Search

In order to investigate the microscopic physicochemical properties and macroscopic coal-oxygen complex thermal effects in the low-temperature oxidation of coal under gas atmosphere, different metamorphic coal and secondary oxidized coal samples as research objects were selected in this paper. Fourier infrared spectrometer and C80 microcalorimeter were employed to study the changes of physicochemical structural properties, kinetic parameters and thermal effects in the low-temperature oxidation of coal under different gas atmospheres. By analysing the microstructure and macroscopic exothermic characteristics of different gas content during coal spontaneous oxidation, the ultimate influence of gas on the oxidation characteristics of coal was clarified. The results show that gas delays the low-temperature oxidation process of coal by inhibiting the relative content of key active groups in the low-temperature oxidation process of coal. 4% gas has the most obvious inhibitory effect. The degree of inhibition on the four active groups is: oxygen-containing functional groups (66.5%) > Aromatic hydrocarbons (47.0%) > Aliphatic hydrocarbons (29.7%) > Hydroxyl (24.7%). In the rapid exothermic stage, due to the large adsorption capacity of coal to gas molecules, gas occupies the adsorption sites in coal molecules, which hinders the process of coal-oxygen recombination reaction, resulting in the exothermic effect being suppressed by gas; at the same time, gas content significantly affects coal oxygen. The amount of activation energy required for the recombination process. For high metamorphic non-stick coal, lean coal and anthracite, gas has a more significant inhibitory effect on its low temperature oxidation reaction; it has less effect on low metamorphic long flame coal. For secondary oxidized coal samples, the inhibitory effect of gas on coal samples increases with the increase of gas content, while the effect of gas on primary oxidized coal samples decreases as the degree of metamorphism decreases, and the degree of inhibition when the gas content is 2% is stronger than 4%. The results of the work have great significance to the theoretical study of the prevention and control of the coupling of gas and coal spontaneous combustion causing accidents.

The effects of water soaking on the microstructure and spontaneous combustion characteristics of coal samples were investigated by scanning electronic microscopy (SEM), Fourier transform infrared (FTIR) spectrometer, and temperature programmed testing system (TPTS). The SEM results showed that the pore structures on the surface of water−soaked coal were more developed than raw coal, the pores increased and enlarged, and the phenomenon of water absorption swelling occurred. At the same time, water soaking had a certain influence on the functional groups in coal. The results of FTIR clearly illustrated that the surface functional groups of water−soaked coal were more active, and the contents of functional groups such as hydroxyl, methylene, aliphatic ether and aromatic ether all increased to varying degrees. During the low−temperature oxidation process, the analysis results of TPTS indicated that the oxygen consumption rate and the production of CO, C2H4, and other gases of water−soaked coal were higher. Based on the analysis method of CO, CO/CO2 and C2H4 gas growth rate, the three peaks of the curve obtained correspond to the characteristic temperatures of each oxidation stage of the coal samples. The critical temperature, dry cracking temperature and fission temperature of water−soaked coal were 60 ± 10 ℃, 90 ± 10 ℃ and 120 ± 10 ℃, respectively, which was 10 ℃ lower than raw coal. The apparent activation energy (Ea) of coal was calculated by the CO model and fitted in sections. It can be seen that the Ea of water−soaked coal at different stages of low−temperature oxidation was lower, and the maximum difference was 2.1 kJ/mol. Therefore, from the above results, it inferred that the activity of bituminous coal became stronger after soaking in water, which may be due to the effect of soaking on the surface structure and active groups of coal, thus showing a higher risk of spontaneous combustion. [ABSTRACT FROM AUTHOR]

To investigate the oxidation combustion heat effect and thermokinetic behavior of lean coal, the pulverized coal samples were tested using C80 micro caloric system and thermogravimetric experimental device, respectively. The thermal effects of lean coal samples during the low-temperature oxidation and oxidation combustion were analyzed, and the influence of the heating rate on the combustion process of lean coal was also studied. In addition, the apparent activation energy and the most probable mechanism function of the coal sample during the combustion process were analyzed. The results indicated that the low-temperature oxidation process of lean coal pulverized coal could be divided into slow oxidation, accelerated oxidation and fast oxidation stages. Moreover, the five characteristic temperature points during the oxidation combustion of pulverized coal were determined by the variations of TG/DTG curves; with the increase of the heating rate, the TG and DTG curves of the coal sample shifted to the high temperature zone, and the peak value of the DTG curve increased with the ignition temperature increased; the apparent activation energy of coal sample in the pyrolysis combustion stage described a trend of first increasing and then decreasing with the increase in the conversion rate. The maximum apparent activation energy were observed when the conversion rate is 0.2, which was 32.4 kJ/mol; heating rates had tiny effect on the most probable mechanism function of the oxidation reaction. The most probable mechanism functions of the reaction under the four heating rates were all basically in line with the A-E equation random nucleation and subsequent growth model, and the peak value of the function curve increased with the heatingrate increased.

To promote the efficient utilization of coal resources and develop the green, economic, and scientific fire-fighting technologies, current situation of coal fire disasters in China was briefly introduced, and the basic theoretical research status of coal spontaneous combustion (CSC) mechanism and characteristics are explained. A technical scheme for fire prevention at different stages is proposed. Then, this paper summarizes the technological progresses of CSC prevention, control, and fire extinguishment. Among them, prevention and control are mainly based on plugging wind, grouting and glue injection, and fire extinguishment technology is changed from water injection and grouting to inert gas. Finally, the main problems and challenges of current fire prevention and control technology, including acquisition of characteristic information of coal spontaneous combustion fire, implementation of detection means, location of fire sources, research and development of fire protection materials and equipment are summarized. The prevention and control of coal spontaneous combustion fire should follow the principles of precision, speed and intelligence, so as to realize the fundamental change from passive control to active prevention and control of coal spontaneous combustion fire.