2947 r2010 American Chemical Society pubs.acs.org/EF Energy Fuels 2010, 24, 2947–2955 : DOI:10.1021/ef901220m Published on Web 04/14/2010 Recovery of Methane from a Variable-Volume Bed of Silica Sand/Hydrate by Depressurization Cef Haligva, † Praveen Linga, † John A. Ripmeester, ‡ and Peter Englezos* ,† † Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3, and ‡ Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6 Received October 26, 2009. Revised Manuscript Received April 1, 2010 Methane hydrate was formed in water occupying the interstitial spaces of a cylindrical bed of silica sand particles. The sand particles have an average diameter equal to 329 μm. The amount of methane consumed during the experiment (methane gas uptake) was determined through pressure and temperature measure- ments and mass balance calculations. Three different sized beds of silica sand particles were used. Water conversion to hydrates in the range of 73-84% was achieved for all of the formation experiments. Hydrate formation was followed by decomposition at 4.0 °C driven by depressurization at 3.1 MPa (nine experiments) and 2.3 MPa (one experiment). Methane recovery measurement curves were determined for each experiment. The initial rate of recovery was found to be strongly dependent on the silica sand bed size. The rate of recovery was found to depend weakly on the size during the second stage, and after 1.25 h, it was constant. During decomposition at 2.3 MPa, the temperature in some locations inside the bed dropped below the freezing point of water and the gas recovery rate was enhanced. This is in agreement with recently reported conclusions by Tsypkin [Fluid Dynamics 2005, 40 (1), 117-125] and Zhou et al. [Ind. Eng. Chem. Res. 2009, 48 (6), 3142-3149]. Finally, the gas recovery data was correlated with an empirical model with one parameter that was found to depend linearly on the bed size. 1. Introduction Efforts to extract natural gas from naturally occurring gas hydrates in the Earth date back to the early 1980s. 3-8 It is estimated that natural gas trapped in solid gas hydrates in the Earth represents a potentially huge resource. 9-12 Holder et al. 13 concluded that the decisive factors that enable a gas hydrate reservoir to produce gas efficiently are the reservoir porosity and the thermal properties of the hydrates and reservoir. Other than these factors, knowledge of the rate of hydrate decomposition is also required. In order to assess the feasibility of producing natural gas from the Earth’s hydrates, reservoir-specific infor- mation, together with laboratory data and models, is needed. 14 *To whom correspondence should be addressed. Tel: 1-604-822- 6184. Fax: 1-604-822-6003. E-mail: englezos@interchange.ubc.ca. 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