Low-grade waste heat energy storage system and utilization method

Abstract

The invention relates to the technical field of environment and energy systems, in particular to a low-grade waste heat energy storage system and a utilization method. The system comprises a waste heat upgrading device, a high-grade heat source storage device, a Brayton cycle power generation device, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a first low-grade waste heat supply device and a second low-grade waste heat supply device, the first low-grade waste heat supply device is connected with the waste heat upgrading device through a first heat exchanger; the waste heat upgrading device is connected with the high-grade heat source storage device through the second heat exchanger; the high-grade heat source storage device is connected with the Brayton cycle power generation device through a fourth heat exchanger; and the second low-grade waste heat supply device is connected with the Brayton cycle power generation device through the third heat exchanger. The method is combined with peak-valley power grid load time period operation, low-grade waste heat is fully utilized, the overall load rate of a power system is increased, the comprehensive utilization rate of power assets is increased, and the electricity price difference income is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental and energy systems, and in particular to a low-grade waste heat energy storage system and a utilization method thereof. Background Art

[0002] Industrial energy consumption accounts for more than 70% of the total consumption, while the energy utilization rate is relatively low. A large amount of low-grade waste heat is directly discharged, resulting in waste of resources and environmental pollution. Industrial waste heat resources are very rich and widely exist in various production processes, such as industries like coal, oil, steel, chemical industry, building materials, machinery, and light industry. Data centers are a new growth point for waste heat utilization. They are characterized by a high energy consumption density but a low waste heat temperature. At the same time, due to the continuous operation of data center servers throughout the year, there is a stable and large amount of waste heat. Since the waste heat quality is relatively low, in most scenarios, the waste heat temperature is below 60°C, making it difficult to directly utilize. Therefore, a method is proposed to improve the quality of low-grade waste heat and couple it with an energy storage system to increase the system efficiency to solve this problem. Summary of the Invention

[0003] To solve the above problems, the present invention provides a low-grade waste heat energy storage system and a utilization method thereof, and the present invention provides the following technical solutions:

[0004] A low-grade waste heat energy storage system, the system includes a waste heat upgrading device, a high-grade heat source storage device, a Brayton cycle power generation device, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a first low-grade waste heat supply device, and a second low-grade waste heat supply device.

[0005] Among them,

[0006] The first low-grade waste heat supply device is connected to the waste heat upgrading device through the first heat exchanger;

[0007] The waste heat upgrading device is connected to the high-grade heat source storage device through the second heat exchanger;

[0008] The high-grade heat source storage device is connected to the Brayton cycle power generation device through the fourth heat exchanger;

[0009] The second low-grade waste heat supply device is connected to the Brayton cycle power generation device through the third heat exchanger.

[0010] Furthermore, the waste heat upgrading device includes a compressor, a motor, a throttle valve, and a buffer storage unit, where

[0011] The compressor is connected to the motor;

[0012] The compressor and the first buffer storage unit are connected through a pipeline to form a circulation loop;

[0013] A second heat exchanger and a throttle valve are sequentially arranged on the pipeline between the outlet of the compressor and the inlet of the first buffer storage unit;

[0014] A first heat exchanger is arranged on the pipeline between the outlet of the buffer storage unit and the inlet of the compressor.

[0015] Furthermore, the high-grade heat source storage device includes a first storage unit, a first delivery pump, a second storage unit, and a second delivery pump that are sequentially connected. Among them,

[0016] The first delivery pump is used to heat-exchange the fluid with a temperature lower than the threshold value in the first storage unit through the second heat exchanger to obtain a fluid with a temperature higher than the threshold value; and input the fluid with a temperature higher than the threshold value into the second storage unit;

[0017] The second delivery pump is used to heat-exchange the fluid with a temperature higher than the threshold value in the second storage unit through the fourth heat exchanger to obtain a fluid with a temperature lower than the threshold value; and input the fluid with a temperature lower than the threshold value into the first storage unit.

[0018] Furthermore, the second storage unit is connected to the high-grade heat source utilization demand unit and is used to supply the high-temperature heat storage medium stored in the second storage unit to the outside.

[0019] Furthermore, the first low-grade waste heat supply device includes a first waste heat source, a first waste heat storage unit, and a first cold source demand unit that are sequentially connected through pipelines;

[0020] The first heat exchanger is arranged on the pipeline between the first waste heat storage unit and the first cold source demand unit.

