Ninety$-$five percent of the acetone vapor in an $86\mathrm{.}5$vol$\%$ air $($rest acetone$)$ stream is to be

absorbed by a countercurrent contact with pure water in a sieve$-$tray column with an expected

overall tray efficiency of $50\%.$ The gas feed rate to the column is $100$kmo$\frac{l}{h}.$ The column will

operate at $20C$ and $101$kPa. Equilibrium data for acetone$-$water at these conditions are given

in the attached graph. Calculate $($a$)$ the minimum $(\frac{L^{\text{'}}}{V^{\text{'}}})($i$.$e$.,$ the ratio of molH$2\frac{O}{m}ol$ air$)$ ;

$($b$)$ the total number of equilibrium stages using a value of $(\frac{L^{\text{'}}}{V^{\text{'}}})$ of $1\mathrm{.}5$ times the minimum;

and $($c$)$ the concentration of acetone in the exit water.

$($Hint: When the equilibrium line is curved concavely downward, the minimum value of $L^{\text{'}}$ is

reached by the operating line becoming tangent to the equilibrium line, instead of intersecting

it$.)$