Occurrence And Emission Characteristics Of PAHs In Thermal Power Plants

The rapid development of industrialization and urbanization drives the demand for electricity.The production and consumption of electric power in China have been abundantly increasing since 1990.In 2017,China's thermal power generation capacity was 4662.7 billion k Wh,accounting for about 72%of the total power generation.The impact of thermal power plants on the environment is not only connected to the economy,but also important to human health.This work first analyzes the 16 priority polycyclic aromatic hydrocarbons?PAHs? specified by the US Environmental Protection Agency?US-EPA?at the inlet and outlet of bag filter of the circulating fluidized bed boiler in a coal-fired power plant;and then analyzes the halogenated polycyclic aromatic hydrocarbons?HPAHs?in combustion products.Finally,the effect of different processes on the formation of halogenated polycyclic aromatic hydrocarbons in thermal power plants was investigated.The main conclusions include:?1?the distribution of gas-phase and particulate-phase PAHs in coal-fired power plants is of great significance for predicting the removal efficiency of PAHs by dust removal devices;the removal efficiency of PAHs in gas phase and particulate phase is 45.59%and 70.67-89.06%,respectively;the gas phase is dominated by 2–and 3–ring PAHs,while the particle phase is dominated by 4–to 6–ring PAHs;as the particle size decreases,low molecular weight?LMW?PAHs have a downward trend;the gas-particle partitioning of PAHs is mainly controlled by the absorption of organic carbon,which shows a clear dependence on the particle size;the relationship between log?TPAH/PM?against D_p shows that PAHs are mainly adsorbed on the particles;the particle size separation of PAHs in PMs shows that the adsorption effect of high molecular weight?HMW?PAHs is more obvious than that of low molecular weight PAHs;?2?the particle size distribution of individual PAHs shows that most PAHs have a bimodal structure,one of which is in the range of 2.1-1.1?m,and the other in the range of 5.8-4.7?m;the intensity of these two peaks changes with the number of polycyclic aromatic hydrocarbon rings,which may be caused by the Kelvin effect;the emission factor of PAHs calculated in this study is 3.53 mg/kg coal-fired,and the total average EF_PAH is 0.55 and 2.98 mg/kg,respectively;in addition,the average PAHs emissions of CFPP studied were 1016.6 g/day and 371073.6 g/year,respectively;?3?the study of halogenated polycyclic aromatic hydrocarbons?HPAHs?content diagrams,composition characteristic diagrams,source analysis and toxicity equivalent?TEQ?of HPAHs content show that the structure of HPAHs in fly ash of different thermal power plants is similar,yet the combustion products and media of which are quite different;among Br-PAHs,9-Br Ant accounts for a relatively large amount;among Cl-PAHs,9,10-Cl₂Ant accounts for a relatively small amount;the HPAHs halogenated by Ant are different from other HPAHs pollution sources,and Cl-PAHs and Br-PAHs also come from different pollution sources;the main sources of HPAHs for combustion products and media are the same,but there are new sources of HPAHs pollution after deacidification and chelation of fly ash;the concentration of HPAHs in the combustion products of the power plant is comparable to the TEQ of dioxins compared with literature studies;the power plant emits about 66225g/year of HPAHs from fly ash at most.