A system and method for simultaneous recovery of nitrogen and carbon dioxide from boiler flue gas.

Abstract

This invention provides a system and method for simultaneously recovering nitrogen and carbon dioxide from boiler flue gas. The system includes: a flue gas pretreatment system for dehydrating and cooling the boiler flue gas; a carbon-nitrogen separation system connected to the flue gas pretreatment system for pressure swing adsorption (PSA) of the pretreated flue gas to separate nitrogen-containing vent gas and crude carbon dioxide gas, wherein the adsorption pressure of the carbon-nitrogen separation system is 0.20-0.40 MPa; a carbon dioxide secondary purification system connected to the carbon-nitrogen separation system for secondary purification of the crude carbon dioxide gas separated by the carbon-nitrogen separation system; and a nitrogen concentration and purification system connected to both the carbon-nitrogen separation system and the carbon dioxide secondary purification system for purifying the nitrogen-containing vent gas separated by the carbon-nitrogen separation system and the vent gas generated by the carbon dioxide secondary purification system. The system of this invention can recover carbon dioxide and nitrogen to the maximum extent, generates no waste, and has low energy consumption.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of recycling of boiler flue gas, and particularly relates to a system and method for synchronous recovery of nitrogen and carbon dioxide from boiler flue gas. BACKGROUND

[0002] Carbon dioxide capture and reuse of coal-fired boiler flue gas is an important measure to reduce carbon emissions, and the nitrogen content in the venting gas after recovery of carbon dioxide is about 90%, and recovery thereof can improve nitrogen production efficiency and reduce energy consumption, thereby further reducing carbon emissions.

[0003] Chinese Patent Application CN107899376A discloses a combined capture and recovery device and method for carbon dioxide and nitrogen in flue gas, which comprises a flue gas treatment system, a first CO2 membrane separation unit, a second CO2 membrane separation unit and an N2 membrane separation unit. The device belongs to a membrane recovery mode, and although it can simultaneously capture carbon dioxide and nitrogen, the product purity is low, the membrane barrel has a high requirement for the cleanliness of the gas source, the device is prone to blockage during use, has a short service life, and the membrane barrel is expensive, which is not suitable for industrial mass production.

[0004] Chinese Patent Application CN110498416A discloses a system for synchronous recovery of carbon dioxide and nitrogen from boiler flue gas of a coal-fired power plant, which comprises 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 high-purity nitrogen system. The system can capture carbon dioxide and nitrogen to the maximum extent, and the product purity is high, but the device operation is not flexible, and the energy consumption is high. When the nitrogen yield of the later stage is reduced or no capture is performed, the pressure compression value of the former stage is too high, and the power consumption is large.

[0005] Therefore, it is necessary to provide an improved technical solution for the above-mentioned deficiencies of the prior art. SUMMARY

[0006] The present application aims to provide a system and method for synchronous recovery of nitrogen and carbon dioxide from boiler flue gas to solve or alleviate the problems in the prior art.

[0007] In order to achieve the above-mentioned purpose, the present application provides the following technical solution:

[0008] A system for synchronous recovery of nitrogen and carbon dioxide from boiler flue gas, the system comprising:

[0009] a flue gas pretreatment system for dehydrating and cooling the boiler flue gas;

[0010] A carbon-nitrogen separation system, connected to the flue gas pretreatment system, is used for pressure swing adsorption of pretreated flue gas and separation of nitrogen-containing vent gas and crude carbon dioxide gas. The adsorption pressure of the carbon-nitrogen separation system is 0.20-0.40 MPa.

[0011] A secondary carbon dioxide purification system, connected to the carbon-nitrogen separation system, is used to further purify the crude carbon dioxide gas separated by the carbon-nitrogen separation system.

[0012] A nitrogen concentration and purification system is connected to the carbon-nitrogen separation system and the carbon dioxide secondary purification system, and is used to purify the nitrogen-containing vent gas separated by the carbon-nitrogen separation system and the vent gas generated by the carbon dioxide secondary purification system.

[0013] The boiler flue gas synchronous recovery system for nitrogen and carbon dioxide as described above may optionally include a first cooler, a first gas-liquid separator, and a flue gas induced draft fan. The inlet of the first cooler is connected to the boiler flue, the outlet of the first cooler is connected to the inlet of the first gas-liquid separator, the outlet of the first gas-liquid separator is connected to the inlet of the flue gas induced draft fan, and the outlet of the flue gas induced draft fan is connected to the carbon-nitrogen separation system.