[0021] Furthermore, the system further includes a fifth heat exchanger and an air cooling tower,

[0022] The air cooling tower is connected to the Brayton cycle power generation device through the fifth heat exchanger.

[0023] Furthermore, the Brayton cycle power generation device includes an expander, a generator, a fifth heat exchanger, a second buffer storage unit, and a booster pump. Among them,

[0024] The expander is connected to the generator;

[0025] The expander and the second buffer storage unit are connected through pipelines to form a circulation loop;

[0026] A booster pump, a third heat exchanger, and a fourth heat exchanger are sequentially arranged on the pipeline between the outlet of the second buffer storage unit and the inlet of the expander;

[0027] A fifth heat exchanger is arranged on the pipeline between the outlet of the expander and the inlet of the second buffer storage unit.

[0028] Furthermore, the second low-grade waste heat supply device includes a first waste heat heat source, a second waste heat storage unit, and a second cold source demand unit that are sequentially connected by pipelines;

[0029] The third heater is arranged on the pipeline between the second waste heat storage unit and the second cold source demand unit.

[0030] A utilization method of the low-grade waste heat energy storage system as described above is also provided, and the method includes,

[0031] The first low-grade waste heat supply device heats the fluid in the waste heat upgrading device through the first heat exchanger (4) to obtain the first fluid;

[0032] The waste heat upgrading device transfers the heat of the first fluid to the fluid in the high-grade heat source storage device through the second heat exchanger, and the high-grade heat source storage device obtains the second fluid;

[0033] The second low-grade waste heat supply device transfers the second low-grade waste heat to the fluid in the Brayton cycle power generation device through the third heat exchanger to preheat the fluid in the Brayton cycle power generation device;

[0034] The high-grade heat source storage device transfers the heat of the obtained second fluid to the preheated fluid in the Brayton cycle power generation device through the fourth heat exchanger.

[0035] Furthermore, the waste heat upgrading device raises the temperature of the fluid obtaining the first low-grade waste heat to obtain the first fluid, including:

[0036] The first low-grade waste heat heats the fluid flowing out of the first buffer storage unit in the waste heat upgrading device through the first heat exchanger;

[0037] The fluid heated by the first low-grade waste heat is compressed by a compressor and the temperature rises to the first threshold value to obtain the first fluid.

[0038] Furthermore, the waste heat upgrading device transfers the heat of the first fluid to the fluid in the high-grade heat source storage device through the second heat exchanger, and the high-grade heat source storage device obtains the second fluid, including:

[0039] After the first fluid transfers the heat of the first fluid to the high-grade heat source storage device through the second heat exchanger, the temperature of the first fluid drops to the second threshold value;

[0040] The first fluid after the temperature drop enters the first buffer storage unit through a throttle valve;

[0041] The first delivery pump raises the temperature of the fluid in the first storage unit to the third threshold value through heat exchange by the second heat exchanger to obtain the second fluid;

[0042] The second fluid enters the second storage unit for storage.

[0043] Furthermore, the high-grade heat source storage device transfers the heat obtained from the second fluid to preheat the fluid in the Brayton cycle power generation device through the fourth heat exchanger, including:

[0044] The first low-grade waste heat in the second waste heat source enters the second waste heat storage unit for storage.

[0045] The first low-grade waste heat is preheated to the fluid in the Brayton cycle power generation device after heat exchange through the third heat exchanger and then the temperature decreases. The first low-grade waste heat after the temperature decrease enters the second cold source demand unit for storage.

[0046] The second delivery pump cools the second fluid in the second storage unit through heat exchange by the fourth heat exchanger, and the cooled second fluid enters the first storage unit.

[0047] The fluid flowing out of the second buffer storage unit is boosted by a booster pump, and the boosted fluid is preheated through the third heat exchanger to obtain the preheated fluid.

[0048] The preheated fluid is heated up after obtaining the heat of the second fluid through the fourth heat exchanger to obtain the third fluid.

[0049] Furthermore, the high-grade heat source storage device transfers the heat obtained from the second fluid to the preheated fluid in the Brayton cycle power generation device through the fourth heat exchanger, and further includes:

[0050] The third fluid enters the expander to expand and do work to drive the generator to generate electricity.

[0051] The expanded third fluid enters the second buffer storage unit for storage after condensation through the fifth heat exchanger.

