High ash coal pyrolysis at different heating rates to analyze its char structure, kinetics and evolved species

Abstract

Mass losses of high ash coal and the mole fractions of evolved species were measured during pyrolysis using a thermo-gravimetric analyzer (TGA) and a mass spectrometric analyzer, respectively. Coal samples of three sizes from Bilaspur, India were pyrolyzed using the TGA in an argon atmosphere under dynamic conditions at atmospheric pressure under the heating rates of 40, 100, 500, and 1000°C/min until the furnace temperature reached 1000°C and maintain the temperature to complete the pyrolysis process. The structural properties of the produced char such as pore surface area (BET) obtained by N2 adsorption method and SEM analysis were performed in order to explain the differences in structure based on char generation method. The BET surface area is increased by more than twofold when the heating rate is raised from 40°C/min to 1000°C/min. The kinetic parameters of activation energies (E) and Arrhenius constant (A) of thermal pyrolysis for different sized coal particles at various conversion levels were correlated from the thermogravimetric data under four heating rates. The dependencies of kinetic parameters on particle size and conversion levels during coal pyrolysis were estimated. The results revealed that higher pyrolysis rate of coal would greatly increase the yield of light gases such as CO, H2 when compared to slower pyrolysis process.