| Nitric oxide（NO）and nitrogen dioxide（NO2）are often referred to as nitrogen oxides（NOX）,which can produce acid rain or photochemical smog,destroy the ozone layer,and cause serious pollution to the atmosphere.As an emerging economy,there is a strong demand in coal source,which causes the main NOX emissions,for China.With the deepening of the national ultra-low emission policy and the continuous decline of emission limits,monitoring the emission of NOX in industrial flue gas and improving the accuracy of emission data are of great significance to NOX prevention and control.Related scholars have proposed a whole-process high-temperature direct-pumping measurement method based on absorption spectroscopy,but the water vapor content in the flue gas is as high as 5%to 20%.There is a wide absorption band in the mid-infrared region for water vapor,which coincide with the characteristic absorption position of NO and NO2,causing the uncertainty of measuring the concentration of NOX.It is necessary to establish an accurate measurement method for low-concentration NOX under high-temperature water-containing conditions.This research is based on Fourier transform infrared spectroscopy technology.Combined with the dynamic gas distribution system based on the mass flow controller,the stable and accurate gas required for the experiment is obtained by calibrating the mass flow controller;the Peltier condenser is used as the experimental object to study its water removal efficiency and simplify the flue gas pre-treatment system based on the measurement principle.The industrial flue gas measurement environment is taken as a reference,parameters such as sampling gun/sampling pump temperature,spectrometer resolution,acquisition band and number of acquisitions are determined;the spectrum preprocessing technology and the corresponding processing method is determined,and then the mid-infrared absorption spectra required for the experiment were obtained;the absorption spectra of NO,NO2 and H2O were studied and analyzed in detail,and the measurement model under the single-component condition of NO,NO2 and H2O,and the model of NO and NO2 under water-containing conditions was established.The specific research results are as follows:（1）It has been shown in the experimental results of condenser water removal efficiency that,with the concentration of water vapor in the sample gas increasing,the water vapor content in the sample gas after treatment shows an upward trend.Based on the principle of high temperature direct extraction measurement method,simplifying the traditional flue gas pretreatment system can effectively eliminate the measurement error caused by the change of the condenser’s water removal efficiency.（2）A mathematical model between the single-component single-peak absorbance/multi-peak absorbance sum and concentration of NO,NO2 and H2O is established.Compared with different measurement models,the result shows that the relative errors of the measurement models established using multi-peak spectral data for NO,NO2,and H2O are respectively less than 1.42%,1.72%,and 2%,which are better than the single-peak measurement model.At the same time,it is found that there is a nonlinear deviation between the absorbance and concentration of the infrared absorption spectrum of gaseous H2O,and the nonlinear relationship between the multi-peak absorbance and concentration of gaseous H2O is established.（3）A measurement model of determining the concentration of NO and NO2 is established,by analyzing the absorption spectra of NO and NO2 under water-containing conditions,and correcting the absorbance of H2O in the mixture.It has been shown that the measurement error of NO and NO2 under water-containing conditions are increasing,and the measurement result of H2O is not affected by NO and NO2.Uncertainty evaluation results show that the maximum extended relative standard uncertainties of NO and NO2 measurement results are 2.8%and 4.16%（k=2）,respectively. |
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