ABSORPTION COLUMN -...

CHATTANOOGA ENGINEERING ASSOCIATION

ABSORPTION COLUMN TEAM BP

Brad Gibson, Brooke Washburn, Philip George

10/23/2013

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the document. Type the abstract of the document here. The abstract is typically a short summary of the

contents of the document.]

T e a m B P | 1

Letter of Transmittal

To the Chattanooga Engineering Association,

This report was done by Team BP at the University of Tennessee at Chattanooga over the absorption

column in the Engineering, Math, and Computer Sciences building. This report and our work on the

column was authorized and supervised by Dr. Ennis and Dr. Henry. This report will go over all of the

steps we have taken to get this system running, data we have compiled, conclusions we have made, and

hardships we have overcome with this task. Thank you for your time and we, Team BP, hope that you

find this project was worth the effort.

Sincerely,

Team BP

T e a m B P | 2

Contents

Letter of Transmittal ..................................................................................................................................... 1

Introduction .................................................................................................................................................. 3

Theory ........................................................................................................................................................... 3

Equipment ..................................................................................................................................................... 5

Procedure ...................................................................................................................................................... 7

Results ........................................................................................................................................................... 8

Discussion of Results ................................................................................................................................... 13

Conclusions ................................................................................................................................................. 17

Recommendations ...................................................................................................................................... 17

References .................................................................................................................................................. 17

Appendix ..................................................................................................................................................... 17

T e a m B P | 3

Introduction

The objectives set for this lab by the Chattanooga Engineering Association was to repair and test

the Absorption Column located in EMCS 120. Through the utilization of two junior engineering teams,

this objective was successfully met.

The absorption column that is used for this experiment is a packed column. The absorption of a

gas that takes place in a packed column is the result of a physical reaction. This physical reaction is best

achieved as the surface area is increased. To aid with this, UTC’s packed column is filled with 1/4”

Rasching rings.

Initially the absorption column was found to be inoperable. Repairs and adjustments were

required for the air valve, water valve, LabView interface, CO2 sensor, and CO2 tank and line. The junior

lab groups were utilized in the testing of the apparatus with each adjustment.

Once the first objective was met, Team BP guided the junior engineering teams to develop

future experiments that monitor the effect of absorption of CO2 as air and water flow is adjusted. These

experiments were successfully conducted and the data and results obtained are included in this lab

report.

Theory

Gas absorption is a unit operation where a soluble gas compound (CO2 for this lab) is brought

into contact with a liquid with the goal of reducing the volatile components of the relevant compound in

the gas mixture. Absorption is typically integrated to reach a minimum acceptable level for industrial

regulation of harmful emissions. The absorption process is done inside of a tall packed column. The

column is vertical, such that packed columns are used for absorption to increase the surface contact

between the water and the inlet gas by sending both streams through a packed region. The solute in the

rich gas, or solute-containing gas, is absorbed by the fresh liquid. The solute containing liquid, called

strong liquor, and then leaves the bottom of the tower. The packing material used in this particular

column is ¼ inch Rasching rings and is categorized as a dumped packing (McCabe 546-9).

The liquid distributed over the packing material will ideally flow as a thin film over each of the

Rasching rings, providing a large area of contact for the CO2 to be absorbed. However, in most packed

columns, channeling occurs. Channeling is a phenomenon where water flows through a specific,

localized region instead of filling the volume of the column equally. This leaves much of the packing

material covered in a stagnant film of water or even dry. In columns with a tower diameter to packing

material diameter ratio of less than 8 to 1, the liquid will tend to flow out of the packing material onto

the sides of the column itself. Channeling is the main reason for loss of efficiency inside of packed

columns (McCabe 549-50).

Absorption processes take two forms: chemical and physical. The absorption column in this lab

performs physical absorption, as there is no chemical reaction taking place. If compounds were present

in the inlet liquid to react with the volatile organic compounds (or various other pollutants), the

chemical absorption process would occur.

T e a m B P | 4

Figure 1: Classic Absorption Column

In the absorption process, three central concepts are considered: material balances, rate of

absorption, and the height of the packed tower. Material balances are calculated by the equation below,

where Va is the lean gas, La is the inlet liquid stream, Vb is the rich gas, and Lb is the strong liquor. Note

that The inlet liquid stream is located at the top of the column and the inlet gas stream is located at the

bottom of the column. ��

Where

La = inlet liquid stream

Va = lean gas (inlet gas stream, polluted)

Vb = rich gas (solute-containing gas)

Lb = strong liquor (solute-containing liquid)

The absorption of a soluble gas makes the total gas rate V decrease as the gas passes through

the column. The flow rate of water varies inversely to the total gas rate (McCabe 557-8).

