Absorbent out-tower regeneration and deoxygenization method and absorbent out-tower regeneration and deoxygenization system

Abstract

The method comprises the following steps: 1) barren liquor discharged from the bottom of a regeneration tower enters a negative pressure buffer tank, the top of the negative pressure buffer tank is connected with a steam compressor, and the barren liquor extracted by the steam compressor enters a barren-rich liquor heat exchanger through a barren liquor pump; 2) water vapor containing a small amount of CO2 enters a vapor compressor, is regulated by a regulating valve I and then enters a regeneration deaerator; (3) the rich liquid enters the top of a regeneration deaerator from top after going out of the rich and lean liquid heat exchanger, and steam enters the regeneration deaerator from bottom to top; (4) the rich liquid enters a regeneration tower from the top after being subjected to heating regeneration and air stripping; and (5) after heating regeneration and air stripping of the rich liquid are completed, regenerated gas I and regenerated gas II from the top of the regeneration tower pass through a gas cooler together and then enter a gas-liquid separator, separated condensate water returns to the regeneration tower from the top, and separated gas enters a membrane separation device after being compressed by a CO2 compressor. According to the method, the energy consumption of the system is reduced, and deoxygenation and energy conservation are coordinated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical absorption carbon capture, and particularly relates to a rich liquid regeneration and oxygen removal technology in a chemical absorption carbon capture system. BACKGROUND

[0002] With the increasing global concern about climate change, carbon capture, utilization and storage (CCUS) technology is considered as one of the important means to reduce carbon dioxide (CO2) emissions. Among various carbon capture technologies, chemical absorption method is widely used in the industrial field due to its high capture efficiency and mature process. The chemical absorption carbon capture system usually includes an absorption tower and a regeneration tower. In the absorption tower, the lean liquid (fresh or regenerated absorbent solution used for absorbing CO2) absorbs CO2 in the flue gas to become rich liquid (absorbent solution after absorbing CO2); then, the rich liquid is transported to the regeneration tower for desorption to release CO2, and the regenerated lean liquid returns to the absorption tower for cyclic absorption. However, in the actual operation process, the absorbent will inevitably absorb part of O2 while absorbing CO2, that is, a certain amount of O2 will inevitably be dissolved in the rich liquid, especially when carbon capture is performed on flue gas with a high oxygen content (>15%) such as fuel gas flue gas, the amount of dissolved O2 is more. These O2 will cause the oxidation degradation of the absorbent when the rich liquid enters the regeneration tower in a high temperature environment. The oxidation degradation of the absorbent not only reduces its CO2 absorption capacity and affects the capture efficiency of the carbon capture system, but also increases the loss of the absorbent, thereby increasing the operating cost of carbon capture. For example, in some carbon capture projects using MEA (ethanolamine) as the absorbent, the oxidation degradation of the absorbent caused by O2 in the rich liquid increases the annual replenishment amount of the absorbent by 20%, directly leading to a 3% increase in operating cost. The existing technologies have deficiencies in solving the problem of O2 in the rich liquid of the chemical absorption carbon capture system, and most of the related measures increase the overall material consumption or energy consumption level of the carbon capture system and increase the carbon capture cost. Therefore, there is an urgent need for an efficient, stable and cost-effective rich liquid oxygen removal technology.

[0003] To solve the problem of O2 in the rich liquid, some existing technologies currently use the method of adding antioxidants. However, this method has many limitations. On the one hand, it is difficult to accurately control the amount of antioxidant added. Adding too little cannot effectively inhibit oxidation degradation, and adding too much may affect the performance of the absorbent itself and the absorption and desorption process of CO2; on the other hand, the persistence of antioxidant is not significant, and long-term use of antioxidants may accumulate impurities in the system, affecting the normal operation of the system.

[0004] In addition, some existing technologies attempt to reduce the oxygen content in the rich solution by deeply removing oxygen from the flue gas entering the absorption tower, but this way of processing flue gas has a large processing capacity and high cost, and can only reduce the initial dissolved oxygen level of the rich solution to a certain extent, and cannot fundamentally solve the problem of repeated accumulation of dissolved oxygen in the rich solution.

