LAB REPORT GAS ABSORPTION PDF

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UNIVERSITI TEKNOLOGI MARA FAKULTIKEJURUTERAAN KIMIAHEAT AND MASS TRANSFER LABORATORY (CHE504)No. Title Allocated Marks (%) Marks1 Abstract/Summary 52 Introduction 53 Aims 54 Theory 55 Apparatus 56 Methodology/Procedure 107 Results 108 Calculations 109 Discussion 2010 Conclusion 1011 Recommendations ...

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UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA HEAT AND MASS TRANSFER LABORATORY (CHE504) NAME

EXPERIMENT DATE PERFORMED SEMESTER PROGRAMME / CODE SUBMIT TO No. 1 2 3 4 5 6 7 8 9 10 11 12 13

Title Abstract/Summary Introduction Aims Theory Apparatus Methodology/Procedure Results Calculations Discussion Conclusion Recommendations Reference Appendix TOTAL MARKS

Remarks: Checked by : Date :

ABDUL RAZAK BIN ABDUL KARIM (2019468322) NAJWA IZZATIE BINTI AZLAN (2019229978) NAJWA QISTINA BINTI MOHAMMAD KHAIRUDIN (2019819692) NUR AFIZA BINTI MAHMUD (2019488502) GAS ABSORPTION 5 APRIL 2021 4 EH220 MADAM SUFFIYANA BINTI AKHBAR Allocated Marks (%) 5 5 5 5 5 10 10 10 20 10 5 5 5 100

Marks

GAS ABSORPTION Abdul Razak Bin Abdul Karim (2019468322) Najwa Izzatie Binti Azlan (2019229978) Najwa Qistina Binti Mohammad Khairudin (2019819692) Nur Afiza Binti Mahmud (2019488502) Abstract—Gas absorption is a mass transfer operation which a gaseous mixture is brought into contact with a liquid and during this contact one or more species is removed from a gaseous stream by dissolution in a liquid. This experiment is aimed to examine the air pressure drop across the column as a function of air flow rate for different water flow rates through the column by using Rashchig Rings packings. When the air pressure is drop to a certain limit, it can’t longer operate as it is and known as ‘flooding’. Thus, this ‘flooding point’ need to be determine to make sure that the process operate under the ‘flooding point’. So for this experiment, the pressure drop is observed at air flowrate of 20 LPM, 40 LPM, 60 LPM, 80 LPM, 100 LPM, 120 LPM, 140 LPM, 160 LPM, 180 LPM while water flowrate is observed at 1 LPM, 2 LPM and 3 LPM. The experiment is continue for the respective water flowrate until flooding occurs and after that, the water flowrate is changed. The pressure drop increases as the air flowrate is increases. Comparing to the theoretical data, the pressure drop at 1 LPM and 2 LPM shows higher value but lower value at 3 LPM. The percentage error for water flowrate at 1 LPM, 2 LPM and 3 LPM are 12.5%, 0% and 20% respectively. At lower liquid flow rate, packing tower work more efficiently and make the absorption rate to be maximize. The objectives are successfully obtained, thus the experiment is successfully done. Keywords—gas absorption; pressure drop;

water flow rate;

I. INTRODUCTION Gas absorption or known as gas liquid absorption is the process where one or more solute components in the gas phase are absorbed to liquid phase which contain less solute components as the two phases are in contact. This process can happen when there is different concentrations

between the two phases. Ajibola, B. K (2010) stated that gas absorption can be either physical process or chemical process. In chemical industry, this process is use for gas purification, gas recovery, removal of air pollutants from the exhaust gases and many more. According to A. Perez Sanchez et al (2016, as cited from Perry and Chilton, 2008), packed towers are widely used for gas-liquid absorption operations and, to a limited extent, for distillations. Geankoplis, C. J (1993) stated that gas-liquid contact in absorption and vapor-liquid contact in distillation occurs by continuous countercurrent flows in packed tower. In this experiment, SOLTEQ-QVF Absorption Column Unit (Model: BP 751-B) is used to measure the pressure drop using different air flow rate and water flow rate by using air mix with carbon dioxide (CO₂) and water. This unit is designed to operate at atmospheric pressure. For this experiment, it is assume that as the gas flow rate and liquid flow rate increase, the pressure drop will rise rapidly. II. OBJECTIVES 1. To examine the air pressure drop across the column as a function of air flow rate for different water flow rates through the column. 2. To plot the graph of column pressure drop against the air flow rate in a log-log graph. 3. To obtain the pressure drop from the generalized correlation chart as in Appendix. 4. To compare the experimental value and with the correlated value. III. THEORY Gas absorption is a mass transfer operation which a gaseous mixture is brought into contact with a liquid and during this contact one or more species is removed from a gaseous stream by dissolution in a liquid. The species that is extracted from the gaseous stream is known as solute and

