Effect of Quenching Temperatures on Melting Characteristics of Coal Ash in a Reducing Atmosphere

Abstract

Two representative Chinese bituminous coals (one with rich Ca content, having a low melting temperature, and the other with rich Fe content, having a high melting temperature) were selected for this study to investigate the effect of quenching temperatures on melting characteristics of coal ash in a reducing atmosphere (6:4 CO/CO2). The final structures were characterized by X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray (SEM–EDX), and differential thermal analysis (DTA). The results show that, with the quenching temperature increasing, the crystalline volume percentage experiences a maximum value. However, the thermal properties (the glass transition temperature and the melting temperature) determine the maximum crystalline volume percentage temperature. There is a large variation in the phase compositions with an increase of the quenching temperatures, but the maximum diffraction peak intensities of most minerals simultaneously occur. A comparison of the coal ash samples after quench and direct heat treatment shows that there is a low crystalline volume percentage and simple phase compositions for the quenching process at corresponding temperatures, which are due to a preheat treatment at high temperatures prior to quench. Anorthite can form a better crystal shape in the coal ash sample with a low melting temperature and high Ca content for the quenching process. The diffusion controls the dissolution of the Fe–O particle, especially for the high melting temperature coal ash with a high Fe content.

Influence of isothermal temperature and cooling rates on crystallization characteristics of a synthetic coal slag

“…The temperature has a greater influence in the high temperature region with a more significant increase in crystal formation when cooled from 1250 to 1200°C than in the low temperature region in which viscosity is more significant. This increasing tendency seems contrary to a previous study of quenching a slag sample in which a maximum crystalline volume occurred as temperature decreased [5]. However, as mentioned before, the crystals are likely two different phases under high and low temperature.…”

“…Despite increasing attention on crystals in coal slags, the effects of factors such as temperature and cooling rate [4][5][6] on crystallization behavior have not been extensively studied. Several researchers [5,11] have investigated the influence of quenching temperature on crystallization of coal slags through semi-quantitative analysis of XRD to determine the volume of crystals. But more quantitative methods developed for study of other types of slags with similar composition can also be applied.…”

Phase Change Cooling and Crystallization Characteristics of Blast Furnace Slags with Various MgO/Al2O3 Ratios

“…For the BF slag cooling process, it has to be noted that the main components (CaO, SiO 2 , MgO, and Al 2 O 3 ) of BF slag significantly affect the physical parameters and crystallization characteristics. , Furthermore, the main components of BF slag vary with time due to the variation of the iron ore composition and blast furnace operating conditions. , Consequently, a good understanding of the effects of the main components of BF slag on the coupling relationship between the BF slag phase change cooling and crystal phase evolution is essential and crucial to achieving the simultaneous collection of high-performance glassy slag and high temperature air during the dry heat recovery process. Until now, the effects of the main components of the slag on the crystallization behaviors have been widely investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), − and the single/double hot thermocouple technique (S/DHTT). ,, Recently, the research of Qin et al indicated that the lower contents of CaO and MgO and higher contents of SiO 2 and Al 2 O 3 were beneficial to form the crystal phase in the BF slag. However, it should not be neglected that the variation of other components was inevitable when the content of one component is varied to explore its effect on the crystallization behaviors of slag.…”