二氧化碳水合物形成原因分析

从万金塔二氧化碳气田向气站内输送原料二氧化碳过程中,经常发生二氧化碳与水形成水合物堵塞输气管道的现象,给二氧化碳的净化提纯生产带来不利的影响。研究人员在参阅相关文献的基础上,提出应用统计热力学方法来求取二氧化碳形成水合物的具体条件,并且基于实践的基础上分析了防止水合物形成的预防方法,对二氧化碳气田的开发具有一定的借鉴意义。     

The clathrate hydrate process for post and pre-combustion capture of carbon dioxide

One of the new approaches for capturing carbon dioxide from treated flue gases (post-combustion capture) is based on gas hydrate crystallization. The basis for the separation or capture of the CO(2) is the fact that the carbon dioxide content of gas hydrate crystals is different than that of the flue gas. When a gas mixture of CO(2) and H(2) forms gas hydrates the CO(2) prefers to partition in the hydrate phase. This provides the basis for the separation of CO(2) (pre-combustion capture) from a fuel gas (CO(2)/H(2)) mixture. The present study illustrates the concept and provides basic thermodynamic and kinetic data for conceptual process design. In addition, hybrid conceptual processes for pre and post-combustion capture based on hydrate formation coupled with membrane separation are presented.     

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.     

气体水合物分解与生成技术应用研究进展

水合物技术应用可归纳为分解应用和生成应用,本文就这两大应用方向对水合物进行了分类综述。从水合物分解角度,阐述了天然气水合物资源勘探开发、管道水合物解堵、水合物抑制防控等技术应用的研究进展;从水合物分解的逆过程(生成)角度,阐述了水合物储气、二氧化碳捕获与封存、海水淡化、溶液提浓、污水处理、混合气体分离、蓄冷等应用技术。同时论文结合气体水合物发展历程,概括了气体水合物技术在诸多领域的应用,指出了水合物技术发展取得的诸多成果,也提出了新形势下水合物发展所面临的问题,希望能为今后水合物技术的发展带来一定指导。     

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。     

天然气水合物合成实验

为提高天然气水合物的生产效率及储气密度,在专门设计的水合物合成实验装置上,进行了纯甲烷水合物的合成实验。实验结果表明:对于纯净甲烷水合物,压力越高,合成速率越大;但当压力大于5 MPa时,压力的提高对生成速率的影响不大。水合物合成前抽真空时间越长,生成的水合物吸收的气体量越大,表明抽真空可以排出水中溶解的气体,提高水合物的储气密度。     

A Perspective on Rheological Studies of Gas Hydrate Slurry Properties

Gas hydrates are solid inclusion compounds that are composed of a three-dimensional hydrogen-bonded network of water cages that can trap small gas molecules, such as methane and carbon dioxide. Understanding the rheological properties of gas hydrate crystals in solution can be critical in a number of energy applications, including the transportation of natural gas in subsea and onshore operations, as well as technological applications for gas separation, desalination, or sequestration. A number of experimental and modeling studies have been done on hydrate slurry rheology; however, the link between theory and experiment is not well-defined. This article provides a review on the current state of the art of hydrate slurry viscosity measurements from high- and low-pressure rheometer studies and high-pressure flowloops over a range of different sub-cooling (ΔT_sub = T_equil − T_exp) and fluid conditions, including for water and oil continuous systems. The theoretical models that have been developed to describe the gas hydrate slurry relative viscosity are also reviewed. Perspectives’ linkage between the experiments and theory is also discussed.     

海洋环境二氧化碳水合物生成的实验研究

温室气体CO2的海洋封存是CO2处理的重要设想,对减缓全球气候变化有着深远的意义。CO2水合物在海洋环境中与在纯水溶液中的生成条件有很大的不同。为了研究海洋环境中CO2水合物的生成特性,设计了一套CO2气体水合物实验装置和一套实验流程,利用这套实验装置模拟海洋深度500 m处海水环境,在海水—CO2体系中合成CO2水合物,探讨了温度、压力和盐度等对海洋环境中CO2水合物生成特性的影响。     

