Rotatable insert for heat exchanger tube

Abstract

The present invention relates to an insert for a heat exchanger tube (10) for improving the heat transfer efficiency and / or 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 comprises a rotatably movable element in the form of a spring (1) having a pitch p1 that is smaller at the inlet of the tube (10) as compared with the rest of the movable element.

Description

[0001] ROTATING INSERT FOR HEAT EXCHANGER TUBE

[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 rotating, spring-shaped moving element with a tighter pitch at the tube inlet.

[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 faced 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 through the tube. The rigid insert is configured to allow the winding to rotate freely about 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 axis X 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] A common problem encountered when using rotary inserts is a lack of flexibility regarding the operating range of the fluid flow velocity within the tube: their operation is generally optimal only within a limited range. Indeed, the mechanical effect provided by the insert's rotation decreases rapidly when the flow velocity is low, typically below approximately 1 lm / s, resulting in reduced insert efficiency in fouling reduction (and therefore heat transfer) and a higher pressure drop.

[0017] This lack of flexibility is therefore detrimental to addressing a wide range of fluids circulating in heat exchangers, and especially fluids with low flow rates such as certain heavy hydrocarbon loads which can, for example, be particularly viscous under given temperature and pressure conditions, or in the event of fluctuation in the flow rate or viscosity of the circulating fluid, linked to changes in the nature / composition of the circulating fluids or operating conditions leading to a slowing down of the circulating fluid.

[0018] Objectives and Summary of the Invention

[0019] The present invention aims to overcome, at least in part, the prior art problems described above, and in particular to improve the operational flexibility of a rotary tubular heat exchanger insert, specifically by providing an insert that can be operated at low fluid flow velocities in the tube, typically below 1 m / s, to ensure a mechanical effect by rotating it at these low flow velocities. It is thus proposed to provide a rotary insert with a low rotation threshold, enabling it to operate at low fluid flow velocities in the tube.

[0020] In general, the present invention aims to provide a device for reducing fouling and / or improving heat exchange for heat exchanger tubes that is robust (risk of breakage minimized), that limits pressure losses while being able to be used at low fluid flow velocities in the tube.

[0021] 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 a rotating movable element having a rigid helical winding of a rod comprising several turns, said element having: a first end fixed to a mechanical link of a system for fixing said element to the tube, the mechanical link allowing the free rotation of the element on itself around the axis (X) of the tube under the action of a fluid passing through the tube, a second free end, and the rigid helical winding being constituted by a first section of length L1 originating at the first end and a second section of length L2 in the extension of the first section, the first pitch pl of the turns of the first section being smaller than the second pitch p2 of the turns of the second section.

[0022] According to one or more embodiments of the invention, the pitch pl is between 5 mm and 20 mm, preferably between 5 mm and 15 mm.

[0023] According to one or more embodiments of the invention, the pitch p2 is between 10 mm and 60 mm, preferably between 20 mm and 40 mm, it being understood that p2 > pl.

[0024] According to one or more embodiments of the invention, the length L1 is between 100 mm and 3000 mm, preferably between 200 mm and 1000 mm.

[0025] According to one or more embodiments of the invention, the insert has a total length between 50% and 100% of the total length L t of the heat exchanger tube.

[0026] According to one or more embodiments of the invention, the insert is inserted into a tube of total length L t between 500 mm and 15,000 mm, preferably between 1,000 mm and 6,000 mm.

[0027] According to one or more embodiments of the invention, the rigid helical winding has a circular or square cross-section, preferably circular. According to one or more embodiments of the invention, the diameter e1 of the winding stem of the first section and the diameter e2 of the winding stem of the second section are between 0.5 mm and 5 mm, preferably between 1 mm and 3 mm.

[0028] According to one or more embodiments of the invention, the diameter e1 of the winding stem of the first section and the diameter e2 of the winding stem of the second section are identical.

[0029] According to one or more embodiments of the invention, the diameter of the turns of the winding D is between 80% and 99% of the internal diameter of the exchanger tube Dt, preferably between 85% and 95%.

[0030] According to one or more embodiments of the invention, the stem of the rigid helical winding is metallic.

[0031] According to a second aspect, the present invention relates to a heat exchanger comprising a plurality of tubes through which a fluid passes, said heat exchanger comprising an insert according to the invention, fixed to the upstream end of at least one of said tubes.

