A multi-working fluid coupled vaporization system and method for LNG cold energy cascade utilization

Abstract

The application discloses a multi-working medium coupling vaporization system and method for LNG cold energy stepwise utilization, which recycles and utilizes LNG cold energy through intermediate medium primary refrigerant and secondary refrigerant CO2, and recovers the cold energy of low-temperature NG (60 DEG C to 5 DEG C) of a shallow cold temperature level through gaseous secondary refrigerant CO2 first E3 section heat exchange. The application not only realizes LNG cold energy stepwise recycling and utilization, but also reduces equipment pipe diameter, lowers equipment cost, and improves heat exchange efficiency by 5% to 10%. In addition, the application can flexibly adjust different temperature level cold energy supply and refrigerant supply temperature through refrigerant shunting and substock treatment, and improves the operation flexibility of the whole system.

Description

Technical Field

[0001] This invention belongs to the field of LNG cold energy recovery and utilization, specifically relating to a multi-working-medium coupled vaporization system and method for LNG cold energy cascade utilization. Background Technology

[0002] Natural gas is a clean energy source that the country is vigorously promoting, while LNG has gradually become an important strategic reserve energy source. According to statistics from China Customs, my country's cumulative natural gas imports reached 121.36 million tons in 2021, of which LNG imports reached 78.93 million tons.

[0003] LNG is a liquid formed from natural gas after purification and cooling to approximately -162°C. It contains a large amount of cold energy, and LNG needs to be vaporized before it can be transported through centralized pipeline networks. Traditional LNG vaporization involves direct vaporization using a vaporizer, which comes in three types: open-frame vaporizer (ORV), submerged combustion vaporizer (SCV), and in-flight vaporizer (IFV). Traditional IFV vaporizers use large amounts of seawater as a heat source for reheating, requiring forced circulation with a water pump. Furthermore, the vaporizers need to be manufactured using titanium alloys, resulting in significant energy consumption and investment. Simultaneously, traditional IFV vaporizers do not consider the recovery and utilization of LNG's cold energy, leading to extreme waste. On one hand, the large amount of cold energy released during this vaporization process will impact the surrounding marine ecosystem; on the other hand, under continuous operation, the vaporizer faces the risk of icing, affecting vaporization efficiency. In summary, the traditional IFV vaporization method not only wastes a significant amount of cold energy but also increases the investment required by companies. Therefore, how to achieve LNG cold energy recovery and utilization under the conditions of low energy consumption, high energy utilization rate and low cost has become a problem that the natural gas industry has been facing.

[0004] Chinese patent application CN105378370A discloses a vaporization device with heat recovery function and a heat recovery device. This invention utilizes heat exchange between a heat source medium, an intermediate medium, and a refrigerant. It includes an evaporator that evaporates at least a portion of the intermediate medium, a vaporizer that vaporizes low-temperature liquefied gas using the evaporated intermediate medium, and a process where the liquefied intermediate medium is removed and returned to the intermediate medium flow path of the vaporizer. A heat exchanger facilitates heat exchange between the intermediate medium flowing in the intermediate medium flow path and the refrigerant circulating in the refrigerant circulation loop. This invention achieves the recovery and utilization of cold energy through different loops. It can use low-temperature liquefied gas as an auxiliary cooling device, saving some cost of the intermediate medium vaporization device. However, this invention does not provide specific details on the downstream application of LNG cold energy recovery, especially regarding the use of cold energy, failing to achieve cascaded utilization of cold energy. As an auxiliary cooling device, its LNG cold energy recovery and utilization rate is low.

[0005] Chinese patent application CN110094239A discloses an integrated intermediate medium vaporizer with LNG cold energy utilization function, and also relates to a power generation system based on the aforementioned integrated intermediate medium vaporizer. It includes a heat exchange cavity within a shell, divided into a front heat exchange zone and a rear heat exchange zone. The shell also contains a first partition and a second partition that sequentially divide the heat exchange cavity into an LNG heat exchange channel, an intermediate medium heat exchange channel, and a seawater heat exchange channel. A middle partition connecting the first and second partitions divides the intermediate medium heat exchange channel into two sections. Both the first and second partitions have several through holes into which heat pipe assemblies are inserted. The invention also relates to a power generation system based on the aforementioned integrated intermediate medium vaporizer. This invention utilizes LNG vaporization cold energy for power generation while saving on equipment investment and reducing space requirements through the use of an integrated intermediate medium vaporizer. However, this invention recovers LNG cold energy for power generation, resulting in a low LNG cold energy recovery rate, and it does not consider the cascade utilization and overall control of LNG cold energy. Summary of the Invention

[0006] This invention is based on the current favorable development trend of LNG in China, and in view of the fact that traditional LNG gasification methods result in a large waste of cold energy. Previously, there have been proposals to use LNG cold energy for power generation, but the utilization rate of cold energy is low. Based on the above situation, this invention proposes a multi-working-medium coupled gasification system and device for the cascade utilization of LNG cold energy, which can recover and utilize LNG cold energy in stages to achieve energy recycling.

