SYSTEM FOR TRANSPORTING A FLUID

Abstract

A system for transporting a fluid, in particular a fluid containing hydrocarbons, has a first pipe (2), which is made of an electrically conductive material and has an internal diameter (D1); a second pipe (3), which is made of an electrically conductive material, has an external diameter (D2) smaller than the internal diameter (D1), and is placed inside the first pipe (2) at a distance from the first pipe (2) to form an annular space (4) between the first and second pipes (2, 3); an electrically conductive layer (5) placed in the annular space (4) at a distance from the first pipe (2); an electrically insulating layer (6) placed between the second pipe (3) and the electrically conductive layer (5); and an electrical power supply (7) to apply an electrical potential difference between the second pipe (3) and the electrically conductive layer (5).

Description

SYSTEM FOR TRANSPORTING A FLUID CROSS-REFERENCE WITH RELATED APPLICATIONS This patent application claims priority over Italian patent application No. 102020000024460 filed on October 16, 2020, the description of which is incorporated herein by reference in its entirety. TECHNICAL CHANGE The present invention relates to a system for transporting a fluid, in particular a fluid containing hydrocarbons. More specifically, the present invention relates to a system for transporting a fluid of the tube-in-tube type, used to transport hydrocarbons in a body of water, therefore, without limiting the wide range of possible uses of the present invention. PRIOR ART Generally, operations for the extraction and production of hydrocarbons from a reservoir located in the bed of a body of water require that the fluid extracted from the underwater reservoir be transported from the reservoir along transport systems comprising pipes laid in the bed of the body of water and together with additional pipes known as riser pipes, which rise to the surface to a 52 / 1828 / 23 i cztrnn / cznz / e / YiAi surface infrastructure, such as, for example, a fixed platform or a floating plant. The fluid extracted from the reservoir is typically a mixture of hydrocarbons and organic compounds of carbon and hydrogen, which often also contains sulfur, nitrogen, oxygen, water, and other unwanted compounds. This mixture may be in a liquid or gaseous state, or it may contain both phases. The flow of fluid within the pipes must be ensured by keeping the fluid within an appropriate thermodynamic range of pressure and temperature, outside of which some components tend to precipitate as solid deposits of hydrates and / or paraffins that could obstruct the pipes. In particular, conditions that lead to the formation of hydrates and / or paraffins should be avoided, whether in the case of continuous or partial nominal production or during the start-up or stop-up of production, due to the loss of heat from the fluid to the environment. Conventionally, these disadvantages can be mitigated by thermal insulation of the pipeline and / or the injection of chemical additives into the hydrocarbons. Additional alternatives traditionally used to solve these disadvantages include the use of tube-in-tube fluid transport systems, i.e., comprising two coaxial pipes thermally insulated from each other by means of an annular space between the two pipes in order to reduce heat losses. In recent decades, technological development has made it possible to exploit marginal underwater reservoirs—reservoirs that would not be economically viable with conventional technologies due to their particular conditions. For example, these marginal reservoirs are located far from existing infrastructure (on the order of tens of kilometers), have a great depth in the water body (more than 2,000 m), low reservoir temperature, and very low ambient temperature. For these marginal reservoirs, specific solutions must be implemented to maintain the fluid within the appropriate thermodynamic range, both during normal production and during production shutdowns, when the fluid tends to cool naturally. As a result, a new approach has been adopted in recent decades, which involves actively heating the transport pipelines to ensure that the fluid is kept at the desired temperature under all operating or shutdown conditions. The term active heating refers to systems that supply energy to the fluid, thus differentiating them from passive systems that simply store energy within the pipes through thermal insulation. Active heating systems can use, for example, hot fluids circulating in heating tubes arranged around the transport pipes or electrical heating of the transport pipes. Currently, the most widely used system is the electrical heating of fluid transport pipes, which is based on heating due to ohmic losses in direct or induced currents. As is known, electrical heating of transport pipes can be of different types: direct electric