[0005] In addition, the patent CN 202311360702 “Method and system for reducing degradation loss of flue gas carbon capture absorption solvent” mentions stripping oxygen from the absorption solvent rich solution to obtain oxygen-containing stripping gas and spent absorption solution, and then regenerating the spent absorption solution to obtain regenerated gas and absorption solvent lean solution. Although this method can regenerate the oxygen physically dissolved in the absorption solvent rich solution and reduce the oxygen concentration in the absorption solvent, it still has some problems. First, using CO2 product gas at about 40℃ to strip the rich solution will cause the rich solution to absorb CO2 product gas again, reducing the actual yield of CO2 and increasing the CO2 content (CO2 load) in the rich solution, causing repeated absorption of CO2 and reducing the temperature of the rich solution, thereby increasing the amount of steam required for the regeneration of the rich solution in the regeneration tower and increasing the energy consumption of the system. The pressure of the compressed CO2 gas is about 2Mpa, and high-pressure stripping has a greater impact on the performance of the absorbent. Second, the oxygen-containing stripping gas stripped out may cause the O2 concentration in the product to exceed the standard and the CO2 purity in the product to be substandard. Third, the backflow of CO2 product will cause the pressure of the product gas to be lost, increasing the compression work and the energy consumption of the system. Fourth, the oxygen-containing stripping gas is sent to the top of the regeneration tower 3 through the demister 7, and the regenerated gas in the regeneration tower 3 is extracted through the Venturi ejector 19 to obtain the carbon capture product. If the extraction effect is to be achieved, the regeneration tower will be under negative pressure, which cannot guarantee the pressure at the top of the regeneration tower 3 to be in the range of 10-50kPaA, posing a safety risk to the operation of the regeneration tower. Therefore, it is difficult to achieve the reduction of the operating temperature of the regeneration tower and the reduction of the regeneration energy consumption cost. In summary, the above scheme cannot achieve the simultaneous reduction of the oxygen concentration in the rich solution and the carbon capture energy consumption, and has the disadvantages of substandard product gas purity and increased unit heat consumption due to repeated absorption of CO2.

[0006] In summary, the existing technologies have deficiencies in solving the problem of O2 in the rich solution of the chemical absorption method carbon capture system, and increase the overall energy consumption level of the carbon capture system and the cost of carbon capture. Therefore, there is an urgent need for an efficient, stable and cost-effective rich solution oxygen removal technology. SUMMARY

[0007] In view of the problem that the high oxygen content in the rich solution of the chemical absorption method carbon capture system causes the oxidation and degradation of the absorbent, affecting the carbon capture effect and increasing the operating cost, the present application provides an absorbent tower regeneration and oxygen removal method and system.

[0008] To solve the above technical problems, the application adopts the following technical solutions:

[0009] A method for regenerating and removing oxygen outside an absorbent rich liquid column, comprising the following steps:

[0010] 1) The lean liquid from the bottom of the regeneration tower enters a negative pressure buffer tank, and the temperature of the lean liquid is 100-110 DEG C; the top of the negative pressure buffer tank is connected with a steam compressor through a variable diameter pipeline, and the steam compressor provides negative pressure for the negative pressure buffer tank, and part of the water and a small part of CO2 (CO2 not completely desorbed in the lean liquid) in the lean liquid are extracted out of the negative pressure buffer tank, the water accounts for about 94-96% in the extracted gas, and the CO2 accounts for about 4-6%, the steam temperature entering the steam compressor is 90-95 DEG C, the pressure is 0.05-0.07 MPa, and the lean liquid after extraction by the steam compressor enters a lean-rich liquid heat exchanger through a lean liquid pump, and the temperature is 88-93 DEG C;

[0011] 2) The water vapor containing a small amount of CO2 enters the steam compressor, and after compression, the temperature is 115-120 DEG C, and the pressure is 0.17-0.2 MPa, and after adjusting the pressure to 0.2-0.3 MPa by adjusting valve I, it enters the regeneration oxygen remover; under this pressure condition, the oxygen stripping efficiency is high and the influence on the absorbent performance is small;