the species that extracting the solute is known as solvent. Carrier gas is the insoluble species appear in the gas that is not absorbed by the solvent. The transfer is based on the preferential solubility of solutes in the solvent (Gas Absorption And Desorption, n.d.). Packed towers are used for continuous counter current contacting of gas and liquid in absorption (Geankoplis, 1993).The mechanism in packed tower is when the liquid and gas phases flows counter-currently while they interact on the packing interface. The liquid flows in downward direction, which is over the surface of the packing, whereas the gas flows in upward direction through the space or voids of the packing. The gas flow is driven by pressure while the liquid flow is driven by the gravity force. When the packing is dry, the line is straight, thus giving a strong relationship between pressure drop and gas flow rate. However, if the packing is irrigated with a constant flow of liquid, the relationship between pressure drop and gas flow rate initially follows a line parallel to that of dry packing. This pressure drop is higher than that for the same gas flow rate in dry packing because liquid in the column reduces the space available for gas flow. However, for higher gas flow rates, the line for the irrigated packing becomes steeper because the gas now impedes the down flowing liquid. But, the slope of the pressure drop changes at a point in which liquid holdup starts to increase. This is called the loading point. With a further increase in gas flow rate, the pressure drop rises rapidly until the lines become almost vertical and the liquid becomes the continuous phase. This is called the flooding point, in which liquid will accumulate at higher gas flows until the entire column is filled with liquid. A widely used correlation for estimating pressure drops in packed column with the following parameters is shown below:

Figure 1: Generalized Correlation for Pressure Drop in Packed Columns

x-axis: y-axis:

G𝑥

√ 2

𝑝𝑥𝑝−𝑝 y 𝑦

G𝑦 F 𝜇 0.1 G𝑦 𝑝 𝑥

g𝑐(𝑝𝑥 −𝑝𝑦 )𝑝𝑦

Gx = liquid mass velocity (lb/ft2 .s) Gy = gas mass velocity (lb/ft2 .s) ρx = liquid density (lb/ft3) ρy = gas density (lb/ft3) μx = liquid viscosity (cP) gc = gravitational constant (32.174 lb.ft/lbf.s2) FP = packing factor There are two types of packings types which is random and structured.

Figure 2: Typical Packed Tower Packings: (a) Raschig ring, (b) Lessing ring, (c) Berl Saddle, (d) Pall Ring

Raschig rings are one of the oldest random packings and still in general use (Separation Columns (Distillation, Absorption and Extraction). It provide a large surface area for the interaction between gas and liquid within the volume of the column. It also increase the contact time between gas and liquid. (iitb.vlab.co.in, 2011). IV. PROCEDURES General Start-up 1. All the valves were ensured to close except the ventilation valve V13. 2. All the gas connections were checked to makes sure that they are properly fitted. 3. The valve on the compressed air supply line was opened. Then the supply pressure was set between 2 to 3 Bar by turning the regulator knob clockwise. 4. The shut-off valve on CO₂ gas cylinder was opened. The CO₂ cylinder pressure was checked to ensure it is sufficient. 5. The power for the control panel was turned on.

Experiment Procedures 1. The receiving vessel B2 through the charge port was filled with 50 L of water by opening valve V3 and V5. 2. Valve V3 was closed. 3. Valve V10 and valve V9 were slightly opened. The flow of water from vessel B1 through pump P1 was observed. 4. Pump P1 was switched on, then valve V11 were slowly opened and adjusted to give a water flow rate around 1 L/min. The water was allowed to enter the top of column K1, flow down the column and accumulate at the bottom until it overflows back into vessel B1.

V.

