Low-position heat conduction oil expansion tank system

Abstract

The invention provides a low-position heat-conducting oil expansion tank system. The low-position heat-conducting oil expansion tank system comprises an expansion tank, an inert gas supply unit, a control system and a heat-conducting oil circulation unit, the heat-conducting oil circulating unit comprises a heat-conducting oil tank, heat-conducting oil heating equipment, a heat-conducting oil pump and at least one heat utilization equipment; the heat-conducting oil tank, the heat-conducting oil pump, the heat-conducting oil heating equipment and the heat utilization equipment are communicated through pipelines to form a closed heat-conducting oil circulating loop; the expansion tank is arranged below the conduction oil heating equipment and the heat utilization equipment or is basically positioned in the same height range with the conduction oil heating equipment and the heat utilization equipment; according to the low-position heat conduction oil expansion tank system, the problems that in the related technology, an expansion tank must be arranged at the highest position of the system, and oil supplementing, exhausting and pressure stabilizing functions can be achieved only by means of a liquid column pressure head formed by gravity; and therefore, a series of problems of limited layout, easy oxidation of oil products, high energy consumption, unstable operation, difficult maintenance and the like of the whole heat-conducting oil heat supply system are solved.

Description

Technical Field

[0001] This invention belongs to the field of heat transfer oil heating technology, and in particular relates to a low-level heat transfer oil expansion tank system. Background Technology

[0002] In thermal oil heating systems, the expansion tank is a key component for achieving thermal oil volume compensation, venting, replenishment, and system pressure stabilization. Its conventional arrangement usually relies on the static pressure head formed by gravity to complete the functions of replenishment, return, and venting. Therefore, the industry generally installs the expansion tank at the highest position of the system. According to GB / T 38450-2020 "Safety Technical Specification for Organic Heat Carrier Heating Systems", the lowest liquid level of the expansion tank should be 1.5 to 2.0 meters higher than the highest point of the system to ensure that the system still has sufficient liquid column pressure head and normal circulation path under complex operating conditions such as heating, pump shutdown, or gas evolution. However, in modern industrial plants, due to the compact equipment layout, limited floor height, and increasingly large thermal systems, the traditional "high-level layout - gravity pressure head" approach has gradually revealed more limitations in engineering practice. In particular, when multiple dispersed thermal oil furnaces are running simultaneously, it is difficult to form a unified pressure reference between the independent expansion tanks, and the high-level pipelines are complex and difficult to maintain, making it difficult to meet the requirements of smart factories, high-density equipment areas, and other scenarios for system flexibility, safety, and maintainability.

[0003] As heat transfer oil systems develop towards larger scale, centralization, and parallel operation of multiple furnaces, traditional high-level expansion tanks, which must be maintained above the highest point of the system to establish an effective liquid column head, suffer from limited system layout flexibility, reduced plant space utilization, and high installation and maintenance costs. In actual operation, the inability of multiple system points to share a unified pressure reference can easily lead to problems such as uneven pressure, air blockage, and unstable circulation. At the same time, the high-level expansion tanks are mostly open or semi-open in structure, with direct or indirect contact with air, making the high-temperature heat transfer oil more prone to oxidation, deterioration, coking, and carbon buildup during long-term operation, thereby affecting heat transfer efficiency and shortening the service life of the oil. In addition, the long-distance return / replenishment oil pipelines arranged at high levels introduce significant frictional and local resistance, significantly increasing the energy consumption of the circulating pump, reducing the overall energy efficiency of the system, and increasing safety hazards due to frequent maintenance work at heights.

[0004] Because the expansion tank in the relevant technology must be located at the highest position of the system and rely on the liquid column pressure head formed by gravity to complete the functions of oil replenishment, venting and pressure stabilization, the entire heat transfer oil heating system suffers from a series of problems such as limited layout, easy oxidation of oil, increased energy consumption, unstable operation and difficult maintenance. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially solve one of the related technical problems.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A low-level heat transfer oil expansion tank system includes an expansion tank, an inert gas supply unit, a control system, and a heat transfer oil circulation unit;

[0008] The heat transfer oil circulation unit includes a heat transfer oil tank, a heat transfer oil heating device, a heat transfer oil pump, and at least one heat-using device. The heat transfer oil tank, the heat transfer oil pump, the heat transfer oil heating device, and the heat-using device are connected by pipelines to form a closed heat transfer oil circulation loop. The outlet of the heat transfer oil pump is connected in sequence to the heat transfer oil heating device and the heat-using device. The outlet of the heat-using device is connected to the heat transfer oil interface of the expansion tank through a return oil pipeline. The expansion tank is connected to the heat transfer oil tank through a bottom heat transfer oil interface.