[0012] 3) The regeneration oxygen remover is a packed tower structure, the rich liquid out of the lean-rich liquid heat exchanger enters the liquid distributor (such as a groove plate distributor or a nozzle type distributor) at the top of the regeneration oxygen remover from the top, to ensure that the rich liquid is uniformly dispersed on the cross section of the packed tower, and a uniform liquid film is formed on the surface of the packing, which flows down and fully contacts with the stripping gas source, and after contacting with the steam spray, it flows out from the bottom and enters the top of the regeneration tower; the steam enters the gas distribution device (such as a perforated plate or a bubble cap tray) at the bottom of the regeneration oxygen remover from bottom to top, so that the regeneration gas uniformly enters the packed tower, and after the heating regeneration and stripping of the rich liquid, it enters the gas-liquid separator;

[0013] 4) The rich liquid after heating regeneration and stripping enters the regeneration tower from the top; at this time, the rich liquid has been heated by the compressed steam, and the temperature entering the regeneration tower is further increased to 87-92 DEG C, and part of the CO2 has been desorbed, the heat required for desorption of the rich liquid entering the regeneration tower is reduced, and the amount of steam required is reduced, thereby realizing the reduction of regeneration heat consumption, and it is expected to reduce the regeneration heat consumption by about 5-7%;

[0014] 5) The gas after the liquid-rich heating regeneration and stripping is used as regenerated gas 1, the gas at the top of the regeneration tower is used as regenerated gas 2, the regenerated gas 1 and the regenerated gas 2 are introduced into a gas-liquid separator after passing through a gas cooler, the condensed water separated is returned to the regeneration tower from the top, and the gas separated is compressed by a CO2 compressor and then introduced into a membrane separation device, gaseous CO2 product is obtained by allowing CO2 gas to pass through the membrane, and water and other gases (oxygen and possibly nitrogen) are discharged after being intercepted by the membrane.

[0015] As a further improvement of the present application, the method further comprises step 6) of monitoring the oxygen removal effect of the liquid-rich in real time, oxygen content detectors are arranged on the pipeline after the liquid-rich pump and the bottom outlet pipeline of the regeneration oxygen remover respectively, when the oxygen content of the liquid-rich in the pipeline after the liquid-rich pump exceeds a set threshold value (such as 25 ppm or more), the flow of the stripping gas source can be adjusted by supplementing nitrogen, the regulating valve II of the nitrogen tank outlet pipeline is opened, the flow of the stripping gas source is increased by 10-30%, the stripping oxygen removal process is optimized, and the oxygen content of the liquid-rich entering the regeneration tower is ensured to be maintained at a low level, such as 10 ppm or less.

[0016] As a further improvement of the present application, the lean liquid out of the regeneration tower can be further desorbed and regenerated to reduce the CO2 load in the lean liquid, the load of the lean liquid before and after extraction is 0.115-0.122 mol / mol 吸收剂 , 0.094-0.103 mol / mol 吸收剂 , and the reduction of the load of the lean liquid can improve the absorption rate of the lean liquid in the absorption tower to the CO2 in the flue gas, thereby reducing the overall energy consumption of the system (it is expected to reduce the overall energy consumption by about 3-5%).

[0017] As a further improvement of the present application, in step 3), the temperature of the liquid-rich before entering the regeneration oxygen remover is 82-87℃, the CO2 load is 0.384-0.392 mol / mol 吸收剂 , and the temperature after the regeneration oxygen remover is 87-92℃, the CO2 load is 0.341-0.355 mol / mol 吸收剂 .

[0018] As a further improvement of the present application, the oxygen content detector in step 6) can use an electrochemical oxygen content sensor or an optical oxygen content sensor, which can quickly and accurately measure the oxygen content in the liquid-rich.

