Solar dual phase change cascade heat storage system under oilfield continuous heat load scene

Abstract

The application provides a solar double-phase-change cascade heat storage system under an oilfield continuous heat load scene, and relates to the technical field of solar heat storage. The system comprises a heat collection, double-phase-change cascade heat storage, heat supply and flow control subsystem. The double-phase-change cascade heat storage subsystem is provided with first and second phase-change heat storage tanks with different phase-change temperatures in parallel. The flow control subsystem switches the fluid path based on the dynamic comparison criterion of the heat collection and heat storage temperatures, and directs the solar energy into the double tanks for cascade latent heat storage according to the heat energy grade. The heat supply subsystem guides the cold crude oil to sequentially absorb the heat released by the double tanks to perform cascade heating. The application overcomes the defect of low fluctuating solar energy capture rate of the traditional single-phase-change system, greatly reduces the irreversible exergy loss of heat transfer through cascade heat storage and release, improves the comprehensive utilization rate of full-band solar energy, and realizes efficient and low-carbon heat supply for oilfields.

Description

Technical Field

[0001] This invention relates to the field of solar thermal storage technology, and in particular to a solar dual-phase change cascade thermal storage system for continuous heat load scenarios in oil fields. Background Technology

[0002] Crude oil gathering and transportation processes require continuous heating of the fluid within the pipeline to a target temperature of approximately 85 degrees Celsius. This heating process is characterized by its continuous, 24 / 7 operation and high energy consumption. Traditional gathering and transportation heating relies heavily on natural gas boilers. Natural gas boilers have high fuel operating costs and significant carbon dioxide emissions. In recent years, researchers have begun exploring the introduction of solar thermal technology into the crude oil heating process (see the crude oil solar heating system disclosed in Chinese Patent Publication No. CN202675677U). Solar radiation has an inherent intermittent characteristic in its temporal and spatial distribution. Intermittent heat sources are difficult to directly match with continuous and stable heat load demands. Therefore, the heating system architecture must incorporate thermal storage devices to mitigate fluctuations in solar energy input.

[0003] Traditional solar thermal storage systems often use large water tanks for sensible heat storage. These tanks suffer from significant technical bottlenecks, including large footprint and substantial heat loss from their external surfaces, especially in high-temperature operating zones. Furthermore, the heat storage and release efficiency of water decreases sharply as the system's operating temperature rises. Phase change latent heat storage technology utilizes phase change materials to absorb or release latent heat through a solid-liquid phase transition. Phase change storage devices can achieve high-density thermal energy storage within a narrow temperature range. Replacing sensible water tanks with phase change materials has become an important evolutionary direction in the field of high-quality solar heating (see "Research on Continuous Drying Performance of Phase Change Thermal Storage Solar Drying System" published in the *Transactions of the Chinese Society of Agricultural Engineering*, Vol. 41, No. 7, 2025).

[0004] Existing single-phase change solar heating systems suffer from structural defects when addressing the demand from the gradual temperature rise of crude oil. Current system designs generally only utilize high-temperature phase change materials with a single phase change point. The heat quality of evacuated tube solar collectors is highly dependent on meteorological conditions. The collector outlet fluid temperature exhibits wide-range frequency fluctuations. During winter or low-radiation periods, the large amount of low-to-medium grade heat generated by the collectors cannot reach the melting point of the high-temperature phase change materials. Unmelted phase change materials can only store sensible heat with extremely low heat capacity. A significant amount of low-to-medium temperature solar heat is passively discarded by the heating system. These physical limitations result in a low overall solar energy capture rate for single-phase change systems.

[0005] Furthermore, the preheating process of low-temperature crude oil is a continuous fluid sensible heat absorption process. A single high-temperature phase change unit releasing heat to low-temperature crude oil inevitably generates a large heat exchange temperature difference. This wide temperature difference in a single-stage heat release mode leads to severe irreversible exergy losses. Exergy losses significantly weaken the system's ability to buffer against heat fluctuations. When the phase change unit's heat release is insufficient, the heating system must frequently start and stop the backup gas-fired boiler. The deep involvement of the gas-fired boiler contradicts the original intention of introducing solar energy and reduces the emission reduction benefits throughout its entire life cycle. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a solar dual-phase change cascade thermal storage system for continuous heat load scenarios in oil fields. This invention solves the problems of low capture rate of fluctuating heat sources and large loss of exergy due to concentrated high-temperature heat release in the existing single-phase change heating technology.

[0007] To achieve the above objectives, the present invention provides the following solution: A solar dual-phase variable cascade thermal storage system for continuous heat load scenarios in oil fields includes: The system includes a heat collection subsystem, a two-phase change cascade thermal storage subsystem, a heating subsystem, and a flow control subsystem. The heat output terminal of the heat collection subsystem is connected to the heat input terminal of the two-phase change cascade thermal storage subsystem; the heat release terminal of the two-phase change cascade thermal storage subsystem is connected to the heating subsystem; wherein, the two-phase change cascade thermal storage subsystem includes a first phase change thermal storage tank and a second phase change thermal storage tank arranged in parallel, and the phase change temperature of the second phase change thermal storage tank is higher than that of the first phase change thermal storage tank; the flow control subsystem is located on the fluid pipeline between the heat collection subsystem and the two-phase change cascade thermal storage subsystem; The solar collector subsystem is used to absorb solar radiation and supply thermal energy to the dual-phase change cascade thermal storage subsystem; the flow control subsystem is used to obtain the solar collector temperature of the solar collector subsystem and the thermal storage temperature in the first phase change thermal storage tank, and switch the fluid conduction path based on the dynamic comparison criterion of the solar collector temperature and the thermal storage temperature, so as to selectively introduce the thermal energy into the first phase change thermal storage tank or the second phase change thermal storage tank for latent heat storage; the heating subsystem is used to introduce the heated crude oil, and make the heated crude oil absorb the heat released by the first phase change thermal storage tank and the second phase change thermal storage tank in sequence, so as to raise the temperature of the heated crude oil in stages.

