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Gas absorbtion


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Gas absorbtion

  1. 1. Abstract The experiment is based on pressure drop, the air flow rate , the water flow rate and also the packed column. The pressure drop is increased when the water flow rate and air flow rate is increased. 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 graph of log pressure drop against log of air flow rate is plotted. The graph of generalized theoretical pressure drop correlation chart for random packing is also plotted. Both of the graph have same principle where high flow rate parameter is meant for high liquid flowand high pressure drop while low flow rate parameter is meant for low liquid flow and low pressure drop. Introduction Absorption is a mass transfer process in which a vapor solute A in a gas mixture is absorbed by means of a liquid in which the solute more or less soluble. The gas mixture consists mainly of an inert gas and the soluble. The liquid also is primarily in the gas phase; that is, its vaporization into the gas phase is relatively slight. A typical example is absorption of the solute ammonia from an air-ammonia mixture by water. Subsequently, the solute is recovered from the solution by distillation. In the reverse process desorption or stripping, the same principle and equations hold. Gas absorption is the unit operation in which one or more soluble components of a gas mixture are dissolved in a liquid. The gas phase or gas mixture is inert gas while the liquid phase is immiscible in the gas phase. Therefore, the liquid phase will vapourize very slightly in gas phase. Gas absorption (also known as scrubbing) is an operation in which a gas mixture is contacted with a liquid for the purpose of preferentially dissolving one or more components of the gas mixture and to provide a solution of them in the liquid. We can see that there is a mass transfer of the component of the gas from the gas phase to the liquid phase. The solute so transferred is said to be absorbed by the liquid.
  2. 2. There are 2 types of absorption processes which are physical absorption and chemical absorption, depending on whether there is any chemical reaction between the solute and the solvent (absorbent). When water and hydrocarbon oils are used as absorbents, no significant chemical reactions occur between the absorbent and the solute, and the process is commonly referred to as physical absorption. When aqueous sodium hydroxide (a strong base) is used as the absorbent to dissolve an acid gas, absorption is accompanied by a rapid and irreversible neutralization reaction in the liquid phase and the process is referred to as chemical absorption or reactive absorption. More complex examples of chemical absorption are processes for absorbing CO2 and H2S with aqueous solution of monoethanolamine (MEA), diethanolamine (DEA), diethyleneglycol (DEG) or triethyleneglycol (TEG), where a reversible chemical reaction takes place in the liquid phase. Chemical reactions can increase the rate of absorption, increase the absorption capacity of the solvent, increase selectivity to preferentially dissolve only certain components of the gas, and convert a hazardous chemical to a safe compound. Aim 1. To determine the pressure drop across the dry column as a function of air flowrate. 2. To examine the air pressure drop across the column as a function of air flow rate for different water flow rates through the column. Theory Packed columns are used for efficient gas-liquid contact processes β€˜contact interface’ into the bulk of the liquid. The driving force for absorption involves a concentration gradient across the gas-liquid interface. Figure 1 provides a visual of the gas-liquid β€˜contact
  3. 3. interface’. Packed columns are used for efficient gas-liquid contact processes .It is used in processes like gas absorption, desorption(stripping) , distillation etc. It mainly consists of a cylindrical column filled with packings , liquid inlet and distributor at the top, gas inlet at the bottom, liquid and gas outlets at the bottom and top respectively. Column packings can be of two types mainly: dumped and structured . A distributor consists of several perforated pipes used for spreading the liquid uniformly throughout the cross- section of column. Figure 1: gas liquid interface Loading: Amount of liquid accumulate in side packed column that generate pressure drop.
  4. 4. Figurer 2 : loading in side packed column Flooding : Amount of the liquid flood in the top of column with increasing pressure drop due to accumulation of liquid in side packed column Figure 3 :flooding in packed column Pressure drop is the result of fluid friction between liquid flow and the packings. loading flooding
  5. 5. The graph above shows the relationship between pressure drop and gas flow rate and fordry column, a straight line is plotted and wet column three curvy lines are plotted. The three curves are parallel to the straight line. The point where liquid holdup starts to increase is the point where the slope starts to change. This point is known as the loading point. When the gas flow rate is further increased, pressure drop rises tremendously untilthe lines plotted are almost vertical and at this point, liquid is of continuous phase. This point is known as the flooding point and happens when liquid accumulates due to hi ghgas flow rate and this accumulation continues until the packed column is completely filled with liquid.