Rate of absorption typically involves volumetric calculations to determine total absorber volume

with coefficients based on the gas or liquid phase. The rate of absorption also depends on the

temperature and flow rate of both the liquid and the rich gas streams. The rate of absorption is defined

through the common expression: rate of absorption = driving force/resistance (Earle). The rate of

absorption per unit volume is defined as follows: � � ��

Where

r = rate of absorption

T e a m B P | 5

kya= individual coefficient based on a unit volume

a= interfacial are per unit volume

y = mole fraction of component being absorbed

The operating line can be plotted on a graph with the equilibrium curve to show if absorption

will take place. For absorption to be possible, the operating line must lie above the equilibrium. � � ��

Where

V = molal flow rate of the gas phase

L = molal flow rate of the liquid phase

x = composition of the liquid

y = composition of the gas

This concept is vital to ensure that intended emissions levels are reached, having considered

column efficiency. One must be careful when operating an absorption column such that both of the flow

streams are in equilibrium. Failure to follow may yield low or unpredictable absorption.

The height of the column must provide ample time for the liquid and gas to interact but be small

enough to be economically feasible for the system size.

This equation takes the product of the number of heat-transfer units and the height of a transfer

unit to find column height, and is much simpler than the integral form of the equation. Absorption is

distinct from adsorption, where reagents are adsorbed to a solid catalyst surface.

Equipment

The absorption column used for this experiment is located in the EMCS building at the University

of Tennessee at Chattanooga. The column is in room 107 and the 3rd floor. The column, depicted in

figure 2, is 12 feet in height, 3 inches in diameter, and packed with ¼ inch diameter Rasching rings. The

column is equipped with a flood control device; for extreme flow rate experiments, a flood control

device will activate. A pressure relief vent is also included in the absorption column (Poe). The CO2 tank

is located on the first floor of room 107 but a CO2 line connects the tank to the apparatus. The CO2 line

had an inlet pressure of 725 psi for the time the data for this system was gathered.

The column is currently equipped with three web-cameras, each of the circled pink regions in

figure 2, however they are digitally inaccessible. There are future plans for utilizing these three webcams

to detect turbulent flows, flooding, and general flow through the packed column. The absorption

column apparatus is controlled through a digital control interface called LabView.

T e a m B P | 6

Figure 2: Absorption Column Diagram (Poe)

In the LabView program for the absorption column, one may toggle system power, toggle excel

output, toggle the solenoids for the CO2 controls and the CO2 meter itself, and change the % input

values for both air and water. The systems output values for any particular run may then be checked on

T e a m B P | 7

the systems website, depicted in the bottom right hand corner of figure 3.

Figure 3: LabView of Absorber Column

This particular column can only handle so much fluid flow before it starts becoming turbulent

along the bottom tube, known as the ‘U Tube.’ The BP team determined that the flow became turbulent

around 70% water input.

Procedure

1. Scroll to the application for the absorption column on the desktop.

2. Run the program labeled <Absorber library.llb>.

3. Within this folder, select “LLB manager select <Absorber.vi>.

4. The program display will appear with CO2 gages along with input selections for valve percentage,

water percentage, and time interval for the duration of each trail as well as an area for the

naming of the experiment.

5. The experiment should first be labeled so that identification of raw data may be done easily at

the conclusion of the trials.

6. Label the trial with a name indicating the type of experiment being run in the item box just

above the label “E-mail Address” at the bottom right hand side. An example for labeling the

experiment would be: “Experiment1-air input 60-water varies.”

T e a m B P | 8

7. Set time interval to 3 (minutes) for the desired output recording of data to excel under the Write

to Spreadsheet quadrant.

8. After setting the time interval for the amount of minutes for intervals within the trial press the

green collect data button just below this input section, “Don’t forget this!!!”

9. Now start the program so it may begin the collection of data. Run the program by pressing the

“arrow” at the top left hand side. The arrow is to the left of the red stop button.

10. Processing will not begin until the System Power is switched on. To power the system, press the

“System power button” at the top left hand side. It will be a green oval button just below the

arrow and the red stop button.

