TWI839793B - Method and equipment for recovering carbon dioxide by absorption and homogeneous crystallization technology - Google Patents

Abstract

A method for recovering carbon dioxide by absorption and homogeneous crystallization technology, wherein waste gas containing _CO2 reacts with an alkaline absorbent aqueous solution to obtain ^a product containing _CO32- and _HCO3 ^- a first solution of at least one of the above; monitoring and adjusting the pH value of the first solution so that it falls within a range of 6 to 10 to become a reaction solution; reacting the reaction solution with a crystallizing agent solution containing alkaline earth metal ions at a pH value of 8 to 11 in a fluidized bed crystallization device to obtain carbonate crystal precipitated particles and a mixed solution containing carbonate crystal suspended particles; filtering the mixed solution to obtain a residue containing carbonate crystal suspended particles; and conveying the residue back to the fluidized bed crystallization device to continue the crystallization reaction to form larger carbonate crystal precipitated particles, thereby eliminating the need to remove sludge and increasing the total yield of carbonate crystal precipitated particles.

Description

Method and equipment for recovering carbon dioxide by absorption and homogeneous crystallization technology

The present invention relates to a gas treatment method and equipment, and in particular to a method and equipment for recovering carbon dioxide by absorption and homogeneous crystallization technology.

Carbon dioxide is one of the components in exhaust gas, and how to capture and recycle it has become an important environmental protection issue today. At present, the technologies used to capture and recycle carbon dioxide in heavy industry, petrochemical industry or power plants mainly include solvent absorption method, adsorption method or gas separation membrane separation method, among which, the solvent absorption method, for example, uses potassium hydroxide solution as an absorbent to separate carbon dioxide from exhaust gas containing carbon dioxide, and converts carbon dioxide into carbonate ions to dissolve in potassium hydroxide solution, and then converts carbonate ions in potassium hydroxide solution dissolved with carbonate ions into carbonate crystals to achieve the purpose of carbon dioxide storage.

At present, the solvent absorption method can be carried out in combination with the fluidized bed crystallization technology. However, the existing method of using the fluidized bed crystallization technology to convert carbonate ions in a potassium hydroxide solution containing carbonate ions into carbonate crystals cannot completely precipitate and recover the carbonate crystals, and there is a problem of low carbonate crystal yield.

Therefore, the first object of the present invention is to provide a method for recovering carbon dioxide using absorption and homogeneous crystallization technology.

Therefore, the method of recovering carbon dioxide by absorption and homogeneous crystallization technology of the present invention comprises the following steps: (a) mixing exhaust gas containing carbon dioxide with an alkaline absorbent aqueous solution having a pH value of 7.3 or above in an absorption tower so that the carbon dioxide in the exhaust gas is dissolved in the alkaline absorbent aqueous solution to obtain a first solution containing at least one of carbonate ions and hydrogen carbonate ions and water; (b) monitoring the pH value of the first solution, and when the pH value of the first solution falls within the range of 6 to 10, transporting the first solution to a fluidized bed crystallization device as a solution to be reacted; when the pH value of the first solution does not fall within the range of 6 to 10, adjusting the pH value of the first solution and then transporting it to the fluidized bed crystallization device as a solution to be reacted, and the pH value of the solution to be reacted ranges from 6 to 10, and the solution to be reacted contains at least one of carbonate ions and hydrogen carbonate ions and water; (c) introducing a crystallization agent solution containing alkali earth metal ions into the fluidized bed crystallization device to allow the reaction solution to mix with the crystallization agent solution and the pH value after mixing is in the range of 8 to 11, so that the existing carbonate ions react with the alkali earth metal ions in the crystallization agent solution to form carbonate crystal precipitate particles, and obtain a mixed solution containing water and carbonate crystal suspended particles; (d) filtering the mixed solution to obtain a filtrate containing water and a residue containing carbonate crystal suspended particles; (e) transporting the residue back to the fluidized bed crystallization device, and reacting the carbonate crystal suspended particles in the residue with the alkaline earth metal ions in the crystallizer solution to form carbonate crystal precipitated particles; and (f) monitoring the pH value of the filtrate, and when the pH value of the filtrate falls within the range of 8 to 11, transporting the filtrate back to the absorption tower for use as an alkaline absorbent aqueous solution, and when the pH value of the filtrate does not fall within the range of 8 to 11, adjusting the pH value of the filtrate and transporting it back to the absorption tower for use as an alkaline absorbent aqueous solution, and the pH value of the alkaline absorbent aqueous solution ranges from 8 to 11.

The second object of the present invention is to provide a device for recovering carbon dioxide by absorption and homogeneous crystallization technology.

Therefore, the device for recovering carbon dioxide by absorption and homogeneous crystallization technology of the present invention is suitable for treating a waste gas containing carbon dioxide, and the device for recovering carbon dioxide by absorption and homogeneous crystallization technology comprises an absorption tower, a first pH value adjusting device, a crystallizing agent supplying device, a fluidized bed crystallization device, a filtering device, a reflux device and a second pH value adjusting device.

