Thermo-Chemo-Mechanical Modeling of Coal Pyrolysis
Résumé
This work deals with the modeling of coal pyrolysis to coke for blast furnace which corresponds to the thermal decomposition process of organic substances in the absence of air. The final aim of the European project SPRITCO which includes this work is the prediction of the coal pushing on the heating wall in the coke oven battery to prevent their damage and then to increase their lifetime. The goal of this work is to develop a thermo-chemo-mechanical model of the coal cake which emphasizes the mechanical effects of the pyrolysis. During pyrolysis, as function of temperature, 4 steps are obtained: drying, plastic phase, semi-coke and coke. Considering the structure of coal, the presence of moisture and volatile matter, fully coupled thermo-chemo-mechanical model for unsaturated porous media is used to simulate the complex coupling mechanisms involved. Transfer of heat, moisture air and volatile matter in a deformable and unsaturated medium involves interaction of three different physics (thermal, mechanical and fluid) and three different phases (solid, liquid and gas). The mathematical formulation of the problem is a set of partial differential equations that combine mass balance, energy balance, momentum balance and state laws of each phase. During coal drying, the observed mechanisms are: evaporation, condensation, phase change and temperature plateau. The second stage concerns the change from coal to plastic phase which induces a mechanical behavior evolution of the skeleton, from elasticity to viscoplasticity. Then the transformation of plastic phase to semi-coke and semi-coke to coke. The proposed presentation will fully develop a model of coal pyrolysis which predicts the pressure on the walls of a coke oven during coking.