FR2793548A1 - Plate vaporizer-condenser operating as a thermosiphon in which the exchange corrugations of the second passage are vertical and the exchange body has two inlet boxes spaced over its length - Google Patents

Abstract

The width (l) of the plates (11) is vertical and is less than their length (L). The exchange corrugations of the second passages are vertical. The exchanger body has at least two inlet boxes (9) spaced over its length An exchanger body (8) contains a stack of identical vertical rectangular plates (11), wave bracing made of heat exchange corrugations (13) and closing bars (12) which define a number of first passages (15) for vaporization of a cooling fluid, open towards the top and bottom and with wave bracing in the principal vertical direction, and a number of second passages for condensation of a heating fluid. Inlet (9) and outlet (10) boxes for the heating fluid enclose the inlets and outlets of the second passages. The exchanger body has at least two outlet boxes spaced over its length. Each second passage extends over at least most of the length of the exchanger body and an inlet (9) and an outlet (10) box are fitted at each end. An intermediate inlet box and/or an intermediate outlet box are placed on the top and bottom faces respectively at an intermediate point on the exchanger's length. Each second passage has a first dead zone between the intermediate inlet box and the intermediate outlet box and each first passage has a second dead zone with regard to this first dead zone. Each first and second passage includes a zone which carries out a different function from heat exchange, for example recirculation of liquids. Each gap between two adjacent plates defines a second passage over a length L/2+e, where L is the length of the heat exchanger and e the length of a heating fluid distribution zone, and defines a first passage over the rest of its length, with the disposition alternating from one gap to the next. The exchanger body is topped with a dome for collecting the gas from vaporization of the liquid and/or a bottom supply done supplying the liquid to be vaporized to the first passages. The width of the plates (l) is greater than 1220 mm. Double column for distillation of air, with a medium pressure column, a low pressure column and a vaporizer-condenser as described above which puts the head gas from the medium gas column in heat exchange with the base liquid from the low pressure column. The vaporizer-condenser is placed in the bottom of the low pressure column or is outside the double column, with a dome above and/or below the exchanger body.

Description

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  The present invention relates to a vaporizer-condenser with plates operating as a thermosyphon, of the type comprising on the one hand an exchanger body consisting of a stack of vertical rectangular plates, all identical, of spacer waves comprising waves of heat exchange, and closing bars, which delimit a plurality of first vaporization passages for a refrigerant, open upwards and downwards and provided with spacers of spacers with main vertical direction, and a plurality of second passages of condensation for circulating fluid, and on the other hand inlet and outlet boxes for circulating fluid which cover rows of inlet and outlet windows opening into the second passages. The invention applies in particular to the main condenser vaporizers of double air distillation columns, which vaporize low pressure liquid oxygen by heat exchange with nitrogen

medium pressure gas.

  These vaporizers-condensers work either in thermosiphon, or

by liquid runoff.

  In vaporizers-condensers operating in thermosiphon, which are of the type indicated at the beginning, the exchanger body is more or less completely immersed in a bath of liquid oxygen. This liquid oxygen enters the first passages from below, is heated there to its bubble point and is then partially vaporized. The rate of recirculation of the liquid, that is to say the ratio of the flow of excess liquid leaving the first passages at the vaporized flow, is very high and between 5 and 100, to avoid any risky dry vaporization lead to the deposition of heavy impurities, in particular hydrocarbons. Indeed, such a deposit can be

  translate into local explosions in the presence of oxygen.

  To have a significant heat exchange height despite the presence of the nitrogen gas distribution and liquid nitrogen collection zones at the top and bottom of the exchanger body, the latter is arranged with the large dimension ( or length) of the vertical plates. However, this leads to a significant hydrostatic height which decreases the performance.

heat exchanger.

  To reduce this hydrostatic height while retaining a large exchange surface, the plates can be arranged with their length in the horizontal direction. However, a difficulty then arises for

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  second passages: if a general vertical orientation of the exchange waves is kept in these, the height occupied by the distribution and collection waves becomes too great compared to the height of the exchange waves. If, on the contrary, these exchange waves are arranged horizontally, a cross-current exchanger is obtained, which leads on the one hand to a dissymmetry of heating which can penalize the overall thermal performance, on the other hand to evacuation faults of the liquid nitrogen, dragged downwards by gravity, which also penalizes

  locally the heat exchange coefficient.

