Regimes of methane recovery from gas hydrate on injection of “warm” carbon dioxide into a porous medium

Specificities of an injection of “warm” liquid carbon dioxide into a porous medium saturated with methane and its gas hydrate are studied using a mathematical model presented in this work. The release of methane from gas hydrate during injection can proceed in two different regimes. In the first regime, the injection is accompanied by the replacement of methane with carbon dioxide in methane hydrate without the release of free water. In the second one, the injection is accompanied by the decomposition of methane hydrate into methane and water and by the formation of carbon dioxide gas hydrate. For each regime, selfsimilar solutions are constructed and critical conditions separating these regimes are found.     

天然气水合物试样制备及力学性质研究进展

天然气水合物是天然气与水在低温高压条件下形成的笼形物。天然气水合物储量丰富,是人类理想的潜在替代能源,被认为是21世纪具有商业开发前景的战略资源。分析了国内外水合物实验装置设计及相应的实验研究内容,重点介绍了我国天然气水合物试样制备研究现状及取得的成果。     

Experiments on fast nucleation and growth of HCFC141b gas hydrate in static water columns

A major technical issue in the realization of refrigerants gas hydrates energy storage systems is to develop a practical means for rapid hydrate formation. In this paper, the nucleation and growth processes of HCFC141b (CH₃CCl₂F, HCFC141b) gas hydrate in a column of water added with 0.038 wt% sodium dodecylbenzenesulfonate-6 and with a metal rod which was placed in the center of the column has been studied. The water solution column, in a cylindrical glass container, was placed in a thermostatic bath ranged 274.15–280.15 K and under atmospheric pressure. The experimental results show that, comparing to that of pure water and HCFC141b system, the properly placed metal rods combined with proper amount of sodium dodecylbenzenesulfonate-6 considerably promotes the hydrate formation speed and reduces the nucleation time. The growth rate of HCFC141b hydrate is significantly effected by the surrounding bath temperature and the formation can be finished in 8 h with a short nucleation time when the bath temperature ranged 274.15–279.15 K and the iron rod penetrating the interface between the water solution and liquid HCFC141b. The experimental results suggest a new way for fast formation of gas hydrates.     

On the theory of formation of gas hydrate in partially water-saturated porous medium when injecting methane

We present a planar one-dimensional theoretical model and numerical solutions for the process of the formation of methane gas hydrate by injecting gas into a porous reservoir partially saturated with water. The case where the intensity of formation of the gas hydrate is limited by the diffusion of gas through a hydrate layer formed between water and gas in the pore channel core is considered. Within this process, the kinetics of hydrate formation is determined by empirical parameter D, having the dimension of a diffusion coefficient (m²/s). The effect of the value of this parameter on the characteristics of the hydrate formation process is studied depending on the parameters that determine the initial state of the porous reservoir and its porosity and permeability characteristics. The equilibrium mechanism of hydrate formation is considered, which is a limit adopted by the diffusion pattern that corresponds to the case of D → ∞.     

高压DSC在气体水合物形成及分解机理研究中的运用

随着海底矿物开采越来越普遍,技术人员面对越来越复杂的钻探技术挑战。特别是极端条件下的深海开采,开采矿产之前,要先处理好表层的可燃冰。通过PVT仪器直接目测来观察气体水合物的形成是一种比较常用的方法。通过记录测量过程中的温压变化来确定气体水合物的形成热力学条件。但是笨重的PVT仪使得实验受限制,并且实验过程中不能有固体微粒出现。本文通过微量热法来确定水合物的成分,研究形成及分解机理,测量比热容。为了满足高压微量热试验需求,法国塞塔拉姆公司特别提出了完全革新的测试手段（法国石油学会专利技术）,运用高压MICRODSC来建立气体水合物的形成热力学模型及生成动力学理论,表征水合物相变与时间、温度、压力的对应关系。MicroDSCVII是研究气体水合的专业高压微量热仪,一经推出就广受好评,样品量为0．7ml的全新样品池,并可与专业的高压控制面板相接,最大压力可以达到1000bars,温度范围为-45℃andl20℃。目前,高压MicroDSCVII已经被运用于各种条件下的气体水合物研究,诸如：气体水合物的形成机理,特别是甲烷气体水合物的研究;气体水合物在海底沉积物中的成藏机理;石油开采中水合物形成的抑制;天然气运输及储存过程中气体水合物的形成;冷藏过程中的气体水合的形成及分解等。     

