【作者】 高颖；

【导师】 戴连奎；

【作者基本信息】 浙江大学 ， 控制科学与工程， 2019， 硕士

【摘要】 天然气因清洁低碳、使用高效和储量丰富等优点而被广泛应用于当今社会,国际标准《ISO 13686天然气质量指标》中对天然气的成分作出了明确规定,因此天然气组分的定量分析变得十分重要。在众多的在线多组分气体检测技术中,拉曼光谱分析技术以其分析速度快、无需样品预处理、测量便捷等优点可用于天然气组分分析。因此本文对天然气组分的拉曼光谱分析方法进行深入研究。论文的具体研究开发工作包括:(1)针对由采样池材料等造成的背景噪声和基线漂移状况,提出了天然气光谱的预处理算法。光谱预处理算法包括背景光谱扣除、基线校正以及光谱归一化处理。利用400条连续测量的天然气光谱对上述算法进行检验,得到较好地处理效果。(2)提出了一种拉曼光谱谱峰的自动分解算法,能将可能含有少量未知组分的待测样本的拉曼光谱分解为已知纯组分拉曼光谱和未知组分拉曼光谱之和,其中未知组分的拉曼光谱由洛伦兹谱峰组拟合得到。该自动分解算法不仅能够准确地分解天然气拉曼光谱,也能够适用于其他混合体系的拉曼光谱分解。(3)建立了天然气组分的拉曼定量分析模型。天然气组分可分为甲烷、乙烷、丙烷、二氧化碳、氮气、氢气、一氧化碳以及C4以上未知烷烃成分(记为C4+)等物质,其中前7种组分为天然气中的主要组分。首先,基于上述拉曼谱峰自动分解算法将天然气拉曼光谱分解为7种纯物质组分的拉曼光谱分量和若干个洛伦兹谱峰之和的形式,其中C4以上未知烷烃成分的含量采用各种烷烃分子共有的C-H变形振动峰来反映。然后,利用训练样本建立除甲烷以外的其他物质相对于甲烷的特征峰面积和对应的浓度之间的模型。实验表明,该方法对甲烷、乙烷、丙烷、二氧化碳、氮气、氢气、一氧化碳和C4+的最大绝对测量误差分别达到了 0.57%、0.37%、0.21%、0.07%、0.18%、0.04%、0.13%和0.26%;与气相色谱检测结果的相关系数也分别达到了 0.997、0.986、0.991、0.998、0.993、1.000、0.995、0.982。(4)开发了一套天然气组分在线拉曼分析系统。该系统由硬件和软件两部分组成。对该系统的重复性和准确性进行了检验:在重复性方面,某一天然气样气中甲烷、乙烷、丙烷、二氧化碳、氮气、氢气、一氧化碳和C4+的分析标准差分别为 0.072%,0.002%,0.000%,0.013%,0.018%,0.02%,0.014%,0.037%;在准确性方面,与气相色谱方法分析值的对比,在线分析系统对甲烷、乙烷、丙烷、二氧化碳、氮气、氢气、一氧化碳和C4+这8种组分的标准偏差分别为0.234%,0.141%,0.176%,0.068%,0.056%,0.01 7%,0.015%,0.35 8%,结果说明系统有较好的准确性。更多还原

【Abstract】 Natural gas is widely used in today’s society due to its advantages of clean and low carbon,high efficiency and abundant reserves.The international standard ISO 13686:2013 Natural gas—Quality designation specifies the composition of natural gas.Therefore,quantitative analysis of natural gas components has become very important.Among many online multi-component gas detection technologies,Raman spectroscopy can be used in the analysis of natural gas components because of its fast analysis speed,no need for sample pretreatment and convenient measurement.This paper studied Raman spectroscopy method for natural gas components.The specific research and development work include:(1)A preprocessing algorithm for natural gas spectrum is proposed to reduce baseline drift and background noise.The above algorithm was tested using 400 continuously measured natural gas spectra,and the pretreatment effect was excellent.(2)An automatic decomposition algorithm for Raman spectral peaks is proposed.It can decompose the Raman spectrum of a mixture sample,which may contain a small amount of unknown components,into the sum of several known pure component spectra and a synthetic unknown component spectrum.The synthetic spectrum of the unknown components is obtained by fitting some Lorentz peaks.The automatic decomposition algorithm not only can accurately decompose natural gas Raman spectra,but also can be applied to the Raman spectral decomposition of other mixture.(3)A Raman quantitative analysis model of natural gas components was established.Natural gas components can be divided into methane,ethane,propane,carbon dioxide,nitrogen,hydrogen,carbon monoxide and unknown alkane components of Ca or more(denoted as C4+).The first seven components are the main components in natural gas.The Raman spectrum of a natural gas sample could be decomposed into the sum of the Raman spectra of pure constituents and several Lorentz peaks by a nonlinear least-square optimization algorithm based on the automatic decomposition algorithm.The concentration of the unknown alkane component C4+was determined according to the area of the C-H deformation vibration peak which was common for most alkane molecules.Some training samples were used to establish the model between Raman characteristic peak areas and corresponding concentrations for each component.The experiments showed that the maximum absolute errors of this algorithm for methane,ethane,propane,carbon dioxide,nitrogen,hydrogen,carbon monoxide,C4+ respectively reached 0.57%,0.37%,0.21%,0.07%,0.18%,0.04%,0.13%,0.26%and the correlation coefficient to gas chromatographic results also reached 0.997,0.986,0.991,0.998,0.993,1.000,0.995,0.982,respectively.(4)An online Raman analysis system for natural gas component was developed.The system consists of two parts:hardware and software.The repeatability and accuracy of the system were examined.For a sample,the analytical repeatability of methane,ethane,propane,carbon dioxide,nitrogen,hydrogen,carbon monoxide and C4+were 0.072%,0.002%,0.00%,0.013%,0.018%,0.029%,0.014%,and 0.037%,respectively.For 26 mixture samples of natural gas,the standard deviation of the online analysis system for the 8 components were 0.234%,0.141%,0.176%,0.068%,0.056%,0.017%,0.015%,0.358%respectively,compared with the analytical values of the gas chromatography.The results prove that the system has good accuracy.更多还原