A method and system for capturing CO2 from a low CO2 concentration gas mixture.

Abstract

The present disclosure relates to a method and system for capturing CO2 from a low CO2 concentration mixed gas, which adopts five parallel adsorption towers to realize medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling and low-temperature cooling of CO2 respectively, and utilizes the once medium-temperature adsorption tail gas after medium-temperature adsorption to cool the adsorbent after desorption, and utilizes the once low-temperature adsorption tail gas after low-temperature adsorption to cool the adsorbent after medium-temperature cooling, effectively coupling the internal heat of the system, avoiding the introduction of external air in the cooling link, improving the heat utilization efficiency of the system, realizing the internal energy recovery of the system, and reducing the energy consumption of the system.

Description

Technical Field

[0001] This disclosure relates to a CO2 capture technology, and more specifically, to a method and system for capturing CO2 from a mixture of gases with low CO2 concentrations. Background Technology

[0002] Adsorption and membrane separation CO2 capture technologies have low energy consumption and low environmental risk, making them good carbon emission reduction technologies. By utilizing the performance differences of adsorption and membrane methods under different feed gas CO2 concentration ranges and different temperature ranges, a CO2 capture system that couples adsorption and membrane methods can be established to achieve efficient capture of carbon dioxide in mixed gases with low carbon dioxide concentrations. Summary of the Invention

[0003] The purpose of this disclosure is to provide a method and system for capturing CO2 from a low CO2 concentration gas mixture. This method effectively couples the internal heat of the system, avoids the introduction of external air during the cooling process, and reduces the system's energy consumption.

[0004] To achieve the above objectives, a first aspect of this disclosure provides a method for capturing CO2 from a low-CO2-concentration gas mixture, the method comprising:

[0005] S1. A medium-temperature mixed gas containing CO2 is introduced into the first adsorption tower for medium-temperature adsorption to obtain a primary medium-temperature adsorption tail gas.

[0006] S2. After the medium-temperature adsorption in the first adsorption tower is completed, the medium-temperature mixed gas is switched to the second adsorption tower for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the low-temperature mixed gas containing CO2 is introduced into the first adsorption tower for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0007] S3. After the medium-temperature adsorption in the second adsorption tower is completed, the medium-temperature mixed gas is switched to the third adsorption tower for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the first adsorption tower is subjected to a desorption process, and the low-temperature mixed gas is switched to the second adsorption tower for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0008] S4. After the medium-temperature adsorption in the third adsorption tower is completed, the medium-temperature mixed gas is switched to the fourth adsorption tower for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the first adsorption tower is cooled at medium temperature, the second adsorption tower is desorbed, and the low-temperature mixed gas is switched to the third adsorption tower for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0009] S5. After the medium-temperature adsorption of the fourth adsorption tower is completed, the medium-temperature mixed gas is switched to the fifth adsorption tower for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower is cooled at low temperature, the second adsorption tower is cooled at medium temperature, the third adsorption tower is desorbed, and the low-temperature mixed gas is switched to the fourth adsorption tower for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0010] S6. After the medium-temperature adsorption in the fifth adsorption tower is completed, the medium-temperature mixed gas is switched to the first adsorption tower for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the second adsorption tower is cooled at low temperature, the third adsorption tower is cooled at medium temperature, the fourth adsorption tower is desorbed, and the low-temperature mixed gas is switched to the fifth adsorption tower for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0011] S7. After the medium-temperature adsorption in the first adsorption tower is completed, the medium-temperature mixed gas is switched to the second adsorption tower for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the low-temperature mixed gas is switched to the first adsorption tower for low-temperature adsorption to obtain a low-temperature adsorption tail gas; the third adsorption tower is cooled at low temperature, the fourth adsorption tower is cooled at medium temperature, and the fifth adsorption tower is desorbed.

[0012] S8. After the medium-temperature adsorption in the second adsorption tower is completed, the medium-temperature mixed gas is switched to the third adsorption tower for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower is subjected to desorption, and the low-temperature mixed gas is switched to the second adsorption tower for low-temperature adsorption to obtain a low-temperature adsorption tail gas; the fourth adsorption tower is subjected to low-temperature cooling, and the fifth adsorption tower is subjected to medium-temperature cooling.

[0013] S9. After the medium-temperature adsorption in the third adsorption tower is completed, the medium-temperature mixed gas is introduced into the fourth adsorption tower for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower is cooled at medium temperature, the second adsorption tower is desorbed, the low-temperature mixed gas is switched to the third adsorption tower for low-temperature adsorption to obtain a low-temperature adsorption tail gas; the fifth adsorption tower is cooled at low temperature.

[0014] S10. After the medium-temperature adsorption of the fourth adsorption tower is completed, the medium-temperature mixed gas is switched to the fifth adsorption tower for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower is cooled at low temperature, the second adsorption tower is cooled at medium temperature, the third adsorption tower is desorbed, and the low-temperature mixed gas is switched to the fourth adsorption tower for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0015] Repeat steps S6 to S10;

[0016] The first, second, third, fourth, and fifth adsorption towers each contain a CO2 adsorbent; the primary medium-temperature adsorption tail gas is used as the medium-temperature cooling gas and contacts the CO2 adsorbent; the primary low-temperature adsorption tail gas is used as the low-temperature cooling gas and contacts the CO2 adsorbent.

[0017] Optionally, the conditions for the mesophilic adsorption include: the mesophilic mixed gas entering the adsorption tower from the inlet at the bottom of the adsorption tower, and the CO2-removed tail gas from the outlet at the top of the adsorption tower; the duration of the mesophilic adsorption is 5–120 min; the volume content of CO2 in the mesophilic mixed gas is 15–25%; the inlet temperature of the mesophilic mixed gas is 60–80°C; the outlet temperature of the tail gas from the first mesophilic adsorption is 40–60°C; the temperature of the CO2 adsorbent in the adsorption tower is 20–40°C before the mesophilic adsorption begins; and the condition for determining the completion of the mesophilic adsorption is that the volume content of CO2 in the tail gas from the first mesophilic adsorption is 3–7%.

[0018] Optionally, the conditions for the low-temperature adsorption include: the low-temperature mixed gas entering the adsorption tower from the inlet at the bottom of the adsorption tower, and obtaining the primary low-temperature adsorption tail gas with CO2 removed from the outlet at the top of the adsorption tower; the low-temperature adsorption time is 5–120 min; the volume content of CO2 in the low-temperature mixed gas is 8–20%; the inlet temperature of the low-temperature mixed gas is 20–40°C; the outlet temperature of the primary low-temperature adsorption tail gas is 25–45°C; the temperature of the CO2 adsorbent in the adsorption tower is 40–60°C before the low-temperature adsorption begins; and the condition for determining the completion of the low-temperature adsorption is that the volume content of CO2 in the primary low-temperature adsorption tail gas is 1.5–5%.

[0019] Optionally, the desorption process includes: allowing high-temperature steam to enter the adsorption tower from the inlet at the bottom of the adsorption tower, and obtaining CO2-rich desorbed gas from the outlet at the top of the adsorption tower; the desorption process lasts for 5–120 minutes; the inlet temperature of the high-temperature steam is 100–150°C, the outlet temperature of the desorbed gas is 60–80°C, and the temperature of the CO2 adsorbent in the adsorption tower is 20–40°C before the desorption process begins; the condition for determining the completion of the desorption process is that the volume content of CO2 in the desorbed gas is 40–60%.

