System and method for coupling cryogenic liquid energy storage using LNG cold energy with air separation

Abstract

The present invention provides a system and method for coupling cryogenic liquid energy storage and air separation by utilizing the cold energy of LNG, which relates to the technical field of electric energy storage systems. The system for coupling cryogenic liquid energy storage and air separation by utilizing the cold energy of LNG includes an air compression, purification and pressurization unit, an air liquefaction and air separation cold box, a liquid air storage and pressurization unit, an air expansion power generation unit and an LNG cold box. The method for coupling cryogenic liquid energy storage and air separation by utilizing the cold energy of LNG includes the following steps: during energy storage, the raw air is cooled and purified, absorbs the cold energy of LNG for air separation rectification and liquid air storage, and part of the liquid air is sent to the air separation rectification to ensure the stable production of products; during energy release, the stored liquid air is sent to an expansion generator set for expansion power generation. The present invention solves the problem of asynchronous supply of LNG cold energy and air separation demand, ensures the efficient and stable operation of the cold energy air separation device, improves the utilization rate of LNG cold energy and the energy conversion efficiency of the LAES system.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy storage systems, and particularly to a system and method for coupling cryogenic liquid energy storage and air separation using LNG cold energy. Background Art

[0002] At large LNG receiving stations, to meet the requirements of natural gas pipeline transportation, LNG needs to be pressurized by a high-pressure pump and vaporized into a normal-temperature gas before being sent into the natural gas pipeline. During the vaporization process, LNG releases a large amount of cold energy. Theoretically, the released cold energy is about 830 kJ / kg. For a receiving station with a receiving capacity of 3 million tons per year, the available cold power is 65 MW, equivalent to about 10×10 8 kWh / year. Reasonably and efficiently utilizing the LNG cold energy of large receiving stations is of great significance.

[0003] In recent years, cryogenic energy storage technology (CES) has attracted much attention due to its high energy density, geographical flexibility, and relatively low investment cost. This technology uses cryogenic liquefaction technology to absorb renewable energy power, stores cryogenic liquids as products, and pressurizes, heats up, and expands them to output electricity during peak electricity consumption. Compared with traditional compressed air energy storage systems, cryogenic liquid energy storage systems greatly reduce the required storage volume and are suitable for popularization and application in a wider area.

[0004] In the prior art, the main way to utilize LNG cold energy is cold energy air separation, and the overall cold energy utilization rate of LNG is relatively low. The cold energy of the LNG cold energy air separation device is provided by the LNG supplied by the receiving station. Therefore, the continuous and stable supply of LNG is a prerequisite for the stable operation of the LNG cold energy air separation device. Currently, restricted by the external transportation conditions of the receiving station, the LNG cold energy fluctuates in temperature, and there is a problem of temporal and spatial asynchrony between the supply of LNG cold energy and the demand for cold energy air separation, resulting in the inability of air separation to operate continuously and stably, and high operation energy consumption. For example, Chinese Patent No. CN 113587551 B discloses an air separation system and method for producing liquid oxygen, liquid nitrogen, and liquid argon using LNG cold energy, and Chinese Patent No. CN 113587552 B discloses an air separation system and air separation method using LNG cold energy.

[0005] Liquid air energy storage (LAES) is a long-duration energy storage method with application demonstrations. However, in traditional LAES, air needs to be liquefied under high pressure, and the cooling capacity is provided by a compressor driven by electricity, resulting in high energy consumption, low energy storage conversion efficiency, and poor economy. During the charging process of the LAES system, cold energy is required to liquefy air. However, during the discharging stage, there is a shortage of recovered cold energy. Therefore, an external cold source needs to be utilized to improve the electrical conversion efficiency of the system. Summary of the Invention

[0006] The present invention provides a system and method for coupling cryogenic liquid energy storage and air separation using the cold energy of LNG, which solves the problem of asynchronous cold energy supply of LNG and air separation demand, ensures the efficient and stable operation of the LNG cold energy air separation device, improves the utilization rate of LNG cold energy, and improves the energy conversion efficiency of LAES.

[0007] The present invention is achieved through the following technical solutions:

[0008] A system for coupling cryogenic liquid energy storage and air separation using the cold energy of LNG includes an air compression, purification, and boosting unit, an air liquefaction and air separation cold box, a liquid air storage and pressurization unit, an air expansion power generation unit, and an LNG cold box;

[0009] Among them, the air liquefaction and air separation cold box includes a main air separation heat exchanger and an air separation rectification system, the liquid air storage and pressurization unit includes a liquid air storage tank, the air expansion power generation unit includes multiple expansion generator sets, the LNG cold box includes an LNG heat exchanger, and a nitrogen circulation pipeline is provided between the LNG heat exchanger and the main air separation heat exchanger;

[0010] The air compression, purification, and boosting unit pressurizes, cools, and purifies the raw air and then inputs it into the main air separation heat exchanger in two paths. One path enters the air separation rectification system after being output from the main air separation heat exchanger, and the other path becomes liquid air after being output from the main air separation heat exchanger and enters the liquid air storage tank of the liquid air storage and pressurization unit. The liquid air storage tank can send the liquid air into the air separation rectification system and the air expansion power generation unit. LNG enters the LNG heat exchanger to exchange heat with the nitrogen in the nitrogen circulation pipeline, and the nitrogen in the nitrogen circulation pipeline exchanges heat with the air in the main air separation heat exchanger.

[0011] Optionally, the air compression, purification, and boosting unit includes an air compressor, an inter-stage heat exchanger of the air compressor, and an adsorption system connected in sequence. The adsorption system outputs two pipelines. One pipeline enters the air separation rectification system after passing through the main air separation heat exchanger, and the other pipeline sequentially passes through an air booster and an inter-stage heat exchanger of the air booster and then is connected to the liquid air storage tank through the main air separation heat exchanger.

