EP1067344B1 - Bath vaporiser-condenser with brazed plates and use thereof in an air distillation device - Google Patents

Description

The present invention relates to a vaporizer-condenser bath of the brazed plate type according to the preamble of claim 1. Such a vaporizer-condenser is known from DE-A-1 152 432 and US-A-5 775 129.

The invention applies in particular to main vaporizers-condensers of air distillation, which vaporizes liquid oxygen under low pressure (typically slightly higher than the atmospheric pressure) by medium nitrogen condensation pressure (typically 5 to 6 at absolute bars), and it will be explained below in this app.

Bath vaporizers / condensers operate in thermosyphon. The bottom-up circulation of oxygen is vaporizing is ensured by hydrostatic pressure due to the height of the liquid oxygen bath.

For safety reasons, the oxygen flow recirculating liquid must be several times greater than the flow of vaporized oxygen. For this reason, we impose that the height of the liquid oxygen bath is approximately equal to the height of the exchanger, that is to say that it is can almost completely immersed in the liquid.

If you want to reduce the temperature difference between the fluid that condenses and one that vaporizes, in order to decrease the pressure of the heating nitrogen and therefore the compression energy of the treated air, it is necessary to increase the heat exchange surface. As the dimensions heat exchangers are limited by space available at the bottom of the distillation column pressure, the height of the exchanger must be increased.

However, such an increase in height increases the hydrostatic pressure of the liquid at the bottom, i.e. at the inlet, spray passages, which creates in the lower part of the exchanger a region containing free liquid sub-cooled and neutralizes at least partially the beneficial effect of increasing the exchange surface.

To avoid this drawback, it has been proposed (see for example US-A-4,606,745) to subdivide the exchanger into several superimposed exchangers each of which is immersed in a reduced height bath. However, this solution does not has not been found satisfactory because a weak bath height leads to a low speed of the vaporized gas leaving of the exchanger. This results in a circulation of fluid insufficient two-phase and deterioration of the exchange thermal.

The invention aims to provide a vaporizer-condenser with thermal performance improved.

• des moyens de transfert de la vapeur issue du sommet des premiers passages de vaporisation à une entrée inférieure des deuxièmes passages de vaporisation; et
• des moyens de distribution de liquide à vaporiser dans le flux de vapeur qui pénètre dans chacun des deuxièmes passages de vaporisation.

To this end, the bath vaporizer-condenser, of the brazed plate type, according to the invention is characterized in that it comprises:

• means for transferring the vapor from the top of the first vaporization passages to a lower inlet of the second vaporization passages; and
• means for distributing liquid to be vaporized in the vapor flow which enters each of the second vaporization passages.

• le vaporiseur-condenseur comprend des moyens d'accélération du flux de vapeur qui pénètre dans chacun des deuxièmes passages de vaporisation, notamment une restriction de la section de passage de ce flux ;
• les premiers et deuxièmes passages de vaporisation sont délimités respectivement par deux corps d'échanges distincts, et lesdits moyens de transfert comprennent un collecteur de l'ensemble de la vapeur issue du sommet des premiers passages de vaporisation, ce collecteur étant relié globalement aux entrées inférieures de tous les deuxièmes passages de vaporisation ;
• les premiers et deuxièmes passages de vaporisation sont délimités par les mêmes plaques, les parties d'échangeur formant un corps d'échangeur unique dans lequel les ondes-entretoises de chaque passage de vaporisation sont interrompues pour la réception desdits moyens de distribution de liquide ;
• le vaporiseur-condenseur comporte une amenée de liquide à vaporiser uniquement auxdits moyens de distribution, lesdits moyens d'alimentation en source recevant le liquide en excès issu de la partie d'échangeur supérieure ;
• ladite amenée de liquide débouche dans un réservoir de liquide ouvert vers le haut, adapté pour créer une hauteur hydrostatique au-dessus desdits moyens de distribution, ce réservoir recevant également le liquide en excès issu du sommet de la partie d'échangeur supérieure et débordant dans un espace qui fait partie desdits moyens d'alimentation en source ;
• lesdits moyens d'alimentation en source sont adaptés pour recevoir le liquide en excès issu du sommet des premiers passages de vaporisation ; et
• lesdits moyens de distribution de liquide comprennent des tubes perforés disposés à l'entrée de chacun desdits deuxièmes passages de vaporisation et dans ces passages, les perforations de ces tubes étant orientées vers le haut.

