Planning ahead

12th November, 2007

The production of fuel ethanol from grains has been developing rapidly in recent years in the Americas and this trend is now spreading to Europe and further east. The principal crops processed are corn and wheat, though other crops such as rye, triticale or sorghum have been considered in a few cases.

By far the largest cost for grain processors is the grain itself. The grain and bioethanol produced are commodities.

Producers are looking at energy efficiency and value added coproducts to improve the profitability of their plants. Each type of grain can have different co-products depending on the ethanol process. In a simple dry grind plant the whole grain is milled to a powder before saccharification, fermentation and distillation. This produces the most common coproduct, distillers dried grains with solubles (DDGS).

Pre-treatment of maize or corn

The most established preseparation technique for the pre-treatment of corn is wet milling where the grain is soaked in dilute sulphurous acid before it is broken up and separated by screening and centrifugation into germ, corn gluten, fibre and starch milk. The starch milk can then be converted into a number of products, one of which is ethanol. The germ is crushed to produce corn oil and the corn gluten is used as a high protein feed for poultry. Wet milling requires economies of scale and is generally only used where very pure starch is needed for high value added starch products. Germ is dried in a fluidised bed dryer and corn gluten is dried in a ring dryer.

In ethanol production less intense separations such as dry fractionation are used. This type of process generally removes a significant amount of the fibre from outside the kernel and the germ from the remainder of the material.

These separations are not as good as wet milling but reduce the amount of solids going through the ethanol process. Dry fractionation usually requires some wetting of the grain to make the separation possible so the germ usually has to be dried in a fluidised bed dryer before going out for oil processing. The fibre can be by-passed around the ethanol process to meet the rest of the non fermentable material at the DDGS dryer. This reduces the suspended solids in the system and the evaporative load on the DDGS dryer.

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