Structural reinforcement of unsupported diagonals of gasketed plate heat exchangers

Abstract

The present invention discloses a structural reinforcement of unsupported diagonals of gasketed plate heat exchangers, wherein the structural reinforcement comprises at least one primary segment that corresponds to the shape of respective corrugations of the unsupported diagonals of the heat exchanger, and at least one secondary segment that allows fluid to pass through the unsupported diagonals.

Description

[0001] STRUCTURAL REINFORCEMENT OF UNSUPPORTED DIAGONALS OF GASKETED PLATE HEAT EXCHANGERS Field of the invention

[0001] The present invention relates to the technical fields of sealing arrangements and structural elements in heat exchangers. More specifically, the present invention relates to a structural reinforcement of the unsupported diagonals of gasketed plate heat exchangers. Background of the invention

[0002] Heat exchangers are devices that transfer heat between two or more fluids based on the temperature difference between the fluid streams. These devices are widely used in various segments of the chemical industry, food processing, refrigeration, oil and gas, and others.

[0003] Different heat exchanger models have been developed to meet diverse application needs. The equipment is primarily classified according to the heat transfer process, construction, heat exchange mechanism, flow arrangement, and compactness.

[0004] Heat transfer can be direct or indirect. In indirect contact, heat energy is transferred through a wall separating the two fluids, meaning the fluids do not come into contact. In direct contact, heat transfer occurs at the interface between the fluids in contact.

[0005] Regarding the heat exchange mechanism, the main classifications are: single-phase convection in both branches, single-phase convection in one branch and convection with phase change in the other branch, or convection with phase change in both branches.

[0006] The three basic flow arrangements are: parallel, countercurrent, and crossflow. In parallel flow, the fluids enter the heat exchanger at the same end, flow in the same direction, and exit at the other end. In countercurrent flow, the fluids flow in the same direction but in opposite directions. In crossflow, the fluids flow perpendicular to each other.

[0007] To classify heat exchangers according to their compactness level, the compactness factor is used. This is calculated by the ratio of the total heat transfer area to the volume occupied by the equipment. Compact heat exchangers typically have a compactness factor greater than 700 m2 of heat transfer area per m3 of equipment.

[0008] Additionally, heat exchangers can be classified based on their construction characteristics. The most commonly used models in industry are shell-and-tube, tubular, finned, or plate heat exchangers.

[0009] Plate heat exchangers are classified into three main types: gasketed, brazed, or fully welded. Less common models include spiral plate, lamella, or printed circuit board. This invention focuses on improving the robustness of gasketed plate heat exchangers.

[0010] The gasketed plate heat exchanger emerged around 1878 to prevent milk contamination during pasteurization. Since then, its use has spread to various segments, from the food industry to the pharmaceutical industry. One of the equipment's advantages is the ease of cleaning and sanitizing the plates. After the 1960s, its effectiveness increased significantly with the development of new plate geometries (corrugated plates) and the use of advanced materials. The extreme process conditions for gasketed plate heat exchangers can involve temperatures up to 275°C and pressures up to 20 bar.

[0011] A typical gasketed plate heat exchanger consists of a series of thin, corrugated plates with holes at opposite ends to allow fluid flow. As illustrated in Figure 1, to allow fluid flow in a channel, a gasket (also called a gasket) placed at the ends of a pair of plates seals the channel. Furthermore, as illustrated in Figure 2, exchangers can have different configurations according to application needs, altering the number of plates, passes, channels, inlet and outlet connections, as well as the type of flow in the channels. In this sense, gaskets can be used in different ways depending on the desired flow distribution.

[0012] Furthermore, these heat exchangers typically consist of a series of alternating plates and gaskets, compressed at the ends by thick plates, known as fixed and movable plates. The flow configurations in the ports or manifolds can be "U" or "Z" shaped. Frequently, a single-pass countercurrent arrangement is adopted, where hot and cold fluid flows are alternated. Each plate has four holes for flow passage, forming ducts for distributing the hot and cold fluids, and ducts for collecting the fluids leaving the channels.

[0013] Figure 3 illustrates, for illustrative purposes, a typical chevron plate with some of the main regions highlighted, namely: plate guide, distribution region, heat exchange area, gasket, unsupported diagonal and nozzle.

