Structure-I and Structure-H Hydrate Formation Using Water Spraying

Abstract

An attempt has been made to form continuously either a structure-I or a structure-H hydrate using methane as the common guest substance and methylcyclohexane as the second guest for the structure-H hydrate. The experimental technique we tested was to spray water into a high-pressure chamber charged with methane gas. In the experiments to form the structure-I hydrate, water droplets sprayed from a single nozzle at the top of the chamber coalesced into a water pool underlying the methane gas phase. In the experiments to form the structure-H hydrate, the water droplets fell onto a methylcyclohexane layer superposed on a pool of water then merged with the pool. Water was continuously drained from the bottom of the chamber and circulated back through the spray nozzle. During this circulation, the water passed through a heat exchanger outside the chamber to release the heat generated by hydrate formation. The pressure in the chamber was maintained at a prescribed level (typically 2.5−3.7 MPa) by supplying methane gas through a port at the top of the chamber. The rate of methane flowing into the chamber was continuously measured to determine the instantaneous rate of hydrate formation in the chamber. The results of the measurements indicate that comparable methane-storing rate may be obtained for structure-H and structure-I hydrates, but with the structure-H hydrate formed at lower pressures. The process of hydrate formation was observed visually through a pair of glass windows in the chamber wall, alternatively using a digital video camera and a microscope connected to a high-speed video-recording system. This paper discusses the mechanisms of hydrate formation revealed by these observations and by the measurements of the rate of hydrate formation.

On the Scale-up of Gas-Hydrate-Forming Reactors: The Case of Gas-Dispersion-Type Reactors

“…The injection of discrete gas bubbles in a continuous aqueous phase [3][4][5]8] or the spraying or sprinkling of liquid water in a continuous gas phase [9][10][11][12][13] significantly increases the gas-liquid interfacial area across which the gas dissolves into the aqueous phase, thereby promoting the hydrate formation at, or in the vicinity of, the interface. Such an external work for dispersing either the fluid phase into the other may be neglected in the case that a surfactant is added to the aqueous pool occupying a lower portion of the tank-shaped reactor, resulting in a capillarity-driven, spontaneous hydrate-layer growth over the reactor wall above the free surface of the quiescent aqueous pool (consult, for example [14][15][16]).…”

“…In general, these methods may be broadly divided into two types: one is to directly cool each reactor itself [4,5,10] or a specific location inside the reactor [22], and the other is to pump the liquid water (or a hydrate slurry) through an external loop in which a heat exchanger is installed [8,9,11]. The latter type may be extended such that, in addition to the water circulation, a hydrophobic liquid coolant is circulated through a separate loop to be cooled to a temperature far below the water freezing point, thereby conveying a large cool energy to the reactor [23][24][25].…”

Capture of carbon dioxide from flue or fuel gas mixtures by clathrate crystallization in a silica gel column

“…Mori (2003) reviewed and discussed the various hydrate formation vessels and their limitations. For example, other arrangements such as bubbles dispersed in water or water droplets injected into a gas atmosphere have been proposed (Gudmundsson et al, 2000;McCallum et al, 2007;Ohmura et al, 2002;Tsuji et al, 2004). Tsouris and co-workers have presented novel and efficient crystallizers in the context of CO 2 sequestration work (Lee et al, 2003;Tsouris et al, 2004Tsouris et al, , 2007West et al, 2001).…”

Static Formation and Dissociation of Methane+Methylcyclohexane Hydrate for Gas Hydrate Production and Regasification

“…The kinetic behaviors of sH methane hydrate formation and decomposition with stirring or spraying have been studied by several researchers [9][10][11][12][13][14]. According to their studies, the rate of methane fixation by sH hydrate formation at lower pressures may even exceed that by sI hydrate formation at higher pressures [11,15].…”