ROTATING INSERT FOR HEAT EXCHANGER TUBE WITH ROTATIONAL ASSISTANCE

Abstract

The present invention relates to an insert (300) for a heat exchanger tube (100) for improving heat transfer efficiency and / or reducing fouling of heat exchanger tubes in industrial units, for example, units used in petroleum refining, petrochemicals, or the chemical industry in general. The insert comprises a rotating movable element including a rotating drive piece (30) connected to a rigid helical winding of a metal rod comprising several turns (10). The drive piece (30) includes a shaft (3a) coaxial with the winding and provided with at least two blades (30b) fixed to the shaft. Figure 3 to be published

Description

Title of the invention: ROTARY INSERT FOR HEAT EXCHANGER TUBE WITH ROTATIONAL ASSISTANCE technical field

[0001] 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 rotating drive component. Previous technique

[0002] Heat exchanger insert technologies are used to improve heat transfer efficiency and reduce fouling of industrial heat exchanger tubes.

[0003] In many fields, such as oil refining, petrochemicals, and other fields 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 may come from impurities present in the liquid streams from various processes that pass through the heat exchangers, and / or from the decomposition or formation of organic products such as polymers or hydrocarbons and mineral products in said liquid streams.

[0004] These may be suspended impurities accumulating, deposits of mineral salts dissolved in liquid streams, coke forming, or sulfur compounds soluble in hydrocarbon streams. These deposits can be generated by excessive fluid temperatures or result from corrosion. These deposits, which gradually accumulate on the walls of the heat exchanger tubes over time, impair the performance of the heat exchangers, which thus lose efficiency over time. 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. 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.

[0005] The use of inserts in heat exchangers is thus aimed at improving heat transfers, in particular because the inserts promote turbulence which leads to a reduction in the thermal boundary layer, which decreases the resistance to heat transfer and therefore improves the efficiency of heat transfer, and at preventing fouling of heat exchangers.

[0006] They constitute a very interesting and promising solution for supporting the reduction of energy consumption and consequently CO2 emissions from industrial processes using heat exchangers, as can be the case in all the fields mentioned above. In the field of oil refining, for example, there are many units using heat exchangers that are susceptible to fouling. Refining crude oil involving preheating said crude oil with the hot atmospheric residue exiting an atmospheric distillation unit is one example. Many so-called heavy crude oils are very rich in asphaltenic compounds that can form sediments, as well as in sulfur and other corrosive compounds that are prone to forming deposits on the internal walls of the heat exchanger tubes through which they circulate.

[0007] There are many different forms of inserts in the industry, such as a winding of a metal wire, a twisted band, a central shaft with blades, said inserts being able to include moving and / or static parts, and being able to be fixed or not to the tube, and where appropriate in different ways, for example on one end only or at 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 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 a mechanical effect linked to 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 resistance to fluid flow, which can be problematic if this resistance is too high. Typically, excessive pressure drop affects the capacity and energy consumption of the pumps and turbines that circulate the fluid. fluid(s) that will compensate for the pressure drop. Therefore, a minimal pressure drop is generally desired, meaning one that is limited compared to the pressure drop of a tube without an insert, in order to avoid compromising the heat exchanger's energy efficiency and even to avoid having to change the fluid circulation equipment upstream of the exchanger. A rotating insert generally induces less pressure drop than a fixed insert, for example, up to 40% less pressure drop.

[0008] An example of a rotating insert for a heat exchanger tube is described, for instance, 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 free rotation of the winding about the axis of the tube. The pitch of the metal winding can be fixed or variable.

[0009] 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 coinciding with the axis Z 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 passing 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 washer-shaped head designed to hold it captive in the bearing.

[0010] A problem often encountered when using rotary inserts is a lack of flexibility regarding the possible operating range for the flow velocity of the fluid sent through the tube: their operation is generally optimal only within a limited range. Indeed, the mechanical effect provided by the rotation of the insert decreases rapidly when the flow velocity is low, typically below approximately 1 m / s, resulting in lower insert efficiency in reducing fouling (and therefore heat transfer) and a greater pressure drop.

[0011] This lack of flexibility is therefore a disadvantage for addressing a wide range of fluids circulating in heat exchangers, and especially low-flow fluids such as certain heavy hydrocarbon loads which can, for example, be particularly viscous under certain temperature conditions and given pressure, 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. Objectives and Summary of the Invention

[0012] 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 to provide an insert that can be operated at low fluid flow velocities in the tube, typically at flow velocities 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.

[0013] 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.

[0014] 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, said insert comprising a rotating movable element having a rotating drive piece to a rigid helical winding of a rod comprising several turns, said rotating movable element having: a first end on the side of the rotating drive piece, attached to a mechanical link of a fixing system for said rotating movable element to said tube, said mechanical link allowing the free rotation of said rotating movable element on itself around the axis of said tube under the action of a fluid passing through said tube, a second free end on the side of the rigid helical winding, and said rotating drive piece having a shaft coaxial with said winding and provided with at least two blades attached to said shaft.

[0015] According to one or more embodiments of the invention, the rod of the rigid helical winding is metallic.

[0016] According to one or more embodiments of the invention, the rotating drive part comprises 2 to 6 blades, preferably 3 to 5 blades.

[0017] According to one or more embodiments of the invention, the rotating drive part is in the form of a screw with a pitch p3 between 10 mm and 50 mm, has 4 blades, and has a length L3 between 10 mm and 500 mm.

[0018] According to one or more embodiments of the invention, the rotating drive part comprises one or more propellers fixed to the shaft and each comprising at least two blades, said blades being flat and inclined with respect to the Z axis at an angle

[33] between 50° and 80°.

[0019] According to one or more embodiments of the invention, the rotating drive part comprises one or more propellers fixed to the shaft and each comprising 2 to 6 blades, preferably 4 blades, said blades each comprising a convex face and a concave face.

[0020] According to one or more embodiments of the invention, the rotating drive part comprises one or more propellers mounted on the shaft and each comprising 2 to 6 twisted blades, preferably three twisted blades, the blades having angular overlap q> between -(360 / Nb)° and +(360 / Nb)° defined between a leading edge of a first blade and a trailing edge of a second consecutive blade on the shaft, Nb being the number of blades.

[0021] According to one or more embodiments of the invention, the rotating drive part comprises an assembly of an upstream part comprising one or more propellers having at least 2 twisted blades with a downstream part comprising one or more propellers having at least 2 flat blades inclined with respect to the shaft at an angle a3 between 50° and 80° or having four blades each comprising a convex face and a concave face.

