Spread law of loose coal combustion under lateral wind flow conditions on the surface

Abstract

Spontaneous combustion of coal increases the risk of fires during its storage and transportation, posing a challenge to the sustainable development of the coal industry. This study employs various similarity criteria, including geometric, time, kinematic, dynamical, Euler’s, Strohal’s, Vernold’s, and Reynolds’ criteria, to investigate the rules of the spread of loose coal body combustion under wind flow conditions using a self-built, open-vehicle coal transportation simulation experimental device. The device recreates the temperature rise process in loose coal bodies, the formation of high-temperature areas, and their subsequent spread. It also analyzes the internal high-temperature area spread and gas distribution rules under wind flow. During the experiment, the temperature of each measurement point changed as the constant temperature time increased, with the measurement points closer to the heat source showing a significant temperature increase compared with those farther away. The experiments were conducted for 70, 54, and 48 h under wind flows of 0, 1, and 2 m·s−1, respectively. The results reveal that the crosswind flow on the surface significantly accelerates the spread of the seed of coal sample combustion. Compared to wind flow at 0 m·s−1, the high-temperature area spread time is 0.3 times quicker (wind flow at 1 m·s−1) and 0.5 times quicker (wind flow at 2 m·s−1); moreover, the maximum temperature of the high-temperature area increases by 120 ± 20 ℃, eventually stabilizing at 510 ℃–560 ℃. The spreading path of the high-temperature area drifts toward the wind under the influence of crosswind flow on the surface. When the wind flow is 0 m·s−1 the difference between the time when the CO concentration peaks at the critical point of each layer and when the critical point reaches 300 ℃ (Δh1) gradually increases with the number of layers. However, under the effect of wind flow, Δh1 is maintained at 1.4 ± 1 h (wind flow at 1 m·s−1) and 0.9 h (wind flow at 2 m·s−1), thus intensifying the coal–oxygen reaction and causing the combustion to spread more rapidly. For each critical point of the oxygen volume fraction of the layers, the time elapsed during the rapid decline phase of the O2 volume fraction at the high-temperature point of combustion gradually increases with depth. When the wind flow is 0 m·s−1, the difference between the time to reach the limiting O2 volume fraction at the critical point and the time to reach 300 ℃ at the critical point (Δh2) increases with depth. However, under the effect of wind flow, Δh2 is maintained at 0.6 ± 0.3 h (wind flow at 1 m·s−1) and 1 ± 0.2 h (wind flow at 2 m·s−1), indicating that surface airflow can exacerbate the rate of O2 consumption during the downward spread of high temperatures. Therefore, controlling air leakage can delay the spread of coal fires. These findings offer valuable insights for developing guidelines to control coal fires during coal transportation and storage.

Keywords

• coal spontaneous combustion
• cross wind flow
• temperature field
• gas spreading
• open-vehicle coal transportation