Study of the Kinetics and Morphology of Gas Hydrate Formation

The kinetics and morphology of ethane hydrate formation were studied in a batch type reactor at a temperature of ca. 270–280 K, over a pressure range of 8.83–16.67 bar. The results of the experiments revealed that the formation kinetics were dependant on pressure, temperature, degree of supercooling, and stirring rate. Regardless of the saturation state, the primary nucleation always took place in the bulk of the water and the phase transition was always initiated at the surface of the vortex (gas‐water interface). The rate of hydrate formation was observed to increase with an increase in pressure. The effect of stirring rate on nucleation and growth was emphasized in great detail. The experiments were performed at various stirring rates of 110–190 rpm. Higher rates of formation of gas hydrate were recorded at faster stirring rates. The appearance of nuclei and their subsequent growth at the interface, for different stirring rates, was explained by the proposed conceptual model of mass transfer resistances. The patterns of gas consumption rates, with changing rpm, have been visualized as due to a critical level of gas molecules in the immediate vicinity of the growing hydrate particle. Nucleation and decomposition gave a cyclic hysteresis‐like phenomena. It was also observed that a change in pressure had a much greater effect on the rate of decomposition than it did on the formation rate. Morphological studies revealed that the ethane hydrate resembles thread or is cotton‐like in appearance. The rate of gas consumption during nucleation, with different rpm and pressures, and the percentage decomposition at different pressures, were explained precisely for ethane hydrate.     

Kinetics of ethane hydrate formation

The kinetics of ethane hydrate formation after commencement of nucleation were studied at temperatures from 274 to 282 K over a pressure range of 0.6–2.6 MPa. Gaseous ethane was reacted with liquid water in a semi-batch stirred tank reactor. The results of the experiments revealed that the reaction rates were governed by the same kinetic parameters as those found for the methane hydrate formation, i.e. interfacial area, pressure, temperature and degree of supercooling. A semi-empirical model was used to correlate the experimental data.     

甲烷水合物在纯水中的生成动力学

The kinetic behavior of methane hydrate formation in pure water was investigated.12 sets of experimental data on methane hydrate formation were determined at temperatures ranging from 273.65 to 276.15K and pressures ranging from 4.47 to 8.47MPa.The duration of three stages in methane hydrate formation,known as the dissolution,nucleation and growth periods,that are lacking in open literature,was obtained.The effect of pressure and temperature on the kinetics of methane hydrate formation was also studied.     

甲烷水合物在纯水中的生成动力学

引言一些低分子量气体,如石油和天然气中C_1～C_4轻烃、氮气、硫化氢、二氧化碳和惰性气体等,在一定压力和温度的条件下可与水形成一类笼形结构的冰状晶体,即所谓的气体水合物．气体水合物是一类较为特殊的包络化合物：主体水分子通过氢键相互结合形成一种内含空隙的笼形框架,客体分子则被笼罩于这些空隙中．主、客体分子之间的作用力为vanderWaals力．水合物晶体最为常见的两种结构分别称为结构I（体心立方构型）和结构Ⅱ（金刚石构型）．甲烷和水形成结构I水合物．文献阐述了开展水合物生成动力学研究的重要意义．但由于水合物生成…     

螺旋内槽管内天然气-水-表面活性剂体系的水合物生成动力学计算

针对多组分气体（天然气）-水-表面活性剂体系在螺旋内槽管内的水合物生成过程,首先采用CFD方法结合群体平衡模型（PBM）,基于溶质渗透模型和Kolmogorov各向同性湍流理论对螺旋内槽管内气液传质系数进行了模拟;其次基于Kashchiev和Firoozabadi的经典水合物成核和生长理论,将其体系从单组分-水系统扩展到多组分气体（天然气-水-十二烷基硫酸钠）系统,同时结合经典结晶理论利用传质系数对水合物生长模型进行了修正,建立了适用于螺旋内槽管流动体系内天然气水合物生成动力学模型。通过模拟计算,获得不同水合物生产条件下天然气在水中的平均传质系数;进而利用Microsoft Visual C++编程计算得到不同条件下水合物生成动力学数据,在考察范围内,天然气水合物的成核速率随着反应体系有效表面能的增大而锐减,而水合物生成驱动力和生长速率未受影响,同时水合物生长速率随着流速和反应压力的增大及温度的降低而增大,成核速率随着压力的增大和温度的降低而增大。     

Experimental study of hydrate formation in oil–water systems using a high-pressure visual autoclave

