Synergistic Effect Of Na/Ca Based Flux On Coal Char Gasification Characteristics And Coal Ash Fusion Properties

Coal gasification reaction activity and ash melting characteristics are the two key factors affecting the coal gasification process.The energy utilization efficiency,long-term and stable operation of the gasification furnace can be improved by the enhancement of gasification reaction activity of coal char and the improvement of ash melting characteristics of coal.In this paper,Huainan coal with high ash melting point was selected to study the gasification reactivity and ash melting characteristics with the addition of Na/Ca based fluxes.The crystalline mineral composition,morphology and microscopic chemical composition of the gasification residue were studied by X-ray diffraction(XRD)and scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDX),respectively.The kinetic data from TGA analysis of coal with different flux addition were fitted by different models to obtain the kinetic parameters of the gasification reaction.The optimum model was determined to reveal the reaction mechanism of Na/Ca compound additives on coal gasification.The results show that the flow temperature of coal ash with the addition of 4%Na/Ca compound additive(Na2CO3/CaCO3=7:3)can be reduced to 1370? which is lower than that of 4%single sodium-based or calcium-based additive.Thus,the fluxing effect of the compound additive is better than that of the single additive.The gasification reaction activity can be significantly increased by sodium-based additives with the activity strength Na2CO3>Na2SO4>NaCl>Na2SiO3.The calcium-based additives have relatively weak catalytic effects,and the activity strength is:CaCl2>CaO?CaCO3?CaSiO3>CaSO4.The actual reactivity index of 2.5%Na2CO3-2.5%CaO and 2.5%Na2CO3-2.5%CaCO3 in the Na/Ca compound additive is greater than the theoretical reactivity index,showing a significant synergistic effect.The bimetallic carbonate(Na2Ca(CO3)2)which increases the dispersion of elemental calcium on the surface of coal char particles is formed during gasification process with the addition of Na/Ca compound additive.The result of dynamic calculations show that the fitting effect of random hole model is the optimum,but the homogeneous model has the worst fit effect,and the shrinking kernel model is in between.The introduction of Na/Ca additives can significantly reduce the activation energy.Figure[37]Table[7]Reference[83]...