Question

A tray tower is designed to absorb acetone from air stream using pure water at 293 K and 101.3 kPa. The inlet air flow rate is 483.33 kg/min (MW air = 29) and it contains 5 mol % of acetone. It is desired to remove 95 % of the acetone from air stream. The equilibrium relationship for this dilute stream is given by the equation of y= 1.186 x. * All the solutions should be presented in the unit of kg mol/h. (a) Compute the minimum liquid flow rate, L’min for this absorption process. (10 marks) (b) By assuming the liquid flow rate (L') is 1.3 to 1.5 times of L’min, compute the number of trays needed for the design of absorption tower with graphical solution. * Select only 1 value within the range for the computation of solution. Assumption: the mole fraction is in dilute range which is not more than 0.05. (10 marks)

Answer 1

= nemore Solution: Given: The inlet air flowrate = 483.33 kg /min = G is . = -186 x y rare . 2 that we con • Molecular Equilibrium sue relationship for the diente system • The inlet a'r Flow Centeons 5% acutene by mal Desired to remore 95% of the acetone. from Jair stream. Assumption. The more praction is in diewe range which is not more than 0.05 under this condition. is appro- anmption mole frection say -ximately equal to (molefraction) - ~ Y (more vario) Considering tray to war absorption as Counter Cument System, Yusif -05 walo (as solvent) (95%. = 0 (bes water is of acetene) Top (2) i pure) of tower liquid mole ratio ie y solens x = 0 of Under the Condition minimum Glowrate, Lwin, bo Hom compositions of the tower are troy in equilibrium nie y = 11864, y = f of tower Bottom (1) or for dirute System, Y,= 1.1868 x = In equiebrium 91 -0.05 x 0.05 = 0.0421 1.186 X = 0.0421 is the ineet If G Glowrate then garfair flowrate and his liquid kg 160 min mit Ihr 483.33 ke G = - 999.99 mal Thr 29

soom Material Balance, we have Lmin G Y-Y2 x, x2 0.05 -0.0025 Lmin 999.99 0.0421-0 Emin = 1 128.25 mol/her (6) L - 1.3 to 1.5 * L min. L = 1.48 1128.25 L = 1579.55 reg mehr two methods for Computing of trays needed for the design of absorption tower Kremser equation) the no. There are generally Analytical tical Method (We use Graphical Methol •Analytical Method using Kremser equation: So Y,-Y2 x-X2 1579.55 a 0.05-0.0025 999.99 sex, -o X = 0.030 Absorption facter, A= mๆ MG 1579.55 = 1:33 > 1 1.1868 999.99 So As A FI Method: to kremser analysis according [G N = en Y, - mx2 12-mx, x 2) (1 - 1) + + 4 In A

Na unico 0.05 -1.186 (0) 0.0025-1.18610) :) I 1.33 1.33 In (1.33) N- 6.1117 Graphical Methael; Construction of operating line Poi P(X2,2)-P(0, 0.0025) Q(X1, X)= 0 (0.030, 0.05) Construction of equlibri brium line y=1.1868 ) X O 0.01 0.02 0.03 0.04 O.O у 0.01186 0.023 0.035 10.047 0.059 (0.03,0.05) 0.05 0.04 1 2 Y 0.03 sequilibrium line 0.02 Hence, from graphical Construction obtained is 7. no. of triangles Henu no. of ideal 0.01 stages is 7. P (0,0.0025) 0 0.01 0.03 0.02 Х 0.04 0,05