Gradient phase change heat storage composite pipeline for heavy oil transportation of thermal power plant

Abstract

The invention relates to the technical field of heavy oil transportation, in particular to a cascade phase change heat storage composite pipeline for heavy oil transportation of a thermal power plant, the composite pipeline comprises a heavy oil transportation pipeline, a heat storage layer and a heat preservation layer, the heat storage layer and the heat preservation layer are sequentially coated outside the heavy oil transportation pipeline from inside to outside, and a heating module is arranged between the heat storage layer and the heat preservation layer. The heat storage layer comprises multiple layers of phase change materials with gradually-changed melting points which are sequentially arranged from inside to outside in the radial direction, a temperature difference power generation module is arranged between the pipe wall of the heavy oil transportation pipeline and the phase change material located in the inner layer, and the phase change material located in the middle layer is filled with an electric response heat conduction medium in a dispersed mode; the medium forms an ordered heat conduction network under the action of an electric field generated by the thermoelectric power generation module, the system adapts to complex working conditions of a thermal power plant, the energy-saving performance and the operation reliability of the system are remarkably improved, and the system has wide industrial application value.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy oil transportation, and particularly to a cascaded phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant. Background Art

[0002] In the operation system of a thermal power plant, heavy oil, as a high-viscosity liquid fuel refined from crude oil, has become an important energy carrier for peak shaving units, oil-fired boilers, and gas-steam combined cycle units due to its calorific value advantage of up to 40 - 42 MJ / kg and stable combustion characteristics. However, the complex component composition of heavy oil makes its physical properties extremely sensitive to temperature changes. The freezing points of typical heavy oils generally range from 80 to 120 °C, which means that when the temperature in the transportation pipeline is lower than this threshold, components such as wax and asphaltene will rapidly crystallize and precipitate, forming colloidal deposits adhering to the pipe wall. Over time, such deposits gradually accumulate, resulting in a reduction in the effective diameter of the pipeline and even causing serious accidents such as complete blockage. According to industry statistics, a single unplanned shutdown of a million-kilowatt coal-fired power plant due to heavy oil pipeline blockage can result in direct economic losses of up to several million yuan. Moreover, the steam purging or chemical cleaning process required to resume transportation not only consumes a large amount of energy but may also cause secondary problems such as corrosion of the inner wall of the pipeline and environmental pollutant emissions.

[0003] To ensure the fluidity of heavy oil, traditional transportation technologies mainly rely on two continuous heating methods: steam tracing and electric tracing. The steam tracing system indirectly heats the heavy oil pipeline by arranging a high-temperature steam pipeline in parallel with the heavy oil pipeline and utilizing the latent heat released by steam condensation. Although this technology has the characteristics of stable heat source and suitability for long-distance pipelines, its inherent high energy consumption problem has always been difficult to solve: the heat loss rate of steam during transportation due to pipeline heat dissipation is usually as high as 15% - 20%, and the complexity of the condensate recovery system further exacerbates energy waste. Taking a 300 MW unit as an example, the steam tracing system of its heavy oil transportation pipeline consumes approximately 2000 tons of standard coal equivalent in steam per year on average, accounting for more than 8% of the auxiliary production energy consumption of the whole plant. In addition, there is an obvious lag in the temperature response of steam tracing. When the power plant load changes rapidly, the adjustment delay of steam pressure and flow will cause a temperature fluctuation of ±15 °C in the pipeline. In a low-temperature environment in winter, the heat dissipation of the pipeline outer wall is intensified, and the temperature in local areas may quickly drop below the freezing point of heavy oil.

[0004] The electric tracing technology converts electrical energy into heat energy through resistance wires or heating cables to directly heat the pipeline. It has the advantages of flexible installation and relatively high temperature control accuracy (±5°C), and is suitable for local heating of valves, elbows, and short-distance pipelines. However, the electricity consumption cost of this technology is significantly higher than that of steam tracing. Taking constant-power electric tracing as an example, the power per unit length is usually 50 - 100 W / m. The annual power consumption of a 1000-meter heavy oil pipeline exceeds 500,000 kWh, and the operating cost reaches 2 - 3 times that of steam tracing. More seriously, the electric tracing system is highly dependent on the stability of the power grid. Once there is a power supply interruption or power fluctuation, the heating function immediately fails, and the pipeline temperature will drop at a rate of 5 - 10°C / min, far exceeding the allowable safe temperature drop rate of heavy oil (≤2°C / min). In addition, the heating cable operates in a high-temperature environment for a long time, and the insulation layer is prone to aging, posing a safety hazard of short-circuit and fire. Moreover, the dot heating method results in uneven circumferential temperature distribution of the pipeline, and the local overheating area may exceed the flash point of heavy oil (130°C), leading to the risk of coking.

