A LOW-ENERGY LIQUID PRODUCTION DEVICE USING FLUE GASES AND METHOD OF USING THE SAME

Abstract

The present invention relates to a low-energy liquid production device using flue gas. This device comprises a medium-pressure and low-temperature CO₂ and N₂ adsorption system, an energy utilization system, a low-temperature compression system for the low-temperature filtered gases, a low-temperature CO₂ purification system (101) and a liquid nitrogen production system (100); these systems are connected together by pipelines and valves, the medium-pressure and low-temperature CO₂ and N₂ adsorption system comprises a flue gas cooler (1A), a first gas-liquid separator (1B), a compression system (1C), a drying system (1D), a gas expansion valve system and a medium-pressure and low-temperature adsorption device (1H); the energy utilization system comprises an electric heater (2E), a CO₂ compressor (2A). (Figure for the abstract: Fig.1).

Description

Title of the invention: A LOW-ENERGY LIQUID PRODUCTION DEVICE USING FLUE GASES AND METHOD OF USING THE SAME Technical field

[0001] The present invention belongs to the technical field of flue gas and relates to a low-energy liquid production device using flue gas and its method of use. Prior art

[0002] In the process of energy utilization, the main CO2 separation and recovery technologies include: absorption technology, adsorption technology, membrane separation technology and low-temperature phase transition separation technology. The solution absorption process is the most mature method for CO2 capture and has been widely applied in many flue gases around the world. It can not only separate CO2 from low-concentration flue gases under atmospheric pressure, but also process large quantities and obtain high-purity CO2. However, the regeneration of the solution after absorption requires a large amount of heat. In addition, the preparation of the absorbent not only consumes resources, but the absorbent also becomes ineffective after a certain period of use and must be constantly renewed.Chemical absorbents also have certain toxicity and corrosiveness, which has a significant impact on the environment, and their manufacture and recovery are relatively expensive. The membrane separation method uses membranes made of polymer materials to separate gases based on the differences in permeation rates of different gases, with the driving force being the pressure difference, this technology is relatively limited for large-scale applications. Pressure reversal adsorption technology has many advantages such as easy adsorbent regeneration, long adsorbent life, and simple equipment, but for flue gas with low carbon dioxide concentration, room temperature pressure reversal adsorption technology has high costs and energy consumption.

[0003] Chinese patent CN107899376A discloses a device and method for jointly capturing and recovering carbon dioxide and nitrogen in exhaust gases. flue, belonging to membrane separation recovery, but the membrane has high requirements for gas source cleanliness, short service life, low product purity, relatively high cost, and is not suitable for large-scale industrial production.

[0004] Chinese patent CN210825439U discloses a system for simultaneously recovering carbon dioxide and nitrogen from flue gas of a coal-fired power plant boiler, comprising 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 nitrogen production system. This system can capture carbon dioxide and nitrogen to the greatest extent, but the purity of the products is only about 99.9%, and there are problems of inflexible equipment operation and high energy consumption.

[0005] Chinese patent CN216481836U discloses a system for simultaneously recovering nitrogen and carbon dioxide from boiler flue gas, comprising: a flue gas pretreatment system, a carbon-nitrogen separation system, a carbon dioxide secondary purification system, and a nitrogen concentration and purification system. This system can recover carbon dioxide and nitrogen to the greatest extent, but the carbon-nitrogen separation system, the carbon dioxide secondary purification system, and the nitrogen concentration and purification system all use pressure reversal adsorption technology at room temperature, with an adsorption pressure reaching 0.2-1.0 MPa, resulting in relatively high energy consumption.

[0006] Chinese patent CN115790076A discloses a device and method for recovering carbon dioxide and nitrogen from flue gas, comprising: a pretreatment system, a CO2 and N2 separation system, an N2 purification and liquefaction system, and a CO2 purification and liquefaction system. This system can utilize the large amount of cold released during LNG gasification to entrain and liquefy carbon dioxide and nitrogen in flue gas, thereby greatly reducing energy consumption and recovery costs, but this system requires a large amount of LNG, with high requirements for the LNG source, and this low-temperature adsorption is carried out under atmospheric pressure, with poor adsorption effect, large volume of the adsorption device, and high cost. Statement of the invention

[0007] Considering the above-mentioned technical background, the present invention aims to provide a low-energy liquid production device using flue gas and its method of use, utilizing the cold released after the expansion of the pressurized gas, combined with the medium-pressure and low-temperature adsorption technology, and coupled with the technologies of compression by various compressors and refrigeration by expanders in the device, to produce liquids from the flue gas, having high economic and social value.

[0008] To achieve the above objective, the present invention adopts the following technique: a low-energy liquid production device using flue gas and its use method, said device comprising a medium-pressure and low-temperature CO2 and N2 adsorption system, an energy utilization system, a low-temperature compression system of low-temperature filtered gases, a low-temperature CO2 purification system and a liquid nitrogen production system; these systems are connected together by pipelines and valves.Said CO2 and N2 medium pressure and low temperature adsorption system comprises a flue gas cooler, a first gas-liquid separator, a compression system, a drying system, a gas expander system and a medium pressure and low temperature adsorption device, used for cooling, compressing, dehydrating and separating by low temperature adsorption CO2 and N2 from the flue gas. Said energy utilization system comprises an electric heater, a CO2 compressor, a heat recovery device, a second cooler, used for compressing, recovering heat and cooling the desorbed gas obtained from the CO2 and N2 medium pressure and low temperature adsorption system.Said low-temperature compression system for low-temperature filtered gases comprises a low-temperature compressor, used for compressing at low temperature the filtered medium-pressure and low-temperature gases obtained from the medium-pressure and low-temperature adsorption system of CO2 and N2. Said low-temperature purification system of CO2 is used for further purifying and liquefying the medium-pressure and low-temperature gases obtained from the energy utilization system, thereby producing liquid CO2 as a product. Said liquid nitrogen production system is used for rectifying and liquefying the medium-pressure gases exiting from the low-temperature compression system, thereby producing liquid nitrogen as a product. .

[0009] Preferably: in said medium pressure and low temperature CO2 and N2 adsorption system, one end of the flue gas cooler is connected to the flue gas discharge outlet, and the other end is connected to the first gas-liquid separator. In the first gas-liquid separator, the liquid is discharged from the liquid outlet of the first gas-liquid separator, and the gases enter into the compression system through the gas outlet of the first gas-liquid separator to be compressed, cooled and dehydrated. After compression, cooling and dehydration, the flue gases enter the drying system via a first pipeline for complete dehydration, so that the water content of the flue gases leaving the drying system is in the ppm range. Said drying system is connected to the downstream gas expander system, consisting of a boost stage of the first expander, a first cooler and a gas expansion stage. The flue gases with a water content in the ppm range successively enter the boost stage of the first expander, the first cooler and the gas expansion stage via a second pipeline.Said gas expansion stage is connected to the medium-pressure and low-temperature adsorption device by a third downstream pipeline, using the medium-pressure and low-temperature adsorption principle to adsorb and capture CO2 present in the medium-pressure and low-temperature flue gas, raw carbon dioxide with a carbon purity of 85-90% is obtained at the desorbed gas outlet of said medium-pressure and low-temperature adsorption device, and medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm is obtained at the medium-pressure and low-temperature filtered gas outlet of said medium-pressure and low-temperature adsorption device; the nitrogen purity of this medium-pressure raw nitrogen is 87-93%, thus achieving the purpose of separating carbon and nitrogen.Said medium pressure low temperature filtered gas outlet is also connected to said medium pressure low temperature adsorption device by a fourth pipe, so that a part of the low temperature filtered gas passes through the fourth pipe as cold purge regeneration gas and enters said medium pressure low temperature adsorption device, cold purging the adsorbent in the medium pressure low temperature adsorption device.

[0010] Preferably: the desorbed gas outlet of said medium-pressure and low-temperature adsorption device is connected to the CO2 compressor in the energy utilization system, to pressurize the raw carbon dioxide gas; the CO2 compressor is successively connected to the heat recovery unit, the second cooler and the low-temperature CO2 purification system, wherein the pressurized raw carbon dioxide gas is further cooled by the second cooler, so that the pressurized raw carbon dioxide gas exiting from the second cooler can meet the temperature and pressure requirements of the raw material of the low-temperature CO2 purification system. Said low-temperature CO2 purification system is used to purify and refine the low-temperature pressurized CO2, to obtain carbon dioxide. of industrial or food grade carbon. Said low temperature CO2 purification system is connected to the heat recovery unit by a ninth pipe, the heat recovery unit is connected to the fourth pipe on said medium pressure low temperature adsorption device, used to heat the low temperature regeneration gas exiting said low temperature CO2 purification system before it enters the medium pressure low temperature adsorption device as heated regeneration gas.

[0011] Preferably: the medium-pressure low-temperature filtered gas outlet of said medium-pressure low-temperature adsorption device is successively connected to the low-temperature compressor in the low-temperature compression system of the low-temperature filtered gases and to the liquid nitrogen production system, allowing all or most of the low-temperature filtered gas to enter the liquid nitrogen production system after being pressurized by the low-temperature compression system. Said liquid nitrogen production system is used to further rectify and liquefy the pressurized low-temperature filtered gas using the low-temperature rectification principle, thereby obtaining liquid nitrogen as a product.A tenth pipeline is arranged downstream of said liquid nitrogen production system, and two paths are respectively arranged downstream of this tenth pipeline, one of which is successively connected to the heat recovery unit and the electric heater, the electric heater is connected to the sixth pipeline, the sixth pipeline is connected to the drying system, used for heating the waste gas regeneration gas exiting the liquid nitrogen production system to the required temperature before it enters the drying system as heated regeneration gas. The other path of said tenth pipeline is directly connected to the sixth pipeline, used for directly entering the waste gas regeneration gas exiting the liquid nitrogen production system into the drying system as cold purge gas.

