Grindability of Torrefied Camelina Straw and Microparticle Evaluation by Confocal Laser Scanning Microscopy for Use as Biofuel

Abstract

This study examined the combined effect of torrefaction and microwave absorbers on improving biomass thermochemical characteristics and grindability for heat, power, and value-added products. Camelina straw in two grinds, ground (6.4 mm screen size) and chopped with biochar addition (0%, 10% and 20%), was torrefied in a bench-scale microwave reactor at torrefaction temperatures of 250 °C and 300 °C with residence times of 10, 15 and 20 min under inert conditions and nitrogen-activated. After torrefaction, the geometric mean particle and size distribution, moisture content, ash content, bulk and particle densities were determined, and the grinding performance values of torrefied ground and chopped with and without biochar were determined and compared with the raw camelina straw. The results showed that the geometric diameter decreased after torrefaction in both grinds. The specific energy required for grinding torrefied biomass decreased significantly with biochar addition, longer residence times, and increased torrefaction temperatures. Torrefied ground camelina straw with biochar after grinding had the lowest grinding energy of 34.30 kJ at 300 °C/20 min. The surface morphology by confocal laser scanning microscopy of torrefied camelina straw particles indicated that biochar addition (>10%) and a torrefaction temperature at 250 °C can create profound surface distortion, and beyond 300 °C, colossal surface damage and carbonized weight fractions were produced.