[0020] Optionally, the conditions for the intermediate-temperature cooling include: the primary intermediate-temperature adsorption tail gas enters the adsorption tower from the inlet at the bottom of the adsorption tower and exits from the outlet at the top of the adsorption tower; the intermediate-temperature cooling time is 5–120 min; the inlet temperature of the primary intermediate-temperature adsorption tail gas is 40–60°C, and the volume content of CO2 in the primary intermediate-temperature adsorption tail gas is 4–7%; the outlet temperature of the intermediate-temperature adsorption tail gas is 45–65°C, and the volume content of CO2 in the intermediate-temperature adsorption tail gas is 1.5–4%; the temperature of the CO2 adsorbent before the intermediate-temperature cooling is 60–80°C; and the condition for determining the completion of the intermediate-temperature cooling is that the temperature of the CO2 adsorbent in the adsorption tower is 40–60°C.

[0021] Optionally, the conditions for the low-temperature cooling include: the primary low-temperature adsorption tail gas enters the adsorption tower from the inlet at the bottom of the adsorption tower and exits from the outlet at the top of the adsorption tower; the low-temperature cooling time is 5–120 min; the inlet temperature of the primary low-temperature adsorption tail gas is 20–40°C, and the volume content of CO2 in the primary low-temperature adsorption tail gas is 3–5%; the outlet temperature of the low-temperature adsorption tail gas is 25–45°C, and the volume content of CO2 in the low-temperature adsorption tail gas is 0.5–3%; the temperature of the CO2 adsorbent before the low-temperature cooling is 40–60°C; and the condition for determining the completion of the low-temperature cooling is that the temperature of the CO2 adsorbent in the adsorption tower is 20–40°C.

[0022] Optionally, the method further includes: passing the desorbed gas into a membrane separation unit for CO2 separation to obtain CO2 product gas and membrane separation tail gas; allowing the CO2 product gas to enter a purification unit for refining and purification to obtain liquid CO2 product; allowing the membrane separation tail gas to enter an adsorption tower as the medium-temperature mixed gas for medium-temperature adsorption; the CO2 volume content in the CO2 product gas is above 95%, and the CO2 purity in the liquid CO2 product is above 99%; the outlet temperature of the membrane separation tail gas is 60-80℃, and the CO2 volume content in the membrane separation tail gas is 8-30%.

[0023] The second aspect of this disclosure provides a system for capturing CO2 from a low CO2 concentration mixed gas using the method described in the first aspect of this disclosure. The system comprises at least five adsorption towers connected in parallel: a first adsorption tower, a second adsorption tower, a third adsorption tower, a fourth adsorption tower, and a fifth adsorption tower. Each adsorption tower has five parallel inlet programmable valves at its bottom inlet and five parallel outlet programmable valves at its top outlet. At any given time, the five towers are in the operating states of medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling, and low-temperature cooling, respectively. Each adsorption tower sequentially cycles through these five operating states.

[0024] Optionally, each inlet programmable valve includes a first inlet programmable valve, a second inlet programmable valve, a third inlet programmable valve, a fourth inlet programmable valve, and a fifth inlet programmable valve; each outlet programmable valve includes a first outlet programmable valve, a second outlet programmable valve, a third outlet programmable valve, a fourth outlet programmable valve, and a fifth outlet programmable valve; the first inlet programmable valve of each adsorption tower is connected to and connected to the membrane separation tail gas outlet main pipeline; the second inlet programmable valve of each adsorption tower is connected to and connected to the low-temperature mixed gas inlet main pipeline; the third inlet programmable valve of each adsorption tower is connected to and connected to the high-temperature steam inlet main pipeline; the fourth inlet programmable valve of each adsorption tower is connected to and connected to the first outlet programmable valve of the adsorption tower; the fifth inlet programmable valve of each adsorption tower is connected to and connected to the second outlet programmable valve of the adsorption tower.

[0025] Optionally, the system further includes a membrane separation unit and a purification unit. The membrane separation unit includes a gas inlet, a membrane separation tail gas outlet, and a CO2 product gas outlet. The purification unit includes a gas inlet and a liquid outlet. The third outlet programmable valve of each adsorption tower is connected to the gas inlet of the membrane separation unit. The fourth outlet programmable valve of each adsorption tower is connected to the outside atmosphere. The fifth outlet programmable valve of each adsorption tower is connected to the outside atmosphere.

[0026] Through the above technical solution, this disclosure provides a method and system for capturing CO2 from a low-CO2 concentration mixed gas. The method employs five parallel adsorption towers to achieve medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling, and low-temperature cooling of CO2, respectively. The tail gas from the first medium-temperature adsorption stage is used to cool the desorbed adsorbent at medium temperature, and the tail gas from the first low-temperature adsorption stage is used to cool the medium-temperature cooled adsorbent at low temperature. This effectively couples the internal heat of the system, avoids introducing external air during the cooling process, improves the system's heat utilization efficiency, achieves internal energy recovery, and reduces system energy consumption. In this system, at least one adsorption tower is simultaneously engaged in the medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling, and low-temperature cooling stages, effectively removing carbon dioxide from the mixed gas and achieving automatic continuous operation of the adsorption unit.

[0027] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0028] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0029] Figure 1 This is a schematic diagram of the CO2 capture system used in Embodiment 1 of this disclosure.

[0030] Explanation of reference numerals in the attached figures

[0031] I. First Adsorption Tower IV. Fourth Adsorption Tower

[0032] II. Second Adsorption Tower V. Fifth Adsorption Tower

[0033] III. Third Adsorption Tower Detailed Implementation

[0034] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0035] The first aspect of this disclosure provides a method for capturing CO2 from a low CO2 concentration gas mixture, the method comprising:

[0036] S1. A medium-temperature mixed gas containing CO2 is introduced into the first adsorption tower I for medium-temperature adsorption to obtain a primary medium-temperature adsorption tail gas.

[0037] S2. After the medium-temperature adsorption in the first adsorption tower I is completed, the medium-temperature mixed gas is switched to the second adsorption tower II for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the low-temperature mixed gas containing CO2 is introduced into the first adsorption tower I for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0038] S3. After the medium-temperature adsorption of the second adsorption tower II is completed, the medium-temperature mixed gas is switched to the third adsorption tower III for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the first adsorption tower I is subjected to a desorption process, and the low-temperature mixed gas is switched to the second adsorption tower II for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0039] S4. After the medium-temperature adsorption of the third adsorption tower III is completed, the medium-temperature mixed gas is switched to the fourth adsorption tower IV for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the first adsorption tower I is cooled at medium temperature, the second adsorption tower II is desorbed, and the low-temperature mixed gas is switched to the third adsorption tower III for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0040] S5. After the medium-temperature adsorption of the fourth adsorption tower IV is completed, the medium-temperature mixed gas is switched to the fifth adsorption tower V for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower I is cooled at low temperature, the second adsorption tower II is cooled at medium temperature, the third adsorption tower III is desorbed, and the low-temperature mixed gas is switched to the fourth adsorption tower IV for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0041] S6. After the medium-temperature adsorption of the fifth adsorption tower V is completed, the medium-temperature mixed gas is switched to the first adsorption tower I for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the second adsorption tower II is cooled at low temperature, the third adsorption tower III is cooled at medium temperature, the fourth adsorption tower IV is desorbed, and the low-temperature mixed gas is switched to the fifth adsorption tower V for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0042] S7. After the medium-temperature adsorption of the first adsorption tower I is completed, the medium-temperature mixed gas is switched to the second adsorption tower II for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the low-temperature mixed gas is switched to the first adsorption tower I for low-temperature adsorption to obtain a low-temperature adsorption tail gas; the third adsorption tower III is cooled at low temperature, the fourth adsorption tower IV is cooled at medium temperature, and the fifth adsorption tower V is desorbed.