  6. 6. Material and apparatus 1. Solteq-QVF absorption column (model: BP 751-B) Procedure 1. All valves is ensured are closed except the ventilation valve V13. 2. All the gas connection is checked properly fitted. 3. The power for control panel is on. 4. The receiving vessel B2 is filled through the charge port with 50 L of water by opening valve V3 and V5.
  7. 7. 5. Valve V3 is closed. 6. Valve V10 and V9 is opened slightly. The flow of water from vessel B1 through pump P1 is observed. 7. Pump P1 is switch on, valve V11 is open and adjusted slowly to give a water flow rate of around 1L/min. The water is allowed to enter the top of the column K1, flow down the column and accumulate at the bottom until it overflows back into vessel B1. 8. Valve V11 is adjusted and open to give a water flow rate of 1L/min into the column K1. 9. Valve V1 is open and adjusted to give an air flow rate of 20L/min into column K1. 10. The pressure drop is recorded . 11. Step 9 is repeated with the different values of air flow rate, each time increasing by 20 L/min while maintaining the same flow rate. 12. Step 8 to 9 is repeated with different values of water flow rate, each time increasing by 1L/min by adjusting valve V11. Result Flow rate (L/min) Pressure drop (mm H20) Air water 20 40 60 80 100 120 140 160 180 1 0 1 2 4 8 14 28 51 - 2 0 1 3 5 10 17 73 - - 3 0 4 8 16 48 58 - - - Table 1: Flow rate and pressure drop Flow rate Pressure drop (mm H20)
  8. 8. (L/min) Air water 1.3 1.6 1.8 1.9 2.0 2.1 2.15 2.2 2.3 1 0 0 0.3 0.6 0.9 1.1 1.4 1.7 - 2 0 0 0.5 0.7 1 1.2 1.9 - - 3 0 0.6 0.9 1.2 1.7 1.8 - - - Table 2: Log air flow rate and Log pressure drop Calculation Data: Density of air = 1.175 kg/m3 density of water = 996 kg/m3 Column diameter =80 mm Area of packed column diameter = 0.005027m2 Packing Factor = 900 m-1 0 0.5 1 1.5 2 1.3 1.6 1.8 1.9 2 2.1 2.15 2.2 LogPressureDrop,mmH20 Log Gas Flow Rate, Gy Graph of Log PressureDrop against Log Gas Flow Rate 1LPM 2LPM 3LPM
  9. 9. Water viscosity = 0.001Ns/m2 Theoretical flooding point: GG, gas flow rate (kg/m2s) GG = πΊπ‘¦π‘‹πœŒ 𝐴 = 20𝐿 π‘šπ‘–π‘› x 1π‘šπ‘–π‘› 60𝑠𝑒𝑐 π‘₯ 1.175π‘˜π‘” π‘š3 π‘₯ 1π‘š3 1000𝐿 0.005027 =0.0779kg/m2s Capacity parameter, y-axis y-axis = 13.1 ( 𝐺 𝐺 )2 𝐹𝑝( πœ‡ 𝐿 𝜌 𝐿 )0.1 𝑃 𝐺 (𝑃𝐿 βˆ’π‘ƒ 𝐺 ) = 13.1 (0.0779)2 900 ( 0.001 996 )0.1 1.175 (996βˆ’1.175) = 0.0154 GL, liquid flow rate per unit column cross-sectional area GL = 𝐺𝐿 π‘‹πœŒ 𝐴 = 1𝐿 π‘šπ‘–π‘› x 1π‘šπ‘–π‘› 60𝑠𝑒𝑐 π‘₯ 1.175π‘˜π‘” π‘š3 π‘₯ 1π‘š3 1000𝐿 0.005027 =3.3002 kg/m2s Flow parameter, x-axis x-axis = 𝐺𝐿 𝐺 𝐺 (√ 𝜌 𝐺 𝜌 𝐿 ) = 3.3002 0.0779 (√ 1.175 996 )
  10. 10. = 1.4551 Water flow rate (L/min) GL (kg/m2s) 1.0 3.3002 2.0 6.6004 3.0 9.9006 Air flow rate (L/min) GG (kg/m2s) Capacity parameter (y-axis) Flow parameter (x-axis) 1 LPM 2 LPM 3 LPM 20 0.0779 0.0154 1.4551 2.9102 4.3653 40 0.1557 0.0614 0.7280 1.4560 2.1840 60 0.2336 0.1383 0.4852 0.9705 1.4557 80 0.3115 0.2459 0.3639 0.7278 1.0917 100 0.3893 0.3841 0.2912 0.5823 0.8735 120 0.4672 0.5532 0.2428 0.4852 0.7279 140 0.6229 0.7531 0.2079 0.4159 0.6238 160 0.6229 0.9832 0.1820 0.3639 0.5459