[0005] The core defect of the above traditional tracing technologies lies in that the heating power cannot be dynamically adjusted according to the actual heat demand of the pipeline, resulting in the coexistence of overheating and insufficient heating. When the heat source supply is stable, the system continuously consumes energy to maintain a constant temperature. When the heat source fluctuates or is interrupted, there is no effective heat buffer mechanism, and the pipeline temperature drops linearly, making it difficult to meet the strict requirements of heavy oil transportation for temperature stability. This technical limitation is particularly prominent under the background of the "dual carbon" goal. Thermal power plants are facing the pressure of energy consumption reduction and emission control, and there is an urgent need for a more efficient and reliable temperature management technology for heavy oil transportation.

[0006] To solve the above problems, introducing a cascaded phase change heat storage composite pipeline is an innovative idea. The cascaded phase change heat storage material can efficiently store and release heat during temperature fluctuations through its unique phase change process. When the steam tracing or electric tracing system is operating, the multi-stage phase change material absorbs and stores the excess heat. When the tracing system pauses, the phase change material can continuously release the stored heat to maintain the pipeline temperature above the solidification point of heavy oil. Compared with traditional technologies, this method has the following significant advantages: 1. Temperature stability: The melting point of the phase change material is constant, which can accurately control the pipeline temperature and avoid overheating or too low temperature; 2. Energy-saving and efficient: By storing excess heat and releasing it in a timely manner, the consumption of steam or electricity can be significantly reduced, achieving the purpose of energy conservation and emission reduction; 3. Improved reliability: Even if the tracing system is interrupted for a short time, the heat stored in the phase change material can still maintain the pipeline temperature, thus avoiding the problem of heavy oil solidification and blockage.

[0007] However, although the cascade phase change heat storage technology significantly improves the temperature stability and energy-saving effect, there are still the following two key problems in practical applications: 1. Insufficient heating rate in the low-temperature area inside the pipeline: Due to the relatively low thermal conductivity of the phase change material, the efficiency of heat transfer to the inner wall of the pipeline is limited, resulting in a slow heating rate in the local low-temperature area inside the pipe. Measured data shows that when the ambient temperature is 20°C, it takes 4-6 hours for the inner wall temperature to rise to 80°C, which cannot meet the rapid start-up requirements of the power plant; 2. Limited heat distribution uniformity: When the temperature fluctuates greatly, it is difficult for the phase change material to quickly match the heat storage and release rates with the demand. The heat release rate of the phase change material, that is, the melting and solidification processes, is limited by heat transfer dynamics. When the heat source power suddenly changes, the phase change speed of the phase change material cannot match the temperature change in time, resulting in a 5-8°C drop in the inner wall temperature of the pipeline within 10 minutes, breaking through the safety temperature threshold. In the circumferential distribution of the pipeline cross-section, due to the weak natural convection ability of the phase change material, the temperature difference of "hot on top and cold at the bottom" can reach more than 10°C. Especially in local structures such as elbows and valves, the phenomenon of heat accumulation or loss caused by flow resistance is more obvious, forming a temperature blind spot. According to the measured data, the temperature at the bottom of the pipeline within 5 meters downstream of the valve is 15°C lower than that at the top, becoming a high-incidence area for heavy oil solidification. These problems indicate that with the current thermal management efficiency of the cascade phase change heat storage composite pipeline, it is difficult to completely solve the problem of uniform heat distribution under complex flow fields and temperature fields. It may lead to insufficient temperature in some areas, affecting the stability of the transportation system. Summary of the Invention

[0008] In view of the above-mentioned prior art, the present invention provides a cascade phase change heat storage composite pipeline for heavy oil transportation in thermal power plants, which can effectively maintain the pipeline temperature, thus avoiding the problem of heavy oil solidification and blockage. It aims to solve the problems of large heat loss, unstable temperature control and high energy consumption in the prior art. This pipeline system realizes efficient heat management, dynamic temperature control and energy recovery, effectively improving the temperature stability and operation efficiency during heavy oil transportation.

[0009] To achieve the above object, the technical solution of the embodiment of the present invention is realized as follows: A cascade phase change heat storage composite pipeline for heavy oil transportation in thermal power plants, the composite pipeline includes a heavy oil transportation pipeline, a heat storage layer and a heat insulation layer that are sequentially coated on the outside of it from inside to outside. A heating module is provided between the heat storage layer and the heat insulation layer. The heat storage layer contains multiple layers of phase change materials with gradually increasing melting points arranged radially from inside to outside. A thermoelectric generation module is arranged between the pipe wall of the heavy oil transportation pipeline and the phase change material in the inner layer. An electric field-responsive heat conduction medium is dispersed and filled in the phase change material in the middle layer, and the medium forms an ordered heat conduction network under the action of the electric field generated by the thermoelectric generation module.

[0010] Optionally, the heat storage layer is composed of a high-temperature phase change material wrapping layer, a medium-temperature phase change material wrapping layer, and a low-temperature phase change material wrapping layer. The high-temperature phase change material wrapping layer is filled with a high melting point phase change material, the medium-temperature phase change material wrapping layer is filled with a medium melting point phase change material, and the low-temperature phase change material wrapping layer is filled with a low melting point phase change material. The melting point range of the high melting point phase change material is 160 - 180 °C, the melting point range of the medium melting point phase change material is 100 - 120 °C, and the melting point range of the low melting point phase change material is 40 - 60 °C.