[0052] Furthermore, the method further includes:

[0053] The first low-grade waste heat in the first waste heat source enters the first waste heat storage unit for storage.

[0054] The first low-grade waste heat is preheated to the fluid in the waste heat upgrading device after heat exchange through the first heat exchanger and then the temperature decreases. The first low-grade waste heat after the temperature decrease enters the first cold source demand unit for storage.

[0055] The technical effects and advantages of the present invention:

[0056] The present invention provides a novel energy storage system and an operation method for improving the quality and efficiency of low-grade waste heat utilization. During the low-load period of the power grid, the low-grade waste heat is raised in temperature and stored through an inverse Brayton cycle. During the peak-load period of the power grid, the Brayton cycle is used to sequentially absorb the low-grade heat and the stored high-grade heat for power generation. By adjusting the system parameters, the system can supply cold, heat, and electricity resources separately or in a combined manner.

[0057] In the system of the present invention, during the low-load period of the power grid, the low-grade waste heat above 50 °C is raised in temperature and stored through an inverse Brayton cycle. During the peak-load period of the power grid, the Brayton cycle is used to sequentially absorb the low-grade heat and the stored high-grade heat for power generation. By adjusting the system parameters, the system can supply cold, heat, and electricity resources separately or in a combined manner. The system makes full use of the low-grade waste heat and improves the resource utilization efficiency. Combined with the operation during the peak and valley periods of the power grid load, electricity is consumed during the low-load period of the power grid, and electricity is supplied during the peak-load period, which can smooth the power grid load fluctuations, improve the overall load rate of the power system, increase the comprehensive utilization rate of power assets, and obtain the price difference income.

[0058] Other features and advantages of the present invention will be described in the following specification, and in part, will become apparent from the specification or be understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained through the structures pointed out in the specification and the drawings. Description of the Drawings

[0059] Figure 1 It is a diagram of a low-grade waste heat energy storage system provided by an embodiment of the present application.

[0060] In the figure: 1 - the first low-grade waste heat heat source; 2 - the first waste heat storage unit; 3 - the first cold source demand unit; 1' - the second low-grade waste heat heat source; 2' - the second waste heat storage unit; 3' - the second cold source demand unit; 4 - the first heat exchanger; 5 - the compressor; 6 - the motor; 7 - the second heat exchanger; 8 - the throttle valve; 9 - the first buffer storage unit; 10 - the first storage unit; 11 - the first delivery pump; 12 - the second storage unit; 13 - the second delivery pump; 14 - the high-grade heat source utilization demand unit; 15 - the booster pump; 16 - the third heat exchanger; 17 - the fourth heat exchanger; 18 - the expander; 19 - the generator; 20 - the fifth heat exchanger; 21 - the air cooling tower; 22 - the second buffer storage unit. Detailed Embodiments

[0061] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0062] To solve the deficiencies of the prior art, the present invention discloses a low-grade waste heat energy storage system. As Figure 1 shown, the system includes a waste heat upgrading device, a high-grade heat source storage device, a Brayton cycle power generation device, a first heat exchanger 4, a second heat exchanger 7, a third heat exchanger 16, a fourth heat exchanger 17, a first low-grade waste heat supply device, and a second low-grade waste heat supply device. Among them,

[0063] The first low-grade waste heat supply device is connected to the waste heat upgrading device through the first heat exchanger 4, and the first heat exchanger 4 is used to transfer the waste heat in the first low-grade waste heat supply device to the waste heat upgrading device;

[0064] The waste heat upgrading device is connected to the high-grade heat source storage device through the second heat exchanger 7, and the second heat exchanger 7 is used to transfer the heat in the waste heat upgrading device to the high-grade heat source storage device;

[0065] The high-grade heat source storage device is connected to the Brayton cycle power generation device through the fourth heat exchanger 17, and the fourth heat exchanger 17 is used to transfer the heat in the high-grade heat source storage device to the Brayton cycle power generation device;

[0066] The second low-grade waste heat supply device is connected to the Brayton cycle power generation device through the third heat exchanger 16, and the third heat exchanger 16 is used to preheat the fluid in the Brayton cycle power generation device with the waste heat in the first low-grade waste heat supply device.

