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

¹ University of Food Technologies / Department of Machines and Apparatuses for Food and Biotechnological Industry, Bulgaria
² University of Food Technologies / Department of Cereals, Fodder, Bread and Confectionery Products, Bulgaria
³ University of Food Technologies / Department of Tobacco, Sugar, Vegetable and Essential Oil, Bulgaria
⁴ University of Food Technologies / Department of Nutrition and Tourism, Bulgaria

^* corresponding author:asimitchiev@gmail.com

Abstract

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/cm³ and 2) black pine twigs with d ≥ 500 μm and ρ_n = 0.297 g/cm³, were obtained. Wheat bran with d_p ≥ 500 μm and bulk density ρ_n = 0.258 g/cm³ 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.