EP0546947B1 - Indirect plate-type heat exchanger - Google Patents

Description

The present invention relates to indirect plate heat exchangers, that is to say of the type comprising a series of parallel plates delimiting between them passages of generally flat shape containing spacer waves, a first set of these passages, constituting heat exchange passages, comprising means for entering / leaving fluids intended to exchange heat between them and comprising annex passages, over at least part of its length and width, arranged to fill at least an auxiliary function of the heat exchanger, in particular a liquid storage and / or liquid recirculation and / or liquid / vapor separation function.

Brazed plate heat exchangers are particularly efficient to build. Indeed, it suffices to stack all their elements (plates, waves serving as spacers and fins, bars for closing the passages) and to connect them to one another in a single operation by brazing in an oven.

However, this advantage is in practice partially lost by the need to connect numerous accessories to the exchanger, such as pipes or phase separators, ensuring the auxiliary functions of the exchanger: recirculation of the liquid, stabilization of the supply. in liquid, phase separation of two-phase fluids, etc. In addition, in many cases, it is necessary to position the exchanger in a liquid retention enclosure such as the tank of a distillation column. All these operations constitute sheet metal work, which is less efficient than brazing in the oven.

An exchanger having passages fulfilling an additional function is known from FR-A-2,431,103 in which the nitrogen supply passages exchange heat with the heat exchange passages.

This heat exchange hampers the operation of the annex nitrogen supply passages.

The object of the invention is to improve the operation of the passages which fulfill a function annexed to that of the exchanger.

To this end, the invention relates to an indirect heat exchanger of the aforementioned type, characterized in that the annex passages are all adjacent and in reduced or almost zero heat exchange relationship with the heat exchange passages.

• les passages annexes sont plus épais que les passages d'échange thermique ;
• les passages annexes contiennent des ondes moins denses que celles des passages d'échange thermique ;
• les passages annexes sont distincts des passages d'échange thermique et, de même que ces derniers, s'étendent chacun sur toute la longueur et sur toute la largeur de l'échangeur ;
• au moins certains passages de l'échangeur constituent sur une partie de la largeur de celui-ci un passage d'échange thermique et sur le reste de sa largeur un passage annexe ;
• au moins certains passages de l'échangeur constituent sur une partie de la longueur de celui-ci un passage d'échange thermique et sur le reste de sa longueur un passage annexe ;
• les passages annexes comprenant des passages de séparation liquide/vapeur, ces passages de séparation contiennent un garnissage de séparation liquide/vapeur disposé en regard d'une fenêtre d'entrée de fluide diphasique ;
• le garnissage est constitué par une onde "serrated" à génératrices obliques ;
• les passages de séparation liquide/vapeur comportent à leur extrémité supérieure une fenêtre de sortie de vapeur coiffée par une boîte de sortie, cette dernière communiquant avec des passages de renvoi de vapeur à un niveau différent de l'échangeur.

According to other characteristics:

• the annex passages are thicker than the heat exchange passages;
• the annex passages contain less dense waves than those of the heat exchange passages;
• the annex passages are separate from the heat exchange passages and, like the latter, each extend over the entire length and over the entire width of the exchanger;
• at least certain passages of the exchanger constitute over a part of the width thereof a heat exchange passage and over the rest of its width an annex passage;
• at least certain passages of the exchanger constitute over a part of the length thereof a heat exchange passage and over the rest of its length an annex passage;
• the annex passages comprising liquid / vapor separation passages, these separation passages contain a liquid / vapor separation lining disposed opposite a two-phase fluid inlet window;
• the lining consists of a "serrated" wave with oblique generatrices;
• the liquid / vapor separation passages have at their upper end a vapor outlet window capped by an outlet box, this last communicating with steam return passages at a different level from the exchanger.

