LNG (Liquefied Natural Gas) cold energy utilization system and method

Abstract

The invention discloses an LNG (Liquefied Natural Gas) cold energy utilization system and method, and the system comprises an organic Rankine cycle power generation unit which is used for heating LNG to-70 DEG C to-40 DEG C and conveying the heated LNG to an intermediate medium cold storage unit; the intermediate medium cold storage unit is used for transferring the cold energy of the LNG to an intermediate medium and heating the LNG into gaseous NG at the same time; and the gas-liquid carbon dioxide energy storage unit is used for transferring the cold energy of the intermediate medium to carbon dioxide. The ultralow-temperature LNG cold energy at the front end is recycled through the organic Rankine cycle power generation unit, direct contact between carbon dioxide and LNG is avoided through the intermediate medium cold storage unit, the LNG tail end cold energy is effectively recycled and effectively transmitted to all links of the gas-liquid carbon dioxide energy storage unit, efficient recycling of the LNG cold energy is achieved, and the energy storage peak shaving capacity is achieved.

Description

Technical Field

[0001] The present invention relates to an LNG cold energy utilization system, belonging to the technical field of surplus energy recovery. Background Art

[0002] As a clean fossil energy source, natural gas can play an important stabilizing role in peak load regulation. However, natural gas is bulky and, for ease of transportation and storage, is typically stored in a cryogenic liquid state at -162°C. This process, when re-gasified, releases a significant amount of cold energy. This cold energy can often be directly used for cryogenic pulverization, seawater desalination, or power generation via the Rankine cycle, generating significant economic benefits.

[0003] On the other hand, CO2, as an emerging compressed energy storage technology, offers great potential for long-term energy storage due to its large storage capacity, stable operation, and environmentally friendly characteristics. CO2 energy storage systems can use electricity to compress CO2 during low-demand periods and release the compressed CO2 to generate electricity during peak periods, potentially generating significant profits through the difference in peak and valley electricity prices. However, CO2 storage typically requires additional cold energy for cooling and liquefaction. Using LNG cold energy in CO2 energy storage systems not only recovers LNG cold energy but also improves the efficiency of the CO2 energy storage system, further enhancing economic benefits.

[0004] However, the triple point temperature of CO2 is -56.6°C, much higher than the -162°C of LNG storage. Directly exchanging heat between CO2 and LNG can lead to the risk of CO2 solidification. Furthermore, a significant portion of the LNG's cold energy cannot be effectively utilized. Therefore, it is necessary to adopt appropriate measures to ensure that CO2 energy storage systems can safely and effectively utilize LNG's cold energy while also fully utilizing it. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that low-temperature cold energy is required for cooling and liquefaction during the carbon dioxide energy storage and charging process. However, since the triple point temperature of carbon dioxide is -56.6°C, which is much higher than the -162°C during LNG storage, directly exchanging heat between carbon dioxide and LNG will lead to the risk of carbon dioxide solidification. The utilization efficiency of LNG cold energy is low, there is a large loss of refrigeration energy, and it may also interfere with the original gasification process of LNG.

[0006] To solve the above technical solution, the present invention provides an LNG cold energy utilization system, comprising: Organic Rankine cycle power generation unit, used to heat LNG to -70~-40℃ and transport the heated LNG to the intermediate medium cold storage unit; The intermediate medium cold storage unit is used to transfer the cold energy of LNG to the intermediate medium and heat the LNG into gaseous NG; The gas-liquid carbon dioxide energy storage unit is used to transfer the cold energy of the intermediate medium to carbon dioxide.

[0007] In the aforementioned LNG cold energy utilization system, in the organic Rankine cycle power generation unit, the output pipeline of the LNG storage tank is connected to the cold end inlet of the ORC condenser through an LNG pump, and the cold end outlet of the ORC condenser is connected to the intermediate medium cold storage unit; The hot end outlet of the ORC condenser is connected to the hot end inlet of the ORC condenser through the ORC pump, ORC evaporator, and ORC turbine.

[0008] The aforementioned LNG cold energy utilization system includes an intermediate medium cooler in the intermediate medium cold storage unit, wherein the cold end inlet of the intermediate medium cooler is connected to the cold end outlet of the ORC condenser of the organic Rankine cycle power generation unit, and the cold end outlet of the intermediate medium cooler is connected to the NG user; The hot end outlet of the intermediate medium cooler is connected to the cold end inlet of the carbon dioxide cooler, the carbon dioxide condenser, and the water cooler after passing through the low-temperature intermediate medium storage tank; the cold end outlets of the carbon dioxide cooler, the carbon dioxide condenser, and the water cooler are connected to the inlet of the high-temperature intermediate medium storage tank respectively; The outlet end of the high-temperature intermediate medium storage tank is connected to the hot end inlet of the intermediate medium cooler.

