Influence of Coal Blending on Ash Fusibility in Reducing Atmosphere
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.
Prediction of Chinese Coal Ash Fusion Temperatures in Ar and H2 Atmospheres
The ash fusion temperatures (AFTs) of 21 typical Chinese coal ash samples and 60 synthetic ash samples were measured in Ar and H{sub 2} atmospheres. The computer software package FactSage was used to calculate the temperatures corresponding to different proportions of the liquid phase and predict the phase equilibria of synthetic ash samples. Empirical liquidus models were derived to correlate the AFTs under both Ar and H{sub 2} atmospheres of 60 synthetic ash samples, with their liquidus temperatures calculated by FactSage. These models were used to predict the AFTs of 21 Chinese coal ash samples in Ar and H{sub 2} atmospheres, and then the AFT differences between the atmospheres were analyzed. The results show that, for both atmospheres, there was an apparently linear correlation and good agreement between the AFTs of synthetic ash samples and the liquidus temperatures calculated by FactSage (R > 0.89, and {sigma} < 30{sup o}C). These models predict the AFTs of coal ash samples with a high level of accuracy (SE < 30{sup o}C). Because the iron oxides in coal ash samples fused under a H{sub 2} atmosphere are reduced to metallic iron and lead to changes of mineral species and micromorphology, the AFTs in amore » H{sub 2} atmosphere are always higher than those with an Ar atmosphere. 34 refs., 9 figs., 7 tabs.« less
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