  As for liquid-vaporizer-condensers (see for example US-A-4 599 097), they avoid the problem of the hydrostatic height of liquid, but they require the use of a liquid ascent pump

  and also present a risk of local dry vaporization.

  The object of the invention is to provide a plate vaporizer-condenser operating as a thermosyphon with a counter-current heat exchange and having a low hydrostatic height and a large exchange surface, while being able to be produced in very large dimensions. in a way

particularly economical.

  To this end, the invention relates to a vaporizer-condenser of the aforementioned type, characterized in that: - the width! plates is arranged vertically and is significantly less than their length L; - The exchange waves of said second passages are in the main vertical direction; and - the exchanger body is provided with at least two inlet boxes

spaced along its length.

  The vaporizer-condenser according to the invention may include one or more of the following characteristics, taken in isolation or in all their technically possible combinations: - the exchanger body is provided with at least two outlet boxes spaced along its length; each second passage extends over at least most of the length of the exchanger body and this body is provided at each longitudinal end with an inlet box and an outlet box;

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  - The exchanger body is provided with at least one intermediate inlet box located on its upper face at an intermediate location of its length; - The exchanger body is provided with at least one intermediate outlet box located on its lower face at an intermediate location of its length; each second passage comprises a first dead zone situated between the intermediate inlet box and the intermediate outlet box, and each first passage comprises a second dead zone opposite

this first dead zone.

  - At a location along the length of the exchanger body, each first passage and each second comprises an area which performs at least one function different from the heat exchange, in particular a liquid recirculation function; each interval between two adjacent plates defines a second passage over a length L / 2 + e, where L denotes the length of the exchanger body and e the length of a distribution zone of circulating fluid, and defines a first passage over the rest of the length of said body, the arrangement being alternated from one interval to the next; - The exchanger body is capped with an upper dome for collecting the gas resulting from the vaporization of the liquid; the exchanger body is provided with a lower dome supplying the source of the first passages of liquid to be vaporized;

  - the width of the plates is clearly greater than 1220 millimeters.

  The invention also relates to a double air distillation column which comprises a medium pressure distillation column, a column

  low pressure distillation and a vaporizer-condenser as defined above

  above which puts the head gas of the medium pressure column in indirect heat exchange relationship with the bottom liquid of the column

pressure.

  The vaporizer-condenser can be placed in the bottom of the column

  low pressure or, alternatively, outside the double column.

  Embodiments of the invention will now be described with reference to the accompanying drawings, in which: - Figure 1 schematically shows part of a double air distillation column according to the invention;

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  - Figure 2 is a view of the vaporizer-condenser of this double column, taken in vertical section along line 11-II of Figure 1; Figure 3 is a view of the same vaporizer-condenser, taken in vertical section along line 111-111 of Figure 1; - Figures 4 and 5 are views similar to Figures 2 and 3 respectively of another embodiment of the vaporizer-condenser according to the invention; - Figures 6 and 7 are views, taken respectively in section

  in two adjacent passages, of another embodiment of the vaporizer-

condenser according to the invention;

  - Figure 8 is a perspective view of another vaporizer-

  condenser according to the invention; - Figure 9 is a plan view of the exchanger body of this vaporizer-condenser; - Figures 10 and 11 are views of the same exchanger body taken

  respectively in section in two adjacent passages, along the lines X-

  X and XI-XI of Figure 9; - Figure 12 is a perspective view of another embodiment of the vaporizer-condenser according to the invention; and - Figures 13 and 14 are views of the same vaporizer-condenser

  taken respectively in section in two adjacent planes.

  FIG. 1 shows schematically the intermediate part of a double air distillation column 1. We see the shell 2 of the double column, common to the medium pressure column 3 and to the low pressure column 4 which is attached to it superimposed. The domed upper bottom 5 of column 3 separates the two columns and retains in the bottom of column 4 a bath of liquid oxygen 6. The nitrogen at the top of column 3 is condensed by indirect heat exchange with liquid oxygen in the main vaporizer-condenser 7 of the double column, which is arranged in the tank of column 4

  and is almost completely immersed in the bath 6.

