Molten salt thermal storage coupled with a two-stage compression electric heat pump system and its operation method

Abstract

This invention discloses a coupled system and operation method of molten salt thermal storage and a two-stage compression electric heat pump, relating to the field of energy storage technology in industrial production. During off-peak hours, a Brayton cycle heat pump unit uses electricity to drive the heat pump cycle, raising the low-temperature working fluid to a high-temperature working fluid. The heat carried by the high-temperature working fluid is then used to heat feedwater to generate industrial steam. A molten salt thermal storage and release unit stores the heat from the Brayton heat pump unit and releases the stored heat during peak hours to heat feedwater and generate industrial steam. An ambient heat pump unit extracts heat from ambient air or low-grade waste heat during off-peak hours to heat the working fluid of the Brayton heat pump unit and preheats the feedwater entering the molten salt thermal storage and release unit during peak hours, achieving peak shaving and valley filling of the power grid and maximizing energy efficiency.

Description

Technical Field

[0001] This invention relates to the field of energy technology in industrial production, specifically to a coupled system of molten salt thermal storage and a two-stage compression electric heat pump, and its operation method. Background Technology

[0002] The demand for high-temperature steam is widespread in industrial production. The continuity of production in industries such as chemical engineering, papermaking, and printing and dyeing largely depends on stable and reliable high-temperature steam supply. Currently, industrial steam supply solutions primarily rely on the combustion of fossil fuels such as coal and natural gas. While these methods can meet the output requirements for steam parameters, the combustion process releases large amounts of greenhouse gases such as carbon dioxide, contradicting the current overall direction of energy conservation, emission reduction, and near-zero carbon emissions. From an energy efficiency perspective, fossil fuel combustion temperatures are high, and after the heat exchange stage, a large amount of waste heat is released into the environment with the flue gas. The loss during heat transfer and conversion is significant, limiting the overall energy utilization rate.

[0003] Steam supply systems also have relatively limited capacity to regulate grid load fluctuations. During off-peak hours, surplus electricity is difficult to absorb effectively; during peak hours, the stability of steam supply may be compromised due to energy shortages, thus disrupting continuous industrial production. In terms of heating technology, single heat pump systems can utilize low-temperature heat sources to enhance heat quality, but they are limited in providing high-parameter steam, making it difficult to meet the stringent pressure and temperature requirements of industrial applications. Molten salt thermal storage technology possesses considerable heat storage capacity and exhibits good thermal stability and specific heat capacity, but its flexibility in energy conversion and scheduling remains insufficient in adapting to grid load changes and the coordinated use of multiple heat sources.

[0004] Currently, high-parameter steam supply in industry mainly relies on the combustion of fossil fuels such as coal and natural gas. While this can meet pressure and temperature requirements, it results in high carbon emissions and significant waste heat loss from combustion flue gas, limiting overall energy efficiency. Meanwhile, chemical heat pumps and organic Rankine cycle heat pumps are constrained by the thermal stability of the working fluid or the circulation temperature range, making it difficult to independently produce high-grade steam above 300°C. At the same time, surplus electricity during off-peak hours cannot be effectively converted into high-quality heat energy for storage, while the stability of steam supply during peak hours is affected by power shortages. Industrial production faces a dual challenge in terms of both continuity and economic efficiency.

[0005] The primary purpose of using Brayton heat pumps is to extract the high-temperature heat they generate. Currently, Brayton heat pumps are mainly used as a source of energy for long-term electrothermal energy storage via Carnot batteries. To expand the application of Brayton heat pumps and make them suitable for a wider range of scenarios, organic Rankine heat pumps, limited by the thermal stability of the working fluid, typically have a condensation heat release temperature range below 150°C, producing only low-parameter steam. They cannot effectively supply high-parameter steam. Coupled with a Brayton cycle, this not only enables the supply of high-parameter steam but also improves the efficiency of the Brayton cycle heat pump, achieving substantial applications in thermodynamic matching and energy cascade utilization. Mechanical vapor recompression systems are inherently complex and expensive, with stringent requirements for steam quality and operational control. Adding such complex components to an already complex system involving high-temperature rotating machinery and molten salt heat exchange will concentrate system failure points, easily triggering cascading shutdowns during industrial load fluctuations, making operational reliability difficult to guarantee.

[0006] Existing industrial steam supply solutions have room for improvement in terms of carbon emission levels, energy efficiency, and steam supply parameters. To achieve near-zero carbon emissions and high energy efficiency, a new steam supply system and its operation method are needed. Summary of the Invention

[0007] Based on the problems mentioned above, the purpose of this invention is to provide a coupled system and operation method of molten salt thermal storage and two-stage compression electric heat pump, which solves the problems of existing technologies that are difficult to stably output high-parameter industrial steam above 300°C under the premise of low carbon emissions, and cannot effectively utilize surplus power during off-peak hours for cross-period thermal storage, resulting in peak steam supply being constrained by power fluctuations and insufficient system economy and continuity.

[0008] This invention is achieved through the following technical solution:

[0009] The first aspect of the present invention provides a coupled system of molten salt thermal storage and a two-stage compression electric heat pump, comprising:

[0010] The Brayton cycle heat pump unit is used to drive the heat pump cycle with electricity during off-peak hours, raising the low-temperature working fluid to a high-temperature working fluid, and using the heat carried by the high-temperature working fluid to heat the feedwater to generate industrial steam.

