Pipeline Electric Heating System

Abstract

A pipeline electric heating system for a transportation pipeline (12) having a pipe (14) and surrounding insulation (7), comprising a power transformer (18), a supply terminal (22), a terminal terminal (24), one or more service terminals (26) disposed between the supply terminal and the terminal terminal, a parameter control / monitoring system, and a heating cable assembly (28) connected to three phases (8a, 8b, 8c) of a three-phase power source and having three resistive heating cables (8) extending along the pipe from the supply terminal (22) to the terminal terminal (24) and through the one or more service terminals (26). Each of the resistive cables is individually mounted in a corresponding cable guide (9a, 9b, 9c), and the cable guides and their associated resistive cables mounted therein are attached beneath the insulation (7) and to the exterior surface of the pipe. Each of the resistive cables comprises an inner conductor and a shield surrounding the inner conductor, the shields in each of the resistive cables being connected to ground and interconnected together at the end terminals and / or the supply terminals, and the shields or the inner conductors being transposed at at least one service terminal.

Description

[Technical field]

[0001] The present invention relates to electric heating systems used in transmission pipelines in the oil and gas industry. [Background technology]

[0002] Nowadays, heating of transmission pipelines over long distances (more than 10 kilometers) requires the construction of an appropriate power supply system, which requires the placement of power plants approximately every 1-10 kilometers depending on the electric heating system.

[0003] The associated power supply network makes the electric heating system more complex and less cost effective, and in places where it is not possible to build an associated network, such as on the seabed, there is no opportunity to heat the pipes.

[0004] At distances of 25 km, skin effect electric heating systems are the most cost-effective heating system. The heating device in these systems is a ferromagnetic pipeline called a heating pipe, which contains an insulated conductor inside. At one end, the heating pipe and the insulated conductor are interconnected, and at the other end, they are connected via an alternating current (AC) power supply. An applied AC voltage generates a current in the conductor, which returns along the inner surface of the pipe. The magnetic field induced by the current in the insulated conductor and the ferromagnetic pipeline causes a countercurrent to crowd the inner surface of the pipe. This current flows in the pipe for a distance called the skin depth (Non-Patent Document 1).

[0005] The above phenomenon removes any measurable voltage on the outer surface of the pipe, thus grounding the pipeline. Current collects on the inner surface of the heated pipe, and the generated heat spreads throughout the pipe, raising the temperature of the pipe surface and its contents to the required level.

[0006] A heating cable based on the skin effect, comprising a coaxially arranged central conductor, an inner insulating layer, and a ferromagnetic outer conductor, is disclosed in US Pat. No. 5,399,366. The inner insulating layer is made of a polymer, while the outer conductor is made of a crimped steel pipe, with a wall thickness less than three skin depths thick at the operating supply voltage frequency.

[0007] An electric heating system having a heating cable with a three-phase power supply system is disclosed in US Pat. No. 5,399,433. The heating cable comprises current-carrying wires insulated with a heat-resistant coating. At one end these current-carrying wires are free to be connected to a power supply source, while at the other end they are interconnected into a complete electric circuit.

[0008] Disadvantages of known systems and resistance cables include insufficient distance for electrical heating with a single power supply, which is limited to 25 km, low heat generation, and poor utilisation of the generated heat for heating the product in the transport pipeline. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Russian Patent No. 2589553 [Patent Document 2] Russian Utility Model Application Publication No. 127273 [Non-patent literature]

[0010] [Non-Patent Document 1] ML Strupinskiy, Analysis of the self-adjusted cable properties at low temperatures / Analytical scientific technical journal / / ML Strupinskiy, NN Khrenkov, 2011 : Industrial electric heating: Hager: 2011. - P. 6-11 Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to provide a pipeline electric heat system capable of generating a certain amount of heat over distances of more than 25 km, for example up to a maximum distance of 200 km, using a single power supply without an associated network. [Means for solving the problem]

[0012] Advantages of the present invention include increased efficiency of heat production and utilization of a specific amount of heat to heat the product in a transport pipe over a significant distance (e.g., up to 200 km), improved constructability of the system, ease of maintenance, and simplification of the electric heating system.

