A system and method for absorbing carbon dioxide in flue gas using slag flushing wastewater

Abstract

The present invention discloses a system and method for absorbing carbon dioxide from flue gas using slag flushing wastewater. The system comprises: a flue gas input pipeline, a spray absorption unit, a sedimentation unit, a supernatant return pipeline, and a slag flushing wastewater input pipeline. The spray absorption unit is provided with a multi-stage spray device at the upper portion, with a gas aeration disk correspondingly provided below each stage of the spray device. The spray device is connected to the slag flushing wastewater input pipeline. The flue gas input pipeline comprises a main line connected to the lower portion of the spray absorption unit and branches connected one-to-one with the gas aeration disks. The spray absorption unit is provided with a gas outlet at the top and an outlet at the bottom connected to the sedimentation unit. The sedimentation unit is provided with a supernatant outlet, which is connected to the slag flushing wastewater input pipeline via the supernatant return pipeline.

Description

Technical Field

[0001] The present invention relates to the field of carbon dioxide capture in the steel industry, and in particular to a system and method for absorbing carbon dioxide in flue gas by utilizing slag flushing wastewater. Background Art

[0002] Currently, the main CO2 capture technologies in the steel industry include waste heat and energy recovery. The use of this technology reduces fossil energy consumption and can effectively reduce CO2 emissions. A second key approach is carbon capture, utilization, and storage (CCUS), which is a key technology for addressing global climate change. Currently, the main CO2 capture methods include pre-combustion capture, oxyfuel combustion, and post-combustion capture. Post-combustion capture has the fastest industrialization progress and is already in the industrial application stage, while pre-combustion capture and oxyfuel combustion capture are still in the industrial demonstration and pilot demonstration stages, respectively. Post-combustion capture is a capture system that separates CO2 from flue gases, forming a high concentration of CO2. The steel industry primarily utilizes post-combustion capture, using commonly used technologies such as physical adsorption, chemical absorption, and membrane separation. Post-combustion capture effectively captures CO2 emitted from various processes.

[0003] The primary blast furnace slag treatment process involves water quenching. High-temperature slag, at 1400-1500°C, flows from the blast furnace through the slag outlet. As it flows through the slag trough, it is impact-quenched into qualified slag using a specific water volume, pressure, and trough slope to create a desired angle between the water and the slag. During the ironmaking process, slag quenching accounts for over 50% of total fresh water consumption. Producing one ton of slag quenching consumes approximately 11.2 tons of fresh water, with approximately 10 tons of recycled water. The blast furnace slag and ash produced by the steel industry contain alkaline substances such as calcium, magnesium, sodium, and potassium. Therefore, the large amount of slag quenching water generated during this process can be used for decarbonization. For example, slag typically contains alkaline substances such as activated calcium oxide (fCaO). The slag quenching wastewater is applied to the flue gas carbon dioxide absorption system, fully utilizing the alkaline substances in the ash to absorb and capture carbon dioxide from the flue gas, thereby reducing the CO2 concentration in the flue gas. Summary of the Invention

[0004] The present invention aims to provide a system and method for absorbing carbon dioxide from flue gas using slag flushing wastewater. The present invention proposes using blast furnace slag flushing wastewater generated by steel enterprises as an absorbent to simply flush carbon dioxide from flue gas, thereby achieving a certain degree of carbon dioxide absorption, reducing the carbon dioxide concentration in the flue gas, and thus reducing carbon dioxide emissions.

[0005] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0006] On one hand, the present invention provides a system for absorbing carbon dioxide in flue gas by using slag flushing wastewater, the system comprising: a flue gas input pipeline, a spray absorption unit, a precipitation unit, a supernatant return pipeline, and a slag flushing wastewater input pipeline;

[0007] The upper part of the spray absorption unit is provided with a multi-stage spray device, and a gas aeration disk is correspondingly provided under each stage of the spray device; the spray device is connected to the slag flushing wastewater input pipeline; the flue gas input pipeline includes a main line connected to the lower part of the spray absorption unit, and branches connected to the gas aeration disks one by one;

[0008] The top of the spray absorption unit is provided with a gas outlet, and the bottom is provided with an outlet connected to the precipitation unit. The precipitation unit is provided with a supernatant outlet, and the supernatant outlet is connected to the slag flushing wastewater input pipeline through the supernatant return pipeline.

[0009] In the system of the present invention, the gas aeration disc is preferably densely covered with fine holes and has protrusions on its edges, thereby retaining the sprayed absorption liquid within the disc. Approximately 20% of the flue gas in the flue gas input line is fed through a branch and enters the gas aeration disc, where it reacts with the absorption liquid layer on the disc to generate bubbles, thereby increasing gas-liquid mass transfer efficiency.

