Water vapor and carbon dioxide species measurements in narrow channels

Classical spectroscopic techniques have been applied in a novel manner to measure the concentration of gas species, water vapor and carbon dioxide, within a narrow channel flow field non-invasively. Tunable diode laser absorption spectroscopy (TDLAS) was used in conjunction with a laser modulated at a high frequency [Wavelength Modulation Spectroscopy (WMS)] tuned to the ro-vibrational transition of the species. This technique measures the absorption profile which is a strong function of the species concentration across short path lengths and small time spans, as in PEM fuel cells during high load cycles. This method has been verified in a transparent circular flow 12 cm path length and a 12 mm rectangular flow channel. Distinct absorption peaks for water vapor and carbon dioxide have been identified, and concentrations of water vapor and carbon dioxide within the test cells have been measured in situ with high temporal resolutions. A comparison of the full-width at half-maximum (FWHM) of the absorption lineshapes to the partial pressure of water vapor and carbon dioxide showed strong relationships, except in the lower partial pressure regions. Test section temperature was observed to have very minimal impact on these curves at low partial pressure values. A porous media like a membrane electrode assembly (MEA) similar to those used in PEM fuel cells sandwiched between two rectangular flow channels was also tested. Some of the scattered radiation off the MEA was observed using a photodiode at high gain, allowing for more localized species detection. The technique was used to monitor the humidity on either side of the MEA during both temperature controlled and super-saturated conditions. The measurements were observed to be repeatable to within 10%.     

基于TDLAS技术的硫化氢气体浓度检测应用

摘? 要：硫化氢因其有毒有害的特性,在工业生产过程中对其浓度检测具有重要意义。本文以监测天然气脱硫过程中的硫化氢为应用案例,采用可调谐二极管激光吸收光谱技术（TDLAS）作为分析平台进行浓度分析。TDLAS气体分析系统基于分子选择吸收原理、比尔-朗伯定理和波长调制技术,包括分析模块、气体模块和人机交互模块。在应用案例中,采用1570nm激光器,通过气体模块模拟天然气背景产生0-100ppm硫化氢混合气体,采用化学计量学方法计算硫化氢浓度,结果显示该分析系统满足2%FS的测量需求。因此,具有非接触式、反应迅速、测量精确等优点的TDLAS技术满足现在石化行业的痕量气体测量需求。     

Improvement of Tunable Diode Laser Absorption System with a Novel Multipass Cell and Wavelet Transform

Combination of Tunable Diode Laser Absorption Spectroscopy(TDLAS)technique and multipass cell is an attractive approach for ultrahigh sensitive detection of trace gases.Theoretically,based on Beer-Lambert law,the longer optical path length and the larger gas absorption,the lower concentration gas could be detected.However,lower radiation intensity and inevitable etalon fringe resulted from multiple reflections would greatly weaken the Signal-to-Noise Ratio(SNR)and thus an expected ultrahigh sensitive detection system is difficult to achieve.In order to fully make use of the advantages of TDLAS and multipass cell,the base length and the total optical path length of the multipass cell are needed to be carefully balanced.Furthermore,the harmonic signals contaminated by various noises are processed with wavelet transform method.As a demonstration of this method,few low concentrations of gas CO in N2 are measured employing TDLAS technique and a novel sealed multipass cell with total optical length of 114 m.The detection limit is about 5×10-6(volume ratio),which is one order of magnitude better than earlier noise reduction.     

激光锁相放大技术在顶空分析中的应用

基于FPGA研究了激光数字锁相放大技术,利用Lorentz线型模拟CO2吸收曲线,研究了调制系数、调制相位对吸收曲线二次谐波信号的影响,实现了调制参数的最优化。在此基础上,搭建了激光检测系统并对培养瓶内CO2浓度进行了顶空测量。结果表明:研制的顶空分析系统检测性能良好,输出二次谐波信号与CO2浓度的线性拟合度达99.98 %,测量范围为0~20 %,1σ检测限达到0.05 %。     

