Method for Extracting Carbon Dioxide from Flue Gas

Abstract

To provide a method for extracting carbon dioxide from a flue gas.SOLUTION: A method for extracting carbon dioxide from a flue gas includes a preparing process, an acid removing process, and a purifying and liquefying process. The preparing process is implemented by collecting the flue gas generated by oxygen-enriched combustion of a glass raw material with methane from a glass furnace. The flue gas includes the carbon dioxide, nitrogen, water vapor, oxygen, fluoric acid compounds, and boric acid compounds. The acid removing process is implemented by performing a first acid removing operation. The first acid removing operation is implemented by using a sodium hydroxide aqueous solution to remove the fluoric acid compounds and the boric acid compounds in the flue gas. The purifying and liquefying process is implemented by using a purifying and liquefying unit to extract the flue gas that already undergoes the acid removing process, so as to obtain liquid carbon dioxide having a purity greater than 99%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for extracting carbon dioxide, and particularly to a method for extracting carbon dioxide from flue gas generated by a melting furnace.

Background Art

[0002] A glass melting furnace generates high-temperature flue gas. Conventional methods for treating flue gas are to remove fluorine compounds by adding alkali, then cool the flue gas using a large amount of air, precipitate boron compounds, and discharge the flue gas.

[0003] However, after implementing the conventional method for treating flue gas, the volume ratio of carbon dioxide in the flue gas (which is about 2% - 3%) is too low, making it difficult to recycle carbon dioxide.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The technical problem to be solved by the present invention is, in view of the deficiencies of the prior art, to provide a method for extracting carbon dioxide from flue gas to solve the problem that after implementing the method for extracting carbon dioxide from conventional flue gas, the volume ratio of carbon dioxide in the flue gas is too low and it is difficult to recycle carbon dioxide.

Means for Solving the Problems

[0005] To solve the above technical problems, one technical means adopted by the present invention is to provide a method for extracting carbon dioxide from flue gas. The method for extracting carbon dioxide from flue gas includes a preparation step of collecting flue gas from the combustion of methane-oxygen enrichment of glass raw materials in a glass melting furnace, an acid removal step of performing a first acid removal operation on the flue gas to remove hydrofluoric acid compounds and boric acid compounds in the flue gas with an aqueous sodium hydroxide solution, and a purification and liquefaction step of extracting from the flue gas on which the acid removal step has been performed in a purification and liquefaction unit to obtain liquid carbon dioxide with a purity exceeding 99%. The flue gas includes carbon dioxide, nitrogen gas, water vapor, oxygen gas, hydrofluoric acid compounds, and boric acid compounds.

[0006] Preferably, in the preparation step, the temperature of the flue gas is 1,000°C to 1,500°C. Taking the volume of the flue gas as 100%, the carbon dioxide content is 30% to 34%, the nitrogen gas content is 1% to 5%, the water vapor content is 58% to 62%, and the oxygen gas content is 2% to 6%.

[0007] Preferably, in the preparation step, the content of hydrofluoric acid compounds exceeds 0 milligrams per cubic meter and is less than 500 milligrams per cubic meter, and the content of boric acid compounds exceeds 0 milligrams per cubic meter and is less than 15 milligrams per cubic meter.

[0008] Preferably, the method for extracting carbon dioxide from flue gas further includes a cooling step in which the flue gas is cooled with water so as to reduce the temperature of the flue gas to 200°C to 400°C after the preparation step and before the acid removal step.

[0009] Preferably, in the acid removal step, a second acid removal operation is further performed on the flue gas to remove hydrofluoric acid compounds and boric acid compounds in the flue gas with sodium bicarbonate powder.

[0010] Preferably, in the acid removal step, in the first acid removal operation, the hydrofluoric acid compound and boric acid compound in the flue gas are removed by an aqueous sodium hydroxide solution in a semi-dry acid removal tower, and in the second acid removal operation, the hydrofluoric acid compound and boric acid compound in the flue gas are removed by sodium bicarbonate powder in a dry acid removal unit. After the first acid removal operation, the temperature of the flue gas is reduced to 170°C to 200°C, and after the second acid removal operation, the temperature of the flue gas is maintained at 170°C to 200°C.

