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The objective of this study was to examine the ash deposition tendencies of biomass fuels and the biomass-coal blended fuels against the base fuel (coal) during co-firing and how the operating parameters influence the ash deposition tendencies. In this study, ash deposition behaviors during combustion and cocombustion of white pine pellets (WPP) and lignite coal were investigated in a pilot-scale, fluidized-bed combustor. Employing a custom-designed, air-cooled probe installed in the freeboard zone of the reactor to simulate a heat-transfer surface, effects of various operating parameters on the ash deposition rate and compositions of the ash deposits were studied, including the fuel type, fuel blending ratio (0-100% biomass on a thermal basis), moisture content, and air/fuel ratio. A new parameter, "relative deposition rate" (RD A ), was proposed in this study to evaluate the relative deposition tendencies of biomass fuels and biomass-coal mixed fuels against the coal as the base fuel for co-firing. As expected, co-firing of the lignite and the wood pellets (with a much lower ash content than the lignite) resulted in a decreased superficial rate of ash deposition. However, co-firing of WPP and crushed lignite (CL) did not significantly increase the ash deposition tendency in terms of the values of RD A , and more interestingly, co-firing of the 50% CL-50% WPP fuel blend produced a lower RD A . Another new and interesting discovery of this study was that fluidized-bed combustion of an individual fuel or a mixture fuel with a higher moisture content produced not only a more uniform temperature profile along the fluidized-bed column but also a reduced ash deposition rate.

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