Research On Performance Test Of Gas Sensor Equipment

Volatile organic compounds(VOCs)have become one of the key pollutants of air pollution control in China.Recently,VOCs have replaced sulfur dioxide and become one of the targets of air quality assessment in China’s 14th Five-Year Plan cities.The development of grid-based environmental monitoring networks is an important means of current VOCs management and control.Sensors have the advantages of simple operation,real-time,sensitive,remote monitoring and early warning,intelligence.However,the commonly used photoionization sensors(PID)and metal oxides Sensors(MOS),etc.present large uncertainties in practical applications.Therefore,research on the performance of typical gas sensors and the effectiveness of VOCs in various application scenarios is important for promoting grid monitoring networks.In this thesis,photoionization sensors(PID)and metal oxide sensors(MOS)are selected as the research objects,and toluene,isopropanol,ethyl acetate and other key industries VOCs characteristic pollutants are selected as the detection objects,and the gas sensor is simulated in the laboratory.The linearity,stabilization time,accuracy,repeatability,24-hour drift and other performances of the product were evaluated;the sensor response of different relative humidity conditions to three kinds of plastic incineration simulated exhaust gas was compared;finally,the coating manufacturer(chemical industry),Packaging and printing companies(solvent use industry),gas stations(gasoline evaporation)carried out on-site monitoring and comparison,and compared with portable GC/MS and other equipment,the main conclusions are as follows:1.Three PIDs of different specifications and one MOS sensor were used to perform performance tests on five representative gaseous pollutants(toluene,isopropanol,ethyl acetate,isobutylene,and hydrogen sulfide).The results show that within the concentration range of 0～20 ppm,the linear regression coefficients of the five pollutants in PID and MOS can reach more than 0.96,with good linearity;in terms of stabilization time,PID and MOS have their own advantages.Among the five gaseous pollutants,toluene with the lowest response factor(RF)and ethyl acetate with the highest response factor(RF)are the substances with long stabilization time and poor repeatability of PID detector.;in general,the repeatability of MOS is better than PID.In the five types of gas test,when isopropanol is used as the gas to be tested,the PID accuracy is the worst,and the 24-hour drift is large,which may be related to its larger ionization energy(IE).In general,the three PID devices under investigation showed differences in linearity,stabilization time,repeatability,accuracy,and 24-hour drift,indicating the necessity of a preliminary comparison study.PID has a certain selectivity to the type of gas to be measured,and the IE and RF of the gas to be measured can be used as a reference basis for the applicability of PID.2.In order to explore the influence of environmental humidity factors on the performance of different PIDs to detect VOCs,the exhaust gas generated during the incineration experiment of three plastic materials(PP plastic bags,PE plastic syringes,and PVC water pipes)was used as the detection object,and the response of PID with two different specifications to the waste gas composition under different humidity was studied.It was found that the presence of water vapor significantly interfered with the response of the photoionization detector to detect VOCs.As the humidity increased,the response value tended to decrease;PID I was more susceptible to humidity than PID Ⅱ.When the relative humidity changed from(15+2)%RH rises to(90±2)%RH,the average response of PID I to PE,PP,PVC incineration decreases by 79%,61.9%,and 70.4%;PID Ⅱ decreases by 70.0%,49.3%,55.0%.3.Field observation and comparison were carried out in coating manufacturing,packaging printing and gas station.The workshop monitoring results of paint manufacturing company A showed that in the closed workshop with high concentration(higher than 10 ppm),the response of PID Ⅱ,PID Ⅲ,MOS sensors to VOCs There is a significant correlation;but in a low-concentration closed workshop,the correlation between the three sensors is weakened.According to the monitoring results of PID,the concentration of VOCs in the oil feeding workshop is the highest,which is roughly 10～52 ppm.VOCs characteristic pollutants are xylene and butyl acetate.The monitoring results of the printing workshop show that the concentration of pollutants at 2 meters away from the VOCs unorganized emission source is 3 times that at 5 meters.The response of PID and FID in the printing workshop has a good linear relationship.The main characteristic pollutants measured by GC/MS were propylene glycol methyl ether,ethanol and propyl acetate.The measured results of the gas station show that the concentration of VOCs measured by PID is 0～1 ppm at the downwind of 1 meter of the gas station.VOCs characteristic pollutants include toluene,n-pentane,butane and so on,the concentration is 0.03 ppm,0.72 ppm,0.98 ppm respectively.