[0011] Preferably, taking the volume of the flue gas as 100%, the carbon dioxide content is 21% to 25%, the nitrogen gas content is 1% to 3%, the water vapor content is 70% to 74%, and the oxygen gas content is 1% to 3%.

[0012] Preferably, the method for extracting carbon dioxide from the flue gas further includes a removal step in which solid waste is filtered and removed by a bag filter after the acid removal step and before the purification and liquefaction step, and the solid waste is formed after the hydrofluoric acid compound and boric acid compound in the flue gas have undergone the acid removal step.

[0013] Preferably, the method for extracting carbon dioxide from the flue gas further includes a cooling and water removal step in which the temperature of the flue gas is reduced to 20°C to 40°C and the water vapor content in the flue gas is reduced before the purification and liquefaction step. After the cooling and water removal step, taking the volume of the flue gas as 100%, the carbon dioxide content is 75% or more, and the water vapor content is 10% or less.

[0014] Preferably, in the cooling and water removal step, the flue gas is first cooled by water with a temperature of 50°C to 80°C in a heat recovery unit. After the water absorbs the thermal energy of the flue gas, it changes to hot water or steam with a temperature of about 95°C to 165°C, and the hot water or steam is cooled by an absorption refrigerator connected to the heat recovery unit to change to low-temperature water, and the low-temperature water reduces the temperature of the flue gas in the cooling and water removal step.

[0015] Preferably, after the cooling and dewatering step, taking the volume of the flue gas as 100%, the carbon dioxide content is 78% - 82%, the nitrogen gas content is 5% - 9%, the water vapor content is 2% - 6%, and the oxygen gas content is 7% - 11%.

Advantages of the Invention

[0016] As an advantageous effect of the present invention, the method for extracting carbon dioxide from flue gas according to the present invention, through technical features such as "collecting the flue gas from the methane-oxygen enriched combustion of glass raw materials in a glass melting furnace" and "removing fluorine compounds and boric acid compounds in the flue gas with an aqueous sodium hydroxide solution", effectively solves the problem that after implementing the conventional flue gas treatment method, the volume ratio of carbon dioxide in the flue gas is too low and it is difficult to recycle carbon dioxide.

[0017] Furthermore, in the cooling and dewatering step, after the hot water or the water vapor obtained by absorbing the thermal energy of the flue gas passes through the absorption refrigerator and is cooled to change into low-temperature water, the flue gas is further cooled with the low-temperature water to achieve the recycling of thermal energy.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0019] For a better understanding of the features and technical content of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings. However, the provided accompanying drawings are only for reference and explanation, and are not intended to limit the scope of the claims of the present invention.

[0020] Hereinafter, the "method for extracting carbon dioxide from flue gas" according to the embodiments of the present invention will be described according to a specific embodiment, and those skilled in the art can understand the advantages and effects of the present invention based on the content disclosed in this specification. The present invention can be implemented or applied according to other different specific embodiments, and for each detail in this specification, various modifications and changes can be made based on different viewpoints and applications without departing from the concept of the present invention. Also, as explained in advance, the accompanying drawings of the present invention are simple schematic explanations and are not drawn based on actual sizes. The technical content of the present invention will be described in more detail based on the following embodiments, but the disclosed content does not limit the protection scope of the present invention.

[0021] It should be understood that in this specification, terms such as "first", "second", "third" may be used to describe various elements or signals, but these elements or signals are not limited by these terms. These terms are mainly used to distinguish one element from another element, or one signal from another signal. Also, the term "or" used in this specification may include any one or a combination of more than one of the related items according to the actual situation.

[0022] [First Embodiment] As shown in FIG. 1, which is a flowchart of a method for extracting carbon dioxide from flue gas according to the first embodiment of the present invention, and FIG. 2, which is a block diagram of a flue gas extraction system according to the first embodiment of the present invention, the first embodiment of the present invention provides a method for extracting carbon dioxide from flue gas. The method for extracting carbon dioxide from the flue gas includes at least a preparation step S110, an acid removal step S120, and a purification and liquefaction step S130.

