Insert for tubes of a two-phase heat exchanger

Abstract

The present invention relates to an insert for a tube (10) of a heat exchanger tube, in particular a two-phase heat exchanger, for improving the heat transfer efficiency and optionally reducing the fouling of the heat exchanger tubes of industrial units, for example units used in the fields of petroleum refining, petrochemistry or chemistry in general. The insert has an element which can be static or, preferably, rotatably movable and comprises several successive series of a first portion (S1) in the form of a spring and a second portion (S2) in the form of a straight rod.

Description

[0001] INSERT FOR TWO-PHASE HEAT EXCHANGER TUBES

[0002] technical field

[0003] The present invention relates to the field of inserts for tubular heat exchangers used to improve heat transfer efficiency and / or reduce fouling of heat exchanger tubes in industrial units, for example, units used in oil refining, petrochemicals, or the chemical industry in general. In particular, the present invention relates to a tubular heat exchanger insert comprising a fixed or rotating element consisting of a periodic alternation of a spring-shaped section and a straight rod section.

[0004] Previous technique

[0005] Heat exchanger insert technologies are used to improve heat transfer efficiency and reduce fouling of industrial heat exchanger tubes.

[0006] In many fields, such as oil refining, petrochemicals, and other areas of chemistry, food processing, and energy, industrialists are indeed concerned with optimizing heat transfer in the heat exchangers used, but also confronted with the problem of deposits in said exchangers, which can come from impurities present in the liquid streams from various processes that pass through the heat exchangers, and / or come from the decomposition or formation of organic products such as polymers or hydrocarbons and mineral products in said liquid streams.

[0007] These deposits can consist of accumulating suspended impurities, deposits of dissolved mineral salts in liquid streams, forming coke, or soluble sulfur compounds in hydrocarbon streams. They can be generated by excessive fluid temperatures or result from corrosion. These deposits, which gradually accumulate on the walls of heat exchanger tubes over time, impair the performance of the heat exchangers, causing them to lose efficiency over time.

[0008] The deposits form a solid substance with low thermal conductivity which has the effect of insulating the walls and reducing heat transfer in the exchanger, ultimately damaging the energy efficiency of the industrial processing or manufacturing unit in question implementing the heat exchanger.

[0009] Another consequence of the formation of these deposits on the internal walls of heat exchanger tubes can be reduced flow rates, which are detrimental to the proper functioning of the downstream process, and / or hot spots on the tube's internal surface. These restrictions and / or hot spots can lead to deterioration of the tube structure and thus cause product leaks that can be hazardous to the operator and / or equipment.

[0010] The use of inserts in heat exchangers aims to improve heat transfer, in particular because the inserts promote turbulence which leads to a reduction in the thermal boundary layer, thus decreasing the resistance to heat transfer and improving heat transfer efficiency, and to prevent fouling of heat exchangers.

[0011] They constitute a very interesting and promising solution to support the reduction of energy consumption and consequently CO2 emissions from industrial processes using heat exchangers, as can be the case in all the areas mentioned above.

[0012] In the oil refining sector, for example, there are many units that use heat exchangers, which are particularly susceptible to fouling. Refining crude oil by preheating it with the hot atmospheric residue exiting an atmospheric distillation unit is one such example. Many heavy crude oils are very rich in asphaltenes, which can form sediments, as well as in sulfur and other corrosive compounds that can deposit on the internal walls of the heat exchanger tubes through which they circulate.

[0013] Many different types of inserts exist in the industry, such as a wire winding, a twisted band, or a central shaft with blades. These inserts may have moving and / or static parts and may or may not be attached to the tube, and if so, in various ways, for example, on one end or both ends of the tube. Two main types of inserts for tubular heat exchangers can be distinguished: static inserts and rotating inserts driven by the flow of the liquid through the tube. Both types of inserts promote heat transfer and reduce fouling. However, rotating inserts generally offer better performance, both in terms of fouling reduction, thanks to the mechanical effect of the insert's rotation, and in terms of pressure drop, which is a factor to consider for insert performance.Indeed, the presence of the insert, which occupies part of the tube, increases the resistance to fluid flow. This can be problematic if the resistance is too high. Typically, excessive pressure drop affects the capacity and energy consumption of the pumps and turbines that circulate the fluid(s) and compensate for the pressure loss. Therefore, a minimal pressure drop is generally desired—one that is limited compared to the pressure drop of a tube without an insert—to avoid compromising the heat exchanger's energy efficiency and even to prevent the need to replace the fluid circulation equipment upstream of the exchanger. A rotating insert generally results in less pressure drop than a fixed insert, for example, up to 40% less.

[0014] An example of a rotating insert for a heat exchanger tube is described in patent FR2569829. The insert comprises a rigid, solenoid-shaped metal winding that is rotated by the fluid flowing in the tube. The rigid insert is configured to allow the winding to rotate freely around the tube axis. The pitch of the metal winding can be fixed or variable.

[0015] Figure 1 illustrates a rotating insert of this type, comprising a rigid helical metal winding with a plurality of turns, of length L, diameter D, pitch p, and angle of inclination α(a) defined with respect to the central axis of the winding, which coincides with the Z-axis of the heat exchanger tube in which the insert is mounted. The metal rod forming the winding has a thickness e. The metal winding has a free end and an end fitted with a ring that passes through the hook of a rotating trunnion held in the bore of a bearing, allowing the insert to rotate freely about the axis of the heat exchanger tube. The bearing consists of a stirrup-shaped part with two prongs at its ends for attachment to the tube (tube not shown), and a central part with a bore for retaining the trunnion.At its end opposite the hook, the trunnion has a head in the form of a washer suitable for holding it captive in the bearing.

[0016] The pressure drop constraint is even more important in the case of two-phase heat exchangers, adapted to a circulation of a gas phase and a liquid phase for the fluid on the tube side, such as those used for feed / effluent heat exchanges for example in hydrotreating hydrocarbon cuts processes in the field of oil refining.

[0017] Indeed, any increase in pressure drop is often critical for the operation of this type of heat exchanger, compared to single-phase heat exchangers. Not only are pressure drops generally higher in two-phase heat exchangers compared to single-phase ones, but two-phase feed-to-effluent heat exchangers used in hydrotreating or hydroconversion processes of hydrocarbon feedstocks operate at high pressure. The hydrogen compressor(s) used in these processes are expensive pieces of equipment, designed to operate at a specific target pressure drop that must be maintained by the feed-to-effluent heat exchanger.The variation around this target pressure loss value, in particular the additional pressure loss which can also be called additional or supplementary pressure loss, or extra pressure loss, must be minimal, typically less than 10 mbar / m (l,0.10. _4 IVIPa / m) or even less.

