Torrefaction process could improve use of biomass

Many UK power stations are now burning plant matter, or biomass, as well as coal in a bid to cut their carbon footprint. Unlike fossil fuels, plants like willow, Miscanthus and poplar are a virtually carbon-neutral source of energy: the carbon dioxide emitted when they burn is absorbed during photosynthesis by the next batch of ‘energy crops’ planted in their place.

But the environmental benefits of biomass are countered by some practical and economic challenges that are forcing power stations to restrict the amount of biomass used. Biomass is moist and bulky, making it relatively expensive to transport and difficult to store for long periods without going mouldy. The fibrous plant matter is also extremely difficult to process in the mills that are used to grind dry lumps of coal into dust before they are burned.

A roasting process known as torrefaction could be the answer, according to Prof Jenny Jones and colleagues from Leeds University’s School of Process, Environmental and Materials Engineering. This process, which sees the plant matter heated to around 300^oC in an air-free container, transforms bulky biomass into a dry, energy-rich fuel that is cheaper and easier to move around and has a much longer shelf life.