Research On Near Infrared Absorption Spectrum Theory And Detection Technology For Acetylene

With the rapid development of chemical industry,acetylene has been the most important raw materials of organic synthesis in the chemical production process.However,because of the explosion of acetylene that would be mixed with air to form the explosive mixture,it would be threat to the safety in chemical production process.Therefore,the accurate detection of acetylene gas concentration to ensure the safety of industrial production has the vital significance.With the development of laser spectroscopy,tunable diode laser absorption spectroscopy(TDLAS)has been applied in the area of trace gas detection for the advantages of high detection sensitivity,rapid respond and nondestructive detection.Target molecule species concentration can be calculated.Direct absorption spectroscopy(DAS)is a direct method of spectrum,which can be used for inversion of gas concentration via measuring light intensity variation induced by molecules interacting with laser.The HITRAN12 database spectroscopic parameters are just theoretical calculation results.In order to improve the precision of inversing concentration,it is necessary to measure and calibrate for the parameters in practical application.In this paper,tunable diode laser absorption spectroscopy(TDLAS)is applied for detecting acetylene v1+v3 absorption band near 1.5 ?m with the Agilent laser working in the near infrared range used as light source.The spectroscopic parameters of the main strong absorption lines have been calculated,of which the lineintensity is greater than 10-20 cm/molecule.In comparison to HITRAN12 database,the relative error is lower than 2%for the spectra parameters including lineintensity and broadening coefficients.In the experiment,for the spectral range between 6526 cm-1 and 6532 cm-1,a number of new lines of acetylene have been found,which have not been reported,and their absorption are relatively weak.Combined with Multipass cell absorption spectroscopy(MCAS),we have measured the lineintensities of known lines and new lines and place the center position of the new lines.Finally,the lineintensities of the known lines and new lines have been calculated.According to the accuracy of the calculated results for the known lines,of which the relative error is mainly lower than 10%comparing to the HITRAN12 database,this paper reported line parameters of acetylene would contribute to the database upgrade.Moreover,the trace acetylene gas detection system is built on the base of multipass cell absorption spectroscopy(MCAS).The line of R 9e located in 6578.5761 cm-1 is selected as target line,of which the lineintensity is equal to 1.34 × 10-20 cm/molecule.The direct absorption spectroscopy is utilized to measuring acetylene concentration through selecting different wavelength scanning mode of laser.The system has achieved the detection sensitivity of 1.8 ppm for the signal to noise ratio of 1 as the rapid wavelength scanning mode is elected.When using the slow wavelength scanning mode,according to the Allan variance analysis,the detection limit of 43.6 ppb can be obtained with 1-s integration time,which can be further improved to 9.6 ppb by increasing the average time to 80s.In order to suppress noiseof experimental signal,Savitzky-Golay(SG)2nd derivative algorithm has been applied to processing spectral signal for the first time.Simulation is used to evaluate the effect of noise reduction of SG 2nd derivative algorithm in the case of selecting different filtering parameters.The results of simulation and experiment prove that the algorithm has a powerful ability to denoise.The algorithm are used to process experimental data and the outcome shows that it has a good linear relation between the acetylene concentration and the amplitude of SG 2nd derivative signal.