[0018] Few inserts have been developed for use in such two-phase heat exchangers. For example, French patent FR2975754 describes a rotary scraper insert, similar to that of French patent FR2569829, featuring a rigid helical metal winding, in a steam boiler flue containing both liquid and steam. The scraper insert is used to prevent the accumulation of impurities in the flue or to slow the rate at which such accumulation occurs.

[0019] Patent J P2014152948 describes various devices for improving heat exchange and reducing pressure losses in the ducts of a flue gas heat recovery boiler, in which water circulates in both liquid and vapor forms. Among these devices is a static insert comprising twisted strips whose edges are in contact with the inner wall of the tube, arranged intermittently along the ducts and which can be connected by rods. However, such ribbon-shaped inserts are expensive to manufacture, not optimal in terms of pressure drop due to their size within the tubes and their static nature, and the large surface area created by the ribbon shape can serve as a substrate for deposits, making the device more susceptible to fouling.

[0020] Thus, there is a need to develop inserts adapted to two-phase heat exchangers, which make it possible to reduce as much as possible the pressure loss caused by the operation of the insert, the presence of which is required to improve heat transfers and possibly limit fouling in the tubes.

[0021] Objectives and Summary of the Invention

[0022] The present invention aims to overcome at least in part the prior art problems described above, and in particular aims to provide an insert for tubular heat exchanger limiting the pressure loss related to the operation of the insert, and thus offer an insert particularly well suited, but not exclusively, to two-phase tubular heat exchangers.

[0023] In general, the present invention aims to provide a device for improving heat exchange, and possibly reducing fouling, for heat exchanger tubes, advantageously two-phase, which limits pressure losses, while being robust (risk of breakage minimized).

[0024] Thus, to achieve at least one of the aforementioned objectives, among others, the present invention proposes, according to a first aspect, an insert for a heat exchanger tube, the insert comprising an element comprising a sequence of several successions of a first section of length L1 comprising a rigid helical winding of a rod comprising several turns and a second section of length L2 comprising a straight rod.

[0025] According to one or more embodiments of the invention, the element comprises a first end connected to a system for attaching said element to an inlet of the tube. According to one or more embodiments of the invention, the element is rotationally mobile, said first end of the element being fixed to a mechanical link of the attachment system, said mechanical link allowing free rotation of said element about itself around the axis (Z) of said tube under the action of a fluid passing through said tube, said element comprising a second free end opposite the first end.

[0026] According to one or more embodiments of the invention, the diameter D of the turns of the helical winding of the first section is between 70% and 99% of the internal diameter of the exchanger tube Dt, preferably between 90% and 95%.

[0027] According to one or more embodiments of the invention, the rotating moving element further comprises a rotating drive piece positioned upstream and connected to the first section of the sequence positioned first in the sequence, said rotating drive piece comprising a shaft coaxial with the helical winding of the first section and provided with at least two blades attached to said shaft.

[0028] According to one or more embodiments of the invention, the sequence comprises n successions, n being a positive integer between 2 and 15, preferably between 2 and 10.

[0029] According to one or more embodiments of the invention, the sequences of events are all identical.

[0030] According to one or more embodiments of the invention, the pitch pl of the helical winding of the first section SI is between 10 mm and 50 mm.

[0031] According to one or more embodiments of the invention, the length L1 and the length L2 are between 50 mm and 12000 mm, preferably between 500 mm and 5000 mm.

[0032] According to one or more embodiments of the invention, the insert has a total length Ll between 50% and 100% of the total length Lt of the heat exchanger tube, Lt being between 500 mm and 15000 mm, preferably between 1000 mm and 6000 mm.

[0033] According to one or more embodiments of the invention, the rod of the rigid helical winding and / or the straight rod are metallic.

[0034] According to one or more embodiments of the invention, the rod of the rigid helical winding and / or the straight rod have a circular or square cross-section, preferably circular, and have a diameter preferably between 0.5 mm and 5 mm.

[0035] According to a second aspect, the present invention relates to a two-phase heat exchanger comprising a plurality of tubes through which a fluid flows, at least one of said tubes comprising an insert according to the invention, said two-phase heat exchanger being configured for the circulation of a gas phase and a liquid phase within said tubes. According to a third aspect, the present invention relates to the use of an insert according to the invention for a tubular heat exchanger, for preheating crude oil in an atmospheric distillation process, or for preheating a hydrocarbon feedstock in a hydroconversion or hydrotreating process of said hydrocarbon feedstock, or for the evaporation or condensation of a fluid in a nuclear power plant.

[0036] Other objects and advantages of the invention will become apparent from the following description of particular embodiments of the invention, given by way of non-limiting examples, the description being made with reference to the attached figures described below.

[0037] List of figures

[0038] Figure 1, already described above, represents an insert and its method of attachment to the heat exchanger tube according to the prior art.

[0039] Figure 2 is a three-dimensional (3D) schematic view of a first embodiment of the insert according to the invention.

[0040] Figure 3 represents the same embodiment as that illustrated in Figure 2, further showing a portion of a heat exchanger tube and a system for attaching the insert to the tube.

[0041] Figure 4 shows a rear view of a portion of the insert and heat exchanger tube in the same embodiment as that illustrated in Figures 2 and 3.

[0042] Figure 5 is a three-dimensional (3D) schematic view of a second embodiment of the insert according to the invention comprising non-permanent rod assembly means.

[0043] Figure 6 is a schematic 3D view of a third embodiment of the insert according to the invention in which the element is rotationally mobile and includes an additional piece for rotating the rods.

[0044] Description of the implementation methods

[0045] In this description, the term "include" is synonymous with (means the same as) "comprise," "include," and "contain," thus being inclusive or open-ended and not excluding other elements not mentioned. It is understood that the term "include" includes the exclusive and closed term "consist."

[0046] In this description, the expression "between ... and ..." means that the limit values ​​of the interval are included in the range of values ​​described, unless otherwise specified.

