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Coalfield subsurface fires can result in ecological disasters of global dimensions. These fires are difficult to control therefore can result in colossal wastage of resources (the coal itself but the resources devoted to suppression), a serious negative impact on the environment and acute health problems for large populations. However, if the heat can be effectively recycled and utilized, the combustion energy will be recovered but also heat extraction can promote suppression. Thus, leading not only to a positive energy impact but to a reduction polluting emissions and consequent health issues. This paper presents the results of a feasibility analysis of the overall recovery of underground thermal resources of a novel system of Waste Heat Recovery Units (WHRUS) that combines thermosyphon and thermoelectric technologies. Both thermal equivalent model and numerical assessment are presented. A series of realistic-scale field experiment conducted in the Xinjiang's fire zone for an extended period are discussed. Using a local geothermic assessment, the heat recovered from subsurface coal fire can be estimated as the summation of the convective and conductive components of the energy generated. The average heat generated for the fire district is estimated at approximately 495 W/m 2 and the average extraction efficiency at approximately 58%. The WHRUS shows and excellent heat transfer performance with an effective lower resistance of approximately 0.0049 W/°C and maximum thermal recovery rate greater than 90%. Finally, while the thermoelectric

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To understand the adsorption mechanism of methane in heterogeneous nanopore structures of coal, integral adsorption models based on linear, exponential, hyperbolic and quadratic energy distribution functions are established. The adsorption energy domain of the new models is assumed to be a finite interval. These new adsorption models can describe both the adsorption isotherm and the adsorption heat. A volumetric method of adsorption with a microcalorimetry system is used to measure the adsorption isotherms and integral heat, and then the parameters of the new models are obtained by fitting the experimental data. Since the adsorption heat can be different for different adsorption models, it is necessary to fit the adsorption isotherms and heat simultaneously. The fitting results of the adsorption isotherms and heat show that the new models are able to describe the experimental data better than the Langmuir model. By comparing the fitting results and the effective range of adsorption energy of the different adsorption models, it is shown that the exponential energy distribution function is the most reasonable model for methane adsorption in coals, which can be used to evaluate the energetic heterogeneity of nanopores in coal samples. The decreasing exponential energy distributions of three coal samples indicate that a larger adsorption energy corresponds to fewer adsorption sites in the coal samples. The proportion of high adsorption energy is related to the micro-nanopore volume in the coal samples.

<p>In the coal fire control project, the multiple water injections used to extinguish coal fires and the coal fires that reignite can cause many forms of ground collapse to occur, threatening project safety. Therefore, studying the thermal damage and capturing disaster signals of sandstone, a main weight bearer in coal measure strata, exposed to heating-cooling, cycles is critical to ensure the engineering safety. In this work, the coal-measure sandstones from Urumqi, Xinjiang and Yulin, Shaanxi, China, were collected. For the sandstones from Urumqi, China (Type A sandstone), the samples were first heated to 800 °C, and cooled using water, heated to a setting temperature (100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C and 800 °C), and cooled using water again. The ultrasonic p-wave velocity, density and water absorption of the sandstones were tested. Uniaxial compression tests and shear tests were conducted on the sandstones. The thermal damage in sandstones were analysed using rock energy theory. For the sandstones from Yulin, China (Type B sandstone), the X-ray diffraction test, scanning electron microscope test and uniaxial compression experiment with AE monitoring were carried out for the raw sandstone and the sandstone exposed to 800 °C and water cooling twice (cooling shock sandstone), respectively. The results show that, for the type A sandstone, compared with the mechanical strength of the sandstone at room temperature, the mechanical strength of the sandstone exposed to 800 °C for the first time is decreased by less than 20%. When the sandstone is exposed to high temperature again, the critical threshold temperature is 400 °C. When the temperature exceeds 400 °C, the thermal damage aggravated again and the mechanical strength rapidly degraded. For the type B sandstone, the results showed that the crack density and volume of cooling shock sandstone increased by 8.79% and 2.69%, respectively, and p-wave velocity decreased by 51.83%, compared with those of the raw sandstone. The mechanical strength of cooling shock sandstone decreased, including a 50.68% reduction in elastic modulus. The AE attenuation coefficient<em> α=(1-E<sub>c</sub>/E<sub>0</sub>)</em> /<em>k<sub>c</sub></em>, related to the elastic modulus and the crack change rate, was derived, which providing an approach to count the attenuation of AE signal caused by thermal damage for cooling shock sandstone. Increasing the preamplifier amplification factor is feasible to improve the accuracy for monitoring the fracture of cooling shock sandstone in coal-fire control project.</p>

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