RESULT AND DISCUSSIONS

The experiment is conducted to examine the experimental air pressure-drop across the column as a function of air flow rate for different water flow rates through the column, in the meantime to obtain the theoretical pressure drop from the generalized correlation chart. Gas absorption is the process of dissolving one or more components of a gas mixture in a liquid (solvent) in which the gas and liquid phase are in contact. An absorption column BP 751-B is used in this experiment to measure the pressure drop at different flow rates.

Below is the experimental and theoretical data achieved 5. Valve V11 was opened and adjusted to give a water flow from the study. From the results below, it can be compared that the experimental pressure drop is higher that the rate of 0.5 L/min into column K1. theoretical pressure drop. Theoretically, flooding should 6. Valve V1 was opened and adjusted to give an air flow occur at 160 LPM and 100 LPM when the water flow rate rate of 40 L/min into column K1. is at 1 LPM and 3 LPM respectively. Instead, flooding 7. The liquid and gas flow in the column K1 were observed occurs experimentally at 140 LPM and 80 LPM and a flow and the pressure drop across the column at dPT-201 was rate of 1 LPM and 3 LPM respectively. At a water flow recorded. rate of 2 LPM, both experimental and theoretical give out 8. Steps 6 and 7 were repeated with different values of air the same flooding point which is at 120 LPM. Percentage flow rate, each time increasing by 40 L/min while error calculated are 12.5%, 0% and 20%. maintaining the same water flow rate. Table 1: Experimental pressure drop at different water flow 9. Steps 5 to 8 were repeated with different values of water flow rate, each time increasing by 0.5 L/min by adjusting valve V11.

rate and air flow rate

General Shut-Down 1. Pump P1 was switched off 2. Valves V1, V2 and V12 were closed. 3. The valve on the compressed air supply line was closed and the supply pressure was exhausted by turning the regulator knob counterclockwise all the way.

Table 2: Theoretical pressure drop at different water flow rate and air flow rate

4. The shut-off valve on the CO₂ gas cylinder was closed. 5. All the liquid in the column K1 was drained by opening valve V4 and V5. 6. All liquid from receiving vessels B1 and B2 were drained by opening valves V7 and V8. 7. All liquid from the pump P1 was drained by opening valve V10. 8. The power for the control panel was turned off.

Figure 3 below shows the generalized correlation for pressure drop in packed column while figure 4 shows the graph plotted for the log pressure drop versus log air flow rate for both experimental and theoretical data. Graph

plotted shows that the higher the gas flow rate, the higher the pressure drop.

previous batch, thus, there might be an error in the flow of gas through the column and affect the pressure. VI.

CONCLUSION

It can be concluded that the pressure drop increases when the gas flow rate increases as well as water flow rate too. Experimentally, at a water flow rate of 1 LPM, 2 LPM and 3 LPM, the flooding are 140 LPM, 120 LPM and 80 LPM respectively while theoretically flooding are 160 LPM, 120 LPM and 100 LPM at a flow rate of 1 LPM, 2 LPM and 3 LPM. This gives the percentage error of 12.5%, 0% and 20%. VII.

RECOMMENDATIONS

Figure 3: Generalized correlation for pressure drop in packed column In order to achieve an accurate result, the experiment must

be conducted properly. First and foremost, in order to improve the packed column's efficiency and achieve better absorption with less pressure drop and flooding, the packed column should be upgraded to a structured packing which operates at a lower pressure drop. Next, readings must be observed and taken properly for at least three times, plus, students’ eyes must be perpendicular to the meniscus to avoid any parallax errors. REFERENCES

Figure 4: Log pressure drop for experimental and theoretical data

When the gas flow remains steady, adding more liquid to the column causes the pressure drop to rise before the liquid flooding is achieved. Any excess liquid that cannot pass through will remain at the top of the packing at this stage, filling the entire column with liquid and amplifying the pressure drop. According to Zent (1980), increase in gas flow will cause a rise in pressure drop before the flooding rate is reached, at which point any further increase will prevent the flow of liquid, resulting in liquid accumulation at the top of the column and a continual increase in pressure drop. These differences between the experimental and theoretical value occur due to experimental error which is equipment used in this experiment were used by the

