基于QCL波长调制光谱技术的SO3高灵敏度测量系统OA

[Objective]A High-Sensitivity optical sensor is developed for detection of sulfur trioxide(SO3)using a quantum cascade laser(QCL)and wavelength modulation spectroscopy(WMS)to address the practical SO3 measurement challenges of low concentration,high reactivity,and difficult separation.It includes functional modules such as high-temperature SO3 gas generation and synchronous measurement of low-concentration SO2 and SO3,utilizing mid-infrared absorption spectroscopy to enable simultaneous measurement of SO2 and SO3 under high-temperature conditions.[Methods]The experimental system uses a multi-reflection high-temperature optical measurement cavity and combines the WMS algorithm to improve the detection limit of SO3.The SO3 gas obtained by the high temperature reaction of SO2 and O2 under the action of vanadium-based catalyst is used as the basis for the calibration of SO3 spectrum and real-time calibration of laser center frequency.The concentrations of SO2 and SO3 were measured synchronously in the process of SO2 catalytic oxidation.The relationship between the conversion rate of the catalytic oxidation reaction and the temperature(550～1 000 K)and pressure(3～20 kPa)was calculated to obtain the best SO3 gas preparation conditions.[Results]The results showed that the conversion of SO2 and O2 increased first and then decreased with the increase of temperature,and reached 92.2%at T=797 K during the catalytic oxidation of vanadium-based catalysts.Under the condition of T=797 K,the reaction conversion rate increases with the increase of pressure,but the rate of change gradually decreases.When P>17.5 kPa,the conversion rate is greater than 90%.The detection limit of the high-sensitivity integrated measurement system for SO2 and SO3 is obtained by calculating the Allan variance.The detection limit of SO2 is 0.7 μL/L when the optimal integration time is about 10 s,and the detection limit of SO3 is 1.75 μL/L when the optimal integration time is about 40 s.It shows that the measurement system has a good detection limit for low-concentration acidic gases.[Conclusion]TThe WMS measurement method and integrated measurement system based on mid-infrared absorption spectroscopy technology can provide an effective means for simultaneous real-time online monitoring of low-concentration SO2 and SO3 in industrial sites.