| Hydrogen is an important raw material in the hydrogenation process of the petrochemical industry,and an important reducing agent in the production process.By deep hydro-desulfurization,it can produce low-sulfur clean oil,which is of great significance for preventing and controlling air pollution.Limited by the hydrogen production process,the hydrogen in its carrying pipeline contains a certain concentration of impurity gas.This impurity gas will not only affect the quality of the product,but also increase the procurement cost of the enterprise.Due to the flammable and explosive nature of gases such as hydrogen and methane,petrochemical companies usually employ offline analysis technology to periodically sample and analyze hydrogen components.However,the automation of this kind of technology is relatively low,in particular,the manual sampling brings high security risks,and its analysis results often have a certain lag.In view of this problem,this paper proposes an optical fiber sensing technology for online measurement of the gas composition of hydrogencarrying pipelines,which has intrinsic safety and long-distance measurement features.Furthermore,this paper studies an online gas composition measurement system with the use of optical fiber sensing based Raman spectroscopy.The main work of this thesis is summarized as follows:(1)Based on the analysis and comparison of the commonly used gas composition analysis methods,combined with the advantages of optical fiber sensing technology,a new idea of online gas composition measurement system using fiber sensing based Raman spectroscopy is proposed.(2)The basic theory of Raman spectroscopy is investigated.According to the characteristics of Wuhan Petrochemical’s hydrogen-carrying pipeline,a gas sample cell which is based on the optical Fabry-Perot(F-P)enhancement cavity is designed.The enhancement effect of this F-P cavity is theoretically analyzed and the actual optical path is debugged.The results show that the enhancement cavity can enhance the Raman scattering signal by about 50 times.(3)According to the characteristics of the gas composition of Wuhan Petrochemical’s hydrogen-carrying pipeline,an optical fiber sensing system has been built to simulate gas changes in the pipeline,and a variety of Raman spectroscopy detection experiments of standard-mixed methane/hydrogen gas have been carried out.After wavelet denoising and background subtracting,a single variable calibration curve is established for the characteristic peaks of methane and hydrogen Raman spectra.The cross-check standard error values for methane and hydrogen are 0.5139% and 0.6684%,respectively.In addition,a multivariate analysis model for two gases is constructed using the partial least-squares algorithm.The cross-check standard error values for methane and hydrogen are reduced to 0.3600% and 0.4825%,respectively.(4)An online measurement system is designed and installed on the petrochemical hydrogen-carrying pipelines,and based on the LabVIEW platform,an online gas component measurement software is developed,with the use of optical fiber sensing based Raman spectroscopy.This software implements functions such as spectral data acquisition,data preprocessing,gas concentration calculation,and real-time display.(5)The online measurement system is tested using both the single variable calibration curve and the partial least squares model.The components of unknown methane/hydrogen gas in the pipeline are quantitatively analyzed,and the results are compared with the results of off-line chromatographic analysis at Wuhan Petrochemical.The results show that the partial least squares model has a higher stability and accuracy,and the maximum measurement errors for methane and hydrogen are 0.654% and 0.612%,respectively.These results have met the requirements of the manufacturer,and this technology can also be used for the online measurement of gas components in the chemical industry. |
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