[0008] The present invention discloses the following technical effects: This invention provides a solar dual-phase change cascade thermal storage system for continuous heat load scenarios in oilfields. The system dynamically switches the direction of heat flow based on temperature comparison criteria through a flow control subsystem. When solar radiation is insufficient or the collector temperature is low, the first phase change storage tank in the low phase change point region effectively captures medium- and low-grade heat energy, overcoming the extremely low capture rate of low-grade heat energy in traditional single high-temperature phase change systems. This significantly improves the overall utilization rate of solar energy across the entire frequency band. Simultaneously, the heating subsystem uses the dual-phase change tank to sequentially preheat and raise the temperature of low-temperature crude oil. This cascaded heat release mode significantly reduces the heat exchange temperature difference between hot and cold fluids, fundamentally reducing irreversible exergy losses and effectively mitigating disturbances caused by intermittent heat sources. This, in turn, significantly reduces the forced start-up and shutdown frequency of the backup gas boiler and fossil fuel consumption, ultimately achieving low-carbon, efficient, and stable operation in continuous high-energy-consumption heating scenarios in oilfields. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of a solar dual-phase change cascade thermal storage system under continuous heat load in an oilfield, provided as an embodiment of the present invention. Attached image description: 1-Heat collection subsystem; 2-Two-phase change cascade thermal storage subsystem; 3-Heating subsystem; 4-Flow control subsystem; 21-First phase change thermal storage tank; 22-Second phase change thermal storage tank. Detailed Implementation

[0012] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0013] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] like Figure 1 As shown, this invention provides a solar dual-phase variable cascade thermal storage system for continuous heat load scenarios in oil fields, comprising: The system comprises: a heat collection subsystem 1, a two-phase change cascade heat storage subsystem 2, a heating subsystem 3, and a flow control subsystem 4. The heat output terminal of the heat collection subsystem 1 is connected to the heat input terminal of the dual-phase change cascade thermal storage subsystem 2; the heat release terminal of the dual-phase change cascade thermal storage subsystem 2 is connected to the heating subsystem 3; wherein, the dual-phase change cascade thermal storage subsystem 2 includes a first phase change thermal storage tank 21 and a second phase change thermal storage tank 22 arranged in parallel, and the phase change temperature of the second phase change thermal storage tank 22 is higher than the phase change temperature of the first phase change thermal storage tank 21; the flow control subsystem 4 is located on the fluid pipeline between the heat collection subsystem 1 and the dual-phase change cascade thermal storage subsystem 2; The heat collection subsystem 1 is used to absorb solar radiation and supply heat energy to the dual-phase change cascade heat storage subsystem 2; the flow control subsystem 4 is used to obtain the heat collection temperature of the heat collection subsystem 1 and the heat storage temperature in the first phase change heat storage tank 21, and switch the fluid conduction path based on the dynamic comparison criterion of the heat collection temperature and the heat storage temperature, so as to selectively introduce the heat energy into the first phase change heat storage tank 21 or the second phase change heat storage tank 22 for latent heat storage; the heating subsystem 3 is used to introduce the heated crude oil, and make the heated crude oil absorb the heat released by the first phase change heat storage tank 21 and the second phase change heat storage tank 22 in sequence, so as to raise the temperature of the heated crude oil in stages.

[0015] Specifically, the solar collector subsystem 1 is responsible for capturing and initially converting the thermal energy at the bottom layer of the system. Under operating conditions, the solar collector subsystem 1 absorbs solar radiation through solar collectors exposed to the external environment, converts light energy into physical thermal energy of the internal circulating medium, and continuously or intermittently supplies the fluid carrying the thermal energy to the two-phase change cascade thermal storage subsystem 2.

[0016] The dual-phase change cascade thermal storage subsystem 2 constitutes the core of energy buffering and grade classification. Physically, this subsystem includes a first phase change thermal storage tank 21 and a second phase change thermal storage tank 22 arranged in parallel pipelines. To meet the physical requirements of continuous heating of crude oil from low to high temperatures, the inherent phase change temperature of the medium loaded inside the second phase change thermal storage tank 22 is strictly higher than the inherent phase change temperature of the medium loaded inside the first phase change thermal storage tank 21.

[0017] The flow control subsystem 4 is responsible for optimizing the addressing and allocation of the heat storage path. The flow control subsystem 4 is equipped with temperature sensing components and a computing unit. During real-time heat collection operation, the flow control subsystem 4 acquires the heat collection temperature of the fluid output from the heat collection subsystem 1 in real time through the sensing components, and simultaneously acquires the heat storage temperature of the internal material of the first phase change heat storage tank 21. The computing unit within the flow control subsystem 4 establishes a corresponding dynamic comparison criterion based on the acquired heat collection temperature and the heat storage temperature. According to the dynamic comparison criterion, the flow control subsystem 4 outputs an electrical control signal to switch the fluid conduction path on the fluid pipeline, selectively forcing the heat energy into the first phase change heat storage tank 21 or the second phase change heat storage tank 22 for latent heat storage.

[0018] In the specific workflow of this embodiment: when solar radiation is limited or during the early morning or late evening, resulting in a low heat collection temperature (i.e., only possessing medium-to-low grade thermal energy), but the heat collection temperature is still higher than the thermal storage temperature of the first phase change thermal storage tank 21, the flow control subsystem 4 unidirectionally opens the flow path to the first phase change thermal storage tank 21 to preferentially capture easily dissipated low-grade solar energy; when the high radiation period such as noon arrives, the heat collection temperature rises, and the material in the first phase change thermal storage tank 21 reaches the saturation capacity limit due to heat absorption, the flow control subsystem 4 triggers a pipeline switching action, unidirectionally opening the flow path to the second phase change thermal storage tank 22 to perform constant-temperature latent heat storage of high-grade thermal energy.