The absorption tower defines an absorption space for containing an alkaline absorbent aqueous solution with a pH value of 7.3 or above, and is used to receive the exhaust gas containing carbon dioxide, so that the carbon dioxide in the exhaust gas is absorbed by the alkaline absorbent aqueous solution and dissolved in the alkaline absorbent aqueous solution to obtain a first solution containing at least one of carbonate ions and hydrogen carbonate ions and water.

The first pH adjusting device is arranged downstream of the absorption tower, and is used for receiving the first solution from the absorption tower and monitoring the pH value of the first solution from the absorption tower. When the pH value of the first solution falls within the range of 6 to 10, the first solution is transported to the fluidized bed crystallization device as a solution to be reacted. When the pH value of the first solution does not fall within the range of 6 to 10, the pH value of the first solution is adjusted and then transported to the fluidized bed crystallization device as a solution to be reacted. The pH value range of the solution to be reacted is 6 to 10, and the solution to be reacted contains at least one of carbonate ions and hydrogen carbonate ions and water.

The crystallizing agent supply device is spaced apart from the first acid-base value adjusting device and is used to provide a crystallizing agent solution containing alkaline earth metal ions.

The fluidized bed crystallization device is connected to the first pH value adjusting device and the crystallization agent supply device, and the fluidized bed crystallization device defines a reaction space, and the reaction space is used for mixing the solution to be reacted with the crystallization agent solution from the crystallization agent supply device, and the pH value after mixing ranges from 8 to 11, so that the existing carbonate ions and the alkaline earth metal ions in the crystallization agent solution undergo a crystallization reaction to form carbonate crystal precipitated particles, and obtain a mixed solution containing water and carbonate crystal suspended particles.

The filtering device is connected to the fluidized bed crystallization device and is used to filter the mixed solution from the fluidized bed crystallization device to obtain a water filtrate and a residue containing carbonate crystal suspended particles.

The recirculation device is arranged downstream of the filtering device and is in communication with the fluidized bed crystallization device, and is used to transport the residue from the filtering device back into the reaction space, so that the carbonate crystal suspended particles in the residue react with the alkaline earth metal ions in the crystallization agent solution to form carbonate crystal precipitated particles.

The second pH value adjusting device is arranged downstream of the filtering device and is connected to the absorption tower, and is used for receiving the filtered liquid from the filtering device and monitoring the pH value of the filtered liquid from the filtering device. When the pH value of the filtered liquid falls within the range of 8 to 11, the filtered liquid is transported back to the absorption tower for use as an alkaline absorbent aqueous solution. When the pH value of the filtered liquid does not fall within the range of 8 to 11, the pH value of the filtered liquid is adjusted and then transported back to the absorption tower for use as an alkaline absorbent aqueous solution. The pH value of the alkaline absorbent aqueous solution is in the range of 8 to 11.

The efficacy of the present invention lies in that the method of the present invention can effectively increase the total yield of carbonate crystallization precipitated particles by monitoring whether the pH value of the first solution falls within the range of 6 to 10 and determining whether to adjust the pH value of the first solution according to the monitoring result, filtering the mixed solution to obtain a residue containing carbonate crystallization suspended particles, and transporting the residue containing carbonate crystallization suspended particles back to the fluidized bed crystallization device, thereby preventing waste sludge containing carbonate crystallization suspended particles from being generated. On the other hand, the device for recovering carbon dioxide by absorption and homogeneous crystallization technology of the present invention can effectively increase the total output of carbonate crystallization precipitated particles through the arrangement of the first pH value adjustment device, the filtering device and the reflux device and the coordination with other devices without generating waste sludge containing carbonate crystallization suspended particles.

The present invention is described in detail below.

《Method for recovering carbon dioxide by absorption and homogeneous crystallization technology》

The method of recovering carbon dioxide by absorption and homogeneous crystallization technology of the present invention comprises the following steps: (a) mixing exhaust gas containing carbon dioxide with an alkaline absorbent aqueous solution having a pH value of 7.3 or above in an absorption tower so that the carbon dioxide in the exhaust gas is dissolved in the alkaline absorbent aqueous solution to obtain a first solution containing at least one of carbonate ions and hydrogen carbonate ions and water; (b) monitoring the pH value of the first solution, and when the pH value of the first solution falls within the range of 6 to 10, transporting the first solution to a fluidized bed crystallization device as a solution to be reacted; when the pH value of the first solution does not fall within the range of 6 to 10, adjusting the pH value of the first solution and then transporting it to the fluidized bed crystallization device as a solution to be reacted, and the pH value of the solution to be reacted ranges from 6 to 10, and the solution to be reacted contains at least one of carbonate ions and hydrogen carbonate ions and water; (c) introducing a crystallization agent solution containing alkali earth metal ions into the fluidized bed crystallization device to allow the reaction solution to mix with the crystallization agent solution and the pH value after mixing is in the range of 8 to 11, so that the existing carbonate ions react with the alkali earth metal ions in the crystallization agent solution to form carbonate crystal precipitate particles, and obtain a mixed solution containing water and carbonate crystal suspended particles; (d) filtering the mixed solution to obtain a filtrate containing water and a residue containing carbonate crystal suspended particles; (e) transporting the residue back to the fluidized bed crystallization device, and reacting the carbonate crystal suspended particles in the residue with the alkaline earth metal ions in the crystallizer solution to form carbonate crystal precipitated particles; and (f) monitoring the pH value of the filtrate, and when the pH value of the filtrate falls within the range of 8 to 11, transporting the filtrate back to the absorption tower for use as an alkaline absorbent aqueous solution, and when the pH value of the filtrate does not fall within the range of 8 to 11, adjusting the pH value of the filtrate and transporting it back to the absorption tower for use as an alkaline absorbent aqueous solution, and the pH value of the alkaline absorbent aqueous solution ranges from 8 to 11.