Absorption in Plate and Packed Towers. (1993). In C. J. Geankoplis, Transport Processes And Unit Operations (pp. 610-613). Prentice-Hall International Inc. Ajibola, B. K. (2010, September). Optimization of Flooding in An Absorption Desoprtion Unit. Retrieved from 19 April 2021: https://www.theseus.fi/bitstream/handle/10024/20671/Bal ogun_Kamorudeen.pdf?sequence=1&isAllowed=y Products: Process & Reaction Engineering. (n.d.). Retrieved from SOLTEQ: www.solution.com.my Sanchez, A. P., Sanchez, E. P., & Silva, R. S. (2016). Design Of A Packed-bed Asorption Column Considering Four Packing Types and Applying Matlab. Nexo Scientific Journal, 83-104. Coughlin, R. W. (1969). Effect of liquid‐packing surface interaction on gas absorption and flooding in a packed column. AIChE Journal.

APPENDICES Experimental Data

Table 3: Experimental Pressure Drop At Different Water Flow Rate and Air Flow Rate (mBar). Flow rate (L/min)

Air

Pressure drop (mBar) 20

40

60

80

100

120

140

160

180

1.0

2

4

8

15

21

30

60 (F)

F

F

2.0

4

4

9

14

23

39 (F)

F

F

F

3.0

1

4

10

56 (F)

F

F

F

F

F

Water

*F = Flooding Table 4: Log pressure drop and log air flow rate value (mm H2O/m) Flow rate (L/min)

Air

Log Pressure drop (mm H2O/m) 1.3010

1.6021

1.7782

1.9031

2.0000

2.0792

2.1461

2.2041

2.2553

1.0

1.4064

1.7075

2.0085

2.2815

2.24276

2.5825

2.8835 (F)

F

F

2.0

1.7075

1.7075

2.0596

2.2515

2.4671

2.6617 (F)

F

F

F

3.0

1.1054

1.7075

2.1054

2.8536 (F)

F

F

F

F

F

Water

Figure 5: Log pressure drop versus log air flow rate (Experimental)

THEORETICAL DATA

Table 5: Theoretical Pressure Drop At Different Water Flow Rate and Air Flow Rate (in H₂O/ft). Flow Rate (L/min)

Theoretical Pressure Drop (in H₂O/ft).

Air

20

40

60

80

100

120

140

160

180

-

0.1

0.25

0.375

0.42

0.75

1.5

F

F

2.0

0.08

0.25

0.5

0.75

1.0

F

F

F

F

3.0

0.1

0.5

0.75

1.5

F

F

F

F

F

Water 1.0

Table 6: Log pressure drop and log air flow rate value (mm H2O/m) Flow rate (L/min)

Air

Log Pressure drop (mm H2O/m) 1.3010

1.6021

1.7782

1.9031

2.0000

2.0792

2.1461

2.2041

2.2553

1.0

-

0.921

1.319

1.495

1.544

1.796

2.096

F

F

2.0

0.824

1.319

1.620

1.796

1.921

F

F

F

F

3.0

0.921

1.620

1.796

2.096

F

F

F

F

F

Water

Figure 6: Log pressure drop versus log air flow rate (Theoretical)

Sample of calculations: Density of Air,

ρy = 1.175kg/m3

Density of Water,

ρx = 996kg/m3

Packing Factor,

FP = 990m3

Column Diameter,

D = 80mm

Water viscosity,

μx = 0.0008 kg/ms

Sample Calculation for Kinematic Viscosity of water, Vx

Sample Calculation for Cross Sectional Area of Packed Column

Ac = 0.0050 m₂ Sample Calculation for Mass Velocity, Gy 𝐺𝑎𝑠𝑠 𝑚𝑎𝑠𝑠 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦, 𝐺𝑦 =

𝑉𝑜𝑙𝑢𝑚𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑉𝑦 (𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑔𝑎𝑠, 𝜌𝑦 ) 𝐶𝑟𝑜𝑠𝑠 𝑆𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝐴𝑟𝑒𝑎, 𝐴𝑐

20𝐿 1𝑚3 1𝑚𝑖𝑛 1.175𝑘𝑔 𝑚𝑖𝑛 ( 1000𝐿)( 60𝑠 )( 𝑚3 ) 𝐺𝑦 = 0.0050𝑚2 𝐺𝑦 = 0.0783 𝑘𝑔/𝑚2 𝑠

Sample Calculation for Liquid Mass Velocity, Gx 𝐺𝑎𝑠𝑠 𝑚𝑎𝑠𝑠 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦, 𝐺𝑥 =

