gas absorption - carlisle
TRANSCRIPT
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Absorption of Carbon
Dioxide by a Sodium
Hydroxide Solution in aPacked Tower
Trevor Carlisle
Thad Ivey
Sara York
ChE 414 Winter 2005
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Presentation Overview
Requested information
Project objectives
Planning and execution
Unit operation background
Experimental design
Results and conclusions Recommendations
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For what purpose?
Request from Environmental Systems Design
They need to finalize their tower design given Waste gas contains 3% CO2 0.05N NaOH scrubbing solution at 40 mL/s
Empirical analysis of mass transfercoefficients and effluent compositions of CO2
Theoretical analysis for comparison
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Objectives
1. Verify calibration data
2. Find the dependence of KGa and outlet
compositions on gas flow3. Determine flooding points
4. Theoretically calculate KGa
5. Statistically analyze the data
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Action Items
1. Understand unit operation
2. Identify safety issues
3. Calibrate flow meters
4. DOE and gas sampling
5. Organize and evaluate the data
6. Identify appropriate mass transfer relations
7. Calculate empirical results8. Compare with theoretical predictions
9. Reach conclusions and present results
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Team member roles
Sara- Operations Manager Run the GC
Ensure Proper tower operation
Responsible for data management
Thad- Safety Manager Identify safety issues
Develop the safety plan
Monitor safe lab behavior
Trevor- Team Leader Develop and the project plan
Ensure lab work moves forward
Coordinate group tasks
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Lessons Learned
Do not rush experimental design
Emphasize background information prior to
lab work
Do not leave any ambiguity in action items
Perform theoretical calculations prior to
experimentation
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The Gas Absorption Tower
Packing Material:
Ceramic RaschigRings
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[0.05N] NaOH
40 mL/s
3% CO2
Air
Treated Gas
Water
Unreacted NaOH
Na2CO3
4'
4'
Ceramic Raschig Rings
Tower
Schematic
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Mass Transfer with Reaction
Mechanism: liquid film controlling
CO2
CO2
CO2
CO2
GAS FILM
CO2
LIQUID FILM
H2O
H2O
H2O
H2O
NaOH Na2CO3
H2O
NaOH
NaOH
Theoretical concentration
profile of CO2
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The rapid, 2nd order irreversible
reaction
OHCONaNaOHCO aqaqg 2)(32)()(2 2
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*
lmTT
aG
ySPh
naK
2
1
21*
*)(
*)(
*)(*)(
yy
yyLn
yyyyylm
Determination of KGa from experimental data
na= absorption rate of CO2 [lbmol/s]
hT= packing height [ft]
S= cross sectional area [ft2]
PT= system pressure [atm]
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Theoretical calculation of KGa with the
Onda Correlation
3/1
4.0
2/13/2
0051.
L
Lpt
LL
L
LW
ML Da
Da
Lk
0.23/17.0
pt
GG
G
Gt
MGtoG Da
Da
G
RT
DaCk
45.11
eaa tW
2.005.01.075.
Re LLLL
C WeFr
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Theoretical Kga continued . . .
LGG k
H
kK
11
WGG
aKaK
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Experimental Design
Prepare ~0.05N NaOHsolution
Standardize scrubbing
solution Vary gas flowrate (100
1000 mL/s)
Maintain 3% CO2
Constant liquid flow, 40
mL/s
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More on experimental design
Allow time to reach SS
mass transfer
Gas samples taken from top
and bottom of tower
GC used for analysis
Peak areas used to
determine CO2
composition
Four samples taken per flow
setting
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Results: Flooding
Theoretical calculation
Superficial Gas flow
rate at flooding =525 lbm/ft
2-hr
=6016 lbm/hr with our
tower
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Results
Mol % CO2 vs. Gas Flow
% CO2 = 1.6*Ln(G) - 5.2
R2
= 0.99
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
20 40 60 80 100 120
Gas Flow (ft3/hr)
Mol%
CO2
Outlet CO2 Mol % vs Gas Flow
Average Inlet CO2 Mol %
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Results
KGa vs. Gas Flow
KGa = -0.0042*G + 0.66
R
2
= 0.98
0
0.1
0.2
0.3
0.4
0.5
0.6
20 30 40 50 60 70 80 90 100 110 120
Gas Flow KGa (ft3/hr)
K
Ga(lbmol/ft3-hr-atm)
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Results
Theoretical KGa vs Gas Flow
KGa = 0.0279*G0.0053
R2 = 0.98
0.0283
0.02835
0.0284
0.02845
0.0285
0.02855
0.0286
0.02865
0 20 40 60 80 100 120
Gas Flow (ft3/hr)
K
Ga(lbmol/ft3-hr-atm)
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What accounts for theoretical and
empirical differences? kL is affected by the 2
nd order reaction
Rather, kL = c*kLo, where c is a reaction parameter
and kLo is the transfer coefficient without reaction
Wetted surface area, aW, may be decreasing with
increased gas flow
The set up is not completely liquid film controlling
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What accounts for theoretical and
empirical differences?
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Conclusions Theoretical model needs to be re-evaluated by considering
reaction effects
The gas phase resistance is not negligible:
KGa= -.0042G + .66 (lbmol/ft3-hr-atm)
CO2 composition in liquid outlet is zero based on mass balance
CO2 composition in the gas outlet varies as a natural log:
%CO2= 1.6ln(G)5.2
Predictions of yCO2 in tower outlet are not reliable above flows
of 150 ft3/hr Flooding will occur well above reasonable operating flows
Gf= 6016 (lbm/hr) = 6.19x105 (mL/s)
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Recommendations
Obtain more data closer to flooding
Determine the relation between reaction
kinetics and KGa
Use previous experiments contained in
journals to anticipate results and complications
Include theoretical calculations as part of the
lab work
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References
Perry, Robert H. and Green, Don W. 1997. Perrys chemical engineers
handbook (7th Ed). United States of America: R.R. Donnelly and Sons
Company.
Nijsing, R.A.O.T., Hendriksz, R.H, and Kramers, H. 1959. Absorption ofCO2 in jets and falling films of electrolyte solutions, with and without
chemical reaction. Chemical engineering science, 10,88-103.
Rorrer, Gregory L. 2004. Che 411 mass transfer operations lecture notes
supplement. Corvallis, OR: Dept. of Chemical Engineering, Oregon State
University.Spector, Norman and Dodge, Barnett F. (year?). Removal of carbon dioxide
from atmospheric air. American institute of chemical engineers, (vol?),
827-848.