卵磷脂对甲烷水合物形成的影响

建立了用于测定卵磷脂(lecithin)对钻井液中水合物形成影响的实验装置及方法,以理解化学添加剂卵磷脂对北极Cascade地区钻井过程中水合物层的稳定作用。本研究旨在理解卵磷脂对纯水中甲烷水合物形成热力学和动力学的影响。结果表明,卵磷脂基本上不影响甲烷水合物生成的热力学条件,但当卵磷脂在水中的浓度超过0.003 g·g^-1时,它会影响甲烷水合物的生成速度和数量,是很好的水合物生成动力学促进剂。     

两种体系中甲烷水合物生成特性的研究

为了强化甲烷水合物生成,满足工业生产天然气水合物的要求,利用定压鼓泡式反应器对甲烷水合物在冰浆体系中和水体系中的生成特性进行了对比实验研究。结果表明,冰浆体系中水合反应的诱导时间比水体系水合反应的诱导时间短;冰浆体系比水体系拥有更大的导热系数和反应热吸收能力,更有利于反应热的释放;十二烷基硫酸钠浓度改变的过程中,水体系中反应的诱导时间和水合物储气密度的变化比冰浆体系明显;冰浆体系可以提升水合物的储气密度,但是随着有利于水合物反应条件的增加,冰浆的提升效果会逐渐地减弱。     

气水体系甲烷水合物生成和分解动力学

为进一步探明搅拌对甲烷水合物生成和分解动力学特性的影响,借助容积约为522mL,最高操作压力21MPa的高压全透明反应釜装置,开展了不同搅拌条件下甲烷水合物的生成、分解和浆液流动实验,得到了搅拌对水合物生成量、生长速率和分解速率的影响规律,基于搅拌电机扭矩值分析了不同搅拌速率下水合物浆液的流动特性。搅拌电机型号ViscoPakt Rheo-57,带有扭矩测量功能,测量最大范围57N·cm,精度±0.04N·cm。结果表明：在水合物开始快速生成的前期,水合物的最大生成量、最大生长速率及平稳生长速率都随搅拌速率的增大而增大,进一步验证了传质是控制水合物生成过程的首要因素;在水合物分解阶段,搅拌能提高水合物颗粒的分散性,促进分解气的运移产出;此外,不同搅拌速率下,水合物浆液的电机扭矩随着水合物体积分数的增大都呈现先保持平稳再逐渐增大最后剧烈波动的规律,由此得到了水合物浆液携带固相颗粒的临界体积分数。研究结论在一定程度上揭示了水合物的生长和分解机理,为动力学预测模型研究提供了参考。     

两种体系中甲烷水合物生成特性的研究

为了强化甲烷水合物生成,满足工业生产天然气水合物的要求,利用定压鼓泡式反应器对甲烷水合物在冰浆体系中和水体系中的生成特性进行了对比实验研究。结果表明,冰浆体系中水合反应的诱导时间比水体系水合反应的诱导时间短;冰浆体系比水体系拥有更大的导热系数和反应热吸收能力,更有利于反应热的释放;十二烷基硫酸钠浓度改变的过程中,水体系中反应的诱导时间和水合物储气密度的变化比冰浆体系明显;冰浆体系可以提升水合物的储气密度,但是随着有利于水合物反应条件的增加,冰浆的提升效果会逐渐地减弱。     

甲烷水合物生成分解的实验研究

海底存在着大量可燃冰,1 m3可燃冰能够储存160 m3的天然气。因此,可燃冰的开采与利用可燃冰储存与运输天然气具有重要意义。在改变搅拌、过冷度及低浓度动力学抑制剂的条件下,对甲烷水合物生成量与生成速率进行了实验研究。将甲烷水合物进行升温分解,分析水合物分解时的压力变化情况。结果表明:搅拌对甲烷水合物生成的促进效果最好,其次是过冷度,最后是超低浓度动力学抑制剂;水合物生成的传质过程最终被阻碍,采取将水与天然气的上下位置交换的方法,可以生成更多水合物。水合物升温可以得到相平衡曲线;改变初始时刻压力,可以得到不同温度区间的相平衡曲线;降低水合物分解时的升温速度,可以得到更长温度区间的相平衡曲线。     

撞击流反应器内快速生成甲烷水合物

为了快速制备甲烷水合物以利于天然气水合物法储运,在自行搭建的液相连续撞击流反应器内考察了纯水和纯水+十二烷基硫酸钠(SDS)2种体系中撞击强度、反应器内温度、初始压力对甲烷水合物快速生成的影响.实验结果表明:2种体系内撞击强度的增加可明显加快甲烷水合物的生成,在撞击强度为0.38、反应的前30 min,水合速率达到最大...     