[0007] To achieve the objectives of this invention, a multi-working-fluid coupled vaporization system for the cascade utilization of LNG cold energy is provided, comprising two shells, an LNG cold energy recovery and utilization module, a primary refrigerant circulation module, and a secondary refrigerant CO2 circulation module.

[0008] One of the two shells contains a heat exchange chamber E2, and the other shell contains a heat exchange chamber E1 and a heat exchange chamber E3. Heat exchange chamber E1 is the heat exchange area between the primary refrigerant and the secondary refrigerant CO2, heat exchange chamber E2 is the heat exchange area between LNG and the primary refrigerant, and heat exchange chamber E3 is the heat exchange area between the cryogenic NG and the secondary refrigerant CO2. The shell side of heat exchange chamber E3 is connected to the tube side of heat exchange chamber E1.

[0009] The LNG cold energy recovery and utilization module includes a flow meter, a first flow regulating valve, a first pressure sensor, and a first temperature sensor installed on the LNG inlet pipeline. The outlet end of the LNG inlet pipeline is connected to the LNG inlet of the heat exchange chamber E2 section. The low-temperature NG outlet of the heat exchange chamber E2 section is connected to the low-temperature NG inlet of the heat exchange chamber E3 section through the NG pipeline. The NG outlet of the heat exchange chamber E3 section is connected to the second pressure sensor and the second temperature sensor through the NG pipeline.

[0010] The primary refrigerant circulation module includes a first level gauge and a first pump. The primary refrigerant outlet of the heat exchange chamber E2 is connected to the first pump. The first level gauge is located at the primary refrigerant outlet. The primary refrigerant is split into two paths after the first pump. One path is connected to the ultra-low temperature user end through a second flow regulating valve and then flows into the main path. The other path is connected to the primary refrigerant inlet of the heat exchange chamber E1 through a third flow regulating valve.

[0011] The secondary refrigerant CO2 circulation module includes an electric valve, a fourth flow regulating valve, and a fifth pressure sensor installed on the CO2 pipeline. The CO2 pipeline is connected to the gaseous secondary refrigerant CO2 inlet of heat exchange chamber E3. The liquid secondary refrigerant CO2 outlet of heat exchange chamber E3 is connected to the liquid CO2 storage tank via a liquid collection bag and a third pump. The liquid secondary refrigerant CO2 outlet of heat exchange chamber E1 is connected to the liquid CO2 storage tank via a buffer tank and a second pump. The liquid CO2 storage tank is connected to a fourth pump to distribute the liquid CO2 into downstream low-temperature users for refrigeration. Finally, the liquid CO2 flows into the gaseous CO2 storage tank, which is connected to the CO2 pipeline.

[0012] This invention also provides a multi-working-fluid coupled vaporization method for the cascade utilization of LNG cold energy, comprising the following steps:

[0013] The flow rate of LNG is regulated by a flow meter and a first flow regulating valve. LNG enters the heat exchange chamber E2 section and undergoes a first heat exchange with the same refrigerant. After the heat exchange, the temperature rises to low temperature NG. Subsequently, the low temperature NG enters the heat exchange chamber E3 section and undergoes a second heat exchange with the second refrigerant CO2. The temperature rises to the reheating condition and is then transported to the external pipeline network through the NG pipeline via the second pressure sensor, the second temperature sensor, and the second emergency shut-off valve, thus completing the heat exchange work.

[0014] The primary refrigerant flowing out of the primary refrigerant outlet in heat exchange chamber E2 is monitored by the first level gauge to control the opening of the first pump. It then splits into two paths. One path enters the ultra-low temperature user end for cooling. After the temperature rises, it becomes gaseous primary refrigerant and merges into the main path. The other path of primary refrigerant enters heat exchange chamber E1 to exchange heat with secondary refrigerant CO2. After the temperature rises and it becomes gaseous primary refrigerant, it merges into the main path. Together, they enter heat exchange chamber E2 to exchange heat with LNG. After the temperature drops, they liquefy into liquid primary refrigerant and then enter the first pump to complete the cycle.