[0014] As described above, the system for simultaneously recovering nitrogen and carbon dioxide from boiler flue gas may optionally include a flue gas compressor, a second gas-liquid separator, a first dryer, a first adsorption tower group, a first vacuum pump, and a first buffer tank. The first adsorption tower group includes multiple first adsorption towers connected in parallel, each filled with a first adsorbent. The inlet of the flue gas compressor is connected to the flue gas pretreatment system, the outlet of the flue gas compressor is connected to the inlet of the second gas-liquid separator, the outlet of the second gas-liquid separator is connected to the inlet of the first dryer, the outlet of the first dryer is connected to the inlet of the first adsorption tower group, the top outlet of the first adsorption tower group is nitrogen-containing vent gas, and the bottom outlet is crude carbon dioxide gas. The top outlet of the first adsorption tower group is connected to the nitrogen concentration and purification system, the bottom outlet of the first adsorption tower group is connected to the inlet of the first vacuum pump, the outlet of the first vacuum pump is connected to the inlet of the first buffer tank, and the outlet of the first buffer tank is connected to the carbon dioxide secondary purification system.

[0015] In the boiler flue gas synchronous recovery system described above, optionally, the nitrogen volume concentration in the nitrogen-containing exhaust gas is 88%-90%, and the carbon dioxide volume concentration in the crude carbon dioxide gas is 45%-80%.

[0016] The boiler flue gas synchronous recovery system for nitrogen and carbon dioxide as described above may optionally include a carbon dioxide secondary purification system comprising a first carbon dioxide compressor, a third gas-liquid separator, a second adsorption tower group, a second vacuum pump, and a second buffer tank. The second adsorption tower group comprises multiple second adsorption towers connected in parallel, each filled with a second adsorbent. The inlet of the first carbon dioxide compressor is connected to the carbon-nitrogen separation system, the outlet of the first carbon dioxide compressor is connected to the inlet of the third gas-liquid separator, the outlet of the third gas-liquid separator is connected to the inlet of the second adsorption tower group, the top outlet of the second adsorption tower group is connected to the nitrogen concentration and purification system, the bottom outlet of the second adsorption tower group is connected to the inlet of the second vacuum pump, and the outlet of the second vacuum pump is connected to the inlet of the second buffer tank.

[0017] The system for simultaneously recovering nitrogen and carbon dioxide from boiler flue gas, as described above, may optionally include a nitrogen concentration and purification system comprising a third buffer tank, a nitrogen compressor, a second dryer, a filter, and a third adsorption tower group. The third adsorption tower group comprises multiple third adsorption towers connected in parallel, each filled with a third adsorbent. The inlet of the third buffer tank is connected to the carbon-nitrogen separation system and the secondary carbon dioxide purification system; the outlet of the third buffer tank is connected to the inlet of the nitrogen compressor; the outlet of the nitrogen compressor is connected to the inlet of the second dryer; the outlet of the second dryer is connected to the inlet of the filter; the outlet of the filter is connected to the inlet of the third adsorption tower group; and product nitrogen is obtained from the top outlet of the third adsorption tower group.

[0018] In the boiler flue gas synchronous recovery system described above, optionally, the adsorption pressure of the third adsorption tower is 0.7-1.0 MPa, and the volume concentration of the product nitrogen is 99%-99.999%.

[0019] The system for simultaneous recovery of nitrogen and carbon dioxide from boiler flue gas as described above may optionally include a carbon dioxide refining and liquefaction system connected to the secondary carbon dioxide purification system for refining carbon dioxide.

[0020] The boiler flue gas synchronous nitrogen and carbon dioxide recovery system described above may optionally include a carbon dioxide refining and liquefaction system comprising a second cooler, a fourth gas-liquid separator, a second carbon dioxide compressor, a fourth buffer tank, a desulfurization tower group, a drying tower group, a third cooler, a liquefaction module, a distillation module, and a carbon dioxide storage tank. The inlet of the second cooler is connected to the carbon dioxide secondary purification system; the outlet of the second cooler is connected to the inlet of the fourth gas-liquid separator; the outlet of the fourth gas-liquid separator is connected to the inlet of the second carbon dioxide compressor; the outlet of the second carbon dioxide compressor is connected to the inlet of the fourth buffer tank; the outlet of the fourth buffer tank is connected to the inlet of the desulfurization tower group; the outlet of the desulfurization tower group is connected to the inlet of the drying tower group; the outlet of the drying tower group is connected to the inlet of the third cooler; the outlet of the third cooler is connected to the inlet of the liquefaction module; the outlet of the liquefaction module is connected to the inlet of the distillation module; and the bottom outlet of the distillation module is connected to the carbon dioxide storage tank. This invention also proposes a method for simultaneous recovery of nitrogen and carbon dioxide from boiler flue gas. The method employs the system described above for simultaneous recovery of nitrogen and carbon dioxide from boiler flue gas, and includes the following steps:

[0021] Step (1): The boiler flue gas is introduced into the flue gas pretreatment system for dehydration and cooling to obtain pretreated flue gas.