In step (a), the waste gas containing carbon dioxide is, for example but not limited to, flue gas generated by burning fuel (such as oil or coal) in industries such as petrochemical industry, cement industry or power plant.

The alkaline absorbent aqueous solution is used to absorb and dissolve carbon dioxide in the exhaust gas so that the carbon dioxide can be converted into carbonate ions or bicarbonate ions and exist in the alkaline absorbent aqueous solution, thereby achieving the purpose of capturing carbon dioxide. The alkaline absorbent aqueous solution contains water and an alkaline absorbent dissolved in the water. There is no particular limitation on the type of the alkaline absorbent, as long as the reagent can make the pH value of the alkaline absorbent aqueous solution be above 7.3, it is applicable to the present invention. In some embodiments of the present invention, the alkaline absorbent is selected from potassium hydroxide, sodium hydroxide, sodium carbonate, calcium oxide, calcium hydroxide, or any combination thereof. Preferably, the alkaline absorbent is selected from potassium hydroxide or sodium hydroxide. In some embodiments of the present invention, considering that the alkaline absorbent aqueous solution is sufficient to absorb carbon dioxide from the exhaust gas and convert carbon dioxide into carbonate ions or bicarbonate ions and the cost of using the alkaline absorbent, the pH value of the alkaline absorbent aqueous solution ranges from 7.3 to 11.

In order to make the carbon dioxide in the exhaust gas more easily absorbed by the alkaline absorbent aqueous solution after the exhaust gas is mixed with the alkaline absorbent aqueous solution, thereby helping to capture the carbon dioxide and convert it into carbonate ions or bicarbonate ions, in some embodiments of the present invention, the exhaust gas is first cooled to reduce the temperature of the exhaust gas to 50° C. to 55° C.

In the step (b), in order to ensure that the carbon dioxide absorbed by the alkaline absorbent aqueous solution can exist in the first solution in the form of carbonate ions or bicarbonate ions, thereby achieving the purpose of effectively capturing carbon dioxide from exhaust gas, the present invention monitors the pH value of the first solution, and when the pH value of the first solution does not fall within the range of 6 to 10, adjusts the pH value of the first solution to 6 to 10. In some embodiments of the present invention, an alkaline reagent is used to adjust the pH value of the first solution to 6 to 10. The alkaline reagent used to adjust the pH value of the first solution is, for example, but not limited to, sodium hydroxide, potassium hydroxide, calcium oxide or calcium hydroxide. In order to avoid the presence of too much carbonate precipitate in the reaction solution, so as to affect the formation of subsequent carbonate crystallization precipitate particles, in some embodiments of the present invention, the alkaline reagent used to adjust the pH value of the first solution is selected from sodium hydroxide, potassium hydroxide, or a combination thereof. It is worth mentioning that by adjusting the pH value of the first solution to a range of 6 to 10, it is also helpful to make the pH value of the reaction solution after mixing with the crystallization agent solution more likely to fall within the range of 8 to 11, so that the existing carbonate ions and the alkaline earth metal ions in the crystallization agent solution are more likely to undergo a crystallization reaction, thereby facilitating the formation of carbonate crystallization precipitate particles.

In the step (c), the carbonate crystallization precipitated particles refer to the carbonate crystallization particles that will not be washed away by the reaction solution, the crystallization agent solution or the mixed solution and leave the fluidized bed crystallization device during the flow in the fluidized bed crystallization device; the carbonate crystallization suspended particles refer to the carbonate crystallization particles that will be washed away by the reaction solution, the crystallization agent solution or the mixed solution and leave the fluidized bed crystallization device during the flow in the fluidized bed crystallization device. It should be noted that the particle size of the carbonate crystallization precipitated particles is larger than the particle size of the carbonate crystallization suspended particles.