• la Figure 1 représente en perspective, avec arrachements, un échangeur de chaleur conforme à l'invention;
• les Figures 2 à 4 représentent respectivement, en coupe verticale, les trois types de passages de cet échangeur;
• la Figure 5 illustre schématiquement une variante du même échangeur;
• la Figure 6 est une vue analogue à la Figure 1 d'un deuxième mode de réalisation de l'échangeur de chaleur suivant l'invention;
• les Figures 7 et 8 représentent respectivement, en coupe verticale, les deux types de passages de cet échangeur;
• les Figures 9 et 10 sont des vues analogues respectivement aux Figures 7 et 8 d'une variante de l'échangeur de chaleur de la Figure 6;
• les Figures 11 et 12 sont des vues analogues respectivement aux Figures 7 et 8 d'une autre variante de l'échangeur de chaleur de la Figure 6;
• les Figures 13 et 14 sont des vues analogues respectivement aux Figures 7 et 8 d'encore une autre variante de l'échangeur de chaleur de la Figure 6;
• la Figure 15 illustre schématiquement une application d'un troisième mode de réalisation de l'échangeur de chaleur suivant l'invention;
• la Figure 16 est une vue analogue à la Figure 1 de ce troisième mode de réalisation; et
• les Figures 17 et 18 représentent respectivement, en coupe verticale, les deux types de passages de l'échangeur de la Figure 16.

Examples of embodiments of the invention will now be described with reference to the appended drawings, in which:

• Figure 1 shows in perspective, with cutaway, a heat exchanger according to the invention;
• Figures 2 to 4 show respectively, in vertical section, the three types of passages of this exchanger;
• Figure 5 schematically illustrates a variant of the same exchanger;
• Figure 6 is a view similar to Figure 1 of a second embodiment of the heat exchanger according to the invention;
• Figures 7 and 8 show respectively, in vertical section, the two types of passages of this exchanger;
• Figures 9 and 10 are views similar to Figures 7 and 8 respectively of a variant of the heat exchanger of Figure 6;
• Figures 11 and 12 are views similar to Figures 7 and 8 respectively of another variant of the heat exchanger of Figure 6;
• Figures 13 and 14 are views similar to Figures 7 and 8 respectively of yet another variant of the heat exchanger of Figure 6;
• Figure 15 schematically illustrates an application of a third embodiment of the heat exchanger according to the invention;
• Figure 16 is a view similar to Figure 1 of this third embodiment; and
• Figures 17 and 18 show respectively, in vertical section, the two types of passages of the exchanger of Figure 16.

The heat exchanger shown in Figures 1 to 4 is a liquid vaporizer, of the thermosyphon type. It will be described in its application as the main evaporator-condenser of a double air distillation column, bringing the nitrogen gas at the top of the medium pressure column into heat exchange relationship, at about 6 bar absolute, and liquid oxygen from the low pressure column tank, at around 1 bar absolute, in order to vaporize the oxygen by condensing the nitrogen.

The exchanger 1 comprises a parallelepipedic body 2 of aluminum, assembled in a single operation by brazing in the furnace, three semi-cylindrical boxes 3 to 5 for inlet / outlet of fluids, and an upper dome 6, the elements 3 to 6 being attached to watertight seal on body 2 by welding.

The body 2 consists of a large number of parallel vertical plates 7 between which are delimited passages 8 of generally flat shape containing spacer waves 9 with vertical generatrices. These passages are delimited by closing bars 10 indicated by strong lines in FIGS. 2 to 4. In what follows, the vertical dimension of the body 2 will be called "length", "thickness" its horizontal dimension perpendicular to the plates 7, and "width" its horizontal dimension parallel to these plates.

The body 2 is made up of two juxtaposed parts: on the left in FIG. 1, a part 2A for heat exchange, and on the right an annex part 2B ensuring the additional functions of liquid recirculation, liquid / vapor separation, storage liquid and uniform liquid supply from part 2A.

