Superheated steam drying and processing of biological materials.

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Conventional hot-air drying is energy intensive and accounts for about 15% of the industrial energy consumption in most industrial countries. The path to reduced energy consumption and associated with it CO2 emissions will depend on breakthrough technologies. Superheated steam (SS) is dry steam which is produced when its temperature is above the saturation point at a given pressure. SS drying is a novel alternative to conventional hot-air drying as it provides increased efficiency, higher drying rates, reduced emissions and improved safety. Since the technique complies with the new trend toward energy efficiency and low environmental impact, it is becoming an increasingly attractive alternative for drying materials that range from granules (e.g., wood granules, oat groats, brown coal) to slurry (e.g., biomass, spent grain, fish meal). Drying slurries is challenging and can be solved by recycling dry product as inert material and mixing it with wet material. This requires systematic exploration of material properties that continuously change during drying. Therefore, an understanding of the dynamic interaction between the material being dried and the drying SS medium is critical. This research program will develop a mathematical model describing drying in SS of slurry on an inert core of recycled dry material, and will determine the effect of SS parameters on material’s physical integrity in static and dynamic conditions. Stillage obtained from a local distillery will be separated into soluble and coarse fraction. The coarse fraction will be compacted to various shapes (cylinders, and disks) and dried in SS. It will then serve as the inert dry material. The slurry (a composition of the coarse fraction and solubles) will be deposited on the compact inert material and then dried in various temperatures and velocities of SS. The recorded moisture and temperature changes of the compact and the deposited slurry will be the basis for developing mathematical models of drying in SS of the two-layer material. A numerical technique will be used to develop a mathematical model addressing the effect of particle size on moisture diffusivity. Changes in physical properties of the compacts over the course of drying in SS will be determined experimentally and described mathematically. SS has been successfully used in drying of food and non-food products substantially reducing the drying time and size of driers when compared to conventional dryers. Modelling of SS drying on an inert- recycled material and linking that information to materials’ properties will provide in-depth knowledge on the drying process that will be essential to processors and design engineers.