[0019] The application provides an absorbent tower external regeneration and oxygen removal system, which comprises a negative pressure buffer tank, a steam compressor, an adjusting valve I, a regeneration and oxygen removal device, a gas cooler, a gas-liquid separator, a CO2 compressor and a membrane separation device; a lean liquid inlet of the negative pressure buffer tank is connected with a lean liquid outlet at the bottom of a regeneration tower, a lean liquid outlet of the negative pressure buffer tank is connected with a lean-liquid rich-liquid heat exchanger through a lean liquid pump, the top of the negative pressure buffer tank is connected with the inlet of the steam compressor, the outlet of the steam compressor is connected with the bottom of the regeneration and oxygen removal device through the adjusting valve I; a rich liquid outlet of the lean-liquid rich-liquid heat exchanger is connected with the top of the regeneration and oxygen removal device, the bottom outlet of the regeneration and oxygen removal device is connected with the top of the regeneration tower, the top outlet of the regeneration and oxygen removal device is connected with the top outlet of the regeneration tower through a pipeline, the gas outlet of the gas cooler is connected with the inlet of the gas-liquid separator, and the condensate outlet at the bottom of the gas-liquid separator is connected with the top of the regeneration tower; the top outlet of the gas-liquid separator is connected with the inlet of the CO2 compressor, and the outlet of the CO2 compressor is connected with the membrane separation device.

[0020] As a further improvement of the application, the rich liquid outlet at the bottom of the absorption tower is connected with the lean-liquid rich-liquid heat exchanger through a rich liquid pump, and an oxygen content detector is arranged on the pipeline after the rich liquid pump and on the pipeline of the bottom outlet of the regeneration and oxygen removal device.

[0021] As a further improvement of the application, the absorbent tower external regeneration and oxygen removal system further comprises a nitrogen tank, and the gas outlet of the nitrogen tank is connected with the pipeline at the top of the negative pressure buffer tank through an adjusting valve II.

[0022] The technical key points and protection points of the application are as follows:

[0023] 1. The overall method and system for absorbent tower external regeneration and oxygen removal do not need to change the solvent formula, do not consume antioxidants, and can significantly reduce the degradation loss of flue gas carbon capture solvent only by optimizing the process flow, and the whole process flow can also reduce the overall carbon capture energy consumption.

[0024] 2. The combination of lean liquid flash compression and absorbent oxygen removal can recover the heat of the lean liquid, reduce the CO2 load in the lean liquid, realize the reduction of carbon capture energy consumption, realize absorbent oxygen removal, and simultaneously realize the regeneration of the rich liquid, so that the rich liquid is desorbed and regenerated in advance and is heated, the steam required by the regeneration tower is reduced, and the synergy of oxygen removal and energy saving is realized.

[0025] 3. The steam flashed out by the lean liquid is used as the stripping gas source, no additional gas needs to be purchased, compared with the use of CO2 product gas or the purchase of nitrogen gas, the pressure and temperature of the steam are more suitable, and when the oxygen content in the front-end rich liquid is higher than the set threshold in special working conditions, nitrogen gas is used as a supplementary stripping gas source, so that the stripping effect is fully guaranteed.

[0026] 4. Considering the impurities such as water, oxygen and nitrogen in the product gas, a membrane separation device is arranged at the rear end of the compressor, the membrane separation method is combined with the chemical absorption method, and the purity of the product CO2 is further ensured.

[0027] The absorbent tower external regeneration and oxygen removal method and system of the application do not need to change the absorbent formula, do not consume antioxidants, and can realize the synchronous reduction of absorbent oxidation degradation loss and system comprehensive energy consumption through process optimization, have strong applicability, and have many significant beneficial technical effects:

[0028] 1. From the absorbent protection angle, the application can effectively reduce the oxygen content in the rich liquid entering the regeneration tower to below 10 ppm, greatly reducing the oxidation degradation of the absorbent in the high-temperature environment of the regeneration tower. For a 2000-ton / year gas flue gas carbon capture device, the original 30% of the absorbent needs to be supplemented annually due to oxidation degradation, and after applying the technology, the supplement amount can be reduced to 10%-15%. This not only prolongs the service life of the absorbent, but also reduces the use cost of the absorbent, directly reducing the unit cost of carbon capture.

[0029] 2. From the carbon capture efficiency guarantee angle. Due to better maintenance of the absorbent performance, the capture efficiency of the carbon capture system is reduced from 80%-85% due to absorbent oxidation degradation, and can be improved and stably maintained at 90%-95%, significantly improving the carbon capture capacity and ensuring the capture amount of the system and the CO2 yield.