[0015] Gaseous secondary refrigerant CO2 flows out from the gaseous CO2 storage tank and enters the fourth flow regulating valve and pressure regulator to adjust the flow and pressure. Then, the gaseous secondary refrigerant CO2 enters the heat exchange chamber E3 section to exchange heat with the low-temperature NG, and the temperature drops to a gas-liquid mixed state. The liquid secondary refrigerant CO2 is then pumped into the liquid CO2 storage tank through the third pump. The gaseous secondary refrigerant CO2 enters the heat exchange chamber E1 section to exchange heat with the same primary refrigerant. After the temperature drops and it liquefies, it enters the liquid CO2 storage tank through the buffer tank. Then, it enters the downstream low-temperature user end for refrigeration. After refrigeration, the temperature rises and it vaporizes into gaseous secondary refrigerant CO2, and finally, it is pumped back into the gaseous CO2 storage tank to complete the cycle.

[0016] Compared with the prior art and the current situation, the present invention has at least the following beneficial effects:

[0017] 1. Achieving cascaded utilization of cold energy. This invention divides the primary refrigerant after heat exchange with LNG into separate streams, which then flow into freeze dryers / ultra-low temperature cold storage for refrigeration and into the E2 stage for transferring cold energy to the secondary refrigerant CO2. This not only enables the recovery of cryogenic cold energy to ultra-low temperature users such as freeze dryers / ultra-low temperature cold storage, but also allows for the cascaded recovery and utilization of LNG cold energy through cold storage and ice-making businesses.

[0018] 2. High heat exchange efficiency. This invention uses phase change refrigerant CO2, which has a higher heat exchange efficiency than seawater. At the same time, after the secondary refrigerant CO2 exchanges heat with the natural gas after the primary heat exchange, it is treated by gas-liquid separation and then split into streams. The gaseous secondary refrigerant CO2 enters the E1 section for heat exchange, which also improves the heat exchange efficiency compared to the conventional IFV design.

[0019] 3. Reduced equipment costs. The secondary heat exchange refrigerant in the IFV equipment of this invention is CO2. Compared with the seawater used in traditional IFV equipment, CO2 has a smaller flow rate and a smaller pipe diameter. Moreover, the IFV equipment of this invention does not need to be made of titanium alloy. In addition, the secondary refrigerant CO2 at the outlet of E3 section is separated into streams after gas-liquid separation, which can reduce the pipe diameter and heat exchange area of ​​E1 section, thereby reducing equipment costs.

[0020] 4. Ensuring Equipment Safety. Compared to traditional IFV equipment where NG (natural gas) travels through the shell side, this invention uses the pipeline side throughout, resulting in higher safety. Even in the event of a natural gas leak, the entire process is protected by the shell side. Furthermore, combustible gas detectors and pressure gauges can be installed to facilitate the determination of NG leaks. In addition, the secondary refrigerant CO2 gas-liquid separation at the E3 section outlet reduces the impact of the gas-liquid mixture on the E1 section, ensuring the safe operation of the equipment.

[0021] 5. High operational flexibility: In this invention, the primary refrigerant flow regulating valve is used to regulate and distribute the flow of the primary refrigerant, thereby controlling the flow demand at the user end; in addition, the secondary refrigerant CO2 can be controlled by the pump and pressure regulating valve to control the circulation pressure of the secondary refrigerant heat exchange module, thereby regulating the circulation temperature of CO2 and realizing the regulation of different temperature levels, so as to meet the actual production needs, and the operational flexibility is high. Attached Figure Description

[0022] Figure 1 This is a diagram of a multi-working-fluid coupled vaporization system for the cascade utilization of LNG cold energy, provided as an embodiment of the present invention.

[0023] Figure 2 This is a logic control diagram for a multi-working-fluid coupled vaporization method for the cascade utilization of LNG cold energy, provided in an embodiment of the present invention.

[0024] Figure 3 This is a diagram illustrating the heat exchange area in an embodiment of the present invention.

[0025] The diagram shows:

[0026] 1. First emergency shut-off valve, 2. Flow meter, 3. First flow regulating valve, 4. First pressure sensor, 5. First temperature sensor, 6. First level gauge, 7. First pump, 8. Second flow regulating valve, 9. Fourth temperature sensor, 10. Second pressure sensor, 11. Second emergency shut-off valve, 12. Third flow regulating valve, 13. Fourth pressure sensor, 14. Fifth temperature sensor, 15. Third level gauge, 16. Third pressure sensor, 17. Third temperature sensor, 18. Fifth pressure sensor, 19. Pressure regulator, 20. Fourth flow regulating valve, 21. Electric valve, 22. Second pump, 23. Buffer tank, 24. Second level gauge, 25. Third pump, 26. Liquid collection bag, 27. Fourth pump, 28. Detailed Implementation

[0027] To better understand the present invention, the invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the scope described in the embodiments.

