With Quantum Theory Study Of Coal Ash Microstructure Features

With the rapid development of our national economy, the energy and environmentare increasingly become the limitation of our national economy development.Considering our characteristics of energy structure with rich coal, short of petroleumand natural gas, the entrained flow coal gasification technology with high pressure andlarge scale has become one of the important means and directions in clean coal and coalconversion technology in the future. The entrained flow gasifier was almost all slagginggasifier and that needs the coal ash fusion temperature （flow temperature） to below1400℃.Therefore a new require for Chinese coal ash fusion characteristics was broughtforward. There are different on coal ash fusion characteristics between foreign and ours,the high coal ash fusion temperature coal which FT>1400℃was account for about55%of annual output and57%of retain coal reserves. The entrained flow coal gasifiercan not use this high ash fusion temperature coal directly. In addition, it is difficult tooperate that higher ash content result in slagging and viscosity of boiler heating surface.So it is very important to study the coal ash fusion characteristics under coalgasification condition.Firstly, based on the extensive investigation of coal ash characteristics research inforeign and China, the coal-ash minerals microstructure were studied with quantumtheory method hang together computation technology from the view of molecular levels.The results were shown that the mainly initial compositions of high-fusion ash are bothlie in mullite region. Therefore, mullite structure is firstly focused on in our calculationto analyze the microcosmic property of coal ash. Mullite mineral is inclined to combinewith electron acceptor and no-inclination with electron donor. The activity of Si atom ishigher than that of Al atom when mullite combined with electron donor. Moreover, thecations of fluxing agent as electron accepters is easy to enter into the crystal lattice ofmullite especially from the cell which located at O（2）, O（4）, O（8） and cause the ruptureof Al（6）-O（8） and Al（5）-O（7） bond, finally leads to the separation of [SiO₄]-tetrahedraand [AlO₆]-octahedra. The lattice recombination will occur between the unit cells ofmullite, which force mullite transform to other minerals. Moreover, the difference ofcharge distribution and reaction activity site between them was computed. Finally, four kinds of typical high ash melting temperature coals, which coveredwith all of the silica to alumina ratio ranges, were selected in our paper. Fluxing agents,borax （Na₂B₄O₇·10H₂O） and Limestone （CaCO₃） were selected to add into four ashessamples respectively with a series of weight ratios. The mixtures were mixed well anddo ASTM test based on Chinese standard （GB219-74） under reducing （CO/CO₂mixtures） atmosphere in a HR-4ash-fusion testing apparatus. The experiment resultshowed that the coal ash melting temperature can decrease about100²00℃by addingappropriate CaCO3,while the melting temperature will increased again with addingmore CaCO3.It can get well result by adding borax, the ash melting temperature candecrease300℃by only adding10¹5%. According to the analysis by ternary phasediagram, Ca²⁺force mullite transform to anorthite and aedelforsite, while Na⁺forcemullite transform to nepheline and corundum. The difference of binding energy ofbetween mullite and these minerals affect the melting point of them, in agreement withthe experimental observations.