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。     

甲烷-四氢呋喃-水体系水合物生成动力学的实验和模型化研究

研究了透明鼓泡塔中含促进剂四氢呋喃（THF）体系中甲烷水合物的生成动力学.分别考察了进气速率、温度、压力、水合物体积分数对甲烷消耗速率的影响.根据Chen-Guo水合物生成机理,采用基础水合物生成反应的量纲1 Gibbs自由焓变-ΔG/RT作为反应的推动力,建立了水合物生成动力学模型,模型中考虑了体系温度、压力和气液接触比表面积的影响.把模型应用于甲烷气体消耗速率的计算,其模型预算结果与实验数据吻合良好,实验结果和反应动力学模型将有助于工业水合反应器的设计和操作条件的设定.     

Deep ocean bubble transport model coupled with multiple hydrate behavior characteristics

Submarine gas seepage is a widely observed process. In this study, a unified mechanistic model of bubble transport both inside and outside the gas hydrate stability zone (GHSZ) was developed. Multiple hydrate-related behaviors were considered, including hydrate nucleation, hydrate film lateral spread, hydrate shell dynamic growth, hydrate dissolution and decomposition, and collapse and fracture deformation of hydrate-coated bubbles. Using the proposed model, a series of simulation studies about bubble dissolution and rising fate were conducted. The results indicate that the formation of solid hydrates in the deep-sea environment can provide a fairly effective barrier for the dissolution and shrinkage of bubbles, and the deeper the initial release water depth, the smaller the critical size of the bubble required for arriving at the water surface. Furthermore, the majority of gases released from the seafloor would be absorbed by the shallow oceanic layer, but larger bubbles could still pass through the water column to the atmosphere.     

Experimental investigation of hydrate formation behaviour of a natural gas bubble in a simulated deep sea environment

A vertically flowing, closed circuit, high pressure water tunnel was designed and constructed for holding individual gas bubbles stationary against an opposing flow for detailed observations. Hydrate formation behavior of natural gas bubbles was studied at constant pressure as well as under conditions of controlled decompression designed to simulate buoyant rise of the bubble.A bubble of simulated natural gas suspended in 3°C salt water formed hydrates when the pressure was 4826 kPa or higher. The simulated decompression accompanying buoyant rise had very little effect on hydrate formation behavior of a bubble starting from a pressure of 5516 kPa or above. At lower starting pressures, a slight increase in the reaction rate was detected in the initial stages of a run. The conversion of the simulated natural gas to hydrates was complete in runs starting from a pressure of 4826 kPa or above.     

The formation of gas hydrates on bubbles of hydrocarbon gases rising in seawater

Calculations are presented which describe the behaviour of a rising bubble of hydrocarbon gas in seawater under conditions where gas hydrates are formi calculations are compared with independent measurements of bubble lifetimes. For pure methane and for a natural gas mixture containing components up to those calculated.The natural gas mixture is one thought to be typical of those occurring in some Arctic oil fields and the results imply that single bubbles of natural to hydrate before reaching the surface.     

THE EFFECT OF VARIOUS TYPES OF EQUATIONS OF STATE ON DRIVING FORCE CALCULATION AND GAS CONSUMPTION PREDICTION IN SIMPLE AND DOUBLE HYDRATE FORMATION WITH OR WITHOUT THE PRESENCE OF KINETIC INHIBITORS IN BATCH SYSTEMS

This article compares the effects of using various types of equations of state (Peng-Robinson, PR; Soave-Redlich-Kwong, SRK; Esmaeilzadeh-Roshanfekr, ER; Patel-Teja, PT; and Valderrama-Patel-Teja, VPT) on the calculated driving force and rate of gas consumption based on the Kashchiev model in simple and double-gas hydrate formation for methane, ethane, and their mixtures with 1130 experimental published data points with or without the presence of kinetic inhibitors at various pressures and temperatures. For the prediction of gas consumption rate in double-gas hydrate formation, the rate equation based on the Kashchiev model for simple gas hydrate formation was developed using the calculation of gas mole fraction in hydrate phase and then prediction of gas hydrate formation rate for each component in gaseous mixture. The total average absolute deviation was found to be 8.72%, 10.34%, 8.84%, 11.04%, and 14.16% for the PR, ER, SRK, VPT, and PT equations of state for calculating gas consumption in simple and double hydrate formation, respectively.     