[0012] Preferably: said low-temperature CO2 purification system comprises a third condenser, an evaporator, a liquefier and a third rectification column, wherein the third condenser is installed above the third rectification column, the evaporator is installed below, and the liquefier is separately arranged outside the column; said second cooler is connected to the evaporator, the evaporator is connected to the liquefier, said liquefier is connected to the third rectification column by an eighth pipe; said third rectification column is connected to the third condenser, the third condenser is connected to the third rectification column by a seventh pipe forming a loop, said third condenser is also provided with an inlet passage for the condensed liquid and an outlet passage for the condensed gas, said third rectification column is provided with a ninth pipe at the bottom which is connected to the heat recovery unit, the bottom of said third rectification column is provided with a fifth pipe which is used to obtain liquid carbon dioxide as a product.

[0013] Preferably: said liquid nitrogen production system comprises a cyclic compression system, a high and low temperature gas expander, a heat exchanger, a second gas-liquid separator, a rectification column system and subcoolers, wherein said cyclic compression system is composed of a first compressor and a second compressor, said high and low temperature gas expander is respectively equipped with a supercompression stage of the second expander, a first expansion stage and a second expansion stage, said subcoolers comprise a first subcooler, a second subcooler and a third subcooler, the rectification column system is composed of a first rectification column and a second rectification column, wherein a first condenser is installed above the first rectification column,a second condenser is installed above the second rectification column. Said low-temperature compressor is successively connected to the heat exchanger and the first rectification column, said first rectification column is provided with two bypass lines, of which the first bypass of the first rectification column is successively connected to the first subcooler, the first condenser, the second rectification column, the second subcooler and the second condenser, and above the second condenser, it is successively connected by a line to the second subcooler, the first subcooler and the heat exchanger; said heat exchanger is connected to the tenth line for regeneration of the drying system,the second branch of the first rectification column is directly connected to the first condenser and the heat exchanger respectively; said first condenser is also provided with two branch lines, of which the first branch line of the first condenser is connected to the first rectification column, the second branch line of the first condenser is connected to the second gas-liquid separator; said second rectification column is provided with two branch lines, of which the first branch line of the second rectification column is connected to the second condenser, the second branch line of the second rectification column is connected to the heat exchanger; said second condenser is also provided with two branch lines, the first branch line of the second condenser is connected to the second rectification column, the second branch line of the second condenser is successively connected to the ,second gas-liquid separator and to the third subcooler; one end of said third subcooler is connected to the liquid nitrogen product passage, while the other end is connected to the heat exchanger via a first expansion valve and via the third subcooler, said second gas-liquid separator is connected to the heat exchanger, this heat exchanger X is successively connected to the first compressor and to the second compressor, wherein the second compressor is provided with two bypasses, of which the first bypass of the second compressor is successively connected to the high and low temperature gas expander, to the heat exchanger and to the second expansion stage, and finally connected to the second gas-liquid separator via the second expansion stage for recycling, the second bypass of the second compressor is successively connected to the heat exchanger,to the first expansion stage and the heat exchanger, and finally connected to the first compressor via the heat exchanger for recycling, said heat exchanger is directly connected to the second gas-liquid separator, and a second expansion valve is arranged on the connecting pipeline, using the low-temperature rectification principle to further purify and liquefy the low-temperature nitrogen-containing gas obtained from the low-temperature compressor, thereby producing liquid nitrogen as the product.

[0014] A method of using said low energy liquid production device using flue gases, said method comprising the following steps:

[0015] ^Pretreatment of flue gases

[0016] The flue gases are treated by compression, cooling, dehydration and drying, so that the water content of the pressurized flue gases after treatment is < 1 ppm;

[0017] 2) Rough separation of CO2 and N2 gases:

[0018] The gases from step 1) are treated by the gas expander system to obtain raw carbon dioxide with a carbon purity of 85-90% and medium pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm; the nitrogen purity of said medium pressure raw nitrogen is 87-93%;

[0019] 3) Purification and liquefaction to obtain liquid CO2 as product:

[0020] Crude carbon dioxide with a carbon purity of 85-90% from step 2) is treated by the low temperature CO2 purification system 101 to obtain liquid CO2 as product;

[0021] 4) Purification and liquefaction to obtain liquid N2 as product:

[0022] The medium pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm from step 2) is processed by the liquid nitrogen production system 100 to obtain liquid N2 as product.

[0023] Preferably: the concrete method of step 1 is as follows: the flue gas at ambient temperature and pressure enters the inlet of the flue gas cooler, where the cooling medium cools the flue gas. The cooled flue gas passes through the first gas-liquid separator to remove condensed water from the flue gas, the water is discharged through the water outlet of said first gas-liquid separator. The cooled flue gas enters the compression system via the gas outlet of the first gas-liquid separator to be compressed, cooled and dehydrated. The medium-pressure flue gas after pressurization enters the drying system via the first pipeline to be further dehydrated and dried, so that the water content of the medium-pressure flue gas leaving the drying system is less than 1 ppm.

[0024] Preferably: the concrete method of step 2 is as follows: the gases then enter the supercharging stage of the first expander of the gas expander system for pressurization. The gases, after being cooled by the first cooler, then enter the gas expansion stage for expansion refrigeration. The medium pressure and low temperature gases after expansion enter the medium pressure and low temperature adsorption device, using the medium pressure and low temperature adsorption principle to adsorb and capture CO2 in the medium pressure and low temperature flue gases.Raw carbon dioxide with a carbon purity of 85-90% is obtained from the desorbed gas outlet of the medium-pressure and low-temperature adsorption device, and medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm is obtained from the medium-pressure and low-temperature filtered gas outlet of the medium-pressure and low-temperature adsorption device; the nitrogen purity of said medium-pressure raw nitrogen is 87-93%, thus achieving the purpose of separating carbon and nitrogen. The medium-pressure and low-temperature adsorption device switches between adsorption, desorption, regeneration, and cold purge via valves and pipelines.

[0025] Preferably: the concrete steps for obtaining liquid CO2 in step 3 are as follows: the desorbed gas exiting from the desorbed gas outlet of the medium-pressure and low-temperature adsorption device enters the CO2 compressor of the energy utilization system, where the raw carbon dioxide gas is pressurized. The high-temperature and high-pressure gas after pressurization enters the heat recuperator for heat exchange, where the thermal energy of the pressurized raw carbon dioxide gas is absorbed and utilized, the gas itself is cooled, and then it enters the second cooler, where the pressurized and cooled raw carbon dioxide gas is further cooled, so that the pressurized raw carbon dioxide gas exiting from said second cooler meets the raw material temperature and pressure requirements of the low-temperature CO2 purification system, the raw material temperature of which is 20-30 degrees Celsius and the pressure is 2.0-2.5 MPaA, after which it enters the low-temperature CO2 purification system, where the low-temperature pressurized CO2 is purified and refined to obtain industrial or food-grade carbon dioxide.The low-temperature regeneration gas extracted from the ninth pipeline of the low-temperature CO2 purification system can be heated by the heat recovery unit, and the heated regeneration gas enters the medium-pressure low-temperature adsorption device, where it can heat and regenerate the adsorbent that requires regeneration, thereby eliminating the dependence of the medium-pressure low-temperature adsorption device on external heat energy during regeneration.

[0026] Preferably: the concrete steps for obtaining liquid N2 in step 4 are as follows: all or most of the medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm exiting the medium-pressure low-temperature adsorption device is compressed by the low-temperature compressor of the low-temperature filtered gas low-temperature compression system, and then directly enters the liquid nitrogen production system. When the adsorbent of the medium-pressure low-temperature adsorption device requires cold purge for regeneration, a part of the low-temperature filtered gas passes through the fourth pipeline as a cold purge regeneration gas and enters the medium-pressure low-temperature adsorption device, cold purging the adsorbent in the medium-pressure low-temperature adsorption device.The pressurized filtered gas enters the liquid nitrogen production system for rectification and liquefaction. The waste gas regeneration gas leaving the liquid nitrogen production system is heated by the heat recovery unit via the tenth line and then further heated by the electric heater to the required temperature, after which it enters the second inlet of the drying system as heated regeneration gas. The waste gas regeneration gas leaving the liquid nitrogen production system can also directly enter the second inlet of the drying system as cold purge gas via the tenth line.

[0027] Preferably: the concrete method of purifying CO2 gas in said low-temperature CO2 purification system is as follows: the raw carbon dioxide entering the low-temperature CO2 purification system first enters the evaporator to evaporate the liquid at the bottom of the third rectification column, the gas itself is cooled, then enters the liquefier where it is cooled to the saturation temperature, then enters the central part of the third rectification column to participate in the rectification. In the third condenser, the gas from the top of the third rectification column is condensed and then participates in the rectification as reflux liquid at the top of the third rectification column. The condensed liquid that enters the third condenser as a cold supplier via the condensed liquid inlet passage is heated and gasified.The liquid carbon dioxide product is obtained at the bottom of the third rectification column and is extracted through the fifth pipe at the bottom of the third rectification column, then sucked through the ninth pipe located in the upper middle part of the third rectification column and enters the heat recovery unit to be heated.

