EP0035444A1 - Process and installation for reheating a cold fluid - Google Patents

Abstract

The invention relates to the heating of a cold fluid by heat exchange with a hot liquid, generally water. The cold fluid first circulates in a downward tube (2) then in an upward tube (3), while the water flows along the tubes (2) and (3) from an upper supply reserve up to a bottom collector 28. Application in particular to the heating and re-vaporization of liquefied natural gas.

Description

The present invention relates to a method and an installation for heating a cryogenic fluid by heat exchange with a circulating fluid whose solidification temperature is higher than the temperature of the cryogenic fluid before its final heating.

It is particularly applicable to the heating of liquefied natural gas with water available in large quantities (river, sea ...).

The object of the present invention is to make it possible to use water or other fluid at a temperature that is relatively cold while avoiding any risk of solidification of the circulating fluid).

Various solutions have already been proposed, none of which allows this result to be achieved.

French patent n ° 70 26.212 describes a process for heating natural gas by countercurrent exchange in a plurality of vertical tubes mounted in parallel, the natural gas always circulating in an upward direction inside the tubes and the circulating water flowing naturally by gravity on the outside of these tubes which are provided with longitudinal fins. In order to optimize the heat exchange, that is to say to maximize the heat flow while avoiding icing of the water at the external periphery of the tubes, an internal section of tube is provided for the passage natural gas which is increasingly reduced, which leads to successive increases in the speed of natural gas flowing in the tubes. These successive decreases in cross-section have in particular been achieved by the installation of an internal lining constituted by a blind tube with variable section, which constitutes a fairly complex technology.

Japanese Patent No. 54,7403 describes the heating of natural gas by first co-current exchange with natural gas flowing from bottom to top in a tube bundle and water flowing from bottom to top in a calender according to a flow forced, then an exchange against the current with the gas flowing from top to bottom in another tube bundle and the water flowing from bottom to top in the corresponding grille. This is enough complex and leads to significant deterioration, in particular calenders in the event of accidental freezing of the warming water.

Japanese patent n ° 52 144.006 describes a heating comprising a first section in countercurrent exchange with the natural gas flowing from bottom to top in a first plurality of tubes and the water naturally flowing outside, then a second section also in countercurrent exchange, the natural gas flowing from bottom to top in a second plurality of tubes and the water naturally flowing outside, with the particularity that the second plurality of tubes offers a passage section for natural gas lower than the first plurality. This arrangement also does not fulfill the objective of the present invention.

The essential characteristic of the invention is, in a heating process in which the cryogenic fluid is led in a plurality of elements of vertical tubes with fins, connected in series, firstly co-current with the circulating fluid flowing at the periphery of said tube elements, then against the flow of said circulating fluid, to provide that the circulating fluid flows by gravity along said tube elements and that each tube element most upstream is supplied with cryogenic fluid at its upper end.

• D'une part, l'existence d'un premier échange à co-courant est décisive en raison de la limitation du flux thermique pour éviter la prise en glace externe. En effet, si la température de l'eau à l'entrée, c'est-à-dire à l'extrémité supérieure de l'élément de tête par exemple est de + 4°c et de + 2°C à la sortie, c'est-à-dire à l'extrémité inférieure de ce même élément de tube, le débit de gaz naturel liquéfié à une température de - 160°C pouvant entrer dans un tube fonctionnant à co-courant est plus de deux fois supérieur à celui qui peut entrer dans ce même tube fonctionnant à contre-courant.

The advantages of the invention can be explained as follows:

• On the one hand, the existence of a first co-current exchange is decisive due to the limitation of the heat flow to avoid setting in external ice. Indeed, if the water temperature at the inlet, i.e. at the upper end of the head element for example is + 4 ° c and + 2 ° C at the outlet , i.e. at the lower end of this same tube element, the flow rate of liquefied natural gas at a temperature of - 160 ° C which can enter a co-current tube is more than twice as high to one who can enter this same tube operating against the current.

The existence of at least a second countercurrent heat exchange is also decisive due to the small temperature difference between the natural gas leaving the second element and the water. cooling this second element. Indeed, if the temperature of the water at the upper end, that is to say, at the upper outlet of this second element is + 4 ° C and + 2 ° C at the lower inlet, the length of this second element operating against the current is 30% less than that which would be necessary for a similar operation at the co-current.

