Patent Application
20250012520
The invention relates to the technical field of block heat exchangers. It relates more particularly to a heat exchange block, which is provided with an improved geometry with regards to both thermal and mechanical issues. The invention also relates to an exchanger which is equipped with such a heat exchange block.
Numerous types of heat exchangers are known, of which mention shall be made inter alia of plate, tube or fin exchangers. The invention relates more particularly to a block type heat exchanger. The latter typically comprises first an inlet and an outlet for a so-called process fluid, both provided along main axis of the exchanger. Moreover the casing of this exchanger is equipped with transverse inlet and outlet, both for a so-called service fluid. Process fluid is for example an acid while service fluid is a heat transfer fluid, such as water.
The casing accommodates at least one heat exchange block, typically a plurality of these blocks which are stacked on top on one another. Each block is made of a thermally conductive material. The present invention more specifically relates to process fluids which are corrosive to metals. In this respect, said material is typically graphite optionally associated with additives, for example of the polymer type. This block may be parallelepipedic or cylindrical, bearing in mind that the invention more specifically aims cylindrical shaped blocks.
Two series of channels, intended for the circulation of respectively process fluid and service fluid, are hollowed in said block. The first channels, which are longitudinal, continuously extend between the front faces of the body and open onto said front faces. Moreover the second channels, which are transverse, continuously extend between the opposite transverse faces of the body and open onto said transverse faces.
Block heat exchangers of the above known type are described for example in EP-A-0 196 548 and WO-A-2006/081965.
Block heat exchangers of the prior art, such as above disclosed, are however not satisfactory, in particular with regard to mechanical issues. Indeed, some material failures have been observed, which reduce the lifetime of the exchanger. These failures occur in particular at the outer periphery of the front face of the block, which is upstream with reference to the flow of hot process fluid.
U.S. Pat. No. 3,391,016 describes a process for manufacturing a heat exchange element, which is formed by an annular body of graphite. U.S. Pat. No. 2,821,369 discloses a heat exchanger comprising a plurality of hollow cylindrical blocks of graphite, which are arranged in axial alignment to form a column having a central hollow interior. These two documents deal with heat exchange blocks, the type of which is substantially different from that aimed by the invention. Indeed, due to the annular shape of the blocks, the transverse channels do not continuously extend between the transverse faces of the block.
Finally GB-A-1 078 868 discloses a heat exchanger equipped with several graphite blocks, but which is not provided with an external casing. Each of said blocks is formed by two distinct parts, which are mutually fixed by clamping. This further document is not concerned with a heat exchange block of the type according to the invention, since this block does not include longitudinal and transverse channels. Indeed, in this British document, the process fluid and the service fluid flow into two series of channels which both open onto the front faces of the block. That being said, one aim of the present invention is providing a heat exchange block which makes it possible to remedy the drawbacks, inherent to above-mentioned prior art.
A further aim of the present invention is providing such a block which ensures both satisfactory mechanical and thermal performances to the heat exchanger equipped therewith.
A further aim of the present invention is providing such a heat exchanger, which has a relatively simple structure and which can be manufactured without any particular risk of mechanical rupture, particularly with respect to the channels hollowed in the blocks belonging to this exchanger.
One object of the present invention is a heat exchange block (1; 501; 1001, 2001, 3001) comprising:
According to advantageous features of the heat exchange block according to the invention:
One further object of the present invention is a manufacturing method of a heat exchanger block as defined above, said method comprising:
One further object of the present invention is a heat exchanger (I; II; III) comprising
According to advantageous features of the heat exchanger according to the invention:
One further object of the present invention is a method for the implementation of a heat exchanger as defined above, wherein the first and second fluids are circulated in the first and second channels, so as to enable the heat exchange thereof, first fluid flowing through the exchanger under a monophasic form, without significant condensation in case said first fluid is a gas, said first fluid being in particular admitted in the first inlet means at a temperature superior to 80° C., whereas second fluid is in particular admitted in the second inlet means at a temperature between −20° C. and +35° C.
According to a feature of the invention, said first fluid may be admitted into first inlet means at a temperature superior to 200° C.
Still one further object of the present invention is a method for the implementation of a heat exchanger as defined above, wherein the first and second fluids are circulated in the first and second channels, so as to enable the heat exchange thereof, wherein first fluid is submitted to a condensation through the exchanger, the inlet temperature of first fluid being in particular between +80° C. and +300° C. whereas its outlet temperature is in particular between −15° C. and +60° C., the inlet temperature of second fluid being in particular between −20° C. and +35° C., whereas its outlet temperature is in particular between −15° C. and +45° C.
