1. ABSTRACTGas absorption is the process of absorption of gas into a liquid and it possible to breakdown or separate one or more components of a gaseous mixture and producing a liquid that contain a desired quantity of a gas. Process of packed column of gas absorption is under gas-liquid counter current condition. This process can be obtained the value in experiments depends on the packing size, shape and material of construction. The objective in this experiment is to examine the air pressure drop across the column as a function of air flow rate for different water flow rates through the column. The methods in this experiment are where step up the experiment to switch on the pump and valve to run it. Then, the flow rate of water was constant at 1.0 L/min, 2.0 L/min and 3.0 L/min and adjusted the valve that control air flow rate used in different rates at 20, 40,60,80,100,120,140,160 and 180 L/min. These shown that the results of pressure drops reading are increased at increasing air flow rates and water flow rates. For example at 2.0 L/min the pressure drop starting point from 20L/min increase highly at 11 mm H2O,at 40L/min is 22 mm H2O, at 60L/min is 25 mm H2O, at 80 is 38 mm H2O, at 100 is 49 mm H2O and at 120 is 63 mm H2O which It was achieved floading point. When the conditions are achieved at maximum temperature and pressure, the pressure drops are at flooding point.

1. INTRODUCTIONGas absorption processes are widely used in the industry. It can be used for removing contaminants or impurities from a gas stream. There are numerous applications of this approach in the chemical industry. Common example of gas absorption are removal or recovery of NH3 in fertilizer manufacturing, control of SO2 from combustion source, control of odorous gases from rendering plants and removal of CO2 from air. In addition, gas absorption can controlled industrial air pollution and make separation of acidic impurities from mixed gas streams which are including carbon dioxide, hydrogen sulfide and organic sulfur compounds (Jackson, 2008).

There are numerous types of contactors that have been developed to assure a good contact between the gas and liquid streams. This is important to obtain an efficient separation process that requires a minimal size for the absorber. Many of the contactors are similar to those used in distillation. These include bubble cap trays and columns filled with various packing.

Chemical engineers need to be able to design gas absorbers which produce a treated gas of a desired purity with an optimal size and liquid flow. This can be based on existing correlations and when required, laboratory and or pilot plant data. (Cusler, 2009).

Gas absorption is a unit operation in which soluble components of a gas mixture are dissolved in a liquid. The inverse operation, called stripping or desorption, is employed when it is desired to transfer volatile components from a liquid mixture into a gas. Both absorption and stripping, in common with distillation, make use of special equipment for bringing gas and liquid phases into intimate contact. The apparatus consists of a cylindrical column or tower with a gas inlet and a distribution space at the bottom, a liquid inlet and distribution space at the top, gas and liquid outlets at the top and bottom respectively; and a supported mass of tower packing, known as raschig rings. A schematic diagram of the gas absorption column is shown in Figure 1.

Figure 1: Gas Absorption Column System

1. OBJECTIVESThe objective of this experiment is;-To examine the air pressure drop across the column as a function of air flow rate for different water flow rates through the column.-To plot the column pressure drops against the air flow rate for every different water flow rate in the log-log graph paper and compare with the value obtained from generalized correlation chart (APPENDIX).

1. THEORYIn a gas absorption column, a component of the gas stream is absorbed into the liquid stream. The absorption may be purely physical, or it may involve solution of the gas into the liquid followed by chemical reaction. The rate of mass transfer is governed by stream flow rates, interfacial contact area, component diffusivities, temperature, and pressure.

The packed column design is involved the diameter of the column and height of the packing which essential for specific separation. The liquid in the column fills up with increasing flow which can cause the pressure drop increased and the space of gas flow is reduced from the column. However, the pressure drop increased rapidly when gas flow rises and the liquid hold up in the column also increased when the conditions is beyond the loading point. Meanwhile, at up loading point, the pressure drop flow the same relation as in dry run. Since the column is not analyzed for gas absorption, the only equations used are the ones for calculating the values used on the pressure drop correlation chart.X- axis = equation (1)

Y axis = equation (2)

Where: Gx = water flow rate, in lbs/sec*in2Gy = air flow rate, in lbs/sec*in2rx = density of water, in lbs/ft3ry = density of air, in lbs/ft3mx = viscosity of water, in centistokes g = acceleration due to gravity, 32.2 ft/sec2FP = packing factor1. APPARATUS AND MATERIALS

5.1 APPARATUS1. Gas absorption column2. 50 mL buret and buret clamp3. 50 mL graduated cylinder4. Stopwatch5. Erlenmeyer flasks

5.2 MATERIALS1. Phenolphthalein indicator solution2. Sodium hydroxide solution3. Carbon dioxide gas

1. PROCEDURES

General Start-Up Procedures 1. All valves were closed except the ventilation valve V13. 2. All gas connections were checked which in properly fit. 3. Valve on the compressed air supply line was opened. The supply pressure was set between 2 to 3 bar by turning the regulator knob clockwise. 4. The shut-off valve was opened on the CO2 gas cylinder. CO2 cylinder pressure was checked either in sufficient or not. 5. The power was turned on for the control panel.

