absorption gas repot

8/3/2019 Absorption Gas Repot

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ABSTRACT

This experiment is about the absorption- two phase flow through a packed bed. This experiment

is to determine the Loading and Flooding Points in the column and to model the pressure drop as

a function of gas (air) and liquid (water) mass velocities ( m3/hour ) using flexi glass column

packed with Raschig Rings. The results of liquid flow rate for 10 m 3/hour, the gas flow rate starts

from 10 m3/hour until 40 m3/hour with 5 m3/hour of intervals, the pressure drop, P ( mm H2O )

is increasing with increasing of gas flow rate. The pressure drop for 10 m 3/hour are 0.7, 0.8, 1.3,

0.8, 3.4, 12.6 and 40.1 (m3/hour). Next, for the liquid flow rate of 15 m3/hour, the gas flow rate

starts from 10 m3

/hour until 25 m3

/hour. This is due to the early flooding point which we have tostop the operation until 25 m

3/hour only. Hence, the results of pressure drop is decreasing with

increasing gas flow rate, 0.3, 0.2 and 0.1 m3/hour, however at 25 m

3/hour, the pressure drop is

increased to 39.1 mm H2O. The third liquid flow rate is 20 m3/hour. The gas flow rates for 20

m3/hour are 10, 15 ,20 and 25 m

3/hour as at this liquid flow rate the flooding point is exist early.

The pressure drop, P ( mm H2O ) are 0.9, 2.0, 3.0 and 14.3 ( mm H2O ). The pressure drop is

increasing with increasing gas flow rate.


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INTRODUCTION

A two-phase flow occurs in a system containing gas and liquid with a meniscus separating the

two phases. Two-phase flow is a particular example ofmultiphase flow . A two-phase flow isflowing through a packed-bed column.

While, a packed bed is a hollow tube, pipe, or other vessel that is filled with a packing material.

The packing can be randomly filled with small objects like Raschig rings or else it can be a

specifically designed structured packing. Packed beds may also contain catalyst particles or

adsorbents such as zeolite pellets, granular activated carbon, etc.

The purpose of a packed bed is typically to improve contact between two phases in a chemical

or similar process. Packed beds can be used in a chemical reactor, a distillation process, or

a scrubber, but packed beds have also been used to store heat in chemical plants. In this case,

hot gases are allowed to escape through a vessel that is packed with a refractory material until

the packing is hot. Air or other cool gas is then fed back to the plant through the hot bed,

thereby pre-heating the air or gas feed.

AIMS

1. To determine the Loading and Flooding Points in the column.2. To model the pressure drop as a function of gas (air) and liquid (water ) mass velocities (

m3/hour) using flexi glass column packed with Raschig Rings.
http://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Meniscushttp://en.wikipedia.org/wiki/Phase_(matter)http://en.wikipedia.org/wiki/Multiphase_flowhttp://en.wikipedia.org/wiki/Tubinghttp://en.wikipedia.org/wiki/Raschig_ringhttp://en.wikipedia.org/wiki/Structured_packinghttp://en.wikipedia.org/wiki/Phase_(matter)http://en.wikipedia.org/wiki/Chemical_reactorhttp://en.wikipedia.org/wiki/Distillationhttp://en.wikipedia.org/wiki/Scrubberhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Refractoryhttp://en.wikipedia.org/wiki/Refractoryhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Scrubberhttp://en.wikipedia.org/wiki/Distillationhttp://en.wikipedia.org/wiki/Chemical_reactorhttp://en.wikipedia.org/wiki/Phase_(matter)http://en.wikipedia.org/wiki/Structured_packinghttp://en.wikipedia.org/wiki/Raschig_ringhttp://en.wikipedia.org/wiki/Tubinghttp://en.wikipedia.org/wiki/Multiphase_flowhttp://en.wikipedia.org/wiki/Phase_(matter)http://en.wikipedia.org/wiki/Meniscushttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Gas


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THEORY

Absorption is an operation when two contacting phases are a gas and a liquid. A solute A or

several solutes are absorbed from the gas phase into the liquid phase in absorption. This process

involves molecular and turbulent diffusion or mass transfer of solute S through a stagnant, non

diffusing gas B into a stagnant liquid C. An example is absorption of ammonia A from air B by

the liquid C. Usually; the exit ammonia-water is distilled to recover relatively pure ammonia.