[0043] S8. After the medium-temperature adsorption of the second adsorption tower II is completed, the medium-temperature mixed gas is switched to the third adsorption tower III for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower I is subjected to desorption, and the low-temperature mixed gas is switched to the second adsorption tower II for low-temperature adsorption to obtain a low-temperature adsorption tail gas; the fourth adsorption tower IV is subjected to low-temperature cooling, and the fifth adsorption tower V is subjected to medium-temperature cooling.

[0044] S9. After the medium-temperature adsorption of the third adsorption tower III is completed, the medium-temperature mixed gas is introduced into the fourth adsorption tower IV for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower I is cooled at medium temperature, the second adsorption tower II is desorbed, the low-temperature mixed gas is switched to the third adsorption tower III for low-temperature adsorption to obtain a low-temperature adsorption tail gas; the fifth adsorption tower V is cooled at low temperature.

[0045] S10. After the medium-temperature adsorption of the fourth adsorption tower IV is completed, the medium-temperature mixed gas is switched to the fifth adsorption tower V for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower I is cooled at low temperature, the second adsorption tower II is cooled at medium temperature, the third adsorption tower III is desorbed, and the low-temperature mixed gas is switched to the fourth adsorption tower IV for low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0046] Repeat steps S6 to S10;

[0047] The first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V each contain CO2 adsorbent; the primary medium-temperature adsorption tail gas is used as the cooling gas for the medium-temperature cooling and is in contact with the CO2 adsorbent; the primary low-temperature adsorption tail gas is used as the cooling gas for the low-temperature cooling and is in contact with the CO2 adsorbent.

[0048] The method disclosed herein employs five parallel adsorption towers to achieve medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling, and low-temperature cooling of CO2, respectively. The method utilizes the tail gas from the first medium-temperature adsorption after medium-temperature adsorption to perform medium-temperature cooling on the desorbed adsorbent, and utilizes the tail gas from the first low-temperature adsorption after low-temperature adsorption to perform low-temperature cooling on the adsorbent after medium-temperature cooling. This effectively couples the internal heat of the system, avoids the introduction of external air during the cooling process, improves the heat utilization efficiency of the system, realizes internal energy recovery, and reduces system energy consumption.

[0049] In one embodiment of this disclosure, the conditions for the mesophilic adsorption include: the mesophilic mixed gas entering the adsorption tower from the inlet at the bottom of the adsorption tower, and obtaining the primary mesophilic adsorption tail gas with CO2 removed from the outlet at the top of the adsorption tower; the mesophilic adsorption time is 5–120 min; the volume content of CO2 in the mesophilic mixed gas is 15–25%; the inlet temperature of the mesophilic mixed gas is 60–80°C; the outlet temperature of the primary mesophilic adsorption tail gas is 40–60°C; the temperature of the CO2 adsorbent in the adsorption tower before the mesophilic adsorption begins is 20–40°C; and the condition for determining the completion of the mesophilic adsorption is that the volume content of CO2 in the primary mesophilic adsorption tail gas is 3–7%. In the above embodiment, by employing the preferred mesophilic adsorption conditions, most of the CO2 in the mesophilic mixed gas can be captured under mesophilic conditions, resulting in a primary mesophilic adsorption tail gas containing a small amount of CO2.

[0050] In one embodiment of this disclosure, the conditions for low-temperature adsorption include: the low-temperature mixed gas entering the adsorption tower from the inlet at the bottom of the adsorption tower, and obtaining the primary low-temperature adsorption tail gas with CO2 removed from the outlet at the top of the adsorption tower; the low-temperature adsorption time is 5–120 min; the volume content of CO2 in the low-temperature mixed gas is 8–20%; the inlet temperature of the low-temperature mixed gas is 20–40°C; the outlet temperature of the primary low-temperature adsorption tail gas is 25–45°C; the temperature of the CO2 adsorbent in the adsorption tower is 40–60°C before the low-temperature adsorption begins; and the condition for determining the completion of low-temperature adsorption is that the volume content of CO2 in the primary low-temperature adsorption tail gas is 1.5–5%. In the above embodiment, by employing the preferred low-temperature adsorption conditions, most of the CO2 in the low-temperature mixed gas can be captured under low-temperature conditions, resulting in a primary low-temperature adsorption tail gas containing a small amount of CO2.

[0051] In one embodiment of this disclosure, the desorption process includes: allowing high-temperature steam to enter the adsorption tower from the inlet at the bottom of the adsorption tower, and obtaining CO2-rich desorbed gas from the outlet at the top of the adsorption tower; the desorption process lasts for 5–120 minutes; the inlet temperature of the high-temperature steam is 100–150°C, the outlet temperature of the desorbed gas is 60–80°C, and the temperature of the CO2 adsorbent in the adsorption tower before the desorption process begins is 20–40°C; the condition for determining the completion of the desorption process is that the volume content of CO2 in the desorbed gas is 40–60%. In the above embodiment, by employing preferred desorption conditions, the CO2 adsorbent that has adsorbed CO2 in the adsorption tower can be desorbed, achieving one-time purification of CO2. Furthermore, since the desorbed gas contains water vapor, it avoids the need to specifically install a humidifier tank before the membrane separation unit, effectively simplifying the system process.

[0052] In one embodiment of this disclosure, the conditions for the intermediate-temperature cooling include: the primary intermediate-temperature adsorption tail gas enters the adsorption tower from the inlet at the bottom of the adsorption tower and exits from the outlet at the top of the adsorption tower; the intermediate-temperature cooling takes 5 to 120 minutes; the inlet temperature of the primary intermediate-temperature adsorption tail gas is 40 to 60°C, and the volume content of CO2 in the primary intermediate-temperature adsorption tail gas is 4 to 7%; the outlet temperature of the intermediate-temperature adsorption tail gas is 45 to 65°C, and the volume content of CO2 in the intermediate-temperature adsorption tail gas is 1.5 to 4%; the temperature of the CO2 adsorbent before the intermediate-temperature cooling takes place is 60 to 80°C; and the condition for determining the completion of the intermediate-temperature cooling is that the temperature of the CO2 adsorbent in the adsorption tower is 40 to 60°C. In the above embodiments, using the primary medium-temperature adsorption tail gas to cool the desorbed CO2 adsorbent at a medium temperature not only reduces the temperature of the CO2 adsorbent, but also allows the residual CO2 in the primary medium-temperature adsorption tail gas to be further captured. Furthermore, it couples the internal heat of the system, avoids introducing external air during the cooling process, realizes internal energy recovery of the system, and reduces system energy consumption.

