Relationship between Thermal Conductivity and Chemical Structures of Chinese Coals

Three different ranks of Chinese coals were investigated on the thermal conductivity and corresponding molecular structure by thermal analyzer, ¹³C NMR, and HRTEM techniques. The thermal conductivity of coals measured in room temperature first shows a decrease, then a slight increase, and finally a sharp increase with increasing coalification. Ranging from 30 to 150 °C, increasing the temperature slightly improves the thermal conductivity of coals with varying degrees. Water with a higher thermal conductivity than air contributes to the thermal conductivity of porous coal samples. The value of thermal conductivity is higher along coal bedding planes than when perpendicular to beddings, which indicates the anisotropy of coal thermal conductivity. The anisotropy degree increases with the rank of coals and is affected by clay minerals when coals adsorb water. Molecular structure analysis shows that polycondensed aromatic ring related to lattice vibration contributes to the increase of thermal conductivity. The aliphatic bridges among aromatic clusters ensure the continuity of atom vibrations and contribute to energy transport, but the free-ended side chains have the opposite effect. The relative ordered distributions of lattice fringes of anthracite, which were higher than those of bituminous coal, enhance the anisotropy of thermal conductivity.