Qi Xuyao

Changes in active functional groups during low-temperature oxidation of coal

Using Fourier Transform Infrared (FTIR) combined with an adiabatic oxidation test, temperature-programmed oxidation and gas analysis, we studied the changes of active functional groups during low-temperature oxidation of lignite, gas coal, fat coal and anthracite. During slow low-temperature heat accumulation, aliphatic hydrocarbons, such as methyl and methylene, are attacked by oxygen atoms absorbed by pores on coal surfaces, generating unstable solid intermediate carbon-oxygen complexes, which then decompose into gaseous products (CO, CO2) and stable solid complexes. At the accelerated oxidation stage, the stable complexes begin to decompose in large amounts and provided new active sites for further oxidation, while the aliphatic structures gained energy and fell from the benzene rings to produce CxHy and H2.

Characteristics of oxygen consumption of coal at programmed temperatures

Abstract Oxygen consumption is an important index of coal oxidation. In order to explore the coal-oxygen reaction, we developed an experimental system of coal spontaneous combustion and tested oxygen consumption of differently ranked coals at programmed temperatures. The size of coal samples ranged from 0.18∼0.42 mm and the system heat-rate was 0.8°C/min. The results show that, for high ranked coals, oxygen consumption rises with coal temperature as a piecewise non-linear process. The critical coal temperature is about 50 °C. Below this temperature, oxygen consumption decreases with rising coal temperatures and reached a minimum at 50 °C, approximately. Subsequently, it begins to increase and the rate of growth clearly increased with temperature. For low ranked coals, this characteristic is inconspicuous or even non-existent. The difference in oxygen consumption at the same temperatures varies for differently ranked coals. The results show the difference in oxygen consumption of the coals tested in our study reached 78.6% at 100 °C. Based on the theory of coal-oxygen reaction, these phenomena were analyzed from the point of view of physical and chemical characteristics, as well as the appearance of the coal-oxygen complex. From theoretical analyses and our experiments, we conclude that the oxygen consumption at programmed temperatures reflects the oxidation ability of coals perfectly.