[0023] In the preparation step S110, flue gas is collected in the glass melting furnace 10 by methane-oxygen enriched combustion of glass raw materials. The flue gas contains carbon dioxide, nitrogen gas, water vapor, oxygen gas, fluorine compounds, and boric acid compounds. The fluorine compound may be an acidic component such as HF, and the boric acid compound may be an acidic component such as H3BO3, HBO2, B2O3, or BF3, but the present invention is not limited to the specific components of the fluorine compound and the boric acid compound. It should be noted that since the fluorine compound and the boric acid compound are produced by burning glass raw materials, methods for extracting carbon dioxide that do not produce fluorine compounds and boric acid compounds in other technical fields are not applicable to the method for extracting carbon dioxide from flue gas according to the present invention.

[0024] The oxygen enrichment is obtained by removing some nitrogen gas in the air. Usually, the oxygen gas occupies 21% or more of the total volume of the gas. In the preparation step S110 of the present embodiment, the oxygen gas occupies 92% - 96% of the total volume of the gas in the glass melting furnace, and preferably occupies 94% or more.

[0025] Compared with the flue gas generated by introducing air into the glass melting furnace, the volume of carbon dioxide in the flue gas from methane-oxygen enriched combustion is relatively high, which improves the recyclability of carbon dioxide. Specifically, the volume of carbon dioxide in the flue gas from methane-oxygen enriched combustion is 30% or more, and the volume of carbon dioxide in the flue gas from air combustion is about 12%.

[0026] In the flue gas S110 of this embodiment, the temperature of the flue gas is 1,000°C to 1,500°C. Taking the volume of the flue gas as 100%, the carbon dioxide content is 30% to 34%, the nitrogen gas content is 1% to 5%, the water vapor content is 58% to 62%, and the oxygen gas content is 2% to 6%.

[0027] Preferably, the temperature of the flue gas is 1,200°C to 1,400°C. Taking the volume of the flue gas as 100%, the carbon dioxide content is 31% to 33%, the nitrogen gas content is 2% to 4%, the water vapor content is 59% to 61%, and the oxygen gas content is 2% to 6%. More preferably, the temperature of the flue gas is about 1,300°C. Taking the volume of the flue gas as 100%, the carbon dioxide content is about 32%, the nitrogen gas content is about 3%, the water vapor content is about 60%, and the oxygen gas content is about 4%.

[0028] In the preparation step S110 of this embodiment, the content of the fluorine compound is more than 0 milligrams per cubic meter and less than 500 milligrams per cubic meter, and the content of the boric acid compound is more than 0 milligrams per cubic meter and less than 15 milligrams per cubic meter. Preferably, the content of the fluorine compound is more than 0 milligrams per cubic meter and less than 400 milligrams per cubic meter, and the content of the boric acid compound is more than 0 milligrams per cubic meter and less than 10 milligrams per cubic meter.

[0029] In the acid removal step S120, a first acid removal operation is performed on the flue gas. In the first acid removal operation, hydrofluoric acid compounds and boric acid compounds in the flue gas are removed with an aqueous sodium hydroxide solution. Specifically described, in the acid removal step S120 of the present embodiment, in the first acid removal operation, hydrofluoric acid compounds and boric acid compounds in the flue gas are removed with an aqueous sodium hydroxide solution by a semi-dry acid removal tower 20. Further, in the present embodiment, the weight percentage concentration of the aqueous sodium hydroxide solution is 2% to 4%, but the present invention is not limited thereto.

[0030] After the first acid removal operation, the temperature of the flue gas is reduced to 170°C to 200°C, and after the second acid removal operation, the temperature of the flue gas is maintained at 170°C to 200°C. Taking the volume of the flue gas as 100%, the carbon dioxide content is 21% to 25%, the nitrogen gas content is 1% to 3%, the water vapor content is 70% to 74%, and the oxygen gas content is 1% to 3%. Preferably, after the acid removal step S120, taking the volume of the flue gas as 100%, the carbon dioxide content is about 23%, the nitrogen gas content is about 2%, the water vapor content is about 72%, and the oxygen gas content is about 2%.

[0031] In the purification and liquefaction step S130, it is extracted from the flue gas that has undergone the acid removal step S120 by a purification and liquefaction unit 40 so as to obtain liquid carbon dioxide with a purity exceeding 99%.