[0030] 3. From the energy consumption and operation cost angle. First, the lean liquid enters the negative pressure buffer tank, and after extraction, it can further desorb and reduce its CO2 load. After completing heat exchange and cooling into the absorption tower, it can absorb more CO2, thereby reducing the unit carbon capture energy consumption and cost, and it is expected to reduce the overall energy consumption by 3-5%. Second, in the regeneration oxygen remover, the rich liquid is regenerated by steam heating. On the one hand, it further increases the temperature entering the regeneration tower by utilizing the latent heat of the steam, and on the other hand, it also desorbs part of the CO2 under the action of the steam, so that the heat required for desorption of the rich liquid entering the regeneration tower is reduced, and the amount of steam required is reduced, thereby realizing the reduction of regeneration heat consumption, and it is expected to reduce the regeneration heat consumption by 5-7%. In general, the comprehensive application of the absorbent tower external regeneration and oxygen removal technology of the application can realize the reduction of carbon capture heat consumption by about 8-12%, thereby realizing 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) The water vapor containing a small amount of CO2 enters the vapor 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 the adjusting valve I 3, it enters the regenerative deaerator 4. Under this pressure condition, the oxygen stripping efficiency is high and the influence on the performance of the absorbent is small.

[0038] 3) The regenerative deaerator 4 is a packed tower structure. The rich liquid enters the liquid distributor (such as a trough plate distributor or a nozzle type distributor) at the top of the regenerative deaerator 4 after leaving the lean and rich liquid heat exchanger, ensuring that the rich liquid is uniformly 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. After contacting with 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 a bubble cap tray) at the bottom of the regenerative deaerator 4 from bottom to top, so that the regeneration gas uniformly enters the packed tower, completes the heating regeneration and stripping of the rich liquid, and then enters the gas-liquid separator 5. The temperature of the rich liquid before entering the regenerative deaerator 4 is 82-87℃, and the CO2 loading is 0.384-0.392mol / mol 吸收剂 , The temperature of the rich liquid after leaving the regenerative deaerator 4 is 87-92℃, and the CO2 loading is 0.341-0.355mol / mol 吸收剂 .

[0039] 4) After the rich liquid is heated, regenerated and stripped, it enters the regeneration tower from the top. At this time, the rich liquid has been heated by the compressed steam, further increasing the temperature of the rich liquid entering the regeneration tower to 87-92℃, and some CO2 has been desorbed. The heat required for the desorption of the rich liquid entering the regeneration tower is reduced, and the amount of steam required is reduced, thereby reducing the regeneration heat consumption by about 5-7%.

[0040] 5) The gas after completing the heating regeneration and stripping of the rich liquid is used as the first regeneration gas, which mainly contains water and a small amount of CO2 and O2. The gas at the top of the regeneration tower is used as the second regeneration gas. After the first regeneration gas and the second regeneration gas pass through the gas cooler 5, they enter the gas-liquid separator 6. The condensed water separated out returns to the regeneration tower from the top, and the gas separated out is compressed by the CO2 compressor 7 and then enters the membrane separation device 8. The CO2 gas permeates the membrane to obtain gaseous CO2 product, and the water and other gases (oxygen and possibly 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) The energy consumption will increase if a separate stripping oxygen removal device is set up. Therefore, the lean liquid flash compression is combined with the absorbent oxygen removal. On the one hand, the lean liquid flash compression can recover the heat of the lean liquid and reduce the CO2 load in the lean liquid, thereby reducing the energy consumption of carbon capture. On the other hand, the steam after the lean liquid flash compression can be used for stripping gas absorption, and the regeneration of the rich liquid is also achieved. The rich liquid is preheated and desorbed for regeneration, and the steam required by the regeneration tower is reduced. In this way, the gas resources in the system can be fully utilized (the problem of the influence of the compressed CO2 gas as the stripping gas on the performance of the absorbent is also solved), and no other gas needs to be introduced, thereby reducing the operating cost.

