Abstract
Coal blending is an effective way to organize and control coal ash fusibility to meet different requirements of Coal-fired power plants. This study investigates three different eutectic processes and explains the mechanism of how coal blending affects ash fusibility. The blended ashes were prepared by hand-mixing two raw coal ashes at five blending ratios, G:D = 10:90 (G10D90), G:D= 20:80 (G20D80), G:D = 30:70 (G30D70), G:D = 40:60 (G40D60), and G:D = 50:50 (G50D50). The samples were heated at 900 °C, 1000 °C, 1100 °C, 1200 °C, and 1300 °C in reducing atmosphere. XRD and SEM/EDX were used to identify mineral transformations and eutectic processes. The eutectic processes were finally simulated with FactSage. Results show that the fusion temperatures of the blended ashes initially decrease and then increase with the blending ratio, a trend that is typical of eutectic melting. Eutectic phenomena are observed in D100, G10D90, and G30D70 in different degrees, which do not appear in G100 and G50D50 for the lack of eutectic reactants. The main eutectic reactants are gehlenite, magnetite, merwinite, and diopside. The FactSage simulation results show that the content discrepancy of merwinite and diopside in the ashes causes the inconsistent eutectic temperatures and eutectic degrees, in turn decrease the fusion temperature of the blended ash and then increase them with the blending ratio.
Highlights
Coal-fired power plants have different requirements for ash fusibility
D coal belong to high ash fusion temperature coal, but the blended ashes fusion temperatures are lower than the temperature of each of the coals
The eutectic processes in D100, G10D90, and G30D70 were simulated with FactSage based on five elements, Si, Al, Ca, Fe and Mg, and the fusibility was analyzed according to the simulation result, which makes up for the limitation of ternary phase diagram analysis
Summary
Coal-fired power plants have different requirements for ash fusibility. Solid-state slag-tap boilers generally require pulverized coal with a high ash fusion temperature to prevent slagging, whereas the liquid-state slag-tap boilers require a low ash fusion temperature [1]. Coal blending has attracted significant attention because it does not increase ash content and oxygen demand, which are its obvious advantages compared with additive blending [2,3,4]. The ash fusion temperature can be higher or lower than that of individual raw coals, not change linearly with the blending ratios [23]. The mechanism of how coal blending affects ash fusibility requires further research. The additive blending or coal blending can lower ash fusion temperature because a low-temperature eutectic mixture is generated [11,22,23,33]. Limited studies explain the detailed mechanism of how the low-temperature eutectic mixture affects ash fusibility. The simulation results were used to explain why the ash fusion temperatures initially decrease and increase with the blending ratio
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