Biomass Pellet Properties and Processing Techniques

Biomass pellets are a form of densified biofuel produced by compressing finely milled organic residues under controlled temperature and pressure. Key feedstocks include woody biomass, agricultural residues and energy grasses, whose intrinsic properties—cellulose, hemicellulose and lignin content—determine binding behaviour during pelletisation. Moisture content and particle size are adjusted during pre-processing to optimise friction and shear forces in the pellet mill. Under the typical temperature range of 50–100 °C and pressures up to 200 MPa, lignin softens and acts as a natural binder, yielding pellets with high bulk density, mechanical durability and low fines generation. Additives such as starches, clays or biochar can further enhance pellet strength and reduce friability, although they may alter ash content and calorific value. Quality metrics include bulk density (kg/m3), durability (% remaining intact under tumbling), compressive strength (N/mm2) and higher heating value (MJ/kg). Post-production drying and controlled storage are crucial to prevent moisture reabsorption and mechanical degradation. Advances in processing techniques—die geometry optimisation, screw versus flat-die mills and temperature profiling—have improved throughput and energy efficiency. Together, these developments support the global deployment of biomass pellets as a renewable, transportable and storable fuel for heat, power and industrial applications, contributing to decarbonisation across multiple sectors.

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Biomass Pellet Properties and Processing Techniques publication trend

The graph below shows the total number of articles in biomass pellet properties and processing techniques across all publications each year (not limited to Nature Index journals).

Technical terms

Biomass densification: Compression of biomass particles to increase energy density and reduce volume.

Lignin: A natural polymer in plant cell walls that, upon heating, acts as an intrinsic binder during pelletisation.

Higher heating value (HHV): The total energy released per unit mass when a fuel is combusted, including latent heat of vaporisation.

Bulk density: The mass of pellets per unit volume, influencing storage and transport efficiency.

Durability: The proportion of pellets remaining intact after mechanical stress, indicating resistance to fines generation.

Binder: An added material (e.g., starch, clay or biochar) that enhances inter-particle adhesion and mechanical strength.

Pyrolysis: Thermal decomposition of biomass in the absence of oxygen to produce char, oil and gas fractions.

References

1. Assessment of densified fuel quality parameters: A case study for wheat straw pellet. Journal of Bioresources and Bioproducts (2023).
2. Effects of binders and die geometry on quality of densified rice bran using a screw-type laboratory scale pelleting machine. Energy Nexus (2024).
3. Analysis of optimal temperature, pressure and binder quantity for the production of biocarbon pellet to be used as a substitute for coke. Applied Energy (2019).