[0032] According to a third aspect, the present invention relates to the use of a tubular heat exchanger insert according to the invention for preheating crude oil in an atmospheric distillation process of said crude oil, or for preheating a hydrocarbon feed in a hydroconversion or hydrotreating process of said hydrocarbon feed, or for evaporating or condensing a fluid in a nuclear power plant.

[0033] The tubular heat exchanger insert according to the invention is very advantageously used for preheating crude oil in an atmospheric distillation process of said crude oil.

[0034] 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.

[0035] List of figures

[0036] Figure 1, already described above, represents an insert and its method of attachment to the heat exchanger tube according to the prior art.

[0037] Figure 2 is a three-dimensional (3D) schematic view of an embodiment of the insert according to the invention.

[0038] Figure 3 shows 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. Figure 4 shows a rear view of a portion of the insert and the heat exchanger tube according to the same embodiment as that illustrated in Figures 2 and 3.

[0039] Figure 5 is a diagram of the rotational speed V R (RPM) of the insert as a function of the fluid velocity V F standardized (V F / V Fr ef) an example of an insert according to the prior art and an example of an insert according to the invention.

[0040] Figure 6 is a normalized pressure loss diagram (APi / AP tv ) depending on the fluid velocity V F standardized (V F / V Fr ef) generated by the inserts tested in the examples.

[0041] Figure 7 is a schematic three-dimensional (3D) view of an insert not in accordance with the invention.

[0042] In the figures, the same references designate identical or analogous elements.

[0043] Description of the implementation methods

[0044] 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."

[0045] 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.

[0046] 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 could be a value of temperature, pressure, distance, speed, flow rate, compound content, etc.

[0047] 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.

[0048] 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.

[0049] In this description, when mentioned, the positions "front," "back," "horizontal," "vertical," etc., of the various elements of the insert and the heat exchanger tube are defined relative to a tubular heat exchanger in its operating position and relative to the direction of fluid flow through the heat exchanger tube. In this description, the fluid flow velocity in the tube is understood to be the surface velocity of the fluid flowing through the tube, V_SF, commonly accepted as the ratio between the volumetric flow rate of the fluid Q and the internal cross-sectional area of ​​the tube S: V_SF = Q / S. The same applies to the threshold rotation speed of an insert, which is a surface velocity, more precisely a specific value of V_SF unique to the insert used.

[0050] 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 that rotates the moving part containing said winding, 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 speed, viscosity, and / or temperature.

[0051] 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)).

[0052] 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).

[0053] 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.

[0054] In this description, the various embodiments presented can be implemented separately or in combination with each other, without limitation of combinations where technically feasible.

[0055] The present invention proposes an insert for a heat exchanger tube.

[0056] With reference to Figures 2 to 4, which depict an embodiment of the insert according to the invention, said insert comprises a rotating element 1 formed by a rigid helical winding of a rod, preferably metallic, having several turns. The rotating element 1 has a first end fixed to a mechanical link 22 of a fastening system 20 of the element 1 to the tube 10 of the heat exchanger, the mechanical link 22 allowing the free rotation of the element 1 about itself around the axis X of said tube 10 under the action of a fluid flowing through the tube (cylindrical tube with axis X). The second end of the rotating element 1, opposite the first end, is free.According to the invention, the winding consists of a first section SI of length L1 originating at the first end of the element 1 and a second section S2 of length L2 in the extension of the first section SI, the first pitch pl of the turns of the first section SI being smaller (strictly less) than the second pitch p2 of the turns of the second section S2.

[0057] Advantageously, when the insert according to the invention is used in a heat exchanger tube, the moving element is rotated by the circulating fluid. This 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. The rotating 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 insert's rotation, which enhances convective heat transfer.Indeed, the mere presence of the insert, and even more so its rotation, creates turbulence that leads to increased heat transfer by reducing the thickness of the heat transfer boundary layer and thus the 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.

[0058] The rotation threshold 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 rotation threshold.

[0059] Within the framework of the present invention, the insert according to the invention has the capacity to have a low rotation threshold compared to existing rigid helical winding type inserts.

[0060] Surprisingly, the inventors have shown that the presence of an initial section with a tighter pitch compared to the rest of the winding of the moving element of the insert, particularly according to the specifications described below, makes it possible to reduce the threshold for starting rotation of the insert, thus ensuring a mechanical effect in low flow velocity ranges (typically less than 1 m / s) of the fluid in the heat exchanger tube, which improves the flexibility of use of this type of insert.