  The vaporizer-condenser 7 consists of a parallelepipedic exchanger body 8, generally made of aluminum or an aluminum alloy, and four nitrogen inlet / outlet boxes of generally semi-cylindrical shape,

  including two upper inlet boxes 9 and two lower outlet boxes 10.

  The body 8 consists of a stack of a large number of vertical rectangular plates 11, all identical, the length L of which is horizontal and the width / of which is vertical. Between these plates are interposed

  on the one hand peripheral closing bars 12, on the other hand waves-

  spacers, namely main orientation heat exchange waves 13

  vertical and distribution waves 14 of horizontal main orientation.

  The body 8 is assembled in a single operation by brazing in the oven, and

  the four boxes 9 and 10 are welded to this body.

  Between the plates 11 are thus delimited a large number of flat passages which are alternately first vaporization passages 15

  oxygen and second nitrogen condensation passages 16.

  The first passages 15 (FIG. 2) are entirely open on their upper and lower sides, and they are closed on their two vertical sides, over their entire height, by closing bars 12. They contain only exchange waves 13. These waves 13 can be corrugated sheet, possibly perforated, or of the "serrated" type, that is to say at

partial lateral shift.

  The second passages 16 (FIG. 3) are closed over their entire periphery by bars 12, which however leave free, at each longitudinal end, an upper window 17 for the entry of nitrogen gas and a lower window 18

liquid nitrogen outlet.

  Each second passage contains four distribution zones, associated respectively with the four windows 17 and 18. Each of these zones contains a wave 14 in the shape of a very elongated right triangle whose short side coincides with the associated window and whose large side coincides with the adjacent half of the corresponding closure bar 12. The rest of the second passage, which covers a large majority of its surface, is occupied

  by an exchange wave 13. The waves 14 are made of corrugated sheet.

  Each of the two nitrogen inlet boxes 9 covers a horizontal row of windows 17. Likewise, each of the two outlet boxes

  of nitrogen 10 covers a horizontal row of windows 18.

  In operation, the nitrogen gas, coming from the column 3 via pipes 19, is introduced into the second passages 16 via the two boxes 9, is distributed over the entire length of the second passages by the upper waves 14, and condenses in the exchange waves 13. The liquid nitrogen thus obtained, collected in the two boxes 10 by the lower waves 14, is

  returned to reflux in column 3 via lines 20.

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  This condensation causes vaporization of liquid oxygen in the first passages 15. By thermosyphon effect, an ascending circulation of two-phase oxygen is established in these passages. The excess of liquid oxygen joins the bath 6, while the gaseous oxygen resulting from the vaporization rises in the column 4. Thanks to the supply of the second passages 16 by the two ends of the body 8, it is possible to obtain a significant effective exchange area. In fact, the nitrogen distribution zones, which only extend over half of the length L, can have a small height, and the brazing furnaces make it possible to choose very long lengths L while

  that width! is limited by the diameter of the oven (passage to be checked).

  The vaporizer-condenser of Figures 4 and 5 differs from that of

  Figures 2 and 3 with the following points.

  Each passage 15, 16 is split lengthwise. At the length of the passages 16 (Figure 5), the upper and lower closing bars are interrupted to release an upper intermediate window

  21 nitrogen inlet and a lower intermediate window 22 of nitrogen outlet.

  Next to these windows are four additional distribution zones. These zones each contain a secondary distribution wave 23 with an oblique main orientation, in the shape of a roughly isosceles right triangle (?). The adjacent waves 23 each have a horizontal dimension e. and they are opposed by a point. On the height separating the waves 23 is arranged a spacer wave 24 with a vertical main orientation, with a wide pitch. An intermediate nitrogen inlet box 25 covers the row of windows 21, and an intermediate outlet box 26 covers the row

windows 22.