• (1) des passages 8A-1 de condensation d'azote, fermés sur toute leur largeur en haut et en bas, qui comportent latéralement à leur extrémité supérieure une fenêtre 11 d'entrée d'azote gazeux et, en regard de celle-ci, une onde oblique 12 de répartition de cet azote gazeux sur toute la largeur du passage. La boîte 3 précitée recouvre toutes les fenêtres 11 et est alimentée en azote gazeux par une conduite d'alimentation 13. Les passages 8A-1 comportent latéralement, du même côté et à leur extrémité inférieure, une fenêtre 14 de sortie d'azote liquide et, en regard de celle-ci, une onde oblique 15 de collection de cet azote liquide débouchant sur la fenêtre 14. La boîte 4 précitée recouvre toutes les fenêtres 14 pour collecter l'azote liquide sortant de celles-ci et l'évacuer via une conduite 16.
• (2) Des passages 8A-2 de vaporisation d'oxygène, fermés sur toute leur largeur en bas mais ouverts sur toute leur largeur en haut, qui comportent latéralement à leur extrémité inférieure une fenêtre 17A d'entrée d'oxygène liquide, et en regard de celle-ci, une onde oblique 18A de répartition de cet oxygène liquide sur toute la largeur du passage. La boîte 5 précitée recouvre toutes les fenêtres 17A.

The passages 8A of part 2A are alternately of two different types, represented respectively in Figures 2 and 3:

• (1) nitrogen condensation passages 8A-1, closed over their entire width at the top and bottom, which laterally have at their upper end a window 11 for the entry of nitrogen gas and, opposite it , an oblique wave 12 for distributing this gaseous nitrogen over the entire width of the passage. The aforementioned box 3 covers all the windows 11 and is supplied with gaseous nitrogen by a supply line 13. The passages 8A-1 have laterally, on the same side and at their lower end, a window 14 for the exit of liquid nitrogen and , opposite this, an oblique wave 15 for collecting this liquid nitrogen opening out on the window 14. The above-mentioned box 4 covers all the windows 14 to collect the liquid nitrogen leaving them and evacuate it via a driving 16.
• (2) Oxygen vaporization passages 8A-2, closed over their entire width at the bottom but open over their entire width at the top, which laterally have at their lower end a window 17A for the entry of liquid oxygen, and Regarding it, an oblique wave 18A of distribution of this liquid oxygen over the entire width of the passage. The aforementioned box 5 covers all the windows 17A.

The passages 8B of part 2B, shown in FIG. 4, have the same constitution as the oxygen vaporization passages 8A-2, their lower windows 17B also communicating with the box 5. However, their vertical waves 9B are less dense that waves 9A-1 of passages 8A-1 and that waves 9A-2 of passages 8A-2, thanks to a higher wave pitch, and / or their thickness is greater than that of passages 8A-1 than of passages 8A-2.

It follows from the above description that the box 5 extends over the entire thickness of the body of the exchanger, that is to say covers its two parts 2A and 2B, while the boxes 3 and 4 only extend over that of part 2A.

The dome 6 is connected all along the four sides of the upper base of the parallelepiped formed by the body 2. It is provided with a pipe 19 for supplying liquid oxygen and a pipe 20 for discharging gaseous oxygen which leaves from its summit.

In operation, the nitrogen gas is condensed under approximately 6 bar absolute down into passages 8A-1, and passages 8A-2 and 8B are filled with liquid oxygen under approximately 1 bar absolute, up to a level situated in dome 6, as seen in Figure 1.

The heat of condensation of nitrogen boils the liquid oxygen contained in the passages 8A-1, which causes an ascending circulation of the liquid oxygen in these passages by thermosyphon effect. Bubbles of gaseous oxygen gradually form from bottom to top of the same passages, so that it is a two-phase mixture which overflows at the upper end of these passages.

Liquid oxygen which cannot descend either in passages 8A-2, where there is an ascending circulation, or in passages 8A-1, closed at the top, descends in passages 8B and, at the lower end thereof, enters the box 5, via their side windows 17B (Figure 4). This liquid oxygen then flows along the box 5 up to the windows 17A for entry of the passages 8A-2 (FIG. 3), so that these are supplied with liquid oxygen.

The passages 8B therefore ensure the recirculation of the excess liquid oxygen, the separation of the two phases of the oxygen, and a storage of liquid oxygen making it possible to feed smoothly and in a manner uniform in liquid oxygen the vaporization passages 8A-2.

