FR2891901A1 - METHOD FOR VAPORIZATION AND / OR CONDENSATION IN A HEAT EXCHANGER - Google Patents

Abstract

In this method of vaporization and / or condensation of at least one fluid in a heat exchanger consisting of a stack of at least one tube (3) and at least one folded wave (17), the wave and the tube being preferably brazed with each other, a fluid circulates inside at least one tube, and another fluid circulates around the wave (17) .The invention also relates to an installation for separating a mixture of fluids by cryogenic distillation, comprising at least one heat exchanger operating according to such a method.

Description

The present invention relates to a method of vaporization and

  optionally condensing fluid in a heat exchanger and an installation for separating a mixture of fluids by cryogenic distillation comprising at least one heat exchanger operating according to such a method. In particular, it relates to a method of vaporization and possibly condensation of air gas in an installation for separating air gases by cryogenic distillation. Air separation units have for a very long time used brazed aluminum plate heat exchangers for the reboiler / condenser functions of the distillation columns, in particular the double-column reboiler / condenser with nitrogen in it. condensation and oxygen spraying. Two principles of operation of these reboilers / condensers have been proposed: thermosiphon: this is the oldest solution with two variants: 1) The body of the vaporizer can be arranged vertically and completely (or partially) immersed in a bath of water. liquid oxygen. This liquid oxygen enters the bottom of the vaporizer is warmed to its bubble point and then vaporized partially. The recirculation rate (excess flow of liquid output on vaporized flow) is very high, ranging from 5 to 100. The dimensions of the bodies can be of the order of 1220 mm wide x 1200 mm stacking x 2000 mm length. One of the disadvantages is that even if the minimum gap in the exchanger can be small (0.3-0.4 C), the apparent difference (difference between the temperature of the nitrogen that enters the reboiler condenser and the temperature of the vaporized oxygen) remains high (1.2-1.6 C) because of the hydrostatic liquid height which increases the pressure of said liquid at the bottom of the exchanger and therefore its vaporization temperature. It may be thought that it is possible to reduce the hydrostatic head by not completely immersing the vaporizer, but the recirculation would be reduced. However it is dangerous to operate with zero (or low) recirculation because by vaporizing liquid oxygen (globally or locally), the solubility limit of certain heavy constituents (hydrocarbons for example) in the last drop of liquid is reached. to spray. These heavy constituents may settle and cause an explosion in the vaporizer and combustion of aluminum. 2) The body of the vaporizer is disposed horizontally and completely (or partially) immersed in a bath of liquid oxygen. The operation is identical to that of the vertically installed vaporizer. By decreasing the hydrostatic head, the oxygen side operation is improved. On the other hand, the design of the nitrogen passages is not obvious. Either we limit the length of the body of the heat exchanger (the body is cubic) and we use the same plane of passage io as for the vertical bodies, or we keep the same length of body (2000 mm or more) then we are obliged to circulate the nitrogen horizontally (otherwise the dispensers would take the whole height of the body) with crossed current which causes a dissymmetry of heating which can penalize the performance as well as defects of evacuation of the liquid nitrogen (the gravity the driving down the passages) which also locally penalizes the exchange coefficient. - In film: more recent solution described in particular in US-A-4599097. The liquid is distributed on vertical plates. The hydrostatic pressure no longer penalizes the exchange and small differences (less than 1 C) can be obtained. However, if it is desired to ensure an excess of liquid at the outlet of the exchanger 20 to avoid dry vaporization and the deposition of heavy constituents, a pump is necessary. Otherwise, operation is potentially dangerous for the same reasons as reboilers / condensers. EP-A-1008826 proposes a film vaporizer in which the exchanger comprises passages defined by parallel plates. The liquid vaporization passages contain auxiliary passages comprising only curved surfaces, for example cylindrical tubes. Moreover, two types of design exist: reboiler / condenser inside a column or a shell or external vaporizer, described for example in US-A5333683.

