3Elsam Engineering

Kraftvaerksvej 53, DK-7000 Fredericia, Denmark

Wheat straw is an abundant energy source in Denmark and is already used in several combined heat and power plants. However, there is also an increasing need for production of renewable biofuels for the transportation sector. The high content of potassium and chlorine in wheat straw can result in serious problems with regard to deposition and corrosion of heat transfer surfaces as well as increased deterioration rates of SCR catalysts for NO_x reduction. To combine the production a better fuel for the power plants and simultaneously produce other valuable products, a pilot scale pretreatment plant with a capacity of 50-100 kg/h of dry-mass has been constructed. The extract from the counter-current extraction at temperatures from 160 to 200°C contains, besides the alkali salts, a substantial part of the hemicelluloses present in the wheat straw. The removal of alkali salts from the straw results in a fuel with fewer problems in combustion and the hemicellulose sugars can be fermented to ethanol, which can then be used as biofuel in the transportation sector.

The hemicelluloses in the extract from the pretreatment plant are present mostly in the form of oligo- and polysaccharides. The study has employed various commercial enzymes for the hydrolysis thereby producing an extract rich in pentoses, mainly xylose. The low concentration of hexoses, like glucose, is advantageous in the fermentation step due to less influence from glucose repression. The use of enzymes for the post-hydrolysis enables the production of less inhibitors and to run the process as a simultaneous saccharification and fermentation. The presentation will provide an overview of the process and report the results from hydrolysis studies using various enzyme preparations.