富气相和富液相中制备天然气水合物的方法

天然气水合物的制备是天然气水合物储运最主要的环节。由于天然气水合物的形成要经过气体溶解、晶核生成和晶体生长等阶段,而天然气组分气体在水中的溶解度很小,水合物只能在气、液界面形成,水合物的自然生成速度十分缓慢,远远不能满足工业应用的需要。因此该技术成功应用的关键在于如何强化天然气水合物快速生成。介绍了几种国内外在富气相和富液相环境下强化制备天然气水合物的方法,分析了各自的优缺点,并对天然气水合物强化制备技术进行了总结与展望。     

钛合金中ω相变的研究进展

钛合金中的ω相及其相变对合金的组织性能影响较大,因此近年来ω相变也成为钛合金研究中的热点问题之一。从ω相的形成、分解、组织形貌以及ω相辅助α形核的角度总结归纳了相关研究报道,对比了相关模型观点的优缺点,阐述了ω相目前仍存在的学术分歧。     

Nucleation of ice and its management in ecosystems

In addition to the gas and liquid phases, water can exist in many different solid states. Some of these are the well-studied crystalline ice polymorphs and the clathrate hydrates, but at least two distinguishable amorphous solid forms have also been shown to exist. This diversity of possible condensed states implies a multiplicity of transitions, each of them presumably associated with a nucleation step. Disagreement still exists as to whether the amorphous states can be regarded as metastable phases, and whether the phenomenon of polyamorphism can be treated in terms of phase transitions. In the Earth's hydrosphere, several of the crystalline and amorphous water phases can be formed from vapour, under given conditions of temperature, pressure and supersaturation, and classical nucleation theory is believed to account reasonably well for the observed growth of condensed forms of water in the upper atmosphere. Many terrestrial organisms are able to activate mechanisms to control the nucleation and growth of ice when exposed to sub-zero temperatures, thus enabling them to minimize the lethal effects of extreme freeze desiccation. The substances involved in these mechanisms include carbohydrates, amino acids and so-called cold-shock proteins, but the actual mechanisms of interfering with ice nucleation, although quite well documented, are as yet imperfectly understood. This is particularly true for the genetic control associated with biochemical processes that produce freeze resistance and freeze tolerance. The molecular biology of cold stress is currently a subject of intensive study.     

Thermal Shock under the Action of Radiation Energy on a Porous Medium Partially Filled with Gas Hydrate

Consideration has been given to the process of decomposition of a gas hydrate saturating a porous volume under the action of the energy of radiation through its boundary. It has been adopted that the zone lying in the vicinity of the boundary and saturated with the products of decomposition of the gas hydrate is transparent to radiation; the far zone saturated with gas hydrate and gas, conversely, is completely opaque; therefore, the radiation energy is totally absorbed at the boundary of phase transitions between the zones mentioned. The selfsimilar solutions of plane onedimensional and radialsymmetric problems have been constructed. The influence of the radiation intensity and of the parameters of the porous medium–solid gas hydrate–gas system in the initial state on the maximum pressures produced in the zone of decomposition of the gas hydrate has been analyzed based on the analytical solutions obtained.     

表面活性剂促进气体水合物生成的研究

天然气水合物被公认为21世纪的重要后续能源,其生成与压力、温度、气水接触面积以及添加剂等因素有关。文章概述了表面活性剂的基本性质,并从改变反应液的表面张力、形成胶束、改变水合物形貌等方面总结了表面活性剂对促进水合物生成的影响,提出了其促进水合物生成的机理。对于未来的研究,我们不仅要观察水合物的形态,也要从水合物膜的内部结构分析表面活性剂对水合物的生成影响,为水合物生成机理形成统一的认识和气体水合物进一步发展提供参考。     

气体水合物超声结晶实验

实验中将15kHz超声波引入R141b和水体系,反应过程在恒温水浴中进行,对超声探头处于不同位置、不同过冷度情况下分别研究.结果表明在超声启动后5秒内就出现大量水合物浆,成核对过冷度的依赖程度降低,但结晶完成时间随过冷度的增加而减少.在同样条件下,探头位于两相界面处,消耗的能量较低.分析结果认为这可能与超声空化产生的一系列效应有关.     

