Differential heat transfer characteristics of coal macerals and their control mechanism: At the mesoscale

Abstract

The dynamic heat transfer process of coal with different macroscopic types was characterized by a thermal imaging acquisition system, and the differential control mechanism of maceral composition and distribution on coal heat transfer was revealed. The results show that the temperature distribution in bright and dull coal samples are unimodal compared with the bimodal temperature distribution in semibright and semidull coal. With the extension of the heating time, the difference of the temperature distribution in the samples are first decreased, then increased and finally decreased. According to the evolutionary characteristics of the temperature difference, the heat transfer process can be divided into four stages: rapid temperature rise, slow down, fluctuating temperature rise and dynamic equilibrium. Inertinite is heated up faster, forming a high-temperature region, and vitrinite is heated slowly resulting in a low-temperature region. The temperature rise rate and equilibrium temperature in the low-temperature region are inversely proportional to the distance from the high-temperature region. It is difficult for vitrinite to heat up as vitrinite has the largest specific heat capacity and the smallest thermal conductivity and thermal diffusion coefficient. Therefore, the heat transfer capacity of vitrinite is generally weak, featured by a lower rate of temperature transfer disturbance.