Unit 5 - Continuous Distillation - School of Life Sciences

Unit 5: Continuous distillationKEY POINT: In the Coffey Still rectifier the alcohol rich streamat about 94% abv is drawn off about six trays from the top. Afusel oil stream is removed about six trays from the bottom ofthe column.The highly volatile compounds, which concentrate on the highertrays, are collected as vapour. These include ethanol, which iscondensed and fed back to the still, and some sulphur compounds,which are vented to the atmosphere.The spent wash emerging from the analyser contains a very low levelof ethanol (less than 0.05%) but it also contains insoluble solidsincluding grain fragments and yeast together with soluble but nonvolatilesubstances. The more important of these latter substancesare oligosaccharides, unfermentable dextrins and glycerol, which isproduced during fermentation. The spent wash is subjected toseparation processes and sold as animal feed.5.4 Theory of Continuous Distillation.5.4.1 A Column Distillation SystemA modern approach to continuous distillation uses cylindrical columnstills manufactured in stainless steel.Figure 4 shows a continuous distillation system, which can best bedescribed in terms of a two component feed – an ethanol and watermixture.© 2001 The International Centre for Brewing and Distilling 10