  Thus, the nitrogen gas is distributed on the one hand by the two end boxes 9 as above, on the other hand by the box 25. In the latter, the nitrogen is directed by the waves 23 to the waves 14 located from either side. Likewise, the intermediate lower waves 14 direct the liquid nitrogen towards the lower waves 23, which conduct this liquid nitrogen

  towards the box 26. The wave 24 defines a dead zone of the passages 16.

  The passages 15, for their part (FIG. 4), include a dead zone 27 opposite the waves 23 and 24. This zone 27 is delimited by two intermediate vertical bars 12 and by two horizontal bars, upper 28 and

  lower 29 (?), and it contains a spacer wave 24 with a wide pitch.

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  In the embodiment of FIGS. 6 and 7, each gap separating two plates 11 constitutes over a little less than half of its length a vaporization passage 15 and over a little less than half of its length a condensation passage 16. The remaining length e is dedicated to an intermediate distribution of nitrogen, with a configuration similar to the

half that of Figure 5.

  Thus, the interval shown in Figure 6 contains successively along its length, from left to right in the drawing: a vertical closing bar 12; a vertical exchange wave 13; an intermediate vertical closing bar 12; an intermediate zone of length e, defining a window

  upper nitrogen gas inlet 21, a wave 23 in the shape of a triangle-

  rectangle, a vertical spacer wave 24, a triangle-shaped wave 23-

  rectangle, and a lower window 22 for intermediate liquid nitrogen outlet; a vertical exchange wave 13 framed upwards by two waves 14 and downwards by two other waves 14, as in Figures 3 and 5; and a vertical closing bar 12 which leaves an upper entry window 17 free

  nitrogen and a lower window 18 of nitrogen outlet.

  Each adjacent interval of the exchanger body 8 is identical but reversed right-left. There is therefore a window 21 and a window 22 in each interval, and these rows of windows are capped by upper intermediate boxes 25 of nitrogen gas inlet and lower 26 outlet

  liquid nitrogen as before.

  In operation, the nitrogen gas enters each passage through the boxes 9 and 25 and the windows 17 and 21, is distributed by the waves 23 and 14 (alternately from right and left) higher in the corresponding waves 13, and the liquid nitrogen is collected by the lower waves 14 and 23 and discharged through the windows 18 and 22 and the outlet boxes 10

  (alternately from right and left) and 26.

  Oxygen is vaporized in the other part 15 of each interval,

like before.

  The advantage of this embodiment compared to that of Figures 4

  and 5 lies in the halving of the inactive length e.

  The embodiment of Figures 8 to 11 differs from that of Figures 4 and 5 in the following points:

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  - In the vaporization passages 15 (Figure 10), the intermediate zone is open upwards and downwards and constitutes a zone 27A for recirculating liquid oxygen; - in the condensation passages 16 (FIG. 11), the intermediate zone 21 to 26 is replaced by a zone 27B for recirculation of liquid oxygen identical to zone 27A, framed by two intermediate vertical closing bars 12. In addition, the four central waves 14 are deleted; the boxes 25 and 26 are eliminated, and the entire body of the exchanger is capped by an upper dome 31 for collecting gaseous oxygen, provided at its top with a tube 32 for discharging this gas, and through

  a lower dome 33 for collecting and recirculating liquid oxygen.

  Each dome is welded over the entire periphery of the body.

  In operation, in each passage 16, on each side of the zone 27B, the nitrogen gas is introduced by the upper side box 9, distributed by the upper wave 14 and descends along the exchange wave 13 in condensing. The liquid is collected by the lower wave 14 and evacuated by the

lower side box 10.

  In each passage 15, on each side of the zone 27A, the liquid oxygen rises by partially vaporizing, and the excess liquid oxygen falls back into the dome 33 passing through all the recirculation zones 27A

  and 27B. Thus, the dome 33 supplies the passages 15 at source.

  The embodiment of Figures 12 to 14 combines those of Figures 4 and 5 and Figures 8 to 11. Indeed, it consists of two exchanger bodies such as that of Figures 8 to 11, each equipped with two domes 31 and 33, and an intermediate zone which, in the passages 15, is a dead zone 27 (FIG. 13), and, in the passages 16, is a zone for bilateral distribution of nitrogen gas and bilateral collection of liquid nitrogen , this intermediate zone being capped with the upper nitrogen inlet 25 and lower nitrogen outlet boxes

26.