[0009] The expansion tank is arranged below the heat transfer oil heating equipment and the heat-using equipment or at approximately the same height as them. The expansion tank has a closed structure, and its top is provided with a gas phase interface and connected to the inert gas outlet of the inert gas supply unit through a gas pipeline to form a closed gas phase space isolated from the outside.

[0010] The control system includes a pressure detection device, a temperature detection device, and a controller. The pressure detection device is used to detect the pressure of the gas phase space in the expansion tank, and the temperature detection device is used to detect the temperature of the heat transfer oil in the heat transfer oil circulation loop. The controller is electrically connected to the pressure detection device, the temperature detection device, and the actuator installed on the controllable gas passage connected to the inert gas supply unit and / or the expansion tank.

[0011] The controller is configured to adjust the opening degree of the actuator according to the pressure and temperature changes in the expansion tank, so that the pressure in the gas phase space in the expansion tank is maintained within a preset micro-positive pressure range, and to compensate for the volume change caused by the thermal expansion and contraction of the heat transfer oil.

[0012] Furthermore, the system also includes a gas regulating assembly, which includes a first valve assembly and a second valve assembly;

[0013] The first valve assembly is disposed on the gas pipeline between the inert gas supply unit and the expansion tank. The first valve assembly includes a gas supply component for regulating the inert gas entering the expansion tank and a gas venting component for regulating the inert gas exiting the expansion tank. The controller is configured to output control signals to the gas supply component and the gas venting component.

[0014] The second valve assembly is installed on the connecting pipeline connecting the expansion tank and the heat transfer oil tank. It is used to open when the pressure in the gas phase space in the expansion tank exceeds a set value, so as to introduce the inert gas and / or heat transfer oil in the expansion tank into the heat transfer oil tank to achieve pressure relief.

[0015] Furthermore, the inert gas supply unit includes an inert gas storage container and / or an inert gas generating device. The outlet side of the inert gas supply unit is provided with at least one pressure reducing device and at least one controllable valve component for regulating the pressure and flow rate of the inert gas flowing into the expansion tank.

[0016] Furthermore, the temperature detection device is installed on the outlet pipe section of the heat transfer oil heating equipment and / or the outlet pipe section of the heat-using equipment, and the controller is configured to predict the volume change of the heat transfer oil based on the temperature change rate and adjust the opening of the gas regulating component in advance to reduce system pressure fluctuations.

[0017] Furthermore, the expansion tank is equipped with an anti-vortex structure and / or an anti-foaming structure to mitigate the flow impact and foam formation of the heat transfer oil during drastic volume changes.

[0018] Furthermore, a liquid level detection device is provided on the side wall of the expansion tank to detect the liquid level of the heat transfer oil in the expansion tank and transmit the liquid level signal to the controller.

[0019] Furthermore, the heat transfer oil circulation unit includes multiple branch pipelines connected to the main pipeline, and each branch pipeline is equipped with a pressure balancing component. The controller is configured to adjust the corresponding pressure balancing component according to the pressure detection results of each branch.

[0020] Furthermore, the top of the expansion tank is provided with a safety relief component that automatically opens when the pressure in the gas phase space exceeds the safety set value, in order to provide overpressure protection.

[0021] Furthermore, the control system includes a communication interface and a data processing module. The controller interacts with an external monitoring platform through the communication interface to monitor, record, and analyze the operating status of pressure, temperature, liquid level, and inert gas usage.

