Patent Application
20200400392
The invention relates to a plate heat exchanger and to a method for producing such a plate heat exchanger.
Plate heat exchangers which are configured to indirectly transfer the heat from a first fluid to another second fluid are known from the prior art. The fluids in the plate heat exchanger are guided in separate heat exchange passages of the plate heat exchanger block. These heat exchange passages are delimited in each case by two parallel partitions of the plate heat exchanger block, between each of which is arranged a heating surface element, which is also referred to as a fin or lamella.
Such plate heat exchangers are shown and described in, for example, “The Standards of the Brazed Aluminium Plate-Fin Heat Exchanger Manufacturers' Association,” ALPEMA, third edition, 2010.
Furthermore, such aluminum plate heat exchangers are used, in particular, in cryogenic processes—for example, in air separation units. Said partitions or separating plates and fins form the heating surface, on the one hand, and, on the other, must absorb the forces from the internal overpressure. Different partitions and fin types are available for this purpose, but the design possibilities are limited by the pressure-carrying function. An arbitrary reduction in the specific heating surface is, therefore, not possible. It is also usually not desired, since a high heating surface density, and thus as compact a design as possible, is normally desired.
Starting—in particular, restarting—heat exchangers—in particular, aluminum plate heat exchangers—after a short or medium-term unit downtime can lead to very high thermal stresses. This applies, in particular, when the total temperature change in the apparatus is great, as is the case, for instance, with main heat exchangers of air separation units. As a result, such heat exchangers run the risk of being damaged even by a relatively small number of restart processes, due to material fatigue.
In this respect, however, units are desired which can be operated flexibly, which, in particular, includes the aforementioned operating interruptions.
The high thermal stresses are caused as follows: As a rule, all process flows come to a halt in the event of a unit downtime. Starting from a temperature profile with a warm and a cold end, the material temperature differences slowly equalize as a result of thermal conduction within the heat exchanger, and the apparatus assumes a homogeneous (average) temperature which lies between the maximum and minimum temperatures of the initial state. The insulation losses are generally small so that this state changes only slowly.
If the process flows are now started again, they impinge on the heat exchanger with a very high temperature difference. As a result, the wall temperature, temporally, changes rapidly—particularly in the region of the flow inlets—and, locally, very steep wall temperature gradients develop along the main flow direction. The temporal and local temperature gradients cause said thermal stresses. Particularly in the case of large heat exchangers, which are manufactured in modular fashion and have a plurality of plate heat exchanger blocks connected to one another, the thermal stresses can be considerable.
Based thereupon, the aim of the present invention is to provide a plate heat exchanger which is improved with regard to the aforementioned problem.
This aim is achieved by a plate heat exchanger having the features of claim 1.
Accordingly, a plate heat exchanger with a plate heat exchanger block is provided, which has a plurality of partitions (for example, in the form of separating plates) which are arranged parallel to one another and form a plurality of heat exchange passages for fluids which are to be brought into indirect heat exchange with one another, wherein the heat exchange passages are delimited—in particular, closed to the outside—by lateral strips (e.g., in the form of sheet metal strips), which are also referred to as sidebars, provided, in particular, so as to be flush with the edge of the partitions, and wherein at least one heat-conducting element (also referred to as a fin) is arranged between, in particular, each two adjacent partitions, and wherein the heat exchange passages—in particular, each heat exchange passage—has an inlet for inflow of a fluid and an outlet for outflow of the fluid.
According to the invention, it is provided that one or more partitions and/or one or more heat-conducting elements and/or one or more lateral strips each have a coating of a heat-insulating material, which is applied to the respective partition, the respective heat-conducting element, or the respective lateral strip.
The two outermost partitions of the plate heat exchanger block, which delimit the plate heat exchanger block to the outside, are also referred to as cover walls and are formed, in particular, by cover plates.
The respective heat exchange passage is thus delimited by two adjacent partitions and has at least one heat-conducting element (fin) arranged between these partitions.
According to one embodiment, the respective heat-conducting element forms with the two adjacent partitions a plurality of flow channels of the respective heat exchange passage, wherein the coating is applied to the respective heat-conducting element and the two adjacent partition plates such that the respective flow channel has a circumferential inner side which is coated with the heat-insulating coating. The coating is preferably applied in such a way that the respective flow channel in a first section has an unbroken coating, i.e., continuous coating, on its inner wall.
