Two-stage heat pump energy storage device based on non-azeotropic working medium and waste heat utilization

Abstract

The utility model relates to a two-stage heat pump energy storage device based on non-azeotropic working media and waste heat utilization, and belongs to the technical field of energy utilization. According to the two-stage heat pump energy storage device, a low-pressure compressor, a high-pressure compressor, a condenser, a subcooler, an evaporator, a superheater, a low-pressure throttling valve, a high-pressure throttling valve, an intermediate evaporator and a liquid separator are connected in series or in parallel to form a circulating working loop. The circulating working medium is a mixed working medium composed of two working media. Through the synergistic effect of two-stage compression, liquid separation regulation and control and the double evaporators, efficient coupling of low-temperature waste heat recovery, medium-temperature waste heat utilization and heat energy storage is achieved, waste heat utilization of two-stage waste heat sources with different temperature grades is achieved, and the energy efficiency of the system is further improved; the performance coefficient of the system is increased by about 36%-47.5% compared with a single-stage heat pump energy storage system, and the total performance coefficient of the system is increased by 11.2%-19.9% compared with two parallel single-stage heat pump energy storage systems adopting two stages of waste heat at different temperatures.

Description

Technical Field

[0001] This utility model belongs to the field of energy utilization technology, specifically involving heat pump technology, energy storage system and waste heat utilization technology. Background Technology

[0002] With the continuous growth of global energy demand and the aggravation of environmental problems, the utilization of renewable energy sources such as solar and wind power has become increasingly important. However, these energy forms are intermittent and fluctuating, leading to a significant mismatch between electricity supply and demand. To address this, various energy storage technologies have been developed, including pumped hydro storage (PHES) and compressed air energy storage (CAES). Although these technologies have certain advantages in terms of storage capacity and efficiency, they are limited by geographical conditions and technological costs, and cannot meet all application needs.

[0003] In recent years, thermal energy storage technology (PTES) has attracted much attention due to its lack of geographical limitations. However, PTEES systems face several challenges in practical applications: First, low-grade heat sources have low temperatures, requiring PTEES systems to achieve efficient heat energy utilization, which increases the compressor load. Second, traditional heat pump cycles have low efficiency, limiting the energy utilization efficiency of PTEES systems. Furthermore, existing PTEES systems generally suffer from high irreversibility and significant energy loss, restricting their widespread application. Utility Model Content

[0004] To address the issues of high irreversibility and energy loss in existing heat pump energy storage systems and to achieve efficient energy utilization and storage, this invention provides a two-stage heat pump energy storage device based on a non-azeotropic working fluid and waste heat utilization.

[0005] A two-stage heat pump energy storage device based on non-azeotropic working fluid and waste heat utilization includes a low-pressure compressor 1, a high-pressure compressor 2, a condenser 3, a subcooler 4, an evaporator 5, and a superheater 6.

[0006] The outlet of the low-pressure compressor 1 is connected in series with the high-pressure compressor 2, the condenser 3 and the subcooler 4, and the inlet of the low-pressure compressor 1 is connected in series with the superheater 6 and the evaporator 5.

[0007] The outlet of the subcooler 4 is connected to the second working inlet of the distributor 10 through the high-pressure throttle valve 8. The intermediate evaporator 9 is connected in parallel between the first working inlet and the outlet of the distributor 10. The first working inlet of the distributor 10 is connected to the outlet of the low-pressure compressor 1 and the inlet of the high-pressure compressor 2 through a three-way pipe. The outlet of the distributor 10 is connected to the working inlet of the evaporator 5 through the low-pressure throttle valve 7 to form a circulation loop.

[0008] Further technical solutions are as follows:

[0009] The low-pressure compressor 1 is a piston compressor; the high-pressure compressor 2 is a scroll compressor.

[0010] The condenser 3 is a fixed tube sheet condenser.

[0011] The subcooler 4 is a fixed tube sheet type subcooler.

[0012] The evaporator 5 is a fixed tube sheet evaporator.

[0013] The superheater 6 is a plate superheater.

