Apparatus and method for recovering carbon dioxide and nitrogen gases from flue gases

Abstract

To provide a device and a method for recovering CO2 and N2 in a flue gas with low cost and lower energy consumption.SOLUTION: A pretreatment system includes a high-temperature NG cooler, a gas-liquid separator, a booster fan, and a dryer. A CO2 N2 separation system includes a low-temperature LNG cooler and a cryogenic adsorption device. An N2 purification and liquefaction system includes an N2 distillation and liquefaction device composed of a compressor, a cooler, a heat exchanger, a gas-liquid separator, and a distillation tower. A CO2 purification and liquefaction system includes a CO2 distillation and liquefaction device composed of a compressor, a cooler, a condenser, an evaporator, a liquefier, and a purification tower and further purifies and liquefies a desorbed gas obtained from the CO2 N2 separation system. The systems are connected via pipe conduits and valves. The device and method recover the CO2 and N2 from the flue gas, executes the liquefaction of CO2 and N2 by LNG cold heat, and can remarkably reduce energy consumption and costs in revering.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for recovering carbon dioxide and nitrogen gases from flue gases and is in the field of cryogenic technology. [Background technology]

[0002] Fossil fuel emissions account for 40% of the world's total carbon dioxide emissions. China's current energy structure relies heavily on coal, little oil, and little natural gas, making coal combustion flue gas the country's main source of carbon dioxide emissions. Therefore, reducing carbon emissions from coal combustion flue gas is of great environmental importance. In the energy utilization process, the main technologies for CO2 capture include absorption, adsorption, membrane separation, and low-temperature phase change separation. Solution absorption is the most mature CO2 capture method and is used for various flue gases worldwide. It can separate CO2 from atmospheric, low-concentration flue gas, has a large throughput, and produces high-purity CO2. However, this method requires a large amount of heat to regenerate the solution after absorption. The absorbent is resource-intensive to manufacture, and loses its effectiveness after a certain period of use, requiring constant replenishment. Chemical absorbents also have some toxicity and corrosiveness, have a significant impact on the environment, and are expensive to manufacture and recover. Membrane separation is a technology that separates gases by using the difference in permeability of polymeric films to different gases and is driven by pressure differences, but its large-scale application is relatively limited. Pressure swing adsorption technology has many advantages, such as easy regeneration of the adsorbent, long service life of the adsorbent, and simple equipment, but for flue gas with low carbon dioxide concentrations, the cost and energy consumption of ambient temperature pressure swing adsorption technology are both very high.

[0003] China is also a major importer of LNG. LNG is a low-temperature liquid mixture obtained by liquefying and refining gaseous natural gas through a cryogenic process. Its temperature at atmospheric pressure is -162°C. LNG releases a large amount of cold energy during re-vaporization at receiving terminals. Conventional re-vaporization processes use seawater to vaporize LNG, resulting in significant cold energy waste and cold pollution to the surrounding marine and local environments. Coal-fired power plants are built near LNG receiving terminals, and the cold energy released during LNG vaporization is used to capture CO2 and N2 from the flue gas. This reduces the cost of LNG vaporization equipment and the power consumption of the capture equipment, indirectly reducing greenhouse gas emissions and providing significant economic and social benefits.

[0004] Chinese Patent CN107899376A discloses an apparatus and method for liquefying and capturing carbon dioxide and nitrogen gases in flue gas, which belongs to membrane separation and recovery technology. However, membranes have high requirements for the purity of the gas source, short service life, low product purity, and high cost, making them unsuitable for industrial mass production.

[0005] Chinese Patent CN210825439U discloses a system for simultaneously recovering carbon dioxide and nitrogen gas from the flue gas of a coal-fired power plant boiler. The system includes a flue gas pretreatment system, a PSA1 system, a PSA2 system, a carbon dioxide compression and purification system, a carbon dioxide rectification and storage system, and a PSA-based high-purity nitrogen production system. This system can maximize the capture of carbon dioxide and nitrogen gas, and produces high-purity products. However, the system suffers from problems such as inconvenient operation and high energy consumption.

[0006] Chinese Patent CN216481836U discloses a system for simultaneously recovering nitrogen gas and carbon dioxide from boiler flue gas. The system includes a flue gas pretreatment system, a carbon-nitrogen separation system, a carbon dioxide secondary purification system, and a nitrogen gas concentration and purification system. This system maximizes the recovery of carbon dioxide and nitrogen gas. However, the carbon-nitrogen separation in this system uses ambient temperature pressure swing adsorption technology, which requires high adsorption pressures of 0.2 to 0.4 MPa, resulting in high energy consumption. Furthermore, the cold energy production utilizes conventional electrically driven refrigeration, resulting in high recovery costs. Summary of the Invention

[0007] In view of the above circumstances, an object of the present invention is to provide an apparatus and method for recovering carbon dioxide and nitrogen gases from flue gas. The present invention utilizes the cold energy from LNG vaporization in combination with low-temperature adsorption technology to recover and utilize CO2 and N2 from flue gas at low cost and with low energy consumption, and has relatively high economic and social value. To achieve the above object, the present invention utilizes the following technologies: 1. An apparatus for recovering carbon dioxide and nitrogen gas in flue gas, comprising: The apparatus includes a pre-treatment system, a CO2 / N2 separation system, an N2 purification and liquefaction system, and a CO2 purification and liquefaction system, which are connected to each other via pipes and valves. The pre-treatment system includes a high-temperature LNG cooler, a gas-liquid separator, a booster blower, and a dryer, and removes moisture from the flue gas and cools the flue gas. The CO2 / N2 separation system includes a low-temperature LNG cooler and a low-temperature adsorption device, and further cools and adsorbs the pre-treated flue gas to separate CO2 and N2. The N2 purification and liquefaction system includes an N2 rectification and liquefaction device consisting of a feed compressor, a heat exchanger, a cooler, a gas-liquid separator, and a rectification system, and is used to further purify and liquefy the nitrogen-containing gas obtained from the CO2-N2 separation system. The CO2 purification and liquefaction system includes a CO2 rectification and liquefaction device consisting of a CO2 compressor, a cooler, an evaporator, a condenser, a liquefier, and a purification column, and is used to further purify and liquefy the desorbed gas obtained from the CO2-N2 separation system.

[0008] Preferably, the first inlet of the high-temperature NG cooler in the pre-treatment system is connected to the flue gas outlet, and the flue gas is further cooled by the high-temperature cold NG; the cooled flue gas passes through the first outlet of the high-temperature NG cooler, and most of the water in the flue gas is removed by a gas-liquid separator, and the water is discharged from the water outlet of the gas-liquid separator; the cooled flue gas passes through the gas outlet of the gas-liquid separator, is pressurized by the booster blower, and then enters the dryer through a passage to be further dried; and the dryer in the pre-treatment system is connected to the inlet of the low-temperature LNG cooler, and The pre-treated dry flue gas is cooled to about the boiling point of CO2 by using cold energy. The outlet of the low-temperature LNG cooler is connected to the inlet of the low-temperature adsorption device. According to the principle of low-temperature adsorption, the CO2 in the low-temperature flue gas is adsorbed and captured. A crude carbon dioxide gas with a relatively high carbon purity is obtained at the desorbed gas outlet of the low-temperature adsorption device. A nitrogen-containing gas containing less than 1 ppm of carbon dioxide and with a relatively high nitrogen purity is obtained at the exhaust outlet of the low-temperature adsorption device, thereby achieving the purpose of carbon-nitrogen separation. The adsorbents used in the low-temperature adsorption device are mainly molecular sieves and activated carbon.