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.     

Migration of a single gas bubble in water during the formation of stable gas-hydrate crust on its surface

A theoretical model of gas-hydrate formation during the migration of the methane bubble in water under thermobaric conditions of hydrate stability has been considered. Numeric solutions were obtained and analyzed for two limiting cases when the rate of formation of the hydrate crust on bubble surface is constrained by the intensity of heat removal, which is released during hydrate-formation process by the surrounding water or the diffusive resistance of gas hydrate crust against the transfer of hydrate-forming components. A comparative analysis of the numeric results with the experimental data showed that the diffusive transfer of hydrate-forming components through the crust most adequately described the process of hydrate-particle growth that was observed in experiments during the ascent of methane particles in seawater. The conditions of the best agreement between the theoretical and experimental data on changing of radius of gas-hydrate particle allowed numeric estimates to be obtained for values of the reduced coefficient of gas and water diffusion through the hydrate crust.     

泡状流中水合物生成预测模型及实验

针对可燃冰钻采井筒内易发生水合物生成和堵塞的工程问题,本文开展了泡状流条件下甲烷水合物生成实验,发现流速增加会提高水合物生成速率,黄原胶质量分数的增加会降低水合物生成速率。基于传质理论,构建了适用于可燃冰钻采井筒内泡状流条件下水合物生成预测模型,模型考虑了连续相流体流变性、气泡破裂、聚并和形变等因素对泡状流中气液界面分布和气液间传质规律的影响,并耦合实验数据,提出了气泡群间的综合传质系数经验公式,用于描述气泡间相互作用对气液间传质速率的影响。对比实验结果,所建立模型对水合物生成量和水合物生成速率的预测误差分别在±5%和±15%以内,满足工程计算需求。该模型的构建有助于精准预测油气和可燃冰钻采井筒内水合物风险,为建立经济、高效的井筒水合物防治方案奠定理论基础。     

鼓泡塔中水合物法分离混合气体的数值模拟

To develop a new technique for separating gas mixtures via hydrate formation,a set of medium-sized experimental bubble column reactor equipment was constructed.On the basis of the structure parameters of the ex- perimental bubble column reactor,assuming that the liquid phase was in the axial dispersion regime and the gas phase was in the plug flow regime,in the presence of hydrate promoter tetrahydrofuran（THF）,the rate of hydrogen enrichment for CH4＋H2 gas mixtures at different operational conditions（such as temperature,pressure,concentra- tion of gas components,gas flow rate,liquid flow rate）were simulated.The heat product of the hydrate reaction and its axial distribution under different operational conditions were also calculated.The results would be helpful not only to setting and optimizing operation conditions and design of multi-refrigeration equipment,but also to hydrate separation technique industrialization.     

多孔载体海绵对CH4-N2-O2瓦斯气体水合分离影响（英文）

The findings were presented from laboratory investigations on the hydrate formation and dissociation processes employed to recover methane from coal mine gas.The separation process of coal mine methane(CMM) was carried out at 273.15K under 4.00 MPa.The key process variables of gas formation rate,gas volume stored in hydrate and separation concentration were closely investigated in twelve THF-SDS-sponge-gas systems to verify the sponge effect in these hydrate-based separation processes.The gas volume stored in hydrate is calculated based on the measured gas pressure.The CH4 mole fraction in hydrate phase is measured by gas chromatography to confirm the separation efficiency.Through close examination of the overall results,it was clearly verified that sponges with volumes of 40,60 and 80 cm 3 significantly increase gas hydrate formation rate and the gas volume stored in hydrate,and have little effect on the CH4 mole fraction in hydrate phase.The present study provides references for the application of the kinetic effect of porous sponge media in hydrate-based technology.This will contribute to CMM utilization and to benefit for local and global environment.     

