Property of Beehive Engineering Ideality of a CSTR Jordan H. Nelson.

Property of Beehive EngineeringProperty of Beehive Engineering

Ideality of a CSTRIdeality of a CSTR

Jordan H. Nelson


Brief OverviewBrief Overview

Introduction – General CSTR InformationThree Questions

Experimental Conclusions


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


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??


Where is the Best MixingWhere is the Best Mixing??

Impeller selectionImpeller selection

Food Dye TestFood Dye Test

Dead ZonesDead Zones

Impeller SpeedImpeller Speed


Rushton Impeller

Marine Impeller

Flow Patterns of different impellers


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


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


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


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.


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()()(


Plot of an ideal residence time Plot of an ideal residence time distribution functiondistribution function


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


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 )()(


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


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


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


Series Reactor with CSTR Series Reactor with CSTR Before PFR.Before PFR.


Series Reactor with PFR Before Series Reactor with PFR Before CSTR.CSTR.


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


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


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


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


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??


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


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


AcknowledgementsAcknowledgements

Taryn HerreraTaryn Herrera Robert BohmanRobert Bohman Michael VanderhooftMichael Vanderhooft Dr. Francis V. HansonDr. Francis V. Hanson Dr. Misha SkliarDr. Misha Skliar


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).


What to expect from your CSTR.


Question?Question?


Design EquationsDesign Equations)(*)1(** X

a

bCboXCaokra b

22 )1(* XCaokra

220

)1( XkC

XFV

Ao

ACSTR

X

A

PFRXkC

dXV

0 220 )1(


Design EquationsDesign Equations

0

22 *

)(dte

t t

Property of Beehive Engineering Ideality of a CSTR Jordan H. Nelson.

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Transcript of Property of Beehive Engineering Ideality of a CSTR Jordan H. Nelson.