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To explore the application prospects of higher-molecular-weight gases (HMWGs) in forecasting coal spontaneous combustion (CSC), the emission characteristics of HMWGs during the oxidation of seven bituminous coals with different degrees of metamorphism were studied using gas chromatography. By analyzing the gas samples released from the oxidation of experimental samples, a total of 20 HMWGs with hydrocarbons as the main component was detected. The concentration of HMWGs changed regularly during the oxidation of experimental samples. The concentrations of most representative hydrocarbon gases increased significantly with increasing temperature but plateaued or even decreased when the temperature exceeded about 210°C. The relationship between HMWG production and the metamorphic degree indicators was nonlinear. The volatile matter content and vitrinite reflectance of coal cannot be used directly to evaluate HMWG production. The initial appearance temperatures of HMWGs during the oxidation of different coal samples also varied. The accuracy of CSC forecasting technology can be significantly improved if HMWGs are used as complementary index gases to forecast the different development stages of bituminous CSC. [ABSTRACT FROM AUTHOR]

Decomposition of oxygen-containing functional groups simultaneously produces CO and CO2, accompanied by the generation of active sites. Two different methods were applied in the study to speculate the kinetics of gas generation and the formation of active sites in coal pyrolysis. The evolution of CO and CO2 gas generation during isothermal pyrolysis under different temperatures was first analyzed, and the generation of CO and CO2 in the pyrolysis process was divided into three stages: the rapid decline stage, slow decline stage, and stabilization stage. In the early stage of the pyrolysis reaction, functional groups exhibited a rapid decomposition rate and a high conversion rate ($$a$$ a), which rapidly decreased the gas concentrations. With increasing pyrolysis time, the decomposition of functional groups declined with a low conversion rate ($$a$$ a) and showed a steady reaction rate in the later stage. On this basis, a method to calculate the activation energy during pyrolysis based on the data of gases generated in a steady period with a continuous cooling temperature was proposed. Activation energies of 70.12–148.39 kJ/mol for the CO formation and 64.47–127.38 kJ/mol for the CO2 formation were obtained from four different coals. In addition, a thermogravimetric analyzer was used to explore the apparent activation energies in the decomposition process via Coats-Redfern (C-R) method; activation energies of 39.33–126.65 kJ/mol and pre-exponential factors of 1.31–5.15E+08 s−1 were obtained for different coals. The results revealed that the CO had a greater generation activation energy than CO2, and a higher metamorphism degree implies a higher decomposition activation energy, which indicates that the decomposition of carboxyl groups and low-rank coals result in higher active sites. [ABSTRACT FROM AUTHOR]

High temperature causes thermal damage to coal, alters its pore-fracture structure, and then influences its permeability and spontaneous combustion characteristics. In this paper, to study the evolution law of coal pore-fracture in the thermal damage process and the influence mechanism of thermal damage on pore-fracture development, the microfracture evolution characteristics and pore morphology of coal samples treated under different temperatures were qualitatively studied by susing a scanning electron microscope (SEM). Besides, the evolution of coal pore structure as a function of temperatures in the heating process was quantitatively studied based on Nuclear magnetic resonance (NMR) technique. In addition, the pore structure of coal samples was quantitatively characterized in combination with the fractal theory, and the variation of fractal dimension of coal sample pore structure with heat treatment temperature was obtained. The results show that after heat treatment, the development of fractures of coal was promoted, and the connectivity between the fractures was effectively enhanced. Moreover, the higher the temperature is, the more favorable it is for the development, expansion, and connectivity of fractures and for the formation of microfracture networks in coal. The high-temperature thermal damage changes the pore structure of coal, increases the pore volume and porosity of coal and enhances the pore connectivity. Moreover, after high-temperature heat treatment, the pore structure of DL coal with low metamorphism changed more significantly than that of XG coal. The porosity of DL coal and XG coal increased with the rising temperature, while the pore fractal dimension DmNMR, DMNMR, and DNMR of the two kinds coal samples show the opposite trend. Furthermore, the variation amplitude of DmNMR is significantly larger than that of DMNMR, and the variation of three fractal dimensions of DL coal is larger than that of XG coal. The research results can support a reference for coal fire prevention. [ABSTRACT FROM AUTHOR]

