Comparison of pulverized coal combustion in air and in O 2/CO 2 mixtures by thermo-gravimetric analysis

Abstract

Thermo-gravimetric technique was used to study the combustion characteristics of pulverized coal in different O 2/CO 2 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 CO 2 environment can be divided into three stages: moisture release, devolatilization and char gasification by CO 2 in higher temperature zone. In the lower temperature zone, the mass loss rate of coal pyrolysis in CO 2 environment is lower than that in N 2 environment. The burning process of pulverized coal in O 2/CO 2 environment is delayed compared with that in O 2/N 2 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 H 2O, CO 2, CO, CH 4, SO 2 and NO were determined and analyzed using the Fourier-transform infrared (FTIR) spectrometer. Compared with pulverized coal combustion in O 2/N 2 environment, much more CO is produced in O 2/CO 2 coal combustion process, but the releases of SO 2 and NO are less than those released in O 2/N 2 environment. The present results might have important implications for understanding the intrinsic mechanics of pulverized coal combustion in O 2/CO 2 environment.