基于TDLAS的二氧化碳检测技术综述

精确检测CO_(2)气体浓度、控制CO_(2)气体排放是治理大气温室效应过程中最重要的部分。可调谐半导体激光吸收光谱(TDLAS)因具有高灵敏度和高可靠性的特点,广泛应用于在线监测、微量气体检测等方面。分析了TDLAS测量气体浓度的基本原理,重点介绍了直接吸收法和波长调制法并比较了两种方法的优缺点,随后介绍了近几十年来国内外应用TDLAS技术在气体检测方面取得的研究进展。最后总结了基于TDLAS的二氧化碳气体检测技术,并对其未来应用进行了展望。     

天然气集输站场CH4及H2S泄漏检测技术研究

可调谐半导体激光吸收光谱技术是一种新型的气体检测方法,其技术关键是利用半导体激光器的窄线宽和可调谐等特性,结合长光程吸收池技术、波长调制技术,并辅以噪声压缩技术,对CH4、H2S分子的吸收线进行测量,从而实现对CH4、H2S气体泄漏的监测和报警.装置具有灵敏度高、选择性好、精度高、响应速度快和远距离遥测等优点.     

基于TDLAS的批量种子活力检测装置设计

针对我国缺乏对批量种子活力检测装置的研究,以及传统检测方法可能会对种子样品造成不可逆损伤的问题,提出了一种通过可调谐半导体激光吸收光谱(tunable diode laser absorption spectroscopy,TDLAS)技术检测种子呼吸强度来判定其活力等级的无损检测方法,并设计了相应的检测装置,以实现对...     

可调谐激光吸收光谱技术监测燃烧中CO检测方法比较

可调谐二极管激光吸收光谱(TDLAS)技术是利用二极管激光器的波长调谐特性,获得被选定的待测气体特征吸收谱线的吸收光谱,从而对待测气体进行定性或定量分析.TDLAS技术与开放式的多次反射池相结合,分别利用二次谐波探测方法和自平衡加波长调制的新型检测方法,测量了酒精喷灯火焰的CO浓度.测量结果表明,自平衡加波长调制的新型检测方法与二次谐波检测方法相比,不仅使检测限提高了16.3倍,还有效地消除了激光器、火焰的光强波动影响,可以应用在燃烧控制及喷焰气体CO浓度测量等多个领域.     

机动车尾气的道边在线实时监测(下)

利用调谐二极管激光器吸收光谱和紫外差分吸收光谱原理研制了道边实时监测机动车尾气仪,详细讨论了该仪器对几种主要有害气体如CO,CO2,NOx和HC（分别用NO和丁二烯代表）的测试及校正原理．以及各种环境因素对测试结果的影响．全文分上、下两部分．本部分（下）介绍了该仪器的主要技术难点、创新点和性能参数,报道了用该仪器跟美国MD-LaserTech公司商业化产品在北京测试现场的部分路边测试实验结果,讨论了各种环境因素如天气、车型、季节、车速、路况等对测试结果的影响及校正．对仪器的性能参数跟国外同类仪器比较发现,我们研制的仪器性能略优于国外同类仪器90年代后期水平．本技术拥有完整自主知识产权,填补了国内空白．     

天然气中硫化氢的激光吸收光谱法在线分析

硫化氢具有强烈的毒性和腐蚀性,为了贯彻实施新的国家天然气标准,增强含硫天然气生产的安全性,提高生产效益,对含硫天然气气质的在线监测,尤其是硫化氢含量的监测就显得非常重要。但现有的测量方法或者精度不高,或者操作复杂、运行维护困难。为此,提出了基于可调谐半导体激光器吸收光谱技术（TDLAS）的在线硫化氢分析方法,并采用波长调制（WMS）技术减少杂质的影响和提高测量精度,试制了测量范围为1 000～20 000 μmol/mol的在线分析系统。离线标定和在线测试结果表明该系统最快响应时间仅0.25 s,最大测量误差为1.3%。在川东北某含硫气井进行了较长时间的在线测量,结果显示该系统稳定可靠。结论认为,该系统具有维护成本低和操作方便简单等特点,它的成功运用,有望弥补现有方法的不足,为我国高含硫天然气的安全开采服务。