[0022] Step (2): The pretreated flue gas is introduced into the carbon-nitrogen separation system for pressure swing adsorption pretreatment and separation of nitrogen-containing vent gas and crude carbon dioxide gas. The adsorption pressure of the carbon-nitrogen separation system is 0.20-0.4 MPa.

[0023] Step (3): The crude carbon dioxide gas separated by the carbon-nitrogen separation system is passed into the carbon dioxide secondary purification system for secondary purification to obtain purified carbon dioxide gas and generate nitrogen-containing vent gas.

[0024] Step (4): The nitrogen-containing vent gas separated by the carbon-nitrogen separation system and the nitrogen-containing vent gas generated by the carbon dioxide secondary purification system are passed into the nitrogen concentration and purification system for purification to obtain product nitrogen.

[0025] Preferably, after step (3), the method further includes step (31), in which purified carbon dioxide gas is introduced into a carbon dioxide refining and liquefaction system for refining to obtain refined carbon dioxide gas.

[0026] Beneficial effects:

[0027] (1) The boiler flue gas synchronous recovery system of the present invention can recover carbon dioxide and nitrogen to the maximum extent and generate no waste. In addition, the carbon-nitrogen separation system of the present invention uses a low-pressure adsorption mode of 0.20-0.40MPa to separate carbon dioxide and nitrogen, which changes the previous technology of adsorption at 1.0MPa, and effectively reduces energy consumption.

[0028] (2) In the carbon-nitrogen separation system of the present invention, the desorption gas is desorbed by a vacuum pump, which not only reduces energy consumption, but also improves the carbon dioxide recovery rate.

[0029] (3) The nitrogen concentration and purification system of the present invention adopts a secondary compression mode and has a secondary pressure boosting process. The compressor model and compression pressure can be selected according to the actual nitrogen demand of the user, thereby further achieving the purpose of energy saving. Attached Figure Description

[0030] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0031] Figure 1 This is a schematic diagram of the process for the simultaneous recovery of nitrogen and carbon dioxide from boiler flue gas according to an embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of the flue gas pretreatment system according to an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of the carbon-nitrogen separation system according to an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram of the carbon dioxide secondary purification system according to an embodiment of the present invention;

[0035] Figure 5 This is a schematic diagram of the carbon dioxide refining and liquefaction system according to an embodiment of the present invention;

[0036] Figure 6 This is a schematic diagram of the nitrogen concentration and purification system according to an embodiment of the present invention.

[0037] Icon labels:

[0038] 1- Flue gas pretreatment system; 2- Carbon-nitrogen separation system; 3- Carbon dioxide secondary purification system; 4- Carbon dioxide refining and liquefaction system; 5- Nitrogen concentration and purification system;

[0039] 11-First cooler; 12-First gas-liquid separator; 13-Flue gas induced draft fan;

[0040] 21-Flue gas compressor; 22-Second gas-liquid separator; 23-First dryer; 24-First adsorption tower group; 25-First vacuum pump;

[0041] 31-First carbon dioxide compressor; 32-Third gas-liquid separator; 33-Second adsorption tower assembly; 34-Second vacuum pump; 35-Second buffer tank;

[0042] 41-Second cooler; 42-Fourth gas-liquid separator; 43-Second carbon dioxide compressor; 43a-Fourth buffer tank; 44-Desulfurization tower group; 45-Drying tower group; 46-Third cooler; 47-Liquefaction module; 48-Distillation module; 49-Carbon dioxide storage tank;

[0043] 51-Third buffer tank; 52-Nitrogen compressor; 53-Second dryer; 54-Filter; 55-Third adsorption tower group. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0045] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0046] To address the problems existing in the prior art, this invention proposes an energy-saving system for the simultaneous recovery of nitrogen and carbon dioxide from boiler flue gas, such as... Figure 1 As shown, the system includes a flue gas pretreatment system 1, a carbon-nitrogen separation system 2, a carbon dioxide secondary purification system 3, a carbon dioxide refining and liquefaction system 4, and a nitrogen concentration and purification system 5.