The object of the invention is to provide a method of condensation and / or vaporization using a heat exchanger which overcomes the defects of the prior art 2891901 and more generally a method of heat exchange alternative to that carried out in a brazed aluminum plate heat exchanger, derived from the technology currently used in automotive radiators. For this purpose, the subject of the invention is a method of vaporizing and possibly condensing at least one fluid in a heat exchanger consisting of a stack of at least one tube and at least one folded wave, the wave and the tube being preferably brazed with each other, and in which a fluid, possibly to be condensed, circulates inside at least one tube and another fluid to be vaporized circulates in generated channels by waves. The method according to the invention may further comprise one or more of the following characteristics: the folding of the waves is substantially parallel to the axis of the tubes; the tubes and waves are made of aluminum, pure or alloyed; the tubes and waves are made of copper alloy; The tubes and waves are made of iron-based alloy; the tubes are oblong and / or flattened; a portion of the exchange surface is inside the tubes; the tube has parallel channels inside comprising two parallel flat walls and inner walls connected to the two flat walls and defining the parallel channels; - The exchange surface inside the tubes is obtained by folding, extrusion or brazed preference inserts for example waves; and the waves are perforated, straight, serrated and / or louvered. Alternatively, one could imagine that the vaporization is carried out in the tubes and the invention would then relate to a method of vaporization and possibly condensation of at least one fluid in a heat exchanger consisting of a stack of at least a tube and at least one folded wave, the wave and the tube being preferably brazed to each other, and wherein a fluid, to vaporize, circulates within at least one tube and another fluid possibly to be vaporized circulates in channels generated by waves. The invention more particularly relates to a method of vaporization of at least one liquid derived from air and optionally of condensation of at least one gas 5 derived from air, or which is air, as previously described. . The invention also relates to a method of vaporization of at least one liquid having, as main component, methane and / or carbon monoxide and / or hydrogen, and optionally of condensation of at least one gas whose main component is methane and / or carbon monoxide and / or hydrogen as previously described. The invention finally relates to an installation for separating a fluid mixture by cryogenic distillation in at least one column having at least one heat exchanger operating according to a heat exchange method in a heat exchanger consisting of a stack of at least one tube and at least one folded wave, the wave and the tube being preferably brazed with each other, and wherein a fluid circulates within at least one tube and another fluid circulates around the wave, one warming while the other is cooling. . Preferably, at least one of the heat exchangers of such an installation and one of the following types: i) a vaporizer-condenser allowing the vaporization of a liquid by heat exchange with a gas which condenses on the inside or outside of a distillation column or; ii) a subcooler or; iii) a regeneration gas heater of a purification unit used to purify the mixture to be distilled or; iv) a dephlegmator or; v) a heat exchanger having passages for cooling the mixture to be distilled at a cryogenic temperature or; vi) a cooling exchanger of an inter-stage of a compressor of the mixture to be distilled or a product of the distillation.

The advantages of such a solution are numerous: 1) The production of the exchangers will be able to benefit from the infrastructures available for the production of automobile radiators allowing a very substantial reduction in the cost and time of manufacture of these exchangers.

Today, it takes several months to design and manufacture brazed aluminum bodies. By using automotive radiator technology, once defined standard sizes, manufacturing will only take a few days. 2) This technology will also offer other alternatives in terms of materials. Admittedly, aluminum will remain a possibility but lo copper / bronze or stainless steel exchangers will be possible to achieve. At the same time, by avoiding the risk of burning aluminum (using for example copper-based alloys), the use of reboilers, film condenser is made safer. 3) Using the conventional technology of brazed aluminum plate heat exchangers, when one seeks to put them in the circular shell of a distillation column, the useful section (exchange zone) occupies only about 50% of the section of the column; using this type of radiator technology, we no longer need to put the boxes and collectors at the same altitude as the exchange bodies. These can be advantageously placed above and below the exchangers. 4) By no longer brazing large bodies and using copper-based alloys, there is no longer a risk of sagging or risk of burning aluminum because the material is much more resistant and since it does not give off energy in the event of combustion, the thickness of the waves on the vaporisation side (up to 50 μm) can be considerably reduced. Nevertheless, even if automotive radiator technology can be used, some adaptations are necessary to make it even more interesting for reboiler / condenser use: 1) Cross-current replacement by countercurrent in the case of a vaporization in thermosyphon: 6 2891901 The collectors are placed vertically in a car radiator. In a thermosiphon reboiler-condenser, in which the direction of the condensing fluid in the tubes is counter-current to the direction of the fluid vaporizing in the channels generated by the waves, because of the condensation in the tubes, place the gas manifold at the top and the liquid collector at the bottom, so as to facilitate the gravity flow of the liquid. 2) Replacement of the cross-current by co-current in the case of a film vaporization In this case, the direction of the condensing fluid in the tubes is co-current of the direction of the fluid vaporizing in the generated channels by the waves and a device for supplying the liquid to be vaporized must be added at the top of the waves. 3) In a radiator, water is often cooled in the tubes against air in the waves. Since the air-side exchange coefficient is significantly lower than the water side (at least a factor of 10), the air-side exchange surface is increased by the waves. In the case of vaporization / condensation, the exchange coefficients of both sides are of the same order of magnitude. It is therefore advantageous to have similar exchange surfaces hence the solution of having additional surface inside the tubes: inserts, brazed waves (or not), bends, extrusion ... (US Patent 6241012). 4) Such a structure could also work as a dephlegmator. Finally, the use of exchangers derived from automotive radiator technology in cryogenic distillation gas separation, is not limited to vaporizers-condensers, which vaporize a fluid by heat exchange with another fluid that condenses, but can also be used for: - the regeneration gas heaters of the purification units; subcoolers; - Main exchangers, in particular for vaporizing oxygen gas under pressure in air-conductive copper-based alloy tubes; The interstage cooling exchangers of the compressors.

