Development a modified crossing point temperature (CPTHR) method to assess spontaneous combustion propensity of coal and its chemo-metric analysis
基于改进交叉点温度法的煤自燃倾向性评定及其化学定量分析
Journal of Loss Prevention in the Process Industries, Volume 56, November 2018, Pages 359-369
N. K. Mohalik, E. Lester, I. S. Lowndes
摘要：Spontaneous combustion of Indian coals was investigated using sponcomb rig at University of Nottingham, UK to assess their susceptibility. In the present study authors have used eleven coal samples collected from the Jharia coalfield (JCF), India. Both thermal as well as gas profiles from sponcomb rig were studied critically to develop a modified crossing point temperature to assess the spontaneous combustion propensity of coal. The product of combustion gases (CO, CO2, CH4, and H2) emitted from sponcomb rig within the temperature range between ambient and 300 °C of these coal samples were studied. The initial product of combustion gas i.e. CO followed by H2 indicates propensity towards oxidation of coal in laboratory condition for Jharia coalfield. The temperatures at which CO and H2 releases in the level of 50 ppm (TCO50, TH250), crossing point temperature of coal (CPTCT) (temperature of coal and bath temperature is same) and modified crossing point temperature of coal (CPTHR) (temperature where dT/dt is equal to 2.0 oCmin−1 because heating rate is double of programme temperature 1 oCmin−1) determined from sponcomb rig categorises the coal as per their propensity to spontaneous combustion. The results of these methods have been compared with other standard method i.e. crossing point temperature method – India, which is widely adopted in Indian regulatory bodies to verify the suitability of this method.
Risk evaluation of coal spontaneous combustion on the basis of auto-ignition temperature
基于自动点火温度的煤自燃危险评估
Fuel, Volume 233, 1 December 2018, Pages 68-76
Yutao Zhang, Yurui Liu, Xueqiang Shi, Chaoping Yang, Yaqing Li
摘要：The spontaneous combustion of coal, if not eradicated immediately, may lead to coal ignition and even a full-blown fire. A new method, DSC Inflection Point (DSCIP), was proposed to determine the coal auto-ignition temperature (CAIT). Heat fluxes and kinetic parameters before and after CAIT were comparatively investigated through TG/DSC analysis and mathematical model construction. Meanwhile, the impacts of temperature rise rate and oxygen concentration on CAIT were studied and two indexes representing the hazard and destructiveness of coal spontaneous combustion, respectively, were proposed. The results demonstrated that the heat flux curve of coal spontaneous combustion can be well fitted using Gaussian mixture model. Compared to the oxidation stage, the released heat during the combustion stage was greatly increased. Furthermore, the activation energy became larger and the reaction order decreased to zero when the temperature exceeded CAIT. The study also found that CAIT was enhanced with the increase of temperature rise rates or the decrease of oxygen concentrations. Changes of heat flux, free radicals, and the activation energy proved the rationality and feasibility of the DSCIP method in determining CAIT. Additionally, under the same environmental conditions, lignite had the largest hazard of coal spontaneous combustion and the anthracite had the biggest destructiveness. Both the hazard and the destructiveness of coal spontaneous combustion became stronger as oxygen concentrations increased.
Polymorphic foam clay for inhibiting the spontaneous combustion of coal
多形泡沫粘土在抑制煤自燃中的应用
Process Safety and Environmental Protection, In press, accepted manuscript, Available online 18 December 2018
Zhilin Xi, Xiaodong Wang, Xiaoli Wang, Li Wang, Liwei Jin
摘要：Polymorphic foam clay (PFC) was proposed to retard the spontaneous combustion of coal. It is mainly synthesized using foaming clay and auxiliary solutions. When the ratio of foaming clay solution to auxiliary solution was ˜1.0 wt. %, the generated PFCs had the best performance. The sol-gel foams that could be obtained as gas were injected into the synthetic solution, which had an excellent wettability on the coal surface due to the synergistic action of polyethylene oxide and sodium dodecyl sulfate. PFCs were obtained with the reaction of organic acids and sodium silicate, and their times of liquidity and self-hardening loss were 180 and 225 s, respectively. The mechanisms of PFC inhibiting the spontaneous combustion of coal were analyzed by a simultaneous differential scanning calorimeter/thermogravimetric analyzer, an XP-550C polarizing microscope linked to a CK 300 thermal station, scanning electron microscopy, a simultaneous differential thermogravimetric scanning calorimetric analyzer linked to a mass spectrometer and X-ray photoelectron spectroscopy. Before 239 °C, the PFC was always in an endothermic state, so it could adsorb significant heat produced by the low-temperature oxidation of coal to cool the coal body. The fused PFC also could form a thin whole colloid clay layer to cover the coal surface and effectively seal gaps and cracks in the coal from oxygen ingress, thereby preventing coal from contacting oxygen. The colloid clay could retain water to increase the moisture of the coal body, resulting in the prevention of the generation of new alkyl groups from cycloalkanes and bridge bond breakage, thereby decreasing the concentration of active groups in the coal. The colloid clay possessed organic acidity that could consume active free radicals.
