Experimental investigation of double gas hydrate formation in the presence of modified starch as a kinetic inhibitor in a flow mini‐loop apparatus

The main objective of the present work is experimental investigation of double gas hydrate formation with or without presence of modified starch as kinetic inhibitors in a flow mini‐loop apparatus. To this object, a laboratory flow mini‐loop apparatus was set up to measure the induction time for hydrate formation and the rate uptake when a gaseous mixture (such as 75% C1–25% C3, 25% C1–75% C3, 75% C1–25% i‐C4 and 25% C1–75% i‐C4) is contacted with water containing or not containing dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, water blend saturated with gas mixture is circulated up to a required pressure. Pressure is maintained at a constant value during experimental runs by means of required gas mixture make‐up. The effect of pressure on gas consumption during hydrate formation is investigated with or without presence of polyvinylpyrrolidone and modified starch as kinetic inhibitors at various concentrations. Our results were shown that the modified starch can be applied as inhibitors in prevention of double gas hydrate formation in mini‐loop apparatus. © 2011 Canadian Society for Chemical Engineering     

Prediction of induction time for natural gas components during gas hydrate formation in the presence of kinetic hydrate inhibitors in a flow mini‐loop apparatus

The objective of this work is the prediction of induction time (t_i) for simple gas hydrate formation in the presence or absence of kinetic hydrate inhibitors at various conditions based on the Kashchiev and Firoozabadi model in a flow mini‐loop apparatus. For this purpose, the t_i model is developed for simple gas hydrate formation in batch system for natural gas components during hydrate formation in a flow mini‐loop apparatus. A laboratory flow mini‐loop apparatus is designed and built up to measure the t_i for simple gas hydrate formation when a hydrate former (such as C₁, C₃, CO₂ and i‐C₄) is contacted with water in the absence or presence of dissolved inhibitor, such as poly vinylpyrrolidone, PVCap and L ‐tyrosine. In each experiment, a water blend saturated with pure gas is circulated up to a required pressure. Pressure is maintained at a constant value during experimental runs by means of the required gas make‐up. The average absolute deviation (AAD) of the predicted t_i values from the corresponding experimental data are found to be about 11% and 9.4% for gas hydrate formation t_i in the presence or absence of kinetic hydrate inhibitors, respectively. © 2012 Canadian Society for Chemical Engineering     

Experimental and Theoretical Investigation of Double Gas Hydrate Formation in the Presence or Absence of Kinetic Inhibitors in a Flow Mini‐Loop Apparatus

Double gas hydrate formation in the presence or absence of kinetic inhibitors in a flow mini‐loop apparatus was investigated. For the prediction of the gas consumption rate during hydrate formation in this system, the rate equation based on the Kashchiev and Firoozabadi model for simple gas hydrate formation in a batch system was developed for double gas hydrate formation in a flow mini‐loop apparatus. To complete the theoretical evaluation of gas hydrate formation through the mini‐loop apparatus in the presence or absence of kinetic hydrate inhibitors (KHI), a laboratory flow mini‐loop apparatus was set up to measure the induction time for hydrate formation and the uptake rate when a gaseous mixture (such as 75 % C1/25 % C3, 25 % C1/75 % C3, 75 % C1/25 % i‐C4, and 25 % C1/75 % i‐C4) is contacted with water containing or not containing dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, a water blend saturated with gas mixture was circulated up to the required pressure. The pressure was maintained at a constant value during the experimental runs by means of a required gas mixture make‐up. The effect of pressure on gas consumption during hydrate formation was investigated in the presence or absence of polyvinylpyrrolidone (PVP) and L ‐tyrosine as kinetic inhibitors at various concentrations. A good agreement was found between the predicted and experimental data in the presence or absence of KHI. The total average absolute deviation percents between the experimental and predicted values of gas consumption were found to be 16.4 and 17.5 % for the double gas hydrate formation in the presence or absence of the kinetic inhibitors, respectively.     

一种可生物降解水合物动力学抑制剂的研究

目前用于天然气水合物防治的工业动力学抑制剂主要是水溶性聚合物，如聚乙烯基吡咯烷酮（PVP）、聚乙烯基己内酰胺（PVCap）、Gaffix VC-713等，然而生物降解性低限制了其工业应用。因此，开发环保型的抑制剂具有重要意义。实验采用易生物降解的海藻酸钠与PVCap的单体接枝共聚，合成一类新型水合物动力学抑制剂NaAlg-g-PVCap，结合最大过冷度及耗气量评价了新型抑制剂在水合物生成过程中的抑制性能，并通过BOD₅/COD值评价了新型抑制剂的生物降解性。结果表明低剂量[0.25%（质量）]下NaAlg-g-PVCap的最大耐受过冷度优于PVP K90，但低于PVCap，且随着添加剂量增大而微弱降低；在其最大耐受过冷度以下（ΔT_sub=5℃），NaAlg-g-PVCap表现出较好的水合物成核和生长抑制作用，其体系水合物初始生长速率值约只为纯水体系的 1/10，也远高于PVP体系，且总耗气量相比纯水及PVP体系减少了60%以上，与PVCap体系接近，但随着过冷度增大，NaAlg-g-PVCap成核抑制作用下降明显，这可能是共聚物中两部分共同作用的结果；同时，NaAlg-g-PVCap相比PVCap其生物降解性提高了26%， 倾向于易降解。说明PVCap与NaAlg共聚后优化了整体的性能，表现出较好的水合物抑制性能和生物降解性。     

