Enhancing herbaceous biomass pellets quality by blending with woody biomass and plastic additives, and post-pelletization torrefaction and optimization processes: A review

Abstract

Current research emphasizes the use of assorted biomass resources of varying quality for pelletizing. Biomass pellet fuel is one of the most common and essential ways of harnessing biomass energy. Herbaceous biomasses like corn stovers, switchgrass and miscanthus are abundant in nature and when used to produce pellets, they are of low quality. This study provides an overview of methods for enhancing herbaceous biomass pellets quality through blending with woody biomasses like pine, eucalyptus and spruce saw dusts, use of plastic additives like linear lowdensity polyethylene and low-density polyethylene, post-pelletization torrefaction, and production of pellets at optimum conditions. The review revealed that the use of biomasses from wood and plastics as additives to herbaceous biomass, improved the pellet properties like strength, durability and higher heating values to great extents, while ash contents decreased. Post-pelletization torrefaction studies showed that there was a noticeable improvement in higher heating value. Finally, there was a general improvement of pellet qualities when pellets are produced at optimum conditions as depicted by the review of optimization studies on pelletization. Generally, each of these methods improves the pelletization of herbaceous biomass to different extents. Some studies have focused on combination of two or three of these methods in which the pellet properties are further enhanced. Therefore, there is need to explore the combination of these methods reviewed to produce pellets and evaluate them against internationally set pellet standards for commercialization.