According to a further embodiment, it is provided that the respective heat-conducting element has alternating and preferably parallel peaks (or head sections) and valleys (or foot sections), wherein the peaks and valleys are respectively connected to one another via, in particular, vertically running webs. The alternately arranged peaks and valleys together with the webs form a corrugated structure of the respective heat-conducting element.
If the peaks are connected to one partition of the two adjacent partitions, and the valleys are connected to the other partition of the two adjacent partitions, a plurality of flow channels are formed in a respective heat exchange passage. The respective flow channels are thus delimited by the partitions, the peaks or the valleys, and the webs of the respective heat-conducting element.
Such plate heat exchangers or the uncoated components of the plate heat exchanger are preferably formed from an aluminum alloy, wherein the components are preferably connected to one another by brazing. In the production of a plate heat exchanger, heating surface elements, separating plates, cover plates, and sidebars, which are partially provided with solder, are preferably stacked on top of each other in a cuboidal block and are then soldered in a vacuum soldering oven to form a heat exchanger block. However, other production methods are also conceivable.
The heat-conducting elements, which are optionally coated as described above, may, in particular, also be so-called distribution fins, which distribute the fluid flow over the entire width of the respective heat exchange passage, i.e., from sidebar to sidebar. Such distribution fins may also be integrally formed with a downstream, heat-conducting element/fin.
According to one embodiment of the invention, it is provided that the respective partition having the coating and/or the respective heat-conducting element having the coating each have a first section (which is, for example, adjacent to the inlet or is arranged adjacent thereto), arranged at the respective inlet, and a second section, which is connected to the first section and is further away from the inlet than the first section, wherein, in each case, only the first section has the coating, and wherein, in each case, the second section does not have the coating, i.e., in other words, thus has no heat-insulating coating. In other words, the first section is thus arranged in such a way that the fluid flows through it before the fluid flows through the second section.
Accordingly, the flow channels formed by the partitions and heat-conducting elements thus have a first section (closer to the inlet) and a second section (closer to the outlet), wherein, in each case, only one inner side or inner wall of the first section of the respective flow channel has the heat-insulating coating.
Furthermore, according to one embodiment of the invention, it is provided that the plate heat exchanger block has at least first heat exchange passages for receiving a first fluid and second heat exchange passages for receiving a second fluid, wherein the surfaces of the partitions and/or lateral strips assigned to the first heat exchange passages, and/or the heat-conducting elements assigned to the first heat exchange passages, each have, at least in sections, a coating of the heat-insulating material-specifically, in particular, only the first sections of said partitions and/or heat-conducting elements—and/or lateral strips, and wherein the surfaces of the partitions and/or of the lateral strips assigned to the second heat exchange passages, and/or the heat-conducting elements assigned to the second heat exchange passages, do not have a coating of the heat-insulating material.
Here, in particular, only the flow channels of the first heat exchange passages have a heat-insulating coating—specifically, in particular, only the inner sides or inner surfaces of the first sections of the flow channels—whereas the flow channels of the second heat exchange passages, in particular, do not have the heat-insulating coating.
Furthermore, it is provided according to one embodiment of the invention that the heat-insulating material is one of the following materials or has one of the following materials: a plastic, a polymer, or a ceramic.
According to a further embodiment of the invention, it is provided that the partitions and/or the heat-conducting elements and/or the lateral strips (apart from the coating) are formed from one of the following materials or have one of the following materials: aluminum, or an aluminum alloy. As alloys, SB-209 (ASME), SB-221 (ASME), or EN-AW-3003 (EN) can be used, for example.
Furthermore, one embodiment of the invention provides that the heat-insulating material has a thermal conductivity or a thermal conductivity coefficient that is less than 5 W/mK—in particular, less than 1 W/mK.
By way of contrast, the base material of the respective partition or of the respective heat-conducting element, or the respective uncoated partition or the respective uncoated heat-conducting element according to one embodiment typically has a thermal conductivity coefficient (for example, at 70 K) in the range of about 130 W/mK (at 70 K) to about 150 W/mK (at 300 K).