[0012] Optionally, the system further includes an NG reheating unit, which includes an NG heat exchanger. A circulation pipeline is provided between the NG heat exchanger, the inter-stage heat exchanger of the air compressor, and the inter-stage heat exchanger of the air booster. A sixth pump is provided on the circulation pipeline. The LNG output by the LNG heat exchanger is reheated by the NG heat exchanger and then output.

[0013] Optionally, the liquid air storage and pressurization unit includes a liquid air expander, a liquid air liquid separator, a liquid air storage tank, and a first pump connected in sequence. The liquid air input into the liquid air storage and pressurization unit from the main heat exchanger of the air separation cold box first enters the liquid air expander. The top of the liquid air liquid separator is connected to an exhaust pipe passing through the main heat exchanger of the air separation cold box.

[0014] Optionally, the air expansion power generation unit sequentially includes an air reheating heat exchanger and four sets of expansion generator sets. An inter-stage heat exchanger of the expansion generator sets is provided between two adjacent expansion generator sets.

[0015] Optionally, the system further includes a liquid air reheating and cold storage unit, which includes two circulation pipelines. One of the circulation pipelines sequentially includes a first cold storage heat exchanger, a first cold storage medium storage tank, a second pump, a second cold storage medium storage tank, and a third pump. The other circulation pipeline sequentially includes a second cold storage heat exchanger, a third cold storage medium storage tank, a fourth pump, a fourth cold storage medium storage tank, and a fifth pump;

[0016] Among them, the liquid air output from the liquid air storage tank of the liquid air storage and pressurization unit sequentially passes through the first cold storage heat exchanger and the second cold storage heat exchanger and then enters the air expansion power generation unit.

[0017] Optionally, the LNG cold box further includes a liquid nitrogen heat exchanger. The pipeline between the second pump and the second cold storage medium storage tank sequentially passes through the liquid nitrogen heat exchanger and the LNG heat exchanger. The pipeline between the fourth pump and the fourth cold storage medium storage tank passes through the LNG heat exchanger.

[0018] Optionally, a first nitrogen compressor, a second nitrogen compressor, and a liquid nitrogen expander are provided on the nitrogen circulation pipeline. The nitrogen circulation pipeline includes a main path and a first branch, a second branch, a third branch, and a fourth branch;

[0019] The main path sequentially passes through the second nitrogen compressor, the LNG heat exchanger, the liquid nitrogen heat exchanger, and the liquid nitrogen expander;

[0020] The first branch sequentially passes through the liquid nitrogen heat exchanger and the LNG heat exchanger from the outlet end of the liquid nitrogen expander and then communicates with the inlet end of the second nitrogen compressor;

[0021] The second branch sequentially passes through the liquid nitrogen heat exchanger and the LNG heat exchanger from the outlet end of the liquid nitrogen expander and then communicates with the inlet end of the first nitrogen compressor;

[0022] The third branch route sequentially passes through the main heat exchanger of the air separation cold box and the LNG heat exchanger from the outlet end of the liquid nitrogen expander and then communicates with the inlet end of the second nitrogen compressor;

[0023] The fourth branch route sequentially passes through the air separation rectification system, the main heat exchanger of the air separation cold box, and the LNG heat exchanger from the outlet end of the liquid nitrogen expander and then communicates with the inlet end of the first nitrogen compressor;

[0024] Wherein, the outlet end of the first nitrogen compressor communicates with the third branch route before entering the LNG heat exchanger, so that the medium output by the first nitrogen compressor enters the inlet end of the second nitrogen compressor after passing through the LNG heat exchanger.

[0025] Based on the same inventive concept, the present invention also provides a method for coupling cryogenic liquid energy storage and air separation by utilizing LNG cold energy, including an air compression purification and boosting unit, an air liquefaction and air separation cold box, a liquid air storage and pressurization unit, a liquid air reheating and cold storage unit, an air expansion power generation unit, as well as an LNG cold box and an NG reheating unit. There is a nitrogen circulation pipeline between the LNG cold box and the air liquefaction and air separation cold box. Energy is stored during the peak period of new energy power generation or the low electricity consumption period, and energy is released for power generation during the peak electricity consumption period;

[0026] Wherein, during energy storage, the raw air enters the air compression purification and boosting unit for cooling and purification, and then is divided into two paths to enter the air liquefaction and air separation cold box. One path enters the air liquefaction and air separation cold box for cooling and then undergoes air separation rectification. The other path is pressurized, cooled, and then enters the air liquefaction and air separation cold box for cooling to form liquid air. The liquid air is sent to the liquid air storage and pressurization unit for storage. The LNG from the receiving station is sequentially introduced into the LNG cold box and the NG reheating unit to realize two - time recovery and utilization of the LNG cold energy. The cold energy absorbed by the NG reheating unit from the LNG is used for cooling the air in the air compression purification and boosting unit. In the LNG cold box, the nitrogen in the nitrogen circulation pipeline absorbs the cold energy of the LNG and the cold energy of the cold storage medium in the liquid air reheating and cold storage unit, and after absorbing the cold energy, the nitrogen transfers the cold energy to the air sent into the air liquefaction and air separation cold box;

[0027] During energy release for power generation, the raw air enters the air compression purification and boosting unit for cooling and purification, then enters the air liquefaction and air separation cold box for cooling and then undergoes air separation rectification. The liquid air stored in the liquid air storage and pressurization unit is pressurized and first exchanges heat with the cold storage medium in the liquid air reheating and cold storage unit, and then is heated by an external heat source and sent to the air expansion power generation unit for power generation. The LNG from the receiving station is sequentially introduced into the LNG cold box and the NG reheating unit to realize two - time recovery and utilization of the LNG cold energy. The cold energy absorbed by the NG reheating unit from the LNG is used for cooling the air in the air compression purification and boosting unit. In the LNG cold box, after the nitrogen in the nitrogen circulation pipeline absorbs the cold energy of the LNG, it transfers the cold energy to the air sent into the air liquefaction and air separation cold box;

[0028] The liquid air stored in the liquid air storage and pressurization unit partially enters the air liquefaction and air separation cold box for air separation rectification according to the fluctuation of the LNG temperature coming from the receiving station, so as to adjust the output of the air separation liquid product to be stable.