[0022] Compared with existing technologies, the low-level heat transfer oil expansion tank system of the present invention has the following advantages:

[0023] 1. By arranging the expansion tank at a height lower than or at the same height as the heat transfer oil heating equipment and heat-using equipment, and setting a sealed gas phase space at the top of the expansion tank connected to the inert gas supply unit, the system no longer relies on the gravity liquid column pressure head formed by the expansion tank installed at the highest point of the system to complete the replenishment and venting of heat transfer oil. Instead, the controllable positive pressure formed by the inert gas compensates for the volume change caused by the thermal expansion and contraction of the heat transfer oil. Thus, stable control of system pressure can still be achieved under low-position arrangement conditions, effectively freeing up space in the upper part of the plant. The expansion tank can be centrally arranged on the equipment floor or near the ground, reducing the amount and cost of high-altitude installation and pipe laying. At the same time, in the case of multiple heat transfer oil heating equipment sharing the same expansion tank, it is convenient to centrally arrange and manage. Maintenance personnel can complete the inspection and maintenance of the expansion tank and related valves and instruments from the ground or low-position platform, reducing the frequency of high-altitude operations and improving overall operational safety and maintenance convenience.

[0024] 2. By incorporating a gas regulation component that includes both gas replenishment and venting parts, and with the control system automatically adjusting the replenishment and discharge of inert gas based on changes in the pressure of the gas phase space in the expansion tank and the temperature of the heat transfer oil, the system can proactively intervene and dynamically buffer when the heat transfer oil rapidly heats up or cools down. This prevents drastic pressure fluctuations due to excessively high or low pressure within a short period. The anti-vortex and defoaming structures inside the expansion tank further weaken the impact flow and foam accumulation of the heat transfer oil during high-flow-rate inflows or sudden changes in operating conditions, resulting in a more stable gas-liquid interface. This facilitates accurate execution of pressure detection and control algorithms. Simultaneously, the expansion tank maintains a positive pressure environment with inert gas, isolating the heat transfer oil from oxygen in the air, significantly inhibiting oxidation reactions under high-temperature conditions, slowing down oil deterioration and coking tendencies, and providing a safe overpressure release path through a pressure relief valve connected to the heat transfer oil tank. This ensures safe system operation while extending the service life of the heat transfer oil and reducing system maintenance frequency and operating costs. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0026] Figure 1 This is a schematic diagram of a low-level heat transfer oil expansion tank system according to an embodiment of the present invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1. Inert gas supply unit; 2. Expansion tank; 3. Control system; 4. Thermal oil tank; 5. Thermal oil pump; 6. Heat-using equipment; 7. Thermal oil heating equipment; 8. Gas regulating assembly; 81. First valve assembly; 82. Second valve assembly. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0030] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] This embodiment provides a low-level thermal oil expansion tank system. Considering the application background of closed-loop thermal oil heating devices, and addressing the limitations of traditional high-level expansion tanks which rely on gravity liquid column pressure for oil replenishment and venting, are restricted by plant height, and are inconvenient to maintain, this system arranges an expansion tank 2 near the equipment floor or ground level. A controllable inert gas pressure space is constructed above the expansion tank 2, and the control system 3 regulates the pressure and temperature. This allows the expansion tank 2 to still achieve volume compensation for thermal expansion and contraction of the thermal oil and stable control of the system pressure even at low levels. This system is suitable for situations where multiple thermal oil heating devices 7 and multiple heat-using devices 6 share the same expansion tank 2, effectively solving problems such as limited plant height, easy oxidation of oil, and difficulty in unified management of multiple furnace systems.

[0034] like Figure 1As shown, the low-level thermal oil expansion tank system of this embodiment includes an expansion tank 2, an inert gas supply unit 1, a control system 3, and a thermal oil circulation unit. The thermal oil circulation unit includes a thermal oil tank 4, a thermal oil pump 5, a thermal oil heating device 7, and at least one heat-using device 6. The thermal oil tank 4, the thermal oil pump 5, the thermal oil heating device 7, and the heat-using device 6 are connected by pipelines to form a closed thermal oil circulation loop. The outlet of the thermal oil pump 5 is sequentially connected to the thermal oil heating device 7 and the heat-using device 6. The outlet of the heat-using device 6 returns to the thermal oil interface of the expansion tank 2 via a return oil pipeline. The bottom of the expansion tank 2 is connected to the heat transfer oil tank 4 through the heat transfer oil interface, so that the expansion tank 2 can receive a part of the heat transfer oil from the system return oil to absorb the volume expansion, and can also replenish or return heat transfer oil to the heat transfer oil tank 4 through the bottom interface, thereby forming a stable liquid phase path with the heat transfer oil circulation loop. In multi-furnace or multi-circuit heat use applications, multiple branch pipelines can be led out from the main pipeline of the heat transfer oil circulation unit. Each branch pipeline is equipped with a pressure balancing component to cooperate with the control system 3 to regulate the pressure of multiple branches, so that each branch can maintain a basically consistent pressure level under different operating conditions.

