The heat transfer rate requirements described above impose particle size limitations on the feed for some reactors. The cost of size reduction in financial and energy terms is clear qualitatively but data is not available to define such a penalty associated with the small particle sizes demanded of fluid bed and circulating fluid bed systems. Reactor performance as for example liquid yields is, therefore, not an adequate criterion by itself.

Drying is usually required to less than 10% wt water unless a naturally dry material such as straw is available. As moisture is generated in flash pyrolysis, bio-oil always contains at least about 15% water at an assumed product yield of around 60 wt% organics and 11 wt% reaction water. This water cannot be removed by conventional methods such as distillation. The effect of water is complex in that it affects stability, viscosity, pH, corrosiveness, and other liquid properties. Selective condensation may reduce the water content of one or more fractions but at the

expense of operating problems and a possible loss of low molecular weight volatile components,