[0053] In one embodiment of this disclosure, the conditions for low-temperature cooling include: the primary low-temperature adsorption tail gas enters the adsorption tower from the inlet at the bottom of the adsorption tower and exits from the outlet at the top of the adsorption tower; the low-temperature cooling process lasts for 5–120 minutes; the inlet temperature of the primary low-temperature adsorption tail gas is 20–40°C, and the volume content of CO2 in the primary low-temperature adsorption tail gas is 3–5%; the outlet temperature of the low-temperature adsorption tail gas is 25–45°C, and the volume content of CO2 in the low-temperature adsorption tail gas is 0.5–3%; the temperature of the CO2 adsorbent before the low-temperature cooling process is 40–60°C; and the condition for determining the completion of low-temperature cooling is that the temperature of the CO2 adsorbent in the adsorption tower is 20–40°C. In the above embodiment, using the primary low-temperature adsorption tail gas to perform low-temperature cooling on the CO2 adsorbent after medium-temperature cooling not only reduces the temperature of the CO2 adsorbent but also allows for further capture of residual CO2 in the primary low-temperature adsorption tail gas. Furthermore, it couples internal system heat, avoids introducing external air during the cooling process, and reduces system energy consumption.

[0054] In one embodiment of this disclosure, the method further includes: passing the desorbed gas into a membrane separation unit for CO2 separation to obtain CO2 product gas and membrane separation tail gas; allowing the CO2 product gas to enter a purification unit for refining and purification to obtain liquid CO2 product; and allowing the membrane separation tail gas to enter an adsorption tower as the medium-temperature mixed gas for medium-temperature adsorption; the CO2 volume content in the CO2 product gas is above 95%, and the CO2 purity in the liquid CO2 product is above 99%; the outlet temperature of the membrane separation tail gas is 60-80°C, and the CO2 volume content in the membrane separation tail gas is 8-30%. In the above embodiment, the high-temperature desorbed gas obtained from the adsorption tower is directly passed into the membrane separation unit operating under high-temperature conditions. This utilizes the high CO2 flux and high selectivity of the membrane separation material under high-temperature conditions to enhance the separation of CO2 from other gases, thereby improving the operating efficiency of the membrane separation unit. Furthermore, it avoids the need for cooling the first-stage high-temperature desorbed gas, which is required in conventional two-stage pressure swing adsorption processes, thus improving the overall system operating efficiency. In addition, by refluxing the membrane separation tail gas containing a low concentration of CO2 and at a certain temperature into the adsorption tower as a medium-temperature mixed gas and using it for medium-temperature adsorption, the residual CO2 in the membrane separation tail gas can be fully captured, thereby improving the system's CO2 capture efficiency.

[0055] The second aspect of this disclosure provides a system for capturing CO2 from a low CO2 concentration mixed gas using the method described in the first aspect of this disclosure. The system comprises at least five adsorption towers connected in parallel: a first adsorption tower I, a second adsorption tower II, a third adsorption tower III, a fourth adsorption tower IV, and a fifth adsorption tower V. Each adsorption tower has five parallel inlet programmable valves at its bottom inlet and five parallel outlet programmable valves at its top outlet. At any given time, the five towers are in the operating states of medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling, and low-temperature cooling, respectively. Each adsorption tower sequentially cycles through these five operating states.

[0056] In one embodiment, in the first stage, the first adsorption tower I is in a medium-temperature adsorption state, the second adsorption tower II is in a low-temperature adsorption state, the third adsorption tower III is in a desorption state, the fourth adsorption tower IV is in a medium-temperature cooling state, and the fifth adsorption tower V is in a low-temperature cooling state. In the second stage, the first adsorption tower I is switched to a low-temperature adsorption state, the second adsorption tower II is switched to a desorption state, the third adsorption tower III is switched to a medium-temperature cooling state, the fourth adsorption tower IV is switched to a low-temperature cooling state, and the fifth adsorption tower V is switched to a medium-temperature adsorption state. In the third stage, the first adsorption tower I is switched to a desorption state, the second adsorption tower II is switched to a medium-temperature cooling state, the third adsorption tower III is switched to a low-temperature cooling state, the fourth adsorption tower IV is switched to a medium-temperature adsorption state, and the fifth adsorption tower V is switched to a low-temperature adsorption state. In the fourth stage, the first adsorption tower I is switched to a medium-temperature cooling state, the second adsorption tower II is switched to a low-temperature cooling state, the third adsorption tower III is switched to a medium-temperature adsorption state, the fourth adsorption tower IV is switched to a low-temperature adsorption state, and the fifth adsorption tower V is switched to a desorption state. In the fifth stage, the first adsorption tower I is switched to a low-temperature cooling state, the second adsorption tower II is switched to a medium-temperature adsorption state, the third adsorption tower III is switched to a low-temperature adsorption state, the fourth adsorption tower IV is switched to a desorption state, and the fifth adsorption tower V is switched to a medium-temperature cooling state.

[0057] The system disclosed herein has at least one adsorption tower operating simultaneously in the stages of medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling, and low-temperature cooling, effectively removing carbon dioxide from the mixed gas and realizing automatic continuous operation of the adsorption unit.

[0058] In one embodiment of this disclosure, each inlet programmable valve includes a first inlet programmable valve, a second inlet programmable valve, a third inlet programmable valve, a fourth inlet programmable valve, and a fifth inlet programmable valve; each outlet programmable valve includes a first outlet programmable valve, a second outlet programmable valve, a third outlet programmable valve, a fourth outlet programmable valve, and a fifth outlet programmable valve. In a preferred embodiment, the first inlet programmable valve of each adsorption tower is connected to and connected to the membrane separation tail gas outlet main pipeline; the second inlet programmable valve of each adsorption tower is connected to and connected to the low-temperature mixed gas inlet main pipeline; the third inlet programmable valve of each adsorption tower is connected to and connected to the high-temperature steam inlet main pipeline; the fourth inlet programmable valve of each adsorption tower is connected to and connected to the first outlet programmable valve of the adsorption tower; and the fifth inlet programmable valve of each adsorption tower is connected to and connected to the second outlet programmable valve of the adsorption tower.

[0059] In one embodiment of this disclosure, the system further includes a membrane separation unit and a purification unit. The membrane separation unit includes a gas inlet, a membrane separation tail gas outlet, and a CO2 product gas outlet. The purification unit includes a gas inlet and a liquid outlet. Specifically, the CO2 product gas outlet is connected to the gas inlet of the purification unit, and the liquid outlet of the purification unit is connected to the outside environment.

[0060] In one embodiment of this disclosure, the third outlet programmable valve of each adsorption tower is connected to the gas inlet of the membrane separation unit; the fourth outlet programmable valve of each adsorption tower is connected to the outside atmosphere; and the fifth outlet programmable valve of each adsorption tower is connected to the outside atmosphere.

[0061] In the above embodiments, by controlling the automatic opening and closing switching of the inlet programmable valve and the outlet inlet programmable valve, the adsorption tower can realize the medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling and low-temperature cooling of CO2 respectively, and at least one adsorption tower is in the medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling and low-temperature cooling stage at the same time, so as to realize the continuous operation of the adsorption unit.

