The aims of the study were (a) the determination of the physicochemical characteristics of properties of pellets made of shredded residue from hay, wheat straw, and their blend at a ratio of 50:50, and (b) the determination of a mathematical model of pellet durability, using a response surface method. Tests were conducted according to applicable standards. As a result of thermal changes during the pressure agglomeration process, the material moisture content of pellets had slightly decreased versus raw three biomasses by 0.50% w.b. (wet basis) to a final value within the range of 5.56–5.87% w.b. The pellet properties of the blend were not adequately represented by the arithmetic mean of their components. Pellets made of hay, straw, and their blend, had DM (DM—dry matter) specific densities of 1034, 974, and 1102 kg m⁻³, respectively. The densities showed correlation with calorific values (r = 0.637), which were in the range of 16.07–17.00 MJ kg⁻¹. The pellet durability coefficient correlated negatively with particle size and biomass moisture content. On the basis of previous conclusions, a non-linear mathematical model was formulated to account for the pellet durability coefficient relative to pellet moisture, and the relation of particle sizes and specific density to pellet bulk density.

The aim of this study was to determine the characteristics of fine shredded pan fraction of biomass from sieve analyzer of oscillatory motion and as significance it was comparison the geometric mean particle size calculated according to the S319.4 standard with the arithmetic mean particle size that is assumed as half size of the last sieve 1.65 mm, according to the S424.1 standard. It was found that the finest particles size distributions are less varied between types of biomass (straw, hay and their mix) and are more aligned than particle size distributions for whole mixtures. The particles of hay were more uniform and belonged to “well sorted” category than particles of straw and mix, which were non-uniform and belonged to “moderately well sorted” category. All biomass particles size belonged to “very well sorted” category and particle size distribution were “very fine skewed” and “mesokurtic”. The geometric mean of the finest fraction particle size is almost by half smaller than the value resulting from the half value of the last sieve hole size (1.65 mm) of sieve separator with oscillatory motion in the horizontal plane, as these values are 0.45 and 0.82 mm, respectively. Assuming the 0.1 mm for a pan and the last sieve size of 1.65 mm we suggest to calculate the geometric mean (0.41 mm), which is closer to the experimental value. Application of this recommendation to the standard requires further comparative studies.