Prediction of spontaneous combustion in the coal stockpile based on an improved metabolic grey model

基于改进型灰色新陈代谢模型的煤堆自然预测

Process Safety and Environmental Protection, Volume 116, May 2018, Pages 564-577

Shoujun Li, Xiaoping Ma, Chunyu Yang

摘要：Spontaneous combustion of coal can lead to serious environmental pollution, safety hazards and huge economic losses. Hazard prevention and environmental protection requires effective monitoring network and efficient prediction methods. To acquire the real-time data of coal parameters we designed multi-layered Zig-bee based wireless sensor network. The shape of the coal pile is formed by the industrial laser scanner followed by the formation of 3D temperature point cloud field via Kriging interpolation. Afterwards, an integrated evaluation indicator Heat Loss Capacity (HLC) is proposed, which synthesizes various factors inducing spontaneous combustion. The real-time and high accurate HLC prediction is realized by using metabolic method to update the raw sequence of the GM(1,1) grey prediction model in cycle with the latest acquired sensor data. Finally, a hybrid model ABC-MGM(1,1) combining the ABC optimization algorithm with the metabolic GM(1,1) model is proposed. Experiment shows that the ABC-MGM(1,1) model has better performance in parameter optimization as well as HLC prediction, especially for short-term prediction. The proposed method has been utilized to predict spontaneous combustion of the stockpiled coal in Xutang power plant of China. The timely parameter acquisition by 25 Zig-bee nodes and effective prediction by the proposed model shows great practicability in safety and hazard prevention.

Experimental study on thermo-responsive inhibitors inhibiting coal spontaneous combustion

热响应阻化剂防治煤自燃实验研究

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.

Analytical prediction of coal spontaneous combustion tendency: Velocity range with high possibility of self-ignition

煤自燃倾向性分析预测：高自燃可能性速度范围

Fuel Processing Technology, Volume 159, May 2017, Pages 38-47

Qi Lin, Shugang Wang, Yuntao Liang, Shuanglin Song, Tingxiang Ren

摘要：Coal spontaneous combustion is an inherent problem in coal mines throughout the world. The analysis of stationary-states, including stable point and critical point, is an effective method to judge its ignition tendency. A lower critical point temperature means that it is more likely to cause fire. In the past, due to the limitation of mathematical methods, the consumption and distribution of oxygen concentration are usually neglected. In order to accurately analyze coal ignition tendency, this paper takes coal bulk as a porous system and develops an improved model by a combination of oxygen species and energy equation. The model is solved for stationary-states of the system. Qualitative analysis of the stationary-states gives a mechanism explanation for the reason why coal spontaneous ignition is hard to be extinguished and indicates that the temperature of initial endpoint and that of internal site can be uniquely determined from each other. It further points out a trend that the location of critical point moves inward as the inlet air velocity increases, which correlates well with simulation results of the existing literatures. Then, for stationary-states, calculation results of Killoch 6015 coal are obtained. Quantitative analysis of them finds a trend that the temperature of critical point rises rapidly after its slow increase. At last, a velocity range, in which the possibility of fire is extremely high, is presented by simulation computation, e.g., the range of Killoch 6015 coal is determined as 8 × 10− 5–3 × 10− 3 m/s when the critical ignition temperature is set as 150 °C.

Study on the change of organic sulfur forms in coal during low-temperature oxidation process

煤中有机硫在低温氧化过程中的形态变迁研究

Fuel, Volume 222, 15 June 2018, Pages 350-361

Lanjun Zhang, Zenghua Li, Wenjing He, Jinhu Li, Xue Zhang

摘要：Organic sulfur functional groups in coal not only have certain oxidation characteristics at low temperature and but also can break to produce free radicals, which is bound to have a considerable effect on coal spontaneous combustion. However, this area has not been reported yet. There are relatively few studies on variation laws of organic sulfur functional groups in coal in the coal spontaneous combustion process (especially low-temperature oxidation stage), and the release of SO2, the gaseous product of organic sulfur during the low-temperature oxidation, is also rarely reported. Therefore, it is necessary to systematically obtain the change laws of organic sulfur forms in coal during low-temperature oxidation. In this paper, the morphological changes of organic sulfur in coal during low-temperature oxidation were studied first, and then the changes of organic sulfur forms in coal before and after low-temperature oxidation and the release of the low-temperature oxidation product SO2 were studied by using the X-ray photon spectroscopy (XPS) technique and the XLZ-1090 infrared gas analyzer. The XPS analysis results show that the relative contents of mercaptan and sulfide are reduced; the content of thiophene sulfur decreases slightly or remains unchanged; and the contents of sulfone, sulfonate and sulfate all increase. This verifies that the low-temperature oxidation process of active organic sulfur functional groups in coal is: sulfide → sulfoxide → sulfone, mercaptan → disulphide → sulfoxide → sulfone → sulfonic acid. The study reveals that the release of gaseous SO2 is not detected during the low-temperature oxidation of the raw coal samples, whereas it is detected during the low-temperature oxidation of the acid-treated coal samples. This is because the acid treatment can remove alkaline minerals in coal, weakens the inhibitory effect of alkaline minerals on SO2 and enable SO2 to escape almost completely. In addition, the study also discovers that the time and amount of SO2 gas release during the low-temperature oxidation process are directly related to the metamorphic degree and organic sulfur content of coal.

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

巷道上方瓦斯抽放条件下瓦斯控制与煤自燃危险性评估

International Journal of Mining Science and Technology, In press, corrected proof, Available online 7 May 2018

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.

Early extinguishment of spontaneous combustion of coal underground by using dry-ice’s rapid sublimation: A case study of application

干冰快速升华气体技术在煤矿煤自燃早期灭火中的应用研究

Fuel, Volume 217, 1 April 2018, Pages 544-552

Wei Liu, Yueping Qin, Xiaobin Yang, Wenqiang Wang, Youqiang Chen

摘要：Carbon dioxide injection is an ideal approach to prevent and control spontaneous combustion of coal in coal mines, which has higher purity, wider coverage and stronger inerting effect, but its application is limited by how to produce considerable gaseous carbon dioxide underground. Liquid carbon dioxide has high risks to be used underground due to its phase-state instability. Dry-ice has stable properties, but its sublimation in normally is too slow to extinguish the fire. To address this issue, a new type of apparatus for efficiently sublimating dry-ice has been developed independently, which would yield more than 205 times as much carbon dioxide as dry-ice under normal condition. There is no external power supply during its working, but the heat for dry-ice’s rapid sublimation originates from continuously running water in a copper pipe inside the apparatus, thereby greatly improving the security of the use underground. This apparatus has been successfully applied to extinguish several early spontaneous combustion in Yangmeiwu Coal Mine in China. This paper describes the apparatus and its application.