Wet carbon capture process integrating water balance control and in-system heat utilization coupling

Abstract

The present invention relates to the technical field of wet carbon capture, and in particular to a wet carbon capture process integrating water balance control and in-system heat utilization coupling. The wet carbon capture process comprises a pretreatment unit, an absorption unit, a regeneration unit and a separation unit which are connected in sequence, wherein the separation unit decomposes a regenerated gas in the regeneration unit into water and carbon dioxide. The wet carbon capture process further comprises a recycling unit which is arranged between the regeneration unit and the separation unit, the recycling unit comprising a regenerated gas washing tower, wherein a gas intake end at the bottom of the regenerated gas washing tower is in communication with a regenerated gas outlet of the regeneration unit, and a liquid intake end at the top of the regenerated gas washing tower is in communication with an external circulation flow path of a cooling section of the pretreatment tower. In the present invention, by means of the additionally provided regenerated gas washing tower, the regenerated gas discharged from the regeneration tower can be pre-cooled by using washing water overflowing from the absorption tower so as to reduce the workload of a regenerated gas cooler; and by means of an additionally provided secondary washing tower, the washing water discharged from the regenerated gas washing tower can be used to perform secondary spraying on an exhaust gas discharged from the absorption tower.

Description

Wet carbon capture process coupled with water balance control and heat utilization within the system Technical Field

[0001] The present invention relates to the technical field of wet carbon capture, and in particular to a wet carbon capture process that couples water collection balance control with heat utilization within the system. Background Art

[0002] As we all know, carbon emissions from low-partial-pressure gas sources account for more than 70% of the total carbon dioxide that can be captured in the current industry. Therefore, in order to achieve the goal of "carbon neutrality", CO2 in low-partial-pressure gas sources is an unavoidable capture target. Based on existing engineering experience at home and abroad, the use of wet process technology for large-scale carbon capture and recovery of low-partial-pressure gas sources will be the only choice.

[0003] Absorbents are the core of wet process technology. In addition to the problems of absorbent degradation and volatilization loss, water balance control and full utilization of internal heat in the capture device are also difficult. The existing process relies solely on the temperature difference between the flue gas entering and leaving the absorber to achieve water balance. However, the temperature of the flue gas leaving the absorber is restricted by factors such as cooling water temperature and absorbent volatilization. Therefore, the flexibility of the overall system water balance control is relatively small. In recent years, the introduction and use of a series of high-concentration absorbents such as phase change absorbents and low-water absorbents have made water balance control in traditional processes increasingly difficult. In addition, how to achieve highly automated operation of the carbon capture device after engineering will become the next problem that needs to be studied and solved urgently. The flexibility of water balance operation is a crucial part of the automation process.

[0004] Water balance refers to the balance between the amount of water carried by the carbon-containing source gas entering the carbon capture system and the amount of water removed from the system during normal operation. This balance is highly complex in engineering, and constant dynamic equilibrium cannot be guaranteed. The range and frequency of imbalances should be minimized. When capturing power plant flue gas, it is typically saturated with water vapor. It passes through pretreatment systems such as water scrubbers for cooling and impurity removal before entering the absorber. During this cooling process, some water vapor liquefies and remains in the scrubber, causing the amount of alkaline wash liquid in the scrubber to increase continuously. This necessitates continuous drainage and replenishment of alkaline, increasing both wastewater emissions and alkaline consumption. Furthermore, water balance control for the absorption-regeneration unit, where flue gas enters and exits the absorber, is typically achieved only through regulation of the flue gas inlet and outlet temperatures. However, temperature regulation is subject to numerous constraints and cannot be adjusted over a wide range, thus limiting its ability to adjust.

[0005] Current optimization efforts in wet-process capture plants primarily focus on improving internal heat utilization and maximizing the absorbent's absorption efficiency, among other energy-saving techniques. These include optimizing the temperature distribution of the absorption-regeneration unit, utilizing secondary steam in lean liquid flash vaporization (MVR), and using heat pumps to recover heat from the regeneration gas. These methods have achieved some success in some plants, but process improvements and optimization to further enhance regeneration gas heat utilization are relatively limited. Furthermore, there are even fewer reports on controlling system water balance to increase process redundancy and reduce wastewater emissions.