[0009] Preferably, the exhaust pipe at the outlet of the low-temperature adsorption device is connected to the inlet of a feed compressor of an N2 purification liquefaction system to pressurize the nitrogen-containing gas, the outlet of the feed compressor is connected to the first inlet of the cooler, the first outlet of the cooler is connected to the first inlet of the heat exchanger, the second inlet of the cooler is connected to a high-temperature cold NG introduction pipe, the second outlet of the cooler is connected to a NG discharge pipe, the first outlet of the heat exchanger is connected to the rectification system, the nitrogen gas outlet of the rectification system is connected to the second inlet of the heat exchanger, the second outlet of the heat exchanger is connected to the inlet of a circulation compressor, the outlet of the circulation compressor is connected to a third inlet of the heat exchanger, and the third outlet of the heat exchanger is connected to the gas-liquid separation system. The second outlet of the gas-liquid separator is connected to the sixth inlet of the heat exchanger, and the sixth inlet is connected to the second outlet of the heat exchanger. The vent outlet of the rectification system is connected to the fourth inlet of the heat exchanger, and the fourth outlet of the heat exchanger is connected to a vent line. The LNG liquid inlet is connected to the fifth inlet of the heat exchanger. The high-temperature cold LNG outlet is connected to the fifth outlet of the heat exchanger. The nitrogen-containing gas obtained from the CO₂-N₂ separation system is further purified and liquefied according to the principle of low-temperature rectification to obtain high-purity liquid nitrogen product. The rectification system is a single-column rectification or a double-column rectification.

[0010] Preferably, the desorption gas pipe at the outlet of the low-temperature adsorption device is connected to the inlet of a CO2 compressor of a CO2 purification and liquefaction system to compress the raw carbon dioxide gas, the outlet of the CO2 compressor is connected to the first inlet of the cooler, the first outlet of the cooler is connected to the inlet of the evaporator, the second inlet of the cooler is connected to a high-temperature cold NG introduction pipe, the second outlet of the cooler is connected to a NG discharge pipe, the outlet of the evaporator is connected to the first inlet of the liquefier, the first outlet of the liquefier is connected to an intermediate inlet of the purification tower, and the liquefier The second inlet of the liquefier is connected to a high-temperature cold NG inlet pipeline, the second outlet of the liquefier is connected to a NG outlet pipeline, the first inlet of the condenser is connected to a high-temperature cold NG inlet pipeline, and the first outlet of the condenser is connected to a NG outlet pipeline. Industrial-grade liquid carbon dioxide product is obtained at the bottom of the purification tower, which is connected to a storage system through the first outlet at the bottom of the purification tower and may be connected to a carbon dioxide purification system, and food-grade carbon dioxide is obtained by secondary purification of CO2. The second outlet of the purification tower is connected to an exhaust gas vent pipeline.

[0011] 1. A method for recovering carbon dioxide and nitrogen gases in flue gas, comprising: Step 1: In flue gas pretreatment, The flue gas is cooled and dried at room temperature and pressure. Step 2: Separation of CO2 and N2 The gas dried in the dryer passes through a low-temperature LNG cooler and a low-temperature adsorption device, whereby crude carbon dioxide gas is desorbed from the gas and nitrogen-containing gas is discharged. Step 3: Obtaining CO2 and N2 products through purification and liquefaction The crude carbon dioxide gas and the discharged nitrogen-containing gas are passed through a CO2 rectification liquefaction unit and an N2 rectification liquefaction unit to be purified and liquefied.

[0012] Preferably, in the step 1: flue gas pretreatment method, the flue gas at normal temperature and pressure enters the first inlet of the high-temperature NG cooler, and the flue gas is cooled by high-temperature cold NG in the cooler, the cooled flue gas enters the high-temperature NG cooler, and enters the gas-liquid separator from the first outlet of the high-temperature NG cooler, most of the water in the flue gas is discharged from the water outlet of the gas-liquid separator, and the cooled flue gas is discharged from the gas outlet of the gas-liquid separator, and after being pressurized by the booster blower, enters the dryer through a passage and is further dried until the dew point meets the relevant requirements.

[0013] Preferably, in the method for separating CO2 and N2 in step 2, the gas dried by the dryer enters the low-temperature LNG cooler through its inlet, and the dry flue gas is cooled to about the boiling point of CO2 in the low-temperature LNG cooler by the cold heat of LNG. The outlet of the low-temperature LNG cooler is connected to the inlet of a low-temperature adsorption device, and CO2 and other substances in the low-temperature dry flue gas are adsorbed and captured according to the principle of low-temperature adsorption. A crude carbon dioxide gas with a relatively high carbon purity is obtained at the desorption gas outlet of the low-temperature adsorption device, and a nitrogen-containing gas containing carbon dioxide of 1 ppm or less and with a relatively high nitrogen purity is obtained at the exhaust outlet of the low-temperature adsorption device, thereby obtaining a purified raw gas of carbon dioxide and nitrogen gas, and achieving the purpose of carbon-nitrogen separation.