Particular embodiments of the invention will now be described with reference to the accompanying drawings, in which: - Figure 1 is a front elevational view of a heat exchanger of a first type according to the invention; ; Figure 2 is a schematic perspective view of a heat exchanger for carrying out the process according to the invention; - Figure 3 is a perspective view, on a larger scale and in the same direction, of a portion of the exchanger shown in Figure 1, according to a first embodiment; Figure 4 is a perspective view showing a tube section of the exchanger of Figure 2, according to a second embodiment; - Figure 5 is a sectional view, in a vertical plane, of a stack of tubes and waves of a heat exchanger according to a third embodiment; and FIGS. 6 and 7 are diagrammatic views, respectively from above and from the front, of a reboiler-condenser of an installation according to the invention, which contains exchangers of a second type, similar to the first shown on FIG. Figures 1 and 2. In Figure 1, there is shown schematically a heat exchanger 20 1 structure similar to that of the exchangers used in the cooling circuits of motor vehicles. For the convenience of the following description, FIGS. 1 to 5 will be oriented according to the orthogonal coordinate system X, Y, Z, in which: the X and Z axes define the vertical plane of FIG. 1 and the principal directions in FIG. which extends the exchanger 1, the X axis being assumed horizontal, and the Z axis being assumed vertical; and - the Y axis is the transverse horizontal axis. The exchanger shown in FIG. 1 essentially comprises on the one hand a stack of elongated tubes 3, spaced apart and parallel to one another, and extending horizontally along the axis X, and on the other hand folded oblong fins ( not visible in Figure 1), arranged in the intervals between two consecutive tubes 3. The tubes 3 are connected, at one of their ends, to a distribution column 5, and at their other end to a collecting column 7. The two columns 5, 7 are formed of vertical tubular conduits in fluid communication with each of the tubes 3. Preferably, the tubes 3 are brazed on the columns 5, 7 which have been previously formed to allow the tubes 3 to fit into said columns. These columns are not necessarily of cylindrical shape. It may be a tubular plate stamped to allow the tubes to be interlocked on which the tubes will have been preferably brazed and on which a box of typically half-cylindrical shape will be attached for example by welding after the operation of brazing.