11. Input data for the desired valve percentage opening just below and to the right side of the

System Power button.

12. Input water valve % beginning with 0 % and air input at 60%.

13. Click off of the input boxes so that the system may run at the set input values and observe the

gages changing to the prospective settings below. Allow this trial to run for 5 minutes.

14. Once done with this trial, hit the red “stop” button at the top left hand side; it is to the right of

the arrow.

15. Import your data to excel by opening the internet browser; copy and paste the link just below

the “E-mail Address” item box into the internet browser and select to search for it. The excel file

should appear with all the flow rates, input percentage values and internal flow temperature.

16. To begin another experiment, exit the control panel and repeat Step 2.

17. In continuing this experiment, conduct the next trial with changing the water valve input to 20 %

and keep the air input constant at 60%.

18. Repeat Step 2, with each trial; increase water valve input in increments of 20% with each

conducted trial. Go no further than 60% in the experiment’s final trial. Remember to keep the

air input constant at 60% with each trial. The output values from excel should be averaged and

put into table format as in Table 1-1.

19. The next experiment trials should be run with constant input values for water and changing trial

values for air input. The output values from excel should be averaged and put into table format

as in Table 1-1.

20. Next experiment, Repeat step 2 but in this experiment keep the trial values of air constant with

the CO2 flow on. Vary the water input as in step 18.

21. Next experiment, Repeat step 2 but in this experiment keep the trial values of water constant

with the CO2 flow on. Vary the air input as in step 19 (Littlejohn).

Results To begin with, the effects of the CO2 on previous results need to be proven from the raw data.

Comparing runs without CO2 to runs with CO2 at the same water and air valve positions will do this. The

averages and standard deviations were collected for runs without CO2, and they are compared visually

with runs with CO2. The CO2 is kept at 725 psi in all the runs that included it, so it will be constant. Data

will first be analyzed for what happens when the air concentration is changed with the water constant,

then what happens when the water concentration is changed with the air constant.

T e a m B P | 9

When the air and water valves were each at 50% open, the average water flow was 7.0 kg/s and

the airflow was 45.1 SLPM. The standard deviation for the water was 0.02 and was 0.59 for the air over

a 5-minute period. This is shown in Figure 4 below. The flow did not become turbulent. On the other

hand, the flow did become turbulent when CO2 was added. It was run a little longer than 5 minutes

since it seemed as if it was soon to become turbulent, and it did at the 6-minute mark. The water slightly

increased from 7 kg/s to about 9 kg/s, and the airflow increased from 45 SLPM to around 60 SLPM. This

is shown in Figure 5.

Figure 4: Air & Water 50% open

Figure 5: Air & Water 50% Open with CO2

When the air valve was 30% open and the water valve was 50% open, the average water flow

was 7.0 kg/s and the airflow was 1.8 SLPM. The standard deviation for the water was 0.46 and 0.21 for

0

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Flo

w (

kg

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Air

Flo

w (

SLP

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Time (s)

Air-50% Water-50%

Air Flow (SLPM)

Water Flow (kg/s)

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0 50 100 150 200 250 300

TIme (s)

Air-50% Water-50% CO2=725 psi

Air Flow (SLPM)

Water Flow (kg/s)

Outlet CO2 % by Volume

T e a m B P | 10

the air over a 5-minute period. This is shown in Figure 6 below. Here, the water flow actually stayed the

same, but the airflow increased from 2 SLPM to around 6 SLPM. This is shown in Figure 7. Neither run

was turbulent.

Figure 6: Air 30% Open & Water 50% Open

Figure 7: Air 30% Open & Water 50% Open with CO2


was 7.0 kg/s and the airflow was 67.2 SLPM. The standard deviation for the water was 0.08 and was 0.76

for the air over a 5-minute period. This is shown below in Figure 8. The flow did not become turbulent.

On the other hand, the flow did become turbulent when CO2 was added. In Figure 9, one can start to

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Air Flow (SLPM)

Water Flow (kg/s)

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Time (s)


Air Flow (SLPM)

Water Flow (kg/s)


T e a m B P | 11

assume that when the air increases, the CO2 decreases. As before, the water flow stayed the same, but

the airflow increased from 67 SLPM to around 75 SLPM.