[0013] The object of the present invention is achieved by providing a pipeline electric heating system according to claim 1. The dependent claims set out various advantageous features for respective embodiments of the invention.

[0014] Disclosed herein is a pipeline electric heating system for a transportation pipeline having a pipe and insulation therearound, the system comprising a power transformer, a supply terminal, an end terminal, one or more service terminals disposed between the supply terminal and the end terminal, a parameter control / monitoring system, and a heating cable assembly. The heating cable assembly includes three resistive heating cables connected to three phases of a three-phase power source and extending along the pipe from the supply terminal to the end terminal, passing through one or more service terminals. Each resistive cable is individually mounted in a corresponding cable guide. The cable guide and associated resistive cable mounted therein are mounted beneath the insulation and on the outer surface of the pipe. Each resistive cable includes an inner conductor and a shield surrounding the inner conductor, the shields of each resistive cable being connected to ground and interconnected together at the end terminal and / or at the supply terminal, and the shield or the inner conductor being transposed at at least one of the service terminals.

[0015] In an advantageous embodiment, adjacent cable guides are spaced a non-zero distance apart.

[0016] In an advantageous embodiment, the system comprises at least two service terminals.

[0017] In an advantageous embodiment, each phase comprises a solid medium voltage resistive cable provided with a shield and insulation.

[0018] In an advantageous embodiment, the cable guide for each resistive cable has a substantially rectangular, trapezoidal or round cross-section.

[0019] In an advantageous embodiment, each cable guide is sealed along a longitudinal edge to the outer surface of the pipe.

[0020] In an advantageous embodiment, the non-zero distance (L) between adjacent cable guides is substantially constant.

[0021] In an advantageous embodiment, the cable guide and associated resistive cable mounted therein is attached to the top of the pipe.

[0022] In an advantageous embodiment, the cable guide is made from a polymer or aluminum.

[0023] In a preferred embodiment, the resistive cables are star-wired together at the end terminals.

[0024] In an advantageous embodiment, the wires of the resistive cable have a flattened cross-sectional shape.

[0025] In an advantageous embodiment, the parameter control / monitoring system includes a temperature sensor, a current sensor, and a load voltage sensor.

[0026] In an advantageous embodiment, the parameter control / monitoring system is configured for remote measurement and control of the heating system, including measuring ambient temperature, detecting the health of the resistive cables, and controlling the load current and load voltage in each resistive cable.

[0027] Further objects and advantageous features of the present invention will become apparent from the following detailed description of the embodiments of the present invention and the accompanying drawings. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 illustrates a pipeline installation equipped with an electric heating system according to an embodiment of the present invention. [Diagram 2] FIG. 2 illustrates a portion of a pipeline equipped with an electric heating system according to an embodiment of the invention. [Diagram 3] FIG. 3 illustrates a resistive cable for an electric heating system according to an embodiment of the present invention. [Figure 4a] FIG. 4a illustrates a cross section of a pipeline provided with an electric heating system according to an embodiment of the invention. [Figure 4b] FIG. 4b is a detailed view of a portion of FIG. 4a. [Diagram 5] FIG. 5 is a detailed view similar to FIG. 4b but of another embodiment. [Figure 6] FIG. 6 is a schematic diagram of an electric heating system according to an embodiment of the invention illustrating a shield transition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Pipeline electric heat systems according to embodiments of the present invention may be implemented to heat pipelines located on above-ground support piers, underground pipelines, and submerged underwater pipelines.

[0030] A pipeline electric heating system according to an embodiment of the present invention advantageously provides a specific combination, composition and arrangement of its components for heating a pipeline over distances of approximately 150-200 km, which is meaningful for today's oil and gas product transportation facilities.