[0028] Preferably: the concrete method for purifying N2 gas in said liquid nitrogen production system is as follows: the gas entering the liquid nitrogen production system is subcooled to the saturation state by the heat exchanger, and then enters the rectification column system. The rectification column system is a double-column rectification. A portion of the medium-pressure nitrogen gas exiting from the top of the first rectification column returns to the top of the first rectification column as liquid nitrogen after being condensed by the first condenser, and a portion enters the second gas-liquid separator.The liquid extracted from the bottom of the first rectification column is subcooled by the first subcooler and then enters the first condenser as a cold source, and then, after being heated, exits the first condenser and enters the bottom of the second rectification column to participate in rectification. A portion of the low-pressure nitrogen gas exiting from the top of the second rectification column returns to the top of the second rectification column as liquid nitrogen after being condensed by the first condenser, and a portion enters the second gas-liquid separator. Another portion of the medium-pressure nitrogen gas exiting from the top of the first rectification column is heated by the heat exchanger and then enters the second compressor of the cyclic compression system to be compressed.Another portion of the low-pressure nitrogen gas exiting from the top of the second rectification column is heated by the heat exchanger and then successively compressed by the first compressor and the second compressor of the cyclic compression system. The compressed gas of one path exiting the second compressor enters the supercompression stage of the second expander of the high-low temperature gas expander for pressurization, and then enters the heat exchanger. heat for cooling. Part of the gas is extracted from the middle of the heat exchanger and enters the second expansion stage for expansion, the fluid after expansion enters the second gas-liquid separator. The rest of the gas is extracted from the bottom of the heat exchanger and enters the second gas-liquid separator after being expanded by the second expansion valve. The gas from another path enters the heat exchanger directly, and is extracted from the upper middle part of the heat exchanger and then enters the first expansion stage for expansion. The gas after expansion enters the heat exchanger again to be reheated, and is then successively compressed by the first compressor and the second compressor of the cyclic compression system.In the second gas-liquid separator, the fluid undergoes gas-liquid separation and then flows out through the liquid outlet of the second gas-liquid separator and is subcooled by the third subcooler. A portion of the liquid is expanded by the first expansion valve and then re-enters the third subcooler for reheating. The fluid after reheating enters the heat exchanger for further reheating and then exits the liquid nitrogen production system as residual gas. The remaining liquid is extracted through the liquid nitrogen product passage as high-purity liquid nitrogen product. The gas in the second gas-liquid separator flows out through the gas outlet of the second gas-liquid separator, then is reheated by the heat exchanger, and then is successively compressed by the first compressor and the second compressor of the cyclic compression system.The liquid exiting from the bottom of the second rectification column is subcooled by the second subcooler and then enters the evaporation side of the second condenser for evaporation. The gas after evaporation is successively reheated by the second subcooler and the first subcooler. The fluid after reheating enters the heat exchanger for further reheating and then exits the liquid nitrogen production system as waste gas.

[0029] Preferably: the adsorbent used in said low temperature and medium pressure adsorption device is mainly composed of molecular sieve, silica gel and activated carbon, and said device comprises two units which can be used separately or simultaneously, said drying system is composed of two drying tanks in parallel, which can be used separately or simultaneously.

[0030] The present invention provides a low energy consumption liquid production device using flue gases and a method of using the same, having the following advantages:

[0031] l)The present device and its method, according to the different temperature and pressure requirements of each system, adopt a perfect compression coupling and expansion, which is able to meet the needs of different temperature and pressure zones.

[0032] 2)The present device and its method utilize medium pressure and low temperature adsorption to realize the separation of carbon and nitrogen, efficiently obtaining relatively high content carbon dioxide raw gas and nitrogen-rich gas, and utilizing the energy utilization system to efficiently utilize the compression heat of the compressor, thereby reducing the heating power of the device and the level of the electric heater, with low overall energy consumption.

[0033] 3)The present invention utilizes the characteristics of medium pressure and low temperature adsorption separation to efficiently and economically separate CO2 and N2, while enabling the use of low temperature rectification to purify and liquefy CO2 and N2, thereby obtaining high-purity liquid carbon dioxide and liquid nitrogen with high efficiency. Brief description of the figures

[0034] [Fig. 1] represents a process diagram of the present invention;

[0035] [Fig.2] represents a structural diagram of a nitrogen production system liquid according to the invention;

[0036] [Fig. 3] represents a structural diagram of a low temperature carbon dioxide purification system according to the invention. Detailed description of the embodiments

[0037] The present invention is then further described with the figures: according to [Fig.l], a low-energy liquid production device using flue gas, said device comprising a medium-pressure, low-temperature CO2 and N2 adsorption system, an energy utilization system, a low-temperature compression system for the low-temperature filtered gases, a low-temperature CO2 purification system 101 and a liquid nitrogen production system 100;these systems are interconnected by pipes and valves, said CO2 and N2 medium pressure and low temperature adsorption system comprises a flue gas cooler IA, a first gas-liquid separator IB, a compression system IC, a drying system 1D, a gas expander system and a medium pressure and low temperature adsorption device 1H, used for cooling, pressurizing, dehydrating the flue gas and separating CO2 and N2 by low temperature and medium pressure adsorption; said energy utilization system comprises an electric heater 2E, a CO2 compressor 2A, a heat recovery unit 2B, a second cooler 2C, used for pressurizing, recovering heat and cooling the desorbed gas from the system; medium pressure and low temperature adsorption system of CO2 and N2; said low temperature compression system of low temperature filtered gases comprises a low temperature compressor 3A, used for pressurizing to low temperature the medium pressure and low temperature filtered gas obtained from the medium pressure and low temperature adsorption system of CO2 and N2; said low temperature purification system of CO2 101 serves to further purify and liquefy the medium pressure and low temperature gas obtained from the energy utilization system, thereby producing liquid CO2; said liquid nitrogen production system 100 serves to rectify and liquefy the medium pressure gas exiting from the low temperature compression system, thereby producing liquid nitrogen.

[0038] The inlet 10 of the flue gas cooler of the medium pressure and low temperature CO2 and N2 adsorption system is connected to the flue gas discharge outlet, the outlet 11 of the flue gas cooler is connected to the first gas-liquid separator IB, where the liquid is discharged through the water outlet 13 of the first gas-liquid separator, while the gases enter the compression system IC to be compressed, cooled and dehydrated via the gas outlet 12 of the first gas-liquid separator.The gases, after compression, cooling and dehydration, enter the drying system 1D via the first pipe 14 to be completely dehydrated and dried, so that the water content of the flue gases leaving the drying system 1D is in the order of ppm; said drying system 1D is connected to the downstream gas expander system, which is composed of a first expander supercompression stage 1E, a first cooler 1F and a gas expansion stage IG. The flue gases with a water content in the order of ppm successively enter the first expander supercompression stage 1E, the first cooler 1F and the gas expansion stage IG via the second pipe 15.Said gas expansion stage IG is connected to the medium-pressure and low-temperature adsorption device 1H through the third downstream pipeline, using the medium-pressure and low-temperature adsorption principle to adsorb and capture CO2 present in the medium-pressure and low-temperature flue gas, raw carbon dioxide with a carbon purity of 85-90% is obtained at the desorbed gas outlet 19 of the medium-pressure and low-temperature adsorption device, and medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm is obtained at the medium-pressure and low-temperature filtered gas outlet 20 of the medium-pressure and low-temperature adsorption device; the nitrogen purity of this medium-pressure raw nitrogen is 87-93%, thus achieving the purpose of separating carbon and nitrogen.Said medium pressure and low temperature filtered gas outlet 20 is also connected to the medium pressure and low temperature adsorption device 1H via the fourth pipe 32, allowing . a portion of the low-temperature filtered gas to enter the medium-pressure, low-temperature adsorption device 1H via the fourth line 32 as a cold purge regeneration gas, for cold purging the adsorbent in the medium-pressure, low-temperature adsorption device 1H.

[0039] The desorbed gas outlet 19 of said medium pressure and low temperature adsorption device is connected to the CO2 compressor 2A of the energy utilization system to pressurize the raw carbon dioxide; the outlet 141 of said CO2 compressor is connected to the first inlet 21 of the heat recovery unit to absorb and utilize the thermal energy of the pressurized raw carbon dioxide, which is itself cooled.The first outlet 22 of said heat recovery unit is connected to the second cooler 2C, the pressurized and cooled raw carbon dioxide is further cooled in said second cooler 2C, so that the pressurized raw carbon dioxide exiting from the second cooler 2C can meet the temperature and pressure requirements of the raw material of the low-temperature CO2 purification system 101, the outlet 23 of said second cooler is connected to the low-temperature CO2 purification system 101, said low-temperature CO2 purification system 101 is used for purifying and refining the low-temperature pressurized CO2, so as to obtain industrial or food-grade carbon dioxide.Said low temperature CO2 purification system 101 is connected to the second inlet 106 of the heat recovery unit via the ninth line 24, the second outlet 25 of said heat recovery unit is connected to the fourth line 32 on the medium pressure and low temperature adsorption device 1H, serving to heat the low temperature regeneration gas from the low temperature CO2 purification system 101 before it enters the medium pressure and low temperature adsorption device 1H as heated regeneration gas.

[0040] The medium-pressure, low-temperature filtered gas outlet 20 of said medium-pressure, low-temperature adsorption device 1H is connected to the inlet 31 of said low-temperature compressor of the low-temperature compression system for low-temperature filtered gases, the outlet 33 of said low-temperature compressor is connected to the inlet 34 of the liquid nitrogen production system, so that all or most of the low-temperature filtered gas from the medium-pressure, low-temperature adsorption device 1H enters the liquid nitrogen production system 100 after being pressurized by the low-temperature compression system. Said liquid nitrogen production system 100 serves to further rectify and liquefy the pressurized low-temperature filtered gas using the low-temperature rectification principle, thereby producing liquid nitrogen.Said liquid nitrogen production system 100 is connected by one end of the tenth. line 26 to the third inlet 107 of the heat recovery unit, the third outlet 111 of the heat recovery unit is connected to the inlet 103 of said electric heater by the fifth line 27, the outlet 28 of said electric heater is connected to the drying system 1D by the sixth line 102, serving to heat the waste gas regeneration gas exiting the liquid nitrogen production system 100 to the required temperature before it enters the drying system 1D as heated regeneration gas. Said liquid nitrogen production system 100 can also be directly connected to the sixth line 102 of the drying system 1D via the other end of the tenth line 26, serving to directly enter the waste gas regeneration gas exiting said liquid nitrogen production system 100 into said drying system 1D as cold purge gas.