In Figure 10, the water valve was manipulated instead of the air valve. When the air valve was

50% open and the water valve was 25% open, the average water flow was 3.5 kg/s and the airflow was

45.6 SLPM. The standard deviation for the water was 0.03 and was 0.06 for the air over a 5-minute

period. In Figure 11, the water flow stayed the same, but the airflow increased from 46 SLPM to around

50 SLPM. There was no turbulence in this run.

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Flo

w (

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Time (s)

Air-75% Water-50%

Air Flow (SLPM)

Water Flow (kg/s)

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Time (s)


Air Flow (SLPM)

Water Flow (kg/s)


T e a m B P | 12




was 8.9 kg/s and the airflow was 45.0 SLPM. The standard deviation for the water was 0.08 and was 0.05

for the air. In Figure 13, the first noticeable issue is the air valve didn’t kick on until a little over 30

seconds into the run. This is because a wire that plugs into the circuit board on the valve had come

loose. When it did function correctly after plugged back in, the run became turbulent after just 90

seconds, which did not happen without CO2.

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Air Flow (SLPM)

Water Flow (kg/s)

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Time (s)


Air Flow (SLPM)

Water Flow (kg/s)


T e a m B P | 13



Discussion of Results

As seen by the graphs in Figures 1-10, there are a few relationships that have to be discussed.

First and foremost, by looking at the data one can conclude that the airflow is not affected by the water

flow rate, and vice versa. Tables 1-4 and Figure 14-17 were taken from our fellow employees on the

Green Team who have the same results only at different valve positions. Table 1 reveals what was

similarly shown when varying water without CO2 above in Figures 4, 10, and 12. Table 2 reveals what

was similarly shown when varying air without CO2 above in Figures 4, 6, and 8. Figures 14 and 15 show

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Wa

ter

Flo

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.s)

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Flo

w (

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Time (s)

Air-50% W-60%

Air Flow (SLPM)

Water Flow (kg/s)

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0 20 40 60 80 100 120

Time (s)


Air Flow (SLPM)

Water Flow (kg/s)


T e a m B P | 14

how each curve was practically linear, proving that the flow rates for these two parameters do not affect

the other significantly.

Table 1: Water Output when Valve Manipulated

Water output Water Valve % Air Valve %

0 0 60

2.65 20 60

5.74 40 60

8.84 60 60

14.4 80 60

Table 2: Air Output when Valve Manipulated

Air output Air Valve % Water Valve %

0 10 60

0* 20 60

41.67 40 60

60.83 60 60

80.09 80 60

*Air Valve does not give output until 30% open

Figure 14: Water Flow Variation

(Output Water flow) = 0.18(input water %) - 0.7

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0 20 40 60 80 100

Wa

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ou

tpu

t (k

g/s

)

Water Valve %

Water Flow Varied

Water %

T e a m B P | 15

Figure 15: Air Flow Variation

Secondly, by looking at the data one can conclude that when the air and water are each

increased the CO2 concentration decreases. Table 3 reveals what was similarly shown when varying

water without CO2 above in Figures 5, 11, and 13. Table 4 reveals what was similarly shown when

varying air without CO2 above in Figures 5, 7, and 9. Figures 16 and 17 show how each curve was linear

with a negative slope. This reveals the fact that as when air and water and increased, CO2 is decreased.

This is also shown in Figures 9, 11, and 13 when the air finally kicks on.

Table 3: Water Output when Valve Manipulated with CO2

Water Output Water Valve % Air Valve % % CO2 Out

0 0 60 16.25

2.67 20 60 14.95

5.79 40 60 14.64

8.91 60 60 14.51

14.53 80 60 13.7

Table 4: Air Output when Valve Manipulated wih CO2

Air Output Air Valve % Water Valve % % CO2 Out

0 0 60 30.063

0* 20 60 30.063

Output Air Flow = 1.2(input air%) - 15

0

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80

90

0 20 40 60 80 100

Air

(S

LPM

)

Air Valve %

Air Flow Varied

Air Valve %

T e a m B P | 16

42.05 40 60 20.78

57.17 60 60 14.51

78.96 80 60 9.95

*Air Valve does not give output until 30% open

Figure 16: Water Flow Variation with CO2

Figure 17: Air Flow Variation with CO2

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tpu

t

CO2 Output %

CO2 Absorbed with Water Varied

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Air

Ou

tpu

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CO2 Output %

CO2 Absorbed with Air Varied

T e a m B P | 17

Conclusions

When looking at the results, there are five conclusions that can be made. First off, the airflow is

not affected by the water flow rate. Secondly, the water flow is not affected by the airflow rate. Thirdly,

when airflow is increased, CO2 is decreased. Fourthly, when water flow is increased, CO2 is decreased.

