Thermal conductivity properties of high temperature molten slag layer based on microstructure

Entrained flow gasifier is the main trend of large-scale high-efficiency coal industrial gasification technology. To ensure smooth slagging, the operation temperature of entrained flow gasifier is generally higher than the ash melting point, thereby forming a stable slag layer deposit on the wall of gasifier. The built up of the slag layer is a characteristic of the entrained-flow gasifier, and its thickness distribution and heat transfer characteristics affect the stable operation of gasification, which is closely related to the thermal conductivity of molten slag. A non-stationary hot wire experimental method and molecular dynamics simulation method were combined to investigate the thermal conductivity of the CaO-Al2O3-SiO2-MgO-Fe2O3 molten slag under its microstructure. A good agreement between the measured and calculated thermal conductivity over the entire operating temperature range is observed, and one can find that thermal conductivity of all slag samples gradually decreases as the temperature increases. A linear relationship between the logarithm of the thermal conductivity of the high-temperature slag and the reciprocal of the temperature is constructed under the determined composition. An empirical formula between the thermal conductivity and temperature and the silicon-aluminum is established when w(SiO2/Al2O3) is around 2.43. The empirical formula is verified on the actual coal ash. A good agreement within the deviation of 18% between the measured and calculated thermal conductivity over the entire operating temperature range is observed. Based on the research of the slag microstructure, it is found that the increasing temperature promotes the enhancement of slag disorder and weakens the bonding force between atoms, resulting in lengthening the interatomic distance in the tetrahedral structure. High temperature also reduces the number of bridging oxygens, and strengthens the anharmonicity of the tetrahedral structure. As a result, the thermal conductivity decreases sharply with increasing temperature and then tends to level off. © 2022, Editorial Office of Journal of China Coal Society. All right reserved.