BIOMASS ASH FLUIDISED-BED AGGLOMERATION: HYDRODYNAMIC INVESTIGATIONS

Agglomeration and defluidisation (A/D) processes in fluidised-bed reactors (FBR) are a real difficulty encountered when gasifying feedstock with high ash content. According to the elemental ash composition, a liquid phase may form at the operating temperature and glue the bed particles together, thus starting disturbing the hydrodynamic of the bed, as well as the conversion efficiency. Finally, it leads to the complete defluidisation of the reactor. This work aims to investigate the influence of agglomeration on the hydrodynamic behaviour of a FBR. The identification of the main parameters involved in A/D and the study of their influence on these processes are carried out inside both a laboratory fluidised-bed operating at high temperature (700-1000 degrees C) and a cold-flow fluidised-bed at ambient temperature. The effect of the in-bed liquid fraction, the liquid properties and the operating parameters are investigated in relation to the agglomeration process and the hydrodynamic behaviour. Based on these results, a simplified modelling approach is given in order to predict the operating time before the complete defluidisation of the reactor.