Hydrates in the ocean and evidence for the location of hydrate formation

There is substantial evidence that the oceans of the world will pose the most important challenges in the area of hydrate formation. This work indicates three areas of concern for hydrate formation in the ocean: (1) deposits of natural gas in ocean hydrates, which will serve as an energy resource and environmental concern in the next tnillenium, (2) a recent proposal for the ocean storage of carbon dioxide in the form of hydrates, and (3) the prevention of hydrate formation in ocean pipelines. To address such applications, fundamental knowledge on the site of hydrate formation was determined. Results are presented for quiescent, high-pressure experiments done in a sapphire tube to determine the site of hydrate formation in deionized water and in mixtures with amorphous silica and sodium dodecyl sulfate. Visual (microscope aided) results are presented for formation with a typical gas mixture and with carbon dioxide.Invited paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, USA.     

Particle size distribution of TBPB hydrates by focused beam reflectance measurement (FBRM) for secondary refrigeration application

The present work investigates TBPB (tetra-n-butylphosphonium bromide) hydrate slurries based on focused beam reflectance measurement (FBRM) method. Hydrates can be used as phase change materials (PCM) for thermal energy storage due to their high latent heat of melting. In this study, hydrates were formed from TBPB-water mixtures, suitable for air-conditioning applications. Moreover, hydrate slurries, composed of hydrate-particles dispersed in liquid, are appropriate solutions for cold distribution. Nevertheless, flow properties of hydrate slurries, depending on hydrate crystallization kinetics, must be controlled. In this work, FBRM was used for analysing TBPB-hydrate-particle size distribution. This work showed that FBRM can detect system phase changes (nucleation, growth, agglomeration). In addition, a bimodal distribution of particles was observed. This work could be useful to understand rheological behaviour of hydrate slurry, not only for secondary refrigeration applications, but also for natural gas hydrate transportation, pipeline plugging prevention, and gas capture.     

Targeted Nanoparticle Thermometry: A Method to Measure Local Temperature at the Nanoscale Point Where Water Vapor Nucleation Occurs

An optical nanothermometer technique based on laser trapping, moving and targeted attaching an erbium oxide nanoparticle cluster is developed to measure the local temperature. The authors apply this new nanoscale temperature measuring technique (limited by the size of the nanoparticles) to measure the temperature of vapor nucleation in water. Vapor nucleation is observed after superheating water above the boiling point for degassed and nondegassed water. The average nucleation temperature for water without gas is 560 K but this temperature is lowered by 100 K when gas is introduced into the water. The authors are able to measure the temperature inside the bubble during bubble formation and find that the temperature inside the bubble spikes to over 1000 K because the heat source (optically‐heated nanorods) is no longer connected to liquid water and heat dissipation is greatly reduced.     

等离子喷涂-物理气相沉积的气相沉积机理

以等离子喷涂-物理气相沉积(PS-PVD)喷涂团聚的 ZrO₂-7wt%Y₂O₃(7YSZ)粉末在五个喷距下制备了热障涂层。通过场发射-扫描电镜(FE-SEM)和X射线衍射(XRD)分析了五个涂层样品的微观结构和相成分差异。另外, 通过发射光谱(OES)诊断研究了射流中7YSZ粉末气相浓度随喷距的变化。最后, 阐述了3种不同的气相沉积涂层生长机制, 说明了射流中粉末的状态和气相浓度对涂层结构的影响。研究表明：(1)350 mm和1800 mm喷距下形成的均是致密结构涂层, 而650~1250 mm喷距下形成的是典型的PS-PVD柱状结构涂层。(2)350 mm喷距下制备的涂层由四方相(t’)和单斜相(m)氧化锆构成; 当喷距大于650 mm时, 涂层以四方相(t’)氧化锆为主。(3)350 mm喷距下涂层是由高浓度气相过饱和自发形核形成的新核和液/固粒子共同作用形成的; 喷距650~1250 mm下, 涂层生长以气相沉积于基体进行非自发形核为主, 气相在射流中的自发形核为辅; 喷距1800 mm下涂层由气相过冷凝固的粒子堆积而成。     