The invention will be described hereinafter, with reference to the appended drawings, given by way of non-limiting example, wherein:
The following reference numbers will be used throughout the present description
These different blocks 1, 101 and 201 are made of any suitable material, in particular adapted to a corrosive environment, such as for example graphite. Each block has a body, which is referenced 10 for what concerns block 1. Said body has a typical cylindrical shape, with a circular cross-section. In a way known as such baffles 12, which are illustrated in particular on
L1 refers to the main or longitudinal axis of each block, which is parallel with the main axis of the exchanger. In a manner known per se, each block is hollowed with different channels, so as to permit the flow of two fluids intended to be placed in mutual heat exchange.
A first series of channels 20, parallel with the axis L1 and referred to as longitudinal channels, open onto the opposite front faces 2 and 6 of each block. With reference to the flow direction of the fluid along longitudinal channels, each front face 2 is called upstream and each opposite front face 6 is called downstream.
Moreover, a second series of transverse channels 60, extending obliquely, particularly perpendicular to the axis L1, open onto the opposite transverse faces 7 and 8 of each block. In operation two fluids, circulating respectively in the first and second series of channels, are placed in heat exchange. These channels 20 and 60 are distant from one another, that is to say they do not open into one another.
Apart from blocks 1 to 201, heat exchanger I also comprises a lower cover 310, an upper cover 320, as well as a peripheral casing 330. Upper cover 320 is hollowed with an opening 322 intended for the inlet of a first so-called process fluid into the longitudinal channels of all three blocks. This inlet is connected with a source of this fluid, which is situated upstream and is not illustrated. Said opening leads to a space 324, provided in the lower face of the cover.
Moreover, the lower cover 310 is hollowed with an opening 312 intended for the outlet of the first fluid outside the longitudinal channels. This outlet is connected with an appropriate downstream equipment, such as a piping. The latter, which is known as such, is not illustrated on the figures.
Casing 330 defines, with the opposite walls of the blocks, a peripheral bowl 335 intended for the circulation of a second so-called service fluid, intended to be placed in heat exchange with the process fluid in the blocks 1 to 201. For this purpose, the casing is equipped with respective inlet 336 and outlet 337 pipes of this second fluid, connected with another appropriate downstream equipment, such as a further piping. The latter, which is also known as such, is not illustrated on the figures.
Above-mentioned space 324 delimits a peripheral collar 326 which rests upon the upstream block 1, in use. So as to avoid any contact between the two fluids, it is critical to ensure a tight seal between the conducting walls of the block 1 and the collar 326. To this end, the interface between said block and said collar is equipped with sealing means, which are known as such and are not illustrated in detail. Moreover upper cover 320 is provided with pressing means, adapted to exert a controlled compressive force on the block, as well as on said sealing means. In the illustrated example, these pressing means are formed by springs 328, in a way known as such
In the present example, downstream front face 6 of upstream block 1, as well as both front faces 102, 106, 202 and 206 of other blocks 101, 201 are manufactured according to prior art. In other embodiments, in particular the one of
Turning back to
Upstream front face 2 of upstream block 1 is on the contrary manufactured according to the invention. Indeed it is not flush but is however provided with a central recess 22, the depth thereof is substantial, thus delimiting:
In the present embodiment, said central bowl 3 is flush and defines a so-called central reference surface S3. As an alternative, this bowl may not be flush, for example may have a corrugated shape. In this event, said reference surface is defined by the average altitude of said bowl.
Said seat 4 protrudes upstream with respect to said central bowl 3 along the longitudinal direction L1. It defines a so-called peripheral reference surface S4 which is flush in the present embodiment. In some variants this seat is not flush, but is provided for example with grooves adapted to receive some seals. Surface S4 is then defined by the average altitude of the seat, the same way as above mentioned surface S3. In use, collar 326 of upper cover 320 rests upon seat 4, while exerting compressing action on this seat due to the springs 328.
It is to be noted that, in the present example, a shoulder 41 is provided at the radial inner end of seat 4. This shoulder, the function of which is typically to maintain an annular seal, exerts no mechanical action.
Transition portion 5 is rectilinear in the present example, when viewed in cross-section on
Let us define some essential representative dimensions of upstream front face 2 of block 1:
According to an essential feature of the invention, which will be detailed below, said distance h4 is far superior to said distance h3. In this respect, it shall be underlined that the applicant has identified explanations with respect to the drawbacks of prior art, as well as the importance of said essential feature.