[0019] The heating subsystem 3 constitutes the final energy consumption and release stage. The first end of the pipeline of the heating subsystem 3 introduces crude oil at a low temperature. As it flows through the heat release zone of this system, the heating subsystem 3 guides the crude oil along a predetermined unidirectional flow path, sequentially passing through the heat release side of the first phase change heat storage tank 21 and the heat release side of the second phase change heat storage tank 22. Through this series flow path design, the crude oil first absorbs the medium-low temperature heat released by the first phase change heat storage tank 21 to complete basic preheating, and then seamlessly transitions to the next stage, absorbing the high temperature heat released by the second phase change heat storage tank 22 to complete the final process heating. This sequential heat absorption process achieves efficient, stepped heating of the crude oil, greatly reducing irreversible exergy losses caused by single-stage centralized heat exchange.

[0020] Furthermore, this embodiment provides a solar collector subsystem 1, which absorbs solar radiation from the external environment and directionally delivers thermal energy to a two-phase change cascade thermal storage subsystem 2. In terms of physical connection architecture, this embodiment defines the solar collector subsystem 1 as including a vacuum tube solar collector array, a collector-side circulation pump, a primary heat exchanger, and a main heat collection output pipe. The heat medium outlet of the vacuum tube solar collector array and the fluid inlet of the collector-side circulation pump are fluidly connected through a rigid insulated pipeline wrapped with polyurethane foam material. The fluid outlet of the collector-side circulation pump is physically connected to the hot end inlet of the primary heat exchanger under pressure. The hot end outlet of the primary heat exchanger is directly connected back to the cold medium inlet of the vacuum tube solar collector array, thereby constructing a sealed closed-loop solar collector circuit in physical space. The closed-loop solar collector circuit is defined as a closed flow path in which the working fluid circulates only internally without physical mixing with the external medium. The cold end outlet of the primary heat exchanger is directly connected to the main heat collection output pipe, making the main heat collection output pipe the sole physical channel for receiving and discharging the thermal energy.

[0021] During the energy capture phase, the vacuum tube solar collector array in this embodiment continuously absorbs full-spectrum solar radiation through its aluminum-nitrogen-aluminum composite absorbing coating, converting the radiant energy into the sensible heat of the heat-collecting medium flowing inside. This embodiment specifies the heat-collecting medium as a 50% (v / v) ethylene glycol aqueous solution. This medium possesses high specific heat capacity, an extremely low freezing point, and a high boiling point, ensuring the system is protected against freezing and cracking in the harsh winter conditions of the oilfield and against boiling and gas lock in the high-radiation summer conditions. As the heat-collecting medium flows through the vacuum collector tubes inside the vacuum tube solar collector array, it absorbs heat passing through the vacuum interlayer, resulting in forced heating and forming a high-temperature fluid carrying high-grade heat energy. This fluid continuously flows out from the heat medium outlet of the vacuum tube solar collector array, realizing the primary form conversion of solar radiation into physical heat energy.

[0022] To maintain continuous unidirectional flow of the fluid within the closed-loop heat collection circuit, this embodiment configures the heat collection-side circulation pump to provide a forced physical driving force to overcome pipeline resistance. This embodiment performs a data processing procedure based on temperature difference comparison logic for starting and stopping the heat collection-side circulation pump. The temperature parameters involved in this data processing are derived from the outlet temperature of the heat collection fluid and the actual temperature of the heat storage medium. The outlet temperature of the heat collection fluid is collected in real-time by a sheathed thermocouple inserted at the outlet of the heat storage medium, while the actual temperature of the heat storage medium is collected in real-time by a longitudinal multi-point temperature probe array penetrating the interior of the dual-phase change cascade heat storage subsystem 2. The arithmetic mean of the longitudinally measured points is used as the final data input for the actual temperature of the heat storage medium to eliminate thermal stratification errors within the phase change container. The industrial programmable logic controller receives the above analog signals and performs difference calculations after processing by the analog-to-digital converter module: when the difference between the outlet temperature of the heat collector fluid and the physical temperature of the heat storage medium is greater than or equal to the set start-up temperature difference threshold, a high-level start signal is generated to trigger the operation of the heat collector-side circulation pump. In this embodiment, the start-up temperature difference threshold is strictly fixed at eight degrees Celsius. This value is derived from the inherent thermal inertia of the fluid inside the long-distance cold pipe network during the initial start-up phase. When the difference between the above two temperature parameters decays and is less than or equal to the set stop temperature difference threshold, a low-level stop signal is generated to trigger the stop operation of the heat collector-side circulation pump. In this embodiment, the stop temperature difference threshold is strictly fixed at two degrees Celsius. This value is derived from the static heat leakage rate of the pipe network insulation layer and is used to prevent reverse heat dissipation from the heat storage tank to the external environment during low radiation periods.

[0023] In the heat transfer process, this embodiment utilizes the primary heat exchanger to perform cross-loop energy transfer. The primary heat exchanger is internally equipped with herringbone corrugated heat transfer plates sealed and fixed by copper brazing, which strictly isolate the internally flowing primary heat-absorbing medium (i.e., the aforementioned ethylene glycol aqueous solution) from the externally introduced secondary heat-conducting medium (i.e., the water medium used to transport heat energy to the storage tank). In this embodiment, the high-temperature heat-collecting medium and the low-temperature heat-storing medium undergo countercurrent heat exchange in the corrugated microchannels isolated within the primary heat exchanger. After releasing sensible heat, the heat-collecting medium returns through the hot-end outlet, completing its own cooling; the heat-storing medium absorbs the heat energy conducted through the isolation plates, causing its temperature to rise, and then overflows from the cold-end outlet of the primary heat exchanger. This achieves massless heat transfer across the physical isolation barrier, fundamentally eliminating the risk of antifreeze leakage contaminating the subsequent pure heat storage medium.