[0009] In the aforementioned LNG cold energy utilization system, the gas-liquid carbon dioxide energy storage unit includes an energy storage charging unit and an energy storage discharging unit; The energy storage and charging unit includes a carbon dioxide gas storage reservoir, the outlet of the carbon dioxide gas storage reservoir is connected to the carbon dioxide liquid storage tank in sequence through the hot end inlet of the carbon dioxide cooler, the hot end outlet of the carbon dioxide cooler, the carbon dioxide compressor, the hot end inlet of the compression heat recovery device, the hot end outlet of the compression heat recovery device, the hot end inlet of the carbon dioxide condenser, and the hot end outlet of the carbon dioxide condenser; the outlet end of the low-temperature water tank is connected to the cold end inlet of the compression heat recovery device, the cold end outlet of the compression heat recovery device, and the inlet of the high-temperature water tank in sequence through pipelines; The energy storage and discharge unit includes a carbon dioxide storage tank, the outlet of which is connected to the carbon dioxide gas storage reservoir through a carbon dioxide evaporator, a cold end inlet of a compression heat releaser, a cold end outlet of a compression heat releaser, a carbon dioxide turbine, and a carbon dioxide heater in sequence; the outlet of the high-temperature water tank is connected to the inlet of the low-temperature water tank through a hot end inlet of a compression heat releaser, a hot end outlet of a compression heat releaser, a hot end inlet of a water cooler, and a hot end outlet of a water cooler in sequence.

[0010] In the aforementioned LNG cold energy utilization system, in the intermediate medium cold storage unit, the intermediate cold storage medium in the low-temperature intermediate medium storage tank enters the carbon dioxide cooler and the carbon dioxide condenser at the same time during the energy storage charging stage, and does not enter the water cooler; during the energy storage discharging stage, it enters the water cooler, and does not enter the carbon dioxide cooler and the carbon dioxide condenser; the flow and time of each channel are controlled by setting an electronic valve on the outlet pipe of the low-temperature intermediate medium storage tank.

[0011] In the aforementioned LNG cold energy utilization system, the organic Rankine cycle power generation unit is composed of multiple Rankine cycles connected in series in the LNG flow direction, but in the ORC condenser of each Rankine cycle, different condensation temperatures are formed from low to high, and the condensation temperature in the ORC condenser closest to the intermediate medium cooler must be greater than -70°C and less than -30°C.

[0012] A method for utilizing LNG cold energy comprises the following steps: Step 1: LNG in the LNG storage tank is pumped out and pressurized by the LNG pump and enters the organic Rankine cycle power generation unit; Step 2: In the organic Rankine cycle power generation unit, the LNG is heated to -70 to -40°C, and the heated LNG is transported to the intermediate medium cold storage unit; Step 3: In the intermediate medium cold storage unit, the cold energy of the LNG is transferred to the intermediate medium, and the LNG is heated into gaseous NG; Step 4: Transfer the cold energy of the intermediate medium to carbon dioxide, including carbon dioxide energy storage charging and carbon dioxide energy storage discharging processes.

[0013] The aforementioned LNG cold energy utilization method, in the organic Rankine cycle power generation unit, heats the LNG to -70~-40°C and transports the heated LNG to the intermediate medium cold storage unit, comprising: The high-pressure liquid organic Rankine cycle fluid is heated in the ORC evaporator, then expanded to atmospheric pressure in the ORC turbine to perform work. It is then cooled in the ORC condenser, then pressurized to a high-pressure liquid in the ORC pump before re-entering the ORC evaporator to begin a new cycle. The pressure of the high-pressure liquid organic Rankine cycle fluid ranges from 0.6 to 2.5 MPa. After being heated by the ORC condenser, the LNG enters the intermediate medium cold storage unit.

[0014] The aforementioned method for utilizing cold energy of LNG, in the organic Rankine cycle power generation unit, in the intermediate medium cold storage unit, is used to transfer cold energy of LNG to the intermediate medium and simultaneously heat the LNG into gaseous NG, comprising: The high-temperature liquid intermediate medium is extracted from the high-temperature intermediate medium storage tank, enters the intermediate medium cooler and is cooled into a low-temperature liquid state, and then stored in the low-temperature intermediate medium storage tank for standby use; During the energy storage and charging phase, the low-temperature liquid intermediate medium is extracted from the low-temperature intermediate medium storage tank, enters the carbon dioxide cooler and the carbon dioxide condenser in parallel, is heated to a high-temperature liquid state, and is then stored in the high-temperature intermediate medium storage tank; During the energy storage and discharge phase, the low-temperature liquid intermediate medium is extracted from the low-temperature intermediate medium storage tank, enters the water cooler, is heated into a high-temperature liquid state, and is then stored in the high-temperature intermediate medium storage tank.

