(60e) Pulverized Coal Pyrolysis & Gasification in N2/O2/CO2 Atmospheres by Thermo-Gravimetric Analysis

The combustion characteristics of Datong coal in the different N2/O2/CO2 environments have been extensively studied by using thermo-gravimetric technique. The effects of combustion environment, oxygen and CO2 concentrations, pyrolysis conditions, particle size and different heating rates were considered. Results showed that, at each temperature zone, the mass loss rate of coal pyrolysis in CO2 environment is higher than that in N2 environment. This may be due to the division of CO2 pyrolysis process into three stages: moisture release, devolatilization and char gasification by CO2 at higher temperature zone or due to the formation of perfectly hexagonal structure of coal. However, the burning process of coal in O2/CO2 environment is almost same compared with that in O2/N2 environment for equivalent oxygen concentrations but slightly lesser than O2/N2 environment at the end of the process. With the increase of oxygen concentration, the burning rate of coal increases and burnout time is shortened. Among the different pyrolysis temperatures, 500 oC was found to be the best temperature as the ignition point in the O2/CO2 atmosphere lies near or just after this temperature. Moreover, the surface area produced by this char at this temperature was much higher in CO2 atmosphere (400 m2/g) than N2 (52 m2/g). This simultaneous process of pyrolysis and gasification seems to be advantageous because of production of the nascent char in one process and avoiding of the excess use of gasifying medium from room temperature to 500 oC. 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 coal. At different heating rates the values of the Arrhenius activation energy (E) and pre-exponentional factor (A) were estimated from the TGA data by applying different methods such as Freeman-Carroll, Doyle and Coats-Redfern. A trend of decrease of activation energy values were observed with the increase of different heating rates.