| Because of its ability to control indoor suspended particles,microorganisms and environmental conditions,the cleanroom can guarantee the production quality of electronic and pharmaceutical products and the quality of laboratory animals,and is widely used in electronics,medicine,biology and other fields.In the production process of cleanroom related products,due to production conditions and process limitations,the toxicants from a variety of raw and auxiliary materials will escape or remain in the indoor air,endangering the health of workers.The fresh air system and the three-stage filter of air conditioning and cleaning system are used to reduce the concentration of indoor pollutants.The total air supply volume is composed of fresh air volume and return air volume,and the return air volume is usually over 70%,and the three-stage filter mainly deals with suspended particles in the air,so the dilution effect of the fresh air system on toxicants is limited,it is difficult to effectively reduce the concentration of indoor toxicants.How to effectively reduce the concentration of toxicants in cleanroom is an urgent problem to be solved.With the rapid development of air purification technology,researchers have found that activated carbon adsorption and photocatalytic degradation have better purification effects on toxicants.The former has the advantages of simple operation,safety,and simple equipment,and the latter has the advantages of high efficiency,stability,safety and non-toxicity.At present,the two are widely used in the field of indoor air purification in public places,and are rarely used in the field of air purification in cleanroom.In view of the fact that pharmaceutical cleanrooms commonly use formaldehyde for disinfection and sterilization,electronic cleanrooms often use isopropanol as cleaning solvents,and laboratory animals in the laboratory animal room will produce a large amount of ammonia.In this study,formaldehyde,isopropanol and ammonia are selected as representative of typical toxicants in electronic,pharmaceutical cleanrooms,and laboratory animal room respectively.The 100.0m2 simulated cleanroom was designed and constructed by Suzhou Goldswallow Purification Equipment Co.,Ltd,and the efficiency of purifying formaldehyde,isopropanol and ammonia in the return air purification device installed with activated carbon purification net,photocatalyst purification net,activated carbon and photocatalyst purification nets are measured respectively in the simulated cleanroom.According to the design concentration,a certain amount of formaldehyde,isopropanol and ammonia solution are taken,heated and volatilized in a water bath,and then mixed with a fan in 24.0m2 simulated clean area.The 5 sampling points of formaldehyde are arranged according to the plum blossom point method,and6-minute air samples are collected at a flow rate of 0.5L/min.Two parallel samples were taken at each sampling point,then the formaldehyde concentration is determined by solution absorption-phenol reagent spectrophotometry.The indoor isopropanol and ammonia concentration are measured by a chemical sensor connected to the simulated cleanroom automation system and capable of detecting display data in real time.Using a one-factor experimental design approach,compare the purification effect of 1.4kg and 2.8kg,8-16 mesh and6-12 mesh coconut shell charcoal,1-3mm and 3-5mm bamboo charcoal on formaldehyde,isopropanol and ammonia,then the performance optimization parameters of the activated carbon purification net in the return air purifying device are determined.The L9（21×33）orthogonal test was used to investigate the effects of nano-Ti O2（UV lamp irradiation）and nano-WO3（fluorescence lamp irradiation）,the photocatalyst dosage of 10g/m2,20g/m2,30g/m2,and the light intensity of 10W,20W,30W on the purification efficiency of formaldehyde,isopropanol and ammonia,then the performance optimization parameters of photocatalyst purification net in the return air purifying device are determined.Comparing the toxicants（formaldehyde,isopropanol,ammonia）purification effect of the return air first passes 30g/m2 of nano-Ti O2（formaldehyde and ammonia:20W,isopropanol:10W）and then 2.8kg of 8-16 mesh coconut shell carbon purification net,the return air first passes 2.8kg of 8-16 mesh coconut shell carbon and then 30g/m2 of nano-Ti O2purification net.The effects of the return air purifying device（the return air first passes 30g/m2 of nano-Ti O2 and then 2.8kg of 8-16 mesh coconut shell carbon purification net）on the purification efficiency of formaldehyde,isopropanol and ammonia were studied by L18（37）orthogonal test under the conditions of the return air volume of 315m3/h,475m3/h,626m3/h,the initial concentration of toxicants of 0.5OEL,OEL,2OEL（formaldehyde,isopropanol,ammonia OEL are 0.50mg/m3,350mg/m3,20mg/m3 respectively）,temperature of 20°C,22°C,24°C,relative humidity of 45%,55%,65%.The results are as follows:1.The efficiency of the same activated carbon purification net for formaldehyde purification for 30 min is higher than 15 min,and the difference is statistically significant（P<0.05）.The 15min,30min formaldehyde purification efficiency of the 2.8kg of 8-16 mesh coconut shell charcoal purification net are（65.49±1.19）%,（86.55±4.40）%,and it higher while the purification nets of 1.4kg of 8-16 mesh coconut shell charcoal are（50.62±1.07）%,（59.66±2.88）%,2.8kg of 6-12 mesh coconut shell charcoal are（57.51±2.17）%,（69.86±2.02）%,2.8kg of 1-3mm bamboo charcoal are（52.62±1.07）%,（67.13±1.51）%,the differences are statistically significant（P<0.05）.The results of repeated measures analysis of variance showed that the purification efficiency of isopropanol and ammonia in the same type of purification net increased with