Study On The Emission Characteristic Of Polycyclic Aromatic Hydrocarbons In Coking Process

Coking industry occupies an important position in the national economy. But a large number of pollutants were emitted to surroundings including physiological and toxic organic compounds such as polycyclic aromatic hydrocarbons (PAHs)during coking process, The potent carcinogens, biological and mutagenic effects of some PAHs have been well demonstrated. Considering the obvious adverse effects on local environmental and human health, great attentions have been focused on PAHs emission from coking industry.Four coke ovens with different dimensions were selected in present study, including 6.0 m,4.3 m and 3.2 m. The gas phase samples flue gases, air on the top of coke oven and solid phase samples fume during coaling and coke discharge processes were collected based on "Integrated emission standard of air pollutants", the PAHs absorbed on solid samples were extracted by Gerhardt Soxhlet using dichloromethane as the extraction solvent and that existed in gas samples were extracted by ordinary Soxhlet. The 16 PAHs which were priority controlled internationally were detected by Gas Chromatography-mass Spectrometer (GC-MS). Blended coals used in four mentioned different coke ovens were first extracted by dichloromethane and the corresponding PAHs contents escaped accompanied with volatile in the coal heating process were got for discussing the emission factors on PAHs during coking process,. And then, the flash pyrolysis experiments with a heating rate 10℃/ms were run in PY-GC-MS and the formation rule of 16 PAHs were studied. The main conclusions are as following:1. The absorption amounts and distribution characters of the 16 PAHs that emitted from different working procedure in four different coking plants were discovered. Whether stamp-charging or top-coaling coke oven, the PAHs emission amounts of per ton coals in coaling, coke discharge and the top of coke oven all decreased with the coke oven volume increased. To the same volume stamp-charging and top-coaling coke oven, the PAHs emission amounts in different working procedure of the former are always lower than the latter.2. It was found no obvious differences on PAHs amount when the blended coals that used in four different coke ovens were pyrolysised in our lab, but which are all higher than the extracted amounts from the raw coal. It indicated that the main source of PAHs from pyrolysis process is the chemical reactions during coal pyrolysis. However, there were the larger differences of the releasing amount of PAHs from the four coking plants under the same pyrolysis temperature and that should attribute to operation factors.3. To the blended coals that used in four different coking plants, the main components of PAHs that could be extracted and that produced by pyrolysis emission are naphthalene and phenanthrene. However, the PAHs in particle-phases during coaling procedure and coke discharge process are taken pentacyclic Benzo[b]fluorathene and Benzo[k]fluorathene as main components. It means naphthalene and phenanthrene released from the process of coaling and coke discharge had been discharged into gas phase. And at the process of coaling and coke discharge, the materials occured the incomplete combustion reaction.4. The content of particles of coal that less than 3mm in tamping coking blended colas are 15% higher than that in a top-coaling condition. And these small particles, which are more easily be absorbed by PAHs and fly into surroundings, is the main reason that cause the emission of PAHs. Through advanced dust removal system, large-scaled dimensions coke oven and improving of operation level at all procedure of coke oven are all effective measures of reducing emission of PAHs of coking plant.