[0011] A molten salt heat storage and release unit is used to store heat from the Brayton heat pump unit and release the stored heat during peak electricity demand periods to heat feedwater and generate industrial steam.

[0012] An ambient heat pump unit is used to extract heat from ambient air or low-grade waste heat during off-peak electricity demand to heat the circulating working fluid of the Brayton heat pump unit, and to preheat the feedwater entering the molten salt heat storage and release unit during peak electricity demand.

[0013] In the above technical solutions,

[0014] In one optional embodiment, the Brayton cycle heat pump unit includes: a compressor 1, a molten salt heater 2, a compressor 3, a steam generator 4, a molten salt heater 23, a feedwater preheater 6, a feedwater pump 22, a regenerator 5, an air preheater 8, an air heater 9, and an expander 7.

[0015] The compressor 1 is connected in sequence to the molten salt heater 2 and the compressor 3; the compressor 3 is connected to the parallel steam generator 4 and the molten salt heater 23; a parallel regenerator 5 and a feedwater preheater 6 are connected after the parallel steam generator 4 and the molten salt heater 23; the parallel regenerator 5 and the feedwater preheater 6 are connected in sequence to the expander 7, the air preheater 8, and the air heater 9, and are connected to the compressor 1 through the regenerator 5; the feedwater pump 22 is connected to the feedwater preheater 6.

[0016] The parallel regenerator 5 and feedwater preheater 6 are used for flow diversion.

[0017] In one optional embodiment, a valve 26 is provided between the compressor 3 and the steam generator 4; a valve 28 is provided between the compressor 3 and the molten salt heater 23; a valve 27 is provided between the steam generator 4 and the feedwater preheater 6; and a valve 24 is provided at the end of the feedwater pump 22 connected to the water source.

[0018] In an optional embodiment, the molten salt heat storage and release unit includes: a Hitec molten salt high-temperature heat storage tank 13, a Hitec molten salt low-temperature heat storage tank 14, a molten salt pump 15, a steam generator 18, a feedwater preheater 17, and a feedwater pump 16.

[0019] The Hitec molten salt high-temperature thermal storage tank 13 is connected to the steam generator 18 via the molten salt pump 15; the steam generator 18 is directly connected to the Hitec molten salt low-temperature thermal storage tank 14; the water supply pump 16 is sequentially connected to the water supply preheater 17 and the steam generator 18; a valve 25 is provided at the end of the water supply pump 16 connected to the water source.

[0020] In one optional embodiment, the Hitec salt molten salt high-temperature storage tank 13 contains Hitec salt at a temperature of 380°C, and the Hitec salt molten salt low-temperature storage tank 14 contains Hitec salt at a temperature of 190°C.

[0021] In one optional embodiment, the environmental heat pump unit includes: a first environmental heat pump unit and a second environmental heat pump unit;

[0022] The first environmental heat pump unit is connected to the Brayton cycle heat pump unit via the air heater 9;

[0023] The second environmental heat pump unit is connected to the molten salt heat storage and release unit through the water preheater 17.

[0024] In one optional embodiment, the first environmental heat pump unit includes: a waste heat recovery unit 10, a compressor 11, and a throttle valve 12; wherein the throttle valve 12 is connected in sequence to the waste heat recovery unit 10 and the compressor 11, and forms a circuit through the air heater 9;

[0025] The second environmental heat pump unit includes: a waste heat recovery unit 21, a compressor 19, and a throttle valve 20; wherein, the throttle valve 20 is connected in sequence to the waste heat recovery unit 21 and the compressor 19, and forms a circuit through the water preheater 17.

[0026] A second aspect of the present invention provides an operation method for a coupled system of molten salt thermal storage and a two-stage compression electric heat pump, comprising:

[0027] When the power grid is in peak electricity demand, the heating working fluid function of the Brayton heat pump unit and the ambient heat pump unit is stopped, allowing the molten salt heat storage and release unit to enter the heat release state; at the same time, the preheating water function of the ambient heat pump unit is started, and the feed water is preheated by the ambient heat pump unit and then sent to the molten salt heat storage and release unit, which further heats and evaporates the preheated feed water into industrial steam.

[0028] When the power grid is in a non-peak electricity consumption period, the first steam supply threshold, the second steam supply threshold, and the third steam supply threshold are set to decrease sequentially according to the operating conditions.

[0029] When the steam demand is not less than the second steam supply threshold, the first operating mode is executed.

[0030] When the steam demand is not less than the third steam supply threshold, the second operating mode is executed.

[0031] When the steam demand is less than the third steam supply threshold, the third operating mode is executed.

[0032] In an optional embodiment, the first operating mode includes: controlling the heat flow direction so that all the heat generated by the Brayton heat pump unit is directly used to heat the feedwater to generate industrial steam, while stopping the heat storage in the molten salt heat storage and release unit; starting the heating cycle working fluid function of the Brayton heat pump unit and the ambient heat pump unit, and keeping the molten salt heat storage and release unit in a non-heat release state.