[0024] After completing the heat transfer across the loop, this embodiment configures the heat collection output manifold to complete the final directional physical migration of thermal energy. The heat collection output manifold receives the heated storage medium flowing out of the primary heat exchanger and forces the fluid carrying the thermal energy to be transported unidirectionally to the two-phase change cascade thermal energy storage subsystem 2. The heat collection output manifold is equipped with a mechanical spring-pressed one-way valve that opens based on the forward pressure difference of the fluid. This physical structure compresses the spring to achieve conduction under the push of the forward water flow, and at the moment the pump stops, the spring rebound force strictly blocks any reverse flow of liquid working medium, ensuring that all and only the high-grade thermal energy produced by the primary heat exchanger is injected into the subsequent thermal storage node. This embodiment, with this complete thermophysical transfer chain and coordinated control process, fully realizes the engineering technical objective of the heat collection subsystem 1 to efficiently absorb and stably transport thermal energy.

[0025] Furthermore, this embodiment provides a flow control subsystem 4, whose hardware topology and spatial connection relationship constitute the physical execution basis for thermal energy addressing and allocation. The flow control subsystem 4 of this embodiment includes a heat collector temperature sensor, a heat storage temperature sensor, a logic control unit, and a flow diversion control valve group. In terms of assembly structure, this embodiment radially inserts the probe end of the heat collector temperature sensor into the fluid output pipeline of the heat collector subsystem 1, with its physical insertion depth strictly set to half the inner diameter of the fluid pipeline, to penetrate the thermal boundary layer of the pipe wall and accurately obtain the true heat of the fluid in the central layer of the pipeline; simultaneously, this embodiment inserts the probe end of the heat storage temperature sensor through and into the solid inner cavity of the first phase change heat storage tank 21. The command issuing end of the logic control unit is electrically connected to the controlled execution end of the flow diversion control valve group. In this embodiment, the flow diversion control valve group is defined as a Y-type electric three-way proportional directional valve with valve position feedback. This directional valve is connected in series at the junction of the main trunk and the two branches of the fluid pipeline to achieve precise cutoff and reversal of the physical flow path.

[0026] In the data sensing and analysis phase, this embodiment utilizes the aforementioned physical probes to collect basic environmental variables. The collector temperature sensor is used to detect the thermodynamic state of the primary working fluid flowing through the pipeline in real time and convert it into an analog voltage signal for transmission back. This signal is defined as the collector temperature in the data stream of this embodiment. The storage temperature sensor is used to detect the real-time heat within the first phase change storage tank 21. The signal acquired by this node is defined as the storage temperature. To ensure the anti-interference capability of the control logic, this embodiment sets the sensor data channel to continuously capture the two analog signals at a fixed sampling frequency of 10 times per second. After receiving the analog signals, the logic control unit uses a built-in high-precision analog-to-digital converter to analyze them into discrete digital temperature parameters, completely eliminating electromagnetic noise during long-distance transmission and providing stable underlying data for subsequent algorithm calculations.

[0027] The logic control unit of this embodiment internally includes a data comparison subunit, a basic thermal storage control subunit, and a high-temperature transition control subunit. The data comparison subunit executes the preset algorithm described in the claims. In this embodiment, the preset algorithm is specifically implemented as a difference hysteresis comparison operation with a dead zone. During the physical process of data processing, the data comparison subunit extracts the digital parameters of the heat collection temperature and the thermal storage temperature, performs arithmetic subtraction to obtain the instantaneous temperature difference, and performs a hysteresis comparison with the reference dead zone value locked at the system's bottom layer. The expression for the instantaneous temperature difference is: ; in, This represents the instantaneous temperature difference. The heat collection temperature; The static heat loss rate per unit length of the fluid output pipeline; This is the equivalent physical length of the fluid output pipeline; The specific heat capacity at constant pressure of the primary working fluid flowing through the pipeline; This refers to the real-time mass flow rate of the primary working fluid. This represents the total number of probes in the longitudinal multi-point temperature probe array. For the first i Local entity temperature collected by a probe.

[0028] In this embodiment, the reference dead zone value is strictly set to 2 degrees Celsius. Its physical function is to offset the static heat leakage of the pipeline network environment and prevent mechanical oscillation of the downstream three-way reversing valve when the difference fluctuates near zero. After the data comparison subunit completes the above difference hysteresis comparison, it outputs the corresponding dynamic comparison criterion. This dynamic comparison criterion is essentially a set of digital control matrices containing positive and negative polarity flags and Boolean logic high and low levels.

[0029] In this embodiment, the basic thermal storage control subunit performs the logical decision-making function of prioritizing the capture of low-grade thermal energy. When the value of the collecting temperature, as indicated by the dynamic comparison criterion, is greater than the value of the storage temperature, and the absolute value of the storage temperature has not reached the preset capacity threshold, the basic thermal storage control subunit generates a first electrical command. In this embodiment, the preset capacity threshold is defined as the physical inflection point temperature at which the phase change material inside the first phase change thermal storage tank 21 completes the solid-liquid phase change, the latent heat storage plateau period ends, and it re-enters the sensible heat heating stage; in this embodiment, the absolute value of the preset capacity threshold is fixed at 65 degrees Celsius. The first electrical command, as a 24-volt DC constant voltage drive signal, is directly fed into the electromagnetic coil of the Y-type electric three-way proportional directional valve, driving the pilot valve core to undergo mechanical displacement, unidirectionally opening the fluid conduction path to the first phase change thermal storage tank 21, forcing all primary thermal energy to flow into the first phase change thermal storage tank 21 to perform basic latent heat storage.

