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Experimental Study on Greenhouse Gas Emissions Caused by Spontaneous Coal Combustion

Wang, Haiyan, Chen, Chen
Energy & Fuels 2015 v.29 no.8 pp. 5213-5221
air, carbon dioxide, coal, combustion, emissions factor, greenhouse gas emissions, greenhouse gases, methane, mining, oxygen, seepage, sulfur, temperature, China
There are large areas of spontaneous coal combustion in northern and northwestern China. The quantification of greenhouse gas (GHG) emissions resulting from spontaneous coal combustion is an important step toward determining proper management practices to reduce such emissions in the future. The present study investigated the GHG emission characteristics of the spontaneous combustion of 10 typical coal types. Furthermore, this study examined the estimation method applied to the GHG emissions caused by spontaneous coal combustion. The experimental results showed that the rates of CH₄ and CO₂ emissions from spontaneous coal combustion resulting from mining activities were greater than the same rates of emissions resulting from mere surface air seepage (by factors of ∼1.8 and ∼1.6, respectively). The emission rate of CH₄ was significantly correlated with the volatile content of coal, while the emission rate of CO₂ was significantly correlated with the moisture, oxygen, and sulfur contents of coal. Three different characteristic phases were observed for the emission of CH₄, with critical temperatures of 200, 400, and 600 °C, respectively. Below 200 °C, CH₄ emissions were very slow; between 200 °C and 450 °C, the emissions increased slowly; and above 450 °C, the emissions increased rapidly. Similarly, the CO₂ emissions were very low at temperatures below 200 °C, slowly grew between 200 °C and 450 °C, and quickly grew after 450 °C. The experimental emission factors of CO₂ and CH₄ caused by spontaneous coal combustion were obtained at different stages of spontaneous combustion. We subsequently determined that the annual GHG emissions from the Wuda coal field fire area of China were ∼956 700 tons of CO₂ equivalents. The results of this research offer a technical basis for quantifying GHG emissions from spontaneous coal combustion.