Analyzing the effect of recirculation on the methane dilution process at the working surface of underground coal mines.
Nandita Suri Kallo(a*), Shulha Muzakkir(a),Deksarina(a), Safira Salsabila(a), Ririn Yulianti(a,b), Nuhindro Priagung Widodo(a), Ahmad Ihsan(a,c), Fadli Zaka Waly(a), Kamran Ali(a)

a) Rekayasa Pertambangan, Fakultas Teknik Pertambangan dan Perminyakan Institut Teknologi
Bandung, Bandung 400191, Indonesia.
*22122016[at]mahasiswa.itb.ac.id
b)Teknik Pertambangan, Fakultas Teknologi Kebumian dan Energi, Universitas Trisakti, Jakarta 1140, Indonesia.
c) Safety Engineering, China University of Mining and Technology, Xuzhou, Jiangsu, 221116, China.

Abstract

Methane is typically located amidst fractures, voids, and coal seam pores within coal mines. Excavating tunnels in underground coal mines can induce shifts in pressure gradients, leading to methane emissions. Elevated methane levels surpassing safety thresholds at the working surface pose explosion risks for underground mining personnel. One approach to mitigate methane concentration in underground mines involves diluting methane gas by augmenting the flow of fresh air. Enhancing clean airflow is achievable through the implementation of a Ventilation-on-demand (VoD) system. VoD operates as a mine ventilation system regulating fan power based on surface air conditions to ensure a safe working environment.
This study utilized Computational Fluid Dynamics (CFD) numerical methodology employing Ansys 2024 R1 Student software to simulate airflow, airspeed, methane gas dilution, and distribution within the system pre and post-dilution. Numerical modeling was conducted on an underground mining tunnel measuring 4 x 0.4 x 0.4 m, with fresh air introduced via a duct measuring 0.06 m in diameter and 3.8 m in length. Two conditions were simulated: first, the gas dilution process without methane recirculation in the incoming fresh air, and second, the gas dilution process with methane recirculation.
Before dilution, airspeed in the duct measured 0.8 m/s, escalating to 2 m/s during the dilution process. Modeling outcomes revealed that in the initial condition, the dilution process required 230 seconds to decrease methane concentration from 0.6% to 0.2%. Conversely, in the second condition with methane recirculation, it took 241 seconds for methane concentration to decline from 1% to 0.8%. This suggests that recirculation prolongs the dilution process and prevents the attainment of permissible threshold concentrations.

Keywords: Methane- Ventilation on demand- Computational fluid dynamics- Dilution- Recirculation

Topic: Healthy, Safety, Environmental (HSE), and Hazard Mitigation