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 N 2 and then switching N 2 to air of 150 °C. When N 2 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 N 2 or only air as the carrier gas throughout the whole retorting process cannot produce such a good effect. In this N 2 -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.