[0031] 1 and 2, a pipeline installation 10 including an oil or gas transportation pipe and a pipeline electric heat system according to an embodiment of the present invention may advantageously include the following elements important for low maintenance functionality: a power transformer 18, a supply terminal 22, a terminal terminal 24, and at least one intermediate service terminal 26. The pipeline electric heat system 20 according to an embodiment of the present invention includes a heating cable assembly 28 including a plurality of heating resistive cables 8, a connecting terminal sleeve 30, a line parameter control / monitoring system (not shown) including at least one temperature sensor 20 attached to the transportation pipe 12, as well as a fixing element 32 for installing the resistive cables 8 of the heating cable assembly 28 on the transportation pipe 12.

[0032] Power for the system according to the embodiment of the invention is provided by a special power transformer 18, which is provided with a changeover key with a wide adjustment range for the secondary voltage. Depending on the electric heating power demand, it may be necessary to provide the transformer with air barrier insulation, cast insulation or oil insulation.

[0033] The heating cable assembly 28 may advantageously comprise three resistive cables 8a, 8b, 8c which may advantageously carry three corresponding phases of a three-phase power supply system. Each resistive cable 8a, 8b, 8c is preferably mounted inside a corresponding cable guide 9a, 9b, 9c which is attached to the surface of the structural pipe 14 (usually made of steel or other metal) of the transport pipeline. Each of the three resistive cables 8 is thus arranged in a separate cable guide 9 which is attached directly to the outside of the structural metal pipe 14 and is surrounded by the thermal insulation 7 of the transport pipeline 12. For pre-insulated pipelines, the resistive cables 8 may be installed inside the cable guide 9 at the site of the transport pipeline manufacture. The cable guide 9 contributes to the effectiveness of the heat transfer of the heat generated by the resistive cables to the structural metal pipe and the oil or gas 16 flowing therein.

[0034] The phases of a three-phase power supply system, each installed separately and surrounded by insulation 7, allow cables 8 with a large cross-section to be installed in a very small area, which allows for higher phase-to-ground voltages in each phase and longer heated lengths of the pipeline. Cables 8 with flat or rectangular wires allow even larger cross-sections.

[0035] The multiple resistive cables 8 a , 8 b , 8 c are preferably star-connected together at end terminals 24 .

[0036] Advantageously, the separate locations of the multiple phases in the individual cable guides allows for more efficient transfer of the generated heat to the pipes 12 and the fluid therein by reducing heat transfer between the cables 8, which also contributes to increasing the phase-to-ground voltage and therefore to longer pipeline heating lengths.

[0037] The cable guides 9 are configured to ensure separation of the phases and to prevent the insulation 7 from contacting the resistive cable 8 or coming between the resistive cable and the structural pipe 12. The cable guides 9, which are attached directly to the surface of the structural pipe 12, allow for efficient installation of the heating cables 8a, 8b, 8c while minimizing damage during system assembly.

[0038] In an embodiment, the cable guide 9a, 9b, 9c for each resistive cable 8a, 8b, 8c can advantageously be provided with an elongated box section having a substantially rectangular, trapezoidal or round (e.g. U-shaped) cross section. The cable guide 9 for multiple resistive cables can be made from a single piece with interconnected cable guide sections 9a, 9b, 9c or can be made from multiple individual guides mounted independently of the pipe.

[0039] The cable guides 9a, 9b, 9c with the resistive cables 8a, 8b, 8c therein can be spaced at approximately equal intervals L on the pipe 12, which contributes to a good distribution of the generated heat and heating. The cable guides 9 with the resistive cables 8 therein are preferably mounted in contact with the top of the pipeline, which is the most efficient from a thermodynamic point of view for transferring the generated heat to the pipeline transport products, taking into account that the ground in which the pipeline is buried is usually cooler closer to the surface during low temperature periods.

[0040] The cable guide 9 can be made of polymer or aluminum or other material with similar physical properties. The choice of material for the cable guide 9 can also be determined by the required heat transport from the heating phases 8a, 8b, 8c to the pipes 12 and the transport oil or gas 16.