[0062] In one embodiment, the membrane separation tail gas outlet main pipeline is connected to the inlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V via five parallel medium-temperature mixed gas inlet branch pipelines and a first inlet programmable valve.

[0063] The low-temperature mixed gas inlet main pipeline is connected to the inlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V through five parallel low-temperature mixed gas inlet branch pipelines and the second inlet programmable valve, respectively.

[0064] The high-temperature steam inlet main pipeline is connected to the inlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V through five parallel high-temperature steam inlet branch pipelines and the third inlet programmable valve.

[0065] The main pipeline for the primary medium-temperature adsorption tail gas flow is connected to the inlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V via five parallel primary medium-temperature adsorption tail gas inlet branch pipelines and a fourth inlet programmable valve.

[0066] The primary low-temperature adsorption tail gas circulation main pipeline is connected to the inlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V via five parallel primary low-temperature adsorption tail gas inlet branch pipelines and a fifth inlet programmable valve.

[0067] In another embodiment, the outlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V are connected to the primary medium-temperature adsorption tail gas circulation main pipeline through five parallel first outlet programmable valves and a primary medium-temperature adsorption tail gas outlet branch pipeline.

[0068] The outlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V are connected to the main pipeline of the primary low-temperature adsorption tail gas through five parallel second outlet programmable valves and the primary low-temperature adsorption tail gas outlet branch pipeline.

[0069] The outlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V are connected to the gas inlet of the membrane separation unit through five parallel third outlet programmable valves and desorption gas outlet branch pipelines.

[0070] The outlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V are connected to the outside atmosphere through five parallel fourth outlet programmable valves and medium-temperature adsorption tail gas outlet branch pipelines.

[0071] The outlets of the first adsorption tower I, the second adsorption tower II, the third adsorption tower III, the fourth adsorption tower IV, and the fifth adsorption tower V are connected to the outside atmosphere through five parallel fifth outlet programmable valves and low-temperature adsorption tail gas outlet branch pipelines.

[0072] The present disclosure is further described in detail below through examples. All raw materials used in the examples are commercially available. The CO2 adsorbent is a porous honeycomb adsorbent, such as honeycomb activated carbon or honeycomb molecular sieve.

[0073] Example 1

[0074] A system for capturing CO2 from a low-CO2 concentration gas mixture, such as Figure 1 As shown, the system comprises an adsorption unit, a membrane separation unit, and a purification unit. The adsorption unit consists of five adsorption towers connected in parallel: adsorption tower I, adsorption tower II, adsorption tower III, adsorption tower IV, and adsorption tower V. Each adsorption tower is packed with 14 tons of CO2 adsorbent. Five parallel inlet control valves are installed at the bottom inlet of each tower, and five parallel outlet control valves are installed at the top outlet of each tower. This ensures that the five adsorption towers are simultaneously operating in the following stages: meso-temperature adsorption, cryogenic adsorption, desorption, meso-temperature cooling, and cryogenic cooling, with each stage lasting 10 minutes.

[0075] The membrane separation unit is a single-stage, single-section membrane system with 100 gas separation membrane modules connected in parallel. Each gas separation membrane module is equipped with a 30m³ membrane. 2 The effective area of ​​the gas separation membrane, with a CO2 permeation rate of 1000 GPU (i.e., 1000 × 10⁻⁶ cm⁻¹) under standard test conditions. 3 / cm 2 The membrane separation unit has a permeation rate selectivity of 80 for CO2 and N2 (permeate gas per second / cmHg), an inlet pressure of 0 MPaG, and a vacuum operation at a pressure of -0.08 MPaG on the product gas side. The membrane separation unit includes a gas inlet, a membrane separation tail gas outlet, and a CO2 product gas outlet. The purification unit includes a gas inlet and a liquid outlet. The CO2 product gas outlet is connected to the gas inlet of the purification unit, and the liquid outlet of the purification unit is connected to the outside environment.

[0076] Each of the five adsorption towers includes a first inlet control valve, a second inlet control valve, a third inlet control valve, a fourth inlet control valve, and a fifth inlet control valve; and each of the five adsorption towers includes a first outlet control valve, a second outlet control valve, a third outlet control valve, a fourth outlet control valve, and a fifth outlet control valve.

[0077] The first inlet control valve of each adsorption tower is connected to the main outlet pipeline of the membrane separation tail gas; the second inlet control valve of each adsorption tower is connected to the main inlet pipeline of the low-temperature mixed gas; the third inlet control valve of each adsorption tower is connected to the main inlet pipeline of the high-temperature steam; the fourth inlet control valve of each adsorption tower is connected to the first outlet control valve of the adsorption tower; the fifth inlet control valve of each adsorption tower is connected to the second outlet control valve of the adsorption tower. The third outlet control valve of each adsorption tower is connected to the gas inlet of the membrane separation unit; the fourth outlet control valve of each adsorption tower is connected to the outside atmosphere; the fifth outlet control valve of each adsorption tower is connected to the outside atmosphere.

[0078] The method for capturing CO2 from a low-CO2 concentration gas mixture using this system includes the following steps:

[0079] S1. Separate the tail gas through the membrane (flow rate 2587 Nm). 3 A medium-temperature mixed gas (containing 25% CO2 by volume and an inlet temperature of 60℃) enters the first adsorption tower I (CO2 adsorbent temperature 30℃) via the medium-temperature mixed gas inlet branch pipe and the first inlet programmable valve for medium-temperature adsorption, yielding a primary medium-temperature adsorption tail gas (flow rate 1811 Nm³) after CO2 removal. 3 / h, when the outlet temperature is 50℃ and the CO2 volume content is 3.57%, the medium temperature adsorption is completed. The tail gas of the first medium temperature adsorption flows out of the first adsorption tower I through the first inlet programmable valve and the first medium temperature adsorption tail gas outlet branch pipeline.

[0080] S2. After the meso-temperature adsorption in the first adsorption tower I is completed, the above-mentioned membrane separation tail gas (meso-temperature mixed gas) is switched to the second adsorption tower II via the meso-temperature mixed gas inlet branch pipe and the first inlet programmable valve to undergo the above-mentioned meso-temperature adsorption, thus obtaining a first-stage meso-temperature adsorption tail gas; and a low-temperature mixed gas containing CO2 (flow rate of 10000 Nm³) is introduced. 3 The gas (CO2 adsorbent temperature 40℃) is introduced into the first adsorption tower I (CO2 adsorbent temperature 40℃) via the low-temperature mixed gas inlet branch pipe and the second inlet programmable valve, and undergoes low-temperature adsorption to obtain the primary low-temperature adsorption tail gas (flow rate 7800 Nm³ / h) after CO2 removal. 3 / h, with an outlet temperature of 40℃ and a CO2 volume content of 1.92%, the primary low-temperature adsorption tail gas flows out of the first adsorption tower I through the second outlet programmable valve and the primary low-temperature adsorption tail gas outlet branch pipeline.