heating, where an electric current flows through the transport pipes, heating the metal of the transport pipes by means of the Joule effect; - Electrical tracing of the tube-in-tube type, where several electrical wires are laid on the outer surface of an inner pipe arranged coaxially within an outer pipe. The thermal power loss of the electrical wires due to the Joule effect is transferred to the inner pipe with which they are in contact, thus heating the fluid. This system has excellent thermal insulation and optimal efficiency, but it has a complex mechanical design and high installation costs. As is known, the direct electrical heating of a system for transporting a fluid can in turn be: - with an open loop, where the current passes through a circuit comprising a transport pipe and a cable laid over the transport pipe. This solution is mechanically simple, but has significant current losses because the transport pipe through which the current passes is in galvanic contact with the body of water; This is a tube-in-tube type system where the inner pipe, used to transport the fluid, and the outer pipe are integral parts of the electrical circuit. This system is characterized by excellent thermal performance due to significant thermal insulation in the annular space between the inner and outer pipes. Although this system has no current losses in the water body, its efficiency is limited because the current passing through the outer pipe does not contribute to heating the fluid. Furthermore, the fact that the electrical circuit essentially comprises two coaxial pipes requires special attention to the presence of contaminants in the annular space, which can generate electrical discharges capable of damaging the thermal insulation and compromising the system's efficiency. Examples of tube-in-tube conveying systems with direct electric heating are described in US 6,142,707, WO 2015 / 148162 and FR 3,083,841. OBJECT OF THE INVENTION An objective of the present invention is to implement a system for transporting a fluid that mitigates the disadvantages of the prior art. According to the present invention, a system is provided for transporting a fluid, in particular a fluid containing hydrocarbons; the system comprises: a first pipe, which is made of an electrically conductive material and has an internal diameter; a second pipe, which is made of an electrically conductive material, has a second outer diameter smaller than the inner diameter of the first pipe, and is placed inside the first pipe at a distance from the first pipe to form an annular space between the first and second pipe; an electrically conductive layer, which is placed in the annular space at a distance from the first pipe and is in electrical contact with the first pipe; - an electrically insulating layer placed between the second pipe and the electrically conductive layer; and an electrical power supply to apply an electrical potential difference between the second pipe and the electrically conductive layer. Thanks to the present invention, the electrically conductive layer and the second pipe define two parts of the electrical circuit, limiting heat loss in the water body and consequently increasing the system's efficiency. Furthermore, the voltage in the annular space is limited, thus ensuring greater tolerance to any contaminants present in the annular space. In general, the first pipe is also laid parallel to the electrically conductive layer, and both are grounded. This limits the electrical potential difference between the first pipe and the conductive layer. Furthermore, since the electrically conductive layer has a lower electrical impedance than the electrical impedance of the first pipe, most of the electric current will pass through the electrically conductive layer. In particular, the system comprises a layer 52 / 1828 / 23 thermally insulating placed in the annular space around the second pipe. In this way, the heat generated by the Joule effect in the second pipe is kept as much as possible in the second pipe where the fluid flows, making the system particularly efficient in terms of energy balance. In particular, the electrical insulation layer covers the second pipe. This solution is particularly practical and easy to implement thanks to common pipe coating machines. In particular, the electrically conductive layer covers the electrically insulating layer. In particular, the thermally insulating layer covers the electrically conductive layer. In this way, the heat generated by the Joule effect in the electrically conductive layer is also largely directed to the second pipe, which directly carries the fluid. Consequently, this technical solution is particularly efficient in terms of energy balance. According to an alternative embodiment of the present invention, the thermally insulating layer covers the electrically insulating layer. 