[0015] In the aforementioned method for utilizing LNG cold energy, in the organic Rankine cycle power generation unit, when the high-temperature intermediate medium storage tank detects that the storage volume has reached 3 / 4 of the maximum capacity, it begins to extract the high-temperature liquid intermediate medium and sends it into the intermediate medium cooler to start a new cycle.

[0016] The aforementioned LNG cold energy utilization method transfers the cold energy of the intermediate medium to carbon dioxide, including carbon dioxide energy storage charging and carbon dioxide energy storage discharging processes. The carbon dioxide energy storage charging process includes: Carbon dioxide at room temperature and pressure is extracted from the carbon dioxide storage reservoir and enters the carbon dioxide cooler to be cooled into low-temperature gas. The temperature of the low-temperature gas is -50~-25℃. Low-temperature gaseous carbon dioxide enters the carbon dioxide compressor and becomes high-pressure, high-temperature gaseous carbon dioxide. At this time, the pressure is 0.6-0.9MPa and the temperature is 100-150℃; The high-pressure and high-temperature gas carbon dioxide enters the compression heat recovery device and is cooled by water from the low-temperature water tank into a high-pressure medium-temperature gas. At this time, the temperature is 5-15°C and the pressure is 0.6-0.9MPa. The high-pressure, medium-temperature gas enters the carbon dioxide condenser and is condensed into a high-pressure, low-temperature liquid. At this time, the pressure is 0.6-0.9MPa and the temperature is -45~-55℃. The high-pressure, low-temperature liquid carbon dioxide then enters the carbon dioxide storage tank for storage.

[0017] The aforementioned method for utilizing cold energy of LNG is described. The water from the low-temperature water tank is heated up after cooling carbon dioxide in the compression heat recovery device, and is converted into high-temperature liquid water and stored in the high-temperature water tank.

[0018] The aforementioned LNG cold energy utilization method, during the carbon dioxide energy storage and discharge process, includes: High-pressure and low-temperature liquid carbon dioxide is extracted from the carbon dioxide storage tank and enters the carbon dioxide evaporator to be heated and turned into gas. At this time, the temperature of the carbon dioxide is 10~20℃. The gaseous carbon dioxide enters the compression heat releaser and is further heated by the high-temperature water from the high-temperature water tank to increase the temperature, forming high-temperature and high-pressure gaseous carbon dioxide with a pressure of 0.6-0.9 MPa and a temperature of 90-140°C; The high-temperature and high-pressure gaseous carbon dioxide enters the carbon dioxide turbine to expand and do work. The outlet of the carbon dioxide turbine is low-temperature and low-pressure gaseous carbon dioxide with a pressure of 0.1 MPa and a temperature of -10-10°C. The low-temperature and low-pressure gaseous carbon dioxide is heated to ambient temperature by a carbon dioxide heater and then sent to the carbon dioxide storage reservoir for storage.

[0019] In the aforementioned method for utilizing LNG cold energy, the high-temperature water from the high-temperature water tank heats carbon dioxide in the compression heat releaser and its temperature is lowered. The water then enters the water cooler, is cooled to the set temperature of the low-temperature water tank, and is then sent to the low-temperature water tank for storage.

[0020] The beneficial effects achieved by the present invention are as follows: the LNG cold energy utilization system of the present invention rationally transfers part of the LNG cold energy to carbon dioxide through an intermediate medium, so that the carbon dioxide energy storage cycle process is not frozen and does not interfere with the stable gasification of LNG; and the efficient utilization of LNG cold energy is achieved through the rational combination of Rankine cycle and carbon dioxide energy storage.

[0021] The present invention may only require seawater as a heat source, but may also utilize heat sources with higher temperatures such as solar energy, geothermal energy, and industrial waste heat, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the system in Example 1 of the present invention.

[0023] Figure 1: LNG storage tank; 2: LNG pump; 3: ORC condenser; 4: intermediate medium cooler; 5: seawater heater; 6: ORC pump; 7: ORC evaporator; 8: ORC turbine; 9: low-temperature intermediate medium storage tank; 10: high-temperature intermediate medium storage tank; 11: CO2 cooler; 12: CO2 compressor; 13: compression heat recovery device; 14: CO2 condenser; 15: CO2 storage tank; 16: CO2 heater; 17: CO2 turbine; 18: compression heat release device; 19: CO2 evaporator; 20: CO2 storage tank; 21: high-temperature water tank; 22: water cooler; 23: low-temperature water tank. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings. Example 1

[0025] like Figure 1As shown, this embodiment provides an LNG cold energy utilization system, including: Organic Rankine cycle power generation unit, used to heat LNG to -70~-40℃ and transport the heated LNG to the intermediate medium cold storage unit; The intermediate medium cold storage unit is used to transfer the cold energy of LNG to the intermediate medium and heat the LNG into gaseous NG; The gas-liquid carbon dioxide energy storage unit is used to transfer the cold energy of the intermediate medium to carbon dioxide.