[0014] The intermediate evaporator 9 is a microchannel shell-and-tube evaporator.

[0015] The beneficial technical effects of this utility model are reflected in the following aspects:

[0016] 1. System efficiency is significantly improved.

[0017] This invention significantly improves the system's energy return efficiency through a multi-stage compression structure. By introducing a distributor 10 and an intermediate evaporator 9, waste heat from additional heat sources is recovered and utilized. The COP of the high and low pressure stages is optimized through the control of the non-azeotropic working fluid composition, reducing energy loss and improving overall energy efficiency. In this invention, when the heat absorbed by the system through the intermediate evaporator 9 and the low-pressure stage evaporator 5 is in a 1:1 ratio, using the same working fluid (R152a, R1234ze, and mixtures thereof), the system's coefficient of performance (COP) is improved by approximately 36% to 47.5% compared to a single-stage heat pump energy storage system, and by 11.2% to 19.9% ​​compared to two parallel single-stage heat pump energy storage systems using waste heat from these two stages at different temperatures.

[0018] 2. Flexible adaptation to various application scenarios

[0019] This invention, through its multi-stage compression structure design, enables the heat pump system to achieve multi-stage cooling. It has wide applications depending on the situation: it can utilize waste heat from two different temperature levels of waste heat sources, further improving system energy efficiency; it can achieve low-pressure stage cooling and intermediate stage waste heat utilization, improving energy storage efficiency while achieving cooling. This flexibility gives the system higher adaptability and reliability in different application scenarios. In practical applications, it is often necessary to recover waste heat from multiple waste heat sources at different temperatures. In the process of recovering low-temperature waste heat, using a single-stage heat pump cycle results in high compressor load and high energy loss due to its high temperature rise ratio and high compression ratio, while using a multi-stage heat pump cycle results in energy loss due to the increased number of intermediate stages. This invention uses a multi-stage heat pump cycle to recover waste heat in the low-temperature range while reducing the compressor load by lowering the compression ratio through multi-stage circulation. Simultaneously, the intermediate-stage evaporator achieves the absorption of heat in the medium-temperature range. In actual production, it can be used for waste heat recovery from medium-temperature waste heat sources or for cooling in this temperature range, improving energy utilization while flexibly adapting to various application scenarios. The system recovers waste heat from the low-temperature zone by absorbing heat from the low-temperature zone through a low-pressure evaporator. The heat is then compressed to an intermediate temperature by a low-pressure compressor and mixed with a working fluid that has absorbed heat from the medium-temperature zone through an intermediate evaporator. The intermediate evaporator allows for the utilization of intermediate-stage waste heat or for refrigeration in the intermediate temperature zone, improving system efficiency by using waste heat or refrigeration capacity. The mixed working fluid is then compressed to the condensing temperature by a high-pressure compressor, and the heat is stored in a heat storage medium through a condenser. After condensation and heat exchange, the fluid enters the expansion valve and then the distributor.

[0020] 3. Economic and environmental friendliness

[0021] This invention utilizes low-grade waste heat sources, improving energy efficiency and reducing reliance on high-grade energy sources, thus demonstrating good economic viability. Simultaneously, by improving energy efficiency and reducing energy loss, this invention is more environmentally friendly, contributing to reduced carbon emissions and energy waste. Attached Figure Description

[0022] Figure 1 This is a system diagram of a utility model.

[0023] Figure 2 Ts diagram for waste heat utilization in a two-stage heat pump energy storage device.

[0024] Figure 1 Intermediate components: 1. Low-pressure compressor; 2. High-pressure compressor; 3. Condenser; 4. Subcooler; 5. Evaporator; 6. Superheater; 7. Low-pressure throttling valve; 8. High-pressure throttling valve; 9. Intermediate evaporator; 10. Liquid distributor. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0026] See Figure 1 A two-stage heat pump energy storage device based on non-azeotropic working fluid and waste heat utilization includes a low-pressure compressor 1, a high-pressure compressor 2, a condenser 3, a subcooler 4, an evaporator 5, and a superheater 6.