[0014] Preferably, in the method for purifying and liquefying N2 in step 3, the exhaust from the exhaust outlet of the low-temperature adsorption device is connected to the inlet of a feed compressor via a pipe to pressurize the nitrogen-containing gas, the outlet of the feed compressor is connected to the first inlet of a cooler, the first outlet of the cooler is connected to the first inlet of a heat exchanger, the second inlet of the cooler is connected to a high-temperature cold NG introduction pipeline, and the second outlet of the cooler is connected to an NG discharge pipeline, the nitrogen-containing gas after pressurization and cooling exchanges heat with LNG, rectification circulating nitrogen gas, and rectification purge gas from the outside in the heat exchanger, and is connected to a rectification system via the first outlet of the heat exchanger, and separation and purification are performed in the rectification system, and the nitrogen gas outlet of the rectification system is connected to the second inlet of the heat exchanger, and this nitrogen gas is used as circulating nitrogen gas. The second outlet of the heat exchanger is connected to the inlet of the circulation compressor. The outlet of the circulation compressor is connected to the third inlet of the heat exchanger. The third outlet of the heat exchanger is connected to the gas-liquid separator. High-purity liquid nitrogen product is obtained at the bottom of the gas-liquid separator and flows out from the first outlet of the gas-liquid separator. The gas from the gas-liquid separator enters the sixth inlet of the heat exchanger through the second outlet of the gas-liquid separator, is reheated by the heat exchanger, and then flows into the circulation compressor through the second outlet and compressed. The purge gas from the rectification system is connected to the fourth inlet of the heat exchanger, is reheated, and then purged through the fourth outlet of the heat exchanger. The LNG liquid inlet is connected to the fifth inlet of the heat exchanger. The high-temperature liquefied natural gas (LNG) flows out from the fifth outlet of the heat exchanger to become a source of high-temperature liquefied natural gas for other systems. In the method for CO2 purification and liquefaction in step 3, the desorbed gas from the low-temperature adsorption device is connected to the inlet of a CO2 compressor via the desorbed gas outlet to compress the crude carbon dioxide gas; the outlet of the CO2 compressor is connected to the first inlet of a cooler; the second inlet of the cooler is connected to a high-temperature cold NG introduction pipe; the second outlet of the cooler is connected to a NG discharge pipe; the compressed crude carbon dioxide gas is cooled by the high-temperature cold NG in the cooler; the first outlet of the cooler is connected to the inlet of an evaporator; the cooled crude carbon dioxide gas serves as a heat source for the evaporator to supply heat for vaporization of liquid carbon dioxide; the outlet of the evaporator is connected to the first inlet of a liquefier; the second inlet of the liquefier is connected to a high-temperature cold NG introduction pipe; and the second outlet of the liquefier is connected to a NG discharge pipe. The first inlet of the overhead condenser is connected to the high-temperature cold NG inlet line, and the first outlet of the condenser is connected to the NG outlet line. The high-temperature cold NG is used to condense and reflux the overhead gas. At the same time, some of the exhaust gas is purged from the second outlet of the purification tower. Industrial-grade liquid carbon dioxide is obtained at the bottom of the purification tower, which is connected to a storage system via the first outlet at the bottom of the purification tower. The industrial-grade liquid carbon dioxide product can be connected to a carbon dioxide purification system, and the CO2 is further purified to obtain food-grade carbon dioxide.

[0015] Preferably, the cold source for the cooler, the liquefier, the condenser and the cooler in the N2 purification liquefaction system is derived from high-temperature cold energy (NG) generated during the LNG vaporization process, which consumes less energy than a method of producing cold energy using a conventional electrically driven refrigerator, is safe and environmentally friendly, and can also realize the recovery and utilization of high-temperature cold energy from LNG.

[0016] Preferably, the N2 purification liquefaction system produces liquid nitrogen products by being driven by the cold generated by vaporizing LNG in the heat exchanger, instead of the conventional method of generating cold by compression and expansion using electrical energy. This significantly reduces the energy consumption for producing high-purity liquid nitrogen products, and the high-temperature cold generated when LNG is vaporized in the N2 purification liquefaction system and releases energy can be used as a cold source for other components of the recovery system, allowing for cascading use of cold sources of different temperatures from LNG.

[0017] The apparatus and method for recovering carbon dioxide and nitrogen gases in flue gas provided in the present invention have the following beneficial effects: 1) The device and method of the present invention uses LNG as the source of cold energy for the system, eliminating the need for an external electric refrigeration system and achieving more energy savings. Furthermore, the device and method realize efficient use of LNG cold energy by combining LNG cold energy at different temperatures according to the different temperature requirements of each system. 2) The device and method of the present invention achieve carbon and nitrogen separation through low-temperature adsorption, and can obtain crude carbon dioxide gas and nitrogen-containing gas with relatively high contents at low pressure, which results in a higher pressure power usage rate for the subsequent purification system and lower overall energy consumption. 3) In this invention, CO2 and N2 in flue gas are recovered by LNG cryogenic liquefaction, and the CO2 and N2 are efficiently separated by the characteristics of low-temperature adsorption separation. The CO2 and N2 are then purified and liquefied by low-temperature rectification, thereby making it possible to obtain high-purity liquid carbon dioxide and high-purity liquid nitrogen with low energy consumption and low cost. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a flowchart of the present invention. [Figure 2] 1 is a schematic diagram of the N2 purification and liquefaction structure of the present invention. [Figure 3] 1 is a schematic diagram of the CO2 purification and liquefaction structure of the present invention. [Figure 4] FIG. 1 is a schematic diagram of another N2 purification and liquefaction structure of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] In order to clarify the technical problems, technical solutions and beneficial effects of the present invention, the present invention will be described in more detail below with reference to Figures 1-4 and specific embodiments. It should be noted that those skilled in the art can make multiple improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications are also within the scope of protection of the present invention.

[0020] Fig. 1 shows an apparatus for recovering carbon dioxide and nitrogen gas from flue gas. The apparatus includes a pre-treatment system 01, a CO2 / N2 separation system 02, an N2 purification and liquefaction system 03, and a CO2 purification and liquefaction system 04, which are connected to each other via pipes and valves. The pre-treatment system 01 includes a high-temperature LNG cooler 1a, a gas-liquid separator 1b, a booster blower 1c, and a dryer 1d, and removes moisture from the flue gas and cools it. The CO2 / N2 separation system 02 includes a low-temperature LNG cooler 2a and a low-temperature adsorption device 2b, and further cools and adsorbs the pre-treated flue gas to separate CO2 and N2. The N2 purification and liquefaction system 03 includes an N2 rectification and liquefaction apparatus consisting of compressors 3a and 3k, a cooler 3b, a heat exchanger 3c, a gas-liquid separator 3i, and a rectification system 3m, and further purifies and liquefies the nitrogen-containing gas obtained from the CO2-N2 separation system. The CO2 purification and liquefaction system 04 includes a CO2 rectification and liquefaction apparatus consisting of a CO2 compressor 4a, a cooler 4b, an evaporator 4c, a condenser 4f, a liquefier 4d, and a purification column 4e, and further purifies and liquefies the desorbed gas obtained from the CO2-N2 separation system.

[0021] The pretreatment system 01 includes a high-temperature NG cooler 1a, a gas-liquid separator 1b, a booster blower 1c, and a dryer 1d. The first inlet 10 of the high-temperature NG cooler 1a is connected to the flue gas outlet, and the flue gas is further cooled by high-temperature cold NG. The cooled flue gas passes through the first outlet 11 of the high-temperature NG cooler 1a and passes through the gas-liquid separator 1b, where most of the water in the flue gas is removed. The water is discharged from the water outlet 12 of the gas-liquid separator 1b. The cooled flue gas passes through the gas outlet 13 of the gas-liquid separator 1b, is pressurized by the booster blower 1c, and then passes through a passage 14 into the dryer 1d, where it is further dried until its dew point meets the relevant requirements.