[0026] In the organic Rankine cycle power generation unit, the output pipeline of the LNG storage tank 1 is connected to the cold end inlet of the ORC condenser 3 through the LNG pump 2, and the cold end outlet of the ORC condenser 3 is connected to the intermediate medium cold storage unit; The hot end outlet of the ORC condenser 3 is connected to the hot end inlet of the ORC condenser 3 through the ORC pump 6 , the ORC evaporator 7 , and the ORC turbine 8 .

[0027] The intermediate medium cold storage unit includes an intermediate medium cooler 4, the cold end inlet of the intermediate medium cooler 4 is connected to the cold end outlet of the ORC condenser 3 of the organic Rankine cycle power generation unit, and the cold end outlet of the intermediate medium cooler 4 is connected to the NG user; The hot end outlet of the intermediate medium cooler 4 is connected to the cold end inlets of the carbon dioxide cooler 11, the carbon dioxide condenser 14, and the water cooler 22 respectively after passing through the low-temperature intermediate medium storage tank 9; the cold end outlets of the carbon dioxide cooler 11, the carbon dioxide condenser 14, and the water cooler 22 are respectively connected to the inlet of the high-temperature intermediate medium storage tank 10.

[0028] The outlet end of the high-temperature intermediate medium storage tank 10 is connected to the hot end inlet of the intermediate medium cooler 4 .

[0029] The cold energy is transferred through the intermediate medium storage tank and used for carbon dioxide cooling and circulating water heat balance in specific time periods without interfering with the LNG gasification process.

[0030] The gas-liquid carbon dioxide energy storage unit includes an energy storage charging unit and an energy storage discharging unit; The energy storage and charging unit includes a carbon dioxide gas storage reservoir 15, and the outlet of the carbon dioxide gas storage reservoir 15 is connected to the carbon dioxide liquid storage tank 20 in sequence through the hot end inlet of the carbon dioxide cooler 11, the hot end outlet of the carbon dioxide cooler 11, the carbon dioxide compressor 12, the hot end inlet of the compression heat recovery device 13, the hot end outlet of the compression heat recovery device 13, the hot end inlet of the carbon dioxide condenser 14, and the hot end outlet of the carbon dioxide condenser 14; the outlet end of the low-temperature water tank 23 is connected to the cold end inlet of the compression heat recovery device 13, the cold end outlet of the compression heat recovery device 13, and the inlet of the high-temperature water tank 21 in sequence through pipelines.

[0031] The energy storage and discharge unit includes a carbon dioxide storage tank 20, the outlet of which is connected to the carbon dioxide storage reservoir 15 through the carbon dioxide evaporator 19, the cold end inlet of the compression heat releaser 18, the cold end outlet of the compression heat releaser 18, the carbon dioxide turbine 17, and the carbon dioxide heater 16 in sequence; the outlet of the high-temperature water tank 21 is connected to the inlet of the low-temperature water tank 23 through the hot end inlet of the compression heat releaser 18, the hot end outlet of the compression heat releaser 18, the hot end inlet of the water cooler 22, and the hot end outlet of the water cooler 22 in sequence.

[0032] Through the coordination of water, intermediate cold storage medium, and waste heat source, water is used to transfer and convert compression heat, the intermediate medium is used to cool carbon dioxide, and the waste heat source is used to gasify carbon dioxide, which simplifies the complexity of the heat recovery unit while achieving high round-trip efficiency.

[0033] A method for utilizing LNG cold energy comprises the following steps: Step 1: LNG in the LNG storage tank is pumped out and pressurized by the LNG pump and enters the organic Rankine cycle power generation unit.

[0034] Step 2, in the organic Rankine cycle power generation unit, heating the LNG to -70 to -40°C and delivering the heated LNG to the intermediate medium cold storage unit, comprising: The high-pressure liquid organic Rankine cycle working fluid is heated in the ORC evaporator 7, converted from liquid to gas. It then expands in the ORC turbine 8, reducing its pressure to normal to perform external work. It is then cooled in the ORC condenser 3, converted from gas to liquid, and pressurized in the ORC pump 6 to a high-pressure liquid state before re-entering the ORC evaporator 7 to begin a new cycle. The pressure of the high-pressure liquid organic Rankine cycle working fluid ranges from 0.6 to 2.5 MPa.

