Fast pyrolysis and combustion characteristic of three different brown coals

三种褐煤的快速热解与燃烧特征

Fuel Processing Technology, Volume 176, July 2018, Pages 15-20

Jun Han, Li Zhang, Hee Joon Kim, Yuichi Kasadani, Tadaaki Shimizu

摘要：In this study, brown coals fast pyrolysis/combustion was carried out in a moving furnace coupled with a balance, and the mass change of sample and emission of hydrocarbon components were online recorded. On the basis of the experimental results, the pyrolysis/combustion kinetic parameters were calculated. In the fast pyrolysis process, the apparent activation energy of Loy Yang brown coal, Wara brown coal and Usibelli brown coal was 36.9, 33.1 and 28.1 kJ/mol respectively, which was far lower than that obtained under the slow pyrolysis process. The main light hydrocarbon gases evolved from brow coal fast pyrolysis were CH4, C2H6 and C3H8. At the same time, it was found that the reaction rate of brown coal fast pyrolysis was strongly influenced by the oxygen content of the raw coal. The high oxygen content of the raw coal was beneficial to pyrolytic reaction. The combustion process of the brown coal could be divided two stages: in the first stage, the evolution and combustion of volatile matter occurred simultaneously. In the secondary stage, only char combustion occurred. The apparent activation energy of char combustion was 2.3–20.8 kJ/mol.

A random forest approach for predicting coal spontaneous combustion

预测煤自燃的随机森林方法

Fuel, Volume 223, 1 July 2018, Pages 63-73

Changkui Lei, Jun Deng, Kai Cao, Li Ma, Lifeng Ren

摘要：The accurate prediction of coal temperature plays a vital role in preventing and controlling the spontaneous combustion of coal in coal mines. In this study, a large-scale 2-ton experimental furnace was constructed to implement an oxidation experiment by using a Dafosi coal sample. The aim was to simulate the spontaneous combustion of coal at low temperatures (<100 °C). A random forest (RF) approach based on the oxidation experiment was proposed to predict coal spontaneous combustion, which exhibited satisfactory results. Moreover, to verify the performance and effectiveness of the RF approach in a practical application, a long-term in-situ observation test was conducted in a fully mechanized caving mining face (the Dafosi Coal Mine), where the in-situ data were employed to establish the RF model. Methods such as back-propagation neural network (BPNN) and multiple linear regression (MLR) were also adopted and compared with the RF model. The results indicated that the MLR model had the least reliable predicted results, regardless of whether the model was based on the oxidation experiment data or the in-situ data. This demonstrated that linear regression methods are not ideal for determining the complicated relationship between the temperature and gaseous products of coal spontaneous combustion. The BPNN model exhibited the most reliable prediction results during the training stage; however, overfitting occurred in the training stage, and the predictive performance at the testing stage was poorer than that of the RF model. The RF model accurately predicted the temperature of coal spontaneous combustion when it was applied to the in-situ data, and almost no deviation existed in the predictive performance indicators between the training and testing stages. The modeling and application results suggested that the RF model, which possesses high precision, strong generalization ability, and sound practical performance is more suitable for the prediction of coal spontaneous combustion. This method can potentially be further applied as reliable approach for the assessment of intricate relationships through fuel and energy investigations.

Spontaneous combustion of coals and coal-shales

煤与煤矸石的自燃

International Journal of Mining Science and Technology, In press, corrected proof, Available online 18 May 2018

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.

Inhibiting effects of three commercial inhibitors in spontaneous coal combustion

三种商业阻燃剂在防治煤自燃中的抑制效果

Energy, In press, accepted manuscript, Available online 11 July 2018

Jun Deng, Yi Yang, Yan-Ni Zhang, Bo Liu, Chi-Min Shu

摘要：Three commercial inhibitors were investigated for their suitability in preventing the spontaneous combustion of noncaking coal (NCC) and gas coal (GC), two coals of low metamorphic grades. Simultaneous thermal analysis, Fourier transform infrared spectroscopy, and kinetic analysis demonstrated that Zn/Mg/Al-CO3-layered double hydroxides (LDHs) and diammonum phosphate ([NH4]2HPO4) both exhibited substantial inhibiting effects. Therefore, Zn/Mg/Al-CO3-LDHs and (NH4)2HPO4 may be used for the prevention of spontaneous coal combustion. The reaction mechanisms and kinetic models for NCC and GC mixed with inhibitors were also determined. Na3PO4 demonstrated poor inhibiting ability in NCC and GC and even promoted the combustion of GC. Therefore, Na3PO4 is not recommended as an inhibitor for NCC and GC. Finally, the results indicated that (NH4)2HPO4 and Zn/Mg/Al-CO3-LDHs can be used to decrease CO2 release, limiting the oxidation reaction of coal and attenuating greenhouse gas emissions. This study can serve as a reference for efforts to prevent spontaneous coal combustion and for the development of new inhibitors.

The PAHs release characters during spontaneous combustion of coal and gangue in the same coal seam

同一煤层煤与矸石自燃过程中的PAHs释放特征

Journal of Loss Prevention in the Process Industries, In press, accepted manuscript, Available online 9 July 2018

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.