[0011] Optionally, the thermoelectric power generation module is disposed between the high melting point phase change material and the pipe wall, and the medium melting point phase change material is dispersedly filled with an electro-responsive heat conducting medium.

[0012] Optionally, the electro-responsive heat conducting medium includes one or more of graphene, carbon nanotubes, or metal particles.

[0013] Optionally, the hot end face of the thermoelectric power generation module is in direct contact with the pipe wall, and its cold end face is in direct contact with the high melting point phase change material.

[0014] Optionally, the thermoelectric power generation module generates a potential difference by using the radial temperature difference existing between the pipe wall and the high melting point phase change material. The potential difference generates a radial electric field between the pipe wall and the medium-temperature phase change material coating layer, and the radial electric field drives the electro-responsive heat conducting medium to be oriented along the electric field direction.

[0015] Optionally, heat conducting fins are embedded in the heat storage layer, and one end of the heat conducting fin is connected to the heavy oil transportation pipeline. The material of the heat conducting fin includes a high thermal conductivity metal or a high thermal conductivity composite material, the thickness is 1 - 2 mm, the length includes 4 mm, 6 mm, or 8 mm, and they are evenly distributed along the circumferential direction of the pipeline and rotated at a preset angle.

[0016] Optionally, the heating module includes a steam channel connected to an external heat source and an electric heating unit, and the steam channel adopts an annular or spiral structure.

[0017] Optionally, the heat insulation layer is made of polyurethane foam or rock wool and is externally coated with a waterproof and anti-corrosion coating.

[0018] Optionally, the heat storage layer is encapsulated with a metal film, and an expansion space is reserved between the inner wall of the metal film and the heat storage layer.

[0019] The beneficial effects of the present invention are as follows: Through the innovative design of the cascade phase change heat storage structure, the present invention effectively solves the core problems of high energy consumption and insufficient reliability in traditional tracing technologies. Phase change materials with different melting points form a gradient distribution along the radial direction of the pipeline. During the operation of the tracing system, they absorb and store excess heat instead of continuously relying on external heating, fundamentally changing the "passive heating" mode of traditional technologies. When the tracing system pauses or the heat source fluctuates, the phase change materials continuously supply heat to the pipeline through latent heat release, avoiding sudden temperature drops caused by steam supply interruptions or power supply failures, significantly improving the operating reliability of the system under complex working conditions, ensuring that the heavy oil transportation temperature is always maintained above the freezing point, and reducing the risk of unplanned shutdowns caused by pipeline blockages.

[0020] Aiming at the problems of difficult precise temperature control and low thermal conductivity of phase change materials in traditional technologies, the thermoelectric generation module utilizes the radial temperature gradient of the pipeline to convert thermal energy into electrical energy, forming a directional electric field in the phase change material layer, promoting the orderly arrangement of the electro-responsive heat-conducting medium and constructing an efficient heat-conducting path, significantly enhancing the heat transfer efficiency to the inner wall of the pipeline. This design not only shortens the pipeline heating time in low-temperature environments but also effectively improves the phenomenon of uneven temperature in local areas, avoids the occurrence of overheating or low-temperature blind spots, significantly improves the pipeline temperature control accuracy, meets the strict requirements of heavy oil transportation for temperature stability, reduces the risk of pipeline material damage caused by temperature fluctuations, and can maintain efficient operation without an external power supply. While improving the energy-saving effect, it enhances the adaptability of the overall system, providing an innovative solution that combines high efficiency, reliability, and energy conservation for the field of industrial pipeline transportation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the two-dimensional structure diagram of the cascade phase change heat storage composite pipeline in the embodiment of the present application;

[0022] Figure 2 is the three-dimensional structure diagram of the pipeline, fin, heating module, and thermoelectric module in the embodiment of the present application;

[0023] Figure 3 is the three-dimensional structure diagram of the cascade phase change heat storage composite pipeline in the embodiment of the present application;

[0024] Explanation of the reference numerals in the drawings:

[0025] 1. Transport pipeline, 2: High melting point phase change material, 3: Medium melting point phase change material, 4: Low melting point phase change material, 5: Thermal insulation layer, 6: Long fin, 7: Low temperature phase change material wrapping layer, 8: Medium fin, 9: Medium temperature phase change material wrapping layer, 10: Short fin, 11: High temperature phase change material wrapping layer, 12: Inlet, 13: Heating module, 14: Outlet, 15: Thermoelectric generation module, 16: Electro-responsive heat-conducting medium. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The technical solution of the present invention will be further elaborated in detail below in conjunction with the accompanying drawings of the specification and specific embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. In the following description, the expression "some embodiments" is used, which describes a subset of all possible embodiments. However, it should be understood that "some embodiments" may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0027] In the following description, a large number of specific details are given to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, some well-known technical features are not described to avoid confusion with the present invention.

