Study on mass transfer property of oxygen molecules and kinetic regimes of pressured pulverized coal combustion

Abstract

The effects of pressure on diffusion of oxygen molecules during the coal combustion could not be ignored. The compressibility factor of real oxygen is investigated to evaluate the deviation between real and ideal oxygen, and obtain the mean free path of real oxygen. Comparing the Knudsen pore diameter with the minimum pore diameter, it is found that with the increase of pressure, Knudsen diffusion cannot exist at low pressure and may delay to occur at higher temperature. When pressure exceeds 3.5 MPa, no Knudsen diffusion occurs within the whole temperature range of our research. Comparing the diffusion rate at 1 MPa with the burning rate, one can conclude that the combustion mainly take place on the internal and external surfaces, and the reaction is controlled by the chemical kinetics below 1400 K. When themperature is between 1400 K and 1600 K, the reaction is controlled by both the diffusion and the chemical kinetics. When the temperature is more than 1600 K, the combustion primarily happens on the external surfaces and is controlled by the diffusion.