Characterization of Ash Materials From Fluidized Bed Combustion of Agricultural Wastes. Effect on System Performance, Environmental Impact and Valorization
The use of secondary fuels for power production, such as animal and agricultural wastes, is becoming important nowadays, in view of the declining reserves of fossil fuels. Fluidized bed furnaces offer many advantages, such as fuel flexibility, high efficiency and low pollutant emissions. However, bottom or fly ashes produced from these appliances may create technical and environmental problems. In this study, agricultural wastes from the island of Crete (S. Europe) were co-fired in a fluid bed unit and bottom and fly ashes were characterized by mineralogical, chemical and fusibility analyses. The effect of ash materials on system’s performance, as well as their environmental impact and valorization were assessed. The results showed that all ashes were enriched in Ca, Si, Mg, P, K. These elements were principally associated with calcite, anhydrite, quartz, dolomite, whitlockite, hydroxylapatite, fairchildite and arcanite minerals. Arcanite, sylvite and hydroxylapatite were partly vaporized during combustion and condensed on fly ashes. Initial deformation temperatures of ashes were quite low for systems other than fluidized bed. Heavy metals showed less preference for fly ashes. Cu, Zn and Sr dominated in fly ashes. Toxic metal ion values were below the legislative limit for disposal in landfills. All ashes could be used as liming agents on acidic soils or for fertilizing applications.