[0033] The second operating mode includes: controlling the heat flow direction so that the heat generated by the Brayton heat pump unit is divided into two parts, one part is directly used to heat the feed water to generate industrial steam, and the other part is transported to the molten salt heat storage and release unit for storage; at the same time, the heating cycle working fluid function of the Brayton heat pump unit and the ambient heat pump unit is activated, and the molten salt heat storage and release unit is in a non-heat release state.

[0034] The third operating mode includes: controlling the heat flow direction so that all the heat generated by the Brayton heat pump unit is transferred to the molten salt heat storage and release unit for storage; and simultaneously activating the heating cycle working fluid function of the Brayton heat pump unit and the ambient heat pump unit so that the molten salt heat storage and release unit is in a non-heat-releasing state.

[0035] In an alternative embodiment, the first operating mode, the second operating mode, and the third operating mode are achieved by controlling the valves in the Brayton heat pump unit.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] 1. A parallel flow path is set up between the regenerator and the feedwater preheater before the expander, so that before the high-temperature and high-pressure air enters the turbine, part of the heat is used to preheat its own circulating working fluid, and the other part is used to heat the feedwater in stages. This does not affect the expansion performance, but also realizes the efficient recovery of medium and low temperature heat and achieves energy cascade utilization.

[0038] 2. During periods of low electricity demand, low-priced electricity is used for heat generation and storage, while during peak periods, the system switches to molten salt heat release for steam supply. This effectively reduces the burden on the power grid during peak hours and improves the absorption rate of renewable energy sources such as wind power and photovoltaic power. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0040] Figure 1 This is a schematic diagram of the structure of the molten salt thermal storage and two-stage compression electric heat pump coupling system provided in an embodiment of the present invention;

[0041] Figure 2 A schematic diagram of the structure of each node in the molten salt thermal storage and two-stage compression electric heat pump coupling system provided in an embodiment of the present invention;

[0042] Figure 3A schematic diagram illustrating the effects of the Brayton cycle heat pump unit, molten salt heat storage and release unit, and ambient heat pump unit provided in the embodiments of the present invention.

[0043] Figure 4 A schematic diagram of the operation of the first operating mode provided in an embodiment of the present invention;

[0044] Figure 5 This is a schematic diagram of the second operating mode provided in an embodiment of the present invention;

[0045] Figure 6 This is a schematic diagram of the third operating mode provided in an embodiment of the present invention.

[0046] In the attached diagram:

[0047] 1. Compressor; 2. Molten salt heater; 3. Compressor; 4. Steam generator; 5. Regenerator; 6. Feedwater preheater; 7. Expander; 8. Air preheater; 9. Air heater; 10. Waste heat recovery unit; 11. Compressor; 12. Throttling valve; 13. Hitec molten salt high-temperature thermal storage tank; 14. Hitec molten salt low-temperature thermal storage tank; 15. Molten salt pump; 16. Feedwater pump; 17. Feedwater preheater; 18. Steam generator; 19. Compressor; 20. Throttling valve; 21. Waste heat recovery unit; 22. Feedwater pump; 23. Molten salt heater; 24. Valve; 25. Valve; 26. Valve; 27. Valve; 28. Valve. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0049] Example 1

[0050] Embodiment 1 of this invention provides an implementation method for a coupled system of molten salt thermal storage and a two-stage compression electric heat pump, see [link to documentation]. Figure 1 A molten salt thermal storage and two-stage compression electric heat pump coupling system includes:

[0051] The Brayton cycle heat pump unit is used to drive the heat pump cycle with electricity during off-peak hours, raising the low-temperature working fluid to a high-temperature working fluid, and using the heat carried by the high-temperature working fluid to heat the feedwater to generate industrial steam.

[0052] A molten salt heat storage and release unit is used to store heat from the Brayton heat pump unit and release the stored heat during peak electricity demand periods to heat feedwater and generate industrial steam.

[0053] An ambient heat pump unit is used to extract heat from ambient air or low-grade waste heat during off-peak electricity demand to heat the circulating working fluid of the Brayton heat pump unit, and to preheat the feedwater entering the molten salt heat storage and release unit during peak electricity demand.

[0054] It should be noted that Embodiment 1 of the present invention proposes to use a Brayton cycle heat pump unit to drive the heat pump cycle with electricity during off-peak electricity demand, thereby raising the low-temperature working fluid to a high-temperature working fluid, and using the heat carried by the high-temperature working fluid to heat the feedwater to generate industrial steam; to store the heat from the Brayton heat pump unit through a molten salt heat storage and release unit, and to release the stored heat to heat the feedwater to generate industrial steam during peak electricity demand; and to extract heat from ambient air or low-grade waste heat through an ambient heat pump unit during off-peak electricity demand to heat the working fluid of the Brayton heat pump unit, and to preheat the feedwater entering the molten salt heat storage and release unit during peak electricity demand.

[0055] The coupled architecture of the Brayton cycle heat pump unit, molten salt heat storage and release unit, and environmental heat pump unit integrates the high-temperature heating capacity of the Brayton cycle, the cross-period heat storage and release capacity of molten salt, and the low-grade waste heat recovery capacity of the organic Rankine cycle into a coordinated whole. The entire process replaces coal with electricity and achieves zero carbon emissions, while simultaneously realizing peak shaving and valley filling of the power grid and maximizing energy efficiency.

