In a bioprocess, molasses is fermented to produce a liquor containing ethyl alcohol. A CO2-rich vapor with a small amount of ethyl alcohol is evolved. The alcohol is recovered by absorption with water in a sieve-tray tower. Determine the number of equilibrium stages required for countercurrent flow of liquid and gas, assuming isothermal, isobaric conditions and absorption of ethanol only. Entering gas is 150 km/h, 95% CO2 and 3.5% ethyl alcohol, 30 °C, 110 kPa. Entering liquid absorbent is 99.5% water and 0.5% ethyl alcohol, 30 °C, 110 kPa. Required recovery (absorption) of ethyl alcohol is 97.5%.