[0067] In the first low-grade waste heat supply device or the first low-grade waste heat supply device, the low-grade waste heat source comes from low-grade waste heat in petrochemical, steel, and data centers, etc. The low-grade waste heat is stored in the waste heat storage device. When the waste heat upgrading device and the Brayton cycle power generation device are operating, the heat storage medium storing the waste heat exchanges heat through the first heat exchanger 4 or the third heat exchanger 16. The heat storage medium of the waste heat after heat exchange and cooling is supplied to the cold source demand 3 outside.

[0068] Exemplarily, the first low-grade waste heat supply device includes a first waste heat source 1, a first waste heat storage unit 2, and a first cold source demand unit 3 connected in sequence through pipelines; the first heat exchanger 4 is arranged on the pipeline between the first waste heat storage unit 2 and the first cold source demand unit 3.

[0069] The second low-grade waste heat supply device includes a first waste heat heat source 1', a second waste heat storage unit 2', and a second cold source demand unit 3' connected in sequence through pipelines; the third heater 16 is arranged on the pipeline between the second waste heat storage unit 2' and the second cold source demand unit 3'.

[0070] In a specific embodiment of the present invention, the waste heat upgrading device includes a compressor 5, a motor 6, a throttle valve 8, and a first buffer storage unit 9. Among them, the compressor 5 is connected to the motor 6; the compressor 5 and the first buffer storage unit 9 are connected through pipelines to form a circulation loop; a second heat exchanger 7 and a throttle valve 8 are sequentially arranged on the pipeline between the outlet of the compressor 5 and the inlet of the first buffer storage unit 9; a first heat exchanger 4 is arranged on the pipeline between the outlet of the first buffer storage unit 9 and the inlet of the compressor 5.

[0071] Exemplarily, the inlet of the compressor 5 is connected to the first heat exchanger 4, and the outlet of the compressor 5 is connected to the second heat exchanger 7; the outlet of the second heat exchanger 7 is connected to the throttle valve 8; the outlet of the throttle valve 8 is connected to the inlet of the first buffer storage unit 9; the outlet of the first buffer storage unit 9 is connected to the first heat exchanger 4.

[0072] According to different operating conditions, the state of the working fluid may be gaseous or liquid after passing through the throttle valve 8. On the one hand, the first buffer storage unit 9 serves as a working condition buffer and stabilizing device during operation to ensure the stability of the inlet and outlet parameters of each device, and on the other hand, it serves as a fluid storage place in the system shutdown state. Through the first heat exchanger 4, the waste heat upgrading device absorbs the waste heat from the low-grade waste heat supply device. Through the second heat exchanger 7, the waste heat upgrading device provides a high-grade heat source for the high-grade heat source storage system device. The compressor 5 in the waste heat upgrading device is the main power-consuming device of the system of the present invention, and the power and operation duration can be reasonably set according to the heat and working medium (or fluid) requirements of the system of the invention, so that the operation stage is in the low electricity price stage, significantly reducing the power consumption cost.

[0073] In a specific embodiment of the present invention, the high-grade heat source storage device includes a first storage unit 10, a first delivery pump 11, a second storage unit 12, and a second delivery pump 13 connected in sequence. Among them, the first delivery pump 11 is used to exchange heat of the fluid with a temperature lower than the threshold in the first storage unit 10 through the second heat exchanger 7 to obtain a fluid with a temperature higher than the threshold; and input the fluid with a temperature higher than the threshold into the second storage unit 12; the second delivery pump 13 is used to exchange heat of the fluid with a temperature higher than the threshold in the second storage unit 12 through the fourth heat exchanger 17 to obtain a fluid with a temperature lower than the threshold; and input the fluid with a temperature lower than the threshold into the first storage unit 10.

[0074] Exemplarily, in the high-grade heat source storage device, the heat storage fluid enters the second heat exchanger 7 in the waste heat upgrading device from the first storage unit 10 through the first delivery pump 11 to absorb heat and increase the temperature, and then enters the second storage unit 12. During the operation stage of the Brayton cycle power generation device, the heat storage fluid enters the fourth heat exchanger 17 in the Brayton cycle power generation device from the second storage unit 12 through the second delivery pump 13 to release heat and reduce the temperature, and then enters the first storage unit 10 for storage. In addition, the high-temperature heat storage medium stored in the second storage unit 12 can supply the high-grade heat source utilization demand unit 14 to the outside world.