[0028] This invention provides a multi-working-medium coupled vaporization system based on the cascade utilization of LNG cold energy, comprising two shells, an LNG cold energy recovery and utilization module, a primary refrigerant circulation module, and a secondary refrigerant CO2 circulation module. One shell contains a heat exchange chamber E2, and the other shell contains heat exchange chambers E1 and E3. The heat exchange chamber E1 is the heat exchange area between the primary refrigerant and the secondary refrigerant CO2, the E2 is the heat exchange area between LNG and the primary refrigerant, and the E3 is the heat exchange area between low-temperature LNG and the secondary refrigerant CO2.

[0029] The LNG cold energy recovery and utilization module includes a first emergency shut-off valve 1, a flow meter 2, a first flow regulating valve 3, a first pressure sensor 4, and a first temperature sensor 5, which are sequentially connected to the LNG inlet pipeline. It then enters the E2 section of the pipeline, enters the E3 section of the pipeline via the cryogenic NG pipeline, and is then connected to the second pressure sensor 10, the second temperature sensor 11, and the second emergency shut-off valve 12 via the NG pipeline.

[0030] The primary refrigerant circulation module includes a first level gauge 6 and a first pump 7 connected in sequence. The primary refrigerant is split into two paths after the first pump 7. One path goes through the second flow regulating valve 8 and enters the freeze dryer / ultra-low temperature cold storage, and then connects to the fourth temperature sensor 9 and merges into the main path. The other path goes through the third flow regulating valve 13 and enters the shell side of the E1 section before merging into the main path and entering the shell side of the E2 section together.

[0031] The secondary refrigerant CO2 circulation module includes an electric valve 22, a fourth flow regulating valve 21, a pressure regulator 20, and a fifth pressure sensor 19, all connected sequentially to the CO2 pipeline. The CO2 then enters the shell side of section E3. A third temperature sensor 18 and a third pressure sensor 17 monitor the temperature and pressure of the shell side of section E3. Afterward, the CO2 splits into two paths: one path flows through a liquid collector 27 and a third pump 26, converging into the liquid CO2 storage tank; the other path enters the pipe side of section E1 (the shell side of E3 connects to the pipe side of E1, with the remaining sections sealed by welding; this is because the pressure in the pipe side of E1 is higher than that in the shell side of E3). Because the pressure is low, CO2 will flow from the shell side of E3 to the tube side of E1 due to the pressure difference, achieving unidirectional flow. The third level gauge 16, the fourth pressure sensor 14, and the fifth temperature sensor 15 are connected to the collection bag 27 to monitor the pressure and temperature at the outlet of the tube side of E1, respectively. Then it enters the buffer tank 24, which is connected to the second level gauge 25. Subsequently, it flows into the liquid CO2 storage tank through the second pump 23, and then into the liquid CO2 storage tank. It is then connected to the fourth pump 28, and flows into the downstream low-temperature cold storage and ice-making plants for refrigeration. Finally, it flows into the gaseous CO2 storage tank.

[0032] In section E3, NG travels through the tube side, while the heat source travels through the shell side. At the same time, a liquid collection bag 27 is installed at the shell side outlet to facilitate CO2 gas-liquid separation.

[0033] This invention provides a multi-working-fluid coupled vaporization method for the cascade utilization of LNG cold energy, comprising the following steps:

[0034] The flow rate of LNG is regulated by flow meter 2 and first flow regulating valve 3. LNG enters heat exchange chamber E2 and undergoes heat exchange with the same stage refrigerant. After heat exchange, the temperature rises to low temperature NG. Then, low temperature NG enters heat exchange chamber E3 and undergoes heat exchange with the secondary refrigerant CO2. After the temperature rises to the reheating condition, it is transported to the external pipeline through NG pipeline via second pressure sensor 10, second temperature sensor 11, and second emergency shut-off valve 12, thus completing the heat exchange work.

[0035] The primary refrigerant flowing out of the primary refrigerant outlet in heat exchange chamber E2 is monitored by the first level gauge 6 to control the opening of the first pump 7. It then splits into two paths. One path enters the ultra-low temperature user end for cooling. After the temperature rises, it becomes gaseous primary refrigerant and merges into the main path. The other path of primary refrigerant enters heat exchange chamber E1 to exchange heat with secondary refrigerant CO2. After the temperature rises and it becomes gaseous primary refrigerant, it merges into the main path. Together, they enter heat exchange chamber E2 to exchange heat with LNG. After the temperature drops, they liquefy into liquid primary refrigerant and then enter the first pump 7 to complete the cycle.