purification time,and the difference was statistically significant（P<0.05）.As the purification time prolonged,the purification efficiency of 2.8kg of 8-16mesh coconut shell carbon purification net for isopropanol and ammonia is higher than 1.4kg of 8-16 mesh coconut shell charcoal and 2.8kg of 6-12 mesh coconut shell charcoal purification net（P<0.05）;the purification efficiency of 2.8kg of 1-3mm bamboo carbon purification net for isopropanol and ammonia is higher than 1.4kg of 1-3mm bamboo carbon and 2.8kg of 3-5mm bamboo carbon purification net（P<0.05）;there is no significant difference in the purification efficiency of isopropanol and ammonia between the 8-16 mesh coconut shell carbon purification net with the same dosage of 2.8kg and the 1-3mm bamboo carbon purification net（P>0.05）.The results indicated that the purification efficiency of formaldehyde,isopropanol and ammonia in the same activated carbon purification net is improved with the prolongation of purification time.The quality,particle size and type of activated carbon have an effect on the purification efficiency of the purification net.The 2.8kg 8-16 mesh coconut shell carbon purification net has better purification effect on formaldehyde than 1-3mm bamboo charcoal purification net.The purification effect of isopropanol and ammonia is better when the purification net are 2.8kg of 8-16 mesh coconut shell carbon or 2.8kg of 1-3mm bamboo carbon.2.Direct analysis of L9（21×33）orthogonal test found that the optimal level of photocatalyst species and dosage,light intensity on formaldehyde and ammonia purification efficiency are nano-Ti O2,0.3g/m2,20W;the optimal level of photocatalyst species and dosage,light intensity on isopropanol purification efficiency are nano-Ti O2,0.3g/m2,10W.The effect of photocatalyst dosage on the purification efficiency of isopropanol is statistically significant（P<0.05）,and there is no significant difference in the purification efficiency of formaldehyde and ammonia（P>0.05）.Under the above experimental conditions,the purification efficiency of ammonia in the return air purification device is（61.00±0.56）%,which is higher than the detection results of other groups in the orthogonal test;the purification efficiency of formaldehyde and isopropanol in the return air purifying device are（71.00±1.14）%and（61.27±0.35）%respectively,which are higher than the detection results in the orthogonal test.3.The 15 min formaldehyde purification efficiency of the combined method of purification nets of 2.8kg of8-16 mesh coconut shell charcoal and 0.3g/m2 nano-Ti O2are（65.30±1.34）%and（65.81±0.74）%,respectively;the20 min isopropanol purification efficiency of their are（89.29±0.12）%and（88.95±1.68）%,respectively;the 30min ammonia purification efficiency of their are（73.77±1.32）%,（74.07±1.07）%,respectively,and there are no significant difference between the groups（P>0.05）.It is suggested that the change of purification net the combination mode does not affect the toxicants purification effect of the return air purifying device.Direct analysis of L18（37）orthogonal test observed that the optimal level of return air volume,initial concentration,temperature and relative humidity on formaldehyde,isopropanol,ammonia purification efficiency in the return air purifying device are 626m3/h,1.00mg/m3,24°C,65%;475m3/h,175mg/m3,22°C,45%and475m3/h,40mg/m3,22°C,55%respectively.Variance analysis showed that the effect of return air volume on the purification efficiency of formaldehyde,isopropanol and ammonia is statistically significant（P<0.05）;the difference of the initial concentration of toxicants on the purification efficiency of formaldehyde and isopropanol is statistically significant（P<0.05）,and the effect on the purification efficiency of ammonia is not statistically significant（P>0.05）;there is no significant difference in the effects of temperature and relative humidity on the purification efficiency of formaldehyde,isopropanol and ammonia（P>0.05）.Least significant difference t test indicated that there was no significant difference in the difference in the efficiency of formaldehyde purification between 475m3/h and 626m3/h（P>0.05）.When the return air volume is 475m3/h,the purification efficiency of isopropanol and ammonia is higher than 315m3/h and 626m3/h,the difference is statistically significant（P<0.05）.The efficiency of purifying 1.00mg/m3 formaldehyde in the return air purifying device is higher than0.25mg/m3 and 0.50mg/m3,the difference is statistically significant（P<0.05）;the efficiency of purifying175mg/m3 isopropanol is higher than 350mg/m3,700mg/m3,the difference is statistically significant（P<0.05）.The results proved that the temperature and relative humidity changes do not affect the purification effect of the return air purifying device on formaldehyde,isopropanol and ammonia;the purification efficiency of isopropanol and ammonia is better when the return air volume is 475m3/h;the purification efficiency of 1.00mg/m3 formaldehyde and 175mg/m3 isopropanol is better.In summary,the 2.8kg of 8-16 mesh coconut shell charcoal purification net in the return air purification device has good purification effect on formaldehyde,isopropanol and ammonia.The 0.3g/m2of nano-Ti O2 has good purification effect on formaldehyde and ammonia after being irradiated by 20W UV lamp,and it has good purification effect on isopropanol after being irradiated by 10W UV lamp.The return air purifying device can exert a good purifying effect on 1.00 mg/m3 of formaldehyde and 175 mg/m3 of isopropanol when the return air first passes 0.3g/m2 of nano-Ti O2 and then 2.8kg of 8-16 mesh coconut shell carbon purification net,and the return air volume is set to 475m3/h. |
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