[0046] 3) The above scheme not only realizes the oxygen removal of the rich liquid, but also does not increase the system energy consumption, but also reduces the system energy consumption, thereby realizing the synergy of oxygen removal and energy saving. In order to further ensure the stripping effect, nitrogen gas is also set as a supplementary stripping gas source. In addition, considering that the product gas may contain water, oxygen and nitrogen and other impurities, a membrane separation device is set at the rear end of the compressor, and the membrane separation method is combined with the chemical absorption method, thereby further ensuring the purity of the product CO2.

[0047] The initial inlet flue gas parameters and operating parameters of a certain 2000 tons / year scale gas flue gas carbon capture device are as follows:

[0048] Table 1 Inlet flue gas parameters of a 2000 tons / year scale gas flue gas carbon capture device

[0049] Item Parameter Flue gas volume 6500 Nm 3 / h]] CO2 3.2% O2 14.2% [N2] 75.2% H2O 7.4% Dust concentration ≤ 1 mg / Nm 3 ]] SO2 concentration ≤ 5 mg / Nm 3 ]] NO x concentration ≤ 5 mg / Nm 3 ]] Temperature 90°C (washed to 40°C) Pressure 4 kPa

[0050] Table 2 Operating parameters of a 2000 tons / year scale gas flue gas carbon capture device

[0051] Item Parameter Absorbent circulation volume 13m 3 / h]] Total amine concentration 30% Lean liquid out of the regeneration tower temperature 104℃ Lean liquid load 0.121 mol / mol 吸收剂 ]] Rich liquid into the regeneration tower temperature 85℃ Rich liquid load 0.389 mol / mol 吸收剂 ]] Rich liquid oxygen content 25~30 ppm Inter-stage cooling temperature drop 10℃ Regeneration heat consumption 3.2 GJ / tCO2 Regeneration power consumption 84 kWh / tCO2 Absorbent loss 2.7 kg / tCO2

[0052] When the 2000 tons / year scale carbon capture device is normally operated, the oxidation and volatilization loss of the absorbent reaches 2.7 kg / tCO2 due to the high oxygen content in the flue gas, and the entire absorbent needs to be replaced after one year of operation. In addition, the regeneration heat consumption and capture cost are high due to the low CO2 concentration in the flue gas. Therefore, in order to realize the synergistic reduction of the absorbent loss and the regeneration heat consumption, an absorbent tower external regeneration and oxygen removal device is configured for the system.

[0053] 1, Device parameters

[0054] (1) Original absorption and regeneration system

[0055] The absorption tower has a diameter of 1.5 m and a height of 40 m, and the regeneration tower has a diameter of 1 m and a height of 28 m. Energy-saving processes such as inter-stage cooling and rich liquid splitting are configured.

[0056] (2) Lean liquid flash compression system

[0057] A horizontal lean liquid flash tank is configured, with a size of 1.5 m in diameter and 2.25 m in length, and an internal volume of 4 m 3 ; a compressor with a shaft power of 30 kW is configured, and related pipelines are configured.

[0058] (3) Regeneration deoxygenation system

[0059] A set of steam regeneration deoxygenators is configured, which are in the form of a packed tower, with a tower body of φ800*8000 mm, internally filled with a Pall ring packing, and with a packing height of 3 m; an electrochemical oxygen content sensor is arranged on a rich liquid outlet pipeline at the bottom of the packed tower. The rich liquid enters the top of the regeneration deoxygenation packed tower from above after passing through a lean-rich liquid heat exchanger, and flows out from the bottom after being contacted with steam spraying to enter the top of the regeneration tower. Steam enters the bubble cap tray at the bottom of the deoxygenation packed tower from bottom to top, completes the heating regeneration and stripping of the rich liquid, and then enters the gas-liquid separator at the rear end.

[0060] (4) Membrane separation system

[0061] A set of membrane separation treatment systems is configured, and a PVAm mixed matrix membrane is selected to realize separation of CO2, with a design treatment capacity of 200 Nm 3 , and a compressor pressure rise of 4 Mpa.

[0062] 2. Implementation effect

[0063] When the original carbon capture system is normally operated, the oxidation and volatilization loss of the absorbent reaches 2.7 kg / tCO2 due to the high oxygen content in the flue gas, and the absorbent needs to be replaced after one year of operation; in addition, the regeneration heat consumption reaches 3.2 GJ / tCO2 due to the low CO2 concentration in the flue gas.