[0030] In this embodiment, the high-temperature transition control subunit performs the logical decision-making function for the cross-stage transfer of high-grade thermal energy. When the dynamic comparison criterion indicates that the heat storage temperature reaches the preset capacity threshold of 65 degrees Celsius, and the heat collection temperature meets the high-temperature heat storage conditions, the high-temperature transition control subunit outputs a second electrical command. In this embodiment, the high-temperature heat storage conditions are strictly defined as follows: the absolute value of the heat collection temperature must be greater than or equal to the sum of the phase change point temperature of the second phase change heat storage tank 22 and the physical heat exchange driving temperature difference. In this embodiment, the phase change point of the second phase change heat storage tank 22 is fixed at 85 degrees Celsius, and the physical heat exchange driving temperature difference is set to 3 degrees Celsius, that is, the condition can only be triggered when the heat collection temperature is not lower than 88 degrees Celsius. Among them, the theoretical calculation expression of the physical heat exchange driving temperature difference (explained from the bottom of heat transfer) The theoretical basis for driving temperature differences.

[0031] ; in, Temperature difference driven by physical heat exchange; The rated stepped heat release power of the second phase change heat storage tank 22; The total area of ​​the solid-liquid phase heat exchange interface of the phase change material encapsulation tube bundle; The convective heat transfer coefficient of the internal thermal fluid; This refers to the wall thickness of the stainless steel seamless pipe. The thermal conductivity of stainless steel seamless pipe; The dominant heat transfer equivalent thickness of the solidified layer of the phase change material; The overall thermal conductivity of organic paraffin-based phase change materials.

[0032] The second electrical command triggers the Y-type electric three-way proportional directional valve to complete its mechanical rotation within 3 seconds, cutting off the passage to the first phase change heat storage tank 21 and unidirectionally opening the fluid flow path to the second phase change heat storage tank 22. This physical action precisely cuts off the low-grade thermal resistance circulation, guiding the qualified high-temperature fluid directly into the second phase change heat storage tank 22, thus realizing the system's cascade latent heat storage purpose.

[0033] Furthermore, this embodiment provides a heating subsystem 3, whose physical pipeline topology constitutes the execution carrier for the cascade heating of the heated crude oil. This embodiment defines the heating subsystem 3 as including a crude oil inlet manifold, a primary heating heat exchanger, a secondary heating heat exchanger, and a backup auxiliary heating furnace. In terms of fluid assembly, this embodiment establishes a rigid connection between the fluid output end of the crude oil inlet manifold and the cold-side input end of the primary heating heat exchanger via a seamless carbon steel pressure-bearing pipeline; the cold-side output end of the primary heating heat exchanger is connected in series with the cold-side input end of the secondary heating heat exchanger; the cold-side output end of the secondary heating heat exchanger is connected to the fluid input end of the backup auxiliary heating furnace, and finally, the fluid output end of the backup auxiliary heating furnace is connected to the downstream export trunk line. This physical series structure restricts the heated crude oil to sequentially traverse each heat exchange node in a single downstream direction, strictly prohibiting reverse flow or bypass, thereby locking the physical sequence of cascade heating in the spatial path.

[0034] In the initial introduction phase of the heating operation, this embodiment configures the crude oil inlet manifold to extract and buffer the low-temperature crude oil to be heated from the upstream pipeline network. The crude oil inlet manifold, as defined in this embodiment, is internally fitted with a labyrinthine pressure-stabilizing baffle and a stainless steel porous filter screen. These physical structures are used to eliminate pressure pulsations in the upstream fluid and filter out mechanical impurities, ensuring the uniformity of the flow field in the cold-side channel of the heat exchanger. This embodiment limits the initial temperature parameters of the introduced crude oil to a cold state range of 25°C to 30°C. Driven by a rated pipeline transport pressure of 1.5 MPa, the crude oil inlet manifold forces the cold-state crude oil to be heated into the cold-side channel of the primary heating heat exchanger at a constant mass flow rate. This 1.5 MPa pressure value is derived from the standard wellhead back pressure of the oilfield gathering and transportation pipeline network, providing a realistic basis for fluid transport dynamics.

[0035] In the basic preheating stage, this embodiment utilizes the primary heating heat exchanger to perform the transfer of primary heat energy. This embodiment defines the primary heating heat exchanger as a shell-and-tube heat exchanger with an expanded diameter design. This expanded diameter structure aims to provide a large flow cross-section, its physical function being to offset the significant frictional resistance loss caused by the extremely high kinematic viscosity of the 25°C cold crude oil. The hot-side input end of the primary heating heat exchanger receives the latent heat fluid released from the first phase change heat storage tank 21. In this physical heat exchange interface, the fluid carrying medium-to-low grade heat energy releases latent heat of phase change, penetrating the heat transfer tube wall to transfer heat to the cold-side flowing crude oil being heated. After absorbing the primary heat, the oil temperature of the heated crude oil rises from the initial 25°C to 55°C. This temperature rise precisely consumes the latent heat released by the medium-temperature phase change material with a reference physical phase change temperature of 60°C within the first phase change heat storage tank 21, completing the first-stage basic preheating.

