STUDY OF THE STABILITY OF METHANE HYDRATES IN NORMAL CONDITIONS (original) (raw)
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Physical and Chemical Properties of Gas Hydrates: Theoretical Aspects of Energy Storage Application
MATERIALS TRANSACTIONS, 2007
A model has been developed permitting to accurately predict on molecular level phase diagram of the clathrate hydrates. This model allows to take into account the influence of guest molecules on the host lattice and to extend the interval of temperatures and pressures of computed thermodynamic potentials and significantly improves known van der Waals and Platteeu theory. The theoretical study of phase equilibrium in gas-gas hydrate-ice Ih system for methane and xenon hydrates has been performed. The obtained results are in a good agreement with experimental data. A new interpretation of so-called self-preservation effect has been proposed. The self-preservation of gas hydrates can be connected with differences in thermal expansions of ice Ih and gas hydrates. This is confirmed by calculations performed for methane and mixed methane-ethane hydrates.
ACS Omega, 2021
The estimation of thermodynamic equilibrium conditions of methane hydrates in the presence of crude oil based on experiments is shown in this research work. This pipeline system replicated the gas-dominant multiphase transmission pipelines at deep-sea regions. An experimental study is done by the usage of a Raman gas hydrate reactor. The pressure was maintained in the range of 3−8 MPa for the experimental study. The water cut is kept constant throughout the system as 30%. Initially, the experimental setup is calibrated by using carbon dioxide gas. Then, methane hydrates are formed with and without crude oil. The methane hydrates that are created without the presence of crude oil are validated with simulation that is performed using CSMGEM, PVTSIM software, and literature data. Then, the thermodynamic conditions are found for the methane hydrate formation in the presence of crude oil with an addition of a 15% oil cut to the system. From these results, the phase behavior of a multiphase system is evaluated. The formation of methane hydrates in the system was found to be affected by the presence of an additional oil phase that exhibited an inhibition behavior. This research validates all the multiphase systems that contain similar hydrocarbon and gas compositions.
Semiclathrate hydrates of natural gas have shown potential applications in natural gas storage and transportation. Promoters, viz., tetra-n-alkyl ammonium bromide (TBAB) and tetrahydrofuran (THF) have positive impacts on the phase stability condition in lowering the required pressure for hydrate formation. As part of this work, a predictive model for the phase stability of gas hydrate, which are necessary to understand the phase behavior of methane (CH 4) hydrate in promoters, has been proposed. The fugacity of hydrate former in the gaseous phase is calculated from Peng-Peng-Robinson equation of state (PR-EoS), while the fugacity of water in the liquid phase is computed from recently proposed Pitzer-Mayorga-Zavitsas-Hydration (PMZH) model for TBAB system and non-random two liquid (NRTL) model for THF system. The van der Waals Plattew model is employed for the hydrate phase. The vapor pressure of water in the empty hydrate lattice as well as Langmuir adsorption constants have been expressed in terms of concentration of the promoters. The predictions of the proposed model are found to be match well with experimental data on phase stability of CH 4 hydrate formed using TBAB and THF aqueous systems. Furthermore, the developed model is employed for the prediction of phase stability conditions of the semiclathrate hydrates of CH 4 in TBAB þ NaCl system. The developed model is found to interpret the promotion effects of both TBAB (with or without NaCl) and THF on phase stability conditions of CH 4 hydrate. AARD-P% with PMZH model are observed to be 3.21% and 8.73% for semiclathrate hydrates of CH 4 in TBAB and TBAB þ NaCl, respectively, and 8.56% for clathrate hydrate of CH 4 in THF. The model may be extended to evaluate the phase stability conditions of hydrates of multicomponent gas systems in TBAB/THF which are necessary for real field applications.
Dyczko Pedchenko: Journal of Ecological Engineering, 2016
The technology of transportation and storage of gas in a gas-hydrated form under atmospheric pressure and slight cooling-the maximum cooled gas-hydrated blocks of a large size covered with a layer of ice are offered. Large blocks form from pre-cooled mixture of crushed and the granulated mass of gas hydrate. The technology of forced preservation gas hydrates with ice layer under atmospheric pressure has developed to increase it stability. The dependence in dimensionless magnitudes, which describes the correlation-regressive relationship between the temperature of the surface and the center gas hydrate block under its forced preservation, had proposed to facilitate the use of research results. Technology preservation of gas hydrate blocks with the ice layer under atmospheric pressure (at the expense of the gas hydrates energy) has designed to improve their stability. Gas hydrated blocks, thus formed, can are stored and transported during a long time in converted vehicles without further cooling. The high stability of gas hydrate blocks allows to distributed in time (and geographically) the most energy expenditure operationsproduction and dissociation of gas hydrate. The proposed technical and technological solutions significantly reduce the level of energy and capital costs and, as a result, increase the competitiveness of the stages NGH technology (production, transportation, storage, regasification).
Current Applications & developments of Gas Hydrates
In recent years the topic of naturally occurring gas hydrates has attracted major interest worldwide due to the fact that they may play a dominant role as possible energy resources in the future. Other positive applications include carbon dioxide sequestration, water desalination and natural gas storage and transportation. Finally the use of their dissociation energy can be applied in refrigeration processes and cool storage. In this article the historical background and development of gas hydrates and natural gas hydrates and the applications of gas hydrates is reviewed as well as the necessary fundamental information about the structure of gas hydrates.
Hydrate Formation during Transport of Natural Gas Containing Water and Impurities
Journal of Chemical & Engineering Data, 2016
The upper limit of water content permitted in a natural gas stream during its pipeline transport without a risk of hydrate formation is a complex issue. We propose a novel thermodynamic scheme for investigation of different routes to hydrate formation, with ideal gas used as reference state for all components in all phases including hydrate phase. This makes comparison between different hydrate formation routes transparent and consistent in free energy changes and associated enthalpy change. From a thermodynamic point of view natural gas hydrate can form directly from water dissolved in natural gas but quite unlikely due to limitations in mass and. The typical industrial way to evaluate risk of hydrate formation involves calculation of water condensation from gas and subsequent evaluation of hydrate from condensed water and hydrate formers in the natural gas. Transport pipes are rusty even before they are mounted together to transport pipelines. This opens up for even other routes to hydrate formation which starts with water adsorbing to rust and then leads to hydrate formation with surrounding gas. Rust consist on several iron oxide forms but Hematite is one of the most stable form and is used as a model in this study, in which we focus on maximum limits of water content in various natural gas mixtures that can be tolerated in order to avoid water dropping out as liquid or adsorbed and subsequently forming hydrate. Calculations for representative gas mixtures forming structure I and II hydrates are discussed for ranges of conditions typical for North Sea. The typical trend is that the estimated tolerance for water content is in the order of 20 times higher if these numbers are based on water dew-point rather than water dropping out as adsorbed on Hematite. For pure methane the maximum limits of water to be tolerated decrease with increasing pressures from 50 to 250 bars at temperatures above zero Celsius and up to six Celsius. Pure ethane and pure propane show the opposite trend due to the high density non-polar phase at the high pressures. Typical natural gas mixtures is, however, dominated by the methane so for systems of 80 per cent methane or more the trend is similar to that of pure methane with some expected shifts in absolute values of water drop-out mole-fractions.