While, for the packing, its primary purpose is to provide a large surface area for mass transfer.

Packing materials may be arranged in either of two ways. The packing may be dumped into the

column randomly or stacked as structured material. Randomly packed towers provide a higher

surface area per unit volume ( ft2/ft3 ), but also caused a higher pressure drop than stacked

packing. In addition to the low pressure drop, the stacked packing provides better liquid

distribution over the entire surface of packing.

APPARATUS

UOP7 gas absorption column ; Armfield


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PROCEDURE

Manometer calibration

Diagram below is for the calibration of manometers and during operation of the column.All

valves must be in the position as in the diagram.

a) U-tube (left)VT-1

VT-2

VT-3

VT-4

VT-5

V-2 (OPEN)

b) U-tube (right)VT-1

VT-2

VT-3

VT-4

VT-5

V-3 (OPEN)

c) Sphere ballV-1 (OPEN)

VT-1

VT-2

VT-3

d) OperationVT-1

VT-2

VT-4

VT-5


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Operation

1. The manometer U-tube is filled with water by arranging the values according to the U-tubearrangement.

2. The values is set to operating arrangemenr before the operation is started.3. All valves are checked carefully (closed) before the column is safe to use.4. Valve VR-3 and VR-4 are opened such that the liquid flow rate is set at 10 m3/h.

Note : The level of liquid returning to the water reservoir must always be higher than the

bottom of the reservoir. This is to avoid air being trapped in line. Valve VR-4 is adjusted

accordingly to avoid this phenomena.

5. Valve VR-1 is opened and the airflow rate is set to be 10 m3/h. Wait for 2 minutes andduring this time the flow rate of air and water is make sure to be constant. The pressure drop

(P) mmH2O is read in the monotube.

6. The gas flow rate is increased by adding an extra of 5 m3/h to the column. Wait for 2minutes and the pressure drop is read again.

7. Part 4 is repeated until Flooding Point is reached.8. The curve of Ln(V) versus Ln(P / m packing) is plotted.9. Step 2 to 6 are repeated with different kind of liquid flow rate.


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RESULTS

For 10 m3/h ,

Gas flow

(m3/h)

Monotube

low(mmH2O)

Monotube

high(mmH2O)

P (mmH2O) Ln (V) Ln (P / m

packing)

10 20.5 19.8 0.7 2.30 4.47

15 20.3 19.5 0.8 2.71 4.61

20 20.7 19.4 1.3 3.00 5.09

25 20.4 19.6 0.8 3,21 4.61

30 21.8 18.4 3.4 3,40 6.05

35 26.4 13.8 12.6 3.56 7.36

40 40.4 0.3 40.1 3.69 8.52

For 15 m3/h ,

Gas flow

(m3/h)

Monotube

low(mmH2O)

Monotube

high(mmH2O)

P (mmH2O) Ln (V) Ln (P / m

packing)

10 19.7 20.0 0.3 2.30 4.73

15 19.8 19.6 0.2 2.71 5.52

20 19.8 19.7 0.1 3.00 5.93

25 39.3 0.2 39.1 3.21 7.49

30

35

40

For 20 m3/h ,

Gas flow(m3/h)

Monotubelow

(mmH2O)

Monotubehigh(mmH2O)

P (mmH2O) Ln (V) Ln (P / mpacking)

10 20.2 19.3 0.9 2.30 3.62

15 20.6 18.6 2.0 2.71 3.22

20 21.2 18.2 3.0 3.00 2.5325 26.5 12.3 14.3 3.21 8.49

30

35

40


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For 10 m3/h ,

Graph of Ln (V) versus Ln (P / m packing)

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7 8

Ln(P/mp

acking)

Ln (V))

Ln (V) Ln (P / m packing)

