Tar Yield and Collection from the Pyrolysis of Large Biomass Particles

Abstract

Tar yield collection from the pyrolysis of relatively large particles of biomass are investigated using the model of Miller and Bellan (1997).A variety of feedstocks are considered by varying the ratios of cellulose, hemicellulose and lignin within the biomass. Effectsof secondary tar reactions, quenching, temperature, particle size and carrier gas are assessed. Secondary tar reactions occuring in both the particle's interior and the exterior boundary layer strongly reduce the potential amount of tar available for collection compared to the maximum given by kinetic predictions. The primary effect of these reactions is the existence of an optimal reactor temperature range for maximizing tar yields. This range is a function of both the quenching location and the initial particle size. For rapid qvenching near the particle surface, tar collection is maximized at high temperatures for small particles, and at low temperatures for large particles. For delayed quenching, low temperatures slow the secondary reactions and provide larger tar yields for all particle sizes investigated. Tar yields are also dependent on the choice of the inert carrier gas; primarily due to changes in heat capacity. A sensitivity study is performed in order to assess the influence of the biomass apparent density, thermal conductivity, heat capacity and primary heats of reaction.