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.     

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     

Performance Improvement of Various Kinetic Hydrate Inhibitors Using 2-Butoxyethanol for Simple Gas Hydrate Formation in a Flow Mini-Loop Apparatus

The effect of 2-butoxyethanol as an additive on simple gas hydrate formation in the presence of kinetic hydrate inhibitors such as modified starch, polyvinylcaprolactam, and Gaffix VC-713 under various conditions in a flow mini-loop apparatus has been studied. A laboratory flow mini-loop apparatus has been designed and manufactured to measure the induction time of simple gas hydrate formation. Hydrate formers (such as C1, C2, C3, i-C4, and CO₂) are contacted with water containing dissolved inhibitor in the presence of 2-butoxyethanol as an additive at desired temperature and pressure. The effect of 2-butoxyethanol on the induction time during gas hydrate formation was investigated in the presence and absence of modified starch, polyvinylcaprolactam, and Gaffix VC-713 as kinetic inhibitors. Results show that the induction time is prolonged in the presence of Gaffix VC-713 compared to polyvinylcaprolactam and modified starch as inhibitors. Moreover, the induction time in the presence of 2-butoxyethanol is greater than in the absence of this additive for simple gas hydrate formation. As a result, the performance of kinetic hydrate inhibitors was enhanced in the presence of 2-butoxyethanol for natural gas components during gas hydrate formation.     

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     

X射线衍射分析聚乙烯吡咯烷酮对水合物分解过程的影响

深水油气资源的勘探开发以及开采过程中的环保要求,使得天然气水合物动力学抑制剂使用不可避免,含动力学抑制剂的分解研究对水合物生成后的解堵具有重要的指导意义。本文在高压反应釜内采用甲烷和丙烷混合气,合成天然气水合物,并用X射线粉晶衍射仪分析了含动力学抑制剂聚乙烯吡咯烷酮的水合物分解过程。结果显示甲烷和丙烷气体会形成SⅡ型水合物,但伴随有SⅠ型甲烷水合物的生成;添加动力学抑制剂后,水合物的分解速率变慢,在-60℃,添加0.5%的聚乙烯吡咯烷酮后,分解起始的20 min内,无抑制剂体系水合物分解可达69%,而在含抑制剂体系分解约18%;SⅡ型甲烷丙烷混合气水合物分解过程中晶胞各晶面分解速率相同,没有偏好性,水合物笼作为一个整体分解,添加抑制剂不改变这种分解方式,仍以整体分解。     

Experimental and theoretical study of gas hydrate formation in a high‐pressure flow loop

A set of mathematical models are developed based on thermodynamics, mass transfer, and crystallisation concepts to predict hydrate formation rate and the aqueous phase composition in the flow loop. In order to validate the model, experimental study is carried out in a 10 m loop with the inside diameter of 10.6 mm using gas mixture of 73% methane and 27% propane to measure the hydrate formation rate. The experimental conditions include temperature from 4 to 5°C and pressures between 2 and 3 MPa. Good agreements are noticed when the experimental and theoretical hydrate formation rates are compared at different operating conditions.     

Dual function inhibitors for methane hydrate

The performance of five imidazolium-based ionic liquids as a new class of gas hydrate inhibitors has been investigated. Their effects on the equilibrium hydrate dissociation curve in a pressure range of 30-110 bar and the induction time of hydrate formation at 114 bar and a high degree of supercooling, i.e., about 25 °C, are measured in a high-pressure micro differential scanning calorimeter. It is found that these ionic liquids, due to their strong electrostatic charges and hydrogen bond with water, could shift the equilibrium hydrate dissociation/stability curve to a lower temperature and, at the same time, retard the hydrate formation by slowing down the hydrate nucleation rate, thus are able to act as both thermodynamic and kinetic inhibitors. This dual function is expected to make this type of inhibitors perform more effectively than the existing inhibitors.     

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.     

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.     

天然气水合物生成焓的实验研究

This paper reports the measurements of enthalpies of natural gas hydrates in typical natural gas mixture containing methane, ethane, propane and iso-butane at pressure in the vicinity of 2000 kPa (300 psi) and 6900 kPa(1000psi). The measurements were made in a multi-cell differential scanning calorimeter using modified high pressure cells. The enthalpy of water and the enthalpy of dissociation of the gas hydrate were determined from the calorimeter response during slow temperature scanning at constant pressure. The amount of gas released from the dissociation of hydrate was determined from the pumped volume of the high pressure pump. The occupation ratio (mole ratio) of the water to gas and the enthalpy of hydrate formation are subject to uncertainty of 1.5%.The results show that the enthalpy of hydrate formation and the occupation ratio are essentially independent of pressure.     