[0041] The straight lengths of resistive cable 8 may be interconnected by high voltage connection sleeves configured to the same voltage as the cable phases, and each end of the resistive cable is designed to have an end sleeve (not shown).

[0042] For routine maintenance, the management of line parameters including the insulation resistance of the heating cable 8 and the detection of defective parts can be performed by utilizing the service terminal 26, the end terminal 24 and the supply terminal 22, which are intended to increase the adaptability of the electric heating system as well as to improve maintenance convenience.

[0043] The pipeline electric heat system according to the present invention significantly reduces the need for numerous transformer substations and associated electrical networks over distances of 150-200 km.

[0044] A resistive cable 8 according to an advantageous embodiment of the invention comprises a single-conductor medium voltage phase cable. The cable 8 is selected such that the generated heat matches the heat required for the pipeline, with respect to losses in the protective shield, for example 10 or 8 W / m. Figure 3 shows the elements of a resistive cable 8 according to an embodiment of the invention, comprising a current carrying wire 1 made of aluminium or copper, a layer 2 of semiconductive material, for example of combined sheathed cable type (CSC), an insulating layer 3 made for example of cross-linked polyethylene, a semiconductive material 4, for example of CSC type, a shield 5 made for example of braided copper wires and an outer jacket 6 made for example of a thermoplastic elastomer.

[0045] The direction of current flow in the metallic cable shields 5 is the distinguishing feature of the separately located phases 8a, 8b, 8c. The shields 6 of each resistive cable 8 have intermediate and terminal earth connections and are also interconnected at the pipeline terminals.

[0046] According to an advantageous embodiment of the invention, the shields of the three phases are transposed at midpoints along the cable length, located at the service terminals 26, as shown in Fig. 6. For example, if there are two service terminals 26 located between the end terminal 24 and the supply terminal 22 of each cable, the cable shields can be rotated twice, so that each shield runs along all three phases of the section. Shield transposition as such is known in medium voltage (MV) and high voltage (HV) underground power cables, to reduce power losses by counterbalancing the direction of induced currents in each shield. It can be noted that the transposition is relative and that either the shields of the three phase cables can be transposed or the wires of the cable can be transposed.

[0047] In the present invention, the shield transposition reduces the loss of cable shield 5 for better heat distribution over longer cable length of pipeline electric heat system. The heat generation due to the transposition connection in some system components does not affect the good operation of the system, but it needs to be taken into consideration in the estimation and design of electric heat system.

[0048] The transposition advantageously allows to adjust the location of heat generation (wire or shield) and the value of the generated heat. The lack of a transposition would result in significantly higher losses in the shield 5, which would result in a shorter maximum length of the heated area. In addition to this, the lack of a transposition would result in higher currents in the shield 5 over a significant length, which would result in less safety and increased risk of damage, as well as a shorter usable life of the cable.

[0049] The resistive cable 8 may be multi-wire.

[0050] The following Table 1 shows an example of advantageous specifications for a heating cable according to an embodiment of the electric heating system of the present invention. [Table 1]

[0051] A control / monitoring system for the parameters of the electric heating system ensures energy efficiency and safe operation of the system. The control / monitoring system includes temperature sensors, current sensors, and load voltage sensors. Using management algorithms, the system remotely manipulates the parameters of the heating system based on measured temperatures of, for example, oil, ambient temperature, resistive cables, and transmission pipelines. The control system controls electrical parameters such as load current, voltage, and circuit health for each phase.

[0052] The control / monitoring system can use a programmable logic controller (PLC), a discrete / analog signal I / O module, an operation panel, and a serial interface module. The circuit parameter control / monitoring system communicates the state parameters of the target object to the high-level control system using industrial data protocols known per se (e.g. ModBus RTU, Ethernet, CAN, HART, PROFIBUS).

[0053] Short circuit currents require direct and separate current measurements on each phase 8a, 8b, 8c and analysis of the line conditions. The same mechanism can be used to identify the damage and expedite repair efforts.