[0036] Gaseous secondary refrigerant CO2 flows out from the gaseous CO2 storage tank, is heated by the heater, and then enters the fourth flow regulating valve 21 and pressure regulator 20 to regulate the flow and pressure. Subsequently, the gaseous secondary refrigerant CO2 enters the heat exchange chamber E3 section to exchange heat with the low-temperature NG, and the temperature drops to a gas-liquid mixed state. The liquid secondary refrigerant CO2 is then pumped into the liquid CO2 storage tank by the third pump 26. The gaseous secondary refrigerant CO2 enters the heat exchange chamber E1 section to exchange heat with the same primary refrigerant. After the temperature drops and it liquefies, it enters the liquid CO2 storage tank through the buffer tank 24. Subsequently, it enters the downstream low-temperature user end for refrigeration. After refrigeration, the temperature rises and it vaporizes into gaseous secondary refrigerant CO2, and finally flows into the gaseous CO2 storage tank to complete the cycle.

[0037] In some embodiments of the present invention, the flow meter 2 is a Venturi flow meter.

[0038] In some embodiments of the present invention, the types of refrigerants applicable to the primary refrigerant that exchanges heat with LNG include Freon refrigerants such as R23, R507, and R410a, as well as various light hydrocarbon refrigerants such as ethane and propane, and their mixtures.

[0039] The primary refrigerant enters the E2 section and exchanges heat with the LNG before being split into two streams. One stream flows into ultra-low temperature users such as freeze dryers / ultra-low temperature cold storage facilities to recover and utilize ultra-low temperature cold energy; the other stream flows into the E1 section to transfer cold energy to the secondary refrigerant CO2, which then transfers the cold energy to low-temperature users such as low-temperature cold storage facilities / ice plants, thereby achieving cascade recovery and utilization of cold energy.

[0040] The primary refrigerant circulation module controls the distribution of primary refrigerant flow by monitoring the outlet temperature of the freeze dryer / ultra-low temperature cold storage in real time through the fourth temperature sensor 9. If the fourth temperature sensor 9 detects that the temperature is too low, the primary refrigerant flow into the freeze dryer / ultra-low temperature cold storage is reduced through the second flow regulating valve 8, and the primary refrigerant flow into the E1 section is increased through the third flow regulating valve 13. If the temperature is too high, the primary refrigerant flow into the E1 section is reduced through the third flow regulating valve 13, and the primary refrigerant flow into the freeze dryer / ultra-low temperature cold storage is increased through the second flow regulating valve 8.

[0041] The secondary refrigerant CO2 is in a gas-liquid mixed state after exchanging heat with the low-temperature NG after the first heat exchange in the E3 section. After the liquid CO2 is collected by the liquid collection bag 27, it enters the liquid CO2 storage tank through the third pump 26. This avoids the gas-liquid mixture from impacting the E1 section, and at the same time improves the heat exchange efficiency and reduces the heat exchange area of ​​the E1 section by 5% to 10%.

[0042] In the secondary refrigerant CO2 circulation module, the pressure of the secondary refrigerant CO2 circulation module can be regulated by the fourth pump 28, the pressure regulator 20, and the fifth pressure sensor 19. By controlling the CO2 circulation pressure, the liquefaction temperature of the secondary refrigerant CO2 in sections E1 and E3 can be adjusted, thereby realizing the temperature control of low-temperature users such as low-temperature cold storage / ice plants.

[0043] The fourth pressure sensor 14 and the fifth temperature sensor 15 monitor the secondary refrigerant CO2 pressure and temperature at the outlet of the E1 section pipe, respectively. When the pressure is higher than the set pressure or the temperature is higher than the set temperature, the opening of the fourth flow regulating valve 21 is reduced to reduce the secondary refrigerant CO2 flow. When the pressure is lower than the set pressure or the temperature is lower than the set temperature, the opening of the fourth flow regulating valve 21 is increased to increase the secondary refrigerant CO2 flow, thus ensuring stable system operation.

[0044] In the LNG cold energy recovery and utilization module, the flow rate of LNG is regulated by the flow meter 2 and the first flow regulating valve 3. It enters the E2 section and undergoes a heat exchange with the same stage refrigerant. After the heat exchange, the temperature rises to low temperature NG. The low temperature NG then enters the E3 section and undergoes a second heat exchange with the secondary refrigerant CO2. After the temperature rises to the reheating condition, it enters the external transmission pipeline to complete the heat exchange work.

[0045] In the primary refrigerant circulation module, the primary refrigerant is monitored by the first level gauge 6 to control the opening of the first pump 7. Then, it is divided into two paths. One path enters the freeze dryer / ultra-low temperature cold storage for refrigeration. After the temperature rises, it becomes gaseous primary refrigerant and merges into the main path. The other path of primary refrigerant enters the E1 section to exchange heat with the secondary refrigerant CO2. After the temperature rises, it becomes gaseous primary refrigerant and merges into the main path. Together, they enter the E2 section to exchange heat with LNG. After the temperature drops, they liquefy into liquid primary refrigerant and then enter the first pump 7 to complete the circulation.

