scholarly journals Influence Mechanism of Nitrogen Injection Into Closed Fire Zone On the Re-Ignition For Residual Coal in Goaf

2021 ◽  
Author(s):  
Yong-liang XU ◽  
Ze-jian LIU ◽  
Xing-lin WEN ◽  
Lan-yun Wang ◽  
Zhi-guang LV ◽  
...  
Keyword(s):  
Functional Groups ◽  
Uniaxial Stress ◽  
Filling Material ◽  
Nitrogen Injection ◽  
Fire Zone ◽  
Ignition Mechanism ◽  
Mine Fires ◽  
Ignition Characteristics ◽  
Temperature Programmed ◽  
Residual Coal

Abstract Coal is the foundation of Chinese energy and economic structure, and the unsealing of coal mine fires would cause a great risk of coal re-ignition. The uniaxial compression equipped with a temperature-programmed (UCTP) device was built to explore the influence of pressure-bearing state on the re-ignition characteristics of residual coal. The Scanning Electron Microscope (SEM), Synchronous Thermal Analyzer (STA) and Fourier Transform Infrared Absorption Spectrometer (FTIR) was applied to investigate the microscopic structure and thermal effect of the coal samples. Moreover, the microscopic effect of uniaxial stress on coal re-ignition was revealed, and the re-ignition mechanism was also obtained. As the uniaxial stress increases, the number, depth and length of the fractures in the pretreated coal increase, and the filling material increases. The application of uniaxial stress causes the thermal conductivity to change periodically, which enhances the heat transfer inhibition effect of nitrogen and prolongs the oxidation exothermic stage. The content of oxygen-containing functional groups has a high correlation with apparent activation energy, and coal samples at 6 MPa are more likely to re-ignition when the fire zone is unsealed. Uniaxial stress controls the re-ignition mechanism by changing the structure of fractures and pores. The side chains and functional groups in the coal structure are easier to break under thermal-stress coupling. The higher the ·OH content, the more difficult it is to re-ignition. The research results have laid a solid theoretical foundation for the safe unsealing of coal field fire areas, tightened the common bond between the actual industry and the experimental theory in the closed fire area, and provided theoretical guidance for preventing coal re-ignition.

Effect Analysis of Nitrogen Injection on the Variation of “Oxidation Zone” in Coal Mine Gob Based on Numerical Simulation

2016 ◽  
Vol 9 (1) ◽  
pp. 47-54
Author(s):  
Jing Shen ◽  
Mingran Chang
Keyword(s):  
Numerical Simulation ◽  
Coal Mine ◽  
Heat Dissipation ◽  
Spontaneous Combustion ◽  
Oxidation Zone ◽  
Effect Analysis ◽  
Mine Fire ◽  
Nitrogen Injection ◽  
The Difference ◽  
Residual Coal

One of the main reasons for coal mine fire is spontaneous combustion of residual coal in gob. As the difference of compaction degree of coal and rock, the underground gob can be considered as a porous medium and divided into “three zones” in accordance with the criteria. The “three zones” are “heat dissipation zone”, “oxidation zone” and “choking zone”, respectively. Temperature programming experiments are taken and numerical simulation with obtained experimental data is utilized to analyze the distribution of “three zones” in this paper. Different width and depth of “oxidation zone” are obtained when the inlet air velocity is changed. As the nitrogen injection has inhibition effect on spontaneous combustion of residual coal in gob, nitrogen is injected into the gob. The widths of “oxidation zone” are compared before and after nitrogen injection. And ultimately the optimum location and volume of nitrogen injection are found out.

Temperature-Programmed Oxidation Experiments on Typical Bituminous Coal Under Inert Conditions

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Yansong Zhang ◽  
Houwang Wang ◽  
Wenzhou Du ◽  
Kuo Niu ◽  
Xiangrui Wei
Keyword(s):  
Bituminous Coal ◽  
Co2 Concentration ◽  
Inert Gases ◽  
Slow Heating ◽  
Fast Heating ◽  
Temperature Programmed Oxidation ◽  
Heating Stage ◽  
Temperature Programmed ◽  
Residual Coal ◽  
Two Stages

Abstract In this study, an experimental investigation was presented on the oxidation behaviors of bituminous coal for different inert gases (N2 and CO2) at different concentrations (oxygen concentration indexes 21%, 18.4%, 15.8%, and 13.1%) using a temperature-programmed experimental device. The purpose of this research was to examine the oxidation patterns of bituminous coal under different inert conditions. The results showed that: (1) the oxidative heating of the coal underwent two stages: an initial slow heating stage and a fast heating stage. The injection of both inert gases would result in a delay in the crossing point temperature (CPT) of the coal, but the injection of N2 resulted in greater delays in the CPT of the coal; (2) the injection of both N2 and CO2 inhibited the concentrations of CO and alkane/olefin gases produced from the oxidative heating of the coal, with CO2 displaying higher inhibition efficiencies than that of N2; (3) Under a non-inerting environment, the C2H4 and C2H6 generation temperatures were 110 °C and 100 °C. Under an inerting environment, when N2 was injected, the higher the N2 concentration, the higher the initial C2H4 and C2H6 generation temperatures; when CO2 was injected, the higher the CO2 concentration, the lower the initial C2H4 and C2H6 generation temperatures; and (4) under a non-inerting environment, the C3H8 generation temperature was 90 °C; and when an inert gas was injected, there was a hysteresis in the C3H8 generation temperature for all concentrations. The above research results can be used to predict the spontaneous combustion of residual coal in an inert environment and prevent fires.

