Integrating spent coffee grounds and silver skin as biofuels using torrefaction

This study used the torrefaction method to innovatively integrate spent coffee grounds (SCG) and silver skin into biofuels. The biofuels were dried, pelletized, and torrefied at 300 degrees C for 3 h. The mass yields and energy yields of the biofuels ranged from 41% to 43% and from 52% to 58%, respectively. The high heat value (HHV) range of the biofuels (24.23-27.28 MJ/kg) was higher than that reported in previous studies. The results revealed that an increase in the percentage of silver skin increased the hygroscopicity of the biofuels, which was unfavorable for storage. On average, the weight increased by 0.24-0.57 wt% with a 10 wt% increase of silver skin in the biofuels. The biofuels had zero sulfur and chlorine content and thus would be cleaner energy sources than coal. The elemental compositions of the biofuels were similar to that of lignite with 0.063-0.070 H/C and 0.34-0.44 O/C ratios. The sample most similar to coal, based on heating value, element content, proximate analysis results, and combustion characteristics, exhibited 62% similarity. Integrating silver skin with other materials may be unsuitable for biofuels, but it is helpful for reducing the environmental burden of landfilling or incineration. (C) 2019 Elsevier Ltd. All rights reserved.