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Abstract

Biomass is one of the most frequently used sources of renewable energy. For centuries, wood has been used by people to heat their homes, and nowadays it is also used to generate electricity. The article discusses legal issues related to biomass, classification of biomass for energy purposes, quality parameters of selected ecological fuels, quality requirements for biomass, as well as biomass trade in the world. The article compares the quality requirements for biomass purchased by individual companies from the power sector (mainly dimensions, calorific value, moisture content, ash content, sulfur and chlorine). An analysis of the price of wood pellets on international markets, represented by the biomass stock exchanges: RBCN, EEX and BALTPOOL was also performed. The market analysis clearly shows that the international market for industrial pellets is dominated by intercontinental trade, which mainly concerns exchanges between the United States of America as a producer and Europe as a consumer. The largest amount of biomass is imported by the United Kingdom, mainly for its Drax biomass power plant, and this biomass comes from the USA and Canada. In addition to Great Britain, significant importers of wood pellets are the Netherlands, Belgium and Denmark. Judging by the interest of Polish energy companies in the purchase of biomass, also in Poland, the development of the biomass market should be expected.
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Abstract

Results of experimental and numerical investigations of wood chips drying are described in the paper. Experiments are carried out on two test facilities: a small laboratory rig and a larger pre-prototype dryer. Both facilities are thorough-circulation convective air dryers. The first one is a batch dryer, whereas the second one is a continuous dryer with wood chips flowing down by gravity from a charging hopper to a gutter with the aid of screw-conveyor. The latter is considered a half scale model (preprototype) for professional drying installations. A low feeding rate of wood chips into the pre-prototype dryer makes the process quasi-stationary and the difference between it and a batch drying is negligible. So, most experiments at this facility were carried out as batch dryers with non-agitated packed beds. The investigations exhibit the same linear correlation between the mass of evaporated water from the packed bed and the drying air velocity for both facilities. Numerical analysis of the drying process is conducted using the Ansys Fluent software enriched in drying capabilities by means of self-written procedures – user defined functions. Simulations confirmed a phenomenon of a drying front observed in the small laboratory rig. A thin layer of wood chips comprises the whole heat exchange and moisture evaporation phenomenon. The drying front travels downstream in the course of the process separating the already dried layer and still wet layer.
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