Question

An off-gas stream consists of a mixture of chlorine (20mol%) in air. The stream is to be contacted with water in a packed absorption column, to reduce the chlorine concentration to Smol%. The column operates isothermally, at 20C and at atmospheric pressure. Equilibrium data for the chlorine air system from different references sources are presented in Tables 6.1(a) and (b). The molecular weight of chlorine is 70.9 kg kmol? Table 6.1(a) Equilibrium data for chlorine in air-water at 20°C x 0.0001 0.0002 0.0003 y 0.006 0.024 0.06 Table 6.1(b) Paz (torr) gCl2 L Solubility data for chlorine in water at 20°C 100 150 200 1.773 2.27 2.74 For a feed gas flow rate of 100kmol h , calculate: (a) The minimum water flow rate; (b) The NTU, at twice the minimum water flow rate.

Answer 1

solution: given data are mixture of chlorine in air = 20%, mol%. chlorine concentration reduce to = 5 molt operating condition is 200 and I atmospheric pressure from tabie 6:1 (9) stope of equilibrium curne m= - 93-92 23-* 0.06-0.006 0000 3-0.00% - 270 so equilibrium - nelation is - Ls x2 = 0 (Pure water) Y2 B Y = 270x where, as = gas How rate isolute free ... basis Ls = water flow rate, salute G=G(1-9) free basis a mole of c mole of B apply mok ofc c-solute mole of A camer B- solvent overall material balance Gs (Y-Y2) = L (X-X2) - 0 Y = 8:2 = 0.25 ES = 100 (1-042) = 80km) Y = = 6.0526 from equation ④ 80 (0.23-0-0526) = ls l -X2) O we assume water steam is pure, so X2=0 1-0.2 so

and in are counter ciment absorption bottom composition always in equilibaium = may= 270x Y = MAL xia y = 0.25 = 9.25 x 104 270 C 80(0.25-0.0526) = 19.258104-0) LS - 17072.43 kmol Many we know 5 tsmin . 50 Lsm = 17072.43 = 41381.62 kmol. part (6) To dy from derivation of NTU Y = y = = √ (x-2) + 9 mx-may ty, mr.muty, man equation of operating line ½ = m = slope of operating line - 2X140724 = 426087 so y - y 9 dy so - y Ju dy y-mng 91-42 Y - may NTU= - NTU = 0.250.0526 = 3.7524 0.25- 4264 x 7.25x10 - 213.4 3.752 so NTU =
so minimum water rate is 17072.43kmol/hr and NTU is 3.75 meter