Let us refer now to
Let us firstly note R the so-called rest zone where the upper cover 420 rests upon the upstream graphite block 401. In this zone a minimum clamping force has to be applied, which induces a noticeable compressive stress on the area of the graphite column, where the cover 420 is bearing. The compressive load on the rest zone R leads to tensile stresses close to the maximum allowable tensile stress. This problem is compounded by the presence of the upstream transverse channels 460a passing under the surface supporting the cover.
To ensure mechanical performance heat exchangers according to prior art are provided with a substantial thickness of material, which forms a flush front face 402. In other words, as shown on said
Even though this design is theoretically advantageous as far as mechanical matter are concerned, it however creates an undesired thermal-stress issue. The latter, which is illustrated on
In the center C′ of front face 402 the graphite surface is firstly in contact with the hot incoming process fluid. Moreover it is far away from the first cooling channel, due to the high value of h402. In periphery P′ of this front face, the graphite surface is also in contact with the hot incoming process fluid. However, contrary to center C′, this periphery P′ is also quite close from the service fluid, the temperature of which is far inferior to that of process fluid.
As a consequence temperature TC′ in the center is far superior to temperature TP′ in the periphery. As a result the volume of graphite in the vicinity of the center expands more than the volume of graphite in the vicinity of the periphery, which induces the development of a thermal stress across the heat exchanger. This stress is likely to cause some material failure, especially in the periphery area P′.
The latter is indeed submitted to a combination of a mechanical stress due to clamping force, as well as of a thermal stress due to thermal gradient through the graphite block. This failure phenomenon is likely to occur especially in transient modes, when the heat exchanger starts receiving some hot process fluid, after being idle for a time long enough to have an even and low temperature. As a summary the applicant has identified that, even though upstream end of prior art exchange blocks are provided with a substantial thickness of material, it paradoxically leads to mechanical fragility.
As mentioned above one essential feature of the invention is to significantly increase ratio h4/h3. In this respect
As shown by this
In theory this increase of ratio h4/h3 can be achieved, either by increasing the value of h4 and/or by reducing the value of h3. In practice it is preferred to keep h4 at a value, which is similar to that of prior art blocks. In this respect, h4 is advantageously set so that the stress applied by the clamping force, through the upper cover, is compatible with the material mechanical properties. Due to the specific geometry of the front face 2 of the block, the clamping force is mostly carried by the annular seat 4, as well as subsidiary by the transition portion 5.
On the other hand, h3 is significantly reduced so as to reach values that are far inferior to prior art. In other words the central portion of the front face is rendered much thinner than the periphery of the block. Moreover, in a surprising way, this reduction of h3 is not prejudicial to the global mechanical behavior. This makes it possible to lower by far thermal stress, with respect to prior blocks with flush front face such as illustrated on
When compared to the prior art, there is an improved thermal exchange between the column top surface in contact with the hot process fluid and the first layer of channels in contact with the cold service fluid. As a consequence the center portion C of the front face 2, as illustrated on
As a consequence, the thermal stress generated by this thermal gradient is far lower than in prior art, so that lifetime of both block 1 and heat exchanger according to the invention is much longer than in prior art. This reduction of blocks breakages leads to a decrease of the global volume of impregnated graphite to be manufactured. In addition, less wastes of such impregnated graphite are to be handled. These advantages will be illustrated by the comparative example, recited at the end of the present description.
As a summary, the invention takes the side to remove graphite material in a targeted zone. This makes it possible to improve thermal performances, due to this local thinning, while preserving high mechanical performances. Therefore, in a surprising way, removing material is not prejudicial to global mechanical behaviour.
Turning back to graph of
This improvement is due to a technical effect of temperature homogenization throughout the block, the magnitude of which increases with the value of above ratio h4/h3. Let us call threshold ratio, the ratio above which this technical effect becomes significant. According to the general scope of the invention, this threshold ratio h4/h3 is advantageously superior to 1.2, preferably superior to 2.
Moreover those skilled in the art will choose this ratio, so as to preserve the global mechanical strength of the block as well as of the exchanger. In this respect said ratio h4/h3 is advantageously inferior to 50, preferably inferior to 15.
In an advantageous way, with reference in particular to
Turning back to
Block 1 may be manufactured starting from a standard block according to prior art, opposite front faces of which are substantially flush. In this respect, recess 22 is provided in one single of these front faces. This stage may be carried out typically by a machining process. Once said recess has been provided, this leads to the formation of both central bowl 3 and transition portion 5. Typically no material is removed in the periphery of said standard block, at the level of seat 4. Such a manufacturing method is advantageous, since it makes it possible to revamp a classic heat exchange block.
