A method and system for oxygen removal and solvent regeneration outside an absorber column
By using a regeneration and deoxygenation system outside the absorbent tower, supplemented with lean liquor flash-compressed steam and nitrogen, the problem of absorbent oxidation and degradation caused by oxygen in the rich liquor is solved, thus achieving absorbent stability and reducing system energy consumption, improving carbon capture efficiency and reducing operating costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHONGQING UNIV
- Filing Date
- 2026-01-28
- Publication Date
- 2026-07-07
Smart Images
Figure CN121715041B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of chemical absorption carbon capture technology, and more particularly to the regeneration and deoxygenation technology of rich solution in chemical absorption carbon capture systems. Background Technology
[0002] With increasing global attention on climate change, carbon capture, utilization, and storage (CCUS) technology is considered a crucial means of reducing carbon dioxide (CO2) emissions. Among numerous carbon capture technologies, chemical absorption (CEA) has been widely used in industry due to its high capture efficiency and mature process. A CEA carbon capture system typically includes an absorption tower and a regeneration tower. In the absorption tower, lean solution (fresh or regenerated absorbent solution used to absorb CO2) absorbs CO2 from the flue gas, becoming rich solution (the absorbent solution after absorbing CO2). Subsequently, the rich solution is transported to the regeneration tower for desorption, releasing CO2, while the regenerated lean solution returns to the absorption tower for recycling. However, in actual operation, the absorbent inevitably absorbs some O2 along with CO2; that is, a certain amount of O2 inevitably dissolves in the rich solution, especially when capturing flue gas with high oxygen content (>15%), such as combustible gas, where the amount of dissolved O2 is even greater. When the O2 enters the regeneration tower with the rich solution, it causes oxidative degradation of the absorbent under high-temperature conditions. This oxidative degradation not only reduces the absorbent's CO2 absorption capacity, affecting the carbon capture system's efficiency, but also increases absorbent loss, leading to higher operating costs. For example, in some carbon capture projects using MEA (ethanolamine) as the absorbent, the oxidative degradation of the absorbent caused by O2 in the rich solution increased the annual replenishment of absorbent by 20%, directly resulting in a 3% increase in operating costs. Existing technologies are insufficient in addressing the O2 problem in the rich solution of chemical absorption carbon capture systems, and most related measures increase the overall material or energy consumption of the carbon capture system and raise carbon capture costs. Therefore, there is an urgent need for a highly efficient, stable, and cost-effective rich solution deoxygenation technology.
[0003] To address the problems caused by O2 in rich solutions, some existing technologies employ the addition of antioxidants. However, this method has several limitations. On the one hand, the amount of antioxidant added is difficult to control precisely; too little antioxidant will not effectively inhibit oxidative degradation, while too much may affect the performance of the absorbent itself and the CO2 absorption and desorption process. On the other hand, the effect of antioxidants is not significant, and long-term use of antioxidants may lead to the accumulation of impurities in the system, affecting its normal operation.
[0004] In addition, some existing technologies attempt to reduce the oxygen content in the rich liquid by performing deep deoxygenation on the flue gas entering the absorption tower. However, this method requires a large amount of flue gas to be treated and is costly. Moreover, it can only reduce the initial dissolved oxygen level of the rich liquid to a certain extent and cannot fundamentally solve the problem of repeated accumulation of dissolved oxygen in the rich liquid.
[0005] Furthermore, patent CN 202311360702, "Method and System for Reducing Degradation Loss of Flue Gas Carbon Capture and Absorption Solvent," mentions stripping oxygen from the rich absorbent solvent to obtain oxygen-containing stripped gas and a pre-regenerated absorbent solution. The pre-regenerated absorbent solution is then regenerated to obtain regenerated gas and a lean absorbent solvent solution. While this method can regenerate oxygen physically dissolved in the rich absorbent solvent solution and reduce the oxygen concentration, it also presents several problems. First, stripping the rich solution with CO2 product gas at around 40°C causes the rich solution to reabsorb the "CO2 product gas," reducing the actual CO2 yield, increasing the CO2 content (CO2 load) in the rich solution, resulting in repeated CO2 absorption, and lowering the temperature of the rich solution. This increases the amount of steam required for regeneration in the regeneration tower, increasing system energy consumption. Furthermore, the compressed CO2 gas pressure is around 2 MPa, and high-pressure stripping significantly impacts absorbent performance. Second, the oxygen-containing stripped gas, after entering the downstream compressor, may cause excessive O2 concentration in the product. The product's CO2 purity is substandard; thirdly, the reflux of CO2 from the product causes a loss of product gas pressure, increasing compression work and system energy consumption; fourthly, the method of "extracting the regenerated gas in regeneration tower 3 by sending the oxygen-containing top gas through demister 7 to Venturi ejector 19 at the top of regeneration tower 3 to obtain carbon capture product" would require the regeneration tower to become negative pressure to achieve the extraction effect, making it impossible to guarantee that the pressure at the top of regeneration tower 3 is within the range of 10-50 kPaA, posing a safety risk to the operation of the regeneration tower. Therefore, achieving "reducing the operating temperature of the regeneration tower and reducing regeneration energy consumption costs" is difficult. In summary, the above solutions are difficult to achieve a synergistic reduction in oxygen concentration in the rich liquid and carbon capture energy consumption, and have drawbacks such as substandard product gas purity and increased unit heat consumption due to repeated CO2 absorption.
