Wastewater containing dissolved hydrogen sulfide (H₂S) at concentration of 2.50 gmole/m³(85 mg/L) enters an open tank at a volumetric flow rate of 20 m³/h, and exits at the same volumetric flow rate, as shown in the figure on the next page. The open tank is within a large enclosed building. The ventilation for the air surrounding the open tank is such that the composition of H₂S in the bulk, well-mixed air over the tank is 0.5 mole% H₂S (gas-phase mole fraction of 0.005), which has a pungent odor. The total system pressure is 1.0 atm, and the temperature is 20°C. The diameter of the cylindrical tank is 5.0 m, and the depth of the liquid in the tank is 1.0 m. At the conditions of operation, the film mass-transfer coefficients for H₂S transfer are k_L= 2.0 · 10^-4 m/s in the liquid film, and k_G= 5.0 · 10^-4kgmole/m²· s · atm in the gas film. The solute H₂S (solute A) is sparingly soluble in water, with the linear equilibrium distribution data at 20°C described by Henry€™s law with H = 9.34 m³· atml/kgmole. At 20°C, the mass density of the wastewater is 1000 kg/m³. The molecular weight of H₂S is 34 g/gmole, and H₂O is 18 g/gmole.

a. Estimate m, the equilibrium distribution constant based upon the mole fraction equilibrium relationship€“e.g., y_A,i = mx_A,i. Plot out the operating point (x_A, y_A) and the equilibrium line in mole fraction coordinates. Is the process gas absorption or liquid stripping? 

b. What is the overall mass-transfer coefficient K_y based upon the overall gas-phase mole fraction driving force? 

c. Perform a material balance on the process. At the conditions of operation, what is the concentration of dissolved H₂S exiting the tank, c_AL, in units of gmole/m³?

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Open Tank YA = 0.005, P = 1.0 atm Wastewater A = H2S D = 5.0 m Effluent wastewater CAL well-mixed Vo = 20 m³/h CALO = 2.5 gmole/m³ CAL = ? %3D