[0075] In a specific embodiment of the present invention, the Brayton cycle power generation device includes an expander 18, a generator 19, a fifth heat exchanger 20, a second buffer storage unit 22, and a booster pump 15, wherein,

[0076] The expander 18 is connected to the generator 19; the expander 18 and the second buffer storage unit 22 are connected by a pipeline to form a circulation loop; a booster pump 15, a third heat exchanger 16, and a fourth heat exchanger 17 are sequentially arranged on the pipeline between the outlet of the second buffer storage unit 22 and the inlet of the expander 18; a fifth heat exchanger 20 is arranged on the pipeline between the outlet of the expander 18 and the inlet of the second buffer storage unit 22.

[0077] Exemplarily, the Brayton cycle power generation device includes an expander 18, a second buffer storage unit 22, and a booster pump 15. The inlet of the third heat exchanger 16 is connected to the outlet of the booster pump 15, and the outlet of the fourth heat exchanger 17 is connected to the inlet of the expander 18; the outlet of the expander 18 is connected to the inlet of the second buffer storage unit 22 through the fifth heat exchanger 20; the outlet of the second buffer storage unit 22 is connected to the inlet of the booster pump 15. The air cooling tower 21 is connected to the Brayton cycle power generation device through the fifth heat exchanger 20.

[0078] The waste heat upgrading device and the compressor 5 and the expander 18 in the Brayton cycle power generation device may include multiple stages, and heat exchangers are arranged at the outlet of each stage of the compressor and the inlet of the turbine.

[0079] According to the system design and the different temperatures of the low-grade waste heat, the waste heat upgrading device and the Brayton cycle power generation device can select different working fluids (or working media), such as carbon dioxide, ammonia, propane, isobutane, etc.

[0080] According to the system design and the different temperatures of the low-grade waste heat, the heat storage media of the low-grade waste heat supply device and the high-grade heat source storage device can be selected as normal pressure water, pressurized water, heat transfer oil, etc.

[0081] The low-grade waste heat supply device can be provided with a waste heat storage device according to requirements. By matching the heat demand and operation time of the waste heat upgrading device and the Brayton cycle power generation device for low-grade waste heat, the size of the waste heat storage device is reasonably selected, so that the waste heat upgrading device operates during the low grid load period or uses abandoned wind and photovoltaic power, reducing the electricity cost.

[0082] The waste heat upgrading device, high-grade heat source storage device, Brayton cycle power generation device and low-grade waste heat supply device involve the heat balance and material balance of the operating medium. According to different requirements, the system operating parameters can be adjusted to achieve the consumption trough of the waste heat upgrading device, the energy storage of abandoned wind and photovoltaic power, the supply of the grid peak load power generation by the Brayton cycle power generation device, the supply of the external high-grade heat source by the high-grade heat source storage device, and the provision of cold energy resources by the low-grade waste heat supply device. The system of the present invention can supply and co-supply cold, heat and power resources by adjusting the system parameters.

[0083] The present invention also provides a method for improving the quality and efficiency of low-grade waste heat utilization, and the method includes,

[0084] Step 1: The first low-grade waste heat in the first waste heat heat source 1 enters the first waste heat storage unit 2 for storage. The first low-grade waste heat is preheated to the fluid in the waste heat upgrading device through the first heat exchanger 4 and then the temperature is reduced. The first low-grade waste heat with reduced temperature enters the first cold source demand unit 3 for storage.

[0085] Step 2: The first low-grade waste heat supply device transfers the first low-grade waste heat to the fluid in the waste heat upgrading device through the first heat exchanger 4; the specific process is: the first low-grade waste heat heats the fluid flowing out of the first buffer storage unit 9 in the waste heat upgrading device through the first heat exchanger 4;

[0086] The fluid heated by the first low-grade waste heat is compressed by the compressor 5 and the temperature rises to the first threshold value to obtain the first fluid.

[0087] Step 3: The waste heat upgrading device raises the temperature of the fluid obtaining the first low-grade waste heat to obtain the first fluid;

[0088] Step 4: The waste heat upgrading device transfers the heat of the first fluid to the fluid in the high-grade heat source storage device through the second heat exchanger 7, and the high-grade heat source storage device obtains the second fluid. The specific process is:

[0089] After the first fluid transfers the heat of the first fluid to the high-grade heat source storage device through the second heat exchanger 7, the temperature of the first fluid drops to the second threshold; the first fluid after the temperature drop passes through the throttle valve 8 and enters the first buffer storage unit 9; the first delivery pump 11 heats the fluid in the first storage unit 10 through the second heat exchanger 7 until the temperature rises to the second threshold, obtaining a second fluid which enters the second storage unit 12 for storage.

