Assessment of spontaneous combustion status of coal based on relationships between oxygen consumption and gaseous product emissions

 

基于氧消耗与气体产物排放关系的煤自燃状态评估

 

Fuel Processing Technology, Volume 179, October 2018, Pages 60-71

 

Junfeng Wang, Yulong Zhang, Sheng Xue, Jianming Wu, Liping Chang

 

摘要：It is imperative to have an in-depth understanding of the relationship between oxygen consumption and gaseous product emissions during coal self-heating not only for preventing fires in the coal industry but also for reducing emissions of hazardous gases. Two typical coal samples with high tendency of spontaneous combustion were heated to 230 °C with a programmed temperature of 1.0 K min−1 using a pilot-scale test apparatus. The trends for oxygen consumption and gaseous product emissions were obtained from continuous measurements of the gas samples at the reactor outlet via a gas chromatography equipped with a Flame Photometric Detector. Based on the rates of oxygen consumption and gaseous product emissions, the relationship between oxygen consumption and each gaseous product emission was studied. Multi-linear regressions of the oxygen consumption and gaseous product emissions were performed. The coefficients for the emission rates of CO2, CO and H2 in the regression equations of the two coals with three different particle sizes are found to be all positive, while the coefficients for the CH4 emission rates are all negative. These results indicate that the oxygen consumption of coal facilitates the release of CO2, CO and H2, while the increase of oxygen consumption rate may not enhance the release of hydrocarbon gas. Based on the results, an evaluation index defined as the ratio of oxygen consumption rate to the gaseous product emission rate is proposed to assess the state of coal spontaneous combustion.

 

 

Surface-based radon detection to identify spontaneous combustion areas in small abandoned coal mine gobs: Case study of a small coal mine in China

 

基于地面氡探测确定废弃小煤矿采空区自燃位置：中国小煤矿实例研究

 

Process Safety and Environmental Protection, Volume 119, October 2018, Pages 223-232

 

Bin Zhou, Jianming Wu, Junfeng Wang, Yuguo Wu

 

摘要：In China, small coal mines refer to non-state-run coal mines with an annual production of less than 300,000 tons. The mining recovery rate of these small Chinese coal mines is low, and large amounts of coal remain in the gob. The mining seams of small coal mines are shallow, which induces extensive fissures between the gob and ground and provides easy pathways for air leakage. Consequently, long-term air leakage and oxygen supplies can result in spontaneous coal combustion in the gob, forming fire areas for many years. Determination of spontaneous combustion areas in the gob of small coal mines is difficult because fire sources are hidden underground and the geological data and roadway layout are poorly documented. Surface-based radon detection provides a fast, accurate, and low-cost method to identify spontaneous combustion areas in the gob of small coal mines. This study focuses on a small abandoned coal mine in Shanxi Province, China, using surface-based radon detection. Three abnormal temperature areas (A, B, C) and a potential abnormal temperature area (D) were identified. Drilling was subsequently performed to measure the temperature distribution in these areas. The results show that spontaneous combustion areas in small abandoned coal mine gobs can be successfully identified.

 

 

Characteristics of polycyclic aromatic hydrocarbon release during spontaneous combustion of coal and gangue in the same coal seam

 

同煤层煤与煤矸石自燃过程中的热解芳烃释放特征

 

Journal of Loss Prevention in the Process Industries, Volume 55, September 2018, Pages 392-399

 

Haiyan Wang, Chaofeng Cheng, Cheng Chen

 

摘要：Based on the influence of temperature, coal quality, oxygen supply and other factors, the formation characters of PAHs during spontaneous combustion of coal and gangue in the same coal seam were experimentally studied. The results showed that the amount of PAHs released from coal and gangue first increased and then decreased with the rising of coal and gangue spontaneous combustion temperature. And it reached a peak value about 5.76–7.17 times of the minimum value at 400 °C–500 °C. The types of PAHs released during the high temperature stage of spontaneous combustion were up to 9. The release amount of PAHs generally increased with the rising of the volatile content, sulfur content, carbon content, fixed carbon content and calorific value of coal and gangue, but decreased with the rising of ash content. The amount of PAHs produced by spontaneous combustion of raw coal was generally higher than that of gangue, and the difference was more obvious at high-temperature stage. The total toxicity amount of PAHs produced by spontaneous combustion of raw coal was higher than that of gangue, up to 9.93 times. Its law of change with temperature was consistent with the total amount of PAHs, which increased and then decreased with the rising of temperature; and reached the peak at 300 °C–400 °C with a peak value of 6.72–14.60 times of the minimum value.

