CO_(2)/CO干扰下基于腔衰荡吸收光谱的痕量H_(2)S浓度测量

Accurate measurement of trace H_(2)S concentration based on cavity ring-down absorption spectroscopy under CO_(2)/CO disturbance

H_(2)S作为一种有毒且腐蚀性较强的气体污染物,实现其浓度的准确测量意义重大.实际工业过程中,H_(2)S测量常受其他排放产物的干扰,本文基于腔衰荡吸收光谱技术(CRDS)通过扫描6336—6339 cm^(-1)范围内的吸收光谱,实现了H_(2)S/CO_(2)/CO三组分物质浓度的同步测量,为实际工业过程中物质干扰下的H_(2)S浓度测量提供新思路.首先,对不同采样长度下提取衰荡时间的准确性进行分析,发现衰荡信号的采样长度约为衰荡时间的8倍时,衰荡时间提取效果最好;通过不同压力对比实验确定最佳实验压力工况为50 kPa,并将最佳采样长度与压力工况应用于H_(2)S浓度测量.随后,改变H_(2)S浓度对CO_(2)/CO干扰下系统对痕量H_(2)S浓度的测量效果进行检验,并对不同稀释比例下浓度测量结果的线性度进行分析.最后,对本文CRDS系统的检测限进行分析,通过对4组低浓度H_(2)S光谱的信噪比进行分析,得到H_(2)S的检出限为6.9 ppb (1 ppb=10^(-9));通过对系统长期测量结果进行Allan方差分析,得到系统对H_(2)S物质浓度的检测下限约在2 ppb左右.

Since H_(2)S is a corrosive and toxic gas pollutant,the accurate measurement of its concentration is significant.However,in the practical industrial processes,it is difficult to implement because of the disturbance caused by other emissions such as CO_(2)and CO.Therefore,in this work,the concentration of H_(2)S,CO_(2)and CO are measured simultaneously based on cavity ring-down spectroscopy(CRDS) as a viable alternative to measure the concentration of H_(2)S accurately when CO_(2)and CO exist.First,the wavelength of mixed gas within a range of 6336-6339 cm^(-1)is selected as the target region where the spectral line intensity of H_(2)S is stronger than 10times that of CO_(2)or CO and the water absorption is extremely weak.Second,the influence of the sampling length(Tm) on the accuracy of the ring-down time is analyzed by evaluating average(accuracy),standard deviation(precision) and consumption time(speed).Third,the experiments are carried out at different pressures in order to obtain the optimal pressure condition.Fourth,the concentration of trace H_(2)S is measured when the disturbances caused by CO_(2)or CO are added,and the error of the measured concentration is analyzed.Finally,the detection limit of CRDS-based system is calculated to be 6.9 ppb by analyzing the SNR of four groups of low concentration H_(2)S spectra,while the lower limit of detection of CRDS-based system is calculated to be 2 ppb by analyzing the Allan variance of long-term data.The measured concentration and its desired value show a good linearity at different dilution ratios.Both the high linearity and the low detection limit of H_(2)S indicate the effectiveness of the CRDS-based measurement system to measure H_(2)S when CO_(2)and CO exist.The successful application of the CRDS-based system to the measurement of H_(2)S shows its promising prospect in gas concentration measurement for practical industrial processes.