[0035] The cooling energy used to condense the organic Rankine cycle working fluid in the ORC condenser 3 is derived from LNG, which is also heated. The working fluid and heat source of the organic Rankine cycle power generation unit can be selected based on existing technologies, and the corresponding operating parameters can also be designed based on the specific working fluid and heat source, which will not be further described here.

[0036] After being heated by the ORC condenser 3, the LNG enters the intermediate medium cold storage unit.

[0037] Step 3, in the intermediate medium cold storage unit, transfers the cold energy of the LNG to the intermediate medium and heats the LNG into gaseous NG, including: The high-temperature liquid intermediate medium (temperature 0-25°C) is extracted from the high-temperature intermediate medium storage tank 10, enters the intermediate medium cooler 4 and is cooled into a low-temperature liquid (temperature -65~-30°C), and then stored in the low-temperature intermediate medium storage tank 9 for standby use.

[0038] During the energy storage and charging stage, the low-temperature liquid intermediate medium is extracted from the low-temperature intermediate medium storage tank 9 and enters the carbon dioxide cooler 11 and the carbon dioxide condenser 14 in parallel to be heated into a high-temperature liquid state, and then stored in the high-temperature intermediate medium storage tank 10.

[0039] During the energy storage and discharge phase, the low-temperature liquid intermediate medium is extracted from the low-temperature intermediate medium storage tank 9 , enters the water cooler and is heated into a high-temperature liquid state, and then stored in the high-temperature intermediate medium storage tank 10 .

[0040] When the high-temperature intermediate medium storage tank 10 detects that the storage volume has reached 3 / 4 of the maximum capacity, it starts to extract the high-temperature liquid intermediate medium and sends it to the intermediate medium cooler 4 to start a new cycle.

[0041] The cold energy for cooling the intermediate medium in the intermediate medium cooler 4 comes from the LNG at the outlet of the ORC condenser.

[0042] After passing through the intermediate medium cooler 4, the temperature of LNG is heated to -20~0°C, and then heated to above 0°C by the seawater heater, and becomes NG near room temperature and is delivered to users.

[0043] Step 4: Transfer the cold energy of the intermediate medium to carbon dioxide, including carbon dioxide energy storage charging and carbon dioxide energy storage discharging processes.

[0044] The energy storage and charging unit of the gas-liquid carbon dioxide energy storage unit includes a carbon dioxide cooler 11, a carbon dioxide condenser 14, a carbon dioxide gas storage reservoir 15, a carbon dioxide compressor 12, a compression heat recovery device 13, a carbon dioxide liquid storage tank 20, a low-temperature water tank 23, and a high-temperature water tank 21.

[0045] The carbon dioxide energy storage charging process includes: 411) Carbon dioxide in normal temperature and pressure gaseous state is extracted from the carbon dioxide storage reservoir 15 and enters the carbon dioxide cooler 11 to be cooled into low-temperature gaseous state. The temperature of the low-temperature gaseous state is -50~-25℃; 412) The low-temperature gaseous carbon dioxide enters the carbon dioxide compressor 12 and becomes a high-pressure, high-temperature gaseous state, at which the pressure is 0.6-0.9 MPa and the temperature is 100-150°C; 413) The high-pressure, high-temperature gaseous carbon dioxide enters the compression heat recovery device 13 and is cooled by water from the low-temperature water tank 23 into a high-pressure, medium-temperature gaseous state with a temperature of 5-15°C and a pressure of 0.6-0.9 MPa; 414) The high-pressure, low-temperature saturated gas enters the carbon dioxide condenser 14 and is condensed into a high-pressure, low-temperature liquid. At this time, the pressure is 0.6-0.9 MPa and the temperature is -45~-55°C. The high-pressure, low-temperature liquid carbon dioxide then enters the carbon dioxide storage tank 20 for storage.

[0046] The water from the low-temperature water tank is heated up after cooling the carbon dioxide in the compression heat recovery device 13 , and is converted into high-temperature liquid water and is stored in the high-temperature water tank 21 .

[0047] The energy storage and discharge unit of the gas-liquid carbon dioxide energy storage unit includes the carbon dioxide gas storage reservoir 15, the carbon dioxide liquid storage tank 20, the low-temperature water tank 23, the high-temperature water tank 21, the water cooler 22, the compression heat release device 18, the carbon dioxide turbine 17, the carbon dioxide evaporator 19, and the carbon dioxide heater 16. The water temperature in the low-temperature water tank 23 is 1-10°C, and the water temperature in the high-temperature water tank 21 is 95-145°C.

