TDLAS直接吸收法和波长调制法在线测量CO2的比较

据统计，2015年我国消耗了39.65亿吨煤炭，而其中发电及热力供应占据了煤炭消耗总量的46.38%。发电及热力供应行业排放的CO2占据了我国温室气体排放量的很大比例，因此对于燃煤电厂CO2气体排放的实时监测是非常重要的。利用测量精度高、响应迅速、非接触测量的可调谐半导体激光吸收光谱（TDLAS）技术对CO2浓度检测。选用了中心波长在1 580 nm的分布式反馈激光器作为光源，参考电厂尾部烟气CO2浓度配置实验气体，分别使用直接吸收和波长调制方法对CO2浓度进行反演。对比研究结果表明，直接吸收和波长调制法重复测量的相对标准偏差分别为0.94%和0.22%，最大相对误差分别为2.64%和1.65%，检测限分别为0.013 6%和0.001 4%。波长调制法比直接吸收法在测量性能指标上更具优势，但由于波长调制法在现场应用时受定标方式的影响很大，且谐波线宽会受到压力、温度等参数变化的干扰，而直接吸收法无需标定，且测量精度足以满足电厂CO2在线监测的需求。因此在电厂锅炉烟气等高浓度CO2的测量中，直接吸收法是更好的选择。

Comparison of direct absorption and wavelength modulation methods for online measurement of CO2 by TDLAS

According to the statistics, 39.65 billion tons of coal has been consumed up from China in 2015. Obviously, CO2 emission from power generation and thermal supply industry segment contributes a large part to global warming. Therefore, it is of great importance for online monitoring of CO2 emissions from coal-fired power plants. The CO2 concentration was measured by tunable semiconductor laser absorption spectrum(TDLAS), which had the benefits of high accuracy, rapid response, non-contact, etc. In order to prevent interference from absorption of other gases, a distributed feedback laser with a center wavelength of 1 580 nm was chosen as the light source. Simulated flue gas was made referring to the concentration of CO2 in the flue gas of the power plant. The direct absorption(DA) and wavelength modulation(WM) methods were used to measure the CO2 concentration. The results show that the relative standard deviation(RSD) for DA and WM are 0.94% and 0.22%, while the maximum relative errors and detection limits for DA and WM are 2.64% and 1.65%, 0.013 6% and 0.001 4%. It is found that WM is better than DA in measurement qualities. But the WM method is influenced by the calibration method in field application and the line width is interfered by the fluctuations of the parameters such as pressure and temperature, resulting in reduced long-term stability. In the case of the DA method, the concentration can be calculated directly by measuring the absorbance, line strength and pressure without calibration. It has a high signal-to-noise ratio for the measurement of gas with high concentration. Meanwhile, the measurement accuracy is high enough to meet the requirement for CO2 online measurement in power plants. Therefore, the DA method is a better choice for the CO2 measurement in the flue gas of power plant boiler.