Effect of multi-walled carbon nanotubes on methane hydrate formation

1 m³ of methane hydrate can be decomposed into a maximum of 216 m³ of methane gas under standard conditions. If these characteristics of hydrates are utilized in the opposite sense, natural gas can be fixed into water in the form of a hydrate solid. Therefore, the use of hydrates is considered to be a great way to transport and store natural gas in large quantities. However, when methane hydrate is formed artificially, the amount of gas that is consumed is relatively low, due to the slow reaction rate between water and methane gas. Therefore, for practical purposes in the application, the present investigation focuses on increasing the rate of formation of the hydrate and the amount of gas consumed by adding multi-walled carbon nanotubes (MWCNTs) to pure water. The results show that when 0.004 wt% of multi-walled carbon nanotubes was added to pure water, the amount of gas consumed was about 300% higher than that in pure water and the hydrate formation time decreased at a low subcooling temperature.     

A kinetic study of methane hydrate formation

The kinetics of methane hydrate formation, after commencement of nucleation, were studied using a semibatch stirred tank reactor. The temperatures studied in the experiments were from 274 to 284 K over a pressure range of 3–10 MPa. The results of the experiments revealed that the formation kinetics were dependent on the interfacial area, pressure, temperature and degree of supercooling. The history of water sample affected the induction delay times for nuclei formation, but it had no observable effects on the overall kinetics of hydrate formation after the nucleation had commenced. A consistent semi-empirical model was formulated to correlate the experimental kinetic data.     

煤层气水合物定容生成实验研究

为了有效利用与回收直接排放的大量抽放瓦斯,提出了利用水合物技术处理与储运的新方法,根据气体成分确立了水合物生成的温度与压力条件,通过对气体进行初始压力为9.5 MPa的定容法实验,研究了含表面活性剂下水合物生成过程中温度-压力与CH4转化率的变化规律。实验结果表明,水合反应的进行应保持一定的反应驱动力,根据不同温度下反应驱动力进而确定最佳反应条件,同时反应过程中CH4能被有效提取,但要进行高效生产,应进行多级水合分离技术以提高产率。     

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).     

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.     

SDS对甲烷水合物生成动力学和微观结构的影响

表面活性剂是促进水合物生成的有效手段之一。在高压反应釜中研究了十二烷基硫酸钠（SDS）对水合物生成过程的动力学影响,利用XRD和拉曼光谱探究了SDS存在条件下水合物的微观结构。宏观结果表明SDS缩短了诱导时间,加快了水合物生长速率。微观结果表明SDS没有影响sI型水合物的晶型结构,晶面间距与理想sI型水合物及纯水甲烷对比误差在千分之几。水合物中甲烷在大笼小笼中的拉曼位移分别为2904和2915 cm^-1,SDS没有改变大笼小笼结构。大笼绝对占有率（q_L）接近饱和时,SDS可以进一步提高小笼绝对占有率（q_S）,从微观角度证明了SDS可以减少水合数,提高储气率。     

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。     

Optimal wetting of active carbons for methane hydrate formation

In a recent paper (Perrin A, Celzard A, Marêché JF, Furdin G. Methane storage within dry and wet active carbons: a comparative study. Energy and Fuels 2003;17(5):1283–1291), methane storage by formation of methane hydrates within wet commercial active carbons (wetting ratio R=mass ratio water/carbon≈1) was investigated at 2 °C and up to 8 MPa. It was suspected from this study that more methane hydrate could be formed if more water was added. The present article is the continuation of this former work, and the pore volumes of the same materials were now saturated by water and investigated in the same T–P conditions. It is shown that, doing this, hydrate formation occurs at the lowest possible pressures (i.e. corresponding to those observed in bulk water) but poor results in terms of stored amounts are obtained. An optimal wetting ratio leading to the highest stored amounts was evidenced and found to be close to 1 whatever the pore texture of the carbon materials. Additionally, saturating the pore space with water further slows down the formation kinetics, which were already very long at R≈1. Finally, the role of an additive like sodium dodecyl sulphate (SDS) was investigated in one carbon; it is found that hydrates are formed at a rather low methane pressure, but the final amount stored is not higher than that previously obtained without adding SDS.     

温度对多孔介质中甲烷水合物生成过程的影响

采用自行设计的实验装置,分别进行了0℃以上(274.7 K)、0℃附近(272.8±0.5 K)和0℃以下(267.4 K)3种不同温度下,在20～40日石英砂中甲烷水合物的生成实验.结果表明甲烷水合物在0℃以上生成比较快;在0℃附近储气量大,水合物在整个砂层中的分布比较均匀.针对实验结果,本文提出了水合物在三种不同温度下的生成机理.     