[0028] It should be understood that the present invention can be implemented in different forms and should not be construed as limited to the embodiments presented herein. On the contrary, providing these embodiments will make the disclosure thorough and complete and will fully convey the scope of the present invention to those skilled in the art. And the purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present invention. When used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, determine the presence of the described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. When used herein, the term "and / or" includes any and all combinations of the related listed items.

[0029] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "inner", "outer", "left", "right" and similar expressions used herein are only for the purpose of illustration and do not represent the only implementation.

[0030] To thoroughly understand the present invention, detailed structures will be presented in the following description to illustrate the technical solutions proposed by the present invention. The optional embodiments of the present invention are described in detail below. However, in addition to these detailed descriptions, the present invention may have other embodiments.

[0031] Please refer to the attached Figure 1 In a first aspect of the present invention, a cascaded phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant is provided. The composite pipeline includes a heavy oil transportation pipeline 1, a heat storage layer and a heat insulation layer 5 that are sequentially coated on the outside of the heavy oil transportation pipeline 1 from the inside to the outside. A heating module 13 is provided between the heat storage layer and the heat insulation layer 5. The heat storage layer contains a plurality of layers of phase change materials with gradually increasing melting points arranged sequentially from the inside to the outside in the radial direction. A thermoelectric generation module 15 is arranged between the pipe wall of the heavy oil transportation pipeline 1 and the phase change material located in the inner layer. A charge-responsive heat conducting medium 16 is dispersed in the phase change material located in the middle layer. The medium forms an ordered heat conducting network under the action of the electric field generated by the thermoelectric generation module 15.

[0032] Specifically, the heavy oil transportation pipeline 1 is made of a high heat-conducting metal material, and the inner wall is polished to reduce the flow resistance. The heat storage layer is arranged with a plurality of layers of phase change materials with gradually increasing melting points from the inside to the outside in the radial direction. The melting point of the inner layer phase change material is the highest, and it gradually decreases outward, forming a gradient heat storage structure. When it is necessary to increase the temperature of the pipeline, a heat source is provided through the heating module 13. The high-grade heat generated by the heating module 13 is first absorbed by the inner layer phase change material, and the heat is stored in the form of latent heat through solid-liquid phase change, avoiding overheating of the inner wall of the pipeline. The middle layer and outer layer phase change materials sequentially absorb the remaining heat, forming a multi-level heat buffer system. This design enables the heat storage layer to automatically adjust the storage state according to the heat input, store the excess heat in a hierarchical manner, rather than continuously heating through traditional tracing technology, fundamentally reducing energy consumption;

[0033] The thermoelectric power generation module 15 located between the inner-layer phase change material and the wall of the heavy oil transportation pipeline 1 utilizes the temperature difference between the two to stimulate the thermoelectric effect, converting the high temperature on the inner wall of the pipeline and the relatively low temperature on the outer side of the inner-layer phase change material into electrical energy. This electrical energy forms a directional electric field in the middle-layer phase change material region, acting on the dispersed and filled electro-responsive heat-conducting medium 16, which will be directionally arranged along the direction of the electric field under the action of the electric field, forming an ordered heat-conducting network that penetrates the middle-layer phase change material. This network significantly enhances the heat conduction capacity of the phase change material, enabling heat to be transferred from the heat storage layer to the inner wall of the pipeline more efficiently. Especially when the pipeline starts or in a low-temperature environment, it can accelerate the heating speed of the inner wall and avoid the problem of heating lag caused by the low intrinsic thermal conductivity of the phase change material. Even if the heat tracing system is interrupted briefly, the heat stored in the heat storage layer can still be continuously transferred to the inner wall of the pipeline through the ordered heat-conducting network. At the same time, the thermoelectric power generation module 15 utilizes the remaining temperature difference to maintain the existence of the electric field, ensuring that the heat-conducting medium remains in a highly efficient heat-conducting state. The overall structure realizes the efficient storage, intelligent distribution, and precise transfer of heat through the hierarchical heat storage of the cascade phase change material, the energy conversion of thermoelectric power generation, and the heat conduction enhancement of the electro-responsive medium, effectively solving the problems of high energy consumption, large temperature fluctuations, and local low temperatures in traditional heavy oil transportation.

[0034] In an optional embodiment, the heat storage layer is composed of a high-temperature phase change material wrapping layer 11, a medium-temperature phase change material wrapping layer 9, and a low-temperature phase change material wrapping layer 7. Among them, the high-temperature phase change material wrapping layer 11 is filled with a high-melting-point phase change material 2, the medium-temperature phase change material wrapping layer 9 is filled with a medium-melting-point phase change material 3, and the low-temperature phase change material wrapping layer 7 is filled with a low-melting-point phase change material 4. The melting point range of the high-melting-point phase change material 2 is 160 - 180 °C, the melting point range of the medium-melting-point phase change material 3 is 100 - 120 °C, and the melting point range of the low-melting-point phase change material 4 is 40 - 60 °C.