[0006] Summary of the Invention

[0007] The present invention addresses the problems in the prior art and provides a wet carbon capture process that couples water balance control with heat utilization within the system. The specific technical solutions are as follows:

[0008] A wet carbon capture process coupled with water balance control and heat utilization within the system includes the following steps connected in sequence:

[0009] A pretreatment unit, comprising a pretreatment tower, wherein the pretreatment tower is provided with an alkali washing section and a cooling section in sequence from bottom to top, the alkali washing section is sprayed with an alkali washing liquid, and the cooling section of the pretreatment tower is sprayed with washing water;

[0010] Absorption unit, which absorbs carbon dioxide in the flue gas through absorbent and produces rich liquid;

[0011] A regeneration unit, used to desorb the rich liquid of 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 flow path;

[0012] and a separation unit for decomposing the regeneration gas in the regeneration unit into water and carbon dioxide;

[0013] The system further comprises a recovery unit disposed between the regeneration unit and the separation unit, the recovery unit comprising a regeneration gas washing tower, the bottom air inlet end of the regeneration gas washing tower being connected to the regeneration gas outlet of the regeneration unit, and the top liquid inlet end of the regeneration gas washing tower being connected to the external circulation flow path of the cooling section of the pretreatment tower;

[0014] The washing water overflowing from the water washing section of the pretreatment tower can enter the regeneration gas washing tower to spray and pre-cool the regeneration gas.

[0015] As a further technical solution of the present invention, the absorption unit includes:

[0016] An absorption tower, the absorption tower comprising an absorption section and a retention section from bottom to top, wherein an absorbent is sprayed in the absorption section;

[0017] A water washing liquid cooler is connected to the retention section of the absorption tower through a one-way pipe outside the tower. The retention section of the absorption tower is sprayed with water washing liquid and cooperates with the water washing liquid cooler to form a circulation flow path for the water washing liquid.

[0018] As a further technical solution of the present invention, the recovery unit further includes:

[0019] A secondary scrubber, wherein the liquid inlet of the secondary scrubber is connected to the liquid outlet of the regeneration gas scrubber, the gas inlet of the secondary scrubber is connected to the gas outlet of the absorption tower, and the secondary scrubber is externally connected to an external one-way pipe to form a scrubbing water circulation pipeline;

[0020] The washing water flowing out from the bottom of the regeneration gas washing tower can enter the secondary washing tower to circulate and spray the flue gas out of the absorption tower to evaporate and release the washing water.

[0021] As a further technical solution of the present invention, the regeneration unit includes:

[0022] 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;

[0023] a reboiler connected to the regeneration tower through a one-way pipe outside the tower;

[0024] a lean liquid cooler, provided on the connecting pipe between the liquid outlet of the regeneration tower and the liquid inlet of the absorption tower, for cooling the lean liquid;

[0025] The rich and lean liquid heat exchanger is used for heat exchange between the rich liquid and the lean liquid.

[0026] The beneficial effects of the present invention are as follows:

[0027] (1) In the present application, the washing water overflowed from the absorption tower can be used to pre-cool the regenerated gas discharged from the regeneration tower by adding a regeneration gas washing tower, thereby reducing the workload of the regeneration gas cooler. At the same time, the washing water discharged from the regeneration gas washing tower can be used to spray the flue gas discharged from the absorption tower for a second time by adding a secondary washing tower. On the one hand, the washing water is evaporated and released to achieve water balance. On the other hand, the washing water can also intercept the absorbent escaping from the flue gas to reduce the escape loss of the absorbent.

