System and method for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas

Abstract

The present application belongs to the field of environmental protection, and in particular to a system and method for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas. The system provided by the present application comprises a flue gas boosting and cooling system, a CO2/N2 front-end separation system, a liquid CO2 preparation system and a high-purity liquid nitrogen preparation system The present application can maximize the use of flue gas to produce high-purity liquid nitrogen and liquid CO2 at low cost, and realize the synchronous resource utilization of carbon/nitrogen components.

1 . A system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas, comprising: a flue gas boosting and cooling system, a CO 2 /N 2  front-end separation system, a liquid CO 2  preparation system and a high-purity liquid nitrogen preparation system;
 wherein the flue gas boosting and cooling system comprises a flue gas booster ( 1 ), a flue gas cooling tower ( 2 ), a water cooling tower ( 3 ), a low-temperature water pump ( 4 ) and a chiller unit ( 5 ), configured to pressurize, cool, dewater and wash raw flue gas;   the CO 2 /N 2  front-end separation system is configured to separate CO 2  by using a pressure swing adsorption method, and comprises a plurality of pressure swing adsorption towers ( 13 ,  14 ), a switching flow path and a valve, a vacuum pump ( 15 ), a CO 2  buffer device ( 16 ) and an adsorption tail gas buffer device ( 19 ); when the system is in operation, the plurality of pressure swing adsorption towers ( 13 ,  14 ) are configured to adsorb CO 2  in the flue gas, and then the vacuum pump ( 15 ) depressurizes to desorb and obtain a CO 2  product gas;   the liquid CO 2  preparation system comprises a CO 2  booster ( 20 ), a CO 2  purification tower ( 22 ), a CO 2  condenser ( 24 ), a CO 2  evaporator ( 23 ) and a CO 2  subcooler ( 46 ), configured to further purify and liquefy the desorbed CO 2  product gas to obtain a high-purity liquid CO 2  product;   the high-purity liquid nitrogen preparation system comprises a blower ( 47 ), a nitrogen booster ( 34 ), a nitrogen cooler ( 32 ), an expansion cooling system ( 31 ), a nitrogen liquefier ( 33 ), a gas-liquid separator ( 43 ) and a low-temperature separation system ( 42 ), configured to further purify and liquefy exhaust gas of the plurality of pressure swing adsorption towers ( 13 ,  14 ) to obtain a liquid nitrogen product;   when the system is in operation, compression heat generated by compressing CO 2  in the liquid CO 2  preparation system is used to assist the operation of the plurality of pressure swing adsorption towers ( 13 ,  14 ); a part of fluid produced by the nitrogen liquefier ( 33 ) of the high-purity liquid nitrogen preparation system is drawn out to be used as a cold source for the liquid CO 2  preparation system; dry exhaust gas produced by the high-purity liquid nitrogen preparation system is used in the water cooling tower ( 3 ) of the flue gas boosting and cooling system to recover cooling capacity;   the flue gas boosting and cooling system, the CO 2 /N 2  front-end separation system, the liquid CO 2  preparation system and the high-purity liquid nitrogen preparation system, as well as various devices and equipments in each system, are connected through pipelines and valves.   
     
     
         2 . The system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas according to  claim 1 , wherein in the flue gas boosting and cooling system, the flue gas is pressurized to a required pressure by the flue gas booster ( 1 ), and the pressurized flue gas is sent to the flue gas cooling tower ( 2 ) for washing and cooling; the flue gas cooling tower ( 2 ) is structurally divided into two sections, and one part of ambient temperature circulating water is pumped into a middle and lower part of the flue gas cooling tower ( 2 ) through a first water valve ( 6 ), and another part of ambient temperature circulating water is pumped into the water cooling tower ( 3 ) through a second water valve ( 7 ); low-temperature water is pumped into an upper part of the flue gas cooling tower through a third water valve ( 8 ) and the low-temperature water pump ( 4 ), which is cooled by the dry nitrogen discharged from the high-purity liquid nitrogen preparation system and chiller unit ( 5 ); during the shutdown of the high-purity liquid nitrogen preparation system, a fourth water valve ( 9 ) is opened to cool the flue gas by circulating the low-temperature water in the upper part. 
     
     
         3 . The system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas according to  claim 1 , wherein in the CO 2 /N 2  front-end separation system, inlets of the plurality of pressure swing adsorption towers ( 13 ,  14 ) are connected to the flue gas treated by the flue gas cooling tower ( 2 ) through a first gas valve ( 12 ) to continuously adsorb and capture CO 2  in the flue gas; an inlet of the vacuum pump ( 15 ) is connected to the plurality of pressure swing adsorption towers ( 13 ,  14 ), and after the adsorption is completed, the vacuum pump ( 15 ) is used to desorb and regenerate the pressure swing adsorption towers that have been saturated with adsorption; an outlet of the vacuum pump ( 15 ) is connected to the CO 2  buffer device ( 16 ), and desorbed gas is sent to the CO 2  buffer device ( 16 ); a gas that is not adsorbed by the plurality of pressure swing adsorption towers ( 13 ,  14 ) is sent to the adsorption tail gas buffer device ( 19 ) through a second gas valve ( 18 ) as an adsorption tail gas. 
     