[0022] According to one or more embodiments of the invention, the propeller comprises a central cylindrical piece serving as a support for the blades, said central piece being fixed and centered on the shaft so as to be integral with the shaft.

[0023] According to one or more embodiments of the invention, the winding consists of a single section of turns with a fixed pitch p.

[0024] According to one or more embodiments of the invention, the winding consists of a first section of length L1 originating at the connection with said rotating drive piece 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, the pitch pl being between 5 mm and 20 mm, the pitch p2 being between 10 mm and 60 mm, and the length L1 being preferably 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 LT of the heat exchanger tube.

[0026] According to one or more embodiments of the invention, the diameter of the blades Dr3 of said rotating drive part and / or 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%.

[0027] According to a second aspect, the present invention relates to a heat exchanger comprising a plurality of tubes through which a fluid passes, comprising an insert according to the invention, fixed to the upstream end of at least one of said tubes.

[0028] 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 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.

[0029] 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. List of figures

[0030] [Fig.1]

[0031] Fig. 1, already described above, represents an insert and its method of attachment to the heat exchanger tube according to the prior art.

[0032] [Fig.2]

[0033] Fig. 2 is a three-dimensional (3D) schematic view of an example of an insert according to a first embodiment of the invention.

[0034] [Fig.3]

[0035] Fig. 3 represents the same embodiment of the insert as that illustrated in Fig. 2, with an additional portion of a heat exchanger tube and a system for attaching the insert to the tube.

[0036] [Fig.4]

[0037] Fig. 4 is a schematic 3D view of the screw-shaped rotating drive part of the insert according to the embodiment illustrated in Figures 2 and 3.

[0038] [Fig.5]

[0039] Fig. 5 corresponds to three schematic 3D views a), b) and c) of an example of a rotating drive part according to a second embodiment of the insert according to the invention, comprising propellers with inclined flat blades.

[0040] [Fig.6]

[0041] Fig. 6 corresponds to three schematic 3D views a), b) and c) of an example of a rotating drive part according to a third embodiment of the insert according to the invention, comprising propellers with four convex-concave curved blades.

[0042] [Fig.7]

[0043] Fig. 7 corresponds to three schematic 3D views a), b) and c) of an example of a rotating drive part according to a fourth embodiment of the insert according to the invention, comprising propellers with three twisted blades.

[0044] [Fig.8]

[0045] Fig. 8 corresponds to a two-dimensional (2D) representation a) of two consecutive blades of an example of an insert according to the fourth embodiment of the invention as represented in Fig. 7, in a cylindrical coordinate reference detailed in diagram b).

[0046] [Fig.9]

[0047] [Fig.9] represents diagrams a) and b) illustrating the geometric profile of the blades of an example of an insert according to the fourth embodiment of the invention as shown in [Fig.7].

[0048] [Fig. 10]

[0049] Fig. 10 is a three-dimensional (3D) schematic view of an example of an insert according to a fifth embodiment of the invention, comprising a rigid helical winding with an initial section with a tight pitch.

[0050] [Fig. 11]

[0051] The [Fig. 11] is a diagram of the rotational speed VR (RPM) of the insert as a function of the normalized fluid speed VF (VF / VFref) of an example of an insert according to the prior art and an example of an insert according to the invention.

[0052] In the figures, the same references designate identical or analogous elements. Description of the implementation methods

[0053] In this description, the term "include" is synonymous with (means the same as) "comprise", "include", and "contain", thus being inclusive or open, and not excluding other elements not mentioned. It is understood that the term "include" includes the exclusive and closed term "consist".

[0054] 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.

[0055] Furthermore, in this description, the terms "essentially" or "substantially" or "approximately" with respect to a reference value correspond to an approximation of ±10%, ±5%, preferably ±1%, most preferably ±0.5%. This may be a value of temperature, pressure, distance, speed, flow rate, content of compound(s), etc.

[0056] In this description, the different parameter ranges characterizing a given device, or relating to a step in a process implementing said device, Ranges such as those relating to dimensions (lengths, diameters, etc.), angles, pressure ranges, or temperature ranges can be used alone or in combination. For example, in the context of the present invention, a preferred range of pressure values ​​can be combined with a more preferred range of temperature values.

[0057] According to the present invention, the pressures are absolute pressures, also noted as abs., and are given in absolute MPa (or abs. MPa), unless otherwise indicated.

[0058] 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 with respect to a tubular heat exchanger in its operating position and with respect to the direction of fluid flow through the heat exchanger tube. The direction of fluid flow is represented by a solid arrow in the figures.

[0059] In this description, the fluid flow velocity in the tube refers to the surface velocity of the fluid flowing in the tube V_SF, commonly understood to be the ratio between the volumetric flow rate of the fluid Q and the internal cross-section of the tube S: V_SF = Q / S. The same applies to the threshold speed for starting rotation of an insert, which is a surface velocity, more precisely a specific value of V_SF particular to the insert used.

[0060] 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.

[0061] 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 the present invention are classically shell-and-tube heat exchangers 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 usually taken at their extremities. The tubes are held in perforated plates called tube sheets, which also serve to separate the fluids. These tubes can be supported between the tube sheets by intermediate support plates (perforated plates transverse to the tubes). The tubes can also be U-shaped, and their ends can, for example, be attached to a single tube sheet.

[0062] In this description, the pitch of a helical winding comprising several 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).

[0063] Embodiments of the insert, its use in a heat exchanger, and their applications are described in detail below. Many specific details are given 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.

[0064] In the present description, the different embodiments presented can be implemented separately or in combination with each other, without limitation of combinations when this is technically feasible.

[0065] The present invention proposes an insert for a heat exchanger tube.

[0066] Reference is made to Figures 2 to 4, which represent an example of a first The following embodiment of the insert according to the invention is provided to describe the insert in general, without the specific features of the embodiment illustrated in Figures 2 to 4 limiting the invention. These specific features relating to the first embodiment are detailed further in the description.

[0067] Thus, the insert according to the invention comprises a rotating movable element 300 having a rotating drive piece 30 connected to a rigid helical winding of a rod, preferably metallic, having several turns 10. The rotating movable element 300 has a first end 3c, on the side of the rotating drive piece, fixed to a mechanical link 22 of a fastening system 200 of the element 300 to the tube 100 of the heat exchanger, the mechanical link 22 allowing the free rotation of the element 300 about itself around the Z-axis of said tube 100 under the action of a fluid flowing through the tube (cylindrical tube with axis Z). The second end of the rotating movable element 300, on the side of the rigid helical winding, and opposite to the first end 3c, is free. According to the invention, the rotating drive element 30 comprises a shaft 3a coaxial with the winding and which is provided with at least two blades 30b attached to said shaft 3a.

