Methane Gas Detection Based on Tunable Diode Laser Absorption Spectroscopy and Optical Fiber Sensing

With the advancement of clean energy, natural gas (methane) in the proportion of energy consumption increased year by year. Methane gas detection technology has become an important research direction in fire alarm area. Tunable diode laser absorption spectroscopy (TDLAS) is a new method of measuring trace methane gas, this gas detection technology has many unique advantages, such as intrinsic safe, good stability, good selectivity, and long working life etc. The technique of detection methane with tunable diode laser absorption spectroscopy in the near-infrared region is introduced. The linear relationship between the gas concentration and second harmonic (2f) is analyzed. And the relationship between the second harmonic spectrum of methane in Lorentzian line shape and the modulation amplitude is also presented. A methane gas detection system is set up by current modulation a tunable diode laser, and slowly ramping the wavelength to scan methane absorption lines at 1.65 micron. Orthogonal lock-in amplifiers detect the first harmonic (1f) and the second harmonic (2f) of the modulation frequency. Optical fiber sensing net is built to monitor up to 64 points, and can synchronously detect 8 points. A series of experiments are carried out and results are applicable to methane gas detection using tunable diode lasers, and to other fields of atmospheric chemistry and monitoring pollutant gases where tunable diode laser absorption spectroscopy techniques are applied.

I. Introduction

Methane is the main components of natural gas, is colorless and odorless, inflammable and explosive, the lower explosive limit is 5.0% VOL in the atmosphere, explosion when meet fire. In recent years, the accidents caused by gas leakage common occur, caused many deaths and huge economic losses, constitutes a great fire safety hidden trouble. Therefore, should promote the use of natural gas detection alarm in the relevant place using natural gas, reduce that such accidents to avoid. Currently, methane detection and alarm at home and abroad is mainly in the traditional techniques, include catalytic combustion, metal oxide semiconductor-type, electrochemical sensors. There are generally easy to drift, poisoning failure, cross-sensitivity, short life and other issues, that makes a serious impact on the actual performance. In comparison, methane sensors using near-infrared absorption spectroscopy has unique advantages, such as intrinsically safe, good stability, good selectivity, low maintenance, long service life etc [1], [2]. Therefore, promote the use of methane detection alarm based on spectral absorption, eliminate the gas fire safety hidden trouble, has important practical significance for using of natural gas resources safely and effectively.