[0047] Furthermore, in this description, the terms "essentially," "substantially," or "approximately" relative to a reference value correspond to an approximation of ±10%, ±5%, preferably ±1%, and most preferably ±0.5%. This may be a value of temperature, pressure, distance, speed, flow rate, compound content, etc.

[0048] In this description, the various parameter ranges characterizing a given device, or relating to a step in a process implementing said device, such as ranges relating to dimensions (lengths, diameters, etc.), angles, pressure ranges, or temperature ranges, may be used alone or in combination. For example, in the context of the present invention, a preferred range of pressure values ​​may be combined with a more preferred range of temperature values.

[0049] According to the present invention, pressures are absolute pressures, also noted as abs., and are given in absolute MPa (or abs. MPa), unless otherwise indicated.

[0050] In this description, when mentioned, the positions "front", "rear", "horizontal", "vertical", etc. of the various elements of the insert and the heat exchanger tube are defined in relation to a tubular heat exchanger in the operating position and in relation to the direction of flow of the fluid passing through the heat exchanger tube.

[0051] In this description, the flow velocity of the fluid in the tube is understood to be the surface velocity of the fluid flowing in the tube V_SF, commonly accepted as being the ratio between the volumetric flow rate of the fluid Q and the internal section of the tube S: V_SF = Q / S.

[0052] In this description, "rigid" refers to the helical winding of a rod, preferably metallic, meaning a winding that does not deform, or hardly deforms, irreversibly under the action of the fluid flowing through the heat exchanger tube in which the insert containing such a winding is integrated, under normal operating conditions of the heat exchanger tubes. In particular, said winding does not deform, or hardly deforms, irreversibly when the circulating fluid exhibits variations in velocity, viscosity, and / or temperature.

[0053] In this description, a tube-side heat exchanger, or tubular heat exchanger, is defined as a heat exchanger comprising at least one tube inside which flows a fluid commonly referred to as the "tube-side fluid," exchanging heat with a fluid flowing outside said tube. The heat exchangers referred to in this invention are classically shell-and-tube heat exchangers, with straight (straight) tubes, in which the tube-side fluid flows inside a set of parallel tubes called a tube bundle. These tubes are enclosed in a shell called a shell. The other fluid, called the "shell-side fluid," flows inside the shell but outside the tubes. The flow of the fluids on the tube and shell sides can be co-current and / or counter-current. The tubes are often long, typically up to 6 m, and of small diameter to optimize the surface area to volume ratio.They are generally held at their ends in perforated plates called tube sheets, which serve to support the tubes and also to separate the fluids, and may be supported between the tube sheets by intermediate support plates (perforated plates transverse to the tubes). The tubes may also be U-shaped, and their ends may, for example, be attached to a single tube sheet. Shell and tube heat exchangers can be single-pass or multi-pass, for example, two-pass (the fluid on the tube side flows through the tubes in one direction, then returns in the opposite direction thanks to an internal configuration (such as a partition in a plenum, or via a U-shaped tube configuration)).

[0054] In this description, the pitch of a helical winding with multiple turns is understood by the commonly accepted definition, which is the distance measured between the centers of two turns. In a two-dimensional representation, it is the distance between two crests on the same side of the winding axis, and in a 3D representation, it is the length (distance) between two turns around the axis of revolution of the turn (or the distance traveled along the axis of revolution of the turn to make one complete turn).

[0055] Embodiments of the insert, its use in a heat exchanger, and their applications are described in detail below. Numerous specific details are presented to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the insert, the heat exchanger incorporating such an insert, and their use can be implemented without necessarily including all these specific details. In other cases, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0056] In this description, the various embodiments presented can be implemented separately or in combination with each other, without limitation of combinations where technically feasible.

[0057] The present invention proposes an insert for a heat exchanger tube.

[0058] With reference to figures 2 to 4, which represent a first embodiment of the insert according to the invention, said insert comprises an element 1 comprising a sequence of several successions of a first section SI of length L1 comprising a rigid helical winding of a rod, preferably metallic, comprising several turns and a second section S2 of length L2 comprising a straight rod, preferably metallic.

[0059] The sequence consisting of a first section SI comprising a rigid helical winding of a rod with several turns and a second section S2 comprising a straight rod is repeated n times in the sequence. The sequences are preferably identical to each other, i.e., have the same geometric characteristics (e.g., same lengths L1 and L2, same pitch of the first section, rod thickness, etc.). However, a sequence of different sequences does not fall outside the scope of the present invention. For example, the value of the length L1 and / or L2 may be the same from one sequence to the next or different. For example, the length L1 of the first section SI of the first sequence in the sequence may be different from the length L1 of the section SI of the subsequent sequences, because it is the first section SI of the first sequence that primarily drives the rotation of the rest of the insert.

[0060] The total length of the insert Li is essentially equal to the sum of the lengths L1 and L2 of all the sequences S1 / S2. The length Li can be equal to n times the sum of the lengths L1 and L2 if the lengths L1 and L2 are identical from one sequence to the next.

[0061] Element 1 has a first end, which is preferably connected to a fixing system 20 of element 1 to the tube 10 of the heat exchanger.

[0062] According to this first embodiment, permanent joining means preferably connect the first section SI and the second section S2, as well as the sequences between them, to form an element 1 in the form of a single part. Such permanent joining means are, for example, welds or any other suitable permanent joining means for said parts. Alternatively, the first section SI and the second section S2, as well as the sequences between them, form an element 1 in the form of a single part without joining means, the different parts being manufactured directly as a single piece.

[0063] According to this first embodiment, the first SI section of the sequence positioned first in the chain from the entrance of the tube 10 takes its origin at the first end of the element 1.

[0064] Element 1 can be static or rotationally mobile during its operation in said tube 10 of the heat exchanger. In the case where element 1 is rotationally mobile, the insert according to the invention further scrapes the walls of the tube and further limits the pressure drop compared to a static insert, as explained in detail.

[0065] In the case of a static element 1, the first end of the element 1 may be attached by a mechanical link to the fastening system 20, which allows the element 1 to be positioned axially and securely within the tube 10 through which a fluid flows. The fastening of the static element 1 within the tube may be reinforced by other means of fastening to the tube, which may be located at a second end opposite the first end and / or along the element 1. The static element 1 may also be secured without dedicated fastening means, as detailed later in the description.Preferably, the element 1 is rotationally mobile, said first end of the element 1 then being fixed to a mechanical link 22 of the fixing system 20 which allows the free rotation of said element 1 on itself around the axis (Z) of said tube 10 under the action of a fluid passing through said tube 10, as shown in figure 3, and said rotationally mobile element 1 having a second free end opposite said first end.

