Fuel Gas Hydrate Formation Probability Distributions on Quasi-free Water Droplets

Abstract

We systematically studied the formation probability distributions of methane−propane (C 1 /C 3 ) mixed gas hydrates on a quasi-free water droplet as a function of the mixed gas pressure of up to 14 MPa. It was found that the maximum achievable subcooling temperature (ΔT) distributions of C 1 /C 3 mixed gas hydrates on a quasi-free water droplet were significantly greater than those on a water sample contained in a glass sample cell, for all of the mixed gas pressures studied. The most probable subcooling was on average around 31 K on quasi-free water droplets, which was significantly greater than that on the water sample in a glass sample cell of around 14 K. The minimum subcooling was around 18 K on a quasi-free water droplet, which was significantly greater than that on a water sample in a glass sample cell of 4 K. The width of the T f distribution showed a wide variation, from 6 to 22 K. This range of variation was similar to that of a water sample contained in a glass sample cell. We also carried out a series of control experiments using nitrogen gas at elevated gas pressures to decouple the C 1 /C 3 mixed gas hydrate formation events from the ice formation events. Finally, the effect of ethanol vapor, a thermodynamic hydrate inhibitor (THI), which had been reported to enhance the rate of methane hydrate growth when seeded with ice, was also studied. The results showed that ethanol vapor reliably inhibited nucleation of C 1 /C 3 mixed gas hydrate at all gas pressures studied.

Statistical Study of the Memory Effect in Model Natural Gas Hydrate Systems

“…It is not possible to repeat the measurement of a particular nucleation event and produce a standard deviation from the resulting ensemble, because each nucleation event is stochastic (i.e., not repeatable). In our previous studies, we showed the whole range of nucleation probability distribution in the form of “stochasticity bars”. ,, A “stochasticity bar” is not a traditional error bar or standard deviation of a Gaussian distribution but includes both the ubiquitous random error and the genuine stochasticity that is unique to nucleation phenomena. In the current study, however, the “net amount” of the memory effect is defined as the most probable difference between two probability distributions.…”

“…We have been developing a class of high pressure automated lag time apparatus (HP-ALTA) over the last several years. − HP-ALTA can repeatedly apply hundreds of linear cooling ramps to a small volume of sample water under an isobaric condition of up to 15 MPa and record the maximum achievable subcooling for each cooling ramp. Because of the extremely long induction times involved in the nucleation phenomena of gas hydrates at shallow subcoolings, a systematic study of induction time distributions at constant subcoolings has not been feasible without introduction of an arbitrary cutoff maximum waiting time. , Instead, we select an approach to use the maximum achievable subcooling distributions as a measure of nucleation probability distributions of gas hydrates.…”

Interfacial Nanobubbles and the Memory Effect of Natural Gas Hydrates

“…This may not be surprising given that the heterogeneous nucleation rate of gas hydrates was measured only very recently in the absence of a solid wall. 8,29,30 In the present study, we investigated the nucleation rates of natural gas hydrates in the absence of a solid wall (with the use of a quasi-free water droplet suspended in squalane) and compared the results to those in the presence of a solid wall to assess the impact of a solid wall on the memory effect. It was found that the memory effect was not detected in the quasi-free water droplet, which supported the idea that the presence of a solid wall is required for the manifestation of the memory effect.…”

“…No attempt has hitherto been made to investigate the memory effect in the absence of a solid wall, even though its presence has been invoked as a possible cause of the memory effect. This may not be surprising given that the heterogeneous nucleation rate of gas hydrates was measured only very recently in the absence of a solid wall. ,, …”

Synergistic effect of combination of surfactant and oxide powder on enhancement of gas hydrates nucleation

“…Distribution functions for accessible supercooling in hydrate nucleation (methane, a mixture of methane and propane) on the surface of water were studied by Maeda et al [20] . The studies were continued in the works dealing with heterogeneous nucleation of hydrates on quasi-free water drops, for the purpose of obtaining an empirical description of the regularities under investigation [21,22] . The effect of the type of hydrate-forming agent on hydrate nucleation was studied [23] .…”