General Shut-Down Procedures 1. Pump P1 was switched off. 2. Valves V1, V2 and V12 were closed. 3. Valve on the compressed air supply line was closed and the supply pressure was exhausted by turning the regulator knob counterclockwise all the way. 4. The shut-off valve on the CO2 gas cylinder was closed. 5. All liquid in the column K1 was drained by opening valve V4 and V5. 6. All liquid from the receiving vessels B1 and B2 were drained by opening valves V7 and V8. 7. All liquid from the pump P1 were drained by opening valve V10. 8. The power for the control panel then was turned off.

EXPERIMENT : Hydrodynamics of a Packed Column (Wet Column Pressure Drop)1. The general start-up procedures were performed as aboved.2. The receiving vessel B2 was filled through the charge port with 50 L of water by opening valve V3 and V5. 4. Then valve V3 was closed. 5. Valve V10 and valve V9 were opened slightly. The flow of water from vessel B1 through pump P1 was observed. 6. Pump P1 was switched on, then V11 was opened and adjusted slowly to give a water flow rate of around 1 L/min. The water was allowed to enter the top of column K1, flow down the column and accumulated at the bottom until it overflows back into vessel B1. 7. Valve V11 was opened and adjusted to give a water flow rate of 0.5 L/min into column K1. 8. Valve V1 was opened and adjusted to give an air flow rate of 40 L/min into column K1. 9. The liquid and gas flow in the column K1 was observed, and the pressure drop across the column at dPT-201 was recorded. 10. Steps 6 to 7 were repeated with different values of air flow rate, each time increasing by 20 L/min while maintaining the same water flow rate. 11. Steps 5 to 8 were repeated with different values of water flow rate, each time increasing by 1.0 L/min by adjusting valve V11.

7.0RESULTFlowrate(L/min)Pressure drop (mm H2O)

AirWater20406080100120140160180

1.0002357112142

2.0112225384963---

3.02527334751----

Table 1: Flowrate and Pressure drop

Log Flowrate(L/min)Log Pressure drop (mm H2O)

AirWater1.31.61.81.92.02.12.152.22.3

1.0000.30.50.7811.31.2

2.011.31.41.61.71.8---

3.01.41.41.51.71.7----

Table 2: Flowrate and pressure drop

Flow rate(L/min)Pressure drop(mm H2O)

AirWater20406080100120140160180

1.0002357112142

2.01112225384963--

3.02527334751----

Table 3 Pressure drop across the column

Air Flow rate (L/min)Pressure drop (mm H2O)

Graph 1 Pressure drop against air flow rate.

Flow rate(L/min)Pressure drop(mm H2O)

AirWater20406080100120140160180

1.004.39.225.739.9NANANANA

2.006.928.562.4NANANANANA

3.0021.176.2NANANANANANA

Table 4 Pressure drop (in inch H20/foot) across the column (Theoretical data)

Air Flow rate (L/min)Pressure drop (mm H2O)

Graph 2 Pressure drop (in inch H20/foot) across the column (Theoretical data)

Graph 3 Pressure drop of experimental data and theoretical data against air flow rate 1.0 L/min

Graph 4 Pressure drop of experimental data and theoretical data against air flow rate 2.0 L/min

Graph 5 Pressure drop of experimental data and theoretical data against air flow rate 3.0 L/min

8.0Calculations

1. Calculation of column diameter = 75 =0.075

2. Conversion of flowrate, L/min to mass flowrate, kg/m2.s

, = = = 4.42 103 2

() = =

= 0.08/ (2) == =

=3.77 103 /

=1.2 /3,

= 1000 /3

= = (0.08 /) (1.2 /3) = 0.10 /2.

= = (3.77103 /) (1000 /3) =3.77 /2.