[0048] The process of carbon dioxide energy storage and discharge includes: 421) High-pressure, low-temperature liquid carbon dioxide is extracted from the carbon dioxide storage tank 20 and enters the carbon dioxide evaporator 19 where it is heated and converted into gas. At this point, the temperature of the carbon dioxide is 10-20°C. 422) The gaseous carbon dioxide enters the compression heat releaser 18 and is further heated by the high-temperature water from the high-temperature water tank to increase the temperature, forming high-temperature and high-pressure gaseous carbon dioxide with a pressure of 0.6-0.9 MPa and a temperature of 90-140°C; 423) The high-temperature and high-pressure gaseous carbon dioxide enters the carbon dioxide turbine 17 to expand and perform work. The outlet of the carbon dioxide turbine 17 is low-temperature and low-pressure gaseous carbon dioxide with a pressure of 0.1 MPa and a temperature of -10-10°C. 424) The low-temperature and low-pressure gaseous carbon dioxide is heated to ambient temperature by the carbon dioxide heater 16 and then sent to the carbon dioxide storage reservoir 15 for storage.

[0049] The high-temperature water from the high-temperature water tank heats the carbon dioxide in the compression heat releaser 18, and then enters the water cooler 22, where it is cooled to the set temperature of the low-temperature water tank and then sent to the low-temperature water tank 23 for storage to prepare for the next round of charge and discharge cycles.

[0050] To save costs, the intermediate medium cold storage unit operates at atmospheric pressure. Methanol can be used as the intermediate medium. HFE-7100, HFE-7200, or other intermediate mediums can also be used. The intermediate medium must have a boiling point greater than 45°C and a freezing point less than -70°C at atmospheric pressure, and exhibit good fluidity. Example 2

[0051] This embodiment provides an LNG cold energy utilization system, comprising: Organic Rankine cycle power generation unit, used to heat LNG to -70~-40℃ and transport the heated LNG to the intermediate medium cold storage unit; The intermediate medium cold storage unit is used to transfer the cold energy of LNG to the intermediate medium and heat the LNG into gaseous NG; The gas-liquid carbon dioxide energy storage unit is used to transfer the cold energy of the intermediate medium to carbon dioxide.

[0052] The intermediate medium cold storage unit, containing the intermediate cold storage medium in the low-temperature intermediate medium storage tank 9, enters both the CO2 cooler 11 and the CO2 condenser 14 during the energy storage charging phase, but not the water cooler 22. During the energy storage discharging phase, the intermediate cold storage medium enters the water cooler 22, but not the CO2 cooler 11 or the CO2 condenser 14. Electronic valves are installed on the outlet pipe of the low-temperature intermediate medium storage tank 9 to control the flow and timing of each channel. This minimizes the intermediate medium flow rate, reduces the tank volume, and thus reduces costs. Example 3

[0053] This embodiment provides an LNG cold energy utilization system, comprising: Organic Rankine cycle power generation unit, used to heat LNG to -70~-40℃ and transport the heated LNG to the intermediate medium cold storage unit; The intermediate medium cold storage unit is used to transfer the cold energy of LNG to the intermediate medium and heat the LNG into gaseous NG; The gas-liquid carbon dioxide energy storage unit is used to transfer the cold energy of the intermediate medium to carbon dioxide.

[0054] The organic Rankine cycle power generation unit has a condensing pressure of atmospheric pressure and an evaporation pressure calculated based on the heat source temperature. Propane can be selected as the circulating working fluid. Other alternative working fluids should at least have a boiling point greater than -70°C and less than -30°C at atmospheric pressure.

[0055] In addition, the organic Rankine cycle power generation unit, in addition to Figure 1 The single Rankine cycle configuration shown can also be constructed by connecting multiple Rankine cycles in series in the direction of LNG flow. However, the ORC condenser in each Rankine cycle has varying condensing temperatures, from low to high. The condensing temperature in the ORC condenser closest to the intermediate medium cooler must be greater than -70°C and less than -30°C. These varying condensing temperatures help create a heat exchange temperature gradient with the LNG, thereby reducing exergy losses during the LNG vaporization process and improving cold energy recovery efficiency. Example 4

[0056] This embodiment provides an LNG cold energy utilization system, comprising: Organic Rankine cycle power generation unit, used to heat LNG to -70~-40℃ and transport the heated LNG to the intermediate medium cold storage unit; The intermediate medium cold storage unit is used to transfer the cold energy of LNG to the intermediate medium and heat the LNG into gaseous NG; The gas-liquid carbon dioxide energy storage unit is used to transfer the cold energy of the intermediate medium to carbon dioxide.