[0054] The circuit parameter control / monitoring system is in some cases configured to maintain operation with one or two phases instead of three, since it is necessary to maintain some working capacity of the electrical heating essential for the heating pipeline. The parameter control / monitoring system is also configured to regulate the generated heat by safe switching on and off and by varying the supply voltage (switching of transformer windings).

[0055] The system according to the embodiment of the invention can work as follows: From the power source, the required linear voltage is fed via a feeding transformer to the feeding terminal, which distributes the voltage to three phases (phase voltages). The power is fed from one feeding substation. The claimed electric heating system maintains the specific electrical parameters in the heating circuit up to 100 km. Thus, if the feeding substation is located in the middle of the heating pipeline area, one substation can heat the pipeline at a distance of up to 100 km in one direction and 100 km in the other direction. Thus, one feeding substation can heat the pipeline at a distance of up to 200 km in total. The parameter control / monitoring system remotely fully controls and manages the system according to the embodiment of the invention.

[0056] Each phase is provided with a resistive cable 8 which generates heat towards the cable guide 9 and the transport pipeline. Each separately installed heating phase 8a, 8b, 8c increases the passing phase voltage of each phase in the area limited by the insulation 7. A higher passing phase voltage increases the length of the heating arm. A flat or rectangular wire increases the cross-sectional area of ​​the heating phase in a given limited area of ​​the insulation 7. Furthermore, the separation of the heating phases 8a, 8b, 8c prevents overheating of each phase, which also contributes to a higher passing phase voltage.

[0057] Examples of calculations and applications of a pipeline electric heat system according to an embodiment of the present invention are described below.

[0058] The parameters of the electric heating system for the pipeline are: 2 The calculation was performed using an example having aluminum wire.

[0059] A commercial software (Elcut Professional app) was used to calculate the heat losses and temperature parameters. To calculate the heat losses, the convective heat transfer condition was selected as the boundary condition at the ground surface: a = 30 V / (m 2 *K),T amb= 18°C. The ground temperature at 10 m depth was chosen to be +21°C. The product temperature at the inner pipeline wall was chosen to be +50°C.

[0060] The cable parameters are as follows: Wire: Aluminum, 70mm 2 (AC-70) ·Thermal performance: 30W / m Number of wires: 3 Heating arm length: 100km Supply voltage (line): 8899V Supply voltage (phase): 5138V The heat loss value with a reduction factor of 1.07 is 25.3 W / m.

[0061] It is assumed that the three heating wires are installed in an aluminum cable guide (GOST 18475) having dimensions of 55x40 mm and a wall thickness of 2.5 mm.

[0062] The thermal parameters of the system in power-on and shutdown modes are given in Table 2 below. [Table 2] Calculation of electrical parameters of systems with wires AC-70 / 11.

[0063] Input data: 3 heating wires Required heating power of one wire: 10W / m Heating arm length: L=100km Current carrying wire: AC-70 / 11 according to GOST 839-80 Current carrying wire material: Aluminum Electrical resistance of 1 km cable for DC current at 20℃: 0.4218Ω Cable linear power at wire temperature 64℃ Temperature resistance coefficient: a=4.3·10 -3 1 / ℃. Resistance of 100km length of wire at 64℃

number

number

[0064] Straight heating capacity of one heating wire at wire temperature 64°C

number

[0065] Due to the defined arrangement of the heating phases and the large linear heating sections, it is possible to increase the length of the heated section of the pipeline up to 200 km and distribute the heat along the pipeline without changing the size and value of the insulation section 7 of the heating pipeline, which contributes to more efficient utilization and allocation of the rated heat capacity for heat tracing the product in the transport pipe over distances of up to 200 km.

[0066] The cable guides 9, which are attached directly to the pipes, contribute to distributing the heat generated by each heating phase in a more efficient manner.