[0066] Advantageously, when the insert according to the invention is used in a heat exchanger tube, the presence of element 1 increases the turbulence of the circulating fluid, improves heat exchange, and homogenizes the temperature of the circulating fluid throughout the tube's cross-section. This prevents the formation of hot spots on the tube wall and consequently significantly reduces the risk of solid deposit formation and improves heat transfer, which is typically hampered by this type of deposit. If rotated, the insert also scrapes away any deposits that may have formed on the wall, thus reducing fouling. In addition to reducing deposits, heat transfer is improved due to the increased turbulence of the circulating fluid caused by the presence of the insert, which enhances convective heat transfer.Indeed, the mere presence of the insert, and even more so its rotation when element 1 is rotating, creates turbulence that leads to increased heat transfer by reducing the thickness of the heat transfer boundary layer and thus the heat transfer resistance near the wall. The heat transfer performance of tubular heat exchangers incorporating such inserts is therefore improved, as is the lifespan of the heat exchangers.

[0067] In the case of a rotating element 1, the threshold (threshold speed) for initiating rotation of an insert corresponds to the minimum surface velocity of the circulating fluid that allows the insert's moving element to rotate. The moving element, rotating in the opposite direction to the helical winding of the spring, with a speed that depends on its weight, geometric characteristics, flow rate, viscosity, and density of the circulating fluid, therefore has its own specific threshold for initiating rotation.

[0068] The presence of an insert in the heat exchanger tube induces a pressure drop.

[0069] Within the scope of the present invention, the insert according to the invention has the capacity to limit the pressure drop associated with the operation of the insert, and is thus particularly well-suited for use in two-phase tubular heat exchangers that may have more demanding operating conditions with respect to pressure drop, i.e., have a low acceptable pressure drop threshold, as is the case in applications such as preheating a hydrocarbon feedstock with the effluent produced in a hydroconversion or hydrotreating process of said hydrocarbon feedstock. According to the invention, an insert can be provided sized to meet the pressure drop requirements of an existing unit.Surprisingly, the inventors have shown that a sequence of several successions of a first section SI comprising a rigid helical winding of a rod comprising several turns followed by a second section S2 comprising a straight rod, in particular according to the specificities described below, makes it possible to improve heat exchanges, and possibly reduce fouling, while limiting the pressure loss induced by the insert.

[0070] The pressure loss is further reduced if the moving element 1 of the insert is rotationally mobile.

[0071] The number of S1 / S2 successions, called n, is determined in such a way as to obtain optimal heat transfer.

[0072] Preferably, n, which is a positive integer, is between 2 and 15, preferably between 2 and 10, more preferably between 4 and 8.

[0073] Preferably, the pitch pl of the first SI section is between 10 mm and 50 mm, preferably is between 20 mm and 40 mm.

[0074] The pitch can be generally defined as a function of the turn inclination angle and the turn diameter of the rigid helical winding D, according to the following relationship: pitch = (K x D) / tana. The turn inclination angle α is defined with respect to the winding axis coinciding with the Z-axis of the heat exchanger tube in which the insert is mounted. The angle αi refers to the turn inclination angle of the first SI section.

[0075] From one S1 / S2 sequence to the next in the chain, the length of a given section (S1, S2) is preferably identical. In this case, the lengths L1 and L2 can be estimated using equations (1) and (2) below:

[0076] (1) L1 ~ (Li / n) • (APs / (APi -APv)) in which:

[0077] Li: the total length of the sequence of S1 / S2 successions (approximately the length of the insert according to the first embodiment), n: the number of S1 / S2 successions of the insert,

[0078] APs: the maximum additional pressure drop specified for one meter of heat exchanger tube; APi: the pressure drop generated for one meter of heat exchanger tube equipped with an insert. APi can be calculated or measured, and the insert used is a conventional rigid helical winding with given geometric parameters; APv: the pressure drop generated by one meter of heat exchanger tube without an insert.

[0079] Advantageously, the length L2 of the second section can be expressed as follows: (2) L2 = (Li / n) - Ll

[0080] Preferably, the length L1 of the first SI section is between 50 mm and 12000 mm, preferably between 500 mm and 5000 mm.

[0081] Preferably, the length L2 is between 50 mm and 12000 mm, preferably between 500 mm and 5000 mm.

[0082] The first section SI and the second section S2 are joined together, as are the successions between them, and can form an element 1 in the form of a single piece (a final single piece), typically when permanent joining means such as welds connect the first section SI and the second section S2 on the one hand, and the successions between them on the other hand.

[0083] The total length of the insert is less than or equal to the total length of tube 10 of the heat exchanger, and preferably between 50% and 100% of the total length of tube 10 of the heat exchanger: the total length of the insert is preferably between L t / 2 and L t , with L t the length of tube 10 of the exchanger.

[0084] The total length of the insert may be slightly less than the tube length to take into account possible elongation due to mechanical stress applied by the fluid and / or thermal expansion.

[0085] The heat exchanger tube 10 can have a total length of between 500 mm and 15,000 mm, preferably between 1,000 mm and 6,000 mm. For example, heat exchangers commonly used in oil refining, such as for preheating crude oil in atmospheric distillation or preheating a hydrocarbon feedstock in a hydroconversion or hydrotreating process using a so-called "feed / effluent" heat exchanger that heats the hydrocarbon feedstock with the effluent from said process, can include heat exchanger tubes ranging from 1 meter to 6 meters in length. In the nuclear sector, heat exchangers in nuclear power plant condensers can have tubes up to 14 meters long.

[0086] The rigid helical winding of the first section SI has a diameter D, which corresponds to the diameter of the turns of the winding.

[0087] Advantageously, the diameter D of the turns of the rigid helical winding of the first section SI is greater than or equal to 80% of the diameter Dt of the tube 10 of the heat exchanger, preferably greater than or equal to 90% of the diameter Dt, in order to generate optimal turbulence of the circulating fluid and possibly to scrape deposits from the tube wall efficiently. Preferably, the diameter D of the turns of the rigid helical winding of the first section SI is between 80% and 100% of the diameter Dt of the heat exchanger tube 10, more preferably between 85% and 100% of the diameter Dt. In the case of a rotating element 1, the diameter D of the turns of the rigid helical winding of the first section SI is preferably between 80% and 99% of the diameter Dt of the heat exchanger tube 10, more preferably between 85% and 95% of the diameter Dt.

