Pyrolysis of biomass in the rotating cone reactor: modelling and experimental justification

In the rotating cone reactor, wood particles fed to the bottom of the rotating cone, together with an excess of inert heat carrier particles, are converted while being transported spirally upwards along the cone wall. The cone geometry is specified by a top angle of π/2 radians and a maximum diameter of 650 mm. Products obtained from the flash pyrolysis of wood dust in a rotating cone reactor are non-condensable gases, bio-oil and char. This paper reports on results of computations and measurements to determine the influence of process parameters like the cone rotational speed (6-15 Hz), the reactor volume (3-200 l), the wood-dust feed rate (1-3.5 g s^-1) and the reactor temperature (550-700°C) on the product composition. The experimental results are compared with predictions of an integrated reactor model which accounts for: (i) the type of particle flow in the reactor; (ii) the wood decomposition kinetics; (iii) the rate of heat transfer to the wood particles; (iv) the kinetics of gas phase reaction (tar cracking); and (v) gas exchange with the space in which ash, char and partially unconverted wood is collected. For the conditions applied, the difference between predicted and measured weight fractions of gas, tar and char produced was always less than 10%. If further appeared that the wood particles were always completely converted inside the reactor and that the product distribution is only affected by the gas-phase reaction kinetics and residence time. The gas-phase residence time is determined by the available reactor volume and the feed rate of the wood particles. At optimal reactor conditions, the tar yield is almost maximal (70% d.a.f. wood base).