基于TDLAS的烟气中CO浓度混合取样式在线监测

燃煤锅炉烟气中不完全燃烧产物CO是燃烧效率监测的重要依据,其存在浓度高、波动剧烈、分布不均匀等特点,采用TDLAS技术中波长调制光谱结合稀释法对烟气中CO浓度进行了混合取样式在线监测。首先基于谐波理论推导出4次谐波与1次谐波免标法测量公式,其次对CO激光器频率调制和光强调制的相位差及电流调谐系数进行了标定,并采用标准气体结合直接吸收法对赫里奥特池光程进行了测量,然后在此基础上对浓度与谐波比值曲线进行了数值计算和实验验证。最后将该装置应用于燃煤电厂,将省煤器出口烟道分为6个区域,各区域安装一个稀释取样探头,在稀释取样过程由于降低了烟气露点无需做除水处理,6路经过稀释后的烟气混合后进入赫里奥特池后实现免标定高精度测量。该监测装置实现了连续稳定运行,运行中使用Testo350便携式分析仪与现场测量数据进行了对比,二者测量结果一致,误差小于1×10~(-6)。

On line measurement of CO concentration in flue gas based on TDLAS in mixed sampling mode

CO as the incomplete combustion product in flue gas of coal fired unit is an important basis for combustion efficiency monitoring, which has the characteristics of high concentration, strong fluctuation and uneven distribution. In this paper, the mixed sampling on line measurement of CO concentration in flue gas is carried out using wavelength modulation spectroscopy in TDLAS technology combined with dilution method. Firstly, based on the harmonic theory, the measurement formulas of the fourth harmonic and first harmonic calibration free method were deduced. Secondly, the phase difference between frequency modulation and light intensity modulation, the current tuning coefficient of the CO laser were calibrated, and the optical path of Herriott cell was measured through standard gas combined with direct absorption method. On this basis, the curve of concentration versus harmonic ratio was numerically calculated and verified in experiment. Finally, the monitoring device was applied in a coal fired power plant. During installation, the outlet flues of the economizer were divided into six areas, and a dilution sampling probe was installed in each area. During the dilution sampling process, because the dew point of flue gas was reduced, no dewatering was needed. The diluted flue gases in the six channels were mixed and then entered into the Herriott cell to realize the calibration free and high precision measurement. The monitoring device realized continuous and stable operation, and in the operation Testo350 portable analyzer was used to make measurement and the measurement results were compared with the measurement data obtained from the field measurement device. The comparison results show that the two measurement results are consistent and the error between them is less than 1×10-6.