integration of process design and control system

control process

1. Integration of Design & Control
CHEN 4470 –Process Design Practice
Dr. Mario Richard Eden
Department of Chemical Engineering
Auburn University
Lecture No. 15 –Integration of Design and Control I
February 28, 2013
Contains Material Developed by Dr. Daniel R. Lewin, Technion, Israel

2. Outline
PartI:ThisLecture
Providemotivationforhandlingflowsheet
controllabilityandresiliencyasanintegralpartof
thedesignprocess
Outlinequalitativeapproachforcontrolvariable
selectionandunitbyunitcontrolstructuring
PartII–NextLecture
Introduceaqualitativeplantwidecontrolstructure
selectionmethod

3. •ImportanceofEarly-StageDecision
Motivation 1:2

4. •ProcessDesignStagesandTools
Motivation 2:2

5. •ProcessObjectives
•ClassificationofVariables
•DegreeofFreedom(DOF)Analysis
•UnitbyUnitControl
Basic Control Concepts 1:7

6. •ProcessObjectives
–Thedesignofacontrolsystemforachemicalplantis
guidedbytheobjectivetomaximizeprofitsby
transformingrawmaterialsintousefulproductswhile
satisfying:
•Productspecifications:quality,rate.
•Safety
•Operationalconstraints
•Environmentalregulations-onairandwaterqualityaswell
aswastedisposal.
Basic Control Concepts 2:7

7. •ClassificationofVariables
–Variablesthateffectandareaffectedbytheprocess
shouldbecategorizedaseithercontrol(manipulated)
variables,disturbancesandoutputs.
–Itisusuallynotpossibletocontrolalloutputs(why?)
–Thus,oncethenumberofmanipulatedvariablesare
defined,oneselectswhichoftheoutputsshouldbe
controlledvariables.
Basic Control Concepts 3:7
Process
Outputs
Manipulated
variables
Disturbances

8. •SelectionofControlledVariables
–Rule 1:Select variables that are not self-regulating.
–Rule 2:Select output variables that would exceed the
equipment and operating constraints without control.
–Rule 3:Select output variables that are a direct
measure of the product quality or that strongly affect it.
–Rule 4:Choose output variables that seriously interact
with other controlled variables.
–Rule 5:Choose output variables that have favorable
static and dynamic responses to the available control
variables.
Basic Control Concepts 4:7

9. •SelectionofManipulatedVariables
–Rule 6:Select inputs that significantly affect the
controlled variables.
–Rule 7:Select inputs that rapidly affect the controlled
variables.
–Rule 8:The manipulated variables should affect the
controlled variables directly rather than indirectly.
–Rule 9:Avoid recycling disturbances.
Basic Control Concepts 5:7

10. •SelectionofMeasuredVariables
–Rule 10:Reliable, accurate measurements are
essential for good control.
–Rule 11:Select measurement points that are
sufficiently sensitive.
–Rule 12:Select measurement points that minimize
time delays and time constants.
Basic Control Concepts 6:7

11. •DegreeofFreedomAnalysis
–Beforeselectingthecontrolledandmanipulated
variables,onemustdeterminethenumberofvariables
permissible.Thenumberofmanipulatedvariables
cannotexceedthedegreesoffreedom,whichare
determinedusingaprocessmodelaccordingto:
Basic Control Concepts 7:7
N
D = N
Variables-N
Equations
N
D= N
manipulated + N
ExternallyDefined
Degrees of
freedom
Number of
variables
Number of
equations
N
Manipulated = N
Variables-N
externally defined-N
Equations

12. •ClassificationofVariables
–ND=N
Variables=10
–Externallydefined(disturbances):C
Ai,T
i,T
co
Example 1: CSTR Control 1:6T, CA
Ti, CAi
Fc
T, CA
Tc
h
Tco
Fo
Fi
h, T, C
A, C
Ai, T
i,
F
i, F
o, F
c, T
c, T
co

13. •BalanceEquations
Example 1: CSTR Control 2:6T, CA
Ti, CAi
Fc
T, CA
Tc
h
Tco
Fo
Fi oi
FF
dt
dh
A    TCrAhCFCFhC
dt
d
A
AAoAiiA
, 
    
csA
oii
TTUAHTCrAh
CpTFCpTFTh
dt
d
CpA


,  
csccccocc
c
cc
TTUATCpFTCpF
dt
dT
CpV 
Overall Mass Balance
Component Balance
Energy Balance Mixture
Energy Balance Coolant
N
Equations= 4

14. •DegreesofFreedom
–N
Manipulated=N
Variables–N
Ext.Defined–N
Equations
–N
Manipulated=10–3–4
–N
Manipulated=3
Example 1: CSTR Control 3:6T, CA
Ti, CAi
Fc
T, CA
Tc
h
Tco
Fo
Fi
Thus we need to select 3
variables to be controlled.
Each must be controlled by
varying one or more of the
remaining variables

15. •SelectionofControlledVariables
–C
Ashouldbeselectedsinceitdirectlyaffectsthe
productquality(Rule3).
–Tshouldbeselectedbecauseitmustberegulated
properlytoavoidsafetyproblems(Rule2)andbecause
itinteractswithC
A(Rule4).
–hmustbeselectedasacontrolledoutputbecauseitis
non-self-regulating(Rule1).
Example 1: CSTR Control 4:6T, CA
Ti, CAi
Fc
T, CA
Tc
h
Tco
Fo
Fi

16. •SelectionofManipulatedVariables
–F
ishouldbeselectedasitdirectlyandrapidlyaffectsC
A
(Rules6,7and8).
–F
cshouldbeselectedasitdirectlyandrapidlyaffectsT
(Rules6,7and8).
–F
oshouldbeselectedasitdirectlyandrapidlyaffectsh
(Rules6,7and8).
Example 1: CSTR Control 5:6T, CA
Ti, CAi
Fc
T, CA
Tc
h
Tco
Fo
Fi

17. •SuggestedControlStructure
Example 1: CSTR Control 6:6T, CA
Ti, CAi
Fc
T, CA
Tc
h
Tco
Fo
Fi
TC
CCLC

18. Summary
PartI:ThisLecture
Providemotivationforhandlingflowsheet
controllabilityandresiliencyasanintegralpartof
thedesignprocess
Outlinequalitativeapproachforcontrolvariable
selection
PartII–NextLecture
Introduceaqualitativeplantwidecontrolstructure
selectionmethod

19. •EvonikSiteVisit–March5
–Whattobring?
•PhotoID(driverslicenseispreferred)
–Whatnottobring?
•Cameras(includingcameraphones)
•CellPhoneuseisonlyallowedinbuildings
•Guns,DrugsorAlcohol(Ihopethisoneisobvious)
–Whattowear?
•LongPants
•ClosedShoes(nosandalsorflipflops)
•ShirtswithSleeves(notanktops)
•SafetyGlasses
Other Business

20. •EvonikSiteVisit–March5(Cont’d)
–Tentativeschedule
Other Business

21. •NextLecture–March7
–Integrationofdesignandcontrol–PartII(Plantwide)
–SSLW322-340
•ProgressReport2
–TurninFridayMarch8
–Remembertofillouttheteamevaluationforms
Other Business