[0061] Preferably, the pitch pl of the first SI section is between 5 mm and 20 mm, preferably is between 5 mm and 15 mm, and more preferably between 7 mm and 12 mm.

[0062] Preferably, the pitch p2 of the second section S2 is between 10 mm and 60 mm, preferably is between 20 mm and 40 mm, it being understood that p2 > pl.

[0063] Advantageously, the ratio between the pitch pl and the pitch p2 is between 0.1 and 0.7, preferably between 0.20 and 0.45. The pitch can be defined in general as a function of the angle of inclination of the turns and the diameter of the turns of the rigid helical winding D, according to the following relation: pitch = (it x D) / tana.

[0064] The turn inclination angle a is defined with respect to the winding axis coinciding with the X-axis of the heat exchanger tube in which the insert is mounted. Angle ai refers to the turn inclination angle of the first winding section, and angle a2 to the turn inclination angle of the second winding section, as shown in Figure 2.

[0065] Advantageously, the rotation threshold of an insert according to the invention is less than 1 m / s, preferably between 0.1 m / s and 0.9 m / s. For example, the rotation threshold of an insert according to the invention is between 0.5 m / s and 0.9 m / s. Advantageously, the length L1 of the first section SI is between 100 mm and 3000 mm, preferably between 200 mm and 1000 mm.

[0066] The first section SI and the second section S2 are joined together, and can form a single piece or be two separate pieces connected in such a way as to be joined together by means of assembly such as a hook-washer assembly or any other means of assembly.

[0067] The total length of the insert is essentially made up of the total length of the rigid helical winding which is the sum of the lengths L1 and L2 of the first and second sections.

[0068] The length L2 of the second section S2 can therefore be defined as the total length of the insert, related to the length of the heat exchanger tube, minus the length L1 of the first section. For example, if the total length of the insert is equal to that of the tube and is 6000 mm, the length L2 is approximately between 5900 mm and 4000 mm, and preferably approximately between 5800 mm and 4000 mm.

[0069] 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.

[0070] The heat exchanger tube 10 can have a total length ranging from 500 mm to 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, can have heat exchanger tubes ranging from 1 meter to 6 meters in length. In the nuclear industry, heat exchangers in nuclear power plant condensers can have tubes up to 14 meters long.

[0071] The rigid helical winding has a diameter D, which corresponds to the diameter of the turns of the winding. The diameter D is common to the first and second sections SI and S2 constituting the rigid helical winding.

[0072] Advantageously, the diameter D of the winding turns is greater than or equal to 80% of the diameter Dt of the heat exchanger tube 10, preferably greater than or equal to 90% of the diameter Dt, in order to generate optimal turbulence in the circulating fluid and to scrape deposits from the tube wall effectively. Preferably, the diameter D of the winding turns is between 80% and 99% of the diameter Dt of the heat exchanger tube 10, more preferably between 85% and 95% of the diameter Dt.

[0073] The diameter of the tubes (internal diameter Dt) can be between 10 mm and 100 mm, preferably between 10 mm and 50 mm. Advantageously, there is a gap "c" between the insert and the inner wall of the tube 10 so that the helical winding of the moving element does not touch the tube wall, as shown in Figure 4, which depicts a rear view of a portion (part of the first section) of the insert and the heat exchanger tube. This gap is designed to prevent damage to the tube wall, for example, by avoiding scratches that could create surface irregularities and promote corrosion. This gap "c" is preferably between 1 mm and 3 mm.

[0074] The winding can have a cross-section of various shapes, and preferably a circular or square cross-section, and more preferably 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 * Cross-sectional area / perimeter of the cross-section.

[0075] The rod, preferably metallic, forming the rigid helical winding has a diameter e1 at the first section SI, and has a diameter e2 at the second section S2.

[0076] The diameters el and e2 are preferably between 0.5 mm and 5 mm, more preferably between 1 mm and 3 mm.

[0077] 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.

[0078] The winding direction, 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 X axis in the figures).

[0079] The first end of the rotating movable element 1, attached to the mechanical link 22, may include a ring la or any other means of attachment to the mechanical link 22.

[0080] 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.

[0081] For highly corrosive fluids, the material forming the insert can be coated with a layer of protective material, typically a polymer layer.

[0082] In another embodiment, the material forming 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 reinforcements, such as fibers, particles, etc., with different matrices, such as a polymer, metallic, or ceramic matrix). The rigid helical winding of the freely rotating moving element is a robust element, i.e., one with a low risk of breakage.

