(49b) Review of Fast Pyrolysis of Biomass

Renewable energy is of growing importance in satisfying environmental concerns over fossil fuel usage. Wood and other forms of biomass including energy crops and agricultural and forestry wastes are some of the main renewable energy resources available. The potential for biomass to supply much larger amounts of useful energy with reduced environmental impacts compared to fossil fuels has stimulated substantial research and development of systems for handling, processing, and converting biomass to heat, electricity, solid, liquid and gaseous fuels, and other chemicals and products. Greater use of biomass has also been motivated by improvements experienced in local and global environmental quality. The increasing dependence on imported oil as well as the urgency to reduce Greenhouse emissions abounds in justifying an energy policy that carefully considers the role of renewable sources as energy carrier.

Pyrolysis and other thermochemical conversion processes offer an important opportunity for the utilization of biomass and waste. Biomass fast pyrolysis is of rapidly growing interest all around the world as it is perceived to offer significant logistical and hence economic advantages over other thermal conversion processes. The principle of fast pyrolysis is rapid heating of relatively small biomass particles (> 5 mm) to approx. 500⁰C in absence of oxygen. Fast pyrolysis is meant for the conversion of biomass to an intermediate, liquid bio-fuel that has a significantly increased volumetric energy density and much lower ash content than the original biomass.

The objective of this review is to analyze the design considerations faced by the developers of fast pyrolysis, upgrading and utilization processes in order to successfully implement the technologies. Aspects of design of a fast pyrolysis system include feed drying; particle size; pretreatment; reactor configuration; heat supply; heat transfer; heating rates; reaction temperature; vapour residence time; secondary cracking; char separation; ash separation; liquids collection. Each of these aspects is reviewed and discussed. The primary liquid product obtained is characterized by many properties that impact its usage in many applications. Applications of bio-oil in various fields have also been critically discussed.