| Volatile organic compounds（VOCs）generated by coal coking process significantly affects environmental air quality and poses great harm to human health.It is of great significance to clarify emission concentration and composition characteristics,photochemical reactivity and emission factors of VOCs during coal coking process to improve the regional environment affected by coking industry.The construction of VOCs source composition profiles and isotope composition characteristics of coking industry can also provides important data support for VOCs source analysis in ambient air.In this paper,taking typical coking plants as the research object,samples from the coking process（flue gas of coke oven,charging,pushing,blocking and the top of coke oven）,chemical byproduct recovery process and sewage treatment process in each coke plant were sampled.VOCs concentration level,ozone and secondary organic aerosol generation potential,the isotopic composition of aromatic VOCs characteristic were analyzed,and VOCs emission factors and emissions were calculated in the different types of coking plants.The main conclusions are as follows:VOCs emission characteristics from coal coking process:（1）The concentration of total volatile organic compounds（TVOCs）in the flue gas of coke oven,charging,pushing and blocking in coking process were 10.01 mg/m3,6.45 mg/m3,152.41 mg/m3 and 11.93 mg/m3,respectively.Alkanes and aromatics were the main VOCs compounds,benzene,ethylene,ethane and 1-butene were the main components in coking process.（2）The concentration of TVOCs in the waste gas from the chemical byproduct recovery process was 15.19 mg/m3,alkene was the main VOCs compounds,and the main VOCs species included ethylene,benzene,ethane,acetylene,propylene and toluene.Alkene and aromatics were the main compounds of waste gas in different production processes,and the characteristic components included benzene,ethylene,ethane and acetylene.（3）The concentration of TVOCs in waste gas from the sewage treatment process was 43.15 mg/m3,aromatics was the main VOCs compounds,and the characteristic components were benzene,toluene.（4）According to the coefficient of divergence and source component profiles of different emission sources in coking plants,the VOCs source component profiles of various emission sources in coking plants had certain similarity,and benzene,ethylene,ethane,1-butene and propylene were characteristic compounds.（5）The B/T,B/E and B/X values from coking plants were significantly different from other emission sources,which can be used as one of the main indicators to distinguish other emission sources.Ozone and SOA formation potential of VOCs emission during coal coking process:（1）Alkene had the highest contribution to ozone formation potential（OFP）in coking and chemical byproduct recovery process.The compounds with the highest OFP contribution from waste gas of sewage treatment process were aromatics.The OFP value of VOCs released from each emission source ranked as charging flue gas>waste gas from chemical byproduct recovery process>waste gas in sewage treatment process>coke oven flue gas>blocking flue gas>pushing flue gas,and coal charging process should be the priority emission sources.Benzene had the highest OFP proportion of VOCs in charging flue gas,and ethylene had the highest OFP proportion of other emission sources.Benzene,ethylene,propylene and 1-butene were the key components to reduce OFP values in coking plants.（2）The secondary organic aerosol formation potential（SOAFP）of VOCs in each emission source is ranked as waste gas in sewage treatment process>blocking flue gas>charging flue gas>waste gas from chemical byproduct recovery process>coke oven flue gas>pushing flue gas,and the sewage treatment was the priority SOAFP control process.Aromatics and benzene were the compounds and components with the highest VOCs contribution to SOAFP in coke oven flue gas,pushing flue gas,blocking flue gas and waste gas from chemical byproduct recovery and sewage treatment,while alkene and ethylene were the compounds and components with the highest VOCs contribution to SOAFP in charging flue gas.Benzene,toluene,ethylbenzene,o-xylene and m/p-xylene were the key to control the SOA generation in coking plants.Stable carbon isotopic compositions of monocyclic aromatics during coal coking:（1）Theδ13C values of benzene,toluene,ethylbenzene and xylene（BTEX）ranged from-27.10‰to-32.58‰,and there was no significant difference in the carbon isotope composition of BTEX in the flue gas emitted from chemical product recovery process,pushing,blocking,coke oven,sewage treatment process and in the ambient air on the top of coke oven during the coking processes.（2）Theδ13C values of benzene in the VOCs discharged from coke pushing process（pushing and blocking）,coke oven,chemical byproduct recovery process,sewage treatment process and the top of coke oven were-31.84±1.44‰,-30.37±0.88‰,-27.10±3.68‰,-31.47±0.63‰and-30.66±1.46‰,respectively.It is found that theδ13C values of benzene in different emission sources were different,which could be used as one of the indicators to analyze the source of VOCs in ambient air.VOCs emission factors and emissions during coal coking process:（1）The emission factors of TVOCs in flue gas fromcoke oven,pushing,charging and blocking in coking process were 16.64 g/t coke,2.85 g/t coke,35.11 g/t coke and 9.5 g/t coke,respectively.The emission factors of TVOCs in waste gas from sewage treatment and chemical byproduct recovery were 5.52 g/t coke and 0.56 g/t coke,respectively.（2）The emission factors of aromatics in coke oven flue gas,coke blocking flue gas and sewage treatment exhaust gas were higher than other VOCs components.The emission factor of alkene was the highest in the waste gas from the charging and chemical byproduct recovery,and the emission factor of alkane was the highest in the coke pushing flue gas.Ethylene,benzene,ethane,n-butane and propylene had the highest emission factors in coking plants（3）Based on the VOCs emission factors obtained in this study,it was estimated that the annual VOCs emissions of China’s coking industry from 2018 to 2020 were 31464.64 tons,33066.09 tons and 33073.14 tons,respectively.VOCs emissions in China showed obvious spatial distribution characteristics,and VOCs emissions in north were significantly higher than those in south in China.VOCs emissions from coking process in Shanxi were the highest,accounting for 22.27%of China’s total emissions,followed by Shaanxi（10.39%）,Hebei（10.24%）,Inner Mongolia（8.96%）and Shandong（6.71%）.Based on Monte Carlo simulation,the uncertainty of VOC emissions estimated in 2020 ranged from-68%to 115%,and the uncertainty of emissions in each province was basically the same. |
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