52 / 1828 / 23 In practice, this involves carrying out two successive coatings. In accordance with the alternative modality, the electrically conductive layer covers the thermally insulating layer and is oriented directly towards the first pipe. Specifically, this power supply comprises a voltage generator. Depending on the length of the first and second pipes, the electrical potential difference can be applied to various points along the longitudinal axis of the first and second pipes and, in particular, along sections of the first and second pipes of discrete length. From a construction standpoint, the electrically conductive layer comprises a plurality of electrically conductive sheets, preferably aluminum, placed longitudinally side by side in the annular space between the first and second pipes. The electrically conductive sheets wrapped around the pipe are joined together by welding or brazing, partial overlapping, or first electrically conductive connecting elements. In this way, an electrically conductive layer is created. With particular reference to the modality of the first i cztrnn / cznz / e / YiAi and second pipes, the system comprises a plurality of first pipes joined together at their opposite ends by means of first weld seams to form the first pipe; a plurality of second pipes joined together at their opposite ends by means of second weld seams; and at least one second connecting element, which is placed at each second weld seam, is made of an electrically conductive material, and is configured to electrically connect two electrically conductive sheets arranged on opposite sides with respect to the second weld seam. This ensures the electrical continuity of the first and second pipes and the electrically conductive sheet. In particular, each connecting element is in contact with two electrically conductive sheets arranged on opposite sides with respect to the second weld seam. In practice, each connecting element forms a connecting bridge between two spaced electrically conductive sheets. Alternatively, the system comprises at least two connecting elements, each of which is in contact with a respective electrically conductive sheet and with the first pipe. 52 / 1828 / 23 i cztrnn / cznz / e / YiAi In this way, the first pipe becomes an integral part of the bridge. In particular, the system comprises a sleeve wrapped around the second weld seam and the free ends of two adjacent tubes. Thus, the sleeve, usually made of polymeric material, restores the continuity of the electrically insulating layer over two adjacent tubes. Advantageously, the system comprises a plurality of annular spacers arranged between the first and second pipes to space the first and second pipes and maintain the annular space substantially constant; in particular, each annular spacer is arranged between the electrically conductive layer and the first pipe. In this way, it is possible to center the first pipe with respect to the second pipe in a simple and precise manner. In particular, the system comprises a plurality of annular shear stops placed between the first and second pipes to limit relative longitudinal displacements between the first and second pipes, i.e., relative displacements along a direction substantially parallel to the longitudinal axis of the first and second pipes. i cztrnn / cznz / e / YiAi In other words, the annular shear stops have the function of absorbing part of the shear forces acting on the first and second pipes. In particular, each annular cut stop breaks the continuity of the electrically conductive layer; the system comprises a plurality of third connecting elements connected to the electrically conductive layer and the first pipe on opposite sides of each annular cut stop. This restores the electrical continuity of the electrically conductive layer. According to an alternative variant, each annular cut stop has openings to ensure the continuity of the annular space along the longitudinal axis of the first and second pipe. This makes it possible to lay cables or optical fibers in the annular space for signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will be clarified from the following description of its exemplary and non-limiting embodiments, with reference to the accompanying figures where: Figure 1 is a longitudinal sectional view, with parts removed for clarity, of a system for transporting fluids made in accordance with a first embodiment of the present invention; - Figure 2 is a cross-sectional view, with parts removed for clarity, of the system in Figure 1; - Figures 3 to 6 are longitudinal section views, enlarged to scale and with parts removed for clarity, of a construction detail of the system in Figure 1 and related variants; Figure 7 is a longitudinal sectional view, with parts removed for clarity, of a detail of the system in Figure 1; Figure 8 is a perspective view, with parts removed for clarity, of a variant of the detail