In view of the use of the above heat exchanger I, process fluid and service fluid are admitted in a way known as such, via inlets 322 and 336. Exchanger I is more specifically adapted for a so-called cooling operation, which corresponds to a substantially monophasic flow of process fluid. In this respect, said process fluid may be a liquid or, in case it is a gas, it does not undergo any significant condensation.
In a typical way, admission temperature of process fluid is superior to 80° C. As it will be detailed hereafter, the invention also encompasses the possibility of bowls, which are deeper than the one 3 of the present embodiment. With that in mind, block 1 and exchanger I are more particularly dedicated to treat a process fluid with an admission temperature inferior to 200° C. In this range of temperatures, the specific geometry of this first embodiment is advantageous with regard to prior art designs, for what concerns thermal issues. Moreover, due to its relatively shallow bowl, the manufacturing of the block is convenient.
On the other hand, admission temperature of service fluid is typically between −20° C. and +35° C. Once these two fluids have been admitted in the exchanger, they are placed in heat exchange in a usual way. Cooled process fluid is discharged via the outlet opening 312, at a typical temperature between −15° C. and +60° C., whereas warmed up service fluid is discharged via the outlet tube 337 at a typical temperature between −15° C. and +45° C.
Heat exchange block 501 of this second embodiment mainly differs from above described block 1, in that it is provided with a deeper bowl 503. In a more detailed manner, for a same global size of blocks, the upstream transverse channel 560a is positioned far below transverse channel 60a. In other words, block 501 is provided with less transverse channels with respect to block 1, in the upstream part of these blocks. Schematic
Turning to
The invention encompasses a possibility, according to which upper wall 561 is located under superior wall 838 of the pipe. However this latest possibility is less preferred since it renders the manufacturing more complicated and it reduces heat transfer area, while bringing no further thermal effect.
The values of some other characteristic parameters of this second embodiment are analogous, with respect to the ones of above described first embodiment. Indeed h504 is analogous to h4, h503 is analogous to h3, ratio h504/503 is analogous to ratio h4/h3 and angle a505 is analogous to angle a5.
This second embodiment, provided with a so-called deep bowl 503, is more specifically adapted for cooling operation of the exchanger with high inlet temperature of process fluid, typically superior to 200° C. The applicant has discovered that, for these inlet values of process fluid temperature, a bowl such as the one 3 of first embodiment, does not ensure a completely satisfactory temperature homogenization.
The applicant has in particular discovered that service fluid flow has specific properties, in the very upstream part of block 1. On schematic
These upper lines of channels 60a to 60d therefore form a so-called dead zone, which is referenced DZ on
As a consequence, digging a deeper bowl 503 permits an increased technical effect of temperature homogenization, while reducing the dead zone phenomenon, as above described. In this respect the specific advantages, linked to block 501 provided with a deep bowl according to this second embodiment, will be illustrated by the comparative example recited at the end of the present description.
It shall also be noted that, even though the manufacturing process of block 501 is less convenient than that of block 1, block 501 remains satisfactory for what concerns mechanical strength.
The two above embodiments of the invention, which are dedicated to cooling operations, refer to an exchanger I/II equipped with one single block 1/501 according to the invention. Said block, which is provided upstream with respect to the process fluid flow, is equipped with one single bowl 3/503 which is turned towards fluid process inlet. Indeed, in case of such a cooling, graphite temperature tends to decrease from the top surface S3 or S503 of the block towards the outlet of process fluid, in a substantial linear way. As a consequence the need for temperature homogenization is more particularly required at the upstream part of upstream block, which explains the provision of this single bowl
As a variant, the exchanger may be equipped with an upstream so-called neutral block. In a way known as such, this neutral block does not ensure any exchange function, but an auxiliary function such as the fluid distribution. In this respect the single block according to the invention is positioned upstream, adjacent said neutral block.
Heat exchanger III of this third embodiment mainly differs from above described exchangers I and II, essentially in that it is equipped with blocks 1001, 2001 and 3001 which are according to the invention. In addition, each of these blocks is provided with two temperature homogenization bowls, each located on a respective front face.
In a more detailed manner, upstream block 1001 is provided with an upstream bowl 1003 on its upstream front face 1002, as well as with a downstream bowl 1103 on its downstream front face 1006. Moreover intermediate block 2001 is provided with an upstream bowl 2003 on its upstream front face 2002, as well as with a downstream bowl 2103 on its downstream front face 2006. Finally downstream block 3001 is provided with an upstream bowl 3003 on its upstream front face 3002, as well as with a downstream bowl 3103 on its downstream front face 3006.