[0047] The system comprises: a flue gas pretreatment system 1 for dehydrating and cooling boiler flue gas; a carbon-nitrogen separation system 2 connected to the flue gas pretreatment system 1 for pressure swing adsorption of the pretreated flue gas and separation of nitrogen-containing vent gas and crude carbon dioxide gas, wherein the adsorption pressure of the carbon-nitrogen separation system 2 is 0.20-0.40 MPa; a carbon dioxide secondary purification system 3 connected to the carbon-nitrogen separation system 2 for secondary purification of the crude carbon dioxide gas separated by the carbon-nitrogen separation system 2; a nitrogen concentration and purification system 5 connected to the carbon-nitrogen separation system 2 and the carbon dioxide secondary purification system 3 for purifying the nitrogen-containing vent gas separated by the carbon-nitrogen separation system 2 and the vent gas generated by the carbon dioxide secondary purification system 3; and a carbon dioxide refining and liquefaction system 4 connected to the carbon dioxide secondary purification system 3 for refining carbon dioxide.

[0048] The carbon-nitrogen separation system 2 of the present invention uses a low-pressure adsorption mode of 0.20-0.40 MPa (e.g., 0.20 MPa, 0.22 MPa, 0.25 MPa, 0.27 MPa, 0.30 MPa, 0.32 MPa, 0.35 MPa, 0.37 MPa or 0.40 MPa) to separate carbon dioxide and nitrogen, which changes the previous technology that adsorbed at 1.0 MPa, and effectively reduces energy consumption.

[0049] like Figure 2 As shown, in an optional embodiment of the present invention, the flue gas pretreatment system 1 includes a first cooler 11, a first gas-liquid separator 12, and a flue gas induced draft fan 13. The inlet of the first cooler 11 is connected to the boiler flue, the outlet of the first cooler 11 is connected to the inlet of the first gas-liquid separator 12, the outlet of the first gas-liquid separator 12 is connected to the inlet of the flue gas induced draft fan 13, and the outlet of the flue gas induced draft fan 13 is connected to the carbon-nitrogen separation system 2.

[0050] like Figure 3 As shown, in an optional embodiment of the present invention, the carbon-nitrogen separation system 2 includes a flue gas compressor 21, a second gas-liquid separator 22, a first dryer 23, a first adsorption tower group 24, a first vacuum pump 25, and a first buffer tank (not shown). The first adsorption tower group 24 includes multiple first adsorption towers arranged in parallel, each first adsorption tower being filled with a first adsorbent. The inlet of the flue gas compressor 21 is connected to the outlet of the flue gas induced draft fan 13 of the flue gas pretreatment system 1, and the outlet of the flue gas compressor 21 is connected to the inlet of the second gas-liquid separator 22. The outlet of separator 22 is connected to the inlet of the first dryer 23, the outlet of the first dryer 23 is connected to the inlet of the first adsorption tower group 24, the top outlet of the first adsorption tower group 24 is nitrogen-containing vent gas, the bottom outlet is crude carbon dioxide gas, the top outlet of the first adsorption tower group 24 is connected to the nitrogen concentration and purification system 5, the bottom outlet of the first adsorption tower group 24 is connected to the inlet of the first vacuum pump 25, the outlet of the first vacuum pump 25 is connected to the inlet of the first buffer tank, and the outlet of the first buffer tank is connected to the carbon dioxide secondary purification system 3.

[0051] The nitrogen volume concentration in the nitrogen-containing exhaust gas of the present invention is 88%-90% (e.g., 88%, 89% or 90%), and the carbon dioxide volume concentration in the crude carbon dioxide gas is 45%-80% (e.g., 45%, 46%, 47%, 48%, 49%, 50%, 60%, 70% or 80%).

[0052] Furthermore, a first pneumatic valve is installed on the pipe connecting to the outlet of the flue gas compressor 21, and a first solenoid valve is installed on the first pneumatic valve. The first solenoid valve is electrically connected to the PLC, so that the first pneumatic valve is controlled by the PLC through the first solenoid valve.

[0053] In this embodiment, the flue gas treated by the flue gas pretreatment system 1 is compressed to about 0.25 MPa by the flue gas compressor 21 and enters the first adsorption tower group 24. The PLC controls the first pneumatic valve through the first solenoid valve to ensure the different working states of the different first adsorption towers. The gas at the top of the tower is nitrogen-rich gas, which enters the nitrogen concentration and purification system as raw material gas. The gas at the bottom of the tower is about 50% crude carbon dioxide gas, which is used as raw material gas for the next stage.

[0054] like Figure 4 As shown, in an optional embodiment of the present invention, the carbon dioxide secondary purification system 3 includes a first carbon dioxide compressor 31, a third gas-liquid separator 32, a second adsorption tower group 33, a second vacuum pump 34, and a second buffer tank 35. The second adsorption tower group 33 includes multiple second adsorption towers connected in parallel, each of which is filled with a second adsorbent. The inlet of the first carbon dioxide compressor 31 is connected to the outlet of the first buffer tank in the carbon-nitrogen separation system 2, the outlet of the first carbon dioxide compressor 31 is connected to the inlet of the third gas-liquid separator 32, the outlet of the third gas-liquid separator 32 is connected to the inlet of the second adsorption tower group 33, the top outlet of the second adsorption tower group 33 is connected to the nitrogen concentration and purification system 5, the bottom outlet of the second adsorption tower group 33 is connected to the inlet of the second vacuum pump 34, and the outlet of the second vacuum pump 34 is connected to the inlet of the second buffer tank 35.

