Adiabatic Operation of a Tray Absorber

The temperature of stream Ln can be obtained from equation (5-30). Stream Vn is then at the same temperature as Ln and in composition equilibrium with it. Equations (5-28) to (5-30) are then applied to tray n - 1, and so forth. To get started, since usually only the temperatures of the entering streams LQ and V +1 are known, it is necessary to make an initial estimate of the temperature Tx of the gas leaving E,. An energy balance over the entire absorber, 

Example 5.5 Tray Tower for Adiabatic Pentane Absorption 

One kmol/s of a gas consisting of 75 mol% methane and 25% n-pentane at 300 K and 1 atm is to be scrubbed with 2 kmol/s of a nonvolatile paraffin oil entering the absorber free of pentane at 308 K. Estimate the number of ideal trays for adiabatic absorption of 98.6% of the pentane. Neglect the solubility of methane in the oil, and assume operation to be at constant pressure. The pentane forms ideal solutions with the paraffin oil. The average molecular weight of the oil is 200 and the heat capacity is 1.884 kJ/kg-K. The heat capacity of methane over the range of temperatures to be encountered is 35.6 kJ/kmol-K for liquid pentane, is 177.5 kJ/kmol-K for pentane vapor, is 119.8 kJ/kmol-K. The latent heat of vaporization of n-pentane at 273 K is 27.82 MJ/kmol (Treybal, 1980). 

It is convenient to refer all enthalpies to the condition of pure liquid solvent, pure diluent gas, and pure solute at some base temperature TQ, with each substance 

In this case, equilibrium is described by Raoult s law, y. = PAx/P = mxv The vapor 

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