The alkali earth metal ions in the crystallizer solution are, for example but not limited to, calcium ions, magnesium ions or barium ions. In some embodiments of the present invention, the alkali earth metal ions in the crystallizer solution are selected from calcium ions, magnesium ions or barium ions, and the carbonate crystallization precipitate particles corresponding to the above alkali earth metal ions are calcium carbonate crystallization precipitate particles, magnesium carbonate crystallization precipitate particles or barium carbonate crystallization precipitate particles. In addition, during the crystallization reaction between the existing carbonate ions and the alkali earth metal ions in the crystallizer solution, alkali earth metal hydroxides are also produced, and the alkali earth metal hydroxides corresponding to the above alkali earth metal ions are calcium hydroxide, magnesium hydroxide or barium hydroxide.

It should be noted that, since there are no carbonate ions in the solution to be reacted when the pH value of the solution to be reacted is within the range of 6 or more and less than 8, in the step (c) of the method of the present invention, the pH value of the solution to be reacted and the crystallizing agent solution after mixing is within the range of 8 to 11, so that the presence of carbonate ions can be ensured, thereby obtaining carbonate crystal precipitate particles through the crystallization reaction.

In order to achieve high reaction efficiency between the existing carbonate ions and the alkali-earth metal ions in the crystallizer solution, thereby increasing the yield of carbonate crystallization precipitated particles, in some embodiments of the present invention, the ratio of the volume molar concentration of the alkali-earth metal ions in the crystallizer solution to the sum of the volume molar concentrations of the carbonate ions and the bicarbonate ions contained in the solution to be reacted is in the range of 0.5 to 3. More preferably, the ratio of the volume molar concentration of the alkali-earth metal ions in the crystallizer solution to the sum of the volume molar concentrations of the carbonate ions and the bicarbonate ions contained in the solution to be reacted is in the range of 1 to 1.5.

In order to achieve high reaction efficiency between the existing carbonate ions and the alkaline earth metal ions in the crystallizer solution, thereby increasing the yield of carbonate crystallization precipitated particles, in some embodiments of the present invention, the hydraulic retention time of the solution to be reacted in the fluidized bed crystallization device ranges from 10 minutes to 50 minutes.

In step (d), the filtering method is not particularly limited, and any method that can separate the filtrate containing water and the residue containing carbonate crystal suspended particles from the mixed solution is applicable to the present invention. In some embodiments of the present invention, the mixed solution is filtered using a filter membrane. Specifically, the residue contains carbonate crystal suspended particles and alkaline earth metal ions.

In the step (e), in order to increase the reactivity between the carbonate crystal suspension particles in the residue and the alkaline earth metal ions in the crystallization agent solution after the carbonate crystal suspension particles in the residue come into contact with the alkaline earth metal ions, thereby further increasing the total yield of carbonate crystal precipitation particles, in some embodiments of the present invention, the pH value of the residue is monitored, and When the pH value of the residue falls within the range of 6 to 10, the residue is transported back to the fluidized bed crystallization device to react with the alkaline earth metal ions in the crystallizer solution. When the pH value of the residue does not fall within the range of 6 to 10, the pH value of the residue is adjusted and then transported back to the fluidized bed crystallization device to react with the alkaline earth metal ions in the crystallizer solution.

It should be noted that the residue containing carbonate crystal suspended particles is obtained by filtering the mixed solution, and the residue is transported back to the fluidized bed crystallization device, so that the carbonate crystal suspended particles in the residue can react with the alkaline earth metal ions in the crystallization agent solution to form carbonate crystal precipitated particles, which can effectively increase the total yield of carbonate crystal precipitated particles. In addition, since the residue will be transported back to the fluidized bed crystallization device again, the present invention will not discharge waste sludge containing carbonate crystal suspended particles, and has the advantage of being environmentally friendly.

In the step (f), in order to ensure that when the filter liquid is transported back to the absorption tower for use as an alkaline absorbent aqueous solution, the carbon dioxide in the exhaust gas can be dissolved in the alkaline absorbent aqueous solution in the form of carbonate ions or bicarbonate ions after being absorbed by the alkaline absorbent aqueous solution, thereby smoothly capturing carbon dioxide from the exhaust gas, the present invention adjusts the pH value of the filter liquid to 8 to 11. The method of adjusting the pH value of the filter liquid to 8 to 11 is, for example, but not limited to, using an alkaline reagent. The alkaline reagent used to adjust the pH value of the filter liquid is, for example, but not limited to, potassium hydroxide, sodium hydroxide, sodium carbonate, calcium oxide, or calcium hydroxide. In some embodiments of the present invention, an alkaline reagent is used to adjust the pH value of the filter solution to 8 to 11, and the alkaline reagent used to adjust the pH value of the filter solution is selected from potassium hydroxide, sodium hydroxide, sodium carbonate, calcium oxide, calcium hydroxide, or any combination thereof.

