Combustion behavior of large size coal over a wide range of heating rates in a concentrating photothermal reactor

Abstract

Combustion behaviors of large size coal pellets were studied in a novel room temperature chamber type concentrating photothermal apparatus. 4 heating rates of 4.0 °C/s, 15.1 °C/s, 52.4 °C/s and 69.4 °C/s were realized by adjusting the voltage-up rates of the heating lamps. The temperature, image, gas emission, and mass loss were synchronously detected and the reliabilities of data were strictly verified. Coal pellets presented “heterogeneous” ignition mechanism at slow (4.0 °C/s) heating rate, “joint homo-heterogeneous” at moderate (15.1 °C/s) heating rate, and “homogeneous” at sub-fast (52.4 °C/s) and fast (69.4 °C/s) heating rates. High concentrations of CO and CH4 were evident at all heating rates. The increase of heating rate accelerated all gas generation rates and leaded to the gas yield reduction of CO but rising of CO2. Kinetics studies of the reactions around the maximum mass loss rate were carried out ultimately. 1-dimensional diffusion mechanism model (D1) showed best correlation coefficients with the reactions at slow, moderate and sub-fast heating rates and the apparent activation energies slightly decreased from 84.45 and 66.18 to 62.28 kJ/mol. The fitting curve of reactions at fast heating rate was two-stage-style and correlated best to the 3-dimensional diffusion mechanism model based on Jander equation (D3) with activation energies of 33.74 and 11.54 kJ/mol.