[0035] Specifically, the heat storage layer adopts three layers of phase change material wrapping layers with different melting points and is arranged in sequence from the inside out to form a gradient heat storage system. The innermost high-temperature phase change material wrapping layer 11 is filled with the high-melting-point phase change material 2, which can preferentially absorb the high-grade heat generated by the steam heat tracing or the electric heating unit. When the external heat source works, the high-melting-point phase change material 2 reaches its melting point and undergoes solid-liquid phase change, stabilizing the temperature of the inner wall of the pipeline within a safe range through latent heat storage, avoiding damage to the pipeline material due to overheating, and preventing high heat from directly dissipating to the outside;

[0036] The intermediate layer of medium-temperature phase change material wrapping layer 9 is filled with medium-melting point phase change material 3, which receives and further stores the remaining heat transferred from the high-temperature layer. Its melting point range matches the safe transportation temperature range of heavy oil. After the inner wall temperature of the high-temperature layer stabilizes, the medium-melting point phase change material 3 absorbs and stores medium-grade heat through the phase change process, forming a temperature stability zone. When the external heat source fluctuates or is temporarily out of use, the medium-melting point phase change material 3 first releases the stored heat and continuously supplies heat to the inner wall of the pipeline to ensure that the temperature remains above the freezing point of the heavy oil. This gradient design enables the heat storage layer to automatically adjust the energy release sequence according to the heat demand, avoiding the "fault" problem of heat supply in traditional technologies and significantly improving the continuity and reliability of temperature control.

[0037] The outermost low-temperature phase change material wrapping layer 7 is filled with a low-melting-point phase change material 4, which primarily absorbs low-grade heat transferred from the intermediate temperature layer and reduces heat loss from the heat storage layer to the insulation layer 5. Its melting point range is below the freezing point of heavy oil, forming an external thermal barrier when ambient temperatures are low, slowing the rate of heat transfer from the heat storage layer to the outside world. When the system is in a low-temperature environment or the heat source is interrupted for a long time, the low-melting-point phase change material 4 synergizes with the intermediate- and high-melting-point phase change materials 2 to release energy, releasing latent heat sequentially in descending order of melting point, thereby extending the duration of pipeline temperature maintenance. The three layers of phase change material form a "relay" heat storage and release pattern through a melting point gradient, enabling hierarchical heat management in the radial direction of the pipeline: the inner layer stabilizes the high-temperature boundary, the middle layer controls the core temperature, and the outer layer blocks the influence of the low-temperature environment. Together, they create an efficient heat management system covering a wide temperature range. This layered design not only solves the problem of one-time heat consumption in traditional heating technology, but also enables on-demand heat storage and orderly release through the latent heat properties of the phase change material.

[0038] In an optional embodiment, the heating module 13 includes a steam channel and an electric heating unit with an external heat source. Steam or electric heating is used as the main heat source. The inlet 12 and outlet 14 of the steam channel are connected in parallel to the steam heat source. The electric heating unit is embedded in the steam channel to provide auxiliary heat when the steam channel is unstable or works intermittently. The electric heating unit is connected to the intelligent temperature control system and can dynamically adjust the heating power according to real-time temperature monitoring data to ensure stable temperature inside and outside the pipeline.

[0039] The steam channel adopts an annular or spiral structure. In the case of an annular structure, the annular steam channel is arranged concentrically around the heavy oil pipeline 1, allowing high-temperature steam to evenly circumscribe the pipeline, ensuring that all areas surrounding the heat reservoir are heated simultaneously. This avoids the localized overheating or hypothermia caused by uneven steam distribution in traditional linear channels. The steam flows through the annular channel with balanced resistance, allowing it to contact the low-temperature phase change material on the outer layer of the heat reservoir at a stable flow rate. Heat is evenly transferred to the heat reservoir through convection, improving circumferential temperature uniformity.

[0040] When it is a spiral structure, the steam channels of the spiral structure are spirally wound along the axial direction of the pipeline, forming a spiral steam flow path, which significantly increases the contact area and heat exchange time between the steam and the heat storage layer compared with the straight channels. When the steam flows in the spiral channels, it is closer to the outer wall of the heat storage layer due to the centrifugal force, strengthening the convective heat transfer effect. Especially in long-distance oil pipelines, it can reduce the heat loss along the way of the steam, enabling the heat to be absorbed by the heat storage layer more efficiently. The spiral design can also make the steam flow direction cooperate with the radial heat transfer direction of the pipeline, prompting the heat to uniformly penetrate into each layer of the phase change material along the spiral path, avoiding heat accumulation or deficiency caused by flow dead zones, and further optimizing the temperature distribution of the heat storage layer.

[0041] In an optional embodiment, the thermoelectric power generation module 15 is arranged between the high-melting-point phase change material 2 and the pipe wall, and the hot end face of the thermoelectric power generation module 15 is in direct contact with the pipe wall, and its cold end face is in direct contact with the high-melting-point phase change material 2. The medium-melting-point phase change material 3 is dispersedly filled with an electro-responsive heat-conducting medium 16, and the electro-responsive heat-conducting medium 16 includes one or more of graphene, carbon nanotubes or metal particles.