[0029] Optionally, the liquid air reheating and cold storage unit includes two circulation pipelines;

[0030] The cold storage medium in one of the circulation pipelines exchanges heat with nitrogen in the nitrogen circulation pipeline twice. The cold storage medium is one or a mixture of alkane compounds and fluorides. The alkane compounds include ethane, ethylene, propane, and propylene, and the fluorides include CHF3, CF4, and CClF3;

[0031] The cold storage medium in the other circulation pipeline exchanges heat with nitrogen in the nitrogen circulation pipeline once. The cold storage medium is one or a mixture of methanol, ethanol, butane, isobutane, butene, dimethyl ether, ammonia, R115, R123, R134a, R143a, and R152a.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The present invention can not only combine large-scale LNG cold energy with large-scale green electricity and apply it to liquid air energy storage and power generation, store energy during the peak period of new energy power generation or the low valley period of power consumption, and release energy for power generation during the peak period of power consumption. At this time, the system can be used to absorb the green electricity of offshore wind and solar power and meet the requirements of green electricity energy storage. At the same time, it can continuously produce air separation liquid products for 24 hours a day to keep the output constant. It can also apply liquid air energy storage to air separation, solve the problem of asynchronous cold energy supply and air separation demand, ensure the efficient and stable operation of the cold energy air separation device, and the output of the air separation liquid product is large and stable. At the same time, the system can be used to store energy during the trough electricity period and release energy for power generation for the self-use of the air separation system during the peak electricity period. Through the price difference between the peak and trough electricity prices, the production cost of the air separation system can be reduced;

[0034] During the charging process, cold energy is required to liquefy air. However, during the discharging stage, there is a shortage of recovered cold energy. Therefore, an external cold source needs to be used to improve the electro-chemical conversion efficiency of the system. In terms of external cooling energy, LNG is the best choice, which fits the requirements of LAES. Through LNG-LAES, the cold energy utilization rate can be maximized, the LAES efficiency can be improved, and the system economy can be improved;

[0035] Using circulating nitrogen as the carrier to transfer the cold energy during the gasification process of LNG, and simultaneously liquefying air by liquid nitrogen for storage and producing air separation liquid products, which greatly improves the safety of using LNG cold energy for liquid air energy storage and air separation systems;

[0036] The conversion efficiency of the liquid air energy storage system is improved. When introducing an external heat source at 150°C, the electrical conversion efficiency of the LNG-LAES system can reach over 75%. The liquid air reheating and cold energy storage unit can store the cold energy generated by the vaporization of the reheated liquid air during the energy release and power generation process, and is used for the heat exchange between LNG and circulating nitrogen during the energy storage process. Different temperature zone cold energy storage media are used for cascade cold energy storage to improve the matching of cold energy in different temperature zones and the cold energy storage efficiency;

[0037] It can be flexibly combined with various external heat sources from 50°C to 250°C and above, improving the system conversion efficiency and the application scenarios of energy storage. This system is used to consume green electricity and valley electricity, and output electrical energy, cold energy or heat energy during the peak electricity consumption period, becoming a new type of integrated energy system;

[0038] Large-scale low-temperature energy storage is carried out during the electricity trough, and electricity is generated during the electricity peak to meet the self-use electricity demand of the air separation unit, greatly reducing the electricity cost of the air separation system and improving the economy of the air separation. After the low-temperature liquid energy storage system using LNG cold energy is coupled with the air separation system, equipment such as compression, purification, pressurization, refrigeration, and heat exchange can be shared, greatly saving the investment cost and floor area, and improving the economy of low-temperature liquid energy storage. Brief Description of the Drawings

[0039] Figure 1 It is a schematic structural diagram of the system for coupling low-temperature liquid energy storage using LNG cold energy and air separation according to the present invention.

[0040] Reference Numerals: C1, air compressor; C2, air booster; C3-1, first nitrogen compressor; C3-2, second nitrogen compressor; E1, inter-stage heat exchanger of air compressor; E2, inter-stage heat exchanger of air booster; E3, NG heat exchanger; E4, air reheating heat exchanger; E5, inter-stage heat exchanger of expansion generator set; E11, LNG heat exchanger; E12, liquid nitrogen heat exchanger; E13, main heat exchanger of air separation cold box; E21, first cold energy storage heat exchanger; E22, second cold energy storage heat exchanger; T1, liquid nitrogen expander; T2, liquid air expander; VP1, liquid air-liquid separator; SP1, liquid air storage tank; SP2, first cold energy storage medium storage tank; SP3, second cold energy storage medium storage tank; SP4, third cold energy storage medium storage tank; SP5, fourth cold energy storage medium storage tank; P1, first pump; P2, second pump; P3, third pump; P4, fourth pump; P5, fifth pump; P6, sixth pump; AT, expansion generator set. Detailed Embodiments

[0041] In the following, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary in nature rather than restrictive.

[0042] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0043] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. Such repetition is for the purpose of simplification and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art may be aware of the application of other processes and / or the use of other materials.

[0044] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0045] As Figure 1 shown, the present invention discloses a system for coupling low-temperature liquid energy storage and air separation using the cold energy of LNG, which includes an air compression purification and pressurization unit, an air liquefaction and air separation cold box, a liquid air storage and pressurization unit, a liquid air reheating and cold storage unit, an air expansion power generation unit, an LNG cold box, and an NG reheating unit.

[0046] Air enters the air compression purification and pressurization unit for cooling, purification, and pressurization. A part of the low-pressure air enters the air liquefaction and air separation cold box for heat exchange cooling and then is sent to the air separation rectification system. Another part of the air is pressurized and then enters the air liquefaction and air separation cold box for heat exchange cooling to become liquid air, and the liquid air enters the liquid air storage and pressurization unit.