[0081] S3. After the medium-temperature adsorption in the second adsorption tower II is completed, the medium-temperature mixed gas is switched to the third adsorption tower III for the above-mentioned medium-temperature adsorption to obtain the tail gas of the first medium-temperature adsorption; and high-temperature steam (flow rate of 500 Nm³) is used. 3 The CO2 gas (at an inlet temperature of 120℃) enters the first adsorption tower I (CO2 adsorbent temperature 40℃) through the high-temperature steam inlet branch pipe and the third inlet programmable valve. Under high-temperature steam purging, the CO2 gas captured by the CO2 adsorbent is completely desorbed, and the resulting desorbed gas (flow rate 4053 Nm³) is produced. 3 The gas (flow rate of 2587 Nm³ / h, outlet temperature of 60℃, CO2 volume content of 50.32%) enters the membrane separation system through the third outlet programmable valve, the desorbed gas outlet branch line, and the gas inlet of the membrane separation unit. After membrane separation, the membrane separation tail gas (flow rate of 2587 Nm³ / h) is obtained. 3 (flow rate of 1466 Nm³ / h, outlet temperature of 60℃, CO2 volume content of 25%) and membrane separation product gas (flow rate of 1466 Nm³ / h). 3 The membrane separation tail gas (flow rate of 1466 Nm³ / h, outlet temperature of 60℃, CO2 volume content of 95.71%) is returned to the adsorption tower for the above-mentioned mesotemperature adsorption operation; the membrane separation product gas (flow rate of 1466 Nm³ / h) is also returned to the adsorption tower for the above-mentioned mesotemperature adsorption operation. 3A gas mixture with a flow rate of 2735 kg / h, an outlet temperature of 60°C, and a CO2 volume content of 95.71% is introduced into the purification unit. After compression, liquefaction, and purification, a liquid CO2 product (2735 kg / h, 99.95% purity) is obtained. The low-temperature mixed gas is then switched to the second adsorption tower II for the above-mentioned low-temperature adsorption, resulting in a primary low-temperature adsorption tail gas.

[0082] S4. After the intermediate-temperature adsorption in the third adsorption tower III is completed, the intermediate-temperature mixed gas is switched to the fourth adsorption tower IV for the above-mentioned intermediate-temperature adsorption to obtain the primary intermediate-temperature adsorption tail gas; and the flow rate of the primary intermediate-temperature adsorption tail gas (1811 Nm³) is controlled. 3 The gas (at an inlet temperature of 50℃ and a CO2 volume content of 3.57%) enters the first adsorption tower I (CO2 adsorbent temperature of 60℃) via the primary medium-temperature adsorption tail gas inlet branch pipe and the fourth inlet programmable valve for medium-temperature cooling. Once the CO2 adsorbent temperature drops to 50℃, medium-temperature adsorption tail gas (1691 Nm³) is formed. 3 The medium-temperature adsorption tail gas (with an outlet temperature of 50℃ and a CO2 volume content of 1.91%) is discharged to the atmosphere through the fourth outlet programmable valve and the medium-temperature adsorption tail gas outlet branch pipeline. The second adsorption tower II then undergoes the above desorption process, and the low-temperature mixed gas is switched to the third adsorption tower III for the above low-temperature adsorption, resulting in a primary low-temperature adsorption tail gas.

[0083] S5. After the intermediate-temperature adsorption in the fourth adsorption tower IV is completed, the intermediate-temperature mixed gas is switched to the fifth adsorption tower V for the above-mentioned intermediate-temperature adsorption to obtain the first-stage intermediate-temperature adsorption tail gas; and the first-stage low-temperature adsorption tail gas (flow rate 7800 Nm³) is... 3 The gas (at an inlet temperature of 40℃ and a CO2 volume content of 1.92%) enters the first adsorption tower I (CO2 adsorbent temperature of 50℃) via the first low-temperature adsorption tail gas inlet branch pipe and the fifth inlet programmable valve for low-temperature cooling. Once the CO2 adsorbent temperature drops to 40℃, low-temperature adsorption tail gas (7342 Nm³) is formed. 3 The low-temperature adsorption tail gas (with an outlet temperature of 40℃ and a CO2 volume content of 1.02%) is discharged to the atmosphere through the fifth outlet programmable valve and the low-temperature adsorption tail gas outlet branch pipeline. The second adsorption tower II undergoes the above-mentioned medium-temperature cooling, the third adsorption tower III undergoes the above-mentioned desorption process, and the low-temperature mixed gas is switched to the fourth adsorption tower IV for the above-mentioned low-temperature adsorption, resulting in a primary low-temperature adsorption tail gas.

[0084] S6. After the medium-temperature adsorption of the fifth adsorption tower V is completed, the medium-temperature mixed gas is switched to the first adsorption tower I for the above-mentioned medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the second adsorption tower II is subjected to the above-mentioned low-temperature cooling, the third adsorption tower III is subjected to the above-mentioned medium-temperature cooling, the fourth adsorption tower IV is subjected to the above-mentioned desorption process, and the low-temperature mixed gas is switched to the fifth adsorption tower V for the above-mentioned low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0085] S7. After the medium-temperature adsorption of the first adsorption tower I is completed, the medium-temperature mixed gas is switched to the second adsorption tower II for the above-mentioned medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the low-temperature mixed gas is switched to the first adsorption tower I for the above-mentioned low-temperature adsorption to obtain a low-temperature adsorption tail gas; the third adsorption tower III is subjected to the above-mentioned low-temperature cooling, the fourth adsorption tower IV is subjected to the above-mentioned medium-temperature cooling, and the fifth adsorption tower V is subjected to the above-mentioned desorption process.

[0086] S8. After the medium-temperature adsorption of the second adsorption tower II is completed, the medium-temperature mixed gas is switched to the third adsorption tower III for the above-mentioned medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the first adsorption tower I is subjected to the above-mentioned desorption process, and the low-temperature mixed gas is switched to the second adsorption tower II for the above-mentioned low-temperature adsorption to obtain a low-temperature adsorption tail gas; the fourth adsorption tower IV is subjected to the above-mentioned low-temperature cooling, and the fifth adsorption tower V is subjected to the above-mentioned medium-temperature cooling.

[0087] S9. After the medium-temperature adsorption of the third adsorption tower III is completed, the medium-temperature mixed gas is introduced into the fourth adsorption tower IV for the above-mentioned medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower I is subjected to the above-mentioned medium-temperature cooling, the second adsorption tower II is subjected to the above-mentioned desorption process, the low-temperature mixed gas is switched to the third adsorption tower III for the above-mentioned low-temperature adsorption to obtain a low-temperature adsorption tail gas; the fifth adsorption tower V is subjected to the above-mentioned low-temperature cooling.

[0088] S10. After the medium-temperature adsorption of the fourth adsorption tower IV is completed, the medium-temperature mixed gas is switched to the fifth adsorption tower V for the above-mentioned medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the first adsorption tower I is subjected to the above-mentioned low-temperature cooling, the second adsorption tower II is subjected to the above-mentioned medium-temperature cooling, the third adsorption tower III is subjected to the above-mentioned desorption process, and the low-temperature mixed gas is switched to the fourth adsorption tower IV for the above-mentioned low-temperature adsorption to obtain a low-temperature adsorption tail gas.

[0089] Repeat steps S6 to S10 above.

[0090] Comparative Example 1

[0091] The method of Example 1 is adopted, except that the tail gas of the first medium-temperature adsorption and the tail gas of the first low-temperature adsorption are not returned to the adsorption tower for use as cooling gas, but are directly discharged; air is used as the cooling gas for medium-temperature cooling and low-temperature cooling, respectively.

