Comparison of pulverized coal combustion in air and in O2/CO2 mixtures by thermo-gravimetric analysis

Thermo-gravimetric technique was used to study the combustion characteristics of pulverized coal in different O2/CO2 environments. The effects of combustion environment, oxygen concentration, particle size and heating rate were considered and the differences of pulverized coal pyrolysis, combustion and gaseous compounds release under two environments were analyzed. Results show that the coal pyrolysis in CO2 environment can be divided into three stages: moisture release, devolatilization and char gasification by CO2 in higher temperature zone. In the lower temperature zone, the mass loss rate of coal pyrolysis in CO2 environment is lower than that in N2 environment. The burning process of pulverized coal in O2/CO2 environment is delayed compared with that in O2/N2 environment for equivalent oxygen concentrations. With the oxygen concentration increase or the coal particle size decrease, the burning rate of coal increases and burnout time is shortened. As the heating rate increases, coal particles are faster heated in a short period of time and burnt in a higher temperature region, but the increase in heating rate has almost no obvious effect on the combustion mechanism of pulverized coal. During the programmed heating process, species in flue gas including H2O, CO2, CO, CH4, SO2 and NO were determined and analyzed using the Fourier-transform infrared (FTIR) spectrometer. Compared with pulverized coal combustion in O2/N2 environment, much more CO is produced in O2/CO2 coal combustion process, but the releases of SO2 and NO are less than those released in O2/N2 environment. The present results might have important implications for understanding the intrinsic mechanics of pulverized coal combustion in O2/CO2 environment.