Furthermore, it is provided according to one embodiment of the invention that the respective coating has a thickness (in particular, normal with respect to the extension plane or to the surface of the respective partition or of the respective heat-conducting element) of less than or equal to 0.2 mm.
Furthermore, one embodiment of the invention provides that the respective uncoated partition (in particular, normal with respect to the extension plane of the surface of the respective partition) has a thickness in the range of 1 mm to 2 mm.
According to one embodiment of the invention, it is furthermore provided that the respective uncoated heat-conducting element (in particular, normal with respect to the extension plane of the surface of the respective base body) has a thickness in the range of 0.2 mm to 0.6 mm.
In order to introduce fluids, a collector with a nozzle is in each case, according to one embodiment of the invention, attached above the inlet of the at least one first heat exchange passage as well as above the inlet of the at least one second heat exchange passage, wherein the nozzles serve to connect supply pipelines.
Such collectors can be designed, for example, as half-cylinders which are closed at the two opposite end faces. Furthermore, such a collector preferably has a peripheral edge, via which the collector is welded to the plate heat exchanger block. The partitions and fins preferably run perpendicularly to a longitudinal axis of the collector when said collector is welded to the plate heat exchanger block as per its intended purpose. In this way, inlets or outlets of the respective heat exchange passage, each delimited by two adjacent partitions, can open into the respective collector. Furthermore, the nozzle associated with the collector is preferably cylindrical and is welded to the collector via an end face of the nozzle so that the nozzle is in flow connection with a through-opening of the collector or with the collector.
According to one embodiment, the plate heat exchanger has, per fluid, at least two collectors with nozzles, which is fed into the plate heat exchanger, wherein the fluid can be introduced via the one first nozzle and collector into the associated heat exchange passages and can be discharged again via the other second collector or nozzle.
Also, with respect to the collectors/nozzles, one embodiment of the invention provides that the collector and/or the nozzle of the first heat exchange passages have a coating of the heat-insulating material on its respective inner sides (or inner walls or inner surfaces). By way of contrast, the collectors and/or nozzles of said second heat exchange passages according to one embodiment of the invention have no coating of the heat-insulating material.
Furthermore, it is provided according to one embodiment of the invention that the respective heat-conducting element has a corrugated structure with alternating foot sections and head sections, wherein the respective foot section is connected via a web to an adjacent head section so that said corrugated structure results. The corrugated structure, in the transition from the foot sections or head sections to the respective webs, can be formed so as to be rounded. However, it can also have a rectangular or stepped shape. Flow channels for guiding the relevant fluid in the respective heat exchange passage are formed by the corrugated structure, together with the partitions on both sides.
According to one embodiment of the invention, it is provided that the respective heat-conducting element is not coated with the heat-insulating coating at the contact surfaces via which the respective heat-conducting element is connected (in particular, soldered) to an adjacent partition.
According to a further embodiment, it is provided that the webs of the respective heat-conducting element (in particular, in the first section of the respective heat-conducting element) have the heat-insulating coating or are coated with the heat-insulating coating.
Furthermore, one embodiment of the invention provides that the respective heat-conducting element has the heat-insulating coating or is coated with the heat-insulating coating only in the region of the webs.
A further embodiment provides that the respective heat-conducting element (in particular, in the first section) has the heat-insulating coating or is coated with the heat-insulating coating only in the region of the surface facing the respective flow channel.
Due to the preferably corrugated structure of the heat-conducting elements, a coating of the webs has already proven to be very effective due to the comparatively large total surface area of the webs (in comparison to the surface of the respective partition).
A further aspect of the present invention relates to a method for producing a plate heat exchanger according to the invention, wherein a flowable material, which in the hardened state forms a heat-insulating material, is introduced into heat exchange passages of the plate heat exchanger block whose partitions and/or heat-conducting elements and/or lateral strips are to receive said coating, wherein the material is cured so as to form said coatings. In this case, the flowable material is introduced, in particular, into said flow channels of the heat exchange passages which are formed by the respective heat-conducting element, the two adjacent partitions, and, optionally, the lateral strips.