[0068] The shaft 3a of the rotating drive element 30 has a diameter da3, preferably between 1 mm and approximately 50% of the internal diameter of the tube, typically between 1 mm and 50 mm, more preferably between 2 mm and 10 mm. The diameter of the shaft 3a influences the fluid passage area, and large values ​​of the diameter da3 make it possible to increase the fluid velocity locally at the rotor. The diameter da3 of the shaft 3a can be constant along the Z axis, or can be variable along the Z axis.

[0069] The rotating drive part 30 has a length La (not shown in the figures), 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.

[0070] 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 100, 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 100, and more preferably between 85% and 95% of the diameter Dt. Advantageously, there is a gap e between the rotating drive component, more precisely the tips of the blades of said component 30, and the inner wall of the tube 100, so that the blades do not touch the tube wall, thus preventing damage to the tube wall. This gap e is preferably between 1 mm and 3 mm. This gap e is preferably constant in the direction of the shaft axis.However, it can vary along said axis, for example decreasing, preferably continuously, from the inlet to the outlet of the tube (in the direction of fluid flow in an operating situation of the insert).

[0071] The diameter of the tubes (internal diameter Dt) can be between 10 mm and 100 mm, preferably between 10 mm and 50 mm. 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 or may vary in the direction of the shaft axis.

[0072] The blades of the rotating drive part 30 have a thickness e3, preferably between 0.3 mm and 5 mm, preferably between 0.3 mm and 3 mm, more preferably between 1 mm and 3 mm. The thickness of the blades must be minimal while still meeting the mechanical constraints, in order to reduce the overall size and thus the pressure loss.

[0073] Preferably, the rotating drive part 30 comprises 2 to 6 blades, and more preferably 3 to 5 blades.

[0074] Preferably, for a given embodiment, all the blades are identical, that is to say, they have the same geometric characteristics (length, diameter, thickness, etc.).

[0075] Each blade has a pitch angle [33, which can be defined between the Z axis and the tangent to the blade's camber line 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 (see [Fig.8] b) for the representation of the cylindrical coordinate system).

[0076] The length of a blade L3 is the distance, along the Z-axis, between the leading edge of a 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. The length of an L3 blade can be between 5 mm and 500 mm, preferably between 5 mm and 200 mm, more preferably between 8 mm and 100 mm, even more preferably between 8 mm and 50 mm.

[0077] 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.

[0078] The first end 3c of the rotating moving element 300, which is integral with the mechanical link 22 of the fastening system 200, said end 3c being that of the rotating drive piece 30, may include a ring, a hook, or any other means of securing it to the mechanical link 22. The rotating drive piece 30 has an end 3d opposite the end 3c, which also has a means of fastening to one end of the rigid helical winding, such as a hook or any other means of making the rotating drive piece 30 and the rigid helical winding 10 integral, so that the piece 30 drives the rigid helical winding 10 in rotation during the operation of the insert.

[0079] The material forming the insert, in particular the rotating drive part and the rigid helical winding, preferably metallic, may be carbon steel, stainless steel, or any other metal or metal alloy material such as Inconel®, providing the insert with the required rigidity and preferably resistant to high temperatures and corrosion. The insert material is preferably less hard than the heat exchanger tube duct material to prevent degradation of said tube.

[0080] For highly corrosive fluids, the material forming the insert can be coated with a layer of a protective material, typically a polymer layer.

[0081] According to 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).

[0082] The rigid helical winding and the rotating drive part of the moving element that are set in rotation are robust elements, i.e., their risk of breakage is low. The materials used for the rigid helical winding 10 and for the rotating drive part may be the same or different.

[0083] Figures 2 to 4 illustrate a first embodiment of the insert according to the invention, in which the rotating drive part 30 is screw-shaped, the blades forming 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.

[0084] Advantageously, as shown, the screw-shaped rotating drive part 30 comprises four identical blades 30b. In the screw-shaped rotating drive part 30, the blades wind around the shaft 3a along the length of the part, giving the part its screw shape.

[0085] The pitch of revolution of the blades is advantageously adjusted so as to generate the moment necessary to rotate the insert while respecting the pressure loss constraint.

[0086] According to this first embodiment, the rotating drive part 30 has a length La, which corresponds substantially to the length L3 of a blade, and is preferably between 10 mm and 500 mm, preferably between 20 mm and 200 mm.

[0087] The surface of the blades is the surface formed by the junction between two propeller curves with two diameters of revolution: da3 and dr3.

[0088] The blades form spirals having an angle of inclination which is constant along Z, and which varies with the radius r according to the equation: [33=arctan((2ir * r) / p3), the pitch p3 being constant.

[0089] Preferably, according to the first embodiment, the number of turns (also called revolutions) for the screw-shaped drive piece is greater than 1, for example, equal to 5 as illustrated in [Fig. 4]. The rotating drive piece 30 can be connected to the rigid helical winding 10 by any fastening means allowing the joint rotation of said rigid helical winding 10 with the drive piece 30, and thus ultimately of the moving element 300, about itself around the Z-axis under the action of a fluid flowing through the tube 100. For example, the piece The rotating drive 30 has an end 3d, opposite end 3c, which includes a hook connected to a ring carried by end la of the rigid helical winding 10. The other end of the rigid helical winding 10, which is also that of the rotating moving element 300 of the insert, is free. Any suitable fastening means other than a hook-washer assembly can be used to secure part 30 and the winding 10.

[0090] According to this first embodiment, the rigid helical winding 10, preferably metallic, is conventional, and as already described in relation to [Fig.1]: the winding comprises a plurality of turns, is of length L, diameter D, pitch p, and angle of inclination alpha (a), defined with respect to the central axis of the winding coinciding with the axis Z of the exchanger tube in which the insert is mounted, and the rod, preferably metallic, forming the winding has a thickness e.

[0091] Preferably, the pitch p of the turns of the rigid helical winding 10 is between 10 mm and 60 mm, preferably is between 20 mm and 45 mm.

[0092] The pitch can be defined in general terms as a function of the angle of inclination of the turns a and the diameter of the turns of the rigid helical winding D, according to the following relation: pitch = (ji D) / tana.

[0093] The total length of the insert is essentially made up of the total length of the rotating drive part 30, corresponding essentially to the length L3 of a blade, and that L of the rigid helical winding 10.