[0088] The diameter of the tubes (internal diameter Dt) can be between 10 mm and 100 mm, preferably between 10 mm and 50 mm.

[0089] Advantageously, a space "c" exists between the rigid helical winding of section SI and the inner wall of tube 10 such that said rigid helical winding of the element does not touch the tube wall, in the case of the rotating insert, as referenced in Figure 4, which shows a rear view of a portion (part of the first section SI) of the insert and the heat exchanger tube, in order to avoid damaging the tube wall, for example, creating scratches that could form surface irregularities that could promote corrosion. This space "c" is preferably between 1 mm and 3 mm.

[0090] The rigid helical winding of the section Sl can have a cross-section taking on different shapes, and preferably has a circular or square cross-section, and more preferably has a circular cross-section. In the case of a square cross-section or another shape, the diameter of the cross-section is understood to be an equivalent diameter D_eq, defined as follows: D_eq = 4 * Area_of_cross-section / perimeter of cross-section.

[0091] The rod, preferably metallic, forming the rigid helical winding of section SI has a diameter el, and the straight rod, preferably metallic, of the second section S2 has a diameter e2. The diameters el and e2 are preferably between 0.5 mm and 5 mm, more preferably between 1 mm and 3 mm.

[0092] The diameters el and e2 can be identical or different. Having identical diameters el and e2 has the advantage of simplifying the manufacture of the insert.

[0093] The direction of the rigid helical winding of the SI section, which can also be defined as the direction of the pitch of the turns, can be clockwise, or counterclockwise (relative to the direction of fluid flow in the tube, represented by an arrow along the Z axis in the figures).

[0094] The first end of element 1, preferably attached to the mechanical link 22, may include a ring la or any other means of attachment to the mechanical link 22.

[0095] The insert material can be carbon steel, stainless steel, or any other metal or metal alloy such as Inconel®, providing the required rigidity and preferably resistance to high temperatures and corrosion. The insert material is preferably less hard than the heat exchanger tube material to prevent tube degradation.

[0096] For highly corrosive fluids, the material forming the insert can be coated with a layer of protective material, typically a polymer layer.

[0097] The material forming the insert can alternatively be a polymer or composite material (metal or metal alloy with a polymer material, or different types of polymers, or a composite material combining different types of reinforcements, such as fibers, particles, etc., with different matrices, such as a polymer, metallic or ceramic matrix).

[0098] The rigid helical winding of the first section SI and the straight rod of the second section S2 of the moving element are robust elements, i.e., whose risk of breakage is low.

[0099] The system for attaching the insert to the tube can be a traditional attachment system, for example, such as that described in patents FR2612267 and FR2639425 in the case of an insert with a rotating element 1. In this case, the attachment system is advantageously arranged along the Z-axis of the heat exchanger tube so that the insert's rotating element can rotate about said axis. The attachment system is typically positioned at the tube inlet, and the rotating element of the insert is connected to the attachment system and positioned downstream in the tube. An example of a traditional attachment system 20 is shown in Figure 3 and includes a bearing 23 and the mechanical linkage 22, typically formed by a rotating trunnion. This trunnion 22 is fixed to the insert's rotating element 1 so that the insert is free to rotate about the Z-axis of the tube 10.The bearing 23 comprises a stirrup-shaped part 23a, typically a single-piece component made of a rigid material capable of elastic deformation, the end of which is in the form of two arms allowing attachment to the tube 10, and a central part 23b comprising an opening for retaining the trunnion 22. The two arms of the stirrup-shaped part 23a are separated by a distance such that the arms can be forcibly engaged in an open end of the tube 10 to bear elastically against the inner wall of the tube, so as to make said part 23a of the bearing 23 rigidly fixed to the tube 10. The trunnion 22 comprises a straight cylindrical rod engaged in the opening of the central part 23b of the bearing 23 and a hook-shaped end 21 that can be hooked onto the ring 1a or any other fastening means comprising the first end of the rotating element 1.The other end of the trunnion 22 has a head in the form of a washer suitable for holding it captive in the bearing 23. An anti-wear washer can also be interposed between the bearing and the head of the trunnion.

[0100] The system for attaching the insert to the tube can also be configured so that element 1 of the insert is fixed, i.e., static, within the insert (no rotation of the insert). Such a fastening system may include various means of attaching element 1 to the tube, at the inlet and / or inside the tube, and possibly at the outlet of the tube, for example, but not limited to:

[0101] - a transverse rod respectively at the inlet and outlet of the tube and to which element 1 is connected;

[0102] - a traditional fastening system similar to that shown in Figure 3 and described above, but without a bearing and without rotation of the trunnion,

[0103] - at least one ring outside the tube and larger than the diameter of the tube, connected to element 1. The insert can also be fixed in the tube without a dedicated fixing system, for example in the case where the diameter of the rigid helical winding is equal to the diameter of the tube, due to the stiffness of the helical winding which is in contact with the wall of the tube and fixes the insert in the tube.

[0104] Each insert advantageously includes its own tube fixing system, although a common fixing system shared between the inserts of the other heat exchanger tubes can be used.

[0105] Other systems for fixing the insert to the tube 10 can be used without departing from the scope of the present invention.

[0106] Figure 5 represents a second embodiment of the insert according to the invention, identical in every respect to the first embodiment described above in relation to Figures 1 to 4, except that non-permanent, preferably detachable, assembly means, such as a hook-washer assembly or any other suitable assembly means, are used to connect the first section SI and the second section S2, as well as the successions between them to form an element 1 in the form of separate parts connected so as to be mechanically joined.

[0107] Figure 6 represents a third embodiment of the insert according to the invention, comprising a rotating movable element 1 as already described above, and identical in every respect to the first and second embodiments described above in relation to Figures 1 to 4 and Figure 5 respectively, except that the rotating movable element 1 further comprises a rotating drive piece 30, positioned upstream and connected to the first section SI of the first succession in the sequence of the element 1 of the insert.

[0108] The rotating drive piece 30 is positioned between the fixing system 20 and the first section SI of the first succession in the sequence of the element 1 of the insert.