Designing Durable Vapor‐Deposited Surfaces for Reduced Hydrate Adhesion

The formation and accumulation of clathrate hydrates inside oil and gas pipelines cause severe problems in deep‐sea oil/gas operations. In the present work, durable and mechanically robust bilayer poly‐divinyl benzene/poly(perfluorodecylacrylate) coatings are developed using initiated chemical vapor deposition (iCVD) to reduce the adhesion strength of hydrates to underlying substrates (silicon and steel). Tetrahydrofuran (THF) dissolved in water with a wt% concentration of 0–70 is used to study the formation of hydrates and their adhesion strength. Goniometric measurements of the THF–water droplets on the substrates exhibit a reduction in advancing and receding contact angles with an increase in the THF concentration. The strength of hydrate adhesion experiences a tenfold reduction when substrates are coated with these iCVD polymers: from 1050 ± 250 kPa on bare silicon to 128 ± 100 kPa on coated silicon and from 1130 ± 185 kPa on bare steel to 153 ± 86 kPa on coated steel. The impact of subcooling temperature and time on the adhesion strength of hydrate on substrates is also studied. The results of this work suggest that the THF–water mixture repellency of a given substrate can be utilized to assess its hydrate‐phobic behavior; hence, it opens a pathway for studying hydrate‐phobicity.     

气体水合及其在空调蓄冷技术中的应用

本文概述了气体水合“暖冰”蓄冷这一技术的研究发展现状,简明地介绍了气体水合现象和水合物的晶体结构、热力学性质、形成条件,影响稳定性和生成速度等的因素,以及混合气体水合物的特点,阐述了气体水合物作为空调蓄冷材料的优越性和在蓄冷技术中的应用方式,并指出了气体水合蓄冷技术研究发展的一些关键问题及该技术的应用前景。     

水合物分解的噪声研究

海洋中水合物在分解后会形成大量气泡并向外辐射噪声信号。基于水合物分解的特点,建立了适用于描述水合物分解的非理想气泡的振动模型,并通过数值方法分别对辐射噪声的频率和辐射声压做了仿真模拟。结合测量二氧化碳水解噪声的实验数据,对分解得到的不同半径气泡辐射噪声频率和声压做了统计分析。结果表明,理论模型与实验结果吻合较好,该研究对监测水合物的泄漏分解等具有重要的意义。     

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.     

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。     

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.     

Phase Equilibrium for Structure-H Hydrates Formed with Methane and Methyl-Substituted Cyclic Ether

Clathrate hydrate formation in a (methane + either 3-methyltetrahydropyran or 2-methyltetrahydrofuran + water) system is demonstrated. The first data of the quadruple (water + structure-H hydrate + either 3-methyltetrahydropyran or 2-methyltetrahydrofuran + methane) equilibrium pressure–temperature conditions are measured over temperatures from 273 to 286 K. In the 3-methyltetrahydropyran system, the equilibrium pressures are lower by 1.6–2 MPa than those of the structure-I methane hydrate formed in the methane + water system at given temperatures. In the 2-methyltetrahydrofuran system, equilibrium pressures at temperatures below 278 K are lower than those for the structure-I methane hydrate, and at temperatures above 278 K, they are higher. These phase equilibria suggest the formation of hydrates other than structure-I methane hydrates in the two systems. The crystallographic structures of the hydrates are determined to be structure H by means of X-ray diffraction as expected from considerations of sizes and shapes of the 3-methyltetrahydropyran and 2-methyltetrahydrofuran molecules     

Solid fraction modelling for CO2 and CO2–THF hydrate slurries used as secondary refrigerants

In the present paper, the suitability of hydrate slurries in secondary refrigeration was investigated by the means of a new hydrate solid-fraction model. Considering the high melting enthalpy of CO₂-containing hydrates, slurries presenting high hydrate solid fractions can carry sufficient latent heat to be useful for a two-phase secondary-refrigerant application. The model presented in this paper allowed to calculate the solid fraction of CO₂ and CO₂–THF hydrate from thermodynamic conditions of pressure and temperature. Contrary to a previous work on single CO₂ hydrates in a closed system, the present model can take into account hydrate mixture and is well adapted to additional CO₂ injections (opened system). By relying on the hydrate-conversion model results, the study of hydrates in suspension in a carrying liquid was also studied in an experimental loop and was based on a formation process by CO₂ injection in a cooled aqueous solution.     

