The present invention relates to a method for vaporization and optionally condensation of a fluid in a heat exchanger and to an installation for separating a mixture of fluids by cryogenic distillation, which includes at least one heat exchanger operating according to such a method. In particular, it relates to a method for vaporization and optionally condensation of air gases in an installation for separating air gases by cryogenic distillation.
Air gas separation units have used brazed aluminum plate heat exchangers for a very long time for reboiler/condenser functions of the distillation columns, especially the reboiler/condenser of the double column with nitrogen condensing and oxygen vaporizing.
Two operating principles for these reboiler/condensers have been proposed:
The liquid is distributed over vertical plates. The hydrostatic pressure therefore no longer adversely affects the exchange and small temperature differences (of less than 1° C.) may be obtained. However, if it is desired to provide excess liquid at the outlet of the exchanger, to avoid dry vaporization and deposition of heavy constituents, a pump is needed. Put another way, the operation is potentially dangerous for the same reasons as for reboilers/condensers.
EP-A-1 008 826 proposes a falling-film evaporator in which the exchanger comprises passages defined by parallel plates. The liquid vaporization passages contain auxiliary passages that have only curved surfaces, for example cylindrical tubes.
Moreover, two design types exist: reboiler/condenser inside a column or a shell, or an external vaporizer, for example described in U.S. Pat. No. 5,333,683.
One object of the invention is to provide a condensation and/or vaporization method using a heat exchanger that alleviates the drawbacks of the prior art and more generally an alternative heat exchange method to that carried out in a brazed aluminum plate exchanger, derived from the technology currently used in automobile radiators.
For this purpose, one subject of the invention is a method for the vaporization and/or condensation of at least one fluid in a heat exchanger consisting of a stack of at least one tube and of at least one corrugated fin, the fin and the tube being preferably brazed to each other and in which heat exchanger a first fluid, optionally to be condensed, flows inside at least one tube and a second fluid, optionally to be vaporized, flows around the fin, in which a) the first fluid condenses and the second fluid vaporizes or b) the first fluid vaporizes and the second fluid condenses.
The method according to the invention may furthermore comprise one or more of the following features:
Alternatively, it would be conceivable for the vaporization to take place in the tubes, and the subject of the invention would then be a method for vaporization and optionally condensation of at least one fluid in a heat exchanger consisting of a stack of at least one tube and at least one corrugated fin, the fin and the tube preferably being brazed to each other, and in which a fluid to be vaporized flows inside at least one tube and another fluid, optionally to be vaporized, flows in channels generated by fins.
The invention aims more particularly to provide a method for vaporization of at least one liquid derived from air and optionally for condensation of at least one gas derived from air, or which is air, as described above.
The aim of the invention is also to provide a method for vaporization of at least one liquid having methane and/or carbon monoxide and/or hydrogen as main component and optionally for condensation of at least one gas having methane and/or carbon monoxide and/or hydrogen as main component, as described above.
Finally, the object of the invention is to provide an installation for separating a mixture of fluids 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 of at least one corrugated fin, the fin and the tube preferably being brazed to each other, and in which a fluid flows inside at least one tube and another fluid flows around the fin, one is heated while the other is cooled.
Preferably, at least one of the heat exchangers of such an installation is one of the types below:
There are many advantages of such a solution:
However, even though the automobile radiator technology may be used, certain adaptations are necessary in order to make it even more beneficial for use in a reboiler/condenser:
Finally, the use of exchangers derived from automobile radiator technology in gas separation by cryogenic distillation is not limited to reboiler/condensers, which vaporize a fluid by heat exchange with another fluid, which condenses, but may also be used for:
Particular embodiments of the invention will now be described with reference to the appended drawings, in which:
For convenience in the following description,
The exchanger shown in
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 from vertical tubular pipes in fluid communication with each of the tubes 3. Preferably, the tubes 3 are brazed to the columns 5, 7, said columns being formed beforehand so as to allow the tubes 3 to be fitted into them. These columns are not necessarily of cylindrical shape. Each may be a tubular plate recessed so as to allow the tubes to be fitted into it, onto which plate the tubes will preferably have been brazed and to which a box, typically of semicylindrical shape, will be attached, for example by welding after the brazing operation.
The distribution column 5 is equipped in an upper part with a fluid inlet coupler 9 allowing the exchanger 1 to be supplied with a first fluid.
The collecting column 7 is correspondingly provided, in a lower part, with an outlet coupler 11 for evacuating the first fluid from the exchanger 1.
The couplers 9, 11 are shown schematically in
The exchanger shown in
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 from vertical tubular pipes placed horizontally and in fluid communication with each of the tubes 3. Preferably, the tubes 3 are brazed to the columns 5, 7, said columns being formed beforehand so as to allow the tubes 3 to be fitted into them. These columns are not necessarily of cylindrical shape. Each may be a tubular plate recessed so as to allow the tubes to be fitted into it, onto which plate the tubes will preferably have been brazed and to which a box, typically of semicylindrical shape, will be attached, for example by welding after the brazing operation.