[0035] The expansion tank 2 is preferably a vertical or horizontal closed container, made entirely of high-temperature and corrosion-resistant metal materials, preferably 316L stainless steel. The inner wall of the expansion tank 2 can be sprayed with a high-temperature resistant ceramic anti-corrosion coating to reduce the tendency of the heat transfer oil to coke during long-term high-temperature operation. The expansion tank 2 is located below the heat transfer oil heating equipment 7 and the heat-using equipment 6, or at approximately the same height as them, with its installation position near the equipment floor or ground level, so that the expansion tank 2 no longer relies on a high-level arrangement to form a liquid column pressure head. The interior of the expansion tank 2 is equipped with an anti-vortex structure along the flow direction of the heat transfer oil, such as several axially arranged baffles or deflectors, to weaken the flow of heat transfer oil at high flow rates. To mitigate the vortex impact during rapid volume changes, a defoaming structure, such as a perforated plate or mesh plate, can be installed near the normal level of the heat transfer oil to break up air bubbles on the surface of the heat transfer oil and stabilize the gas-liquid interface. A level detection device, such as a magnetic level gauge and / or an electronic level sensor, is installed on the side wall of the expansion tank 2 to detect the level of the heat transfer oil in the expansion tank 2 in real time and transmit the level signal to the control system 3. A safety pressure relief component, such as a spring safety valve or a rupture disc, is installed on the top of the expansion tank 2. When the pressure in the gas phase space of the expansion tank 2 exceeds the safety setting value, it will automatically open to discharge some inert gas and / or heat transfer oil to a safe area or the heat transfer oil tank 4, thereby achieving overpressure protection of the system.

[0036] The inert gas supply unit 1 is used to provide a stable source of inert gas to the expansion tank 2. The inert gas supply unit 1 may include an inert gas storage container, such as a high-pressure nitrogen cylinder group or a centralized gas supply main, or an inert gas generating device, such as a pressure swing adsorption nitrogen generator or a membrane separation nitrogen generator. The outlet side of the inert gas supply unit 1 is provided with at least one pressure reducing device and at least one controllable valve component. The pressure reducing device is used to reduce the pressure of the high-pressure inert gas to a positive pressure state that is suitable for forming a slightly higher positive pressure state than atmospheric pressure in the expansion tank 2, such as a positive pressure range that is several kilopascals higher than atmospheric pressure. The controllable valve component is used to finely adjust the flow rate of inert gas to the expansion tank 2 under the control of the control system 3. The system also includes a gas regulating component 8, which includes a first valve component 81 and a second valve component 82. The first valve component 81 is installed on the gas pipeline between the inert gas supply unit 1 and the expansion tank 2. The first valve component 81 can be composed of an electric regulating valve and a controlled-opening vent valve, etc., and is used to regulate the replenishment flow rate of inert gas entering the expansion tank 2 and the vent flow rate discharged from the expansion tank 2. The second valve component 82 is installed on the connecting pipeline connecting the expansion tank 2 and the heat transfer oil tank 4. It can be a high-temperature resistant automatic valve or a pneumatic valve. When the pressure in the gas phase space in the expansion tank 2 exceeds the set value, it automatically opens to introduce the inert gas and / or part of the heat transfer oil entrained in the expansion tank 2 into the heat transfer oil tank 4 to achieve pressure relief, thereby forming a dual pressure relief path for the expansion tank 2.