[0046] In the secondary refrigerant CO2 circulation module, gaseous secondary refrigerant CO2 flows out from the gaseous CO2 storage tank and enters the fourth flow regulating valve 21 and pressure regulator 20 to regulate the flow and pressure. Then, the gaseous secondary refrigerant CO2 enters the E3 section to exchange heat with the low-temperature NG. After the temperature decreases, it becomes a gas-liquid mixed state. The liquid secondary refrigerant CO2 is pumped into the liquid CO2 storage tank through the third pump 26. The gaseous secondary refrigerant CO2 enters the E1 section to exchange heat with the same primary refrigerant. After the temperature decreases and it liquefies, it enters the liquid CO2 storage tank through the buffer tank 24. Then, it enters the downstream low-temperature cold storage / ice plant, etc., for refrigeration. After refrigeration, the temperature rises and it vaporizes into gaseous secondary refrigerant CO2. Finally, it is pumped into the gaseous CO2 storage tank to complete the circulation.

[0047] In some embodiments of the present invention, propane is used as the primary refrigerant, the LNG flow rate is 180t / h, the temperature is -150 to -160℃, and the pressure is 9.2MPa.

[0048] LNG at -150 to -160℃ is regulated by Venturi flow meter 2 and first flow regulating valve 3. It enters section E2 and undergoes a first heat exchange with gaseous primary refrigerant propane at a flow rate of 200 t / h, a temperature of -35 to -45℃, and a pressure of 0.1 to 0.15 MPa. After the heat exchange, the temperature of LNG rises to -55 to -65℃, becoming gaseous natural gas (NG). The gaseous natural gas then enters section E3 and undergoes a second heat exchange with gaseous secondary refrigerant CO2 at a flow rate of 314 t / h, a temperature of 30 to 40℃, and a pressure of 1.3 to 1.5 MPa. After the temperature rises to the reheating condition of 0 to 5℃, it enters the external transmission pipeline network, completing the heat exchange process.

[0049] Gaseous primary refrigerant propane with a flow rate of 200 t / h, a temperature of -35 to -45℃, and a pressure of 0.1 to 0.15 MPa enters section E2 and exchanges heat with LNG with a flow rate of 180 t / h, a temperature of -150 to -160℃, and a pressure of 9.2 MPa. After heat exchange, the temperature drops to -50 to -60℃. The flow rate is then monitored by the first level gauge 6 and the mixture enters the first pump 7. It is then divided into two streams, ① and ②. Stream ① contains 20-30% liquid primary propane, which is then pumped through the first... The second flow regulating valve 8 leads to the refrigeration process in the freeze dryer. After the temperature rises to -35 to -45°C, the gaseous primary refrigerant flows into the main circuit. The second circuit consists of 70-80% propane, a primary refrigerant, which enters the E1 section and exchanges heat with CO2, a gaseous secondary refrigerant with a flow rate of 314 t / h, a temperature of 30-40°C, and a pressure of 1.3-1.5 MPa. After the heat exchange, the temperature rises to -35 to -45°C, at which point it becomes a gaseous primary refrigerant. It then flows into the main circuit and together with LNG enters the E2 section to complete the cycle.

[0050] Gaseous secondary refrigerant CO2 with a flow rate of 314 t / h, a temperature of 30–40℃, and a pressure of 1.3–1.5 MPa flows out of the gaseous CO2 storage tank. After being heated by a heater, the flow rate and pressure are regulated by the fourth flow regulating valve 21 and the pressure regulator 20. Subsequently, the gaseous secondary refrigerant CO2 enters the E3 section and exchanges heat with low-temperature NG with a flow rate of 180 t / h, a temperature of -55 to -65℃, and a pressure of 9.2 MPa. The temperature drops to 10–20℃, at which point it is in a gas-liquid mixed state (gas-liquid ratio of 0.3:0.7–0.35:0.65). After gas-liquid separation, it is divided into two phases: ① and ②. In the first path, the liquid secondary refrigerant CO2 from path ① flows into the liquid CO2 storage tank after its flow rate is regulated by the third pump 26. In the second path, the gaseous secondary refrigerant CO2 enters section E1 and exchanges heat with liquid primary refrigerant propane at a flow rate of 200t / h, a temperature of -50 to -60℃, and a pressure of 0.1 to 0.15MPa. After heat exchange, the temperature drops to -35 to -45℃ and enters the buffer tank 24. Subsequently, it flows into the liquid CO2 storage tank along with path ①. Then, it flows into downstream cold storage facilities or ice plants for refrigeration. After refrigeration, the temperature rises, and it becomes gaseous secondary refrigerant CO2, which flows into the gaseous CO2 storage tank, completing the cycle.