鼓泡器中环戊烷-甲烷-盐水体系水合物的生成动力学

采用鼓泡装置研究了盐水体系中环戊烷（CP）-甲烷水合物的生成动力学,分别考察了进气速率、温度、压力对水合物生成速率和进气速率对气体转化率的影响。结果显示,提高进气速率、压力,降低温度均可提高水合物生成速率。但进气速率对气体转化率有影响,进气速率过大,单位时间内进入到反应器内的气体过多,气体还未参与反应便被排出,导致气体转化率反而减小。通过观察到的实验现象,分析环戊烷-甲烷水合物的生成过程,认为水合物晶体首先在环戊烷-水界面生成,并逐步向内部气相生长,最后水合物壳破裂,气泡逸出。水合物逐渐生长成粒状,并不断聚集在一起。     

13C NMR analysis and gas uptake measurements of pure and mixed gas hydrates: Development of natural gas transport and storage method using gas hydrate

¹³C NMR spectra were obtained for pure CH₄, mixed CH₄+THF, and mixed CH₄+Neohexane hydrates in order to identify hydrate structure and cage occupancy of guest molecules. In contrast to the pure CH₄ hydrates, the NMR spectra of the mixed CH₄+THF hydrate verified that methane molecules could occupy only the small portion of 5¹² cages because the addition of THF, water-soluble guest component, to aqueous solution prevents the complete filling of methane molecules into small cages. Furthermore, from these NMR results one important conclusion can be made that methane molecules can’t be enclathrated at all in the large 5¹²6⁴ cages of structure II. In addition, gas uptake measurements were carried out to determine methane amount consumed during pure and mixed hydrate formation process. The moles of methane captured into pure CH₄ hydrate per mole of water were found to be similar to the full occupancy value, while the moles of methane captured into the mixed CH₄+THF hydrate per moles of water were much lower than the ideal value. The overall results drawn from this study can be usefully applied to storage and transportation of natural gas.     

The combination of 1-octyl-3-methylimidazolium tetrafluorborate with TBAB or THF on CO2 hydrate formation and CH4 separation from biogas

[C₈min] BF₄ was used in this work to combine with TBAB or THF for the investigation about thermodynamic and kinetic additives on CO₂ and CH₄/CO₂ hydrates. The results show that[C₈min] BF₄ has the inhibition effect on the equilibrium of hydrate formation. About the kinetic study,[C₈min] BF₄ could improve the rate of CO₂ hydrate formation and increase the gas uptake in hydrate phase. At the same time, the combination of TBAB and[C₈min] BF₄ could increase the mole friction of CH₄ in residual gas comparing with the data in THF solution. CH₄ separation efficiency was strongly enhanced. Since that the size of CO₂ and CH₄ molecules are similar, CH₄ and CO₂ could form the similar hydrate, so the recovery of CH₄ from biogas decreases lightly. The CH₄ content in biogas can purified from 67 mol% to 77 mol% after one-stage hydrate formation. In addition, the combination of THF and[C₈min] BF₄ do not have obvious promoting effect on CH₄ separation comparing with the gas separation results in pure THF solution.     

Surfactant effects on hydrate formation in an unstirred gas/liquid system: An experimental study using HFC-32 and sodium dodecyl sulfate

This paper deals with the effects of a surfactant additive on the formation of a clathrate hydrate in a quiescent guest-gas/liquid-water system. The paper first presents our strong suspicion against the existing hypothesis that the surfactant-micelle formation in the liquid-water phase promotes the hydrate formation. It is pointed out that the Krafft point for sodium dodecyl sulfate (SDS), a popular anionic surfactant often used in previous hydrate-forming experiments, is presumably higher than the system temperatures set in these experiments and hence that no micelles may have formed in these experiments. The paper then describes our experimental observations of the hydrate formation from a hydrofluorocarbon gas, HFC-32 (CH₂F₂), to show how the hydrate formation behavior is affected by the addition of SDS to the water when brought into contact with HFC-32. In each experiment, HFC-32 gas was continuously supplied to a rectangular chamber partially filled with a quiescent pool of water (pure water or an aqueous SDS solution) to compensate for the gas consumption due to the hydrate formation, thereby maintaining a constant pressure inside the chamber. The present experiments featured the following characteristics: (a) detailed visual observations along horizontal axes through large side windows in the test chamber, and (b) surface tension measurements of the aqueous SDS solutions with the aid of a pendant-drop device inserted in the same chamber to determine the SDS-in-water solubility, which seems to have been misunderstood as the critical micelle concentration (CMC) in some previous studies, under the hydrate-forming conditions. The former revealed that the addition of SDS to the pool-forming water results in the formation of thick, highly porous hydrate layers not only on the liquid-pool surface but also on the chamber walls above the level of the pool surface, leaving the bulk of the liquid pool free from hydrate crystals. The latter led to an important finding that the SDS concentration at which the rate of the hydrate formation peaks is slightly lower than the solubility (the false CMC). An excessive addition of SDS beyond the solubility was found to cause a decrease in the rate of hydrate formation but an increase in the final level of the water-to-hydrate conversion.     

