CSTR IdealityCSTR Ideality

November 29, 2006November 29, 2006

By Taryn HerreraBy Taryn Herrera

Importance of CSTR IdealityImportance of CSTR Ideality

EconomicsEconomics Design of ReactorsDesign of Reactors Higher Conversion of ReactantsHigher Conversion of Reactants

CSTR IdealityCSTR Ideality

The ExperimentThe Experiment The ResultsThe Results Characterization of IdealityCharacterization of Ideality Residence Time Distribution FunctionResidence Time Distribution Function Causes of CSTR Non-IdealityCauses of CSTR Non-Ideality Conclusions and QuestionsConclusions and Questions

The ExperimentThe Experiment

Characterize the ideality of client’s Characterize the ideality of client’s bench CSTR reactor bench CSTR reactor

Operate currently at 30 rpmOperate currently at 30 rpm Determine most ideal conditions and Determine most ideal conditions and

make recommendationsmake recommendations

The Experiment (cont.)The Experiment (cont.)

Injection Impulse Step TestInjection Impulse Step Test Sodium Chloride is the TracerSodium Chloride is the Tracer Concentration Measurements by Concentration Measurements by

ConductivityConductivity Different Mixer SpeedsDifferent Mixer Speeds

Figure 1 Schematic Diagram for CSTR

Item Description

1 Mixing Point

2 Mixing Point

3 Mixing Point

4 Mixing Points

5Water Bath Inlet and

Outlet

6Four Wall Mounted

Baffles

7 Mixer Drive

8 Marine Type Impeller

9 CSTR Vessel

10 Water Bath Vessel

The CSTR Apparatus

Characterization of IdealityCharacterization of Ideality

Ideal Residence Time vs. Mean Ideal Residence Time vs. Mean Residence TimeResidence Time

Residence Time is how long material Residence Time is how long material stays in reactorstays in reactor

Comparison is done numerically and Comparison is done numerically and graphicallygraphically

Ideal Residence TimeIdeal Residence Time

oideal

V

Residence Time DistributionResidence Time Distribution

endt

meanmean dtttEt0

)(

endt

m dttEtt0

2 )()(

endt

dttCtC

tCtCtE

0

)]0()([

)0()()(

Residence Time Distribution Residence Time Distribution (cont.)(cont.)

E(t) or RTD, measures fraction of E(t) or RTD, measures fraction of material in reactor between two material in reactor between two timestimes

ttmm, mean residence time, mean residence time Sigma or variance, measures the Sigma or variance, measures the

distribution’s spreaddistribution’s spread

Residence Time Distribution Residence Time Distribution (cont.)(cont.)

Figure 2 Graph from Fluent Magazine showing RTD functions for different methods (Ring, 2004)

The ResultsThe ResultsConcentration of Sodium Chloride versus Time

10

15

20

25

30

35

0 100 200 300 400 500 600 700 800

Time(s)

Con

cent

ratio

n N

aCl(g

/L)

30 RPM

15 RPM

The Results (cont.)The Results (cont.)

Residence 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

The Results (cont.)The Results (cont.) Mean Residence Time

0

100

200

300

400

500

0 5 10 15 20 25 30 35

RPM

Mea

n R

esid

ence

Tim

e(s)

Ideal Mean Residence Time

Experimental Residence Times

The Results (cont.)The Results (cont.)

RPMMean Residence

Time Standard Deviation Sigma Sigma/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 

Causes of CSTR Non-IdealityCauses of CSTR Non-Ideality

Poor MixingPoor Mixing Dead Zones in CSTRDead Zones in CSTR Short CircuitShort Circuit

CSTR Non-IdealityCSTR Non-Ideality

Figure 3 Impulse Injection for CSTR

CSTR Non-IdealityCSTR Non-Ideality

Rushton Impeller Marine Impeller

CSTR Non-IdealityCSTR Non-Ideality

2ND 53

0

DN

PrPowerNumbe

Turbulent Mixing Turbulent Mixing Done by Baffles and Mixing SpeedDone by Baffles and Mixing Speed Promotes Better Mixing of ReactantsPromotes Better Mixing of Reactants Dead Zones MinimizedDead Zones Minimized Reynolds Number of 4000Reynolds Number of 4000

ReviewReview

Characterization of IdealityCharacterization of Ideality Residence Time Distribution FunctionResidence Time Distribution Function Mean Residence Time vs. Ideal Mean Residence Time vs. Ideal

Residence TimeResidence Time CSTR Non-IdealityCSTR Non-Ideality

ConclusionsConclusions

Use Marine Type ImpellerUse Marine Type Impeller Promote Turbulence in CSTRPromote Turbulence in CSTR Choose Wisely the Mixing Points and Choose Wisely the Mixing Points and

Sampling PointsSampling Points Use FluentUse Fluent Observe other RTD dataObserve other RTD data

Questions?Questions?