[0036] In the high-temperature stepped heating stage, this embodiment utilizes the secondary heating heat exchanger to perform a high-grade thermal energy boosting. The crude oil, after being preheated in the first stage, experiences a significant decrease in viscosity and flows smoothly into the cold-side channel of the secondary heating heat exchanger. Simultaneously, the hot side of the secondary heating heat exchanger introduces high-temperature latent heat fluid released from the second phase change heat storage tank 22. Since the reference phase change point of the medium in the second phase change heat storage tank 22 is set at 85 degrees Celsius, this embodiment utilizes the physical heat transfer temperature difference established on both sides of the heat exchanger to drive the transfer of high-temperature thermal energy to the preheated crude oil. During this stepped heat transfer process, the crude oil continuously absorbs heat, and its temperature further jumps from 55 degrees Celsius to 80 degrees Celsius. This physical process achieves a high-level temperature increase of the crude oil, thoroughly injecting the solar energy of different temperature scales stored in the two-phase change tank into the crude oil in stages, thus performing the second-stage high-temperature heating action.

[0037] During the terminal supplementary heating and process assurance phase, this embodiment configures the backup auxiliary heating furnace and independently configures a microprocessor-based burner controller. In this embodiment, a sheathed thermal resistor is inserted at the cold-side output end of the secondary heating heat exchanger to obtain the actual outlet temperature of the heated crude oil after flowing out of the heat exchange network in real time. The burner controller receives this actual outlet temperature and performs a digital subtraction operation: subtracting the actual outlet temperature from the system's built-in process target temperature (the absolute value is fixed at 85 degrees Celsius) to extract the heating gap value. When the calculated heating gap value is greater than 0 degrees Celsius and exceeds the system dead zone tolerance of 1 degree Celsius, the burner controller determines that there is a gap in solar heat release and then generates a linear mapping adjustment command, which is sent to the natural gas proportional control valve of the backup auxiliary heating furnace. This embodiment strictly locks the control boundary of the linear mapping adjustment command: a 0°C temperature rise gap corresponds to 0% initial closing opening of the natural gas proportional control valve, and a temperature rise gap of 5°C or higher corresponds to 100% full-load absolute opening of the natural gas proportional control valve. When the gap is between 0 and 5°C, the command drives the valve opening to follow proportionally. When the recalculated temperature rise gap value drops to 0°C or below, the burner controller outputs a zero-level cutoff command to forcibly close the proportional valve, thus ensuring that the oil outlet temperature meets the stringent requirements through this closed-loop mechanism. The formula for the linear mapping adjustment command of the target opening of the natural gas proportional control valve is as follows: ; in, The target valve opening for the natural gas proportional control valve; This is the temperature rise gap value, which is the arithmetic difference between the process target temperature and the actual liquid outlet temperature. The lower limit of the allowable deviation set for the system, i.e., the dead zone tolerance; The upper limit of the notch threshold for triggering the full-load absolute opening of the proportional control valve.

[0038] Furthermore, this embodiment provides a dual-phase change cascade thermal energy storage subsystem 2, which constitutes the core physical support network for the independent buffering and orderly release of high and low grade thermal energy within the system. In terms of physical network architecture, this embodiment defines the dual-phase change cascade thermal energy storage subsystem 2 as including a first phase change thermal storage tank 21, a second phase change thermal storage tank 22, a heat release manifold network, and a return flow merging valve group. In the fluid interconnection, the heat release interfaces of the first phase change thermal storage tank 21 and the second phase change thermal storage tank 22 are respectively connected to the two inlet branch pipe systems of the heat release manifold network via flange seals. This embodiment defines the inlet branch pipe system as a parallel, equal-resistance symmetrical pipe network structure to utilize the physical geometric symmetry to forcibly balance the hydraulic pressure drop at both ends, fundamentally eliminating fluid flow deviation. The cooling return interfaces of both the first phase change thermal storage tank 21 and the second phase change thermal storage tank 22 are connected to the fluid input side of the return flow merging valve group. The physical flow path of this parallel structure achieves absolute hydraulic isolation between the two tanks, ensuring that the two tanks perform latent heat storage independently and with complementary temperature scales; the reflux merging valve group merges the cooling fluid after the heat release action and refluxes back, strictly maintaining the mass conservation of the circulating working fluid inside the system.

[0039] To ensure efficient throughput of latent heat of phase change and mitigate phase change expansion stress, this embodiment strictly defines the internal physical hardware topology of the first phase change heat storage tank 21. The internal components of the first phase change heat storage tank 21 include a pressure-bearing support shell, an internal fluid distributor, a phase change material encapsulation tube bundle, and a bottom fluid collector. The pressure-bearing support shell is made of 12 mm thick boiler-grade carbon steel plate, rolled and welded. The internal fluid distributor is fixedly suspended at the top of the cavity. The phase change material encapsulation tube bundle consists of 300 seamless stainless steel tubes with an outer diameter of 25 mm, arranged in a vertical array within the cavity. Considering the physical expansion characteristics of the phase change medium, this embodiment reserves a nitrogen buffer volume, accounting for 15% of the total cavity volume, at the top of each phase change material encapsulation tube bundle. This buffer volume utilizes the high compressibility of nitrogen to flexibly absorb the severe volume expansion of the medium during the solid-liquid phase change process, completely avoiding the risk of stress-induced cracking of the encapsulation tubes.

[0040] Within this three-dimensional hardware topology, this embodiment endows each internal component with a clearly defined flow field control function. The pressure-bearing support shell defines an absolutely closed physical boundary for heat storage and withstands a pipe network rated hydrostatic pressure of up to 1.0 MPa. The internal fluid distributor has 60 radially arranged micropores that completely disperse the high-pressure-introduced heat energy fluid jet and evenly distribute it across the entire cross-section of the lower cavity, eliminating localized thermal stress concentration and fluid short-circuiting. The phase change material encapsulated tube bundle provides a sealed isolation of the internal phase change medium, and its exposed outer surface provides a solid-liquid phase heat exchange interface of up to 45 square meters for the flowing heat carrier fluid. The bottom fluid collector, through an inverted conical funnel structure, collects the fluid that has completely flushed the tube bundle and forms a vortex at the narrow opening to force the flow to the cooling return interface.

