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Technical Issues
3/2016 pp. 126-134

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The fusion behaviour of biomass ash-forming materials is an important factor in assessing the propensity to form undesirable slag and fouling deposits in the boiler. The characteristics of the fuel used affect the extent and severity of the problem, thus growing efforts are put on finding reliable methods for its characterization. Combustion and co-combustion of biomass have gained popularity in combating climate change and reducing carbon dioxide emissions into the atmosphere. Nevertheless, biomass encompasses a wide range of different types and its use increases operational risks due to the diversity of the chemical composition. This study is based on characterising the mineral phase transformations of two kinds of biomass (wood pellets and cereal pellets) using various laboratory-based methods on fuel ashes. Measurements of changes in the electrical properties of the ash during the sintering process (dielectric loss factor) were performed using a QuadTech Plus 7600 bridge in the frequency range 500Hz - 1MHz. Thermodynamic analyses were performed by means of FactSage™ modelling. The results were compared with those of standard tests, AFT and oxide index calculations, which were employed to predict slagging and fouling propensities. The observed changes in dielectric loss depend on the frequency and temperature of sintering. FactSageTM thermodynamic equilibrium calculations proved very useful in predicting the ash melting behaviour and the chemical changes occurring in the ash. The existence of a melt phase, occurring at even lower temperatures of those given by the AFT, is in accordance with the high slagging and fouling hazards predicted by empirical indices.

Key words

biomass, ash, slagging, fouling


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