[0109] The rotating drive piece 30, forming part of element 1, is positioned between the first end of element 1 and the first section SI of the sequence positioned first, in the sequence, from the inlet of the tube 10 to which the piece 30 is connected. The rotating drive piece comprises a shaft 3a coaxial with the helical winding of the first section SI, said shaft being provided with at least two blades 30b integral with said shaft 3a.

[0110] The rotating drive part 30 has Nb blades, Nb being an integer between 2 and 6, preferably between 3 and 5.

[0111] The insert according to this third embodiment of the invention has the capacity to have a low rotation threshold compared to existing rigid helical-wound rotary inserts. Surprisingly, such an embodiment, including the preferred features described below, makes it possible to reduce the insert's rotation threshold, thus ensuring a mechanical effect in low fluid flow velocity ranges within the heat exchanger tube, improving the versatility of this type of insert.

[0112] The rotating drive part 30 has a length La, which corresponds substantially to the length of the shaft 3a, and which is preferably between 10 mm and 500 mm, preferably between 20 mm and 200 mm.

[0113] According to this third embodiment, the total length of the insert is essentially made up of the sum of the length La of the rotating drive part 30 and the length Li of the sequence of successions S1 / S2, the length Li being able to be equal to n times the sum of the lengths L1 and L2 if the lengths L1 and L2 are identical from one succession to the other.

[0114] The length L3 of a blade is the distance, along the Z-axis, between the leading edge of the blade and its trailing edge. The leading and trailing edges follow each other in the direction of fluid flow, with the leading edge initially facing the fluid.

[0115] Each blade has a pitch angle P3, which can be defined between the Z-axis and the tangent to the mean camber line of the blade at a given point on the blade. This pitch angle can be variable or fixed along Z and / or r in a cylindrical coordinate system.

[0116] Preferably, all the blades are identical, that is to say, they have the same geometric characteristics (length, diameter, thickness, etc.).

[0117] The material forming the rotating drive component 30 of the rotating element 1 of the insert can be carbon steel, stainless steel, or any other metal or metal alloy such as Inconel®, providing the insert, as with metal rods, with the required rigidity, and preferably resistant to high temperatures and corrosion. The material forming the rotating drive component of the insert is preferably less hard than the material of the heat exchanger tube conduit to prevent degradation of said tube.

[0118] For highly corrosive fluids, the material forming the rotating drive part 30 of the insert can be coated with a protective layer, typically a polymer layer. Alternatively, the material forming the rotating drive part 30 of the insert can be a polymer or composite material (metal or metal alloy with a polymer material, or different types of polymers, or a composite material combining different types of reinforcement, such as fibers, particles, etc., with different matrices, such as a polymer, metal, or ceramic matrix).

[0119] The rotating drive part 30 of the insert is a robust element, i.e., one with a low risk of breakage.

[0120] The rotating drive component and the S1 / S2 section linkage can be formed from the same or different materials, as described above. Figure 6 illustrates one possible example of a rotating drive component; however, other variations are possible and not shown.

[0121] According to the example illustrated in figure 6, the rotating drive part 30 is screw-shaped, the blades form spirals, and the pitch of each blade p3 (pitch of revolution) is between 10 mm and 50 mm, more preferably between 15 mm and 20 mm.

[0122] The pitch of revolution of the blades is advantageously adjusted so as to generate the moment necessary to start the rotation of the insert while respecting the pressure loss constraint.

[0123] Advantageously, as shown, the screw-shaped rotating drive part 30 has four identical blades 30b. In the screw-shaped rotating drive part 30, the blades wind around the shaft 3a along its entire length, giving the part its screw shape. In this example, the rotating drive part 30 has a length L3, which is also the length of one blade.

[0124] The number of turns (also called revolution) for the screw-shaped drive part 30 is greater than 1, for example equal to 5 as illustrated in Figure 6.

[0125] The shaft 3a of the rotating drive component 30 has a diameter da3, preferably between 1 mm and approximately 50% of the tube's internal diameter, typically between 1 mm and 50 mm, but more preferably between 2 mm and 10 mm. The diameter of shaft 3a influences the fluid passage area, and large values ​​of da3 increase the fluid's surface velocity. The diameter da3 of shaft 3a can be constant along the Z-axis, as shown in Figure 6. Alternatively, it can be variable along the Z-axis.

[0126] The blades of the rotating drive component 30 have a diameter dr3, preferably greater than or equal to 80% of the diameter Dt of the heat exchanger tube 10, and more preferably greater than or equal to 90% of the diameter Dt. Preferably, the diameter dr3 of the blades is between 80% and 99% of the diameter Dt of the heat exchanger tube 10, and more preferably between 85% and 95% of the diameter Dt. Advantageously, there is a gap between the rotating drive component, more precisely the tips of the blades of said component 30, and the inner wall of the tube 10, so that the blades do not touch the tube wall, thus preventing damage to the tube wall. This gap is preferably between 1 mm and 3 mm. This gap is preferably constant along the axis of the shaft.However, it can vary along said axis, for example decrease, preferably continuously, from the inlet to the outlet of the tube (in the direction of fluid flow in an operating situation of the insert).

[0127] Preferably, the diameter dr3 of the blades is between 8 mm and 99 mm, preferably between 8.5 mm and 95 mm, more preferably between 8.5 mm and 50 mm, and even more preferably between 10 mm and 25 mm. The diameter of a blade is constant, as shown in Figure 6, or may vary in the direction of the shaft axis.

[0128] The blades of the rotating drive part 30 have a thickness e3, preferably between 0.3 mm and 3 mm. The blade thickness must be minimal while still meeting mechanical constraints, to reduce the overall size and thus the pressure loss.

[0129] The blade surface is the surface formed by the junction between two propeller curves with two diameters of revolution: da3 and dr3.

[0130] The angle of inclination P3 of the blades of the drive part shown in Figure 6 is constant along X, and varies with the radius r according to the equation: P3=arctan((2pi * r) / p3), the pitch p3 being constant.

[0131] The shaft 3a and the blades can be a single unit (i.e. manufactured in one piece), or alternatively be separate units fixed to each other for example by welding or any other rigid fastening means allowing the whole to be joined together.

