🌱 Unlocking the Energy Potential of Biomass

Every year, millions of tons of waste from forestry, agriculture, and agro-industrial activities are generated worldwide. Often abandoned or burned in open air, they release atmospheric pollutants and greenhouse gases, with harmful effects on health and the environment, contributing to global warming. Yet, biomass waste holds considerable energy potential and represents a sustainable alternative to fossil fuels and conventional biomass-based fuels.

Compared with conventional energy sources, lignocellulosic biomass is characterized by a high moisture content (up to 15-50 wt%), relatively low bulk and energy densities (between 40 and 250 kg/m³ and mainly below 20 MJ/kg) and high heterogeneity in terms of shape and size. Consequently, it is challenging to handle, transport and store in loose form.

Thanks to physical processes (such as densification) and thermochemical processes (such as pyrolysis), it is possible to transform these resources by producing solid, liquid, or gaseous biofuels suitable for various energy applications. With physical methods, which this article focuses on, raw biomass is processed into densified and uniform solids, called briquettes or pellets (see figure 1), which can be used to meet household, commercial or industrial energy needs, and as substitutes for firewood or charcoal. This processing method is a means of increasing energy density, reducing moisture content, overcoming storage and handling difficulties and reducing transport costs.

Figure 1: Densified fuels: (a) pellets and (b) briquettes

To produce high-quality densified fuels, several steps must be taken before the compaction process, notably the preparation and characterization of raw biomass, pretreatment analysis, and the selection of binders. The selection of biomass is a step that involves choosing appropriate feedstocks to produce solid fuels, based on their availability, ease of transportation, and the quality of raw biomass in terms of energy density.   The characterization phase involves determining the physicochemical properties of the feedstocks. Parameters such as moisture content, bulk density, particle size distribution, biochemical composition (cellulose, hemicellulose, and lignin), proximate analysis (contents of ash, volatile matter, and fixed carbon), as well as calorific value, are determined using standard laboratory methods. The results of these analyses indeed provide insights into the feedstocks' densification potential and allow for an estimation of the quality of the densified fuels that will be produced.   Pretreatment analysis, for its part, involves grinding the raw biomass into small particle sizes, drying it to achieve the desired moisture content, and performing torrefaction when the purpose is to produce carbonized densified fuels.  

The quality of densified fuels can be assessed through several parameters, including physical and mechanical properties, chemical composition, combustion characteristics (notably ignition time, burning time, and burning rate), as well as gas emission analysis resulting from the oxidation of solid fuels, further noting that these parameters are significantly impacted by feedstocks properties and operating parameters governing the densification process (i.e., temperature of compaction, die pressure, dwelling time).

To conclude, the use of biomass as an energy source offers numerous environmental benefits, making it a sustainable alternative to conventional energy sources. Biomass contributes to a closed carbon cycle and is considered carbon neutral, since the CO₂ absorbed by plants during their growth is later released during oxidation, without exceeding the amount initially captured. Moreover, energy recovery from biomass facilitates the management of agricultural residues, helping to reduce emissions linked to traditional waste disposal practices. Finally, it promotes the development of a circular economy and enhances energy independence by diversifying the energy mix beyond conventional fossil-based markets.