| Agricutural residues are regarded as key biomass resourse for heat and power production. However, these fules have high alkali contents, which react with other ash forming elements to form low-melt temperature materials and lead to ash sintering and slagging. This has become one of the major obstacles of biomass utilization. Therefore, it’s of great significance to study the regular pattern of alkali transtormation and the influence on slagging during biomass combustion.FactSage, a kind of chemical equilibrium software, was used to simulate the straw combustion process to obtain the type and the state of alkali mental compounds in the combustion product considering temperature, pressure, excess air coefficient, S content and Cl content in the straw. The result shows that the alkali chloride is the main form in the vapor phase and the production increases as the temperature increases. The production of molten materials decreases when the oxygen concentration increases in certain range, which can abate the slagging. The formation of gaseous alkali metal compound is prevented when the pressure increases or the S content of the biomass improves. Besides, increasing the Cl content can promote the formation of HCl(g) and Cl2(g), which may exacerbate the corrosion of boiler heating surface.Straw ash was produced by muffle furnace in different combustion conditions. The alkali content of the straw ash was tested by altomic absorption spectrometer. The result shows that Na is more likely to release into the gas ghase than K during the biomass combustion. The production of gaseous alkali metal compound increases as the temperature increases. Additive kaolin prevents K release and may react with alkali salts to form high-melting point materials, which alleviates the problem of slagging. Additive CaO or MgO promotes the formation of gaseous alkali metal compound and decreases the production of alkali metal silicate to achieve the aim of anti-slagging. |
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