CO2 output is at its highest, 30.5% by volume, when air and water each are not on. Lastly, the addition of

CO2 creates turbulence at a more rapid pace, or at valve positions that did not have turbulence in the

without CO2.

Recommendations

There are four suggestions Team BP suggests. At such a high pressure, there should be a regulator

installed on the CO2 tank. This would increase safety and control over pressure release to the column.

Also, there needs to be more soldering done on the air valve to decrease the amount of interruptions

during runs. Working cameras to allow this experiment to be run and observed digitally would be

preferable. Finally, an instrument needs to be installed that takes a more precise reading on the CO2

input along with CO2 output to see how much may be lost out of the column.

References

Littlejohn, Latoya. "Weekly Activity Report IV." Message to the author. 13 Oct. 2013. E-mail.

Poe, Ashley. Absorption Column Lab. Rep. Chattanooga: ENCH 4350, 2011. Digital.

<http://chem.engr.utc.edu/Student-files/x-2012-Fa/4350-Blue/Absorption-Column-Lab-

powerpoint.pdf>

Smith, Julian C., and Peter Harriott. "18: Gas Absorption." Unit Operations of Chemical Engineering. By

Warren L. McCabe. 6th ed. New York, NY: McGraw-Hill, 2001. 546-95. Print.

"Unit Operations in Food Processing - R. L. Earle." Unit Operations in Food Processing - R. L. Earle. New

Zealand Institute of Food Science and Technology, 1983. Web. 22 Oct. 2013.

Appendix

T e a m B P | 18

Figure 18: Water Flow Calibration

Table 5: Pre-Statistical Analysis (Lagging Variable Check)

AMOUNT OF SECONDS BEFORE STATISTICAL

ANALYSIS CONDUCTED DURING FINAL LAB

RUN AIR WATER CO2

1 15 15 15

2 45 20 0

3 20 20 0

4 15 20 0

5 15 20 0

6 0 20 0

7 45 0 0

8 20 20 0

9 70 20 0

10 40 20 0

11 45 20 0

12 20 20 0

Air varied because of the time it took to register and plugging in blue wire.

Water varied because of the time it took to register.

The first CO2 reading was slow only because it was calibrating.

Mean of Control Variation = 1.0*(Timed Result)0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Me

an

of

Co

ntr

ol

Va

ria

tio

n

Timed Result (lbs/min)

Water Flow Calibrationlbs/min

T e a m B P | 19

Figure 19: Bugged Water Valve

Figure 20: Bugged Water Valve

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Wa

ter

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w (

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Air

Flo

w (

SLP

M)

Elapsed Time (s)

1st Run - Water 40% & Air 40%

Air Flow (SLPM)

Water Flow (kg/s)

0

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ate

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(k

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Flo

w (

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Elapsed Time (s)

2nd Run - Water 20% & Air 40%

Air Flow (SLPM)

Water Flow (kg/s)

T e a m B P | 20

Figure 21: Bugged Air Valve

Figure 22: Bugged Air Valve

This data was collected in our first lab and everything seemed to go incorrectly.

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Elasped Time (s)

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Air

Flo

w (

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M)

3rd Run - Water 40% & Air 40%

Air Flow (SLPM)

Water Flow (kg/s)

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ate

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Flo

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Elapsed TIme (s)

4th Run - Water 20% & Air 40%

Air Flow (SLPM)

Water Flow (kg/s)

T e a m B P | 21

Figure 23: Test Graph

Figure 24: Air as a Lagging Variable

0

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1160 1170 1180 1190 1200

Time (s)

Section 1 A-20 W-40

Air Flow (SLPM) Water Flow (kg/s)

Air Valve Position (20%) Water Valve Position (40%)

0

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1200 1220 1240 1260 1280

Time (s)

Section 2 A-40 W-40

Air Flow (SLPM) Water Flow (kg/s)

AIr Valve Position (40%) Water Valve Position (40%)

Notes.

Theory.

Much of this appears to be taken from a book. If so, you MUST give attribution when you

quote it.

Some of it is confused or confusing, also. Please carefully check all equations and units.

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