Recent developments in biomass pelletization – A review

Abstract

The depletion of fossil fuels and the need to reduce greenhouse gas emissions has resulted in a strong growth of biomass utilization for heat and power production. Attempts to overcome the poor handling properties of biomass, i.e. its low bulk density and inhomogeneous structure, have resulted in an increasing interest in biomass densification technologies, such as pelletization and briquetting. The global pellet market has developed quickly, and strong growth is expected for the coming years. Due to an increase in demand for biomass, the traditionally used wood residues from sawmills and pulp and paper industry are not sufficient to meet future needs. An extended raw material base consisting of a broad variety of fibrous residues from agriculture and food industries, as well as thermal pre-treatment processes, provides new challenges for the pellet industry. Pellet production has been an established process for several decades, but only in the past five years has there been significant progress made to understand the key factors affecting pelletizing processes. A good understanding about the pelletizing process, especially the processing parameters and their effect on pellet formation and bonding are important for process and product optimization. The present review provides a comprehensive overview of the latest insights into the biomass pelletization processes, such as the forces involved in the pelletizing processes, modeling, bonding, and adhesive mechanisms. Furthermore, thermal pretreatment of the biomass, i.e. torrefaction and other thermal treatment to enhance the fuel properties of biomass pellets are discussed.

Characterizing devolatilized wood pellets for fluidized bed applications

“…Gasification of biomass might be one possible approach, to generate synthesis gas from biomass and replace natural gas sustainably and effectively for some applications. To achieve better fuel properties, pelletized biomass can be used [1,27]. Biomass pellets are heterogeneous materials made from dry biomass powder in a pressure-assisted densification process [32].…”

Densification of Biocarbon and Its Effect on CO2 Reactivity

“…Mechanical densification involves applying mechanical pressure to densify the material. A densification like pelletization results generally into an increase of both mechanical strength, mechanical durability and density compared to untreated biomass [18]. Thermochemical densification involves heating the biomass in the absence of oxygen.…”

Size Reduction Characteristics of Yellow Poplar in a Laboratory Knife Mill

“…However an amount of fines (particles smaller than 0.5 mm in diameter) that is too high in the raw material has a negative impact both on friction and pellet quality. As a rule of thumb, the amount of fines should not exceed 10 to 20% unless a binding agent is added (Stelte et al, 2012). In this study the amounts of fines did not exceed 4% with all the aperture diameters of screens in the knife mill.…”