To investigate the characteristics of hydrate formation in oil–water systems, a high-pressure visual autoclave equipped with visual windows was used where a series of hydrate formation experiments were performed from natural gas + diesel oil + water systems at different water cuts (30 and 70%), rotation rates (100, 200, 300 r/min) and thermodynamic conditions (temperature, pressure). According to the temperature and pressure profiles in test experiments, the processes of hydrate formation under two kinds of experimental procedures were analyzed first. Then, based on the experimental phenomenon observed through the visual windows, hydrate morphologies and hydrate morphological evolvements throughout the experiments were mainly investigated. In experiments, the growth and annealing of hydrate films on the wall, the agglomeration and deposition of hydrate coated water droplets, flocculent-like hydrate deposition with water trapped in and the Pickering effect of hydrates were identified. Simultaneously, based on the experimental data of thermodynamic parameters, the kinetics of hydrate formation was studied by calculating the variations of hydrate film area and gas consumption in different experiments. In addition, the influences of temperature, pressure, and rotation rate on hydrate morphologies, hydrate morphological evolvements, and hydrate formation kinetics were also focused on.     

海底沉积物层CO2封存中水合物研究进展

海底沉积物层内CO2封存被认为是缓解全球气候变暖的有效途径,本文介绍了CO2封存时水合物自封机理、水合物形成条件和水合物稳定带范围,描述了水合物生成动力学研究现状,包括成核动力学、生长动力学以及水合物结晶过程驱动力,水合物的成核模型有成簇成核模型、成簇成核扩展模型、界面成核模型、Chen-Guo模型,水合物生长动力学模型有Englezos、Kvamme生长模型、指数增长模型、流体流动模型以及LB模型,水合驱动力有化学势差、温差、吉布斯自由能差、浓度差、压差或逸度差。总结了多孔介质渗透率和孔隙度随水合物成核和生长的演化关系,有KC模型、NR模型、平行毛细管束模型、渗透率下降模型和Morisdis相对渗透率模型,最后介绍了CO2水合实验情况,展望了CO2海底沉积物层内封存与水合物相关的科学问题。     

Studies of hydrate nucleation with high pressure differential scanning calorimetry

Current models for hydrate formation in subsea pipelines require an arbitrary assignment of a subcooling criterion for nucleation. In reality hydrate nucleation times depend on both the degree of subcooling and the amount of time the fluid has been subcooled. In this work, differential scanning calorimetry was applied to study hydrate nucleation for gas phase hydrate formers. Temperature ramping and isothermal approaches were combined to explore the probability of hydrate nucleation for both methane and xenon. A system-dependent subcooling of around 30 K was necessary for hydrate nucleation from both guest molecules. In both systems, hydrate nucleation occurred over a narrow temperature range (2-3 K). The system pressure had a large effect on the hydrate nucleation temperature but the ice nucleation temperature was not affected over the range of pressures investigated (3-20 MPa). Cooling rates in the range of (0.5-3 K/min) did not have any statistically significant effect on the nucleation temperature for each pressure investigated. In the isothermal experiments, the time required for nucleation decreased with increased subcooling.     

气体水合物形成的热力学与动力学研究进展

气体水合物形成过程中涉及复杂的热力学和动力学问题.本文对水合物热力学理论模型、水合物生成动力学机理等方面的研究成果和最新进展进行了综述.热力学方面重点介绍了基于等温吸附理论 (van der Waals-Platteeuw模型)和基于双过程水合物生成机理(Chen-Guo模型)的相平衡热力学模型,同时介绍水合物结构及其转变方面的最新研究成果.动力学方面介绍了成簇成核、界面成核等成核机理模型以及成核后的水合物生长机理.另外还述及了目前水合物热力学和动力学研究中所涉及的微观、亚微观和宏观测量方法.针对目前水合物热力学和动力学研究中存在的问题,对未来的发展方向和重点提出了建议.     

Nucleation of methane hydrate and ice in emulsions of water in crude oils and decane under non-isothermal conditions

Achievable supercooling for the formation of methane hydrate from water emulsions was studied in seven different crude oils and in decane. The experiments were performed under constant rate cooling from + 20 to-15 °C and a pressure of methane of 12 MPa. It was demonstrated that the shapes and positions of the resulting survival curves depend on the density, viscosity and dispersive power of oil samples used in the experiments, as well as on the degree of oil oxidation. In addition, results of the experiments on ice freezing under the same emulsions are presented. The results obtained in the work allowed us to discuss the possibility and features of primary and secondary nucleation of the hydrate and ice in the systems under consideration.     

