# Internal Temperature Variation on Spontaneous Combustion of Coal Gangue Dumps under the Action of a Heat Pipe: Case Study on Yinying Coal Mine in China

^{1}

^{2}

^{3}

^{4}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Overview of the Study Area

^{2}. In 2006, the first spontaneous combustion occurred in the gangue dump, and then the surface of the gangue was covered with about 0.5 m loess layer, and greening measures were taken. In 2018, the area is returning to about 2600 m

^{2}, causing the decline of vegetation on the surface. The site survey found that the surface of the gangue dump has obvious signs of fire, sometimes smoke, and you can smell a strong irritating smell, indicating that spontaneous combustion is still continuing.

#### 2.2. Working Principle of the HP

#### 2.3. Experimental Scheme

#### 2.4. Initial Temperature

#### 2.5. Fitting the Model

^{2}is used to judge the fitting effect; the closer R

^{2}is to 1, the better the fitting effect, and the expression is:

^{2}is the correlation coefficient, and y is the 2 m, 3 m, 4 m, and 5 m depth temperature.

## 3. Results and Discussion

#### 3.1. The Relationship between Shallow and Deep Temperatures

^{2}and a better fit, followed by the quadratic and logarithmic fits for the 1 m temperature and the rest of the depth, respectively, and the results are shown in Table 2.

^{2}of the quadratic model for the 1 m temperature on the 2~6 m temperatures is greater than the R

^{2}of the logarithmic model, so the quadratic fit is better.

#### 3.2. Model Significance Analysis

_{0}= a

_{1}= a

_{2}= 0; alternative assumption H1: at least one a

_{i}≠0 (i =1,2)

_{R}is the sum of squared deviations; Q

_{E}is the sum of squared residuals.

_{0.01}(2, n − 3) of the F distribution was compared with the magnitude of the calculated value of F. If: the test statistic F ≥ F

_{0.01}(2, n − 3), the original hypothesis was rejected and the regression equation was significant, and vice versa, it was not significant. The results of the significance tests are shown in Table 3.

#### 3.3. Effect of the HP on Gangue Dumps

#### 3.4. Horizontal Temperature Variation

#### 3.5. Vertical Temperature Variation

#### 3.6. Maximum Cooling Range in Different Temperature Zones

## 4. Conclusions

- (1)
- The quadratic regression model fits better than the logarithmic function model, and the regression is significant and can be used as an empirical regression formula for the temperature between shallow and deep layers.
- (2)
- The HP has high thermal conductivity and an obvious cooling effect on the coal gangue dump. In the low-temperature oxidation zone below 80~90 °C of the gangue dump, compared with the control group without an HP, the temperature of the HP decreased continuously after 700 h, and the HP needed a stable period of about 100 h in the early cooling period, with an average cooling range of 21.44%, while the control group without HP was in a continuous rising state, with a heating range of 8%. Under the action of the HP, the cooling range of the three single-pipe test groups is different, showing a regular change. The internal temperature drop of the coal gangue dump is inversely proportional to the horizontal distance and directly proportional to the working time, and the control radius for the three groups of tests is 3 m.
- (3)
- In the vertical direction, the temperature difference between the shallow layer and the deep layer is larger, and the internal temperature is proportional to the depth. The decrease is related to the spontaneous combustion, the depth of the HP, the location of the ignition point, and the temperature range. The HP mainly reduces the temperature of the gangue layer with a depth of 1~4 m. HP technology has an obvious control effect on different temperature zones of spontaneous combustion in the coal gangue dump, and can effectively improve the economy of spontaneous combustion treatment of the coal gangue dump.

