In an ethanol plants, the mixture of water and ethanol from the beer column distillate contains about 40% ethanol (molar basis) in water,together with the fusel oils described in the previous problem.This mixture is distilled to give an azeotropic mixture of ethanol and water(89% ethanol) overhead, with 99.9% recovery of ethanol.The fusel oil can cause blending problems if it is allowed to accumulate in the distillate.Fusel oil is a mixture of higher alcohols and ethers that can be approximated as a mixture of n-butanol and diethyl ether.This mixture is usually removed as a side stream from the column.
When the side stream is contacted with additional water, a two phase mixture can be formed and the oil phase can be decanted to leave an ethanol-water phase that is returned to the column.
1. Draw a flowsheet for this process.
2.Estimate the stream flow rates and compositions for a production rate of 200000 U.S. gal/d of dry (100%) ethanol.
3.Optimize the distillation column using the cost correlations given in Section 6.3 and assuming that reboiler heat costs $5/MMBtu. Minimize the total annualized cost of the column.