[0055] Preferably, a second pneumatic valve is provided on the pipe connecting to the outlet of the first carbon dioxide compressor 31, and a second solenoid valve is provided on the second pneumatic valve. The second solenoid valve is electrically connected to the PLC, so that the second pneumatic valve is controlled by the PLC through the second solenoid valve.

[0056] In this embodiment, multiple second adsorption towers are provided, and the second pneumatic valve is controlled by the PLC through the second solenoid valve to ensure different working states of different second adsorption towers. The gas at the top of the tower is nitrogen-rich gas that enters the nitrogen concentration and purification system as raw material gas or is vented. The gas at the bottom of the tower is carbon dioxide gas with a purity of about 95%, which is used as raw material gas for refined carbon dioxide.

[0057] like Figure 5As shown, in an optional embodiment of the present invention, the carbon dioxide refining and liquefaction system 4 includes a second cooler 41, a fourth gas-liquid separator 42, a second carbon dioxide compressor 43, a fourth buffer tank 43a, a desulfurization tower group 44, a drying tower group 45, a third cooler 46, a liquefaction module 47, a distillation module 48, and a carbon dioxide storage tank 49; wherein, the inlet of the second cooler 41 is connected to the desorbed gas of the carbon dioxide secondary purification system 3 (i.e., connected to the outlet of the second buffer tank 35), the outlet of the second cooler 41 is connected to the inlet of the fourth gas-liquid separator 42, and the outlet of the fourth gas-liquid separator 42 is connected to the inlet of the second carbon dioxide compressor 43, compressing carbon dioxide to 2.5 MPa. Carbon dioxide gas enters the inlet of the fourth buffer tank 43a from the outlet of the second carbon dioxide compressor 43. The outlet of the fourth buffer tank 43a is connected to the inlet of the desulfurization tower group 44. After desulfurization by impurity sulfur, it enters the inlet of the drying tower group 45 from the outlet of the desulfurization tower group 44 for deep drying and dehydration. The outlet of the drying tower group 45 is connected to the inlet of the third cooler 46 for cooling. The outlet of the third cooler 46 is connected to the inlet of the liquefaction module 47. The outlet of the liquefaction module 47 enters the inlet of the distillation module 48. The distillation yields food-grade carbon dioxide product with a volume concentration of ≥99.9%, which enters the carbon dioxide storage tank 49 from the bottom outlet of the distillation module 48 for storage.

[0058] It should be noted that the desulfurization tower group 44 includes multiple desulfurization towers arranged in parallel, the drying tower group 45 includes multiple drying towers arranged in parallel, and the distillation module 48 includes a distillation tower.

[0059] like Figure 6 As shown, in an optional embodiment of the present invention, the nitrogen concentration and purification system 5 includes a third buffer tank 51, a nitrogen compressor 52, a second dryer 53, a filter 54, and a third adsorption tower group 55. The third adsorption tower group 55 includes multiple third adsorption towers arranged in parallel, and the third adsorption towers are filled with a third adsorbent. The inlet of the third buffer tank 51 is connected to the vent of the carbon-nitrogen separation system 2 and the carbon dioxide secondary purification system 3. The outlet of the third buffer tank 51 is connected to the inlet of the nitrogen compressor 52. The outlet of the nitrogen compressor 52 is connected to the inlet of the second dryer 53. The outlet of the second dryer 53 is connected to the inlet of the filter 54. The outlet of the filter 54 is connected to the air inlet of the third adsorption tower group 55. Product nitrogen is obtained from the top outlet of the third adsorption tower group 55.

[0060] Optionally, the adsorption pressure of the third adsorption tower is 0.7-1.0 MPa (e.g., 0.7 MPa, 0.75 MPa, 0.8 MPa, 0.9 MPa or 1.0 MPa), and the volume concentration of nitrogen in the product is 99%-99.999%.

[0061] Understandably, the nitrogen concentration and purification system 5 of the present invention recovers the two sections of vent gas generated by the carbon-nitrogen separation system 2 and the carbon dioxide secondary purification system 3. After compression and filtration, the gas at a pressure of 0.7-1.0 MPa enters the third adsorption tower, which is filled with a third adsorbent. It has a high recovery rate for vent gas with complex composition. After multi-tower pressure swing adsorption separation, product nitrogen with a volume concentration of 99%-99.999% is obtained at the top of the tower.

