In the present work, an improved model of the Raman gas analyzer (RGA) of natural gas (NG) developed by us is described together with its operating principle. The sensitivity has been improved and the number of measurable gases has been expanded. Results of its approbation on a real NG sample are presented for different measurement times. A comparison of the data obtained with the results of chromatographic analysis demonstrates their good agreement. The time stability of the results obtained using this model is analyzed. It is experimentally established that the given RGA can reliably determine the content of all molecular NG components whose content exceeds 0.005% for 100 s; moreover, in this case the limiting sensitivity for some NG components is equal to 0.002%.

The use of multipass optical systems as well as the compression of the gaseous test medium to increase the signal intensity of the spontaneous Raman scattering of light has been experimentally studied. A description of a prototype developed for a natural-gas analyzer based on spontaneous Raman scattering spectroscopy is presented. A technique is described for calculating the composition of natural gas from its spectrum. The results are compared with chromatographic-analysis data.

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Raman spectroscopy is a promising method for analyzing natural gas due to its high measurement speed and the potential to monitor all molecular components simultaneously. This paper discusses the features of measurements of samples whose composition varies over a wide range (0.005–100%). Analysis of the concentrations obtained during three weeks of experiments showed that their variation is within the error caused by spectral noise. This result confirms that Raman gas analyzers can operate without frequent calibrations, unlike gas chromatographs. It was found that a variation in the gas composition can change the widths of the spectral lines of methane. As a result, the measurement error of oxygen concentration can reach 200 ppm. It is also shown that neglecting the measurement of pentanes and n-hexane leads to an increase in the calculated concentrations of other alkanes and to errors in the density and heating value of natural gas.

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We have developed a spectrometer designed to record spontaneous Raman scattering (SRS) spectra in gaseous media. The spectrometer has improved sensitivity due to using a high-performance spectral instrument and also a device for compressing the analyte gaseous medium. We present the results of an experimental test of the spectrometer, and show that its limiting sensitivity for methane is <1 ppm.Introduction. Diagnostics of the composition of gaseous media at a new technical level are greatly needed in today's society. Environmental protection agencies and agencies of the Ministry for Civil Defense, Emergencies, and Disaster Response especially need high-sensitivity monitoring instruments solving problems for both environmental monitoring of atmospheric pollution and identifying emergency situations associated with emission of toxic gases into the atmosphere [1]. In connection with development of the corresponding instrumentation, refi ning analysis methods, and improving metrological characteristics of gas analyzers, the list of their fi elds of application is steadily expanding. Today they are acutely needed to solve such problems as diagnosis of diseases from the composition of exhaled air [2][3][4][5], detection of explosives [6-8] and narcotics [9], optimization of combustion processes in heating and power plants [10], high-precision monitoring of the composition of fuel gases [11][12][13], etc.Despite the broad range of physical principles for monitoring gaseous media and instruments based on them, optical diagnostics methods are especially important. This is because of their high sensitivity, selectivity, and speed at which results are obtained. The most attractive optical diagnostics method is spontaneous Raman scattering (SRS) spectroscopy. The SRS method for gas analysis makes it possible to simultaneously record any molecular components of the gaseous medium using a single laser with fi xed wavelength, where the SRS signal for each gaseous component is strictly individual, proportional to its concentration, practically instantaneous, and does not depend on the composition of the gaseous medium. Owing to such a unique set of properties, the SRS method is a general-purpose optical method for analysis of multicomponent molecular gaseous media, including media whose composition is not known ahead of time. The major disadvantage of this method is the low intensity of the SRS signals in a gaseous medium, due to the low density of molecules and the small light scattering cross section (~10 -30 cm 2 /sr). However, when using high-sensitivity multichannel photodetectors, and also with improved effi ciency of detection of the SRS signals, the possibility arose to design a high-sensitivity SRS spectrometer and an SRS gas analyzer.Design of the Spontaneous Raman Spectrometer. An SRS spectrometer for gaseous media was modifi ed in the Environmental Instrumentation Laboratory of the Institute for Monitoring Climatic and Ecological Systems (Siberian Branch, Russian Academy of Sciences). The block diagram for this inst...