The prediction of behaviour of ashes from five different solid fuels in fluidised bed combustion

The behaviour of different ashes was predicted by the combination of extended fuel analysis with advanced global thermodynamic equilibrium calculations. The extended fuel analysis is a fractionation method that consists of sequential leaching of a solid fuel with water, ammonium acetate and hydrochloric acid. In order to cover a broad spectrum of fuels a coal, a peat, a forest residue and Salix (i.e. willow) were studied. The last was taken with and without soil contamination, i.e. with a high and low content of silica, respectively. Results from the fractionation showed clear differences in mineral distribution in the fuels. More ash-forming elements were present as included minerals in the older fuels. In relatively young fuels, almost half of the inorganic material was found in the soluble fractions after leaching with water and ammonium acetate. Fouling and slagging predictions based on the combined use of the extended fuel analysis and the advanced global equilibrium analysis indicated that no ash-related problems should be expected in FBC boilers firing the studied coal. The peat that was studied could cause minor ash depositions in the flue gas channel at temperatures above 700 degrees C. The studied forest residue could form fly ash deposits in the flue gas channel at temperatures between 600 and 860 degrees C. The Salix could cause fly ash depositions at temperatures between 840 and approximately 1000 degrees C. If soil contamination was present as well, Salix could cause bed sintering at temperatures above 1030 degrees C. (C) 2000 Elsevier Science Ltd. All rights reserved.