Study on the Effect of Pore Evolution on the Coal Spontaneous Combustion Characteristics in Goaf
Abstract
:1. Introduction
2. Governing Equations for Goaf CSC
2.1. Momentum Conservation Equation
2.2. Mass Conservation Equation
2.3. Energy Conservation Equation
2.4. Cross-Coupling Relationship
3. Model Construction and Validation
3.1. Engineering Overview
3.2. Assumptions and Physical Modelling
- (1)
- The gas movement in goaf conforms to the non-Darcy Forchheimer’s law, and the oxygen consumption for coal oxidation is determined using the Arrhenius equation.
- (2)
- The gas in the goaf is considered an ideal gas, and the impact of temperature on its kinetic viscosity is disregarded.
- (3)
- Disregarding the gas outflow from the goaf and other gases (CO, CO2, CH4, SO2 and NOX, etc.) produced during CSC, the gases in the goaf are mainly air.
- (4)
- The goaf is simplified to a two-dimensional non-homogeneous porous medium flow field.
- (5)
- Using the 1302 working face as an example, a physical model was established, as shown in Figure 2. The inlet and return airway measure 4 m in width and 8 m in length, the working face measures 7 m in width and 132 m in length, and the goaf measures 140 m in width and 150 m in length. The simulation boundaries and parameters for goaf CSC are shown in Table 1 and Table 2.
3.3. Permeability Evolution of Goaf
3.4. Parameter Setting
3.5. Model Validation
4. Results and Discussion
4.1. Spatial Distribution of Porosity and Permeability
4.2. Spatial Distribution of Oxygen Concentration and Airflow Velocity
4.3. Spatial Distribution of Temperature
4.4. Spatial Distribution of CSC Three Zones
5. Conclusions
- (1)
- Both porosity and permeability decrease with increasing goaf depth. The goaf porosity is positively correlated with the permeability. When the goaf maximum porosity was increased from 25 to 40%, the average flow velocity increased by about 6 times. This demonstrates that porosity has a significant impact on air leakage in the goaf.
- (2)
- The oxygen concentration in the extraction zone increases as the porosity increases and exhibits a trend of initially increasing and then decreasing over time. Similarly, the temperature trend varies with different goaf porosities, increasing over time. As porosity increases, the high temperature zone gradually expands along the goaf depth.
- (3)
- Over time, the CSC three zones in the goaf exhibit a tendency to decrease in the radiator and oxidation zones, while increasing in the asphyxiation zone. The range of the CSC three zones is positively correlated with the goaf porosity. Specifically, the higher the goaf porosity, the greater the area of the oxidation zone and, consequently, the higher the CSC risk.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Coal Sample | Number | Mad (%) | Vad (%) | FCd (%) | Ad (%) |
---|---|---|---|---|---|
Lignite coal | S1 | 16 | 33.5 | 31.7 | 34.8 |
Boundary | Pressure | Concentration | Temperature |
---|---|---|---|
AD | p = p0 + R·Q2·(L − y) | T = T0 | |
AB/BC/CD |
Parameters | Value | Unit | Parameters | Value | Unit |
---|---|---|---|---|---|
Initial expansion coefficient, | 1.5 | - | particle diameter, dp | 0.04 | m |
Compaction expansion coefficient, | 1.12 | - | Initial pressure, p0 | 1 | atm |
Attenuation rate, a0 | 0.0368 | - | Adjustable parameters, | 0.233 | - |
Attenuation rate, a1 | 0.0268 | - | Initial O2 concentration, | 9.375 | mol/m3 |
Initial temperature, T0 | 27 | °C | solid density, | 1250 | Kg/m3 |
Activation energy, Ea | 45.5 | KJ/mol | Gas density, | 1.1 | Kg/m3 |
Indexing factor, A | 180 | 1/s | Solid specific heat capacity, Cps | 1200 | J/(kg·K) |
Ideal gas constant, R | 8.314 | J/(mol·K) | Gases specific heat capacity, Cpg | 1012 | J/(kg·K) |
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Li, J.; Xu, H.; Wu, G. Study on the Effect of Pore Evolution on the Coal Spontaneous Combustion Characteristics in Goaf. Fire 2024, 7, 164. https://doi.org/10.3390/fire7050164
Li J, Xu H, Wu G. Study on the Effect of Pore Evolution on the Coal Spontaneous Combustion Characteristics in Goaf. Fire. 2024; 7(5):164. https://doi.org/10.3390/fire7050164
Chicago/Turabian StyleLi, Jinglei, Hao Xu, and Genshui Wu. 2024. "Study on the Effect of Pore Evolution on the Coal Spontaneous Combustion Characteristics in Goaf" Fire 7, no. 5: 164. https://doi.org/10.3390/fire7050164