A simple method for the rapid heating of biomass particles is to mix them with the moving sand particles of a high-temperature fluid bed. High heat transfer rates can be achieved, as the bed usually contains small sand particles, generally about 250 pm. The heat required is generated by combustion of the pyrolysis gases, and/or char, and eventually transferred to the fluid bed by heating coils. While the sand to biomass heat transfer is excellent (over 500 W/m2 K), the heat transfer from the heating coils to the fluid bed will be low, due to the resistance inside the coils (gas to coil wall heat transfer estimated 100-200 W/m2K), and the limiting driving force of around 300 °C as a maximum. In an optimistic case, at least 10-20 m2 surface area is required per ton/h of biomass fed.