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

- Luo, L.; Li, K.; Fu, W.; Liu, C.; Yang, S. Preparation, characteristics and mechanisms of the composite sintered bricks produced from shale, sewage sludge, coal gangue powder and iron ore tailings. Constr. Build. Mater.
**2019**, 232, 117250. [Google Scholar] [CrossRef] - He, J.; Liu, C.; Hong, P.; Yao, Y.; Luo, Z.; Zhao, L. Mineralogical characterization of the typical coarse iron ore particles and the potential to discharge waste gangue using a dry density-based gravity separation. Powder Technol.
**2018**, 342, 348–355. [Google Scholar] [CrossRef] - Kuenzer, C.; Zhang, J.; Tetzlaff, A.; van Dijk, P.; Voigt, S.; Mehl, H.; Wagner, W. Uncontrolled coal fires and their environmental impacts: Investigating two arid mining regions in north-central China. Appl. Geogr.
**2007**, 27, 42–62. [Google Scholar] [CrossRef] - Heffern, E.; Coates, D. Geologic history of natural coal-bed fires, Powder River basin, USA. Int. J. Coal Geol.
**2004**, 59, 25–47. [Google Scholar] [CrossRef] - Pan, R.K.; Yu, M.G.; Xu, J.; Huang, Z. Harm of Gangue Dump and Cause Analysis of Spontaneous Combustion. Saf. Environ. Eng.
**2006**, 13, 66–70. [Google Scholar] - Zhai, X.W.; Ma, L.; Zhu, G.; Huang, J.; Zheng, X. Study and practices on spontaneous combustion control technology of mine coal waste pile. Coal Sci. Technol.
**2015**, 43, 53–56. [Google Scholar] - Kong, X.; Wang, E.; Hu, S.; Li, Z.; Liu, X.; Fang, B.; Zhan, T. Critical slowing down on acoustic emission characteristics of coal containing methane. J. Nat. Gas Sci. Eng.
**2015**, 24, 156–165. [Google Scholar] [CrossRef] - Stracher, G.B.; Taylor, T.P. Coal fires burning out of control around the world: Thermodynamic recipe for environmental catastrophe. Int. J. Coal Geol.
**2004**, 59, 7–17. [Google Scholar] [CrossRef] - Song, Z.; Kuenzer, C. Coal fires in China over the last decade: A comprehensive review. Int. J. Coal Geol.
**2014**, 133, 72–99. [Google Scholar] [CrossRef] - Zhang, Z.W. Forming Mechanism and Influence Factors of Gangue Hill Spray Explosion. J. Liaoning Technol. Univ.
**2002**, 21, 11–14. [Google Scholar] - Wang, J.; Zhang, J.; Zhu, K.; Zhou, L. Anatomy of explosives spontaneous combustion accidents in the Chinese underground coal mine: Causes and prevention. Process Saf. Prog.
**2016**, 35, 221–227. [Google Scholar] [CrossRef] - Deng, J.; Xiao, Y.; Li, Q.; Lu, J.; Wen, H. Experimental studies of spontaneous combustion and anaerobic cooling of coal. Fuel
**2015**, 157, 261–269. [Google Scholar] [CrossRef] - Wang, H.; Fang, X.; Du, F.; Tan, B.; Zhang, L.; Li, Y.; Xu, C. Three-dimensional distribution and oxidation degree analysis of coal gangue dump fire area: A case study. Sci. Total Environ.
**2021**, 772, 145606. [Google Scholar] [CrossRef] - Pan, W.D.; Lian, F.Y.; Deng, H.Y.; Yu, S.S.; Zhang, X.J. Application principle and prospect of thermal-probe technique in cold region engineering. Chin. J. Rock Mech. Eng.
**2003**, 22, 2673–2676. [Google Scholar] - Xiu, F.; Zhang, Y.; Wang, S.; Li, B.; Jiang, W. Temperature characteristic and inhibition effect on insect pest in grain storehouse based on heat pipe technology. Trans. Chin. Soc. Agric. Eng.
**2013**, 14, 264–269. [Google Scholar] - Chen, X.L.; Li, J.W. Experiments of lowering the temperature of sandy soil speedily at night by heat-pipe technology. J.-Huazhong Univ. Sci. Technol. Nat. Sci. Ed.
**2007**, 35, 82–88. [Google Scholar] - Wang, S.Y.; Cheng, Q.L.; Han, H.S.; Wei, L.X.; Liu, Y.J. Study of Heat Transfer Characteristic in Gravity Heat Pipe of Well bore. Energy Conserv. Technol.