In a typical manner, above mentioned bowls 1003, 1103, 2003, 2103, 3003 and 3103 have the same depths, which advantageously corresponds to the depth of bowl 3 of first embodiment. In particular, it is less preferred to provide deep bowls, such as the one 503 of second embodiment.
The exchanger III of this embodiment is more particularly adapted for a condensation operation, which corresponds to a biphasic flow of process fluid. In this respect, said process fluid is a gas submitted to a condensation, which may be complete or partial. By way of example, the inlet temperature of process fluid is between +80° C. and +300° C., whereas its outlet temperature is between −15° C. and +60° C. Moreover the inlet temperature of service fluid is between −20° C. and +35° C., whereas its outlet temperature is between −15° C. and +45° C.
With reference to
Moreover the location of the zone Z2, Z′2 may vary along the exchanger, depending upon several parameters which may be the type of fluids, but also the operative conditions. In this respect, the solid line curve of
As a consequence the need for temperature homogenization, in the present case of condensation, is required throughout the whole exchanger, and not only in its upstream part like for cooling operation. This acknowledgement, by the applicant, explains the advantageous provision of bowls not only on all blocks, but also on each front face of these blocks.
It can be noted that the gas condensation provokes a significant temperature increase DT, which is likely to break or at least weaken the graphite in prior art. On the contrary, due to the invention, the temperature barely increases in the zone dt, which is favorable to the mechanical integrity of the exchanger. In addition the two above commented curves are mixed in the very upstream part of the exchanger, as well as in its downstream part.
In the embodiment of
Finally, in the three main embodiments of the invention, the exchanger extends vertically with a top inlet of process fluid, as well as a bottom outlet of said process fluid. Alternatively said process fluid may flow from the bottom to the top. As another variant, the exchanger may extend horizontally or in an oblique manner.
As a summary, the invention is based on the identification of the function of the bowl, which makes it possible to homogenize the graphite temperature over at least part of the exchanger. Moreover, depending upon the different applications, several embodiments may be considered, as it has been above detailed. In case of a cooling, one single bowl is preferred, in particular with a deep bowl if admission temperature of process fluid is high. In case of condensation, a plurality of bowls are preferred on every front face of every block.
It is to be noted that the bowl(s), provided in the front face(s) of the block(s) according to the invention, is (are) different from the chambers provided in the blocks disclosed in the above discussed U.S. Pat. Nos. 3,391,016, 2,821,369 and GB-A-1 078 868. Indeed, in these prior arrangements, said chambers only ensure a function of fluid distribution between two adjacent blocks. On the other hand, due to their very low depth, these chambers are not adapted to fulfil a significant function of temperature homogenization. In any case, these documents are not concerned with this homogenization function
The following example illustrates the advantages and the technical effects brought about by the features according to the two main embodiments of the invention.
First a heat exchange block 401 was provided, according to prior art. With reference to
Ten blocks according to prior art were accommodated the one on top of the other, in an enclosure analogous to the one of
Secondly a block 1 was provided, according to the first embodiment of the invention. This block 1 differs from the one 401 according to prior art, essentially in that
This block 1 was accommodated in an enclosure with other blocks according to prior art, which are similar to the one 401.
Thirdly a block 501 was provided, according to the second embodiment of the invention. This block 501 differs from the one 1 according to the first embodiment of the invention, essentially in that
This block 501 was accommodated in an enclosure with other blocks according to prior art, which are similar to the one 401.
The three heat exchangers IV, I and II, equipped with respectively the above blocks 401, 1 and 501 as upstream blocks, were submitted to the same implementation methods. For each exchanger gaseous chloric acid HCl was fed in the process channels at a flow rate of 3142.8 kg/h, at a temperature of 1335° C. and at a pressure of 3.20 barg. At the same time a service fluid, typically water, was fed in the service channels 460 at a flow rate of 87000 kg/h, at a temperature of 63.6° C. and at a pressure of 4.25 barg.
During these implementations, for each exchanger several parameters were measured and put into the following table:
As shown by the different simulation values, the invention makes it possible to substantially lower different characteristic temperatures of the implementation, with respect to prior art. In particular exchanger II and block 501, according to second embodiment of the invention, bring about a further lowering of these temperatures with respect to exchanger I and block 1, according to first embodiment.
This comparative example clearly shows the advantages of the invention, for what concerns thermal issues. Moreover, as explained above, this thermal technical effect does not lead to a significant mechanical weakening of the exchangers according to the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21179189.2 | Jun 2021 | EP | regional |
| 22171766.3 | May 2022 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/055277 | 6/7/2022 | WO |