Kinetic Modeling of Methane Hydrate Formation in the Presence of Low‐Dosage Water‐Soluble Ionic Liquids

The kinetic and thermodynamic effects of three typical low‐dosage imidazolium‐based ionic liquids (ILs) on methane hydrate formation and dissociation were investigated, considering the anion nature and subcooling and/or overpressure driving forces. Isochoric hydrate formation and dissociation data were obtained by the modified slow step‐heating method. ILs proved to have a dual effect on both formation and dissociation of methane hydrate including thermodynamic and kinetic inhibition. Kinetic modeling of methane hydrate inhibition by low‐dosage ILs was performed. Kinetic analysis showed that IL inhibitors mainly cause a delay in the nucleation or hydrate growth step. The related inhibition mechanism was resolved regarding the ionic nature and electrostatic interactions of ILs with water molecules. Two binomial exponential kinetic relations were derived and used for simple methane hydrate formation in the presence of ILs as kinetic hydrate inhibitors. The proposed relations can serve for a quick estimation of the nature, extent, strength, and effectiveness of ILs on various gas hydrates.     

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。     

Rheological evaluation of kinetic hydrate inhibitors in NaCl/n‐heptane solutions

The performance of polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap) as kinetic hydrate inhibitors (KHIs) in the presence of NaCl and n‐heptane was evaluated by using a high‐pressure cell in conjunction with a rotational rheometer. The addition of KHIs was found to prolong the induction time and decrease the hydrate growth. On the other hand, hydrates agglomerated more readily. PVP performed more efficiently than PVCap in delaying nucleation time but PVCap controlled the growth and delayed agglomeration more effectively. Addition of n‐heptane to the system increased induction time and reduced growth. Unexpectedly, addition of KHIs in the presence of n‐heptane decreased nucleation time but controlled growth effectively. Meanwhile, hydrate particles remained dispersed more efficiently and no agglomeration was detected. These observations confirm that high‐pressure rheology is an additional laboratory assessment tool to evaluate KHIs under ocean field conditions. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2654–2659, 2014     

Determining gas hydrate kinetic inhibitor effectiveness using emulsions

In this study we measure the effect of hydrate kinetic inhibition in emulsions. Because hydrate nucleation is stochastic, many experiments normally are needed to obtain accurate analysis of the effectiveness of kinetic inhibitors. Using differential scanning calorimetry (DSC), we show how emulsions can reduce the number of kinetic samples needed to obtain a statistical analysis of the effectiveness of polyvinylcaprolactam, PVCap, a common kinetic inhibitor. PVCap is shown to delay the average hydrate nucleation time and also causes hydrate nucleation to become more stochastic. This novel method uses less material and experimental time compared to traditional methods used to test kinetic inhibitors.     

Enhancement of the performance of kinetic inhibitors in the presence of polyethylene oxide and polypropylene oxide for binary mixtures during gas hydrate formation in a flow mini‐loop apparatus

The objective of this work is to demonstrate the impact of the polyethylene oxide (PEO) and polypropylene oxide (PPO) on the performance of gas hydrate kinetic inhibitors for binary mixtures during gas hydrate formation in a flow mini‐loop apparatus. PEO and PPO are commercially available polymers that they have been considered to be unable to exhibit kinetic hydrate inhibition (KHI) by their self. Prevention of gas hydrate formation experiments in the presence of the KHIs solutions were conducted in a flow mini‐loop apparatus manner under suitable pressures and temperature conditions for binary gaseous mixtures including 70% CH₄/30% C₃H₈, 30% CH₄/70% C₃H₈, 70% CH₄/30% i‐C₄H₁₀, and 30% CH₄/70% i‐C₄H₁₀. In the experiments, induction time for crystallisation of gas hydrate formation and gas consumption rate are investigated in systems without KHI, containing KHI only (such as polyvinylpyrrolidone (PVP) and L ‐tyrosine) and PEO or PPO together with KHI. Pressure is maintained at a constant value during experimental runs by means of required gas make‐up. The addition of a KHI into system delayed the onset of hydrate crystal nucleation. Furthermore, addition of the PEO or PPO to a KHI solution was found to enhance the performance of KHI. In addition, under the same pressure temperature hydrate formation conditions the induction time is longer when the PPO is present. Thus, inclusion of PPO into a KHI solution shows a higher enhancement in its inhibiting performance compare to PEO. © 2011 Canadian Society for Chemical Engineering     

