Solar-driven torrefaction for sustainable bioenergy production: A review

Abstract

Torrefaction is a viable pretreatment method to enhance the fuel properties of various lignocellulosic feedstocks. While electrical torrefaction offers process control flexibility, it typically relies on grid electricity, which is generated mostly from fossil fuel sources. This reliance can undermine the overall sustainability and environmental benefits of the process. To address this issue, solar-driven torrefaction serves as an alternative approach to replace the electrical torrefaction methods that rely on non-renewable energy sources. This innovative approach harnesses renewable solar energy, offering a more sustainable and carbon-neutral solution for biomass conversion. This article aims to review the integration of solar energy into the torrefaction process and evaluate its impact on biomass properties. Following a detailed analysis of solar torrefaction, including experimental setups and the influence of parameters, the paper discusses the challenges associated with solar torrefaction systems and provides insights into future perspectives. The review shows that the solar torrefied products exhibit improved qualities and are highly competitive compared to the electrical torrefied products and commercial coals. Additionally, previous researchers have primarily focused on the impact of temperature and residence time, with limited exploration of other parameters and analyses. Therefore, future research should further explore the impact of other parameters and address the technical challenges such as intermittent nature of solar energy, uneven distribution of heat energy and process control complexity. By addressing these challenges, solar torrefaction can be scaled up and commercialized.