Kinetics of carbon dioxide and methane hydrate formation

Experimental data on the kinetics of carbon dioxide hydrate formation and its solubility in distilled water are reported. The experiments were carried out in a semi-batch stirred tank reactor at nominal temperatures of 274, 276 and 278 K and at pressure ranging from 1.59 to 2.79 MPa for the kinetics experiments and at pressure ranging from 0.89 to 2.09 MPa for the solubility experiments. A minor inconsistency in the kinetic model developed by Englezos et al. (1987a) was removed and the model was modified to determine the intrinsic kinetic rate constant for carbon dioxide hydrate formation. The same model was also used to re-determine the intrinsic kinetic rate constant for methane hydrate formation. The model is based on the crystallization theory coupled with the two-film theory for gas absorption in the liquid phase. The Henry's constant (H) and apparent dissolution rate constant (K_La) required in the model were determined using the experimental solubility data. The kinetic model describes the experimental data very well. The kinetic rate constant obtained for the carbon dioxide hydrate formation was found to be higher than that for methane.     

Kinetic and Phase Behaviors of Catalytic Cracking Dry Gas Hydrate in Water-in-Oil Emulsion

The systematic experimental studies were performed on the hydrate formation kinetics and gas-hydrate equilibrium for a simulated catalytic cracking gas in the water-in-oil emulsion. The effect of temperature, pressure and initial gas-liquid ratio on the hydrate formation was studied, respectively. The data were obtained at pressures ranging from 3.5 to 5 MPa and temperatures from 274.15 to 277.15 K. The results showed that hydrogen and methane can be separated from the C₂₊ fraction by forming hydrate at around 273.15 K which is much higher temperature than that of the cryogenic separation method, and the hydrate formation rate can be enhanced in the water-in-oil emulsion compared to pure water. The experiments provided the basic data for designing the industrial process, and setting the suitable operational conditions. The measured data of gas-hydrate equilibria were compared with the predictions by using the Chen-Guo hydrate thermodynamic model.     

Experimental and modeling study of the kinetics of methane hydrate formation and dissociation

In this work, several experiments were conducted at isobaric and isothermal condition in a CSTR reactor to study the kinetics of methane hydrate formation and dissociation. Experiments were performed at five temperatures and three pressure levels (corresponding to equilibrium pressure). Methane hydrate formation and dissociation rates were modeled using mass transfer limited kinetic models and mass transfer coefficients for both formation and dissociation were calculated. Comparison of results, shows that mass transfer coefficients for methane hydrate dissociation are one order greater than formation conditions. Mass transfer coefficients were correlated by polynomials as relations of pressure and temperature. The results and the method can be applied for prediction of methane production from naturally occurring methane hydrate deposits.     

油水体系内水合物的生成:温度、压力和搅拌速率影响

水合物在管道内的生成对流动安全保障构成了极大威胁。为研究水合物在油水体系内的生成特性,本文以天然气、柴油、水为实验介质,在高压可视反应釜内开展了一系列不同温度、压力和搅拌速率的水合物生成实验。根据测试实验中温度、压力的变化趋势,首先分析了两种不同实验步骤下水合物的生成过程。然后,基于从反应釜可视窗处观察到的实验现象,研究了温度、压力和搅拌速率对水合物生成和分布位置、水合物生成形态及水合物形态演化过程的影响。实验中,可以观察到水合物的聚集、沉积和壁面膜生长现象。同时,实验还研究了温度、压力和搅拌转速对诱导时间、壁面水合物膜生长速率及气体消耗速率等水合物生成动力学参数的影响。本文研究成果可为油气管道水合物防治技术的发展提供理论支持。     

全可视化反应釜内二氧化碳水合物的生成分解特征

二氧化碳水合物封存技术已成为目前碳封存研究的热点。该技术中对于二氧化碳水合物的生成分解特征及其影响因素的研究是当前的重点和难点。本文设计了高压全透明双反应釜实验平台,以高纯度二氧化碳和去离子水作为研究对象,在17℃、7MPa的初始温压条件下,进行了二氧化碳水合物的初次和二次生成分解实验,并设置对照组对搅拌的影响进行了研究,而后与甲烷在相同条件下的实验进行对比。实验结果表明,搅拌会促进二氧化碳水合物的生成,在400r/min的转速条件下,缩短诱导时间可达40%,增大压降速率可达15%,形成更多且更致密厚实的水合物,并延缓了分解;多次生成可以减少水合物的诱导时间,但对于水合物生成的总量几乎没有影响。与甲烷水合物相比,二氧化碳水合物生成的量大且更难以分解,实验结果有利于二氧化碳的海洋水合物封存技术的开发应用。     

