Kinetic characteristics and product distribution of tar-rich coal in-situ underground pyrolysis: Influence of multifunctional proppants

An iron-based multifunctional proppant was developed to enable in-situ pyrolysis of tar-rich coal underground. Thermogravimetric experiments were conducted to deeply explore the influence mechanism of the multifunctional proppants on the pyrolysis of tar-rich coal. By calculating the comprehensive pyrolysis index, it is found that the comprehensive pyrolysis index is increased from 1.13 × 10⁻⁸/%²·min⁻²·°C⁻³ to 1.309 × 10⁻⁸/%²·min⁻²·°C⁻³ by multifunctional proppants. The macro activation energy of pyrolysis weight loss of tar-rich coal is calculated by KAS model and DAEM model. Experimental findings reveal a reduction in activation energy enabled by multifunctional proppants. In addition, the distribution of pyrolysis products and tar components was analyzed through pyrolysis experiments in the tube furnace. Experimental results revealed a 10.5 % enhancement in the light fraction content of tar following the addition of multifunctional proppants. DTG curves peak fitting revealed the action mechanism of multifunctional proppants during pyrolysis reaction stages. Pyrolysis reaction pathways for tar-rich coal in the presence of multifunctional proppants were analyzed. Catalysis of tar upgrading by multifunctional proppants during tar-rich coal pyrolysis is supported by experimental findings. In particular, the Fe₂O₃-loaded multifunctional proppants hold significant potential for underground in-situ pyrolysis of tar-rich coal.