[0056] Example 2

[0057] Embodiment 2 of the present invention provides an implementation method for a Brayton cycle heat pump unit, see [link to documentation]. Figure 1 The Brayton cycle heat pump unit includes: compressor 1, molten salt heater 2, compressor 3, steam generator 4, molten salt heater 23, feedwater preheater 6, feedwater pump 22, regenerator 5, air preheater 8, air heater 9, and expander 7.

[0058] The compressor 1 is connected in sequence to the molten salt heater 2 and the compressor 3; the compressor 3 is connected to the parallel steam generator 4 and the molten salt heater 23; after the parallel steam generator 4 and the molten salt heater 23, there is a parallel regenerator 5 and a feedwater preheater 6; the parallel regenerator 5 and the feedwater preheater 6 are connected in sequence to the expander 7, the air preheater 8 and the air heater 9, and are connected to the compressor 1 through the regenerator 5; the feedwater pump 22 is connected to the feedwater preheater 6.

[0059] Among them, the parallel regenerator 5 and feedwater preheater 6 are used for diversion.

[0060] The key concept of this invention lies in constructing a parallel flow-dividing structure in the Brayton cycle and realizing a cascade heating water supply method. Specifically, the Brayton cycle heat pump unit adopts a two-stage compression and parallel split-flow cascade heating structure. Low-temperature, low-pressure air is sequentially pressurized and heated by compressor 1, molten salt heater 2, and compressor 3, and then split into two paths—one path enters steam generator 4 to directly heat feedwater to produce steam, and the other path enters molten salt heater 23 to store heat in molten salt. The high-temperature, high-pressure air from the two outlets is again split in parallel to regenerator 5 and feedwater preheater 6. Regenerator 5 is used to preheat the circulating working fluid from air heater 9, while feedwater preheater 6 uses feedwater pump 22 to recover heat from the low-temperature range. Subsequently, the air merges and enters expander 7 to do work. The parallel split-flow design of regenerator 5 and feedwater preheater 6 allows some heat to be diverted before the air enters expander 7 for staged preheating of feedwater, thereby widening the heat release temperature range, reflecting the concept of energy cascade utilization, and thus improving the overall electrothermal conversion efficiency of the system.

[0061] After passing through the expander 7, the air then passes through the air preheater 8 and the air heater 9 before returning to the compressor 1 via the regenerator 5. This design, by setting a parallel flow path between the regenerator and the feedwater preheater before the expander, allows the high-temperature, high-pressure air to use part of its heat to preheat its own circulating working fluid and the other part to use for cascade heating of the feedwater before entering the turbine. This not only does not affect the expansion performance but also achieves efficient recovery of medium and low temperature heat, highlighting the technical concept of energy cascade utilization.

[0062] In one optional embodiment, a valve 26 is provided between the compressor 3 and the steam generator 4; a valve 28 is provided between the compressor 3 and the molten salt heater 23; a valve 27 is provided between the steam generator 4 and the feedwater preheater 6; and a valve 24 is provided at the end of the feedwater pump 22 that is connected to the water source.

[0063] Specifically, during periods of low electricity demand, when the steam demand exceeds the steam supply threshold, valves 24, 26, and 27 are opened while valves 28 and 25 are closed. When the steam demand is less than or equal to the steam supply threshold but greater than zero, valves 24, 26, 27, and 28 are opened while valve 25 is closed, allowing some of the heat from the heat pump compressor 3 to be stored in the storage tank. When the steam demand is zero, valve 28 is opened while valves 24, 26, 27, and 25 are closed, allowing all the heat from the heat pump compressor 3 to be stored in the storage tank.

[0064] The operation mode of the Brayton heat pump unit during off-peak electricity demand is achieved by using valves in the unit.

[0065] Example 3

[0066] Embodiment 3 of the present invention provides an implementation method for a molten salt heat storage and release unit, see [link to documentation]. Figure 1 The molten salt heat storage and release unit includes: a Hitec molten salt high-temperature heat storage tank 13, a Hitec molten salt low-temperature heat storage tank 14, a molten salt pump 15, a steam generator 18, a feedwater preheater 17, and a feedwater pump 16.

[0067] The Hitec molten salt high-temperature thermal storage tank 13 is connected to the steam generator 18 via the molten salt pump 15; the steam generator 18 is directly connected to the Hitec molten salt low-temperature thermal storage tank 14; the feed water pump 16 is connected in sequence to the feed water preheater 17 and the steam generator 18; a valve 25 is provided at the end of the feed water pump 16 that is connected to the water source.

[0068] It should be noted that during peak electricity consumption periods, heat release occurs. High-temperature molten salt, driven by the high-temperature storage tank 13 and the molten salt pump 15, flows into the hot side of the steam generator 18, releases heat, cools down, and returns to the low-temperature storage tank 14. Simultaneously, feedwater, controlled by the feedwater pump 16 and valve 25, first flows through the cold side of the feedwater preheater 17 (preheated to medium temperature by the second ambient heat pump unit), and then enters the cold side of the steam generator 18, where it is heated and evaporated by the high-temperature molten salt to generate high-temperature, high-pressure industrial steam. This dual-tank design allows for independent operation of heat storage and release. Valve 25 controls the on / off state of the feedwater branch, and in conjunction with the system's switching of operating modes at different times, it enables flexible heat allocation across time periods.

