Temperature Spreading Characteristics of Water-Bearing Weathered Coal Smoldering Process and Its Gas Emission Behavior Under Parallel Air Supply Conditions

To investigate the temperature propagation characteristics and gas emission behavior of weathered coal during underground smoldering processes, this study conducted oxidative thermal decomposition on water-bearing weathered coal samples. Using a custom-built smoldering simulation platform, we systematically examined the smoldering process under controlled conditions. The experimental results demonstrate three distinct oxidative thermal decomposition stages: moisture evaporation and carboxyl decarboxylation (25–200°C), organic matter pyrolysis with volatile release (300–600°C), and inorganic decomposition with phenolic compound formation (600–800°C). A characteristic temperature plateau of 70–80°C was observed during the ignition phase. Increasing the airflow velocity from 6 mm/s to 60 mm/s increased the vertical forward smoldering propagation speed from 8 mm/h to 180 mm/h and reduced the total duration by 65 ± 3%. The gas yield increased by 35% when moisture content was in the 20–30% range. The primary gaseous emissions identified were CO, CO₂, CₓHy, SO₂, and NOx. This comprehensive study systematically analyzes the effects of airflow direction (forward/reverse) and spatial orientation (vertical/horizontal) on smoldering characteristics, revealing significant nonlinear interactions between moisture content and airflow velocity. The results provide valuable theoretical insights and practical technical parameters for effective coal mine fire prevention and control strategies.