TDLAS测量CO2的温度影响修正方法研究

摘要

Tunable diode laser absorption spectroscopy (TDLAS) is often used to detect CO2concentrations in many fields .But because of the variation of ambient temperature ,the measured the line strength and line-shape are affected and may lead to the monitoring errors .Therefore ,in order to overcome the influence of temperature change on the concentration measurement ,we used the DFB laser with the center wavelength of 1 580 nm and the direct absorption method was used to measure the high con-centration of carbon dioxide gas in the flue of the power plant under the condition of room temperature (298 K) and variable tem-perature (298～338 K ,interval 10 K) .The results showed that the maximum relative error of the concentration measurement was -5.26%,the minimum relative error was 1.25% and the relative error mean square was 3.39%,which indicated that TD-LAS measurement system had good measurement precision and stability at room temperature .But the concentration measure-ment in the temperature measurement error ,the maximum of relative error was more than 25% .Then ,the influence of tempera-ture change on the measurement of the concentration was solved to meet the needs of industrial measurement and on the basis of temperature change measurement ,the least squares method was used to fit the correction relation between the concentration of the measurement system and the gas absorption at different temperatures .After the correction ,the relative error of the CO2con-centration measurement was reduced to below 5%,and the relative error mean square value fell below 3.5% .The correction re-sults showed that the proposed method can effectively suppress the influence of temperature change on the concentration meas-urement and improve the measurement accuracy and stability of the system in the variable temperature environment ,which pro-vides theoretical support and technical support for the TDLAS system field application .%可调谐二极管激光吸收光谱(TDLAS)技术测量CO2浓度时,由于测量氛围温度变化的影响引起气体吸收谱线的线强和线型发生变化,最终导致浓度测量存在较大误差.为了克服温度变化对浓度测量的影响,选用中心波长在1 580 nm的DFB激光器,基于直接吸收法,模拟电厂尾部烟道内的高浓度二氧化碳气体环境,研究了在常温(298 K )和变温(298～338 K 、间隔10 K )不同温度工况下CO2浓度的测量.结果显示,常温浓度测量的最大相对误差为-5. 26%,最小相对误差为1.25%,相对误差均方值为3. 39%,验证了TDLAS测量系统在常温下有着良好的测量精度和稳定性,但其在变温测量时浓度测量结果误差较大,其最大相对误差已经超过25%.为了修正温度变化对浓度测量结果的影响,适应工业测量的需要,在变温测量基础上利用最小二乘法拟合出测量系统在不同温度下的浓度与气体吸收的修正关系式.经过修正后,CO2浓度测量的相对误差降到5% 以下,相对误差均方值降到3.5% 以下.修正结果表明,所提出的修正方法可以有效抑制温度变化对浓度测量结果的影响,显著提高了测量系统在变温环境下的测量精度和稳定性,为TDLAS系统测量CO2浓度的现场应用提供了理论支持和技术保障.