Research On Emission Characteristics Of Main Atmospheric Pollutant And Their Behavior During Mechanical Cokinii Processes

The pollutants emitted from coking can have a significant impact on the environmental quality and human health. To control these emissions effectively, establishing the source profiles of various contaminants is very urgent. In addition, understanding the emission levels, distribution characteristics and emission factors of the various contaminants is very significant for improving the air quality in the coking areas.In the present study, typical coke plants were selected, and the samples from different flues and fugitive emission from each plant were collected. OC、EC and PAHs emission levels, distribution characteristics, PAH gas-particle partitioning and its formation mechanism were discussed. Emission factors and amounts of these pollutants were calculated. On the other hand, emission characteristics of heavy metals and their behavior during coking in a typical coke plant were investigated.Emission characteristics of OC and EC during coking processes:(1) The concentrations of OC and EC in the stack flue gas were significantly higher than those emitted from fugitive emissions, and OC、 EC concentrations from coke pushing were obviously higher than those from coal charging and combustion of coke oven gases.(2) The EC/OC ratios for different coking processes in the same coke plant were similar with each other, however, for the some process, it varied significantly in different plants. It should be cautious to apply EC/OC ratios in source apportionment.Emission levels of PAHs in stack flue gases, fugitive emission and fly ash collected by the air pollution control device during coking:The total PAH concentrations from coal charging (359.55μg/m3) were obviously higher than those from coke pushing (124.20μg/m) and combustion of coke oven gases (226.64μg/m3). PAH concentration from fugitive emission was56.24μg/m3, and it is3-fold higher for coke plant with stamp charging than that for plant with top charging. PAH content in the ashes collected by the air pollution control devices (APCD) was2911.05μg/g, and this content for coal charging was significantly higher than that for coke pushing in the same coke plant.PAHs characteristics in composition, gas-particle partitioning and its formation mechanism:PAH compositions in the stack flue gases and fugitive emission were consistently dominated by low molecular weight (LMW-PAHs), however, middle molecular weight (MMW-PAHs) and high molecular weight (HMW-PAHs) were dominant for the ashes collected by APCD. PAHs emitted from coking processes were mostly present in the gas phases, and different PAH have different distribution characteristics. Absorption into organic carbon dominated the gas-particle partitioning of PAHs from fugitive emission during coking and different mechanisms control this processes for different PAHs.Evaluation of BaP-equivalent carcinogenicity for coking processes: The carcinogenic potency of the total PAHs (total BaPeq) from fugitive emission was higher than that from coal charging and coke pushing. In addition to BaP, DbA was also an important contributor to carcinogenic risk in emissions from stack flue gases, fugitive emission and fly ash collected by APCD. More than90%of carcinogenicity was attributable to particulate smaller than1.4μm.From the point of human health, some effective control measures should be taken to reduce the emission of fine particles, BaP and DbA.Source profile of PAHs from coking processes:PAHs profiles for stack emission and fugitive emission during coking processes showed as bimodal distribution, and the first peak was NaP followed by Flu, PhA and AnT. However, Chr, BaA, and BbF were found to be the most abundant PAHs in the ashes collected by APCD. Source profile of gaseous PAHs was similar with total PAHs, and different from particulate PAHs.Size distributions of PAHs in aerosol emissions from coking:Particulate PAHs emitted from coal charging, coke pushing and fugitive emission mainly distributed in the particles less than1.4μm.2-ring PAHs distributed uniformly in particles with various size ranges, however,5-to6-ring PAHs were mainly in fine particles. PAHs source profile in fine particles (less than1.4μm) from coal charging was similar with that from coke pushing, however, for coarse particles (larger than1.4μm), it was different with each other.Calculation of emission factors and emission amount for OC, EC and PAHs:Emission factors of OC, EC and PAHs from coal charging were1.73,0.78g/t and346.13mg/t coal, respectively. Emission factors of OC, EC and PAHs from coke pushing were1.36、0.67g/t and93.17mg/t coal, respectively. Emission factors of these pollutants from the coke oven with the height of6m were significantly lower than those from the ovens with the height of3.2m and4.3m. During the year of2010, the total emission amount of OC, EC and PAHs from coal charging and coke pushing were1455.38,683.68and207.13t, respectively, among which814.13,367.77and163.20t was from coal charging, and641.25,315.91,43.93t was from coke pushing.Emission characteristics of heavy metals and their behavior during coking processes:During coking, the heavy metals that were contained in the coal showed different partitioning patterns. Cu, Zn, As, Pb and Cr were obviously concentrated in the inlet fly ash compared to the coke; among these metals Cu, As, and Cr were concentrated in the outlet fly ash, whereas Zn and Pb were distributed equally between the outlet fly ash and APCD residue. Ni, Co, Cd, Fe, and V were partitioned equally between the inlet fly ahs and the coke.