[0092] Test case

[0093] The CO2 capture rate in the examples and comparative examples was determined using the following method: CO2 capture rate = volumetric flow rate of CO2 in the membrane separation product gas / volumetric flow rate of CO2 in the low-temperature mixed gas; where the volumetric flow rate of CO2 = total volumetric flow rate of the mixed gas * volumetric content of CO2 in the mixed gas. The total volumetric flow rate of the mixed gas was measured using a vortex flow meter, and the volumetric content of CO2 was measured using an infrared analyzer. The results are shown in Table 1.

[0094] Table 1

[0095]

[0096] According to the data in Table 1, Example 1 uses the method and system disclosed herein, which can effectively capture CO2, remove carbon dioxide from the mixed gas, realize automatic and continuous operation of the adsorption unit, and realize internal energy recovery of the system, thereby reducing system energy consumption.

[0097] In Comparative Example 1, the tail gas from the first-stage medium-temperature adsorption and the tail gas from the first-stage low-temperature adsorption were directly discharged. This resulted in the small amount of residual CO2 in these two tail gases not being captured by the adsorbent again through the adsorption tower, thus reducing the overall CO2 capture capacity of the system. Furthermore, the discharged tail gas from the first-stage medium-temperature adsorption (1328 Nm³)... 3 / h, 3.57%) and primary low-temperature adsorption tail gas (7800Nm 3 / h, 1.92%), resulting in the system finally obtaining a product gas of 1371Nm. 3 / h, 95%. Compared to the product gas in Example 1 (1466 Nm³ / h). 3 / h, 95%), the product gas flow rate decreased by 6.5%.

[0098] Secondly, due to the direct emission of the primary medium-temperature adsorption tail gas and the primary low-temperature adsorption tail gas, the adsorption tower needs to introduce external air for cooling. In Example 1, the primary medium-temperature adsorption tail gas (1811 Nm³) 3 / h, 50℃) is used to lower the temperature of the adsorbent in the adsorption tower from 60℃ to 50℃, and perform a primary low-temperature adsorption of the tail gas (7800Nm). 3 / h, 40℃) is used to reduce the temperature of the adsorbent in the adsorption tower from 50℃ to 40℃. In Comparative Example 1, because of the external air, taking a common air temperature of 30℃ as an example, the required air flow rate is 4503 Nm. 3 / h. On the one hand, it wastes the potential of the original medium-temperature adsorption tail gas and low-temperature adsorption tail gas to cool the adsorption tower; on the other hand, the system needs to introduce additional pressurization equipment to introduce external air into the adsorption tower for cooling, which increases both energy consumption and system complexity.

[0099] In summary, compared to Comparative Example 1, Example 1, which uses the method and system disclosed herein, can effectively couple the internal heat of the system and has the advantages of a simpler system, lower energy consumption, and higher product gas recovery rate.

[0100] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0101] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0102] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for capturing CO2 from a low-CO2 concentration gas mixture, characterized in that, The method includes the following steps: S1. A medium-temperature mixed gas containing CO2 is introduced into the first adsorption tower (I) for medium-temperature adsorption to obtain a primary medium-temperature adsorption tail gas. S2. After the medium-temperature adsorption of the first adsorption tower (I) is completed, the medium-temperature mixed gas is switched to the second adsorption tower (II) for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the low-temperature mixed gas containing CO2 is introduced into the first adsorption tower (I) for low-temperature adsorption to obtain a low-temperature adsorption tail gas. S3. After the medium-temperature adsorption of the second adsorption tower (II) is completed, the medium-temperature mixed gas is switched to the third adsorption tower (III) for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the first adsorption tower (I) is subjected to desorption process, and the low-temperature mixed gas is switched to the second adsorption tower (II) for low-temperature adsorption to obtain a low-temperature adsorption tail gas. S4. After the medium-temperature adsorption of the third adsorption tower (III) is completed, the medium-temperature mixed gas is switched to the fourth adsorption tower (IV) for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the first adsorption tower (I) is cooled at medium temperature, the second adsorption tower (II) is desorbed, and the low-temperature mixed gas is switched to the third adsorption tower (III) for low-temperature adsorption to obtain a low-temperature adsorption tail gas. S5. After the intermediate-temperature adsorption of the fourth adsorption tower (IV) is completed, the intermediate-temperature mixed gas is switched to the fifth adsorption tower (V) for intermediate-temperature adsorption to obtain a first-stage intermediate-temperature adsorption tail gas; the first adsorption tower (I) is cooled to a low temperature, the second adsorption tower (II) is cooled to a medium temperature, the third adsorption tower (III) undergoes a desorption process, and the low-temperature mixed gas is switched to the fourth adsorption tower (IV) for low-temperature adsorption to obtain a first-stage low-temperature adsorption tail gas; S6. After the medium-temperature adsorption of the fifth adsorption tower (V) is completed, the medium-temperature mixed gas is switched to the first adsorption tower (I) for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the second adsorption tower (II) is cooled at low temperature, the third adsorption tower (III) is cooled at medium temperature, the fourth adsorption tower (IV) undergoes desorption, and the low-temperature mixed gas is switched to the fifth adsorption tower (V) for low-temperature adsorption to obtain a low-temperature adsorption tail gas. S7. After the medium-temperature adsorption of the first adsorption tower (I) is completed, the medium-temperature mixed gas is switched to the second adsorption tower (II) for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; and the low-temperature mixed gas is switched to the first adsorption tower (I) for low-temperature adsorption to obtain a low-temperature adsorption tail gas; the third adsorption tower (III) is cooled at low temperature, the fourth adsorption tower (IV) is cooled at medium temperature, and the fifth adsorption tower (V) undergoes desorption. S8. After the medium-temperature adsorption of the second adsorption tower (II) is completed, the medium-temperature mixed gas is switched to the third adsorption tower (III) for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower (I) is subjected to desorption, and the low-temperature mixed gas is switched to the second adsorption tower (II) for low-temperature adsorption to obtain a low-temperature adsorption tail gas; the fourth adsorption tower (IV) is subjected to low-temperature cooling, and the fifth adsorption tower (V) is subjected to medium-temperature cooling. S9. After the medium-temperature adsorption of the third adsorption tower (III) is completed, the medium-temperature mixed gas is introduced into the fourth adsorption tower (IV) for medium-temperature adsorption to obtain a medium-temperature adsorption tail gas; the first adsorption tower (I) is cooled at medium temperature, the second adsorption tower (II) undergoes desorption, the low-temperature mixed gas is switched to the third adsorption tower (III) for low-temperature adsorption to obtain a low-temperature adsorption tail gas; the fifth adsorption tower (V) is cooled at low temperature. S10. After the intermediate-temperature adsorption of the fourth adsorption tower (IV) is completed, the intermediate-temperature mixed gas is switched to the fifth adsorption tower (V) for intermediate-temperature adsorption to obtain a first-stage intermediate-temperature adsorption tail gas; the first adsorption tower (I) is cooled to a low temperature, the second adsorption tower (II) is cooled to a medium temperature, the third adsorption tower (III) undergoes a desorption process, and the low-temperature mixed gas is switched to the fourth adsorption tower (IV) for low-temperature adsorption to obtain a first-stage low-temperature adsorption tail gas. Repeat steps S6 to S10; The first adsorption tower (I), the second adsorption tower (II), the third adsorption tower (III), the fourth adsorption tower (IV), and the fifth adsorption tower (V) each contain a CO2 adsorbent; the primary medium-temperature adsorption tail gas is used as the cooling gas for the medium-temperature cooling and is in contact with the CO2 adsorbent; the primary low-temperature adsorption tail gas is used as the cooling gas for the low-temperature cooling and is in contact with the CO2 adsorbent.