[0051] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A multi-working-fluid coupled vaporization system for the cascade utilization of LNG cold energy, characterized in that, It includes two shells, an LNG cold energy recovery and utilization module, a primary refrigerant circulation module, and a secondary refrigerant CO2 circulation module. One of the two shells contains a heat exchange chamber E2, and the other shell contains a heat exchange chamber E1 and a heat exchange chamber E3. Heat exchange chamber E1 is the heat exchange area between the primary refrigerant and the secondary refrigerant CO2, heat exchange chamber E2 is the heat exchange area between LNG and the primary refrigerant, and heat exchange chamber E3 is the heat exchange area between the cryogenic NG and the secondary refrigerant CO2. The shell side of heat exchange chamber E3 is connected to the tube side of heat exchange chamber E1. The LNG cold energy recovery and utilization module includes a flow meter (2), a first flow regulating valve (3), a first pressure sensor (4), and a first temperature sensor (5) installed on the LNG inlet pipeline. The outlet end of the LNG inlet pipeline is connected to the LNG inlet of the heat exchange chamber E2 section. The low-temperature NG outlet of the heat exchange chamber E2 section is connected to the low-temperature NG inlet of the heat exchange chamber E3 section through the NG pipeline. The NG outlet of the heat exchange chamber E3 section is connected to the second pressure sensor (10) and the second temperature sensor (11) through the NG pipeline. The primary refrigerant circulation module includes a first level gauge (6) and a first pump (7). The primary refrigerant outlet of the heat exchange chamber E2 section is connected to the first pump (7). The first level gauge (6) is located at the primary refrigerant outlet. The primary refrigerant is split into two paths after the first pump (7). One path is connected to the ultra-low temperature user end through the second flow regulating valve (8) and then flows into the main path. The other path is connected to the primary refrigerant inlet of the heat exchange chamber E1 section through the third flow regulating valve (13). The secondary refrigerant CO2 circulation module includes an electric valve (22), a fourth flow regulating valve (21), and a fifth pressure sensor (19) installed on the CO2 pipeline. The CO2 pipeline is connected to the gaseous secondary refrigerant CO2 inlet of the heat exchange chamber E3 section. The liquid secondary refrigerant CO2 outlet of the heat exchange chamber E3 section is connected to the liquid CO2 storage tank via a liquid collection bag (27) and a third pump (26). The liquid secondary refrigerant CO2 outlet of the heat exchange chamber E1 section is connected to the liquid CO2 storage tank via a buffer tank (24) and a second pump (23). The liquid CO2 storage tank is connected to the fourth pump (28) to distribute the liquid CO2 into the downstream low-temperature user end for refrigeration. Finally, it flows into the gaseous CO2 storage tank, which is connected to the CO2 pipeline.

2. A multi-working-fluid coupled vaporization method for the cascade utilization of LNG cold energy, characterized in that, The system described in claim 1 includes the following steps: The flow rate of LNG is controlled by the flow meter (2) and the first flow regulating valve (3). LNG enters the heat exchange chamber E2 section and exchanges heat with the first-stage refrigerant once. After the heat exchange, the temperature rises to low temperature NG. Then, the low temperature NG enters the heat exchange chamber E3 section and exchanges heat with the second-stage refrigerant CO2 for a second time. The temperature rises to the reheating condition and is then transported to the external pipeline network through the NG pipeline via the second pressure sensor (10), the second temperature sensor (11), and the second emergency shut-off valve (12) to complete the heat exchange work. The primary refrigerant flowing out from the primary refrigerant outlet of the heat exchange chamber E2 is monitored by the first level gauge (6) to control the opening of the first pump (7). Then it is divided into two paths. One path enters the ultra-low temperature user end for cooling. After the temperature rises, it becomes gaseous primary refrigerant and merges into the main path. The other path of primary refrigerant enters the heat exchange chamber E1 to exchange heat with the secondary refrigerant CO2. After the temperature rises, it becomes gaseous primary refrigerant and merges into the main path. Together, they enter the heat exchange chamber E2 to exchange heat with LNG. After the temperature drops, they liquefy into liquid primary refrigerant and then enter the first pump (7) to complete the cycle. Gaseous secondary refrigerant CO2 flows out of the gaseous CO2 storage tank and enters the fourth flow regulating valve (21) and pressure regulator (20) to regulate the flow and pressure. Then, the gaseous secondary refrigerant CO2 enters the heat exchange chamber E3 section to exchange heat with the low temperature NG. The temperature drops to a gas-liquid mixed state. The liquid secondary refrigerant CO2 flows into the liquid CO2 storage tank through the third pump (26). The gaseous secondary refrigerant CO2 enters the heat exchange chamber E1 section to exchange heat with the same primary refrigerant. After the temperature drops and it liquefies, it enters the liquid CO2 storage tank through the buffer tank (24). Then, it enters the downstream low temperature user end for refrigeration. After refrigeration, the temperature rises and it vaporizes into gaseous secondary refrigerant CO2. Finally, it flows into the gaseous CO2 storage tank to complete the cycle.

