Absorb ammonia from air into water at 20.0°C and 1.5 atm pressure. Inlet water is recycled from a stripper and contains 0.2 wt% ammonia. Gas flow rate is 100.0 kmol/h. Inlet gas is 3.1 mol% ammonia. Exit gas should be 0.31 mol% ammonia. Assume L/V is constant. Equilibrium data are in Table 12-3. 

a). What is the minimum flow rate of water in kg/h?
b). What is the exit concentration of the liquid, and how many equilibrium stages are needed if L = 1.5 X Lmin?
Note: Keep your units straight. In Table 12-3, 10.0 weight NH3 per 100.0 weight water = 10.0 weight/110.0 weight solution =0.090909 mass fraction.
Approach 1: Convert all units to either mass or to moles. [MW NH3 = 17.0, MW H2O = 18.0, MW air = 28.97
Approach 2: Keep liquid in weight fraction and gas in mole fraction, and plot equilibrium in this form. In the NH3 mass balance, if y is mole fraction NH3 in gas and x is weight fraction ammonia in liquid, Vy (kmol gas/h) (kmol NH3/kmol gas) = kmol NH3/h, and LX = (kg liquid/h) (kg NH3/kg liquid) = kg NH3/h. Then adjust the NH3 mass balance with the molecular weight of NH3 so that all terms are in kg NH3/h. Derive the operating equation from this form of mass balance. 

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Solubility, 93.68 1190.1 4175.4 778.9 213.99 1.8196 2.48 ppm (mol) Although the units of H in Tables 12-1 and 12-2, atm/(mole fraction), are fairly common, other units are also used. The effect of concentration is shown in Table 12-3, in which data for absorption of ammonia in water (Perry et al., 1963) are illustrated. Note that solubilities are nonlinear, and H PNH3/X is not a constant. This behavior is fairly general for soluble gases. TABLE 12-3. Absorption of ammonia in water Weight NH3 per Partial pressure of NH3, mm Hg 100 weight HO 100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 25.0 20.0 0C 10C 20C 30C 40C 50C 60C 947.0- 785.0- 636.0 987.0 14500 500.0 780.0 1170.0- 380.0 600.0 945.0 275.0 439.0 686.0 190.0 301.0 470.0 119.0 190.0 298.0 89.5 144.0 227.0 64.0 103.5 166.0 - = - 3300.0- 2760.0 - 2130.0 1520.0 719.0 1065.0 454.0 692.0 352.0 534.0 825.0 260.0 395.0 596.0 - 15.0 10.0 7.5 5.0 4.0 3.0 2.5 2.0 1.6 1.2 1.0 0.5 42.7 70.1 114.0 25.1 41.8 69.6 17.7 29.9 50.0 11.2 19.1 31.7 16.1 24.9 XB = H sol,B 11.3 | PB, or XB = (Ho 18.2 15.0 12.0 *Extrapolated values. Source: Perry et al. (1963). Copyright 1963. 179.0 273.0 405.0 110.0 167.0 247.0 79.7 120.0 179.0 115.0 51.0 76.5 40.1 60.8 91.1 23.5 29.6 45.0 67.1 19.4 24.4 (37.6)* (55.7) 15.3 19.3 (30.0) (44.5) 12.0 15.3 (24.1) (35.5) 9.1 11.5 (18.3) (26.7) 7.4 (15.4) (22.2) 3.4 Unfortunately, there are other forms of the linear equilibrium equation that are also known as Henry's law. The basic solubility form of Henry's law is sol,B/Ptot)YB (12-5a, b) where Hsol,B = 1/HB and has units (mole fraction)/atm (Smith and Harvey, 2014). The solubility form is also written as Solubility, 93.68 1190.1 4175.4 778.9 213.99 1.8196 2.48 ppm (mol) Although the units of H in Tables 12-1 and 12-2, atm/(mole fraction), are fairly common, other units are also used. The effect of concentration is shown in Table 12-3, in which data for absorption of ammonia in water (Perry et al., 1963) are illustrated. Note that solubilities are nonlinear, and H PNH3/X is not a constant. This behavior is fairly general for soluble gases. TABLE 12-3. Absorption of ammonia in water Weight NH3 per Partial pressure of NH3, mm Hg 100 weight HO 100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 25.0 20.0 0C 10C 20C 30C 40C 50C 60C 947.0- 785.0- 636.0 987.0 14500 500.0 780.0 1170.0- 380.0 600.0 945.0 275.0 439.0 686.0 190.0 301.0 470.0 119.0 190.0 298.0 89.5 144.0 227.0 64.0 103.5 166.0 - = - 3300.0- 2760.0 - 2130.0 1520.0 719.0 1065.0 454.0 692.0 352.0 534.0 825.0 260.0 395.0 596.0 - 15.0 10.0 7.5 5.0 4.0 3.0 2.5 2.0 1.6 1.2 1.0 0.5 42.7 70.1 114.0 25.1 41.8 69.6 17.7 29.9 50.0 11.2 19.1 31.7 16.1 24.9 XB = H sol,B 11.3 | PB, or XB = (Ho 18.2 15.0 12.0 *Extrapolated values. Source: Perry et al. (1963). Copyright 1963. 179.0 273.0 405.0 110.0 167.0 247.0 79.7 120.0 179.0 115.0 51.0 76.5 40.1 60.8 91.1 23.5 29.6 45.0 67.1 19.4 24.4 (37.6)* (55.7) 15.3 19.3 (30.0) (44.5) 12.0 15.3 (24.1) (35.5) 9.1 11.5 (18.3) (26.7) 7.4 (15.4) (22.2) 3.4 Unfortunately, there are other forms of the linear equilibrium equation that are also known as Henry's law. The basic solubility form of Henry's law is sol,B/Ptot)YB (12-5a, b) where Hsol,B = 1/HB and has units (mole fraction)/atm (Smith and Harvey, 2014). The solubility form is also written as