[0032] After the acid removal step and before the purification and liquefaction step, a removal step S121 may be further included in which by-products generated from hydrofluoric acid compounds and boric acid compounds in the flue gas are filtered and removed by a bag filter 30. The by-products may be, for example, alkaline solids containing fluorine or boron (such as sodium hydroxide or sodium bicarbonate), but the present invention is not limited thereto. The by-products can be recycled, but the present invention is not limited to the uses of the by-products.

[0033] In addition, in the present embodiment, the method for extracting carbon dioxide from the flue gas can be implemented by a carbon dioxide extraction system 100, and the carbon dioxide extraction system 100 includes the glass melting furnace 10, the semi-dry acid removal tower 20, the bag filter 30, and the purification / liquefaction unit 40.

[0034] [Second Embodiment] As shown in FIG. 3, which is a flowchart of the method for extracting carbon dioxide from the flue gas according to the second embodiment of the present invention, and FIG. 4, which is a block diagram of the flue gas extraction system according to the second embodiment of the present invention, since this embodiment is similar to the first embodiment, the parts where the two embodiments are the same will not be described repeatedly. In addition, the differences between the two embodiments are as follows.

[0035] In the present embodiment, after the preparation step S110 and before the acid removal step S120, a cooling step S111 is further included, in which the flue gas is cooled with water so that the temperature of the flue gas is reduced to 200°C to 400°C. Preferably, after the cooling step S111, the temperature of the flue gas is about 300°C. In the cooling step S111 of other embodiments, the flue gas may be cooled with air, or the flue gas may be cooled with air first and then with water, but the present invention is not limited thereto.

[0036] In the cooling step of the present embodiment, the flue gas is cooled with boiler water in the heat recovery cooling unit 11, and after the boiler water absorbs the thermal energy of the flue gas, it changes into steam.

[0037] [Third Embodiment] As shown in FIG. 5, which is a flowchart of the method for extracting carbon dioxide from the flue gas according to the third embodiment of the present invention, and FIG. 6, which is a block diagram of the flue gas extraction system according to the third embodiment of the present invention, since this embodiment is similar to the second embodiment, the parts where the two embodiments are the same will not be described repeatedly. In addition, the differences between the two embodiments are as follows.

[0038] The acid removal step S120a further includes a second acid removal operation of removing fluorine compounds and boric acid compounds in the flue gas with sodium bicarbonate powder for the flue gas. Preferably, in the acid removal step, after the first acid removal operation is performed, the second acid removal operation is performed.

[0039] In the second acid removal operation, the fluorine compounds and boric acid compounds in the flue gas are removed with sodium bicarbonate powder by the dry acid removal unit 21.

[0040] [Fourth Embodiment] As shown in FIG. 7 which is a flowchart of a method for extracting carbon dioxide from flue gas according to the fourth embodiment of the present invention, and FIG. 8 which is a block diagram of a flue gas extraction system according to the fourth embodiment of the present invention, since this embodiment is similar to the third embodiment, the parts where the two embodiments are the same will not be described repeatedly. Also, the differences between the two embodiments are as follows.

[0041] The method for extracting carbon dioxide from the flue gas further includes a cooling and water removal step S122 of reducing the temperature of the flue gas to 20°C to 40°C and reducing the water vapor content in the flue gas before the purification and liquefaction step S130 and after the removal step S121. Preferably, after the cooling and water removal step S122, the temperature of the flue gas is reduced to about 30°C.

[0042] In the cooling and water removal step S122 of this embodiment, the cooling and water removal unit 31 reduces the temperature of the flue gas and the water vapor content in the flue gas. Also, before the flue gas is introduced into the cooling and water removal unit 31, the flue gas may first pass through the heat recovery unit 32 and be cooled. The heat recovery unit 32 may be connected to the absorption refrigerator 33, and the heat recovery unit 32 can cool the flue gas with return water having a temperature of 50°C to 80°C.

[0043] After the return water absorbs the thermal energy of the flue gas, it changes into hot water or steam with a temperature of about 95°C to 165°C. The hot water or the steam is cooled by the absorption chiller 33 and changes into low-temperature water. The low-temperature water is introduced into the cooling and dewatering unit 31 in the cooling and dewatering process S122, and the temperature of the flue gas can be reduced. The low-temperature water may be at 4°C to 7°C, but the present invention is not limited thereto. It should also be noted that the hot water or steam formed after the return water absorbs the thermal energy of the flue gas is not limited to being applied to the cooling and dewatering unit 31. The thermal energy of the hot water or the steam may be recycled to heat other units (for example, other units not included in the flue gas extraction system 100) so as to realize the recycling of thermal energy.

