Shells as Fuels

Can nutshells power the future?

Researchers at the University of Nottingham, working with CSIRO Australia, have developed an innovative model that evaluates shells as fuels, including pistachio and walnut shells, as potential low-carbon energy sources. This pioneering research could help diversify the UK’s bioenergy portfolio, improve efficiency, and support progress toward net zero emissions.

Unlocking agricultural residues

The study, published in the Journal of the Energy Institute, tested five biomass types: pistachio shells, walnut shells, rice husks, palm kernel shells, and wood pellets. These underused agricultural by-products could become viable alternatives to conventional wood pellets, which currently dominate the UK’s biomass market.

Biomass in the UK

Biomass is the second largest renewable energy contributor in the UK, generating 31.1 terawatt-hours of electricity in 2022 (UK Government renewables statistics). The sector relies heavily on imported wood pellets, with the US and Canada supplying most of the demand. Agricultural residues, however, currently make up just 1% of the fuel mix — highlighting the opportunity for diversification.

Milling and combustion performance

Selecting suitable fuels for combustion requires understanding how materials behave during milling and burning. The Nottingham team created a new metric to predict milling efficiency and a unique burnout prediction tool that uses image analysis of unburnt fuel to assess carbon loss. These innovations allow power generators to evaluate new fuels more quickly and accurately.

Improving efficiency

By combining milling and combustion models, the researchers have provided a more holistic view of how particle size and composition affect energy output. This insight helps power plants identify fuels that burn efficiently while minimising waste — a win for both cost-effectiveness and sustainability.

Supporting net zero

The UK has set a legally binding target to achieve net zero by 2050. Developing tools to assess alternative fuels supports this aim by enabling the energy sector to reduce emissions while maintaining reliable electricity supply. Using agricultural residues like pistachio and walnut shells not only diversifies fuel sources but also reduces reliance on imports.

Looking ahead

Dr Orla Williams, from the University of Nottingham’s Department of Mechanical, Materials and Manufacturing Engineering, explained: “By combining milling and combustion modelling, we can now predict fuel performance more accurately, helping power plants improve efficiency and reduce emissions, whilst diversifying their supply chains.”

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How can CNR help?

Innovations in low carbon fuels highlight the need for robust engineering solutions to bring research into practice. At CNR, we can support this transition by providing engineering design expertise, test rigs, detailed analysis, and prototype development. Whether it’s assessing new combustion technologies or designing systems for sustainable energy applications, we help turn promising concepts into engineered reality.