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Ideality of a CSTRIdeality of a CSTR
Jordan H. Nelson
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Brief OverviewBrief Overview
Introduction – General CSTR InformationThree Questions
Experimental Conclusions
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Item Description
1 Mixing Point
2 Mixing Point
3 Mixing Point
4 Mixing Points
5 Water Bath Inlet and Outlet
6 Four Wall Mounted Baffles
7 Mixer Drive
8 Marine Type Impeller
9 CSTR Vessel
10 Water Bath Vessel
Schematic of the CSTRSchematic of the CSTR
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3 Questions3 Questions ??
Where is the best mixing in the Where is the best mixing in the CSTRCSTR??
What is τWhat is τmeanmean and how does it and how does it compare to τcompare to τidealideal??
What configuration of PFR-CSTR will What configuration of PFR-CSTR will produce the greatest conversionproduce the greatest conversion??
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Where is the Best MixingWhere is the Best Mixing??
Impeller selectionImpeller selection
Food Dye TestFood Dye Test
Dead ZonesDead Zones
Impeller SpeedImpeller Speed
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Rushton Impeller
Marine Impeller
Flow Patterns of different impellers
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ττMeanMean vs vs ττIdealIdeal ??
ττMeanMean – Measured mean residence – Measured mean residence timetime
The amount of time a molecule The amount of time a molecule spends in the reactorspends in the reactor
ττIdealIdeal – Ideal residence time is – Ideal residence time is calculated from the following calculated from the following equationequation
oideal
V
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ExperimentExperiment
Fill reactor with low concentration salt Fill reactor with low concentration salt (baseline)(baseline)
Spike reactor at most ideal mixingSpike reactor at most ideal mixing Create spike concentration at least one Create spike concentration at least one
order of magnitude larger than baselineorder of magnitude larger than baseline Measure change in conductivity over Measure change in conductivity over
timetime Run experiment at different impeller Run experiment at different impeller
speedsspeeds
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Yikes!Yikes!
10
15
20
25
30
35
0 100 200 300 400 500 600 700 800
Time(s)
Co
nce
ntr
atio
n N
aCl(
g/m
L)
30 RPM
15 RPM
Plot of Concentration vs Time with Error
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20
21
22
23
24
25
26
0 200 400 600 800
Time(s)
Co
nce
ntr
atio
n N
aCl(
g/m
L)
30 RPM
15 RPM
Measured Concentration over Measured Concentration over time in the CSTR.time in the CSTR.
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RTD Function E(t)RTD Function E(t)
Measured concentrations are used to Measured concentrations are used to create the residence time distribution create the residence time distribution functionfunction
endt
dttCtC
tCtCtE
0
)]0()([
)0()()(
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Plot of an ideal residence time Plot of an ideal residence time distribution functiondistribution function
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Residence time distributionsResidence time distributions
0.0005
0.0007
0.0009
0.0011
0.0013
0.0015
0.0017
0.0019
0.0021
0.0023
0 20 40 60 80 100 120 140 160 180 200
Time(s)
E(t
)
Ideal E(t)
E(t) Conductivity 15 RPM
E(t) Conductivity 30 RPM
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Mean Residence TimeMean Residence Time
Using E(t) the following equations Using E(t) the following equations produce the mean residence timeproduce the mean residence time
endt
meanmean dtttEt0
)(
endt
m dttEtt0
2 )()(
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Comparison of Residence Comparison of Residence TimesTimes
RPM
Mean Residence
TimeStandard
Deviation SigmaSigma/
Tau
15 357.57 11.58 206.87 0.58
30 358.14 11.58 206.35 0.58
Ideal CSTR 466.97 5.90
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Loss of DataLoss of Data
Over an hour of data was lost from Opto Over an hour of data was lost from Opto 2222
Calculation of Reynolds number over Calculation of Reynolds number over 4000 (Turbulent)4000 (Turbulent)
Equation applies to a baffled CSTREquation applies to a baffled CSTR RPM speed of 300 obtained full RPM speed of 300 obtained full
turbulenceturbulence
2ND
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CSTR-PFR ConfigurationsCSTR-PFR Configurations ??
Schematic of arrangementsSchematic of arrangements Levenspiel PlotLevenspiel Plot Conduct saponification reaction in Conduct saponification reaction in
the reactor at different RPM’sthe reactor at different RPM’s Use Equimolar flow rates and Use Equimolar flow rates and
concentrations of reactantsconcentrations of reactants Quench reaction with a HCl and Quench reaction with a HCl and
titrate with NaOHtitrate with NaOH
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Series Reactor with CSTR Series Reactor with CSTR Before PFR.Before PFR.
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Series Reactor with PFR Before Series Reactor with PFR Before CSTR.CSTR.