[0022] The CO₂-N₂ separation system includes a low-temperature LNG cooler 2a and a low-temperature adsorption device 2b. The inlet 15 of the low-temperature LNG cooler 2a is connected to the outlet of the dryer 1d in the pretreatment system 01, and uses the cold energy of the LNG to cool the dried pretreated flue gas to approximately the boiling point of CO₂. The outlet 16 of the low-temperature LNG cooler 2a is connected to the inlet of the low-temperature adsorption device 2b, which uses the principle of low-temperature adsorption to adsorb and capture CO₂ in the low-temperature flue gas. A crude carbon dioxide gas with a relatively high carbon purity is obtained at the desorbed gas outlet 18 of the low-temperature adsorption device, and a nitrogen-containing gas containing less than 1 ppm of carbon dioxide and with a relatively high nitrogen purity is obtained at the exhaust outlet 17 of the low-temperature adsorption device, thereby achieving the purpose of carbon-nitrogen separation.

[0023] As shown in FIG. 2, the inlet 19 of the feed compressor 3a of the N2 purification liquefaction system 03 is connected to the exhaust outlet 17 of the low-temperature adsorption device 2b to compress the nitrogen-containing gas. The outlet of the raw material compressor 3a is connected to the first inlet 20 of the cooler 3b, the first outlet of the cooler 3b is connected to the first inlet 21 of the heat exchanger 3c, the second inlet 80 of the cooler 3b is connected to a high-temperature cold NG introduction pipe, the second outlet 90 of the cooler 3b is connected to an NG discharge pipe, the first outlet 22 of the heat exchanger 3c is connected to the rectification system 3m, the nitrogen gas outlet of the rectification system 3m is connected to the second inlet 33 of the heat exchanger, the second outlet 34 of the heat exchanger 3c is connected to the inlet of a circulation compressor 3k, the outlet of the circulation compressor 3k is connected to a third inlet 35 of the heat exchanger 3c, and the third outlet 36 of the heat exchanger is connected to the first inlet of the gas-liquid separator 3i. The gas-liquid separator 3i is connected to a sixth inlet 37 of the heat exchanger 3c, and the sixth inlet 37 is connected to the second outlet 34 of the heat exchanger 3c. The vent outlet of the rectification system 3m is connected to the fourth inlet 29 of the heat exchanger. The fourth outlet 30 of the heat exchanger is connected to a vent line. The LNG liquid inlet is connected to the fifth inlet 39 of the heat exchanger. The high-temperature cold LNG outlet is connected to the fifth outlet 40 of the heat exchanger. The nitrogen-containing gas obtained from the CO2 / N2 separation system is further purified and liquefied according to the principle of low-temperature rectification to obtain a high-purity liquid nitrogen product.

[0024] As shown in Figure 3, the CO2 purification and liquefaction system 04 includes a CO2 rectification and liquefaction apparatus consisting of a CO2 compressor 4a, a cooler 4b, an evaporator 4c, a liquefier 4d, a condenser 4f, and a purification column 4e. The inlet 41 of the CO2 compressor 4a is connected to the desorbed gas outlet 18 of the low-temperature adsorption device 2b and compresses the crude carbon dioxide gas. The outlet of the CO2 compressor 4a is connected to a first inlet 42 of a cooler 4b, a first outlet 43 of the cooler 4b is connected to the inlet of the evaporator 4c, a second inlet 47 of the cooler 4b is connected to a high-temperature cold NG inlet line, and a second outlet 52 of the cooler 4b is connected to a NG outlet line. The outlet of the evaporator 4c is connected to the first inlet 44 of the liquefier 4d. The first outlet 45 of the liquefier 4d is connected to the intermediate inlet of the purification tower 4e. The second inlet 48 of the liquefier 4d is connected to the high-temperature, cold-energy natural gas (NG) inlet line, and the second outlet 53 of the liquefier 4d is connected to the NG outlet line. The first inlet 46 of the condenser 4f is connected to the high-temperature, cold-energy natural gas (NG) inlet line, and the first outlet 51 of the condenser 4f is connected to the NG outlet line. Industrial-grade liquid carbon dioxide product is obtained at the bottom of the purification tower 4e. This is connected to a storage system via the first outlet 49 at the bottom of the purification tower 4e, and may be connected to a carbon dioxide purification system for secondary purification to obtain food-grade carbon dioxide. The second outlet 50 of the purification tower 4e is connected to the exhaust gas vent line.

[0025] A specific embodiment includes the following steps: Step 1: Flue gas at normal temperature and pressure enters the first inlet 10 of the high-temperature NG cooler 1a, where it is cooled by high-temperature cold NG. The cooled flue gas enters the high-temperature NG cooler 1a and enters the gas-liquid separator 1b from the first outlet 11 of the high-temperature NG cooler 1a. Most of the water in the flue gas is discharged from the water outlet 12 of the gas-liquid separator. The cooled flue gas is discharged from the gas outlet 13 of the gas-liquid separator 1b and pressurized by the booster blower 1c. Then, it enters the dryer 1d through the passage 14 and is further dried until the dew point meets the relevant requirements.

[0026] Step 2: The gas dried by the dryer 1d enters the low-temperature LNG cooler 2a through its inlet 15, where it uses the cold energy of the LNG to cool the dried flue gas to approximately the boiling point of CO2. The outlet 16 of the low-temperature LNG cooler 2a is connected to the inlet of the low-temperature adsorption device 2b, which uses the principle of low-temperature adsorption to adsorb and capture CO2 and other substances in the low-temperature dried flue gas. A crude carbon dioxide gas with a relatively high carbon purity is obtained from the desorbed gas outlet 18 of the low-temperature adsorption device 2b, and a nitrogen-containing gas containing carbon dioxide of 1 ppm or less and with a relatively high nitrogen purity is obtained from the exhaust outlet 17 of the low-temperature adsorption device 2b, thereby obtaining a purified raw gas of carbon dioxide and nitrogen gas, and achieving the purpose of carbon-nitrogen separation.

[0027] Step 3: The exhaust from the exhaust outlet 17 of the low-temperature adsorption device 2b is connected to the inlet 19 of the feed compressor 3a via a pipe to pressurize the nitrogen-containing gas. The outlet of the feed compressor 3a is connected to the first inlet 20 of the cooler 3b. The first outlet of the cooler 3b is connected to the first inlet 21 of the heat exchanger 3c. The second inlet 80 of the cooler 3b is connected to the high-temperature cold NG introduction pipe. The second outlet 90 of the cooler 3b is connected to the NG discharge pipe. The pressurized and cooled nitrogen-containing gas exchanges heat with LNG, rectified circulating nitrogen gas, and rectified purge gas from the outside in the heat exchanger 3c. The heat exchanger 3c then connects the nitrogen gas outlet of the rectification system 3m via the first outlet 22 of the heat exchanger 3c. Separation and purification are performed in the rectification system 3m. The nitrogen gas outlet of the rectification system 3m is connected to the second inlet 33 of the heat exchanger 3c. This nitrogen gas is used as circulating nitrogen gas. The second outlet 34 is connected to the inlet of the circulation compressor 3k, the outlet of which is connected to the third inlet 35 of the heat exchanger 3c, the third outlet 36 of which is connected to the gas-liquid separator 3i, and a high-purity liquid nitrogen product is obtained at the bottom of the gas-liquid separator 3i and flows out from the first outlet 38 of the gas-liquid separator 3i. The gas from the gas-liquid separator 3i enters the sixth inlet 37 of the heat exchanger 3c from the second outlet of the gas-liquid separator 3i, is reheated by the heat exchanger, and then enters the circulation compressor 3k from the second outlet 34 and is compressed. The purge gas from the distillation system 3m is connected to the fourth inlet 29 of the heat exchanger 3c, is reheated, and then purged from the fourth outlet 30 of the heat exchanger 3c. The LNG liquid inlet is connected to the fifth inlet 39 of the heat exchanger 3c, and the high-temperature cold NG flows out from the fifth outlet 40 of the heat exchanger 3c to become a source of high-temperature cold for other systems.

