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Zhang B.-Y.,Heilongjiang University | Zhang B.-Y.,National Central Laboratory of Hydrocarbon Gas Transportation Pipeline Safety | Zhou H.-J.,Heilongjiang University | Zhou H.-J.,National Central Laboratory of Hydrocarbon Gas Transportation Pipeline Safety | And 3 more authors.
Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis | Year: 2016

CH4/C2H6/N2 mixed hydrate formation experiments were performed at 2 ℃ and 5 MPa for three different mine gas concentrations (CH4/C2H6/N2, G1=54:36:10, G2=67.5:22.5:10, G3=81:9:10). Raman spectra for hydration products were obtained by using Microscopic Raman Spectrometer. Hydrate structure is determined by the Raman shift of symmetric C-C stretching vibration mode of C2H6 in the hydrate phase. This work is focused on the cage occupancies and hydration numbers, calculated by the fitting methods of Raman peaks. The results show that structure I (sI) hydrate forms in the G1 and G2 gas systems, while structure II (sII) hydrate forms in the G3 gas system, concentration variation of C2H6 in the gas samples leads to a change in hydrate structure from sI to sII; the percentages of CH4 and C2H6 in sI hydrate phase are less affected by the concentration of gas samples, the percentages of CH4 are respectively 34.4% and 35.7%, C2H6 are respectively 64.6% and 63.9% for gas systems of G1 and G2, the percentages of CH4 and C2H6 are respectively 73.5% and 22.8% for gas systems of G3, the proportions of object molecules largely depend on the hydrate structure; CH4 and C2H6 molecules occupy 98%, 98% and 92% of the large cages and CH4 molecules occupy 80%, 60% and 84% of the small cages for gas systems of G1, G2 and G3, respectively; additionally, N2 molecules occupy less than 5% of the small cages is due to its weak adsorption ability and the lower partial pressure. © 2016, Science Press. All right reserved. Source


Zhang B.-Y.,Heilongjiang University | Zhang B.-Y.,National Central Laboratory of Hydrocarbon Gas Transportation Pipeline Safety | Yu Y.,Heilongjiang University | Yu Y.,National Central Laboratory of Hydrocarbon Gas Transportation Pipeline Safety | And 3 more authors.
Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis | Year: 2015

The research on micro crystal structure of mine gas hydrate is especially significant for the technology of gas hydrate separation. Using Raman spectroscopy to observe hydration process of 3 kinds of mine gas mixture on line which contains high concentration of carbon dioxide, this experiment obtained the information of the hydrate crystals including large and small cage occupancy. Meanwhile obtained the hydration number indirectly based on the statistical thermodynamic model of van der Waals and Platteeuw. The results show that cage occupancy and hydration number of mine gas hydrates change little during different growth stages. The large cages of hydrate phases are nearly full occupied by carbon dioxide and methane molecules together, with the occupancy ratios between 97.70% and 98.68%. Most of the guest molecules in large cages is carbon dioxide (78.58%~94.09%) and only a few (4.52%~19.12%) is filled with methane, it is because carbon dioxide concentration in the gas sample is higher than methane and there is competition between them. However the small cage occupancy ratios is generally low in the range from 17.93% to 82.41%, and the guest molecules are all methane. With the increase of methane concentration in gas sample, the cage occupancy both large and small which methane occupied has increased, meanwhile the large cage occupancy which methane occupied is lower than small cage. The hydration numbers of mine gas hydrate during different growth stages are between 6.13 and 7.33. Small cage occupancy has increased with the increase of methane concentration, this lead to hydration number decreases. Because of the uneven distribution of hydrate growth, the hydration numbers of 3 kinds of gas samples show irregular change during different growth stages. ©, 2015, Science Press. All right reserved. Source


Zhang B.-Y.,China University of Mining and Technology | Zhang B.-Y.,Heilongjiang University | Zhang B.-Y.,National Central Laboratory of Hydrocarbon Gas Transportation Pipeline Safety | Liu C.-H.,Heilongjiang University | And 5 more authors.
Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis | Year: 2014

Accurate determination of coal mine gas separation product characteristics is the key for gas separation application based on hydrate technology. Gas hydrate was synthesized from two types of gas compositions (CO2-CH4-N2). The separation products were measured by in situ Raman spectroscopy. The crystal structure of mixed-gas hydrate was determined, and the cavity occupancy and hydration index were calculated, based on the object molecular various vibrational mode, "loose cage-tight cage" model and the Raman bands area ratio, combined with the model of van der Waals-Platteeuw. The results show that the mixed-gas hydrates are both structure I for the two gas samples; Large cages of mixed-gas hydrate are nearly occupied by guest molecules, and the large cavity occupancies are 98.57% and 98.52%, respectively; but small cages are not easy to be occupied, and the small cavity occupancies are 29.93% and 33.87%, respectively; hydration index of the two gas samples hydrate is 7.14 and 6.98, respectively, which is greater than the theoretical value of structure I. Source


Wu Q.,Heilongjiang University | Wu Q.,National Central Laboratory of Hydrocarbon Gas Transportation Pipeline Safety | Yue Y.-B.,Heilongjiang University | Yue Y.-B.,National Central Laboratory of Hydrocarbon Gas Transportation Pipeline Safety | And 6 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2015

To explore the effect of THF-SDS complex solution on the distribution characteristics of the temperature field in gas hydrate reaction process, using the hydration reaction apparatus with arraying temperature sensors, distribution characteristics of temperature field in hydrate separation process of gas mixtures(85%CH4, 7%N2, 3%O2, 5%CO2) in three groups of promoter solution (1 mol/L THF, 1 mol/L THF+0.02 mol/L SDS, 1 mol/L THF+0.1 mol/L SDS) were investigated. Studies show that accompanying the increasing of the SDS concentration of the gas hydration systems, the exothermic reaction rate shows an increasing trend (0.030-0.230 kJ/min). The reaction rate changes results in the variation of the temperature distribution in the hydration systems, the upper temperature is the highest and the lower is the lowest in the system, and the higher the SDS concentration is, the more significant temperature gradient is. Gas hydrate thermal conductivity changes while the temperature distribution (0.529-0.534 W/(m·K)) is altering, and the higher the SDS concentration is, the greater the gas hydrate thermal conductivity is. Analysis suggests that THF-SDS complex solution improves the thermodynamic conditions of gas hydrate separation process, advances the air-water conversion rate, and affects the temperature field distribution of different hydration systems. ©, 2015, China Coal Society. All right reserved. Source


Zhang B.-Y.,Heilongjiang University | Zhang B.-Y.,China University of Mining and Technology | Zhang B.-Y.,National Central Laboratory of Hydrocarbon Gas Transportation Pipeline Safety | Yu Y.,Heilongjiang University | And 6 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2014

Phase equilibrium conditions and its influencing factors are especially significant for the rapid generation of gas hydrate. Using visual and high pressure-resisting experimental setup and graphical method, this paper investigated the phase equilibrium conditions of mine gas hydrate formed by gas samples in three different concentrations of NaCl solution. The results show that NaCl could change the phase equilibrium condition and make it more demanding. At the same temperature, the phase equilibrium pressure increases from 0.50 to 2.98 MPa than that in pure water during nine experiments. The hypothesis model of influence mechanism of NaCl on the phase equilibrium was established based on hydrated ion ionization equilibrium theory. This paper concludes that the strong electric field of Na+ and Cl- ionized from NaCl produces an interaction on water molecules. This interaction will destroy the clusters structure of water molecules that surrounds gas molecules. ©, 2014, Meitan Xuebao/Journal of the China Coal Society. All right reserved. Source

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