[0069] In one optional embodiment, the Hitec salt molten salt high-temperature storage tank 13 contains Hitec salt at a temperature of 380°C, and the Hitec salt molten salt low-temperature storage tank 14 contains Hitec salt at a temperature of 190°C.

[0070] Example 4

[0071] Embodiment 4 of the present invention provides an implementation of an environmental heat pump unit, which includes: a first environmental heat pump unit and a second environmental heat pump unit;

[0072] The first ambient heat pump unit is connected to the Brayton cycle heat pump unit via an air heater 9.

[0073] The second environmental heat pump unit is connected to the molten salt heat storage and release unit via the feedwater preheater 17.

[0074] Specifically, see Figure 1 The first environmental heat pump unit includes: a waste heat recovery unit 10, a compressor 11, and a throttle valve 12; wherein, the throttle valve 12 is connected in sequence to the waste heat recovery unit 10 and the compressor 11, and forms a circuit through the air heater 9;

[0075] The second environmental heat pump unit includes: a waste heat recovery unit 21, a compressor 19, and a throttle valve 20; wherein, the throttle valve 20 is connected in sequence to the waste heat recovery unit 21 and the compressor 19, and forms a circuit through the feed water preheater 17.

[0076] The environmental heat pump unit consists of a first environmental heat pump unit and a second environmental heat pump unit, both of which are independent organic working fluid heat pump loops. The working fluids in both loops absorb low-grade heat energy, such as industrial waste heat, in their respective waste heat recovery units. After being boosted to the medium-temperature range by the compressor, the first loop releases heat in the air heater 9 to heat the inlet air of the Brayton cycle, increasing its pre-compression temperature and thus reducing the compression power consumption of the Brayton heat pump and improving heating efficiency. The second loop releases heat in the feedwater preheater 17 to preheat the feedwater entering the molten salt heat release unit, ensuring the feedwater reaches a medium-temperature level before entering the molten salt heat release stage, reducing irreversible temperature loss due to molten salt heating. The two loops can operate independently or alternately according to the grid load period and steam supply demand—the first loop is mainly activated during off-peak hours to optimize the Brayton cycle, while the second loop is mainly activated during peak hours to assist molten salt heat release—thus achieving efficient utilization of low-grade waste heat resources across time periods and for different purposes, effectively reducing the system's dependence on high-grade electrical energy or high-temperature heat sources.

[0077] Furthermore, the salt heater 2, steam generator 4, molten salt heater 23, feedwater preheater 6, regenerator 5, air preheater 8, air heater 9, waste heat recovery unit 10, steam generator 18, feedwater preheater 17, and waste heat recovery unit 21 all adopt shell-and-tube heat exchangers.

[0078] Furthermore, compressors 1, 3, 11, and 19 are centrifugal compressors.

[0079] Furthermore, expander 7 adopts a vortex expander.

[0080] Furthermore, a distributor (not shown in the figure, but placed before the regenerator 5 and the feedwater preheater 6) is used to divert the working fluid of the Brayton heat pump system, thereby improving the efficiency of the heat pump cycle and preheating the feedwater to highlight the concept of energy cascade utilization.

[0081] Furthermore, the parameters of the coupled system of molten salt thermal storage and two-stage compression electric heat pump at each node are shown in Table 1:

[0082] Table 1: Parameters of each node in the Carnot battery system

[0083]

[0084] As shown in the table above, combined with Figure 2Molten salt heaters 2 and 23 have air and molten salt as their hot and cold working fluids, respectively; steam generator 4 has air and steam / water as its hot and cold working fluids, respectively; feedwater preheaters 6 and 17 have air and water as their hot and cold working fluids, respectively; regenerators and air preheaters 8 have air and air as their hot and cold working fluids, respectively; air heater 9 has organic and air as its hot and cold working fluids, respectively; waste heat recovery units 10 and 21 have waste hot water and organic working fluids as their hot and cold working fluids, respectively; and steam generator 18 has molten salt and steam as its hot and cold working fluids, respectively.

[0085] Table 2 shows the energy storage, energy release, and round-trip efficiency parameters of the Carnot battery system:

[0086] Table 2: Energy storage, energy release, and round-trip efficiency parameters of the Carnot battery system

[0087]

