N-Hexane is used to extract oil from soybeans. The solid residue from the extraction unit, which contains 0.78 kg liquid hexane/kg dry solids, is contacted in a dryer with nitrogen that enters at 85°C. The solids leave the dryer containing 0.05 kg liquid hexane/kg dry solids, and the gas leaves the dryer at 80°C and 1.0 atm with a relative saturation of 70%. The gas is then fed to a condenser in which it is compressed to 5.0 atm and cooled to 28°C, enabling some of the hexane to be recovered as condensate.

(a) Calculate the fractional recovery of hexane (kg condensed/kg fed in wet solids).

(b) A proposal has been made to split the gas stream leaving the condenser, combining 90% of it with fresh makeup nitrogen, heating the combined stream to 85°C, and recycling the heated stream to the dryer inlet. What fraction of the fresh nitrogen required in the process of part (a) would be saved by introducing the recycle? What costs would be incurred by introducing the recycle?