[0028] Step 4: The desorbed gas from the low-temperature adsorption device 2b is connected to the inlet 41 of the CO2 compressor 4a via the desorbed gas outlet 18 to compress the crude carbon dioxide gas. The outlet of the CO2 compressor 4a is connected to the first inlet 42 of the cooler 4b. The second inlet 47 of the cooler 4b is connected to the high-temperature cold NG introduction line. The second outlet 52 of the cooler 4b is connected to the NG discharge line. The compressed crude carbon dioxide gas is cooled by the high-temperature cold NG in the cooler 4b. The first outlet 43 of the cooler 4b is connected to the inlet of the evaporator 4c. The cooled crude carbon dioxide gas serves as a heat source for the evaporator to supply heat for vaporization of liquid carbon dioxide. The outlet of the evaporator 4c is connected to the first inlet 44 of the liquefier 4d. The second inlet 48 of the liquefier 4d is connected to the high-temperature cold NG introduction line. The second outlet 53 of the liquefier 4d is connected to the NG discharge line. The first outlet 45 of the liquefier 4d is connected to the intermediate inlet of the purification tower 4e, where the crude carbon dioxide is purified by heat and mass transfer within the purification tower. The first inlet 46 of the overhead condenser 4f is connected to the high-temperature cold NG inlet line, and the first outlet 51 of the condenser 4f is connected to the NG outlet line, where the high-temperature cold NG is used to condense and reflux the overhead gas. At the same time, some of the exhaust gas is purged through the second outlet 50 of the purification tower 4e, and industrial-grade liquid carbon dioxide is obtained at the bottom of the purification tower 4e. This is connected to a storage system via the first outlet 49 at the bottom of the purification tower 4e, whereby industrial-grade liquid carbon dioxide product is obtained. This product may be connected to a carbon dioxide purification system, and the CO2 is further purified to obtain food-grade carbon dioxide.

[0029] The adsorbent used in the low-temperature adsorption device 2b is mainly molecular sieve or activated carbon.

[0030] The rectification system 3m in the N2 purification and liquefaction system 03 may be a single-column rectification process or a double-column rectification process.

[0031] The device and method of the present invention utilizes the cold energy released during vaporization of LNG as the source of cold energy for the system, eliminating the need for an external electric refrigeration system and achieving greater energy savings. Furthermore, the device and method realize efficient utilization of the cold energy of different gradients of LNG combined with the cold energy at different temperatures according to the different temperature requirements of each system.

[0032] The apparatus and method of the present invention achieve carbon and nitrogen separation by low-temperature adsorption, and can obtain relatively high-content raw carbon dioxide gas and nitrogen-containing gas at low pressure, with low overall energy consumption.

[0033] FIG. 4 is a schematic diagram of a modified example of the N2 purification and liquefaction system 03 in the apparatus and method, and the rectification system 3m of the N2 purification and liquefaction system 03 mainly includes a first pressure column 3d, a first condenser-evaporator 3e, a subcooler 3f, a second pressure column 3g, a second condenser-evaporator 3h, and a liquid nitrogen pump 3j.

[0034] The specific implementation procedure is as follows: The first outlet 22 of the heat exchanger 3c is connected to the bottom inlet of the first pressure column 3d, the liquid at the bottom outlet of the first pressure column 3d is connected to the first inlet 23 of the subcooler 3f, the first outlet 24 of the subcooler 3f is connected to the inlet of the first condenser-evaporator 3e, the bottom liquid of the first pressure column 3d is subcooled by the subcooler 3f and then enters the first condenser-evaporator 3e to be used as a cold source. The outlet 25 of the first condenser-evaporator 3e is connected to the bottom inlet of the second pressure column 3g, and the nitrogen gas at the top outlet of the first pressure column 3d is connected to the second inlet 33 of the heat exchanger. The bottom outlet of the second pressure column 3g is connected to the second inlet 26 of the subcooler 3f, and the second outlet 27 of the subcooler 3f is connected to the inlet of the second condenser-evaporator 3h. The bottom liquid of the second pressure column 3g is subcooled by the subcooler 3f and then enters the second condenser-evaporator 3h to be used as a cold source. The outlet of the second condenser-evaporator 3h is connected to the third inlet 28 of the subcooler 3f, and the third outlet of the subcooler 3f is connected to the fourth inlet 29 of the heat exchanger. Liquid nitrogen is extracted from the top 31 of the second pressure column 3g, pressurized by a liquid nitrogen pump 3j, and then returned to the top 32 of the first pressure column 3d.

[0035] Specific Examples Example 1 Please refer to Figures 1, 2 and 3. 1. Normal-temperature, normal-pressure flue gas 10 (approximately 50°C, 0.1 MPaA), which is boiler flue gas that meets the national ultra-low emission standards, flows into the inlet of high-temperature NG cooler 1a via a pipe. In this cooler, the flue gas is further cooled to approximately 5°C using high-temperature cold NG. After cooling, the flue gas enters the first inlet 11 of gas-liquid separator 1b, and most of the water in the flue gas is discharged from the gas-liquid separator's water outlet 12. After cooling, the flue gas is discharged from the gas-liquid separator's gas outlet 13, pressurized by booster blower 1c, and then passes through passage 14 to dryer 1d at approximately 0.12 MPaA, where it is further dried until the dew point meets the relevant requirements.

[0036] 2. The dry gas at the outlet of the dryer 1d is connected to the inlet 15 of the low-temperature LNG cooler 2a, where it is cooled to approximately the boiling point of CO2 (-78°C, approximately 0.11 MPaA) using the cold energy of the LNG. The outlet 16 of the low-temperature LNG cooler 2a is connected to the inlet of the low-temperature adsorption device 2b, which adsorbs and captures CO2 and other substances in the low-temperature flue gas using the principle of low-temperature adsorption. A crude carbon dioxide gas with a relatively high carbon purity is obtained at the desorbed gas outlet 18 of the low-temperature adsorption device 2b, and a nitrogen-containing gas containing less than 1 ppm of carbon dioxide and with a relatively high nitrogen purity is obtained at the exhaust outlet 17 of the low-temperature adsorption device 2b. This produces a purified raw gas of carbon dioxide and nitrogen gas, achieving the goal of carbon-nitrogen separation.

