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A method for vaporizing a liquid stream includes cycling a heat transfer fluid in a closed circuit; feeding the heat transfer fluid to a first heat transfer zone; feeding a liquid stream to be vaporized to the first heat transfer zone; providing heat from the heat transfer fluid to the liquid stream

A method for vaporizing a liquid stream includes cycling a heat transfer fluid in a closed circuit; feeding the heat transfer fluid to a first heat transfer zone; feeding a liquid stream to be vaporized to the first heat transfer zone; providing heat from the heat transfer fluid to the liquid stream in the first heat transfer zone thereby vaporizing the liquid stream and at least partially condensing the heat transfer fluid; removing the vaporized liquid stream and the at least partially condensed heat transfer fluid and passing the latter to a second heat transfer zone; providing heat from ambient air to the at least partially condensed heat transfer fluid thereby vaporizing the heat transfer fluid; recycling the vaporized heat transfer fluid to the first heat transfer zone using gravitational force exerted on the heat transfer fluid being cycled in the closed circuit.

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1. A method for vaporizing a liquid stream, the method at least comprising the steps of: a) feeding a heat transfer fluid to a first heat transfer zone, the heat transfer fluid being cycled in a closed circuit;b) feeding a liquid stream to be vaporized to the first heat transfer zone;c) providing he