[0057] The ORC evaporator 7, CO2 evaporator 20, and CO2 heater 16 can be heated using seawater, geothermal energy, or industrial waste heat. The higher the heat source temperature, the higher the temperature of the Rankine cycle fluid and CO2 before entering the turbines, resulting in greater power generation.

[0058] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An LNG cold energy utilization system, characterized in that: include: Organic Rankine cycle power generation unit, used to heat LNG to -70~-40℃ and transport the heated LNG to the intermediate medium cold storage unit; The intermediate medium cold storage unit is used to transfer the cold energy of LNG to the intermediate medium and heat the LNG into gaseous NG; The gas-liquid carbon dioxide energy storage unit is used to transfer the cold energy of the intermediate medium to carbon dioxide.

2. The LNG cold energy utilization system according to claim 1, characterized in that: In the organic Rankine cycle power generation unit, the output pipeline of the LNG storage tank (1) is connected to the cold end inlet of the ORC condenser (3) through the LNG pump (2), and the cold end outlet of the ORC condenser (3) is connected to the intermediate medium cold storage unit; The hot end outlet of the ORC condenser (3) is connected to the hot end inlet of the ORC condenser (3) through the ORC pump (6), the ORC evaporator (7), and the ORC turbine (8).

3. The LNG cold energy utilization system according to claim 1, characterized in that: In the intermediate medium cold storage unit, an intermediate medium cooler (4) is included, a cold end inlet of the intermediate medium cooler (4) is connected to a cold end outlet of an ORC condenser (3) of an organic Rankine cycle power generation unit, and a cold end outlet of the intermediate medium cooler (4) is connected to an NG user; The hot end outlet of the intermediate medium cooler (4) is connected to the cold end inlets of the carbon dioxide cooler (11), the carbon dioxide condenser (14), and the water cooler (22) respectively after passing through the low-temperature intermediate medium storage tank (9); the cold end outlets of the carbon dioxide cooler (11), the carbon dioxide condenser (14), and the water cooler (22) are connected to the inlet of the high-temperature intermediate medium storage tank (10); The outlet end of the high-temperature intermediate medium storage tank (10) is connected to the hot end inlet of the intermediate medium cooler (4).

4. The LNG cold energy utilization system according to claim 1, characterized in that: The gas-liquid carbon dioxide energy storage unit includes an energy storage charging unit and an energy storage discharging unit; The energy storage and charging unit includes a carbon dioxide gas storage reservoir (15), the outlet of the carbon dioxide gas storage reservoir (15) is connected to the carbon dioxide liquid storage tank (20) in sequence through the hot end inlet of the carbon dioxide cooler (11), the hot end outlet of the carbon dioxide cooler (11), the carbon dioxide compressor (12), the hot end inlet of the compression heat recovery device (13), the hot end outlet of the compression heat recovery device (13), the hot end inlet of the carbon dioxide condenser (14), and the hot end outlet of the carbon dioxide condenser (14); the outlet end of the low-temperature water tank (23) is connected to the cold end inlet of the compression heat recovery device (13), the cold end outlet of the compression heat recovery device (13), and the inlet of the high-temperature water tank (21) in sequence through pipelines; The energy storage and discharge unit comprises a carbon dioxide liquid storage tank (20), wherein the outlet of the carbon dioxide liquid storage tank (20) is connected to the carbon dioxide gas storage reservoir (15) through a carbon dioxide evaporator (19), a cold end inlet of a compression heat releaser (18), a cold end outlet of the compression heat releaser (18), a carbon dioxide turbine (17), and a carbon dioxide heater (16) in sequence; and the outlet of the high-temperature water tank (21) is connected to the inlet of a low-temperature water tank (23) through a hot end inlet of a compression heat releaser (18), a hot end outlet of the compression heat releaser (18), a hot end inlet of a water cooler (22), and a hot end outlet of the water cooler (22) in sequence.

5. The LNG cold energy utilization system according to claim 1, characterized in that: In the intermediate medium cold storage unit, the intermediate cold storage medium in the low-temperature intermediate medium storage tank (9) enters the carbon dioxide cooler (11) and the carbon dioxide condenser (14) simultaneously during the energy storage charging phase, and does not enter the water cooler (22); during the energy storage discharging phase, it enters the water cooler (22) and does not enter the carbon dioxide cooler (11) and the carbon dioxide condenser (14); and the flow rate and time of each channel are controlled by arranging an electronic valve on the outlet pipe of the low-temperature intermediate medium storage tank (9).

