Key Techniques Research For Continuous Emission Monitoring System

Differential absorption spectrometry （DOAS） with the in situ probe applied tothe concentration measurements of flue gas always has the advantages of highprecision, real-time and simultaneous measurement of gas concentrations. However,the monitoring system has many shortcomings. The probe susceptible to the adverseenvironmental impact in the flue gas causes the corrosion of the probe, especially inthe desulphurization environment. Those effects always result in measurement errors.Besides, CEMS with the direct measurements type have difficult in achieving acomplete on-line calibration. The following work is described in this paper:（1） An analysis of the basic laws of the UV absorption spectra is made in thepaper and a laboratory measurement system is designed. New SO₂, NO gas algorithmbased on analysis summarizing are proposed. The proposed statistic SO₂algorithmimproves the measurement accuracy. The low concentration algorithm of SO₂solvesthe measurement problems under desulphurization. The Wavelet decompositionalgorithm of NO gas at the same time, improves the accuracy of the measurement ofthe gas mixture.（2） Analysis of the internal parameters of the spectrometer is made in this paper.The internal parameters of the spectrometer, including the integration time of theCCD spectrometer, CCD slit size, the dynamic signal to noise ratio of thespectrometer, the spectrometer wavelength, CCD number of pixels, average smoothfrequency. Through the experiment, the specific implications for the scope and role ofthe results of the corresponding parameters are given. Selection and the correspondingsolution for the adjustment of the integration time are given. The compensationmethod for the temperature effect is proposed. And the characteristic line of thedeuterium lamp is used for automatic wavelength calibration.（3） The advantages and disadvantages of many direct measurement probecalibration design are discussed. On the basis of summing up the characteristics ofdomestic flue gas environment, a new calibration method is proposed. The method isto take a slide calibration cover emptying measurement of regional flue-linecalibration of the system-wide. This method will meet the complete calibration of the optical path, easy to put into practice. The field experiments determined the method isable to reach the national standard requirements.（4） An UV-hot wet CEMS system is proposed in this paper. The system is basedon the UV spectra measurement principle, heat and moisture sampling, combined withthe advantages of high accurate DOAS algorithm and the simultaneous measurementof multi-component. The experimental results show that the system can adapt to themonitoring environment of ammonia desulphurization, limestone desulphurizationsite as well as the denitration site with selective catalytic reduction.