[0094] The length L of the rigid helical winding 10 can therefore be defined as being substantially equal to the total length of the insert, related to the length of the exchanger tube, from which is subtracted the length L3 of the rotating drive part 30. For example, if the total length of the insert is equal to that of the tube and is 6,000 mm, the length L is approximately between 5,500 mm and 5,990 mm, and preferably approximately between 5,800 mm and 5,950 mm.

[0095] Advantageously, the length L of the rigid helical winding 10 is between 400 mm and 14000 mm.

[0096] The total length of the insert is less than or equal to the total length of the heat exchanger tube 100, and preferably between 50% and 100% of the total length of the heat exchanger tube 100: the total length of the insert is preferably between Lt / 2 and Lt, with Lt being the length of the heat exchanger tube 100.

[0097] The total length of the insert may be slightly less than the tube length in order to take into account possible elongation related to the mechanical force applied by the fluid and / or thermal expansion.

[0098] The heat exchanger tube 100 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 the field of Oil refining, for example in the preheating of crude oil in atmospheric distillation, may involve 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.

[0099] The rigid helical winding has a diameter D, which corresponds to the diameter of the turns of the winding. Advantageously, the diameter D of the winding turns is greater than or equal to 80% of the diameter Dt of the heat exchanger tube 100, preferably greater than or equal to 90% of the diameter Dt, in order to generate optimal turbulence in the circulating fluid and to effectively scrape deposits from the tube wall. 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. The diameter D of the turns may be equal to or different from the diameter dr3 of the rotating drive component.

[0100] Advantageously, there is a space "c" between the insert and the inner wall of the tube 100 such that the rigid helical winding of the moving element does not touch the tube wall, as referenced in [Fig. 3], so as not to damage the tube wall, for example, by creating scratches that could form surface irregularities that could promote corrosion. Said space "c" is preferably between 1 mm and 3 mm.

[0101] The winding may have a cross-section of various shapes, and preferably has a circular or square cross-section or of another shape, and more preferably has a circular cross-section. In the case of a square cross-section or of another shape, the diameter of the square cross-section is understood to be an equivalent diameter D_eq, defined as follows: D_eq = 4 * Area_of_section / perimeter of section.

[0102] The rod, preferably metallic, forming the rigid helical winding has a diameter e. The diameter e is preferably between 0.5 mm and 5 mm, more preferably between 1 mm and 3 mm. The winding direction, which can also be defined as the direction of the twist pitch, 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).

[0103] The direction of the rigid helical winding 10 is the same as the direction of winding of the blades around the shaft 3a of the rotating drive part 30.

[0104] Advantageously, when the insert according to the invention is used in a heat exchanger tube, the moving element is set in rotation by the circulating fluid, which has This increases the turbulence of the circulating fluid, improves heat exchange, and homogenizes the fluid temperature across the entire tube cross-section, thus preventing the formation of hot spots on the tube wall and significantly reducing the risk of solid deposits. It also improves heat transfer, which is typically hampered by such deposits. The rotating insert also scrapes away any deposits that may have formed on the wall, further reducing fouling. Beyond the reduction of 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 which 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.

[0105] The rotation threshold of an insert corresponds to the minimum surface velocity of the circulating fluid allowing the rotation of the moving element of the insert. The moving element, rotating in the opposite direction to the helical winding of the spring, with a speed that depends on its weight, its geometric characteristics, the flow rate, the viscosity and the density of the circulating fluid, therefore has its own rotation threshold.

[0106] 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.

[0107] Surprisingly, the inventors have demonstrated that the presence of a specific drive element positioned upstream and connected to a rigid helical winding of a rod, preferably metallic, comprising several turns, in particular such a drive element having a shaft coaxial with said winding and equipped with at least two blades integral with said shaft, described in more detail below, makes it possible to reduce the rotation threshold 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, thereby improving the flexibility of use of this type of insert. This drive element assists in the rotation of the rigid helical winding.

[0108] Advantageously, the rotation threshold of an insert according to the invention is less than Im / 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.

[0109] 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 Z-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 inlet of the tube, 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 [Fig. 3], and comprises a bearing 23 and the mechanical linkage 22 typically formed by a rotating trunnion. Said trunnion 22 is fixed to the moving element 300 of the insert so that the insert is free to rotate about the Z-axis of the tube 100.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 100, 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 100 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 100. 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 or any other fastening means included in said first end 3c of the moving element 300.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.

[0110] 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.

[0111] Other systems for fixing the insert to the tube 100 can be used without departing from the scope of the present invention.

[0112] Other embodiments are described below, in which the rotating moving element of the insert always includes a rotating drive part connected to a rigid helical winding of a rod, preferably metallic, comprising several turns, the description of which is not repeated, but in which said rotating drive part differs from that of the first embodiment according to the characteristics described in more detail below.

[0113] Figure 5 illustrates a second embodiment, in particular an example of an insert according to this second embodiment in which the rotating moving element comprises a rotating drive part 31 including one or several propellers 31e fixed to the shaft, each propeller comprising at least two blades 31b, said blades being flat and inclined with respect to the axis of the shaft at an angle

[33] between 50° and 80°, preferably between 60° and 70°. The angle of inclination

[33] is constant along Z and along r (flat blades which have zero camber).

[0114] Figure 5 shows a propeller 31e comprising five blades 31b, distributed regularly around the axis of the shaft 3a. The angle of inclination of the blades 33 is advantageously chosen so as to generate the torque necessary to rotate the insert while respecting the pressure loss constraint. The blades have a length L31, which is also substantially that of the propeller 31e.

[0115] The propeller 31e may include a central cylindrical part (hub) that serves as a support for the blades. The blades are then preferably distributed evenly around this part. The central part is then fixed and centered on the shaft 3a, so as to be rigidly connected to the rotating shaft. Fig. 5 c) illustrates such a configuration of a five-plane-bladed propeller 31e comprising a central piece of diameter dc3, and more specifically an example of an insert whose movable element 1 comprises a rotating drive piece 31 comprising several propellers 31e, e.g. two propellers 31e, each propeller being provided with a central piece of diameter dc3 fixed and centered on the shaft 3a of diameter da3, the two propellers 31e being spaced on the shaft by a distance Es3. The diameter dc3 of the central part is defined identically to the diameter da3 of the shaft 3a: it may be equal to or greater than the diameter 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. The diameter dc3 of the central part, like the diameter of the shaft 3a, influences the fluid passage area, and large diameter values ​​allow for an increase in fluid velocity locally at the rotor. The diameter dc3 of said central part can be constant or variable along the Z axis. The cylindrical central part 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 assembly to be joined together.

