Effect of Reciprocating Impact on Methane Hydrate Formation and Dissociation

Morphology observation is an important approach to studying the mechanism of one method of improving hydrate formation. In this study, morphology change in methane hydrate formation and dissociation was investigated at 274.15 K to study the promoting mechanism of reciprocating impact on hydrate formation. The results suggested that, under reciprocating impact, a synthetic effect consisted of the agitating of water and the extruding of water, and the forming and fracturing of hydrate shells significantly improved the hydrate formation. The hydrate shells formed in hydrate slurry were the key factor that affected the formation kinetics in hydrate slurry and after the hard hydrate block had formed. On the basis of the excellent water conversion under reciprocating impact, the impact method was adopted to study the re-formation of methane hydrate. The results indicated that the memory effect not only affected the nucleation rate but also influenced the gas storage capacity and the morphology of re-formed hydrate. The performance of the memory effect in hydrate re-formation perhaps was affected by the melting time via regulating the amount of residual structures in the meltwater. The induction time was found to increase with the decrease of the melting time. The storage capacity of the re-formed hydrate increased with the increase of melting time, and when hydrate re-formed in meltwater that experienced a long melting time, the storage capacity of re-formed hydrate was close to that formed in fresh water. Conversely, a large amount of free water remained in the reactor when meltwater with short melting time was used. The results of this study could be helpful in improving the impact reactor and applying the memory effect to accelerate hydrate formation.

Automated summary

Morphology observation is an important approach for studying hydrate formation mechanisms. The study found that under reciprocating impact, forming and fracturing of hydrate shells significantly improved hydrate formation, and the memory effect during re-formation affected nucleation rate and gas storage capacity.