Research On Simultaneous Monitoring Of Sulfur Dioxide,Nitrogen Oxides And Mercury Based On UV Differential Optical Absorption Spectroscopy

Coal-fired power plant is the main power supply of China, and this situation will not change in the short term. Coal-fired power plant has caused severe environmental pollution problems. SO₂, NOX and Hg in the flue gas are the main components of the coal-fired power plant emissions, and can cause great harm to the atmospheric environment. Increasing attention from the environmental protection departments has been paid to the reduction and monitoring of these substances, for which the latest Coal-fired power plant air pollutant emission standards has made strict rules. Compared with the last emission standards, the new ones slashed the indicators, which propose more stringent requirements for the Continuous Emission Monitoring. Existing flue gas monitoring techniques can not achieve simultaneous online monitoring of SO₂, NOX and Hg in the flue gas. Appropriate technology and products should be developed to fill technology gaps and to meet the requirements of environmental monitoring.In this paper, UV differential optical absorption spectroscopy is used for the simultaneous online monitoring of SO₂, NOX（NO₂ dollars） and Hg0. An experimental system was built, of which the components, including gas distribution systems, optical systems, data acquisition and processing systems, software analysis system are introduced. A pulsed xenon lamp- fiber optic spectrometer optical measurement system was built to meet the molecules spectra absorption of SO₂, NO₂. The spectral range of SO₂, NO₂ were determined to 297-315 nm, 425-455 nm, by the experiment result. Least squares, Fourier transform and chirp Z transform are used for the spectral processing. Inversion error of the three methods was less than 5%. The inversion error of least squares of error is generally small, and the error level is more stable than the other two algorithms. The SO₂, NO₂ mixed gas measurement has found that, due to the selected cross-interference-free absorption spectrum band, the measurement accuracy is not affected by the mixture. Low pressure mercury lamp- monochromator measurement system was applied to meet the atomic absorption of Hg0 around 253.65 nm. The results show that the integrated area measurement inversion method, of which he error can be controlled within 5%, is better than the peak method. Optical simultaneous online measurements of SO₂, NO₂ and Hg0 showed that the three gas are interference free with each other, thanks to the relatively independence of the optical absorption band, and the quite difference of absorption intensity. The measurement accuracy can meet and is better than the environmental emission standards, and this approach is field operable.