in Figure 7; - Figure 9 is a cross-sectional view, with parts removed for clarity, in accordance with the variant of Figure 8; - Figure 10 is a cross-sectional view, with parts removed for clarity, of an additional variant of the detail in Figure 7; - Figure 11 is a longitudinal section view, with parts removed for clarity, of the additional variant of Figure 10; - Figures 12, 13 and 14 are longitudinal section views, with parts removed for clarity, of respective variants of an additional construction detail of the system in Figure 1; Figures 15 and 16 are longitudinal section views, with parts removed for clarity and reduced scale, of an additional variant of the detail in Figure 13; - Figure 17 is a longitudinal section view, with parts removed for clarity, of a detail of the system in Figure 1; Figure 18 is a longitudinal sectional view, with parts removed for clarity, of a fluid transport system made in accordance with a second embodiment of the present invention; and Figure 19 is a cross-sectional view, with parts removed for clarity, of the system of Figure 18. PREFERRED MODALITY OF THE INVENTION With reference to Figures 1 and 2, (1) denotes a complete system for transporting a particular fluid, a fluid containing hydrocarbons. System (1) is adapted to operate in a body of water at a considerable depth and low temperature. The system (1) comprises a pipe (2), which extends along an axis (A1), is made of an electrically conductive material, and has an internal diameter (DI); a pipe (3), which is substantially coaxial with the pipe (2), is made of an electrically conductive material, has an external diameter (D2) smaller than the internal diameter (DI), and is positioned inside the pipe (2) at a distance from the pipe (2) to form an annular space (4) between the pipes (2) and (3); an electrically conductive layer (5) positioned in the annular space (4) at a distance from the pipe (2); an electrically insulating layer (6) positioned between the pipe (3) and the electrically conductive layer (5); and a potential electrical power supply (7) connected to the pipe (3), the electrically conductive layer (5), and the pipe (2). In fact, the electrically conductive layer (5) and the pipe (2) are grounded and have the same potential. In practice, the electrically insulating layer (6) covers the outer face of the pipe (3) while the electrically conductive layer (5) covers the outer face of the electrically insulating layer (6). The system (1) comprises a thermally insulating layer (8) placed in the annular space (4) around the second pipe (3). In particular, the thermally insulating layer (8) covers the electrically conductive layer (5). As shown in Figures 1 and 2, part of the annular space (4) is kept free and the pipe (2) is provided with an external protective layer (9). With reference to Figure 3, the electrically conductive layer (5) is made of electrically conductive sheets (10), usually aluminum, with a thickness ranging from a few tens of mm to a few mm. The sheets (10) of discrete length are wrapped around the pipe (3) and are arranged adjacent to each other, but must be joined in the longitudinal direction to ensure electrical continuity. In the case shown in figure 3, the sheets (10) are joined by welding or brazing. In the variant of figure 4, electrical continuity between adjacent sheets (10) is achieved by means of connecting elements (11), whose opposite ends are in contact with two adjacent sheets (10). In the variant of figure 5, the electrical continuity of the electrically conductive layer (5) is ensured by the partial overlap of the ends of the adjacent sheets (10). In the variant shown in Figure 6, electrical continuity is ensured by the connecting elements (12), which in this case are additional sheets of reduced length overlapping the ends of the adjacent sheets (10). 52 / 1828 / 23 With reference to figures 1 and 2, the annular spacers (13) are arranged between the pipes (2) and (3) their function is to keep the pipes (2) and (3) substantially coaxial; and the annular shear stops (14), whose function is to limit the relative longitudinal displacements between the pipes (2) and (3), i.e., the relative displacements substantially parallel to the axis (Al). In the case shown, each annular spacer (13) is arranged to support the electrically conductive layer (5) and is arranged to be in contact with the inner face of the pipe (2). Each annular cut stop (14) adheres to the pipe (2) and the pipe (3) and breaks the continuity of the electrically conductive layer (5). In the detail shown in Figure 7, the annular cutting stops (14) are shown arranged directly in contact with both pipes (2) and (3), specifically attached to pipes (2) and (3). In this case, the continuity of the electrically conductive layer (5) is broken, which is connected to pipe (2) by means of connecting elements (15) made of electrically conductive material. An