Roasting biomass

Pre-roasting plant matter could lead to more green fuel being burned in coal-fired power stations say researchers from the University of Leeds.

Professor Jenny Jones and colleagues from the School of Process, Environmental and Materials Engineering has found the roasting process torrefaction – heating plant matter to 300°C in an air-free container – transforms bulky biomass into a dry, energy-rich fuel.

Energy crops like willow, Miscanthus and poplar – virtually neutral carbon energy sources – are grown specifically for making green fuels, but they are moist and bulky. They are expensive to transport, hard to process and go mouldy if stored for long periods.

Torrefaction turns them into a cheap, easy to move resource with long shelf life. The biomass can be ground into powder meaning containers of coal could be replaced with biomass in existing power stations. The team are investigating whether the process could be scaled up and hope to produce a design blueprint for industrial engineers.

“If we can show that torrefaction is feasible on an industrial scale then we would hope to end up with a demonstration plant here in the UK,” Jones said. “More farmers would be interested in growing energy crops in areas of poorer quality soil if the economic barriers were lowered and the power companies could use more biomass without losing out financially.”

The project will address outstanding questions about the safety, practicality and environmental impact of large-scale torrefaction. Researchers will investigate the liquid and gaseous by-products of the roasting process, and assess how likely it is for dust generated by the milling process to trigger explosions.

They will work with a range of different materials that could potentially replace coal in the future – including waste matter from forestry plantations and farms, such as branches of harvested pine trees and straw.

“These are all materials that grow well in the UK but not at the expense of food crops,” said Jones. “We do not want farmers to have to choose between planting a field of wheat or barley and a field of willow. Ultimately, this is all about providing a secure energy supply for the future and one that is sustainable on all levels.”