In most passages 8B, the downward circulation of liquid oxygen is not hampered by any vaporization phenomenon, since these passages are not in heat exchange relationship with the nitrogen passages. The situation is slightly different for passage 8B adjacent to part 2A of body 2, but the heat exchange is reduced there considerably on the one hand by the proximity of passage 8A-2, on the other hand by the greater thickness of the passages 8B and / or by the lower density of the wave 9B, leading to a reduced fin effect.

The variant of FIG. 5 differs from that which has just been described only in that the part 2B of the body 2 is divided into two sub-parts 2B-1 and 2B-2 surrounding the heat exchange part 2A. This shows that the auxiliary passages 8B can be distributed in different ways. However, the arrangement of FIG. 1 is currently preferred, where the heating of the passages 8B is minimal.

The embodiment of the heat exchanger shown in FIGS. 6 to 8 differs essentially from the previous one in that the parts 2A and 2B of the body 2 are no longer distributed according to the thickness of the exchanger, but according to its width, that is to say that part of each passage 8 is used for heat exchange and the rest for additional functions.

Thus, one passage in two consists, over most of its width (FIG. 7), of a nitrogen condensation passage 8A-1 having the constitution described above with regard to FIG. 2 and, on the rest of its width, of an annex passage 8B-1 open at the top and at the bottom and containing a simple vertical wave 9B, the passages 8A-1 and 8B-1 being sealed over the entire length of the body 2 by a vertical bar 10.

The other passages consist (Figure 8) of an oxygen vaporization passage 8A-2 open at its two ends, of the same width as the passages 8A-1 and located opposite these, this passage 8A-2 containing a simple vertical wave, and an annex passage 8B-2 similar to passages 8B-1, with the interposition of a vertical bar 10 between passages 8A-2 and 8B-2.

The box 5 of FIG. 1, intended for the supply of liquid oxygen to the passages 8A-2, is eliminated and replaced by a lower dome 21 connected to a tight seal at the four lower sides of the body 2. Thus, the passages 8A-2 are supplied with liquid oxygen directly from below.

Alternatively (Figures 9 and 10), the passages 8B-1 are closed at the bottom, and the lower dome 21 is replaced by perforations 22 provided in the lower part of the plates 7, in the passages 8B-1. The liquid oxygen then passes into the vaporization passages 8A-2 via a lower side window 17A provided at the base of one strip 10 of two, then is distributed by an oblique wave 18A along the length of the passages 8A-2, the same way as in Figure 3.

This variant can be modified as illustrated in Figures 11 and 12: the holes 22 are deleted; each passage 8B-1 has at its base an outlet window 17B-1 and an oblique wave 18B as in Figures 1 to 4, and each of the passages 8B-2 has at its base an inlet window 17B-2. We find the box 5 of Figures 2 to 4, which covers all the windows 17B-1 and 17B-2. In addition, the lower part of the passages 8B-2 comprises a wave 23 with horizontal generators, for example, as shown, of the "serrated" type, that is to say comprising at intervals regular punctures vertically offset by a quarter of a wave step.

In another variant (Figures 13 and 14), the vertical bars 10 may only be provided between the passages 8A-1 and 8B-1, no partition separating the passages 8A-2 and 8B-2, which comprise only one non-perforated vertical common wave and, in their lower part, a horizontal wave 24 of triangular shape which extends over the entire width of the exchanger.

In such a variant, in one passage out of two, the liquid oxygen follows a downward path in the zone 8B-2, horizontal along the wave 24 then ascending in the zone 8A-2. In this latter zone, the liquid oxygen is in an indirect heat exchange relationship with the nitrogen which condenses in the passages 8A-1, and the passages 8B-1 are dead zones, which can be opened upwards. and therefore filled with liquid oxygen, as shown, or alternatively, closed at their two ends.