[0010] According to the system of the present invention, the pore diameter should not be too small, as too small a size will increase gas resistance and be detrimental to diffusion. The pore diameter is preferably 5 mm to 10 mm.

[0011] According to the system of the present invention, preferably, the gas aeration disc and the spray device are connected to the inner wall of the spray absorption unit on alternate sides from bottom to top, while the opposite side is unconnected, forming a baffle channel within the spray absorption unit. Approximately 80% of the flue gas in the flue gas input pipeline passes through the main line from bottom to top within the spray absorption unit through the baffle channel at the edge of the gas aeration disc. The provision of the baffle channel can increase the contact time between this portion of flue gas and the slurry, thereby improving the absorption and capture efficiency of carbon dioxide.

[0012] According to the system of the present invention, preferably, the spraying device is provided with an automatic control unit for adjusting the spraying amount in real time according to the flue gas volume of the flue gas input pipeline.

[0013] According to the system of the present invention, preferably, a slurry pump is provided on the slag flushing wastewater input pipeline.

[0014] According to the system of the present invention, preferably, the slag flushing wastewater input pipeline is further provided with a buffer unit before the slurry pump, and the supernatant return pipeline is connected to the slag flushing wastewater input pipeline before the buffer unit.

[0015] According to the system of the present invention, preferably, a regulating control valve is provided on the supernatant return pipeline.

[0016] According to the system of the present invention, preferably, an adjusting control valve is provided at the inlet of the slag flushing wastewater input pipeline.

[0017] According to the system of the present invention, preferably, the sedimentation unit is provided with a conveyor belt device for transporting the solids settled in the sedimentation unit out for subsequent processing.

[0018] The sedimentation tank in the system of the present invention is used to collect the slurry after absorbing carbon dioxide. The supernatant after precipitation is returned for recycling through the supernatant return pipeline. The precipitated solids are regularly cleaned and transported to the sintering batching system for return ore batching, and then returned to the sintering system to realize closed-loop harmless treatment of solid waste in steel production.

[0019] Another aspect of the present invention provides a method for absorbing carbon dioxide in flue gas by utilizing slag flushing wastewater, which is carried out by the above system.

[0020] According to the method of the present invention, preferably, the method comprises:

[0021] The flue gas after desulfurization and denitrification enters the bottom of the spray absorption unit and the gas aeration plate through the main line and branch of the flue gas input pipeline respectively; the slag flushing wastewater as the absorption liquid enters the spraying device through the slag flushing wastewater input pipeline for spraying;

[0022] The flue gas at the bottom moves upward and reacts with the absorption liquid sprayed from the upper part in a reverse manner. The flue gas entering the gas aeration plate reacts with the absorption liquid remaining on the plate. The flue gas from which carbon dioxide has been removed by the reaction is discharged from the gas outlet at the top of the spray absorption unit.

[0023] The absorption liquid that has absorbed carbon dioxide is collected from the bottom outlet of the spray absorption unit to the precipitation unit, and the supernatant after precipitation is returned to the slag flushing wastewater input pipeline through the supernatant return pipeline for recycling.

[0024] Preferably, the precipitated solids (calcium bicarbonate, calcium carbonate) are regularly cleaned and transported to the sintering batching system for return ore batching, and then returned to the sintering system to achieve closed-loop harmless treatment of solid waste in steel production.

[0025] The system and method of the present invention fully utilize the blast furnace slag flushing wastewater generated inside the steel plant to absorb carbon dioxide in the flue gas at low cost, reduce the carbon dioxide concentration in the exhaust flue gas, and achieve clean production and green circular development. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1This is a schematic diagram of a system for absorbing carbon dioxide in flue gas using slag flushing wastewater in a preferred embodiment.

[0027] Figure 2 Schematic diagram of the spray device and the gas aeration disk in the spray absorption unit 2 in a preferred embodiment.

[0028] Description of reference numerals:

[0029] 1. Flue gas input pipeline;

[0030] 2. Spray absorption unit;

[0031] 3. Sedimentation unit;

[0032] 4. Supernatant return line;

[0033] 5. Slag flushing wastewater input pipeline;

[0034] 6. Spraying device;

[0035] 7. Gas aeration plate;

[0036] 8. Main pipe of flue gas input pipeline;

[0037] 9. Branch of flue gas input pipeline;

[0038] 10. Slurry pump;

[0039] 11. Buffer unit;

[0040] 12 and 13, regulating control valve;

[0041] Regulating control valves;

[0042] 14. Conveyor belt device;

[0043] 15. Flue. DETAILED DESCRIPTION

[0044] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. Those skilled in the art should understand that the following specific description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0045] The present invention provides a system for absorbing carbon dioxide in flue gas by using slag flushing wastewater. Figure 1 and Figure 2 As shown, the system includes: a flue gas input pipeline 1, a spray absorption unit 2, a precipitation unit 3, a supernatant return pipeline 4, and a slag flushing wastewater input pipeline 5;