3. Computation of X-axis

=

=

=1.31

4. Computation of Y-axis Y =

=

=

= 0.047

Sample Calculation of Error At air =60 mmH2O, water = 2L/min

, % = 100 %

= 100% = 22.81 %

9.0 DISCUSSION

The experiment was done by conducting the different flow rate of water and flow rate of gas. All the data of pressure drops were tabulated in Table 1 which shows the increasing air flow rate caused the rises of pressure drop. When the result obtained at water flow rate 1.0 L/min, the air flow rates were increased to get resulted of the pressure drop from 20 L/min until 180 L/min of gas flow rate. The reading of pressure drop at 20 L/min of air flow rate at constant water flow rate at 1.0 L/min shown in Table 1 is 0 mmH2O. However, the air flow rate increased at 60 L/min, the reading pressure drop increased at 1 mmH2O and the results of pressure drop were obtained through increasing the air flow rate. Although the increasing of air flow rate from 20 L/min until 180 L/min give the resulted that pressure drop rises but the pressure drop achieved at flooding point at 180 L/min of air flow rate. Whereas this explained that the pressure drops at this point have maximum pressure and achieved maximum temperature.

The table 1 result also shows that the 2.0 L/min of water flow rate also gets the increasing of pressure drop when the flow rate of air increased from 20 L/min to 180 L/min. The initial flow rate of air at 20 L/min shows that resulted of pressure drop at 1 mmH2O. However, the resulted at 2.0 L/min of water flow rate, the pressure drop only can be calculated or read at point 20 L/min until 140 L/min of air flow rate and after 140 L/min of air flow rate, there were flooding of pressure drop occurred and achieved the maximum temperature and pressure.

The tabulated result show that at 3.0 L/min of water flow rate and at initial of air flow rate was increased at 25 mmH2O compared to 1.0 L/min and 2.0 L/min. At this 3.0 L/min of water flow rate also shows that the increasing air flow rate at 20 L/min until 60 L/min caused to increase the pressure drops. Even though the air flow rate increased highly at this water flow rate level, the flooding point of pressure drop was achieved at point 100 L/min until 180 L/min. The highest water flow rate and air flow rate used, produced the highest result of pressure drop where it caused the flooding point at maximum temperature and pressure.

From the experiment, there also having calculation of pressure drop from the correlation graph for pressure drop in the packed column. This pressure drops were compared with pressure drop that recorded from the experiment. The value pressure drop was finding from graph pressure-drop correlation for random packing by Strigle as shown in appendix. The result of pressure drop calculation can be shown in Table 4, Table 5 and Table 6 depending on the water flow rate. Based on that result, there have quite different value pressure drop get from experiment and calculation. Besides that, for all different water flow rate, the pressure drop were most of at flooding point.

Regarding to this result, there may be some errors or problems during conducting the experiment. One of the problem is it is hard to have accurate flow rate values for water and air. This is because, it is difficult to control the valve manually. This resulted that the reading of pressure drops also not stable. As a result, the pressure drop is not accurate and the value quite different from calculation.

10.0CONCLUSIONBased on these experiment, it can concluded that the objective of the experiment were achieved which is to determine the pressure drop across the dry column as a function of the air flow rate for different water flow rates through the column. For the graph of log pressure drop against log gas flow rate, it can concluded that the log gas flow rate enters to the packed column is increases, the log pressure drop of the packed column also increases. While for the graph of for generalized theoretical pressure drop correlation, it concluded that the value of the flow parameter, x-axis is higher, the value of the capacity parameter, y-axis is lower. Furthermore, we manage to visualize pressure drop as a function of gas(air) and liquid(water) using packed column and Rashing Ring.

11.0 RECOMMENDATIONS

1. Before starting the experiment, Material Safety Data Sheets (MSDS) was reviewed on NaOH. The sheets can be found in the MSDS notebook located in the laboratory.2. Personal protective equipment should include goggles and mask. Disposable nitrile gloves should be worn when handling NaOH solutions.3. Safety requirements should be checked and needed to be aware of when using high pressure gas cylinders.4. When starting up the system, always use low initial air and water velocities. Be sure the recycle valve to the sump pump is always at least partially open to prevent buildup of liquid and flooding. Open the tank valve slowly.5. Remember to plug in the gas heater 5 minutes before turning on the gas.

12.0 REFERENCES

1. E. L. Cussler, (2009). Diffussion: Mass Transfer in Fluid Systems,(3rd Ed.) .Cambridge University Press, New York.Page 993-9981. Jackson Y.Z. (2008). Modeling gas absorption. Project number: WMC 4028, page 5-57. 1. McCabe, W. L., Smith, J. C., & Marriott, P, (1985). "Unit Operations of Chemical Engineering", 4th Edition, McGraw-Hill.1. Treybal, Robert E., (1980). "Mass-Transfer Operations", McGraw-Hill Book Company, Inc., New York, N.Y.1. Washburn, E. W., Editor, "International Critical Tables of Numerical Data, Physics, Chemistry, and Technology", McGraw-Hill Book Company, Inc., New York, N.Y.13.0Appendices

Figure 2: Gas absorption column

Figure 3: Generalized correlation for pressure drop in packed columns (1 in.H2O/ft = 817 Pa/m)

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