CN110115910A - A kind of energy-saving carbon dioxide capture system and method - Google Patents

Abstract

The invention discloses an energy-saving carbon dioxide capture system and method, belonging to the technical field of flue gas purification. By setting up a gas-liquid separation system, the rich liquid is partially regenerated before entering the regeneration tower, and the carbon dioxide is separated and discharged into the regeneration tower, which reduces the heat load of the regeneration tower and can keep the regeneration tower at a higher temperature, which is different from the conventional Compared with the system of carbon dioxide capture by chemical absorption method, it can greatly reduce the regeneration energy consumption and reduce the size of the regeneration tower. In addition, sending part of the condensate from the reflux tank at the upper stage of the regeneration tower to the washing device of the absorption tower for reuse can greatly reduce the consumption of demineralized water. The purpose of washing is to prevent the diffusion of absorbent vapor. Reasonable design, energy saving and environmental protection, and can significantly reduce the cost of equipment manufacturing and system maintenance.

Description

An energy-saving carbon dioxide capture system and method

technical field

The invention belongs to the technical field of flue gas purification, and in particular relates to an energy-saving carbon dioxide capture system and method.

Background technique

In recent years, the technical route of reducing greenhouse gas emissions through the capture and storage of carbon dioxide (CCS) has become one of the important measures for the world to deal with climate change. To achieve this goal, various methods such as chemical absorption, adsorption, membrane separation, and cryogenics have been developed to capture carbon dioxide at home and abroad. Among them, the chemical absorption method of removing acid gas carbon dioxide produced by such as coal-fired power plants by using absorbents is one of the most common methods, which has the advantages of high efficiency and stable technology. The capture process based on alcohol ammonia absorbent is an example of a technically sound chemical absorption technology that has been successfully used in petrochemical decarbonization processes. Nevertheless, this separation technology still needs process improvement before it can be used to treat flue gas from boiler combustion.

Figure 1 shows the workflow of carbon dioxide capture using conventional chemical absorption. The cooled flue gas 1 is generally in contact with the absorbent at a temperature of 40-60°C; the carbon dioxide in the flue gas is absorbed by the absorbent and discharged from the bottom of the absorption tower 9, and the decarbonized flue gas 4 is discharged from the top of the absorption tower 9 . The circulating washing water in the circulating washing water pipeline 3 plays the role of recovering the absorbent diffused with the flue gas. The absorbent that has absorbed carbon dioxide is called rich liquid, and the rich liquid in the rich liquid pipeline 5 is heated by the poor-rich heat exchanger 10 and then sent to the upper end of the packing of the regeneration tower 11 . The rich liquid is regenerated at 110-140°C and a pressure of 150-200kPa, and carbon dioxide gas is desorbed. The regeneration process of the regeneration tower consumes heat energy, which is provided by the reboiler 12 . The regeneration gas 6 mainly consists of carbon dioxide and steam, with a small amount of absorbent steam. The regeneration gas in the regeneration gas pipeline 6 is cooled by the condenser 13, and the condensate separated from the reflux tank 7 is transported to the regeneration tower 11 through the condensate pipeline 8, and the separated carbon dioxide is discharged through the carbon dioxide discharge pipeline on the reflux tank 7. The regenerated absorbent is called lean liquid, and the lean liquid in the lean liquid pipeline 2 passes through the lean-rich heat exchanger 10 to recover heat and then is pumped to the absorption tower 9 .

In the above process flow, the carbon dioxide regeneration process consumes a lot of energy. The rich liquid is heated through the rich-poor heat exchanger before entering the regeneration tower, forming a gas-liquid two-phase medium and entering the regeneration tower, resulting in a decrease in the heat transfer efficiency in the tower and increasing the Renewable energy consumption. In addition, the condensate separated from the regeneration gas condensation is not reused as the scrubbing liquid of the absorption tower, which increases the amount of desalted water in the scrubbing section.

Contents of the invention

In order to solve the above defects in the prior art, the object of the present invention is to provide an energy-saving carbon dioxide capture system and method, which can greatly reduce the consumption of desalted water and regeneration energy, and reduce the size of the regeneration tower. The system has reasonable design, simple construction, energy saving and environmental protection, and can significantly reduce the cost of equipment manufacturing and system maintenance.

