Mechanism And Modification Of Slagging During Biomass Conversion

Due to the high content of alkali metal and alkaline-earth metal elements in biomass,ash-related slagging problems were easily generated during the process of conversion（combustion and gasification）.In this paper,the mechanism and regulation of slagging during biomass conversion were investigated.It could provide basic data and theoretical guidance for solving slagging problem.The slagging mechanism of the ash/slag from biomass water-cooled vibrating grate boiler and their formation process were investigated.According to the chemical composition,surface morphology of ash/slag,fusion characteristics and the mineral transformation behavior in the cotton stalk（CS）ash,it might be deduced that slagging mechanism and the ash/slag formation process during biomass water-cooled vibrating grate combustion.During CS combustion process,deposits(D_CS)was formed on the surface of the vibrating grate super-heater.The ash fusion temperature（AFT）of and its modification by additives were investigated.The kalsilite and leucite formation made the mixture AFT increase with increasing kaolinite proportion.The formations of high melting point calcium silicates with increasing calcite proportion,which made their AFT increase.Additives could further alleviate the formation of D_CS by changed the AFT.Paper-making sludge（Ca-W）could be used as a substitute for calcium-based additives,the formation of anorthite with increasing Ca-W mass ratio made the AFTs of D_CS and CS increase.The migration of potassium in biomass gasification was the main factor to determine its behavior.To illustrate potassium behaviors during biomass gasification,the potassium migration of wheat straw（WS）or maize stalk（MS）ashes and their modification mechanisms by additives were investigated.The results showed that the K content in WS or CS increased with increasing kaolonite content and decreased with increasing dolomite content.Kaolinite could delay the release of potassium in ash and reduced the slagging problem induced by alkali.The addition of dolomite could promoted alkali-induced slagging,and reduced the slagging induced by silicate melt,the effect of dolomite on slagging characteristics of biomass is needed to explore further.