甲烷+氨水体系水合物生成条件实验测定及计算

甲烷在氨水体系中生成水合物的实验数据对于开发水合法回收合成氨驰放气工艺以及操作条件的确定具有重要意义。本文测定了氨摩尔分数为1.018、3.171、5.278氨水溶液中甲烷气体水合物的生成条件。结果表明：氨的加入对甲烷水合物的生成起着明显抑制作用,而且随着氨浓度的增加,生成压力越高。采用Chen-Guo模型对甲烷在氨水中生成水合物的数据进行了计算,得到了较为满意的计算结果,平均误差为2.71%,说明Chen-Guo模型能够较好地预测该类体系的水合物的生成条件。     

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.     

石英砂中甲烷溶解运移体系水合物生成与聚集实验分析

建立了可模拟海底天然气水合物形成环境的大型三维成藏实验模拟装置,其主体高压反应釜内径500 mm,高1000 mm。在此基础上,采用填砂模型,进行了甲烷溶解运移体系下甲烷水合物生成与聚集过程的实验模拟分析。实验流程为：甲烷溶解于NaCl溶液中,再泵送进入高压反应釜,在沉积层中渗流并生成甲烷水合物。通过30个电阻率传感器监测甲烷水合物的生成和聚集过程。实验结果表明,甲烷溶解运移体系下甲烷水合物生成之后首先分散在溶液中,当溶液的总甲烷浓度（溶解的甲烷及水合物分散相中的甲烷）达到操作条件下盐溶液体系甲烷饱和溶解度后,甲烷水合物从溶液中析出。电阻率分布实验结果表明,析出甲烷水合物的聚集区域受溶液流动控制。     

0℃以下含SDS的甲烷水合物生成方式及过程对其分解速率的影响

The dissociation rates of methane hydrates formed with and without the presence of sodium dodecyl sulfate(methane-SDS hydrates),were measured under atmospheric pressure and temperatures below ice point to investigate the influence of the hydrate production conditions and manners upon its dissociation kinetic behavior.The experimental results demonstrated that the dissociation rate of methane hydrate below ice point is strongly dependent on the manners of hydrate formation and processing.The dissociation rate of hydrate formed quiescently was lower than that of hydrate formed with stirring;the dissociation rate of hydrate formed at lower pressure was higher than that of hydrate formed at higher pressure;the compaction of hydrate after its formation lowered its stability,i.e.,increased its dissociation rate.The stability of hydrate could be increased by prolonging the time period for which hydrate was held at formation temperature and pressure before it was cooled down,or by prolonging the time period for which hydrate was held at dissociation temperature and formation pressure before it was depressurized to atmospheric pressure.It was found that the dissociation rate of methane hydrate varied with the temperature(ranging from 245.2 to 272.2 K) anomalously as reported on the dissociation of methane hydrate without the presence of surfactant as kinetic promoter.The dissociation rate at 268 K was found to be the lowest when the manners and conditions at which hydrates were formed and processed were fixed.     

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…     

Mathematical model of formation of carbon dioxide hydrate upon injection of carbon dioxide into a methane hydrate stratum

A mathematical model of formation of carbon dioxide gas hydrate upon injection of warm carbon dioxide into a natural stratum saturated with methane and methane hydrate has been presented. The case when methane hydrate decomposes into gas and water on two frontal boundaries and the subsequent formation of carbon dioxide hydrate from carbon dioxide and water has been discussed. The regions where this mode is implemented depending on stratum permeability have been studied based on the pressure–temperature plane of the gas being injected into the stratum.     

初始压力对冰冻石英砂中CO2水合物生成特性的影响

利用冰冻石英砂模拟冻土水合物的赋存条件，研究了压力对二氧化碳水合物生成特性的影响，在300 mL高压水合物反应釜中于271 K下进行了多组CO2液化压力以上及以下的霰状冰粉包裹的石英砂中水合物生成实验。结果表明，充入的CO2未液化时，初始压力越大，水合反应速率越快，压力越早达稳定状态；充入压力达液化压力后，注入的CO2越多，水合反应速率越快。压力作为水合反应的驱动力，压力越高水合物生成越多，冰的最终转化率越高。采用CO2置换冻土区中甲烷水合物时，控制压力低于液化压力或注入过量的CO2，置换效果更好。     

Characteristics of methane hydrate formation in carbon nanofluids

When methane hydrate is formed artificially by simply reversing its process of natural generation, the amount of methane gas consumed by hydrate formation is fairly low, which is problematic for its large scale synthesis and application. Therefore, this study examined methods for increasing the amount of gas consumed by adding MWCNTs (multi-walled carbon nanotubes) and OMWCNTs (oxidized multi-walled carbon nanotubes). The surfaces of the MWCNTs were oxidized chemically, and dispersed uniformly in distilled water after a dispersion operation. The amount of methane gas consumed during the formation of methane hydrate in the oxidized carbon nanofluid was approximately 4.5 times higher than that in distilled water. The hydrate-nanocarbon fluid phase boundary line was shifted to the right side of the hydrate-pure water phase boundary line in the pressure–temperature phase diagram. The carbon nanofluid system accelerated the rate of methane hydrate formation at low subcooling temperatures (<8 K).     

