Method For Vaporizing Cryogenic Liquid Through Heat Exchange Using Calorigenic Fluid
A method of vaporizing cryogenic liquid, for example liquefied natural gas, by heat exchange with a calorigenic fluid, for example gaseous nitrogen is provided.
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The present invention relates to a method of vaporizing cryogenic liquid, for example liquefied natural gas, by heat exchange with a calorigenic fluid, for example gaseous nitrogen.
In order to heat up and vaporize cryogenic liquids of the liquefied natural gas (LNG) or equivalent type against a calorigenic fluid, in order to recover the cold energy from the LNG, use has, in the past, been made of one of the following three options:
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- a technology that consists in coiling into the form of a pancake coil a system comprising two tubes that are joined together by a tie. The tubes are welded or expanded onto manifolds transverse to the pancake coils;
- brazed plate and fin exchangers;
- wound tubular exchangers.
If there is a wish to recover the cold energy in order to liquefy air gases, it is absolutely essential to avoid accidental contamination of the nitrogen or the oxygen with a hydrocarbon gas, especially when the natural gas is circulating through the exchanger at a pressure higher than that of the air gas.
Tubular geometries are not very thermally efficient and often lead to costly over engineering.
Moreover, existing methane terminals and existing air separation plants do not always have the equipment required to avoid sharp thermal transients during shut downs and restarts, and this leads to thermal shock and therefore damage to the exchangers.
One subject of the invention is a method for heating up a first fluid by heat exchange with a second fluid in a plate and fin heat exchanger in which the first fluid is heated up in a first series of separated passages and the second fluid is cooled down in a second series of separated passages, characterized in that each passage of the first series is separated from the nearest passage of the second series by an auxiliary passage containing fins in which an inert gas circulates.
Optionally:
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- the first fluid consists of liquefied natural gas which is vaporized or heated up in the first series of separated passages;
- the second fluid consists of gaseous nitrogen which is cooled down or liquefies in the second series of separated passages;
- the inert gas is at a pressure of at least 0.1 bar or even at least 0.5 bar higher than those of the first fluid and of the second fluid;
- the inert gas is at a pressure of at least 0.1 bar, or even at least 0.5 bar lower than those of the first fluid and of the second fluid;
- the inert gas is gaseous nitrogen;
- the inert gas sent into at least certain auxiliary passages is then sent to the atmosphere or to a flare;
- at least one inlet and/or outlet box of one of the first and second fluids is separated from the passages in which the other of the first and second fluids circulates by means of a double bar system, the bars possibly being separated by a dead zone;
- the first fluid is heated up at a pressure of at least 60 bar abs.
Another subject of the invention is a method of starting a plate and fin heat exchanger in which, at full capacity, a first fluid is heated up by heat exchange with a second fluid in a plate and fin heat exchanger, the first fluid being heated up in a first series of separated passages and the second fluid being cooled down in a second series of separated passages, characterized in that each passage of the first series is separated from the nearest passage of the second series by an auxiliary passage containing fins and in which during start-up an inert gas at a temperature lower than ambient temperature, possibly at cryogenic temperature, is sent into at least one auxiliary passage in order to get down to temperature more swiftly.
The invention will be described in greater detail with reference to the figures.
To avoid the nitrogen becoming contaminated with the liquefied natural gas, an auxiliary passage is interposed between each pair of nitrogen and LNG passages. The exchange of heat between the nitrogen and LNG passages will be via the fins of the auxiliary passage, by conduction. Obviously, the corrugation chosen for the auxiliary passage will have an optimal height/thickness ratio.
In the case illustrated, the auxiliary passages will be swept with low-pressure gaseous nitrogen (at a pressure lower than that of the LNG of
The boxes which cover the stack and may therefore be sources of contamination, will therefore be isolated from the other fluid using dead zones Z.
Gas from the dead zones Z will be collected, and these zones may possibly be swept with low-pressure nitrogen.
The above dead zones may be isolated from the LNG and nitrogen circuits by means of a double bar 2 system in order to improve sealing. Gases from the clearance space between the double bars 2 may itself be collected in order to improve intrinsic safety. This is explained in greater detail in respect of the method of
The passages of
According to another aspect of the invention which is illustrated in
As can be seen in
Claims
1-10. (canceled)
11. A method for heating up a first fluid by heat exchange with a second fluid in a plate and fin heat exchanger in which the first fluid is heated up in a first series of separated passages and the second fluid is cooled down in a second series of separated passages, comprising:
- separating each passage of the first series from the nearest passage of the second series by an auxiliary passage containing fins in which an inert gas circulates.
12. The method of claim 11, wherein the first fluid consists of liquefied natural gas which is heated in the first series of separated passages.
13. The method of claim 11, wherein the first fluid consists of liquefied natural gas which is vaporized in the first series of separated passages.
14. The method of claim 11, wherein the second fluid consists of gaseous nitrogen which cools in the second series of separated passages.
15. The method of claim 11, wherein the second fluid consists of gaseous nitrogen which liquefies in the second series of separated passages.
16. The method of claim 11, wherein the inert gas is at a pressure at least 0.1 bar higher than those of the first fluid and of the second fluid.
17. The method of claim 11, wherein the inert gas is at a pressure at least 0.5 bar higher than those of the first fluid and of the second fluid.
18. The method of claim 11, wherein the inert gas is at a pressure at least 0.1 bar lower than those of the first fluid and of the second fluid.
19. The method of claim 11, wherein the inert gas is at a pressure at least 0.5 bar lower than those of the first fluid and of the second fluid.
20. The method of claim 11, wherein the inert gas is gaseous nitrogen.
21. The method of claim 11, wherein the inert gas sent into at least certain auxiliary passages is then sent to the atmosphere.
22. The method of claim 11, wherein the inert gas sent into at least certain auxiliary passages is then sent to a flare.
23. The method of claim 11, wherein at least one inlet and/or outlet box of one of the first and second fluids is separated from the passages in which the other of the first and second fluids circulates by means of a double bar system.
24. The method of claim 23, wherein said double bar system comprises bars separated by a dead zone.
25. The method of claim 11, wherein the first fluid is heated up at a pressure of at least 60 bar abs.
26. A method of starting a plate and fin heat exchanger in which, at full capacity, a first fluid is heated up by heat exchange with a second fluid in a plate and fin heat exchanger, the first fluid being heated up in a first series of separated passages and the second fluid being cooled down in a second series of separated passages, comprising
- separating each passage of the first series from the nearest passage of the second series by an auxiliary passage containing fins and in which during start-up an inert gas at a temperature lower than ambient temperature, possibly at cryogenic temperature, is sent into at least one auxiliary passage in order to get down to temperature more swiftly.
27. The method of claim 26, wherein during start-up said inert gas has a cryogenic temperature.
Type: Application
Filed: Mar 12, 2009
Publication Date: Jan 27, 2011
Applicant:
Inventors: Maurice Bosquain (Sommecaise), Marc Wagner (Saint Maur Des Fosses), Philippe Grigoletto (Villeparisis), Daniel Machon Diez De Baldeon (Paris), Alain Briglia (Corze)
Application Number: 12/933,571
International Classification: F28D 15/00 (20060101);