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Levenspiel Plot for NaOh+EtOAc
0
2
4
6
8
0 0.1 0.2 0.3 0.4 0.5 0.6
Conversion
-1/r
a
Levenspiel Plot forNaOh+EtOAc
OHEtNaAcNaOHAcEt
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CSTR-PFR ConfigurationsCSTR-PFR Configurations ??
Schematic of arrangementsSchematic of arrangements Levenspiel PlotLevenspiel Plot Conduct saponification reaction in Conduct saponification reaction in
the reactor at different RPM’sthe reactor at different RPM’s Use Equimolar flow rates and Use Equimolar flow rates and
concentrations of reactantsconcentrations of reactants Quench reaction with a HCl and Quench reaction with a HCl and
titrate with NaOHtitrate with NaOH
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Measured Conversion for PFR-Measured Conversion for PFR-CSTR ConfigurationCSTR Configuration
Speed (RPM)
Conversion (%)
Conversion Error (%)
30 19.7 +/- 4.30
60 21.7 +/- 3.91
200 21.2 +/- 4.00
400 24.3 +/- 3.48
875 24.7 +/- 3.41
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Measured Conversion for CSTR-Measured Conversion for CSTR-PFR ConfigurationPFR Configuration
Speed (RPM)
Conversion (%)
Conversion Error (%)
30 21.5 +/- 3.94
60 21.2 +/- 4.00
200 21.4 +/- 3.97
400 20.9 +/- 4.06
875 21.5 +/- 3.94
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3 Questions3 Questions ??
Where is the best mixing in the Where is the best mixing in the CSTRCSTR??
What is τWhat is τmeanmean and how does it and how does it compare to τcompare to τidealideal??
What configuration of PFR-CSTR will What configuration of PFR-CSTR will produce the greatest conversionproduce the greatest conversion??
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ConclusionsConclusions Better mixing for a Rushton impeller Better mixing for a Rushton impeller
is below the impelleris below the impeller The reactor is far from ideal at low The reactor is far from ideal at low
impeller speedsimpeller speeds The PFR-CSTR arrangement provided The PFR-CSTR arrangement provided
better conversionsbetter conversions Run the PFR-CSTR reactor at RPM’s Run the PFR-CSTR reactor at RPM’s
of higher than 300of higher than 300
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OpportunitiesOpportunities
Run the experiment again to obtain Run the experiment again to obtain the lost residence time valuesthe lost residence time values
Run the saponification reaction at Run the saponification reaction at higher temperatureshigher temperatures
Exit sampling stream should be at Exit sampling stream should be at the bottom of the reactorthe bottom of the reactor
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AcknowledgementsAcknowledgements
Taryn HerreraTaryn Herrera Robert BohmanRobert Bohman Michael VanderhooftMichael Vanderhooft Dr. Francis V. HansonDr. Francis V. Hanson Dr. Misha SkliarDr. Misha Skliar
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REFERENCESREFERENCES De Nevers, Noel, De Nevers, Noel, Fluid MechanicsFluid Mechanics, McGraw Hill, New York , McGraw Hill, New York
N.Y. (2005)N.Y. (2005) Fogler, H. Scott, Fogler, H. Scott, Elements of Chemical Reaction Elements of Chemical Reaction
EngineeringEngineering, Prentice Hall, Upper Saddle River, N.J. (1999), Prentice Hall, Upper Saddle River, N.J. (1999) Havorka, R.B., and Kendall H.B. “Tubular Reactor at Low Havorka, R.B., and Kendall H.B. “Tubular Reactor at Low
Flow Rates.” Flow Rates.” Chemical Engineering ProgressChemical Engineering Progress, , Vol. 56.Vol. 56. No. No. 8 (1960).8 (1960).
Ring, Terry A, Choi, Byung S., Wan, Bin., Phyliw, Susan., Ring, Terry A, Choi, Byung S., Wan, Bin., Phyliw, Susan., and Dhanasekharan, Kumar. “Residence Time and Dhanasekharan, Kumar. “Residence Time Distributions in a Stirred Tank-Comparison of CFD Distributions in a Stirred Tank-Comparison of CFD Predictions with Experiments.” Predictions with Experiments.” Industrial and Engineering Industrial and Engineering Chemistry. Chemistry. (2003).(2003).
Ring, Terry A, Choi, Byung S., Wan, Bin., Phyliw, Susan., Ring, Terry A, Choi, Byung S., Wan, Bin., Phyliw, Susan., and Dhanasekharan, Kumar. “Predicting Residence Time and Dhanasekharan, Kumar. “Predicting Residence Time Distribution using Fluent” Distribution using Fluent” Fluent MagazineFluent Magazine. (2003).. (2003).
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What to expect from your CSTR.
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Question?Question?
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Design EquationsDesign Equations)(*)1(** X
a
bCboXCaokra b
22 )1(* XCaokra
220
)1( XkC
XFV
Ao
ACSTR
X
A
PFRXkC
dXV
0 220 )1(
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Design EquationsDesign Equations
0
22 *
)(dte
t t