[0083] 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. The attachment system is advantageously arranged along the X-axis of the heat exchanger tube so that the moving element of the insert can rotate about said axis. The attachment system is typically positioned at the tube inlet, and the rotating moving 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 moving element 1 of the insert so that the insert is free to rotate about the X-axis of the tube 10.The bearing 23 comprises a stirrup-shaped portion 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 portion 23b comprising an opening for retaining the trunnion 22. The two arms of the stirrup-shaped portion 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 portion 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 portion 23b of the bearing 23 and a hook-shaped end 21 that can be hooked onto the ring 1a or any other fastening means included in the first end of the movable 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.

[0084] Each insert advantageously includes its own tube fixing system, although a common fixing system shared between the inserts of the other heat exchanger tubes would not fall outside the scope of the present invention.

[0085] Other systems for fixing the insert to the tube 10 can be used without departing from the scope of the present invention.

[0086] The present invention also relates to a heat exchanger comprising a plurality of tubes 10 through which a fluid flows, comprising an insert according to the invention, in particular fixed to the upstream end of at least one of these tubes.

[0087] The heat exchanger according to the invention is advantageously a shell and tube heat exchanger as defined above.

[0088] 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 single-phase.

[0089] The length of the tubes can be between 500 mm and 15,000 mm, preferably between 1,000 mm and 6,000 mm.

[0090] 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.

[0091] 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.

[0092] The present invention also relates to the use of an insert for a tubular heat exchanger.

[0093] In particular, the present invention relates to the use of such an insert during the preheating of crude oil in an atmospheric distillation process. In the field of petroleum refining, it is common practice to perform 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 the atmospheric distillation.

[0094] The present invention relates to the use of an insert for a tubular heat exchanger according to the invention 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. The use of such an insert in this context notably provides operational flexibility at both low and high flow rates, which can be linked to a transient or steady-state regime.

[0095] 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.

[0096] The present invention thus relates, for example, to the use of a tubular heat exchanger insert as described in this description in a hydrotreating or hydroconversion process of hydrocarbon feedstocks, in particular petroleum cuts, typically for preheating such a feedstock by means of so-called "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.

[0097] 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.

[0098] Examples

[0099] The examples below are based on the implementation of a so-called "cold" experimental model, and aim to show some of the advantages of the heat exchanger insert and its use according to the invention.

[0100] The cold model includes a transparent PVC heat exchanger tube with a length of 3 m and a diameter of 21 mm (internal diameter Dt), in which water at ambient temperature and pressure is circulated, over a surface velocity range in the tube of between 0.5 and 2 m / s.

[0101] Three examples of inserts are tested:

[0102] - example A: example of an insert according to the prior art, as illustrated in figure 1, in which the rigid helical winding consists of a single section of fixed pitch p.

[0103] - Example B: Example of an insert according to the invention, according to an embodiment as illustrated in Figure 2, in which the rigid helical winding consists of two successive sections SI and S2 of different pitches pl and p2, with pl less than p2.

[0104] - example C: example of an insert not conforming to the invention, as illustrated in figure 7, in which the rigid helical winding consists of two successive sections SI and S2 of different pitches pl and p2, with pl less than p2, repeated twice (RI and R2).

[0105] The rigid helical winding of the moving element of the inserts in examples A, B, and C is made of carbon steel and has a circular cross-section. The winding direction is clockwise relative to the position of the insert at the tube inlet.

[0106] The main geometric parameters of the rigid helical winding of the moving element of the inserts according to examples A, B, and C are shown in Table 1 below. Table 1

[0107] In Table 1:

[0108] - 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;

[0109] - L1 and L2 are respectively the lengths of section SI and section S2 of the rigid helical metal winding of the insert according to example B. These lengths L1 and L2 are also those of sections SI and S2 of each of the two repetitions of the assembly S1 / S2 of the rigid helical metal winding of the insert according to example C.

[0110] (*) Thus, according to example C, the rigid helical winding has a total length of 3 m broken down as follows: 2 times the length L1 (0.5 m) for each section SI, i.e. 0 1 m, plus 2 times the length L2 (1 m) of the section S2, i.e. 2 m;

[0111] - pl and p2 are respectively the pitches of sections SI and S2 of the rigid helical metal winding of the insert according to example B and according to example C.

[0112] - el and e2 are respectively the thicknesses of sections SI and S2 of the rigid helical metal winding of the insert according to example B and according to example C.

