Analysis on the Governing Reactions in Coal Oxidation at Temperatures up to 400°C

Jing Zhan, Haihui Wang, Feng Zhu, Shengnan Song

State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, China.

DOI: 10.4236/ijcce.2014.32003                

Abstract

The present study aims to further understanding of the principal reactions that occur during coal oxidation at moderate temperatures. Mass change and heat evolution of a sample were monitored by thermo-gravimetric analysis coupled with differential thermal analysis (TGA/DTA). Gaseous and solid products were traced using online or in situ Fourier trans- form infrared spectroscopy (FTIR). Measurements were conducted by heating the samples up to 400?C, with the O₂ concentration in the reaction medium set at 0, 10, 21, and 40 vol%, respectively. It was observed that the mass increase of a sample between 150?C and ~275^oC was a result of the accumulation of C=O containing species in the coal structure, whereas substantial mass loss and heat evolution of a sample at ~400^oC can be attributed to the significant involvement of the direct “burn-off” reaction. Enrichment of O₂ inthe reaction medium leads to the acceleration in oxygen chemi- sorption, formation and decomposition of the solid oxygenated complexes, as well as the “burn-off” reaction. With the temperature increasing, the oxidation process governed by oxygen chemisorption gradually shifts to that by significant decomposition reactions, and eventually to that by the direct “burn-off” reaction. Temperature boundaries of these stages can be determined using parameters defined based on a set of TG/DTA data. Shift in the governing reactions is essentially due to the diverse requirements of reactants of the reactions and their energy barriers to be overcome. In en- gineering practice, the phenomena of self-heating and spontaneous combustion of coal correspond to chemisorption and the direct “burn-off” reaction, respectively.

Keywords

Coal; Oxidation at Moderate Temperatures; Reaction Product; Governing Reaction; Self-Heating; Spontaneous Combustion

Conflicts of Interest

The authors declare no conflicts of interest.

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