| The effects of adding single flux(CaO,MgO,Na2CO3,Na2SO4),and sodium-based compound calcium-magnesium flux(WNa/WCa?WNa/WMg)on the melting properties of high ash melting coal and mullite in this article were studied.The coal ash melting temperature of high ash melting point coal was measured using an intelligent ash melting point tester.The analysis of the crystalline minerals changes in mullite slag added with flux at different temperatures was performed using X-ray diffraction(XRD).The apparent morphology and chemical composition of mullite slag with flux addition at different temperatures was investigated by scanning electron microscopy combined with X-ray energy spectrum analysis(SEM-EDX).The minerals transformation of mullite slag at high temperature with the addition of different fluxes were simulated with the help of FactSage and Materials studio software.The phase equilibrium composition change process and the lattice structure damage process of kaolinite and mullite molecules while adding sodium-based compound calcium-magnesium flux have been explored from different point of views.Adding single flux Na2CO3,Na2SO4,CaO,MgO,sodium calcium(WNa/WCa=X)and sodium magnesium(WNa/WMg=X)compound flux to high ash melting coal,the effect of the addition percentage of flux on reducing the melting temperature of coal ash was studied.When adding 6%calcium sodium and calcium magnesium compound flux(WNa/WCa,WNa/WMg),the melting temperature trend of coal ash showed "U" shape.When the ratio of sodium-based Na2CO3 to CaO and MgO is 1:1,the flow temperature of coal ash is reduced to 1336? and 1333?,which is more obvious than adding single flux at same addition percentage.Adding different fluxes will cause mullite slag to form different minerals at high temperature.Through XRD analysis,the low temperature eutectic in which the main element composition is same as that of single flux is formed.When adding sodium calcium,sodium magnesium compound flux,two or more different low melting point minerals which coexist at low temperature will be formed.As the temperature rises,these minerals co-melt to eutectic slag.Combined with the SEM spectrum analysis,at the same magnification and temperature of 1300?,the surface of the ash residue gradually showed agglomeration from small particles to large particles,indicating that it tended to be smooth,and there were still obvious gaps between the single and large particles.It shows that at 1300?,the addition of single flux failed to reach the ash flow temperature.Thermodynamic calculation results show that the types of minerals in the ash and minerals reaction process at low temperatures are increased with the addition of sodium calcium(WNa/WCa=1)and sodium magnesium compound(WNa/W/Mg=1)flux to mullite.As the temperature increases,the solid-phase minerals gradually co-melt with each other,which causes the initial temperature of liquid slag formation to decrease.At the same time,the low-temperature eutectic occurs between the sodium minerals and calcium minerals,magnesium minerals and other minerals,so that the liquid phase is generated in advance,which is shown as a decrease in the ash melting temperature.Combined with the structural characteristics of mullite,alkali metal cations such as Na+,Ca2+ and Mg2+ enter through the two bonds of Al(6)-O(8)and Al(5)-O(7)which are more easily broken in the mullite.The mullite lattice is destroyed in the structure of Al-O tetrahedron and Si-O tetrahedron to producing low-temperature molten minerals,which explains the reason why the melting temperature of coal ash decreases at the molecular level.Figure[24]Table[13]Reference[83]... |
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