**2013**, 31, 46–60. [Google Scholar] - Yu, F.W. Role of Liquid Filling Ratio on Heat Transfer Characteristics in Miniaturized Gravitational Heat Pipe. J. Eng. Thermophys.
**2018**, 39, 2749–2754. [Google Scholar] - Wu, X.D. Laboratory Experiment and Field Test of Gravity Heat Pipe. J. Southwest Petrol. Univ.
**2008**, 1, 140–142. [Google Scholar] - Schmidt, M.; Suhendra, S.; Rüter, H. Heat pipes-Suitable for extinguishing underground coal fires? Fed. Minist. Educ. Res.
**2010**, 2, 433–437. [Google Scholar] - Rui, Q.U. Experimental Research of Gravity Heat Pipe Used to Extract Spontaneous Heat Storage in the Coal. Master’s Thesis, Xi’an University of Science and Technology, Xi’an, China, 2014. [Google Scholar]
- Zhang, Y.P.; Wang, J.G.; Ji, C.F.; Ma, L.; So, E. Cooling effect analysis of heat pipe suppressing coal spontaneous combustion. Coal Eng.
**2017**, 49, 100–102. [Google Scholar] - Wang, L.W. Study on Influence Factors of Heat Transfer Capacity of Heat Pipe Used for Coal Storage Pile. Master’s Thesis, Xi’an University of Science and Technology, Xi’an, China, 2017. [Google Scholar]
- Chen, Q.H.; Sun, M.H.; Su, G.Y. Influence of Gravity Heat Hipe on Temperature Field in Coal Pile. Saf. Coal Mines.
**2018**, 49, 211–214. [Google Scholar] - Deng, J.; Li, B.; Ma, L. Influence of heat pipes on temperature distribution in coal storage pile. China Saf. Sci.
**2015**, J25, 62–67. [Google Scholar] - Cheng, F.M.; Chang, Z.C.; Li, B. Numerical simulation on thermal migration behavior of spontaneous combustion coal pile based on heat pipe cooling technology. J. Xian Univ. Sci. Technol.
**2019**, 4, 581–588. [Google Scholar] - Li, B.; Deng, J.; Xiao, Y.; Zhai, X.; Shu, C.-M.; Gao, W. Heat transfer capacity of heat pipes: An application in coalfield wildfire in China. Heat Mass Transf.
**2018**, 54, 1755–1766. [Google Scholar] [CrossRef] - Deng, J.; Li, B.; Xiao, Y.; Ma, L.; Wang, C.P.; Lai-Wang, B.; Shu, C.M. Combustion properties of coal gangue using thermogravimetry-Fourier transform infrared spectroscopy. Appl. Therm. Eng.
**2017**, 116, 244–252. [Google Scholar] [CrossRef] - Senthilkumar, R.; Vaidyanathan, S.; Sivaraman, B. Comparative study on heat pipe performance using aqueous solutions of alcohols. Heat Mass Transf.
**2012**, 48, 2033–2040. [Google Scholar] [CrossRef] - Shen, C.; Zhang, Y.; Wang, Z.; Zhang, D.; Liu, Z. Experimental investigation on the heat transfer performance of a flat parallel flow heat pipe. Int. J. Heat Mass Transf.
**2021**, 168, 120856. [Google Scholar] [CrossRef] - Lu, P.; Liao, G.; Sun, J.; Li, P. Experimental research on index gas of the coal spontaneous at low-temperature stage. J. Loss Prev. Process Ind.
**2004**, 17, 243–247. [Google Scholar] [CrossRef] - Smith, M.A.; Glasser, D. Spontaneous combustion of carbonaceous stockpiles. Part I: The relative importance of various intrinsic coal properties and properties of the reaction system. Fuel
**2005**, 84, 1151–1160. [Google Scholar] [CrossRef] - Wu, Y.G.; Wu, J.M. Experimental study on significant gases of coal spontaneous combustion by temperature programmed (TP)-Science Direct. Proc. Eng.
**2011**, 26, 120–125. [Google Scholar] - Cao, K.; Zhong, X.; Wang, D.; Shi, G.; Wang, Y.; Shao, Z. Prevention and control of coalfield fire technology: A case study in the Antaibao Open Pit Mine goaf burning area, China. Int. J. Min. Sci. Technol.
**2012**, 22, 657–663. [Google Scholar] [CrossRef]