[0037] 3. The exhaust outlet 17 (approximately -70°C, 0.1 MPaA) of the outlet of the low-temperature adsorption device 2b was connected via a pipe to the inlet 19 of the feed compressor 3a, where the nitrogen-containing gas was pressurized to approximately 0.75 MPaA. The outlet of the feed compressor 3a was connected to the first inlet 20 of the cooler 3b, and the first outlet (approximately 5°C) of the cooler 3b was connected to the first inlet 21 of the heat exchanger 3c. The second inlet 80 of the cooler 3b was connected to the high-temperature cold NG inlet line, and the second outlet 90 of the cooler 3b was connected to the NG outlet line. The pressurized nitrogen-containing gas exchanged heat with LNG, rectification circulating nitrogen gas, and rectification purge gas in the heat exchanger 3c, and was connected to the rectification system 3m via the first outlet 22 (approximately -172°C, 0.72 MPaA) of the heat exchanger 3c, where it was separated and purified. Nitrogen gas (approximately 0.71 MPaA) at the outlet of the rectification system 3m is connected to the second inlet 33 of the heat exchanger 3c. This nitrogen gas is used as circulating nitrogen gas and is connected to the inlet of the circulation compressor 3k via the second outlet 34 of the heat exchanger 3c (approximately -121°C, 0.7 MPaA). The outlet of the circulation compressor 3k (approximately -50°C, 6.0 MPaA) is connected to the third inlet 35 of the heat exchanger 3c. The third outlet 36 of the heat exchanger 3c is connected to the gas-liquid separator 3i. High-purity liquid nitrogen product is obtained at the bottom of the gas-liquid separator 3i and discharged from the first outlet 38 of the gas-liquid separator 3i (approximately -191°C, 0.6 MPaA). The gas in the gas-liquid separator 3i is connected to the sixth inlet 37 of the heat exchanger 3c via the second outlet at the top. The sixth inlet 37 is connected to the second outlet 34 of the heat exchanger 3c and returns to the inlet of the circulation compressor. The purge gas from the rectification system 3m was connected to the fourth inlet 29 (approximately -178°C, 0.14 MPaA) of the heat exchanger 3c, where it was reheated to room temperature and then purged from the fourth outlet 30 of the heat exchanger 3c. The LNG liquid inlet (approximately -140°C, 10.0 MPaA) was connected to the fifth inlet 39 of the heat exchanger 3c, and after passing through the high-temperature cold NG, it flowed out from the fifth outlet 40 of the heat exchanger 3c (approximately -70°C, 9.7 MPaA) to serve as a source of high-temperature cold for other systems.

[0038] The desorbed gas outlet 18 of the low-temperature adsorption device 2b was connected to the inlet 41 of the CO2 compressor 4a, which pressurized the crude carbon dioxide gas to approximately 2.4 MPaA. The outlet of the CO2 compressor was connected to the first inlet 42 of the cooler 4b, the first outlet 43 of the cooler 4b was connected to the inlet of the evaporator 4c, the second inlet 47 of the cooler 4b was connected to the high-temperature cold NG inlet line, and the second outlet 52 of the cooler 4b was connected to the NG outlet line, and the compressed crude carbon dioxide gas was cooled by the high-temperature NG in the cooler 4b. The first outlet 43 (approximately 6°C) of the cooler 4b was connected to the inlet of the evaporator 4c, and the cooled crude carbon dioxide gas served as the heat source for the evaporator, supplying heat for vaporizing the liquid carbon dioxide. The outlet (about 15°C) of the evaporator 4c was connected to a first inlet 44 of a liquefier 4d, a first outlet 45 of the liquefier 4d was connected to an intermediate inlet of the purification column 4e, a second inlet 48 of the liquefier 4d was connected to a high-temperature cold NG introduction line, and a second outlet 53 of the liquefier 4d was connected to an NG discharge line, and the crude carbon dioxide gas was liquefied and condensed by the high-temperature cold NG in the liquefier. The crude carbon dioxide that entered the purification column was subjected to heat and mass transfer within the purification column and further purified. The first inlet 46 of the overhead condenser 4f is connected to the high-temperature cold NG inlet pipeline, and the first outlet 51 of the condenser 4f is connected to the NG outlet pipeline. The high-temperature cold NG is used to condense and reflux the overhead rising gas. At the same time, some of the exhaust gas is purged from the second outlet at the top of the purification tower 4e, and industrial-grade liquid carbon dioxide product is obtained at the bottom of the purification tower 4e. This is connected to a storage system via the first outlet 49 (approximately -17°C, 2.3 MPaA) at the bottom of the purification tower 4e, and may be connected to a carbon dioxide purification system for secondary purification of CO2, resulting in food-grade carbon dioxide.

[0039] Example 2 As shown in Figure 4, the first outlet 22 (approximately -172°C, 0.72 MPaA) of the heat exchanger 3c was connected to the bottom inlet of the first pressure column 3d, where separation and purification were performed. The liquid at the bottom outlet of the first pressure column 3d was connected to the first inlet 23 of the subcooler 3f, and the first outlet 24 (approximately -175°C, 0.72 MPaA) of the subcooler 3f was connected to the inlet of the first condenser-evaporator 3e. The liquid at the bottom of the first pressure column 3d was subcooled by the subcooler 3f and then entered the first condenser-evaporator 3e to be used as a cold source. The outlet 25 (approximately -180°C, 0.4 MPaA) of the first condenser-evaporator 3e was connected to the bottom inlet of the second pressure column 3g, where the cold source evaporated and entered the second pressure column 3g for secondary separation and purification. Nitrogen gas (approximately 0.71 MPaA) at the top outlet of the first pressure column 3d was connected to the second inlet 33 of the heat exchanger 3c. The bottom outlet of the second pressure column 3g (approximately -180°C, 0.4 MPaA) was connected to the second inlet 26 of the subcooler 3f, and the second outlet 27 of the subcooler 3f was connected to the inlet of the second condenser-evaporator 3h. The liquid at the bottom of the second pressure column 3g was subcooled by the subcooler 3f and then entered the second condenser-evaporator 3h to be used as a cold source. The outlet of the second condenser-evaporator 3h was connected to the third inlet 28 of the subcooler, and the third outlet of the subcooler 3f was connected to the fourth inlet 29 (approximately -178°C, 0.14 MPaA) of the heat exchanger 3c. Liquid nitrogen was extracted from the top 31 of the second pressure column 3g, pressurized to approximately 1.0 MPaA by a liquid nitrogen pump 3j, and returned to the top 32 of the first pressure column 3d.

