Study of the Straw Compaction Degree as a Function of Moisture Content, Particle Size and Process Temperature

The paper presents research on the process of densifying rye-wheat straw for its use in producing mouldable biofuel. The straw used in the research is a waste material from a farm located in Wielkopolska, resulting from the cultivation of triticale for the purpose of producing feed for pig farming. The aim of the study is to determine the utilisation of this material for the production of an agglomerate for energy purposes, such as heating the farm's infrastructure. The research was conducted for two moisture levels of straw: <i>M</i> = 10% and 30%. Before the experiment, the straw was cut into particles of the desired size: <i>S</i> = 10, 20, 30, 40, 50 and 60 mm. The densification process was carried out at temperatures <i>T</i> = 25, 50, 100, 150 and 200 °C, subjecting the straw to a compaction pressure of 15 MPa. Based on experimental studies, two values of the densification degree were determined: <i>x</i>₁-the densification degree under load; and <i>x</i>₂-the densification degree after unloading. The densification degree <i>x</i>₂ is more relevant from the perspective of storage and transport. ANOVA analysis of the results showed that the most significant factors affecting <i>x</i>₁ were particle size S and process temperature T, with higher <i>x</i>₁ values obtained for straw moisture of 30%. The ANOVA analysis of the densification degree after unloading (<i>x</i>₂) revealed that higher x₂ values were achieved for straw with 10% moisture and the smallest particle size of 10 mm. The most significant factors affecting <i>x</i>₂ were particle size and moisture content. Studies of the friction coefficient between the straw and the materials of the densification equipment components indicated that the optimal process temperature is 150 °C. The conducted research and the obtained results determined the optimal input parameters for the process and also provided a solid support for further studies, including investigation of the influence of other factors, such as binders.