[0042] Specifically, the number of the thermoelectric power generation modules 15 is multiple, and they are all arranged between the high-melting-point phase change material 2 and the heavy oil transportation pipeline 1 pipe wall. The multiple thermoelectric power generation modules 15 are connected in series to provide sufficient voltage for the subsequent generation and drive of the electric field. When the thermoelectric power generation module 15 utilizes the temperature difference between the two to stimulate the thermoelectric effect, it converts the high temperature of the pipeline inner wall and the relatively low temperature outside the high-melting-point phase change material 2 into electric energy. When the pipeline inner wall is at a high temperature due to heavy oil transportation or external heating, the high-melting-point phase change material 2 absorbs heat and undergoes a phase change, and its outer temperature is lower than the inner wall temperature, forming a radial temperature gradient. The hot end of the thermoelectric power generation module 15 is attached to the pipeline inner wall, and the cold end is in contact with the high-melting-point phase change material 2. This temperature difference prompts the carrier migration in the semiconductor material inside the module, and finally forms an electric potential difference at both ends of the module, and then forms a directional electric field along the pipeline radius in the medium-melting-point phase change material 3 region.

[0043] The medium-melting-point phase change material 3 is dispersedly filled with one or more electro-responsive heat-conducting media 16 including graphene, carbon nanotubes or metal particles. The above materials have good electrical conductivity or dielectric properties and can be oriented under the action of an electric field. Taking graphene as an example, its sheet structure generates a dipole moment due to electrostatic induction in an electric field, and the interaction between the dipole moment and the electric field direction drives the graphene sheets to be orderly arranged along the electric field direction; as a one-dimensional material, carbon nanotubes will be oriented along the electric field direction due to the anisotropy of the length-diameter ratio in the electric field, forming a continuous heat-conducting channel; metal particles accumulate charges on the surface through electrostatic induction and migrate in the direction of high electric field strength under the action of the electric field force, and finally form a chain-like structure along the radial direction. These orderly arranged media construct an efficient heat-conducting network penetrating the radial direction in the medium-melting-point phase change material 3, significantly reducing the thermal resistance of the phase change material and enabling heat to be transferred from the heat storage layer to the inner wall of the pipeline more quickly.

[0044] Furthermore, the thermoelectric power generation module 15 utilizes the radial temperature difference existing between the pipe wall and the high-melting-point phase change material 2 to generate a potential difference. The potential difference generates a radial electric field between the pipe wall and the medium-temperature phase change material coating layer, and the radial electric field drives the electro-responsive heat-conducting medium 16 to be oriented along the electric field direction.

[0045] When the two ends of the thermoelectric power generation module 15 are respectively in contact with the pipe wall (hot end) and the high-melting-point phase change material 2 (cold end), based on the thermoelectric effect, this temperature difference promotes the generation of carrier migration in the semiconductor material inside the module. The electrons at the hot end obtain higher kinetic energy and move towards the cold end, and finally accumulate charges at both ends of the module, forming a potential difference consistent with the direction of the radial temperature gradient.

[0046] The existence of this potential difference causes a radial electric field to be formed between the pipe wall of the pipeline and the medium-temperature phase change material coating layer, and the electric field direction points from the pipe wall (high potential end) to the medium-temperature phase change material layer (low potential end). The electro-responsive heat-conducting medium 16 filled in the medium-temperature phase change material, such as graphene, carbon nanotubes or metal particles, generates a response in the electric field due to its own electrical conductivity or dielectric property: charge separation will occur on the surface of the metal particles with high electrical conductivity due to electrostatic induction, forming a dipole moment consistent with the electric field direction; one-dimensional / two-dimensional materials such as graphene sheets or carbon nanotubes will rotate under the action of the electric field torque due to the anisotropic polarizability until their main axes are parallel to the electric field direction; polar dielectric particles will generate a directional force due to dipole polarization and overcome the viscous resistance of the phase change material matrix to migrate along the electric field direction. These behaviors jointly promote the electro-responsive medium to form a highly ordered arrangement structure in the medium-temperature phase change material, constructing an efficient heat-conducting channel penetrating along the radial direction.

[0047] The ordered heat conduction network formed under the drive of the radial electric field significantly improves the heat conduction ability of the medium-temperature phase change material. During the start-up phase of the pipeline, when the wall temperature needs to rise rapidly, this network can accelerate the transfer of heat from the heat storage layer to the inner wall, shortening the heating time. During normal operation, it can balance the circumferential temperature distribution of the pipeline, avoiding the "hot on top, cold on the bottom" phenomenon caused by the low thermal conductivity of traditional phase change materials. Especially at positions such as elbows and valves where flow dead zones are likely to form, local low-temperature hazards can be effectively eliminated through directional heat conduction. In addition, the thermoelectric power generation module 15 does not require an external power source and completely relies on the radial temperature difference of the pipeline itself to generate electric energy to maintain the existence of the electric field, forming a "self-powered - self-reinforcing" closed-loop system. This design not only reduces the dependence on external energy, but also ensures the stable release of heat from the heat storage layer through the continuous heat conduction enhancement of the electro-responsive medium during fluctuations or short-term interruptions of the tracing system, maintaining the pipeline temperature above the freezing point of heavy oil, fundamentally improving the reliability and energy efficiency of the transportation system.