On the other hand, as the critical temperature of natural gas is generally close to - 60 ° C, its density in the vicinity of this temperature varies rapidly with temperature, even under a pressure higher than the critical pressure (6 kg / m3 / ° C under 75 bars). However, the flow rate of natural gas in the second tube element is still necessarily low at this temperature to avoid setting in external ice. Under these conditions, a "downward" flow of natural gas would lead to flow disturbances due to the untimely influence of gravity and generating thermodynamic irreversibilities. On the other hand and according to the invention, an upward flow in the second element leads to a natural stratification according to the density and the temperature of the natural gas which therefore does not create any disturbance of flow. Since the intermediate temperature between the first and second tube elements is close to the critical temperature, it is therefore preferable to provide for an upward circulation of natural gas in the second tube element in order to ensure a final heating of the natural gas. without untimely irreversibilities, which should then be compensated for by a noticeable increase in the exchange surface.

The present invention also relates to an installation for heating a cold fluid by heat exchange with a hot liquid, of the type comprising heat exchange passages with substantially vertical extension with means for distributing a runoff liquid to the high end of the passages and this installation is characterized in that said passages comprise at least one module with at least one first tube element or head element, connected at its lower end to the lower end of at least one second element of tube, and means for supplying fluid to be heated at the end su of each head tube element.

• - la figure 1 est une vue partielle en coupe verticale d'une installation de réchauffement de liquide cryogénique selon l'invention;
• - la figure 2 est un détail, à échelle agrandie, d'une partie de la figure 1 ;
• - la figure 3 est une vue, à échelle agrandie, en coupe selon la ligne III-III de la figure 2;
• - les figures 4 - 5 - 6 - 7 - 8 et 9 sont des variantes de réalisation d'une installation selon l'invention.

The characteristics and advantages of the invention will emerge from the description which follows with reference to the appended drawings in which:

• - Figure 1 is a partial view in vertical section of a cryogenic liquid heating installation according to the invention;
• - Figure 2 is a detail, on an enlarged scale, of a part of Figure 1;
• - Figure 3 is a view, on an enlarged scale, in section along the line III-III of Figure 2;
• - Figures 4 - 5 - 6 - 7 - 8 and 9 are alternative embodiments of an installation according to the invention.

With reference to FIGS. 1 to 3, it can be seen that an installation comprises a plurality of heating tubes 1 forming heat exchange passages, made of aluminum, each consisting of a tube element “upstream” or head 2 and of a "downstream" tube element 3, connected by a lower bend 4..The head tube element 2 is connected to a pipe 5 to a source of cryogenic fluid to be heated by means of a box of connection 10, while the "downstream" tube element 3 is connected directly to a pipe 6 for withdrawing heated fluid: the tube elements 2 and 3 are suspended so as to extend substantially vertically, and all around and along these tube elements, which have external fins 7, flow streams of heating liquid in the form of sheets 8 and 9 which are previously formed by upper distribution devices 11.

The connection box 10 here comprises (see FIG. 2) welded as an extension of the head element 2, an envelope tube 12 having a constant wall thickness in a lower section 12 ′ and increasing radially in a middle portion 12 ″, with a constant internal diameter, at the upper end, this casing 12 extends at 13 to a connection end 14 of the pipe 5 for the cryogenic fluid. All of these parts are made of aluminum to be suitably welded between - They and with the heat exchange tube element 1. The end piece 14 has an internal bore of small diameter 16 in which is welded a conduit element 17 leading largely inside the tubular head element 2. Between the conduit element 17 on the one hand and on the other hand the casing 13 - 12 and the upper part of the 'tube element 2 is placed a thermal insulation product 18. The assembly which has just been described is housed inside a distribution well 20 having a ring of perforations 21. This well 20 is fixed on the distribution device 11 enveloping at a short distance the tube element 2 with its fins 7 and the perforations 21 are located at the upper level of the portion 12 "of oversized thickness. In practice, and as noted in the drawings, the liquid runoff caloric, which is intended to flow in layers such as 8 and 9 along the tube elements "upstream '2 and" downstream "3, comes from a general reserve of liquid 25, which itself is supplied by a 25 'source.