Figure 15 shows schematically an application of a plate heat exchanger serving as a dephlegmator, for example to produce nitrogen. In one passage out of two, the air, introduced at approximately 6 bar absolute, is partially condensed upward, as illustrated by the arrows 25, which produces at the bottom of these passages "rich liquid" (air enriched in oxygen) LR and, at the top of the same passages, nitrogen gas NG.

To ensure the condensation of the air, the rich liquid is expanded to 1 bar absolute in an expansion valve 26, which produces a flash. The upper part of the aforementioned passages is used to separate the two phases, which are then recombined in the remaining passages, where the low-pressure two-phase refrigerant rich liquid circulates from top to bottom and is then discharged in the form of a vaporized rich liquid. LRV.

The constitution of the heat exchanger is shown in Figures 16 to 18.

• (1) Une partie principale d'échange thermique 28, s'étendant à partir du bas de l'échangeur, qui comporte, de bas en haut, une zone 29 de distribution d'air et de collection de liquide riche, une zone de déphlegmation 30 et une zone 31 de collection et d'évacuation d'azote gazeux. La zone 29 contient une onde oblique 32 perforée débouchant sur une fenêtre latérale 33 d'entrée d'air et, sous cette onde, une onde verticale 34 qui débouche sur une fenêtre inférieure 35 de sortie de liquide riche. La zone 30 contient une onde verticale 36, et la zone 31 contient une onde oblique 37 débouchant sur une fenêtre latérale 38 d'évacuation d'azote. Des boîtes 39 d'entrée d'air, 40 de sortie de liquide riche et 41 de sortie d'azote communiquent respectivement avec les fenêtres 33, 35 et 38.
• (2) Une partie annexe supérieure 42 formant séparateur de phases. Cette partie contient, de bas en haut, une zone de faible hauteur, sans onde, où chaque plaque verticale présente une rangée horizontale de trous 43, une première zone contenant une onde verticale 44, une zone contenant une onde "serrated" 45 à génératrices obliques, communiquant avec une fenêtre latérale d'entrée 46, une seconde zone contenant une onde verticale 47, et une zone contenant une onde oblique 48 débouchant sur une fenêtre latérale de sortie 49. Des boîtes 50 d'entrée de liquide riche diphasique et 51 de sortie de liquide riche vaporisé recouvrent les fenêtres 46 et 49 respectivement.

One passage in two (Figure 17) is subdivided into two parts by a horizontal bar 27:

• (1) A main heat exchange part 28, extending from the bottom of the exchanger, which comprises, from bottom to top, an area 29 for air distribution and collection of rich liquid, an area for dephlegmation 30 and a zone 31 for collecting and discharging nitrogen gas. The area 29 contains a perforated oblique wave 32 opening onto a side window 33 for air inlet and, under this wave, a vertical wave 34 which opens onto a lower window 35 for outlet of rich liquid. Zone 30 contains a vertical wave 36, and zone 31 contains an oblique wave 37 opening onto a side window 38 for discharging nitrogen. Boxes 39 for air inlet, 40 for rich liquid outlet and 41 for nitrogen outlet communicate with windows 33, 35 and 38 respectively.
• (2) An upper annex part 42 forming a phase separator. This part contains, from bottom to top, a zone of low height, without wave, where each vertical plate presents a horizontal row of holes 43, a first zone containing a vertical wave 44, a zone containing a "serrated" wave 45 with generatrices oblique, communicating with a lateral entry window 46, a second zone containing a vertical wave 47, and a zone containing an oblique wave 48 leading to a lateral exit window 49. Boxes 50 for entering two-phase rich liquid and 51 vaporized rich liquid outlet cover windows 46 and 49 respectively.

The remaining passages 60 (FIG. 18) have, from top to bottom, a vaporized rich liquid inlet zone communicating with a lateral inlet window 52 and containing an oblique wave 53, a zone containing a vertical wave 54, a zone without wave, of low height, into which the holes emerge 43, a heat exchange zone with vertical wave 55, and a liquid outlet zone rich vaporized containing an oblique wave 56 which leads to an outlet window 57. The box 51 also communicates with the windows 52, and an outlet box 58 communicates with the windows 57.

