Experimental study on CO and CO2 emissions from spontaneous heating of coals at varying temperatures and O2 concentrations

Abstract

Laboratory experiments were conducted to investigate carbon monoxide (CO) and carbon dioxide (CO2) emissions from spontaneous heating of three U.S. coal samples in an isothermal oven at temperatures between 50 and 110 °C. The oxygen (O2) concentration of an oxygen/nitrogen (N2) mixture flowing through the coal sample was 3, 5, 10, 15, and 21%, respectively. The temperature at the center of the coal sample was continuously monitored, while the CO, CO2, and O2 concentrations of the exit gas were continuously measured. The results indicate that the CO and CO2 concentrations and the CO/CO2 ratio increased when the initial temperature was increased. As the inlet O2 concentration increased, the CO and CO2 concentrations increased, while the CO/CO2 ratios tended to converge to the same value. The ratio of CO/CO2 was found to be independent of coal properties, approaching a constant value of 0.2. The maximum CO production rate correlated well with the maximum coal temperature rise. The apparent order of reaction for coal oxidation was estimated to be between 0.52 and 0.72. The experimental results in this study could be used for early detection and evaluation of a spontaneous heating in underground coal mines.

The influence of oxygen concentration on the composition of gaseous products occurring during the self-heating of coal and wood sawdust

“…At the end of measurements, the concentrations of carbon monoxide were 120 ppm (at 15% of oxygen in air) and 152 ppm (at 21% of oxygen in air). The finding that more carbon monoxide results from the heating of coal at 21% of oxygen in air, compared to 15% of oxygen in air, corresponds to the findings stated in Yuan and Smith (2013). Based on the results, it can be stated that the oxygen concentration influences substantially the amount of products of low-temperature oxidization of coal, since higher concentrations were registered for the sample exposed to 21% of oxygen, for the whole time of measurement.…”

“…That is why it can be used for the assessment of the influence of oxygen concentration on the two materials. The use of the ratio of CO concentration to CO 2 concentration after their becoming steady after two and more hours is stated in Yuan and Smith (2013) in connection with the use of this ratio for early detection of self-ignition.…”

“…However Veznikova (1993), Davidi et al (1995), Lohrer et al (2005), Malow and Krause (2008) and Yuan and Smith (2013) also looked at coal with lower oxygen concentrations. Nitrogen is sometimes used in storage and processing of solids to reduce the oxygen concentration.…”

“…The change of carbon monoxide and carbon dioxide when heating coal in the temperature range from 50 to 110 • C at 3, 5, 10, 15, and 21% of oxygen in air was established by Yuan and Smith (2013). The concentration of carbon oxides rises slowly at 3-15% of oxygen in air, while it rises rapidly at 21%.…”

Numerical and experimental simulation of spontaneous combustion of coal

“…Experimental simulation is undoubtedly the most effective way to study the formation characteristics and the evolution law of coal self-heating. However, as there are extremely complex internal and external factors, a small-scale experimental method can better reveal the thermodynamics characteristics, temperature variation, and law of production for indicator gases, although it cannot monitor the position of the fire source due to passive heating or altering the external environment [4][5][6][7][8]. A largescale test of the spontaneous heating of coal can well simulate the field conditions and investigate the coal oxidation and exothermic features [9].…”