2.3 4.47

2.71 4.61

3 5.09

3,21 4.61

3,40 6.05

3.56 7.36

3.69 8.52


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For 15 m3/h ,


2.3 4.73

2.71 5.52

3 5.93

3.21 7.49


0

1

2

3

4

5

6

7

8

0 0.5 1 1.5 2 2.5 3 3.5

Ln(P/mp

acking)

Ln (V)


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For 20 m3/h ,


2.3 3.62

2.71 3.22

3 2.53

3.21 8.49


0

1

2

3

4

5

6

7

8

9

0 0.5 1 1.5 2 2.5 3 3.5

Ln(P/mp

acking)

Ln (V)


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CALCULATION

For 10 m3/h ,

To calculate for P ,

P = Monotube lowMonotube high

Gas flow(m3/h)

Monotubelow

(mmH2O)

Monotubehigh(mmH2O)

P (mmH2O)

10 20.5 19.8 20.519.8 = 0.7

15 20.3 19.5 20.319.5 = 0.8

20 20.7 19.4 20.719.4 = 1.3

25 20.4 19.6 20.4 - 19.6 = 0.8

30 21.8 18.4 21.818.4 = 3.435 26.4 13.8 26.413.8 = 12.6

40 40.4 0.3 40.40.3 = 40.1

To obtain Ln(V) , we can calculate by using calculator.

Gas flow(m3/h)

Ln (V)

10 Ln (10) =2.30

15 Ln (15) =

2.7120 Ln (20)

=3.00

25 Ln (25)

=3,21

30 Ln (30)

=3,40

35 Ln (35)

=3.56

40 Ln (40)

=3.69


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We can calculate the Ln (P / m packing) such that m packing is equal to 8 x 10-3

m.

Gas flow(m3/h)

P (mmH2O) Ln (P / m packing)

10 0.7 ( 0.7 / 8 x 10

-3

) = 4.4715 0.8 ( 0.8 / 8 x 10

-3) = 4.61

20 1.3 ( 1.3 / 8 x 10-3

) = 5.09

25 0.8 ( 0.8 / 8 x 10-3 ) = 4.61

30 3.4 ( 3.4 / 8 x 10-3 ) = 6.05

35 12.6 ( 12.6 / 8 x 10-3

) = 7.36

40 40.1 ( 40.1 / 8 x 10-3

) = 8.52


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DISCUSSION

This experiment is conducted to determine the Loading and Flooding points in the column and to

model the pressure drop as a function of gas (air) and liquid (water) mass velocities ( m3

/hour )

using flexi glass column packed with Raschig Rings. Mass transfer between liquids and vapor is

often achieved by flowing these two phases, countercurrent through a packed column. It turns

out that these packed columns are at their most efficient when they are operated close to the

column flooding point. Flooding point is the point where the capacity of the column to carry both

these stream which are liquids and vapor is exceeded. This provides large surface area per unit

volume for the liquid and vapor to interact. When the liquid flow rate is set to 10m3/hour, the gas

flow rate starts from 10 m3/hour until 40 m

3/hour with 5 m

3/hour of intervals. At this liquid flow

rate, the pressure drop P (mm H2O) is increasing with increasing of gas flow rate. The pressure

drop for 10 m3/hour are 0.7, 0.8, 1.3, 0.8, 3.4, 12.6 and 40.1 (m

3/hour). During at this flow rate,

the packed columns are operated at Loading point. Next, for the liquid flow rate of 15 m3/hour,

the gas flow rate starts from 10 m3/hour until 25 m

3/hour. This is because of the flooding point

that has been occurred in the column. At this point, the liquid cannot flow down as fast as it is

coming into the column is the. The actual flooding point is partly dependent on how fast the

liquid can flow down with no vapor flowing upwards and the rate at which vapor is trying to

flow upwards. Cross sections of the column occupied by vapor are not available for liquid flow

thus, effectively reducing the cross-section for downward flow of the liquid. . Hence, the results

of pressure drop is decreasing with increasing gas flow rate, 0.3, 0.2 and 0.1 m3/hour, however at

25 m3/hour, the pressure drop is increased to 39.1 mm H2O. The third liquid flow rate is 20

m3/hour. The gas flow rates for 20 m3/hour are 10, 15, 20 and 25 m3/hour as at this liquid flow

rate the flooding point is exist early. The pressure drop, P (mm H2O) are 0.9, 2.0, 3.0 and 14.3

(mm H2O). The pressure drop is increasing with increasing gas flow rate.