进气方式影响CO2水合物喷雾合成的实验研究

为探讨进气方式对二氧化碳水合物生成特性的影响,利用自行设计的喷雾强化水合物制备实验系统,分析和比较连续式进气和振荡进气两种进气方式下喷雾合成水合物的耗气量和反应釜内温度的变化,研究其生成特性。实验结果表明:采用振荡进气方式,相对连续进气方式,单位时间内耗气量更多,生成的水合物速率更快。该方式下可以产生较大的驱动力,这种气体间变化性的扰动,使得水合物快速生长。在前期溶解阶段,适当调节进气阀门,加大进气速率,利于水合物生长。     

热丝碳化促进CVD金刚石成核增强的物理机制

采用扫描电镜、X射线衍射及喇曼光谱等手段研究了HFCVD过程中热丝碳化对金刚石成核特性的影响。热丝经充分碳化后能发射出更多热电子，进而从反应气体中激发出更多原子H和CH3^ ，使金刚石晶核的孕育期大为缩短，3min内即可在未经表面预处理Si衬底上获得10^10cm^-2以上的高晶核密度。     

Modeling of phase decomposition of supersaturated solid solutions using the free-energy density functional method

The nucleation and growth of particles of the second phase in a one-dimensional binary alloy is considered based on the Cahn–Hilliard equation with allowance for fluctuations. Using the results of modeling, it is shown that the second phase is occupied by the mechanism of solid solution decomposition, which involves simultaneous processes of the fluctuational nucleation of the second phase, diffusion-type growth of precipitations, and absorption of small clusters by coarse ones at the coalescence stage. Composition fluctuations are among the main factors influencing the distribution of solid solution phases.

     

On the migration of a single gas bubble in water

A theoretical model of a single gas bubble rising in open water is considered. It is revealed that methane bubble rising is accompanied by the formation of the hydration shell on its surface under the thermobaric conditions of the stability of hydrates. Numerical solutions for two limiting cases were obtained and analyzed, when the formation rate of the hydrated crust on the bubble surface is limited by the intensity of heat removal released in the process of hydrate formation by the surrounding liquid or the diffusion resistance of the gas hydrate crust to the transfer of hydrate-forming components. The comparison of numerical results with experimental data showed that the scheme of the diffusion transfer of hydrate-forming components through the crust describes most adequately the process of the growth of the gas hydrate particle observed in experiments of methane bubbles rising in sea water. It is established that argon bubble rising under the corresponding thermobaric conditions can occur without the formation of the hydrate on its surface. The migration of the gas bubble is accompanied by its dissolution in water. Numerical estimates for the values of the argon diffusion coefficient in water and reduced diffusion coefficients of gas (methane) and water through the hydrate crust are obtained from the conditions of matching theoretical and experimental data from the change of the argon bubble radius and the gas hydrate particle.     

Formation Conditions of Clathrates Between HFC Alternative Refrigerants and Water

There are two promising candidates as alternative refrigerants for air-conditioners and heat pumps. The first is R407C, which is composed of HFC-32 (23 mass%), HFC-125 (25 mass%), and HFC-134a (52 mass%). The second is R410A, which is composed of HFC-32 (50 mass%) and HFC-125 (50 mass%). In this study, formation conditions of clathrate compounds between water and HFC alternative refrigerants such as HFC-32, HFC-125, HFC-134a, and their mixtures, R407C and R410A, were investigated. Phase diagrams of clathrates of these HFC alternative refrigerants and their mixtures were determined. From the phase diagrams, the critical decomposition temperature and the critical decomposition pressure were determined. The relationship between the critical decomposition points for the clathrates of HFC-32, HFC-125, HFC-134a, R410A, and R407C were studied. It is found that R407C and R410A form clathrate compounds with water under the evaporating temperature condition in the refrigeration cycle of air-conditioners and heat pumps.