cstr ideality
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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?
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