  11. 11. Discussion In this experiment, we are going to determine the pressure drop across the dry column as a function of air flow rate and the air pressure drop across the column as a function of air flow rate for different flow rates through the column. These two objectives are achieved by using the same apparatus but different method. The experiment is bases on the flow rate of liquid and gas in the packed. Firstly, the water flow rate is kept constant to 1L/min and air flow rate reading is recorded when achieved 1 minute. The air flow rate is kept rising constantly by 20 L/min by each minute. All reading of pressure drop is recorded until flooding point is reached. The pressure drop for flow rate of air are 1, 2, 4, 8 , 14, 28 and 51 mm H20 consequently to 20, 40, 60, 80, 100, 120, 140, and 160 L/min. It cannot reach 180 of air flow rate, which the water will sprayed out from the column due to the high flow rate. The the flow rate is adjusted to 2L/min, by using the same step as recording the 1L/min. the data recorded are 0, 1, 3, 5, 10, 17 and 73 mm H20 consequently to 20, 40, 60, 80, 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0.0154 0.0614 0.1383 0.2459 0.3841 0.5532 0.7531 0.9832 CapacityParameter Flowrate parameter Generalised Thepretical Pressure Drop CorrelationChart for Random Packings 1LPM 2LPM 3LPM
  12. 12. 100, 120, and 140 L/min. Whereby, for flow rate of water 3L/min is 0, 4, 8, 16, 48 and 58 consequently to 20, 40, 60, 80, 100, and 120. With these data record, the graph of log of pressure drop against the log of air flow rate is plotted. From the graph plotted, all the log pressure drop is directly proportional log gas flow rate. We can conclude that the higher the log of gas flow rate the higher the log of pressure drop. But the higher the water flow rate, the lower the log gas flow rate. For correlated value of the pressure drop is calculated and the graph of capacity parameter against flow rate parameter is plotted. The capacity parameter is indirectly proportional to flow rate parameter. Two of the graph is different as one is directly proportional while the other one is indirectly proportional. Conclusion In conclusion, the aim of experiment which is to determine the pressure drop across the column as a function of air flow rate for different water flow rate through the column is achieved. They are some errors made when the experiment is being conducted resulting in a slight in accuracy of the experimental chart plotted. Recommendation When conducting this experiment, there are several recommendations that will produce better observation which will not differ much from the theoretical observations. Firstly, safety is very important when doing experiment. Thus, we need to wear laboratory coat, helmet and fully cover shoes to avoid any danger for safety precaution. Titration must take place in fume chamber and must be stop when the solution turns to light pink. Next, when taking the reading of volume of sodium hydroxide solution, make sure that eyes is directly perpendicular with the level of sodium hydroxide solution inside the burrette to avoid any parallax error. Before conducting the experiment, we must
  13. 13. ensure that all the apparatus are in good condition and follow all the procedures in order to get more accurate result. Reference I. II. III. /theory1_1.htm IV.'s_for_techniques/Liquid_ Liquid.pdf V. Lab Manual