In a water purification system, a stream of water-and-acetone mixture (1.0 mol% acetone) is contacted with a stream of pure nitrogen to recover the acetone, using a counter-current multistage operation.
the liquid solution is fed at 100 kmol/hr, and the nitrogen at 200 kmol/hr. the vapor-liquid distribution of acetone under the operating condition is characterized by equilibrium constant k of 1.5.
a) determine the number of equilibrium stages to recover 97.5% of the feed acetone into the vapor.
b) consider the case where the entering gas is no longer pure nitrogen, but may contain acetone. assuming the same total flow rates and number of stages in a), determine the allowable range of acetone content in the nitrogen stream (in kmol/hr) to obtain at least 91% recovery of the acetone into the vapor.
c) go back to the original problem where the entering nitrogen is pure. instead of using 200 kmol/hr, suppose we want to use a smaller flow rate of nitrogen. determine the minimum flow rate of nitrogen that we must use, if such a limit exists, to recover 97.5% of the feed acetone. hint: re-doing part a) with decreasing flow rates of nitrogen may be useful. consider the limits of number of stages.