused

Infusion pumps

Patient

Measured variables

MAP CO

SNP DPM

setpoints

Flourine MeasurementRF PowerVoltage Bias

Measurement

Computer Control

Power

Throttle

[F]V

bias

Reactive Ion Etcher

Gases In Gases Out

Heater

flow

Flow, % of range

voltage

Voltage, V

fluorine

Fluorine, % of range

throttle, %

power, W

Clock

t

time

power disturbance, W

Etcher

LC

PC

u1

u2

heat input

inlet flowrate

y1

substrate concentration

y2

temperature

Anaerobic Digester

biogas

disgested sludge

MIMO Control

Project Stages

Literature review Week 1Model development Week 2Single input-single output (SISO) controller design Week 3Multiple loop design Week 4Oral presentation Week 5Final written report Week 5

Primary Goals: Learn MIMO Modeling, Analysis and ControlIntegrate basic concepts learned throughout the semester

Twin-Screw Cooking Food Extruder

Common food processing unit, mostly in baking industryFast-speed bioreactor with heating, cooling, compressing, mixing, evaporating, cutting, and aerating in one unitTwin-screw is now becoming more common, as it is easier to manipulate a number of parameters

www.foodprocessing-technology.comScrew Speed manipulated

Moisture content manipulated

Motor torquemeasured

Product temperature measured

Process Simulation (MATLAB/Simulink)

Step Tests to Develop Model

Input 1 Input 2

Output 1 Output 2

Step Tests to Develop ModelNoise and mismatch

Output 1 Output 2

Input 1 Input 2

SS-MT SISO ControlEffect of tuning parameter values

Relative Gain Analysis (RGA) for “Pairing”

Process Gain matrix =

λ11 & λ22 are closer to one, and therefore are the better control loop pairings.

This means the two control loops are:

SS (screw speed) controlling MT (motor torque)

MC (moisture content) controlling PT (product temperature)

⎥⎦

⎤⎢⎣

⎡=

⎥⎥⎦

⎤

⎢⎢⎣

⎡=⎥

⎦

⎤⎢⎣

⎡λλλλ

=Λ−−

−−

−−

88.12.

12.88.

21122211

2211

21122211

2112

21122211

2112

21122211

2211

kkkkkk

kkkkkk

kkkkkk

kkkkkk

2221

1211

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=⎥⎦

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⎡4.212.

87.32.

kk

kk

2221

1211

Best “Pairing” based on RGA

Simultaneous Setpoint Changes

Simultaneous Setpoint Changes

Disturbance Rejection(change in barrel temperature)

RGA Validation: Opposite Pairing

Textbook

Chapters1. Introduction 2. Fundamental Models3. Dynamic Behavior 4. Empirical Models5. Introduction to Feedback Control6. PID Controller Tuning7. Frequency-Response Analysis8. Internal Model Control 9. The IMC-Based PID Procedure10. Cascade and Feed-Forward Control11. PID Enhancements12. Ratio, Selective, and Split-Range Control13. Control-Loop Interaction14. Multivariable Control15. Plantwide Control16. Model Predictive Control17. Summary

Modules1. Introduction to MATLAB2. Introduction to Simulink3. Ordinary Differential Equations 4. MATLAB LTI Models 5. Isothermal Chemical Reactor 6. First-Order + Time-Delay Processes7. Biochemical Reactors8. Continuously Stirred Tank Reactor (CSTR)9. Steam Drum Level10. Surge Vessel Level11. Batch Reactor12. Biomedical Systems13. Distillation Control14. Case Study Problems15. Flow Control 16. Digital Control

SummaryLaptop Studio-based Course

Lectures followed by simulation-based reinforcement of theory

Case Study ProjectsChoice of 5 projects, final 1/3 of course

Integrates concepts learned throughout course

Multivariable focus

Twin screw food extruder