非平衡级法气体混合物吸收-水合双塔分离单元的模拟计算

水合物技术应用于低沸点气体混合物分离的优势在于其可在0℃左右操作,因此可极大地降低制冷所消耗的能量。由于此分离方法尚处在理论研究阶段,还不能实现工业化,因此对操作流程模拟计算的研究很有必要。采用非平衡级法(速率法)对水合塔-吸收塔串联操作流程进行了模拟计算,其中涉及水合物生成动力学模型、水合物分解动力学模型以及混合气体在乳液相的吸收传质动力学模型。探讨了两个串联分离塔操作参数,如温度、压力等,对分离效率的影响,所得结果对水合物技术分离低沸点气体混合物流程的设计有重要意义,同时也可为以后的工业化奠定一定的理论基础。     

Growth kinetics of hydrate formation from water–hydrocarbon system

Gas hydrates have drawn global attentions in the past decades as potential energy resources. It should be noted that there are a variety of possible applications of hydrate-based technologies, including natural gas storage, gas transportation, separation of gas mixture, and seawater desalination. These applications have been critically challenged by insufficient understanding of hydrate formation kinetics. In this work, the literatures on growth kinetic behaviors of hydrate formation from water-hydrocarbon were systematically reviewed. The hydrate crystal growth, hydrate film growth and macroscopic hydrate formation in water system were reviewed, respectively. Firstly, the hydrate crystal growth was analyzed with respect to different positions, such as gas/liquid interface, liquid–liquid interface and gas–liquid–liquid system. Secondly, experimental and modeling studies on the growth of hydrate film at the interfaces between guest phase and water phase were categorized into two groups of lateral growth and thickening growth considering the differences in growth rates. Thirdly, we summarized the promoters and inhibitors reported (biological or chemical, liquid or solid and hydrophobic or hydrophilic) and analyzed the mechanisms affecting hydrate formation in bulk water system. Knowledge gaps and suggestions for further studies on hydrate formation kinetic behaviors are presented.     

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.     

Assessment of commercial hydrate inhibitors using the 3‐in‐1 method

Phase equilibria, kinetics, and morphology studies of gas hydrates require separate pieces of equipment and experimentation times in the order of days. Recently, we designed a reactor that allows for tight control of the crystallization temperature. Coupled with a novel method, this reactor can screen the crystal morphology, phase equilibria, and apparent kinetics of gas hydrates. Compared to traditional multi‐trial methods, the main advantage of this method is that only a single experiment, completed in the order of hours, is required to assess: (a) the change in hydrate growth velocity with respect to temperature, (b) the HLV equilibrium temperature at the experimental pressure, and (c) the change in crystal morphology with respect to driving force. Using this 3‐in‐1 method, methane hydrate growth and dissociation was studied in the presence of four commercial inhibitors. Phase equilibria, kinetics, and morphology were obtained for all hydrate systems with inhibitors. The standard uncertainty for the HLV equilibrium temperature was 0.05 K and for pressure 0.005 MPa. The apparent rates of growth were measured for all systems (standard uncertainty was 0.008 mm · s^?1) and the difference between the inhibited systems and the pure system was very clear. Crystal habits varied considerably among inhibitors and radically with respect to the uninhibited system. Overall, we present an innovative technology to assess the morphology, kinetics, and thermodynamics of hydrate forming systems with a single apparatus. Furthermore, with little time investment, small sample sizes can be used to obtain replicates with minimum temperature and pressure uncertainties.     

低浓度瓦斯气体水合分离过程中十二烷基硫酸钠和高岭土的影响

为了探寻有效改善瓦斯水合分离动力学条件的方法,本文研究了十二烷基硫酸钠(SDS)和高岭土对瓦斯水合物生成过程及CH₄分离效果的影响。实验获取了低浓度瓦斯在4个体系中,即：SDS质量分数为10.34%的SDS溶液及高岭土质量分数为1.47%、5.64%和8.23%的SDS-高岭土复配溶液中瓦斯水合物生成过程压力-温度-时间（p-T-t）曲线,利用气相色谱仪测定了分离产物中CH₄的浓度。结果表明：SDS和SDS-高岭土复配体系缩短了瓦斯水合物生成诱导时间,提高了瓦斯水合物生成速率。4个体系中,瓦斯水合物生成诱导时间最短为72 min,平均生成速率最大可达5.261×10^-6 m³·h^-1;一级水合分离产物中CH₄浓度比原料气提高了12.40%～20.61%;在SDS-高岭土复配溶液中,瓦斯水合物分形生长,CH₄提纯浓度最高可达58.41%。     

