【作者】 李宁；

【导师】 严建华； 倪明江； 池涌；

【作者基本信息】 浙江大学 ， 热能工程， 2008， 博士

【摘要】 近年来，随着国家对于环境保护的日趋重视，以及出于保证工业生产安全高效进行的需要，光学非接触式的气体检测技术发展十分迅速。基于可调谐激光吸收光谱的气体测量技术具有无需预处理，响应快速，数据准确，多参数同时检测等优势，成为了当前气体实时在线检测的代表性技术之一。本文研究的主要目的是利用可调谐激光吸收光谱技术，针对于燃烧领域中具有重要意义的气态物质进行在线检测，并同时对气体温度，以及气体分布的二维重建进行研究。本文首先利用工作波长位于1．53μm波段的可调谐激光二极管，针对于利用SCR技术脱除燃烧产生烟气中NOx的工作环境，对其中的NH₃浓度进行了在线测量。实验室内借助于波长位于1527nm的NH₃特征气体吸收谱线，在常温常压下利用直接吸收测量的方法达到10ppm-m的浓度测量下限。在小型燃烧试验台上，通过对燃烧产生的烟气中喷洒NH₃，以模拟现场测量工况，实现对烟气中NH₃的实时在线检测。其次，利用工作波长位于1．58μm处的可调谐激光二极管，针对于泛频区内的CO₂与CO气体吸收谱线，分别利用直接吸收测量技术以及波长调制技术对其浓度检测进行了试验研究，在常温下实验室内达到的浓度测量下限分别为0．14％-m与400ppm-m。讨论了环境温度压力等条件变化时线宽对于二次谐波信号的影响，采用二次谐波峰谷比值的方法来对其进行修正，大大提高了利用波长调制方法进行浓度测量的精度。设计加工了适合于现场安装和在线检测使用的测枪，对不同工况下燃油炉燃烧产生烟气中的CO₂进行了连续测量。其次，通过利用高精度分子光谱数据库，在1．58μm波段内选择两条CO₂特征吸收谱线，利用其线强比值来实现对于光路中均匀气体温度的测量研究。在373K至773K的温度范围内，温度测量误差均方值为17K。针对于光路中存在明显温度梯度的测量环境，通过扫描多条CO₂气体吸收谱线，借助于离散化的数学模型并利用带约束的最小二乘拟合方法来进行求解。在实验室内对两段温度分布重建进行了相应的数值模拟和试验研究，并讨论了相关影响因素。针对于焦炉煤气中O₂的在线检测，在实验室内采用工作波长位于763nm处的可调谐激光二极管在不同的气体组分，温度，压力，激光透射率等工况下对其浓度检测进行了测量试验，验证了浓度测量结果的准确性，以保证在O₂超标时可以及时进行报警从而确保工业生产安全。另外，对波长调制过程中颗粒对于二次谐波信号的影响进行了理论分析。分别采用180μm与800μm两种不同粒径的石英沙颗粒，对颗粒存在环境下的气体浓度测量进行试验研究。并结合基于Mie理论上的消光法，进行了颗粒物浓度的测量试验。搭建了小型气固两相流动试验台，利用固定浓度的CO₂气体吹动石英沙颗粒进行流化，实现了对于不同流化位置处的气体浓度与颗粒物浓度的同时在线测量。最后，将CT断层重建技术与TDLAS技术相结合，在实验室内搭建了高速CT重建测量系统，以实现对于气体二维分布的重建。通过利用四个高速旋转台进行重建断面的扫描，使得扫描时间控制在100ms。利用数值模拟的方法验证了测量的准确性与精度。借助于NH₃气体吸收谱线，通过采用ART代数重建算法，成功实现了对于气体浓度分布的快速二维重建。并通过采用扫描两条特征谱线的方法，利用变量轮换的最优化策略，对气体浓度与温度场同时重建进行了初步试验研究，为今后针对于燃烧环境中的气体重建工作提供借鉴。更多还原

【Abstract】 As much more attention has been paid on the environment protection and demand to improve the safety and efficiency of industry, the optical techniques for gas sensing are developing very rapidly. Tunable diode laser absorption spectroscopy （TDLAS） is the one of the representative measurement method, with features of fast response, high precision, and simultaneous measurement of multi-parameter. The purpose of this paper is to develop the method of on-line remote sensing for the gases in the flue, and do research on the gas temperature and distribution reconstruction with computed tomography （CT） for further investigation in combustion.NH₃ sensing is carried out with tunable diode laser working at the wavelength of 1.53nm for detection in the process of decreasing NOx by SCR in the flue gas. The concentration can be obtained accurately by scanning the spectral line at 1527nm, with minimum detectable concentration of about 10 ppm-m at normal temperature and pressure. By injecting the gaseous NH₃ into the flue gas after combustion, the real time and on line measurement is completed at the small-scale experimental setup.The VCSEL diode laser at 1580 nm is utilized to measure the gas concentration of CO₂ and CO in the range of over-tone by direct absorption and wavelength modulation strategy separately, yielding to a minimum detectable concentration of 0.14%-m and 400ppm-m. The effect of line width variety on the second-harmonic signal casued by pressure or temperature is discussed, and corresponding correction method by introducing the ratio of peak to valley from the second-harmonic signal is accepted to improve the wavelength modulation measurement. The apparatus designed for convenient installation and continuous running is applied to the oil-burning boiler for CO₂ detection continuously.Based on the high-resolution transmission molecular absorption database, two spectral lines of CO₂ near 1.58μm are selected, and the ratio of the linestrengths is utilized to infer the uniform temperature in the optical path. The experiment is carried out during the range from 373K to 773K by direct absorption method, leading to the mean square error of 17K. The light-of-sight gas temperature distribution is also studied to obtain the temperature distribution at non-uniform path. Discretization model is established for the tempmerature reconstruction, and solved by constrained linear least-square fitting method. The simulation and experiement are completed for the two-temperature distribution, and the relative factors are discussed here.For the purpose of on-line monitoring of O₂ in the coke oven gas to ensure the industry safety, the diode laser working at 763 nm is utilized in the lab to detect the O₂ concentration and validate the precision in the conditions of different gas components, pressure and temperature.Theory analysis about the effect of particles in the gas on the second-harmonic signal is presented, together with the experiment on gas detection in the condition of mixture by gas component and quartz sands with different size. Combined with the extinction methods based on Mie theory, the particles concentration can be also obtained in the TDLAS system. The simultaneous measurement of gas and particle concentration is proved in the small-scale system with gas-solid two-phase flow.A multi-source optical computed tomography system for gas distribution based on the tunable diode laser absorption spectroscopy technique is established here, with tomography scanning time about 100ms to cover the region of interest by projections from four fast rotation platforms. The 2D reconstruction image of NH3 concentration distribution is calculated by algebraic reconstruction technique （ART） method using the projections from gas absorption. The pilot research on simultaneous reconstruction of both concentration and temperature distribution with a pair of spectral lines is continued with optimization strategy of cyclic variable method. The research can be useful for the investigation of chemical distribution in the combustion further.更多还原