The distribution column 5 is equipped, in an upper part, with a fluid inlet connector 9 for supplying the exchanger 1 with a first fluid. The collecting column 7 is correspondingly provided, in a lower part, with an outlet connection 11 ensuring the evacuation of the first fluid 20 from the exchanger 1. The connections 9, 11 have been schematically represented on the Figure 2. Like that of Figure 1, the exchanger shown in Figure 2 essentially comprises firstly a stack of elongate tubes 3, 25 spaced and parallel to each other, and second oblong elbows folded (not visible in Figure 2), arranged in the intervals between two consecutive tubes 3. However, in the case of the invention, the elongate tubes 3 extend vertically along the Z axis and the direction of waviness or folding of the fins 17 of FIG. 2 is parallel to the longitudinal axis of the tubes 3, c that is, the Y axis; The tubes 3 are connected, at their upper end, to a distribution column 5, and at their other end to a collecting column 7. The two columns 5, 7 are formed of vertical tubular conduits placed horizontally and in fluid communication. with each of the tubes 3. Preferably, the tubes 3 are brazed to the columns 5, 7 which have been previously formed to allow the tubes 3 to fit into said columns. These columns are not necessarily cylindrical. It can be a stamped tubular plate to allow the tubes to be interlocked on which the tubes have preferably been brazed and on which a box of typically half-cylindrical shape will be attached for example by welding after the operation. brazing. The distribution column 7 is equipped, on the left, with an inlet connector 11 making it possible to supply the exchanger 1 with a first fluid in gaseous form. The connector extends perpendicularly to the axis of the distribution column and to the axis of the tubes. This connection could nevertheless extend in another direction, for example along the Z axis or possibly Y. The collecting column 5 is correspondingly provided, in a lower part, with an outlet connection 9 ensuring the evacuation. of the first fluid of the exchanger 1. The connection extends perpendicularly to the axis of the distribution column and to the axis of the tubes. This connection could nevertheless extend in another direction, for example along the Z axis or possibly Y. The connections 9, 11 have been shown schematically in FIG. 2. In the case of a thermosiphon vaporization, a spray fluid (a second fluid) flows through fin 17 in an upward vertical direction (i.e., the fluid to be vaporized is circulated through the channels generated by the waves), and a fluid of higher temperature (first fluid) is circulated inside the tubes 3 in a downward vertical direction.

In the case of a film vaporization, a fluid possibly to be condensed circulates through the fin 17, in a downward vertical direction 2891901 (that is to say that the fluid possibly to be condensed is circulated in the channels generated by the waves), and circulating a lower temperature fluid to vaporize, inside the tubes 3 in a downward vertical direction.

In Figure 3, there is shown a portion of a portion of the exchanger 1 of Figure 1, consisting of two consecutive tubes 3, and a corrugated fin 17 formed between these two tubes. As is apparent from this Figure, the tubes 3 have a running section, in the vertical plane XY, of elongated shape transversely along the X axis, so that they each have two substantially planar and parallel opposite faces. In other words, the tubes 3 have an oblong section along the transverse axis X, and of flattened shape. The fin 17 is corrugated in a direction of corrugation or folding Y, perpendicular to the longitudinal axis of the tubes 3. The fin 17 is fixed to the tubes 3, preferably by soldering, at its vertices 19. This brazing operation may be concomitant with the brazing of the tubes 3 on the columns 5.7. The fins 17 may be of any suitable type, for example one of the following types, commonly used in plate heat exchangers, namely: perforated, straight, serrated (partially offset), herringbone (in zigzag) and shutters. The fins 17 may have, in section in the YZ plane, a sinusoidal, crenellated or triangular shape, or may have any other suitable type of geometric pattern. The hydraulic diameter of the channels formed by the fins 17 is typically between 100 μm and 10 mm. These fins may be of solid sheets, perforated sheets, sintered metal or any other metal structure (foam, ...). The tubes 3 and the fins 17 may be made of pure aluminum or alloyed. Alternatively, the tubes 3 and the fins 17 may be made of copper base alloy.

In another variant, the tubes 3 and the fins 17 may be made of iron-based alloy. The exchanger 1 of FIG. 2 comprises fins 17 oriented no longer along the X axis but along the Z axis.