[0047] A part of the liquid air in the liquid air storage and pressurization unit enters the air separation rectification system to adjust and maintain the stability of the output of the air separation liquid products. Another part of the liquid air in the liquid air storage and pressurization unit passes through the liquid air reheating and cold storage unit to exchange heat with the cold storage medium and then enters the air expansion power generation unit.

[0048] A nitrogen circulation pipeline is provided between the LNG cold box and the air liquefaction and air separation cold box. LNG exchanges heat with the nitrogen medium in the nitrogen circulation pipeline through the LNG cold box. The cold storage medium in the liquid air reheating and cold storage unit also exchanges heat with the nitrogen medium in the nitrogen circulation pipeline in the LNG cold box, and then the nitrogen medium exchanges heat with the air entering the air liquefaction and air separation cold box.

[0049] The NG reheating unit and the air compression, purification and boosting unit use a set of thermodynamic cycles. The thermodynamic cycle in the air compression, purification and boosting unit absorbs the heat of the air to cool the air. The LNG output after heat exchange with the medium nitrogen in the LNG cold box enters the NG reheating unit. In the NG reheating unit, the LNG absorbs the heat of the thermodynamic cycle, realizing the use of the cold energy in the LNG output from the LNG cold box for air cooling.

[0050] Specifically, the air compression, purification and boosting unit includes an air compressor C1, an inter-stage heat exchanger E1 of the air compressor and an adsorption system connected in sequence. The adsorption system outputs two pipelines into the air liquefaction and air separation cold box. One pipeline directly enters the air liquefaction and air separation cold box, and the other pipeline is sequentially provided with an air booster C2 and an inter-stage heat exchanger E2 of the air booster.

[0051] The air liquefaction and air separation cold box includes a main heat exchanger E13 of the air separation cold box and an air separation rectification system. In the air compression, purification and boosting unit, both pipelines output by the adsorption system are located on the main heat exchanger E13 of the air separation cold box. Among the two pipelines, the pipeline passing through the air booster C2 enters the liquid air storage and pressurization unit after passing through the main heat exchanger E13 of the air separation cold box, and the other pipeline enters the air separation rectification system after passing through the main heat exchanger E13 of the air separation cold box. The air separation rectification system is also provided with a pipeline for discharging nitrogen through the main heat exchanger E13 of the air separation cold box.

[0052] The liquid air storage and pressurization unit includes a liquid air expander T2, a liquid air-liquid separator VP1, a liquid air storage tank SP1, and a first pump P1 connected in sequence. The top of the liquid air-liquid separator VP1 is connected to an exhaust pipe passing through the main heat exchanger E13 of the air separation cold box. The liquid air-liquid separator VP1 is also connected to a product regulating pipe communicating with the air separation rectification system. The pipeline passing through the air booster C2 enters the liquid air expander T2 of the liquid air storage and pressurization unit after passing through the main heat exchanger E13 of the air separation cold box. The liquid air coming out of the liquid air expander T2 enters the liquid air-liquid separator VP1. The gas returns to the main heat exchanger E13 of the air separation cold box through the exhaust pipe and is reheated to room temperature and discharged. Part of the liquid air can enter the air separation rectification system through the product regulating pipe to adjust the output of the air separation liquid product to keep it stable.

[0053] The liquid air reheating and cold storage unit includes two circulation pipelines. One circulation pipeline sequentially includes a first cold storage heat exchanger E21, a first cold storage medium storage tank SP2, a second pump P2, a second cold storage medium storage tank SP3, and a third pump P3. The internal cold storage medium is one or a mixture of alkane compounds and fluorides. The alkane compounds include ethane, ethylene, propane, propylene, etc., and the fluorides include CHF3, CF4, CClF3, etc. The other circulation pipeline sequentially includes a second cold storage heat exchanger E22, a third cold storage medium storage tank SP4, a fourth pump P4, a fourth cold storage medium storage tank SP5, and a fifth pump P5. The internal cold storage medium is one or a mixture of fluorides such as methanol, ethanol, butane, isobutane, butene, dimethyl ether, ammonia, R115, R123, R134a, R143a, R152a, etc. Among them, the liquid air output from the liquid air storage and pressurization unit's liquid air storage tank SP1 sequentially passes through the first cold storage heat exchanger E21 and the second cold storage heat exchanger E22 and then enters the air expansion power generation unit. When the first cold storage heat exchanger E21 and the second cold storage heat exchanger E22 are plate-fin heat exchangers, the outlet pressure of the first pump P1 is not higher than 11 MPa; when the first cold storage heat exchanger E21 and the second cold storage heat exchanger E22 are wound-tube heat exchangers, the outlet pressure of the first pump P1 is not higher than 15 MPa.

[0054] The air expansion power generation unit sequentially includes an air reheating heat exchanger E4 and four sets of expansion generator sets AT. An expansion generator set inter-stage heat exchanger E5 is provided between adjacent expansion generator sets AT. The liquid air input into the air expansion power generation unit is first heated by an external heat source and then sent to the four sets of expansion generator sets AT for power generation.

[0055] The LNG cold box includes an LNG heat exchanger E11 and a liquid nitrogen heat exchanger E12. The LNG pipeline enters the NG reheating unit after passing through the LNG heat exchanger E11. Among the two circulation pipelines of the liquid air reheating and cold storage unit, the pipeline between the second pump P2 and the second cold storage medium storage tank SP3 sequentially passes through the liquid nitrogen heat exchanger E12 and the LNG heat exchanger E11, and the pipeline between the fourth pump P4 and the fourth cold storage medium storage tank SP5 passes through the LNG heat exchanger E11.