Claims

1. 1. An apparatus for recovering carbon dioxide and nitrogen gas in flue gas, comprising: The device comprises a pre-treatment system (01) and a CO ２ ・N ２ Separation system (02) and N ２ A purification and liquefaction system (03), and ２ and a purification and liquefaction system (04), the pretreatment system (01) including a high-temperature NG cooler (1a), a gas-liquid separator (1b), a booster blower (1c), and a dryer (1d) for removing moisture from the flue gas and cooling the flue gas, and the CO ２ ・N ２ The separation system (02) includes a low-temperature LNG chiller (2a) and a low-temperature adsorption unit (2b) for further cooling and adsorbing the pre-treated flue gas to remove CO ２ and N ２ and N ２ The purification and liquefaction system (03) is a N liquefaction system comprising a feed compressor, a heat exchanger (3c), a cooler (3b), a gas-liquid separator (3i), and a rectification system (3m). ２ Including a rectification liquefaction unit, ２ ・N ２ The nitrogen-containing gas obtained from the separation system is further purified and liquefied, ２ The purification and liquefaction system (04) ２ A CO refrigeration system comprising a compressor (4a), a cooler (4b), an evaporator (4c), a condenser (4f), a liquefier (4d), and a purification column (4e). ２ Including a rectification liquefaction unit, ２ ・N ２ The desorbed gas obtained from the separation system is further purified and liquefied, The first inlet (10) of the high-temperature NG cooler (1a) in the pre-treatment system (01) is connected to a flue gas outlet, and the flue gas is further cooled by the cold heat of the high-temperature NG. The cooled flue gas passes through a first outlet (11) of the high-temperature NG cooler (1a) and enters a gas-liquid separator (1b), where most of the water in the flue gas is removed, and the water is discharged from a water outlet (12) of the gas-liquid separator (1b). The cooled flue gas passes through a gas outlet (13) of the gas-liquid separator (1b), is pressurized by the booster blower (1c), and then enters the dryer (1d) through a passage (14) and is further dried. The dryer (1d) in the pre-treatment system (01) is used to dry the CO ２ ・N ２ The separation system (02) is connected to the inlet (15) of the low-temperature LNG cooler (2a) and uses the cold energy of the LNG to convert the pre-treated dry flue gas into CO ２ The outlet (16) of the low-temperature LNG cooler (2a) is connected to the inlet of the low-temperature adsorption device (2b), and the low-temperature flue gas is cooled to about the boiling point temperature. ２ and adsorb and capture the carbon dioxide gas, so that a raw carbon dioxide gas having a relatively high carbon purity is obtained at the desorption gas outlet (18) of the low-temperature adsorption device (2b), and a nitrogen-containing gas containing carbon dioxide of 1 ppm or less and having a relatively high nitrogen purity is obtained at the exhaust outlet (17) of the low-temperature adsorption device (2b), thereby achieving the purpose of carbon-nitrogen separation; the adsorbent used in the low-temperature adsorption device (2b) is mainly at least one of molecular sieve and activated carbon; The exhaust outlet (17) of the cryogenic adsorption device (2b) is ２ The compressor (3k) is connected to an inlet (19) of a feed compressor (3a) of a purification and liquefaction system (03) and compresses a nitrogen-containing gas. The outlet of the feed compressor (3a) is connected to a first inlet (20) of the cooler (3b). The first outlet of the cooler (3b) is connected to a first inlet (21) of the heat exchanger (3c). The second inlet (80) of the cooler (3b) is connected to a high-temperature NG introduction pipe. The second outlet (90) of the cooler (3b) is connected to a NG discharge pipe. The first outlet (22) of the heat exchanger (3c) is connected to the distillation system (3m). The nitrogen gas outlet of the distillation system (3m) is connected to a second inlet (33) of the heat exchanger. The second outlet (34) of the heat exchanger (3c) is connected to an inlet of a circulation compressor (3k). The outlet of the rectification system (3m) is connected to the third inlet (35) of the heat exchanger (3c), the third outlet (36) of the heat exchanger is connected to the first inlet of the gas-liquid separator (3i), liquid nitrogen product is obtained at the bottom of the gas-liquid separator (3i) and flows out from the first outlet (38) of the gas-liquid separator (3i), the second outlet of the gas-liquid separator (3i) is connected to the sixth inlet (37) of the heat exchanger (3c), the sixth inlet (37) is connected to the second outlet (34) of the heat exchanger (3c), the vent outlet of the rectification system (3m) is connected to the fourth inlet (29) of the heat exchanger, the fourth outlet (30) of the heat exchanger is connected to a vent line, the LNG inlet is connected to the fifth inlet (39) of the heat exchanger, and the high-temperature NG outlet is connected to the fifth outlet (40) of the heat exchanger, ２ The purification and liquefaction system (03) ２ ・N ２ The nitrogen-containing gas obtained from the separation system (2) is further purified and liquefied to obtain a high-purity liquid nitrogen product, and the rectification system (3m) is a single-column rectification or a double-column rectification; The desorbed gas outlet (18) of the cryogenic adsorption device (2b) is ２ CO of the purification and liquefaction system (04) ２ The compressor (4a) is connected to the inlet (41) of the compressor (4a) to compress the raw carbon dioxide gas and ２ An outlet of the compressor (4a) is connected to a first inlet (42) of the cooler (4b), a first outlet (43) of the cooler (4b) is connected to an inlet of the evaporator (4c), a second inlet (47) of the cooler (4b) is connected to a high-temperature NG introduction pipe, a second outlet (52) of the cooler (4b) is connected to a high-temperature NG discharge pipe, an outlet of the evaporator (4c) is connected to a first inlet (44) of the liquefier (4d), a first outlet (45) of the liquefier (4d) is connected to an intermediate inlet of the purifying column (4e), and The second inlet (48) of the liquefier (4d) is connected to a high-temperature NG introduction pipeline, the second outlet (53) of the liquefier (4d) is connected to a NG discharge pipeline, the first inlet (46) of the condenser (4f) is connected to a high-temperature NG introduction pipeline, and the first outlet (51) of the condenser (4f) is connected to a NG outlet pipeline. An industrial-grade liquid carbon dioxide product is obtained at the bottom of the purification tower (4e), and is connected to a storage system via a first outlet (49) at the bottom of the purification tower (4e) and is also connected to a carbon dioxide purification system. ２ and a second outlet (50) of the purification column (4e) is connected to an exhaust gas vent line.

2. 10. A method for recovering carbon dioxide and nitrogen gases in flue gas using the apparatus of claim 1, comprising the following steps 1 to 3: Step 1: In flue gas pretreatment, The flue gas is subjected to a cooling and drying process, Step 2: CO ２ and N ２ In the separation of The gas dried in the dryer passes through a low-temperature LNG cooler and a low-temperature adsorption device (2b) to desorb crude carbon dioxide gas from the gas and discharge nitrogen-containing gas; Step 3: CO purification and liquefaction ２ and N ２ In acquiring the product, The crude carbon dioxide gas and the discharged nitrogen-containing gas were treated with CO ２ Rectification liquefaction unit and N ２ A method for purifying and liquefying the liquefied product by passing the liquefied product through a rectification and liquefaction apparatus.