[0006] In summary, existing technologies are insufficient in solving the O2 problem in the rich solution of chemical absorption carbon capture systems, and all of them increase the overall energy consumption and cost of the carbon capture system. There is an urgent need for a high-efficiency, stable and cost-effective rich solution deoxygenation technology. Summary of the Invention
[0007] To address the problem in existing chemical absorption carbon capture systems where high oxygen content in the rich solution leads to oxidative degradation of the absorbent, affecting carbon capture efficiency and increasing operating costs, this invention provides an absorbent external regeneration and deoxygenation method and system.
[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0009] A method for external regeneration and deoxygenation of absorbent in a rich liquid tower, the method comprising the following steps:
[0010] 1) The lean liquid from the bottom of the regeneration tower enters the negative pressure buffer tank, with a lean liquid temperature of 100-110℃; the top of the negative pressure buffer tank is connected to the steam compressor through a reducing pipe, and the steam compressor provides negative pressure to the negative pressure buffer tank, extracting some water and a small amount of CO2 (CO2 that has not been completely desorbed in the lean liquid) from the negative pressure buffer tank. The extracted gas contains approximately 94-96% water and approximately 4-6% CO2. The steam entering the steam compressor has a temperature of 90-95℃ and a pressure of 0.05-0.07 MPa. The lean liquid after extraction by the steam compressor enters the lean-rich liquid heat exchanger through the lean liquid pump, with a temperature of 88-93℃.
[0011] 2) Water vapor containing a small amount of CO2 enters the steam compressor. After compression, the temperature is 115-120℃ and the pressure is 0.17-0.2 MPa. After the pressure is adjusted to 0.2-0.3 MPa by regulating valve I, it enters the regeneration deaerator. Under this pressure condition, the oxygen stripping efficiency is high and the impact on the absorbent performance is small.
[0012] 3) The regenerating deaerator is a packed tower structure. After the rich liquid exits the lean-rich liquid heat exchanger, it enters the liquid distributor (such as a tray distributor or a nozzle distributor) at the top of the regenerating deaerator from the top, ensuring that the rich liquid is evenly dispersed on the cross-section of the packed tower, forming a uniform liquid film on the surface of the packing and flowing down, fully contacting the stripping gas source, and after contacting the steam spray, it flows out from the bottom into the top of the regeneration tower; the steam enters the gas distribution device (such as a perforated plate or bubble cap plate) at the bottom of the regenerating deaerator from the bottom up, so that the regeneration gas enters the packed tower evenly, completing the heating, regeneration, and stripping of the rich liquid before entering the gas-liquid separator.
[0013] 4) After being heated, regenerated, and stripped, the rich liquid enters the regeneration tower from the top. At this time, the rich liquid has been heated by the compressed steam, which further increases the temperature of the liquid entering the regeneration tower to 87-92℃, and some CO2 has been desorbed. The heat required for desorption of the rich liquid after entering the regeneration tower is reduced, and the amount of steam required is reduced, thereby reducing the regeneration heat consumption. It is expected to reduce the regeneration heat consumption by about 5-7%.
[0014] 5) The gas after heating and regenerating the rich liquid and stripping is called regeneration gas one, and the gas coming out of the top of the regeneration tower is called regeneration gas two. Regeneration gas one and regeneration gas two are passed through the gas cooler and then enter the gas-liquid separator. The separated condensate returns to the regeneration tower from the top. The separated gas is compressed by the CO2 compressor and then enters the membrane separation device. CO2 gas permeates through the membrane to obtain gaseous CO2 product. Water and other gases (oxygen and possible nitrogen) are trapped by the membrane and discharged.
[0015] As a further improvement of the present invention, the method also includes step 6). Step 6) is to monitor the deoxygenation effect of the rich liquid in real time. Oxygen content detectors are installed on the pipeline after the rich liquid pump and the bottom outlet pipeline of the regeneration deoxygenator. When the oxygen content of the rich liquid in the pipeline after the rich liquid pump exceeds the set threshold (e.g., above 25 ppm), nitrogen can be added to increase the flow rate of the stripping gas source. The regulating valve II of the nitrogen tank outlet pipeline is opened to increase the flow rate of the stripping gas source by 10-30%, optimize the stripping deoxygenation process, and ensure that the oxygen content of the rich liquid entering the regeneration tower is always maintained at a low level, such as below 10 ppm.
[0016] As a further improvement of the present invention, step 1) can further desorb and regenerate the lean liquor exiting the regeneration tower to reduce the CO2 load in the lean liquor, so that the loads of the lean liquor before and after extraction are 0.115~0.122 mol / mol. 吸收剂 0.094~0.103 mol / mol 吸收剂 Reducing the lean liquor load can improve the absorption rate of CO2 in the flue gas by the lean liquor in the absorption tower, thereby reducing the overall energy consumption of the system (expected to reduce the overall energy consumption by about 3-5%).