[0088] This invention integrates the high-temperature heating capacity of the Brayton cycle, the inter-period heat storage and release capacity of molten salt, and the low-grade waste heat recovery capacity of the organic Rankine cycle into a cohesive whole through a coupled architecture of a Brayton cycle heat pump unit, a molten salt heat storage and release unit, and an environmental heat pump unit. (See also...) Figure 3 The dashed box A shows that the system can stably output high-parameter industrial steam with a pressure exceeding 1MPa and a temperature above 300℃, operating with a near-zero carbon emission path. It provides green and low-carbon heat energy to end users and can actively absorb surplus renewable energy by converting it into high-quality steam for storage and utilization, thus significantly improving the level of new energy consumption. Dashed box B shows that the Brayton heat pump unit adopts a feedwater preheater 6 design connected in parallel with the regenerator, expanding the supply temperature range of the Brayton heat pump and fully recovering low-temperature heat. Simultaneously, during the molten salt heat release process, the environmental heat pump unit assists in heating the feedwater to supplement the low-temperature heat. This cascade utilization design significantly improves the overall electrothermal conversion efficiency of the system. Dashed box C reveals that the environmental heat pump unit uses an organic working fluid as the Rankine cycle working fluid to recover low-grade industrial waste heat. The working fluid evaporates during heat exchange with low-temperature waste heat, and after being heated and pressurized by the compressor to the medium-temperature range, it condenses and releases heat, thus achieving efficient utilization of waste heat resources. These three components work together to form a high-parameter, high-efficiency, and low-carbon-emission industrial steam supply system.

[0089] Example 5

[0090] Embodiment 5 of the present invention provides the operation mode of the molten salt thermal storage and two-stage compression electric heat pump coupling system of Embodiments 1 to 4, see [link to embodiment 5]. Figures 4 to 6 The operating modes of the molten salt thermal storage and two-stage compression electric heat pump coupled system include:

[0091] When the power grid is in peak electricity demand, the heating working fluid function of the Brayton heat pump unit and the ambient heat pump unit is stopped, allowing the molten salt heat storage and release unit to enter the heat release state; at the same time, the preheating water function of the ambient heat pump unit is started, and the feed water is preheated by the ambient heat pump unit and then sent to the molten salt heat storage and release unit, which further heats and evaporates the preheated feed water into industrial steam.

[0092] When the power grid is in a non-peak electricity consumption period, the first steam supply threshold and the second steam supply threshold are successively reduced according to the operating conditions.

[0093] When the steam demand is not less than the first steam supply threshold, the first operating mode is executed.

[0094] When the steam demand is not less than the second steam supply threshold, the second operating mode is executed.

[0095] When the steam demand is less than the second steam supply threshold, the third operating mode is executed.

[0096] It should be noted that during peak electricity consumption periods, the heat storage sections of the Brayton heat pump unit, the molten salt heat storage and release unit, and the air heating section of the ambient heat pump unit all cease operation; the heat release section of the molten salt heat storage and release unit and the water heating section of the ambient heat pump unit are put into operation. The water heating section of the ambient heat pump unit uses a separate independent organic working fluid circulation loop to preheat the initial feedwater to a medium temperature; the preheated feedwater then enters the heat release section of the molten salt heat storage and release unit, where it is further heated and evaporated using the heat stored in the Hitec salt during off-peak electricity consumption, similarly generating high-temperature and high-pressure steam of 0.8MPa to 1.5MPa and 250℃ to 350℃ to meet industrial steam supply needs.

[0097] During off-peak electricity consumption periods, the operating conditions of thermal storage need to be flexibly adjusted according to specific industrial demands. Different operating conditions have corresponding maximum steam supply thresholds. In this embodiment, the first and second steam supply thresholds, whose values ​​decrease sequentially according to the operating conditions, are used. When the steam demand is not less than the first steam supply threshold, the first operating mode is executed; when the steam demand is not less than the second steam supply threshold, the second operating mode is executed; and when the steam demand is less than the second steam supply threshold, the third operating mode is executed. It should be noted that the first and second steam supply thresholds in this embodiment are only the basis for dividing the operating conditions; the specific values ​​can be set by those skilled in the art according to specific industrial needs.

[0098] Specifically, the heat storage sections of the Brayton heat pump unit, the molten salt heat storage and release unit, and the air heating section of the environmental heat pump unit are operational, while the heat release section of the molten salt heat storage and release unit and the water heating section of the environmental heat pump unit are inactive. The Brayton heat pump unit uses low-cost electricity to drive the compressor, pressurizing low-temperature, low-pressure air to high-temperature, high-pressure gas. After releasing heat, the air expands and cools down. The air heating section of the environmental heat pump unit then uses low-cost electricity to raise the low-temperature waste heat to a medium temperature, reheating the circulating air before returning it to the compressor. This environmental heat pump unit has an independent organic refrigerant circulation loop that specifically recovers low-grade heat energy, such as industrial waste heat, during off-peak electricity consumption periods to increase the inlet air temperature of the Brayton heat pump, thereby significantly improving the heating efficiency of the Brayton cycle.

[0099] In an optional embodiment, the first operating mode includes: controlling the heat flow direction so that all the heat generated by the Brayton heat pump unit is directly used to heat the feedwater to generate industrial steam, while stopping the heat storage in the molten salt heat storage and release unit; starting the heating cycle working fluid function of the Brayton heat pump unit and the ambient heat pump unit, and keeping the molten salt heat storage and release unit in a non-heat release state.

[0100] The second operating mode includes: controlling the heat flow direction so that the heat generated by the Brayton heat pump unit is divided into two parts, one part is directly used to heat the feed water to generate industrial steam, and the other part is transported to the molten salt heat storage and release unit for storage; at the same time, the heating cycle working fluid function of the Brayton heat pump unit and the ambient heat pump unit is activated, and the molten salt heat storage and release unit is in a non-heat release state.

