Christmas Trees Turned into Green Fuel

Once Christmas is gone and the tinsel and balls have been removed from the fir, most Christmas trees end up in the trash.

But soon, thanks to a brilliant idea of a researcher from the University of Leeds, UK, Xmas trees could be useful even after they lose their glow.

Jenny Jones thought of a special roasting process that could make it economically viable for power stations to burn large quantities of biomass, like pine and spruce trees, instead of coal.

There are already coal-fired power stations that burn biomass, but because of the difficulty and expense of pulverizing wood to a powder that can be burned alongside processed coal dust, only small amounts can be used.

To eliminate this problem, and because unlike fossil fuels, biomass can provide a carbon-neutral form of energy, Jones and colleagues have carried out several experiments involving torrefaction.

Torrefaction is a roasting process, where plant matter is heated in an air-free container, but it may sound more familiar when talking about coffee – torrefying coffee beans is the oldest application of this process.

But back to trees, the torrefaction process is already used to produce biochar – a processed form of plant material that improves soils and avoids carbon dioxide emissions that would have resulted from the plants decomposition.

After several tests, Jones and her colleagues discovered a different roasting method that could make biomass suitable to burn alongside coal.

They worked with willow and also with Miscanthus grass, and they found that both types of plant matter had to be heated to about 300 °C – with the cooking time depending on the diameter of the branches.

This process caused the plant material to lose a small fraction of their mass but managed to retain almost all of their capacity to generate heat when burned, yielding nearly 75% of the coal's energy.

Also, by roasting the plant matter, it became more brittle, thus easier to grind into a fine powder just like good-quality coal, New Scientist reports.

Another benefit of the torrefaction process is that “it makes the biomass hydrophobic, which means it doesn't absorb moisture and can be stored more easily without the fuel rotting,” added Jones.

The team is currently working with the utilities RWE NPower and Alstom, and the Drax power station in Selby, UK, and they are experimenting on other biomass sources, like spruce and pine trees.

The new experiments include assessing whether it would be practical to carry out the process on an industrial scale and what the safety and environmental implications could be.