[0017] As a further improvement of the present invention, in step 3), the temperature of the rich liquid before entering the regenerator is 82-87℃, and the CO2 load is 0.384-0.392 mol / mol. 吸收剂 The temperature after exiting the regeneration deaerator is 87-92℃, and the CO2 load is 0.341-0.355 mol / mol. 吸收剂 .
[0018] As a further improvement of the present invention, the oxygen content detector in step 6) can be an electrochemical oxygen content sensor or an optical oxygen content sensor, which can quickly and accurately measure the oxygen content in the rich solution.
[0019] This invention provides an absorbent tower external regeneration and deoxygenation system, comprising a negative pressure buffer tank, a steam compressor, a regulating valve I, a regenerating deaerator, a gas cooler, a gas-liquid separator, a CO2 compressor, and a membrane separation device. The lean liquid inlet of the negative pressure buffer tank is connected to the lean liquid outlet at the bottom of the regeneration tower. The lean liquid outlet of the negative pressure buffer tank is connected to a lean-rich liquid heat exchanger via a lean liquid pump. The top of the negative pressure buffer tank is connected to the inlet of the steam compressor. The outlet of the steam compressor is connected to the bottom of the regenerating deaerator via the regulating valve I. The rich liquid outlet of the lean-rich liquid heat exchanger is connected to the top of the regenerating deaerator. The bottom outlet of the regenerating deaerator is connected to the top of the regeneration tower. The top outlet of the regenerating deaerator and the top outlet of the regeneration tower are connected to the inlet of the gas cooler via pipelines. The outlet of the gas cooler is connected to the inlet of the gas-liquid separator. The condensate outlet at the bottom of the gas-liquid separator is connected to the top of the regeneration tower. The top outlet of the gas-liquid separator is connected to the inlet of the CO2 compressor. The outlet of the CO2 compressor is connected to the membrane separation device.
[0020] As a further improvement of the present invention, the rich liquid outlet at the bottom of the absorption tower is connected to the lean and rich liquid heat exchanger after the rich liquid pump, and oxygen content detectors are respectively installed on the pipeline after the rich liquid pump and on the bottom outlet pipeline of the regeneration deaerator.
[0021] As a further improvement of the present invention, an absorbent tower external regeneration and deoxygenation system further includes a nitrogen tank, wherein the outlet of the nitrogen tank is connected to a pipe at the top of a negative pressure buffer tank via a regulating valve II.
[0022] The key technical points and protection points of this invention are as follows:
[0023] 1. An integrated method and system for external regeneration and deoxygenation of absorbent towers, which does not require changes to solvent formulation or consumption of antioxidants, can significantly reduce the degradation loss of flue gas carbon capture solvents simply by optimizing the process flow, and the entire process flow can also reduce the overall energy consumption of carbon capture.
[0024] 2. Combining lean liquor flash evaporation and compression with absorbent deoxygenation can, on the one hand, recover heat from the lean liquor and reduce the CO2 load in the lean liquor, thereby reducing carbon capture energy consumption; on the other hand, it can achieve absorbent deoxygenation and simultaneously regenerate the rich liquor, pre-desorbing and regenerating the rich liquor and raising its temperature, thus reducing the amount of steam required for the regeneration tower. This achieves a synergistic effect of deoxygenation and energy saving.
[0025] 3. The steam generated from the flash evaporation of lean liquor is used as the stripping gas source, eliminating the need for additional gas purchases. Compared to using CO2 product gas or purchased nitrogen, the pressure and temperature of steam are more suitable. Furthermore, in special operating conditions—that is, when the oxygen content in the front-end rich liquor is high and exceeds the set threshold—nitrogen is used as a supplementary stripping gas source to fully ensure the stripping effect.
[0026] 4. Considering the impurities such as water, oxygen and nitrogen that may be present in the product gas, a membrane separation device is installed at the back end of the compressor, combining membrane separation with chemical absorption to further ensure the purity of the product CO2.
[0027] The absorbent tower external regeneration and deoxygenation method and system of the present invention does not require changes to the absorbent formulation, does not consume antioxidants, and can achieve a simultaneous reduction in absorbent oxidative degradation loss and overall system energy consumption simply by optimizing the process flow. It has strong applicability and has many significant beneficial technical effects:
[0028] 1. From the perspective of absorbent protection, this invention can effectively reduce the oxygen content in the rich liquid entering the regeneration tower to below 10 ppm, significantly reducing the oxidative degradation of the absorbent under the high-temperature environment of the regeneration tower. For a 2000-ton / year flue gas carbon capture unit, previously 30% of the absorbent needed to be replenished annually due to oxidative degradation; after applying this technology, the replenishment amount can be reduced to 10%-15%. This not only extends the service life of the absorbent but also reduces its usage cost, directly lowering the unit cost of carbon capture.
[0029] 2. From the perspective of ensuring carbon capture efficiency. Because the performance of the absorbent is better maintained, the capture efficiency of the carbon capture system, which was reduced to 80%-85% due to the oxidative degradation of the absorbent, can be improved and stabilized at 90%-95%, which significantly improves the carbon capture capacity and ensures the capture volume and CO2 production of the system.