In the example of Figure 4, the interior volume delimited by each tube is divided in two longitudinally. For this, the tube 103 has its upper face cut along a median longitudinal line, the two edges 21, 22 separated by this line being folded towards the inside of the tube and welded to the bottom wall. The strips thus folded are contiguous and form a double wall separation io between the two longitudinal compartments 103A, 103B thus defined. These compartments are called channels. The welding of the edges 21, 22 on the bottom wall can for example be performed by laser. A heat exchanger formed from tubes of this type is likely to withstand the pressure of the fluid flowing in the channels 103A, 103B because of smaller size than the tube 3. Such a design can be used to generate a number more than 2. Also, a heat exchanger formed from such tubes is capable of operating with three different fluids, one circulating around the fins, another flowing in one of the channels 103A, and the last flowing in the other 1038 channels. In the two channels 103A, 103B, it is thus possible to circulate two different fluids between which heat exchange occurs, so that a part of the exchange surface, which is obtained by folding the edges 21, 22, is located inside the tube 103. In Figure 5, there is illustrated another embodiment of a stack of tubes and fins, adapted for the implementation of the method according to the invention. In this stack, the tubes 203 are also cross-sectionally elongate tubes with opposite flat and parallel faces. Their internal volume, however, is divided into a plurality of parallel longitudinal channels 203A, separated by plane walls 23 parallel to each other, here vertical. The hydraulic diameter of these channels is typically between 100 μm and 10 mm. The walls 23 may be integral with the outer walls of the tube 203, for example by extrusion, or may consist of inserts, preferably brazed. These inserts may be very similar to the fins 17. In the example shown, each layer of tubes consists of two adjacent parallel tubes arranged in the same plane. Thus, a portion of the exchange surface is located inside the tubes 203. Optionally, a wall 204 surrounds the tubes 203 and the fins 17 so as to make the heat exchanger vis-à-vis its environment . This wall can be brazed on the tubes 203 or simply circled around the tubes 203.

In the embodiment of FIG. 5, and contrary to the embodiment of FIG. 3, the fluid to be vaporized circulating around the wave 17 circulates in parallel with the fluids to be condensed circulating in the tubes 203. Preferably, the fluids to be condensed on the one hand, and the fluid to vaporize on the other hand, will be circulated in opposite directions.

FIGS. 6 and 7 diagrammatically show part of the installation according to the invention, which comprises, inside a ferrule 31 of generally cylindrical shape, a series of heat exchangers 301a-301n of Same type, analogous to that of Figures 1 and 2. For these figures, the orthogonal coordinate system Xo, Yo, Zo shown is defined as follows: the axis Zo is the vertical axis oriented from bottom to top; the axis Xo is the horizontal axis defining with the axis Zo the principal planes in which the exchangers 301 extend; and the axis Yo is the horizontal axis orthogonal to the axis Xo.

The exchangers 301a-301n are all arranged parallel and centered on a diametral plane of the cylindrical shell 31, as can be seen in FIG. 6. The length of each exchanger 301a-n is adjusted to the length, along the axis Xo, of the vertical section of the shell 31 on the axis Yo. Thus, the length along the axis Xo of the exchangers 301a-301n increases towards the central axis Zo of the cylindrical shell 31. In contrast to the orientation of the exchanger 1 shown in FIG. Exchangers 301a-n are such that the distribution columns 305a-n extend horizontally on the upper side of the ferrule 31, while the collector columns 307a-n extend on the lower side of the ferrule 31, also horizontally. Thus, the stacks of tubes 303 extend between the columns 305a-n, 307a-n, along the vertical axis Z. Above the distribution columns 305a-n is arranged a gas collector 41 provided for supplying gas the group of exchangers 301 year. The depicted installation further comprises a liquid collector 43, arranged under the collector columns 307a-n, and provided to collect the liquid phase from the group of exchangers 301a-n. The fins stop before the columns 307a-n and 305a-n so as to allow entry and exit of the fluid. The outer wall as shown in FIG. 5 (204) substantially stops at the same levels as the fins also to allow entry and exit of the fluids. The vaporization and condensation process which has been described above, as well as the installation described with reference to FIGS. 6 and 7, applies to the vaporization of at least one liquid derived from air or a liquid which is liquefied air and the condensation of at least one gas derived from the air, this gas can also be the air itself. The method and the installation also apply to the vaporization of at least one liquid having as its main component methane and / or carbon monoxide and / or hydrogen, and the condensation of at least one gas. having as main component methane and / or carbon monoxide and / or hydrogen.

Such a method can be applied to many types of fluid mixing separation facilities, operating by cryogenic distillation, in at least one column having one or more heat exchangers, as previously described.

