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Biomass tends to form deposits and tends to slag during combustion. This study focused on deposits obtained from a circulating fluidized bed (CFB) in a biomass power plant. Analyses using scanning electron microscopy, energy-dispersive spectrometry, and X-ray diffraction are also included. The results indicate that the deposits are dense with a certain hardness, which resulted from the erosion of particles in the CFB. The deposits are high in K, Na, Cl, and Ca, whereas Si, Al, Mg, and S contents are relatively lower. KCl and K 2 SO 4 are the main components of the deposits. The particles in the flue are captured by the viscous layer that was formed by the condensation of gaseous KCl and K 2 Ca(SO 4 ) 2 on the surface of the tubes. Moreover, deposits are formed under the effect of the adhesion and capturing processes, in alternation.

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In the present study, the NO and N2O formation characteristics during combustion of five biomass fuels (rice straw, wheat straw, corn stalk, sugarcane leaf, and eucalyptus bark) and one bituminous coal, as a comparison, were investigated in a horizontal fixed-bed reactor. It showed that there was still a considerable degree of N2O conversion for biomass fuels, although NO was formed in a much larger amount. Most of NO and N2O were formed during the devolatilization stage for biomass fuels; therefore, optimizing the supply of air and fuel during biomass combustion in actual boilers can be expected to achieve ultralow emissions of nitrogen oxides. There was no clear correlation between the NO and N2O yields and fuel N content, which indicated that the nitrogen functionality and other components, such as inherent mineral matter, present in biomass must have great influence on the nitrogen transformation during thermal processing. When rice straw was co-fired with eucalyptus bark, nonlinear behavior could be seen and the fuel N conversion to NO was largely enhanced. In the temperature range of 700–900 °C, the fuel N conversion to NO first increased and then decreased slightly, while the conversion to N2O showed a continuous decreasing trend. The fuel N conversion to NO and N2O showed a general increasing trend with the increase of the inlet oxygen concentration, and this phenomenon was more obvious at higher temperatures. The results presented in this study will help to gain some insight onto the fundamental mechanism of fuel N conversion during biomass combustion.

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