基于紫外吸收的烟气中NO和NO2成分浓度的同时测量

利用高分辨率光栅单色仪测量到的不同浓度的NO和NO2混合气体综合紫外吸收光学厚度,将光学厚度中的快变离散吸收与NO浓度相关,将慢变连续吸收与NO2浓度相关,同时反演NO和NO2的摩尔浓度。研究结果表明:(1)当气体总压接近一个大气压时,NO2反映出很强的转换为N2O4的倾向,转化率R最大值约为22.5%,远大于低气压下的R值,导致NO2吸收截面主要取决于N2O4的吸收特性,表现为慢变的连续吸收特征;(2)离散吸收截面随NO分压增大产生谱线增宽现象,吸收截面在增宽区域的积分值和NO浓度的线性相关性优于吸收截面峰值。测量和反演结果表明:当NO2分压在17～100Pa范围变化时,NO2摩尔浓度反演的平均相对误差为11.7%。当NO分压在63.8～181.62Pa范围变化时,基于积分法的NO浓度反演的最大相对误差为16.9%,平均相对误差为9.6%,而基于峰值法的NO浓度反演的最大相对误差为38.2%,平均相对误差为14.4%。因此,积分法反演较峰值反演具有更好的线性度和更高的精确度。利用上述测量技术,采用相对简单的测试装备,实现了NO和NO2多种成分浓度的同时测量。

Synchronous Measurement of Concentrations of Nitric Oxide and Nitric Dioxide in Flue Gas by Ultraviolet Absorption Analysis

Ultraviolet absorption optical depths of NO and NO2 gas mixture with different concentrations were measured,using a high resolution grating monochromator.By correlating fast-varying discrete absorption and slow-varying continuous absorption with NO and NO2 contributions respectively,the mole concentrations of NO and NO2 were derived synchronously.The study results indicated that,when the total pressure of gas mixture approached to one atmospheric pressure,a strong tendency that two moles of NO2 were combined into one mole of N2O4 was found.The maximum conversion rate from NO2 to N2O4 was roughly 22.5%,resulting in the fact that the effective absorption cross-section of NO2-N2O4 mixture mainly depended on that of N2O4,which exhibited continuous characteristics in its absorption spectrum.The discrete absorption cross-section spectrum was broadened with the increase in the partial pressure of NO.It was shown that the integral of absorption cross-sections within a discrete absorption band had better linear correlation with NO concentration than the discrete absorption cross-section peak.The measurement and derivation results indicated that,when the partial pressure of NO2 varied within 17-100 Pa,the average relative error for the derived NO2 concentration was 11.7%.When the partial pressure of NO varied within 63.8-181.62 Pa,the maximum and average relative error for the derivation of NO concentration was 16.9% and 9.6% respectively by using the spectrum integral method,while the corresponding data rose to 38.2% and 14.4% by using the spectral peak method.The technique can be applied to synchronous monitoring of NO and NO2 concentration with relatively simple measurement hardware.