Insights into Properties of Biomass Energy Pellets Made from Mixtures of Woody and Non-Woody Biomass: A Meta-Analysis

There is a widespread global shift toward renewable energy sources, where the emphasis is on enhancing the utilization of renewable energy due to the rising costs associated with fossil fuels. In this light, biomass pellets made from woody and non-woody biomass and blends have gained increased attention. Extensive research has been conducted globally to enhance the quality of biomass pellets and to explore the potential to combine woody biomass with other non-woody forms of biomass in biomass pellet production. The heterogeneity of the raw materials used and resulting properties of the biomass pellets have led to the establishment of internationally recognized benchmarks such as the International Organization for Standardization (ISO) 17225 standard to regulate pellet quality. In this article, the key mechanical, physical, chemical, and energy properties of pellets made of different non-woody herbaceous biomass are investigated, and the available test values for such properties of the pellets were meta-analyzed. A comparison of the properties of these pellets with the relevant standards was also performed. A meta-analysis of studies on biomass pellet production was conducted via a comprehensive Systematic Literature Review (SLR). The SLR focuses on determining and analyzing the average values for the key physical properties of biomass pellets using woody biomass as a component in concert with other biomass materials. In addition, the optimal range of mixtures of woody and non-woody biomass was reviewed to produce biomass pellets with potential acceptance in the marketplace. The majority of studies included in the SLR concentrate on pellets made from a mixture of biomass materials. The results show that the average values for wood/non-wood mixtures such as pellet diameter, pellet length, moisture content, ash content, fine particle content, gross calorific value, and bulk density were found to adhere to the ISO standards. However, the average mechanical durability fell short of meeting the requirements of the standards. Additional comparisons were nitrogen, sulfur, volatile matter, and fixed carbon content. The findings in this meta-analysis could be useful in directing future research focused on producing high-quality and efficient biomass pellets derived from biomass blends and mixtures.