| Tunable diode laser absorption spectroscopy?TDLAS?could derive the spectral characteristics of sampling gases.It has the properties of high sensitivity,high resolution,selectivity,real-time response and non-intrusion.Therefore,spectroscopic sensors have been widely used in environment detection,medical diagnose,industrial process control and food industry.With the development of industrialization,the demand of natural gas is daily growing and its main ingredient is CH4.There is a little content of H2S that is deadly not only for environment but also for human health.Therefore,it is requisite for real-time detecting the CH4 and H2S.In the thesis,it mainly investigates the implementation of TDLAS in the security area of natural gas utility.First,a setup of opening cell TDLAS system was constructed for recording the concentration of leaking CH4 gas.Then the free calibration of WMS-2f/DS-sine was employed for reducing the interference of external environment.It was verified the ability of wavelength modulation spectroscopy WMS-2f/DS-sine could be immune to environmental fluctuations.Additionally,the laser spectroscopic sensor of H2S was developed for on-line monitoring the domestic natural gas.The main parts of the thesis consist of the following two parts:1.According to the theory of WMS,an open absorption spectroscopy for CH4 was built based on the distributed feedback?DFB?laser emitting at 1.654?m.The minimum CH4 detection is 5 ppb after Allan deviation analysis.Furthermore,it was proved by simulating the leakage case through natural gas bag.2.The WMS-2f/DS-sine was testified that it was effectively immune to the laser intensity variations caused by atmosphere,and mechanical vibration.Employed a compact Herriott cell and FPGA electronic system,the concentration of H2S mixing into natural gas was measured by a DFB laser at1.632?m.The selected line of H2S is not affected by the absorption of CH4.When the integration time is at 178 s,the limited detection of system can reach to 0.14 ppm. |
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