One technique used to recover oil from ground oil shale, or to burn oil shale semicoke, consists of propagating a smoldering front through a packed bed. One drawback of this technique is that the mineral structure of the shale is decarbonated due to the high temperature of the front. This phenomenon causes 70% of the CO 2 emissions released during such processes. The remaining 30% result from the fixed carbon oxidation. With the aim of decreasing the front temperature and thus avoiding decarbonation at the front passage, the impact of two parameters was experimentally tested in this work: first, increasing the amount of carbonates, as they may play the role of a heat sink, and second, decreasing the amount of fixed carbon in the medium. It is shown that increasing the amount of carbonates can only decrease the front temperature to 800°C but not lower, which is still too high to avoid decarbonation. On the other hand, the front temperature can be decreased enough for decarbonation to be almost completely avoided by reducing the amount of fixed carbon. At the low temperatures reached, almost all the fixed carbon is oxidized, but not all the oxygen transported in the air is consumed by the chemical front. The velocity of the front is consequently decreased.

A one dimensional (1-D) numerical model to describe forward filtration combustion in a porous bed is proposed. The numerical model is based on mass and momentum conservation law (generalized Darcy's law). We assume local thermal equilibrium between gas and solid phases. The effect of carbon and calcium carbonate content on the propagation of the high temperature combustion front has been investigated. A simple carbon oxidation reaction, producing CO and CO 2 , describes the combustion. We found that increasing the carbon content of the bed increases the peak temperature. However, the combustion front velocity versus carbon content does not show a monotone behaviour. The front velocity increases while carbon content increases up to a certain value and then decreases. Also, we observed that higher the temperature is, stronger the calcium carbonate decomposition is. Consequently, the calcium carbonate decomposition is closely linked to the peak temperature. Moreover, increasing the calcium carbonate content of the porous bed resulted a decrease of the peak temperature. These results as well as the composition of produced gases are consistent with the previous published experimental study. Results of this paper show that using a 1-D model with a simple reaction scheme for combustion and for calcium carbonate decomposition produces satisfactory results for simulation of filtration combustion process.

One way of recovering oil is to propagate a co-current feed smoldering front in oil shale. This can be performed either in situ or as an ex situ process. Smoldering in oil shale semicoke achieves both thermal valorization and carbon release. In both cases, two phenomena cause CO 2 formation and release: the oxidation of fixed carbon and the decarbonation of CaCO 3 . It is shown in this work that enriching the gas fed to the front with CO 2 significantly impacts both phenomena, potentially in a positive way: (i) the oxidation of fixed carbon to CO is encouraged, leading to the production of a richer gas and limiting the amount of CO 2 formed, and (ii) the decarbonation of CaCO 3 is limited, which also contributes to reducing the formation of CO 2 .