[0044] After the cooling and dewatering process S122, taking the volume of the flue gas as 100%, the carbon dioxide content is 75% or more, and the water vapor content is 10% or less. Specifically, after the cooling and dewatering process S122, taking the volume of the flue gas as 100%, the carbon dioxide content is 78% to 82%, the nitrogen gas content is 5% to 9%, the water vapor content is 2% to 6%, and the oxygen gas content is 7% to 11%.

[0045] Preferably, after the cooling and dewatering process S122, taking the volume of the flue gas as 100%, the carbon dioxide content is 79% to 81%, the nitrogen gas content is 6% to 8%, the water vapor content is 3% to 5%, and the oxygen gas content is 8% to 10%. More preferably, after the cooling and dewatering process S122, taking the volume of the flue gas as 100%, the carbon dioxide content is about 80%, the nitrogen gas content is about 7%, the water vapor content is about 4%, and the oxygen gas content is about 9%.

[0046] [Measurement of experimental data] When comparing the methods for extracting carbon dioxide from flue gas according to Examples 1 to 4 and the comparative example, the arrangement of each step in Examples 1 to 4 and the comparison is as shown in Table 1.

[0047] Further, the flue gas before performing the acid removal step is defined as the first flue gas, and the flue gas before performing the purification and liquefaction step is defined as the second flue gas. The gases and volume ratios contained in the first flue gas, as well as the temperature of the first flue gas, are as shown in Table 2 below. The gases and volume ratios contained in the second flue gas, as well as the temperature of the second flue gas, are as shown in Table 3 below.

[0048] [Table 1]

[0049] [Table 2]

[0050] [Table 3]

[0051] [Examination of Measurement Results] In the comparative example, since the glass raw material was burned by air combustion, the volume ratios occupied by carbon dioxide in both the first flue gas and the second flue gas were lower than the volume ratios occupied by carbon dioxide in the first flue gas and the second flue gas in Example 1.

[0052] Since the method for extracting carbon dioxide from the flue gas according to Example 2 includes a cooling step, the temperature of the first flue gas was relatively low.

[0053] Since the method for extracting carbon dioxide from the flue gas according to Example 3 includes the first acid removal operation and the second acid removal operation, the fluorine-containing compounds contained in the second flue gas were relatively few.

[0054] Since the method for extracting carbon dioxide from flue gas according to Example 4 includes a cooling and water removal step, the proportion of carbon dioxide contained in the second flue gas is relatively high, and the amount of fluorine compounds contained in the second flue gas is relatively small.

[0055] [Advantageous Effects According to Embodiment] As an advantageous effect of the present invention, the method for extracting carbon dioxide from flue gas according to the present invention has technical features such as "collecting flue gas by methane-oxygen enriched combustion of glass raw materials in a glass melting furnace" and "removing fluorine compounds and boric acid compounds in the flue gas with an aqueous sodium hydroxide solution", which effectively solve the problem that after implementing the conventional flue gas treatment method, the volume ratio of carbon dioxide in the flue gas is too low and it is difficult to recycle carbon dioxide.

[0056] Furthermore, in the cooling and water removal step, the hot water or the water vapor obtained by absorbing the thermal energy of the flue gas is cooled by passing through the absorption refrigerator and changed into low-temperature water, and then further cooled with the low-temperature water to achieve the recycling of thermal energy.

[0057] The content disclosed above is only a preferred feasible embodiment of the present invention, and the scope of the claims of the present invention is not limited thereto. Therefore, all equivalent technical changes made using the content of the specification and drawings of the present invention are included in the scope of the claims of the present invention.