[0067] This therefore provides a pipeline electric heat system capable of generating a certain amount of heat from one supply point (one substation) over considerable distances of up to 200 km without the need for an associated network.

[0068] Overall, the absence of an associated supply network contributes to the simplification of the electric heating system. [Explanation of symbols]

[0069] Pipeline Equipment 10 Transportation Pipeline 12 Structural (metal) pipes 14 Insulation section 7 Oil, Gas 16 Power Transformer 18 Pipeline Electric Heating System Supply Terminal 22 Terminal 24 Service Terminal 26 Heating cable assembly 28 Resistive Cable 8 Current-carrying conductor 1 Aluminum or copper wire Semiconductor material layer 2 Composite armored cable type (CSC) Insulation Layer 3 Cross-linked polyethylene layer Semiconductor material layer 4 CSC type Electric Shield 5 Copper Wire Shield Outer insulation layer 6 Thermoplastic elastomer coating Connection end sleeve 30 Temperature Sensor 20 Cable guide 9 Fixing element 32 Distance L between cables on the pipe

Claims

1. A pipeline electric heat system for a transportation pipeline (12) comprising a pipe (14) and a surrounding insulation (7), comprising: A power transformer (18); A supply terminal (22); A terminal (24); one or more service terminals (26) disposed between said supply terminal and said end terminal; A parameter control / monitoring system; a heating cable assembly (28) connected to three phases (8a, 8b, 8c) of a three-phase power source and having three resistive heating cables (8) extending along said pipe from said supply terminal (22) to said end terminal (24) through said one or more service terminals (26); Equipped with each of the three resistive heating cables (8) is individually mounted in a corresponding cable guide (9a, 9b, 9c), the cable guide and the associated resistive cable mounted therein being mounted beneath the insulation (7) and on the outer surface of the pipe; and each of the three resistive heating cables (8) comprises an inner conductor and a shield surrounding the inner conductor, the shields of each of the three resistive heating cables (8) are connected to ground and are interconnected together at the end terminals and / or at the supply terminals, and the shield or the inner conductor is transposed at at least one of the service terminals.

1. A pipeline electric heating system comprising:

2. 2. The pipeline electric heat system of claim 1, wherein adjacent cable guides are separated by a non-zero distance (L).

3. 3. A pipeline electric heat system as claimed in claim 1 or 2, comprising at least two service terminals (26).

4. 4. A pipeline electric heating system according to claim 1, characterized in that each of the phases comprises a solid medium voltage resistive cable provided with a shield (5) and an insulation (3).

5. 5. A pipeline electric heating system as claimed in any one of claims 1 to 4, characterized in that the cable guide for each of the three resistive heating cables has a substantially rectangular, trapezoidal or round cross-section.

6. 6. The pipeline electric heat system of claim 5, wherein each of said cable guides is sealed to an exterior surface of said pipe along a longitudinal edge thereof.

7. 3. The pipeline electric heat system of claim 2, wherein the non-zero distance (L) between adjacent cable guides is substantially constant.

8. 8. A pipeline electric heating system as claimed in any one of claims 1 to 7, characterized in that the cable guide and associated resistive cable installed therein are attached to the top of the pipe.

9. The pipeline electric heating system according to any one of claims 1 to 8, characterized in that the cable guide is made of polymer or aluminum.

10. 10. A pipeline electric heating system according to any one of claims 1 to 9, wherein the three resistive heating cables are star-connected together at the end terminals.

11. 11. A pipeline electric heating system according to any one of claims 1 to 10, characterized in that the wires of the three resistive heating cables have a flattened cross-sectional shape.

12. The pipeline electric heat system of claim 11, wherein the parameter control / monitoring system comprises a temperature sensor, a current sensor, and a load voltage sensor.

13. 13. The pipeline electric heating system of claim 12, wherein the parameter control / monitoring system is configured for remote measurement and control of the pipeline electric heating system, including measuring ambient temperature, detecting the health of the three resistive heating cables, and controlling load current and load voltage in each resistive cable.

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