The vaporizer-condenser according to the invention may include one or more of the following characteristics, taken individually or according to all their technically possible combinations:

• the vaporizer-condenser comprises means for accelerating the flow of vapor which penetrates into each of the second vaporization passages, in particular a restriction of the passage section of this flow;
• the first and second vaporization passages are delimited respectively by two separate exchange bodies, and said transfer means comprise a collector of all of the vapor coming from the top of the first vaporization passages, this collector being connected overall to the lower inlets all second spray passes;
• the first and second vaporization passages are delimited by the same plates, the exchanger parts forming a single exchanger body in which the spacer waves of each vaporization passage are interrupted for the reception of said liquid distribution means;
• the vaporizer-condenser comprises a supply of liquid to be vaporized only to said distribution means, said source supply means receiving the excess liquid from the upper exchanger part;
• said liquid supply opens into a liquid tank open upwards, adapted to create a hydrostatic height above said distribution means, this tank also receiving excess liquid from the top of the upper exchanger part and overflowing into a space which is part of said source supply means;
• said source supply means are adapted to receive the excess liquid from the top of the first vaporization passages; and
• said liquid distribution means comprise perforated tubes disposed at the entrance to each of said second spray passages and in these passages, the perforations of these tubes being oriented upwards.

The invention also relates to an apparatus air distillation comprising a vaporizer-condenser for spray liquid oxygen under low pressure by nitrogen condensation under medium pressure, this vaporizer-condenser being as defined above.

• la Figure 1 représente schématiquement, en coupe verticale dans des passages de vaporisation, un vaporiseur-condenseur conforme à l'invention ;
• la Figure 2 est une vue analogue d'un autre mode de réalisation ;
• la Figure 3 est une vue analogue à plus grande échelle de la région de liaison des deux parties d'échangeur du vaporiseur-condenseur de la Figure 2 ;
• la Figure 4 est une vue partielle prise en coupe suivant la ligne IV-IV de la Figure 1 ; et
• la Figure 5 est une vue partielle prise en coupe suivant la ligne V-V de la Figure 2 ou de la Figure 3.

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

• Figure 1 shows schematically, in vertical section in vaporization passages, a vaporizer-condenser according to the invention;
• Figure 2 is a similar view of another embodiment;
• Figure 3 is a similar view on a larger scale of the connection region of the two exchanger parts of the vaporizer-condenser of Figure 2;
• Figure 4 is a partial view taken in section along the line IV-IV of Figure 1; and
• FIG. 5 is a partial view taken in section along the line VV of FIG. 2 or of FIG. 3.

The vaporizer-condenser 1 shown in Figure 1 is the main vaporizer-condenser of a double air distillation column (not shown in Figure 1) consisting essentially of a distillation column medium pressure and a low distillation column pressure. The vaporizer-condenser 1 is intended to vaporize liquid oxygen from the low pressure column tank by condensation of nitrogen gas at the top of the middle column pressure.

The vaporizer-condenser 1 consists of a body 2A lower heat exchanger surmounted by a heat exchanger body higher 2B. Each exchanger body, of general shape rectangular, consists of a stack of plates vertical rectangles 3A, 3B aluminum, all identical, of peripheral closing bars 4A, 4B and of spacer waves 5A, 5B, for example of corrugated sheet perforated. The whole is brazed in the oven in one surgery. On each body 2A, 2B are welded two boxes of generally semi-cylindrical shape, namely a box upper side 6A, 6B of nitrogen gas inlet and a lower side box 7A, 7B for liquid nitrogen outlet.

