Study of the bed fouling problems in a biomass fired commercial CFB boiler

摘要

The use of biomass fuels in circulated fluidised bed (CFB) combustion is becoming more important because of increasing energy demand and the polluting nature of existing fossil fuel energy sources. The commercial circulating fluidised bed boiler at VEAB (Vaxjo Energy Limited) has a large fuel flexibility, and can be fired with low moisture, high grade fuels, as well as high moisture, low grade fuels like biomass. The major ash-related problem encountered at VEAB is bed agglomeration which, in the worst case, may result in total defluidisation and unscheduled shutdown. Non-agglomerated and agglomerated ash samples resulting from the firing of 50 % sawdust and 50 % forestry residues were analysed using inductively coupled plasma atomic emission spectroscopy (ICP-AES), x-ray fluorescence analysis (XRF), scanning electron microscopy (SEM) equipped with energy dispersive x-ray spectroscopy (EDS), atomic force microscopy (AFM), and x-ray diffraction (XRD). An increase of the concentration of the trace elements in the agglomerated samples was observed by ICP-AES and XRF. On the basis of the AFM experimental results and evidence of the non-height difference in the topography of the agglomerated samples, formation of binary or ternary eutectic melts was proposed.