Study on electrical properties of coal at spontaneous combustion characteristic temperature
煤在自燃特征温度点的电性能研究
Journal of Applied Geophysics, Volume 159, December 2018, Pages 707-714
Hongqing Zhu, Wei Wang, Haoran Wang, Hongru Zhao, Miao Xin
摘要：In order to study the variation of electrical parameters in the process of spontaneous combustion of coal, first, 9 characteristic temperature points of 5 kinds of coal samples at low temperature oxidation stage and high temperature spontaneous combustion stage were obtained based on temperature programmed experiment and thermogravimetric experiment. According to these experiments samples at characteristic temperature points were prepared. Then, the complex impedance parameters of each coal sample are measured at the alternating current of 20 Hz to n × 106 Hz, and the volume resistivity and the complex permittivity of the coal sample are obtained by calculation. Finally, the volume resistivity temperature model and the complex dielectric constant temperature model of coal samples are obtained by fitting the electrical parameters at 100 kHz test frequency. The results showed that the volume resistivity of coal samples decreased rapidly in the mid-low frequency and slowly in the mid-high frequency. Under the fixed test frequency, the volume resistivity of coal samples rises first and then decreases with the increase of temperature. Both the real and imaginary parts of the complex relative permittivity of coal samples decrease with the increase of temperature, and the slope of the curve decreases gradually.
Experimental study on prevention and control of coal spontaneous combustion with heat control inhibitor
热控阻燃剂防治煤自燃实验研究
Journal of Loss Prevention in the Process Industries, Volume 56, November 2018, Pages 272-277
Zhengyan Wu, Shanshan Hu, Shuguang Jiang, Xinjian He, Wanrong Li
摘要：Traditional inhibitors have such disadvantages as unstable inhibitory effects and short active lifetimes. Sodium bicarbonate, stable in nature, is expected to absorb heat and lower the temperature upon heated and decomposition, enabling its decomposition product to be effective for preventing coal oxidation and spontaneous combustion. Accordingly, the present study investigates the characteristics of sodium bicarbonate and proposes a novel method for preventing the spontaneous combustion of coal using sodium bicarbonate. By establishing a programmed temperature experimental system of coal spontaneous combustion in the laboratory, the researchers added sodium bicarbonate (0.5–3 g) to the coal samples, and analyzed changes in CO and O2 concentration. The results out of the present experimental conditions, compared with those of coal samples treated with magnesium and calcium chlorides, show that adding different amounts of sodium bicarbonate can inhibit coal oxidation with an optimal addition amount of 3 g. When the amount of sodium bicarbonate added was larger than 2 g and the temperature above 130 °C, its inhibitory effect is more significant than that of existing inhibiting agents.
Spontaneous combustion of coals and coal-shales
煤及煤页岩的自燃
International Journal of Mining Science and Technology, Volume 28, Issue 6, November 2018, Pages 933-940
M. Onifade, B. Genc
摘要：Spontaneous combustion of coal is a well-known phenomena around the globe. Apart from the coal itself, burning coal-shales is becoming a problem in the South African coal mines. Serious incidents of spontaneous combustion have been reported as a result of self-heating of reactive coal-shales. The intrinsic properties and spontaneous combustion tests of 28 selected coal and coal-shale samples were conducted and a relationship between the two has been established. Intrinsic properties were obtained by using the proximate and ultimate analysis, and spontaneous combustion liability tests results were obtained by using the Wits-Ehac and Wits-CT indices. The experimental results show that intrinsic properties of these materials complement to the spontaneous combustion liability tests results. Comparative analyses of intrinsic properties and spontaneous combustion characteristics indicate similarities between the mechanism of coal oxidation and that of the oxidative processes undergone by coal-shales. For the tested samples, coal samples have a higher intrinsic spontaneous combustion reactivity rating than the coal-shales. Furthermore, an increase in carbon, moisture, hydrogen, volatile matter, nitrogen and a decrease in ash content indicate an increased proneness to self-heating. The concentration of pyrite found in the coal-shales accelerates self-heating. The event of spontaneous combustion can occur if coal-shales absorb sufficient oxygen when subjected to atmospheric conditions.
Experimental study on the effect of mechanochemistry on coal spontaneous combustion
力化学对煤自燃影响的实验研究
Powder Technology, Volume 339, November 2018, Pages 102-110
Jinhu Li, Zenghua Li, Yongliang Yang, Chaojie Wang, Liutao Sun
摘要：Although the mechanical grinding process is often involved in coal mining and processing, the effect of this process on coal spontaneous combustion has been scarcely investigated in the literature. The changes of the content of oxygen-containing functional groups in coal caused by mechanochemical effect and their effects on coal spontaneous combustion were studied. The low-temperature oxidation experiment, grinding experiment, infrared spectrum experiment, and electron spin resonance (ESR) experiment were carried out. Firstly, the cross-point temperatures (CPTs), CO gas production, and the content of oxygen-containing functional groups of coal with different particle sizes were compared. Furthermore, changes in gas composition and functional groups during the grinding of coal samples under different gas conditions were also analyzed. Finally, the mechanism of mechanochemical reaction was revealed by studying the change of free radical concentration during the grinding process. The experiments have shown that coal will oxidize and generate large amounts of oxygen-containing functional groups under mechanical grinding. The effect of particle size on coal spontaneous combustion is not only caused by the change of surface area which was traditionally considered, but also the mechanochemical action during the crushing and grinding process. The research results can provide a new way for the prevention of coal spontaneous combustion.