It should be noted that by filtering the mixed solution to obtain the filtrate containing water, adjusting the pH value of the filtrate to 8 to 11, and then transporting it back to the absorption tower for use as an alkaline absorbent aqueous solution, the purpose of resource regeneration can be achieved. At the same time, the amount of alkaline absorbent aqueous solution added can be reduced, thereby reducing the cost of the entire treatment process. In addition, by adjusting the pH value of the filtrate to 8 to 11, it is also helpful to ensure that the carbon dioxide in the exhaust gas can exist in the alkaline absorbent aqueous solution in the form of carbonate ions or hydrogen carbonate ions after dissolving in the alkaline absorbent aqueous solution, thereby facilitating the capture of carbon dioxide in the exhaust gas and the subsequent formation of carbonate crystal precipitation particles.

The method of the present invention for recovering carbon dioxide by using absorption and homogeneous crystallization technology can be carried out by using an apparatus for recovering carbon dioxide by using absorption and homogeneous crystallization technology.

《Equipment for recovering carbon dioxide by absorption and homogeneous crystallization technology》

Referring to FIG. 1 , the first embodiment of the device for recovering carbon dioxide by absorption and homogeneous crystallization technology of the present invention is applicable to treating a waste gas containing carbon dioxide. The waste gas containing carbon dioxide is as described above, so it will not be described in detail.

The equipment for recovering carbon dioxide by absorption and homogeneous crystallization technology comprises an absorption tower 1, a first pH value adjusting device 2, a crystallizing agent supplying device 3, a fluidized bed crystallizing device 4, a filtering device 5, a reflux device 6 and a second pH value adjusting device 7.

The absorption tower 1 defines an absorption space 11 for containing an alkaline absorbent aqueous solution with a pH value of 7.3 or above, and is used to receive the exhaust gas containing carbon dioxide, so that the carbon dioxide in the exhaust gas is absorbed by the alkaline absorbent aqueous solution and dissolved in the alkaline absorbent aqueous solution to obtain a first solution containing at least one of carbonate ions and hydrogen carbonate ions and water.

The first pH value adjusting device 2 is disposed downstream of the absorption tower 1 and communicated with the absorption tower 1 to receive the first solution from the absorption tower 1 and monitor the pH value of the first solution from the absorption tower 1. When the pH value of the first solution falls within the range of 6 to 10, the first solution is transported to the fluidized bed crystallization device 4 as a solution to be reacted. When the pH value of the first solution does not fall within the range of 6 to 10, the pH value of the first solution is adjusted and then transported to the fluidized bed crystallization device as a solution to be reacted, and the pH value of the solution to be reacted ranges from 6 to 10. The solution to be reacted includes at least one of carbonate ions and hydrogen carbonate ions and water.

The crystallizer supply device 3 is spaced apart from the first acid-base value adjusting device 2 and is used to provide a crystallizer solution containing alkali-earth metal ions. The alkali-earth metal ions in the crystallizer solution are as described above, so they will not be described in detail.

The fluidized bed crystallization device 4 is connected to the first pH value adjustment device 2 and the crystallization agent supply device 3, and the fluidized bed crystallization device 4 defines a reaction space 41. The reaction space 41 is used for mixing the solution to be reacted with the crystallization agent solution from the crystallization agent supply device 3, and the pH value after mixing is in the range of 8 to 11, so that the existing carbonate ions and the alkaline earth metal ions in the crystallization agent solution undergo a crystallization reaction to form carbonate crystal precipitated particles, and obtain a mixed solution containing water and carbonate crystal suspended particles.

The filtering device 5 is connected to the fluidized bed crystallization device 4 and is used to filter the mixed solution from the fluidized bed crystallization device 4 to obtain a filtrate containing water and a residue containing carbonate crystal suspended particles and alkaline earth metal ions.

The recirculation device 6 is disposed downstream of the filtering device 5 and is in communication with the fluidized bed crystallization device 4, and is used to transport the residue from the filtering device 5 back into the reaction space 41, so that the carbonate crystal suspended particles in the residue react with the alkaline earth metal ions in the crystallization agent solution to form carbonate crystal precipitated particles.

The second pH value adjusting device 7 is arranged downstream of the filtering device 5 and is connected to the absorption tower 1, and is used for receiving the filtered liquid from the filtering device and monitoring the pH value of the filtered liquid from the filtering device 5. When the pH value of the filtered liquid falls within the range of 8 to 11, the filtered liquid is transported back to the absorption tower 1 for use as an alkaline absorbent aqueous solution. When the pH value of the filtered liquid does not fall within the range of 8 to 11, the pH value of the filtered liquid is adjusted and then transported back to the absorption tower 1 for use as an alkaline absorbent aqueous solution, and the pH value of the alkaline absorbent aqueous solution ranges from 8 to 11.

It should be noted that, through the filtering device 5, the filtrate containing water and the residue containing carbonate crystallization suspended particles can be separated from the mixed solution, especially the residue containing carbonate crystallization suspended particles, so that the residue can be transported back to the fluidized bed crystallization device 4 in cooperation with the reflux device 6, so that the carbonate crystallization suspended particles in the residue react with the alkaline earth metal ions in the crystallization agent solution, thereby increasing the total yield of carbonate crystallization precipitated particles. In addition, since the recycle device 6 can transport the residue back to the fluidized bed crystallization device 4 for reaction, the use of the device for recovering carbon dioxide using the absorption and homogeneous crystallization technology can also ensure that waste sludge containing carbonate crystal suspended particles is not discharged.

