VISUAL OBSERBATION OF HCFC141b GAS HYDRATE FORMATION/DECOMPOSITION PROCESS OUTSIDE OF A TUBE

In order to design a kind of heat exchanger suitable to the indirect-touched gas hydrate cool storage vessel, a visual observation of HCFC141b gas hydrate formation/decomposition process was presented through a self-designed small-scale visualization apparatus of gas hydrate cool storage. Based on the shooted photos and recorded temperatures, the formation/decomposition process of HCFC141b are described, some characteristics are concluded, and some suggestions of designing heat exchanger are indicated according to the specific characteristics of HCFC141b gas hydrate formation/decomposition process.

Experimental Study on the Characteristics of CO_2 Hydrate Formation in Porous Media below Freezing Point

Porous medium has an obvious effect on the formation of carbon dioxide hydrate. In order to study the characteristics of CO2 hydrate formation in porous medium below the freezing point, the experiment of CO2 hydrate formation was conducted in a high-pressure 1.8-L cell in the presence of porous media with a particle size of 380 μm, 500 μm and 700 μm, respectively. The test results showed that the porous medium had an important influence on the process of CO2 hydrate formation below the freezing point. Compared with porous media with a particle size of 500 μm and 700 μm, respectively, the average hydrate formation rate and gas storage capacity of carbon dioxide hydrate in the porous medium with a particle size of 380 μm attained 0.016 14 mol/h and 65.094 L/L, respectively. The results also indicated that, within a certain range of particle sizes, the smaller the particle size of porous medium was, the larger the average hydrate formation rate and the gas storage capacity of CO2 hydrate during the process of hydrate formation would be.

Experimental Study on Preparation of Natural Gas Hydrate by Crystallization

In this paper, the saturated solution crystallization method is proposed to promote the formation of hydrate by means of the known similarities between the hydrate formation process and the crystallization process. In this method,adding the second phase crystals was used to replace the spontaneous formation of hydrate crystal nuclei to form hydrate.The effects of saturated Na_2SO_4, MgSO_4, NH_4HCO_3 and CuSO_4 solutions on the formation rates of natural gas hydrate and gas storage capacity were investigated. The results showed that the saturated solution had an influence on the hydrate formation process. Under the given experimental conditions, the saturated Na_2SO_4 solution showed a highest increase in the hydrate formation rate, and the average hydrate formation rate in its presence was 11.8 times higher than that obtained in the deionized water. Moreover, the largest formation rate of gas hydrates observed in the saturated Na_2SO_4 solution was 386 times bigger than that in the deionized water, and the gas storage capacity increased by 10 times. In addition, the average hydrate formation rate in the saturated Mg SO_4 solution was faster than that in water by 20 times. The largest formation rate of gas hydrates in the saturated MgSO_4 solution was 165 times faster than that obtained in the deionized water, and the gas storage capacity increased by 6.2 times. The saturated NH_4HCO_3 and saturated CuSO_4 solutions also influenced the formation process of hydrate. Therefore, the crystallization method of saturated solution can be used to achieve a highefficiency preparation of natural gas hydrates, which provides theoretical guidance for the storage of natural gas in the form of hydrate.

Analysis of sensitivity to hydrate blockage risk in natural gas gathering pipeline

During the operational process of natural gas gathering and transmission pipelines,the formation of hydrates is highly probable,leading to uncontrolled movement and aggregation of hydrates.The continuous migration and accumulation of hydrates further contribute to the obstruction of natural gas pipelines,resulting in production reduction,shutdowns,and pressure build-ups.Consequently,a cascade of risks is prone to occur.To address this issue,this study focuses on the operational process of natural gas gathering and transmission pipelines,where a comprehensive framework is established.This framework includes theoretical models for pipeline temperature distribution,pipeline pressure distribution,multiphase flow within the pipeline,hydrate blockage,and numerical solution methods.By analyzing the influence of inlet temperature,inlet pressure,and terminal pressure on hydrate formation within the pipeline,the sensitivity patterns of hydrate blockage risks are derived.The research indicates that reducing inlet pressure and terminal pressure could lead to a decreased maximum hydrate formation rate,potentially mitigating pipeline blockage during natural gas transportation.Furthermore,an increase in inlet temperature and terminal pressure,and a decrease in inlet pressure,results in a displacement of the most probable location for hydrate blockage towards the terminal station.However,it is crucial to note that operating under low-pressure conditions significantly elevates energy consumption within the gathering system,contradicting the operational goal of energy efficiency and reduction of energy consumption.Consequently,for high-pressure gathering pipelines,measures such as raising the inlet temperature or employing inhibitors,electrical heat tracing,and thermal insulation should be adopted to prevent hydrate formation during natural gas transportation.Moreover,considering abnormal conditions such as gas well production and pipeline network shutdowns,which could potentially trigger hydrate formation,the installation of methanol injection connectors remains necessary to ensure production safety.

CO_2水合物喷雾合成的生长特性实验研究

利用自行设计的可视化喷雾强化水合物制备实验系统,分析和比较了不同初始温度和初始压力条件下,喷雾合成CO2水合物的耗气量和反应釜内温度的变化,研究其生长特性.实验结果表明,初始压力越高,或者初始温度越低,那么诱导时间越短,单位时间内CO2耗气量越多,水合物生成速率越快.同时,通过对水合物生长过程的摄像在线观察,发现CO2水合物在接触界面紧贴反应釜壁面的两相接触处最先诱导成核并迅速扩展,生成水合物后,随着反应进行,吉布斯自由能差增大,水合物颗粒由圆滑状向数枝状变化.

