Dynamic and kinetic studies on the oxy-coal combustion using multi-parameter high-speed diagnostics

Abstract

Non-intrusive measurement of dynamic and kinetic parameters during oxy-coal combustion has been carried out in an enclosed downward laminar flow reactor. High-speed OH-PLIF, CH* chemiluminescence, and pyrometer were used to determine the luminescence species, particle velocity, and particle temperature. A two-step model was established to predict the release of coal combustible based on the Arrhenius expression. The experimental data from traditional coal char analysis methods verified the optical kinetic model. Experiments showed that homogeneous ignition first occurred and dominated the upstream volatile combustion. The heterogeneous reaction was activated upstream due to volatile oxidization and became dominant downstream. The coal combustion formed an overlapping region between volatile and char oxidations. This region played a critical role in enhancing flame stability. The duration of the overlapping region was smaller in oxy-fuel combustion than in air-alike combustion due to the higher reaction rate and lower heat and mass diffusion. A temperature-dependent kinetic model was found to obey a two-step first-order Arrhenius expression with two pre-exponential factors (103.59±0.22 and 105.81±0.31 s−1) and two activation energies (173.1 and 278.0 kJ/mol) in air-alike combustion, and two pre-exponential factors (105.02±0.47 and 106.37±0.24 s−1) and two activation energies (217.0 and 291.1 kJ/mol) in oxy-fuel combustion. The kinetic predictions agree well with the experimental results of the combustible release in the corresponding tests.