Gas Absorption - Carlisle

8/3/2019 Gas Absorption - Carlisle

1/25

Absorption of Carbon

Dioxide by a Sodium

Hydroxide Solution in aPacked Tower

Trevor Carlisle

Thad Ivey

Sara York

ChE 414 Winter 2005


2/25

Presentation Overview

Requested information

Project objectives

Planning and execution

Unit operation background

Experimental design

Results and conclusions Recommendations


3/25

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


4/25

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


5/25

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


6/25

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


8/25

The Gas Absorption Tower

Packing Material:

Ceramic RaschigRings


9/25

[0.05N] NaOH

40 mL/s

3% CO2

Air

Treated Gas

Water

Unreacted NaOH

Na2CO3

4'

4'

Ceramic Raschig Rings

Tower

Schematic


10/25

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


12/25

*

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]


13/25

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


14/25

Theoretical Kga continued . . .

LGG k

H

kK

11

WGG

aKaK


15/25

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


16/25

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


17/25

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 %


19/25

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)


21/25

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


22/25

What accounts for theoretical and

empirical differences?


23/25

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)


24/25

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


25/25

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.

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Gas Absorption - Carlisle