Integrated water balance control and system heat utilization coupled wet carbon capture process

Abstract

The present application relates to the technical field of wet carbon capture, in particular to a wet carbon capture process coupled with water balance control and system heat utilization, comprising a pretreatment unit, an absorption unit, a regeneration unit and a separation unit connected in sequence, wherein the regeneration gas in the regeneration unit is decomposed into water and carbon dioxide; further comprising a recovery unit arranged between the regeneration unit and the separation unit, wherein the recovery unit comprises a regeneration gas washing tower, the bottom gas inlet end of the regeneration gas washing tower is in communication with the regeneration gas outlet of the regeneration unit, and the top liquid inlet end of the regeneration gas washing tower is in communication with the outer circulation flow path of the cooling section of the pretreatment tower. The added regeneration gas washing tower can use the overflow washing water of the absorption tower to pre-cool the regeneration gas discharged from the regeneration tower, thereby reducing the working burden of the regeneration gas cooler; meanwhile, the added secondary washing tower can use the washing water discharged from the regeneration gas washing tower to perform secondary spraying on the tower exit flue gas discharged from the absorption tower.

Description

Technical Field

[0001] This invention relates to the field of wet carbon capture technology, specifically a wet carbon capture process coupled with water balance control and internal heat utilization. Background Technology

[0002] As is well known, carbon emissions from low-partial-pressure gas sources account for more than 70% of the total captureable carbon dioxide in current industry. Therefore, to achieve the goal of "carbon neutrality", CO2 from low-partial-pressure gas sources is an unavoidable target for capture. Based on existing engineering experience at home and abroad, using wet process technology for large-scale carbon capture and recovery from low-partial-pressure gas sources is the only option.

[0003] As the core of wet process technology, the absorbent faces challenges beyond its own degradation and volatilization losses. Water balance control and efficient utilization of internal heat within the capture unit are also significant challenges. Current processes rely solely on the temperature difference between the flue gas entering and exiting the absorption tower to achieve water balance. However, the flue gas exiting the absorption tower is constrained by cooling water temperature and absorbent volatilization, resulting in limited flexibility in overall system water balance control. In recent years, the emergence and use of high-concentration absorbents such as phase change absorbents and low-water absorbents have made water balance control in traditional processes increasingly difficult. Furthermore, achieving highly automated operation of the carbon capture unit after its engineering will be another pressing issue, with water balance operational flexibility being a crucial element of this automation process.

[0004] Water balance refers to the balance between the amount of water carried by the carbon-containing gas entering the carbon capture system and the amount of water carried away by the gas exiting the system during normal operation of a carbon capture device. This balance is very important in engineering; constant dynamic balance cannot be guaranteed, and the range and frequency of imbalance fluctuations should be controlled as much as possible. When power plant flue gas is used as the capture target, the flue gas usually contains saturated water vapor. After being cooled and impurities removed by pretreatment systems such as water scrubbing towers, it enters the absorption tower. During this cooling process, some water vapor liquefies and remains in the water scrubbing tower, leading to a continuous increase in the amount of alkaline scrubbing liquid in the tower. This necessitates continuous liquid drainage and alkali replenishment, increasing both waste liquid discharge and alkali consumption. Furthermore, for the water balance control of the absorption-regeneration unit, the inlet and outlet temperatures of the flue gas are typically controlled only by adjusting the temperature. However, temperature adjustment is subject to many constraints and cannot be adjusted over a wide range, thus its adjustment capability is very limited.

[0005] Current optimization of wet scrubbing processes mainly focuses on energy-saving techniques such as improving heat utilization within the system and maximizing absorbent efficiency. Examples include optimizing temperature distribution in the absorption-regeneration unit, utilizing secondary steam in lean liquid flash MVR, and recovering heat from regenerated gas using heat pump principles. While these methods have yielded some results in some systems, further improvements to enhance regenerated gas heat utilization are lacking. Furthermore, there are even fewer reports on improving system water balance control to increase process redundancy and reduce wastewater discharge. Summary of the Invention

[0006] This invention addresses the problems in existing technologies by providing a wet carbon capture process that couples water balance control with internal system heat utilization. The specific technical solution is as follows:

[0007] A wet carbon capture process coupled with water balance control and internal heat utilization includes the following sequentially connected components:

[0008] The pretreatment unit includes a pretreatment tower, which is provided with an alkaline washing section and a cooling section from bottom to top. The alkaline washing section is sprayed with alkaline washing liquid, and the cooling section of the pretreatment tower is sprayed with washing water.