3. The multi-working-fluid coupled vaporization method for LNG cold energy cascade utilization according to claim 2, characterized in that, The primary refrigerant enters the heat exchange chamber E2 section and exchanges heat with the LNG before being split into two streams. One stream enters the ultra-low temperature user end to recover and utilize the ultra-low temperature cold energy; the other stream enters the E1 section to transmit cold energy to the secondary refrigerant CO2, which then transmits the cold energy to the low temperature user end, thereby realizing the cascade recovery and utilization of cold energy.

4. The multi-working-fluid coupled vaporization method for LNG cold energy cascade utilization according to claim 2, characterized in that, A third temperature sensor (18) and a third pressure sensor (17) are installed on the heat exchange chamber E3 section to monitor the temperature and pressure of the shell side of the E3 section, respectively.

5. The multi-working-fluid coupled vaporization method for LNG cold energy cascade utilization according to claim 2, characterized in that: A fourth pressure sensor (14) and a fifth temperature sensor (15) are installed on the heat exchange chamber E1 section. The fourth pressure sensor (14) and the fifth temperature sensor (15) monitor the pressure and temperature of the secondary refrigerant CO2 at the tube outlet, respectively. When the pressure is higher than the set pressure or the temperature is higher than the set temperature, the opening of the fourth flow regulating valve (21) is reduced to reduce the flow of the secondary refrigerant CO2. When the pressure is lower than the set pressure or the temperature is lower than the set temperature, the opening of the fourth flow regulating valve (21) is increased to increase the flow of the secondary refrigerant CO2, thus ensuring the stable operation of the system.

6. A multi-working-fluid coupled vaporization method for LNG cold energy cascade utilization according to claim 2, characterized in that: The primary refrigerant used for heat exchange with LNG is a Freon-based refrigerant, which includes, but is not limited to, any one of R23, R507, and R410a.

7. A multi-working-fluid coupled vaporization method for LNG cold energy cascade utilization according to claim 2, characterized in that: The primary refrigerant applicable to heat exchange with LNG includes, but is not limited to, light hydrocarbon refrigerants such as ethane and propane, and their mixtures.

8. A multi-working-fluid coupled vaporization method for LNG cold energy cascade utilization according to claim 2, characterized in that: The primary refrigerant circulation module controls the distribution of primary refrigerant flow by monitoring the outlet temperature of the ultra-low temperature user terminal in real time through the fourth temperature sensor (9). If the fourth temperature sensor (9) detects that the temperature is lower than the preset value, the primary refrigerant flow entering the ultra-low temperature user terminal is reduced through the second flow regulating valve (8), and the primary refrigerant flow entering the heat exchange chamber E1 section is increased through the third flow regulating valve (13). If the temperature is higher than the preset value, the primary refrigerant flow entering the heat exchange chamber E1 section is reduced through the third flow regulating valve (13), and the primary refrigerant flow entering the ultra-low temperature user terminal is increased through the second flow regulating valve (8).

9. A multi-working-fluid coupled vaporization method for LNG cold energy cascade utilization according to claim 2, characterized in that: After the secondary refrigerant CO2 exchanges with the low-temperature NG after the first heat exchange in the heat exchange chamber E3 section, it is in a gas-liquid mixed state. After the liquid CO2 is accumulated by the liquid collection bag (27), it enters the liquid CO2 storage tank through the third pump (26). This avoids the gas-liquid mixture from impacting the heat exchange chamber E1 section, and at the same time improves the heat exchange efficiency and reduces the heat exchange area of ​​E1 section by 5% to 10%.

10. A multi-working-fluid coupled vaporization method for LNG cold energy cascade utilization according to any one of claims 2-9, characterized in that: In the secondary refrigerant CO2 circulation module, the secondary refrigerant CO2 is regulated by the fourth pump (28), the pressure regulator (20), and the fifth pressure sensor (19). By controlling the CO2 circulation pressure, the liquefaction temperature of the secondary refrigerant CO2 in the heat exchange chamber E1 and E3 is adjusted, thereby achieving the control of the low temperature user end temperature.

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