Each pair of adjacent plates 3 delimits a passage of generally flat shape. These passages are alternately 8A oxygen vaporization passages, 8B (Figure 1) and nitrogen condensation passages. The bars 4 close the periphery of these passages, except inlet / outlet openings for fluids.

Thus, the passages 8 are closed laterally on their full height and completely open at their ends upper and lower.

On the contrary, passages 8 are closed on all their periphery except for a side window upper nitrogen gas inlet, which leads to the box 6, and a lower side outlet window liquid nitrogen, on which the box 7 opens.

The waves 5 of the vaporization passages have vertical generators over the entire height of these passages. Those of condensation passages have vertical generators over most of the height of these passages, but are extended at the top and bottom by oblique distribution waves which emerge in the nitrogen inlet / outlet side windows, so classic.

• une réserve d'oxygène liquide adaptée pour réaliser une immersion quasi-totale du corps 2A dans ce liquide. Cette réserve peut être la cuve de la colonne basse pression, ou bien, comme représenté, une cuve inférieure 11 disposée sous le corps d'échangeur et dans laquelle débouchent une ou plusieurs conduites de descente 12 ;
• un dôme supérieur 13 qui coiffe l'extrémité supérieure 14A du corps 2A. L'extrémité supérieure des conduites 12 est reliée à ce dôme au niveau de cette extrémité 14A.

Associated with the heat exchanger body 2A:

• a reserve of liquid oxygen suitable for achieving almost total immersion of the body 2A in this liquid. This reserve can be the tank of the low pressure column, or, as shown, a lower tank 11 disposed under the exchanger body and into which open one or more downpipes 12;
• an upper dome 13 which covers the upper end 14A of the body 2A. The upper end of the pipes 12 is connected to this dome at this end 14A.

• un dôme inférieur 15 qui coiffe l'extrémité inférieure 16B du corps 2B et qui communique avec le dôme 13 par une conduite 17 ; et
• un réservoir latéral 18 qui s'étend sur toute l'épaisseur, considérée perpendiculairement au plan du dessin, et sur toute la hauteur du corps 2B. Ce réservoir est ouvert vers le haut sensiblement au niveau de l'extrémité supérieure 14B de ce corps 2B. Au-dessus du réservoir 18 se trouve l'unique alimentation 19 en oxygène liquide du vaporiseur-condenseur. L'extrémité inférieure du réservoir 18 communique uniquement avec des dispositifs 20 d'injection d'oxygène liquide dans l'oxygène gazeux prévus respectivement à l'entrée de chaque passage de vaporisation 8B.

Associated with the heat exchanger body 2B:

• a lower dome 15 which covers the lower end 16B of the body 2B and which communicates with the dome 13 via a pipe 17; and
• a lateral reservoir 18 which extends over the entire thickness, considered perpendicular to the plane of the drawing, and over the entire height of the body 2B. This reservoir is open upwards substantially at the level of the upper end 14B of this body 2B. Above the reservoir 18 is the only supply 19 of liquid oxygen to the vaporizer-condenser. The lower end of the reservoir 18 communicates only with devices 20 for injecting liquid oxygen into the gaseous oxygen provided respectively at the inlet of each vaporization passage 8B.

As seen in Figure 4, each device 20 consists of a perforated tube which extends over the entire the horizontal width of passage 8B, at the lower entrance of it, the 5B wave starting above this tube. The tube diameter 20 is less than the spacing of the two plates 3B which delimit the passage, and the perforations 21 are directed upwards. Each tube 20 is connected by a end at the bottom of tank 18, while its other end is closed.

The vaporizer-condenser also has a downpipe 22 which constitutes the sole supply of the lower body 2A. The entrance to this pipe forms a manifold 23 open upwards, attached to the upper edge of the reservoir 18, while its outlet is stitched at a point intermediate the height of at least one pipe 12.

Furthermore, the upper edge of the body 2B is provided vertical edges 24 which lead into the reservoir 18 all of the liquid oxygen coming out of the end upper 14B, and which direct in the collector 23 the all of the liquid overflowing from the reservoir 18.