Probability distributions of gas hydrate formation

Induction time distributions for gas hydrate formation were measured for gas mixtures of methane + propane at pressures up to 11.3 MPa using a high‐pressure automated lag time apparatus (HP‐ALTA). Measurements were made at subcooling temperatures between 4.3 and 13.5 K and, while isothermal induction times between 0 and 15,000 s were observed, the median isothermal induction times for the distributions ranged from 100 to 4000 s. A hyperbolic relationship between median induction time and subcooling was used to correlate the data. A graphical interpretation is presented that relates the two types of data that can be acquired by using the HP‐ALTA in one of two modes to study hydrate formation: induction time distributions at constant subcooling and formation temperature distributions observed during linear cooling ramps. The equivalence of these two modes provides a robust method for studying the variation of formation phenomena in different hydrate systems. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2640–2646, 2013     

A water droplet size distribution dependent modeling of hydrate formation in water/oil emulsion

Experimental data on chord length distributions and growth rate during methane hydrate formation in water‐in‐oil emulsions were obtained in a high pressure stirring reactor using focused beam reflectance measurement and particle video microscope. The experiments were carried out at 274.2 K for 10–30% water cuts and agitation rates ranging from 200 to 500 rpm initially at 7.72 MPa. Rapid growth was accompanied by gradually decrease in rate. Free water was observed to become depleted during rapid growth while some water remained encapsulated inside hydrate layers constituting a mass transfer barrier. The apparent kinetic constants of methane hydrate formation and free‐water fractions were determined using a newly developed kinetic model independent of the dissolution rate at the gas–oil interface. It was illustrated that continued growth depends on distribution and transfer of water in oil‐dominated systems. This perception accords with observations of hydrate film growth on suspended water droplet in oil and clarifies transfer limits in kinetics. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1010–1023, 2017     

次氯酸钙对水合物中甲烷储气量的影响

1 INTRODUCTION At present,natural gas accounts for 3% of the total energy consumption in China.It will go up to 5% in 2005 and 8% in 2010. Natural gas storage is a subject of great interest to many industries and particularly to transportation.Compressed natural gas,liquefied natural gas and adsorbed natural gas are techniques widely used.The possibility of developing a convenient storage system based on hydrate has been explored for about ten years around the world[1-5].Gudmundsson[1] has focused on the storage and transportation of gas as hydrate at atmospheric pressure since 1990.Khokhar[2] used 1,3-dimethylcyclohexane and polyvinyl-pyrrolidone as additives to lower hydrate formation pressure. Saito[3] surveyed the effects of tetrahydrofuran and acetone.Rogers[3] used sodium dodecyl sulfate as accelerator to natural gas hydrate formation. In this work,the effects of calcium hypochlorite on hydrate formation are investigated.The data show that it can lower the degree of supercooling and enhance the relative cage occupancy.     

Nucleation curves of model natural gas hydrates on a quasi‐free water droplet

Heterogeneous nucleation probability distributions of gas hydrates on a water droplet that was supported by inert and immiscible perfluorocarbon oil, perfluorodecalin is studied. The guest gas used was a mixture of 90 mol % methane and 10 mol % propane. The probability distribution was measured using a high pressure automated lag time apparatus under the guest gas pressure range of 6.7–12.5 MPa and the cooling rate range of 0.002–0.02 K/s. Nucleation curves were derived for unit area of water surface. The nucleation rate per unit area of water surface that was contained in a glass sample cell, which differed significantly from that on a quasi‐free water droplet, is also derived. It is concluded that the nucleation curves in the presence of a solid wall should be normalized to the unit length of the three‐phase line at which water, guest gas, and the solid wall meet. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2611–2617, 2015     

Experimental study of natural gas hydrates and a novel use of neural network to predict hydrate formation conditions

A novel high-pressure apparatus with various abilities in hydrate investigation fields has been designed, constructed and fully described in the present paper. In order to achieve an appropriate understanding of the gas hydrate behavior in formation and destabilization, series of laboratory experiments with six different gas mixtures were done and more than 130 hydrate equilibrium points in the pressure range of about 450–3000 psia were recorded. Different methods of hydrate formation prediction were discussed and finally the new promising neural networks method was used. Because of the previous works defects in accurate hydrate formation prediction via neural networks, a new use of neural networks was introduced. Testing and validation of the new neural networks method indicates that it is a reliable technique for the accurate prediction of hydrate formation conditions for generalized gas systems and can be used in future automatic inhibitor dosing devices.