[0062] It should be noted that the first adsorbent, the second adsorbent, and the third adsorbent used in this invention are all existing adsorbents.

[0063] This invention also proposes a method for simultaneous recovery of nitrogen and carbon dioxide from boiler flue gas, employing the system for simultaneous recovery of nitrogen and carbon dioxide from boiler flue gas as described above. The method includes the following steps:

[0064] Step (1): The boiler flue gas is introduced into the flue gas pretreatment system for dehydration and cooling to obtain pretreated flue gas.

[0065] Step (2): The pretreated flue gas is introduced into the carbon-nitrogen separation system for pressure swing adsorption pretreatment and separation of nitrogen-containing vent gas and crude carbon dioxide gas. The adsorption pressure of the carbon-nitrogen separation system is 0.20-0.40 MPa.

[0066] Step (3): The crude carbon dioxide gas separated by the carbon-nitrogen separation system is passed into the carbon dioxide secondary purification system for secondary purification to obtain purified carbon dioxide gas and generate venting air.

[0067] Step (4): The nitrogen-containing vent air separated by the carbon-nitrogen separation system and the vent air generated by the carbon dioxide secondary purification system are passed into the nitrogen concentration and purification system for purification to obtain product nitrogen.

[0068] Preferably, after step (3), the method further includes step (31), in which purified carbon dioxide gas is introduced into a carbon dioxide refining and liquefaction system for refining to obtain refined carbon dioxide gas.

[0069] The system and method for simultaneous recovery of nitrogen and carbon dioxide from boiler flue gas according to the present invention will be described in detail below through a specific embodiment.

[0070] This invention relates to the recovery of carbon dioxide and nitrogen from flue gas in a coal-fired power plant. The carbon dioxide is used for increased income in smart agriculture, and the nitrogen is used for displacement and purging in the plant's chemical workshop. The composition of the flue gas is shown in Table 1.

[0071] Table 1 Composition of flue gas

[0072]

[0073] refer to Figures 1 to 6 As shown, the required flue gas is drawn from the flue gas emission chimney after desulfurization and denitrification, enters the first cooler 11 for preliminary cooling to about 35°C, enters the first gas-liquid separator 12 for gas-liquid separation, and then enters the flue gas induced draft fan 13. The outlet pressure of the flue gas induced draft fan 13 is 5 kPa.

[0074] Flue gas exiting the flue gas induced draft fan 13 enters the flue gas compressor 21, is compressed to 0.23 MPa, then enters the second gas-liquid separator 22, and then enters the first dryer 23 for deep dehydration. Finally, it enters the first adsorption tower group 24 for adsorption separation. At the top of the tower, vent gas with a nitrogen content of 88-90% is obtained, which serves as the feed gas for the nitrogen concentration and purification system. At the bottom of the tower, after desorption by the first vacuum pump 25, the desorbed gas is crude carbon dioxide gas with a volume content of 45% and a pressure of 15 kPa.

[0075] Crude carbon dioxide gas with a content of 45% is compressed to 0.25 MPa by the first carbon dioxide compressor 31 and enters the third gas-liquid separator 32 for gas-liquid separation. Then it enters the second adsorption tower group 33 for further purification of carbon dioxide. The carbon dioxide secondary purification venting air obtained at the top of the tower is introduced into the raw material gas pipe of the nitrogen concentration and purification system 5. The carbon dioxide gas with a purity of 95% and a pressure of about 15 kPa is obtained by desorption by the second vacuum pump 34 at the bottom of the tower and stored in the second buffer tank 35.

[0076] 95% of the carbon dioxide gas passes through the second cooler 41 and the fourth gas-liquid separator 42 for further cooling and dehydration. Then, it is pressurized to 2.5 MPa by the second carbon dioxide compressor 43 and enters the inlet of the fourth buffer tank 43a. The outlet of the fourth buffer tank 43a is connected to the inlet of the desulfurization tower group 44. Afterward, it sequentially enters the desulfurization tower group 44 and the drying tower group 45 for desulfurization, impurity removal, and drying. Then, it enters the third cooler 46 for further cooling and enters the liquefaction module 47, where it is cooled to -18°C to a liquid state. The liquid carbon dioxide then enters the distillation module 48 for further purification. The bottom of the tower contains 99.9% food-grade carbon dioxide, which is stored in the carbon dioxide storage tank 49. Air is released from the top of the tower as a regeneration gas source for the desulfurization tower group and the drying tower group, saving product gas and reducing energy consumption.