[0028] (2) In the present application, the cooling structure of the traditional alkaline washing liquid is divided into an alkaline washing section and a cooling section. The alkaline washing section only performs impurity removal operations on the flue gas, thereby eliminating the need to continuously replenish alkali to the pretreatment unit, thereby reducing the consumption of alkali. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 shows a schematic diagram of the overall structure of a wet carbon capture process coupled with water balance control and heat utilization within the system;

[0030] FIG2 shows a schematic structural diagram of a pretreatment unit and an absorption unit;

[0031] FIG3 shows a schematic structural diagram of a regeneration unit and a separation unit;

[0032] FIG4 shows a schematic structural diagram of a recovery unit and a separation unit.

[0033] Description of the drawings: 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 scrubber; 520, secondary scrubber. DETAILED DESCRIPTION

[0034] In order to make the purpose, 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.

[0035] The present application provides a wet carbon capture process coupled with water balance control and system heat utilization. FIG1 shows a schematic diagram of the overall structure of the wet carbon capture process coupled with water balance control and system heat utilization. In FIG1 , the wet carbon capture process coupled with water balance control and system heat utilization includes:

[0036] Pretreatment unit, used to remove impurities from flue gas and reduce flue gas temperature;

[0037] Absorption unit, which absorbs carbon dioxide in the flue gas through absorbent and produces rich liquid;

[0038] A regeneration unit, used to desorb the rich liquid of 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 flow path;

[0039] and a separation unit for decomposing the regeneration gas in the regeneration unit into water and carbon dioxide.

[0040] FIG2 shows a schematic structural diagram of a pretreatment unit and an absorption unit; in FIG2 , the pretreatment unit includes:

[0041] The pretreatment tower 110 is provided with an alkali washing section and a cooling section from bottom to top. The alkali washing section is sprayed with alkali washing liquid. The alkali washing section of the pretreatment tower 110 is connected to an external one-way pipe to form a circulation flow path for the alkali washing liquid.

[0042] 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 cooperates with the washing water cooler 120 to form a circulating flow path for the washing water.

[0043] It should be noted that a pump body is provided on the one-way pipe outside the tower to drive the flow of liquid. At the same time, referring to Figure 1, a washing tank 600 is also provided in this application. The washing tank 600 is unidirectionally connected to all the pump bodies in this application and contains liquid to avoid empty suction of the pump body. It is a conventional technical means known to those skilled in the art and will not be elaborated on here.

[0044] It should be noted that the water washing section and the alkali washing section are separated by a liquid collecting tray. The liquid in the water washing section will be retained by the liquid collecting tray, while the gas in the alkali washing section can pass through the liquid collecting tray and enter the water washing section.

[0045] It should be noted that, in the present application, the alkaline washing liquid uses sodium hydroxide or sodium hydrogen nitrate to deal with flue gas. In some other embodiments, it can be specifically set according to the different processing gases, which is not a limitation of the present application.

[0046] During use, the flue gas enters from the air inlet of the pretreatment tower 110 and passes through the alkali washing section and the cooling section in sequence before being discharged from the exhaust port. The flue gas is removed from the air by the alkali washing section and cooled by the cooling section. In this application, the traditional alkaline washing liquid cooling structure is divided into an alkali washing section and a cooling section. The alkali washing section only removes impurities from the flue gas, thereby eliminating the need to continuously replenish alkali to the pretreatment unit, thereby reducing the consumption of alkali.

[0047] Continuing to refer to Figure 2, the absorption unit includes:

[0048] Absorption tower 210, which includes an absorption section and a retention section from bottom to top, and an absorbent is sprayed in the absorption section;

[0049] 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 cooperates with the washing liquid cooler 220 to form a circulating flow path for the washing liquid.

[0050] It should be noted that in this application, the absorbent can be selected from traditional organic amine absorbents represented by monoethanolamine, diethanolamine, aminomethyl propanol, piperazine, etc.; amino acid salts such as potassium glycine or phase change absorbents can also be used.

[0051] 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 spraying of the absorption section. Since part of the absorbent will evaporate and escape with the flue gas, the circulating water washing in the retention section can re-liquefy the absorbent brought out of the flue gas to achieve interception, thereby reducing the loss of the absorbent.

