An oil containing 2.35 mole % of a hydrocarbon is stripped by running the oil down a column up which live steam is passed, so that 4 kmol of steam are used per 100 kmol of oil stripped. Determine the number of theoretical plates required to reduce the hydrocarbon content to 0.05 mole%, assuming that the oil is non-volatile.
The vapour-liquid relation of the hydrocarbon in the oil is given by ye = 33x, where ye is the mole fraction in the vapour and x the mole fraction in the liquid. The temperature is maintained constant by internal heating, so that steam does not condense in the tower.