[0116] Figure 6 represents a third embodiment, in particular an example of insert according to this third embodiment in which the rotating moving element comprises a rotating drive part 32 which includes one or more propellers 32e fixed to the shaft (shaft not shown in [Fig. 6]), and each comprising at least 2 blades, preferably between 2 and 6 blades, for example 4 blades, preferably identical. Each of said blades comprises a convex face and a concave face, and the blades have a curvature chosen to create a pressure difference between the concave face and the convex face, advantageously in order to minimize drag and maximize lift (or torque) thus generating a lift force which allows the fluid, e.g. liquid, to flow efficiently in the tube through the insert by ensuring the rotation of the drive part and minimizing the minimum pressure loss.

[0117] The propeller 32e may include a central cylindrical part serving as a support for the blades. The blades are then preferably distributed regularly around said part. The central part is then fixed and centered on the shaft 3a, so as to be integral with the rotating shaft.

[0118] The diameter dc3 of said central part is defined identically to the diameter da3 of shaft 3a: it may be equal to or greater than the diameter da3, and is preferably between 1 mm and approximately 50% of the internal diameter of the tube, typically between 1 mm and 50 mm, more preferably between 2 mm and 10 mm. The diameter dc3 of said central part, like the diameter of shaft 3a, influences the fluid passage area, and large diameter values ​​allow for an increase in fluid velocity, locally at the rotor. The diameter of said central part can be constant or variable along the Z axis.

[0119] 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.

[0120] As with the first embodiment, the surface of the blades is the surface formed by the junction between two propeller curves with two diameters of revolution: da3 or dc3 and dr3.

[0121] The length of the propeller 32e is substantially equal to the length L32 of the blade 32b (distance, along the Z axis, between the leading edge and the trailing edge of the blade).

[0122] The angle of inclination [33 of the blade (not referenced in [Fig.6]) is constant along Z.

[0123] The blades do indeed have an angle of inclination which is constant along Z but which varies with the radius r according to the equation: [33 = arctan((2pi * r) / step), the step being the revolution step, which is constant.

[0124] Preferably, according to the third embodiment, the number of turns (also called revolution) for the drive part 32 is a fraction of 1, more precisely is equal to 1 / Nb (Nb: number of blades), and is for example equal to 0.25, as illustrated with the 4 blades in [Fig.6], or is for example equal to 0.2 (5 blades), or to 0.33 (3 blades).

[0125] The pitch of revolution is equal to the length L32 of the 32nd propeller divided by the number of revolutions. For example, if the length of the propeller L32 is 10 mm and the propeller has 4 blades (number of revolutions = 0.25), then the pitch of revolution is 40 mm.

[0126] The length L32 of the propeller 32e is equal to the pitch of revolution divided by the number of blades Nb, and is preferably between 5 mm and 30 mm, preferably between 8 mm and 20 mm.

[0127] Figure 7 illustrates a fourth embodiment, in particular an example of an insert according to this fourth embodiment in which the rotating moving element comprises a rotating drive part 33 which includes one or more propellers 33e fixedly to the shaft (not shown) and having from 2 to 6 twisted blades, preferably three twisted blades. Figure 7 shows three schematic 3D views of such an example: a three-quarter view for diagrams a) and b) and a side view for diagram c).

[0128] The propeller 33e may include a central cylindrical part serving as a support for the blades. The blades are then preferably distributed regularly around said part. The central part is then fixed and centered on the shaft 3a, so as to be integral with the rotating shaft.

[0129] The diameter dc3 of said central part is defined identically to the diameter da3 of shaft 3a: it may be equal to or greater than the diameter da3, and is preferably between 1 mm and approximately 50% of the internal diameter of the tube, typically between 1 mm and 50 mm, more preferably between 2 mm and 10 mm. The diameter dc3 of said central part, like the diameter of shaft 3a, influences the fluid passage area, and large diameter values ​​allow for an increase in fluid velocity, locally at the rotor. The diameter of said central piece can be constant or variable along the Z axis, in the same way as detailed below regarding shaft 3a.

[0130] 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.

[0131] The twisted blades each have a first face 33i (extrados) and a second face 33j (intrados) opposite the first face, an inner edge 33g contiguous with the shaft or the central piece mounted on the shaft ("hub" in Anglo-Saxon terminology) and an outer edge 33h opposite the inner edge and away from the shaft ("shroud" in Anglo-Saxon terminology), as well as a leading edge 33k ("leading edge" in Anglo-Saxon terminology) and a trailing edge 331. The distance between the two inner edges 33g and outer edges 33h of a blade, along an axis orthogonal to the Z-axis, constitutes the width R of The blade (twisted strip). In a cylindrical coordinate system, the blade width is defined by its radius r (see [Fig. 8] b) for the conversion from a Cartesian coordinate system (x, y, z) to a cylindrical coordinate system (r, 0, z), where r is the radius or magnitude, 0 is the azimuth, and z is the elevation. The distance between the leading and trailing edges of a blade, along the Z-axis, forms the length L33 of the blade (twisted strip), which is distinct from the displacement length along a blade edge. The length of the helix 33e is approximately equal to the length of a blade L33. Generally, the upper surface of a non-symmetrical airfoil (exhibiting camber) is the face on the same side as the camber, regardless of the lift direction. It is in this area that the depression is located. The intrados of a non-symmetrical lifting profile (exhibiting a camber) is the face opposite the camber, regardless of the direction of lift.

[0132] Each blade 33b is designed as an extrusion of layers, at least two in number, along the radius r in a cylindrical coordinate system (see [Fig. 8]b for the cylindrical coordinate system (r, 0, z)). As shown in [Fig. 7], each blade comprises, for example, five profiles 33m, represented by lines on the blades, between which the layers are defined to form the 3D blade. In other words, the surface of each blade is the junction between the profiles 33m, given that the number of profiles 33m is greater than 2 (3 minimum), and the definition of the profile depends on r.

[0133] The blades of the propeller 33e of the rotating drive part 33 form a circular cross-section assembly having a diameter dr3, as generally defined above: 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 dr3 is constant or can vary in the direction of the shaft axis (Z-axis).

[0134] The number of blades Nb is equal to 3 for the example of the fourth embodiment shown in [Fig.7], without this constituting a limitation to the invention. The number of blades Nb of the 33e propeller is a minimum of two, and can preferably go up to 6.