[0090] Step 5: The second low-grade waste heat supply device transfers the second low-grade waste heat to the fluid in the Brayton cycle power generation device through the third heat exchanger 16 to preheat the fluid in the Brayton cycle power generation device. The specific process is as follows: The second delivery pump 13 cools the second fluid in the second storage unit 12 through the fourth heat exchanger 17, and the second fluid after the temperature drop enters the first storage unit 10.

[0091] The first low-grade waste heat in the second waste heat heat source 1' enters the first waste heat storage unit 2' for storage.

[0092] The first low-grade waste heat preheats the fluid in the Brayton cycle power generation device through the third heat exchanger 16 and then the temperature drops. The first low-grade waste heat after the temperature drop enters the second cold source demand unit 3' for storage.

[0093] The fluid flowing out of the second buffer storage unit 22 is boosted by the booster pump 15. After the boosted fluid is preheated through the third heat exchanger 16, preheated fluid is obtained.

[0094] The preheated fluid obtains the heat of the second fluid through the fourth heat exchanger 17 and then the temperature rises, obtaining a third fluid. The third fluid enters the expander 18 to expand and do work to drive the generator 19 to generate electricity.

[0095] After expansion, the third fluid is condensed through the fifth heat exchanger 20 and then enters the second buffer storage unit 22 for storage.

[0096] Step 6: The high-grade heat source storage device transfers the heat obtained from the second fluid to the preheated fluid in the Brayton cycle power generation device through the fourth heat exchanger 17.

[0097] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0098] In the first low-grade waste heat supply device and the second low-grade waste heat supply device, the 60°C waste heat heat source from petrochemical, steel, and data centers, etc. is stored in the first low-grade waste heat supply device and the second low-grade waste heat supply device in the form of hot water. When the waste heat upgrading device and the Brayton cycle power generation device are operating, the hot water exchanges heat through the first heat exchanger 4 and the third heat exchanger 16, and the hot water cools down to 50°C after heat exchange.

[0099] In the waste heat upgrading device, the working fluid is R11. At night during the low valley electricity period, the motor 6 drives the fluid heated by the first heat exchanger 4 to be compressed by the compressor 5. The fluid at the inlet of the compressor 5 is gaseous (0.2 MPa, 50°C), and the fluid at the outlet of the compressor 5 is gaseous (0.95 MPa, 120°C). Then the fluid exchanges heat through the second heat exchanger 7 and becomes liquid (0.94 MPa, 85°C), and then passes through the throttle valve 8 and becomes a gas-liquid mixture state (0.202 MPa, 44°C), and then enters the first buffer storage unit 9 for buffer storage. The fluid in the first buffer storage unit 9 absorbs heat from the 60°C hot water through the first heat exchanger 4, evaporates and warms up to gaseous (0.2 MPa, 50°C) and enters the compressor 5 for compression, and the cycle continues. The waste heat upgrading device operates for 6 hours every day, the fluid flow rate is 293 kg / s, and the power consumption is 10.7 MW.

[0100] In the high-grade heat source storage device, the hot water enters the second heat exchanger 7 of the waste heat upgrading device from the first storage unit 10 through the first delivery pump 11 to absorb heat and increase the temperature to 90°C, and then enters the second storage unit 12. The hot water flow rate is 800 kg / s, and the operating time is 6 hours. During the operation stage of the Brayton cycle power generation system, the heat storage medium enters the fourth heat exchanger 17 in the Brayton cycle power generation device from the second storage unit 12 through the 13 - high-temperature heat storage medium delivery pump to release heat and reduce the temperature to 75°C, and then enters the first storage unit 10 for storage. The hot water flow rate is 1200 kg / s, and the operating time is 4 hours.