[0037] The control system 3 is used to detect and comprehensively control operating parameters such as the pressure of the gas phase space, the temperature of the heat transfer oil, and the pressure of multiple branches in the expansion tank 2. The control system 3 includes a pressure detection device, a temperature detection device, a liquid level signal acquisition module, and a controller. The pressure detection device is installed on the pipeline connected to the gas phase space at the top of the expansion tank 2, and is used to detect the pressure of the gas phase space in the expansion tank 2 in real time and transmit the pressure signal to the controller. The temperature detection device is installed on the outlet pipe section of the heat transfer oil heating equipment 7 and / or the outlet pipe section of the heat-using equipment 6, and is used to detect the temperature change of the heat transfer oil at key locations. The controller can be a programmable logic controller or a control unit of a distributed control system. The controller is electrically connected to the pressure detection device, the temperature detection device, and the liquid level detection device through analog or digital signals, and is also connected to the first valve assembly 81, the second valve assembly 82, and the inert gas. The controllable valve component at the outlet of supply unit 1 is electrically connected. The controller has a pre-stored pressure-temperature coordinated control algorithm, which can calculate the required gas supply or release volume based on the heat transfer oil operating temperature, temperature change rate, and real-time pressure in expansion tank 2, and output the corresponding opening control signal to the actuator of each valve. In multi-branch operation, control system 3 can also collect the output signal of the pressure detection device on each branch pipeline, and achieve automatic pressure balance between multiple branches by adjusting the opening of the pressure balancing component on each branch. Control system 3 also includes a communication interface and a data processing module. The communication interface can be connected to the host computer or monitoring platform via industrial Ethernet or fieldbus to upload data such as pressure, temperature, liquid level, and inert gas usage to the monitoring platform. The data processing module can record and analyze historical operating data to provide a basis for maintenance decisions and operating condition optimization.

[0038] How this example works

[0039] Step 1, System Start-up and Pre-pressurization Stage: When the system is first put into operation or restarted after maintenance, heat transfer oil is first injected into the heat transfer oil circulation loop through the heat transfer oil tank 4, so that the heat transfer oil fills the expansion tank 2, heat transfer oil tank 4, heat transfer oil pump 5, heat transfer oil heating equipment 7 and heat-using equipment 6, and the residual air or other gases in the system are discharged through the high-level vent point or dedicated exhaust port. Subsequently, inert gas is slowly injected into the gas phase space at the top of the expansion tank 2 through the inert gas supply unit 1. Under the monitoring of the control system 3, the pressure in the gas phase space in the expansion tank 2 is established within the preset positive pressure range by adjusting the pressure reducing device at the outlet of the inert gas supply unit 1 and the opening of the first valve assembly 81. The working conditions of the liquid level detection device, pressure detection device and valve actuator are checked to ensure that the basic operating conditions of the system and the safety interlock parameters are set.

[0040] Step two, normal operation and dynamic adjustment phase: After the heat transfer oil pump 5 starts, the heat transfer oil is transported from the heat transfer oil tank 4 through the bottom connection interface of the expansion tank 2 and the heat transfer oil pump 5 to the heat transfer oil heating equipment 7. In the heat transfer oil heating equipment 7, it is heated to the required process temperature and then transported to the heat-using equipment 6 for heat exchange. The heat transfer oil at the outlet of the heat-using equipment 6 returns to the expansion tank 2 via the return oil pipeline, completing a closed loop. As the process load changes, the temperature and volume of the heat transfer oil will fluctuate within a certain range. The control system 3 continuously collects the pressure of the gas phase space and the temperature of the heat transfer oil in the expansion tank 2 and calculates the temperature change rate. When it detects that the heat transfer oil temperature rises and causes expansion... When the pressure in expansion tank 2 approaches the set upper limit, the controller automatically adjusts the opening of the venting component in the first valve assembly 81 to release some inert gas. If necessary, it will cooperate with the second valve assembly 82 to open briefly and guide some of the gas-liquid mixture back to the heat transfer oil tank 4, thereby controlling the pressure in expansion tank 2 within the preset positive pressure range. When the heat transfer oil cools down and the system pressure approaches the set lower limit, the controller controls the venting component in the first valve assembly 81 to open appropriately and replenish inert gas into expansion tank 2 to counteract the effect of volume shrinkage on system pressure, so that the system can still maintain relatively smooth pressure fluctuations and stable heating capacity under varying operating conditions.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-level heat transfer oil expansion tank system, characterized in that: It includes an expansion tank (2), an inert gas supply unit (1), a control system (3), and a heat transfer oil circulation unit; The heat transfer oil circulation unit includes a heat transfer oil tank (4), a heat transfer oil heating device (7), a heat transfer oil pump (5), and at least one heat-using device (6). The heat transfer oil tank (4), the heat transfer oil pump (5), the heat transfer oil heating device (7), and the heat-using device (6) are connected by pipelines to form a closed heat transfer oil circulation loop. The outlet of the heat transfer oil pump (5) is connected to the heat transfer oil heating device (7) and the heat-using device (6) in sequence. The outlet of the heat-using device (6) is connected to the heat transfer oil interface of the expansion tank (2) through a return oil pipeline. The expansion tank (2) is connected to the heat transfer oil tank (4) through the bottom heat transfer oil interface. The expansion tank (2) is arranged below the heat transfer oil heating device (7) and the heat-using device (6) or at approximately the same height as them. The expansion tank (2) adopts a closed structure, and its top is provided with a gas phase interface and connected to the inert gas outlet of the inert gas supply unit (1) through a gas pipeline to form a closed gas phase space isolated from the outside. The control system (3) includes a pressure detection device, a temperature detection device and a controller. The pressure detection device is used to detect the pressure of the gas phase space in the expansion tank (2). The temperature detection device is used to detect the temperature of the heat transfer oil in the heat transfer oil circulation loop. The controller is electrically connected to the pressure detection device, the temperature detection device and the actuator set on the controllable gas passage connected to the inert gas supply unit (1) and / or the expansion tank (2). The controller is configured to adjust the opening degree of the actuator according to the pressure in the expansion tank (2) and the temperature of the heat transfer oil, so that the pressure of the gas phase space in the expansion tank (2) is maintained within a preset micro-positive pressure range, and to compensate for the volume change caused by the thermal expansion and contraction of the heat transfer oil.