[0052] FIG3 shows a schematic structural diagram of a regeneration unit and a separation unit; in FIG3 , the regeneration unit includes:

[0053] The regeneration tower 310 has its top connected to the liquid outlet of the absorption tower 210 and its bottom connected to the liquid inlet of the absorption tower 210;

[0054] The reboiler 320 is connected to the regeneration tower 310 through a one-way pipe outside the tower;

[0055] The lean liquid cooler 330 is provided on the connecting pipe between the liquid outlet of the regeneration tower 310 and the liquid inlet of the absorption tower 210, and is used to cool the lean liquid;

[0056] The rich-lean liquid heat exchanger 340 is used for heat exchange between the rich liquid and the lean liquid. The rich liquid flows through the rich liquid heat exchanger 340 before entering the regeneration tower 310 and the lean liquid flows out of the regeneration tower 310.

[0057] During 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, and then converges and enters the reboiler 320 through a one-way pipe outside the tower. The carbon dioxide and water in the rich liquid are evaporated and desorbed by the reboiler 320. The high-temperature lean liquid after desorption passes through the lean-rich liquid heat exchanger 340 and the lean liquid cooler 330 in turn and enters the absorption tower 210, forming a recycling of the absorbent. In this application, the absorbent is desorbed by 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.

[0058] It should be noted that the rich solution is the absorbent that has been saturated, and the lean solution is the absorbent that has not yet been saturated.

[0059] It should be noted that the reboiler 320 is heated by external steam, preferably steam discharged from other combustion units.

[0060] Continuing to refer to FIG3 , the separation unit includes:

[0061] 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;

[0062] The gas-liquid separator 420 is used to separate carbon dioxide and water.

[0063] It should be noted that the regeneration gas is a mixture of water vapor and carbon dioxide.

[0064] During use, the regeneration gas cooler 410 can cool the water vapor to liquefy the water vapor in the regeneration gas, and the gas-liquid mixture is separated by the gas-liquid separator 420 to discharge the low-temperature regeneration gas of the mixture of carbon dioxide and part of the water vapor.

[0065] FIG4 shows a schematic structural diagram of a recovery unit and a separation unit. In FIG4 , the wet carbon capture process coupled with water balance control and heat utilization within the system further includes a recovery unit disposed between the regeneration unit and the separation unit. The recovery unit includes:

[0066] The regeneration gas washing tower 510 has its air inlet connected to the air outlet of the regeneration tower 310, and its liquid inlet connected to the external circulation flow path of the cooling section of the pretreatment tower 110;

[0067] The secondary washing tower 520 has a liquid inlet connected to the liquid outlet of the regeneration gas washing tower 510, and an air inlet connected to the air outlet of the absorption tower 210. The secondary washing tower 520 is connected to an external one-way pipe to form a washing water circulation pipeline.

[0068] During use, when the washing water from the water washing section of the pretreatment tower 110 overflows to the top of the regeneration gas washing tower 510 and is sprayed, the regeneration gas enters from the bottom of the regeneration gas washing tower 510 and exchanges heat with the washing water. The design of the regeneration gas washing tower 510 can use 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 washing tower 520 uses the washing water discharged from the regeneration gas washing tower 510 to perform a secondary circulation spray on the flue gas out of the absorption tower 210, so that the washing water evaporates and is discharged from the exhaust port of the secondary washing tower 520 to achieve water balance. At the same time, the washing water can also intercept the absorbent escaping in the flue gas out of the tower for a secondary time to reduce the escape loss of the absorbent.

[0069] It should be noted that, in specific use, the liquid outlet of the regeneration gas washing tower 510 may be set at a higher height than the liquid inlet of the secondary washing tower 520 so that the washing liquid can flow directly into the secondary washing tower 520 by gravity.