Explanation of Reference Numerals

[0058] 100... Carbon Dioxide Extraction System 10... Glass Melting Furnace 11... Heat Recovery Cooling Unit 20... Semi-Dry Acid Removal Tower 21... Dry Acid Removal Unit 30... Bag Filter 31... Cooling and Water Removal Unit 32... Heat Recovery Unit 33... Absorption Refrigerator 40...Purification and Liquefaction Unit S110...Preparation Process S111...Cooling Process S120, S120a...Acid Removal Process S121...Removal Process S122...Cooling and Dewatering Process S130...Purification and Liquefaction Process

Claims

1. A preparation step of collecting flue gas from the combustion of methane-oxygen enrichment of glass raw materials in a glass melting furnace, wherein the temperature of the flue gas is 1,000°C to 1,500°C, and performing a first acid removal operation and a second acid removal operation on the flue gas. In the first acid removal operation, a hydrofluoric acid compound and a boric acid compound in the flue gas are removed with an aqueous sodium hydroxide solution by a semi-dry acid removal tower. In the second acid removal operation, a hydrofluoric acid compound and a boric acid compound in the flue gas are removed with sodium bicarbonate powder by a dry acid removal unit. After the first acid removal operation, the temperature of the flue gas is reduced to 170°C to 200°C. After the second acid removal operation, the temperature of the flue gas is maintained at 170°C to 200°C. An acid removal step; a purification and liquefaction step of extracting carbon dioxide from the flue gas that has undergone the acid removal step in a purification and liquefaction unit so as to obtain liquid carbon dioxide with a purity exceeding 99%, including The method for extracting carbon dioxide from flue gas, wherein the flue gas contains carbon dioxide, nitrogen gas, water vapor, oxygen gas, a hydrofluoric acid compound, and a boric acid compound.

2. In the preparation step, taking the volume of the flue gas as 100%, the carbon dioxide content is 30% to 34%, the nitrogen gas content is 1% to 5%, the water vapor content is 58% to 62%, and the oxygen gas content is 2% to 6%. The method for extracting carbon dioxide from flue gas according to Claim 1.

3. In the preparation step, the content of the hydrofluoric acid compound exceeds 0 milligrams per cubic meter and is less than 500 milligrams per cubic meter, and the content of the boric acid compound exceeds 0 milligrams per cubic meter and is less than 15 milligrams per cubic meter. The method for extracting carbon dioxide from flue gas according to Claim 1.

4. After the preparation step and before the acid removal step, further including a cooling step in which the flue gas is cooled with water so as to reduce the temperature of the flue gas to 200°C to 400°C. The method for extracting carbon dioxide from flue gas according to Claim 1.

5. After the acid removal step, taking the volume of the flue gas as 100%, the carbon dioxide content is 21% - 25%, the nitrogen gas content is 1% - 3%, the water vapor content is 70% - 74%, and the oxygen gas content is 1% - 3%. A method for extracting carbon dioxide from the flue gas according to Claim 1.

6. After the acid removal step and before the purification and liquefaction step, it further includes a removal step in which by-products are filtered and removed by a bag filter. The by-products are formed after the fluoric acid compound and boric acid compound in the flue gas have undergone the acid removal step. A method for extracting carbon dioxide from the flue gas according to Claim 1.

7. Before the purification and liquefaction step, it further includes a cooling and dewatering step of reducing the temperature of the flue gas to 20°C - 40°C and reducing the water vapor content in the flue gas. After the cooling and dewatering step, taking the volume of the flue gas as 100%, the carbon dioxide content is 75% or more, and the water vapor content is 10% or less. A method for extracting carbon dioxide from the flue gas according to Claim 1.

8. In the cooling and dewatering step, the flue gas is first cooled by water with a temperature of 50°C - 80°C in a heat recovery unit. After the water absorbs the thermal energy of the flue gas, it changes to hot water or steam with a temperature of 95°C - 165°C. The hot water or steam is cooled by an absorption refrigerator connected to the heat recovery unit to change to low-temperature water. The low-temperature water reduces the temperature of the flue gas in the cooling and dewatering step. A method for extracting carbon dioxide from the flue gas according to Claim 7.

9. After the cooling and dewatering step, taking the volume of the flue gas as 100%, the carbon dioxide content is 78% - 82%, the nitrogen gas content is 5% - 9%, the water vapor content is 2% - 6%, and the oxygen gas content is 7% - 11%. A method for extracting carbon dioxide from the flue gas according to Claim 7.

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