[0030] 3. From the perspective of energy consumption and operating costs: First, the lean liquid enters the negative pressure buffer tank, where it undergoes extraction, further desorbing and reducing its own CO2 load. After heat exchange and cooling before entering the absorption tower, it can absorb more CO2, thereby reducing the unit energy consumption and cost of carbon capture. It is expected to achieve an overall energy consumption reduction of 3-5%. Second, in the regeneration deaerator, the rich liquid is regenerated by steam heating. On the one hand, the latent heat of steam further increases the temperature entering the regeneration tower; on the other hand, some CO2 is desorbed first under the action of steam, reducing the heat required for desorption after the rich liquid enters the regeneration tower and reducing the amount of steam required, thus achieving a reduction in regeneration heat consumption. It is expected to achieve a reduction in regeneration heat consumption of 5-7%. In summary, by comprehensively applying the absorbent tower external regeneration and deaeration technology of this invention, carbon capture heat consumption can be reduced by about 8-12%, thereby reducing the cost of capture.
[0031] 4. Utilizing the steam generated from the flash evaporation of lean liquor as the stripping gas source eliminates the need for additional gas purchases, saving on gas procurement costs. Furthermore, in special operating conditions—specifically, when the oxygen content in the rich liquor exceeds a set threshold—nitrogen can be used as a supplementary stripping gas source. This ensures effective stripping, and the chemical stability of nitrogen prevents it from reacting with the rich liquor components, guaranteeing the stability and reliability of the deoxygenation process and providing strong support for the long-term stable operation of the carbon capture system. Attached Figure Description
[0032] Figure 1 This is a schematic diagram of an absorbent tower external regeneration and deoxygenation system according to the present invention.
[0033] In the attached diagram, 1: negative pressure buffer tank, 2: steam compressor, 3: regulating valve I, 4: regenerator deaerator, 5: gas cooler, 6: gas-liquid separator, 7: CO2 compressor, 8: membrane separation device, 9: oxygen content detector, 10: nitrogen tank, 11: regulating valve II. Detailed Implementation
[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.
[0035] A method for external regeneration and deoxygenation of an absorbent tower, comprising the following steps:
[0036] 1) The lean solution from the bottom of the regeneration tower enters negative pressure buffer tank 1, such as... Figure 1 As shown, the lean solution temperature is 100-110℃. The top of the negative pressure buffer tank 1 is connected to the steam compressor 2 via a reducing pipe. The steam compressor 2 provides negative pressure to the negative pressure buffer tank 1, extracting some water and a small amount of CO2 (CO2 that has not been completely desorbed from the lean solution) from the negative pressure buffer tank 1. The extracted gas contains approximately 94-96% water and 4-6% CO2. This step further desorbs and regenerates the lean solution exiting the regeneration tower, reducing the CO2 load in the lean solution. The loads of the lean solution before and after extraction are 0.115~0.122 mol / mol, respectively. 吸收剂 0.094~0.103 mol / mol 吸收剂 Reducing the lean liquor load can improve the absorption rate of CO2 in the flue gas by the lean liquor in the absorber, thereby reducing the overall energy consumption of the system (expected to reduce the overall energy consumption by about 3-5%). The steam temperature entering the steam compressor 2 is 90-95℃ and the pressure is 0.05-0.07Mpa. The lean liquor extracted by the steam compressor 2 enters the lean-rich liquor heat exchanger through the lean liquor pump, and the temperature is 88-93℃.
[0037] 2) Water vapor containing a small amount of CO2 enters the steam compressor 2. After compression, the temperature is 115-120℃ and the pressure is 0.17-0.2Mpa. After the pressure is adjusted to 0.2-0.3Mpa by the regulating valve I3, it enters the regeneration deaerator 4. Under this pressure condition, the oxygen stripping efficiency is high and the impact on the absorbent performance is small.
[0038] 3) The regenerating deaerator 4 is a packed tower structure. After the rich liquid exits the lean-rich liquid heat exchanger, it enters the liquid distributor (such as a tray-type distributor or a nozzle-type distributor) at the top of the regenerating deaerator 4 from the top, ensuring that the rich liquid is evenly dispersed on the cross-section of the packed tower, forming a uniform liquid film on the packing surface and flowing down. This film fully contacts the stripping gas source and, after contact with the steam spray, flows out from the bottom into the top of the regeneration tower. Steam enters the gas distribution device (such as a perforated plate or bubble cap plate) at the bottom of the regenerating deaerator 4 from the bottom up, ensuring that the regeneration gas enters the packed tower evenly. After completing the heating, regeneration, and stripping of the rich liquid, it enters the gas-liquid separator 6. The temperature of the rich liquid before entering the regenerating deaerator 4 is 82-87℃, and the CO2 load is 0.384-0.392 mol / mol. 吸收剂 The temperature after exiting regeneration deaerator 4 is 87-92℃, and the CO2 load is 0.341-0.355 mol / mol. 吸收剂 .