When the relaxed rich liquid enters the two-phase form in the box 50 then in the zones 42 of FIG. 17, it encounters a forest of small obstacles created by the punctures of the "serrated" wave 46. This causes the separation of its two phases. The liquid phase collects on the bar 27 and, crossing the holes 43, penetrates, in the form of as many jets, into the adjacent passages 60 of FIG. 18. At the same time, the vapor phase is returned by the box 51 in the windows 52 of these adjacent passages, so that this vapor circulates downward along the waves 54 and recombines with the liquid at the level of the holes 43, to form a two-phase refrigerant fluid which vaporizes as it descends along the waves 55.

In a variant not shown, it is possible to use the phase separation zone 42 to return the separated vapor phase, via the box 51 and the passages containing the wave 54, to a different level from the exchanger, for example at its end. lower. In this case, the vapor phase is released laterally at said level, taken up by an outlet box and sent by the latter in other passages of the exchanger.

Claims (12)

1. Indirect heat exchanger of the type comprising a series of parallel plates (7) delimiting between them passages (8A, 8B; 28, 42, 60) having a generally flat shape containing corrugated spacers (9, 32, 34, 36, 37, 44, 47, 48, 53 to 56), a first assembly (8A; 28, 60) of these passages constituting heat exchange passages, having means (3 to 5; 39 to 41, 51), for the entry/exit of fluids intended to exchange heat between each other, comprising on at least one part of its length and width, supplementary passages (8B; 42) arranged to fulfil at least one subsidiary function of the heat exchanger, in particular a function of storing liquid and/or recirculating liquid and/or separating liquid from vapour, characterized in that the supplementary passages are all adjacent to each other, in a reduced, or practically zero, heat exchange relationship with the heat exchange passages 8A; 28, 60).
2. Heat exchanger according to claim 1, characterized in that the supplementary passages (8B; 42) are thicker than the heat exchange passages (8A; 28, 60).
3. Heat exchanger according to claim 1 or 2, characterized in that the supplementary passages (8B; 42) contain corrugations (9) that are less dense than those of the heat exchange passages (8A; 28, 60).
4. Heat exchanger according to any one of claims 1 to 3, characterized in that the supplementary passages (8B) are distinct from the heat exchange passages (8A) and, as with the latter, each extends throughout all the length and throughout all the width of the exchanger.
5. Heat exchanger according to claim 4 wherein a means of entry for a first fluid (5) extends through all the thickness of the body of the exchanger while the means of entry for a second fluid (3) and a means of exit for the second fluid (4) only extend through the thickness of the part (2A) of the exchanger comprising solely heat exchange passages (8A).
6. Heat exchanger according to any one of claims 1 to 3, characterized in that at least certain passages of the exchanger constitute a heat exchange passage (8A) over part of the width of the latter and a supplementary passage (8B) over the rest of its width.
7. Heat exchanger according to claim 6 wherein the heat exchange passages (8A; 2) are supplied with liquid from a lower dome (21) connected with a gasket to the lower sides of the exchanger.
8. Heat exchanger according to claim 6 wherein the heat exchange passages (8A; 2) communicate with the supplementary passages (8B; 1) by means of perforations (22) in a plate (7) separating the passages.
9. Heat exchanger according to any one of claims 1 to 3, characterized in that at least certain passages of the exchanger constitute a heat exchange passage (8A) over part of the length of the latter and a supplementary passage (8B) over the rest of its length.
10. Heat exchanger according to any one of claims 1 to 9, wherein the supplementary passages comprise passages for liquid/vapour separation (42), characterized in that these separating passages contain a packing (45) for the separation of liquid from vapour arranged opposite a window (46) for the entry of two-phase fluid.
11. Heat exchanger according to claim 10 characterized in that the packing (45) consists of a corrugation with oblique generating lines.
12. Heat exchanger according to claim 10 or 11, characterized in that the passages for liquid/vapour separation (42) have a vapour outlet window (49) at their upper end covered by an outlet chamber (51), the latter communicating with passages for returning vapour to a different level of the exchanger.

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