6. A method for utilizing LNG cold energy, characterized in that: The following steps are involved: The LNG in the LNG storage tank is pumped out and pressurized by the LNG pump and enters the organic Rankine cycle power generation unit; In the organic Rankine cycle power generation unit, LNG is heated to -70~-40°C and the heated LNG is transported to the intermediate medium cold storage unit; In the intermediate medium cold storage unit, the cold energy of LNG is transferred to the intermediate medium, and the LNG is heated into gaseous NG at the same time; The cold energy of the intermediate medium is transferred to carbon dioxide, including carbon dioxide energy storage charging and carbon dioxide energy storage discharging processes.

7. The method for utilizing LNG cold energy according to claim 6, characterized in that: In the organic Rankine cycle power generation unit, LNG is heated to -70~-40°C and the heated LNG is transported to the intermediate medium cold storage unit, including: The high-pressure liquid organic Rankine cycle working fluid is heated from liquid to gas in the ORC evaporator (7), undergoes expansion in the ORC turbine (8) and is reduced to normal pressure to perform external work, is cooled from gas to liquid in the ORC condenser (3), is pressurized to high-pressure liquid in the ORC pump (6), and enters the ORC evaporator (7) again to start a new cycle. The pressure range of the high-pressure liquid organic Rankine cycle working fluid is 0.6-2.5 MPa; After being heated by the ORC condenser (3), the LNG enters the intermediate medium cold storage unit.

8. The method for utilizing LNG cold energy according to claim 6, characterized in that: In the intermediate medium cold storage unit, the cold energy of LNG is transferred to the intermediate medium, and the LNG is heated into gaseous NG, including: The high-temperature liquid intermediate medium is drawn from the high-temperature intermediate medium storage tank (10), enters the intermediate medium cooler (4) and is cooled into a low-temperature liquid state, and then stored in the low-temperature intermediate medium storage tank (9) for future use; During the energy storage and charging phase, the low-temperature liquid intermediate medium is extracted from the low-temperature intermediate medium storage tank (9), enters the carbon dioxide cooler (11) and the carbon dioxide condenser (14) in parallel, is heated to a high-temperature liquid state, and is then stored in the high-temperature intermediate medium storage tank (10); During the energy storage and discharge phase, the low-temperature liquid intermediate medium is drawn from the low-temperature intermediate medium storage (9) tank, enters the water cooler and is heated to a high-temperature liquid state, and is then stored in the high-temperature intermediate medium storage tank (10).

9. The method for utilizing LNG cold energy according to claim 6, characterized in that: The cold energy of the intermediate medium is transferred to carbon dioxide, including the carbon dioxide energy storage charging and carbon dioxide energy storage discharging processes. The carbon dioxide energy storage charging process includes: Carbon dioxide in a normal temperature and pressure gaseous state is extracted from the carbon dioxide gas storage (15) and enters the carbon dioxide cooler (11) to be cooled into a low-temperature gaseous state, the temperature of which is -50 to -25°C. The low-temperature gaseous carbon dioxide enters the carbon dioxide compressor (12) and becomes a high-pressure, high-temperature gaseous state, at which the pressure is 0.6-0.9 MPa and the temperature is 100-150°C; The high-pressure and high-temperature gaseous carbon dioxide enters the compression heat recovery device (13) and is cooled by water from the low-temperature water tank (23) into a high-pressure and medium-temperature gaseous state, at which the temperature is 5-15°C and the pressure is 0.6-0.9MPa; The high-pressure, medium-temperature gas enters the carbon dioxide condenser (14) and is condensed into a high-pressure, low-temperature liquid. At this time, the pressure is 0.6-0.9 MPa and the temperature is -45~-55°C. The high-pressure, low-temperature liquid carbon dioxide then enters the carbon dioxide storage tank (20) for storage.

10. The method for utilizing LNG cold energy according to claim 6, characterized in that: The process of carbon dioxide energy storage and discharge includes: High-pressure and low-temperature liquid carbon dioxide is extracted from the carbon dioxide storage tank (20) and enters the carbon dioxide evaporator (19) to be heated and converted into gaseous state. At this time, the temperature of the carbon dioxide is 10-20°C. The gaseous carbon dioxide enters the compression heat releaser (18) and is further heated by the high-temperature water from the high-temperature water tank to increase the temperature, thereby forming high-temperature and high-pressure gaseous carbon dioxide with a pressure of 0.6-0.9 MPa and a temperature of 90-140°C; The high-temperature and high-pressure gaseous carbon dioxide enters the carbon dioxide turbine (17) to expand and perform work. The outlet of the carbon dioxide turbine (17) is low-temperature and low-pressure gaseous carbon dioxide with a pressure of 0.1 MPa and a temperature of -10-10°C. The low-temperature and low-pressure gaseous carbon dioxide is heated to ambient temperature by the carbon dioxide heater (16) and then sent to the carbon dioxide storage reservoir (15) for storage.

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