| The two high-ash-fusion-temperature coals C and Z were selected,and the fusion temperature of coal ash can be reduced to meet the gasification requirements by adding flux.The paper mainly study of the effect of different kind of fluxes and different flux concentration on fusion temperature of coal ash,and the influence of flux on the minerals transformation and morphology of slag by scanning electron microscopy and energy dispersive X-ray spectroscopy(SEM-EDX)and X-ray diffraction(XRD).Moreover,the molecular structure and the existent form and evolution of element were characterized by Raman,X-ray photoelectron spectroscopy(XPS)and quantum chemical calculation.From the mineral bonding properties,the mechanism of calcium and magnesium compound flux was elaborated.The main results were shown as follows:The effect of CaO,MgO and compound flux(WCaO/WMgO =X)on the melting temperature of C coal and Z coal ash was studied.The effect of compound flux was more obvious than single CaO or MgO.At the same gasification temperature of 1300?,C coal and Z coal added 6%CaO present loose network or block structure,which indicated mullite transformed into anorthite in slag.When added 6%Mg0,all two slags were partly molten with large pores which indicated that a large amount of magnesium-based minerals in slag reduced the melting temperature.When added 6%CaO/MgO(WCaO/WMgO=1),the two slags showed dense molten structure,indicating that eutectic melting occured between the calcium minerals and magnesium minerals,and the compound flux had a positive impact on the formation of eutectic minerals,which greatly impacted the molecular structure of slag.When Z coal was added CaO(6%)or MgO(6%),the temperatures of eutectic formed at 1421? and 1355?,while the temperature of Z coal added compound flux CaO/MgO(WCaO/WMgO=1,6%)is only 1290?.The results of XPS and quantum chemistry showed that the compound flux reduced ash melting temperature mainly because of structure change of silicon,aluminum and oxygen.The coordination mode of aluminum and oxygen was changed,namely aluminum-oxide tetrahedron[AlO4]and aluminum-oxide octahedron[AlO6]varied with temperature changes.The addition of Ca2+ and Mg2+ destroyed the silica chain,which making bridging oxygen silicon changed into non-bridge oxygen silicon.Besides,oxo-bridged oxygen bond is broken and non-bridge oxygen bond formed.Ca2+ and Mg2+ easily reacted with non-oxygen bonds in silicon oxide or aluminum oxide tetrahedron and aluminum oxygen octahedrons to produce low-melting feldspars and magnesite minerals. |
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