[0041] Said low temperature CO2 purification system 101 comprises a third condenser 4F, an evaporator 4D, a liquefier 4E and a third rectification column 4G, wherein the third condenser 4F, the third rectification column 4G and the evaporator 4D are arranged in a unified manner inside the column and arranged from top to bottom, the liquefier 4E is arranged separately outside the column. The outlet 23 of said cooler is connected to the inlet 104 of the evaporator, and the outlet 45 of the evaporator is connected to the liquefier 4E. Said liquefier 4E is connected to the first inlet 108 of said third rectification column by the eighth pipe 46; the first outlet 42 of said third rectification column is connected to the inlet 109 of the third condenser, and the outlet of the third condenser is connected to the second inlet 43 of the third rectification column by the seventh pipe 110.Said third condenser 4F is also provided with an inlet passage 48 for the condensed liquid and an outlet passage 49 for the condensed gas. The bottom of said third rectification column 4G is provided with a ninth pipe 24 connected to the second inlet 106 of the heat recuperator, and the bottom of said third rectification column 4G is provided with a fifth pipe 47 for obtaining the liquid carbon dioxide product.

[0042] Said liquid nitrogen production system 100 comprises a cyclic compression system, a high and low temperature gas expander, a heat exchanger 5A, a second gas-liquid separator 5H, a rectification column system and subcoolers. Said cyclic compression system is composed of a first compressor 5K1 and a second compressor 5K2. Said high and low temperature gas expander is respectively equipped with a supercompression stage of the second expander 5P, a first expansion stage 5T and a second expansion stage 5U. Said subcoolers comprise a first subcooler 5D, a second subcooler 5F and a third subcooler 5J, the rectification column system is composed of a first rectification column 5B, a first condenser 5C, a second rectification column 5E and a second condenser 5G. The outlet 33 of the low temperature compressor is connected to the inlet 34 of the first passage of the heat exchanger, the outlet 112 of the first passage of the heat exchanger is connected to the first inlet 60 of the first rectification column, the first outlet 61 of the first rectification column is connected to the inlet 113 of the first passage of the first subcooler, the outlet 114 of the first passage of the first subcooler is connected to the first inlet 62 of the first condenser, the first outlet 64 of the first condenser is connected to the first inlet 115 of the second rectification column. The second outlet 50 of the first rectification column is connected on the one hand to the second inlet 116 of the first condenser and on the other hand to the inlet 117 of the third passage of the heat exchanger.The second outlet 63 of the first condenser is connected on the one hand to the second inlet 118 of the first rectification column and on the other hand to the first inlet 119 of the second gas-liquid separator.The first outlet 65 of the second rectification column is connected to the inlet 120 of the first passage of the second subcooler, the outlet 121 of the first passage of the second subcooler is connected to the first inlet 66 of the second condenser, the first outlet 70 of the second condenser is connected to the inlet 122 of the second passage of the second subcooler, the outlet 71 of the second passage of the second subcooler is connected to the inlet 123 of the second passage of the first subcooler, the outlet 72 of the second passage of the first subcooler is connected to the inlet 84 of the second passage of the heat exchanger, the outlet 124 of the second passage of the heat exchanger is connected to the tenth line 26, used for the regeneration of said drying system 1D.The second outlet 68 of the second rectification column is connected on the one hand to the second inlet 160 of the second condenser and on the other hand to the inlet 67 of the fourth passage of the heat exchanger. The second outlet 69 of the second condenser is connected on the one hand to the second inlet 125 of the second rectification column and on the other hand to the second inlet 126 of the second gas-liquid separator.The liquid outlet 80 of the second gas-liquid separator is connected to the inlet 138 of the first passage of the third subcooler, the outlet 81 of the first passage of the third subcooler is connected to the inlet 137 of the first expansion valve V4, the outlet 82 of the first expansion valve V4 is connected to the inlet 127 of the second passage of the third subcooler, the outlet 83 of the second passage of the third subcooler is connected to the inlet 84 of the second passage of the heat exchanger, the outlet 81 of the first passage of the third subcooler is connected to the liquid nitrogen product passage 85, the liquid nitrogen from the bottom of the second gas-liquid separator 5H flows through the liquid nitrogen product passage 85 after subcooling by the third . subcooler 5J. The gas outlet 78 of the second gas-liquid separator is connected to the inlet 128 of the fifth passage of the heat exchanger, the outlet 74 of the fourth passage of the heat exchanger and the outlet 79 of the fifth passage of the heat exchanger are connected to the inlet 52 of the first compressor of the cyclic compression system, the outlet 51 of the third passage of the heat exchanger and the outlet 53 of the first compressor are connected to the inlet 129 of the second compressor of the cyclic compression system, the outlet 54 of the second compressor is connected on the one hand to the inlet 55 of the high and low temperature gas expander and on the other hand to the inlet 130 of the eighth passage of the heat exchanger, the outlet 131 of the eighth passage of the heat exchanger is connected to the inlet 58 of the first expansion stage of the high and low temperature gas expander,the outlet 59 of the first expansion stage is connected to the inlet 132 of the seventh passage of the heat exchanger, the outlet 133 of the seventh passage of the heat exchanger is connected to the inlet 52 of the first compressor, the outlet 56 of the overcompression stage of the high and low temperature gas expander is connected to the inlet 134 of the sixth passage of the heat exchanger, the outlet 1 of the sixth passage of the heat exchanger is connected to the inlet 75 of the second expansion stage of the high and low temperature gas expander, the outlet 76 of the second expansion stage is connected to the fourth inlet 139 of the second gas-liquid separator, the outlet 2 of the sixth passage of the heat exchanger is connected to the inlet 77 of the second expansion valve V3, the outlet 140 of the second expansion valve V3 is connected to the third inlet 135 of the second gas-liquid separator,using the low-temperature rectification principle to further purify and liquefy the low-temperature nitrogen-containing gas obtained from the low-temperature compressor, thereby producing liquid nitrogen.

[0043] A method of using a low energy liquid production device using flue gases, said method comprising the following steps:

[0044] ^Pretreatment of flue gases

[0045] The flue gases are treated by compression, cooling, dehydration and drying, so that the water content of the pressurized flue gases after treatment is < 1 ppm;

[0046] 2) Rough separation of CO2 and N2 gases:

[0047] The gases from step 1) are treated by the gas expander system to obtain raw carbon dioxide with a carbon purity of 85-90% and medium pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm; the nitrogen purity of said medium pressure raw nitrogen is 87-93%;

[0048] 3)Purification and liquefaction to obtain liquid CO2 as product:

[0049] The crude carbon dioxide with a carbon purity of 85-90% from step 2) is processed by the low temperature CO2 purification system 101 to obtain liquid CO2 as product;

[0050] 4)Purification and liquefaction to obtain liquid N2 as product:

[0051] The medium pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm from step 2) is processed by the liquid nitrogen production system 100 to obtain liquid N2 as product.

[0052] The concrete method of the above-mentioned step 1 is as follows: the discharged flue gas at ambient temperature and pressure enters the inlet 10 of the flue gas cooler, where the cooling medium cools the flue gas, the cooled flue gas passes through the first gas-liquid separator 1B to remove condensed water from the flue gas, the water is discharged through the water outlet 13 of said first gas-liquid separator; the cooled flue gas enters said compression system via the gas outlet 12 of the first gas-liquid separator to be compressed, cooled and dehydrated. The medium-pressure flue gas after pressurization enters the first pipeline 14 of the drying system 1D to be further dehydrated and dried, so that the water content of the medium-pressure flue gas leaving the drying system 1D is less than 1 ppm.

[0053] The concrete method of the above-mentioned step 2 is as follows: the gases then enter the supercharging stage 1E of the first expander of the gas expander system for pressurization. The gases, after being cooled by the first cooler 1F, then enter the gas expansion stage IG for expansion refrigeration. The medium-pressure and low-temperature gases after expansion enter the medium-pressure and low-temperature adsorption device 1H, using the medium-pressure and low-temperature adsorption principle to adsorb and capture CO2 in the medium-pressure and low-temperature flue gases.Raw carbon dioxide with a carbon purity of 85-90% is obtained at the desorbed gas outlet 19 of the medium-pressure and low-temperature adsorption device, and medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm is obtained at the medium-pressure and low-temperature filtered gas outlet 20 of the medium-pressure and low-temperature adsorption device; the nitrogen purity of said medium-pressure raw nitrogen is 87-93%, thereby achieving the purpose of separating carbon and nitrogen. The medium-pressure and low-temperature adsorption device switches between adsorption, desorption, regeneration, and cold purge via valves and pipelines.

[0054] The concrete steps for obtaining liquid CO2 in the above-mentioned step 3 are as follows: the desorbed gas leaving the desorbed gas outlet 19 of the medium pressure and low temperature adsorption device enters the compressor of C02 2A of the energy utilization system, where the raw carbon dioxide gas is pressurized.The high-temperature and high-pressure gas after pressurization enters the heat recovery unit 2B for heat exchange, where the heat energy of the pressurized raw carbon dioxide gas is absorbed and utilized, the gas itself is cooled, and then it enters the second cooler 2C, where the pressurized and cooled raw carbon dioxide gas is further cooled, so that the pressurized raw carbon dioxide gas exiting said second cooler 2C meets the raw material temperature and pressure requirements of the low-temperature CO2 purification system 101, the raw material temperature of which is 20-30 degrees Celsius and the pressure is 2.0-2.5 MPaA, after which it enters the low-temperature CO2 purification system 101, where the low-temperature pressurized CO2 is purified and refined to obtain industrial or food-grade carbon dioxide.The low-temperature regeneration gas extracted from the ninth pipeline 24 of the low-temperature CO2 purification system 101 can be heated by the heat recovery unit 2B, and the heated regeneration gas enters the medium-pressure low-temperature adsorption device 1H, where it can heat and regenerate the adsorbent that requires regeneration, thereby eliminating the dependence of the medium-pressure low-temperature adsorption device 1H on external heat energy during regeneration.