The present invention is realized through the following technical solutions:

The invention discloses an energy-saving carbon dioxide capture system, which includes an absorption tower, a rich-poor heat exchanger, a regeneration tower, a reflux tank, and a flash tank; the bottom of the absorption tower communicates with the flash tank through a liquid-rich pipeline, and the The liquid outlet is connected to the rich liquid inlet on the regeneration tower, and the rich liquid pump is provided on the rich liquid pipeline; the washing section of the absorption tower is provided with a circulating washing water pipeline; the carbon dioxide in the flue gas is absorbed by the absorbent in the absorption tower and becomes decarbonized The flue gas exits the absorption tower;

The lean liquid outlet at the bottom of the regeneration tower communicates with the lean liquid inlet on the absorption tower through the lean liquid pipeline, and the lean liquid pump and the lean liquid cooler are arranged on the lean liquid pipeline; Heat; the regeneration tower is connected with a reboiler; the regeneration gas outlet on the regeneration tower is connected to the reflux tank through the regeneration gas pipeline, the regeneration gas pipeline is equipped with a condenser, and the liquid outlet of the reflux tank is connected to the condensate inlet of the regeneration tower through the condensate pipeline Connected; the condensate pipeline communicates with the circulating washing water pipeline through the condensate return pipeline.

Preferably, a semi-lean liquid-lean liquid heat exchanger is provided on the lean liquid pipeline between the lean liquid outlet and the lean-rich heat exchanger, a semi-lean liquid circulation pipe is provided on the regeneration tower, and a semi-lean liquid circulation pipe is connected to the semi-lean liquid The liquid-lean liquid heat exchanger is connected, and the semi-lean liquid in the semi-lean liquid circulation pipeline exchanges heat with the lean liquid in the lean liquid pipeline in the semi-lean liquid-lean liquid heat exchanger and returns to the regeneration tower.

Further preferably, the semi-poor liquid-poor liquid heat exchanger is a shell-and-tube heat exchanger.

Preferably, the condenser is a plate cooler or a tube cooler.

Preferably, the lean liquid cooler is a plate cooler or a tube cooler

Preferably, the absorbent is one or more of amine solution, amino acid salt, inorganic salt solution and ammonia solution.

Preferably, the gas outlet of the flash tank communicates with the reflux tank.

The invention discloses a method for capturing carbon dioxide by adopting the above-mentioned energy-saving carbon dioxide capture system, comprising: after the flue gas enters the absorption tower, the carbon dioxide in the flue gas is absorbed by the absorbent, and becomes decarbonized flue gas, which passes through the washing section and then is discharged from the absorption tower The absorbent that has absorbed carbon dioxide, that is, the rich liquid is pumped into the flash tank from the bottom of the absorption tower through the rich liquid pipeline through the rich liquid pump, and the rich liquid is separated from the carbon dioxide in the flash tank and enters the regeneration tower from the rich liquid inlet. The carbon dioxide is heated by the reactor to separate the carbon dioxide, and the carbon dioxide enters the reflux tank from the regeneration gas pipeline through the condenser, and part of the condensate generated in the reflux tank enters the regeneration tower through the condensate pipeline, and the other part enters the circulating washing water pipeline through the condensate return pipeline; The absorbent of carbon dioxide is the lean liquid, which is pumped from the lean liquid pipeline through the lean liquid pump to the lean liquid cooler and then enters the absorption tower to start the next absorption/regeneration cycle. During the cycle, the rich liquid pipeline and the lean liquid pipeline pass through the rich and poor The heat exchanger performs heat exchange.

Preferably, a semi-poor liquid-poor liquid heat exchange system is provided outside the regeneration tower, and the semi-poor liquid in the regeneration tower returns to regeneration after exchanging heat with the poor liquid in the poor liquid pipeline in the semi-poor liquid-poor liquid heat exchange system tower.

Compared with the prior art, the present invention has the following beneficial technical effects:

An energy-saving carbon dioxide capture system disclosed in the present invention, by setting a flash tank, the rich liquid is partially regenerated before entering the regeneration tower, and the carbon dioxide is separated and discharged into the regeneration tower, which reduces the heat load of the regeneration tower and can Keeping the regeneration tower at a higher temperature can greatly reduce the regeneration energy consumption and reduce the size of the regeneration tower compared with the conventional chemical absorption method for carbon dioxide capture system. In addition, part of the condensate from the reflux tank in the upper section of the regeneration tower is sent to the washing device of the absorption tower for reuse through the circulating washing water pipeline, which can greatly reduce the consumption of demineralized water. The purpose of washing is to prevent the diffusion of absorbent vapor. The system is reasonably designed, energy-saving and environmentally friendly, and can significantly reduce the cost of equipment manufacturing and system maintenance.

