Pellet Production from Pruning and Alternative Forest Biomass: A Review of the Most Recent Research Findings

Abstract

Typically, coniferous sawdust from debarked stems is used to make pellets. Given the high lignin content, which ensures strong binding and high calorific values, this feedstock provides the best quality available. However, finding alternative feedstocks for pellet production is crucial if small-scale pellet production is to be developed and used to support the economy and energy independence of rural communities. These communities have to be able to create pellets devoid of additives and without biomass pre-processing so that the feedstock price remains low. The features of pellets made from other sources of forest biomass, such as different types of waste, broadleaf species, and pruning biomass, have attracted some attention in this context. This review sought to provide an overview of the most recent (2019–2023) knowledge on the subject and to bring into consideration potential feedstocks for the growth of small-scale pellet production. Findings from the literature show that poor bulk density and mechanical durability are the most frequent issues when making pellets from different feedstocks. All of the tested alternative biomass typologies have these shortcomings, which are also a result of the use of low-performance pelletizers in small-scale production, preventing the achievement of adequate mechanical qualities. Pellets made from pruning biomass, coniferous residues, and wood from short-rotation coppice plants all have significant flaws in terms of ash content and, in some cases, nitrogen, sulfur, and chlorine content as well. All things considered, research suggests that broadleaf wood from beech and oak trees, collected through routine forest management activities, makes the best feasible feedstock for small-scale pellet production. Despite having poor mechanical qualities, these feedstocks can provide pellets with a low ash level. High ash content is a significant disadvantage when considering pellet manufacture and use on a small scale since it can significantly raise maintenance costs, compromising the supply chain’s ability to operate cost-effectively. Pellets with low bulk density and low mechanical durability can be successfully used in a small-scale supply chain with the advantages of reducing travel distance from the production site and storage time.

Sustainable reduction of sulfate contained in gypsum waste: perspectives and applications for agroforestry waste and sanitary sewage

“…These wastes, if not managed correctly, can contribute to environmental problems. Still, on the other hand, they offer opportunities for sustainable use, such as in producing renewable energy and improving soil quality (Picchio et al, 2023).…”

Energy-based break-even transportation distance of biomass feedstocks

“…Mechanical densification and thermal treatment processes, such as torrefaction, were shown to improve the bulk density and specific energies of the biomass feedstocks (Tumuluru et al, 2011;10.3389/fenrg.2024.1347581 2021; Tumuluru, 2015;Pradhan et al, 2018;Picchio et al, 2023;Tumuluru, 2023). Torrefied and densified biomass reduced the shipping costs due to increased bulk density and specific energy (Searcy et al, 2014).…”