[0056] A first nitrogen compressor C3-1, a second nitrogen compressor C3-2, and a liquid nitrogen expander T1 are provided on the nitrogen circulation pipeline. The nitrogen circulation pipeline passes through the LNG heat exchanger E11, the liquid nitrogen heat exchanger E12, and the main heat exchanger E13 of the air separation cold box. In the LNG heat exchanger E11 and the liquid nitrogen heat exchanger E12, the medium nitrogen exchanges heat with the LNG and the cold storage medium and liquefies. In the main heat exchanger E13 of the air separation cold box, the medium nitrogen exchanges heat with the air and reheats.

[0057] The nitrogen cycle pipeline includes a main path and four branches, namely the first branch, the second branch, the third branch, and the fourth branch. The main path sequentially passes through the second nitrogen compressor C3-2, the LNG heat exchanger E11, the liquid nitrogen heat exchanger E12, and the liquid nitrogen expander T1. The first branch starts from the outlet end of the liquid nitrogen expander T1, sequentially passes through the liquid nitrogen heat exchanger E12 and the LNG heat exchanger E11, and then communicates with the inlet end of the second nitrogen compressor C3-2. The second branch starts from the outlet end of the liquid nitrogen expander T1, sequentially passes through the liquid nitrogen heat exchanger E12 and the LNG heat exchanger E11, and then communicates with the inlet end of the first nitrogen compressor C3-1. The third branch starts from the outlet end of the liquid nitrogen expander T1, sequentially passes through the main heat exchanger E13 of the air separation cold box and the LNG heat exchanger E11, and then communicates with the inlet end of the second nitrogen compressor C3-2. The fourth branch starts from the outlet end of the liquid nitrogen expander T1, sequentially passes through the air separation rectification system, the main heat exchanger E13 of the air separation cold box, and the LNG heat exchanger E11, and then communicates with the inlet end of the first nitrogen compressor C3-1. Among them, the outlet end of the first nitrogen compressor C3-1 is connected to the third branch before entering the LNG heat exchanger E11, so that the medium output by the first nitrogen compressor C3-1 enters the inlet end of the second nitrogen compressor C3-2 after passing through the LNG heat exchanger E11.

[0058] The NG reheating unit includes a sixth pump P6 and an NG heat exchanger E3 arranged in sequence. The NG heat exchanger E3, the sixth pump P6, the inter-stage heat exchanger E1 of the air compressor, and the inter-stage heat exchanger E2 of the air booster are connected by pipelines, and ethylene glycol solution circulates internally as a heat exchange medium, constituting a thermal cycle between the NG reheating unit and the air compression purification and boosting unit. The LNG output from the LNG heat exchanger E11 enters the NG heat exchanger E3 for reheating to no less than 0°C and then is output. During this process, the heat absorbed by the ethylene glycol solution from the air in the inter-stage heat exchanger E1 of the air compressor and the inter-stage heat exchanger E2 of the air booster is absorbed by the LNG, and the sixth pump P6 circulates the ethylene glycol solution. Embodiment

[0059] The system stores energy during the peak period of new energy power generation for 8 hours; the system releases energy for power generation during the peak period of electricity consumption for 8 hours; during the period when the system neither stores nor releases energy for power generation (also called the flat section), it operates for 8 hours. The temperature of the LNG leaving the receiving station is -135°C and the pressure is 10 MPa, and the inlet temperature of the air expansion power generation unit is 200°C. The operating data of the system is shown in Table 1:

[0060] Table 1

[0061]

[0062] The power generation of the energy release period system is divided by the operating energy consumption during the energy storage period minus the energy consumption during the flat operation period, and the system's electricity-to-electricity conversion efficiency can be obtained, that is, (30626 kW - 1383 kW) × 8 h / (43706 kW × 8 h - 9758 kW × 8 h) ≈ 86.1%. This embodiment can reach 86.1%, which can be used to consume the green electricity of offshore wind and solar power, meet the requirements of green electricity with energy storage, with a daily green electricity generation of 800 MWh. The system can meet the peak shaving of 30 MW of energy storage power generation for 8 hours, and at the same time produce 800 TPD of air separation liquid products continuously for 24 hours a day to keep the output constant. Embodiment

[0063] The system stores energy during the low electricity consumption period for 8 hours; the system releases energy for power generation during the high electricity consumption period for 8 hours; the system neither stores energy nor releases energy for power generation (also called the flat period), and operates for 8 hours. The LNG temperature at the receiving station is -135 °C and the pressure is 10 MPa, the inlet temperature of the air expansion power generation unit is 150 °C, the electricity price during the trough period is 0.3 yuan / kWh, the electricity price during the peak period is 1.1 yuan / kWh, the electricity price during the flat period is 0.6 yuan / kWh, and the average electricity price for the whole day is 0.67 yuan / kWh. The system operation data is shown in Table 2:

[0064] Table 2

[0065]

[0066] The power generation of the energy release period system is divided by the operating energy consumption during the energy storage period minus the energy consumption during the flat operation period, and the system's electricity-to-electricity conversion efficiency can be obtained, that is, (10149 kW - 367 kW) × 8 h / (22524 kW × 8 h - 9758 kW × 8 h) ≈ 76.6%. This embodiment can reach 76.6%. The system can be used to store energy during the trough electricity period and release energy for power generation for the self-use of the air separation system during the peak electricity period. At the same time, it produces air separation liquid products continuously for 24 hours a day to keep the output constant, and reduces the production cost of the air separation system through the price difference between the peak and trough electricity prices.

[0067] The electricity price during the off-peak period of the whole day is 0.3 yuan / kWh, the energy storage duration is 8 hours, the electricity price during the peak period is 1.1 yuan / kWh, and the energy release duration is 8 hours. The electricity price during the flat period is 0.6 yuan / kWh, and the average electricity price for the whole day is 0.67 yuan / kW. Calculated based on the energy consumption of 10,000 kW of the cold energy air separation system, the average production electricity cost of this system is: (0.3×10,000×8 + 0.6×10,000×8 + 0.3×1 / 0.766×10,000×8) / (24×10,000) = 0.43 yuan / kWh. Without considering the increased production income of the air separation system due to the LNG temperature fluctuation in this system, (0.67 - 0.43) / 0.67 ≈ 35.8%. The production cost of the air separation system products has been reduced by approximately 35.8%.