 

Comparative analysis of thermokinetic behavior and gaseous products between first and second coal spontaneous combustion  

 

初始与二次煤自燃期间的热动特征和气体产物比较分析

Fuel, Volume 227, 1 September 2018, Pages 325-333

 

Yang Xiao, Shuai-Jing Ren, Jun Deng, Chi-Min Shu

 

摘要：To investigate the entire process of first and second coal spontaneous combustion, a 15-t experimental furnace for coal spontaneous combustion and synchronous thermal analyzer coupled with Fourier transform infrared spectroscopy were employed. The process of experimental tests was as follows: First, coal temperature was increased from 31.0 °C (room temperature) to 452.7 °C without intervention. Second, the coal sample was cooled to approximately 90.0 °C in an anaerobic atmosphere. Third, air was supplied until the sample reached 418.0 °C. Finally, the coal was cooled again to 100.0 °C in an anaerobic atmosphere. The variations of temperature, mass, heat energy intensity, and gaseous products were investigated. The results indicated that the temperature change rate first increased and then decreased during the first and second coal spontaneous combustion. Compared with the first coal spontaneous combustion, the rates of temperature and mass loss change with a heating rate of 2.5 °C/min were higher at the combustion stage of the second coal spontaneous combustion, but the variations of the exothermic reaction rate and mass loss with other heating rates (5.0, 10.0, and 15.0 °C/min) were lower. The differences among CO, CO2, alkanes, and alkenes during the first and second coal spontaneous combustions were insignificant until 300.0 °C. However, the emission of CO and CO2 during the second coal spontaneous combustion was significantly higher than during the first coal spontaneous combustion, whereas the release of alkanes and alkenes was substantially weaker when the temperature was higher than 300.0 °C. Moreover, the amount of H2O during the first coal spontaneous combustion was higher than that during the second coal spontaneous combustion.

 

An experimental study for characterization the process of coal oxidation and spontaneous combustion by electromagnetic radiation technique  

 

电磁辐射技术在煤氧化与自燃过程特征实验研究中的应用

 

Process Safety and Environmental Protection, Volume 119, October 2018, Pages 285-294

 

Biao Kong, Zenghua Li, Enyuan Wang, Wei Lu, Guansheng Qi

 

摘要：Coal spontaneous combustion results from a complex reaction between coal and oxygen. Previous studies on coal oxidation spontaneous combustion process provided guidance for fire prevention and control. In this work, we present a novel electromagnetic radiation (EMR) method to detect spontaneous combustion of coal. We established a multi-index experimental system for estimating various factors during coal oxidation (heating) and combustion and analyzed the characteristic temperature, index gases, and EMR signals. With the increase of temperature, the central temperature of coal varies significantly with the temperature around the coal oxidation heating device. Besides, we simultaneously tested the EMR signals generated during coal oxidation and combustion. EMR signals showed a positive correlation with temperature changes (i.e., EMR signal intensity increases with the increase in temperature and vice versa). The change trend of EMR signals with the CO is notable, and there is a good correspondence between the EMR signals and the change rule of CO gas. With the increase of temperature, the dielectric properties of coal change quickly, resulting in the occurrence of thermal deformation and rupture in the coal body, which produces significant EMR signals. The research results are of great significance for applying the EMR technique to directly detect hidden fire hazards in coal mines.