[0009] The absorption unit absorbs carbon dioxide from the flue gas using an absorbent and produces a rich liquid.

[0010] The regeneration unit is used to desorb the rich liquid from the absorption unit and produce lean liquid and regeneration gas, and to return the lean liquid to the absorption unit to form an absorbent circulation path.

[0011] And a separation unit that decomposes the regeneration gas in the regeneration unit into water and carbon dioxide;

[0012] It also includes a recovery unit located between the regeneration unit and the separation unit. The recovery unit includes a regeneration gas scrubbing tower. The bottom air inlet of the regeneration gas scrubbing tower is connected to the regeneration gas outlet of the regeneration unit, and the top liquid inlet of the regeneration gas scrubbing tower is connected to the external circulation path of the cooling section of the pretreatment tower.

[0013] The washing water overflowing from the pretreatment tower's washing section can enter the regenerated gas washing tower to spray and pre-cool the regenerated gas.

[0014] As a further technical solution of the present invention, the absorption unit includes:

[0015] An absorption tower, comprising, from bottom to top, an absorption section and a retention section, wherein an absorbent is sprayed in the absorption section;

[0016] A washing liquid cooler is provided, which is connected to the retention section of the absorption tower via a one-way pipe outside the tower. The retention section of the absorption tower is sprayed with washing liquid, which, together with the washing liquid cooler, forms a circulating flow path for the washing liquid.

[0017] As a further technical solution of the present invention, the recycling unit further includes:

[0018] The secondary scrubbing tower has its liquid inlet connected to the liquid outlet of the regenerated gas scrubbing tower, and its gas inlet connected to the gas outlet of the absorption tower. The secondary scrubbing tower is connected to an external one-way pipe to form a circulating pipeline for the scrubbing water.

[0019] The washing water flowing out from the bottom of the regenerated gas scrubbing tower can enter the secondary scrubbing tower to circulate and spray the flue gas exiting the absorption tower to evaporate and release the washing water.

[0020] As a further technical solution of the present invention, the regeneration unit includes:

[0021] A regeneration tower, wherein the top of the regeneration tower is connected to the liquid outlet of the absorption tower, and the bottom of the regeneration tower is connected to the liquid inlet of the absorption tower;

[0022] The reboiler is connected to the regeneration tower via a one-way pipe outside the tower.

[0023] A lean liquor cooler is installed on the connecting pipe between the outlet of the regeneration tower and the inlet of the absorption tower, and is used to cool the lean liquor.

[0024] The rich and lean liquid heat exchanger is used for heat exchange between the rich and lean liquids, both before the rich liquid enters the regeneration tower and after the lean liquid exits the regeneration tower.

[0025] The beneficial effects of this invention are as follows:

[0026] (1) In this application, the added regeneration gas scrubbing tower can use the scrubbing water overflowing from the absorption tower to pre-cool the regeneration gas discharged from the regeneration tower, reducing the workload of the regeneration gas cooler. At the same time, the added secondary scrubbing tower can use the scrubbing water discharged from the regeneration gas scrubbing tower to spray the flue gas discharged from the absorption tower for a second time. On the one hand, the scrubbing water is evaporated and released to achieve water balance. On the other hand, the scrubbing water can also intercept the absorbent escaping in the flue gas discharged from the tower for a second time, so as to reduce the loss of absorbent.

[0027] (2) In this application, by dividing the cooling structure of the traditional alkaline washing liquid into an alkaline washing section and a cooling section, the alkaline washing section only performs impurity removal operation on the flue gas, thereby eliminating the need to continuously replenish alkali to the pretreatment unit and reducing the consumption of alkali. Attached Figure Description

[0028] Figure 1 A schematic diagram of the overall structure of a wet carbon capture process that couples water balance control and internal heat utilization is shown.

[0029] Figure 2 A schematic diagram of the pretreatment unit and the absorption unit is shown.

[0030] Figure 3 A schematic diagram of the regeneration unit and the separation unit is shown;

[0031] Figure 4 A schematic diagram of the recycling unit and the separation unit is shown.

