Carbon dioxide fixation method and carbon dioxide fixation apparatus

Abstract

The present invention provides a carbon dioxide fixation method and apparatus that can fix carbon dioxide at low cost by suppressing energy consumption during manufacturing. [Solution] The carbon dioxide fixation method comprises: a slurrying step to produce a strongly alkaline intermediate 18 by mixing water 12 with powdered waste 3 containing calcium and magnesium without adding an alkaline agent to form a slurry; an immobilization step to produce a solid 5 containing calcium carbonate and magnesium carbonate by reacting the intermediate 18 produced in the slurrying step with a gas 4 containing carbon dioxide; and a separation and drying step to produce a powder 2 with fixed carbon dioxide by solid-liquid separation of the solid 5 produced in the immobilization step together with the waste 3 that has not reacted with carbon dioxide and drying.

Description

Technical Field

[0001] The present invention relates to a carbon dioxide fixation method and a carbon dioxide fixation apparatus.

Background Art

[0002] Conventionally, there has been known a method of producing a powder by adding water to concrete sludge, supplying a gas containing carbon dioxide to fix carbon dioxide to produce a calcium carbonate-containing solid, and performing solid-liquid separation (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the powder produced by the above manufacturing method has low water removability and is difficult to dry, so it takes time to dry. Therefore, it is desired to produce a powder containing calcium carbonate with lower energy consumption.

[0005] The present invention has been made in view of such points, and an object thereof is to provide a carbon dioxide fixation method and a carbon dioxide fixation apparatus capable of suppressing energy consumption during production and fixing carbon dioxide at low cost.

Means for Solving the Problems

[0006] The carbon dioxide fixation method of the present invention is neutral without adding an alkaline agent to a powdery waste containing calcium and magnesium waterThe method comprises: a slurrying step to produce a strongly alkaline intermediate by mixing and forming a slurry; an immobilization step to produce a solid containing calcium carbonate and magnesium carbonate by reacting the calcium and magnesium eluted from the waste in the intermediate produced by the slurrying step with a gas containing carbon dioxide; and a separation and drying step to produce a powder with immobilized carbon dioxide by solid-liquid separation of the solid produced by the immobilization step together with the waste that has not reacted with carbon dioxide and drying. [Effects of the Invention]

[0007] According to the present invention, carbon dioxide can be sequestrated inexpensively while suppressing energy consumption. [Brief explanation of the drawing]

[0008] [Figure 1] This is an explanatory diagram showing a manufacturing apparatus used in a method for producing powder according to one embodiment of the present invention. [Modes for carrying out the invention]

[0009] Hereinafter, one embodiment of the present invention will be described with reference to Figure 1.

[0010] In Figure 1, 1 represents a carbon dioxide fixation device. The carbon dioxide fixation device 1 is a manufacturing device for producing powder 2. Powder 2 is a CCU (Carbon dioxide Capture, Utilization) powder containing calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) from which carbon dioxide has been fixed. This powder 2 is generally produced by using powdered waste 3 containing calcium and magnesium as a raw material, reacting the calcium and magnesium components in the waste 3 with a gas 4 containing carbon dioxide by bubbling to artificially produce a solid 5 containing calcium carbonate and magnesium carbonate, and then separating the solid 5 together with the unreacted waste 3 contained in the gas 4 and drying it. Therefore, in addition to calcium carbonate and magnesium carbonate, powder 2 also contains unreacted waste 3.

[0011] Waste 3 is an industrial waste called lime residue, which is generated in the manufacturing process of magnesium hydroxide. Specifically, waste 3 is an industrial waste generated in the process of manufacturing magnesium hydroxide using quicklime (a calcium source), light-calcined dolomite (a calcium and magnesium source), and seawater (a magnesium source) as raw materials, and its main raw materials are a strongly alkaline material (pH 13) containing large amounts of calcium hydroxide and magnesium hydroxide. Lime residue is generally treated as industrial waste and has not been reused in the past. Lime residue may be either quenching residue or reaction residue, or a mixture thereof.

[0012] Gas 4 is preferably a gas whose main component is carbon dioxide, and is even more preferably, from the standpoint of environmental impact, exhaust gas emitted from combustion equipment (factories, etc.), such as exhaust gas from a thermal power plant or exhaust gas from a city gas boiler. The carbon dioxide concentration in gas 4 is, for example, 25% or less.