[0039] 4) After being heated, regenerated, and stripped, the rich liquid enters the regeneration tower from the top. At this time, the rich liquid has been heated by the compressed steam, which further increases the temperature of the liquid entering the regeneration tower to 87-92℃. Some CO2 has also been desorbed. The heat required for desorption of the rich liquid after entering the regeneration tower is reduced, and the amount of steam required is reduced, thereby reducing the regeneration heat consumption. It is expected to reduce the regeneration heat consumption by about 5-7%.
[0040] 5) The gas after heating and regenerating the rich liquid and stripping is called regeneration gas one. The main substance of regeneration gas one is water, containing a small amount of CO2 and O2. The gas coming out from the top of the regeneration tower is called regeneration gas two. Regeneration gas one and regeneration gas two enter the gas-liquid separator 6 after passing through the gas cooler 5. The separated condensate returns to the regeneration tower from the top. The separated gas is compressed by the CO2 compressor 7 and enters the membrane separation device 8. CO2 gas permeates through the membrane to obtain gaseous CO2 product. Water and other gases (oxygen and possible nitrogen) are intercepted by the membrane and discharged.
[0041] 6) To monitor the deoxygenation effect of the rich solution in real time, oxygen content detectors 9 are installed on the pipeline after the rich solution pump and the bottom outlet pipeline of the regeneration deaerator 4. The oxygen content detectors 9 can be electrochemical oxygen content sensors or optical oxygen content sensors, which can quickly and accurately measure the oxygen content in the rich solution. When the oxygen content of the rich solution in the pipeline after the rich solution pump exceeds the set threshold (e.g., above 25 ppm), the stripping gas source flow rate can be increased. For example, the stripping gas source flow rate can be increased by supplementing nitrogen. The regulating valve II 11 of the outlet pipeline of the nitrogen tank 10 can be opened to increase the stripping gas source flow rate by 10~30%, optimize the stripping deoxygenation process, and ensure that the oxygen content of the rich solution entering the regeneration tower is always maintained at a low level, such as below 10 ppm.
[0042] An absorbent tower external regeneration and deoxygenation system includes a negative pressure buffer tank 1, a steam compressor 2, a regulating valve I 3, a regenerator deaerator 4, a gas cooler 5, a gas-liquid separator 6, a CO2 compressor 7, a membrane separator 8, an oxygen content detector 9, a nitrogen tank 10, and a regulating valve II 11, as shown below. Figure 1 As shown. The lean liquid inlet of the negative pressure buffer tank 1 is connected to the lean liquid outlet at the bottom of the regeneration tower. The lean liquid outlet of the negative pressure buffer tank 1 is connected to the lean-rich liquid heat exchanger via a lean liquid pump. The top of the negative pressure buffer tank 1 is connected to the inlet of the steam compressor 2. The outlet of the steam compressor 2 is connected to the bottom of the regeneration deaerator 4 via a regulating valve I3. The rich liquid outlet of the lean-rich liquid heat exchanger is connected to the top of the regeneration deaerator 4. The bottom outlet of the regeneration deaerator 4 is connected to the top of the regeneration tower. The top outlet of the regeneration deaerator 4 and the top outlet of the regeneration tower are connected to the inlet of the gas cooler 5 via a pipeline. The outlet of the gas cooler 5 is connected to the inlet of the gas-liquid separator 6. The condensate outlet at the bottom of the gas-liquid separator 6 is connected to the top of the regeneration tower. The top outlet of the gas-liquid separator 6 is connected to the inlet of the CO2 compressor 7. The outlet of the CO2 compressor 7 is connected to the membrane separation device 8. The rich liquid outlet at the bottom of the absorption tower is connected to the lean-rich liquid heat exchanger via a rich liquid pump. Oxygen content detectors 9 are installed on the pipeline after the rich liquid pump and on the bottom outlet pipeline of the regeneration deaerator 4, respectively. The outlet of the nitrogen tank 10 is connected to the pipeline at the top of the negative pressure buffer tank 1 via a regulating valve II 11.
[0043] The specific improvements made in this invention are as follows:
[0044] 1) First, the rich solution is deoxygenated using a stripping deoxygenation method. Stripping is an effective method for removing dissolved gases and volatile substances from water based on the theory of gas-liquid phase equilibrium and mass transfer rate. In this invention, when stripping gas is introduced into the rich solution, under the action of the packing material, the dissolved oxygen in the rich solution will cross the gas-liquid interface and enter the gas phase, thereby achieving the purpose of removing oxygen from the rich solution.
[0045] 2) Considering that setting up a separate stripping and deoxygenation unit would increase energy consumption, the lean liquor flash compression is combined with absorbent deoxygenation. On the one hand, lean liquor flash compression can recover the heat of the lean liquor and reduce the CO2 load in the lean liquor, thereby reducing the energy consumption of carbon capture. On the other hand, the steam after lean liquor flash compression can also be used as stripping gas for absorbent deoxygenation, and the rich liquor can be regenerated simultaneously. The rich liquor is preheated and desorbed for regeneration, reducing the amount of steam required for the regeneration tower. This can make full use of the gas resources in the system (and also solve the problem of the impact of using compressed CO2 gas as the purge gas pressure for high-pressure stripping on the performance of the absorbent), without the need to introduce other gases, thus reducing operating costs.