[0027] The outlet of the low-pressure compressor 1 is connected in series with the high-pressure compressor 2, the condenser 3 and the subcooler 4, and the inlet of the low-pressure compressor 1 is connected in series with the superheater 6 and the evaporator 5.

[0028] The outlet of the subcooler 4 is connected to the second working inlet of the distributor 10 through the high-pressure throttle valve 8. The intermediate evaporator 9 is connected in parallel between the first working inlet and the outlet of the distributor 10. The first working inlet of the distributor 10 is connected to the outlet of the low-pressure compressor 1 and the inlet of the high-pressure compressor 2 through a three-way pipe. The outlet of the distributor 10 is connected to the working inlet of the evaporator 5 through the low-pressure throttle valve 7 to form a circulation loop.

[0029] Low-pressure compressor 1 is a reciprocating compressor, and high-pressure compressor 2 is a scroll compressor. Condenser 3 is a fixed tube sheet condenser. Subcooler 4 is a fixed tube sheet subcooler. Evaporator 5 is a fixed tube sheet evaporator. Superheater 6 is a plate superheater. Intermediate evaporator 9 is a microchannel shell-and-tube evaporator.

[0030] In this embodiment, the circulating working medium of the two-stage heat pump energy storage device is a mixture of two working media: 1,1-difluoroethane (R152a) and trans-1,3,3,3-tetrafluoropropylene (R1234ze). The two working media are mixed in different proportions in different components to form different working media. However, due to the difference in boiling points between the two working media, the saturated liquid and saturated vapor obtained after passing through the separator have some differences in composition. The circulating working media between the high-pressure stage and the low-pressure stage of the system have certain differences in the proportion of the two working media.

[0031] The proportions of 1,1-difluoroethane (R152a) and trans-1,3,3,3-tetrafluoropropylene (R1234ze) in the low-pressure compressor 1, superheater 6, evaporator 5, low-pressure throttling valve 7, and intermediate evaporator 9 follow proportion 1; the proportions of 1,1-difluoroethane (R152a) and trans-1,3,3,3-tetrafluoropropylene (R1234ze) in the high-pressure compressor 2, condenser 3, subcooler 4, and high-pressure throttling valve 8 follow proportion 2.

[0032] The advantages of using 1,1-difluoroethane (R152a) and trans-1,3,3,3-tetrafluoropropylene (R1234ze) as the non-azeotropic working fluids in this invention are: their excellent thermophysical property matching within the operating temperature range allows them to work synergistically under different pressure and temperature conditions, thereby optimizing energy cycle efficiency. Furthermore, the selection of these two working fluids also considers environmental friendliness, as both have low global warming potential (GWP). For example, R152a has a GWP of approximately 138, while R1234ze has a GWP of less than 1. Compared to traditional high-GWP working fluids, these low GWP values ​​mean that using these working fluids can significantly reduce greenhouse gas emissions from the system and mitigate environmental impact.

[0033] In a specific embodiment, the heat absorbed by the system through the intermediate evaporator 9 and the low-pressure stage evaporator 5 is in a 1:1 ratio.

[0034] The working principle of this utility model is explained in detail below:

