Method of producing gas hydrate in two or more hydrate forming r

Details Method of producing gas hydrate in two or more hydrate forming r Method of producing gas hydrate in two or more hydrate forming r

1997-10-07

2000-08-29

Griffin, Walter D.

Chemistry of hydrocarbon compounds

Hydrate or production thereof

C07C 720

Patent

active

061111554

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a method of producing gas hydrate from an hydrate forming gas.
The hydrate forming gas may be substantially a single gaseous substance, or the hydrate forming gas may comprise a mixture of hydrate forming gaseous substances, for example natural gas.
A gas hydrate is an ice-like crystal structure comprising mainly water molecules and during the formation of the hydrate the gas molecules are incorporated into molecular scale cavities within the crystal structure. A unit volume of typical hydrate can contain in excess of 100 volumes of gas when the gas is measured at 20.degree. C. and atmospheric pressure.
Hydrates can only be formed by a limited range of gaseous compounds including methane, ethane, propane, butane, carbon dioxide, hydrogen sulphide, tetra-hydro furan, and chlorofluorocarbons. The first six of these gaseous compounds form the bulk of most natural gas fields.
FIG. 1 of the drawings shows a calculated hydrate equilibrium curve for a typical North Sea natural gas composition, in which the curve represents the pressure and temperature conditions at which the natural gas hydrate forms. Thus gas hydrate forming conditions for this particular natural gas are when it is at pressure and temperature values which are either on the curve or to the left-hand side of the curve. The natural gas to which FIG. 1 relates is of the following composition or mixture of gaseous substances in mol %:


______________________________________ Gaseous Substance mol % ______________________________________ Nitrogen 2.07 - reluctant to form hydrate Carbon Dioxide 0.575 - forms hydrate Methane 91.89 - forms hydrate Ethane 3.455 - readily forms hydrate Propane 0.900 - easily forms hydrate Butane 0.395 - easily forms hydrate Pentane 0.177 - non-hydrate former Hexane 0.0108 - non-hydrate former Heptane 0.0105 - non-hydrate former Octane 0.0102 - non-hydrate former Water 0.5065 - non-hydrate former ______________________________________
Under appropriate conditions of pressure and temperature known to those skilled in the art the mixing of a hydrate forming gas with water results in the formation of the gas hydrate.
According to the invention a method of producing a gas hydrate from an hydrate forming gas comprises passing the gas into an hydrate forming region in which hydrate of the gas is formed and passing residual gas which has not formed hydrate in said region from said region into at least one other hydrate forming region in which hydrate of said gas is formed.
The invention will now be further described, by way of example, with reference to the accompanying drawings in which:
FIG. 2 is a diagramatic section of a pressure vessel used in the method according to the invention;
FIG. 3 is a diagramatic section on line III--III in FIG. 2;
FIG. 4 is a perspective view on a larger scale than FIG. 2 of a gas distribution nozzle used in the pressure vessel in FIG. 2;
FIG. 5 shows diagramatically a plant for forming gas hydrate by the method according to the invention using a plurality of pressure vessels each of the kind in FIG. 2;
FIG. 6 shows diagramatically another array of such pressure vessels which can be substitutes for the array of pressure vessels in FIG. 5, and
FIG. 7 shows diagramatically another embodiment of a pressure vessel which can be used in the method according to the invention and can be used as an alternative to the plurality of pressure vessels in the plant in FIG. 5.
In the drawings like reference numerals or letters identify similar or comparable parts. Also the drawings have been simplified by omitting therefrom certain flow direction control valves, fluid pressure control valves and pumps which the skilled addressee will readily be able to provide to operate the plant.
With reference to FIGS. 2 to 4 a pressure vessel or chamber A of generally cylindrical shape has a plurality of substantially radially disposed baffle plates 2 extending along the interior of the vessel and spaced from an interior wall of the vessel. Leading into a bo

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