[0046] The upper part of the spray absorption unit 2 is provided with a multi-stage spray device 6, for example Figure 1 and Figure 2A five-stage spraying device 6 is provided. Figure 2 As shown, a gas aeration plate 7 is correspondingly provided under each spray device 6, specifically, a gas aeration plate 7 is provided below the liquid distributor 6-1 in the spray device 6. The spray device 6 is connected to the slag flushing wastewater input pipeline 5; the flue gas input pipeline 1 is led out from the flue 15 and includes a main line 8 connected to the lower part of the spray absorption unit 2, and branches 9 connected one-to-one with the gas aeration plates 7;

[0047] The spray absorption unit 2 is provided with a gas outlet at the top and an outlet at the bottom connected to the sedimentation unit 3. The sedimentation unit 3 is provided with a supernatant outlet, and the supernatant outlet is connected to the slag flushing wastewater input pipeline 5 through the supernatant return pipeline 4.

[0048] like Figure 2 As shown, the gas aeration disk 7 is densely covered with fine pores. The pore diameter should not be too small, as this increases gas resistance and hinders diffusion. A pore diameter of 5 mm to 10 mm is preferred. The edges of the gas aeration disk 7 are provided with protrusions to retain the sprayed absorption liquid within the gas aeration disk 7. Approximately 20% of the flue gas in the flue gas input pipeline is input through branch 9 and enters the gas aeration disk 7. This creates bubbles with the absorption liquid layer on the gas aeration disk 7, thereby increasing gas-liquid mass transfer efficiency.

[0049] The gas aeration plate 7 and the spray device 6 are connected to the inner wall of the spray absorption unit on one side from bottom to top, and are not connected on the opposite side, forming a baffle channel in the spray absorption unit 2. Figure 1 As shown, about 80% of the flue gas in the flue gas input pipeline passes through the main line 8 and passes through the deflection channel at the edge of the gas aeration plate 7 from bottom to top in the spray absorption unit 2. The setting of the deflection channel can increase the contact time between this part of the flue gas and the slurry, thereby improving the absorption and capture efficiency of carbon dioxide.

[0050] In a more preferred solution, the spraying device 6 may also be provided with an automatic control unit for adjusting the spraying amount in real time according to the amount of flue gas in the flue gas input pipeline 1 .

[0051] The slag flushing wastewater input pipeline 5 is provided with a slurry pump 10 to pump the absorption liquid into the spray absorption unit 2 for spraying. Further preferably, the slag flushing wastewater input pipeline 5 is also provided with a buffer unit 11 before the slurry pump 10, which can specifically be a buffer pool or a buffer tank; the supernatant return pipeline 4 is connected to the slag flushing wastewater input pipeline 5 before the buffer unit 11, first enters the buffer unit 11 to mix with the slag flushing wastewater and then enters the spray absorption unit 2. The inlet of the slag flushing wastewater input pipeline 5 is also provided with a regulating control valve 13 to control the amount of slag flushing wastewater entering the system. The supernatant return pipeline 4 is provided with a regulating control valve 12 to control the supernatant entering the buffer unit 11.

[0052] The sedimentation tank 3 in the system of the present invention is used to collect the slurry after absorbing carbon dioxide. The supernatant after precipitation is returned for recycling through the supernatant return pipeline 4. The precipitated solids are regularly cleaned and transported to the sintering batching system through the conveyor belt device 14 for return ore batching, and then returned to the sintering system to realize closed-loop harmless treatment of solid waste in steel production.

[0053] A method for absorbing carbon dioxide in flue gas by using slag flushing wastewater using the above system includes the following process:

[0054] After the sintering flue gas passes through the existing dust removal, denitrification and desulfurization purification system, the purified flue gas temperature is between 100 and 110°C. The outlet of the purification system enters the carbon dioxide absorption system of the present invention through a flue. Specifically, the flue gas after desulfurization and denitrification passes through the flue 15 through the main line 8 and branch 9 of the flue gas input pipeline 1 and enters the bottom of the spray absorption unit 2 and the gas aeration plate 7 respectively; the slag flushing wastewater is used as the absorption liquid through the slag flushing wastewater input pipeline 5 and enters the spray device 6 for spraying; the flue gas at the bottom (about 80% of the original flue gas) flows upward and reacts with the absorption liquid sprayed from the top in a reverse direction. Preferably, this part of the flue gas flows upward along the deflection channel at the edge of the gas aeration plate 7 to extend the contact reaction time with the absorption liquid. The flue gas entering the gas aeration plate 7 (about 20% of the original flue gas) reacts with the absorption liquid retained on the plate; the flue gas from which carbon dioxide has been removed by the reaction is discharged from the gas outlet at the top of the spray absorption unit 2. The absorption liquid that has absorbed carbon dioxide is collected from the bottom outlet of the spray absorption unit 2 to the precipitation unit 3, and the supernatant after precipitation is returned to the slag flushing wastewater input pipeline 5 through the supernatant return pipeline 4 for recycling.