[0046] 3) The above solution achieves deoxygenation in rich liquid without increasing system energy consumption; on the contrary, it reduces system energy consumption, achieving a synergistic effect of deoxygenation and energy saving. To further ensure the stripping effect, nitrogen is also provided as a supplementary stripping gas source. Furthermore, considering the impurities such as water, oxygen, and nitrogen that may be present in the product gas, a membrane separation device is installed at the end of the compressor, combining membrane separation with chemical absorption to further ensure the purity of the product CO2.
[0047] Taking a 2000-ton / year flue gas carbon capture unit as an example, its initial inlet flue gas parameters and operating parameters are as follows:
[0048] Table 1. Inlet flue gas parameters for a 2000-ton / year gas-fired flue gas carbon capture unit.
[0049] project parameter flue gas volume <![CDATA[6500Nm 3 / h]]> <![CDATA[CO2]]> 3.2% <![CDATA[O2]]> 14.2% <![CDATA[N2]]> 75.2% <![CDATA[H2O]]> 7.4% dust concentration <![CDATA[≤1mg / Nm 3 ]]> <![CDATA[SO2 concentration]]> <![CDATA[≤5mg / Nm 3 ]]> <![CDATA[NO x Concentration <![CDATA[≤5mg / Nm 3 ]]> temperature 90℃ (wash temperature drops to 40℃) pressure 4 kPa
[0050] Table 2 Operating parameters of a 2000-ton / year flue gas carbon capture unit
[0051] project parameter absorbent circulation rate <![CDATA[13m 3 / h]]> Total amine concentration 30% Lean liquor outlet temperature of regeneration tower 104℃ Lean liquid load <![CDATA[0.121mol / mol 吸收剂 ]]> Temperature of rich liquid entering the regeneration tower 85℃ Rich liquid loading <![CDATA[0.389mol / mol 吸收剂 ]]> oxygen content in rich solution 25~30ppm Interstage cooling temperature drop 10℃ Regeneration heat consumption <![CDATA[3.2 GJ / tCO2]]> Regenerative power consumption <![CDATA[84 kWh / tCO2]]> Absorbent loss <![CDATA[2.7 kg / tCO2]]>
[0052] During normal operation of a 2000-ton / year carbon capture unit, the high oxygen content in the flue gas leads to an absorption loss of 2.7 kg / tCO2 due to oxidation and volatilization, requiring replacement of the entire absorption medium after one year of operation. Furthermore, the low CO2 concentration in the flue gas results in high regeneration heat consumption and capture costs. Therefore, to synergistically reduce absorption loss and regeneration heat consumption, an external absorption medium regeneration and deoxygenation device was installed on the system.
[0053] 1. Device parameters
[0054] (1) Original absorption and regeneration system
[0055] The absorption tower has a diameter of 1.5m and a height of 40m, while the regeneration tower has a diameter of 1m and a height of 28m. It is equipped with energy-saving processes such as interstage cooling and rich liquid diversion.
[0056] (2) Lean liquid flash compression system
[0057] Configure one horizontal lean liquid flash evaporator with a diameter of 1.5m, a length of 2.25m, and an internal volume of 4m³. 3 It is equipped with a compressor with a shaft power of 30 kW and related piping.
[0058] (3) Regeneration and deoxygenation system
[0059] A steam regeneration deaerator is configured. This deaerator is a packed tower type, with a tower body of φ800*8000mm, filled with Pall ring packing at a height of 3m. An electrochemical oxygen content sensor is installed on the rich liquor outlet pipe at the bottom of the packed tower. After exiting the rich-lean-rich liquor heat exchanger, the rich liquor enters the tray-type distributor at the top of the regeneration deaerator packed tower from the top. After contacting the steam spray, it flows out from the bottom and enters the top of the regeneration tower. Steam enters the bubble cap tray at the bottom of the deaerator packed tower from the bottom to the top, completing the heating, regeneration, and stripping of the rich liquor before entering the gas-liquid separator at the rear.
[0060] (4) Membrane separation system
[0061] A membrane separation system is configured, using a PVAm hybrid matrix membrane to separate CO2, with a designed processing capacity of 200 Nm³. 3 The compressor pressure rises to 4 MPa.
[0062] 2. Implementation Results
[0063] When the original carbon capture system is operating normally, due to the high oxygen content in the flue gas, the oxidation and volatilization loss of the absorbent reaches 2.7 kg / tCO2, and all absorbents need to be replaced after one year of operation; in addition, due to the low CO2 concentration in the flue gas, its regeneration heat consumption reaches 3.2 GJ / tCO2.