[0135] Fig. 8 a) is a 2D representation of two consecutive blades of the example drive part shown in Fig. 7, and more specifically illustrates a layer used to form the blades 33b, according to a 2D projection. Such a representation is also called a cascade view, as is common in the field of turbines, and allows certain important geometric parameters of the blade and its interaction with the fluid to be defined. Figure 8 a) shows a projection of the cross-section of two consecutive blades 33bi and 33b2 of a propeller 33e, along (o, Z, 0) of the cylindrical coordinate system (cf. [Fig.8] b) for the cylindrical coordinate system). Some geometric characteristics are thus represented for the blades of the drive part 33 of the insert according to this fourth embodiment.

[0136] The blades preferably have an angular overlap q>, defined as the angular distance (in degrees, expressed in the cylindrical coordinate system (r,0,Z)) between the leading edge 33ki of a first blade 33bi and the trailing edge 3312 of a second blade 33b2 following the first blade 33b, which is advantageously between - (360 / Nb)° and + (360 / Nb)°, Nb being the number of blades of the propeller 33e. For Nb=3, q> is thus between -120° and +120°, for example is equal to approximately 80°. In [Fig.8] a), the blades 33bi and 33b2 are two consecutive blades, and the angular overlap q> between these two blades is the angular distance between the leading edge 33ki of the blade 33bi and the trailing edge 33L of the blade 33b2.

[0137] For each blade, the blade pitch angle

[33] varies along Z and along r in the cylindrical coordinate system (r,0,z). This angle

[33] varies along Z between the leading edge and the trailing edge of the same blade, as also seen in [Fig. 9] a) described below. It is thus possible to define a blade pitch angle [3pi] at the leading edge 33k of a blade 33b, and a blade pitch angle [3po] at the trailing edge 331 of the same blade.

[0138] The flow angle [3f, visible in [Fig. 8] a), is the angle representing the fluid flow in the tube 100 that impacts the insert and primarily the rotating drive part 33, defined between the axial direction Z and the direction of the fluid flow. The angle of incidence i, shown in [Fig. 8] a), is the difference between the flow angle [3f] and the blade inclination angle

[33] , representing the angle formed between the blade and the fluid flow arriving at the blade. The blade pitch angle at the trailing edge [33in] can be greater or less than the blade pitch angle at the leading edge [33ft]. The angle [33in] is, for example, greater than the angle [33ft] in [Fig. 8] a).

[0139] Preferably, the angle of inclination of the blade at the leading edge [33ft] is between 0 and 80°, preferably between 20° and 60°, preferably between 30° and 49°.

[0140] Preferably, the angle of inclination of the blade at the trailing edge [33in] is between 0 and 80°, preferably between 0° and 60°, preferably between 40° and 60°.

[0141] The variation of the blade's inclination angle

[33] is illustrated in [Fig. 9] a), which gives an example of the variation of the inclination angle

[33] as a function of Z, conferring a particular geometric profile (camber line) used to form one of the layers of the blade 33b. The function |33(Z) can be, but is not limited to, a spline, a polynomial curve, or a Bézier curve.

[0142] Figure 9 illustrates an example of 33m profiles between which the layers forming the blades 33b. A profile 33m of a blade 33b is defined at a given distance r, expressed in the cylindrical coordinate system (r,0,z). Fig. 9 a) illustrates such a profile along (33,Z) and Fig. 9 b) illustrates such a profile along (0,Z), in the cylindrical coordinate system (r,0,z).

[0143] The length L33 of a blade 33b (and therefore of the propeller 33e) can be expressed as a function of the angular overlap q>, the variation of the angle of inclination of the blade

[33] as a function of Z (|33(Z)), and the width R of the blade, according to the relations defined by equations (1), (2), (3) and (4) below: (1) 9 (Z) = Oend (Z) - 360 / Nb (2) Oend = SA0(Z), Oend being the final azimuth of a given blade (3) A0(Z) ~ AC(Z) / R, C(Z) being the circumferential distance of a given blade (distance in the azimuthal direction 0) (4) AC(Z) = AZ x tan([33(Z))

[0144] Preferably, the length L33 of the blades is between 5 mm and 100 mm, preferably between 10 mm and 50 mm.

[0145] The thickness of the blades e3 may be constant or vary continuously from the leading edge to the trailing edge of the blade (along the Z-axis). For example, the thickness e3 of the blade may be the same from the leading edge 33k to the trailing edge 331 of the blade, or decrease constantly from the leading edge 33k to the trailing edge 331 of the blade. Preferably, the thickness e3 of the propeller blades 33e is between 0.3 mm and 5 mm, preferably between 1 mm and 3 mm.

[0146] The diameter da3 of the shaft 3a can be constant along the Z-axis, or can be variable along the Z-axis, preferably varying continuously over at least a portion of said shaft, and for example decreasing from the leading edge to the trailing edge of the blade (along the Z-axis). A variation in the diameter da3 of the shaft along the Z-axis makes it possible to influence the fluid flow velocity by varying the axial force exerted by the blades. A variable diameter da3 also has a structural role, notably by allowing greater mechanical resistance at points where the stresses are greatest. For example, a larger diameter da3 of the shaft upstream than downstream (in the direction of the general fluid flow) provides greater mechanical resistance at the drive component, which is the first to come into contact with the fluid. Preferably, the diameter da3 of the shaft is between 1 mm and 50 mm, preferably between 2 mm and 10 mm.

[0147] A variation in the diameter of the shaft (or central part) along the Z-axis and in the width R of the blades (and consequently in the space c between the insert and the inner wall of the tube 100) can modify the axial force exerted between the leading edge of the blade and the trailing edge. The axial force can be identical at the leading edge and at the trailing edge of the blades in the case of a constant shaft diameter da3 and a constant blade width, or alternatively be different if the shaft diameter da3 is larger (and consequently the blade width smaller) at the leading edge than at the trailing edge of the blades.

[0148] The leading edges 33k and trailing edges 331 of the blades may be of identical or different shapes, said shape being able to be chosen from circular, square, oval, triangular, etc. cross-section shapes.

[0149] Advantageously, the clearance “c” between the insert and the inner wall of the tube 100, more precisely between the blades of the propellers of the rotating drive part of the moving element of the insert, can be between 1 mm and 3 mm. This clearance c can be constant or variable along the blade along the Z-axis, preferably smaller on the leading edge 33k side than on the trailing edge 331 side, and more preferably decreasing continuously between these two edges.

[0150] Fig. 10 illustrates a fifth embodiment, in particular an example of an insert comprising a rotating drive piece 30 as described for the first embodiment, or according to the other embodiments described above, said drive piece being connected to a specific rigid helical winding of a rod, preferably metallic, comprising several turns 11, having an initial section with a tight pitch. The said specific rigid helical winding 11 is in fact made up of a first section SI of length L1 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. Unexpectedly, 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 further reduce the threshold for starting rotation of the insert, which further improves the flexibility of use of this type of insert.