alternative solution to ensure the electrical continuity of the electrically conductive layer i cztrnn / cznz / e / YiAi (5) consists of making windows (16) in the electrically conductive layer (5) and in the electrically insulating layer (6), as shown in Figure 8, and making an annular cut stop (17) by molding which holds the outer surface of the pipe (3) in the windows (16) as shown in Figure 9. An additional alternative solution shown in Figures 10 and 11 allows for an annular cut stop (18) with a slotted inner face which holds the pipe (3) in the window (19) formed along the electrically conductive layer (5) while the slotted parts ensure the continuity of the electrically conductive layer (5). With reference to Figure 12, pipes (2) and (3) are formed by respective tubes (20) and (21) of unit length, generally 12 m, which are joined together at their opposite ends by respective weld seams (22) and (23). Along the length of pipe (3), the electrically insulating layer (6), the electrically conductive layer (5), and the thermally insulating layer (8) are interrupted at the opposite ends of each tube (21). After joining the tubes (21), the continuity of the electrically insulating layer (6) is restored by means of a sleeve (24) made of polymeric material around the free ends of the tubes (21). Subsequently, electrical continuity is achieved between the electrically conductive layers (5) of two adjacent tubes (21) by means of connecting elements (25) attached to the adjacent electrically conductive layers (5). Finally, the two adjacent tubes (20) are welded together. In the variant shown in Figure 13, the connecting elements 25 connect an electrically conductive layer (5) to the corresponding tube (20). In this way, the pipe (2) ensures electrical continuity throughout the system (1). In the variant of figure 14, the system (1) comprises a connecting element (26), which is a strip of conductive sheet material applied over the weld seam (23) which electrically connects the layers of conductive material (5) disposed over the weld seam (23). The variant in Figures 15 and 16 shows a solution similar to that in the variant in Figure 13, in which the connecting elements (25) are sufficiently long and flexible to allow the axial sliding of at least one of the two tubes (20) to allow the restoration of the continuity of the electrically conductive layer (5) obtained by means of the weld seam (22) in a simple and quick manner. With reference to figure 17, the system (1) comprises a bulkhead (27) of electrically conductive material, which is arranged at the ends of the pipes (2) and (3) and is configured to ensure the closure of the electrical circuit by bringing the pipes (2) and (3) into contact. During use, with reference to figure 1, the pipe (2) and the electrically conductive layer (5) are grounded, while, on one side, a potential difference is applied to the pipe (3), and on the other side to the electrically conductive layer (5) and the pipe (2), in the central part of the system (1). The thermal energy generated by the Joule effect along the pipe (3) is transferred to the fluid. Some of the heat generated by the Joule effect along the electrically conductive layer (5) is also confined to the fluid by the thermally insulating layer (8) arranged around the electrically conductive layer (5). Although the electrically conductive layer (5) and the pipe (2) are connected in parallel, the lower resistance of the electrically conductive layer (5) results in most of the current passing through the electrically conductive layer (5), significantly limiting thermal energy losses to the environment outside the system (1). This increases the efficiency of the system (1) because the heat generation by the Joule effect is concentrated in the pipe (3) through which the fluid flows. In some variations of the described modality, when the continuity of the electrically conductive layer (5) is broken, a branch is made through the pipe (2) which, as already mentioned, is subject to the same potential as the electrically conductive layer (5). In the embodiment of Figures 18 and 19, the thermally insulating layer (8) is applied over the electrically insulating layer (6), and the electrically conductive layer (5) is applied over the thermally insulating layer (8). The system (1) comprises annular spacers (28) arranged in contact with the electrically conductive layer (5), and annular cutting stops (29), which adhere to the pipe (2) and the pipe (3) and break the continuity of the electrically conductive layer (5). This embodiment of the invention has a lower efficiency because the thermally insulating layer (8) does not cover the electrically conductive layer (5). Finally, it is evident that variations can be made to the present invention with respect to the described modalities, however, without departing from the scope of protection of the attached claims.