[0101] In the Brayton cycle power generation device, the fluid is carbon dioxide. The fluid flows out of the second buffer storage unit 22 as a liquid (6.5 MPa, 25.4 °C), is pressurized by the booster pump 15 to a liquid state (9.8 MPa, 32.7 °C), and then enters the third heat exchanger 16 to absorb the 50 °C hot water from the low-grade waste heat supply device to initially raise the temperature to a gaseous state (9.7 MPa, 55 °C), and then enters the fourth heat exchanger 17 to absorb the 90 °C hot water from the high-grade heat source storage device to further raise the temperature to a gaseous state (9.6 MPa, 85 °C). After that, the fluid enters the expander 18 to expand and do work to drive the generator 19 to generate electricity, and the temperature and pressure of the fluid drop to a gaseous state (6.57 MPa, 54.2 °C). The expanded fluid passes through the fifth heat exchanger 2 to be condensed to a liquid state (6.5 MPa, 25.4 °C) and then enters the second buffer storage unit 22 for storage, and the cycle continues. The Brayton cycle power generation device operates for 4 hours during the peak power stage every day, the fluid flow rate is 1100 kg / s, and the power generation is 10 MW.

[0102] The electrical conversion efficiency of the system of the present invention exceeds 62%. According to the low valley power consumption of 0.2 yuan / kWh and the peak power supply of 0.8 yuan / kWh, the daily income of the system is 19,000 yuan. In addition, the system can also obtain peak shaving benefits, etc.

[0103] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A low-grade waste heat energy storage system, characterized in that The system includes a waste heat upgrading device, a high-grade heat source storage device, a Brayton cycle power generation device, a first heat exchanger (4), a second heat exchanger (7), a third heat exchanger (16), a fourth heat exchanger (17), a first low-grade waste heat supply device, and a second low-grade waste heat supply device. Among them, The first low-grade waste heat supply device is connected to the waste heat upgrading device through the first heat exchanger (4); The waste heat upgrading device is connected to the high-grade heat source storage device through the second heat exchanger (7); The high-grade heat source storage device is connected to the Brayton cycle power generation device through the fourth heat exchanger (17); The second low-grade waste heat supply device is connected to the Brayton cycle power generation device through the third heat exchanger (16).

2. The low-grade waste heat energy storage system according to claim 1, characterized in that The waste heat upgrading device includes a compressor (5), a motor (6), a throttle valve (8), and a buffer storage unit (9). Among them, The compressor (5) is connected to the motor (6); The compressor (5) and the first buffer storage unit (9) are connected by a pipeline to form a circulation loop; A second heat exchanger (7) and a throttle valve (8) are sequentially arranged on the pipeline between the outlet of the compressor (5) and the inlet of the first buffer storage unit (9); A first heat exchanger (4) is arranged on the pipeline between the outlet of the buffer storage unit (9) and the inlet of the compressor (5).

3. The low-grade waste heat energy storage system according to claim 1 or 2, characterized in that, The high-grade heat source storage device includes a first storage unit (10), a first delivery pump (11), a second storage unit (12), and a second delivery pump (13) connected in sequence. Among them, The first delivery pump (11) is used to exchange heat of the fluid with a temperature lower than the threshold in the first storage unit (10) through the second heat exchanger (7) to obtain a fluid with a temperature higher than the threshold; and input the fluid with a temperature higher than the threshold into the second storage unit (12); The second delivery pump (13) is used to exchange heat of the fluid with a temperature higher than the threshold in the second storage unit (12) through the fourth heat exchanger (17) to obtain a fluid with a temperature lower than the threshold; and input the fluid with a temperature lower than the threshold into the first storage unit (10).

4. The low-grade waste heat energy storage system according to claim 3, characterized in that The second storage unit (12) is connected to a high-grade heat source utilization demand unit (14) and is used to supply the high-temperature heat storage medium stored in the second storage unit to the outside.

5. The low-grade waste heat energy storage system according to claim 1, characterized in that The first low-grade waste heat supply device includes a first waste heat heat source (1), a first waste heat storage unit (2), and a first cold source demand unit (3) connected in sequence through a pipeline; The first heat exchanger (4) is arranged on the pipeline between the first waste heat storage unit (2) and the first cold source demand unit (3).

6. The low-grade waste heat energy storage system according to claim 1, characterized in that The system further includes a fifth heat exchanger (20) and an air cooling tower (21), The air cooling tower (21) is connected to the Brayton cycle power generation device through the fifth heat exchanger (20).

7. The low-grade waste heat energy storage system according to claim 6, characterized in that The Brayton cycle power generation device includes an expander (18), a generator (19), a fifth heat exchanger (20), a second buffer storage unit (22), and a booster pump (15), wherein, The expander (18) is connected to the generator (19); The expander (18) and the second buffer storage unit (22) are connected by a pipeline to form a circulation loop; On the pipeline between the outlet of the second buffer storage unit (22) and the inlet of the expander (18), a booster pump (15), a third heat exchanger (16), and a fourth heat exchanger (17) are sequentially arranged; A fifth heat exchanger (20) is arranged on the pipeline between the outlet of the expander (18) and the inlet of the second buffer storage unit (22).

