Microwave-aided pyrolysis and fragmentation of tar-rich coal and rocks for in situ coal conversion and clean utilization

British Petroleum predicts that coal will account for the largest share in energy resources for power generation until 2040. The U.S. Energy Information Administration forecasts that coal will remain a key component of the country's national electricity portfolio at least until 2040. However, due to serious issues including high carbon emissions, environmental pollution, surface subsidence, resource wastage, and mining accidents associated with traditional coal mining and utilization patterns, international communities have called for the abandonment of coal use and adoption of renewable resources. To overcome the disadvantages, we proposed a novel approach for achieving in situ conversion and power generation using subsurface coal. An earthworm-shaped intelligent unmanned mining machine (IUMM) was designed to use high-power microwave energy to pulverize and py-rolyze coal into particles that can be used for power generation via chemical conversion. In this study, we used IUMM-based technology for in situ conversion and utilization of tar-rich coal and recovery of oil and gas from the coal. We quantified the pyrolysis efficiency of the tar-rich coal and the surrounding sandstone as well as the gas-liquid overflow rate of the coal under various high-power microwave irradiation conditions. The critical microwave energy threshold for discriminating tar-rich coal from the surrounding sandstone was determined, which will help to realise automatic pyrolysis of tar-rich coal by IUMM and minimise the damage caused by high-energy microwave radiation to the surrounding rock. This work aids in the production of cleaner energy, while ensuring energy security.