Retorting Oil Shale by a Self-Heating Route

Abstract

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-energyinput 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.

Identifying the reaction mechanism of oil-shale self-heating retorting by thermal analysis techniques

“…The strongest peak at 1033 cm À1 , the bands of low wavenumbers at 797, 694, 532 and 469 cm À1 as well as the bands near 3620 and 3710 cm À1 are all attributed to mineral matter, such as the OH stretching in kaolinite and Si-O bond [33]. The main bands associated with kerogen are at 2923 and 2851 cm À1 and they are attributed to the characteristic peaks of aliphatic C-H bonds [18][19][20]33], indicating that the kerogen mainly consists of aliphatic alkyl groups [34]. It can be seen from Fig.…”

“…The first weight-loss region around $250-500°C is dominated by the desired pyrolysis of kerogen [31]. The second weight-loss region located above 650°C is dominated mainly by the decomposition of carbonates such as calcite in the [31,18]. However, there are some obvious differences between anaerobic and aerobic processes.…”

“…This means that almost all the kerogen is consumed by reacting with air, however, practical SHR shows no marked loss in shale-oil yield as compared to anaerobic retorting [18][19][20]. To investigate the reason, the OS fine powder, used for thermal analysis with a < 70 lm particle size (Fig.…”

“…In SHR process, because external heat supply is needed only for preheating raw OS to $300°C (i.e., the required energy input and external-heating terminal temperature are low), the retorting process is much simplified. Moreover, the study on the composition of shale oil showed that the oil still mainly consists of various hydrocarbons, like that obtained from anaerobic process [18][19][20], indicating that SHR does not cause an obvious oxidation of the obtained oil.…”

“…Independent from Sun et al, our group developed a low-energy-input retorting route but without marked loss in the shale-oil yield [18][19][20], which is achieved by spontaneously increasing retorting temperature in the absence of external heat supply. This self-heating retorting (SHR) process starts with preheating OS from room temperature to 300°C by external heating in N 2 and then switching N 2 into air of 150°C (or preheating OS to 350°C by external heating in N 2 and then switching N 2 into air of room temperature).…”