Experimental study on thermo-responsive inhibitors inhibiting coal spontaneous combustion

热响应阻化剂抑制煤自燃实验研究

Fuel Processing Technology, Volume 175, 15 June 2018, Pages 113-122

Chuanbo Cui, Shuguang Jiang, Hao Shao, Weiqing Zhang, Zhengyan Wu

摘要：Due to its strong fluidity and easy evaporation characteristic, high water-cut physical inhibitors (HWPIs) cause the decrease in moisture content of coal, so that its inhibitory effect on coal spontaneous combustion weakens or even fails. Aiming at solving the problem, this paper proposes to inhibit coal spontaneous combustion using thermo-responsive inhibitors (TRIs). These inhibitors are sensitive to specific temperatures and can retain their effects as long as the temperatures have not been reached. Besides, when the temperatures are reached, they are able to absorb heat and undergo physical and chemical changes to release H2O and inert gases (defined as gases that are not involved into the coal oxidation reaction in this paper) such as NH3 and CO2, so as to inhibit the low-temperature oxidation of coal. Based on the temperature-programmed experiment of coal spontaneous combustion, this paper analyzed the effects of types and amounts of TRIs on coal spontaneous combustion by using differential scanning calorimetry (DSC), scanning electron microscope (SEM), thermogravimetry-derivative thermogravimetric analysis-differential scanning calorimetry (TG-DTG-DSC) and nitrogen adsorption test methods. The results show that CaCl2•6H2O achieves the most stable inhibitory effect, as its inhibiting rate rises steadily in the heating process to reach a maximum value of 79.9% at 200 °C.

Thermogravimetric and infrared spectroscopic study of bituminous coal spontaneous combustion to analyze combustion reaction kinetics

烟煤自燃的热重-红外光谱研究及其燃烧反应动力学分析

Thermochimica Acta, Volume 676, June 2019, Pages 84-93

Xiaokun Chen, Teng Ma, Xiaowei Zhai, Changkui Lei

摘要：Thermogravimetry and in-situ Fourier transform infrared spectroscopy were used to study spontaneous combustion in bituminous coal. The results show that the coal’s spontaneous combustion can be divided into five stages, Stages I–V. Qualitative analysis of changes in the molecular functional groups allowed the chemical reactions in each stage to be deduced. Through semi-quantitative calculations of alkyl side bond length, and the degrees of aromatic condensation and oxygen enrichment degree, the critical temperature T1, mass maximum temperature T2 and ignition temperature T3 were identified as important characteristic temperature points for spontaneous combustion which shows that coal spontaneous combustion is produced by multi-stage reactions. Isoconversional calculations found that the apparent activation energies of the oxygen absorption and weight gain and slow chemical reaction stages gradually increased as the temperature increased but the apparent activation energy decreased after T3. Calculations also show that different stages have different reaction mechanism functions. Recognizing that these stages exist is important for deepening our understanding of coal oxidation reactions.

Risk assessment of gas control and spontaneous combustion of coal under gas drainage of an upper tunnel

上巷瓦斯抽采下瓦斯控制与煤自燃风险评估

International Journal of Mining Science and Technology, Volume 29, Issue 3, May 2019, Pages 491-498

Tingxiang Chu, Pin Li, Yuexia Chen

摘要：The adjustment of the gas drainage rate has an immediate impact on air leakage in gob, thus resulting in the change of self-heating of coal. While regulating the gas drainage parameters, the risk of spontaneous combustion of coal should be considered. The risk assessment of gas control and spontaneous combustion of coal under gas drainage in a tunnel was investigated at different gas drainage rates. The distributions of the air volume along the working face, the gas management effects and the width of the oxidation zone were subjected to risk analysis. As the simulation results showed, with increasing gas drainage rate, although the safety of gas dilution by ventilation was assured, the intensifying air leakage caused the oxidation zone to move into the deeper gob and led to an increase in the width of the oxidation zone. A risk assessment method was proposed to determine a suitable gas drainage rate for the upper tunnel. The correctness of the risk assessment and the validity of the numerical modelling were confirmed by the field measurements.

Novel sodium silicate/polymer composite gels for the prevention of spontaneous combustion of coal

防治煤自燃的新型硅酸钠/聚合物复合胶

Journal of Hazardous Materials, Volume 371, 5 June 2019, Pages 643-654

Xiaofeng Ren, Xiangming Hu, Di Xue, Yongsheng Li, Wei Lu

摘要：Novel gel materials are proposed for fire prevention and extinction in coal mines, where spontaneous combustion of coal continues to pose a significant risk. Cationic polyacrylamide (CPAM), anionic polyacrylamide (HPAM), and carboxymethyl cellulose (CMC) were each introduced separately into a sodium silicate (WG) gel, to obtain three gels labeled as CPAM/WG, HPAM/WG, and CMC/WG. A crosslinking agent, aluminum citrate, was subsequently added to the HPAM/WG and CMC/WG gels to afford two novel interpenetrating network hydrogels, HPAM-Al3+/WG and CMC-Al3+/WG, respectively. Among the various gels, the HPAM-Al3+/WG hydrogel exhibits the best seepage capacity, water retention capacity, compressive strength, and inhibition characteristics, which effectively resolve the post-water-loss cracking and pulverization problems commonly associated with inorganic consolidated silica gels. The microstructures of all the gels were investigated by scanning electron microscopy and their inhibitory effects on the oxidation of hydroxyl and methylene groups in coal at high temperatures were analyzed by Fourier transform infrared spectroscopy. Elemental mapping by energy dispersive X-ray spectroscopy indicated that the inorganic silica gel blends uniformly with the polymeric gel. Fire extinction experiments indicated that the HPAM-Al3+/WG gel reduces the fire-source temperature, heat radiation, and CO generation. Thus, the HPAM-Al3+/WG gel is an ideal fire prevention and extinction material.

Correlation analysis of the functional groups and exothermic characteristics of bituminous coal molecules during high-temperature oxidation

高温氧化过程中烟煤分子官能团与放热特征的关联分析

Energy, Volume 181, 15 August 2019, Pages 136-147

Jingyu Zhao, Jun Deng, Long Chen, Tao Wang, Qiang Zeng

摘要：Coal spontaneous combustion is characterized by high-temperature oxidation and microscopic mechanisms. These are essential aspects to understand when attempting to control or prevent spontaneous combustion. Three fresh bituminous coal samples were collected for experimentation from Huainan, China. X-ray diffraction and Fourier-transform infrared spectrometry were conducted to determine the microscopic characteristics of coal during high-temperature oxidation. The mineral structures and functional groups were ascertained to ensure that the original structural characteristics of the coals were obtained. Thermogravimetry–differential scanning calorimetry was used to divide the high-temperature oxidation into four substages and obtain detailed exothermic characteristics. The heat energy release exhibited a positive correlation with an increase in temperature. Moreover, to investigate the relationship between the functional groups and their exothermic characteristics, correlation analysis was conducted for describing the quantitative phenomena within the four oxidation stages. The results revealed that the oxygen-containing groups were initially the most active and reactive among the 14 types of functional groups. The most rapid stage of spontaneous combustion, in which should be the most cautious and aware of risks, was the oxygen adsorption and mass gain stage because the heat energy output increased rapidly and passed this stage, thus leading to dangerous and possibly unrecoverable situations.