Continuous Regasification of LNG Using Ambient Air

Abstract

Liquefied natural gas is regasified to form natural gas, including circulation of an intermediate fluid between a vaporizer and an ambient air heater, where the intermediate fluid is warmed by exchanging heat with the ambient air as the intermediate fluid passes through the ambient air heater, and the intermediate fluid is cooled by exchanging heat with LNG as the intermediate fluid passes through the vaporizer. The ambient air heater is subjected to a defrosting cycle by intermittently regulating the temperature of the intermediate fluid fed to the ambient air heater to a temperature greater than zero degrees Celsius using a source of supplemental heat.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate a more detailed understanding of the nature of the invention several embodiments of the present invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic side view of the RLNGC moored at a turret mooring buoy through which the natural gas is from the onboard regasification facility is transferred via a marine riser associated with a sub-sea pipeline to shore;

FIG. 2 is a flow chart illustrating a first embodiment of the regasification facility suitable for tropical climates where the minimum ambient temperature is about 10 to 15° C.;

FIG. 3 illustrates one embodiment of the ambient air heater of FIG. 2 provided with a horizontal tube bundle and a vertical tube bundle;

FIG. 4 is a flow chart illustrating a second embodiment of the regasification facility suitable for mildly cold climates; and,

FIG. 5 is a flow chart illustrating a third embodiment of the regasification facility suitable for much colder climates using supplemental heat provided by heat recovery and also from a back-up heater operating using a closed loop system in which a water-glycol mixture or other auxiliary fluid is heated using heat from a fired heater.

Claims

1. A process for regasification of LNG to form natural gas, said process comprising the steps of: (a) circulating an intermediate fluid between a vaporizer and an ambient air heater, the intermediate fluid being warmed by exchanging heat with the ambient air as the intermediate fluid passes through the ambient air heater, the intermediate fluid being cooled by exchanging heat with LNG as the intermediate fluid passes through the vaporizer; and,(b) subjecting the ambient air heater to a defrosting cycle by intermittently regulating the temperature of the intermediate fluid fed to the ambient air heater to a temperature greater than zero degrees Celsius using a source of supplemental heat.

2. The process of claim 1, wherein step (b) is conducted downstream of the ambient air heater.

3. The process of claim 1, wherein the source of supplemental heat is selected from the group consisting of an exhaust gas heater, an electric water or fluid heater, a propulsion unit of a ship, a diesel engine, a gas turbine propulsion plant, and an exhaust gas stream from a power generation plant.

4. The process of claim 1, wherein regasification of the LNG is conducted onboard an LNG carrier and the source of supplementary heat is heat recovered from the engines of the LNG carrier.

5. The process of claim 1, wherein heat exchange between the ambient air and the intermediate fluid in the ambient air heater is encouraged through use of forced draft fans.

6. The process of claim 1, wherein the intermediate fluid is selected from the group consisting of a glycol, a glycol-water mixture, methanol, propanol, propane, butane, ammonia, a formate, fresh water and tempered water.

7. The process of claim 1, wherein the intermediate fluid comprises a solution containing an alkali metal formate or an alkali metal acetate.

8. The process of claim 7, wherein the alkali metal formate is potassium formate, sodium formate or an aqueous solution of ammonium formate.

9. The process of claim 7, wherein the alkali metal acetate is potassium acetate or ammonium acetate.

10. The process of claim 1, wherein the ambient air heater is one of a plurality of ambient air heaters and step (b) is performed on each of the plurality of ambient air heaters sequentially.

11. The process of claim 1, wherein the ambient air heater comprises a horizontal tube bundle for exchanging heat with the intermediate fluid when the temperature of the ambient air is above 0° C. and a vertical tube bundle for exchanging heat with ambient air when the temperature of the ambient temperature falls below 0° C.

12. The process of claim 11, wherein heat exchange between the ambient air and the intermediate fluid in the ambient air heater is encouraged through use of forced draft fans and the horizontal tube bundle lies above the vertical tube bundle in closer proximity to forced draft fans.

13. A regasification facility for regasification of LNG to form natural gas, said apparatus comprising: a vaporizer for regasifying LNG to natural gas;an ambient air heater for heating an intermediate fluid using ambient air as the primary source of heat;a circulating pump for circulating the intermediate fluid between the vaporizer and the ambient air heater, the intermediate fluid being warmed by exchanging heat with the ambient air as the intermediate fluid passes through the ambient air heater, the intermediate fluid being cooled by exchanging heat with LNG as the intermediate fluid passes through the vaporizer; anda control device for regulating the temperature of the intermediate fluid fed to the ambient air heater to a temperature greater than zero degrees Celsius using a source of supplemental heat to subject the ambient air heater to a defrosting cycle.

14. The apparatus of claim 13, wherein the source of supplemental heat is located downstream of the ambient air heater.

15. The apparatus of claim 13, wherein the source of supplemental heat is selected from the group consisting of an exhaust gas heater, an electric water or fluid heater, a propulsion unit of a ship, a diesel engine, a gas turbine propulsion plant, and an exhaust gas stream from a power generation plant.

16. The apparatus of claim 13, wherein the regasification facility is provided onboard an LNG carrier and the source of supplementary heat is heat recovered from the engines of the LNG carrier.

17. The apparatus of claim 13, further comprising a forced draft fan for encouraging heat exchange between the ambient air and the intermediate fluid in the ambient air heater.

18. The apparatus of claim 13, wherein the ambient air heater is one of a plurality of ambient air heaters and the control device is arranged to subject each of the plurality of ambient air heaters sequentially to a defrosting cycle.

19. The apparatus of claim 13, wherein the ambient air heater comprises a horizontal tube bundle for exchanging heat with the intermediate fluid when the temperature of the ambient air is above 0° C. and a vertical tube bundle for exchanging heat with ambient air when the temperature of the ambient temperature falls below 0° C.

20. The apparatus of claim 19, wherein heat exchange between the ambient air and the intermediate fluid in the ambient air heater is encouraged through use of forced draft fans and the horizontal tube bundle lies above the vertical tube bundle in closer proximity to forced draft fans.