2. The low-level heat transfer oil expansion tank system according to claim 1, characterized in that: The system also includes a gas regulating assembly (8), which includes a first valve assembly (81) and a second valve assembly (82); The first valve assembly (81) is disposed on the gas pipeline between the inert gas supply unit (1) and the expansion tank (2). The first valve assembly (81) includes a gas supply component for regulating the inert gas entering the expansion tank (2) and a gas venting component for regulating the inert gas exiting the expansion tank (2). The controller is configured to output control signals to the gas supply component and the gas venting component. The second valve assembly (82) is installed on the connecting pipeline connecting the expansion tank (2) and the heat transfer oil tank (4), and is used to open when the pressure in the gas phase space in the expansion tank (2) exceeds a set value, so as to introduce the inert gas and / or heat transfer oil in the expansion tank (2) into the heat transfer oil tank (4) to achieve pressure relief.

3. The low-level heat transfer oil expansion tank system according to claim 1 or 2, characterized in that: The inert gas supply unit (1) includes an inert gas storage container and / or an inert gas generating device. The outlet side of the inert gas supply unit (1) is provided with at least one pressure reducing device and at least one controllable valve component for regulating the pressure and flow rate of the inert gas flowing into the expansion tank (2).

4. The low-level heat transfer oil expansion tank system according to claim 1, characterized in that: The temperature detection device is installed on the outlet pipe section of the heat transfer oil heating device (7) and / or the outlet pipe section of the heat-using device (6). The controller is configured to predict the volume change of the heat transfer oil according to the temperature change rate and adjust the opening of the gas regulating component (8) in advance to reduce system pressure fluctuations.

5. The low-level heat transfer oil expansion tank system according to claim 1, characterized in that: The expansion tank (2) is equipped with an anti-vortex structure and / or an anti-foaming structure to reduce the flow impact and foam formation of the heat transfer oil during the process of drastic volume change.

6. The low-level heat transfer oil expansion tank system according to claim 1, characterized in that: The expansion tank (2) is equipped with a liquid level detection device on its side wall, which is used to detect the liquid level of the heat transfer oil in the expansion tank (2) and transmit the liquid level signal to the controller.

7. The low-level heat transfer oil expansion tank system according to claim 1, characterized in that: The heat transfer oil circulation unit includes multiple branch pipelines connected to the main pipeline. Each branch pipeline is equipped with a pressure balancing component. The controller is configured to adjust the corresponding pressure balancing component according to the pressure detection results of each branch.

8. The low-level heat transfer oil expansion tank system according to claim 1, characterized in that: The top of the expansion tank (2) is provided with a safety relief component that automatically opens when the pressure in the gas phase space exceeds the safety setting value, in order to provide overpressure protection.

9. The low-level heat transfer oil expansion tank system according to claim 1, characterized in that: The control system (3) includes a communication interface and a data processing module. The controller interacts with an external monitoring platform through the communication interface to monitor, record and analyze the operating status of pressure, temperature, liquid level and inert gas usage.

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