Study on the Reoxidation Characteristics of Soaked and Air-Dried Coal

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Lulu Sun ◽  
Yanbo Zhang ◽  
Yue Wang ◽  
Qiqi Liu
Keyword(s):  
High Energy ◽  
Gas Generation ◽  
Cross Point ◽  
Point Temperature ◽  
Oxidation Stage ◽  
The Cross ◽  
Temperature Programmed ◽  
Residual Coal ◽  
Seam Mining ◽  
Index Gases

After coal seam mining, the residual coal is soaked with the accumulated water in goaf, and its spontaneous combustion characteristics were changed after air-dried. To study the reoxidation characteristics of soaked and air-dried coal, temperature-programmed experiments were carried out, and the cross point temperatures and index gases were investigated. Results showed that the cross point temperature of raw coal (146.3 °C) was reduced to 137.1 °C after it was pre-oxidized at 90 °C. The cross point temperature of water-soaked, and air-dried coal (96 h) was 122.5 °C, while the cross point temperature of water-soaked, air-dried (96 h) and pre-oxidized (90 °C) coal was 111.5 °C. Although CO was produced in the initial slow oxidation phase, it was found that C2H4 and C3H8 were not generated. In the rapid oxidation stage, different pretreatments affected the gas generation and the overall oxidative degree was consistent with the cross point temperature. The generation temperature and the concentration of C2H4 and C3H8 were decreased after the coal was water-soaked, air-dried, and pre-oxidized. Furthermore, the high-energy chemicals and functional groups were studied, which could be used to explain the physical experiment oxidation characteristics of different coals.

Ignition mechanism of mechanically activated Me–Si(Me = Ti, Nb, Mo) mixtures

2004 ◽  
Vol 19 (5) ◽  
pp. 1558-1566 ◽  
Author(s):  
U. Anselmi-Tamburini ◽  
F. Maglia ◽  
S. Doppiu ◽  
M. Monagheddu ◽  
G. Cocco ◽  
...  
Keyword(s):  
High Temperature ◽  
Reaction Mechanism ◽  
Mechanical Activation ◽  
Ignition Temperature ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Ignition Mechanism ◽  
Ignition Characteristics ◽  
Different Response

The influence of mechanical activation on the characteristics and mechanism of ignition of self-propagating high-temperature synthesis processes of different silicides in the systems Me–Si (Me =Ti, Nb, Mo) was investigated. The results show that mechanical activation does not alter the mechanism involved but influences significantly the ignition characteristics. The influence, however, strongly depends on the stoichiometry of the mixtures. The composition Ti:Si = 1:2 shows the largest influence, with the ignition temperatures decreasing from 1400 °C for unmilled powders to about 600 °C for powders milled for several hours. The compositionsTi:Si = 5:3, Nb:Si = 1:2 show less pronounced decreases, while the compositionMo:Si = 1:2 shows no decrease. These differences are discussed in terms of the role of microstructure in the reaction mechanism and the different response of the systems to contamination, particularly from oxygen. The results suggest that for these systems self-ignition processes during milling cannot be explained only on the basis of the decrease in the ignition temperature.

Hysteresis characteristics of oxidation-thermodynamic for residual coal in goaf under uniaxial stress

Fuel ◽  
2021 ◽  
Vol 306 ◽  
pp. 121750
Author(s):  
Yong-liang Xu ◽  
Ze-jian Liu ◽  
Lan-yun Wang ◽  
Zhi-guang Lv ◽  
Jin-dong Wu ◽  
...  
Keyword(s):  
Uniaxial Stress ◽  
Residual Coal ◽  
Hysteresis Characteristics

scholarly journals Distribution of spontaneous combustion three zones and optimization of nitrogen injection location in the goaf of a fully mechanized top coal caving face

PLoS ONE ◽  
2021 ◽  
Vol 16 (9) ◽  
pp. e0256911
Author(s):  
Yun Qi ◽  
Wei Wang ◽  
Qingjie Qi ◽  
Zhangxuan Ning ◽  
Youli Yao
Keyword(s):  
Combustion Zone ◽  
Heat Dissipation ◽  
Spontaneous Combustion ◽  
Simulation Analysis ◽  
Distribution Area ◽  
Nitrogen Injection ◽  
Residual Coal ◽  
Controlling Measures ◽  
And Control ◽  
The Impact

In order to effectively prevent and control spontaneous combustion of residual coal in the goaf and reduce the waste of nitrogen caused by setting the position of nitrogen injection, 1303 fully mechanized coal caving faces of the Jinniu Mine are studied. By deploying a bundle tube monitoring system in the inlet air side and return air side of the goaf, changes in gas concentration in the goaf are continuously monitored. In addition, the distribution area for spontaneous combustion three-zone in the goaf is divided into heat dissipation zone, oxidized spontaneous combustion zone, and suffocation zone. Simulations from the COMSOL Multiphysics 5.3 software provide insight based on the three zones division standard of spontaneous combustion in the goaf. The gradual deepening of the nitrogen injection position into the goaf affects the lower limit of the oxidized spontaneous combustion zone significantly, but the impact on the upper limit of the oxidized spontaneous combustion zone is not obvious and is negligible. With regard to the width of the oxidized spontaneous combustion zone, it initially decreases followed by a gradual increase. Numerical calculations suggest the optimal nitrogen injection position is 40 m from the roof cutting line, with an oxidized spontaneous combustion zone width of 28 m. Based on the simulation analysis results, nitrogen injection controlling measures have been adopted for spontaneous combustion of residual coal in the goaf of the 1303 fully mechanized coal caving faces, and coal self-ignition in the goaf has been successfully extinguished.

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