Abstract:
Petroleum coke consumption is an important contributor to energy production in China and is regarded as one of the most important sources of air pollutants that have considerable impacts on human health. Particularly, hazardous organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) generated during combustion process of petroleum coke are highly genotoxic, mutagenic and carcinogenic. The effects of combustion conditions on the formation of PAHs in petroleum coke combustion process were studied in a tube furnace by controlling combustion temperature and atmosphere.The influence of the composition of petroleum coke on the formation of PAHs was further investigated by burning six types of petroleum coke at 800℃. The experimental results show that, the release amount of PAHs increases up to a maximum value at 700℃ as the combustion temperature (600-900℃) is increased in air, while above 700℃, the intensity of oxidation and thermal degradation cause a decrease of the PAHs emission. Similarly, the release of PAHs is initially increased and then decreased with the increasing of pyrolysis temperature in N
2, and the maximum release is reached at 800℃. 2-ring and 3-ring PAHs are the main species at different temperatures and atmosphere conditions. PAHs are generated not only by thermal degradation of petroleum coke structure, but also by the combination of different small molecular free radicals with each other. The higher the volatile substance of petroleum coke is, the more small molecular free radicals are produced during the combustion. Therefore, the release of PAHs increases with of the amount of volatile substance during the petroleum coke combustion. Moreover, the release of PAHs decreases with mass fraction of sulfur element in petroleum coke. The release of PAHs decreases first and then increases with the mass fraction of carbon element in petroleum coke during the combustion.