It is desired to absorb 89% of the ammonia in a gas containing 4.0 mol% in air in a countercurrent stage tower. The total inlet gas flow to the tower is 20.0 kg mol/h, and the total inlet pure water flow to be used to absorb the ammonia is 75 kg mol H2O/h. The process is to operate isothermally at 310 K and a total pressure of 101.3 kPa. The equilibrium relation for the ammonia in the gasliquid is yA = 2.53xA.

Determine the number of theoretical stages required for this separation (a) graphically and (b) using the analytical Kremser equation.