[0132] The rotating drive piece 30 can be connected to the rigid helical winding of the first section SI of the sequence positioned first (from the inlet of the tube 10) of the element 1 by any means of attachment allowing the joint rotation of said rigid helical winding with the drive piece 30, and thus ultimately of the moving element 1, about itself around the Z-axis under the action of a fluid flowing through the tube 10. For example, the rotating drive piece 30 has an end 3d, opposite end 3c, which has a hook connected to a ring la carried by the end of the rigid helical winding of the first section SI of the sequence positioned first. The second end of the element 1, at the end of the sequence of the first and second sections SI and S2, is free.Any suitable means of fastening other than a hook-washer assembly can be used to fasten the rotating drive part 30 and the succession of sections S1 / S2.

[0133] Various variants for the drive component are possible, as described below without limitation, and can be combined. In one variant, the rotating drive component is not screw-shaped but comprises one or more propellers fixed to the shaft, i.e., rigidly attached. Each propeller has at least two flat blades inclined to the Z-axis of the shaft at an angle between 50° and 80°, preferably between 60° and 70°. For example, the flat-bladed propeller has five blades, evenly distributed around the shaft axis. The inclination angle P3 is constant along Z and along r (flat blades with zero camber).

[0134] According to another variant, the rotating drive component comprises one or more propellers rigidly mounted on the shaft, each having between two and six blades, for example, four blades, preferably identical, each with a convex and a concave face. The blades have a curvature chosen to create a pressure difference between the concave and convex faces, advantageously minimizing drag and maximizing lift (or torque), thus generating a lift force that allows the fluid, e.g., the liquid, to flow efficiently through the tube via the insert, ensuring the rotation of the drive component and minimizing pressure loss. According to this variant, the propeller length, defined along the Z-axis between a leading edge and a trailing edge of the blades, is between 5 mm and 30 mm, preferably between 8 mm and 20 mm.The blades have an angle of inclination, defined with respect to the Z-axis of the heat exchanger tube in which the insert is mounted. This angle is constant along Z and varies with the radius r (orthogonal to Z) according to the equation: a = arctan((2π * r) / pitch, where pitch is the rotational pitch, which is constant). The number of revolutions (also called revolutions) is a fraction of 1, more precisely equal to 1 divided by the number of blades Nb, and is preferably equal to 0.25 (4 blades), or, for example, equal to 0.2 (5 blades), or 0.33 (3 blades).

[0135] According to yet another variant, the rotating drive component comprises one or more propellers mounted rigidly on the shaft, each having 2 to 6 twisted blades, preferably three twisted blades. The twisted blades advantageously have an angular overlap between - (360 / Nb)° and + (360 / Nb)°, preferably between -120° and +120° for Nb = 3, defined between a leading edge of the first blade and a trailing edge of a second consecutive blade on the shaft.

[0136] In variants of the propeller drive, the propeller may include a central cylindrical component (hub) that supports the blades. This central component is fixed and centered on shaft 3a, thus being rigidly connected to the rotating shaft. The diameter of this central component is defined identically to the diameter da3 of shaft 3a: it may be equal to or greater than da3, and is preferably between 1 mm and approximately 50% of the tube's internal diameter, typically between 1 mm and 50 mm, and more preferably between 2 mm and 10 mm. Like the diameter of shaft 3a, the diameter of this central component influences the fluid passage area, and larger diameter values ​​allow for increased fluid velocity locally at the rotor. The diameter of this central component may be constant or variable along the Z-axis.The central cylindrical piece and the blades can be a single unit (i.e. manufactured in one piece), or alternatively be separate units fixed to each other, for example by welding or any other rigid fastening means allowing the whole to be joined together.

[0137] The present invention also relates to a heat exchanger comprising a plurality of tubes

[0138] 10 through which a fluid passes, comprising an insert according to the invention, in particular fixed to the upstream end of at least one of these tubes.

[0139] The heat exchanger according to the invention is advantageously a shell and tube heat exchanger as defined above.

[0140] The heat exchanger can be single-phase or two-phase, meaning that the fluid on the tube side can comprise a single phase, for example, liquid, or two phases, typically liquid and gas. Preferably, the heat exchanger comprising at least one insert according to the invention is two-phase.

[0141] 11 is configured for the circulation of a gas phase and a liquid phase in said tubes.

[0142] The heat exchanger according to the invention can be a so-called "feed-effluent" heat exchanger, such as those used in a hydrotreating or hydroconversion process for hydrocarbon feedstocks, particularly petroleum fractions, typically for preheating the hydrocarbon feedstock by means of such "feed-effluent" exchangers incorporating at least one insert according to the invention, in which the feedstock is heated by an effluent from the hydrotreating or hydroconversion unit. This type of "feed-effluent" exchanger is typically a two-phase heat exchanger, the feedstock being able to be in gaseous and liquid form within the exchanger tubes.

[0143] The length of the tubes can be between 500 mm and 15,000 mm, preferably between 1,000 mm and 6,000 mm.

[0144] The diameter of the tubes (internal diameter Dt) can be between 5 mm and 100 mm, preferably between 10 mm and 80 mm, preferably between 10 mm and 50 mm.

[0145] The heat exchanger preferably comprises a plurality of horizontal tubes (the axis of the tubes being horizontal). In this case, the insert itself is horizontal in the operating position. The invention also includes heat exchangers with vertical tubes. In this case, the insert itself is vertical in the operating position.

[0146] The present invention also relates to the use of an insert for a tubular heat exchanger according to the invention. In particular, the present invention relates to the use of such an insert during the preheating of a hydrocarbon feedstock in a hydrotreating or hydroconversion process of such a feedstock, particularly petroleum fractions, by means of at least one feed-effluent heat exchanger incorporating at least one insert according to the invention, in which the hydrocarbon feedstock is heated by an effluent from the hydrotreating or hydroconversion unit. As already described above, this type of heat exchanger is typically two-phase and should preferably operate with low pressure drops.

[0147] The heat exchanger inserts according to the invention can be used in other industrial processes employing tubular heat exchangers and fluids, including, but not limited to, fluids that may foul said exchangers, particularly in the field of oil refining or petrochemicals, without departing from the scope of the present invention.

[0148] In the field of oil refining, it is indeed common to carry out atmospheric distillation of crude oil which is preheated, before being sent to the distillation column, in tubes of one or more heat exchangers in contact with the hot atmospheric residue from atmospheric distillation.