[0014] It will be appreciated that the gasket sealing a channel allows flow between only two orifices. To avoid mixing with the flow from the other branch, flow in the other two orifices is prevented by gasket segments present in the diagonals supported on the periphery of these orifices: these are the supported diagonals. The diagonals around the orifices through which flow passes usually do not have gaskets: these are the unsupported diagonals.

[0015] Heat is transferred by conduction from the hot to the cold medium through the corrugated plates. The most common types of corrugations are chevron (or herringbone) and washboard. In addition to increasing the heat exchange area of ​​the plates, the corrugations continuously disturb the flow in the channel, resulting in high heat transfer coefficients as the flow continues to develop.

[0016] Gaskets provide sealing of channels and direct hot and cold fluids to their respective channels. They are generally manufactured with specific rubbers, which offer good mechanical and chemical properties, as well as good thermal resistance, depending on the selection.

[0017] In the central part of the channels, there are several contact points resulting from the geometry of the corrugations and the tightening of the heat exchanger by tie rods. These contact areas increase the rigidity of the heat exchanger structure. Channel areas with few contact points have low rigidity and present greater deformations, e.g., unsupported diagonals.

[0018] In this sense, the unsupported diagonal region is associated with a high rate of structural failures, such as cracks and visible local deformations, indicating high local mechanical stress. These failures can occur due to an undesirable plastic deformation process of the unsupported diagonal, since stresses greater than the minimum yield strength of the materials used in the plates can occur during the assembly process.

[0019] However, heat exchanger failures can interrupt the production process, causing significant losses. As noted above, in the case of gasketed plate heat exchangers, potential failure locations are the unsupported diagonal regions of the plates, where the highest stress levels are encountered. Therefore, a solution that allows fluid flow while simultaneously providing local support to mitigate local stresses is of significant importance. Prior art

[0020] In the state of the art, there is the publication of some documents that contain teachings on structural reinforcements for gasketed plate heat exchangers.

[0021] EP4015963 discloses a spacer adapted to be sandwiched between the edge regions of two adjacent heat transfer plates of a plate heat exchanger, wherein the spacer is formed with a gasket on the surface adapted to surround an internal cavity of said spacer. The document further teaches that the spacer may comprise support means for the areas adapted to support the areas of the heat transfer plates of the openings of the heat transfer plates allow the flow to pass through the heat transfer area.

[0022] However, this document is primarily focused on variations in spacer insertion and its function of preventing plate contact and ensuring plate alignment. Furthermore, the support means for the heat transfer plate openings are incorporated into this spacer.

[0023] Document GB2164439A discloses a plate heat transfer device. This document discloses that to locate gaskets and possibly also reinforce recesses, the bridge bases and / or door recesses that will receive the gaskets can be provided with pressed cavities that are smaller in height than the recess depth. The cavities extend into the recess of an unsealed recess and outward from the recess of a sealed recess to abut and reinforce the unsealed recesses.

[0024] Document US20200116440A1 discloses a heat transfer plate for a plate heat exchanger. The heat transfer plate comprising: a plate body forming a standardized cross-section and having a first side and a second side opposite the first side; a gasket groove formed by pressing from the plate body in a direction from the first side to the second side, and having a bottom wall, the bottom wall having a bottom wall body; and wherein the gasket groove includes at least a first section with a first recess formed in the bottom wall body, pressed from the bottom wall body in the direction from the first side towards the second side, and a second section with a second recess formed in the bottom wall body, pressed from the bottom wall body in the direction from the second side towards the first side, wherein said second section is adapted to accommodate a gasket.

[0025] Therefore, there remain obvious deficiencies in the prior art. In view of these deficiencies, the features and advantages of the present invention will become clear from the detailed description below and with reference to the accompanying drawings, which are provided only as preferred embodiments and are not limitative. Objectives of the invention

[0026] In view of the foregoing, the objectives of the present invention are to provide structural reinforcement for the unsupported diagonals of gasketed plate heat exchangers, which offers at least the following advantages: - A low-complexity, low-cost solution for increasing the channel stiffness of a gasketed plate heat exchanger while minimizing viscous dissipation. - Use of widely available materials for manufacturing. - Cost reduction. - Operational continuity and increased equipment reliability by reducing downtime for maintenance and / or repair of gasketed plate heat exchangers. - Increased service life of gasketed plate heat exchangers. - Increased robustness of gasketed plate heat exchangers when subjected to transient voltage situations. Brief description of the invention

[0027] The present invention discloses a structural reinforcement of the unsupported diagonals of gasketed plate heat exchangers, in which the structural reinforcement comprises at least one primary segment that corresponds to the shape of the respective corrugations of the unsupported diagonals of the heat exchanger, and at least one secondary segment that allows the passage of fluid through the unsupported diagonals. Brief description of the figures

[0028] In order to complement the present description and obtain a better understanding of the characteristics of the present invention, figures are presented, where in an exemplified and non-limiting manner, preferred embodiments of the same are represented.