[0077] The vent gas produced at the top of the adsorption tower in the carbon-nitrogen separation system 2 and the carbon dioxide secondary purification system 3 enters the third buffer tank 51, and then enters the nitrogen compressor 52, where it is pressurized to 0.8-1.0 MPa. After being dried and filtered by the second dryer 53 and filter 54, it enters the third adsorption tower group 55 for pressure swing adsorption to obtain product nitrogen gas with a purity ranging from 99.5% to 99.9%.

[0078] In this embodiment, the carbon-nitrogen separation system adopts a low-pressure adsorption mode with an adsorption pressure of 0.25 MPa, which changes the previous technology's adsorption at 1.0 MPa. Furthermore, the desorption gas is desorbed using a vacuum pump, which not only reduces energy consumption but also improves the carbon dioxide recovery rate. The nitrogen concentration and purification system employs a secondary compression mode, increasing the pressure from 0.23 MPa to 0.8–1.0 MPa. The compressor model is selected only based on the actual nitrogen volume required by the user. Compared to compressors designed for large volumes of flue gas, the compressed gas volume here is only 68% of the flue gas compression. In this embodiment, the flue gas compression is increased from 0.01 MPa to 0.8–1.0 MPa, and the vent gas compression is increased from 0.23 MPa to 0.8–1.0 MPa. The compressed gas volume is also reduced to 68%, demonstrating the significant energy-saving effect of the system of this invention.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for simultaneous recovery of nitrogen and carbon dioxide from a boiler flue gas, characterized by; The system comprises: a flue gas pretreatment system for dehydrating and cooling the boiler flue gas; a carbon-nitrogen separation system in communication with the flue gas pretreatment system for pressure swing adsorption of the pretreated flue gas and separation of nitrogen-containing vent gas and crude carbon dioxide gas, the adsorption pressure of the carbon-nitrogen separation system being 0.25 MPa, the nitrogen volume concentration of the nitrogen-containing vent gas being 88%-90%, and the volume concentration of carbon dioxide in the crude carbon dioxide gas being 45% and the pressure being 15 kPa; a carbon dioxide secondary purification system in communication with the carbon-nitrogen separation system for secondary purification of the crude carbon dioxide gas separated by the carbon-nitrogen separation system; a nitrogen concentration and purification system in communication with the carbon-nitrogen separation system and the carbon dioxide secondary purification system for purification of the nitrogen-containing vent gas separated by the carbon-nitrogen separation system and the vent gas generated by the carbon dioxide secondary purification system, the pressure of the nitrogen-containing vent gas separated by the carbon-nitrogen separation system and the vent gas generated by the carbon dioxide secondary purification system being 0.23 MPa; the nitrogen concentration and purification system comprises a third buffer tank, a nitrogen compressor, a second dryer, a filter, and a third adsorption tower group, the third adsorption tower group comprising a plurality of third adsorption towers arranged in parallel, the third adsorption towers being filled with a third adsorbent; wherein the inlet of the third buffer tank is in communication with the carbon-nitrogen separation system and the carbon dioxide secondary purification system, the outlet of the third buffer tank is in communication with the inlet of the nitrogen compressor, the outlet of the nitrogen compressor is in communication with the inlet of the second dryer, the outlet of the second dryer is in communication with the inlet of the filter, the outlet of the filter is in communication with the gas inlet of the third adsorption tower group, and the top gas outlet of the third adsorption tower group obtains product nitrogen gas; the adsorption pressure of the third adsorption towers is 0.7-1.0 MPa, and the volume concentration of the product nitrogen gas is 99%-99.999%.

2. The system for simultaneous recovery of nitrogen and carbon dioxide from a boiler flue gas according to claim 1, wherein, the flue gas pretreatment system comprises a first cooler, a first gas-liquid separator, and a flue gas induced draft fan, the inlet of the first cooler is connected to the boiler flue gas, the outlet of the first cooler is connected to the inlet of the first gas-liquid separator, the outlet of the first gas-liquid separator is connected to the inlet of the flue gas induced draft fan, and the outlet of the flue gas induced draft fan is connected to the carbon-nitrogen separation system.

3. The system for simultaneous recovery of nitrogen and carbon dioxide from a boiler flue gas according to claim 1, wherein, the carbon-nitrogen separation system comprises a flue gas compressor, a second gas-liquid separator, a first dryer, a first adsorption tower group, a first vacuum pump, and a first buffer tank, the first adsorption tower group comprises a plurality of first adsorption towers arranged in parallel, each of the first adsorption towers being filled with a first adsorbent; The flue gas compressor is connected with the flue gas pretreatment system at the inlet, and connected with the second gas-liquid separator at the outlet. The outlet of the second gas-liquid separator is connected with the inlet of the first desiccator. The outlet of the first desiccator is connected with the gas inlet of the first adsorption tower group. The top gas outlet of the first adsorption tower group is the nitrogen-containing vent gas, and the bottom gas outlet is the crude carbon dioxide gas. The top gas outlet of the first adsorption tower group is connected with the nitrogen concentration and purification system. The bottom gas outlet of the first adsorption tower group is connected with the inlet of the first vacuum pump. The outlet of the first vacuum pump is connected with the inlet of the first buffer tank. The outlet of the first buffer tank is connected with the carbon dioxide secondary purification system.