 

Experimental investigation of applying MgCl2 and phosphates to synergistically inhibit the spontaneous combustion of coal  

 

应用MgCl2和磷酸盐协同抑制煤自燃的实验研究

 

Journal of the Energy Institute, Volume 91, Issue 5, October 2018, Pages 639-645

 

Yibo Tang

 

摘要：Spontaneous fire hazard in underground collieries threatens the safe production of coal. Thus, globally, there is a growing interest in identifying and adapting novel methods for inhibiting the spontaneous combustion of coal. Although Cl-containing minerals exhibit retardant properties in the low-temperature range, they fail to control the combustion of coal at high temperatures. Therefore, to control the fire hazard caused by spontaneous combustion of coal at high temperatures effectively, phosphates and MgCl2 were innovatively used as synergistic inhibitors for suppressing self-ignition of coal. Laboratory tests such as thermal analysis, infrared spectrum analysis and oxidation analysis were performed to evaluate the behavior of coal samples before and after treatment. Experimental results indicated that the combined utilization of MgCl2, Zn3(PO4)2, and (NH4PO3)n could significantly reduce the heat emission during coal combustion, as well as the yield rate of CO. The optimal effect can be obtained with a Cl-to-P ratio of 2:1. In addition, functional groups such as OH and CH2 in treated samples decreased markedly. Hence, underground coal fire can be prevented more effectively using a combination of Cl and P, instead of using Cl-based retardants alone.

 

Risk forecasting for spontaneous combustion of coals at different ranks due to free radicals and functional groups reaction  

 

自由基和官能团反应引起的不同煤阶煤自燃风险预测

 

Process Safety and Environmental Protection, Volume 118, August 2018, Pages 195-202

 

Qin Xu, Shengqiang Yang, Jiawen Cai, Buzhuang Zhou, Yanan Xin

 

摘要：To explore the reaction mechanism of spontaneous coal combustion and the indicators for forecasting this risk, reaction characteristics of free radicals and functional groups during low-temperature oxidation of coal with different ranks were analyzed by electron spin resonance (ESR) and Fourier transform infrared (FTIR) spectroscopy. Combined with gas chromatography of CO, other indicators besides the main indicator gas CO were researched to forecast spontaneous coal combustion. The results showed that with increasing oxidizing temperature in the range of 30 °C–230 °C, the production of free radicals changed from slow to rapid after being oxidized and heated above characteristic temperatures, depending on the coal grade. The oxygen-containing functional groups in coal of all ranks mainly include OH, CO, CO and COOH, whose reaction trends varied widely. The concentration and production rate of free radicals and the CO functional group in coal can be regarded as the leading indicators.

 

Experimental study on the inhibitory effect of ethylenediaminetetraacetic acid (EDTA) on coal spontaneous combustion  

 

乙二胺四乙酸的煤自燃阻燃效果实验研究

 

Fuel Processing Technology, Volume 178, September 2018, Pages 312-321

 

Jinhu Li, Zenghua Li, Chaojie Wang, Yongliang Yang, Xiaoyan Zhang

 

摘要：The inorganic salts in coal contain a certain number of metal ions, among which transition metal ions can exert a certain catalytic effect on coal spontaneous combustion by reducing the activation energy of coal oxygen reaction. Therefore, the addition of metal chelating agent in coal will definitely reduce the catalytic effect of metal ions, so as to inhibit coal spontaneous combustion. In this paper, the inhibitory effect of a common metal chelating agent ethylenediaminetetraacetic acid (EDTA) on coal spontaneous combustion was studied. Four coal samples were selected in this study. First, basic data such as the types and contents of transition metal elements in coal samples were measured via X-ray fluorescence (XRF). Then, thermal analyses, infrared spectrum experiments, low-temperature oxidation experiments and crossing point temperature experiments were performed on WL coal samples before and after EDTA treatment. The experimental results show that there is no mass gain caused by oxygen adsorption in the EDTA-treated coal sample throughout the heating process. In addition, the treated coal sample exhibit a great reduction in its content of oxygen functional groups, a decrease in the concentration of gas products and a rise of the crossing point temperature, indicating that EDTA has a strong inhibitory effect on coal. The calculation of the apparent activation energy reveals that the activation energies of the inhibited coal sample were 51.18 kJ/mol and 43.42 kJ/mol in the temperature ranges of 30–70 °C and 80–180 °C, respectively, which are 7.94 kJ/mol and 8.28 kJ/mol higher than those of the raw coal. This proves that the metal chelating agent EDTA is able to inhibit coal spontaneous combustion by chelating transition metal ions to increase the activation energy. Finally, experiments were carried out to study the inhibitory effects of EDTA on different coal samples, which suggests that EDTA can exert good inhibitory effects on different coal samples.