[0035] This utility model's two-stage heat pump energy storage device uses a non-azeotropic working fluid (a mixture of R152a and R1234ze) as the circulating medium. Through the synergistic action of two-stage compression, liquid-liquid separation regulation, and dual evaporators, it achieves efficient coupling of low-temperature waste heat recovery, medium-temperature waste heat utilization, and thermal energy storage. During system operation, the liquid non-azeotropic working fluid first enters the evaporator 5 after being depressurized by the low-pressure throttling valve 7. Driven by a low-temperature waste heat source (such as ambient waste heat or solar energy), it evaporates and absorbs heat, forming a low-temperature, low-pressure gaseous working fluid. This gaseous working fluid then enters the superheater 6 to absorb additional waste heat and rise to a superheated state, before being compressed to a medium-pressure, medium-temperature state by the low-pressure compressor 1. The compressed working fluid mixes with the working fluid leaving the liquid separator 10 and the intermediate evaporator 9 and then enters the high-pressure compressor 2 for secondary compression, forming a high-temperature, high-pressure working fluid, which is then transported to the condenser 3. In condenser 3, the working fluid releases latent heat and exchanges heat with the heat storage medium, storing the thermal energy in a high-temperature heat storage system. It is then further cooled by subcooler 4 to increase energy storage density. The subcooled liquid working fluid, after being throttled and depressurized by high-pressure throttling valve 8, enters separator 10, where it is separated into saturated vapor rich in low-boiling-point components and saturated liquid rich in high-boiling-point components based on the boiling point difference between the non-azeotropic working fluids. A portion of the high-boiling-point-rich liquid enters intermediate evaporator 9 to absorb intermediate-temperature waste heat (such as industrial waste heat) and evaporates into a gaseous state. This gas mixes with the low-boiling-point-rich saturated vapor leaving separator 10 and the working fluid exiting low-pressure compressor 1 to form a medium-pressure mixed working fluid, which enters high-pressure compressor 2 to participate in the cycle. The high-boiling-point-rich liquid returns to evaporator 5 via low-pressure throttling valve 7 to restart the low-pressure cycle, forming a closed loop.

[0036] The core function of the distributor 10 is to dynamically regulate the ratio of working fluid components: in the low-pressure stage cycle, the working fluid is balanced to optimize low-temperature evaporation performance and efficiently recover low-grade waste heat; in the high-pressure stage cycle, the working fluid, after being separated, reduces the compression ratio and adapts to high-temperature condensation requirements, significantly reducing compressor power consumption. The intermediate evaporator 9 achieves energy cascade utilization and multi-scenario function switching by absorbing medium-temperature waste heat or providing cooling capacity. The system splits the total compression ratio into low-pressure and high-pressure stages through two-stage compression, and combined with the variable operating condition characteristics of the centrifugal compressor, reduces single-stage load and irreversible losses. This design not only breaks through the high compression ratio bottleneck of traditional heat pump energy storage, but also flexibly adapts to the combined needs of waste heat recovery, multi-temperature zone cooling, and distributed energy storage, providing an innovative solution for renewable energy integration and industrial energy conservation.

[0037] The operating conditions of each heat exchanger are as follows:

[0038] Due to the presence of the separator 10, the working fluid after being throttled by the expansion valve 8 exhibits different proportions of R152a and R1234ze in the separator due to the boiling point differences between the different working fluids. Specifically, the saturated liquid leaving the separator follows proportion 1, the unsaturated vapor entering the separator follows proportion 2, and the saturated vapor leaving the separator follows proportion 3.

[0039] See Figure 2 The operating conditions for each device are described below:

[0040] Evaporator 5 is a low-pressure evaporator: the ratio of R152a and R1234ze in the circulating working fluid follows a ratio 1, the inlet temperature is the f-state point temperature Tf, and the outlet temperature is the a-state point temperature Ta. In this case, the heat exchange working fluid is set to water, with an inlet temperature of T. 5入 The outlet temperature is T 5出 .

[0041] Superheater 6 is a low-pressure superheater: the ratio of R152a and R1234ze in the circulating working fluid follows a ratio 1, the inlet temperature is state point temperature a Ta, and the outlet temperature is state point temperature b Tb. In this case, the heat exchange working fluid is set to water, with an inlet temperature of T. 6入 The outlet temperature is T 6出 .

[0042] Intermediate Evaporator 9: The ratio of R152a and R1234ze in the circulating working fluid follows a ratio of 1. The inlet temperature is the zero-state point temperature To, and the outlet temperature is the m-state point temperature Tn. In this case, the heat exchange working fluid is set to water, with an inlet temperature of T. 9入 The outlet temperature is T 9出 .

[0043] Condenser 3 is a high-pressure condenser: the ratio of R152a and R1234ze in the circulating working fluid follows ratio 2, the inlet temperature is state point temperature hTh, and the outlet temperature is state point temperature iTi. In this case, the heat exchange working fluid is set to water, with an inlet temperature of T. 3入 The outlet temperature is T 3出 .