  This embodiment makes it possible to considerably increase the length L of the plates without significantly affecting the distribution of nitrogen.

  nor the thermal performance of the exchanger.

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Claims (14)

  1. Plate vaporizer-condenser operating as a thermosyphon, of the type comprising on the one hand an exchanger body (8) consisting of a stack of vertical rectangular plates (11) all identical, of spacer waves comprising exchange waves thermal (13), and closing bars (12), which delimit a plurality of first vaporization passages (15) for a refrigerant, open upwards and downwards and provided with spacer waves (13) to vertical main direction, and a plurality of second condensation passages (16) for circulating fluid, and on the other hand inlet (9; 9, 25) and outlet (10; 10, 26) boxes for circulating fluid which cover rows of inlet (17; 17, 21) and outlet (18; 18, 22) windows opening into the second passages, characterized in that: - the width (1) of the plates (11) is arranged vertically and is significantly less than their length (L); - the exchange waves (13) of said second passages (16) are in the main vertical direction; and - the exchanger body (8) is provided with at least two inlet boxes   (9; 9, 25) spaced along its length.   2. Vaporizer-condenser according to claim 1, characterized in that the exchanger body (8) is provided with at least two outlet boxes (10) spaced along its length.   3. vaporizer-condenser according to claim 1 or 2, characterized in that each second passage (16) extends over at least most of the length (L) of the exchanger body (8), and in that this body is provided at each longitudinal end with an inlet box (9) and an outlet box (10).   4. Vaporizer-condenser according to any one of the claims   1 to 3, characterized in that the exchanger body (8) is provided with at least one intermediate inlet box (25) located on its upper face in a   intermediate location of its length.   5. Vaporizer-condenser according to any one of the claims   1 to 4, characterized in that the exchanger body (8) is provided with at least one intermediate outlet box (26) located on its underside in a   intermediate location of its length. 2793548   6. Vaporizer-condenser according to claims 4 and 5 taken   assembly, characterized in that each second passage (16) has a first dead zone (24) located between the intermediate inlet box (25) and the intermediate outlet box (26), and in that each first passage (15 ) -comports a second dead zone (27) opposite this first dead zone.   7. vaporizer-condenser according to any one of claims   1 to 6, characterized in that at a location along the length of the exchanger body (8), each first passage (15) and each second passage (16) comprises a zone (27A, 27B) which provides at least one different function from   heat exchange, including a liquid recirculation function.   8. Vaporizer-condenser according to any one of claims   1 to 7, characterized in that each interval between two adjacent plates (11) defines a second passage (16) over a length L / 2 + e, where L denotes the length of the exchanger body and e the length of a distribution zone for circulating fluid, and defines a first passage (16) over the rest of the length of said body, the arrangement being alternated from one interval to the next.   9. Vaporizer-condenser according to any one of claims   1 to 8, characterized in that the exchanger body (8) is capped with a dome   upper (31) for collecting the gas resulting from the vaporization of the liquid.   10. Vaporizer-condenser according to any one of   Claims I to 9, characterized in that the exchanger body (8) is provided   a lower dome (33) supplying the source of the first passages (15) liquid spray.   11. Vaporizer-condenser according to any one of   Claims 1 to 10, characterized in that the width (1) of the plates (11) is   significantly greater than 1220 millimeters.   12. Double air distillation column, characterized in that it comprises a medium pressure distillation column (3), a low pressure distillation column (4) and a vaporizer-condenser (7) according to one   any of claims 1 to 11 which puts the overhead gas in the column   medium pressure in indirect heat exchange relationship with the liquid low pressure column tank. 1 1 2793548   13. Double column according to claim 12, characterized in that the vaporizer-condenser (7) is arranged in the bottom of the low pressure column (4). 14. Double column according to claim 12, characterized in that   the vaporizer-condenser (7) conforms to claims 9 and 10 taken   together and is arranged outside the double column.