Emission Characteristics Of Volatile Organic Compounds (VOCs) From Typical Chemical Enterprises

Volatile organic compounds(VOCs)was one of the most important pollution incentive which reduced the air quality in China.In recent years,more and more photochemical pollution phenomenon by PM2.5 and ozone occurred in many regions.Since the large emission intensity,high emission concentration and complex types of pollutants,the industrial pollution sources,especially the chemical industry,will become to the difficulties in the comprehensive treatment and control of VOCs in the next few decades.Gradually,a large number of research work has shown that the VOCs emitted by petrochemical,coal chemical,fine chemical can account for more than 80%in total industrial sources.In this paper,the emission laws and pollution sources with the VOCs emission of a few typical chemical enterprises in Shizuishan City were researched through field investigation,distribution sampling,composition detection and data analysis.On the basis,the theoretical and data foundation for the comprehensive control of VOCs and the long-term pollution mechanism of the chemical park was established.The main conclusions are as follows.(1)The results of the classification survey and calculation of the VOCs emissions of VOCs emissions in the industrial park showed that:the VOCs emissions of chemical enterprises usually comes from the leakage of equipment dynamic and static sealing location,the storage and blending of organic liquid,loading/unloading volatilization of organic liquid,collection,storage and disposal of wastewater,cooling tower/circulating water cooling system,abnormal working conditions,and organized emissions,etc.In the source item above,the storage and blending of organic liquid,loading/unloading volatilization of organic liquid,collection,storage and disposal of wastewater were the the three with the largest number of totals.It should be noted that the contribution of wastewater collection and transportation in the three chemical plants A,B and C is the largest,with a maximum value of 96.34%;the proportion of volatile losses in enterprise D organic liquid storage and harmonization is the largest,and its contribution rate can reach 40.50%;the largest proportion of volatile loss rates in organized emissions in E,and the maximum contribution rate can reach 96.01%.(2)The distribution and composition analysis of VOCs in the atmospheric environment in different time periods and different location conditions show that:Although the production raw materials and products are quite different,the chlorinated hydrocarbons(including tetrachloroethylene,trichloromethane,chloropropylene,dichloromethane)and the benzene(benzene,toluene,m-,para-xylene,etc.)are the main characteristic pollutants of the chemical park,and their total number can account for 38.2%and 12%of the total VOCs components,respectively.Meanwhile,the VOCs emissions of the industrial park showed the law of increasing after decreasing under the normal production conditions.From the perspective of spatial distribution,the downwind VOCs concentration is higher than upwind concentration in the industrial park.(3)Different VOCs components contribute differently to ozone formation.The calculation results of ozone generation potential(OFP)show that chloropropylene has the greatest potential trend for ozone generation,up to 67.5%,followed by m-,para-xylene,accounting for 20.6%.Meanwhile,it is showed that although the emission concentration and total emission value of chlorocarbons such as tetrachloroethylene,dichloromethane and trichloromethane are much large,the OFP value is relatively small for it is not easy to be oxidized into free radicals.If the main pollutants are divided into three categories,olefins,aromatic hydrocarbons and alkanes,then it can be obtained that OFP(olefins)>OFP(aromatic hydrocarbons)>OFF(alkanes).Itis maybe due to the high activity of olefins in an unsaturated state,which can form free radicals with hydroxyl groups under light conditions more easily.Then it can be captured by NOx in the atmospheric environment to generate O3.Conversely,the reactivity of alkanes with hydroxyl radicals is much lower,which leading the OFP value is the lowest.(4)On the basis of the above research,it can be seen that the VOCs produced by the factory have complex components and wide sources.We can control them effectively by qualitatively identifying,judging different pollution sources and quantitatively analyzing the contribution rate of various pollution sources.