降温模式对甲烷水合物形成的影响

在定容条件下,以两种不同的降温模式(缓慢降温和快速降温)进行甲烷水合物在沉积物中的形成实验. 结果表明,甲烷水合物在沉积物中的形成过程包括气液溶解、核化、生长、稳定4个阶段. 在相同的初始条件下,降温模式对水合物生成的热力平衡影响较小,但对水合物生成动力学有显著改变. 快速降温下水合物生长速度明显快于缓慢降温,随着水合物初始条件不同,缓慢降温比快速降温水合物形成时间约增加21.4%~28.8%.     

Coalescence behaviour of gas bubbles in aqueous solutions of n-alcohols and fatty acids

Coalescence frequency and coalescence times of bubble pairs formed on two adjacent capillary tubes were determined in aqueous solutions of n-alcoho and fatty acids. The results show, that coalescence times of bubbles are proportional to the surface excess concentration of the solute. Coalescence ti increase with the polarity of the hydrophilic group of the solute, its chain length and the bubble size. Coalescence frequency decrease drastically fro 100% to 0% at a distinct solute concentration. The transition in coalescence behaviour occurs, if the coalescence times becomes greater than the availa contact times of the bubbles. The transition concentration therefore decreases with increasing rate of bubble formation.     

The modelling of hydrocarbon bubble plumes to include gas hydrate formation

Information gained on hydrate formation on a single rising bubble of hydrocarbon gas is applied to the case of a complete bubble plume. When hydrate formation is included in the plume equations there is a strong coupling between small scale bubble behaviour and the total plume buoyancy. The sensitiv of the plume solutions to this coupling is examined for methane and a natural gas typical of certain Arctic oilwells. The results of the latter are app to a hypothetical oilwell blowout under Arctic conditions, and indicate that for wellhead depths greater than 800 m all the gas will be converted to hy before the surface is reached.     

甲烷水合物在纯水和抑制剂体系中的生成动力学

Kinetic data of methane hydrate formation in the presence of pure water,brines with single salt and mixed salts,and aqueous solutions of ethylene glycol(EG) and salt EG were measured.A new kinetic model of hydrate formation for the methane water systems was developed based on a four-step formation mechanism and reaction kinetic approach.The proposed kinetic model predicts the kinetic behavior of methane hydrate formation in pure water with good accuracy.The feasibility of extending the kenetic model of salt(s) and EG containing systems was explored.     

Evidence for pore-filling gas hydrates in the sediments through morphology observation

To provide an evidence of natural gas hydrate occurrence state, a series of experiments on multiple growth and dissociation of 90.0% methane/10.0% propane hydrates at 1.3 MPa and 270.15 K were carried out in two sediments for morphology observation via a visible jacketed-reactor. The gas hydrate crystals were observed to form and grow on the surface of sediments at the initial growth. During the thermal decomposition, gas and liquid products had an unceasingly impact on the sediments, then gas/liquid–solid migration occurred, and a large number of cavitation appeared. In the later growth and dissociation experiments, the gas hydrate particles were in suspension or supporting states in the interstitial pore space between the sediment particles, indicating that the gas hydrate displayed a pore-filling characteristics. Through analyzing the distribution of gas hydrates and bubbles, it was found that the amount of gas hydrates distributed in the sediments was improved with multiple growth-dissociation cycle proceedings. Gas migration enhanced the sediment movement, which led to the appearance of the increasing quantity of gas bubbles in the sediments during cycles. Salts affected the growth of the gas hydrates and the migration of sediment grains, which also restricted the accumulation of gas bubbles in the sediments. According to the Raman analysis, the results showed that sII hydrates were formed for CH₄ and C₃H₈ gas mixtures in different sediments and solutions with hydration number of 5.84–6.53. The Salt restricted the access of gas into the hydrate cages.