[0068] The present invention also discloses a method for coupling cryogenic liquid energy storage using LNG cold energy with air separation. Energy is stored during the peak period of new energy power generation or the off-peak period of electricity consumption for 8 hours of operation, and energy is released for power generation during the peak period of electricity consumption for 8 hours of operation. During the period when there is neither energy storage nor energy release for power generation (also known as the flat period), the operation duration is 8 hours.

[0069] When storing energy during the peak period of new energy power generation, the system can be used to absorb the green electricity of offshore wind and photovoltaic power, meet the requirements of green electricity with energy storage, and at the same time produce air separation liquid products continuously for 24 hours a day and maintain a constant output.

[0070] When storing energy during the off-peak period of electricity consumption, the system can be used to store energy during the off-peak electricity period and release energy for power generation for the self-use of the air separation system during the peak electricity period. At the same time, air separation liquid products are produced continuously for 24 hours a day to maintain a constant output, and the production cost of the air separation system is reduced through the price difference between the peak and off-peak electricity prices.

[0071] When storing energy, the NG reheating unit, the air compression, purification and boosting unit remain in operation. LNG exchanges heat with nitrogen in the nitrogen circulation pipeline in the LNG cold box. The cold storage medium in the liquid air reheating and cold storage unit also exchanges heat with nitrogen in the nitrogen circulation pipeline in the LNG cold box. After the raw air is cooled and purified, a part exchanges heat with nitrogen in the nitrogen circulation pipeline, is cooled and then sent into the air separation rectification system, and another part of the liquid air produced after pressurization and cooling is sent into the liquid air storage and pressurization unit for storage. A part of the liquid air is used to adjust the product output by sending it into the air separation rectification system when the LNG temperature fluctuates, and another part is stored for power generation. Specifically, at this time, the LNG from the receiving station is about -135°C to -150°C, and the LNG at 6 - 10 MPa enters the LNG heat exchanger E11. In the LNG heat exchanger E11, the cold energy generated by the gasification of LNG is transferred to the high-pressure nitrogen, and the high-pressure nitrogen is then liquefied by the liquid nitrogen heat exchanger E12.

[0072] After the liquid nitrogen is depressurized to 1.5 - 3 MPa by the liquid nitrogen expander T1, the nitrogen is divided into two parts. One part sequentially passes through the liquid nitrogen heat exchanger E12 and the LNG heat exchanger E11, then enters the second nitrogen compressor C3-2 for pressurization, and then forms liquid nitrogen after passing through the LNG heat exchanger E11 and the liquid nitrogen heat exchanger E12 again. The other part sequentially passes through the liquid nitrogen heat exchanger E12 and the LNG heat exchanger E11, then enters the first nitrogen compressor C3-1 for pressurization, and after passing through the LNG heat exchanger E11 and the second nitrogen compressor C3-2 for pressurization, finally forms liquid nitrogen after passing through the LNG heat exchanger E11 and the liquid nitrogen heat exchanger E12 sequentially.

[0073] After the liquid nitrogen is depressurized to 1.5 - 3 MPa by the liquid nitrogen expander T1, the liquid nitrogen is divided into two parts. One part directly enters the main heat exchanger E13 of the air separation cold box, is reheated by exchanging heat with air, then returns to the LNG heat exchanger E11, and after being pressurized by the second nitrogen compressor C3-2, is sequentially sent to the LNG heat exchanger E11 and the liquid nitrogen heat exchanger E12 to form liquid nitrogen. The other part is depressurized by a throttle valve and enters the air separation rectification system, and then after being reheated by exchanging heat with air in the main heat exchanger E13 of the air separation cold box, sequentially passes through the LNG heat exchanger E11, is pressurized by the first nitrogen compressor C3-1, the LNG heat exchanger E11, the second nitrogen compressor C3-2, the LNG heat exchanger E11, and the liquid nitrogen heat exchanger E12 to form liquid nitrogen.

[0074] The first nitrogen compressor C3-1 pressurizes the nitrogen to 1.5 - 3 MPa, and the second nitrogen compressor C3-2 pressurizes the nitrogen to 6 - 7.5 MPa. Through the nitrogen cycle, the cold energy for LNG vaporization is utilized.

[0075] After passing through the LNG heat exchanger E11, the LNG enters the NG reheating unit, is reheated to NG not lower than 0 °C by exchanging heat with the medium in the NG heat exchanger E3, and then returns to the receiving station. During this period, the first cold storage medium storage tank SP2 in the liquid air reheating and cold storage unit sequentially exchanges heat with the nitrogen in the nitrogen circulation pipeline through the liquid nitrogen heat exchanger E12 and the LNG heat exchanger E11. After the cold storage medium is reheated, it flows back to the second cold storage medium storage tank SP3. The cold storage medium in the third cold storage medium storage tank SP4 exchanges heat with the nitrogen in the nitrogen circulation pipeline through the LNG heat exchanger E11. After the cold storage medium is reheated, it flows back to the fourth cold storage medium storage tank SP5.

[0076] After the raw material air is pressurized by the air compressor C1, it sequentially passes through the inter-stage heat exchanger E1 of the air compressor and the adsorption system to achieve air cooling and the removal (purification) of carbon dioxide and moisture. Then the air is sent out in two parts. One part of the low-pressure air directly enters the main heat exchanger E13 of the air separation cold box in the air liquefaction and air separation cold box, is heat-exchanged and cooled, and then sent into the air separation rectification system. The other part is pressurized to 1 - 7 MPa by the air booster C2, cooled by the inter-stage heat exchanger E2 of the air booster, and then the pressurized air enters the main heat exchanger E13 of the air separation cold box to be heat-exchanged and cooled into liquid air, and the low-temperature liquid air is sent into the liquid air storage and pressurization unit. The media that exchanges heat with the air in the inter-stage heat exchanger E2 of the air booster and the inter-stage heat exchanger E1 of the air compressor is the media that absorbs the cold energy of LNG in the NG heat exchanger E3.