The Neoproterozoic tectonic evolution of the Jiangnan Orogen is controversial, with one of the issues being whether the ca. 850-820-Ma granitoids were generated by mantle plumes or the collision between the Yangtze and Cathaysia blocks. This paper tackles this problem by examining the age and petrogenesis of one of the granitoids, the Getengling pluton in the central Jiangnan Orogen, and through comparison with a regional geochronological-geochemical database compiled from previous studies. The Getengling pluton is characterized by high A/CNK values (~1.5), slight negative whole-rock εNd(t) values (−2.8 to −3.4), and positive zircon εHf(t) values (0.7 ± 1.1), suggesting S-type granite affinities with juvenile contributions. Rb/Sr, Rb/Ba, and high CaO/Na2O ratios indicate psammitic sources with both clay-rich and clay-poor characters. These geochemical characteristics are distinct from those of the granitoids (typically of A type) associated with mantle plumes. The zircon laser ablation-inductively coupled plasma-mass spectrometry U-Pb age of 845 ± 4 Ma obtained in this study, together with other ca. 835-820 Ma ages of S-type granites in the Jiangnan Orogen, indicates that the felsic magmatism in the Jiangnan Orogen lasted for ca. 25 Ma, which is longer than typical plume-related felsic magmatism. In addition, the mafic rocks in the Jiangnan Orogen and elsewhere in the South China Block are geochemically distinct from the coeval mantle plume-related ones in Australia and west Laurentia. In geochemical diagrams diagnostic of tectonic settings, the Getengling pluton and other ca. 850-820 Ma intrusions plot in the syn- and post-collisional fields, whereas the pre-850 and post-820-Ma igneous rocks plot in the arc and within-plate settings, respectively. This sequential tectonic evolution from plate subduction through collision to within-plate environments further supports the hypothesis that the ca. 850-820-Ma granitoids in the Jiangnan Orogen resulted from the Yangtze-Cathaysia collision rather than from mantle pluming. [ABSTRACT FROM AUTHOR]

As an important part of coal, the existence of soluble organic matters (SOMs) has its own impact on the number of active groups within coal and its pore and fracture structure, which have influence on both spontaneous combustion and inhibitory effect of coal. But some in-depth researches are still lacking on this matter. On the basis of testing the composition of SOMs and analyzing the change of coal’s pore and fracture structure, we conducted an oxidation experiment on model compounds stimulating SOMs, and coal’s spontaneous combustion inhibition experiment before and after extraction. By testing characterization parameters like oxygen consumption rate, activation energy, inhibition rate, and the crossing point temperature, we analyzed how SOMs make a difference on spontaneous combustion and inhibitory effect of coal. It shows that, after the extraction of SOMs, both the amount and rate of oxygen consumption of coal goes down, while the activation energy of coal ascends after extraction. Once being added with model compounds stimulating SOMs, coal’s oxidation degree increases. Between 50°C and 140°C, the inhibition rates of ZHCM, ZHYM, and CTM range from 50.7% to 71.2%, 40.1% to 52.0%, and 18.1% to 27.6%, respectively, and residual coals’ inhibition rates surpass raw coals’ inhibition rates. The crossing point temperature of ZHCM reached 122.5°C, 35.2°C higher compared to that of YM. This shows that adding inhibitors after extract can have a strong effect on restraining coal’s spontaneous combustion. Through free radical reaction and oxidation reaction, SOMs would release the heat to hasten the coal’s oxidation process. After extraction, coal’s permeability increases, which makes it easier for an inhibitor to seep into coal, thereby restraining the intensity of coal’s oxidation. [ABSTRACT FROM PUBLISHER]

Analysis on the source of CO is very important for prevention of coal spontaneous combustion. In this article, a method of identifying primary CO in coal seams based on an oxygen isotope method is proposed through research. Tests on the oxygen isotopes (δ18O) of CO were generated in coal oxidization reaction and coal pyrolysis reaction. It is found that δ18O of CO will reduce with rising temperature in both reactions, with δ18O of CO being 15–20‰ in air atmosphere and that being 25–28‰ in argon atmosphere in the temperature range of 130–220°C, confirming that the sources of oxygen atoms of CO vary with different atmospheric conditions. Through collecting and testing a number of gas samples from the coal seam and roof in the coal mine, their δ18O of CO is found to be 35.2–37.3‰. The result would improve the prevention of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]