Experiments on the effect of the pressure on the mineral transformation of coal ash under the different reaction atmosphere

Abstract

This paper investigated the effect of the pressures, reaction atmospheres and coal ash species on the ash fusibility with high-pressure thermogravimetric analysis (PTGA) apparatus and X-ray diffraction (XRD) analysis. Each specimen analyzed by XRD was observed for the mineral conversion and formation of new minerals with the pressures under different atmospheres. These results indicate that the pressure restrains the transformation and decomposition of minerals. Many low-temperature minerals are still present under the elevated pressure. The different reaction atmospheres have different effects on the formation of coal ash minerals. Under the N₂ atmosphere, the present microcline may decrease the melting temperature of coal ash. And later, it transforms into sanidine at high pressure; thus, the melting temperature of coal ash may increase. Under the CO₂ atmosphere, the minerals such as microcline, lomonitite, geothite and illite are still present with the increase in pressure; this may reduce the melting temperature. While under the H₂O atmosphere, there are magnetite and anorthoclase, which may produce the low-temperature eutectics decreasing the melting temperature. The coal ash abundance in basic oxides or higher SiO₂, Fe₂O₃, K₂O and Na₂O has lower melting temperature. While the ash sample with more SiO₂ and Al₂O₃ and less Fe₂O₃ and basic oxides may lead to higher melting temperature.

Keywords

ash fusibility / XRD analysis / PTGA / low-temperature eutectic

References

[1] Gupta S K, Gupta R P, Bryant G W, Wall T F. The effect of potassium on the fusibility of coal ashes with high silica and alumina levels. Fuel, 1998, 77(11): 1195–1201

[2] Ninomiya Y, Sato A. Ash melting behavior under coal gasification conditions. Energy Convers, 1997, 38(10-13): 1405–1412

[3] Yang J G, Deng F R, Zhao H, Cen K F. Mineral conversion and microstructure change in the melting process of Shenmu coal ash. Asia-Pac J Chem Eng, 2007, 2(3): 165–170

[4] Van Dyk J C, Benson S A, Laumb M L, Waanders B. Coal and coal ash characteristics to understand mineral transformations and slag formation. Fuel, 2009, 88(6): 1057–1063

[5] Vandyk J C, Melzer S, Sobiecki A. Mineral matter transformation during Sasol-Lurgi xed bed dry bottom gasification-utilization of HT-XRD and FactSage modelling. Minerals Engineering, 2006, 19(10): 1126–1135

[6] Bai J, Li W, Li B Q. Characterization of low-temperature coal ash behaviors at high temperatures under reducing atmosphere. Fuel, 2008, 87(4-5): 583–591

[7] Reifensteina A P, Kahramanb H, Coina C D A, Calos N J, Miller G, Uwins P. Behaviour of selected minerals in an improved ash fusion test: quartz, potassium feldspar, sodium feldspar, kaolinite, illite, calcite, dolomite, siderite, pyrite and apatite. Fuel, 1999, 78(12): 1449–1461

[8] Stanislav V V, Kunihiro K, Shohei T, Takashi T. Influence of mineral and chemical composition of coal ashes on their fusibility. Fuel Processing Technology, 1995, 45(1): 27–51

[9] Yang J K, Xiao B, Boccaccini A R. Preparation of low melting temperature glass-ceramics from municipal waste incineration y ash. Fuel, 2009, 88(7): 1275–1280

[10] Wu X J, Zhang Z X, Piao G L, He X, Chen Y S, Mori S, Kobayashi N, Itaya Y. Behavior of mineral matters in Chinese coal ash melting during gasification reaction char-CO₂/H₂O. Energy & Fuels, 2009, 23(5): 2420–2428

[11] You J L, Jiang G C, Xu K D. Temperature dependence of the Raman spectra of Na₂Si₂O₅. Chinese Physics Letters, 2001, 18(3): 408–410

Acknowledgements

The authors acknowledged this work supported by the National Basic Research Program of China (Grant No. 2005CB221201). The authors acknowledged the contributions made by the members of State Key Laboratory of Clean Energy Utilization.

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg