High Subcooling Conditions Research Articles

Molecular dynamics simulations on the anti-memory effect of vinyl lactam-based polymers

Molecular dynamics simulations were carried out to study the microscopic working mechanism of PVCap-co-TBA and PVCap, especially its working mechanism on the memory effect of hydrates. Our simulation results indicate that PVCap-co-TBA could weaken or even eliminate the hydrate memory effect under the higher subcooling conditions compared with PVCap. The hydrogen bonds formed by the double-bond oxygen atoms and nitrogen atoms of the lactam groups in PVCap with water molecules make the hydrate residual structures around PVCap less susceptible to decompose and provide nucleation sites for hydrate reformation at high subcooling conditions. Compared with PVCap, the introduction of strong hydrophobic tertiary butyl functional groups in PVCap-co-TBA accelerates the mass transfer of water and methane molecules, leading to the decomposition of the hydrate residual structures and the aggregation of large nano-bubble, thereby delaying the hydrate re-nucleation even at high subcooling conditions (e.g. 273 K and 30 MPa).

Effective prevention of structure II gas hydrate formation using the newly synthesized kinetic inhibitors

Gas hydrate deposition is a complex issue with significant implications for the oil and gas industry. The formation of solid gas hydrates in the hydrocarbon transportation pipelines leads to production disruptions and potentially even complete blockages, resulting in huge financial losses and operational difficulties. For over two decades, kinetic gas hydrate inhibitors have played a crucial role in preventing the formation of gas hydrates within the flow lines of oil and gas production. They directly influence the kinetics of hydrate formation, hindering nucleation and slowing down crystal growth. In this study, five new waterborne polyurethanes (WPUs) with varying degrees of hydrophobicity as inhibitors for cubic structure II gas hydrates were synthesized and tested using rocking cells and differential scanning calorimetry. The synthesis of WPUs involved the reaction between dialkylamines (diethyl, dipropyl, dibutyl, dibenzyl, and dioctyl) and glycidol under mild conditions. All WPUs effectively prevented gas hydrate formation, and a correlation between their efficiency and the alkyl chain length was observed. The inhibitory efficacy of WPUs increased with the extension of the alkyl chain from ethyl to butyl. WPU-DBuA, featuring butyl groups, exhibited the highest inhibition activity. It provided a subcooling temperature of 12.9 and 15.6 °C at 0.25 and 0.5 wt%, respectively, surpassing commercial samples, such as Luvicap EG and Luvicap 55 W. Additionally, the solutions containing 1 and 2 wt% of WPU-DBu exhibited maximum subcooling temperatures of 16.2 °C and 16.7 °C, respectively, which correspond to a 79.7 % and 85.4 % reduction in gas uptake during hydrate growth compared to pure water. However, the inhibitory power of WPUs diminished with larger alkyl (dioctyl) or aromatic groups (dibenzyl), indicating that dibutyl represents the optimal alkyl length for achieving maximum performance. Moreover, WPUs demonstrated a reduction in hydrate conversion under static conditions, signifying their efficiency when the flow is stopped. WPUs lowered the onset temperature of hydrate formation from 3 °C in pure water to temperatures below −12 °C. Thus, WPUs demonstrated a remarkable ability to prevent the formation of structure II gas hydrates, even under high subcooling conditions. Additionally, WPU-DBuA exhibits a considerable degree of biodegradability, as evidenced by its biodegradation level of 44 %, suggesting that it has the potential to break down more easily in the environment compared to Luvicap 55 W. This research contributes to a deeper understanding of the structure–property relationships of KHIs. This can facilitate the development of more effective and eco-friendly inhibitors, which helps address environmental concerns associated with using KHIs in the oil and gas industry.

Effect of wall subcooling on condensation in a steam-air mixture on a vertical tube

In this study, the effects of wall subcooling on the condensation heat transfer in steam-air mixture on a vertical tube was investigated. The effect of wall subcooling on condensation heat transfer was analyzed experimentally and using heat and mass transfer model. The experimental analysis indicated that wall subcooling effect varied depending on the degree of subcooling, i.e., the decrement of condensation heat transfer became less in low subcooling. In addition, the noncondensable gas fraction affected the wall subcooling effect. Such phenomenon was also found in the analysis using heat and mass transfer model. Through analysis using heat and mass transfer model, it was found that the accumulation of noncondensable gas and steam diffusion have competing effects. The former deteriorates and the latter enhances the condensation heat transfer with increasing wall subcooling. In low subcooling condition, both effects have higher rate of change, resulting in the different subcooling effect with that of high subcooling condition. We then developed an empirical correlation of condensation heat transfer over a wide range of wall subcooling; this predicted the experimental results reasonably well, particularly at low subcooling.

Synthesis and evaluation investigation of novel kinetic hydrate inhibitors at high subcooling conditions

Kinetic hydrate inhibitors (KHIs) have gradually gained more attention in the natural gas and oil transportation field due to their remarkable inhibition performance at low dosages. However, the inhibition performance of most commercial KHIs is poor under high subcooling conditions. In this work, a radical polymerization method was used to synthesize four new KHIs by introducing the 1-vinylimidazole (VI) or vinylacetate (VAc) monomer. These newly-synthesized copolymer KHIs were characterized by Fourier Transform Infrared, 1H nuclear magnetic resonance, and gel permeation chromatography, respectively. The cloud point of HY-201 is remarkably as high as 92.3 °C and the four KHIs are all biodegradable. Under subcooling of 10 K and 15 K, the inhibitory performance of four new KHIs and three commercial KHIs on hydrate nucleation and growth are as follows: PVP < Luvicap EG < Inhibex 501 < HY-101 < HY-201 < HY-301 < HY-401. In addition, the hydrate volume fraction of the four new KHIs at the optimal concentration of 15 K subcooling for 12 h was 13.3 %, 1.7 %, 2.4 %, and 2.1 %, respectively, which did not exceed 1/3 of the tested commercial KHIs. Further, the novel mechanism hypothesis is proposed as follows: the surface charge of the hydrate nuclei is neutralized by KHIs, and the hydrate nuclei aggregates, hindering the gas from entering the hydrate. In addition, the strong entanglement and adsorption of KHIs molecules with better inhibition performance make the hydrate lose the space for growth and expansion. Overall results highlight the great application prospects of these new KHIs in natural gas transmission based on the remarkable inhibition performance under high subcooling conditions.

Correction to: Flow Boiling Burnout in a Hypervapotron Channel Under High Heat Flux and High Sub-Cooling Conditions

Correction to: Flow Boiling Burnout in a Hypervapotron Channel Under High Heat Flux and High Sub-Cooling Conditions

Flow Boiling Burnout in a Hypervapotron Channel Under High Heat Flux and High Sub-Cooling Conditions

Flow Boiling Burnout in a Hypervapotron Channel Under High Heat Flux and High Sub-Cooling Conditions

Molecular dynamics simulation to explore the synergistic inhibition effect of kinetic and thermodynamic hydrate inhibitors

The combined injection of kinetic and thermodynamic hydrate inhibitors (KHIs and THIs) is considered as a promising method to prevent the blockage of oil and gas pipelines caused by the accidental formation of methane hydrate. To develop better strategies for enhancing inhibition effects, molecular dynamics simulation is employed to investigate the synergistic mechanism of a KHI and a THI (PVP-A and methanol, respectively). Our results show that the nucleation time is shortened from 22 ns to about 12 ns by 1.65 wt% PVP-A or 4.8 wt% methanol, exhibiting the promotion effect on hydrate formation under the simulated high subcooling conditions. However, the composite inhibitor composed of PVP-A and methanol with a total concentration of 4.8 wt% prolongs the nucleation time beyond 500 ns, showing amazing inhibition effect. The whole synergistic process of KHIs and THIs is mainly composed of three stages, i.e. gas adsorption, water arrangement destruction and steric hindrance stages, and the first one usually dominates the whole inhibition process. Adding THIs to the aqueous solution containing KHIs enhances the attraction to methane and weakens the driving force for hydrate formation. Therefore, the methane adsorption capacity of the hybrid inhibitors is suggested to be considered in the future development.

Wall heat transfer in the inverted annular film boiling regime

Inverted annular film boiling (IAFB) is one of the post critical heat flux (post-CHF) regimes, which may occur during the core reflooding phase following large-break loss of coolant accidents in water-cooled nuclear reactors. This paper first analyzes wall heat transfer characteristics and summarizes convective wall heat transfer coefficient correlations developed for the IAFB regime in the literature. Parametric effects of the inlet subcooling, mass flux, and pressure on the wall Nusselt number in the IAFB regime are studied. It is found based on the experimental data in the literature that the system pressure has negligible effect on the wall Nusselt number while the effects of the mass flux and inlet subcooling are complex and depend on the flow conditions. The modified Bromley model and laminar flow model with an enhancement factor for the IAFB regime, currently used in COBRA-TF and TRACE, respectively, are compared with Stewart’s experimental data under subcooled and low-quality conditions in the IAFB regime. Both of these two models under-predict the heat transfer coefficients calculated from Stewart’s experimental data for high flow and high subcooling conditions. Based on the analysis of the parametric effects, two new wall heat transfer correlations are proposed by correlating the Nusselt number and non-dimensional vapor film thickness using Stewart’s experimental data and benchmarked against the experimental data in the literature. These two new correlations cover ranges of the system pressure from 2.0 to 9.0 MPa, mass flux from 215 to 923 kg/m2-s, and inlet subcooling up to 50 °C.

The invalidation mechanism of kinetic hydrate inhibitors under high subcooling conditions

Vinyl lactam-based polymers have been shown to be excellent kinetic hydrate inhibitors (KHIs), inhibiting the formation and growth of methane hydrate under low subcooling conditions. However, under moderate/high subcooling conditions, they lose their inhibitory effect and can even be converted into hydrate promoters. In this work, molecular dynamics simulations were employed to explore the invalidation mechanism of two vinyl lactam-based KHIs, namely, PVP-A and PVP, under high subcooling conditions. By analyzing the nucleation and growth trajectories of methane hydrate in the absence/presence of KHIs, we found that the addition of KHIs could shorten the nucleation time of methane hydrate by reducing the mass transfer resistance of methane and water molecules and accelerating the formation of the hydrate precursor. Additionally, KHIs can facilitate the formation and survival of sII hydrate by improving the kinetic superiority of the methane-water homogeneous solution.

Quenching experiment on Cr-alloy-coated cladding for accident-tolerant fuel in water pool under low and high subcooling conditions

A transient pool boiling experiment was conducted to investigate the quenching performance of Cr-alloy-coated cladding in the simulated conditions of a loss-of-coolant accident (LOCA). Cr-alloy-coated cladding is a potential candidate for accident-tolerant fuel (ATF), which is developed to suppress hydrogen generation at high temperature in the event of an LOCA or beyond design basis accident. Cr-alloy-coated cladding and Zircaloy-4 cladding were used in the quenching experiment under low and high subcooling conditions, i.e., 0 °C and 50 °C. The thicknesses of the Cr-alloy-coated layer were 20 and 50 μm. Each cladding specimen was heated up to 600 °C in a furnace and quenched in a water pool at constant temperature. The quenching experiment showed the formation of film boiling and transition to nuclear boiling at the low subcooling temperature of 0 °C. No film boiling was observed at high subcooling at 50 °C. The effect of surface roughness was found to be insignificant for quenching performance. Rather, cladding oxidation, particularly for the Zircaloy-4 specimens, had a remarkable influence on the minimum film boiling temperature (MFBT) and quenching time. The Cr-alloy-coated cladding did not show the effect of surface oxidation as expected because of very low cladding oxidation. There is no significant difference in the quenching performance of the Zircaloy-4 cladding and the Cr-alloy-coated cladding at the high subcooling temperature of 50 °C. Furthermore, the Cr-alloy-coated cladding tends to decrease the quenching time with higher MFBT as the coating thickness decreases.

MODELING OF DEPARTURE FROM NUCLEATE BOILING

Modeling of departure from nucleate boiling (DNB) essentially requires predicting key parameters like bubble departure diameter and nucleation site density. Based on experimental evidence, different hypotheses of DNB occurrence have been envisaged. Among them, the bubble crowding model performs well under high subcooling conditions. Validations of the DNB model are required under a wide range of operating and geometrical conditions. With the scarcity of experimental data for bubble departure diameter and nucleation site densities at high pressure conditions it is difficult to validate the models. It is observed that the computational Quid dynamics model's performance is good compared to mechanistic models, especially for high pressure conditions. The DNB models are still evolving and are less matured as compared to the dry-out modeling of annular flow regime, which has a definite flow pattern and can be mechanistically treated with significantly less uncertainty. On the contrary, DNB involves agitated bubbles, and bubble dynamics are very complex, hence it is a challenging task to mechanistically treat the same. This chapter provides the state-of-the-art approach for predicting the DNB and describes the gray areas requiring further effort for understanding the physics of the same.

Thermal hydraulic performance analysis of a post-CHF heat transfer test facility

Post critical heat flux (post-CHF) heat transfer may occur in loss of coolant accidents (LOCAs) in water-cooled nuclear reactors when makeup water quenches the uncovered fuel rods in the reactor core. The post-CHF regimes are characterized by low heat transfer coefficient and high wall temperature due to the vapor-wall contact. A good understanding of the hydrodynamics and heat transfer process in the post-CHF regimes, especially low-quality film boiling, such as inverted annular film boiling (IAFB) and inverted slug film boiling (ISFB), is imperative for accurately modeling the post-CHF phenomena and predicting the fuel rod cladding temperature and void fraction during accidents. This paper first discusses limitations of existing post-CHF hydrodynamics and heat transfer models/correlations and then identifies needs of post-CHF experimental data under high-flow and high-pressure conditions for model improvement. To narrow down the gap in the available experimental data, a Post-CHF Heat Transfer (PCHT) test facility is designed to perform quasi-steady-state low-quality film boiling experiments under high-pressure (ranging from 0.14 to 3.45 MPa), high-flow (ranging from 150 to 2000 kg/m2-s), and high inlet subcooling (up to 50 °C) conditions. In addition to the experimental study, a numerical model using COMSOL Multiphysics tool is developed to inform the test section design and to investigate wall heat flux and wall temperature distributions in the post-CHF regimes. The COMSOL Multiphysics simulation results show that quasi-steady-state post-CHF phenomena can be achieved in the PCHT test section. Considering thermal non-equilibrium conditions in the post-CHF regimes, a one-dimensional two-fluid model is implemented into a computer code to predict the void fraction using the wall temperature information obtained from the COMSOL simulation results. A correlation for the liquid-side Nusselt number is obtained for the IAFB regime based on previous experimental data and is implemented into the code, which results in an improvement in the agreement between the calculated void fraction and corresponding experimental data. With the new Nusselt number correlation, a parametric study of the effects of the heat flux, pressure, mass flux, and inlet subcooling on the liquid-side Nusselt number is studied. In addition, flow regime transition in the post-CHF regimes is studied by comparing the existing correlation and experimental data. Furthermore, the Weber number and liquid-side Nusselt number are calculated to examine whether there exists any correlation between these two non-dimensional numbers and the flow regime transition. The simulation results provide insights for design improvement of the PCHT test section and assist the development of a test plan for future IAFB and ISFB tests under high-pressure, high-flow, and high-subcooling conditions in the PCHT test facility.

Effect of salt and water cuts on hydrate anti-agglomeration in a gas condensate system at high pressure

Anti-agglomerants (AAs) can be effective molecules in gas hydrate flow assurance in deep-water at high subcooling conditions. Salt and water cut (ratio of water volume to total liquid volume) may have a major effect on hydrate anti-agglomeration. The understanding of the effect of salt and water cut on hydrate anti-agglomeration is limited. There has been no systematic investigation of anti-agglomeration in water-cuts in the 10 to 100% range in rocking cell apparatus at high pressure. In this work, we conduct a systematic investigation of the effect of NaCl and water cut on the performance of a non-ionic anti-agglomerant which is effective at high water cuts (up to 100%). We use a condensate liquid as the liquid hydrocarbon phase and methane as hydrate former to conduct a systematic investigation of the effect of water cut and salt on anti-agglomeration at high pressure. At a low water cut of 10%, the salt makes the AA ineffective. At 20% water cut, NaCl does not have an appreciable effect on AA performance. In water cuts in the range of 30 to 100%, 1wt% AA becomes effective when there is limited amount of NaCl in the aqueous phase. The effect of NaCl includes lowering of water to hydrate conversion and decreasing the solubility of AAs in water. At 95% water cut the mixtures of condensate, salt, water/brine, and AA form a very viscous emulsion. Addition of alcohol allows anti-agglomeration in this complex mixture. The measurements over a broad range of water cuts reveal formation of water-in-oil and oil-in-water emulsions as well as flocculation. To shed light on the mechanisms we perform emulsion studies and measure AA partitioning between the aqueous phase and the hydrocarbon phase. This study presents the mechanisms that their understanding may be essential in application of AA in a broad range of water cuts.

Prevention of methane hydrate re-formation in transport pipeline using thermodynamic and kinetic hydrate inhibitors

Methane gas produced from marine hydrate deposits will flow together with dissociated water in two phases, and the risk of hydrate reformation must be managed. This study used the OLGA multiphase flow simulation software to simulate methane transportation with dissociated water through a vertical 2160m pipeline in order to determine the amount of monoethylene glycol (MEG) as a thermodynamic hydrate inhibitor. When the hydrate saturation ratio in hydrate deposits varies, a large amount of MEG becomes inevitable. Moreover, when undesired water breakthrough occurs, the MEG concentration would decrease to where hydrates may re-form before responding in the offshore platform. A risk management strategy for hydrate reformation is investigated by adopting under-inhibition with MEG and the addition of PVCap as a kinetic hydrate inhibitor (KHI). The experimental results in high pressure autoclave showed that PVCap exhibited a limited performance in delaying the hydrate formation in a high subcooling condition. Considering the vertical flowline of 2160m, the delay time was not sufficient to prevent the hydrate re-formation in the transport pipeline. Complete prevention of hydrate re-formation can be avoided with 35wt% MEG concentration, however decreasing the MEG concentration to 20wt% was also feasible in order to avoid hydrate formation since it was not observed for more than 960min. In the presence of 0.1wt% of PVCap and 10wt% MEG, the hydrate delay time was of about 311.5min. This delay time is 76% longer than the residence time of methane and water mixture in the transport pipeline, thus this synergistic inhibition can significantly reduce the injection rate of MEG while preventing hydrate formation. This is the first work suggesting a risk management strategy for hydrate reformation in hydrate production system, and thus will provide insights to develop advanced hydrate production technologies.

An investigation on flashing instability induced water hammer in an open natural circulation system

The flashing instability induced water hammer phenomenon (FIIWH) is firstly found in an open natural circulation experimental facility, which is used to study the thermalhydraulics characteristic of natural circulation style PCS. The primary mechanism of the FIIWH is that, the periodic movement of flashing front in the upwards channel leads to the periodic violent changes of the local pressure and temperature at the underpart of upwards channel. However, the pressure change rate is more rapid than temperature, which causes the alternately transforms of water from superheated and subcooled at the underpart of upwards channel, and results in the periodic violent evaporation and steam condensation process there. Among them, the rapid condensation causes the sudden acceleration and collision of water columns and forms a transient high pressure peak i.e. the FIIWH. Besides, the horizontal tube at the underpart of upwards channel (pipeline structure) also makes an essential effect on the FIIWH.Furthermore, the influence factors on the region and intensity of FIIWH, e.g. the heating tube outlet temperature, inlet subcooling, loop structure and non-condensable gas in water are experimental studied in detail. The initial and terminal conditions of the FIIWH are also found out by experiments. And the contour map describing the scope and intensity of the FIIWH are drawn in this paper.Finally, a simplified numerical model is carried out to simulate the pressure peak of the FIIWH. The simulation result shows a good agreement with the experimental result on the low inlet subcooling conditions, while it has a disparity with the experiment result on the high inlet subcooling conditions. And the deviation reason and improvement orientation of the model are analyzed in this paper.

Improvement of TASS/SMR code using a simple correlation for subcooled boiling flow prediction

SMART, which was an advanced integral type small modular PWR, was developed by KAERI (Kim et al., 2014). To analyze the thermal hydraulic phenomena including behaviors at the SMART specific components, the TASS/SMR code which can predict a heat transfer for various thermal hydraulic conditions, has been developed. Information of the void distribution in a subcooled boiling flow is important in predicting the inception of a two-phase flow and an onset of the critical heat flux condition. The TASS/SMR code adopts an energy partitioning method and a critical enthalpy correlation determining a point of net vapor generation for subcooling conditions. A range of the subcooling degree investigated is 1.5–50.6K to validate the method for a subcooled boiling flow prediction. The TASS/SMR code predicts well the void distribution along the height for the subcooled boiling flow conditions compared with the experimental data. The predicted location of the onset of void generation is simulated well at most investigated conditions and delayed slightly at the very high subcooling condition.

Experimental study of the formation and deposition of gas hydrates in non-emulsifying oil and condensate systems

Potential flow assurance problems in oil and gas pipelines related to gas hydrates have traditionally been resolved by implementing avoidance strategies, such as water removal, insulation, and injection of thermodynamic inhibitors. As a means of lowering development and operational costs in the industry, hydrate management is becoming a more viable approach, a strategy which seeks to minimize the risk of plugging conditions using methods that allow transportability of hydrate slurries with the hydrocarbon production fluids. A thorough understanding of how hydrates form and behave in different multiphase systems is essential for safe implementation of various hydrate management methods. In order to increase insight into the different processes leading to hydrate plug conditions, a number of experiments have been performed using a visual rocking cell to measure and observe the various stages of hydrate formation, deposition and accumulation during continuous mixing and motion induced by the oscillation of the rocking cell. The fluid combinations studied in these experiments considered oil+water+gas and condensate+water+gas. The effects of added monoethylene glycol (MEG) and a model anti-agglomerant (AA) were also studied in some of the experiments. The experiments showed that hydrate deposition is prevalent in all systems studies, but it was observed that there was a higher tendency to deposit on surfaces exposed to condensate or the gas phase than on oil wetted surfaces. Hydrate growth, agglomeration and bedding were observed in the experiments. Highly porous hydrate deposits formed in conditions with a large temperature gradient between the bulk and the surface, and high subcooling conditions, then suffering from sloughing due to the shear of the fluids on the deposit. Hydrate formation in an experiment with mineral oil, 30% water cut and anti-agglomerant resulted in transportable hydrate slurry. Both the condensate and mineral oil tested were non-emulsifying, but shear-stabilized dispersion of the liquid phases was created prior to hydrate formation by mixing induced by the motion of the cell. Interestingly, the dispersion appeared to completely phase-separate, momentarily, upon hydrate formation onset.

The characteristics of premature and stable critical heat flux for downward flow boiling at low pressure in a narrow rectangular channel

Flow instability and critical heat flux (CHF) especially for downward flow of water in a vertical narrow rectangular channel heated from both sides were experimentally investigated. The gap, width, heated width, and heated length of the channel were 2.35, 40, 30, and 350mm, respectively. The flow boiling was developed as the wall heat flux was increased for the imposed mass flux of 500 and 1000kgm−2s−1 for high inlet subcooling (52–74K) conditions under atmospheric pressure. In this paper, the unstable boiling flow was investigated by monitoring the channel pressure drop and high speed visualization for side view of boiling (HSV-SVB) with the back-lighting method. The results showed that an irremovable pressure drop fluctuation was involved in the flow boiling after the distinct initiating point called as the onset of pressure drop fluctuation (OPDF). We determined that coalescence of bubble (or vapor) layers on opposing heated surfaces triggered the OPDF, since an abrupt increase of pressure drop was occurred as the expansion of the liquid–vapor interface became bounded by the other layer on the opposite side. The fluctuation was amplified as the exit quality was increased and the flow regime passed through the unstable slug or churn flow. For a low inlet throttling condition, premature CHF was induced at the maximum fluctuation during those flow regimes. On the other hand, stable CHF was obtained in the re-stabilized flow regime as the annular flow was developed only for large inlet throttling conditions with an additional pressure drop across the valve of more than 0.4bar for our experimental configuration.

An Experimental Study on the Synergetic Effects of Kinetic and Thermodynamic Gas Hydrate Inhibitors

Gas hydrate can be inhibited by using hydrate inhibitors, such as thermodynamic inhibitors (e.g., methanol and salts) and kinetic inhibitors (KHIs; polymer based). The study of kinetic hydrate inhibitors is paid growing attention in recent years because of its low dosage and environment friendly features, but its application is restricted at high sub-cooling conditions. In this study, the combination of kinetic hydrate inhibitor (polyvinylcaprolactam based) and thermodynamic inhibitors (methanol and NaCl) was investigated in terms of the synergetic effect of the two types of hydrate inhibitors and the effects of pressure and sub-cooling time on the kinetic inhibition effect. The results show that the combined system has a good synergetic effect, which can make the KHIs to stand at higher sub-cooling conditions. The performance of polyvinylcaprolactam and methanol is better than that of polyvinylcaprolactam and NaCl, and the combined system can be also greatly affected by high pressure and long sub-cooling time.

Effectiveness of Alcohol Cosurfactants in Hydrate Antiagglomeration

Hydrates are crystalline inclusion compounds where hydrogen bonded water molecules form cages to trap small hydrocarbon and nonhydrocarbon molecules. Under high subcooling conditions, these crystals grow rapidly into large pieces and may cause enormous problems in transport and deepwater oil capture. One of the most effective methods to address gas hydrate problems is through the formation of small hydrate particles in the nanometer or micrometer range dispersed in the fluid phase. In this approach, special surfactants are required, which are called antiagglomerants (AAs). However, there are major limitations when salt is present in water and when volume ratio of water in fluid (i.e., watercut) is high. In this work, we investigate a wide range of alcohols as cosurfactants along with the rhamnolipid as AA in a multiple screening-tube rocking apparatus by monitoring the temperature of vials and morphology of mixtures. The results show medium-sized alcohols, such as isopropanol (IPA), are effective cosurfac...