Design And Operation Performance Evaluation Of Combustion Exhaust Gas Purification For External Wall Insulation Board

With the development of the construction industry,the insulation board usage rate is increasingrapidly.In order to ensure the quality of insulation board,all of the samples shall be tested by a third party for flame retardant performance.There are few domestic studies on Volatile Organic Compounds?VOCs?emission from thermal insulation board during combustion and the treatment technology is backward.In this experiment,EPS and XPS,which have the largest market share,were selected as the research objects to study the VOCs emission characteristics in the combustion process,calculate the potential of ozone formation potential?OFP?and threshold dilution ratio,and estimate the total annual VOCs emission in the detection industry.According to the composition,concentration and flow rate of flue gas,a set of flue gas purification process based on biological method was designed and in the same time the equipment selection and key technical parameters were calculated,both of which are used to verify the VOC removal capacity of the biological purification system,explorethe removal efficiency of benzene,toluene,xylene and other odorous substances in each processingunit,and analyze the rule of microbial community structure change.The specific research results are as follows:?1?The concentration of VOCs emitted by EPS and XPS during combustion was 194.5 to 47.4 and 88.9 to 12.5 mg·m^-3,respectively,and Alkane,with the77.9%and 95.8%concentration ratio respectively,was the main component.The equivalent propylene concentration method and the maximum incremental reactivity method,were used to calculate theOFP by analyzing the VOCs emitted byburning EPS and XPS,and the results were 27.0 to 278.1 and 11.2 to 151.1 mg O₃?m^-3respectively.Olefin was an important contributor to OFP of XPS board?49.8%?,and the main contributor to OFP of EPS boardwas alkanes?80.0%?.By calculating,EPS and XPS thermal insulation board threshold dilution multiples were 3.7±0.9 and14.2±9.1,respectively,with odor pollution in the exhaust gas,mainly fromxylene,ethylbenzene,styrene and other aromatic hydrocarbons.According to the preliminary estimation,the annual discharge of VOCs in the third-party testing industry of insulation boardnationwide in 2018 was up to 226.7t.?2?According to the characteristics of the pollution source and the actual situation,the designed engineering treatment scale was 2500 m³?h^-1.The exhaust gas purification adopts the"filler absorption tower+electrostatic precipitator+biofilter"coupling treatment process.The absorption tower adopted a segmented packed absorption tower.By calculating,the size of absorption tower was 1200×600×2500mm and itwas filled with pall ring packing with the 500 mm packing layer and the35m³/(m²?h^-1)spray density.The size of the designed biological purifier was2000×2000×1500 mm,with pine bark as the filler,the volume of the filler layer was4.2 m³,and the empty bed contact time was 6s.?3?The internal temperature of the bio-purifier ranged from 32°C to 53°C,and the relative humidity varied from 34%to 63%.The maximum removal efficiency of the TVOC by the biological purification system for the detection of EPS and XPS boards was 59.7%,70.4%,respectively.The removal efficiency of components such as benzene,toluene and xylene discharged from EPS and XPS boards in each processingunitwas 11.4%and 10.4%in the spray section,21.3%and 17.6%in the electric dust removal section,and 89.7%and 91.6%in the biological section.The purification system could effectively remove odor pollution and had a strong impact load resistance and recovery ability.However,particulate matter such as carbon black generated during combustion blocks the filler layer and affects the removal efficiency of the biological purification system.?4?PCR-DGGE technology was used tostudy the changes of microbial community structure in the biological purifierpreliminarly.The microbial diversity was higher at the start-up stage,the distribution was more uniform,and the microbial community structure succession was significant at the stable stage.The microbial community structure in the bio-purifier was dominated by actinomycetes,and the most dominant species was Thermobifida fusca with its abundance ratio increasing from 5.5%at the initial stage to 49.1%.The increase of internal temperature of biological purifier had obvious screening effect on actinomycetes,and the change rule of removal efficiency of biological purification system during operation wasconsistent with the growth,reproduction and degradation functional characteristics of dominant microorganisms.