On the other hand, through the cooperation of the filtering device 5 and the second pH value adjusting device 7, the filtered liquid is transported back to the absorption space 11 to be used as an alkaline absorbent aqueous solution after the pH value is adjusted to 8 to 11 by the second pH value adjusting device 7, and after absorbing the exhaust gas containing carbon dioxide that subsequently enters the absorption tower 1, the carbon dioxide in the exhaust gas can be more effectively converted into carbonate ions or hydrogen carbonate ions to be dissolved in the alkaline absorbent aqueous solution.

Referring to FIG. 2 , the second embodiment of the device for recovering carbon dioxide by absorption and homogeneous crystallization technology of the present invention is different from the first embodiment in that the reflux device 6 is also connected to the first pH adjusting device 2 and is used to transport the residue from the filtering device 5 to the first pH adjusting device 2. More specifically, by transporting the residue to the first acid-base value adjusting device 2, the first acid-base value adjusting device 2 can monitor whether the pH value of the residue falls within the range of 6 to 10. When the pH value of the residue does not fall within the range of 6 to 10, so that the carbonate crystallization suspended particles in the residue cannot effectively react with the alkali earth metal ions in the crystallization agent solution to form carbonate crystallization precipitated particles, the pH value of the residue can be further adjusted and then transported back to the fluidized bed crystallization device 4, thereby further improving the total yield of the carbonate crystallization precipitated particles.

The present invention will be further described with respect to the following embodiments, but it should be understood that the embodiments are only for illustrative purposes and should not be interpreted as limitations on the implementation of the present invention.

[Example 1]

(a) Exhaust gas containing carbon dioxide is mixed with an alkaline absorbent aqueous solution containing water and potassium hydroxide dissolved in the water in an absorption tower so that the carbon dioxide in the exhaust gas is dissolved in the alkaline absorbent aqueous solution to obtain a first solution containing at least one of carbonate ions and hydrogen carbonate ions, potassium hydroxide and water. The concentration of carbonate ions in the first solution is between 0.2 g/L and 6 g/L.

(b) monitoring the pH value of the first solution, and when the pH value of the first solution falls within the range of 6 to 10, transporting the first solution to a fluidized bed crystallization device as a solution to be reacted; when the pH value of the first solution does not fall within the range of 6 to 10, adjusting the pH value of the first solution to a range of 6 to 10 using potassium hydroxide, and then transporting the first solution to the fluidized bed crystallization device as a solution to be reacted. The solution to be reacted comprises carbonate ions, bicarbonate ions, potassium hydroxide and water.

(c) introducing a crystallization agent solution containing calcium ions into the fluidized bed crystallization device, so that the solution to be reacted is mixed with the crystallization agent solution and the pH value after mixing is 10, so that the existing carbonate ions react with the calcium ions in the crystallization agent solution to form calcium carbonate crystal precipitated particles, and obtain a mixed solution containing potassium hydroxide, water and calcium carbonate crystal suspended particles. The ratio of the volume molar concentration of calcium ions in the crystallization agent solution to the sum of the volume molar concentrations of carbonate ions and bicarbonate ions contained in the solution to be reacted is within a range of 0.8 to 1.5.

(d) filtering the mixed solution using a filter membrane to obtain a filtrate containing potassium hydroxide and water, and a residue containing suspended particles of calcium carbonate crystals and calcium ions.

(e) transporting the residue back to the fluidized bed crystallization device to mix the residue with the crystallization agent solution and the pH value after mixing is 10, so that the calcium carbonate crystal suspended particles in the residue react with the calcium ions in the crystallization agent solution to form calcium carbonate crystal precipitated particles.

(f) monitoring the pH value of the filtrate, and when the pH value of the filtrate falls within the range of 8 to 11, directly transporting the filtrate back to the absorption tower for use as an alkaline absorbent aqueous solution; when the pH value of the filtrate does not fall within the range of 8 to 11, adjusting the pH value of the filtrate to 8 to 11 using potassium hydroxide, and then transporting the filtrate back to the absorption tower for use as an alkaline absorbent aqueous solution.

In this Example 1, the total removal rate of carbonate ions was 99.9%, and the crystallization rate of calcium carbonate was 99.1%.

In summary, the present invention is a method for recovering carbon dioxide by absorption and homogeneous crystallization technology. The method monitors whether the pH value of a first solution containing at least one of carbonate ions and hydrogen carbonate ions and water is within the range of 6 to 10 and determines whether to adjust the pH value of the first solution according to the monitoring result. The mixed solution containing water and carbonate crystal suspended particles is filtered to obtain a first solution containing carbonate ions and hydrogen carbonate ions. The residue of the carbonate crystallization suspended particles is transported back to the fluidized bed crystallization device, so that the carbonate crystallization suspended particles in the residue react with the alkaline earth metal ions, thereby effectively increasing the total yield of the carbonate crystallization precipitated particles and no waste sludge containing the carbonate crystallization suspended particles is generated, so the purpose of the present invention can be achieved.

