| In recent years,China's economy has grown significantly with the development of industry,but air pollution has become more and more serious.The concentration of volatile organic compounds?VOCs?has been climbing steadily.The main industrial emission sources include the petroleum refining,mechinery manufacturing,constraction industry,painting industry,printing industry and so on.The components of VOCs are more and more complex and the distribution is wider.As a prerequisite for PM2.5 and O3,VOCs causes great harm to human health and environmental quality by directly and indirectly.The coating manufacturing industry has become a key industry of VOCs emissions due to the large amount of organic solvents used in the production.According to statistics,the most emitted substances in the coating manufacturing industry include ketones,benzenes,esters,alcohols,and aromatic hydrocarbons,which have different degrees of carcinogenic risk to people,and have become a hot spot of global concern.This article conducts research on VOCs emitted during the production process of Bangong workshop and Juangang workshop of a coating company,which is a main emission source of VOCs.According to different coating applications,the raw material of general industrial coating is toluene,xylene and other benzene series in the Bangong workshop,and it is a large number of benzene series and ketones for steal coils in Juangang workshop.According to pollutant emission characteristics,retrofitting integral process“Liposolubility absorption and desorption+Water-based spray absorption+Photocatalytic oxidation combination+Complete oxidation”at terminal of exhaust emissions to governance many kinds of exhaust gas in an efficient way.For evaluating the overall purificating efficiency,collecting exhaust gas by air bag sampling method.Quantitaty and qualitaty the main components of the exhaust gas which are acetone,methyl ethyl ketone,benzene,toluene,xylene,esters,and a small amount of other substances by gas chromatograph.To detect the concentration of VOCs and Characteristics of composition change before and after each link for evaluating efficiency of every sector and its absorption characteristics to various components.Simultaneous sampling with handheld PID detector at the same time as airbag sampling,detecting the instantaneous concentration of VOCs,and then calculate efficiency.Comparing with gas chromatograph's results to determine their accuracy.Use the NMHC online monitor to detect the concentration of NMHC in the tail gas outlet of the overall treatment equipment to determine the tail gas concentration meets the maximum allowable emission concentration stipulated by Shanghai local standards.These results suggest that:?1?The liposolubility absorption tower mainly absorbs high concentrations toluene and xylene,and the absorption efficiency is greater than 50%of the totally absorpt rate.?2?The water-based spray absorption tower mainly absorbs esters and other low-concentration substances in the exhaust gas,and absorbs only a small amount of high-concentration benzenes and ketones.?3?The box of photocatalytic oxidation combination and complete oxidation tower are mainly for the treatment of high-concentration ketones.The absorption of high-concentration acetone and methyl ethyl ketone is more than 50%of the total absorption efficiency.It is the main section to govern ketones.?4?The concentration of volatile organic compounds in the tail vents of the Bangong workshop and the Juangang workshop detected by the NMHC online monitor are 32.19mg/m3 and 45.22mg/m3,respectively,which are in line with the Shanghai local standards--50mg/m3.?5?comparing the detection results of the gas chromatograph and the handheld PID detector,the calculated efficiency of the data obtained by the gas chromatograph is similar to the efficiency obtained by the data of the handheld PID detector.The results are basically reliable. |
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