Further, by setting the semi-lean liquid-lean liquid heat exchanger, the lean liquid can exchange heat with the semi-lean liquid in the middle section of the regeneration tower, making full use of the heat contained in the lean liquid that has been discharged from the regeneration tower, further reducing regeneration Boiler steam consumption.

Furthermore, the semi-poor liquid-poor liquid heat exchanger adopts a shell-and-tube heat exchanger, which has a simple structure and low cost, and can be used under high temperature and high pressure conditions.

Further, the condenser and the lean liquid cooler adopt a plate cooler or a tube cooler, which has high heat exchange efficiency, small heat loss, relatively compact structure and long service life.

Further, the absorbent is used in combination with one or more of amine solution, amino acid salt, inorganic salt solution and ammonia solution, and has a good absorption effect on carbon dioxide.

Furthermore, the gas outlet of the flash tank is connected to the return tank, and the carbon dioxide is collected in the return tank for discharge, which is convenient for unified collection and utilization, and also reduces the cost caused by setting up separate collection equipment.

The method for carbon dioxide capture by adopting the above-mentioned energy-saving carbon dioxide capture system disclosed in the present invention makes full use of the heat of products in each link and reduces energy consumption; sends part of the condensate of the reflux tank in the upper part of the regeneration tower to the washing device of the absorption tower Reuse can greatly reduce the consumption of demineralized water. The process is simple to operate, energy-saving and environment-friendly.

Furthermore, the semi-lean liquid-lean liquid heat exchange system makes full use of the heat contained in the lean liquid, reducing the heat required by the semi-lean liquid and further reducing the steam consumption of the reboiler.

Description of drawings

Figure 1 is a process flow chart of carbon dioxide capture by conventional chemical absorption method;

Fig. 2 is the system process flowchart of embodiment 1 of the present invention;

Fig. 3 is a system process flow diagram of Embodiment 2 of the present invention.

In the figure: 1-flue gas, 2-lean liquid pipeline, 3-circulating washing water pipeline, 4-decarbonization flue gas, 5-rich liquid pipeline, 6-regenerated gas pipeline, 7-reflux tank, 8-condensate pipeline , 9-absorption tower, 10-poor-poor heat exchanger, 11-regeneration tower, 12-reboiler, 13-condenser, 14-lean liquid cooler, 15-flash tank, 16-condensate return pipeline, 17 - Semi-poor liquid-poor liquid heat exchanger.

Detailed ways

The present invention will be described in further detail below in conjunction with accompanying drawing and specific embodiment, and its content is explanation of the present invention rather than limitation:

Example 1

As shown in Figure 2, the energy-saving carbon dioxide capture system of the present invention includes an absorption tower 9, a rich-poor heat exchanger 10, a regeneration tower 11, a reflux tank 7, and a flash tank 15; The steam tank 15 is communicated, the liquid outlet of the flash tank 15 is communicated with the rich liquid inlet on the regeneration tower 11, and the gas outlet of the flash tank 15 can be communicated with the reflux tank 7; the rich liquid pipeline 5 is provided with a rich liquid pump; The washing section of the tower 9 is provided with a circulating washing water pipeline 3; the carbon dioxide in the flue gas 1 is absorbed by the absorbent in the absorption tower 9 and becomes decarbonized flue gas 4 and discharged from the absorption tower 9. The absorbent can be amine liquid, amino acid salt, inorganic One or more of salt solution and ammonia solution; the lean liquid outlet at the bottom of the regeneration tower 11 communicates with the lean liquid inlet on the absorption tower 9 through the lean liquid pipeline 2, and the lean liquid pipeline 2 is provided with a lean liquid pump and a lean liquid Cooler 14; the lean liquid pipeline 2 and the rich liquid pipeline 5 exchange heat through the poor-rich heat exchanger 10; the regeneration tower 11 is connected with a reboiler 12; the regeneration gas outlet on the regeneration tower 11 passes through the regeneration gas pipeline 6 and the reflux tank 7 connection, the regeneration gas pipeline 6 is provided with a condenser 13, and the liquid outlet of the reflux tank 7 is communicated with the condensate inlet of the regeneration tower 11 through the condensate pipeline 8; the condensate pipeline 8 is connected with the circulating washing water pipeline 3 through the condensate return pipeline 16 connected.