[0101] The third operating mode includes: controlling the heat flow direction so that all the heat generated by the Brayton heat pump unit is transferred to the molten salt heat storage and release unit for storage; and simultaneously activating the heating cycle working fluid function of the Brayton heat pump unit and the ambient heat pump unit so that the molten salt heat storage and release unit is in a non-heat-releasing state.

[0102] In an alternative embodiment, the first operating mode, the second operating mode, and the third operating mode are achieved by controlling the valves in the Brayton heat pump unit.

[0103] For the first operating mode, please refer to [link / reference]. Figure 4 In the first operating mode, the Brayton heat pump unit closes its molten salt heater branch 23 through valve control, opens valves 24, 26, and 27, and closes valves 28 and 25. The Brayton heat pump unit uses low-cost electricity to drive the compressor, pressurizing low-temperature, low-pressure air to high-temperature, high-pressure gas. This high-temperature air is used directly to heat the feed water, generating high-temperature, high-pressure steam of 0.8MPa to 1.5MPa and 250℃ to 350℃.

[0104] For the second operating mode, please refer to [link / reference]. Figure 5 In the second operating mode, the Brayton heat pump unit opens valves 24, 26, 27, and 28 and closes valve 25, so that part of the heat after the heat pump compressor 3 is stored in the storage tank. The Brayton heat pump unit uses low-cost electricity to drive the compressor to pressurize low-temperature, low-pressure air into high-temperature, high-pressure gas. Part of the heat from this high-temperature air is stored in the Hitec salt high-temperature storage tank through a bypass via a molten salt heater, while the other part is still directly used to produce steam.

[0105] For the third operating mode, please refer to [link / reference]. Figure 6 In the third operating mode, the Brayton heat pump unit opens valve 28 and closes valves 24, 26, 27, and 25, so that all the heat from the heat pump compressor 3 is stored in the storage tank.

[0106] During periods of low electricity demand, the system utilizes low-cost electricity for heating and heat storage, while switching to molten salt heat release for steam supply during peak demand periods. This effectively reduces the burden on the power grid during peak hours and improves the absorption rate of renewable energy sources such as wind and solar power.

[0107] It should be noted that the mainstream technologies for achieving low-carbon industrial steam supply at high temperatures, besides heat pump thermal storage based on the Brayton cycle, also include electric boilers and high-temperature phase change integrated steam compression heat pumps.

[0108] Compared to existing high-temperature phase change integrated vapor compression heat pumps, which typically require multiple stages and loops to gradually raise temperature and pressure to high parameter levels, resulting in a complex system structure, this invention offers a more efficient solution. Furthermore, these systems often lack heat storage capacity, hindering heat transfer over time and leading to poor operational flexibility and economy. In contrast, this invention achieves high-parameter industrial steam output through direct coupling of a Brayton heat pump and molten salt thermal storage, eliminating the need for complex multi-stage configurations. It also possesses complete heat storage and release functions, offering direct operational control response and superior flexibility and economy.

[0109] Compared to existing electric boilers, which directly convert high-quality electrical energy into lower-grade heat energy, resulting in significant irreversible losses, low electrothermal conversion efficiency, and lack of long-term energy storage capabilities, this invention cannot meet the demands of peak shaving and valley filling in the power grid. This invention employs an electrothermal conversion and heat storage path combining a heat pump and thermal storage. Electrical energy drives the heat pump to improve the heat energy grade, and molten salt thermal storage is used to achieve energy transfer over time. This significantly reduces irreversible losses, improves system energy efficiency, and provides long-term energy storage capabilities.

[0110] Compared to thermochemical thermal storage technology, although thermochemical thermal storage has higher thermal density and long-term storage potential, its system is complex, reaction conditions are harsh, and the technology is less mature. The molten salt sensible heat thermal storage path of this invention has the advantages of simple system structure, direct control response, and high technical reliability, and is easier to promote in engineering and to operate and maintain.

[0111] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A coupled system of molten salt thermal storage and a two-stage compression electric heat pump, characterized in that, include: The Brayton cycle heat pump unit is used to drive the heat pump cycle with electricity during off-peak hours, raising the low-temperature working fluid to a high-temperature working fluid, and using the heat carried by the high-temperature working fluid to heat the feedwater to generate industrial steam. A molten salt heat storage and release unit is used to store heat from the Brayton heat pump unit and release the stored heat during peak electricity demand periods to heat feedwater and generate industrial steam. An ambient heat pump unit is used to extract heat from ambient air or low-grade waste heat during off-peak electricity demand to heat the circulating working fluid of the Brayton heat pump unit, and to preheat the feedwater entering the molten salt heat storage and release unit during peak electricity demand.

2. The molten salt thermal storage and two-stage compression electric heat pump coupling system according to claim 1, characterized in that, The Brayton cycle heat pump unit includes: a compressor (1), a molten salt heater (2), a compressor (3), a steam generator (4), a molten salt heater (23), a feed water preheater (6), a feed water pump (22), a regenerator (5), an air preheater (8), an air heater (9), and an expander (7). The compressor (1) is connected in sequence to the molten salt heater (2) and the compressor (3); the compressor (3) is connected to the parallel steam generator (4) and the molten salt heater (23); a parallel regenerator (5) and a feedwater preheater (6) are connected after the parallel steam generator (4) and the molten salt heater (23); the parallel regenerator (5) and the feedwater preheater (6) are connected in sequence to the expander (7), the air preheater (8), and the air heater (9), and are connected to the compressor (1) through the regenerator (5); the feedwater pump (22) is connected to the feedwater preheater (6); The parallel regenerator (5) and feedwater preheater (6) are used for flow diversion.