Claims

1. A system for transporting a fluid, in particular a fluid containing hydrocarbons, the system (1) comprising: - a first pipe (2), which is made of an electrically conductive material and has an internal diameter (DI); - a second pipe (3), which is made of an electrically conductive material, has a second external diameter (D2) smaller than the internal diameter (DI) of the first pipe (2), and is placed inside the first pipe (2) at a distance from the first pipe (2) to form an annular space (4) between the first and second pipes (2, 3); - an electrically conductive layer (5), which is placed in the annular space (4) at a distance from the first pipe (2) and is in electrical contact with the first pipe (2); an electrically insulating layer (6) placed between the second pipe (3) and the electrically conductive layer (5);and an electrical power supply (7) to apply an electrical potential difference between the second pipe (3) and the electrically conductive layer (5). 52 / 1828 / 23 i cztrnn / cznz / e / YiAi; 2. The system according to claim 1, wherein it comprises a thermally insulating layer (8) placed in the annular space (4) around the second pipe (3).

3. The system according to claim 1 or 2, wherein the electrically insulating layer (6) covers the second pipe (3).

4. The system according to claim 3, wherein the electrically conductive layer (5) covers the electrically insulating layer (6).

5. The system according to any of claims 2 to 4, wherein the thermally insulating layer (8) covers the electrically conductive layer (5).

6. The system according to claim 2 or 3, wherein the thermally insulating layer (8) covers the electrically insulating layer (6).

7. The system according to claim 6, wherein the electrically conductive layer (5) covers the thermally insulating layer (8).

8. The system according to any of the preceding claims, wherein the power supply (7) comprises a voltage generator.

9. The system according to any of the preceding claims, wherein the electrically conductive layer (5) comprises a plurality of electrically conductive sheets (10) positioned side by side longitudinally in the annular space (4) between the first and second pipes (2, 3); the electrically conductive sheets (10) are coupled together by welding or brazing or partial overlap or first electrically conductive connecting elements (11, 12).

10. The system according to any of the preceding claims, wherein it comprises a plurality of first tubes (20) joined together at their opposite ends by means of first weld seams (22) to form the first pipe (2); a plurality of second tubes (21) joined together at their opposite ends by means of second weld seams (23) to form the second pipe (3); and at least one second connecting element (25, 26), which is placed on each second weld seam (23), is made of an electrically conductive material, and is configured to electrically connect two electrically conductive sheets (10) arranged on opposite sides with respect to the second weld seam (23).

11. The system according to claim 10, wherein each connecting element (25, 26) is in contact with two electrically conductive sheets (10) arranged on opposite sides with respect to the second weld seam (23).

12. The system according to claim 10, wherein it comprises at least two connecting elements (25), each of which is in contact with an electrically conductive sheet (10) and with the first pipe (2).

13. The system according to any of claims 10 to 12, wherein it comprises a sleeve (24) wrapped around the second weld seam (23) and the free ends of two adjacent tubes (21).

14. The system according to any of the preceding claims, wherein it comprises a plurality of annular spacers (13, 28) disposed between the first and second pipes (2, 3) to space the first and second pipes (2, 3), in particular, each annular spacer (13, 28) is placed between the electrically conductive layer (5) and the first pipe (2).

15. The system according to any of the preceding claims, wherein it comprises a plurality of annular cutting stops (14, 17, 18, 29) placed between the first and second pipe (2, 3) to limit the relative longitudinal displacements between the first and second pipe (2, 3).

16. The system according to claim 15, wherein each annular cutting stop (14, 29) breaks the continuity of the electrically conductive layer (5), the system (1) comprises a plurality of third connecting elements (15) connected to the electrically conductive layer (5) and to the first pipe (2) on opposite sides of each annular cutting stop (14, 29).

17. The system according to claim 15, wherein each annular cutting stop (18) has openings to ensure the continuity of the annular space (4) along the longitudinal axis of the first and second pipes (2, 3).

18. The system according to claim 15, wherein each annular cutting stop (17) has a plurality of portions arranged to support the electrically conductive layer (5).

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