[0151] Preferably, the pitch pl of the first section SI is between 5 mm and 20 mm, preferably is between 5 mm and 15 mm, and more preferably between 7 mm and 12 mm.

[0152] Preferably, the pitch p2 of the second section S2 is between 10 mm and 60 mm, preferably is between 20 mm and 40 mm.

[0153] Advantageously, the ratio between the step pl and the step p2 is between 0.1 and 0.7, preferably between 0.20 and 0.45.

[0154] The pitch can be defined in general terms 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 = (ji x D) / tana.

[0155] The angle of inclination of the turns a is defined with respect to the axis of the winding coinciding with the Z axis of the exchanger tube in which the insert is mounted. Reference is made to angle ai for the angle of inclination of the turns of the first section of the winding, and to angle a2 for the angle of inclination of the turns of the second section of the winding, as shown in [Fig. 10].

[0156] 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.

[0157] Advantageously, the diameter D of the winding turns is greater than or equal to 80% of the diameter Dt of the heat exchanger tube 100, 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 efficiently. Preferably, the diameter D of the winding turns D is between 80% and 99% of the diameter Dt of the heat exchanger tube 100, more preferably between 85% and 95% of the diameter Dt. The diameter D of the turns may be equal to or different from the diameter dr3 of the rotating drive component.

[0158] Advantageously, there is a clearance “c” between the insert and the inner wall of the tube 100 such that the helical winding of the moving element does not touch the tube wall, similar to that referred to in [Fig. 4] in relation to the first embodiment, 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 clearance “c” is preferably between 1 mm and 3 mm.

[0159] The winding stem can have a cross-section of various shapes, and preferably has a circular or square cross-section or of another shape, and more preferably has a circular cross-section. In the case of a square cross-section or of another shape, the diameter of the square cross-section is understood to be an equivalent diameter D_eq, defined as follows: D_eq = 4 * Area_of_section / perimeter of section.

[0160] The rod, preferably metallic, forming the rigid helical winding has a diameter e1 at the level of the first section S1, and has a diameter e2 at the level of the second section S2. The diameters el and e2 are preferably between 0.5 mm and 5 mm, more preferably between 1 mm and 3 mm. 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.

[0161] The direction of the rigid helical winding 11 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).

[0162] The winding direction is advantageously the same as the winding direction of the blades around the shaft 3a of the rotating drive part 30.

[0163] Advantageously, the length L1 of the first section SI is between 100 mm and 3000 mm, preferably between 200 mm and 1000 mm.

[0164] The first section SI and the second section S2 are joined together, and can form a single piece or be two separate pieces connected so as to be joined together by means of assembly such as a hook-washer assembly or any other means of assembly.

[0165] The total length of the insert is essentially made up of the total length L3 of the rotating drive part 30 and that of the rigid helical winding 11 which is essentially equal to the sum of the lengths L1 and L2 of the first and second sections.

[0166] 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 tube of the exchanger, from which is subtracted the total length L3 of the rotating drive part 30 and the length L1 of the first section of the winding 11. For example, if the total length of the insert is equal to that of the tube and is 6,000 mm, the length L2 is approximately between 2,500 mm and 5,890 mm, and preferably approximately between 4,800 mm and 5,750 mm.

[0167] It is understood that according to the invention, such a rigid helical winding 11 having an initial section with a tight pitch, as shown in [Fig. 10], can be combined with a rotating drive part 30 according to any one of the embodiments described above and examples of which are shown in Figures 5 to 9.

[0168] Various combinations of the embodiments described below are possible. For example, the rotating drive part may comprise an assembly of an upstream part comprising one or more propellers 33e (see [Fig.7]) having at least 2 twisted blades with a downstream part comprising one or more propellers having at least 2 flat blades inclined with respect to the shaft at an angle

[33] between 50° and 80° (propeller 31e of [Fig.5]) or having four blades each comprising a convex face, a concave face, and a curvature chosen so as to create a pressure difference between the concave face and the convex face in order to minimize drag and maximize lift (propeller 32e see [Fig.6]).

[0169] The present invention also relates to a heat exchanger comprising a plurality of tubes 100 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.

[0170] The heat exchanger according to the invention is advantageously a shell and tube heat exchanger as defined above.

[0171] The heat exchanger can be single-phase or two-phase, that is to say, 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.

[0172] The length of the tubes can be between 500 mm and 15,000 mm, preferably between 1,000 mm and 6,000 mm.

[0173] 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.

[0174] The heat exchanger preferably comprises a plurality of horizontal tubes (the axis of the tubes being horizontal). In this case, the insert is itself horizontal in the operating position. The invention also includes heat exchangers with vertical tubes. In this case, the insert is itself vertical in the operating position.

[0175] The present invention also relates to the use of an insert for a tubular heat exchanger.

[0176] In particular, the present invention relates to the use of such an insert during the preheating of crude oil in an atmospheric crude oil distillation process. In the field of oil refining, it is 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. 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.

[0177] 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 liable to fouling said exchangers, particularly in the field of oil refining or petrochemicals, without departing from the scope of the present invention.

[0178] The present invention thus relates, for example, to the use of a tubular heat exchanger insert as described in this description in a process of hydrotreating or hydroconverting 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 hydroconverting unit.

[0179] 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 distillation column reboilers or nuclear power plant condensers. Examples

[0180] The examples below are based on the implementation of a so-called "cold" experimental model, and are intended to show some of the advantages of the heat exchanger insert and its use according to the invention.

[0181] 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 0.2 and 2 m / s.

[0182] 3 examples of inserts are tested: - example A: example of an insert according to the prior art, as illustrated in [Fig.1], whose moving element consists only of a rigid helical winding of fixed pitch p. - Example B: Example of an insert according to the invention, according to the second embodiment as illustrated in [Fig.5] c), in which the moving element comprises a rotating drive part 31 comprising two helices 31e, spaced 10 mm apart, fixedly mounted on a shaft and each comprising 5 flat blades, said part 31 being connected to the same rigid helical winding as in Example A. - Example C: Example of an insert according to the invention, according to the fourth embodiment as illustrated in Figures 7 to 9, in which the moving element comprises a rotating drive part 33 including a propeller 33e fixedly mounted on a shaft and comprising three twisted blades, said part 33 being connected to the same rigid helical winding as in Example A. The blades according to this example are defined by the following parameters: blade pitch angle at leading edge [33ft : 40; blade pitch angle at trailing edge [33in : 54°; angle of overlap q> : 74°.