[0029] It should also be noted that the scales in the figures may vary depending on the dimensions of the exchanger and plates, and on the operating conditions, fluid type, species, process pressure, and temperature. Therefore, the dimensions of the reinforcement segments may vary, such as the width and length of the reinforcements, the number of reinforcements, the fluid passage area, the thickness of the fluid passage region, the gasket thickness, etc.

[0030] Figure 1 illustrates a gasketed plate heat exchanger in operation, according to the state of the art.

[0031] Figure 2 illustrates a typical arrangement of gaskets in a gasketed plate exchanger, according to the state of the art.

[0032] Figure 3 illustrates, by way of example, a typical chevron plate with some of the main regions highlighted, in accordance with the state of the art.

[0033] Figure 4 illustrates an isometric view of an exemplary gasket that incorporates structural reinforcement in unsupported diagonals of a heat exchanger.

[0034] Figure 5 illustrates an assembly view of an exemplary configuration of an individual structural reinforcement according to an embodiment of the invention arranged on the unsupported diagonal of an exemplary plate.

[0035] Figure 6 illustrates possible geometric parameters of the reinforcement.

[0036] Figure 7 illustrates cross sections of the reinforcement with possible additional geometric parameters.

[0037] Figure 8 shows a prototype of the invention used in experimental tests.

[0038] Figures 9a and 9b show, respectively, gasket test configurations without and with structural reinforcements.

[0039] Figure 10 is a graph of the results of the von Mises equivalent stresses for different tightening conditions, with reinforcement (prototype) and without reinforcement (conventional).

[0040] Figure 11 is a graph of the influence of structurally reinforced gaskets on pressure drop. The pressure drop will be greater the smaller the fluid passage area in the unsupported region.

[0041] Figure 12 is a graph of the relative difference between gaskets with and without structural reinforcement. This relationship is a function of the fluid passage area in the structural reinforcement of the unsupported region. Detailed description of the invention

[0042] The present invention relates to a structural reinforcement for the unsupported diagonals of gasketed plate heat exchangers. These diagonals will be filled with structural reinforcements to allow fluid flow while simultaneously increasing the rigidity of this region, which is subject to high deformations and mechanical stresses.

[0043] With this increased stiffness, the stress in the region is reduced. This reduction prevents the material's yield stress from being reached, preventing the possibility of plastic deformation or gasket expulsion, and consequently, the possibility of plate failure.

[0044] This increases the useful life of the board and the campaign time of the equipment, generating economic benefits and reducing man-hours exposed to risk and possible leaks in stationary production units.

[0045] The invention is flexibly applicable to various industrial activities that use pressurized plate heat exchangers.

[0046] Essentially, the invention consists of a structural reinforcement of the unsupported diagonals of gasketed plate heat exchangers, in which the structural reinforcement comprises: at least one primary segment that corresponds to the shape of the respective corrugations of the unsupported diagonals of the heat exchanger; and at least one secondary segment that allows the passage of fluid through the unsupported diagonals.

[0047] The structural reinforcement is arranged between two adjacent plates of the heat exchanger and in which the primary segment is preferably a shoulder while the secondary segment is preferably a recess.

[0048] As illustrated by way of example in Figure 7, the primary segment may have a circular, rectangular, square, trapezoidal, triangular, or airfoil cross-sectional geometry (AA). Furthermore, the secondary segment may also have a circular, rectangular, square, trapezoidal, triangular, or airfoil cross-sectional geometry (BB).

[0049] It will be appreciated that the structural reinforcement may be a fabricated section: integrally with a heat exchanger gasket as illustrated in Figure 4, individually as illustrated in Figure 5, as a modification of an existing gasket in a heat exchanger (not illustrated) or as a modification of the stamping of the unsupported diagonal of the heat exchanger plate (not illustrated).

