New opportunities for the exploitation of energy crops by thermochemical conversion in Northern Europe and the UK

Currently, significant academic and industrial activity is focused on sourcing feed stocks from non-food biomass crops for the sustainable production of energy, power and chemical products. Crops identified as suitable for Northern Europe include Miscanthus, switchgrass (Panicum virgatum), reed canary grass (Phalaris arundinacea) and short rotation coppice willow and poplar (Salix and Populus spp.). All of these crops provide biomass that is amenable for conversion by thermochemical processes i.e. those based on heat and pressure. There are concerns that for some processes the conversion efficiency of biomass is poor compared with coal and oil due to comparatively low energy density, high moisture content, and poor storage and handling properties. Many of these parameters can be improved by pre-processing feed stock materials prior to their conversion. We examine the energy crop species that are suitable for Northern Europe; discuss the processes of combustion, gasification and pyrolysis, and explore how differences in chemical composition influence conversion efficiency. Finally, we review biomass upgrading (pelletisation, torrefaction and treatment with sub-critical (hydrothermal upgrading) and with supercritical water).