Spontaneous combustion of residual coal in longwall goaf is a long standing hazard. Airflow leakage into goaf is a major driver to the hazard and this issue deteriorates where longwalls are operating in multiple seams and shallow covers because mining-induced cracks are very likely to draw fresh airflow into goaf due to presence of pressure differential between longwall face and surface. To study the problem more critically, a ventilation simulation package "Ventsim" is used to conduct a case study from Bulianta colliery. It was found that isolating and pressurizing active longwall panel can mitigate the problem and the pressure differential can be adjusted by varying performance of auxiliary fan and resistance of ventilation regulator. A booster ventilation system can also mitigate the problem by adjusting fan duties. Ventilation simulation is a powerful tool to study spontaneous combustion control in underground coal mine.
ABSTRACT: An experimental study was undertaken to examine the sorption and desorption characteristics of coal at temperatures of 35 °C, 45 °C and 55 °C. The study focused on the effect of changes in temperature and coal particle sizes on gas sorption and desorption characteristics. The coal size used ranged from fragmented coals, 16 mm, 8 mm, 2.4 mm, powdered coal of 150 µm and 54 mm core samples. The samples were tested in pressure vessels, known as bombs, and charged with CO 2 gas at different pressure levels up to a maximum of 4000 kPa. It was found that temperature was a significant influence the sorption and desorption behaviour. The degree of hysteresis phenomenon was found to be influenced by the coal surface area as we ll as temperature. The Langmuir equation was used to model CO 2 sorption and desorption. Both Langmuir volume and Langmuir pressure were assessed in relation to the changes at different temperatures and was found to tally well with the experimental results. INTRODUCTION
Computational fluid dynamics (CFD) is an effective methodology that has been widely used for decades to solve engineering problems involving spontaneous combustionand abnormal gas emissions. However, most of the previous CFD modelling focused on qualitative rather than quantitative analysis, and the factors influencing spontaneous combustion control and gas management are numerically under-researched. The onset of spontaneous heating in the goaf area is dictated by many operational and environmental parameters, including mining method, ventilation and geology. Based on field data from a real mine site, extensive CFD modelling was conducted and analyzed qualitatively and quantitatively to investigate the impact of ventilation design and operational measures on the management and control of spontaneous combustion and gas exceedance. Real-time gas monitoring data was utilized for model validation, and a good agreement between simulation results and monitoring data was reached. The tightness of goaf seals described by permeability was quantitatively investigated, revealing that the permeability should be smaller than 10 -9 m 2 to prevent air leakage effectively. Goaf inertisation parameter optimization is crucial to minimize the risk of spontaneous combustion. The systematic study revealed that the oxidation zone area (OZA) was the largest for nitrogen injection (29706 m 2 ), followed by boiler gas (28396 m 2 ), while it was the smallest for carbon dioxide (11902 m 2 ), which produced the best goaf inertisation performance. Injection flow rate is another significant factor influencing the effectiveness of heating prevention. The simulation results indicated that a critical injection rate of 1750 m 3 /h was determined, and the ratio of the OZA to the goaf area (GA) fluctuated around 7% once the injection rate was beyond this critical value. The installation location of curtains and brattices both on the longwall face and tailgate end was also simulated and optimized. Noticeable methane reduction at the tailgate end was observed with optimal configurations of brattices and curtains. Results from the modelling will be shed light on improving current practices to effectively contain goaf heating in the longwall goaf areas and mitigate methane exceedance on the longwall face.
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