[0064] After the process of the application is applied:

[0065] (1) The lean liquid from the bottom of the regeneration tower enters a negative pressure buffer tank, the temperature of the lean liquid is 104℃, and the steam compressor extracts part of the water and a small part of CO2 from the negative pressure buffer tank, the water accounts for about 95% and the CO2 accounts for about 5% in the extracted gas, the load of the lean liquid after extraction is reduced from 0.121 mol / mol 吸收剂 to 0.098 mol / mol 吸收剂 , the steam temperature entering the steam compressor is 94℃, and the pressure is 0.065 Mpa, the lean liquid after extraction by the steam compressor enters the lean-rich liquid heat exchanger through the lean liquid pump, and the temperature is 90.6℃.

[0066] (2) The 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 is 1305 Nm 3 / h, the pressure is adjusted to about 0.25 MPa by the regulating valve 3 and enters the regenerative deaerator. Due to the latent heat of steam and the pressure, the temperature of the rich liquid before entering the regenerative deaerator is 86.1℃, and the CO2 load is 0.389 mol / mol 吸收剂 , the oxygen content is 17 ppm; the temperature of the rich liquid after entering the regenerative deaerator is 90.5℃, and the CO2 load is 0.348 mol / mol 吸收剂 , the oxygen content is 5 ppm.

[0067] (3) The gas after the rich liquid is heated, regenerated and stripped is cooled together with the regenerator at the top of the regeneration tower and enters a gas-liquid separator. The condensed water separated is returned to the regeneration tower from the top, and the separated gas is compressed by a CO2 compressor and then enters a membrane separation device. The gaseous CO2 product is obtained by the CO2 gas permeating the membrane, and the water and oxygen and possibly existing nitrogen are discharged after being intercepted by the membrane.

[0068] (4) In addition, an electrochemical oxygen content sensor is arranged on the pipeline after the rich liquid pump. When the oxygen content of the rich liquid in the pipeline exceeds 25 ppm, an alarm program is triggered, an instruction is output to prompt the opening of the regulating valve of the nitrogen tank outlet pipeline, and the stripping gas source flow is increased by 10-30%, so that the stripping deoxygenation process is optimized, and the oxygen content of the rich liquid entering the regeneration tower is always maintained below 10 ppm.

[0069] After the process of the present application is applied, the oxidation degradation of the absorbent is greatly reduced, the oxidation and volatilization loss is reduced to 1.05 kg / tCO2 in total, and after one year of continuous operation, the capture efficiency can still be stabilized at more than 90%, without replacing all the absorbent, only supplementing during operation, which significantly improves the carbon capture capacity, enhances the effectiveness of the entire system in dealing with carbon emission problems, and reduces the absorbent cost by about 800,000 yuan / year. In addition, the regeneration heat consumption of the carbon capture system is also reduced from 3.2 GJ / tCO2 to 2.81 GJ / tCO2. Although the process also increases the power consumption of the compressor, the increased heat consumption of the compressor is 0.294 GJ / tCO2, calculated as the unit heat consumption of the compressor shaft power of 30 kW. After considering the increased power consumption of the compressor, the regeneration heat consumption of the system can still be reduced to 3.1 GJ / tCO2. If the steam price is 127.6 yuan / GJ and the electricity price is 0.513 yuan / degree, the total cost can still be reduced by 8 yuan / tCO2. Moreover, the process uses flash-compressed steam as the stripping gas source, without the need for additional gas procurement. In general, the process does not increase the system material consumption or only slightly increases the material consumption (nitrogen used in special working conditions), and reduces the overall energy consumption of the system, achieving the synergistic reduction of the absorbent loss and the regeneration heat consumption of the carbon capture system, and the economic benefits are significant.

[0070] Finally, it is to be explained that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the purpose and scope of the present application, and all of them should be covered in the scope of the claims of the present application.

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 rich and lean 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. A uniform liquid film is formed on the surface of the packing and flows 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. After completing the heating, regeneration, and stripping of the rich liquid, it enters the gas-liquid separator (5). 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).

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