Study Of Coupling Interaction Mechanism Of Calcium And Magnesium On Coal Ash Melt Structure

In this paper,three typical high ash fusion temperature coal samples with different silica-alumina ratios were selected to analyze the regulation of coal ash fusion temperature and ash viscosity-temperature characteristics in a reducing atmosphere by adding different proportions of CaO and MgO reagents to the coal.CCSEM and X-ray diffraction(XRD)were used to examine the relationship between the mineral composition in coal and the coal ash melting characteristics,and the effect of calcium and magnesium fluxes on the crystalline minerals conversion process and cell parameters in coal ash.The Factsage thermodynamic software was adopted to explore the action mechanism of calcium and magnesium fluxes on coal ash fusion process and slag liquid phase production from a theoretical perspective.Quantum chemistry software was combined with X-ray photoelectron spectroscopy(XPS)to study the effects of calcium and magnesium ions on the bond lengths and bond energies of minerals in depth.The microscopic structural properties of the minerals in the ash are calculated in the molecular level to reveal the mechanism of interaction between calcium and magnesium ions on coal ash melt structures.The conclusions were summarized as follows:The conversion of high content of refractory minerals such as kaolinite and quartz in the coal to mullite is the main reason for the high melting temperature of the coal ash.The expression form of calcium and magnesium coupling for B coal and C coal whose Si/Al ratio is bewteen 1.5-2.0 is as follows:the addition of calcium and magnesium accelerated the melting process of coal ash and the mineral conversion process of ash.It can be seen from XRD results that CaO and MgO reacted with the aluminosilicates(mullite)in the coal ash to form Calcium-based minerals and magnesium-based minerals such as anorthite,osmite,forsterite,magnesium spinel and magnesium lolite et al.Crystalline minerals such as mullite anorthite,forsterite and spinel in the ash slag did not change crystal form at 1000?1500 ?.Under the combined action of calcium and magnesium,it caused the collapse of the mullite "skeleton" and reduced size,which would transform into low-melting minerals,resulting in a decrease in coal ash melting temperature and a increase in liquid phase production.There are 2 reasons why the coupling interaction of calcium and magnesium reduced the coal ash melting temperature:(1)Metal cations such as Ca2+ and Mg2+acted as electron acceptors,they destroyed the Si-O or Al-O non-bridge oxygen covalent bond of mullite,then combined with[A104]-,[A106]-and[SiO4]-to form minerals such as anorthite,forsterite and lolite.It is consistent with XRD analysis.(2)According to the results of quantum chemistry calculation,the free Ca2+ in the feldspar easily entered into the lattice structure of the forsterite and reacted with the eutectic at low temperature.It is consistent with the results of cell parameters.The combination of the two reactions leaded to a decrease in the melting temperature of coal ash.