[0041] This embodiment rigidly anchors the physicochemical parameters of the core medium performing phase change heat storage within the first phase change heat storage tank 21. This embodiment limits the loaded medium to an inorganic hydrated salt phase change material, specifically using magnesium chloride hexahydrate at 97% by mass, rigidly blended with 2% strontium chloride hexahydrate as a nucleation accelerator, and 1% carboxymethyl cellulose as a skeleton thickener. The introduction of this composite formulation completely eliminates the fatal defects of supercooling and phase separation that are prone to occur in hydrated salts through isomorphic substitution physical mechanisms. This embodiment locks the reference physical phase change temperature of the composite material at 60 degrees Celsius, precisely matching the endothermic boundary of the process section from 25 degrees Celsius room temperature preheating of cold crude oil to 55 degrees Celsius. Under heat release conditions, the material continuously releases 180 kJ of latent heat of crystallization per kilogram on a constant temperature platform of 60 degrees Celsius, maintaining a stable temperature of the heat release outlet water.

[0042] Collaboratively, this embodiment performs high-level parameter deployment and thermophysical property enhancement across temperature scales on the heat storage medium of the second phase change heat storage tank 22. This embodiment limits the loaded medium to an organic paraffin-based phase change material, specifically using a multi-component mixed microcrystalline wax with a carbon chain length of 28 to 32, and blending it with 5% nano-expanded graphite by mass. Since pure paraffin has extremely low thermal conductivity, the addition of nano-expanded graphite constructs a three-dimensional high thermal conductivity network within the paraffin, exponentially increasing its overall thermal conductivity and ensuring a high-frequency melting and solidification response of the medium in the central region of the tube bundle. The expression for the overall thermal conductivity of the organic composite paraffin after adding nano-expanded graphite is: ; in, The overall thermal conductivity of organic composite paraffin; The background thermal conductivity is that of pure multi-component mixed microcrystalline wax; The intrinsic thermal conductivity of the expanded graphite nanoparticles; In this embodiment, the reference physical phase transition temperature of the organic composite paraffin is strictly set to 85 degrees Celsius, directly aligning with the target temperature for final viscosity reduction during delivery. During the actual heat exchange process, when preheated crude oil is introduced, the medium solidifies within its 85-degree Celsius phase transition isothermal zone, using a high-density latent heat of 210 kJ per kilogram to offset the high-temperature heating load of the crude oil, perfectly establishing a stepped exothermic response surface that coincides with the nonlinear endothermic curve.

[0043] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0044] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A solar dual-phase variable cascade thermal storage system for continuous heat load scenarios in oilfields, characterized in that, include: The system includes a heat collection subsystem, a two-phase change cascade thermal storage subsystem, a heating subsystem, and a flow control subsystem. The heat output terminal of the heat collection subsystem is connected to the heat input terminal of the two-phase change cascade thermal storage subsystem; the heat release terminal of the two-phase change cascade thermal storage subsystem is connected to the heating subsystem; wherein, the two-phase change cascade thermal storage subsystem includes a first phase change thermal storage tank and a second phase change thermal storage tank arranged in parallel, and the phase change temperature of the second phase change thermal storage tank is higher than that of the first phase change thermal storage tank; the flow control subsystem is located on the fluid pipeline between the heat collection subsystem and the two-phase change cascade thermal storage subsystem; The solar collector subsystem is used to absorb solar radiation and supply thermal energy to the dual-phase change cascade thermal storage subsystem; the flow control subsystem is used to obtain the solar collector temperature of the solar collector subsystem and the thermal storage temperature in the first phase change thermal storage tank, and switch the fluid conduction path based on the dynamic comparison criterion of the solar collector temperature and the thermal storage temperature, so as to selectively introduce the thermal energy into the first phase change thermal storage tank or the second phase change thermal storage tank for latent heat storage; the heating subsystem is used to introduce the heated crude oil, and make the heated crude oil absorb the heat released by the first phase change thermal storage tank and the second phase change thermal storage tank in sequence, so as to raise the temperature of the heated crude oil in stages.

2. The solar dual-phase change cascade thermal storage system under continuous heat load in an oilfield as described in claim 1, characterized in that, The solar collector subsystem includes: Vacuum tube heat collection array, heat collection side circulation pump, primary heat exchanger and heat collection output main pipe; The heat medium outlet of the vacuum tube heat collector array is connected to the fluid inlet of the heat collector-side circulation pump; the fluid outlet of the heat collector-side circulation pump is connected to the hot end inlet of the primary heat exchanger; the hot end outlet of the primary heat exchanger is connected to the cold medium inlet of the vacuum tube heat collector array to form a closed-loop heat collection circuit; the cold end outlet of the primary heat exchanger is connected to the heat collection output main pipe, and the heat collection output main pipe constitutes the heat energy output end. The vacuum tube heat collection array is used to absorb solar radiation and generate a heat medium; the heat collection side circulation pump is used to provide physical driving force for the flow of the medium in the closed-loop heat collection circuit; the primary heat exchanger is used to isolate the heat collection medium and the heat storage medium and perform heat transfer across the circuit; the heat collection output manifold is used to unidirectionally transport the fluid carrying the heat energy to the two-phase change cascade heat storage subsystem.