[0183] The rigid helical winding of the moving element of the inserts according to 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.

[0184] The rotating drive parts 30 of the insert according to example B, and that according to example C, are made of polymer (plastic).

[0185] 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, and those of the rotating drive part of the inserts according to examples B and C are shown in Table 2 below.

[0186] [Tables 1] Helical winding Parameters Type D (mm) L (m) P (mm) e (mm) Example A (prior art - non-compliant) Fixed pitch 18.7 3.0 35 1.5

[0187] [Tables2] Drive Part Parameters L3 (mm) dr3 (mm) dc3 (mm) e3 (mm) P (°) Number of propellers Number of helices Es3 (mm) Flat profile Example B (Conforming) 5.0 18.0 9.3 1.0 20 5 2 10 Flat Example C (Conforming) 23.5 18.4 5.1 0.4-2.1 (avg.=l, 6) NA 3 1 NA Variable

[0188] In Table 1: - D, L, p and e are respectively the diameter of the turns, the total length, the pitch and the thickness of the stem of the rigid helical metal winding of the insert according to example A and of the insert according to examples B and C;

[0189] In Table 2: - L3 is the length of a blade of the rotating drive part of the rotating moving element according to examples B and C; - dr3 and dc3 are respectively the diameters of the blades and the hub (central part) of a propeller of the rotating drive part of the rotating moving element according to examples B and C;

[0190] - e3 is the thickness of the blades of the rotating drive part of the element mobile rotating according to examples B and C, it is variable for example C along the Z axis with an average value of 1.6 mm; - [33 is the angle of inclination of the blades of the rotating drive part of the rotating moving element according to example B; - Number of blades is the number of blades of the rotating drive part according to examples B and C;

[0191] - Nb helixes is the number of propellers of the rotating drive part according to the examples B and C;

[0192] - Es3 is the distance (between the end of helix 1 and the beginning of helix 2) that separates two helices on the shaft of the rotating drive part of the rotating moving element according to example B.

[0193] 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 rotating the insert according to example A taken as a reference.

[0194] The diagram in [Fig. 11] thus shows the rotation speed VR (RPM or rpm) of the insert according to example A (rigid helical winding of the moving element of the insert "A") and according to examples B and C according to the invention, as a function of the normalized liquid speed VF: VF / VFref, VFref being the minimum liquid speed for starting rotation of the insert according to example A.

[0195] According to the diagram in [Fig. 11], the relative rotation speed of the insert according to Example A is 1.0, while that of an insert according to Example B or Example C is less than 1.0, in particular that of Example C is less than 0.8, and in absolute terms less than 0.6 m / s. The results indicate that an insert according to the invention, as exemplified in Example B and Example C, reduces the insert rotation threshold by 11% (-11%) and 26% respectively, thus enabling better performance in reducing fouling at low fluid velocities, thanks to the rotary mechanical effect.

Claims

Demands

1. Insert for heat exchanger tube, said insert comprising a rotating movable element (300) having a rotating drive piece (30, 31, 32, 33) connected to a rigid helical winding of a rod comprising several turns (10, 11), said rotating movable element (300) having: a first end (3c) on the side of the rotating drive piece, integral with a mechanical link (22) of a fastening system (200) of said rotating movable element (300) to said tube (100), said mechanical link allowing free rotation of said rotating movable element (300) about itself about the axis (Z) of said tube (100) under the action of a fluid passing through said tube (100), a second free end on the side of the rigid helical winding (10, H), and said rotating drive piece (300) having a shaft (3a) coaxial said winding and equipped with at least two blades (30b, 31b, 32b, 33b, 34b) attached to said shaft.

2. Insert according to claim 1, wherein the rod of the rigid helical winding is metallic.

3. Insert according to claim 1 or 2, wherein said rotating drive part (30, 31, 32, 33) comprises from 2 to 6 blades, preferably from 3 to 5 blades.

4. Insert according to any one of claims 1 to 3, wherein said rotating drive part (30) is in the form of a screw with a pitch p3 between 10 mm and 50 mm, has 4 blades, and has a length L3 between 10 mm and 500 mm.

5. Insert according to any one of claims 1 to 3, wherein said rotating drive part (31) comprises one or more propellers (31e) fixed to the shaft and each comprising at least two blades, said blades being flat and inclined with respect to the Z axis at an angle [33] between 50° and 80°.

6. Insert according to any one of claims 1 to 3, wherein said rotating drive part (32) comprises one or more propellers (32e) fixed to the shaft and each comprising 2 to 6 blades, preferably 4 blades, said blades each comprising a convex face and a concave face.

7. An insert according to any one of claims 1 to 3, wherein said rotating drive part (33) comprises one or more propellers (33e) fixed to the shaft and each comprising 2 to 6 twisted blades, preferably three twisted blades, the blades having angular overlap q> between -(360 / Nb)° and +(360 / Nb)° defined between a leading edge (33k) of a first blade and a trailing edge (331) of a second consecutive blade on the shaft, Nb being the number of blades.

8. Insert according to any one of the preceding claims, wherein said rotating drive part comprises an assembly of an upstream portion comprising one or more propellers (33e) having at least 2 twisted blades with a downstream portion comprising one or more propellers having at least 2 flat blades inclined with respect to the shaft at an angle a3 between 50° and 80° or having four blades each comprising a convex face and a concave face.

9. An insert according to any one of claims 5 to 8, wherein the propeller comprises a central cylindrical piece serving as a support for the blades, said central piece being fixed and centered on the shaft so as to be integral with the shaft.

10. Insert according to any one of the preceding claims, wherein said winding is constituted by a single section of turns with a fixed pitch p.

11. An insert according to any one of claims 1 to 9, wherein said winding consists of a first section (SI) of length L1 originating at the connection with said rotating drive piece (30) and a second section (S2) of length L2 extending from 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), the pitch pl being between 5 mm and 20 mm, the pitch p2 being between 10 mm and 60 mm, and the length L1 being preferably between 100 mm and 3000 mm, preferably between 200 mm and 1000 mm.

12. Insert according to any one of the preceding claims, of a total length between 50% and 100% of the total length LT of the heat exchanger tube.

13. An insert according to any one of the preceding claims, wherein the diameter of the blades Dr3 of said drive part in rotation (30, 31, 32, 33) and / or 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%.

14. Heat exchanger comprising a plurality of tubes (100) 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.

15. Use of a tubular heat exchanger insert according to any one of claims 1 to 13, 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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