In addition, the method of the present invention filters the mixed solution to obtain a filtrate containing water, monitors whether the pH value of the filtrate falls within the range of 8 to 11, and decides based on the monitoring result whether to directly transport the filtrate back to the absorption tower for use as an alkaline absorbent aqueous solution, or to adjust the pH value of the filtrate before transporting it back to the absorption tower for use as an alkaline absorbent aqueous solution, thereby achieving the effects of resource regeneration, cost reduction, and improving the ability of the alkaline absorbent aqueous solution to convert carbon dioxide into carbonate ions or bicarbonate ions. Furthermore, the method of the present invention converts the captured carbon dioxide into carbonate crystal precipitate particles, so that the carbonate crystal precipitate particles can be used as chemical raw materials and subsequently provided to different industries for utilization, thus also having the advantage of increasing additional revenue.

On the other hand, the device for recovering carbon dioxide by absorption and homogeneous crystallization technology of the present invention can effectively increase the total output of carbonate crystallization precipitated particles through the arrangement of the first pH value adjusting device 2, the filtering device 5, the reflux device 6 and the second pH value adjusting device 7 and the cooperation with other devices without generating waste sludge containing carbonate crystallization suspended particles. At the same time, it can also enhance the effect of the alkaline absorbent aqueous solution in absorbing carbon dioxide and converting it into carbonate ions or bicarbonate ions.

However, the above is only an embodiment of the present invention and should not be used to limit the scope of implementation of the present invention. All simple equivalent changes and modifications made according to the scope of the patent application of the present invention and the content of the patent specification are still within the scope of the present patent.

1·············· Absorption tower 11············· Absorption space 2··············· First acid-base value adjustment device 3·············· Crystallizer supply device 4··············· Fluidized bed crystallization device 41············· Reaction space 5··············· Filter device 6·············· Circulation device 7··············· Second acid-base value adjustment device

Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, wherein: FIG. 1 is a schematic diagram illustrating a first embodiment of the device for recovering carbon dioxide by absorption and homogeneous crystallization technology of the present invention; and FIG. 2 is a schematic diagram illustrating a second embodiment of the device for recovering carbon dioxide by absorption and homogeneous crystallization technology of the present invention.

1·············· Absorption tower 11············· Absorption space 2··············· First acid-base value adjustment device 3·············· Crystallizer supply device 4··············· Fluidized bed crystallization device 41············· Reaction space 5··············· Filter device 6·············· Circulation device 7··············· Second acid-base value adjustment device

Claims (8)