𝑉𝑜𝑙𝑢𝑚𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑉𝑥 (𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑔𝑎𝑠, 𝜌𝑥 ) 𝐶𝑟𝑜𝑠𝑠 𝑆𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝐴𝑟𝑒𝑎, 𝐴𝑐

1𝑚3 1𝑚𝑖𝑛 996𝑘𝑔 1𝐿 ( 𝑚𝑖𝑛 1000𝐿)( 60𝑠 )( 𝑚3 ) 𝐺𝑥 = 0.0050𝑚2 𝐺𝑦 = 3.32 𝑘𝑔/𝑚2 𝑠

Sample Calculation for Flow Parameter, y-axis

𝐺𝑦2 𝐹𝑝 𝑉𝑥0.1 𝑦 − 𝑎𝑥𝑖𝑠 = 𝑔𝑐 (𝑝𝑥 − 𝑝𝑦 )𝑝𝑦

2 2 0.1 10−6 𝑠𝑚 ) 0.0783 𝑘𝑔 ) (990𝑚−1 )(0.8032 × ( 𝑚2 𝑠 996𝑘𝑔 1.175𝑘𝑔 1.175𝑘𝑔 ) (1)( 𝑦 − 𝑎𝑥𝑖𝑠 = − )( 𝑚3 𝑚3 𝑚3 𝑦 − 𝑎𝑥𝑖𝑠 = 0.0013

Sample Calculation for Flow Parameter, x-axis 𝑥 − 𝑎𝑥𝑖𝑠 =

𝜌𝑦 𝐺𝑥 √ 𝐺𝑦 𝜌𝑥 − 𝜌𝑦

3.32𝑘𝑔 1.175𝑘𝑔 2𝑠 ) 𝑚 𝑚3 𝑥 − 𝑎𝑥𝑖𝑠 = √ 0.0783𝑘𝑔 996𝑘𝑔 − 1.175 ( ) 𝑚3 𝑚2 𝑠 𝑚3 (

𝑥 − 𝑎𝑥𝑖𝑠 = 1.4572

Sample Calculation for Theoretical Pressure Drop Units, in H₂O/ft to mm H₂O/m 𝑻𝒉𝒆𝒐𝒓𝒆𝒕𝒊𝒄𝒂𝒍 𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆 𝑫𝒓𝒐𝒑, ∆𝑷𝑻𝒉𝒆𝒐𝒓𝒚 =

𝟎. 𝟏 𝒊𝒏 𝑯 𝟐 𝑶 𝟖𝟑. 𝟑𝟏𝒎𝒎 𝑯𝟐 𝑶/𝒎 ) ( 𝟏 𝒊𝒏 𝑯𝟐 𝑶/𝒇𝒕 𝒇𝒕

𝑻𝒉𝒆𝒐𝒓𝒆𝒕𝒊𝒄𝒂𝒍 𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆 𝑫𝒓𝒐𝒑, ∆𝑷𝑻𝒉𝒆𝒐𝒓𝒚 = 8.331 𝑚𝑚 𝐻2 𝑂/𝑚

Sample Calculation for Pressure Drop Units, mBar to mm H₂O/m

∆𝑃𝐸𝑥𝑝 Sample Calculation for Percentage Error

𝐻

= 25.49 𝑚𝑚 𝐻2 𝑂/𝑚

𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 − 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝐸𝑟𝑟𝑜𝑟 (%) = | | × 100% 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 140 − 160 | × 100% 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝐸𝑟𝑟𝑜𝑟 (%) = | 160 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝐸𝑟𝑟𝑜𝑟 (%) = 12.5%

Air Flowrate (𝐕𝐲) LPM 20

Table 7: Data from calculation to determine theoretical pressure drop Gas Mass Capacity Liquid Mass Velocity Flow Parameter Velocity Parameter (x-axis) (𝑮𝒙) 𝐤𝐠/𝐦𝟐𝐬 (y-axis) (𝑮𝐲) 1 2 3 1 2 3 𝐤𝐠/𝐦𝟐 LPM LPM LPM LPM LPM LPM 0.0783

0.0013

3.3200

6.6400

9.9600

1.4572

2.9172

4.3758

40

0.1567

0.0051

3.3200
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