3. The solar dual-phase change cascade thermal storage system under continuous heat load in an oilfield as described in claim 1, characterized in that, The flow control subsystem includes: The heat collection temperature sensor, the heat storage temperature sensor, the logic control unit, and the diversion control valve assembly; The probe end of the heat collection temperature sensor is inserted into the fluid output pipeline of the heat collection subsystem; the probe end of the heat storage temperature sensor is inserted into the solid inner cavity of the first phase change heat storage tank; the signal output ends of the heat collection temperature sensor and the heat storage temperature sensor are both electrically connected to the signal receiving end of the logic control unit; the command issuing end of the logic control unit is electrically connected to the controlled execution end of the diversion control valve group; the diversion control valve group is connected in series at the node of the fluid pipeline. The heat collection temperature sensor is used to detect and transmit the heat collection temperature in real time; the heat storage temperature sensor is used to detect and transmit the heat storage temperature in real time; the logic control unit is used to receive sensor signals and compare them according to a preset algorithm to obtain the dynamic comparison criterion; the diversion control valve group is used to physically cut off or open the fluid conduction path.

4. The solar dual-phase change cascade thermal storage system under continuous heat load in an oilfield as described in claim 3, characterized in that, The logic control unit includes: Data comparison subunit, basic thermal storage control subunit, and high-temperature transition control subunit; The data stream output terminal of the data comparison subunit is connected to the instruction trigger terminal of the basic thermal storage control subunit and the instruction trigger terminal of the high temperature transition control subunit, respectively. The data comparison subunit is used to calculate the numerical relationship between the heat collection temperature and the heat storage temperature in real time, and continuously output the dynamic comparison criterion to the subsequent stage; the basic heat storage control subunit is used to obtain a first electrical command when the dynamic comparison criterion indicates that the heat collection temperature is higher than the heat storage temperature and the heat storage temperature has not reached the preset capacity threshold, so as to drive the diversion control valve group to unidirectionally open the fluid conduction path of the first phase change heat storage tank; the high temperature transition control subunit is used to obtain a second electrical command when the dynamic comparison criterion indicates that the heat storage temperature has reached the preset capacity threshold and the heat collection temperature meets the high temperature heat storage conditions, so as to drive the diversion control valve group to switch action, cut off the first passage and unidirectionally open the fluid conduction path to the second phase change heat storage tank, and perform the latent heat storage.

5. A solar dual-phase variable cascade thermal storage system for continuous heat load scenarios in oilfields according to claim 1, characterized in that, The heating subsystem includes: Crude oil inlet manifold, primary heating heat exchanger, secondary heating heat exchanger and backup auxiliary heating furnace; The fluid output end of the crude oil inlet manifold is connected to the cold side input end of the primary heating heat exchanger; the cold side output end of the primary heating heat exchanger is connected to the cold side input end of the secondary heating heat exchanger; and the cold side output end of the secondary heating heat exchanger is connected to the fluid input end of the backup auxiliary heating furnace. The crude oil inlet manifold is used to introduce the low-temperature crude oil to be heated from the upstream pipeline network; the primary heating heat exchanger is used to transfer the latent heat released by the first phase change heat storage tank to the crude oil to be heated, performing the first-stage basic preheating; the secondary heating heat exchanger is used to transfer the latent heat released by the second phase change heat storage tank to the preheated crude oil to be heated, performing the second-stage high-temperature heating; the backup auxiliary heating furnace is used to provide fossil fuel thermal energy supplement to the crude oil to be heated that flows out of the secondary heating heat exchanger and has not reached the process target temperature, so as to force the completion of the stepped heating.

6. The solar dual-phase change cascade thermal storage system under continuous heat load in an oilfield as described in claim 1, characterized in that, The two-phase variable cascade thermal storage subsystem includes: The first phase change heat storage tank, the second phase change heat storage tank, the heat release manifold network, and the return flow valve assembly; The heat release ports of the first phase change heat storage tank and the second phase change heat storage tank are respectively connected to the two inlet branch pipe systems of the heat release manifold network; the total outlet of the heat release manifold network is connected to the heating subsystem; the cooling return ports of the first phase change heat storage tank and the second phase change heat storage tank are both connected to the fluid input side of the return flow merging valve group. Both the first phase change thermal storage tank and the second phase change thermal storage tank are used to achieve independent and complementary latent heat storage through a parallel physical flow path; the heat release manifold network is used to centrally and physically export the latent heat fluid extracted from the two tanks; the reflux merging valve group is used to merge and guide the cooling fluid after the heat release action is completed to maintain the working fluid conservation inside the dual phase change cascade thermal storage subsystem.

7. A solar dual-phase variable cascade thermal storage system for continuous heat load scenarios in oilfields according to claim 6, characterized in that, The first phase change heat storage tank includes: Pressure-bearing support shell, internal fluid distributor, phase change material encapsulated tubing bundle, and bottom fluid collector; The internal fluid distributor is fixedly suspended at the top of the inner cavity of the pressure-bearing support shell; the bottom fluid collector is fixedly connected to the bottom of the inner cavity of the pressure-bearing support shell; the phase change material encapsulation tube bundle is arranged in a vertical array in the cavity between the internal fluid distributor and the bottom fluid collector. The pressure-bearing support shell is used to define the closed physical boundary of the heat storage and withstand the operating pressure of the pipeline system; the internal fluid distributor is used to disperse the introduced thermal energy fluid and evenly distribute it on the cross-section of the cavity; the phase change material encapsulated tube bundle is used to seal and isolate the phase change medium and provide a solid-liquid phase heat exchange interface with a large specific surface area; the bottom fluid collector is used to collect the fluid that completely overflows the phase change material encapsulated tube bundle and force it to flow to the cooling return interface.

8. A solar dual-phase variable cascade thermal storage system for continuous heat load scenarios in oilfields according to claim 7, characterized in that, The phase change medium encapsulated in the first phase change heat storage tank is an inorganic hydrated salt phase change material, wherein the reference physical phase change temperature is 60°C.

9. A solar dual-phase change cascade thermal storage system for continuous heat load scenarios in oilfields according to claim 8, characterized in that, The phase change medium encapsulated in the second phase change heat storage tank is an organic paraffin-based phase change material, wherein the reference physical phase change temperature is set at 85°C.

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