Mass Transfer 3) The waste gas flow rate entering an absorber is 21,377 standard
ID: 718153 • Letter: M
Question
Mass Transfer
3) The waste gas flow rate entering an absorber is 21,377 standard ft'/min (22,288 actual ft3/min). The pollutant in the waste gas is hydrochloric acid (HCI). There are 1871 ft of HCl entering the absorber in the waste gas per 106 ft of waste gas. The pollutant removal efficiency is 99 % (by mole). The absorbant is a caustic solution with the minimum liquid-to-gas ratio. The maximum HCl concentration in the liquid phase, in equilibrium with the HCl entering the column in the gas phase, is 0.16 Ibmol ! HCl-free solvent. The HCI concentration (Ibmol HCL1bmol solvent) exiting the absorber in the liquid stream is most nearly (A)0.00110 (B)0.106 (C) 0.108 (D)0.160Explanation / Answer
Given data
Waste gas flow rate = 21377 ft3/min
HCl entering flow rate/waste gas flow rate
= (1871 ft3) / (10^6 ft3)
Mol fraction of HCl inlet y1 = 0.001871
Actual Liquid flow / gas flow = 1.5 x Lmin/Gs = L/G
Mol fraction of HCl outlet = 0.16
HCl balance in the absorber column
G(Y1 - Y2) = L(X2 - X1)
X2 = HCl concentration in outlet liquid =?
X1 = HCl concentration in inlet liquid = 0
Y1 = y1/(1 - y1) = (0.001871) / (1 - 0.001871)
= 0.0018745
HCl removed = 99%
HCl remained = 100 - 99 = 1%
Y2 = 0.01 x Y1 = 0.01 x 0.0018745 = 0.000018745
Gs(Y1 - Y2) = Lmin(X2 - X1)
Gs(0.0018745 - 0.000018745) = Lmin(0.16 - 0)
Min liquid flow / gas flow = Lmin/Gs = 0.011598
Actual flow L/G = 1.5 x 0.011598 = 1.7397 x 10^-2
G(Y1 - Y2) = L(X2 - X1)
(0.0018745 - 0.000018745) = L/G(X2 - 0)
0.001855755 = 1.7397 x 10^-2 x X2
X2 = 0.106
Option B is the correct answer