Fundamentals of torrefaction of biomass and its environmental impacts

In response to the EU 2020 target, the markets of biomass energy are developing rapidly and becoming more international. At the same time, there have been concerns with biomass in terms of its characteristics such as high moisture content, poor grindability behaviour, low calorific value and problems in relation to transport, handling and storage. Torrefaction is a pre-thermal treatment that has the potential to improve these characteristics. This thesis covers four areas of investigation work. The first chapter shows how torrefaction has improved the physical and chemical properties of biomass. Torrefied fuels became more hydrophobic, contain higher energy yields and have grindability behaviours that resemble those of low rank coals. Furthermore, microscopic and spectrometric studies were carried out to gain a better insight into any changes in morphology and chemical composition of torrefied biomass. The overall results indicate that careful optimization is required to maximize the benefits of torrefaction whilst maintaining a good energy yield. Torrefaction is still in the development stage and so underpinning knowledge and science is still required. The second chapter examines how different sizes of biomass (≥ 5x5x5 mm) could influence torrefaction. The presence of mass and heat transfer limitations was suggested to explain the observed significant changes. The third chapter provides a short investigation on how torrefied biomass fuels react in response to combustion, where the heating rate of the flame and the rate of char combustion were estimated. Torrefaction in relation to health and safety concerns as well as environmental issues are still unknown. The next chapter provides a preliminary study of an environmental impact assessment was reviewed using any information that is readily available. Several areas of interests that cover from raw materials to the environmental fates of products of torrefaction were considered. Finally, a series of recommendations for future work are discussed at the end of the thesis.