[0149] The present invention also relates to the use of a tubular heat exchanger insert as previously described during the preheating of crude oil, in particular an atmospheric distillation process employing one or more heat exchangers comprising a plurality of tubes through which crude oil flows, said exchanger(s) being equipped with at least one insert according to the invention, in particular fixed to the upstream end of at least one of said tubes. Heat exchangers used for preheating crude oil are generally single-phase. According to certain embodiments of the invention, in particular if an insert according to the third embodiment is used, a high degree of operational flexibility at both low and high flow rates, which may be linked to a transient or steady-state regime, can be conferred to the process.

[0150] The present invention also relates to the use of a tubular heat exchanger insert as described herein for the evaporation or condensation of a fluid in a nuclear power plant. The heat exchangers are then of the evaporator or condenser type, such as reboilers in distillation columns or condensers in nuclear power plants or steam generation boilers equipped with tubular heat exchangers. The heat exchangers used in these applications are generally two-phase.

[0151] Examples

[0152] The examples below are based on calculations and aim to demonstrate some of the advantages of the heat exchanger insert and its use according to the invention. - Reference case "REF": tube without insert.

[0153] - example A: example of an insert according to the prior art, as illustrated in figure 1, comprising a fixed rigid helical winding consisting of a single section of fixed pitch p.

[0154] - Example B: Example of an insert according to the invention, according to the first embodiment as illustrated in Figure 2, in which the element 1 is fixed and comprises a sequence of 6 times (n) the succession of a first section SI of length L1 = 0.56 m and a second section S2 of length L2 = 0.44 m. The total length of the element 1 (and therefore of the insert) is 6 m and corresponds to the length of the tube.

[0155] The metal rods of the inserts in examples A and B (helical winding in example A and helical winding and straight rod in example B) are made of carbon steel and have a circular cross-section. The helical windings rotate clockwise relative to the position of the insert at the tube inlet.

[0156] The main geometric parameters of the inserts according to examples A and B are summarized in Table 1 below, which also gives the results of pressure loss induced by the presence of the insert in the tube.

[0157] The flow conditions for the examples are as follows:

[0158] - liquid velocity = 0.25 m / s;

[0159] - gas velocity = 2.82 m / s.

[0160] Pressure loss and heat transfer efficiency calculations on the tube side are performed for a fixed insert for both examples A and B.

[0161] Table 1

[0162] In Table 1:

[0163] - D, L, p and e are respectively the diameter, total length, pitch of turns and thickness of the rigid helical metal winding of the insert according to example A;

[0164] - L1 and L2 are respectively the lengths of section SI (rigid helical metal winding) and section S2 (straight metal rod) of element 1 of the insert according to example B. According to example B, the succession of sections S1 / S2 is repeated n=6 times, the total length of the insert according to example B being 6 m; - pl is the pitch of the first section SI (rigid helical metal winding) of the insert according to example B.

[0165] - el and e2 are respectively the thicknesses of sections SI and S2 of the insert according to example B.

[0166] To evaluate the performance of the insert in each example, we compare the heat transfer obtained with the reference case REF, and the pressure drop induced by the presence of the insert.

[0167] The results obtained indicate a gain in heat transfer on the tube side of 111% in the case of example B compared to the case of REF, which makes it possible to significantly improve the heat transfer performance of the tubular heat exchanger integrating the insert.

[0168] The results also show that the insert according to Example B generates a pressure drop of 13 mbar / m, or -33% compared to Example A (prior art). Example B also allows for an additional permissible pressure drop of 8 mbar / m compared to the REF case, which has a pressure drop of 5 mbar / m. This is compatible with the operation of tubular heat exchangers of the feed-effluent type, such as those used in a diesel hydrotreating process.

Claims

Demands 1. Insert for heat exchanger tube comprising an element (1) comprising a series of several successions of a first section (SI) of length L1 comprising a rigid helical winding of a rod comprising several turns and a second section (S2) of length L2 comprising a straight rod.

2. Insert according to claim 1, wherein the element (1) has a first end connected to a fastening system (20) of said element (1) to an inlet of said tube (10).

3. Insert according to claim 1, wherein the element (1) is rotationally mobile, said first end of the element (1) being fixed to a mechanical link of the fastening system (20), said mechanical link allowing free rotation of said element (1) about itself around the axis (Z) of said tube (10) under the action of a fluid passing through said tube (10), said element (1) having a second free end opposite said first end.

4. Insert according to claim 3, wherein the diameter D of the turns of the helical winding of the first section (SI) is between 70% and 99% of the internal diameter of the exchanger tube Dt, preferably between 90% and 95%.

5. Insert according to claim 3 or 4, wherein the rotating movable element (1) further comprises a rotating drive piece (30) positioned upstream and connected to the first section (SI) of the sequence positioned first in the sequence, said rotating drive piece comprising a shaft (3a) coaxial with the helical winding of the first section (SI) and provided with at least two blades (30b) integral with said shaft (3a).

6. Insert according to any one of the preceding claims, wherein the sequence comprises n sequences, n being a positive integer between 2 and 15, preferably between 2 and 10.

7. Insert according to any one of the preceding claims, wherein the sequences of the chain are all identical.

8. Insert according to any one of the preceding claims, wherein the pitch pl of the helical winding of the first section SI is between 10 mm and 50 mm.

9. Insert according to any one of the preceding claims, wherein the length L1 and the length L2 are between 50 mm and 12000 mm.

10. Insert according to claim 9, wherein the length L1 and the length L2 are between 500 mm and 5000 mm.

11. Insert according to any one of the preceding claims, of total length Li between 50% and 100% of the total length L t of the heat exchanger tube, L t being between 500 mm and 15000 mm, preferably between 1000 mm and 6000 mm.

12. Insert according to any one of the preceding claims, wherein the rod of the rigid helical winding and / or the straight rod are metallic.

13. Insert according to any one of the preceding claims, wherein the rod of the rigid helical winding and / or the straight rod have a circular or square cross-section, preferably circular, and have a diameter preferably between 0.5 mm and 5 mm.

14. A two-phase heat exchanger comprising a plurality of tubes (10) through which a fluid flows, at least one of said tubes comprising an insert according to any one of the preceding claims, configured for the circulation of a gas phase and a liquid phase within said tubes.

15. Use of an insert for a tubular heat exchanger according to any one of claims 1 to 13 for preheating crude oil in an atmospheric distillation process, or for preheating a hydrocarbon feedstock in a hydroconversion or hydrotreating process of said hydrocarbon feedstock, or for the evaporation or condensation of a fluid in a nuclear power plant.

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