Abstract:
The utilization of coal leads to the emission of organic pollutants that cause significant harm to the environmental. The coal consumption in China is particularly high, making the emissions of organic pollutant an issue that cannot be overlooked. In this work, the organic components of raw lignite, anthracite, and Tianchi coal were analyzed using Fourier transform infrared analysis method. The characteristics and influencing factors of polycyclic aromatic hydrocarbons (PAHs) were investigated with a fixed-bed pyrolysis system. The 16 kinds of PAHs were quantitatively determined by gas chromatography-mass spectrometry (GC-MS), while the composition of released organic pollutants was explored through qualitative analysis. The results indicate that alkanes are the primary organic compounds in coals, accounting for 39%−61%. Lignite contains the greatest variety and quantity of hydroxyl groups, along with more complex oxygen-containing functional groups, whereas anthracite exhibits a higher degree of aromatization. The optimal extraction time for PAHs from raw coal is 12 hours. The PAHs content of anthracite, Tianchi coal, and lignite are 10.34, 15.10 and 0.75 μg/g, respectively. The pyrolysis time is found to be a critical factor influencing PAHs formation. At 30 minutes, pyrolysis can be considered complete, with PAHs fully released. With the increase of the pyrolysis temperature, PAHs emission of lignite and Tianchi coal increases and then decreases. The maximum emissions are observed at 1 000 ℃, with the values of 3 168.15 µg/g and 974.58 µg/g, respectively. For anthracite, PAHs emissions followed a different trend-increasing, then decreasing, and finally rising again, with a maximum of 853.93 μg/g at 1 100 ℃. The volatile matter content has a pronounced effect on PAH emissions, and coals with higher volatile content generate more PAHs. Furthermore, halogen elements in Tianchi coal are found to hinder the aromatization and condensation reactions of benzene rings, thereby affecting PAHs formation. The maximum toxic equivalency of lignite and anthracite occur at 1 000 ℃ and 1 100 ℃, with values of 85.59 μg/g and 75.00 μg/g, respectively. For Tianchi coal, the maximum toxic equivalency is observed at 800 ℃, with a value of 24.33 μg/g.