4. The system for simultaneous recovery of nitrogen and carbon dioxide from a boiler flue gas according to claim 1, wherein, The carbon dioxide secondary purification system comprises a first carbon dioxide compressor, a third gas-liquid separator, a second adsorption tower group, a second vacuum pump and a second buffer tank. The second adsorption tower group comprises a plurality of second adsorption towers connected in parallel. Each second adsorption tower is filled with a second adsorbent. The first carbon dioxide compressor is connected with the carbon-nitrogen separation system at the inlet. The outlet of the first carbon dioxide compressor is connected with the inlet of the third gas-liquid separator. The outlet of the third gas-liquid separator is connected with the gas inlet of the second adsorption tower group. The top gas outlet of the second adsorption tower group is connected with the nitrogen concentration and purification system. The bottom gas outlet of the second adsorption tower group is connected with the inlet of the second vacuum pump. The outlet of the second vacuum pump is connected with the inlet of the second buffer tank.

5. The system for simultaneous recovery of nitrogen and carbon dioxide from a boiler flue gas according to claim 1, wherein, The system further comprises a carbon dioxide refining and liquefaction system connected with the carbon dioxide secondary purification system for refining and liquefying carbon dioxide.

6. The system for simultaneous recovery of nitrogen and carbon dioxide from a boiler flue gas according to claim 5, wherein, The carbon dioxide refining and liquefaction system comprises a second cooler, a fourth gas-liquid separator, a second carbon dioxide compressor, a fourth buffer tank, a desulfurization tower group, a drying tower group, a third cooler, a liquefaction module, a rectification module and a carbon dioxide storage tank. The inlet of the second cooler is connected with the carbon dioxide secondary purification system. The outlet of the second cooler is connected with the inlet of the fourth gas-liquid separator. The outlet of the fourth gas-liquid separator is connected with the inlet of the second carbon dioxide compressor. The outlet of the second carbon dioxide compressor is connected with the inlet of the fourth buffer tank. The outlet of the fourth buffer tank is connected with the inlet of the desulfurization tower group. The outlet of the desulfurization tower group is connected with the inlet of the drying tower group. The outlet of the drying tower group is connected with the inlet of the third cooler. The outlet of the third cooler is connected with the inlet of the liquefaction module. The outlet of the liquefaction module is connected with the inlet of the rectification module. The bottom outlet of the rectification module is connected with the carbon dioxide storage tank.

7. A method of simultaneous recovery of nitrogen and carbon dioxide from a boiler flue gas, characterized by, The method for synchronously recovering nitrogen and carbon dioxide by using the system for synchronously recovering nitrogen and carbon dioxide from boiler flue gas according to any one of claims 1-6 comprises the following steps: Step (1), passing the boiler flue gas into the flue gas pretreatment system to remove water and cool, to obtain pretreated flue gas; Step (2), passing the pretreated flue gas into the carbon-nitrogen separation system to separate carbon dioxide and nitrogen, to obtain a carbon dioxide-containing gas and a nitrogen-containing gas; Step (2), the flue gas after the pretreatment is introduced into a carbon-nitrogen separation system, a pressure swing adsorption pretreatment is carried out, and nitrogen-containing vent gas and crude carbon dioxide gas are separated, wherein the adsorption pressure of the carbon-nitrogen separation system is 0.25 MPa; Step (3), the crude carbon dioxide gas separated by the carbon-nitrogen separation system is introduced into a carbon dioxide secondary purification system, a secondary purification is carried out, purified carbon dioxide gas is obtained, and nitrogen-containing vent gas is generated; Step (4), the nitrogen-containing vent gas separated by the carbon-nitrogen separation system and the nitrogen-containing vent gas generated by the carbon dioxide secondary purification system are introduced into a nitrogen gas concentration purification system, a purification is carried out, and product nitrogen gas is obtained; the pressure of the nitrogen-containing vent gas is 0.23 MPa, and the adsorption pressure of the nitrogen gas concentration purification system is 0.7-1.0 MPa; Step (3) further comprises: step (31), the purified carbon dioxide gas is introduced into a carbon dioxide refining liquefaction system, a refining treatment is carried out, and refined carbon dioxide gas is obtained.

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