Modelling of non-consolidated oil shale semi-coke forward combustion: Influence of carbon and calcium carbonate contents

Abstract

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.

Darcy Scale Modeling of Smoldering: Impact of Heat Loss

“…The experimental results suggest that important heat losses occur at the cell walls as pointed out before. Therefore, a 2D model and not a simpler 1D model like in Fadaei et al (2012) was developed. As the insulating layer around the medium is taken into account, the model is indeed expected to bring insights to explain the observed radial temperature gradients and front curving.…”

“…This remains an indication of the possible effects of both density and viscosity on the front shape. But, in the past, this was mentioned in Fadaei et al (2012), as well as channeling effects. Even if we exhibit that heat losses are the main phenomenon explaining front curvature, they generate on the fluid properties two important effects:…”

“…They clearly demonstrate, using simplified chemistry, the competitive effect between residence time of oxygen in the front and the thermal equilibrium to maintain the combustion process. Increasing the flow rate could lead to unburned carbon and then to transition in thermal wave temperature as in Elayeb (2008). In turn, the front velocity depends on a number of parameters.…”

“…Usually, we lump all of the reactions representing the carbon oxidation process into a simplified model. This has been done in Martins et al (2010) and Fadaei et al (2012). A global description of this very complex process can be given as:…”

“…In addition, to our knowledge, none of the currently available models properly takes into account the heat loss. Heat loss is described as a volumetric sink term in 1D (Fadaei et al, 2012) or as a prescribed heat flux on the external boundary in 2D (Hasan et al, 2011;Maerefat et al, 2015). One should note that these prescribed heat fluxes have to be experimentally monitored, then provided to the model, which hinders the model's actual predictive culpabilities.…”