According to one embodiment of the method according to the invention, it is provided that the plate heat exchanger block is immersed in the flowable material, at least in sections—in particular, with a first section—in order to introduce the flowable material into the corresponding heat exchange passages or flow channels. With such an immersion method, the size of the region to be coated can, advantageously, be precisely controlled.
In this respect, it is provided according to one embodiment of the method that heat exchange passages or flow channels that are not to be coated are suitably sealed beforehand so that the material cannot penetrate there.
A further aspect of the present invention relates to a method for operating a plate heat exchanger according to the invention, wherein at least one first and one second fluid are respectively introduced into at least one heat exchange passage of the plate heat exchanger so that said fluids can exchange heat indirectly.
In the context of the present invention, said (at least two) fluids or fluid streams can be materially identical or differ in their material composition.
Furthermore, in accordance with one embodiment of the method according to the invention, as in the case of the plate heat exchanger according to the invention, all heat exchange passages (or their flow channels) can have a coating of the heat-insulating material (in particular, a coating of the partitions and/or heat-conducting elements, and/or the lateral strips of the respective heat exchange passage).
According to a further embodiment of the method/plate heat exchanger according to the invention, only those heat exchange passages or flow channels which are assigned to a specific fluid (e.g., the first fluid) can have a coating of the heat-insulating material (in particular, a coating of the partitions and/or heat-conducting elements and/or the lateral strips of the respective heat exchange passage), while other heat exchange passages (in particular, their partitions and/or heat-conducting elements) or flow channels have no coating of the heat-insulating material. In this case, the individual coatings can be formed or arranged in one of the ways already described above.
Furthermore, one embodiment of the method according to the invention provides that the first fluid is introduced into the at least one first heat exchange passage and the second fluid is introduced into the at least one second heat exchange passage.
According to one embodiment of the method according to the invention, it is further provided in this case that, when the plate heat exchanger is started up, the first fluid is introduced into the at least one first heat exchange passage before the second fluid is introduced into the at least one second heat exchange passage.
The startup refers, in particular, to a process in which—for example, after a stoppage of all fluids that were previously conducted through the plate heat exchanger or through heat exchange passages of the plate heat exchanger, or after a first provision of the heat exchanger not yet used previously for heat exchange—the fluids involved in the heat exchange are reintroduced into the plate heat exchanger, wherein the first fluid is introduced into the plate heat exchanger prior to the second fluid. In particular, the first fluid is introduced into the plate heat exchanger first (i.e., prior to all other fluids, or at least simultaneously with, optionally, further fluids). Alternatively, the first fluid is at least among those fluids that are introduced into the plate heat exchanger prior to the second fluid.
Furthermore, one embodiment of the method according to the invention provides that the first fluid be introduced into the at least one first heat exchange passage via the nozzle and collector which is arranged above the inlet of the at least one first heat exchange passage.
Furthermore, for example, the at least one first fluid, which is, in particular, introduced during startup prior to all other fluids, can have an inlet temperature in the plate heat exchanger in the range of 3 K to 360 K, wherein the plate heat exchanger can have a temperature—in particular, a homogeneous temperature—in said range of 3 K to 360 K prior to startup.
Furthermore, during startup, the first fluid can have a temperature which differs from a temperature of the plate heat exchanger prior to startup by a temperature differential which is, for example, in the range of 10 K to 100 K—in particular, 20 K to 50 K.
The technical teaching according to the invention advantageously allows temporal and local temperature gradients to be reduced by an optionally partial reduction of the heat transfer. As a result, the thermal stresses are reduced—in particular, in the aforementioned startup processes—in particular, restart processes. The apparatus can accordingly withstand a higher number of such processes, thereby extending the service life.
Further features and advantages of the present invention shall be described in the following figure descriptions of exemplary embodiments of the invention, with reference to the figures. Shown are:
Heat exchange takes place by means of heat transfer via the separating plates 4 and via the heat-conducting elements 2, 3, which are arranged between the separating plates 4 and are also referred to as fins 2, 3. The fins 2 shown in
The heat exchange passages 1a, 1b are delimited by lateral strips 8, also referred to below as sidebars 8, in the form of sheet metal strips 8 which are, in particular, arranged flush with the edge of the separating plates 4. In particular, the heat exchange passages 1a, 1b are closed off by the sidebars 8 to the outside, i.e., to the surroundings of the heat exchanger 10.