3. The molten salt thermal storage and two-stage compression electric heat pump coupling system according to claim 2, characterized in that, A valve (26) is provided between the compressor (3) and the steam generator (4); a valve (28) is provided between the compressor (3) and the molten salt heater (23); a valve (27) is provided between the steam generator (4) and the water preheater (6); and a valve (24) is provided at the end of the water pump (22) connected to the water source.

4. The molten salt thermal storage and two-stage compression electric heat pump coupling system according to claim 2, characterized in that, The molten salt heat storage and release unit includes: a Hitec molten salt high-temperature heat storage tank (13), a Hitec molten salt low-temperature heat storage tank (14), a molten salt pump (15), a steam generator (18), a water preheater (17), and a water pump (16). The Hitec molten salt high-temperature thermal storage tank (13) is connected to the steam generator (18) via the molten salt pump (15); the steam generator (18) is directly connected to the Hitec molten salt low-temperature thermal storage tank (14); the water supply pump (16) is connected in sequence to the water supply preheater (17) and the steam generator (18); a valve (25) is provided at the end of the water supply pump (16) connected to the water source.

5. The molten salt thermal storage and two-stage compression electric heat pump coupling system according to claim 4, characterized in that, The Hitec salt molten salt high-temperature heat storage tank (13) contains Hitec salt at a temperature of 380°C, and the Hitec salt molten salt low-temperature heat storage tank (14) contains Hitec salt at a temperature of 190°C.

6. The molten salt thermal storage and two-stage compression electric heat pump coupling system according to claim 4, characterized in that, The environmental heat pump unit includes: a first environmental heat pump unit and a second environmental heat pump unit; The first environmental heat pump unit is connected to the Brayton cycle heat pump unit through the air heater (9); The second environmental heat pump unit is connected to the molten salt heat storage and release unit through the feed water preheater (17).

7. The molten salt thermal storage and two-stage compression electric heat pump coupling system according to claim 6, characterized in that, The first environmental heat pump unit includes: a waste heat recovery unit (10), a compressor (11), and a throttle valve (12); wherein the throttle valve (12) is connected in sequence to the waste heat recovery unit (10) and the compressor (11), and forms a circuit through the air heater 9; The second environmental heat pump unit includes: a waste heat recovery unit (21), a compressor (19), and a throttle valve (20); wherein the throttle valve (20) is connected in sequence to the waste heat recovery unit (21) and the compressor (19), and forms a circuit through the water preheater (17).

8. The operation method of the molten salt thermal storage and two-stage compression electric heat pump coupling system according to any one of claims 1 to 7, characterized in that, When the power grid is in peak electricity demand, the heating working fluid function of the Brayton heat pump unit and the ambient heat pump unit is stopped, allowing the molten salt heat storage and release unit to enter the heat release state; at the same time, the preheating water function of the ambient heat pump unit is started, and the feed water is preheated by the ambient heat pump unit and then sent to the molten salt heat storage and release unit, which further heats and evaporates the preheated feed water into industrial steam. When the power grid is in a non-peak electricity consumption period, the first steam supply threshold, the second steam supply threshold, and the third steam supply threshold are set to decrease sequentially according to the operating conditions. When the steam demand is not less than the second steam supply threshold, the first operating mode is executed. When the steam demand is not less than the third steam supply threshold, the second operating mode is executed. When the steam demand is less than the third steam supply threshold, the third operating mode is executed.

9. The operation method of the molten salt thermal storage and two-stage compression electric heat pump coupling system according to claim 8, characterized in that, The first operating mode includes: controlling the heat flow direction so that all the heat generated by the Brayton heat pump unit is directly used to heat the feed water to generate industrial steam, while stopping the heat storage in the molten salt heat storage and release unit; starting the heating cycle working fluid function of the Brayton heat pump unit and the ambient heat pump unit, and keeping the molten salt heat storage and release unit in a non-heat release state. The second operating mode includes: controlling the heat flow direction so that the heat generated by the Brayton heat pump unit is divided into two parts, one part is directly used to heat the feed water to generate industrial steam, and the other part is transported to the molten salt heat storage and release unit for storage; at the same time, the heating cycle working fluid function of the Brayton heat pump unit and the ambient heat pump unit is activated, and the molten salt heat storage and release unit is in a non-heat release state. The third operating mode includes: controlling the heat flow direction so that all the heat generated by the Brayton heat pump unit is transferred to the molten salt heat storage and release unit for storage; and simultaneously activating the heating cycle working fluid function of the Brayton heat pump unit and the ambient heat pump unit so that the molten salt heat storage and release unit is in a non-heat-releasing state.

10. The operation method of the molten salt thermal storage and two-stage compression electric heat pump coupling system according to claim 8, characterized in that, The first operating mode, the second operating mode, and the third operating mode are achieved by controlling the valves in the Brayton heat pump unit.

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