The Effect of Temperature and Steam Concentration on the Yields of Tar Compounds in Fluidized Bed Pyrolysis

The effect of temperature and steam concentration on the yields of different tar compounds was investigated. Wood pellets and dried sewage sludge spheres (DSS) were pyrolyzed in a fluidized bed reactor in the temperature range of 500-800ºC. The reactor has two independent electrically heated zones, enabling independent adjustment of the temperature of generation of volatiles (release of volatiles during thermal decomposition of the fuel particle) and secondary conversion of the volatiles on homogeneous phase. The temperatures of the bed and the freeboard were varied independently keeping constant the residence time of volatiles in each zone. This work is one of the tasks within a project whose overall objective is the development of a three stage gasification process to generate a gas with low tar content. The specific aim of this task is to identify the conditions minimizing the heavy tar formation. Parameters such as the air injection points or the steam addition could be adjusted on the gasifier design and they are of capital significance on temperatures distribution and hence on tar formation and conversion. Therefore this works try to clarify the effects of temperature stratification and steam addition on tar formation and conversion in order to be an useful tool during the gasifier design