Influence of temperature and airflow on polycyclic aromatic hydrocarbons (PAHs) by simulated self-combustion of coal partings

Abstract

Simulation of spontaneous combustion of partings in intermediate rank coal, aiming to study the influence of temperature and airflow on the formation and emission of 16 PAHs (Polycyclic Aromatic Hydrocarbons) specified by US Environmental Protection Agency as priority pollutants, and investigate the origin of PAHs. The experiments were performed from 50°C to 950°C, varying the airflow rates from 300mlmin∧1 to 1200mlmin∧1, with a constant interval time of50min. PAHs released from spontaneous combustion were collected by XAD-2 resin and dichloromethane solvent, then extracted with Soxhlet extraction method. High performance liquid chromatography (HPLC) was used to analyze the amount and composition of PAHs. The result indicates that the amount and toxicity of PAHs are much higher after self-combustion of coal wastes. Furthermore, oxidization of coal gangue at lower temperature stage (50°C•450°C) released much more PAHs and toxicity than that of combustion of coal gangue at higher temperature stage (550°C•950°C) basically. LPAHs (Low molecular weight PAHs)with two- and three-ring dominate the total PAHs yields, and the HPAHs (High molecular weight PAHs) ratios at high temperatures are relatively higher than that at low temperatures. The distribution of PAHs from coal wastes self-combustion indicates that the PAHs emitted are most undecomposed PAHs from petrogenic source, but with temperature increasing, the intensity of oxidation and pyrolyzation cause the total amount of PAHs decreased and HPAHs ratio increased.