[0032] Figure descriptions: 110, Pretreatment tower; 120, Wash water cooler; 210, Absorption tower; 220, Wash liquid cooler; 310, Regeneration tower; 320, Reboiler; 330, Lean liquid cooler; 340, Lean and rich liquid heat exchanger; 410, Regeneration gas cooler; 420, Gas-liquid separator; 510, Regeneration gas scrubbing tower; 520, Secondary scrubbing tower. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0034] This application provides a wet carbon capture process that couples water balance control with internal heat utilization. Figure 1 A schematic diagram of the overall structure of a wet carbon capture process that couples water balance control and internal heat utilization is shown. Figure 1 In this process, the wet carbon capture technology coupled with water balance control and internal heat utilization includes the following sequentially connected components:

[0035] The pretreatment unit is used to remove impurities from the flue gas and reduce its temperature.

[0036] The absorption unit absorbs carbon dioxide from the flue gas using an absorbent and produces a rich liquid.

[0037] The regeneration unit is used to desorb the rich liquid from the absorption unit and produce lean liquid and regeneration gas, and to return the lean liquid to the absorption unit to form an absorbent circulation path.

[0038] And a separation unit that decomposes the regeneration gas in the regeneration unit into water and carbon dioxide.

[0039] Figure 2 A schematic diagram of the pretreatment unit and the absorption unit is shown. Figure 2 In this context, the preprocessing unit includes:

[0040] The pretreatment tower 110 is provided with an alkaline washing section and a cooling section from bottom to top. The alkaline washing section is sprayed with alkaline washing liquid. The alkaline washing section of the pretreatment tower 110 is connected to an external one-way pipe to form a circulation path for the alkaline washing liquid.

[0041] The washing water cooler 120 is connected to the cooling section of the pretreatment tower 110 through a one-way pipe outside the tower. The cooling section of the pretreatment tower 110 is sprayed with washing water and forms a circulating flow path for the washing water in conjunction with the washing water cooler 120.

[0042] It should be noted that pumps are installed on all unidirectional pipelines outside the tower to drive the liquid flow; see also... Figure 1 This application also includes a washing tank 600, which is unidirectionally connected to all pump bodies in this application and contains liquid to prevent the pump body from sucking dry. This is a conventional technical means known to those skilled in the art and will not be described in detail here.

[0043] It should be noted that the water washing section and the alkaline washing section are separated by a liquid collection tray. The liquid in the water washing section will be trapped by the liquid collection tray, while the gas in the alkaline washing section can pass through the liquid collection tray and enter the water washing section.

[0044] It should be noted that in this application, sodium hydroxide or sodium hydrogen nitrate is used as the alkaline washing solution to deal with the flue gas. In some other embodiments, the specific settings may be different depending on the gas being treated, which is not a limitation of this application.

[0045] In use, flue gas enters through the inlet of the pretreatment tower 110 and passes through the alkaline washing section and the cooling section in sequence before being discharged through the exhaust port. The alkaline washing section removes impurities from the flue gas, and the cooling section cools the flue gas. In this application, by dividing the traditional alkaline washing liquid cooling structure into an alkaline washing section and a cooling section, the alkaline washing section only performs impurity removal on the flue gas, thereby eliminating the need to continuously replenish alkali to the pretreatment unit and reducing alkali consumption.

[0046] See also Figure 2 The absorption unit includes:

[0047] Absorption tower 210, from bottom to top, includes an absorption section and a retention section, and the absorption section is sprayed with absorbent;

[0048] The washing liquid cooler 220 is connected to the retention section of the absorption tower 210 through a one-way pipe outside the tower. The retention section of the absorption tower 210 is sprayed with washing liquid and forms a circulating flow path for the washing liquid in conjunction with the washing liquid cooler 220.

[0049] It should be noted that in this application, the absorbent may be a traditional organic amine absorbent such as monoethanolamine, diethanolamine, aminomethylpropanol, piperazine, etc.; or an amino acid salt such as potassium glycinate or a phase change absorbent may be used.

[0050] During use, the flue gas discharged from the pretreatment tower 110 enters the absorption tower 210 and passes through the absorption section and the retention section in sequence. The carbon dioxide in the flue gas can be absorbed by the spray in the absorption section. Since some absorbent will evaporate and escape with the flue gas, the circulating water washing in the retention section can re-liquefy the absorbent carried out in the flue gas to achieve interception, thereby reducing the loss of absorbent.