**Figure 6.**Comparison of the temperature with and without an HP. (

**a**–

**d**) show the temperature changes at the detection points at 0m, 1m, 2m and 3m from the HP compared to the without HP.

No. of HP | No. of Measuring Point | Depth/m | |||||||
---|---|---|---|---|---|---|---|---|---|

1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | ||

HP201 | T101 | 383.5 °C | 453 °C | 485 °C | 493.7 °C | ||||

T102 | 104.7 °C | 244 °C | 373.7 °C | ||||||

T103 | 122.2 °C | 260 °C | 394 °C | ||||||

T104 | 106.2 °C | 297.4 °C | 398.2 °C | 471.2 °C | 488.5 °C | 485.2 °C | |||

T105 | 122.2 °C | 246.7 °C | 404.7 °C | ||||||

T106 | 112.2 °C | 287.3 °C | 415 °C | ||||||

HP122 | T201 | 64 °C | 79.5 °C | 88 °C | 98 °C | ||||

T202 | 47.7 °C | 65 °C | 74.5 °C | ||||||

T203 | 49.7 °C | 77.2 °C | 74.2 °C | ||||||

T204 | 48 °C | 74 °C | 71.2 °C | 76 °C | 87.2 °C | 93.2 °C | 99.7 °C | 165 °C | |

T205 | 46.7 °C | 63.5 °C | 71.5 °C | ||||||

T206 | 60.7 °C | 79 °C | 81 °C | ||||||

HP168 | T301 | 260.7 °C | |||||||

T302 | 84.5 °C | 141.7 °C | 254.5 °C | ||||||

T303 | 94.2 °C | 157.5 °C | 251 °C | ||||||

T304 | 101.7 °C | 156.5 °C | 262 °C | 442.7 °C | 528.7 °C | 550.2 °C | 573 °C | 545 °C | |

T305 | 92 °C | 145.7 °C | 238 °C | ||||||

T306 | 101.2 °C | 175.5 °C | 298.2 °C |

Fitted Models | Quadratic Fitting Equations | Logarithmic Fitting Equations |
---|---|---|

1 m and 2 m | y = −0.0022x^{2} + 2.5671x − 43.669 (R^{2} = 0.941) | y = 162.61ln(x) − 543.4 (R ^{2} = 0.8725) |

1 m and 3 m | y = −0.0089x^{2} + 4.7838x − 78.533 (R^{2} = 0.9141) | y = 238.25ln(x) − 778.17 (R ^{2} = 0.8909) |

1 m and 4 m | y = −0.0201x^{2} + 7.9185x − 164.62 (R^{2} = 0.9646) | y = 292.7ln(x) − 945.83 (R ^{2} = 0.9437) |

1 m and 5 m | y = −0.0212x^{2} + 8.1371x − 143.95 (R^{2} = 0.9699) | y = 293.32ln(x) − 920.61 (R ^{2} = 0.953) |

1 m and 6 m | y = −0.0268x^{2} + 9.5022x − 150.73 (R^{2} = 0.9511) | y = 308.68ln(x) − 939.78 (R ^{2} = 0.9364) |

Fitted Models | Freedoms | F-Value | F Critical Value |
---|---|---|---|

1 m and 2 m | 34 | 7.825 | 5.29 |

1 m and 3 m | 29 | 6.438 | 5.42 |

1 m and 4 m | 8 | 11.312 | 8.65 |

1 m and 5 m | 5 | 15.496 | 13.3 |

1 m and 6 m | 6 | 12.852 | 10.9 |

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**MDPI and ACS Style**

Zhao, N.; Zhang, Y.; Zhao, X.; Niu, J.; Shi, H.; Yang, N.; Gao, T.; Guo, L.
Internal Temperature Variation on Spontaneous Combustion of Coal Gangue Dumps under the Action of a Heat Pipe: Case Study on Yinying Coal Mine in China. *Sustainability* **2022**, *14*, 9807.
https://doi.org/10.3390/su14169807

**AMA Style**

Zhao N, Zhang Y, Zhao X, Niu J, Shi H, Yang N, Gao T, Guo L.
Internal Temperature Variation on Spontaneous Combustion of Coal Gangue Dumps under the Action of a Heat Pipe: Case Study on Yinying Coal Mine in China. *Sustainability*. 2022; 14(16):9807.
https://doi.org/10.3390/su14169807

**Chicago/Turabian Style**

Zhao, Na, Yongbo Zhang, Xuehua Zhao, Jinrong Niu, Hong Shi, Na Yang, Tong Gao, and Lina Guo.
2022. "Internal Temperature Variation on Spontaneous Combustion of Coal Gangue Dumps under the Action of a Heat Pipe: Case Study on Yinying Coal Mine in China" *Sustainability* 14, no. 16: 9807.
https://doi.org/10.3390/su14169807