[0055] The concrete steps for obtaining liquid N2 in the above-mentioned step 4 are as follows: all or most of the medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm exiting the medium-pressure low-temperature adsorption device 1H is compressed by the low-temperature compressor 3A of the low-temperature filtered gas low-temperature compression system, and then directly enters the liquid nitrogen production system 100. When the adsorbent of the medium-pressure low-temperature adsorption device 1H requires cold purging for regeneration, a part of the low-temperature filtered gas passes through the fourth pipeline 32 as a cold purging regeneration gas and enters said medium-pressure low-temperature adsorption device 1H, cold purging the adsorbent in said medium-pressure low-temperature adsorption device 1H.The pressurized filtered gas enters the liquid nitrogen production system 100 for rectification and liquefaction. The waste gas regeneration gas exiting the tenth line 26 of the liquid nitrogen production system 100 is heated by the heat recovery unit 2B and then further heated by the electric heater 2E to the required temperature, after which it enters the inlet 136 of the drying system as heated regeneration gas. The exiting waste gas regeneration gas. from the tenth line 26 of the liquid nitrogen production system 100 can also enter directly into the inlet 136 of the drying system as cold purge gas.

[0056] The concrete method of purifying CO2 gas in said low-temperature CO2 purification system 101 is as follows: the raw carbon dioxide entering the low-temperature CO2 purification system 101 first enters the evaporator 4D to evaporate the liquid at the bottom of the third rectification column 4G, the gas itself is cooled, then enters the liquefier 4E where it is cooled to the saturation temperature, and then enters the central part of the third rectification column 4E to participate in the rectification. In the third condenser 4F, the gas from the top of the third rectification column 4G is condensed and then participates in the rectification as a reflux liquid at the top of the third rectification column 4G. The condensed liquid which enters the third condenser 4F as a cold supplier via the condensed liquid inlet passage 48 is heated and gasified.The liquid carbon dioxide product is obtained at the bottom of the third rectification column 4G and is extracted through the fifth pipe 47 at the bottom of the third rectification column 4G, then sucked through the ninth pipe 24 located in the upper middle part of the third rectification column 4G and enters the heat recovery unit 2B to be heated.

[0057] The concrete method for purifying the N2 gas in said liquid nitrogen production system 100 is as follows: the gas entering the liquid nitrogen production system 100 is subcooled to the saturation state by the heat exchanger 5A, and then enters the rectification column system. The rectification column system is a double-column rectification. A portion of the medium-pressure nitrogen gas exiting from the top of the first rectification column 5B returns to the top of the first rectification column 5B as liquid nitrogen after being condensed by the first condenser 5C, and a portion enters the second gas-liquid separator 5H.The liquid extracted from the bottom of the first rectification column 5B is subcooled by the first subcooler 5D and then enters the first condenser 5C as a cold source, and then, after being heated, exits the first condenser 5C and enters the bottom of the second rectification column 5E to participate in the rectification. A portion of the low-pressure nitrogen gas exiting from the top of the second rectification column 5E returns to the top of the second rectification column 5E as liquid nitrogen after being condensed by the second condenser 5G, and a portion enters the second gas-liquid separator 5H. Another portion of the medium-pressure nitrogen gas exiting from the top of the first rectification column 5B is reheated. through the heat exchanger 5A and then enters the second compressor 5K2 of the cyclic compression system for compression. Another part of the low-pressure nitrogen gas exiting from the top of the second rectification column 5E is heated by the heat exchanger 5A and then successively compressed by the first compressor 5K1 and the second compressor 5K2 of the cyclic compression system. The compressed gas of one path exiting the second compressor 5K2 enters the supercharging stage 5P of the second expander of the high-low temperature gas expander for pressurization, and then enters the heat exchanger 5A for cooling. A part of the gas is extracted from the middle of the heat exchanger 5A and enters the second expansion stage 5U for expansion, the fluid after expansion enters the second gas-liquid separator 5H.The remaining gas is extracted from the bottom of the heat exchanger 5A and enters the second gas-liquid separator 5H after being expanded by the second expansion valve V3. The gas from another path directly enters the heat exchanger 5A, and is extracted from the upper middle part of the heat exchanger 5A and then enters the first expansion stage 5T for expansion. The gas after expansion enters the heat exchanger 5A again to be reheated, and is then successively compressed by the first compressor 5K1 and the second compressor 5K2 of the cyclic compression system. In the second gas-liquid separator 5H, the fluid undergoes gas-liquid separation and then flows out through the liquid outlet 80 of the second gas-liquid separator and is subcooled by the third subcooler 5J. Part of the liquid is expanded by the first expansion valve V4 and then enters the third subcooler 5J again to be reheated.The fluid after heating enters the heat exchanger 5A to continue heating, and then exits the liquid nitrogen production system 100 as residual gas. The remaining liquid is extracted through the liquid nitrogen product passage 85 as high-purity liquid nitrogen product. The gas in the second gas-liquid separator 5H flows through the gas outlet 78 of the second gas-liquid separator, is then heated by the heat exchanger 5A, and is then successively compressed by the first compressor 5K1 and the second compressor 5K2 of the cyclic compression system. The liquid exiting from the bottom of the second rectification column 5E is subcooled by the second subcooler 5F and then enters the evaporation side of the second condenser 5G for evaporation. The gas after evaporation is successively reheated by the second subcooler 5F and the first subcooler 5D.The fluid after heating enters the heat exchanger 5A to continue heating, and then exits the liquid nitrogen production system 100 as waste gas.

[0058] The adsorbent used in said 1H low temperature and medium pressure adsorption device is mainly composed of molecular sieve, silica gel and carbon. active, and said device comprises two units which can be used separately or simultaneously, said 1D drying system is composed of two drying tanks in parallel, which can be used separately or simultaneously.

[0059] The outlet pressure of said compression system IC according to the present invention is in coupling relationship with said gas expander system, the low temperature compressor 3A and the CO2 compressor 2A. The outlet pressure of said compression system IC must take into account not only the energy consumption of the three elements itself, the low temperature compressor 3A and the CO2 compressor 2A, but also the refrigeration capacity of said gas expander system, as well as the outlet pressure of the gas expansion stage IG to enable efficient adsorption in the medium pressure and low temperature adsorption device 1H.The outlet temperature of the gas expansion stage IG should also be considered to ensure that the gas exiting from said gas expansion stage 1G does not solidify and can be effectively adsorbed, and also the investment cost of the drying system 1D and the medium pressure and low temperature adsorption device 1H, as well as the drying and adsorption efficiency should be taken into consideration. The adsorbent used in said low temperature and medium pressure adsorption device 1H is mainly composed of molecular sieve, silica gel and activated carbon, and said device has two units which can be used separately or simultaneously, said drying system 1D is composed of two drying tanks in parallel, which can be used separately or simultaneously.

[0060] The present invention uses the energy utilization system to efficiently utilize the compression heat of the CO2 compressor 2A, allowing the heated regeneration gas required by the medium-pressure and low-temperature adsorption device 1H and the drying system 1D to be obtained by heating in the heat recovery unit 2B, thereby eliminating the dependence of the medium-pressure and low-temperature adsorption device 1H on external thermal energy during its regeneration and reducing the heating power of the electric heater 2E, thereby significantly decreasing the overall energy consumption.

[0061] Example of embodiment 1:

[0062] As shown in [Fig.l]: the flue gas at ambient temperature and pressure which reaches the ultra-low emission standards, at a temperature of about 50°C, a pressure of about 0.1 MPaA, and a molar composition of about 12% CO2, 73% N2, 8% H2O, 6% O2, 0.984% Ar, 100ppm CO, 50ppm NO2, 100ppm SO2, enters the inlet 10 of the flue gas cooler, the cooling medium cools the flue gas to about 6°C. After cooling, the flue gases pass through the gas-liquid separator IB to remove the condensed water, which is discharged through the water outlet 13 of the gas-liquid separator; the cooled flue gases exit through the gas outlet 12 of the gas-liquid separator and enter the compression system IC to be compressed, cooled and dehydrated. The saturated flue gases at a pressure of about 0.8 MPaA and a temperature of about 6°C enter the first pipeline 14 of the drying system 1D to be further dehydrated, so that the water content of the flue gases exiting the drying system 1D does not exceed 1 ppm. Then they enter the supercompression stage 1E of the first expander of the gas expander system for pressurization, where they are compressed to about 1.6 MPaA and then cooled to about 6°C by the first cooler 1F before entering the gas expansion stage IG for expansion cooling.The expanded gas, at a pressure of about 0.41 MPaA and a temperature of about -80°C, enters the medium-pressure and low-temperature adsorption device 1H, using the medium-pressure and low-temperature adsorption principle to adsorb and capture CO2 in the medium-pressure and low-temperature flue gas. At the outlet of the filtered medium-pressure and low-temperature gas 20 of the medium-pressure and low-temperature adsorption device, medium-pressure and low-temperature raw nitrogen containing a carbon dioxide concentration of less than 1 ppm with a pressure of about 0.4 MPaA is obtained, thereby achieving the purpose of separating carbon and nitrogen. The medium-pressure and low-temperature adsorption device switches between adsorption, desorption, regeneration, and cold purge via valves and pipelines.The 1H low-temperature medium-pressure adsorption device uses adsorbents mainly based on molecular sieves, silica gel and activated carbon. During desorption of the 1H low-temperature medium-pressure adsorption device, raw carbon dioxide with a purity of 85-90% is obtained at the desorbed gas outlet 19. .