[0051] Figure 3 A schematic diagram of the regeneration unit and the separation unit is shown; Figure 3 In this context, the regeneration unit includes:

[0052] The top of the regeneration tower 310 is connected to the liquid outlet of the absorption tower 210, and the bottom of the regeneration tower 310 is connected to the liquid inlet of the absorption tower 210.

[0053] The reboiler 320 is connected to the regeneration tower 310 via a one-way pipe outside the tower.

[0054] The lean liquor cooler 330 is installed on the connecting pipe between the outlet of the regeneration tower 310 and the inlet of the absorption tower 210, and is used to cool the lean liquor.

[0055] The rich and lean liquid heat exchanger 340 is used for heat exchange between the rich and lean liquids, both before the rich liquid enters the regeneration tower 310 and after the lean liquid flows out of the regeneration tower 310.

[0056] In use, the rich liquid flowing out of the absorption tower 210 enters the regeneration tower 310 after passing through the lean-rich liquid heat exchanger 340. It then converges and enters the reboiler 320 through a one-way pipe outside the tower. In the reboiler 320, the carbon dioxide and water in the rich liquid are evaporated to achieve desorption. The desorbed high-temperature lean liquid then passes through the lean-rich liquid heat exchanger 340 and the lean liquid cooler 330 before entering the absorption tower 210, forming a recycling of the absorbent. In this application, the absorbent is desorbed through the regeneration tower 310, the reboiler 320, and the lean liquid cooler 330 to form a recycling of the absorbent. At the same time, the lean-rich liquid heat exchanger 340 is used to exchange heat between the low-temperature rich liquid and the high-temperature lean liquid. On the one hand, the rich liquid is heated to reduce the workload of the reboiler 320, and on the other hand, the lean liquid is cooled to reduce the workload of the lean liquid cooler 330.

[0057] It should be noted that the rich solution is a saturated absorbent, while the poor solution is an unsaturated absorbent.

[0058] It should be noted that the reboiler 320 is heated by external steam, preferably steam emitted from other combustion units.

[0059] See also Figure 3 The separation unit comprises the following components connected in sequence:

[0060] The regeneration gas cooler 410 is connected to the exhaust port of the regeneration tower 310 and is used to cool the water vapor in the regeneration gas.

[0061] Gas-liquid separator 420 is used to separate carbon dioxide and water.

[0062] It should be noted that the regenerated gas is a mixture of water vapor and carbon dioxide.

[0063] In use, the regenerated gas cooler 410 can cool water vapor, thereby liquefying the water vapor in the regenerated gas, and the gas-liquid mixture is separated by the gas-liquid separator 420, thereby discharging low-temperature regenerated gas containing a mixture of carbon dioxide and part of the water vapor.

[0064] Figure 4 A schematic diagram of the recycling unit and the separation unit is shown. Figure 4 The wet carbon capture process coupled with water balance control and internal heat utilization also includes a recovery unit located between the regeneration unit and the separation unit. The recovery unit includes:

[0065] The regenerated gas scrubbing tower 510 has its inlet end connected to the outlet end of the regeneration tower 310, and its liquid inlet end connected to the external circulation path of the cooling section of the pretreatment tower 110.

[0066] The secondary scrubbing tower 520 has its liquid inlet connected to the liquid outlet of the regenerated gas scrubbing tower 510, and its gas inlet connected to the gas outlet of the absorption tower 210. The secondary scrubbing tower 520 is connected to an external one-way pipe to form a circulating pipeline for the scrubbing water.

[0067] During use, when the washing water from the pretreatment tower 110 overflows to the top of the regeneration gas scrubbing tower 510 and is sprayed, the regeneration gas enters from the bottom of the regeneration gas scrubbing tower 510 and exchanges heat with the washing water. The design of the regeneration gas scrubbing tower 510 can utilize the excess washing water on the pretreatment tower 110 to cool the regeneration gas discharged from the regeneration tower 310, pre-cool the regeneration gas, and reduce the workload of the regeneration gas cooler 410. At the same time, the secondary scrubbing tower 520 uses the washing water discharged from the regeneration gas scrubbing tower 510 to perform secondary circulating spraying on the flue gas exiting the absorption tower 210, so that the washing water evaporates and is discharged from the exhaust port of the secondary scrubbing tower 520 to achieve water balance. At the same time, the washing water can also intercept the absorbent escaping in the flue gas exiting the tower for a second time, so as to reduce the loss of absorbent.