[0048] In an optional embodiment, heat conducting fins are embedded in the heat storage layer, and one end of the heat conducting fin is connected to the heavy oil transportation pipeline 1. The material of the heat conducting fin includes high thermal conductivity metal or high thermal conductivity composite material, with a thickness of 1 - 2 mm, a length including 4 mm, 6 mm or 8 mm, and is evenly distributed along the circumferential direction of the pipeline and rotated at a preset angle.

[0049] Specifically, one end of the heat conducting fin embedded in the heat storage layer is tightly connected to the outer wall of the heavy oil transportation pipeline 1, and the other end extends deep into the heat storage layer. The fin with a length of 4 mm is the short fin 10, the fin with a length of 6 mm is the medium fin 8, and the fin with a length of 8 mm is the long fin 6. They respectively correspond to the phase change material wrapping layers with different melting points. The short fin 10 is mainly embedded in the inner high melting point phase change material 2 area. With its short heat conduction path, it can quickly transfer high-quality heat from the heat storage layer to the inner wall of the pipeline, especially accelerating the heating of the inner wall during the start-up phase and avoiding heat retention caused by insufficient thermal conductivity of the high melting point material. The medium fin 8 extends to the middle medium melting point phase change material 3 to balance the heat conduction rate of medium-quality heat and ensure the stable temperature of the pipeline during normal operation. The long fin 6 extends deep into the outer low melting point phase change material 4 to maximize the absorption of low-quality heat in the edge area and reduce the loss to the insulation layer 5, forming a full radial heat capture from the outside to the inside.

[0050] The heat-conducting fins are made of high heat-conducting metals such as copper and aluminum, or high heat-conducting composite materials such as graphite-reinforced polymers. The 1-2 mm thin design maximizes the heat conduction efficiency per unit area while reducing the material usage. The high heat-conducting property of its material effectively reduces the thermal resistance of the fins themselves, enabling heat to be transferred along the axial direction of the fins at a faster speed. The fins evenly distributed circumferentially around the pipeline are rotated at a preset angle, such as in a spiral or inclined arrangement, breaking the heat flow boundary layer in the heat storage layer and promoting the uniform diffusion of heat in the phase change material towards the inner wall of the pipeline. Especially at positions such as elbows and valves where flow dead zones are likely to form, the rotating fins eliminate the circumferential temperature difference through the guiding effect, further avoiding the uneven phenomenon of "hot on top and cold on the bottom" in traditional technologies.

[0051] Fins of different lengths work in cooperation with the stepped phase change material. The short fins 10 achieve rapid heat response for the inner high-temperature area, the medium fins 8 build a stable heat conduction channel in the middle layer, and the long fins 6 recover the waste heat from the outer low-temperature area, forming a heat transfer network of "layered strengthening and overall coverage". This design not only improves the radial heat exchange efficiency between the heat storage layer and the pipeline, but also evenly transports heat to each area of the pipeline through circumferential uniform distribution and angle optimization, effectively solving the risk of heavy oil solidification caused by local low temperature. In addition, the thin and structured design of the fins does not significantly increase the system heat capacity, ensuring that the heat storage layer can still respond quickly when the heat source fluctuates. Cooperating with the thermoelectric generation module 15 and the electro-responsive heat-conducting medium 16, it jointly constructs an efficient and balanced heat management system.

[0052] In some embodiments, the thermal insulation layer 5 is made of polyurethane foam or rock wool and is coated with a waterproof and anti-corrosion coating, effectively reducing the heat dissipation to the external environment and further improving the overall energy-saving effect of the system. The thermal insulation layer 5 combines the multi-stage heat buffering characteristics of the stepped phase change heat storage layer to ensure the stable operation of the system in high or low temperature environments.

[0053] In some embodiments, the heat storage layer is encapsulated with a metal film, and an expansion space is reserved between the inner wall of the metal film and the heat storage layer.

[0054] Specifically, the material of the metal film is usually selected as metals with good ductility such as aluminum and copper, which can not only withstand the thermal stress in high-temperature environments, but also assist the heat transfer between the heat storage layer and the external heat source or the thermal insulation layer 5 through its own high heat-conducting property, ensuring that the encapsulation structure does not affect the overall heat exchange efficiency.