[0077] In the liquid air storage and pressurization unit, the liquid air transported from the air liquefaction and air separation cold box first expands to 0.3 - 0.7 MPa through the liquid air expander T2. The liquid air coming out of the liquid air expander T2 passes through the liquid air-liquid separator VP1. The gas part returns to the main heat exchanger E13 of the air separation cold box from the top of the liquid air-liquid separator VP1, is reheated to normal temperature and then discharged. The liquid part is sent to the liquid air storage tank SP1 for storage, used for subsequent expansion power generation, and part of the liquid air enters the air separation rectification system to adjust the output of the air separation liquid product to keep it stable.

[0078] When generating energy during the peak electricity consumption period, the NG reheating unit and the air compression purification and boosting unit keep running. LNG exchanges heat with nitrogen in the nitrogen circulation pipeline in the LNG cold box. After the raw material air is cooled and purified, it exchanges heat with nitrogen in the nitrogen circulation pipeline and is cooled and then sent into the air separation rectification system. The liquid air stored in the liquid air storage and pressurization unit, according to the fluctuation of the LNG temperature coming from the receiving station, part of it enters the air separation rectification system to adjust the output of the air separation liquid product to keep it stable, and the other part is pressurized and exchanges heat with the cold storage medium in the liquid air reheating and cold storage unit, so that the cold storage medium obtains cold energy, and then is sent into the air expansion power generation unit for power generation. Specifically, the liquid air in the liquid air storage tank SP1, according to the fluctuation of the LNG temperature coming from the receiving station, part of the liquid air in the liquid air storage tank SP1 enters the air separation rectification system to adjust the output of the air separation liquid product to keep it stable, and the rest of the liquid air is output from the liquid air storage and pressurization unit for expansion power generation. The liquid air output from the liquid air storage and pressurization unit is first pressurized to 50 - 120 MPa by the first pump P1, and then sequentially passes through the first cold storage heat exchanger E21 and the second cold storage heat exchanger E22, exchanges heat and reheats with the cold storage media in the second cold storage medium storage tank SP3 and the fourth cold storage medium storage tank SP5 respectively, and then is heated by an external heat source at 50°C - 250°C and sent to four expansion generator sets AT for power generation. The external heat source has a wide temperature range, strong adaptability, and a wide range of application scenarios for energy storage.

[0079] During the flat period, the NG reheating unit, the air compression purification and pressurization unit keep running. The LNG exchanges heat with the nitrogen in the nitrogen circulation pipeline in the LNG cold box. After the raw material air is cooled and purified, it exchanges heat with the nitrogen in the nitrogen circulation pipeline and then is sent into the air separation rectification system. According to the fluctuating change of the LNG temperature coming from the receiving station, the liquid air stored in the liquid air storage and pressurization unit enters the air separation rectification system to adjust and keep the output of the air separation liquid product stable.

[0080] The above-described embodiments have elaborated on the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements, equivalent replacements, etc. made within the principle scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for coupling cryogenic liquid energy storage and air separation using the cold energy of LNG, characterized in that, It includes an air compression, purification and boosting unit, an air liquefaction and air separation cold box, a liquid air storage and pressurization unit, an air expansion power generation unit, a liquid air reheating and cold storage unit and an LNG cold box; Among them, the air liquefaction and air separation cold box includes an air separation cold box main heat exchanger and an air separation rectification system, the liquid air storage and pressurization unit includes a liquid air storage tank, the air expansion power generation unit includes a plurality of expansion generator sets, the LNG cold box includes an LNG heat exchanger, and a nitrogen circulation pipeline is provided between the LNG heat exchanger and the air separation cold box main heat exchanger; The air compression, purification and boosting unit pressurizes, cools and purifies the raw air and then inputs it into the air separation cold box main heat exchanger in two paths. One path enters the air separation rectification system after being output from the air separation cold box main heat exchanger, and the other path becomes liquid air after being output from the air separation cold box main heat exchanger and enters the liquid air storage tank of the liquid air storage and pressurization unit. The liquid air storage tank can send the liquid air into the air separation rectification system and the air expansion power generation unit. The LNG enters the LNG heat exchanger to exchange heat with the nitrogen in the nitrogen circulation pipeline, and the nitrogen in the nitrogen circulation pipeline exchanges heat with the air in the air separation cold box main heat exchanger; The liquid air reheating and cold storage unit includes two circulation pipelines. One circulation pipeline sequentially includes a first cold storage heat exchanger, a first cold storage medium storage tank, a second pump, a second cold storage medium storage tank, and a third pump. The other circulation pipeline sequentially includes a second cold storage heat exchanger, a third cold storage medium storage tank, a fourth pump, a fourth cold storage medium storage tank, and a fifth pump; Among them, the liquid air output from the liquid air storage tank of the liquid air storage and pressurization unit sequentially passes through the first cold storage heat exchanger and the second cold storage heat exchanger and then enters the air expansion power generation unit; The LNG cold box also includes a liquid nitrogen heat exchanger. The pipeline between the second pump and the second cold storage medium storage tank sequentially passes through the liquid nitrogen heat exchanger and the LNG heat exchanger, and the pipeline between the fourth pump and the fourth cold storage medium storage tank passes through the LNG heat exchanger.

2. The system for coupling cryogenic liquid energy storage and air separation using LNG cold energy according to claim 1, wherein The air compression, purification and boosting unit includes an air compressor, an air compressor inter-stage heat exchanger, and an adsorption system connected in sequence. The adsorption system outputs two pipelines. One pipeline enters the air separation rectification system after passing through the air separation cold box main heat exchanger, and the other pipeline sequentially passes through an air booster, an air booster inter-stage heat exchanger and then is connected to the liquid air storage tank through the air separation cold box main heat exchanger.