Kinetics of methane hydrate formation in aqueous electrolyte solutions

Experimental data on the kinetics of methane hydrate formation in aqueous electrolyte solutions are reported. The experiments were carried out in a semi-batch stirred tank reactor in three NaCl and two KCl solutions as well as in a solution containing a mixture of NaCl and KCl at three different nominal temperatures from 270 to 274 K and at pressures ranging from 3.78 to 7.08 MPa. The kinetic model developed by Englezos et al. (1987a) was adapted to predict the growth of hydrates. The model is based on the crystallisation theory coupled with the two-film theory for gas absorption in the liquid phase. The kinetic rate constant which appears in the model was that obtained earlier for methane hydrate formation in pure water. The effect of the electrolytes was taken into account through the computation of the three-phase equilibrium conditions and the corresponding fugacities. Overall, the model predictions match the experimental data very well with the largest prediction error being less than 10%.     

气液比对表面活性剂复配促进甲烷水合物生成影响

气液比作为影响天然气水合物快速、大量生成的关键因素,有必要对其深入研究。利用天然气水合物装置,设定初始压力为6 MPa,温度为275.15 K,研究了十二烷基硫酸钠(SDS)与烷基多糖苷(APG1214)复配溶液体系在不同气液比条件下对天然气水合物生成影响。结果表明,合理的选取气液比能增强水合物的储气能力以及生成速率,4.00为其最佳气液比,最终储气密度可达到110.2(V/V),实验初始气液比的大小会影响水合物的生成过程,增加气液比能增加水合物的生成速率。因此,合理地将表面活性剂复配以及选取气液比,可显著提高水合物生成速率与储气能力。     

聚乙烯己内酰胺链端改性及其对甲烷水合物形成的抑制作用研究

注入动力学抑制剂是一种有效缓解天然气水合物管道堵塞的方法。本文以动力学抑制剂聚乙烯基己内酰胺(PVCap)结构为基础,将氧乙基和酯基引入PVCap的分子链端,合成了新抑制剂PVCap-XA1,在高压定容反应釜内评价了PVCap-XA1对甲烷水合物形成的抑制作用,并采用粉末X射线衍射、低温激光拉曼光谱和冷冻扫描电子显微镜研究了抑制剂对甲烷水合物结构和形态的影响。实验结果表明,相同实验条件下PVCap-XA1比PVCap具有更好的抑制作用;微观测试表明PVCap-XA1的加入没有改变甲烷水合物的晶体结构,但会使甲烷水合物晶面扭曲变形,可以降低水合物大小笼占有比(I_L/I_S),使得甲烷分子更难进入水合物大笼,同时PVCap-XA1的加入使甲烷水合物的微观形貌由多孔有序变得更致密而不利于气体通过。     

相变浆液中甲烷水合物的生成过程强化

利用相变材料（PCM）正十四烷的固液相变过程,吸收甲烷水合释放的热量,实现了直接换热强化水合过程的目的。正十四烷与水混合制成相变乳液（PCE）,经冷却后形成浆液。在半间歇水合器中,测定并计算了甲烷水合物在此浆液中的收率和生成速率。为了提高计算的准确性,设计了一套PVT装置,通过减压法实验测定了低温条件下甲烷在正十四烷中的溶解度。实验结果表明：低温条件下,甲烷在正十四烷中的溶解度与压力基本呈线性关系;相比于间接传热方式下的水合过程,相变浆液中甲烷水合物收率及生成速率得到了有效提升。     

泡沫铜强化甲烷水合物生成动力学实验研究

提高水合物生成速率和储气密度对天然气水合物技术应用非常重要。将三种孔密度的泡沫铜（CF）分别浸入十二烷基硫酸钠（SDS）溶液中构建水合储气强化体系,在高压静态反应釜中研究泡沫金属对甲烷水合物生成动力学特性。实验结果表明,泡沫铜骨架能为水合物生成提供充足的结晶点,同时可作为水合物生长过程水合热迁移的“高速公路”。甲烷水合物在SDS/CF体系中可快速生成,最大水合储气速率分布在19.24~21.04 mmol·mol^-1·min^-1之间,其中添加15 PPI泡沫铜的SDS溶液储气量最高（139 mmol·mol^-1）,且达到最大储气量90%所用时间最短（10.1 min）。在6.0~8.0 MPa压力下,相比SDS溶液,添加15 PPI泡沫铜的SDS溶液储气量提高了8.8%~35.6%,储气速率提高了4.7%~40.4%;特别在压力为5.0 MPa时,该孔密度SDS/CF体系储气量甚至比SDS溶液增加13倍,储气速率增加16倍。