Methane Hydrate Formation and Dissociation in the presence of Bentonite Clay Suspension

The present work reports the effect of bentonite clay on methane hydrate formation and dissociation in synthetic seawater of salinity 3.55 % of total dissolved salts. Extensive observations of pressure‐temperature equilibrium during formation and decomposition of methane hydrate under different conditions have been made. It is observed that phase equilibrium conditions of hydrate are affected on changing the concentration of bentonite clay in synthetic seawater. Induction time for hydrate nucleation has been measured under different concentrations of clay and subcooling conditions. The presence of bentonite clay in synthetic seawater reduces the induction time of hydrate formation. Enthalpy of hydrate dissociation is calculated by Clausius‐Clapeyron equation using measured phase equilibrium data. The amount of gas consumed during hydrate formation has been calculated using real gas equation. It is found that a larger amount of gas is consumed upon addition of bentonite clay in synthetic seawater.     

Study on the kinetics of hydrate formation in a bubble column

Gas hydrate formation experiments were performed using methane in the presence of tetrahydrofuran (THF) in aqueous solution in a transparent bubble column in which a single pipe or a sintered plate was used to produce bubbles. The mole fraction of THF in aqueous solution was fixed at 6%. The hydrate formation kinetic behaviors on the surface of the rising bubble, the mechanical stability of hydrate shell formed on the surface of the bubble, the interactions among the bubbles with hydrate shell were observed and investigated morphologically. The rise velocities of individual bubbles with hydrate shells of different thickness and the consumption rates of methane gas were measured. A kinetic model was developed to correlate the experimentally measured gas consumption rate data. It was found that the hydrate formation rate on the surface of the moving bubble was high, but the formed hydrate shell was not very easy to be broken up. The bubbles with hydrate shells tended to agglomerate rather than merge into bigger bubble. This kind of characteristic of hydrate shell hindered the further formation of hydrate and led to the lower consumption rate of methane. The consumption rate of methane was found to increase with the decrease of temperature or increase of pressure. The increase of gas flux led to a linear increase in consumption rate of methane. It was demonstrated that the developed kinetic model could be used to correlate the consumption rate satisfyingly.     

Methane hydrate formation and dissociation behaviors in montmorillonite

The methane hydrate formation and the methane hydrate dissociation behaviors in montmorillonite are experimentally studied. Through the analyses of the microstructure characteristic, the study obtains the porous characteristic of montmorillonite. It is indicated that methane hydrate in montmorillonite forms the structure I(sI) crystal.Meanwhile, molecular dynamics simulation is carried out to study the processes of the methane hydrate formation and the methane hydrate dissociation in montmorillonite. The microstructure and microscopic properties are analyzed. The methane hydrate formation and methane hydrate dissociation mechanisms in the montmorillonite nanopore and on the montmorillonite surface are expounded. Combining the experimental and simulating analyses,the results indicate the methane hydrate formation and methane hydrate dissociation processes have little influence upon the crystal structure of porous media from either micro-or macro-analysis. It is beneficial to the fundamental researches on the exploitation and security control technologies of natural gas hydrate in deep-sea sediments.     

甲烷与冰快速形成天然气水合物的影响因素研究

设计了冰-气生成天然气水合物的实验装置,对由冰和甲烷反应生成天然气水合物的影响因素进行实验研究。结果表明,压力越高,温度越低,冰粒越小,越有利于水合物的生成,促进水合物快速形成的搅拌速度和促进剂浓度最佳值分别是800 r/min和800 mg/L。     

离子对甲烷水合物相平衡的影响

自由水盐度直接影响水合物的生成和分解,为了充分研究自由水盐度对甲烷水合物相平衡的影响,本文利用正交实验设计方法研究了不同离子组成和浓度条件下多孔介质中水合物形成与分解特性。运用正交法研究水合物可减少实验次数、缩短实验周期。甲烷水合物相平衡点通过定容压力搜索法测得。与纯水体系相比,添加离子后相同压力条件下甲烷水合物的平衡温度降低,并且随着离子浓度的增加,平衡温度进一步降低。方差分析证明阳离子中Mg²⁺对水合物平衡影响最显著;极差分析结果表明,阳离子的影响程度从大到小依次为Mg²⁺、Ca²⁺、Na⁺、K⁺。SO^2-₄、CO^2-₃、Cl^-三种阴离子浓度对水合物相平衡点影响均显著。水合物诱导时间变化无明显规律,受离子种类、浓度影响不显著。     

