基于TDLAS的气体检测技术研究
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摘要
TDLAS技术由于其非接触性、高灵敏度、在线响应速度快等优点,而成为当前气体浓度在线检测技术的重要发展方向之一。确定分子吸收线型函数是应用该技术的前提条件,但是目前尚没有有效的方法在线测量分子吸收线型函数,以至严重影响了TDLAS技术的测量精度,限制了其应用范围。因此,通过吸收光谱理论和波长调制理论研究TDLAS技术中谐波特征参数与分子吸收线型函数的关系,推导出蕴含分子吸收信息的谐波通项表达式,利用谐波信号间的关系特征来消除背景信号、激光强度、调制系数等因素的影响,建立了一种基于谐波信号的绝对吸收强度测量算法。以CO2分子和H2O分子在6982cm-1附近的谱线为例进行数值分析和实验研究,仿真和实验结果表明,根据算法测得的分子吸收光谐波信号谱与理论吸收光谱之间的相对误差不超过5%,进一步提高了TDLAS技术的测量精度,拓宽了其应用范围。
TDLAS technology has become one of the important development directions of gas concentration on-line detection technology because of its non-contact,high sensitivity and fast on-line response. Determining the molecular absorption line shape function is the prerequisite for applying this technology. However,there is no effective method for on-line measurement of molecular absorption line shape function,which seriously affects the measurement accuracy of TDLAS technology and limits its application. Therefore,studies the relationship between the characteristic parameters and the molecular absorption line shape function in TDLAS technology through the theory of absorption spectrum and wavelength modulation,and deduces the expression of harmonic terms containing molecular absorption information,eliminating the effects of the background signal,laser intensity,and modulation index according to the relationships between the harmonic signals,and finally establishing the measurement algorithm of absolute absorption intensity based on harmonic signal. The absorption spectral lines of CO2 molecule and H2 O molecule near 6982 cm-1 is taken as an example for numerical analysis and experimental research,and the simulation and experimental results show that the relative error between the theoretical absorption spectrum and the measured molecular absorption spectrum according to the algorithm is less than 5%,which further improves the measurement accuracy of TDLAS technology and broadens its application range.
TDLAS technology has become one of the important development directions of gas concentration on-line detection technology because of its non-contact,high sensitivity and fast on-line response. Determining the molecular absorption line shape function is the prerequisite for applying this technology. However,there is no effective method for on-line measurement of molecular absorption line shape function,which seriously affects the measurement accuracy of TDLAS technology and limits its application. Therefore,studies the relationship between the characteristic parameters and the molecular absorption line shape function in TDLAS technology through the theory of absorption spectrum and wavelength modulation,and deduces the expression of harmonic terms containing molecular absorption information,eliminating the effects of the background signal,laser intensity,and modulation index according to the relationships between the harmonic signals,and finally establishing the measurement algorithm of absolute absorption intensity based on harmonic signal. The absorption spectral lines of CO2 molecule and H2 O molecule near 6982 cm-1 is taken as an example for numerical analysis and experimental research,and the simulation and experimental results show that the relative error between the theoretical absorption spectrum and the measured molecular absorption spectrum according to the algorithm is less than 5%,which further improves the measurement accuracy of TDLAS technology and broadens its application range.
引文
[1]卢伟业,朱晓睿,李越胜,等. TDLAS直接吸收法和波长调制法在线测量CO2的比较[J].红外与激光工程,2018,47(7):0717002.
[2]杨雅涵,李国林,李小鹏,等.基于TDLAS技术的天然气中痕量硫化氢分析的PLS算法应用[J].光子学报,2017,46(2):0230002.
[3] Liu Ningwu,Deng Hao,He Tianbo,et al. Measurements of new absorption lines of acetylene at 1. 53μm using a tunable diode laser absorption spectrometer[J]. Spectrochimica Acta Part A:Molecular and Biomolecular Spectroscopy,2017,186(5):1~7.
[4] Wang Fupeng,Chang Jun,Wang Qiang,et al. TDLAS gas sensing system utilizing fiber reflector based roundtrip structure:Double absorption path-length, residual amplitude modulation removal[J]. Sensors and Actuators A:Physical,2017,259(1):152~159.
[5] S. Schilt. Impact of water vapor on 1.51μm ammonia absorption features used in trace gas sensing applications[J]. Applied Physics B,2010,100(2):349~359.
[6] A. D. Sappey,P. Masterson,E. Huelson,et al. Results of closed-loop coal-fired boiler operation using a TDLAS sensor and smart process control software[J]. Combustion Science&Technology,2011,183(11):1282~1295.
[7] S. Wagner,B. T. Fisher,J. W. Fleming,et a. TDLAS based in situ measurement of absolute acetylene concentrations in laminar 2D diffusion flames[J]. Proceedings of the Combustion Institute,2009,32(1):839~846.
[8] J. T. C. Liu,J. B. Jeffries,and R. K. Hanson,Wavelength modulation absorption spectroscopy with 2f detection using multiplexed diode lasers for rapid temperature measurements in gaseous flows[J]. Applied Physics B,2004,78(3):503~511.
[9] J Reid,D Labrie. Second-harmonic detection with tunable diode lasers-Comparison of experiment and theory[J]. Applied Physics B,1981,26(3):203~210.
[10]王雪梅,刘石.基于波长调制光谱技术的二氧化碳浓度测量[J].大气与环境光学学报,2017,12(5):356~361.
[2]杨雅涵,李国林,李小鹏,等.基于TDLAS技术的天然气中痕量硫化氢分析的PLS算法应用[J].光子学报,2017,46(2):0230002.
[3] Liu Ningwu,Deng Hao,He Tianbo,et al. Measurements of new absorption lines of acetylene at 1. 53μm using a tunable diode laser absorption spectrometer[J]. Spectrochimica Acta Part A:Molecular and Biomolecular Spectroscopy,2017,186(5):1~7.
[4] Wang Fupeng,Chang Jun,Wang Qiang,et al. TDLAS gas sensing system utilizing fiber reflector based roundtrip structure:Double absorption path-length, residual amplitude modulation removal[J]. Sensors and Actuators A:Physical,2017,259(1):152~159.
[5] S. Schilt. Impact of water vapor on 1.51μm ammonia absorption features used in trace gas sensing applications[J]. Applied Physics B,2010,100(2):349~359.
[6] A. D. Sappey,P. Masterson,E. Huelson,et al. Results of closed-loop coal-fired boiler operation using a TDLAS sensor and smart process control software[J]. Combustion Science&Technology,2011,183(11):1282~1295.
[7] S. Wagner,B. T. Fisher,J. W. Fleming,et a. TDLAS based in situ measurement of absolute acetylene concentrations in laminar 2D diffusion flames[J]. Proceedings of the Combustion Institute,2009,32(1):839~846.
[8] J. T. C. Liu,J. B. Jeffries,and R. K. Hanson,Wavelength modulation absorption spectroscopy with 2f detection using multiplexed diode lasers for rapid temperature measurements in gaseous flows[J]. Applied Physics B,2004,78(3):503~511.
[9] J Reid,D Labrie. Second-harmonic detection with tunable diode lasers-Comparison of experiment and theory[J]. Applied Physics B,1981,26(3):203~210.
[10]王雪梅,刘石.基于波长调制光谱技术的二氧化碳浓度测量[J].大气与环境光学学报,2017,12(5):356~361.
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