Effect of the Mineral Interaction on Emission of Submicron Fly Ash during Coal Combustion

摘要

Coal ash is China's largest single source of solid waste, of which the submicron fly ash are particularly troublesome, since they are enriched with the toxic heavy metals and have a high probability of escaping common air pollution control devices. To investigate its formation mechanisms during coal combustion, the interaction between different minerals in the coal and its effect on the formation of the submicron fly ash were studied. Four bituminous coals were combusted in the Drop Tube Furnace and the produced ash was collected and separated by Low-pressure impactor. The X-ray fluorescence (XRF), the transmission electron microscopy-energy dispersion spectroscopy (TEM-EDS) and the computer controlled SEM (CCSEM) are used to characterize the minerals in the coal and the submicron ash. With respect to the influence of the modes of occurrence of elements, it was investigated from the consideration of the mineral association in parent coals, i.e., included or excluded particles. According to the experimental results, it was concluded that the association of inherent minerals with the carbonaceous matrix was primarily important for determining their transformation into submicron ash. The excluded minerals barely contribute to submicron ash formation. The transformation behaviors of Si and Al were possibly affected by the amount of excluded in raw coals. A portion of Fe-bearing large particles likely transformed into submicron ash too. Its vaporization was possibly affected by the chemical forms of Fe. On the other hand, the fragmentation of large Fe-bearing compounds was mainly controlled by their particle size.