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The UV absorption spectrometry technique DOAS (Differential Optical Absorption Spectroscopy) has been widely used
in continuous monitoring of flue gas, and has achieved good results. DOAS method is based on the basic law of light
absorption--Lambert-Beer law. SO2, NOX are the principal component of the flue gas. These components are
considered by DOAS method at the same time. And certain mathematical methods are used for concentrations
measuring. The Continuous Emission Monitoring System (CEMS) based on the principle of DOAS mainly has two
probe-styles present: in-situ probe-style and extractive probe-style.
For the in-situ probe-style CEMS based on DOAS method, prolonged use for the UV light source, contaminated lens
caused by floating oil and complex environment of the flue will all bring attenuation of the spectral intensity, it will
affect the accuracy of measurement. In this article, an in-situ continuous monitoring system based on DOAS method is
described, and a component adaptive sensing technology is proposed. By using this adaptive sensing technology, CEMS
can adjust the integral time of the spectrometer according to the non-measuring attenuation of the light source intensity
and automatically compensate the loss of spectral intensity. Under the laboratory conditions, the experiments for SO2,
NO standard gas measurement using adaptive sensing technology is made. Many different levels of light intensity
attenuation are considered in the experiments. The results show that the adaptive sensing technology can well
compensate the non-measuring loss of spectral intensity. In the field measurement, this technology can well reduce the
measurement error brought by attenuation of light intensity, compared with the handheld gas analyzer, the average error
of concentration measurement is less than 2% FS(Full Scale).
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