The absorbent (rich liquid) that has absorbed carbon dioxide in the absorption tower 9 is heated during the heat exchange process with the high-temperature (110-130°C) lean liquid, and then sent to the flash tank 15, and the carbon dioxide gas that flashes out is sent back to the flow tank 7 , the liquid is sent to the regeneration tower 11 upper section. A part of the condensate produced in the reflux tank 7 is sent to the regeneration tower through the condensate pipeline 8, and the other part is sent to the absorption tower 9 washing device through the condensate return pipeline 16.

Condenser 13 and lean liquid cooler 14 can adopt plate cooler or tube cooler;

Example 2

As shown in Figure 3, on the basis of the system of Embodiment 1, a semi-poor liquid-poor liquid heat exchanger 17 is set on the poor liquid pipeline 2 between the poor liquid outlet and the poor-rich heat exchanger 10, and the regeneration tower 11 is provided with The semi-poor liquid circulation pipeline, the semi-poor liquid in the semi-poor liquid circulation pipeline returns to the regeneration tower 11 after exchanging heat with the poor liquid in the poor liquid pipeline 2 in the semi-poor liquid-poor liquid heat exchanger 17. The semi-poor liquid-poor liquid heat exchanger 17 can be a shell-and-tube heat exchanger.

comparative example

As shown in FIG. 1 , the carbon dioxide capture system using the conventional chemical absorption method does not include the flash tank 15 , the semi-lean liquid-lean liquid heat exchanger 17 and the condensate return pipeline 16 .

Effect verification

The flue gas with a temperature of 40°C and a carbon dioxide volume fraction of 15% is sent to the bottom of the system absorption tower 9 of Example 1, Example 2 and Comparative Example respectively at a flow rate of 2.0m ³ /hour, and a 30wt% ethanolamine solution is used as the For the carbon dioxide absorbent, the circulation rate is set at 100ml/min, and the temperature of the absorbent sent into the absorption tower is set at 40°C. The concentration of carbon dioxide in the flue gas 1 at the entrance of the absorption tower 9 and the decarbonized flue gas 4 is measured by a gas analyzer, and the heat consumption of the reboiler in capturing per ton of carbon dioxide is calculated according to the 90% carbon dioxide removal rate, and the results are shown in Table 1 .

The regeneration energy consumption contrast of table 1 embodiment 1, 2 and comparative example

It can be seen from Table 1 that when the same amount of carbon dioxide is captured under the same carbon dioxide removal efficiency (90%), the heat consumption of cooling water and reboiler of Example 1 and Example 2 is lower than that of the comparative example. The result shows that under the same carbon dioxide removal efficiency, the energy-saving carbon dioxide capture system and process of the present invention can reduce the consumption of desalted water and the load of the regeneration tower, and greatly reduce the steam consumption.

The present invention proposes two energy-saving regeneration processes and methods through partial regeneration of the rich liquid and intermediate heating of the regeneration tower, which reduces the heat load of the regeneration tower and allows the regeneration tower to maintain a higher temperature, which is comparable to the traditional amine liquid absorbent carbon dioxide capture system. Ratio, can greatly reduce regeneration energy consumption and regeneration tower size. In addition, because the condensate from the reflux tank in the upper part of the regeneration tower is sent to the washing device of the absorption tower for reuse, the consumption of demineralized water can be greatly reduced. Therefore, it is possible to reduce regeneration energy and water consumption, which are the most important factors in the CO2 capture process.

Compared with the conventional system (comparative example), the system using Embodiment 2 of the present invention can reduce regeneration energy consumption by 0.45GJ/ton CO2. According to the current situation of carbon dioxide treatment in a 500MW coal-fired power plant, about 10,000 tons of carbon dioxide are produced every day, and under the condition of 90% removal rate, the energy consumption can be reduced by about 4,500GJ.

It should be noted that the above description is only one of the embodiments of the present invention, and equivalent changes made according to the system described in the present invention are all included in the protection scope of the present invention. Those skilled in the art to which the present invention belongs can replace the described specific examples in a similar manner, as long as they do not deviate from the structure of the present invention or exceed the scope defined in the claims, they all belong to the protection scope of the present invention.