8. The low-grade waste heat energy storage system according to claim 7, wherein, The second low-grade waste heat supply device includes a first waste heat heat source (1'), a second waste heat storage unit (2'), and a second cold source demand unit (3') connected in sequence through pipelines; The third heater (16) is arranged on the pipeline between the second waste heat storage unit (2') and the second cold source demand unit (3').

9. The utilization method of the low-grade waste heat energy storage system according to any one of claims 1-8, characterized in that, The method includes, The first low-grade waste heat supply device heats the fluid in the waste heat upgrading device through a first heat exchanger (4) to obtain a first fluid; The waste heat upgrading device transfers the heat of the first fluid to the fluid in the high-grade heat source storage device through a second heat exchanger (7), and the high-grade heat source storage device obtains a second fluid; The second low-grade waste heat supply device preheats the fluid in the Brayton cycle power generation device through a third heat exchanger (16); The high-grade heat source storage device transfers the heat of the second fluid to the preheated fluid in the Brayton cycle power generation device through a fourth heat exchanger (17).

10. The utilization method according to claim 9, wherein, The waste heat upgrading device raises the temperature of the fluid obtaining the first low-grade waste heat to obtain a first fluid, including: The first low-grade waste heat heats the fluid flowing out of the first buffer storage unit (9) in the waste heat upgrading device through the first heat exchanger (4); The fluid heated by the first low-grade waste heat is compressed by a compressor (5) and the temperature rises to a first threshold to obtain a first fluid.

11. The utilization method according to claim 9, characterized in that The waste heat upgrading device transfers the heat of the first fluid to the fluid in the high-grade heat source storage device through a second heat exchanger (7), and the high-grade heat source storage device obtains a second fluid, including: After the first fluid transfers the heat of the first fluid to the high-grade heat source storage device through the second heat exchanger (7), the temperature of the first fluid drops to a second threshold; The first fluid with the reduced temperature enters the first buffer storage unit (9) through a throttle valve (8); A first transfer pump (11) raises the temperature of the fluid in the first storage unit (10) to a third threshold through heat exchange by the second heat exchanger (7) to obtain a second fluid; The second fluid enters the second storage unit (12) for storage.

12. The utilization method according to claim 9, wherein The high-grade heat source storage device transfers the heat of the obtained second fluid to preheat the fluid in the Brayton cycle power generation device, including: The first low-grade waste heat in the second waste heat heat source (1') enters the second waste heat storage unit (2') for storage, The first low-grade waste heat is preheated for the fluid in the Brayton cycle power generation device after heat exchange through the third heat exchanger (16), and then the temperature decreases. The first low-grade waste heat after the temperature decrease enters the second cold source demand unit (3') for storage; The second transfer pump (13) cools the second fluid in the second storage unit (12) through heat exchange in the fourth heat exchanger (17), and the second fluid after the temperature decrease enters the first storage unit (10); The fluid flowing out of the second buffer storage unit (22) is pressurized by the booster pump (15), and the pressurized fluid is preheated through the third heat exchanger (16) to obtain the preheated fluid; The preheated fluid obtains the heat of the second fluid through the fourth heat exchanger (17) and then the temperature rises to obtain the third fluid.

13. The utilization method according to claim 12, wherein The high-grade heat source storage device transfers the heat obtained from the second fluid to the preheated fluid in the Brayton cycle power generation device through the fourth heat exchanger (17), and further includes: The third fluid enters the expander (18) to expand and do work to drive the generator (19) to generate electricity; The third fluid after expansion is condensed through the fifth heat exchanger (20) and then enters the second buffer storage unit (22) for storage.

14. The utilization method according to claim 9, characterized in that, The method further includes: The first low-grade waste heat in the first waste heat heat source (1) enters the first waste heat storage unit (2) for storage, The first low-grade waste heat is preheated for the fluid in the waste heat upgrading device after heat exchange through the first heat exchanger (4), and then the temperature decreases. The first low-grade waste heat after the temperature decrease enters the first cold source demand unit (3) for storage.

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