The installation can in particular be: a vaporizer-condenser for vaporizing a liquid by heat exchange with a gas that condenses inside or outside a distillation column, or -cooler, or io - a regeneration gas heater of a purification unit used to purify the mixture to be distilled, or - a dephlegmator, or - a heat exchanger having passages for cooling the mixture todistiller to a cryogenic temperature, or a cooling exchanger of an inter-stage of a compressor of the mixture to be distilled or a product of the distillation. 15

Claims (20)

  A method of vaporizing and / or condensing at least one fluid in a heat exchanger (1; 301) consisting of a stack of at least one tube (3; 103; 203; 303) and at least one a folded wave (17), the wave and the tube being preferably brazed with each other, and in which a first fluid, possibly to be condensed, circulates inside at least one tube, and a second fluid, possibly to be vaporized circulates around the wave (17) in which a) the first fluid condenses and the second fluid vaporizes or b) the first fluid vaporizes and the second fluid is condensed.   2. Method according to claim 1, wherein the folding of the waves (17) is substantially parallel to the axis (X or Z for Figure 2; Zo) of the tubes (3; 103).   3. Method according to claim 1 or 2, characterized in that the tubes (3; 103; 203; 303) and waves (17) are made of aluminum, pure or alloyed.   4. Method according to claim 1 or 2, characterized in that the tubes (3; 103; 203; 303) and waves (17) are made of copper-based alloy.   5. Method according to claim 1 or 2, characterized in that the tubes (3; 103; 203; 303) and waves (17) are made of iron-based alloy.   6. Method according to one of the preceding claims, characterized in that the tubes (3; 103; 203; 303) are oblong and / or flattened.   7. Method according to one of the preceding claims, characterized in that a portion of the exchange surface (23) is inside the tubes (103; 203).   8. Method according to one of the preceding claims, characterized in that the exchange surface inside the tubes (103; 203) is obtained by folding, extrusion or brazed preference inserts. 16 2891901   9. Method according to one of the preceding claims, characterized in that the waves (17) are perforated, straight, serrated (partially offset), herringbone (zigzag) and / or louvers.   10. Method according to one of the preceding claims wherein the first fluid circulates inside at least one tube in a downward vertical direction.   11. The method of claim 10 wherein the first fluid is a fluid that vaporizes in the at least one tube and the second fluid possibly to be condensed circulates around the wave (17) in a downward vertical direction.   12. The method of claim 10 wherein a fluid to be vaporized (second fluid) circulates around the wave (17), in an upward vertical direction.   13. A method of vaporization of at least a liquid derived from air and optionally condensation of at least one gas derived from air or which is air according to one of the preceding claims.   14. Process for the vaporization of at least one liquid containing, as the main component, methane and / or carbon monoxide and / or hydrogen and optionally condensation of at least one gas whose main component is methane and / or carbon monoxide and / or hydrogen according to one of claims 1 to 12.   15. Heat exchanger consisting of a stack of at least one tube (3; 103; 203; 303) and at least one folded wave (17), the wave and the tube being preferably brazed one with the other, a distribution column for sending a first fluid, possibly to be condensed, inside at least one tube at one end of the tube, a collecting column for collecting the first fluid at the other end of the tube means for sending a second fluid, possibly to be vaporized around the wave (17), means for collecting the second fluid, characterized in that the folding of the waves (17) is substantially parallel to the axis (X; ) tubes (3; 103). 17 2891901   16. Heat exchanger according to claim 15 wherein a fluid inlet pipe connected to the distribution column and / or a fluid collection pipe connected to the collector column has an axis perpendicular to the axis of the tubes.   17. Exchanger according to claim 15 or 16 comprising two series of tubes, a first series connected to an inlet and an outlet for the first fluid and the second series connected to an inlet and an outlet for the second fluid, wherein at least one tube of the second series contains the wave (17).   18. Apparatus for separating a mixture of fluids by cryogenic distillation in at least one column having at least one heat exchanger operating according to the method of one of claims 1 to 14 or being according to claim 15, 16 or 17.   19. Installation according to claim 18 wherein at least one of the heat exchangers, operating according to the method of one of claims 1 to 14 or being according to claim 15, 16 or 17, is - a vaporizer-condenser for vaporization d a liquid by heat exchange with a gas that condenses inside or outside a distillation column, or - a subcooler, or - a regeneration gas heater of one unit purification device used to purify the mixture to be distilled, or - a dephlegmator, or - a heat exchanger having passages allowing the cooling of the mixture to be distilled at a cryogenic temperature, or - a cooling exchanger of an inter-stage d a compressor of the mixture to be distilled or a product of the distillation.   20. Apparatus according to claim 19 wherein a condenser vaporizer located inside the distillation column is constituted by several exchangers operating according to claims 1 to 14 or being according to 18 2891901 claims 15, 16 or 17, the exchangers being of different widths to fill the entire section of the column.