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CONCLUSION

Based on our results and collected data, we can conclude that the gas liquid absorption column is

useful tool for predicting absorption rates given specific gas liquid and velocities, mass transfercoefficient.

For all the liquid flow rates used in the absorption lab which were 10 m3/h, 15 m

3/h and 20 m

3/h.

From the three flow rates that we control in this experiment we can conclude that the highest gas

flow rates that we got was at the 10 m3/h that gives 40 m

3/h of gas flow rates. At this liquid flow

rates we got the highest pressure drop as shown in the calculation. In addition, for the flow rates

15 m3/h and 20 m

3/h, we got that the gas flow rates were same which were at 25 m

3/h

.However , the pressure drop for the these flow rates were varied. At liquid flow rates of 20

m3/h, the pressure drop is higher than at the 15 m

3/ h. Included in this conclusion, we knew that

this gas liquid absorption column not only provides a quantitative analysis for the packed tower

,in regards to predicting the amount of carbon dioxide removed, but also a qualitative analysis,

which is essential in understanding the absorption process in its entirety.


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RECOMMENDATIONS

The recommendation that can be taken into account for performing the gas absorption lab

experiment based on the gas liquid absorption column. Firstly, more time should be allotted

before measuring or collecting data. In this experiment, twenty minutes was allowed for the

system to come to equilibrium; however the maximum absorption for that particular liquid

flow rate was not achieved. We believed that the permitting an extra ten minutes would give

more accurate data. Besides, in order to get accurate readings, we should control more

carefully control the valves. In this experiment we have to control the VT-4 which

controlled the level of the water from returning to the water reservoir .It must always be

higher than the bottom of the reservoir. This is to avoid air being trapped in line.

Other than that, all the valves must be ensured closed before used the column make this

experiment running smoothly and surely safe. Lastly, we have to make sure that the gas and

liquid flow rates were constant at that particular flow rates.


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REFERENCES

1. Geankoplis, Transport Processes and Separation Processes Principles, 4th Edition2. http://www.wpi.edu/Pubs/E-project/Available/E-project-042408-

133605/unrestricted/Modeling_Absorption.pdf

3. Laboratory report4. http://www.unb.ca/che/Undergrad/lab/gasab.pdf5. http://www.separationprocesses.com/CourseWare/Experiments/GA_Prac01.htm
http://www.wpi.edu/Pubs/E-project/Available/E-project-042408-133605/unrestricted/Modeling_Absorption.pdfhttp://www.wpi.edu/Pubs/E-project/Available/E-project-042408-133605/unrestricted/Modeling_Absorption.pdfhttp://www.wpi.edu/Pubs/E-project/Available/E-project-042408-133605/unrestricted/Modeling_Absorption.pdfhttp://www.wpi.edu/Pubs/E-project/Available/E-project-042408-133605/unrestricted/Modeling_Absorption.pdfhttp://www.unb.ca/che/Undergrad/lab/gasab.pdfhttp://www.separationprocesses.com/CourseWare/Experiments/GA_Prac01.htmhttp://www.separationprocesses.com/CourseWare/Experiments/GA_Prac01.htmhttp://www.unb.ca/che/Undergrad/lab/gasab.pdfhttp://www.wpi.edu/Pubs/E-project/Available/E-project-042408-133605/unrestricted/Modeling_Absorption.pdfhttp://www.wpi.edu/Pubs/E-project/Available/E-project-042408-133605/unrestricted/Modeling_Absorption.pdf


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APPENDIX

Gas liquid absorption column


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Figure : Raschig Rings

absorption gas repot

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