In operation, the runoff caloric liquid is transferred into a lower part of the distribution well 20 in the form of a plurality of veins or liquid jets 26 coming from the reserve 25 and formed from the perforations 21. Thanks to the arrangement which comes To be described, the cryogenic fluid which circulates inside the pipe 5 and the tube 17 to reach the head tube element 2 is radially isolated from the outside by the insulating body 18. In addition, the significant longitudinal refrigeration flow, which essentially arises, c8té "upstream", at the level of the end piece 14 and which propagates downstream along the tube-envelope 13 - 12 towards the tube element 2, is substantially derived radially outward at the location of the envelope tube 12 with a progressively increasing wall thickness upstream. In fact, in the very thick middle part 12 "of the tube-shell 12, the longitudinal refrigerant flow is transferred as much as possible to the water, which is in the form of jets 26 in free and rapid gravitational flow. This maximum transfer effect radially outwardly thermal results on the one hand from the arrangement, at the level of the jets 26, of a significant excess wall thickness of the part 12 "of the tube-envelope 12, which offers increased thermal conductance in the radial direction, on the other hand, a rapid flow of water in free fall, which has the effect of bringing the coefficient of heat exchange to its maximum value. This arrangement therefore allows a diversion towards the liquid jets 26 of a substantial part of the refrigerating flow with longitudinal propagation, which thereby alleviates the residual refrigerating flow thereby continuing its longitudinal propagation in the weaker walled portion 12 ′ and especially towards the upper part 2 ′ of the head element 2 which is immersed in an individual reserve of distribution water 29 of a substantially stagnant nature, therefore with a low coefficient of heat exchange with the wall of the tube element 2. Without the provision described above, we would witness the arrival of a significant refrigerating flow with longitudinal wall propagation at the level of the part 2 ′ of the tube element 2, enveloped in a reserve of standing water 29, which does not would not fail to cause detrimental surface solidifications of the water at the level of the part 2 'since these solidifications, by propagating radially, could reach all the water reserve 29 and thus make inoperative heat exchange of the tube 2 - 3. On the contrary, thanks to the arrangement described, it is possible to very precisely control the heat flux which reaches the level of the part 2 ′ of the head element 2, since this flux thermal is the sum of a residual thermal flux with longitudinal propagation and a thermal flux with radial propagation which is itself weak thanks to the interposition of the insulating product 18. Besides, in some cases, one can on the contrary slightly increase the heat exchange coefficient between the part 2 'of the tube element 2 with the water reserve 29 by giving the latter a certain convection movement thanks to the presence of relief perforations 21' made in low position in the distribution chimney 20, thus favoring a certain complementary admission of water coming directly from the main reserve 25.

As explained above, the runoff water forms in a runoff layer on the finned external wall of the upstream tube element 2 and gradually cools down to the lower end of this tube element. "upstream" 2, where the runoff water is then evacuated at 30 with, moreover, that which comes from the runoff against the current on the "downstream" tube element 3. It is noted that at this element of "downstream" tube 3, the risks of freezing the runoff liquid are significantly reduced, the fluid being heated The temperature flowing in the tube 1 has seen its temperature increase until it is close to that of the runoff liquid, so that the evacuation of the heated fluid from the "downstream" tube element 3 can be carried out, without setting in use of a connection box as described with reference to FIG. 2, by a simple draw-off line 6, with, however, of course, the distribution device 11 allowing the formation of a uniform run-off ply 9, such as shown in Figure 3.

Instead of using a heating tube whose inlet end "upstream" receives the raw fluid to be heated and whose downstream end delivers the fluid to the desired temperature of heating (or more precisely a plurality of such tubes arranged in parallel and connected directly to intake manifolds 30 and withdrawal 31), it is possible to arrange the upstream tube elements and the "downstream" tube elements in a number of combinations.

Referring to FIG. 4, it can be seen that a plurality of "upstream" tube elements 42a, 42b, ... 42n are all connected between an upper distribution manifold 50 and a lower connection manifold 51 supplying another plurality 43a, 43b ... 43n of "downstream" tube elements thus forming a first multi-tubular module whose upper end is connected by a manifold 52 to a second multi-tubular module made up of another plurality of "upstream" tube elements 44a, 44b ... 44g, the final module having a plurality of "upstream" tube elements 45a, 45b ... 45r and a plurality of "downstream" tube elements 46a, 46b. .. 46s, delivering the heated liquid to a 52 "final manifold.

According to FIG. 5, monotubular modules as described with reference to FIG. 1, each consisting of an upstream tube element (54a, 54b, etc.) are supplied at their upper end by a common supply collector 55, and are connected by individual connectors 58a, 58b ... to a downstream tube element (56a, 56b, etc ...), themselves connected at their upper end to a common withdrawal manifold 57.

According to FIG. 6, several lines 61 and 62, such as those described in FIG. 4, that is to say incorporating each several multi-tubular modules in series 63, 64 ... 63 ', 64' ... are connected in parallel between a main intake manifold 68 and a main withdrawal manifold 69.