[0113] To evaluate the performance of the insert in each example, the evolution of the rotation speed of the insert in revolutions per minute (rpm) is plotted as a function of the surface velocity of the liquid in the tube, normalized by the minimum velocity of the liquid for starting the rotation of the insert according to example A taken as a reference.

[0114] The diagram in Figure 5 thus shows the rotational speed V R (RPM or rpm) of the insert according to example A (rigid helical winding of the moving element of insert "A") and according to example B of the invention (rigid helical winding of the moving element of insert "B"), as a function of the liquid velocity V F standardized: V F / V Fr ef, V Fre f being the minimum liquid speed for starting rotation of the insert according to example A.

[0115] According to the diagram in Figure 5, the rotational speed of the insert according to Example A is 1 m / s, and that of an insert according to Example B is less than 1 m / s. The results indicate that an insert according to the invention, as exemplified in Example B, reduces the rotational threshold of the insert by 20% (-20%), thus enabling better performance in reducing fouling at low fluid velocities, thanks to the rotary mechanical effect.

[0116] The test results for the insert according to example C, which features a helical winding consisting of two repetitions of a SI section followed by an S2 section, show that periodically adding a section with a tighter twist pitch than the other section does not reduce the threshold fluid speed for rotation. On the contrary, using two SI sections with a tighter twist pitch compared to the S2 section located in the extension of the SI section has a counterproductive effect: the insert does not rotate, even at the highest speeds. The tight twist pitch on two periodic SI sections causes vibration rather than rotation.Moreover, this configuration causes a significantly greater increase in pressure loss, visible in the diagram in Figure 6 representing the normalized pressure loss, which is the ratio between the pressure loss of the tested insert APi and the pressure loss of the empty tube, AP. tv , generated by the inserts according to examples A, B, and C, as a function of the fluid velocity V F standardized (V F / V F ref).

Claims

Demands 1. Insert for heat exchanger tube, said insert comprising a rotating movable element (1) having a rigid helical winding of a rod comprising several turns, said element having: a first end fixed to a mechanical link (22) of a fixing system (20) of said element to said tube (10), said mechanical link allowing free rotation of said element (1) about itself around the axis (X) of said tube (10) under the action of a fluid passing through said tube (10), a second free end, and said rigid helical winding being constituted by a first section (SI) of length L1 originating at the first end and a second section (S2) of length L2 in the extension of the first section (SI), the first pitch pl of the turns of the first section (SI) being smaller than the second pitch p2 of the turns of the second section (S2).

2. Insert according to claim 1, wherein the pitch pl is between 5 mm and 20 mm, preferably between 5 mm and 15 mm.

3. Insert according to claim 1 or 2, wherein the pitch p2 is between 10 mm and 60 mm, preferably between 20 mm and 40 mm, it being understood that p2 > pl.

4. Insert according to any one of the preceding claims, wherein the length L1 is between 100 mm and 3000 mm, preferably between 200 mm and 1000 mm.

5. Insert according to any one of the preceding claims, having a total length between 50% and 100% of the total length L t of the heat exchanger tube.

6. Insert according to claim 5, inserted into a tube of total length L t between 500 mm and 15000 mm, preferably between 1000 mm and 6000 mm.

7. Insert according to any one of the preceding claims, wherein the rigid helical winding has a circular or square cross-section, preferably circular.

8. Insert according to any one of the preceding claims, wherein the diameter e1 of the winding stem of the first section (S1) and the diameter e2 of the winding stem of the second section (S2) are between 0.5 mm and 5 mm, preferably between 1 mm and 3 mm.

9. Insert according to any one of the preceding claims, wherein the diameter e1 of the winding stem of the first section (S1) and the diameter e2 of the winding stem of the second section (S2) are identical.

10. Insert according to any one of the preceding claims, wherein the diameter of the winding turns D is between 80% and 99% of the internal diameter of the exchanger tube Dt, preferably between 85% and 95%.

11. Insert according to any one of the preceding claims, wherein the stem of the rigid helical winding is metallic.

12. Heat exchanger comprising a plurality of tubes (10) through which a fluid flows, comprising an insert according to any one of the preceding claims, fixed to the upstream end of at least one of said tubes.

13. Use of a tubular heat exchanger insert according to any one of claims 1 to 11 for preheating crude oil in an atmospheric distillation process of said crude oil, or for preheating a hydrocarbon feedstock in a hydroconversion or hydrotreating process of said hydrocarbon feedstock, or for evaporating or condensing a fluid in a nuclear power plant.

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