The distribution column 7 is equipped on the left with an inlet coupler 11, allowing the exchanger 1 to be supplied with a first fluid in gaseous form. The coupler extends perpendicularly to the axis of the distribution column and to the axis of the tubes. This coupler may nevertheless extend along another direction, for example along the Z axis or possibly the Y axis.
The collecting column 5 is correspondingly provided, in a lower part, with an outlet coupler 9 for evacuating the first fluid from the exchanger 1. The coupler extends perpendicularly to the axis of the distribution column and to the axis of the tubes. However, this coupler could extend in another direction, for example along the Z axis or possibly the Y axis.
The couplers 9, 11 have been shown schematically in
In the case of vaporization in thermosiphon mode, a fluid to be vaporized (a second fluid) flows over the fins 17, in an ascending vertical direction (i.e. the fluid to be vaporized is made to flow in the channels generated by the corrugations), and a fluid at higher temperature (first fluid) is made to flow inside the tubes 3 along a descending vertical direction.
In the case of falling-film vaporization, a fluid optionally to be condensed flows over the fins 17 in a descending vertical direction (i.e. the fluid optionally to be condensed is made to flow in the channels generated by the fins) and a lower temperature fluid to be vaporized is made to flow inside the tubes 3 along a descending vertical direction.
As may be seen in this figure, the tubes 3 have a running section, in the XY vertical plane, of transversely elongate shape along the X axis, so that they each have two approximately plane and parallel opposed faces. In other words, the tubes 3 have an oblong cross section on the transverse axis X that is of flattened shape.
The fin 17 is corrugated along a corrugation or folding direction Y perpendicular to the longitudinal axis of the tubes 3. The fin 17 is fixed to the tubes 3, preferably by brazing, at its peaks 19. This brazing operation may be concomitant with the brazing of the tubes 3 to 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 fins, straight fins, serrated (partially offset) fins, herringbone (zig-zag) fins and louvered fins.
The fins 17 may have, in cross section in the YZ plane, a sinusoidal, rectangular 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 made of solid sheet metal, perforated sheet metal, sintered metal or any other metal structure (foam, etc.).
The tubes 3 and the fins 17 may be made of pure or alloyed aluminum.
As a variant, the tubes 3 and the fins 17 may be made of a copper-based alloy.
As another variant, the tubes 3 and the fins 17 may be made of an iron-based alloy.
The exchanger 1 in
In the example shown in
The edges 21, 22 may for example be welded to the lower wall by laser welding.
A heat exchanger made up from tubes of this type is better able to withstand the pressure of the fluid flowing in the channels 103A, 103B since they are smaller than the tube 3. Such a design may be used to generate a number of channels greater than 2.
Incidentally, a heat exchanger made up from tubes of this type is capable of operating with three different fluids, one flowing over the fins, another flowing in the channel 103A and the third flowing in the other channel 103B.
Thus, it is possible to make two different fluids flow in the two channels 103A, 103B, between which fluids a heat exchange takes place so that part of the exchange area, obtained by folding the edges 21, 22, is inside the tube 103.
In this stack, the tubes 203 are again tubes of transversely elongate cross section having plane and parallel opposed faces. However, their internal volume is divided into a plurality of parallel longitudinal channels 203A separated by mutually parallel plane walls 23, which here are vertical. The hydraulic diameter of these channels is typically between 100 μm and 10 mm.
The walls 23 can be made as a single entity with the external walls of the tube 203, for example by extrusion, or else they may consist of inserts, preferably brazed inserts. These inserts may be very similar to the fins 17.
In the example shown, each layer of tubes consists of two adjacent parallel tubes lying in the same plane.
Thus, part of the exchange area lies inside the tubes 203.
Optionally, a wall 204 surrounds the tubes 203 and the fins 17 so as to seal the exchanger from its environment. This wall may be brazed to the tubes 203 or simply enclosed around the tubes 203.
In the embodiment shown in
In these figures, the orthogonal reference frame X0, Y0, Z0 shown is defined as follows:
The exchangers 301a-301n are all parallel to one another and centered with respect to a diametral plane of the cylindrical shell 31, as may be seen in
Unlike the orientation of the exchanger 1 shown in
Placed above the distribution columns 305a-n there is a gas header 41 designed for supplying the group of exchangers 301a-n with gas.
The installation shown also includes a liquid header 43 placed beneath the collecting columns 307a-n and designed to collect the liquid phase coming from the group of exchangers 301a-n.
The fins stop before the columns 307a-n and 305a-n so as to allow the fluid to enter and leave. The external wall shown in
The vaporization/condensation method that has been described above and the installation described with reference to
The method and the installation also apply to the vaporization of at least one liquid having methane and/or carbon monoxide and/or hydrogen as principal component and to the condensation of at least one gas having methane and/or carbon monoxide and/or hydrogen as principal component.
Such a method may apply to many types of installations for separating mixtures of fluids, operating by cryogenic distillation, in at least one column having one or more heat exchangers such as those described above.
The installation may in particular be:
Number | Date | Country | Kind |
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0553028 | Oct 2005 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR2006/050962 | 9/29/2006 | WO | 00 | 10/6/2008 |