The recovery of ethyl alcohol from brewery effluent.
Brewery effluent, although mainly water, contains a wide range of materials and compounds. Among these is ethyl alcohol often up to 4% in concentration. In cooperation with some breweries the APV Company has developed a number of ways in which the ethanol might be recovered. The first system involves a single free standing distillation column which is fed a stream of preheated and degassed effluent. Depending on the number of trays in the column and the reflux ratio being used this technique can produce a distillate containing 70 to 95% (v/v) of ethanol. Where the height of a building is a problem the single column can be replaced by two shorter columns, often referred to as the stripping column and the rectifying column. A major problem with this system is the difficulty of obtaining sufficient preheating without fouling. The problem can often be reduced by judicious mixing of various effluents before heating. Paraflow plate heat exchangers appear to be very suitable for preheating as the turbulent flow around the plate corrugations reduces fouling and, if flow does become impeded, in place cleaning is relatively easy. A second system available uses evaporator steam for heating in the stripping column and a packed secondary still. The first condensate has an ethanol level of only 3 to 6% but this can easily be raised into the 70 to 95% level by distillation from a packed column. The ethanol recovered by both techniques contains higher boiling compounds such as fusel oils as well as water. The fusel oils can be removed to a large extent during distillation but removal of the remaining 5% of water is very difficult. It involves secondary distillation of a ternary benzene azetrope and is probably too complicated and expensive to be of interest to breweries. However, 95% ethanol is a reasonably valuable product and 70% ethanol can be used in the plant as an auxillary fuel as it is fully combustible.
Keywords: brewery costs effluent ethanol legislation recovery