Claims (9)

1. An energy-saving carbon dioxide capture system, characterized in that it comprises a lean liquid pipeline (2), a rich liquid pipeline (5), a return tank (7), an absorption tower (9), and a rich-poor heat exchanger (10) , regeneration tower (11) and flash tank (15); the bottom of absorption tower (9) is communicated with flash tank (15) by rich liquid pipeline (5), and the liquid outlet of flash tank (15) is connected with regeneration tower (11) ) is connected to the rich liquid inlet, and the rich liquid pipeline (5) is provided with a rich liquid pump; the washing section of the absorption tower (9) is provided with a circulating washing water pipeline (3); the carbon dioxide in the flue gas (1) passes through the absorption tower (9) After the internal absorbent is absorbed, it becomes decarbonized flue gas (4) and discharges the absorption tower (9); The lean liquid outlet at the bottom of the regeneration tower (11) communicates with the lean liquid inlet on the absorption tower (9) through the lean liquid pipeline (2), and the lean liquid pump and the lean liquid cooler (14) are provided on the lean liquid pipeline (2) The lean liquid pipeline (2) and the rich liquid pipeline (5) exchange heat through the poor-rich heat exchanger (10); the regeneration tower (11) is connected with a reboiler (12); the regeneration gas outlet on the regeneration tower (11) The regeneration gas pipeline (6) is connected to the reflux tank (7), the regeneration gas pipeline (6) is provided with a condenser (13), and the liquid outlet of the reflux tank (7) is connected to the regeneration tower (11) through the condensate pipeline (8). ) is communicated with the condensate inlet; the condensate pipeline (8) is communicated with the circulating washing water pipeline (3) through the condensate return pipeline (16). 2. The energy-saving carbon dioxide capture system according to claim 1, characterized in that, the lean liquid pipeline (2) between the lean liquid outlet and the lean-rich heat exchanger (10) is provided with a semi-lean liquid-poor liquid The heat exchanger (17), the regeneration tower (11) is provided with a semi-poor liquid circulation pipeline, and the semi-poor liquid circulation pipeline is connected with the semi-poor liquid-poor liquid heat exchanger (17), and the semi-poor liquid circulation pipeline in the semi-poor liquid The liquid returns to the regeneration tower (11) after exchanging heat with the lean liquid in the lean liquid pipeline (2) in the semi-lean liquid-lean liquid heat exchanger (17). 3. The energy-saving carbon dioxide capture system according to claim 2, characterized in that the semi-poor liquid-poor liquid heat exchanger (17) is a shell-and-tube heat exchanger. 4. The energy-saving carbon dioxide capture system according to claim 1, characterized in that the condenser (13) is a plate cooler or a tube cooler. 5. The energy-saving carbon dioxide capture system according to claim 1, characterized in that the lean liquid cooler (14) is a plate cooler or a tube cooler. 6. The energy-saving carbon dioxide capture system according to claim 1, wherein the absorbent is one or more of amine solution, amino acid salt, inorganic salt solution and ammonia solution. 7. The energy-saving carbon dioxide capture system according to claim 1, characterized in that the gas outlet of the flash tank (15) communicates with the return tank (7). 8. A method for carbon dioxide capture using the energy-saving carbon dioxide capture system described in any one of claims 1 to 7, comprising: After the flue gas (1) enters the absorption tower (9), the carbon dioxide in the flue gas (1) is absorbed by the absorbent, and becomes decarbonized flue gas (4). After passing through the washing section, it is discharged from the absorption tower (9); The rich liquid is pumped into the flash tank (15) from the bottom of the absorption tower (9) through the rich liquid pipeline (5) through the rich liquid pump, and the rich liquid enters from the rich liquid inlet after separating carbon dioxide in the flash tank (15). The regeneration tower (11) is heated by the reboiler (12) to separate carbon dioxide, and the carbon dioxide enters the reflux tank (7) through the regeneration gas pipeline (6) through the condenser (13), and the condensate produced in the reflux tank (7) A part enters the regeneration tower (11) through the condensate pipeline (8), and the other part enters the circulating washing water pipeline (3) through the condensate return pipeline (16); ) is pumped into the lean liquid cooler (14) by the lean liquid pump and enters the absorption tower (9) to start the next absorption/regeneration cycle. During the cycle, the rich liquid pipeline (5) and the lean liquid pipeline (2) pass through the lean liquid The rich heat exchanger (10) performs heat exchange. 9. The energy-saving carbon dioxide capture system clean combustion process according to claim 8, characterized in that a semi-poor liquid-poor liquid heat exchange system is provided outside the regeneration tower (11), and the semi-poor liquid heat exchange system in the regeneration tower (11) The lean liquid returns to the regeneration tower (11) after exchanging heat with the lean liquid in the lean liquid pipeline (2) in the semi-lean liquid-lean liquid heat exchange system.