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1.
Depressurization combined with brine injection is a potential method for field production of natural gas hydrate, which can significantly improve production efficiency and avoid secondary formation of hydrate. In this work, the experiments of hydrate production using depressurization combined with brine injection from a simulated excess-water hydrate reservoir were performed, and the effects of NaCl concentration on hydrate decomposition, temperature change, and heat transfer in the reservoir were investigated. The experimental results indicate that there is little gas production during depressurization in a excess-water hydrate reservoir, and the gas dissociated from hydrate is trapped in pores of sediments. The high-water production reduces the final gas recovery, which is lower than 70% in the experiments. The increasing NaCl concentration only effectively promotes gas production rate in the early stage. The final cumulative gas production and average gas production rate have little difference in different experiments. The NaCl concentration of the produced water is significantly higher than that which is in contact with hydrate in the sediments because the water produced by hydrate decomposition exists on the surface of undissociated hydrate. The high concentration of NaCl in the produced water from the reactor significantly reduces the promoting effect and efficiency of NaCl solution on hydrate decomposition. The injection of NaCl solution decreases the lowest temperature in sediments during hydrate production, and increases the sensible heat and heat transfer from environment for hydrate decomposition. The changes of temperature and resistance effectively reflect the distribution of the injected NaCl solution in the hydrate reservoir. 相似文献
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The purpose of this study is to analyze the dynamic properties of gas hydrate development from a large hydrate simulator through numerical simulation. A mathematical model of heat transfer and entropy production of methane hydrate dissociation by depressurization has been established, and the change behaviors of various heat flows and entropy generations have been evaluated. Simulation results show that most of the heat supplied from outside is assimilated by methane hydrate. The energy loss caused by the fluid production is insignificant in comparison to the heat assimilation of the hydrate reservoir. The entropy generation of gas hydrate can be considered as the entropy flow from the ambient environment to the hydrate particles, and it is favorable from the perspective of efficient hydrate exploitation. On the contrary, the undesirable entropy generations of water, gas and quartz sand are induced by the irreversible heat conduction and thermal convection under notable temperature gradient in the deposit. Although lower production pressure will lead to larger entropy production of the whole system, the irreversible energy loss is always extremely limited when compared with the amount of thermal energy utilized by methane hydrate. The production pressure should be set as low as possible for the purpose of enhancing exploitation efficiency, as the entropy production rate is not sensitive to the energy recovery rate under depressurization. 相似文献
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水流动强化天然气水合物降压分解研究 总被引:1,自引:0,他引:1
降压法被认为是最经济可行的天然气水合物开采方法,但开采后期驱动力不足、甚至产生水合物的二次生成,因此其应用受到限制。本文将降压法与水流动结合提升水合物分解驱动力,研究不同降压模式和水流动对天然气水合物分解特性的影响。发现当降压结合水流动时,压降为水合物分解提供初始驱动力,且压降越大水合物分解驱动力越大。同时水流动能够加快传热传质过程,为水合物分解提供额外的驱动力。在快速降压结合水流动模式中,较高背压下水流动为水合物分解提供主要的驱动力;在梯度降压结合水流动模式中,降压和水流动共同为水合物提供分解驱动力,对水合物分解的促进作用更加显著。 相似文献
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The paper studies the process of floating a gas hydrate particle in liquid. The typical depths when gas bubble floating is accompanied by gas hydrate formation (or with zero gain of hydrate) were calculated. The low depths were identified when floating occurs with hydrate dissociation. The model assumes that the gas hydrate formation is limited by heat transfer from interface to the surrounding liquid. The model for gas hydrate dissociation assumes the rate governed by thermal conductivity of hydrate particle and by convective heat transfer to surrounding water. The temperature of the gas hydrate surface equals the phase transition temperature at the given water pressure. Comparative analysis of thermal conductivity and convective heat transfer effects on hydrate dissociation rate was performed for different initial radius of the particle. 相似文献
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V. Sh. Shagapov Yu. A. Yumagulova O. A. Shepelkevich 《Thermophysics and Aeromechanics》2016,23(4):537-542
The solution was obtained for a problem of gas hydrate growth in water with dissolved gas. The rate of hydrate formation depends on gas diffusion to the contact with gas hydrate. Three versions of problem configuration were considered: planar, radial, and spherical symmetry. For these cases, the values of the self-similarity coordinate were obtained: this parameter controls the growth of gas hydrate in water with gas dissolved and the level of top temperature in the hydrate zone. Analysis was performed for temperature fields related to heat release during hydrate formation. 相似文献
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Inward transport of a magnetized pure positron plasma confined in a Penning-Malmberg trap is produced by applying a rotating electric field to the plasma. Compression is observed over a broad range of frequencies. Compression factors up to 20 in central density were obtained. Positron collisions with a neutral buffer gas are used to counteract the heating due to the rotating electric field. The results have implications for a variety of applications including the production of brightness enhanced positron beams, the study of electron-positron plasmas, and antihydrogen production. 相似文献
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The mathematical model of decomposition of a spherical gas hydrate particle in water behind a 1D wave of the stepped profile
(rarefaction wave) is suggested. Contribution of the outer and inner heat flux in a particle to the process of hydrate decomposition