A method for recovering carbon dioxide by absorption and homogeneous crystallization technology comprises the following steps: (a) mixing exhaust gas containing carbon dioxide with an alkaline absorbent aqueous solution having a pH value of 7.3 or above in an absorption tower so that the carbon dioxide in the exhaust gas is dissolved in the alkaline absorbent aqueous solution to obtain a first solution containing at least one of carbonate ions and hydrogen carbonate ions and water; (b) monitoring the pH value of the first solution, and when the pH value of the first solution falls within the range of 6 to 10, transporting the first solution to a fluidized bed crystallization device as a solution to be reacted; when the pH value of the first solution does not fall within the range of 6 to 10, adjusting the pH value of the first solution and then transporting it to the fluidized bed crystallization device as a solution to be reacted, and the pH value of the solution to be reacted ranges from 6 to 10, and the solution to be reacted contains at least one of carbonate ions and hydrogen carbonate ions and water; (c) introducing a crystallization agent solution containing alkali earth metal ions into the fluidized bed crystallization device to allow the reaction solution to mix with the crystallization agent solution and the pH value after mixing is in the range of 8 to 11, so that the existing carbonate ions react with the alkali earth metal ions in the crystallization agent solution to form carbonate crystal precipitate particles, and obtain a mixed solution containing water and carbonate crystal suspended particles; (d) filtering the mixed solution to obtain a filtrate containing water and a residue containing carbonate crystal suspended particles; (e) transporting the residue back to the fluidized bed crystallization device, and reacting the carbonate crystal suspended particles in the residue with the alkaline earth metal ions in the crystallizer solution to form carbonate crystal precipitated particles; and (f) monitoring the pH value of the filtrate, and when the pH value of the filtrate falls within the range of 8 to 11, transporting the filtrate back to the absorption tower for use as an alkaline absorbent aqueous solution, and when the pH value of the filtrate does not fall within the range of 8 to 11, adjusting the pH value of the filtrate and transporting it back to the absorption tower for use as an alkaline absorbent aqueous solution, and the pH value of the alkaline absorbent aqueous solution ranges from 8 to 11. A method for recovering carbon dioxide by absorption and homogeneous crystallization technology as described in claim 1, wherein, in step (a), the alkaline absorbent aqueous solution comprises water and an alkaline absorbent dissolved in the water, and the alkaline absorbent is selected from potassium hydroxide, sodium hydroxide, sodium carbonate, calcium oxide, calcium hydroxide, or any combination thereof. A method for recovering carbon dioxide by absorption and homogeneous crystallization technology as described in claim 2, wherein in the step (a), the alkaline absorbent is selected from potassium hydroxide or sodium hydroxide. A method for recovering carbon dioxide by absorption and homogeneous crystallization technology as described in claim 1, wherein in step (c), the alkaline earth metal ions in the crystallizer solution are selected from calcium ions, magnesium ions or barium ions. A method for recovering carbon dioxide by absorption and homogeneous crystallization technology as described in claim 1, wherein, in step (f), when the pH value of the filtrate does not fall within the range of 8 to 11, the pH value of the filtrate is adjusted using an alkaline reagent, and the alkaline reagent is selected from potassium hydroxide, sodium hydroxide, sodium carbonate, calcium oxide, calcium hydroxide, or any combination thereof. A method for recovering carbon dioxide by absorption and homogeneous crystallization technology as described in claim 1, wherein in step (e), the pH value of the residue is monitored, and when the pH value of the residue falls within the range of 6 to 10, the residue is transported back to the fluidized bed crystallization device to react with the alkaline earth metal ions in the crystallizer solution, and when the pH value of the residue does not fall within the range of 6 to 10, the pH value of the residue is adjusted and then transported back to the fluidized bed crystallization device to react with the alkaline earth metal ions in the crystallizer solution. A device for recovering carbon dioxide by absorption and homogeneous crystallization technology, suitable for treating a waste gas containing carbon dioxide, comprising: an absorption tower, a first pH value adjustment device, a crystallizer supply device, a fluidized bed crystallization device, a filtering device, a reflux device, and a second pH value adjustment device; wherein, the absorption tower defines an absorption space for containing an alkaline absorbent aqueous solution with a pH value of 7.3 or above, and is used to receive the waste gas containing carbon dioxide, so that the carbon dioxide in the waste gas is absorbed by the alkaline absorbent aqueous solution and dissolved in the alkaline absorbent aqueous solution, and a first solution containing at least one of carbonate ions and hydrogen carbonate ions and water is obtained, The first pH value adjusting device is arranged downstream of the absorption tower, and is used to receive the first solution from the absorption tower, and monitor the pH value of the first solution from the absorption tower, and when the pH value of the first solution falls within the range of 6 to 10, the first solution is transported to the fluidized bed crystallization device as a solution to be reacted, and when the pH value of the first solution does not fall within the range of 6 to 10, the pH value of the first solution is adjusted and then transported to the fluidized bed crystallization device as a solution to be reacted, and the pH value range of the solution to be reacted is 6 to 10, and the solution to be reacted contains at least one of carbonate ions and hydrogen carbonate ions and water, The crystallizer supply device is arranged at intervals from the first pH value adjusting device, and is used to provide a crystallizer solution containing alkali earth metal ions, The fluidized bed crystallization device is connected to the first pH value adjustment device and the crystallization agent supply device, and the fluidized bed crystallization device defines a reaction space, and the reaction space is used for the solution to be reacted to be mixed with the crystallization agent solution from the crystallization agent supply device, and the pH value after mixing is in the range of 8 to 11, so that the existing carbonate ions and the alkaline earth metal ions in the crystallization agent solution undergo a crystallization reaction to form carbonate crystal precipitated particles, and obtain a mixed solution containing water and carbonate crystal suspended particles, The filtering device is connected to the fluidized bed crystallization device and is used to filter the mixed solution from the fluidized bed crystallization device to obtain a filtrate containing water and a residue containing carbonate crystal suspended particles. The reflux device is arranged downstream of the filtering device and is connected to the fluidized bed crystallization device and is used to transport the residue from the filtering device back to the reaction space so that the carbonate crystal suspended particles in the residue react with the alkaline earth metal ions in the crystallization agent solution to form carbonate crystal precipitated particles, and The second pH value adjusting device is arranged downstream of the filter device and is connected to the absorption tower to receive the filter liquid from the filter device and monitor the pH value of the filter liquid from the filter device. When the pH value of the filter liquid falls within the range of 8 to 11, the filter liquid is transported back to the absorption tower for use as an alkaline absorbent aqueous solution. When the pH value of the filter liquid does not fall within the range of 8 to 11, the pH value of the filter liquid is adjusted and then transported back to the absorption tower for use as an alkaline absorbent aqueous solution. The pH value range of the alkaline absorbent aqueous solution is 8 to 11. As described in claim 7, the equipment for recovering carbon dioxide by absorption and homogeneous crystallization technology, wherein the reflow device is also connected to the first acid-base adjustment device and is used to transport the residue from the filtering device to the first acid-base adjustment device.

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