Retorting Oil Shale by a Self-Heating Route

Retorting is a frequently used method for producing shale oil from oil shale. During retorting, heat is usually supplied to the retort by heat-carrier gas of high temperature, such as 700 °C, until retorting ends. In this work, a low-energy-input retorting process using low-temperature carrier gas but without marked loss in oil yield was achieved by a self-heating effect, that is, spontaneously increasing retorting temperature in the absence of external heat provision. The self-heating retorting process starts by preheating oil shale from room temperature to 300 °C by external heating under N2 and then switching N2 to air of 150 °C. When N2 is replaced by air, the self-heating effect starts. Subsequently, the temperature of raw oil shale can increase spontaneously to complete the retorting, so that an external heat supply is no longer required. While using only N2 or only air as the carrier gas throughout the whole retorting process cannot produce such a good effect. In this N2-air sequence retorting process, because an external heat supply is needed only to preheat the raw oil shale to 300 °C (i.e., the required energy input and external-heating terminal temperature are low), the retorting process is significantly simplified. The present work provides a promising starting point for the further development of not only ex situ (aboveground) but also in situ (underground) retorting for the production of shale oil.