Assessment of the energetic and mechanical properties of pellets produced from agricultural biomass

This paper presents an assessment of the energetic and mechanical properties of pellets produced from agricultural biomass. For the production of pellets the following raw materials were used: wheat straw, rape straw, and maize straw. Additionally, the mixtures of wheat-rape straw, wheat-maize straw, and rape-maize straw (each accounting for 50% of the mass) were applied. The studied resources were ground with the use of a universal shredder driven by a 7.5 kW electric engine. A pelleting machine fitted with a fixed flat matrix with two driven thickening rolls was used to produce the pellets. Analyses of the moisture and calorific value of resources as well as the bulk density and mechanical strength of pellets were performed according to biding standards. The moisture of resources ranged from 16.5% to 18.5% for rape and maize straw, respectively. The average calorific value fluctuated between 15.3 MJ kg−1 for a mixture of wheat and rape straw to 16.2 MJ kg−1 for maize straw. The bulk density and mechanical strength of pellets depended on the type of resources used. The lowest bulk density was recorded for wheat straw pellets (386-420 kg m−3), and the highest (561-572 kg m−3) for maize straw pellets. The lowest mechanical strength of pellets was noted for rape (95.4-96.8%), whereas the highest was for pellets made from a wheat and maize straw mixture (96.8-98.9%).