Study On Improvement Of Fusion And Viscosity Properties Of High Aluminosilicate Coal Ash

The fusion and viscosity properties of coal ash is important to the safety and stable operation of the entrained-flow gasifiers,and they are also important reference indexes for coal selection.For the high fusion temperature coal ash with high aluminosilicate content,the addition of flux and coal blending method was used to improve the high temperature fluidity of such low quality coal ash and meet the requirements of gasifier operation.In this paper,the intelligent ash fusion point tester,high temperature viscometer,muffle furnace,high temperature heating furnace,thermodynamic calculation software FactSage,X-ray fluorescence spectrometer and X-ray diffractometer were adopted to study the fusion properties and viscosity characteristics of high fusion temperature and ash content raw coal.The effects of different flux addition and different blending ratio on the fusion characteristics and high temperature viscosity of high aluminosilicate content were investigated in detail.The effect of adding flux and coal blending was analyzed.The rheological properties of typical gasified coal at high temperature were investigated,and the effect of high temperature phase composition on slag flow pattern was studied.?1?The effects of fluxes such as CaCO₃,Fe₂O₃,complex flux,dolomite and typical iron ore?ore powder,srcuff and mineral waste?on the fusion temperature of high aluminosilicate content were studied.Based on the Factsage thermodynamics software,the liquidus temperature and the mineral composition at different temperatures were analyzed.The conversion of minerals in coal ash at high temperature was measured by X-ray diffractometer.The results showed that calcium-based or iron-based fluxes can effectively reduce the fusion temperature of coal ash.Adding calcium-containing flux could change the mineral composition of coal ash from mullite to lower fusion point of cordierite.The addition of iron-containing flux could increase the liquid content in coal ash and reduce the fusion temperature of coal ash.The effect of flux and Fe₂O₃ on coal ash was the best,and iron ore could improve the ash.Of the fusion temperature,iron ore flux fusion effect of the order was:ore powder>srcuff>mineral waste.?2?The effects of CaCO₃ flux on the viscosity characteristics of high aluminosilicate content ash were studied.Based on the thermodynamics software Factsage,the mechanism of the type and content of minerals precipitated during the process of coal ash cooling was obtained.The results showed that CaCO₃ can improve the viscosity characteristics of coal ash.With the increase of CaCO₃ addition,the viscosity curve type gradually changed from crystal slag to glassy slag.The addition of CaCO₃ caused the SiO₂ and Al₂O₃ structures in the slag to be depolymerized and reduced the structural strength of the meshes in the slag.The compound precipitated from the molten coal ash during the cooling process was changed from mullite to anorthite,thereby improving the fluidity of the liquid slag and reducing the slag viscosity at high temperatures.?3?The effects of mixed coal on the fusion characteristics and viscosity characteristics of coal ash with high aluminosilicate content were studied.The different types of coal blending were used to obtain the types and contents of minerals in mixed coal ash at different temperatures,and the mineral types of slag were verified by X-ray diffractometer.Results showed that the ratio of mixed coal had little effect on the fusion temperature of coal ash,but it had a great influence on the viscosity curve of coal ash,especially in the area of critical viscosity temperature.The ratio of coal blending affected the type of precipitated crystals during the cooling process,resulting in significant differences in the viscosity and temperature characteristics of coal ash.?4?The high temperature rheological properties of typical gasified coal species under weak reduced atmosphere were studied.The influence mechanism of precipitated crystals on the rheology of coal ash during cooling process was studied by thermodynamic calculation method.The results showed that when the temperature was higher than liquidus temperature of coal ash,the rheological properties of coal ash were as Newtonian fluid.With the temperature transition,the precipitated crystals and the rheological properties of coal ash were transformed into plastic or pseudoplastic fluid.During the cooling process,the type of crystals precipitated in the slag had a great influence on the rheological properties of coal ash.When the mullite was first precipitated in the slag,the coal ash exhibited a Newtonian fluid form,and the anorthite was first precipitated in the slag,and the coal ash exhibits a non-Newtonian fluid form.