基于化学亲和力模型的水合物生成动力学

水合物生成促进及动力学模型是水合物利用技术的关键问题。本文回顾了水合物生成促进技术的发展,实验研究了氧化石墨烯（GO）与十二烷基硫酸钠（SDS）复配促进剂体系下CO₂水合物的生成动力学,揭示了不同浓度对水合物生成时间、耗气的影响规律。研究结果表明,在GO与SDS复配体系下,CO₂水合物生成速度加快,诱导时间和生成时间缩短,耗气量增大。得出最佳复配浓度为0.005%GO+0.2%SDS,与纯水和单一0.005%GO体系相比,水合物的生成时间分别缩短69.7%和12.2%,耗气量提高11.24%和3.2%。建立了该体系下CO₂水合物生成化学亲和力模型,并从模型角度研究了GO与SDS复配比例、温度和压力对化学亲和力模型参数的影响。利用Matlab对模型编程计算并与实验结果进行了对比分析,吻合很好。通过研究认为,化学亲和力模型可准确预测复配体系水合物的生成。     

一种高效复合型气体水合物抑制剂的研究

在油气运输管道中,气体水合物的形成会造成管道堵塞,给油气行业带来巨大的损失。为了抑制水合物的形成,文章以二氧化碳水合物为实验对象,在低温高压带视镜悬浮搅拌试验装置中,分别采用聚乙烯吡咯烷酮(PVP),氯化钠以及这两者的复合液作为抑制剂进行实验。通过诱导时间和气体耗气量的比较,结果表明,单一的PVP能有效的延长气体水合物生成的诱导时间,单一的氯化钠能降低反应体系的耗气量,而由PVP与氯化钠复配得到的复合型抑制剂能延长反应的诱导时间和降低反应耗气量,是一种高效的气体水合物抑制剂。     

Enhancement of the performance of gas hydrate kinetic inhibitors with polyethylene oxide

Inclusion of polyethylene oxide into a kinetic inhibitor solution was found to enhance the performance of the inhibitor. Polyethylene oxide is a commercially available high molecular weight polymer that is not a kinetic inhibitor by itself. The hydrate formation experiments in the presence of the various inhibitor solutions were conducted in a vessel in a semi-batch manner at constant pressure and using methane and methane-ethane gas mixtures. In some experiments a non-aqueous liquid phase (n-heptane) was also present. The induction time, the gas uptake and the temperature were measured. It was found that the induction time is prolonged in the presence of the additive by an order of magnitude in some cases compared to the inhibitor only.     

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.     

气体水合物蓄冷技术研究进展

综述了国内外制冷剂气体水合物蓄冷技术的研究进展。概括描述了制冷剂气体水合物的相平衡热力学、结晶动力学研究，介绍了水合物蓄冷系统及蓄／释冷过程的研究成果：相平衡研究水合物形成的压力、温度条件；动力学研究水合物的生成，包括添加剂和外场等的作用；蓄冷过程研究系统运行可靠性及优化控制。最后简要展望了今后的主要研究方向。     

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。     

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.     

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.     

水合物动力学抑制剂的作用机理研究进展

水合物动力学抑制剂作为低液量抑制剂,其可应用于深水流动保障风险控制水合物冻堵问题,受到国内外研究者的广泛关注。本文重点阐述了动力学抑制剂的可承受最大过冷度和对诱导时间的延长这两个评价指标,同时梳理了动力学抑制剂对水合物生成及分解过程影响的研究成果。总体而言,可承受最大过冷度越大、延长诱导时间程度越强的动力学抑制剂,抑制水合物生成并保障流动安全的可靠性越高;动力学抑制剂对水合物生成与分解过程存在复杂的影响规律。本文将其对气体消耗速率、气体消耗量和形态,分解温度、时间和分解速率,“记忆效应”等影响进行了分析。结合上述研究成果,总结了动力学抑制剂对水合物的影响机理,特别是提出了化学型动力学抑制剂对水合物吸附抑制机理的概念示意图。最后,给出了未来深入开展动力学抑制剂研究的建议。     

添加剂对二氧化碳水合物形成的影响研究进展

本文介绍了二氧化碳水合物的基本特性,根据二氧化碳水合物的形成机理,提出了几种促进二氧化碳水合物形成的方法。具体分析了不同添加剂对二氧化碳水合物形成过程的影响,阐述了一些添加剂在缩短诱导时间、提高生成速率、降低相平衡条件中取得的研究成果。     

Cationic starches as gas hydrate kinetic inhibitors

This work investigated the kinetic inhibiting effect of a number of cationic starches in hydrate formation experiments with methane and methane/ethane and methane/propane gas mixtures. The starches were found to exhibit a very weak inhibiting effect except for tapioca starch which increased the induction time (delay of onset of crystallization) by an order of magnitude. The addition of polyethylene oxide (PEO) was found to further enhance the performance of tapioca starch as well as some of the other starches. Finally, the presence of tapioca starch and PEO was found to suppress the memory effect. The results were interpreted based on a mechanism proposed by Zeng et al. [2006a. Effect of antifreeze protein on nucleation, growth and memory of gas hydrates. A.I.Ch.E. Journal 52(9), 3304-3309; 2006b. Effect of antifreeze proteins on the nucleation, growth and the memory during tetrahydrofuran clathrate hydrate formation. Journal of the American Chemical Society 128, 2844-2850] whereby the starches interfere with nucleation through interactions with heterogeneous nucleation sites.