[0063] The desorbed gas exiting the outlet 19 of the low temperature and medium pressure adsorption device (temperature of about 10°C, pressure of about 0.11 MPaA, molar composition of about 92% CO2, 8% N2, 50 ppm NO2, 10 ppm SO2) enters the CO2 compressor 2A of the energy utilization system where it is compressed to about 2.3 MPaA, with an outlet temperature of about 100°C. It then passes into the heat exchanger 2B for heat exchange, where the thermal energy of the pressurized raw carbon dioxide gas is absorbed and utilized, the gas itself is cooled, and then it enters the second cooler 2C, where the pressurized and cooled raw carbon dioxide gas is further cooled, so that the pressurized raw carbon dioxide gas exiting from said second cooler 2C is cooled to about 25°C, thereby meeting the temperature and raw material pressure of the cryogenic CO2 purification system. After which it enters the low-temperature CO2 purification system, where the low-temperature pressurized CO2 is purified and refined to obtain industrial or food-grade carbon dioxide.When heating the low-temperature and medium-pressure adsorption device 1H, the low-temperature regeneration gas (temperature of about -12.7°C, pressure of about 2.3 MPaA, molar composition of about 98.5% CO2, 1.5% N2, 20 ppm CO, 2 ppm NO2, 1 ppm SO2) extracted from the ninth pipeline 24 of the low-temperature CO2 purification system can be reheated to about 90°C by the heat recovery unit 2B, and then the heated regeneration gas enters the low-temperature and medium-pressure adsorption device 1H, where it can heat and regenerate the adsorbent that requires regeneration, thereby eliminating the dependence of the low-temperature and medium-pressure adsorption device 1H on external heat energy during regeneration.

[0064] The medium-pressure raw nitrogen exiting the adsorption device 1H, containing less than 1 ppm of carbon dioxide, at a temperature of about -87°C, a pressure of about 0.4 MPaA, and a molar composition of about 92% N2, 7.5% O2, 1.4% Ar, 120 ppm CO, 1 ppm CO2, is fully or mostly compressed by the low-temperature compressor 3A of the low-temperature compression system of the low-temperature filtered gases to about 0.9 MPaA, with a temperature of about -10°C, and then directly enters the liquid nitrogen production system, when the adsorbent of the medium-pressure and low-temperature adsorption device 1H requires a cold purge for regeneration, a part of the low-temperature filtered gas passes through the fourth line 32 as a cold purge regeneration gas and enters the medium-pressure and low-temperature adsorption device 1H,cold purging the adsorbent in the medium-pressure, low-temperature adsorption device 1H, the pressurized filtered gas enters the liquid nitrogen production system for rectification and liquefaction. When the drying system 1D requires heating, the waste gas regeneration gas exiting the tenth pipeline 26 of the liquid nitrogen production system is heated to about 90°C by the heat recovery unit 2B, and then further heated to about 170°C by the electric heater 2E, after which it enters the inlet 136 of the drying system as a heated regeneration gas, when the drying system 1D requires cold purging, the atmospheric pressure waste gas regeneration gas exiting the tenth pipeline 26 of the liquid nitrogen production system can also directly enter the inlet 136 of the drying system as a cold purge gas.

[0065] As shown in [Fig.2]: The gas entering the nitrogen liquefaction system, at a pressure of about 0.9 MPaA and a temperature of about -10°C, is subcooled to the saturation state by the heat exchanger 5A before entering the rectification column system. A portion of the medium-pressure nitrogen gas exiting from the top of the first rectification column 5B returns to the top of the first rectification column 5B as liquid nitrogen after being condensed by the first condenser 5C, and a portion enters the second gas-liquid separator 5H. The liquid extracted from the bottom of the first rectification column 5B is subcooled by the first subcooler 5D and then enters the first condenser 5C as a source of cold, then, after being heated, leaves the first condenser 5C and enters the bottom of the second rectification column 5E to participate in the rectification.A portion of the low-pressure nitrogen gas exiting from the top of the second rectification column 5E returns to the top of the second rectification column 5E as liquid nitrogen after being condensed by the first condenser 5G, and a portion enters the gas-liquid separator 5H. Another portion of the medium-pressure nitrogen gas exiting from the top of the first rectification column 5B is heated by the heat exchanger 5A and then enters the second compressor 5K2 of the cyclic compression system to be compressed to about 2.5 MpaA. Another portion of the low-pressure nitrogen gas exiting from the top of the second rectification column 5E is heated by the heat exchanger 5A and then successively compressed to about 2.5 MpaA by the first compressor 5K1 and the second compressor 5K2 of the cyclic compression system.Compressed gas from one path exiting the second compressor 5K2 enters the supercharging stage 5P of the second expander of the high and low temperature gas expander for pressurization, and then enters the heat exchanger 5A for cooling. Part of the gas is extracted from the middle of the heat exchanger 5A and enters the second expansion stage 5U to expand to about 0.39 MpaA, the fluid after expansion enters the gas-liquid separator 5H. The rest of the gas is extracted from the bottom of the heat exchanger 5A and enters the gas-liquid separator 5H after being expanded by the second expansion valve V3. Gas from another path directly enters the heat exchanger 5A, and is extracted from the upper middle part of the heat exchanger 5A and then enters the first expansion stage 5T for expansion.The gas after expansion re-enters the heat exchanger 5A to be reheated, and then is successively compressed to about 2.5 MpaA by the first compressor 5K1 and the second compressor 5K2 of the cyclic compression system. In the gas-liquid separator 5H, the fluid undergoes gas-liquid separation and then flows out through the liquid outlet of the gas-liquid separator 5H and is subcooled by the third subcooler. 5J. A portion of the liquid is expanded to about 0.13 MpaA by the first expansion valve V4 and then re-enters the third subcooler 5J to be reheated. The fluid after reheating enters the heat exchanger 5A to continue to be reheated, and then exits the liquid nitrogen production system as residual gas; the rest of the liquid is extracted through the liquid nitrogen product passage 85 as high-purity liquid nitrogen product. The gas in the gas-liquid separator 5H flows out through the gas outlet 12 of the gas-liquid separator, then is reheated by the heat exchanger 5A, and then is successively compressed to about 2.5 MpaA by the first compressor 5K1 and the second compressor 5K2 of the cyclic compression system. The liquid exiting the bottom of the second rectification column 5E is subcooled by the second subcooler 5F and then enters the evaporation side of the second condenser 5G for evaporation.The gas after evaporation is successively reheated by the second subcooler 5F and the first subcooler 5D. The fluid after reheating enters the heat exchanger 5A to continue reheating, and then exits the liquid nitrogen production system as waste gas.

[0066] As shown in [Fig.3]: the pressurized raw CO2 (temperature of about 25°C, pressure of about 2.3 MPaA, molar composition of about 92% CO2, 8% N2, 50 ppm NO2, 10 ppm SO2) entering the low-temperature CO2 purification system passes through evaporator 4D where it evaporates the liquid from the bottom of rectification column 4G, thus cooling to about -10°C. It then passes through liquefier 4E where it is cooled to near the saturation temperature (-17°C) before entering the central part of rectification column 4G to participate in rectification. In the third condenser 4F, the gas from the top of the rectification column 4G is condensed and returns as reflux liquid to the top of the rectification column 4G to participate in the rectification.The condensed liquid entering the third condenser 4F as a cold supplier via the condensed liquid inlet passage 48 is heated and gasified, the industrial-grade liquid carbon dioxide product is obtained at the bottom of the third rectification column 4G, and the regeneration gas is extracted through the ninth pipeline 24 of the rectification column 4G.

[0067] Contrary to a limitation of the present invention, the exemplary embodiment described herein is intended to illustrate in an exemplary manner the principles and effectiveness of the present invention. Any person familiar with this technology may make modifications or variations to the above-mentioned exemplary embodiment without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or variations made by persons having ordinary knowledge in the relevant technical field, without departing from the spirit and technical concept disclosed by the present invention, must be covered by the claims of the present invention.

Claims

1.