3. The system for coupling cryogenic liquid energy storage and air separation using LNG cold energy according to claim 2, wherein The system also includes an NG reheating unit. The NG reheating unit includes an NG heat exchanger. A circulation pipeline is provided between the NG heat exchanger and the air compressor inter-stage heat exchanger and the air booster inter-stage heat exchanger. A sixth pump is provided on the circulation pipeline, and the LNG output from the LNG heat exchanger is reheated through the NG heat exchanger and then output.

4. The system for coupling low-temperature liquid energy storage and air separation using LNG cold energy according to claim 1, characterized in that The liquid air storage and pressurization unit includes a liquid air expander, a liquid air liquid separator, a liquid air storage tank, and a first pump connected in sequence. The liquid air input into the liquid air storage and pressurization unit from the air separation cold box main heat exchanger first enters the liquid air expander, and the top of the liquid air liquid separator is connected to an exhaust pipe passing through the air separation cold box main heat exchanger.

5. The system for coupling cryogenic liquid energy storage and air separation using LNG cold energy according to claim 1, wherein The air expansion power generation unit sequentially includes an air reheating heat exchanger and four groups of expansion generator sets, and an inter-stage heat exchanger of the expansion generator sets is provided between two adjacent expansion generator sets.

6. The system for coupling cryogenic liquid energy storage and air separation using LNG cold energy according to claim 1, wherein A first nitrogen compressor, a second nitrogen compressor and a liquid nitrogen expander are provided on the nitrogen circulation pipeline. The nitrogen circulation pipeline includes a main pipeline and a first branch pipeline, a second branch pipeline, a third branch pipeline and a fourth branch pipeline. The main pipeline sequentially passes through the second nitrogen compressor, the LNG heat exchanger, the liquid nitrogen heat exchanger and the liquid nitrogen expander. The first branch pipeline sequentially passes through the liquid nitrogen heat exchanger and the LNG heat exchanger from the outlet end of the liquid nitrogen expander and then communicates with the inlet end of the second nitrogen compressor. The second branch pipeline sequentially passes through the liquid nitrogen heat exchanger and the LNG heat exchanger from the outlet end of the liquid nitrogen expander and then communicates with the inlet end of the first nitrogen compressor. The third branch pipeline sequentially passes through the main heat exchanger of the air separation cold box and the LNG heat exchanger from the outlet end of the liquid nitrogen expander and then communicates with the inlet end of the second nitrogen compressor. The fourth branch pipeline sequentially passes through the air separation rectification system, the main heat exchanger of the air separation cold box and the LNG heat exchanger from the outlet end of the liquid nitrogen expander and then communicates with the inlet end of the first nitrogen compressor. Wherein, the outlet end of the first nitrogen compressor communicates with the third branch pipeline before entering the LNG heat exchanger, so that the medium output by the first nitrogen compressor enters the inlet end of the second nitrogen compressor after passing through the LNG heat exchanger.

7. A method for coupling cryogenic liquid energy storage and air separation by utilizing the cold energy of LNG in the system according to any one of claims 1 to 6, characterized in that, Energy is stored during the peak period of new energy power generation or the low electricity consumption period, and energy is released for power generation during the peak electricity consumption period. Wherein, during energy storage, the raw air enters the air compression purification and pressurization unit for cooling and purification, and then is divided into two paths to enter the air liquefaction and air separation cold box. One path enters the air liquefaction and air separation cold box for cooling and then for air separation rectification. The other path is pressurized and cooled and then enters the air liquefaction and air separation cold box for cooling to form liquid air. The liquid air is sent to the liquid air storage and pressurization unit for storage. The LNG from the receiving station is sequentially introduced into the LNG cold box and the NG reheating unit to realize two-time recovery and utilization of the cold energy of the LNG. The cold energy of the LNG absorbed by the NG reheating unit is used for cooling the air in the air compression purification and pressurization unit. In the LNG cold box, the nitrogen in the nitrogen circulation pipeline absorbs the cold energy of the LNG and the cold energy of the cold storage medium in the liquid air reheating and cold storage unit. After absorbing the cold energy, the nitrogen transfers the cold energy to the air sent into the air liquefaction and air separation cold box. When releasing energy for power generation, the raw air enters the air compression purification and pressurization unit for cooling and purification, then enters the air liquefaction and air separation cold box for cooling and then for air separation rectification. The liquid air stored in the liquid air storage and pressurization unit is pressurized and first exchanges heat with the cold storage medium in the liquid air reheating and cold storage unit, and then is heated by an external heat source and sent to the air expansion power generation unit for power generation. The LNG from the receiving station is sequentially introduced into the LNG cold box and the NG reheating unit to realize two-time recovery and utilization of the cold energy of the LNG. The cold energy of the LNG absorbed by the NG reheating unit is used for cooling the air in the air compression purification and pressurization unit. In the LNG cold box, after the nitrogen in the nitrogen circulation pipeline absorbs the cold energy of the LNG, it transfers the cold energy to the air sent into the air liquefaction and air separation cold box. The liquid air stored in the liquid air storage and pressurization unit partially enters the air liquefaction and air separation cold box for air separation rectification according to the fluctuation of the LNG temperature coming from the receiving station, so as to adjust the output of the air separation liquid products to remain stable; The liquid air reheating and cold storage unit includes two circulating pipelines; The cold storage medium in one of the circulating pipelines exchanges heat with nitrogen in the nitrogen circulation pipeline twice. The cold storage medium is one or more mixtures of alkane compounds and fluorides. The alkane compounds include ethane, ethylene, propane, and propylene, and the fluorides include CHF3, CF4, and CClF3; The cold storage medium in the other circulating pipeline exchanges heat with nitrogen in the nitrogen circulation pipeline once. The cold storage medium is one or more mixtures of methanol, ethanol, butane, isobutane, butene, dimethyl ether, ammonia, R115, R123, R134a, R143a, and R152a.

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