is studied. The effect of the gas hydrate particle size, pressure and temperature jumps in liquid on gas hydrate decomposition
is investigated. 相似文献
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《Heat Recovery Systems and CHP》1988,8(5):393-399
Four different moderator heat recovery circuits are proposed for CANDU-1000 MW (e) reactors. The proposed circuits utilize all, or part, of the 155 MW(th) moderator heat load (at 70°C moderator outlet temperature from calandria) to the first stage of the water heating system. An economics study was carried out and indicated that the direct circulation of feed water through the moderator heat exchanger (with full heat recovery) is the most economical scheme. For this scheme the saved steam from the turbine extraction was found to produce additional electric power of 8 MW(e). This additional power represents a 0.7% increase in the plants nominal electric output. The outstanding features and advantages of the selected scheme are also presented. 相似文献
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D. V. Antonov O. V. Vysokomornaya G. V. Kuznetsov M. V. Piskunov 《Journal of Engineering Thermophysics》2018,27(2):145-154
A predictive model was developed for investigation of high-temperature heating and evaporation of water droplets. The model takes into account the basic interrelated processes of heat transfer and phase transitions. Typical velocity and temperature profiles were found in the high-temperature gas–water droplet system with external gas medium temperature varied from 100 to 800°C. Various formulations of the problem, significantly different in the type of considered processes and factors, are considered.We analyzed temperature conditions of heating and evaporation of water droplets, which allow the use of simplified models and which need consideration of all complex interrelated processes of heat and mass transfer (including convection, conduction and radiant heat transfer in droplets, and also in the surface vapor–gas layer). 相似文献
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用分子动力学模拟方法研究甲烷水合物的热激法,化学试剂法,以及热激法结合化学试剂法分解,系统研究温度为277K和340K时添加液态水(WTR)和30wt%乙二醇(EG)溶液对水合物分解的影响.模拟显示WTR与水合物表面水分子形成氢键,破坏水合物原有的氢键平衡,造成笼状结构坍塌,水合物分解.EG分子中的羟基与水合物表面水分子形成氢键,从而破坏原有的稳定结构,造成水合物笼状结构被破坏,达到促进水合物分解,释放甲烷气体的效果.比较温度为277K和340K时添加WTR和30wt%EG溶液对水合物分解效果得出EG(340K)> WTR(340K)>EG(277K)>WTR(277K),热激法结合化学试剂法能更好促进水合物分解. 相似文献
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The longitudinal wave velocity and attenuation measurements of artificial gas hydrate samples at a low temperature are reported.
And the temperature and pressure dependence of longitudinal wave velocity is also investigated. In order to understand the
acoustic properties of gas hydrate, the pure ice, the pure tetrahydrofuran (THF), the pure gas hydrate samples and sand sediment
containing gas hydrate are measured at a low temperature between 0°C and −15°C. For the pure ice, the pure THF and the pure
gas hydrate samples, whose density is 898 kg/m3, 895 kg/m3 and 475 kg/m3, the velocity of longitudinal wave is respectively 3574 m/s, 3428 m/s and 2439 m/s. For synthesized and compacted samples,
the velocity of synthesized samples is lower than that of compacted samples. The velocities increase when the densities of
the samples increase, while the attenuation decreases. Under the condition of low temperature, the results show that the velocity
is slightly affected by the temperature. The results also show that wave velocities increase with the increase of piston pressures.
For example, the velocity of one sample increases from 3049 up to 3337 m/s and the other increases from 2315 up to 2995 m/s.
But wave velocity decreases from 3800 to 3546 m/s when the temperature increases from −15°C to 5°C and changes significantly
close to the melting point. Formation conditions of the two samples are the same but with different conversion ratios of water.
The results of the experiment are important for exploration of the gas hydrate resources and development of acoustic techniques.
Supported by the National Natural Science Foundation of China (Grant No. 10674148) 相似文献
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V. E. Nakoryakov S. Ya. Misyura S. L. Elistratov A. Yu. Manakov A. A. Sizikov 《Journal of Engineering Thermophysics》2013,22(3):169-173
Kinetics of dissociation of synthetic and natural methane gas hydrates, and also double isopropanol-methane hydrate is investigated. Thermal fields of the sample surfaces are measured by means of thermal imaging in combustion of released methane with clathrate dissociation. The dissociation rates of natural hydrate and double hydrate with isopropanol are many times lower than those of synthetic methane hydrate. Methane combustion is accompanied by formation of a thin water film on the powder surface, which has a strong effect on the heat and mass transfer mechanisms. The experiments demonstrated partial self-preservation for methane hydrate and the absence of self-preservation for double isopropanol-methane hydrate. The experimentally observed dissociation rate of double isopropanol-methane hydrate is considerably lower than that of methane hydrate. 相似文献
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E. A. Bondarev I. I. Rozhin V. V. Popov K. K. Argunova 《Journal of Engineering Thermophysics》2018,27(2):221-231
The paper is devoted to simulation of the initial stage of natural gas hydrate underground storage: gas injection into aquifer just below permafrost rocks. It is based on the mathematical model of multiphase non-isothermal real gas and water flow in porous media. The model takes into account the transformation of gas and water into hydrate at certain temperature, which depends on gas flow pressure. The dynamics of hydrate and water saturation as well as the pressure and temperature fields in a reservoir with given porosity, permeability, and initial values of pressure, temperature and water saturation were studied. An implicit finite-difference scheme is used to approximate the original boundary-value problem. The finite-difference equations are solved using simple iteration and sweeping algorithms. Several examples of calculations corresponding to real cases are given. Calculations have revealed that the final result strongly depends on the combination of porosity and permeability of a reservoir. 相似文献