3. 3. The method according to claim 2, characterized in that in step 1, the flue gas enters the first inlet (10) of the high-temperature NG cooler (1a), and the cooler (1a) cools the flue gas with the cold heat of the high-temperature NG. The cooled flue gas enters the gas-liquid separator (1b) through the first outlet (11) of the high-temperature NG cooler (1a). Most of the water in the flue gas is discharged from the water outlet (12) of the gas-liquid separator. The cooled flue gas is discharged from the gas outlet (13) of the gas-liquid separator (1b), and after being pressurized by the booster blower (1c), enters the dryer (1d) through the passage (14), and is further dried until the dew point meets the relevant requirements.

4. CO in step 2 ２ and N ２ In the separation of (1), the gas dried by the dryer (1d) enters the low-temperature LNG cooler (2a) through the inlet (15) of the low-temperature LNG cooler (2a), and the dried flue gas is converted into CO by the cold heat of the LNG in the low-temperature LNG cooler (2a). ２ The outlet (16) of the low-temperature LNG cooler (2a) is connected to the inlet of a low-temperature adsorption device (2b), and the low-temperature dry flue gas is cooled to about the boiling point temperature. ２ 3. The method according to claim 2, characterized in that the low-temperature adsorption device (2b) adsorbs and captures the carbon dioxide gas having a relatively high carbon purity at the desorption gas outlet (18) of the low-temperature adsorption device (2b), and the low-temperature adsorption device (2b) exhausts the nitrogen-containing gas having a carbon dioxide concentration of 1 ppm or less and a relatively high nitrogen purity at the exhaust outlet (17), thereby obtaining a purified raw material gas of carbon dioxide and nitrogen gas, and achieving the purpose of carbon-nitrogen separation.

5. N in Step 3 ２ In the purification and liquefaction, the exhaust gas from the exhaust outlet (17) of the low-temperature adsorption device (2b) is connected via a pipe to the inlet (19) of the feed compressor (3a) to pressurize the nitrogen-containing gas, the outlet of the feed compressor (3a) is connected to the first inlet (20) of the cooler (3b), the first outlet of the cooler (3b) is connected to the first inlet (21) of the heat exchanger (3c), the second inlet (80) of the cooler (3b) is connected to a high-temperature NG introduction pipeline, and the second outlet (90) of the cooler (3b) is connected to the NG discharge pipeline. The nitrogen-containing gas is connected to a pipeline, and after being pressurized and cooled, the nitrogen-containing gas exchanges heat with external LNG, rectification circulating nitrogen gas, and rectification purge gas in a heat exchanger (3c), and is connected to a rectification system (3m) via a first outlet (22) of the heat exchanger (3c), where separation and purification are carried out. A nitrogen gas outlet of the rectification system (3m) is connected to a second inlet (33) of the heat exchanger (3c), and the nitrogen gas is used as circulating nitrogen gas, and the second outlet (34) of the heat exchanger (3c) ), the outlet of the circulation compressor (3k) is connected to the third inlet (35) of the heat exchanger (3c), the third outlet (36) of the heat exchanger (3c) is connected to the gas-liquid separator (3i), high-purity liquid nitrogen product is obtained at the bottom of the gas-liquid separator (3i), and flows out from the first outlet (38) of the gas-liquid separator (3i), and the gas of the gas-liquid separator (3i) enters the sixth inlet (37) of the heat exchanger (3c) from the second outlet of the gas-liquid separator (3i) and flows into the heat exchanger. After being reheated, the LNG enters the circulation compressor (3k) through the second outlet (34) and is compressed. The purge gas of the rectification system (3m) is connected to the fourth inlet (29) of the heat exchanger (3c), and after being reheated, is purged through the fourth outlet (30) of the heat exchanger (3c). The LNG inlet is connected to the fifth inlet (39) of the heat exchanger (3c). The high-temperature cold NG flows out from the fifth outlet (40) of the heat exchanger (3c) and becomes a source of high-temperature cold for other systems. ２ In the purification and liquefaction, the desorbed gas from the cryogenic adsorption unit (2b) is discharged via the desorbed gas outlet (18) as CO ２ The compressor (4a) is connected to the inlet (41) to compress the raw carbon dioxide gas and ２ The outlet of the compressor (4a) is connected to a first inlet (42) of a cooler (4b), the second inlet (47) of the cooler (4b) is connected to a high-temperature NG introduction pipe, and the second outlet (52) of the cooler (4b) is connected to a NG discharge pipe. The compressed crude carbon dioxide gas is cooled by high-temperature NG in the cooler (4b). The first outlet (43) of the cooler (4b) is connected to an inlet of an evaporator (4c). The cooled crude carbon dioxide gas serves as a heat source for the evaporator and supplies heat for vaporization of liquid carbon dioxide. The outlet of the evaporator (4c) is connected to a first inlet (44) of a liquefier (4d). The second inlet (48) of the liquefier (4d) is connected to a high-temperature NG introduction pipe, and the second outlet (53) of the liquefier (4d) is connected to a NG discharge pipe. The crude carbon dioxide is liquefied and condensed by the high-temperature NG, the first outlet (45) of the liquefier (4d) is connected to the intermediate inlet of the purification tower (4e), and enters the purification tower, where the crude carbon dioxide is purified by heat transfer and mass transfer within the purification tower. The first inlet (46) of the top condenser (4f) is connected to the high-temperature NG inlet line, and the first outlet (51) of the condenser (4f) is connected to the NG outlet line, and the overhead rising gas is condensed and refluxed by the high-temperature NG. At the same time, a part of the exhaust gas is purged from the second outlet (50) of the purification tower (4e). Industrial-grade liquid carbon dioxide is obtained at the bottom of the purification tower (4e), and communicates with a storage system via the first outlet (49) at the bottom of the purification tower (4e). The industrial-grade liquid carbon dioxide product is obtained and also communicates with a carbon dioxide purification system. ２ 3. The method according to claim 2, further comprising subjecting the above-mentioned raw material to secondary purification to obtain food-grade carbon dioxide.

6. The cooler (4b), the liquefier (4d), the condenser (4f) and the N ２ The method according to claim 5, characterized in that the cold source of the cooler (3b) in the purification and liquefaction system (03) is derived from high-temperature NG generated in the LNG vaporization process, and is less energy consuming, safer, and more environmentally friendly than a method of producing cold using a conventional electrically driven refrigerator, and also enables the recovery and utilization of cold from the high-temperature NG generated in the LNG vaporization process.

7. The N ２ The method according to claim 6, characterized in that the purification liquefaction system (03) produces liquid nitrogen products by being driven by the cold generated by vaporization of LNG in the heat exchanger (3c) instead of the conventional method of generating cold by compression and expansion using electrical energy, thereby significantly reducing the energy consumption for producing high-purity liquid nitrogen products and recovering and utilizing the cold from the high-temperature NG generated in the LNG vaporization process as a cold source for other components, thereby realizing cascaded use of cold.

Images