The Solid Deposition Features Of Biomass Combustion

Biomass have broad prospects due to its clean and renewable advantage. But the existence of alkali metals cause many problem during the biomass combustion. This paper combined the theory predict and experiment. Using chemical fractionation analysis, XRD, SEM/EDS and EPMA to analyse the characteristics of the solid phase deposition in different combustion temperature and time, which came from three different kinds biomass straws ( the straw of corn, oats and rice ). For a deep research on the mechanism of the deposition formation.This paper predicted the effects of temperature on the compounds variety on the base of chemical thermal equilibrium calculation. The results show that: K will first react with Cl, Cl can get alkali metals from K2SO4 and Na2SO4 to add gas phase substance after 900℃; Low content Na will cause little Na2SO4 formation, when the content is high, it will make the compounds below 800℃more complex and increase the activities of K; There are many solid phase compounds of aluminum borosilicate with alkali metals, high content Si will cause appearence of these compounds below 850℃.This investigation was carried out in the self-designed deposition furnace which examined the dynamic characteristics during three biomass straw combustion. The results showed that:The deposition weight was close connected with straw ash content, temperature and time, the increase of rice straw deposition weight was significantly affected by combustion time, and so did the combustion temperature on oat straw. The order of deposition hard is corn straw > oats straw > rice straw, the main part of chemical fractionation in all deposition are SiO2 and CaO, the content variety of other compounds like Al2O3, K2O and Na2O can effect crystalline forms and diversity in the deposition; there are three kinds process of deposition formation, agglutination, "bridge connection", "crisscross stand", respectively, and which of them was followed in the actual process depended on the particle size distribution in biomass fragments. Potassium feldspar is the supporting structure of deposition, and the oxide compounds of Al, Fe, Ca, Mg continued to fill the interspace and make the structure closed-grain. The formation process of compounds can be described as from simple to complex and part to whole, finally, elements evenly distributed.At last, the clinkering index of deposition was analyzed by gray association degree theory in different combustion temperature, time and alkali metals content. The results show that apart from alkali metals content, the temperature is the most important element.