2. The method according to claim 1, characterized in that, The conditions for the mesophilic adsorption include: the mesophilic mixed gas enters the adsorption tower from the inlet at the bottom of the adsorption tower, and the CO2-removed tail gas is obtained from the outlet at the top of the adsorption tower; the mesophilic adsorption takes 5 to 120 minutes. The volume content of CO2 in the intermediate-temperature mixed gas is 15-25%, the inlet temperature of the intermediate-temperature mixed gas is 60-80℃, the outlet temperature of the tail gas from the first intermediate-temperature adsorption is 40-60℃, and the temperature of the CO2 adsorbent in the adsorption tower before the intermediate-temperature adsorption is 20-40℃. The condition for determining the completion of the mesophilic adsorption is that the volume content of CO2 in the tail gas after one mesophilic adsorption is 3-7%.

3. The method according to claim 1, characterized in that, The conditions for the low-temperature adsorption include: the low-temperature mixed gas enters the adsorption tower from the inlet at the bottom of the adsorption tower, and the tail gas after CO2 removal is obtained from the outlet at the top of the adsorption tower; the low-temperature adsorption takes 5 to 120 minutes. The volume content of CO2 in the low-temperature mixed gas is 8-20%, the inlet temperature of the low-temperature mixed gas is 20-40℃, the outlet temperature of the tail gas from the first low-temperature adsorption is 25-45℃, and the temperature of the CO2 adsorbent in the adsorption tower before the low-temperature adsorption is 40-60℃. The condition for determining the completion of the low-temperature adsorption is that the volume content of CO2 in the tail gas after one low-temperature adsorption is 1.5~5%.

4. The method according to claim 1, characterized in that, The desorption process includes: allowing high-temperature steam to enter the adsorption tower from the inlet at the bottom of the adsorption tower, and obtaining CO2-rich desorbed gas from the outlet at the top of the adsorption tower; the desorption process takes 5 to 120 minutes. The inlet temperature of the high-temperature steam is 100~150℃, the outlet temperature of the desorbed gas is 60~80℃, and the temperature of the CO2 adsorbent in the adsorption tower before the desorption process is 20~40℃. The condition for determining the completion of the desorption process is that the volume content of CO2 in the desorbed gas is 40-60%.

5. The method according to claim 1, characterized in that, The conditions for the intermediate temperature cooling include: the intermediate temperature adsorption tail gas enters the adsorption tower from the inlet at the bottom of the adsorption tower and exits from the outlet at the top of the adsorption tower; the intermediate temperature cooling process takes 5 to 120 minutes. The inlet temperature of the primary medium-temperature adsorption tail gas is 40~60℃, and the volume content of CO2 in the primary medium-temperature adsorption tail gas is 4~7%; the outlet temperature of the medium-temperature adsorption tail gas is 45~65℃, and the volume content of CO2 in the medium-temperature adsorption tail gas is 1.5~4%; the temperature of the CO2 adsorbent before the medium-temperature cooling is 60~80℃. The condition for determining the completion of the intermediate-temperature cooling is that the temperature of the CO2 adsorbent in the adsorption tower is 40~60℃.

6. The method according to claim 1, characterized in that, The conditions for the low-temperature cooling include: the primary low-temperature adsorption tail gas enters the adsorption tower from the inlet at the bottom of the adsorption tower and exits from the outlet at the top of the adsorption tower; the low-temperature cooling process takes 5 to 120 minutes. The inlet temperature of the primary low-temperature adsorption tail gas is 20~40℃, and the volume content of CO2 in the primary low-temperature adsorption tail gas is 3~5%; the outlet temperature of the low-temperature adsorption tail gas is 25~45℃, and the volume content of CO2 in the low-temperature adsorption tail gas is 0.5~3%; the temperature of the CO2 adsorbent before the low-temperature cooling is 40~60℃. The condition for determining the completion of low-temperature cooling is that the temperature of the CO2 adsorbent in the adsorption tower is 20~40℃.

7. The method according to claim 4, characterized in that, The method further includes: passing the desorbed gas into a membrane separation unit for CO2 separation to obtain CO2 product gas and membrane separation tail gas; allowing the CO2 product gas to enter a purification unit for refining and purification to obtain liquid CO2 product; and allowing the membrane separation tail gas to enter the adsorption tower as the medium-temperature mixed gas for medium-temperature adsorption. The CO2 product gas has a CO2 volume content of over 95%, and the liquid CO2 product has a CO2 purity of over 99%; the outlet temperature of the membrane separation tail gas is 60~80℃, and the CO2 volume content of the membrane separation tail gas is 8~30%.

8. A system for capturing CO2 from a low CO2 concentration gas mixture using the method described in any one of claims 1 to 7, characterized in that, The system comprises at least five adsorption towers connected in parallel: a first adsorption tower (I), a second adsorption tower (II), a third adsorption tower (III), a fourth adsorption tower (IV), and a fifth adsorption tower (V). Each adsorption tower has five parallel inlet control valves at its bottom inlet and five parallel outlet control valves at its top outlet. At any given time, the five towers are in the working states of medium-temperature adsorption, low-temperature adsorption, desorption, medium-temperature cooling, and low-temperature cooling, respectively. Each adsorption tower cycles through these five working states sequentially.

9. The system according to claim 8, characterized in that, Each inlet programmable valve includes a first inlet programmable valve, a second inlet programmable valve, a third inlet programmable valve, a fourth inlet programmable valve, and a fifth inlet programmable valve; each outlet programmable valve includes a first outlet programmable valve, a second outlet programmable valve, a third outlet programmable valve, a fourth outlet programmable valve, and a fifth outlet programmable valve. The first inlet programmable valve of each adsorption tower is connected to the membrane separation tail gas outlet main pipeline; the second inlet programmable valve of each adsorption tower is connected to the low-temperature mixed gas inlet main pipeline; the third inlet programmable valve of each adsorption tower is connected to the high-temperature steam inlet main pipeline; the fourth inlet programmable valve of each adsorption tower is connected to the first outlet programmable valve of the adsorption tower; and the fifth inlet programmable valve of each adsorption tower is connected to the second outlet programmable valve of the adsorption tower.

10. The system according to claim 9, characterized in that, The system also includes a membrane separation unit and a purification unit. The membrane separation unit includes a gas inlet, a membrane separation tail gas outlet, and a CO2 product gas outlet. The purification unit includes a gas inlet and a liquid outlet. The third outlet programmable valve of each adsorption tower is connected to the gas inlet of the membrane separation unit; the fourth outlet programmable valve of each adsorption tower is connected to the outside atmosphere; and the fifth outlet programmable valve of each adsorption tower is connected to the outside atmosphere.

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