[0055] The precipitated solids (calcium bicarbonate, calcium carbonate) are cleaned regularly and transported to the sintering batching system through the conveyor belt device 14 for return ore batching, and then returned to the sintering system. After sintering, the carbon dioxide is solidified in the sintered slag to achieve calcification and storage of carbon dioxide.

[0056] The system can also adjust the injection amount of the spraying device 6 in real time according to the flue gas volume through the automatic control device to ensure sufficient absorption of carbon dioxide and decarbonization efficiency.

[0057] The system and method of the present invention fully utilizes blast furnace slag flushing wastewater generated within steel mills to achieve low-cost absorption of carbon dioxide from flue gas, reducing the concentration of carbon dioxide in exhaust flue gas and achieving clean production and green circular development. This invention enables steel enterprises to capture carbon dioxide from flue gas using steel production wastewater, thereby reducing carbon emissions. The system is applicable to flue gas treatment processes in steel enterprises and includes a proprietary integrated system of integrated equipment and ancillary process equipment.

[0058] use Figure 1 The system shown in the figure processes a sintering flue gas, the components of which mainly include CO2, CO, SO2, NO x , the CO2 content is about 7% by volume, according to Figure 1 After system treatment, the CO2 content in the flue gas is reduced to about 3%.

[0059] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A system for absorbing carbon dioxide in flue gas by using slag flushing wastewater, characterized in that: The system includes: flue gas input pipeline, spray absorption unit, precipitation unit, supernatant return pipeline, slag flushing wastewater input pipeline; The upper part of the spray absorption unit is provided with a multi-stage spray device, and a gas aeration disk is correspondingly provided under each stage of the spray device; the spray device is connected to the slag flushing wastewater input pipeline; the flue gas input pipeline includes a main line connected to the lower part of the spray absorption unit, and branches connected to the gas aeration disks one by one; The top of the spray absorption unit is provided with a gas outlet, and the bottom is provided with an outlet connected to the precipitation unit. The precipitation unit is provided with a supernatant outlet, and the supernatant outlet is connected to the slag flushing wastewater input pipeline through the supernatant return pipeline; The spraying device is provided with an automatic control unit for adjusting the spraying amount in real time according to the amount of flue gas in the flue gas input pipeline; A slurry pump is provided on the slag flushing wastewater input pipeline.

2. The system according to claim 1, wherein: The gas aeration disk is densely covered with fine holes, and the edge of the gas aeration disk is provided with protrusions.

3. The system according to claim 2, characterized in that The diameter of the pores is 5 mm to 10 mm.

4. The system according to claim 1, wherein: The gas aeration disk and the spray device are connected to the inner wall of the spray absorption unit on one side alternately from bottom to top, and are not connected on the opposite side, thereby forming a baffle channel in the spray absorption unit.

5. The system according to claim 1, wherein: The slag flushing wastewater input pipeline is further provided with a buffer unit before the slurry pump, and the supernatant return pipeline is connected to the slag flushing wastewater input pipeline before the buffer unit.

6. The system according to claim 1, wherein: The supernatant return pipeline is provided with a regulating control valve.

7. A method for absorbing carbon dioxide in flue gas by using slag flushing wastewater, characterized in that: The method is carried out by the system according to any one of claims 1 to 6.

8. The method according to claim 7, characterized in that The method includes: The flue gas after desulfurization and denitrification enters the bottom of the spray absorption unit and the gas aeration plate through the main line and branch of the flue gas input pipeline respectively; the slag flushing wastewater as the absorption liquid enters the spraying device through the slag flushing wastewater input pipeline for spraying; The flue gas at the bottom moves upward and reacts with the absorption liquid sprayed from the upper part in a reverse manner. The flue gas entering the gas aeration plate reacts with the absorption liquid remaining on the plate. The flue gas from which carbon dioxide has been removed by the reaction is discharged from the gas outlet at the top of the spray absorption unit. The absorption liquid that has absorbed carbon dioxide is collected from the bottom outlet of the spray absorption unit to the precipitation unit, and the supernatant after precipitation is returned to the slag flushing wastewater input pipeline through the supernatant return pipeline for recycling.

9. The method according to claim 8, characterized in that The precipitated solids are cleaned regularly and transported to the sintering batching system for return ore batching, and then returned to the sintering system.

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