2. Claims A low-energy liquid production device using flue gas, said device comprising a medium-pressure, low-temperature CO2 and N2 adsorption system, an energy utilization system, a low-temperature compression system for low-temperature filtered gases, a low-temperature CO2 purification system (101) and a liquid nitrogen production system (100);these systems are interconnected by pipes and valves, said device is characterized in that said CO2 and N2 medium pressure and low temperature adsorption system comprises a flue gas cooler (IA), a first gas-liquid separator (IB), a compression system (IC), a drying system (1D), a gas expander system and a medium pressure and low temperature adsorption device (1H), used for cooling, compressing, dehydrating and separating by low temperature adsorption the CO2 and N2 from the flue gas; said energy utilization system comprises an electric heater (2E), a CO2 compressor (2A), a heat recovery unit (2B), a second cooler (2C), used for compressing, recovering heat and cooling the desorbed gases obtained from the CO2 and N2 medium pressure and low temperature adsorption system;said low-temperature compression system for low-temperature filtered gases comprises a low-temperature compressor (3A), used for compressing at low temperature the filtered medium-pressure and low-temperature gases obtained from the medium-pressure and low-temperature adsorption system of CO2 and N2; said low-temperature purification system of CO2 (101) is used for further purifying and liquefying the medium-pressure and low-temperature gases obtained from the energy utilization system, thereby producing liquid CO2 as a product; said liquid nitrogen production system is used for rectifying and liquefying the medium-pressure gases exiting from the low-temperature compression system, thereby producing liquid nitrogen as a product.; A low energy liquid production device using flue gases according to claim 1, characterized in that the flue gas cooler (IA) of said system medium pressure and low temperature adsorption of CO2 and N2 is connected on one side to the flue gas discharge outlet, and on the other side to the first gas-liquid separator (IB), the liquid in the first gas-liquid separator (IB) is discharged through the liquid outlet (13) of the first gas-liquid separator, and the gases enter the compression system (IC) through the gas outlet (12) of the first gas-liquid separator to be compressed, cooled and dehydrated, the flue gases after compression, cooling and dehydration, enter the drying system (1D) via a first pipeline (14) for complete dehydration, so that the water content of the flue gases leaving the drying system (1D) is in the order of ppm, said drying system (1D) is connected to the downstream gas expander system, consisting of a supercompression stage (1E) of the first expander, a first cooler (1F) and a gas expansion stage (IG),the flue gases with a water content of the order of ppm successively enter the supercompression stage (1E) of the first expander, the first cooler (1F) and the gas expansion stage (IG) via a second pipe (15), said gas expansion stage (IG) is connected to the medium pressure and low temperature adsorption device (1H) by a third pipe (18) downstream, using the medium pressure and low temperature adsorption principle to adsorb and capture the CO2 present in the medium pressure and low temperature flue gases, raw carbon dioxide with a carbon purity of 85-90% is obtained at the desorbed gas outlet (19) of said medium pressure and low temperature adsorption device,and medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm is obtained at the medium-pressure low-temperature filtered gas outlet (20) of the medium-pressure low-temperature adsorption device; the nitrogen purity of this medium-pressure raw nitrogen is 87-93%, thus achieving the purpose of separating carbon and nitrogen, said medium-pressure low-temperature filtered gas outlet (20) is also connected to the medium-pressure low-temperature adsorption device (1H) by a fourth pipeline (32), so that a part of the low-temperature filtered gas passes through the fourth pipeline (32) as a cold purge regeneration gas and enters said device, medium pressure and low temperature adsorption (1H), cold purging the adsorbent in the medium pressure and low temperature adsorption device (1H).

3. A low-energy liquid production device using flue gas according to claim 2, characterized in that the desorbed gas outlet (19) of said medium-pressure and low-temperature adsorption device is connected to the CO2 compressor (2A) in the energy utilization system, for pressurizing the raw carbon dioxide gas; the CO2 compressor (2A) is successively connected to the heat recovery unit (2B), the second cooler (2C) and the low-temperature CO2 purification system (101), wherein the pressurized raw carbon dioxide gas is further cooled by the second cooler (2C), so that the pressurized raw carbon dioxide gas exiting the second cooler (2C) can meet the temperature and pressure requirements of the raw material of the low-temperature CO2 purification system (101),said low temperature CO2 purification system (101) is used for purifying and refining pressurized CO2 at low temperature, in order to obtain industrial or food grade carbon dioxide, said low temperature CO2 purification system (101) is connected to the heat recovery unit (2B) by a ninth pipeline (24), the heat recovery unit (2B) is connected to the fourth pipeline (32) on said medium pressure and low temperature adsorption device (1H), used for heating the low temperature regeneration gas exiting from said low temperature CO2 purification system (101) before it enters the medium pressure and low temperature adsorption device (1H) as heated regeneration gas.,

4. A low-energy liquid production device using flue gas according to claim 2, characterized in that the medium-pressure, low-temperature filtered gas outlet (20) of said medium-pressure, low-temperature adsorption device is successively connected to the low-temperature compressor (3A) in the low-temperature compression system of the low-temperature filtered gases and to the liquid nitrogen production system (100), allowing all or most of the low-temperature filtered gas to enter the system

5. liquid nitrogen production system (100) after being pressurized by the low-temperature compression system, said liquid nitrogen production system (100) is used to further rectify and liquefy the low-temperature pressurized filtered gas using the low-temperature rectification principle, thereby obtaining liquid nitrogen as a product, a tenth pipeline (26) is provided downstream of said liquid nitrogen production system (100), and two paths are respectively provided downstream of said tenth pipeline (26), one of which is successively connected to the heat recovery unit (2B) and the electric heater (2E), the electric heater (2E) is connected to the sixth pipeline (102), the sixth pipeline (26) is connected to the drying system (1D),used for heating the waste gas regeneration gas exiting the liquid nitrogen production system (100) to the required temperature before it enters the drying system (1D) as heated regeneration gas, the other way of said tenth pipeline (26) is directly connected to the sixth pipeline (102), used for directly entering the waste gas regeneration gas exiting the liquid nitrogen production system (100) into the drying system (1D) as cold purge gas., A low-energy liquid production device using flue gas according to claim 3, characterized in that said low-temperature CO2 purification system (101) comprises a third condenser (4F), an evaporator (4D), a liquefier (4E) and a third rectification column (4G), wherein the third condenser (4F) is installed above the third rectification column (4G), the evaporator (4D) is installed below, and the liquefier (4E) is separately arranged outside the column; said second cooler (2C) is connected to the evaporator (4D), the evaporator (4D) is connected to the liquefier (4E), said liquefier (4E) is connected to the third rectification column (4G) by an eighth pipeline (46);said third rectification column (4G) is connected to the third condenser (4F), the third condenser (4F) is connected to the third rectification column (4G) by a seventh pipe (110) forming a loop, said third condenser (4F) is also provided with a condensed liquid inlet passage (48) and a condensed gas outlet passage (49), said third column;

6. rectification column (4G) is provided with a ninth pipe (24) at the bottom which is connected to the heat recovery unit (2B), the bottom of said third rectification column (4G) is provided with a fifth pipe (47) which is used to obtain liquid carbon dioxide as a product. A low-energy liquid production device using flue gas according to claim 4, characterized in that said liquid nitrogen production system (100) comprises a cyclic compression system, a high and low temperature gas expander, a heat exchanger (5A), a second gas-liquid separator (5H), a rectification column system and subcoolers, wherein said cyclic compression system is composed of a first compressor (5K1) and a second compressor (5K2), said high and low temperature gas expander is respectively equipped with a supercompression stage of the second expander (5P), a first expansion stage (5T) and a second expansion stage (5U), said subcoolers comprise a first subcooler (5D), a second subcooler (5F) and a third subcooler (5J),the rectification column system is composed of a first rectification column (5B) and a second rectification column (5E), wherein a first condenser (5C) is installed at the top of the first rectification column (5B), a second condenser (5G) is installed at the top of the second rectification column (5E), said low-temperature compressor (3A) is successively connected to the heat exchanger (5A) and the first rectification column (5B), said first rectification column (5B) is equipped with two bypass lines, of which the first bypass line of the first rectification column (5B) is successively connected to the first subcooler (5D), the first condenser (5C), the second rectification column (5E), the second subcooler (5F), the second condenser (5G), and above the second condenser (5G),it is successively connected by pipes to the second sub-cooler (5F), to the first sub-cooler (5D) and to the heat exchanger (5A); said heat exchanger (5A) is connected to the tenth pipe (26), used for the regeneration of the drying system (1D), the second bypass pipe of the first column of, rectification (5B) is directly connected to the first condenser (5C) and the heat exchanger (5A); said first condenser (5C) is also equipped with two bypass lines, of which the first bypass line of the first condenser (5C) is connected to the first rectification column (5B), and the second bypass line of the first condenser (5C) is connected to the second gas-liquid separator (5H); said second rectification column (5E) is equipped with two bypasses, of which the first bypass of the second rectification column (5E) is connected to the second condenser (5G), and the second bypass of the second rectification column (5E) is connected to the heat exchanger (5A); said second condenser (5G) is also equipped with two bypasses, the first bypass of the second condenser (5G) is connected to the second rectification column (5E),and the second bypass of the second condenser (5G) is successively connected to the second gas-liquid separator (5H) and to the third subcooler (5J); said third subcooler (5J) is connected on one side to the liquid nitrogen product passage, and on the other side, it is connected to the heat exchanger (5A) via a first expansion valve (V4) and then through the third subcooler (5J), said second gas-liquid separator (5H) is connected to the heat exchanger (5A), which is successively connected to the first compressor (5K1) and the second compressor (5K2), wherein the second compressor (5K2) is equipped with two bypasses, of which the first bypass of the second compressor (5K2) passes successively through the high and low temperature gas expander (5P), the heat exchanger (5A), the second expansion stage (5U),and finally connects to the second gas-liquid separator (5H) for circulation through the second expansion stage (5U), the second branch of the second compressor (5K2) is successively connected to the heat exchanger (5A), the first expansion stage (5T), the heat exchanger (5A), and finally connects to the first compressor (5K1) for circulation through the heat exchanger (5A), said heat exchanger (5A) is directly connected to the second gas-liquid separator (5H), and a second expansion valve (V3) is installed on the connection pipeline, using the low-temperature rectification principle to purify, and further liquefying the low-temperature nitrogen-containing gas obtained from the low-temperature compressor, thereby producing liquid nitrogen as a product.