     
         4 . The system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas according to  claim 1 , wherein in the liquid CO 2  preparation system, an inlet of the CO 2  booster ( 20 ) is connected to a gas in the CO 2  buffer device ( 16 ) through a third gas valve ( 17 ), and a pressurized hot fluid is connected to the plurality of pressure swing adsorption towers ( 13 ,  14 ) through valves to improve regeneration and desorption efficiency of the pressure swing adsorption towers, and the hot fluid is cooled and returned to the CO 2  evaporator ( 23 ) of the liquid CO 2  preparation system through an eighth gas valve ( 21 ) as a heat source, the fluid is then further cooled and sent to the CO 2  subcooler ( 46 ) for condensation and liquefaction, and then it is sent to a middle part of the CO 2  purification tower ( 22 ) for low-temperature separation to obtain the high-purity liquid CO 2  product at a bottom of the CO 2  evaporator ( 23 ). 
     
     
         5 . The system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas according to  claim 1 , wherein a part of low-temperature fluid is drawn out from a middle and upper part of the nitrogen liquefier ( 33 ) of the high-purity liquid nitrogen preparation system and connected to a cold source inlet of the CO 2  subcooler ( 46 ) through a fourth gas valve ( 44 ) to serve as a cold source to condense and liquefy the CO 2  gas from the CO 2  evaporator ( 23 ); after heat exchange in the CO 2  subcooler ( 46 ), the low-temperature fluid is connected from a cold source outlet of the CO 2  subcooler ( 46 ) to an inlet of the blower ( 47 ) of the high-purity liquid nitrogen preparation system through a fifth gas valve ( 25 ), and returned to the high-purity liquid nitrogen preparation system for recycling. 
     
     
         6 . The system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas according to  claim 1 , further comprising an external refrigerant circulation refrigeration system, wherein the external refrigerant circulation refrigeration system comprises a refrigerant compressor ( 26 ), a refrigerant cooler ( 27 ), a refrigerant heat regenerator ( 28 ) and a refrigerant throttle valve ( 29 ); a refrigerant outlet of the CO 2  condenser ( 24 ) is connected to the refrigerant heat regenerator ( 28 ), a refrigerant flowing out of the refrigerant outlet of the CO 2  condenser ( 24 ) is reheated by the refrigerant heat regenerator ( 28 ), pressurized by the refrigerant compressor ( 26 ), cooled by the refrigerant cooler ( 27 ), cooled by the refrigerant heat regenerator ( 28 ) and throttled by the refrigerant throttle valve ( 29 ), and then returns to a refrigerant inlet of the CO 2  condenser ( 24 ) to complete the refrigerant circulation refrigeration. 
     
     
         7 . The system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas according to  claim 1 , wherein in the high-purity liquid nitrogen preparation system, gas from the adsorption tail gas buffer device ( 19 ) is combined with gas from the outlet of the CO 2  subcooler ( 46 ) after boosted by the blower ( 47 ) through a sixth gas valve ( 30 ), and then connected to a hot-end inlet of the nitrogen liquefier ( 33 ) through a seventh gas valve ( 48 ), it is cooled by the nitrogen liquefier ( 33 ), and then sent to the low-temperature separation system ( 42 ) for separation and purification to obtain high-purity nitrogen; meanwhile, a part of the fluid extracted from the middle and upper part of the nitrogen liquefier ( 33 ) is sent to the CO 2  subcooler ( 46 ) of the liquid CO 2  preparation system through the fourth gas valve ( 44 ) to serve as a cold source; the high-purity nitrogen from the low-temperature separation system ( 42 ) is connected to a cold-end inlet of the nitrogen liquefier ( 33 ), reheated by the nitrogen liquefier ( 33 ), and then connected to an inlet of the nitrogen booster ( 34 ); gas from an outlet of the nitrogen booster ( 34 ) is cooled by the nitrogen cooler ( 32 ) and enters the expansion cooling system ( 31 ) for pressurization and expansion, and is connected to the hot-end inlet of the nitrogen liquefier ( 33 ) to provide the cooling capacity required by the nitrogen liquefier ( 33 ); low-temperature high-pressure gas from the nitrogen liquefier ( 33 ) is connected to the gas-liquid separator ( 43 ) through a high-pressure throttle valve ( 45 ); gas at the top of the gas-liquid separator ( 43 ) is reheated by the nitrogen liquefier ( 33 ) and returned to the inlet of the nitrogen booster ( 34 ); liquid at the bottom outlet of the gas-liquid separator ( 43 ) is sent to the low-temperature separation system ( 42 ); low-pressure exhaust gas from the low-temperature separation system ( 42 ) is reheated by the nitrogen liquefier ( 33 ) and is connected to the inlet of the water cooling tower ( 3 ) in the flue gas boosting and cooling system through a ninth gas valve ( 55 ) to cool circulating water; the low-temperature separation system ( 42 ) sends out a subcooled high-purity liquid nitrogen product. 
     
     
         8 . The system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas according to  claim 1 , wherein the flue gas booster ( 1 ) is a multi-stage centrifugal compressor or blower. 
     
     
         9 . The system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas according to  claim 1 , wherein the CO 2  buffer device ( 16 ) and the adsorption tail gas buffer device ( 19 ) are separately selected as an air bag or a buffer tank. 
     
     
         10 . A method for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas, wherein the flue gas is treated in the system for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas according to  claim 1 , to obtain the liquid nitrogen product and the liquid carbon dioxide product.