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This paper proposes a novel energy-efficient oil shale pyrolysis process triggered by a topochemical reaction that can be applied in horizontal oil shale formations. The process starts by feeding preheated air to oil shale to initiate a topochemical reaction and the onset of self-pyrolysis. As the temperature in the virgin oil shale increases (to 250–300°C), the hot air can be replaced by ambient-temperature air, allowing heat to be released by internal topochemical reactions to complete the pyrolysis. The propagation of fronts formed in this process, the temperature evolution, and the reaction mechanism of oil shale pyrolysis in porous media are discussed and compared with those in a traditional oxygen-free process. The results show that the self-pyrolysis of oil shale can be achieved with the proposed method without any need for external heat. The results also verify that fractured oil shale may be more suitable for underground retorting. Moreover, the gas and liquid products from this method were characterised, and a highly instrumented experimental device designed specifically for this process is described. This study can serve as a reference for new ideas on oil shale in situ pyrolysis processes.

As the simplest conversion route, combustion is extensively applied to oil shale utilization. To improve oil shale conversion techniques, we used non-isothermal thermogravimetric analysis to explore the combustion reactivity and kinetics of Huadian oil shale at various oxygen concentrations (10, 20, 30, 50, 65, and 80 vol %) and heating rates (5, 10, and 20 °C min–1). With an increase in oxygen concentration, the combustion performances of oil shale could be significantly improved; the volatile-releasing temperature, ignition temperature, and burnout temperature decreased; the mass loss rate increased; and the integrated combustion characteristics of oil shale were enhanced. These improvements were attenuated when the oxygen concentration exceeded 50 vol %. When the oxygen concentration increased from 10 to 80 vol %, the average activation energy in the second combustion stage increased from 46.85 to 117.98 kJ mol–1 by the Kissinger–Akahira–Sunose method, from 46.85 to 117.98 kJ mol–1 by the Starink method, from 59.08 to 129.17 kJ mol–1 by the Friedman method, and from 36.34 to 57.58 kJ mol–1 by the Coats–Redfern method at a heating rate of 20 °C min–1. Results indicated oxygen enrichments beyond which additional enrichment yields significantly less enhancement to the combustion process.

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