7. A method of using the low-energy liquid production device using flue gases according to any one of claims 1 to 6, characterized in that said method comprises the following steps: 1) pretreatment of flue gases: the flue gases are treated by compression, cooling, dehydration and drying, so that the water content of the pressurized flue gases after treatment is < 1 ppm; 2) rough separation of CO2 and N2 gases: the gases of step 1) are treated by the gas expander system to obtain raw carbon dioxide with a carbon purity of 85-90% and medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm; the nitrogen purity of said medium-pressure raw nitrogen is 87-93%;3) purification and liquefaction to obtain liquid CO2 as product: raw carbon dioxide with a carbon purity of 85-90% from step 2) is treated by the low-temperature CO2 purification system (101) to obtain liquid CO2 as product; 4) purification and liquefaction to obtain liquid N2 as product: raw nitrogen at medium pressure containing a carbon dioxide concentration of less than 1 ppm from step 2) is treated by the liquid nitrogen production system (100) to obtain liquid N2 as product.;

8. A method of using the low-energy liquid production device using flue gases according to claim 7, characterized in that the concrete method of the above-mentioned step 1 is as follows: the flue gases discharged at ambient temperature and pressure enter the inlet (10) of the flue gas cooler, where the cooling medium cools the flue gases, the cooled flue gases pass through the first gas-liquid separator (IB) to remove condensed water from the flue gases, the water is discharged through the water outlet (13) of said first gas-liquid separator; the cooled flue gases enter into the compression system via the gas outlet (12) of the first gas-liquid separator to be compressed, cooled and dehydrated, the medium pressure flue gases after pressurization enter the first pipeline (14) of the drying system (1D) to be further dehydrated and dried, so that the water content of the medium pressure flue gases exiting the drying system (1D) is less than 1 ppm.

9. A method of using the low-energy liquid production device using flue gas according to claim 7, characterized in that the concrete method of the above-mentioned step 2 is as follows: the gases then enter the supercompression stage (1E) of the first expander of the gas expander system for pressurization, the gases, after being cooled by the first cooler (1F), then enter the gas expansion stage (IG) for expansion refrigeration, the medium-pressure and low-temperature gases after expansion enter the medium-pressure and low-temperature adsorption device (1H), using the medium-pressure and low-temperature adsorption principle to adsorb and capture CO2 in the medium-pressure and low-temperature flue gases,raw carbon dioxide with a carbon purity of 85-90% is obtained at the desorbed gas outlet of the medium-pressure and low-temperature adsorption device (1H), and medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm is obtained at the medium-pressure and low-temperature filtered gas outlet (20) of the medium-pressure and low-temperature adsorption device (1H); the nitrogen purity of said medium-pressure raw nitrogen is 87-93%, thereby achieving the purpose of separating carbon and nitrogen, the medium-pressure and low-temperature adsorption device (1H) switches between adsorption, desorption, regeneration and cold purge via valves and pipelines.,

10. A method of using the low-energy liquid production device using flue gases according to claim 7, characterized in that the concrete steps for obtaining liquid CO2 in the above-mentioned step 3 are as follows: the desorbed gas leaving the desorbed gas outlet (19) of the medium-pressure, low-temperature adsorption device between

11. in the CO2 compressor (2A) of the energy utilization system, where the raw carbon dioxide gas is pressurized, the high-temperature and high-pressure gas after pressurization enters the heat recovery unit (2B) for heat exchange, where the heat energy of the pressurized raw carbon dioxide gas is absorbed and utilized, the gas itself is cooled, and then enters the second cooler (2C), where the pressurized and cooled raw carbon dioxide gas is further cooled, so that the pressurized raw carbon dioxide gas exiting from said second cooler (2C) meets the temperature and pressure requirements of the raw material of the CO2 low-temperature purification system (101), the raw material temperature of which is 20-30 degrees Celsius and the pressure is 2.0-2.5 MPaA, after which it enters the CO2 low-temperature purification system (101),where the low-temperature pressurized CO2 is purified and refined to obtain industrial or food-grade carbon dioxide, the low-temperature regeneration gas extracted from the ninth pipeline (24) of the low-temperature CO2 purification system (101) can be heated by the heat recovery unit (2B), and the heated regeneration gas enters the medium-pressure low-temperature adsorption device (1H), where it can heat and regenerate the adsorbent that requires regeneration, thereby eliminating the dependence of the medium-pressure low-temperature adsorption device (1H) on external heat energy during regeneration., A method of using the low-energy liquid production device using flue gas according to claim 7, characterized in that the concrete steps for obtaining liquid N2 in the above-mentioned step 4 are as follows: all or most of the medium-pressure raw nitrogen containing a carbon dioxide concentration of less than 1 ppm exiting from the medium-pressure and low-temperature adsorption device (1H) is compressed by the low-temperature compressor (3A) of the low-temperature filtered gas low-temperature compression system, and then directly enters the liquid nitrogen production system (100), when the adsorbent of the medium-pressure and low-temperature adsorption device (1H) requires cold purging for the

12. regeneration, a portion of the low-temperature filtered gas passes through the fourth line (32) as a cold purge regeneration gas and enters the medium-pressure, low-temperature adsorption device (1H), cold purging the adsorbent in the medium-pressure, low-temperature adsorption device (1H), the pressurized filtered gas enters the liquid nitrogen production system (100) for rectification and liquefaction, the waste gas regeneration gas exiting the tenth line (26) of the liquid nitrogen production system (100) is heated by the heat recuperator (2B), and then further heated by the electric heater (2E) to the required temperature, after which it enters the second inlet of the drying system (1D) as a heated regeneration gas,the waste gas regeneration gas leaving the liquid nitrogen production system (100) can also enter directly into the second inlet of the drying system (1D) via the tenth line (26) as cold purge gas., A method of using the low-energy liquid production device using flue gas according to claim 10, characterized in that the concrete method of purifying CO2 gas in said low-temperature CO2 purification system (101) is as follows: the raw carbon dioxide entering the low-temperature CO2 purification system (101) first enters the evaporator (4D) to evaporate the liquid at the bottom of the third rectification column (4G), the gas itself is cooled, then enters the liquefier (4E) where it is cooled to the saturation temperature, then enters the middle part of the third rectification column (4E) to participate in rectification, in the third condenser (4F), the gas from the top of the third rectification column (4G) is condensed and then participates in rectification as reflux liquid at the top of the third rectification column (4G),the condensed liquid which enters the third condenser (4F) as a cold supplier via the condensed liquid inlet passage (48) is heated and gasified, the liquid carbon dioxide product is obtained at the bottom of the third rectification column (4G) and is extracted through the fifth pipe (47) at the bottom of the third rectification column (4G), and then sucked through the ninth pipe (24) located in the upper middle part of the third column,

13. rectification (4G) and enters the heat recovery unit (2B) to be heated. A method of using the low-energy liquid production device using flue gas according to claim 11, characterized in that the concrete method of purifying N2 gas in said liquid nitrogen production system (100) is as follows: the gas entering the liquid nitrogen production system (100) is subcooled to the saturation state by the heat exchanger (5A), then enters the rectification column system, the rectification column system is a double-column rectification, a part of the medium-pressure nitrogen gas exiting from the top of the first rectification column (5B) returns to the top of the first rectification column (5B) as liquid nitrogen after being condensed by the first condenser (5C), and a part enters the second gas-liquid separator (5H),the liquid extracted from the bottom of the first rectification column (5B) is subcooled by the first subcooler (5D) and then enters the first condenser (5C) as a cold source, then, after being heated, exits the first condenser (5C) and enters the bottom of the second rectification column (5E) to participate in the rectification, a part of the low-pressure nitrogen gas exiting from the top of the second rectification column (5E) returns to the top of the second rectification column (5E) as liquid nitrogen after being condensed by the second condenser (5G), and a part enters the second gas-liquid separator (5H), another part of the medium-pressure nitrogen gas exiting from the top of the first rectification column (5B) is heated by the heat exchanger (5A) and then enters the second compressor (5K2) of the cyclic compression system to be compressed,another part of the low-pressure nitrogen gas exiting from the top of the second rectification column (5E) is heated by the heat exchanger (5A) and then successively compressed by the first compressor (5K1) and the second compressor (5K2) of the cyclic compression system, the compressed gas of one path exiting from the second compressor (5K2) enters the overcompression stage (5P) of the second expander of the high-low temperature gas expander for pressurization, and then enters the exchanger of, heat (5A) for cooling, a part of the gas is extracted from the middle of the heat exchanger (5A) and enters the second expansion stage (5U) for expansion, the fluid after expansion enters the second gas-liquid separator (5H), the rest of the gas is extracted from the bottom of the heat exchanger (5A) and enters the second gas-liquid separator (5H) after being expanded by the second expansion valve (V3), the gas from another path directly enters the heat exchanger (5A), and is extracted from the upper middle part of the heat exchanger (5A) and then enters the first expansion stage (5T) for expansion, the gas after expansion enters the heat exchanger (5A) again to be reheated, and then is successively compressed by the first compressor (5K1) and the second compressor (5K2) of the cyclic compression system,the fluid in the second gas-liquid separator (5H) undergoes gas-liquid separation and then flows out through the liquid outlet of the second gas-liquid separator (5H) and is subcooled by the third subcooler (5J), a part of the liquid is expanded by the first expansion valve (V4) and then enters the third subcooler (5J) again to be reheated, the fluid after reheating enters the heat exchanger (5A) to continue to be reheated, and then exits the liquid nitrogen production system (100) as residual gas; the rest of the liquid is extracted through the liquid nitrogen product passage (85) as high-purity liquid nitrogen product, the gas in the second gas-liquid separator (5H) flows out through the gas outlet of the second gas-liquid separator (5H), then is reheated by the heat exchanger (5A),then is successively compressed by the first compressor (5K1) and the second compressor (5K2) of the cyclic compression system, the liquid exiting from the bottom of the second rectification column (5E) is subcooled by the second subcooler (5F) and then enters the evaporation side of the second condenser (5G) for evaporation, the gas after evaporation is successively reheated by the second subcooler (5F) and the first subcooler (5D), the fluid after reheating enters the heat exchanger (5A) to continue to be reheated, and then exits the liquid nitrogen production system (100) as waste gas.,

14. A method of using the low-energy liquid production device using flue gas according to claim 11, characterized in that the adsorbent used in said low-temperature and medium-pressure adsorption device (1H) is mainly composed of molecular sieve, silica gel and activated carbon, and said device comprises two units which can be used separately or simultaneously, said drying system (1D) is composed of two drying tanks in parallel, which can be used separately or simultaneously.

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