Preparation of gas hydrates by nonequilibrium condensation of molecular beams

Layers of amorphous ice saturated with carbon dioxide were prepared by the deposition of molecular beams of water and gas onto a substrate cooled with liquid nitrogen. Their heating is accompanied by glass transition (softening) and subsequent spontaneous crystallization. The glass transition and crystallization temperatures were determined from the change in dielectric properties during heating. The heat effects of the transformations were detected using differential thermal analysis. The crystallization of amorphous layers under conditions of deep metastability leads to the formation of crystalline hydrates. The avalanche nucleation of crystallization sites captures the gas molecules; therefore, they are not displaced by the movement of the crystallization front.     

Have sudden large releases of methane from geological reservoirs occurred since the Last Glacial Maximum,and could such releases occur again?

Methane emissions from geological reservoirs may have played a major role in the sudden events terminating glaciation, both at the start of the B?lling/Aller?d and also at the end of the Younger Dryas. These reservoirs include Arctic methane hydrates and also methane hydrate stored in offshore marine sediments in tropical and temperate latitudes. Emissions from hydrate stores may have resonated with tropical wetland emissions, each reinforcing the other. Because methane is such a powerful greenhouse gas, much smaller emissions of methane, compared with carbon dioxide, are required in order to have the same short-term impact by climate forcing. The methane-linked hypothesis has much geological support from sea-floor evidence of emission. However, Greenland ice-core records have been interpreted as showing methane as a consequential factor, rather than the leader, of change. This interpretation can be challenged on the grounds that temperature gradients in Greenland ice record local changes and local timing of a step-like shift in weather fronts, while methane concentrations record changes on a hemispheric and global scale. There are large remaining hydrate reservoirs in the Arctic and in shelf sediments globally, and there is substantial risk of further emissions.     

Pyrite crystallization in seep carbonates at gas vent and hydrate site

Pyrite formed by the synergistic metabolism of methane oxidizing archaea and sulfate reducing bacteria has been found in seep carbonates where hydrates usually occur in the subsurface and gas vents out from seafloor in many places worldwide. These bacteria collaborate to oxidize venting methane and reduce seawater sulfate. The hydrogen sulfide and carbon dioxide produced in this process causes pyrite and calcite crystallization (seep carbonate precipitation). We show, using the microscope analysis, that the pyrite crystallization has both bacterial fossilization and crystallization in seep carbonates collected from gas vent and hydrate sites off Louisiana Coast in the Gulf of Mexico and near Dongsha Island in the South China Sea. The pyrite shows bacterial and crystal forms scattered in the calcites. The crystal pyrite occurs as cubic crystals to construct framboid. The bacterial pyrite causes spheroids, rods in nanometer scale to aggregate to layered spheroids, rod-chains, and worm-like forms. These bacterial forms are identical to the characteristic form of live MOA/SRB colonies observed in gas vent and hydrate sites.     

Thermodynamics and kinetics of methane hydrate formation and dissociation in presence of calcium carbonate

Huge amount of gas hydrate deposits are identified in deep marine sediments, which may be considered as a future source of energy. Since carbonate is one of the major components of marine sediments, in the present study attention has been given to characterize methane hydrate formation and dissociation in presence of calcium carbonate. Experiments were performed with 0%, 2%, 4%, 6% and 10% by weight of calcium carbonate in distilled water. Extensive investigations have been done on pressure-temperature equilibrium behavior of hydrate formation and dissociation at varying concentrations of calcium carbonate. Hydrate formation rate was found to vary with concentration of calcium carbonate as the solubility of calcium carbonate in water is controlled by the presence of simultaneous chemical equilibria involving a high number of species like Ca²⁺, CO₃^2?, HCO₃^?, CO₂, etc. Induction time for hydrate formation has also been measured at different concentrations of carbonate. Nucleation point for the hydrate formation was observed to be slightly higher at higher concentration of calcium carbonate due to increased heat absorption. Dissociation enthalpy of hydrates was calculated by using Clausius-Clapeyron at different measured conditions. Moles consumption of methane gas during hydrate formation at different concentrations of carbonate was measured using real gas equation and found to be minimum at 10?wt%.