[0064] After applying the process of this invention:
[0065] (1) The lean liquid from the bottom of the regeneration tower enters the negative pressure buffer tank. The temperature of the lean liquid is 104℃. The steam compressor extracts some water and a small amount of CO2 from the lean liquid into the negative pressure buffer tank. The extracted gas contains about 95% water and about 5% CO2. After extraction, the load of the lean liquid is 0.121 mol / mol. 吸收剂 Reduced to 0.098 mol / mol 吸收剂 The steam entering the steam compressor has a temperature of 94℃ and a pressure of 0.065 MPa. The lean liquor extracted by the steam compressor enters the lean-rich liquor heat exchanger through the lean liquor pump, where the temperature is 90.6℃.
[0066] (2) Water vapor containing a small amount of CO2 enters the steam compressor, and after compression, the temperature is 117.9℃, the pressure is 0.186 MPa, and the flow rate is 1305 Nm³. 3The liquid, at a rate of / h, is pressurized to approximately 0.25 MPa by regulating valve 3 before entering the regeneration deaerator. Due to the latent heat of steam and pressure, the temperature of the rich liquid before entering the regeneration deaerator is 86.1℃, and the CO2 load is 0.389 mol / mol. 吸收剂 The oxygen content was 17 ppm; the temperature exiting the regenerator was 90.5℃, and the CO2 load was 0.348 mol / mol. 吸收剂 Oxygen content 5 ppm.
[0067] (3) The gas after heating and regenerating the rich liquid and stripping is cooled together with the regenerator at the top outlet of the regeneration tower and enters the gas-liquid separator. The separated condensate returns to the regeneration tower from the top. The separated gas is compressed by the CO2 compressor and enters the membrane separation device. The CO2 gas permeates through the membrane to obtain gaseous CO2 product. Water, oxygen and possible nitrogen are trapped by the membrane and discharged.
[0068] (4) In addition, an electrochemical oxygen content sensor is installed on the pipeline after the rich liquid pump. When the rich liquid oxygen content in the pipeline exceeds 25ppm, an alarm program is triggered and an instruction is output to prompt the opening of the regulating valve of the nitrogen tank outlet pipeline, increasing the stripping gas source flow rate by 10-30%, optimizing the stripping and deoxygenation process, and ensuring that the rich liquid oxygen content entering the regeneration tower is always maintained below 10ppm.
[0069] After applying the process of this invention, the oxidative degradation of the absorbent is significantly reduced, and the total loss due to oxidation and volatilization is reduced to 1.05 kg / tCO2. Moreover, after one year of continuous operation, the capture efficiency can still remain stable at over 90%. There is no need to replace all the absorbent; only replenishment is required during operation. This significantly improves the carbon capture capacity, enhances the effectiveness of the entire system in addressing carbon emission issues, and reduces the cost of the absorbent by approximately 800,000 yuan per year. Furthermore, the regeneration heat consumption of the carbon capture system was reduced from 3.2 GJ / tCO2 to 2.81 GJ / tCO2. Although this process also increased the power consumption of the compressor, the increased heat consumption per unit of power (compared to a compressor shaft power of 30kW) is only 0.294 GJ / tCO2. Considering the increased power consumption of the compressor, the system's regeneration heat consumption can still be reduced to 3.1 GJ / tCO2. Based on a steam price of 127.6 yuan / GJ and an electricity price of 0.513 yuan / kWh, the total cost can still be reduced by 8 yuan / tCO2. Moreover, this process uses flash-compressed steam as the stripping gas source, eliminating the need for additional gas purchases. In summary, this process does not increase system material consumption or only slightly increases it (nitrogen is used under special operating conditions), while reducing overall system energy consumption. It achieves a synergistic reduction in absorbent loss and regeneration heat consumption in the carbon capture system, resulting in significant economic benefits.
[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. A method for external regeneration and deoxygenation of an absorbent tower, characterized in that: The method includes the following steps: 1) The lean liquid from the bottom of the regeneration tower enters the negative pressure buffer tank (1), and the temperature of the lean liquid is 100-110℃; the top of the negative pressure buffer tank (1) is connected to the steam compressor (2), and the steam compressor (2) provides negative pressure to the negative pressure buffer tank (1), extracting some water and a small amount of CO2 from the lean liquid into the negative pressure buffer tank (1). The extracted gas contains about 94-96% water and about 4-6% CO2. The steam temperature entering the steam compressor (2) is 90-95℃ and the pressure is 0.05-0.07Mpa. The lean liquid after being extracted by the steam compressor (2) enters the lean-rich liquid heat exchanger through the lean liquid pump, and the temperature is 88-93℃. 2) Water vapor containing a small amount of CO2 enters the steam compressor (2), and after compression, the temperature is 115-120℃ and the pressure is 0.17-0.2Mpa. After the pressure is adjusted to 0.2-0.3Mpa by regulating valve I (3), it enters the regeneration deaerator (4). 3) The regenerator (4) is a packed tower structure. After the rich liquid exits the lean and rich liquid heat exchanger, it enters the liquid distributor at the top of the regenerator (4) from the top, ensuring that the rich liquid is evenly dispersed on the cross-section of the packed tower and forms a uniform liquid film on the surface of the packing to flow down, fully contacting the stripping gas source. After contacting the steam spray, it flows out from the bottom and enters the top of the regeneration tower. The steam enters the gas distribution device at the bottom of the regenerator (4) from the bottom up, so that the regeneration gas enters the packed tower evenly, and after completing the heating, regeneration, and stripping of the rich liquid, it enters the gas-liquid separator (6). 4) After being heated, regenerated, and stripped, the rich liquid enters the regeneration tower from the top. At this point, the rich liquid has been heated by the compressed steam, which further increases the temperature of the liquid entering the regeneration tower to 87-92℃, and some CO2 has been desorbed. 5) The gas after heating and regenerating the rich liquid and stripping is called regeneration gas one, and the gas coming out of the top of the regeneration tower is called regeneration gas two. Regeneration gas one and regeneration gas two are passed through the gas cooler (5) and then enter the gas-liquid separator (6). The separated condensate returns to the regeneration tower from the top. The separated gas is compressed by the CO2 compressor (7) and then enters the membrane separation device (8). CO2 gas permeates through the membrane to obtain gaseous CO2 product. Water and other gases are intercepted by the membrane and discharged.