In operation, the flow of liquid oxygen arriving in 19 is regulated so that with the overflow of the tank 18, the level of the liquid in the lower body 2A is maintained in the vicinity of the upper end 14A of it. This regulation can be carried out for example by regulating the flow rate of liquid products withdrawn from installation, and / or by regulating the turbine refrigeration production thereof.

Liquid oxygen partially vaporizes in the passages 8A, where the bubbles resulting from the vaporization cause an ascending thermosyphon effect. The fluid biphasic which leaves the upper end 14A divides in a liquid phase which overflows in the pipes 12 to return to the lower bath, and in a vapor phase which is collected by dome 13 and then passes into dome 15 via driving 17.

This gaseous oxygen enters all the passages 8B. At the entrance of each of them, it is accelerated in passing of the tube 20, due to the reduced passage section which is offered, and drives up the droplets of liquid coming out of the orifices 21 under the effect of the hydrostatic height of the liquid in the tank 18. The gaseous oxygen is thus intimately mixed with liquid oxygen at the entrance of passages 8B and causes this liquid, and vaporization continues from bottom to top of these passages. The two-phase fluid coming out of the end upper 14B separates into a vapor phase which rises in the low pressure column, and in a liquid phase which overflows into tank 18.

Line 22 is supplied only by overflow of the reservoir 18, which guarantees the supply sufficient passages 8B in liquid to avoid any drying in them. The lower part of this line 22 forms a liquid guard which forces all of oxygen vaporized in the body 2A to pass in the domes 13 and 15.

Thanks to the arrangement described above, a partial height bath for the exchanger body lower, which reduces the hydrostatic height at the inlet passages 8A and therefore the pressure of the heating nitrogen. Simultaneously, in the upper exchanger, a accelerated two-phase circulation, without liquid bath straightforward, which improves heat exchange in the body higher 2B.

Figures 2, 3 and 4 show a vaporizer-condenser 101 which integrates all the functions of the vaporizer-condenser 1 in a single exchanger body 102, with a particularly simple construction.

The vaporizer-condenser 101 is thus constituted of a single stack of vertical rectangular plates 103, closing bars 104 and spacer waves 105.

The nitrogen condensation passages extend continuously over the entire height of the exchanger, with a single upper input box 106 and one single entry box lower outlet 107, both arranged laterally.

The oxygen vaporization passages 108 are closed laterally over their entire height and completely open at the top and bottom. Their spacer waves 105, at vertical generators, are interrupted at one location intermediate their length. In each free space 25 thus defined is arranged a perforated tube 20 with orifices 21 directed upwards (Figure 5), with the arrangement described above next to Figure 4. However, in this case, the tubes 20 are open at their two ends and open into the lower part of a side tank 18 which surrounds the exchanger body, through holes corresponding side closing bars for passageways 108.

In this way are defined, as in the case of Figure 1, a lower exchanger part 102A containing lower spray passages 108A, and an upper exchanger part 102B containing upper spray passages 108B, with between these passages a space 25 for collection and redistribution of gaseous oxygen which corresponds to space 13, 17, 15 previously described.

The lower part 102A of the exchanger, substantially to the level of the upper end 114A passages 108A, is directly immersed in a bath liquid oxygen 26 collected in the bottom column tank pressure 27, which overcomes the medium pressure column 28.

To ensure that all of the vaporized oxygen in part 102A goes into part 102B, a partition vertical 29 starting from the bottom of the reservoir 18 surrounds the upper region of part 102A and plunges into the bath 26.

The vaporizer-condenser is supplied only at 19 in tank 18. Tank 18 also receives excess liquid oxygen which exits at top of the exchanger. As before, the reservoir 18 feeds the tubes 20, and the liquid which leaves the orifices 21 mixes intimately with the vapor phase of the mixture two-phase from the lower part 102A of the exchanger. The liquid phase of this mixture overflows in bath 26. The latter is also supplied by the tank 18 overflow. These various movements of fluids are indicated by arrows in Figure 2, and the resulting benefits are analogous to those discussed more top opposite Figures 1 and 4.

