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Study of the Impact of Alkali on Slagging During Biomass Combustion

Author: LiLi
Tutor: LiGuoZuo
School: Beijing Jiaotong University
Course: Engineering Thermophysics
Keywords: Alkali slagging biomass
CLC: TK6
Type: Master's thesis
Year: 2011
Downloads: 280
Quote: 2
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Abstract

Biomass can be combusted directly in boiler to generate heat and electricity, especially the high efficiency of this technology, leading it to be a promising new energy for future. However, fouling and slagging problems associated with biomass boiler is still a major issue, which limits the utilization of biomass on a large scale.In order to solve this problem, nine typical plants from industry and agriculture were chosen as a research background to study the characteristics of biomass ash, including the chemical elements composition, ash fusibility, volatile properties and so on, especially the way that alkali impacts on these qualities, using XRF, XRD, TG, and muffle furnace. Furthermore, to prevent the interference of organic and trace elements in biomass which limits the interpretation of the influence of alkali, a simulate method was applied in investigating the alkali impacts on ash fusibility and volatility in depth, based on the ratio of Si/Al, distribution range of CaO, alkali and other trace elements in biomass. Then a further study of fusion characteristics and volatilization properties was taken on simulative ashes, using fusion point analyzer and TG. Finally, the relevance between alkali and fusion points was understood further, and the correlation of alkali and volatility was clear. On the basis of these experimental results, a new indicator was obtained for forecasting fouling and slagging property, considering the high volatility of biomass ash resulting from high level of alkalis.The general conclusion is that the content of alkali in biomass is not the direct reason to cause the ash fusion point high or low, but the content of eutectic mixture for low temperature created in the reaction between alkalis and other inorganic elements which reduces the temperature. Meanwhile, when the biomass fuels are combusting in the furnace, the high content of alkali is the direct reason to cause the high volatility of biomass ash, which means mineral substances in ash are tend to volatilize into gas easily then stick on the heating surface as fouling at first, developing into slagging gradually. However, the old indicators for predicting the slagging tendency regard ash fusion or chemical composition as key points without considering of these high volatility of biomass ash, leading a low feasibility. Therefore the new method thinks over not only the ash fusion but the volatility of biomass ash, aiming at providing a more accurate method to forecast the fouling and slagging in biomass boiler.

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