Possibilities for obtaining pellets by single-screw extrusion of biomass from black pine ( Pinus nigra Arn.)

The aim of the present study was to investigate the possibilities for obtaining pellets by single-screw extrusion of black pine ( Pinus nigra Arn.) biomass. Two fractions of black pine needles – 1) with d p ≥ 500 μm and bulk density ρ n = 0.243 g/cm 3 and 2) black pine twigs with d ≥ 500 μm and ρ n = 0.297 g/cm 3 , were obtained. Wheat bran with d p ≥ 500 μm and bulk density ρ n = 0.258 g/cm 3 in a ratio of 1:1 was added to the obtained fractions. The experiments showed that getting pellets by single-screw extrusion of biomass from twigs and needles of black pine was possible when mixing them in a 1:1 ratio with wheat bran. The addition of wheat bran improved the smoothness and homogeneity of the produced pellets and increased their density. High-density pellets with a low sectional expansion index were produced during extrusion. The productivity of extruding mixtures of black pine twigs with wheat bran was 30% higher than that made from a mix of black pine needles and wheat bran. The pellets obtained after mixing biomass from black pine and wheat bran had over 13% higher density than those produced entirely from wheat bran. The presence of black pine biomass increased the quality of the final product while at the same time having a positive effect on both productivity and specific energy consumption.