[0070] The benefits of this application are as follows:

[0071] 1. Use the washing water from the upper section of the pretreatment tower to spray and cool the regenerated gas out of the regeneration tower, perform direct heat exchange, improve heat exchange efficiency, and reduce the cooling water consumption of the regeneration gas cooler;

[0072] 2. Due to the cooling of the upper section of the pretreatment tower, a large amount of condensed water is discharged in the form of water vapor through the secondary washing tower with a higher temperature, which greatly reduces the wastewater discharge and alkali consumption of the pretreatment tower;

[0073] 3. The escape of absorbent in the purified gas can be reduced by secondary washing of the purified gas;

[0074] 4. Improve the operational flexibility of the water balance control of the absorption tower, that is, the temperature adjustment range of the flue gas entering and leaving the capture system is greatly increased, which better ensures the solubility of the system absorbent.

[0075] This application performs flue gas treatment based on the above carbon capture method and compares it with the traditional wet process carbon capture method, as shown in Table 1.

[0076] Table 1

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same.

Claims

1. A wet carbon capture process integrating horizontal balance control and internal heat utilization coupling in the system, characterized in that, Comprising successively connected: A pretreatment unit, the pretreatment unit comprising a pretreatment tower (110), the pretreatment tower (110) being successively provided with an alkali washing section and a cooling section from bottom to top, the alkali washing section being sprayed with an alkali washing liquid, and the cooling section of the pretreatment tower (110) being sprayed with washing water; An absorption unit, which absorbs carbon dioxide in the flue gas by an absorbent and produces a rich liquid; A regeneration unit, which is used for desorbing the rich liquid of the absorption unit and producing a lean liquid and a regenerated gas, and returning the lean liquid to the absorption unit to form an absorbent circulation flow path; And a separation unit, which decomposes the regenerated gas in the regeneration unit into water and carbon dioxide; It further comprises a recovery unit arranged between the regeneration unit and the separation unit, the recovery unit comprising a regenerated gas washing tower (510), the bottom gas inlet end of the regenerated gas washing tower (510) being communicated with the regenerated gas outlet of the regeneration unit, and the top liquid inlet end of the regenerated gas washing tower (510) being communicated with 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.

2. The wet carbon capture process integrating horizontal balance control and internal heat utilization coupling in the system according to claim 1, wherein, The absorption unit comprises: An absorption tower (210), the absorption tower (210) successively comprising an absorption section and a retention section from bottom to top, and the absorption section being sprayed with an absorbent; A water washing liquid cooler (220), the water washing liquid cooler (220) being communicated with the retention section of the absorption tower (210) through an external one-way pipeline, and the retention section of the absorption tower (210) being sprayed with a water washing liquid and cooperating with the water washing liquid cooler (220) to form a circulation flow path of the water washing liquid.

3. The wet carbon capture process integrating horizontal balance control and internal heat utilization coupling in the system according to claim 2, characterized in that, The recovery unit further comprises: A secondary washing tower (520), the liquid inlet end of the secondary washing tower (520) being communicated with the liquid outlet end of the regenerated gas washing tower (510), the gas inlet end of the secondary washing tower (520) being communicated with the gas outlet end of the absorption tower (210), and the secondary washing tower (520) being externally connected with an external one-way pipeline to form a washing water circulation pipeline; The washing water flowing out from the bottom of the regenerated gas washing tower (510) can enter the secondary washing tower (520) to circularly spray the flue gas out of the absorption tower (210) to evaporate and release the washing water.

4. The wet carbon capture process integrating horizontal balance control and internal heat utilization coupling in the system according to claim 3, characterized in that, The regeneration unit comprises: A regeneration tower (310), the top of the regeneration tower (310) being communicated with the liquid outlet of the absorption tower (210), and the bottom of the regeneration tower (310) being communicated with the liquid inlet of the absorption tower (210); A reboiler (320), which is communicated with the regeneration tower (310) through an external one-way pipeline; A lean liquid cooler (330), which is arranged on the communication pipeline between the liquid outlet of the regeneration tower (310) and the liquid inlet of the absorption tower (210) for cooling the lean liquid; A rich-lean liquid heat exchanger (340), both the rich liquid before entering the regeneration tower (310) and the lean liquid after flowing out of the regeneration tower (310) flow through the rich-lean liquid heat exchanger (340) for heat exchange between the rich liquid and the lean liquid.

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