The structure of a combustion front propagating in a fixed bed of crushed oil shale : co-current configuration

摘要

The structure of a combustion front propagating in a fixed bed of crushed oil shale: co-current configuration. The propagation of a combustion front in reactive porous medium involves thermal, chemical and fluid flow mechanisms, with strong couplings. In order to describe the thermal and chemical structure of the combustion front, a new experimental device, finely instrumented, allowing to carry out 1D experiments in co-current combustion was designed and developed. To validate the combustion cell, a porous medium model - a mix of charcoal/sand was used. This fixed bed down flow reactor is equipped with an original system that allows micro sampling gas within the combustion front. For the experiments with the oil shale from Timahdit in Morocco, it was crushed and sieved into particle size at 500-1000 µm and mixed with sand. The combustion was carried out at air velocity of 0.024 m s-1 at STP. The front propagates at 6.13x10-5 m s-1 and its temperature peak is 1100 °C. A mass balance was made based on a detailed chemical and physical characterization of the medium, its solid residue after combustion and flue gas. The organic matter is converted into 1/4 of fixed carbon – which the oxidation reactions provide the energy to propagate the front -1/4 into pyrolysis gas and 1/2 into oil. A two temperature numerical model developed by IMFT was validated. Combining, experimental and numerical approach made it possible in fine to evaluate the thickness of the different reaction zones: oil shale devolatilization, fixed carbon oxidation and CaCO3 decarbonation. A parametric study varying the air velocity and particle size is finally proposed