A型分子筛对甲烷水合物生成的影响

The porous medium has an important effect on hydrate formation. In this paper, the formation process and the gas storage capacity of the methane hydrate were investigated with A-type zeolite and Sodium Dodecyl Sulfate (SDS) existing in the system. The results show that A-type zeolite can influence methane hydrate formation. At the temperature of 273.5 K and pressure of 8.3 MPa, the distilled water with A-type zeolite can form methane hydrate with gaseous methane in 12 hours. The formation process of the system with A-type zeolite was quite steady and the amount of A-type zeolite can influence the gas storage capacity significantly. The adding of A-type zeolite with 0.067 g&#8226;(g water)－1 into 2×10－3 g&#8226;g－1 SDS-water solution can increase the gas storage capacity, and the maxi-mum increase rate was 31%. Simultaneously the promotion effect on hydrate formation of 3A-type zeolite is much more obvious than that of 5A-type zeolite when the water adding amounts are 0.033 g&#8226;g－1 and 0.067 g&#8226;g－1 at the experimental conditions.     

Accelerated methane storage in clathrate hydrates using surfactantstabilized suspension with graphite nanoparticles

In this study, enhanced kinetics of methane hydrate formation in the sodium dodecyl sulfate(SDS) solution with different concentrations of suspended graphite nanoparticles(GNPs) were investigated at 6.1–9.0 MPa and 274.15 K. The GNPs with rough surfaces and excellent thermal conductivity not only provided a considerable number of microsites for hydrate nucleation but also facilitated the fast hydrate heat transfer in the suspension system. At a relatively low pressure of 6.1 MPa, the suspension with 0.4 wt% of GNPs exhibited the minimum induction time of 22 min and maximum methane uptake of 126.1 cm~3·cm~(-3). However, the methane storage performances of the suspensions with higher and lower concentrations of GNPs were not satisfactory. At the applied pressure, the temperature increase arising from the hydrate heat in the suspension system with the optimized concentration(0.4 wt%) of GNPs was more significant than that in the traditional SDS solution. Furthermore,compared with those of the system without GNPs, enhanced hydration rate and storage capacity were achieved in the suspensions with GNPs, and the storage capacities were increased by 3.9%–17.0%. The promotion effect of GNPs on gas hydrate formation at low pressure is much more obvious than that at high pressure.     

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。     

水合物法分离低浓度煤层气中的甲烷

向模拟煤层气(13.11vol% CH4+86.89vol% N2)中添加5.8mol%四氢呋喃(THF)?0.03mol%十二烷基硫酸钠(SDS)促进剂溶液分离提纯煤层气,考察了压力、温度、反应时间对气体消耗量、反应速率、分解气中甲烷浓度、甲烷回收率和甲烷分离因子的影响,采用色谱分析法分别测定了CH4在剩余气相和分解气相中的浓度。结果表明,压力增加,CH4回收率增大,CH4分离因子增大,CH4分离效果越好;温度是影响甲烷分离因子的关键因素,温度降低,氮气和甲烷竞争进入水合物晶体中,导致水合物相中甲烷浓度降低;温度升高有利于提高水合物对甲烷的选择性。甲烷回收效率最高可达98.65%,分离因子最大为14.83。随反应时间增加,分解气中CH4浓度升高。     

Fundamental challenges to methane recovery from gas hydrates

The growing use of natural gas, cleanest of all available fossils fuels, is already raising concern regarding the long-term supply of this precious resource. The amount of methane in gas hydrates is much greater than all other presently known sources of methane. This paper describes some fundamental challenges, the location, magnitude, and feasibility of recovery, which must be addressed to recover methane from dispersed hydrate sources. For methane recovery, we briefly describe kinetic models of methane hydrate decomposition for temperature and pressure conditions that mimic in situ methane hydrate stability. We also propose the catalytic role of sediment impurities, if any, in inducing nucleation sites for hydrate formation. The availability of plentiful methane is important to avoid future energy crises, such as that which crippled the world economy three decades ago.     

Induction time,storage capacity,and rate of methane hydrate formation in the presence of SDS and silver nanoparticles

In this communication, the kinetic parameters of methane hydrate formation (induction time, quantity and rate of gas uptake, storage capacity (SC), and apparent rate constant) in the presence of sodium dodecyl sulfate (SDS), synthetized silver nanoparticles (SNPs), and mixture of SDS?+?SNPs have been studied. Experimental measurements were performed at temperature of 273.65?K and initial pressure of 7?MPa in a 460?cm³ stirred batch reactor. Our results show that adding SDS, SNPs and their mixture increases the quantity of gas uptake, water to hydrate conversion, and SC of methane hydrate formation, noticeably. Using 300?ppm SDS increases the SC and the quantity of methane uptake 615, and 770%, respectively, compared with pure water. Investigating the hydrate growth rate at the start of hydrate formation process shows that, using SNPs, SDS, and their mixture increases the initial apparent rate constant of hydrate rate, considerably. Our results show that the system of methane?+?water?+?SDS 500?ppm?+?SNPs 45?µM represents the maximum value of initial apparent rate constant, compared with other tested systems.