2. The method for external regeneration and deoxygenation of an absorbent tower according to claim 1, characterized in that, The method also includes step 6). In step 6), to monitor the deoxygenation effect of the rich liquid in real time, oxygen content detectors (9) are installed on the pipeline after the rich liquid pump and the bottom outlet pipeline of the regeneration deoxygenator (4). When the oxygen content of the rich liquid in the pipeline after the rich liquid pump exceeds the set threshold, nitrogen can be added to increase the flow rate of the stripping gas source and open the regulating valve II (11) of the outlet pipeline of the nitrogen tank (10) to ensure that the oxygen content of the rich liquid entering the regeneration tower is always maintained at a low level.
3. A method for external regeneration and deoxygenation of an absorbent tower according to claim 1 or 2, characterized in that, Step 1) The lean liquor exiting the regeneration tower can be further desorbed and regenerated to reduce the CO2 load in the lean liquor. The CO2 load of the lean liquor before and after extraction is 0.115~0.122 mol / mol. 吸收剂 0.094~0.103 mol / mol 吸收剂 Reducing the lean liquor load can improve the absorption rate of CO2 in the flue gas by the lean liquor in the absorber, thereby reducing the overall energy consumption of the system.
4. A method for external regeneration and deoxygenation of an absorbent tower according to claim 1 or 2, characterized in that, In step 3), the temperature of the rich liquor before entering the regenerator (4) is 82-87℃, and the CO2 load is 0.384-0.392 mol / mol. 吸收剂 The temperature after exiting the regenerator (4) is 87-92℃, and the CO2 load is 0.341-0.355mol / mol. 吸收剂 .
5. A method for external regeneration and deoxygenation of an absorbent tower according to claim 1 or 2, characterized in that, In step 5), the main component of the regenerated gas is water, with small amounts of CO2 and O2.
6. The method for external regeneration and deoxygenation of an absorbent tower according to claim 2, characterized in that, The oxygen content detector (9) in step 6) can be an electrochemical oxygen content sensor or an optical oxygen content sensor, which can quickly and accurately measure the oxygen content in the rich solution.
7. An absorbent tower external regeneration and deoxygenation system, characterized in that, It includes a negative pressure buffer tank (1), a steam compressor (2), a regulating valve I (3), a regenerating deaerator (4), a gas cooler (5), a gas-liquid separator (6), a CO2 compressor (7), and a membrane separation device (8); The lean liquid inlet of the negative pressure buffer tank (1) is connected to the lean liquid outlet at the bottom of the regeneration tower. The lean liquid outlet of the negative pressure buffer tank (1) is connected to the lean-rich liquid heat exchanger via a lean liquid pump. The top of the negative pressure buffer tank (1) is connected to the inlet of the steam compressor (2). The outlet of the steam compressor (2) is connected to the bottom of the regeneration deaerator (4) via regulating valve I (3). The rich liquid outlet of the lean-rich liquid heat exchanger is connected to the top of the regeneration deaerator (4). The bottom outlet of the regeneration deaerator (4) is... The top outlet of the regenerating deaerator (4) is connected to the top outlet of the regenerating tower via a pipeline to the inlet of the gas cooler (5). The outlet of the gas cooler (5) is connected to the inlet of the gas-liquid separator (6). The condensate outlet at the bottom of the gas-liquid separator (6) is connected to the top of the regenerating tower. The top outlet of the gas-liquid separator (6) is connected to the inlet of the CO2 compressor (7). The outlet of the CO2 compressor (7) is connected to the membrane separation device (8).
8. The absorbent tower external regeneration and deoxygenation system according to claim 7, characterized in that, The rich liquid outlet at the bottom of the absorption tower is connected to the lean and rich liquid heat exchanger after the rich liquid pump. Oxygen content detectors (9) are installed on the pipeline after the rich liquid pump and on the bottom outlet pipeline of the regeneration deaerator (4).
9. The absorbent tower external regeneration and deoxygenation system according to claim 8, characterized in that, It also includes a nitrogen tank (10), the outlet of which is connected to a pipe at the top of the negative pressure buffer tank (1) via a regulating valve II (11).