IAA - Process Economic Modelling of Spent Grain Fractionation and Valorisation

First generation bioethanol processes based on wheat or corn use the starch in the grain to produce ethanol, while the residual grain goes through the fermentation process and is recovered at the end for conversion into “Distillers Dried Grain and Solubles” (DDGS). The latter is a dried product containing grain, yeast and dried “syrup” from the fermentation broth. It is energy costly to produce but has a value as an animal feed, mainly for ruminants (because of the high fibre content). A process concept has been developed at University of Bath to fractionate the wet distillers grains (before conversion to DDGS) to recover additional value before conversion to a higher value animal feed. The feed value is mainly based on the protein content. The other useful components in the grain are polymeric carbohydrates (glucans, xylan and arabinoxylan) which can be used as fermentation substrates, and oil which varies in quantity depending on the grain. Brewers spent grain presents a similar opportunity, although the grain differs and the value of the spent grain is lower because it is not dried. Conditions for recovering oil (using supercritical CO2 extraction), carbohydrate and protein and fermenting the carbohydrate have been developed in our laboratory, but in order to engage effectively with the industrial end-users (Vivergo and Molson Coors) we needed to provide an techno-economic model of various processing scenarios. This was the purpose of the IAA-funded project.