Research On Urban Gas Leakage Detection Technology Based On Infrared Spectroscopy

In recent years,with the acceleration of industrialization,people’s demand for energy is gradually increasing.The use of natural gas has brought great convenience to people’s life,but because of the characteristics of flammable and explosive natural gas,also buried a huge hidden danger.In cities,pipelines are the main way to transport natural gas.Therefore,timely detection of pipeline leakage points can effectively reduce the probability of gas explosion.However,due to the high coverage of urban pipelines,the traditional manual detection method is time-consuming and inefficient,which cannot meet the needs of energy security and environmental protection.Therefore,sensors are installed on mobile platforms,such as vehicles,aircraft and unmanned aerial vehicles,which can achieve a wide range of gas inspection work in a short time,greatly improving the inspection efficiency.The main components of natural gas are methane(CH4)and ethane(C2H6).In this paper,two infrared spectroscopy technologies are used to detect CH4 and C2H6,which are tunable diode laser absorption spectroscopy and off-axis integrated cavity output spectroscopy.For tunable diode laser absorption spectroscopy technology,a compact multipass cell was designed with a gas cell size of 18.5×8×9 cm3 and an effective optical path of9.39 m.A near infrared methane/ethane sensor was designed and implemented based on a compact and compact spot multipass cell and its peripheral optical path.The sensor uses two near-infrared distributed feedback lasers,which are used to detect CH4 and C2H6 respectively.The simultaneous detection of the two gases by one chamber and one detector was realized through time division multiplexing.Allan deviation analysis was used to analyze the performance of dual-gas sensing.The detection limits for CH4 and C2H6 were 78 ppbv and 189 ppbv,respectively,with an average time of 0.8 s.The sensitivity of the sensor meets the need of monitoring atmospheric methane concentration,and the performance of the sensor system was evaluated by measuring atmospheric methane for a long time.For off-axis integrated cavity output spectroscopy technology,an off-axis integrated cavity was designed with a gas cell size of 580×75×95 mm3 and an effective optical path of 2.5 km.Compared with the tunable diode laser absorption spectroscopy system,the designed system has a longer effective optical path.Kalman algorithm was used to improve the sensitivity of the system.Allan deviation analysis was used to analyze the performance of the two-gas sensor.The detection limits of CH4 and C2H6 were 4.3 ppbv and 14.2 ppbv,respectively,with an average time of 1 s.The sensitivity of the sensor meets the needs of monitoring atmospheric methane and ethane concentrations.The optical system was integrated by the off-axis integrated cavity,and the optical system was isolated from the sensor by the vibration absorption module,which effectively improves the stability of the sensor.A multi-stage gas filter was used to preprocess the gas,GPS and anemometer were integrated into the sensor,and trolley leak source detection in campus and vehicle-mounted mobile detection for urban gas leak detection were carried out,which verified the performance of the sensor system.The innovation points of this paper are as follows: in order to detect atmospheric CH4/C2H6 concentration,a compact multipass cell with an optical path of 9.39 m and an off-axis integrated cavity with an optical path of 2.5 km are designed,and two CH4/C2H6 two-component sensor systems are developed.The performance of the sensor systems were verified by atmospheric monitoring experiment and simulated leak source location experiment,respectively,and the rapid location of urban gas leak source is realized.