进气方式影响CO_2水合物喷雾合成的实验研究

为探讨进气方式对二氧化碳水合物生成特性的影响,利用自行设计的喷雾强化水合物制备实验系统,分析和比较连续式进气和振荡进气两种进气方式下喷雾合成水合物的耗气量和反应釜内温度的变化,研究其生成特性。实验结果表明:采用振荡进气方式,相对连续进气方式,单位时间内耗气量更多,生成的水合物速率更快。该方式下可以产生较大的驱动力,这种气体间变化性的扰动,使得水合物快速生长。在前期溶解阶段,适当调节进气阀门,加大进气速率,利于水合物生长。

纳米石墨颗粒与SDS复配对水合物生成特性的影响

为了促进水合物的生成,采用将纳米石墨颗粒与十二烷基硫酸钠(SDS)复配的方法,研究其复配体系对于水合物生成的诱导时间、耗气量以及生成速率的影响。结果表明,纳米石墨颗粒与SDS复配体系能大幅度缩减水合物生成过程的诱导时间,增加耗气量,加快生成速率。其中在277.15K、4.5MPa的条件下,0.5%纳米石墨流体与0.03%SDS的复配效果最佳,其诱导时间与纯水体系相比降幅达到61.77%。在277.15K、3.5MPa的条件下,0.5%纳米石墨与0.05%SDS的复配体系最大气体消耗量与纯水体系相比提高了5.29倍。比较两者的耗气率,复配体系中的峰值更是纯水体系的6.32倍。两者复配是强化水合物生成有力的促进剂。

高压CO_(2)水合物的生成机理实验和模拟

温室气体CO_(2)的捕捉和储存对减缓温室效应具有重大意义。CO_(2)水合物法储存CO_(2)具有效率高、储量大、易运输等优点。为了更高效制备CO_(2)水合物,对其生成机理进行实验和模拟研究。通过建立水合物生成的热力学模型,对水合物生成条件进行预测,利用高压静态釜式反应容器开展水合物生成实验,通过温度压力数据验证模型的准确性。在选取化学势能差作为水合物生成驱动力的基础上建立气体消耗速率模型,并与实验结果对比,结果表明:模型的预测值与实验值相对吻合。在低于水合物相平衡温度的条件下,升高容器的内反应压力可以促进气-液质量交换过程,提高生成效率。在生成过程中测得不同位置的电阻率变化数据,发现容器内的电阻率随固态水合物的生成而升高,并且首先在容器上部靠近壁面处结晶、团聚。

水合物在静态脂肪醇聚氧乙烯醚硫酸钠溶液与纯水搅拌条件下生成分析

促进天然气水合物快速大量生成是天然气水合物技术产业化的关键,因此,对其动力学促进方法进行研究是十分必要的。本文在温度为(2±0.1)℃,压力为(6.6±0.1)MPa条件下研究了不同浓度(60~1350mg/L)脂肪醇聚氧乙烯醚硫酸钠(AES)以及不同搅拌转速0~800r/min对水合物生成的影响,对两种方式的促进效果进行了对比,并从水合物生成动力学角度对AES及搅拌的促进机理进行分析。实验结果表明:AES与搅拌都可以促进液相气过饱和,加速单核生长和多核聚结过程,显著缩短诱导期,提高水合物生成速率及气体消耗量,但不同的是在水合物生长阶段搅拌仅能促进气相向液相单向移动,AES能够使气液交叉移动,显著降低了气液传质阻力,增加了成核位置,因此AES比搅拌进一步提高了水合物生成速率及气体消耗量。

碳纳米管对高浓瓦斯水合分离的动力学影响

为提高煤矿瓦斯利用率,探究了碳纳米管对高浓瓦斯快速水合分离的影响。利用瓦斯水合物生成装置,通过瓦斯水合分离实验,分析了3种碳纳米管添加量对瓦斯水合动力学参数与分离效果的影响。研究结果表明:随着碳纳米管添加量的增加,瓦斯水合物的水合速率、气体消耗量、水合物相中CH_(4)的体积分数都呈现先上升、后下降的特征。与纯水体系相比,水合速率分别增长了0.172×10^(-6)、0.448×10^(-6)、0.004×10^(-6)mol/h,气体消耗量增加了0.282、0.456、0.188 mol,水合物相中CH_(4)的体积分数分别提高了4.46%、9.07%、2.17%。

四丁基氯化铵溶液中瓦斯水合分离实验研究

提高水合物生成速度与生成量是利用水合物法气体分离技术高效利用瓦斯的关键。利用自主搭建的瓦斯水合物合成与分解循环装置,开展了3种不同质量分数的四丁基氯化铵(TBAC)溶液中瓦斯水合分离实验。结果表明,不同质量分数的溶液体系均能在50 min内生成水合物。在相同的时间内,质量分数为5.0%的TBAC溶液获得最大的气体消耗量,平均生长速率达到了2.907 cm^3/min,瓦斯气体中CH4体积分数占比下降了20%,促进效果最佳;质量分数为2.5%的次之;质量分数为7.5%的诱导时间最短,但气体消耗量极少。