[0044] Subcooler 4 is a high-pressure subcooler: the ratio of R152a and R1234ze in the circulating working fluid follows ratio 2, the inlet temperature is state point temperature Ti (i), and the outlet temperature is state point temperature Tj (j). In this case, the heat exchange working fluid is set to water, with an inlet temperature of T. 4入 The outlet temperature is T 4出 .

[0045] The first preferred embodiment is as follows: The two-stage heat pump energy storage device of this invention absorbs heat from heat sources in different temperature zones through two-stage evaporators, and transfers the heat energy to the energy storage system through the condenser 4. The two heat sources that the two-stage heat pump energy storage device obtains heat from can be heat sources at different temperatures, and the system efficiency is improved by simultaneously utilizing the two heat sources. The heat source can be one or more forms of energy, such as solar energy or factory waste heat.

[0046] The second preferred embodiment is as follows: The two-stage heat pump energy storage device of this invention utilizes waste heat source through intermediate evaporator 9, and uses low-temperature evaporator 5 for cooling in the corresponding temperature zone. The two-stage heat pump energy storage device can improve system efficiency by utilizing the absorbed heat while simultaneously providing cooling in the corresponding temperature zone of the low-temperature evaporator 5.

[0047] The third preferred embodiment is as follows: The two-stage heat pump energy storage device of this utility model utilizes a low-temperature evaporator 5 and an intermediate-stage evaporator 9 to perform cooling in their respective temperature zones. While performing cooling in its corresponding multiple temperature zones, the absorbed heat is stored for recovery and reuse.

[0048] Through this design and implementation method, the present invention achieves flexible application in a variety of scenarios and significantly improves the energy conversion efficiency of the system.

Claims

1. A two-stage heat pump energy storage device based on a non-azeotropic working fluid and waste heat utilization, characterized in that: It includes a low-pressure compressor (1), a high-pressure compressor (2), a condenser (3), a subcooler (4), an evaporator (5), and a superheater (6). The outlet of the low-pressure compressor (1) is connected in series with the high-pressure compressor (2), the condenser (3) and the subcooler (4), and the inlet of the low-pressure compressor (1) is connected in series with the superheater (6) and the evaporator (5). The outlet of the subcooler (4) is connected to the second working inlet of the distributor (10) through the high-pressure throttle valve (8), and the intermediate evaporator (9) is connected in parallel between the first working inlet and the outlet of the distributor (10). The first working inlet of the distributor (10) is connected to the outlet of the low-pressure compressor (1) and the inlet of the high-pressure compressor (2) through a three-way pipe, and the outlet of the distributor (10) is connected to the working inlet of the evaporator (5) through the low-pressure throttle valve (7) to form a circulation loop.

2. The two-stage heat pump energy storage device based on a non-azeotropic working fluid and waste heat utilization according to claim 1, characterized in that: The low-pressure compressor (1) is a piston compressor; the high-pressure compressor (2) is a scroll compressor.

3. A two-stage heat pump energy storage device based on a non-azeotropic working fluid and waste heat utilization as described in claim 1, characterized in that: The condenser (3) is a fixed tube sheet condenser.

4. A two-stage heat pump energy storage device based on a non-azeotropic working fluid and waste heat utilization as described in claim 1, characterized in that: The subcooler (4) is a fixed tube sheet type subcooler.

5. A two-stage heat pump energy storage device based on a non-azeotropic working fluid and waste heat utilization according to claim 1, characterized in that: The evaporator (5) is a fixed tube sheet evaporator.

6. A two-stage heat pump energy storage device based on a non-azeotropic working fluid and waste heat utilization according to claim 1, characterized in that: The superheater (6) is a plate superheater.

7. A two-stage heat pump energy storage device based on a non-azeotropic working fluid and waste heat utilization according to claim 1, characterized in that: The intermediate evaporator (9) is a microchannel shell-and-tube evaporator.

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