As you can see, the lower immersed part 8A or 102A of the vaporizer-condenser can, as a variant, be surmounted by more than one exchanger part such as 8B or 102B whose vaporization passages are supplied with a leaves with gaseous oxygen from the exchanger stage underlying, and secondly by liquid oxygen intimately mixed with this gaseous oxygen at their entry. In such a variant, feeding the entire liquid oxygen vaporizer-condenser is preferably only on the highest floor, then each floor on the underlying floor, by overflow.

Claims (9)

1. Bath condenser-reboiler (1; 101), of the type with brazed plates, comprising:

   a lower exchanger part (2A; 102A) comprising a first brazed stack of parallel plates (3A; 3), of corrugated spacers (5A; 105) and of sealing bars (4A; 104), which define a series of first vaporizing passages (8A; 108A) and a series of first heating passages;

   means (11, 12; 26) for supplying, as source, the first vaporizing passages (8A; 108A) with liquid to be vaporized;

   at least one upper exchanger part (8B; 108B) comprising a second brazed stack of parallel plates (3B; 3), of corrugated spacers (5B; 105) and of sealing bars (4B; 104), which define a series of second vaporizing passages (8B; 108B) and a series of second heating passages;

   characterized in that it comprises:

   means (13, 15, 17; 25) for transferring the vapour emanating from the top of the first vaporizing passages (8A; 108A) to a lower inlet of the second vaporizing passages (8B; 108B); and

   means (20) for delivering liquid to be vaporized into the stream of vapour that penetrates each of the second vaporizing passages (8B; 108B).
2. Condenser-reboiler according to Claim 1, characterized in that it includes means for accelerating the stream of vapour that penetrates each of the second vaporizing passages (8B; 108B), especially a restriction in the flow area of this stream.
3. Condenser-reboiler according to Claim 1 or 2, characterized in that the first and second vaporizing passages are respectively bounded by two separate exchange bodies (2A, 2B) and in that the said transfer means comprise a header (13) for all of the vapour emanating from the top of the first vaporizing passages (8A), this header being connected altogether (at 15) to the lower inlets of all of the second vaporizing passages (8B).
4. Condenser-reboiler according to Claim 1 or 2, characterized in that the first (108A) and second (108B) vaporizing passages are bounded by the same plates (103), the exchanger parts (102A, 102B) forming a single exchanger body (102) in which the corrugated spacers (105) of each vaporizing passage are interrupted (at 25) in order to receive the said liquid delivery means (20).
5. Condenser-reboiler according to any one of Claims 1 to 4, characterized in that it includes a feed (19) of liquid to be vaporized to the said delivery means only, the said source supply means (11, 12; 26) receiving the excess liquid emanating from the upper exchanger part (102B).
6. Condenser-reboiler according to Claim 5, characterized in that the said liquid feed (19) runs into a liquid reservoir (18) open at the top, designed to create a hydrostatic head above the said delivery means (20), this reservoir also receiving the excess liquid emanating from the top of the upper exchanger part (102B) and running into a space (12; 26) that forms part of the said source supply means.
7. Condenser-reboiler according to any one of Claims 1 to 6, characterized in that the said source supply means (11, 12; 26) are designed to receive the excess liquid emanating from the top of the first vaporizing passages (8A; 108A).
8. Condenser-reboiler according to any one of Claims 1 to 7, characterized in that the said liquid delivery means (20) comprise perforated tubes placed at the inlet of each of the said second vaporizing passages (8B; 108B) and in these passages, the perforations (21) in these tubes being upwardly oriented.
9. Air distillation unit that includes a condenser-reboiler for vaporizing low-pressure liquid oxygen by condensation of medium-pressure nitrogen, characterized in that the condenser-reboiler (1; 101) is in accordance with any one of Claims 1 to 8.

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