Formation and distribution of polycyclic aromatic hydrocarbons (PAHs) derived from coal seam combustion: A case study of the Ulanqab lignite from Inner Mongolia, northern China

Coalfield fires are hazardous to the environment and human health as a result of the release of polycyclic aromatic hydrocarbons (PAHs). The incomplete combustion processes of the Ulanqab lignite from Inner Mongolia of northern China during coalfield fires were simulated in a tubular furnace, and 16 US Environmental Protection Agency priority pollutant PAHs in the flue gas were absorbed and analyzed. The results indicate that incomplete combustion results in a clear increase in PAH emission compared with other combustion methods; this is attributed to the formation of species with two and three benzene rings, such as naphthalene, acenaphthylene, and acenaphthene. Benzo[a]pyrene, dibenz[a,h]anthracene, and benz[a]anthracene make a large contribution to the toxicity equivalent value (TEQ), although they make up a small proportion of the PAHs. With temperature increasing, the total PAH yield peak occurs at 800 °C with a yield of 923.41 mg/kg at an air/coal ratio of 1 m3/kg. As the air/coal ratio increases, the amount of PAHs varies with the addition of oxygen. At a ratio of 2 m3/kg, the minimum PAH yield of 486.07 mg/kg occurs at 800 °C and the maximum concentrations of the most toxic species, benzo[a]pyrene, and dibenz[a,h]anthracene, are found. Increasing the coal particle size from 0.25 to 20 mm results in a significant growth of both the yields and TEQs of the PAH species.

► Incomplete combustion of coal seam results in a clear increase in PAH emission. ► NaP, AcPy, and AcP are the main PAH species in the flue gas. ► BaP, DbA, and BaA make the biggest contribution to the Total TEQ value. ► PAH formation and toxicity are remarkably affected by air/coal raito.