Biomass Ash Fluidised-Bed Agglomeration: Hydrodynamic Investigations

Abstract

Agglomeration and defluidisation processes in fluidised-bed reactors due to ash melting are a real difficulty encountered when gasifying feedstock with high ash content. This work aims to investigate the influence of agglomeration on the hydrodynamic behaviour of a bubbling fluidised-bed reactor. The identification of the main parameters involved in agglomeration and defluidisation and the study of their influence on these processes are carried out inside both a laboratory fluidised-bed operating at high temperature (700–1000 °C) and a cold-flow fluidised-bed at ambient temperature. Results are then compared to a gasification test performed in a pilot-scale facility (800 °C). Results show that hydrodynamic disturbances and defluidisation are the result of agglomerates segregation. Once formed, the agglomerates tend to segregate at the bottom of the bed causing the formation and the build-up of a fixed bed crossed by multiple channels. In addition, the hydrodynamic behaviour is highly sensitive to the in-bed liquid amount. Complete defluidisation was seen to occur for very low liquid amount (few vol%). Based on these results, a simplified modelling approach is given in order to predict the operating time before the complete defluidisation of the reactor.