[0055] When the phase change material absorbs heat and melts from solid state to liquid state, its volume usually expands by 5%-15%. The reserved space provides a buffer area for this expansion, preventing the metal film from breaking or deforming due to excessive internal pressure caused by volume increase. When the phase change material releases heat and solidifies from liquid state to solid state, the voids generated by volume shrinkage can be naturally filled through the reserved space, preventing the encapsulation layer from failing due to vacuum or stress concentration. This design effectively solves the problem of material leakage caused by thermal expansion and contraction in traditional packaging structures. Especially under the working conditions of multiple repeated phase changes, it can maintain the integrity and tightness of the heat storage layer for a long time.

[0056] It should be noted that the electric heating unit and the thermoelectric power generation module 15 involved in the embodiments of the present application both adopt mature models known in the conventional technical means in the art. Their specific structures, connection methods and control principles all belong to the scope that can be reasonably determined by those skilled in the art based on the prior art, and can be realized without creative labor. Therefore, no specific limitations or explanations are made in this embodiment.

[0057] The second aspect of the present invention provides a method for manufacturing a composite pipeline. The method includes the following steps: manufacturing a heavy oil transportation pipeline 1, using a high thermal conductivity metal material and polishing its inner wall; sequentially coating cascade phase change materials with high melting point, medium melting point and low melting point, and filling an electro-responsive heat conducting medium 16; uniformly arranging thermoelectric power generation modules 15 between the pipe wall and the high melting point phase change material 2, and connecting the modules in series to form an electric field; embedding heat conducting fins in each phase change material layer and optimizing their distribution according to the design; designing steam channels and electric heating units to provide heat for the heat storage layer and the pipeline; finally, coating a low thermal conductivity material on the outer layer of the composite pipeline and applying a waterproof and anti-corrosion coating.

[0058] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, and all of them should be covered by the protection scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A cascaded phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant, characterized in that, The composite pipeline includes a heavy oil transportation pipeline, a heat storage layer and a heat insulation layer that are sequentially coated on the outside of the heavy oil transportation pipeline from the inside to the outside. A heating module is provided between the heat storage layer and the heat insulation layer. The heat storage layer contains a plurality of layers of phase change materials with gradually changing melting points arranged radially from the inside to the outside. A thermoelectric generation module is arranged between the pipe wall of the heavy oil transportation pipeline and the phase change material located in the inner layer. An electric field-responsive heat conduction medium is dispersed and filled in the phase change material located in the middle layer, and the medium forms an ordered heat conduction network under the action of the electric field generated by the thermoelectric generation module.

2. The stepped phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant according to claim 1, characterized in that, The heat storage layer is composed of a high-temperature phase change material wrapping layer, a medium-temperature phase change material wrapping layer, and a low-temperature phase change material wrapping layer. The high-temperature phase change material wrapping layer is filled with a high-melting-point phase change material, the medium-temperature phase change material wrapping layer is filled with a medium-melting-point phase change material, and the low-temperature phase change material wrapping layer is filled with a low-melting-point phase change material. The melting point range of the high-melting-point phase change material is 160-180°C, the melting point range of the medium-melting-point phase change material is 100-120°C, and the melting point range of the low-melting-point phase change material is 40-60°C.

3. The stepped phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant according to claim 2, characterized in that, The thermoelectric generation module is arranged between the high-melting-point phase change material and the pipe wall, and the electric field-responsive heat conduction medium is dispersed and filled in the medium-melting-point phase change material.

4. A cascade phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant according to claim 1, characterized in that The electric field-responsive heat conduction medium includes one or more of graphene, carbon nanotubes, or metal particles.

5. A cascade phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant according to claim 3, characterized in that, The hot end surface of the thermoelectric generation module is in direct contact with the pipe wall, and its cold end surface is in direct contact with the high-melting-point phase change material.

6. The cascade phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant according to claim 5, characterized in that The thermoelectric generation module generates a potential difference by using the radial temperature difference existing between the pipe wall and the high-melting-point phase change material. The potential difference generates a radial electric field between the pipe wall and the medium-temperature phase change material coating layer, and the radial electric field drives the electric field-responsive heat conduction medium to be oriented along the electric field direction.

7. The cascade phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant according to claim 1, wherein Heat conduction fins are embedded in the heat storage layer, and one end of the heat conduction fin is connected to the heavy oil transportation pipeline. The material of the heat conduction fin includes a high-thermal-conductivity metal or a high-thermal-conductivity composite material, with a thickness of 1-2 mm, a length including 4 mm, 6 mm, or 8 mm, and is evenly distributed along the circumferential direction of the pipeline and rotated at a preset angle.

8. A stepped phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant according to claim 1, characterized in that, The heating module includes a steam channel connected to an external heat source and an electric heating unit, and the steam channel adopts an annular or spiral structure.

9. A stepped phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant according to claim 1, characterized in that, The heat insulation layer is made of polyurethane foam or rock wool and is externally coated with a waterproof and anti-corrosion coating.

10. The cascade phase change heat storage composite pipeline for heavy oil transportation in a thermal power plant according to claim 1, characterized in that, The heat storage layer is encapsulated with a metal film, and an expansion space is reserved between the inner wall of the metal film and the heat storage layer.

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