[0050] Therefore, in new gasket designs for heat exchangers, these could already include reinforcement segments in a single component.

[0051] Alternatively, the reinforcements can also be produced in a complementary (individual) manner and inserted into the unsupported diagonals of typical or operating heat exchanger channels, where there is no support from structural reinforcements on the unsupported diagonal.

[0052] Furthermore, if structural reinforcement is achieved by modifying an existing gasket, the gasket could include material in the unsupported diagonal in question (e.g., by injection of material).

[0053] Finally, if structural reinforcement is obtained by modifying the stamping of the unsupported diagonal of the heat exchanger plate, this alternative can be obtained without adding a spacer or any other materials.

[0054] Therefore, regardless of the form of implementation, it will be appreciated that the primary segment of the structural reinforcement has a hydrodynamic shape, which guarantees increased rigidity, and simultaneously presents a geometry that allows the flow in the heat exchanger to occur with low viscous dissipation.

[0055] The primary segment and secondary segment of the structural reinforcement can be manufactured, respectively, from one or a combination of metallic, polymeric or gasket materials.

[0056] If the structural reinforcement material is a gasket, this can be a gasket made from any of EPDM (Ethylene Propylene Diene Methylene rubber), NBR (Nitrile Butadiene Rubber), HNBR (Hydrogenated Nitrile Butadiene Rubber), FKM (fluoroelastomers) or other common gasket materials.

[0057] Furthermore, the structural reinforcement fabricated from gasket can be mounted to the heat exchanger by one or a combination of glue, adhesive, rivet or clips.

[0058] Alternatively, if the structural reinforcement is made of a metallic material, it can be assembled to the heat exchanger by one or a combination of glue, adhesive, welding, brazing or laser melting.

[0059] As illustrated in Figures 6 and 7, possible geometric parameters of the proposed structural reinforcement can be considered in order to ensure ease of flow with low viscous dissipation and, simultaneously, increase stiffness. Some of the main parameters to be considered are: ▪ d1: angle between reinforcement segments; ▪ d2: width of the fluid passage region; ▪ d3: width of the reinforcement / fluid blocking region; ▪ d4: main reinforcement segment; ▪ d5: secondary reinforcement segment; ▪ d6: radius of the central relief of the top of the reinforcement / fluid blocking region; ▪ d7: angle of the top of the reinforcement / fluid blocking region; ▪ d8: radius of the reinforcement bulge; ▪ d9: thickness of the fluid blocking region before angulation; ▪ d10: thickness of the fluid passage region.

[0060] Notwithstanding the above listing of the possible geometric parameters of structural reinforcement, it should be reiterated that reinforcement segments can be manufactured with different dimensions, i.e., width of reinforcements, quantity of reinforcements, fluid passage area, thickness of the fluid passage region, gasket thickness, etc.

[0061] A specialist in the field will also appreciate that the geometric characteristics of the reinforcement can be adapted according to the operating conditions, fluid type, species, pressure, and operating temperature, providing the desired increase in stiffness to extend service life without significantly increasing the pressure drop in the equipment. Tests and experimental results

[0062] To evaluate the mechanical stresses in the unsupported diagonal with and without support, assembly tests were performed in both situations. The unsupported region was instrumented with a triaxial strain gauge to evaluate local deformation and, consequently, local stress.

[0063] The tests performed with the presence of support were conveniently called prototype tests, as shown in Figures 8 and 9b. The tests without the presence of the gasket in the unsupported region are called conventional model tests, as shown in Figure 9a.

[0064] Deformation measurements were initiated during the closing procedure of a 21-plate heat exchanger. Manufacturers suggest maximum and minimum tightness values ​​"A" (structural distance between plates), related to the geometric parameters of the plates. In the 21-plate configuration, the maximum proposed tightness is A max = 64.05mm and the minimum of A min= 67.2 mm. The assembly process must be carried out in stages, with time intervals for gasket relaxation. The distance was 1.3A to 1A, as shown in Table 1 below. Table 1

[0065] The resulting von Mises equivalent stress for each clamping condition is shown in Figure 10.

[0066] In hydrodynamic experimental tests, it was observed that the presence of the prototype promotes a significant change in the mechanical behavior of the unsupported diagonal. Up to 1.2A, when the plates do not significantly compress the gasket, the presence of the support increases local stresses. However, as the plate pack compresses, the presence of the prototype acts as a support for the unsupported diagonal, which previously, with the conventional gasket design, was completely free to deform, resulting in high local deformation.