[0068] It should be noted that, in actual use, the outlet height of the regenerated gas scrubbing tower 510 can be set higher than the inlet height of the secondary scrubbing tower 520, so that the scrubbing liquid can flow directly into the secondary scrubbing tower 520 by gravity.

[0069] The benefits of this application are as follows:

[0070] 1. Utilize the washing water from the upper section of the pretreatment tower to spray and cool the regenerated gas exiting the regeneration tower, thereby achieving direct heat exchange, improving heat exchange efficiency, and reducing the amount of cooling water used in the regenerated gas cooler.

[0071] 2. Due to the cooling process in the upper section of the pretreatment tower, a large amount of condensate is discharged as steam through the secondary washing tower at a higher temperature, which greatly reduces the wastewater discharge and alkali consumption of the pretreatment tower.

[0072] 3. By performing secondary washing on the purified gas, the escape of the absorbent in the purified gas can be reduced;

[0073] 4. Improve the flexibility of water balance control operation of the absorption tower, that is, greatly increase the temperature adjustment range of flue gas entering and leaving the collection system, and better ensure the solubility of the absorbent in the system.

[0074] This application describes flue gas treatment based on the above-mentioned carbon capture method and compares it with traditional wet carbon capture methods, as detailed in Table 1.

[0075]

[0076]

[0077] Table 1

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.

Claims

1. A wet carbon capture process coupled with water balance control and internal heat utilization, characterized in that, Including those connected sequentially: The pretreatment unit includes a pretreatment tower (110), which is provided with an alkaline washing section and a cooling section from bottom to top. The alkaline washing section is sprayed with alkaline washing liquid, and the cooling section of the pretreatment tower (110) is sprayed with washing water. The absorption unit absorbs carbon dioxide from the flue gas using an absorbent and produces a rich liquid. The regeneration unit is used to desorb the rich liquid from the absorption unit and produce lean liquid and regeneration gas, and to return the lean liquid to the absorption unit to form an absorbent circulation path. The separation unit decomposes the regeneration gas in the regeneration unit into water and carbon dioxide; The recovery unit is located between the regeneration unit and the separation unit, and the recovery unit includes a regeneration gas scrubbing tower (510) and a secondary scrubbing tower (520). The bottom air inlet of the regenerated gas scrubbing tower (510) is connected to the regenerated gas outlet of the regeneration unit, and the top liquid inlet of the regenerated gas scrubbing tower (510) is connected to the cooling section of the pretreatment tower (110). The washing water overflowing from the water washing section of the pretreatment tower (110) can enter the regenerated gas washing tower (510) to spray and pre-cool the regenerated gas. The liquid inlet of the secondary scrubbing tower (520) is connected to the liquid outlet of the regenerated gas scrubbing tower (510), the gas inlet of the secondary scrubbing tower (520) is connected to the gas outlet of the absorption tower (210), and the secondary scrubbing tower (520) is connected to an external one-way pipe to form a washing water circulation pipeline. The washing water flowing out from the bottom of the regenerated gas scrubbing tower (510) can enter the secondary scrubbing tower (520) to circulate and spray the flue gas exiting the absorption tower (210) to evaporate and release the washing water.

2. The wet carbon capture process coupled with water balance control and internal heat utilization according to claim 1, characterized in that, The absorption unit includes: The absorption tower (210) includes an absorption section and a retention section from bottom to top, and the absorption section is sprayed with an absorbent. The washing liquid cooler (220) is connected to the stagnation section of the absorption tower (210) through a one-way pipe outside the tower. The stagnation section of the absorption tower (210) is sprayed with washing liquid and forms a circulating flow path for the washing liquid in conjunction with the washing liquid cooler (220).

3. The wet carbon capture process coupled with water balance control and internal heat utilization according to claim 1, characterized in that, The regeneration unit includes: The regeneration tower (310) is connected at the top to the outlet of the absorption tower (210) and at the bottom to the inlet of the absorption tower (210). The reboiler (320) is connected to the regeneration tower (310) via a one-way pipe outside the tower; A lean liquor cooler (330) is installed on the connecting pipe between the outlet of the regeneration tower (310) and the inlet of the absorption tower (210) for cooling lean liquor; The rich and lean liquid heat exchanger (340) is used for heat exchange between the rich and lean liquids before the rich liquid enters the regeneration tower (310) and after the lean liquid flows out of the regeneration tower (310).

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