Method for recovering power according to a cascaded Rankine cycle by gasifying liquefied natural gas and utilizing the cold potential

Claim 1

A method for recovering power according to a cascaded Rankine cycle in which liquefied natural gas is gasified and the cold potential thereof is utilized, comprising the steps of selecting a first medium having a low pressure cooling curve substantially corresponding to a vaporizing curve in gasifying the liquefied natural gas as a mixture of hydrocarbons having 1-6 carbon atoms or a mixture of halogenated hydrocarbons of boiling points close to those of said hydrocarbons, using the first medium in a first Rankine cycle with the liquefied natural gas as a low temperature source, exchanging heat of the liquefied natural gas and high pressure first medium with the low pressure first medium in the first Rankine cycle at a first multifluid heat exchanger during the first Rankine cycle, thereby completely condensing said low pressure first medium, vaporizing said liquefied natural gas and vaporizing said high pressure first medium in the first Rankine cycle, using a first pump means to pressurize said condensed first medium to provide said high pressure flat medium between two successive passages of said first medium through said multifluid heat exchanger, using a first turbine for recovering the power generated during the first Rankine cycle, selecting a second medium, having a higher boiling point than said first medium and having a low pressure cooling curve substantially corresponding to a vaporizing curve of said first medium at a high pressure, from the group consisting of a single hyudrocarbon component having 1-6 carbon atoms of a mixture thereof; one or more halogenatedd hydrocarbons having a boiling point close to that of said hydrocarbon components having 1-6 carbon atoms; and ammonia, using said second medium in a second Rankine cycle, cascading said first and second Rankine cycles by using part of said first Rankine cycle as the low temperature source for said second Rankine cycle, exchanging heat of said second medium at a low pressure in the second Rankine cycle with the high pressure first medium after said first multifluid heat exchanger in the first Rankine cycle at a heat exchanger during the cascading of the first and second Rankine cycle, thereby completely condensing said second medium in the second Rankine cycle and further vaporizing said high pressure first medium, using a second pump means to pressurize said condensed second medium, and using a second turbine to recover power during the second Rankine cycle.

Claim 2

A method for recovering power according to a cascaded Rankine cycle in which liquefied natural gas is gasified and the cold potential thereof is utilized, comprising the steps of selecting a first medium having a low pressure cooling curve substantially corresponding to a vaporizing curve in gasifying the liquefied natural gas as a mixture of hydrocarbons having 1-6 carbon atoms or a mixture of halogenated hydrocarbons of boiling points close to those of said hydrocarbons, using the first medium in a first Rankine cycle with the liquefied natural gas as a low temperature source, exchanging heat of the liquefied natural gas and high pressure first medium with the low pressure first medium in the first Rankine cycle at a first multifluid heat exchanger during the first Rankine cycle, thereby completely condensing said low pressure first medium, vaporizing said liquefied natural gas and vaporizing said high pressure first medium in the first Rankine cycle, using a first pump means to pressurize said condensed first medium to provide said high pressure flat medium between two successive passages of said first medium through said multifluid heat exchanger, using a first turbine for recovering the power generated during the first Rankine cycle, selecting a second medium, having a higher boiling point than said first medium and having a low pressure cooling curve substantially corresponding to a vaporizing curve of said first medium at a high pressure, from the group consisting of a single hyudrocarbon component having 1-6 carbon atoms of a mixture thereof; one or more halogenatedd hydrocarbons having a boiling point close to that of said hydrocarbon components having 1-6 carbon atoms; and ammonia, using said second medium in a second Rankine cycle, cascading said first and second Rankine cycles by using part of said first Rankine cycle as the low temperature source for said second Rankine cycle, exchanging heat of said second medium at a low pressure in the second Rankine cycle with the high pressure first medium after said first multifluid heat exchanger in the first Rankine cycle at a heat exchanger during the cascading of the first and second Rankine cycle, thereby completely condensing said second medium in the second Rankine cycle and further vaporizing said high pressure first medium, using a second pump means to pressurize said condensed second medium, and using a second turbine to recover power during the second Rankine cycle.

Claim 6

A method according to any one of claims 2, 3, 4 or 1, wherein the liquefied natural gas and the high pressure first medium are both at substantially the same temperature after said first exchanging step.