CARBON ELUTRIATION FROM PRESSURISED FLUIDIZED BED COMBUSTION OF AUSTRALIAN BLACK COALS

A batch-fed bench-scale pressurised fluidized bed combustion (PFBC) facility was built at UNSW to research the in-bed processes generating fine char particles during PFBC of Australian black coals. Measured carbon elutriation varied from coal to coal and the results agreed qualitatively with large-scale PFBC performance, allowing definition of satisfactory and unsatisfactory performance criteria. For both of the tested coals, the carbon elutriation rate decreased during burnout due to the decrease of in-bed carbon loading. The specific carbon attrition rates were constant at the early stage of burnout when the in-bed char particles were larger(about >2mm) and then increased at the later stage of burnout. Carbon elutriation in PFBC was correlated tentatively with crucible swelling number (CSN), although the range of values of CSN needs to be extended. Carbon elutriation in PFBC did not correlate with volatile matter for the 5 Australian coals investigated, in contrast with previous PFBC pilot plant studies. The higher swelling coal produced a significantly larger average macro-pore diameter after devolatilisation in PFBC, which caused greater attrition of fine char from the particle surface during the char burnout stage.