单项选择题

Once the decorations have been removed, many of our Christmas trees end up in the trash. Soon they could be put to better use, however: a special roasting process could make it practical for power stations to burn large quantities of biomass(生物质), such as pine and spruce trees, instead of coal. Compared with fossil fuels, biomass can provide a carbon-neutral form of energy. Many coal-fired power stations already burn biomass, but only small amounts can be used because of the difficulty and expense of crushing wood to a powder that can be burned alongside processed coal dust.
To overcome this problem, Jenny Jones at the University of Leeds, UK, and colleagues have been experimenting with "torrefaction" (烘烤). Torrefaction is already used to produce biochar (生物碳). Jones and her colleagues discovered that a different roasting recipe can make biomass suitable to burn alongside coal.
Working with willow and also with Miscanthus(芒草) grass, the team found that both types of plant matter had to be heated to around 300℃, though the cooking time depended on the diameter of the branches. During this process the plant material lost a small fraction of their mass but retained almost all of their capacity to generate heat when burned—their energy yield was about 75 percent that of coal. Furthermore, roasting made the plant matter more brittle, so that it could be ground into a fine powder just as easily as good-quality coal.
The torrefaction process brought other benefits too. "It makes the biomass hydrophobic, which means it doesn’t absorb moisture and can be stored more easily without the fuel rotting," Jones says. The team is now experimenting on other biomass sources, including spruce and pine trees. They are also investigating how practical it will be to carry out the process on an industrial scale and what the safety and environmental implications might be.
Jenny Jones and her colleagues are also exploring ______.