基于菲涅耳透镜开放光路天然气泄漏检测系统设计研究

天然气泄漏直接导致能源浪费和环境污染，造成重大经济损失。以可调谐半导体激光吸收光谱技术为基础的光学检测方法具有精度高、选择性强、响应速度快以及远距离遥测等优点，使其成为天然气站场以及天然气输运管道在线监测的理想方法。可调谐半导体激光吸收光谱与谐波探测相结合，设计了一套开放式长光程的用于天然气泄漏监测的实验系统。它以中心波长为1.65 μm的分布式反馈InGaAS激光器为光源，利用实心角反射器，在发射端以菲涅耳透镜为光学接收系统，把反射回来的光聚焦到InGaAs探测器。同时，在测量过程中，考虑到光强变化对浓度的影响，并通过归一化光强的方法进行消除，使光强波动引起的误差小于1%。在320 m的光程下模拟管道泄漏实验，系统的检测灵敏度为0.1(10-6体积比)，根据光学系统收光效率以及探测器的可探测性能进行分析的最小光强，计算得到该系统可探测的光程可达2 000 m，证明完全满足天然气泄漏检测的需求。

System Design of Open-Path Natural Gas Leakage Detection Based on Fresnel Lens

Based on the technology of tunable diode laser absorption spectroscopy (TDLAS) in conjunction with second harmonic wave detection, a long open-path TDLAS system using a 1.65 μm InGaAsP distributed feedback laser was developed, which is used for detecting pipeline leakage. In this system, a high cost performance Fresnel lens is used as the receiving optical system, which receives the laser-beam reflected by a solid corner cube reflector, and focuses the receiving laser-beam to the InGaAs detector. At the same time, the influences of the concentration to the fluctuation of light intensity were taken into account in the process of measurement, and were eliminated by the method of normalized light intensity. As a result, the measurement error caused by the fluctuation of light intensity was made less than 1%. The experiment of natural gas leakage detection was simulated, and the detection sensitivity is 0.1×10-6 (ratio by volume) with a total path of 320 m. According to the receiving light efficiency of the optical system and the detectable minimum light intensity of the detector, the detectable maximal optical path of the system was counted to be 2 000 m. The results of experiment show that it is a feasible design to use the Fresnel lens as the receiving optical system and can satisfy the demand of the leakage detection of natural gas.