The preferably corrugated fins 2, 3 are arranged within the heat exchange passages 1a, 1b, i.e., between two partitions 4 each, wherein a cross-section of a fin 3 is shown in a detail in
Accordingly, the fins 3 each have a corrugated structure with alternating foot sections 12, hereinafter also referred to as valleys 12, and head sections 14, hereinafter also referred to as peaks 14, wherein the valleys 12 and peaks 14 are arranged parallel to each other. A valley 12 is connected to an adjacent peak 14 via an, in particular, vertically-running web 13 of the relevant fin 3 so that said corrugated structure results. The corrugated structure, in the transition from valleys 12 or peaks 14 to the respective webs 13, can be formed so as to be rounded. However, it can also have a rectangular or stepped shape. Flow channels 40 for guiding the relevant fluid in the respective heat exchange passage 1a, 1b are formed by the corrugated structure, together with the partitions 4 on both sides.
The peaks 14 and valleys 12 of the respective fin 3 are integrally connected to the respectively adjacent separating plates 4—preferably by soldered joints. The fluids participating in the heat exchange are thus in direct thermal contact with the corrugated structures 3 so that the heat transfer is ensured by the thermal contact between the peaks 14 or valleys 12 and separating plates 4, and thus by thermal conduction. In order to optimize the heat transfer, the orientation of the corrugated structure 3 within the heat exchange passages 1a, 1b is selected as a function of the application in such a way that an equal-, cross-, counter-, or cross-counter-flow between adjacent passages 1a, 1b is made possible.
The plate heat exchanger 10 furthermore has inlets 9 to the heat exchange passages 1a, 1b (wherein only an inlet 9 to a second heat exchange passage 1b is shown in
The separating plates 4, fins 3, and sidebars 8 and, optionally, further components (for example, the distribution fins 2 shown) are, for example, connected to one another by brazing. For this purpose, the components, such as heating surface elements (fins) 3, separating plates 4, distribution fins 2, cover plates 5, and sidebars 8, are partially provided with solder and are stacked on top of each other in one block, and are subsequently brazed in a furnace to form a heat exchanger block 11.
For supplying and discharging the heat-exchanging fluids A, B, C, D, E, preferably semi-cylindrical collectors 7 (or headers) are welded on above the inlets 9 and outlets 19, respectively. Furthermore, a cylindrical nozzle 6 is preferably welded to each collector 7. The nozzles 6 serve to connect a supply or discharge pipeline to the respective collector 7.
As already explained above, in the case of plate heat exchangers of the type shown in
According to the invention, it is therefore provided that one or more partitions 4, 5 and/or one or more heat-conducting elements 2, 3 and/or one or more lateral strips 8 each have a coating 41 of a heat-insulating material, which is applied to the respective partition 4, 5 or the respective heat-conducting element 2, 3.
Examples of suitable heat-insulating materials are disclosed herein. The base material is, in particular, an aluminum alloy (for example, of type 3003). Other suitable aluminum alloys/materials are also conceivable.
The heat-insulating coating 41 is preferably applied to the partitions 4 and heat-conducting elements (fins) 2, 3 and, optionally, the sidebars 8 in such a way that the flow channels 40 are coated without gaps with the heat-insulating coating 41, preferably in at least one first section A1 of the heat exchange passages 1a (cf. detail of
In particular, it can be provided according to one embodiment that only a certain region or a first section A1 of the partitions 4, 5 and the heat-conducting elements 2, 3 and/or lateral strips 8 or the flow channels 40 or the heat exchange passages 1a, 1b has a heat-insulating coating 41. This first section A1 can also merge—for example, along the transition plane U indicated by a dashed line in
In this case, the first section A1 preferably adjoins inlets 9 for first heat exchange passages 1a via which a first fluid B is introduced into the block 11 during startup—in particular, restart—prior to other fluids (for example, prior to a second fluid A). Furthermore, such a coating 41 can also be provided on the collector 7 and/or nozzle 6 via which the first fluid B is introduced into the inlets 9.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18020042.0 | Jan 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/025016 | 1/17/2019 | WO | 00 |