[0067] Therefore, at the recommended tightening conditions for gasketed plate heat exchanger (PHE) operation, the prototype reduces the local von Mises equivalent stress by 36%, from 431MPa to 277MPa for Amax and by 27% for the Amín tightening condition, from 222MPa to 162MPa.

[0068] Furthermore, two types of tests were carried out in relation to the measurement of pressure drop in a prototype exchanger channel: one in its standard operational condition (as shown in Figure 9a) and a second with the insertion of structural reinforcement prototypes of the unsupported diagonals of the exchanger (as shown in Figure 9b).

[0069] As illustrated in Figure 11, greater pressure drops were observed in the presence of structural reinforcements for tests with the same mass flow rate (compare circles and triangles in that figure). Furthermore, as illustrated in Figure 12, for flow rates greater than 0.4 kg / s, the pressure drop in the exchanger channel containing reinforcements was 150% higher than the pressure drop in the channel in its standard state. The pressure drop is a function of the fluid passage area, which can be arbitrated when fabricating the structural support for the unsupported region (maximum allowable pressure drop specification).

[0070] Finally, to demonstrate the increased robustness of gasketed plate heat exchangers when subjected to transient stress situations using the present invention, tests were performed to experimentally obtain mechanical stresses at locations in the flow distribution region of a commercial heat exchanger (based on deformation measurements). Tests were performed under single-pressure transient conditions (when only one branch is pressurized). Two types of tests were performed: one with the exchanger in its standard operating condition and a second with the insertion of structural reinforcement prototypes in the unsupported diagonals of the exchanger channel (as shown in Figures 4, 5, and 6). It was found that the heat exchanger operating with the insertion of reinforcement prototypes presented stresses 36% lower than the stresses obtained by the equipment under standard conditions.This reduction was sufficient to avoid entering regions of plastic deformation, which guarantees greater useful life and reliability of the plates.

[0071] Those skilled in the art will appreciate the knowledge presented herein and will be able to reproduce the invention in the presented embodiments and in other variants, covered by the scope of the attached claims.

Claims

CLAIMS 1. Structural reinforcement of the unsupported diagonals of gasketed plate heat exchangers, characterized in that the structural reinforcement comprises: at least one primary segment that corresponds to the shape of respective corrugations of the unsupported diagonals of the heat exchanger; and at least one secondary segment that allows the passage of fluid through the unsupported diagonals.

2. Structural reinforcement, according to claim 1, characterized in that the primary segment is a shoulder and the secondary segment is a recess.

3. Structural reinforcement, according to claim 1, characterized in that the primary segment has a circular, rectangular, square, trapezoidal, triangular or airfoil profile cross-sectional geometry (AA). 4.Structural reinforcement according to claim 1, characterized in that the secondary segment has a circular, rectangular, square, trapezoidal, triangular or airfoil cross-sectional geometry (BB).

5. Structural reinforcement according to claim 1, characterized in that it is located between two adjacent plates of the heat exchanger.

6. Structural reinforcement according to claim 1, characterized in that it is a manufactured section: individually, integrated into a gasket of a heat exchanger, as a modification of an existing gasket in a heat exchanger or as a modification of the stamping of the unsupported diagonals of the plate of the heat exchanger.

7. Structural reinforcement according to claim 1. characterized by the fact that the primary segment has a hydrodynamic shape.

8. Structural reinforcement, according to claim 1, characterized by the fact that the primary segment and secondary segment are manufactured, respectively, from one or a combination of metallic, polymeric or gasket materials.

9. Structural reinforcement, according to claim 6, characterized by the fact that the material of the gasket structural reinforcement can be one of EPDM (Ethylene Propylene Diene Methylene rubber), NBR (Nitrile Butadiene Rubber), HNBR (Hydrogenated Nitrile Butadiene Rubber) and FKM (fluoroelastomers).

10. Structural reinforcement, according to claim 7, characterized by the fact that the structural reinforcement manufactured from gasket can be assembled in the heat exchanger by one or a combination of glue, adhesive, rivet or by clips. 11.Structural reinforcement according to claim 6, characterized in that the structural reinforcement manufactured from metallic material can be assembled into the heat exchanger by one or a combination of glue, adhesive, welding, brazing or laser fusion.

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