An intelligent gel designed to control the spontaneous combustion of coal: Fire prevention and extinguishing properties
防治煤自燃的智能胶：火灾预防与灭火特性
Fuel, Volume 210, 15 December 2017, Pages 826-835
Weimin Cheng, Xiangming Hu, Jun Xie, Yanyun Zhao
Abstract:A new type of mining fire-extinguishing material designed to prevent the spontaneous combustion of coal is presented. Through the graft copolymerization of corn straw, 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and acrylic acid (AA), a corn straw-co-AMPS-co-AA hydrogel was synthesized. A chemical foaming agent was then added to the hydrogel, resulting in a self-foaming gel, which was subsequently mixed with expandable graphite to create an intelligent gel. Compared to temperature-sensitive and polyacrylamide gels, this intelligent gel exhibited good thermal stability, as well as adhesion and swelling at high temperatures. Fire-extinguishing experiments revealed that the intelligent gel could cover the surface of burning coal, thereby significantly reducing the ignition source temperature, thermal radiation, and amount of CO generated. Infrared spectrum analysis showed that the IG sample with 10% expanded graphite could inhibit the oxidation of the hydroxyl group during the heating process. The fire-extinguishing performance of the intelligent gel was found to be superior to those of the other gels, as it prevented re-ignition. Thus, this gel is an ideal fire prevention and control material, especially for controlling the spontaneous combustion of coal.
A quantitative approach to evaluate risks of spontaneous combustion in longwall gobs based on CO emissions at upper corner
基于上隅角CO排放的长壁采空区自燃危险性量化评价方法
Fuel, Volume 210, 15 December 2017, Pages 359-370
Wei Liu, Yueping Qin
Abstract:Carbon monoxide (CO) is an important gas indicator for early detection and evaluation of spontaneous combustion in longwall gobs, and continuous monitoring of this gas is generally located at the upper corner of working face. Although CO emissions during spontaneous heating of coal have been investigated adequately in laboratory, few studies have involved in the migration and generation behavior of CO in longwall gobs. The CO-based early warning threshold for spontaneous combustion in gob is unsettled either. In this study, a fully coupled model of generation and transport of CO in longwall gob is developed by combining with air seepage, oxygen transport, thermal transfer, and exothermic reaction. Standard CO generation rate (SCOGR) as one key parameter is introduced for the better simulation on CO migration in gob. Our previously developed solving software of COMBASS-3D has been improved to investigate the functional relationship between progression of spontaneous combustion in longwall gob and CO emissions at upper corner. The results show that (i) the SCOGR depends strongly on temperature and coal properties, but is independent of ambient oxygen concentration, which is the basis for calculating actual CO generation rate; (ii) the high CO concentration zone overlaps with the oxidative self-heating zone and the high temperature zone in windward side of gob, which is consistent with the theoretical expectation and on-site observation; (iii) increasing longwall advance rate, decreasing ventilation flux and reducing thickness of abandoned coal all can not only reduce risks of spontaneous combustion in longwall gob but also suppress CO emissions from the gob; (iv) the maximum temperature in gob grows linearly with the increase of natural logarithm of CO concentration at upper corner in low temperature stage, and the early warning threshold can be calculated on basis of this relationship with the minimum self-heating temperatures of coal. These works can provide a quantitative approach for early warning the spontaneous combustion fires in longwall gobs.
Determination and prediction on “three zones” of coal spontaneous combustion in a gob of fully mechanized caving face
综采面采空区煤自燃“三区”的确定与预报
Fuel, Volume 211, 1 January 2018, Pages 458-470
Jun Deng, Changkui Lei, Yang Xiao, Kai Cao, Bin Laiwang
Abstract:The precise division into “three zones” of coal spontaneous combustion in the gob plays a key role for coal fire fighting. This paper presents three-dimensional distribution maps and contour plots for the gases and temperature in the gob by the method of griddata interpolation according to the data (O2, CO, CO2, CH4, and temperature) acquired from in-situ test, and the variation of gases and temperature. It is proposed to comprehensively divide “three zones” by using O2 concentration of 5–18 vol%, the appearance and disappearance of CO, and the heating rate K = 0 °C/m. The gas explosion conditions were considered to determine the danger zone of coal spontaneous combustion. The minimum mining speed was calculated to be 4.8 m/day based on the division of the “three zones” in the gob in order to prevent spontaneous combustion phenomenon. Particle swarm optimization (PSO) was employed to optimize the parameters of support vector regression (SVR); the PSO-SVR model was established to predict the temperature of coal spontaneous combustion based on the gases’ concentration in the gob and distance from the measuring points to the working face. Prediction results and performance of PSO-SVR model were compared with standard SVR, back propagation neural network (BPNN), and multiple linear regression (MLR). The results indicated that PSO-SVR model had greater prediction accuracy and generalization ability, which can predict the temperature of coal spontaneous combustion in the gob.
Inhibition of spontaneous combustion for different metamorphic degrees of coal using Zn/Mg/Al–CO3 layered double hydroxides
Zn/Mg/Al–CO3层状双氢氧化物在不同变质程度煤自燃抑制中的应用
Process Safety and Environmental Protection, Volume 113, January 2018, Pages 401-412
Yi Yang, Yun-Ting Tsai, Yanni Zhang, Chi-Min Shu, Jun Deng
Abstract:Layered double hydroxides (LDHs) have excellent physical and chemical properties and are thus widely and effectively used to inhibit spontaneous coal combustion. In this study, Zn/Mg/Al–CO3 LDHs, which are metal ion–LDH complexes, were prepared through coprecipitation and synthesized using three types of coal with different metamorphic degrees to form Zn/Mg/Al–CO3 LDH/coal. Additionally, the spontaneous coal combustion inhibition mechanism of added Zn/Mg/Al–CO3 LDHs was investigated using scanning electron microscopy, in situ Fourier transform infrared spectroscopy, and differential scanning calorimetry to further elucidate prevention and control measures for spontaneous coal combustion. The results demonstrated that Zn/Mg/Al–CO3 LDHs are extremely highly compatible with coal and form a crystalline structure on the surface of coal, which interrupts the diffusion of oxygen for combustion and, consequently, inhibits spontaneous coal combustion. Furthermore, the negative effects of various crucial functional groups on spontaneous coal combustion were weakened by the addition of Zn/Mg/Al–CO3 LDHs. When decomposing, Zn/Mg/Al–CO3 LDHs undergo an endothermic reaction and generate enormous amounts of CO2 and H2O, which could effectively reduce the surface temperature of coal and dilute the oxygen concentration of the environment. A novel material, Zn/Mg/Al–CO3 LDHs can be used to prevent the occurrence of severe accidents caused by spontaneous coal combustion.