According to FIG. 7, several lines 70, 71, each consisting of several multi-tubular modules 72, 73, ..., 72 ', 73' .. are not only connected between a main supply collector 74 and a main collector racking 75, but intermediate equalization collectors 77 connect the homologous modules of several lines in parallel.

According to FIG. 8, a bundle of tube elements is formed of a first set of lines 81a, 81b, 81c (for example three in number) consisting of a multi-tubular module (or several multi-tubular modules in series) between a supply collector 83 and an intermediate collector 84 which supplies a second set of lines 82a and 82b (for example two) between this intermediate collector 84 and the final withdrawal collector 85.

According to FIG. 9, a first set of a plurality of lines 91a, 91b, 91c (for example three) supplied by a supply collector 93 and withdrawn by a withdrawal collector 95a is connected via a pipe. 96 with expansion valve 97 to a second set of another plurality of lines 92a, 92b connected between a supply manifold 95b and a withdrawal manifold 94. This arrangement can be used for example if the network is at 40 bars and the gas available under higher pressure, for example 80 bars, and it is noted that this delayed expansion which causes refrigeration release is not detrimental to the pipes, since the natural gas is then in the already partially heated state. If necessary, a separator can be placed at the outlet of the expansion valve 97 for withdrawing and removing the heaviest condensates, such as ethane, propane or butane, while the gaseous fraction is only warmed up.

The invention is particularly applicable to the heating and re-vaporization of liquefied natural gas.

Claims (10)

1. A method of heating a cryogenic fluid such as liquefied natural gas by heat exchange with a circulating fluid, such as water, the solidification temperature of which is higher than the temperature of said cryogenic fluid before its final cooling, according to which said cryogenic fluid is led into a plurality of elements of vertical tubes with fins connected in series, firstly co-current (2) of said circulating fluid flowing at the periphery of said tube elements (8) then (at 3 ) against the flow of said circulating fluid (at 9), characterized in that the circulating fluid (8) (9) flows by gravity along said tube elements (2) (3) and in that each tube element the most upstream (2) is supplied (at 10, 11) with cryogenic fluid at its upper end. 2. A method of heating a cold fluid according to claim 1, of the type in which the circulating fluid is distributed around a tube element (2) (3) heat exchange from a reserve of fluid circulating (29) individually assigned to each element (2) (3) around the lower part of a tube-envelope (12) extending upwards said element (2) (3) and inside which extends with the interposition of an insulator (18) of a pipe element for supplying fluid to be heated (17), said pipe element (17) and said tube-jacket (12) being connected to a pipe end piece (14), said individual liquid reserve (29) being itself supplied with liquid coming from a general liquid reserve (25) and trickling (at 26) along a part of said tube-envelope situated above said individual reserve (29), characterized in that the thickness of said part (12 ") of said envelope tube (12) is oversized, the oversizing of thickness being preferably all the more marked as one rises above said individual liquid reserve (29). 3. Installation for heating a cryogenic fluid by heat exchange with a hot liquid, of the type comprising heat exchange tube (2) (3) elements with substantially vertical extension, with means for distributing a liquid of runoff (11) at the high end of the elements (2) (3), characterized in that the said tube elements comprise at least one module with at least one first element (2), upstream or head element, connected by fitting (4) at its lower end to the lower end of at least a second tube element (3), or downstream tube element, and means (10) (5) for supplying cryogenic fluid to the upper end of each upstream passage element. 4. Installation according to claim 3, characterized in that a module comprises a first plurality of tube elements (42a, 42b ... 42n) dits'hmont "connected by their lower ends by a" low "collector (51 ) at the lower ends of a second plurality of so-called "downstream" tube elements (43a, 4 ₃₁ ... 43n). 5. Installation according to claim 3 or 4, characterized in that several modules are connected in series by tall collectors (52) (52 ") to form a line. 6. Installation according to claim 3, characterized in that several modules (54a, 56a, 56b) are connected in parallel between an "upstream" supply manifold (55) and an "downstream" withdrawal manifold (57). 7. Installation according to claim 5, characterized in that several lines (61, 62) are arranged and connected at one end of said lines to an intake manifold (68) and at the other end of said lines to a manifold racking (69). 8. Installation according to claim 7, characterized in that a line (70 - 71) is formed of several modules, certain homologous modules (72, 72 ') (73, 73') of several lines in parallel being connected to intermediate collectors (77). 9. Installation according to claim 7, characterized in that several lines are arranged, some (81a, 81b, 81c) in parallel, some in series (81a ... 82a) with intermediate collectors (84). 10. Installation according to claim 9, characterized in that the intermediate collectors incorporate expansion means (97), if necessary followed by a condensate separator.

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