Study On The Real-Time Monitoring Method Of Flue Gas By DOAS

Air pollution is the most important problem of the environmental issue. As the main source of air pollution, flue gas emissions have become the focus of the monitoring and control. In this article, the basic principle and measurement method of gas pollutants is introduced by differential optical absorption spectrometry (DOAS). The spectral feature extraction, the fitting method of the measurement error, as well as the statistical analysis of the scene spectrum are studied in detail. The main contents include:1. The micro-properties of the electric spectrum are described, which is the base of the differential optical absorption spectrum. The amended expression of the Lambert-Beer Law is given for the calculation ofDO AS. A variety of light-scattering properties of the actual light path and the functions of the equipment are taken into account in the formula. The relationship between the theoretical model of the background light and the absorption light, and the actual model of the reference light and measured light is deduced;2. In the aspect of feature extraction, a multi-resolution preprocessing method of original spectrum is adopted to denoise by the signal energy in different scales. On the other hand, the useful signal component is enhanced according to the signal correlation. In addition, the origin of the nonlinear factors is analyzed, that is caused by the actual measurement condition. And the polynomial approximation equation is taken to deal with it. This method improves the signal-noise ratio of scene nomal signal significantly;3. In the aspect of error correction, the three procedures of the spectrum conditioning, the computing of absorption cross-section and the absorption band-weighted, are adopted to amend the errors. This correction method includes the shift and stretching of the spectral curve, the calculation method of the absorption cross-section used for on-site and fitting the spectral function of the measurement system, the different weighted algorithm in the wavelength range for the measured gases that have different absorption wavelength range. The processed scene data error is lower than 3%;4. In order to estimate the main components ratio and changes of the spectrum before and after the ammonia desulfurization, the principle of ammonia desulfurization and the interference materials that may be generated are analyzed. The comparison between the spectrums captured in the lad and at the scene of desulphurization is taken with the help of the cluster and factor analysis. The calculation of the desulphurization spectrums is done by the use of the polynomial fitting in different sections, which increases the desulphurized data accuracy effectively;5. The sulfur dioxide and nitrogen oxides measuring probe is developed. The spectral data processing and analysis software is programmed. And two scenes are chosen to run and do the comparison tests. The on-site data show that, the monitoring system is suitable to the on-site industrial environment, which works stability.