1. A method for vaporizing a liquid stream, the method at least comprising the steps of: a) feeding a heat transfer fluid to a first heat transfer zone, the heat transfer fluid being cycled in a closed circuit;b) feeding a liquid stream to be vaporized to the first heat transfer zone;c) providing heat from the heat transfer fluid to the liquid stream across a heat transfer surface in the first heat transfer zone thereby vaporizing the liquid stream and at least partially condensing the heat transfer fluid;d) removing the vaporized liquid stream obtained in step c);e) removing the at least partially condensed heat transfer fluid obtained in step c) and passing the at least partially condensed heat transfer fluid to a second heat transfer zone such that the at least partially condensed heat transfer fluid flows from the first heat transfer zone into a downward flowing part, wherein the heat transfer fluid flows downward in the downward flowing part;f) providing heat from ambient air to the at least partially condensed heat transfer fluid across a heat transfer surface in the second heat transfer zone thereby vaporizing the heat transfer fluid;g) recycling the vaporized heat transfer fluid to the first heat transfer zone wherein the vaporized heat transfer fluid flows upward in an upward flowing part and from the upward flowing part into the first heat transfer zone;wherein the upward flowing part is provided with heat transfer improvers and wherein the downward flowing part is not provided with heat transfer improvers, wherein the heat transfer fluid is recycled in step g) using gravitational force exerted on the heat transfer fluid being cycled in the closed circuit; and, wherein the first heat transfer zone is supported by a support frame, said support frame comprising through going holes for indirectly exchanging heat between the heat transfer fluid and the ambient air. 2. The method according to claim 1, wherein no pump is used for circulation of the heat transfer fluid in the closed circuit. 3. The method according to claim 1, wherein the heat transfer fluid comprises more than 90 mole % CO2. 4. The method according to claim 1, wherein the heat transfer fluid is cycled at a pressure in the closed circuit and wherein the heat transfer fluid has a boiling point below 5° C. at the pressure. 5. Method according to claim 4, wherein the heat transfer fluid comprises a compound that is selected from the group consisting of CO2, ethane, ethene, propane, propene, butane and a mixture thereof. 6. The method according to claim 1, wherein the heat transfer fluid comprises 100 mole % CO2. 7. The method according to claim 1, wherein the heat transfer fluid is cycled at a pressure in the closed circuit and wherein the heat transfer fluid has a boiling point from −10 to 0° C. at the pressure. 8. The method according to claim 1, wherein said heat transfer improvers comprise at least one of fins and grooves. 9. The method according to claim 1, wherein the downwards flowing part and the upwards flowing part are separated by a separation wall. 10. The method according to claim 9, wherein the separation wall is thermally insulated. 11. The method according to claim 1, wherein the second heat transfer zone comprises separate tubes or bundles of tubes for the downwards flowing part and the upwards flowing part. 12. The method according to claim 1, wherein said heat transfer improvers improve transfer of heat from the ambient air to the heat transfer fluid. 13. The method according to claim 1, wherein the liquid stream to be vaporized is a liquefied natural gas stream. 14. The method according to claim 13, further comprising obtaining the liquefied natural gas stream from a source by use of a pump, whereby the pump passes the liquefied natural gas stream to the first heat transfer zone in step b). 15. The method according to claim 14, further comprising obtaining a gaseous natural gas stream in step c) and sending the gaseous natural gas stream to a gas pipe network. 16. The method according to claim 15, further comprising a back-up heater to provide extra heat to at least one of the heat transfer fluid, the liquefied natural gas stream, and the gaseous natural gas stream so as to provide a vaporized natural gas stream to the gas pipe network. 17. An apparatus for vaporizing a liquid stream, the apparatus at least comprising: a first heat transfer zone having a heat transfer surface for exchanging heat between a liquid stream to be vaporized and a heat transfer fluid;a second heat transfer zone having a heat transfer surface for exchanging heat between the heat transfer fluid and ambient air to vaporize the heat transfer fluid;a closed circuit for the heat transfer fluid comprising a downward flowing part and an upward flowing part for recycling the vaporized heat transfer fluid to the first heat transfer zone whereby the vaporized heat transfer fluid flows upward in the upward flowing part and from the upward flowing part into the first heat transfer zone;wherein the second heat transfer zone is situated gravitationally lower than the first heat transfer zone and wherein the upward flowing part is provided with heat transfer improvers and wherein the downward flowing part is not provided with heat transfer improvers, and wherein the first heat transfer zone is supported by a support frame, said support frame comprising through going holes for indirectly exchanging heat between the heat transfer fluid and the ambient air. 18. Apparatus according to claim 17, wherein the closed circuit comprises one or more closed circuits, the one or more closed circuits forming one or more support legs in the support frame. 19. Apparatus according to claim 18, wherein the support frame includes more than one support leg, the support legs comprising at least a first and a second support leg defining an angle α between them. 20. Apparatus according to claim 17, wherein no pump is present for circulation of the heat transfer fluid in the closed circuit. 21. Apparatus according to claim 17, wherein said heat transfer improvers comprise at least one of fins and grooves. 22. Apparatus according to claim 17, wherein the downwards flowing part and the upwards flowing part are separated by a separation wall. 23. Apparatus according to claim 22, wherein the separation wall is thermally insulated. 24. Apparatus according to claim 17, wherein the second heat transfer zone comprises separate tubes or bundles of tubes for the downwards flowing part and the upwards flowing part. 25. Apparatus according to claim 17, wherein the liquid stream to be vaporized is a liquefied natural gas. 26. Use of CO2 as a heat transfer fluid or as a component thereof, comprising cycling the CO2 in the heat transfer fluid in a closed circuit between a first heat transfer zone and a second heat transfer zone, wherein the heat transfer fluid is at least partially condensed in the first heat transfer zone, and vaporized in the second heat transfer zone having a heat transfer surface for exchanging heat between the heat transfer fluid and ambient air to vaporize the heat transfer fluid, and wherein gravitational force exerted on the heat transfer fluid is used to cycle the heat transfer fluid in the closed circuit, wherein the closed circuit comprises a downward flowing part and an upward flowing part for recycling the vaporized heat transfer fluid in the upward flowing part to the first heat transfer zone whereby the vaporized heat transfer fluid flows upward in the upward flowing part and from the upward flowing part into the first heat transfer zone, and wherein the upward flowing part is provided with heat transfer improvers and the downward flowing part is not provided with heat transfer improvers; and, wherein the first heat transfer zone is supported by a support frame, said support frame comprising through going holes for indirectly exchanging heat between the heat transfer fluid and the ambient air. 27. Use according to claim 26, wherein the heat transfer fluid is intended for vaporizing a fluid, the fluid to be vaporized having a temperature below 5° C.