气体水合物抑制剂的研制与性能评价

针对海洋深水钻井过程中气体水合物的形成严重影响钻井作业的顺利进行等问题,室内经过大量的优选实验,采用甲基丙烯酸乙酯和N-乙烯基吡咯烷酮作为单体,并对单体比例、引发剂、反应温度及反应时间等综合因素进行分析,研制出低剂量气体水合物抑制剂HLA。通过四氢呋喃(THF)测试法和水合物生成模拟实验装置评价其效果,实验结果表明:盐类气体水合物抑制剂能使形成气体水合物的温度和压力条件得到改变,此外还可以有效的抑制气体水合物的形成;低剂量气体水合物抑制剂HLA能使水合物的形成速率得到有效降低,使形成水合物晶核的诱导时间得到一定的延长,使晶体的聚集过程得到一定的改变,但并不能从实际上改变气体水合物形成的相平衡。     

Kinetics of methane hydrate decomposition

The kinetics of methane hydrate decomposition was studied using a semibatch stirred-tank reactor. The decomposition was accomplished by reducing the pressure on a hydrate slurry in water to a value below the three-phase equilibrium pressure at the reactor temperature. The data were obtained at temperatures from 274 to 283 K and pressures from 0.17 to 6.97 MPa. The stirring rates were high enough to eliminate mass-transfer effects. Analysis of the data indicated that the decomposition rate was proportional to the particle surface area and to the difference in the fugacity of methane at the equilibrium pressure and the decomposition pressure. The proportionality constant showed an Arrhenius temperature dependence. An estimate of the hydrate particle diameters in the experiments permitted the development of an intrinsic model for the kinetics of hydrate decomposition.     

蜡晶析出对CO2水合物相平衡及诱导特性的影响

为了探明蜡晶析出对水合物生成相平衡特性及成核特性的影响,本文选用2^#工业白油与60^#昆仑石蜡的混合溶液来模拟含蜡体系,利用高压可视化搅拌釜开展含蜡体系水合物生成实验,结合水合物生成过程中的可视化图像,研究不同蜡晶浓度对水合物生成相平衡曲线、水合物成核诱导时间、诱导时间变化率的影响规律及蜡晶析出对水合物生成机理的影响。结果表明：①随着蜡晶浓度的增加,水合物生成相平衡条件逐渐降低,相平衡曲线较无蜡体系向右偏移,且蜡晶浓度越大,偏移趋势越明显,在温度281.5K时,3.5%（质量分数）的蜡含量比无蜡体系的相平衡压力降低6.5%;②通过分析不同蜡晶浓度对水合物成核诱导时间的影响发现,蜡晶析出加快了水合物结晶,缩短了水合物成核诱导时间,且蜡晶浓度越大,诱导时间缩短越明显;③通过探究不同蜡晶浓度对水合物成核诱导能力的影响发现,随着蜡晶浓度的增加,蜡晶析出对水合物诱导成核的促进能力总体呈现先增大后减小的趋势,即蜡晶对水合物的促进能力不是无限增大的,会随蜡晶浓度的增加逐渐减弱;④通过分析蜡晶析出对水合物生成速率及生成位置的影响发现,当体系达到水合物生成条件时,反应釜中心部分的水合物会先于气液表面及釜壁生成。本文研究成果有助于深海油气开采的应用发展,同时为更好研究蜡晶与水合物耦合特性提供可靠的pVT数据。     

Unusual kinetic inhibitor effects on gas hydrate formation

Gas hydrate formation experiments were conducted with a methane-ethane mixture at 273.7 or 273.9 K and 5100 kPa and using water droplets or water contained in cylindrical glass columns. The effect of kinetic inhibitors and the water/solid interface on the induction time for hydrate crystallization and on the hydrate growth and decomposition characteristics was studied. It was found that inhibitors GHI 101 and Luvicap EG delayed the onset of hydrate nucleation. While this inhibition effects has been reported previously some unusual behaviour was observed and reported for the first time. In particular, the water droplet containing GHI 101 or Luvicap EG was found to collapse prior to nucleation and spread out on the Teflon surface. Subsequently, hydrate was formed as a layer on the surface. Catastrophic growth and spreading of the hydrate crystals was also observed during hydrate formation in the glass columns in the presence of the kinetic inhibitor. Finally, when polyethylene oxide (PEO) was added into the kinetic inhibitor solution the memory effect on the induction time decreased dramatically.     

天然气水合物优化合成实验研究

水合物储运技术实用化的进程中,如何提高水合物制备效率,实现高密度的储存是最为关键的问题。文中对此应用新型雾化系统对气水合物的强化合成技术进行了实验研究。结果表明:压力提高对水合物生长加速作用明显;活性剂组分和雾化方式提供了最优的气液传质条件,极大地加快了溶解、成核及生长过程,其整体反应速度提高了1倍以上,最终含气体积比也显著提高;分解水重复生成、水合物晶种的投入也能极大加快成核过程,缩短诱导期,从而提高反应速率。