[0013] The carbon dioxide fixation apparatus 1 comprises a reaction vessel 10 and stirring means 11 such as a stirring blade for stirring the contents of the reaction vessel 10.

[0014] The reaction vessel 10 is connected to a waste introduction means 13 for introducing the waste material 3, and a water introduction means 14 for introducing the water 12 that will be mixed with the waste material 3. Furthermore, the reaction vessel 10 is connected to a gas introduction means 15 for introducing gas 4. The gas introduction means 15 is connected to the bottom of the reaction vessel 10.

[0015] Each of the introduction means 13, 14, and 15 is generally provided with an adjustment means such as a valve so that the amount introduced can be adjusted.

[0016] Furthermore, the reaction vessel 10 is provided with an outlet 16 for discharging the precipitate inside the reaction vessel 10. Through the outlet 16, the solid material 5 can be removed to the outside along with the unreacted waste 3 that has not reacted with carbon dioxide. The outlet 16 is located, for example, at the bottom of the reaction vessel 10.

[0017] Next, we will explain the method for producing powder 2.

[0018] First, a predetermined amount of powdered waste 3 is introduced into the reaction vessel 10 from the waste introduction means 13, and a predetermined amount of water 12 is added from the water introduction means 14 to produce a slurry of strongly alkaline (pH 13) intermediate 18 (slurrying step). In other words, the intermediate 18 does not have an alkaline agent added separately, and consists of waste 3 and water 12, and basically does not contain any other raw materials. The weight of water 12 added to the waste 3 is preferably about 10 to 30 times the weight of the waste 3. As the water 12 introduced, for example, groundwater or industrial water with a neutral or nearly neutral pH is preferably used.

[0019] Following the slurrying step, gas 4 is supplied to the slurryed intermediate 18 from the bottom of the reaction vessel 10 by a gas introduction means 15 while stirring by a stirring means 11. This causes the calcium and magnesium dissolved in the intermediate 18 to react with carbon dioxide in the gas 4, thereby producing a solid 5 containing calcium carbonate and magnesium carbonate, and fixing the carbon dioxide (fixation step).

[0020] The reaction time in this immobilization step is set until the pH of the strongly alkaline intermediate 18 becomes near neutral, for example, pH 6 to 8.5. Therefore, the reaction time in the immobilization step also varies depending on the carbon dioxide concentration in the gas 4, temperature conditions, etc.

[0021] In this way, in the immobilization step, after the pH of the intermediate 18 reaches 6 to 8.5, the solid matter 5 is precipitated at the bottom of the reaction tank 10 by leaving it for a certain period of time (precipitation step). At this time, in addition to the solid matter 5, the precipitate contains the unreacted waste 3 with respect to carbon dioxide.

[0022] Then, following the precipitation step, the precipitate that has precipitated at the bottom of the reaction tank 10 is separated from the intermediate 18 through the discharge port 16 of the reaction tank 10 and discharged, and then dried to produce the powder 2 containing calcium carbonate, magnesium carbonate, and the unreacted waste 3 with respect to carbon dioxide (separation and drying step).

[0023] The powder 2 produced in this way has a particle size (D50, average particle size) of 10 to 30 μm and a BET specific surface area of 10 to 20 m 2 / g, has good water removal properties, and can be produced in a short drying time. Also, not only is carbon dioxide immobilized during its production process, but it also has an additional carbon dioxide adsorption function inside, and exhibits a function of adsorbing carbon dioxide over time, that is, a slow carbon dioxide adsorption function.

[0024] Thus, according to this embodiment, a strongly alkaline intermediate 18 is produced by mixing water 12 with powdered waste 3 containing calcium and magnesium without adding an alkaline agent to form a slurry. A gas 4 containing carbon dioxide is reacted with the intermediate 18 to produce a solid 5 containing calcium carbonate crystals (light calcium carbonate) and magnesium carbonate crystals (light magnesium carbonate). The solid 5 is then separated from the unreacted waste 3 and dried to produce a powder 2 in which carbon dioxide is fixed. This method allows for inexpensive and large-scale carbon dioxide fixation through a simple flow at room temperature and pressure, while suppressing energy consumption during production. In other words, although the purity of the calcium carbonate and magnesium carbonate contained in this fixation method is low, it is a method for producing an inexpensive powder 2 in which a large amount of carbon dioxide is fixed.

[0025] In the immobilization process, by reacting gas 4 with intermediate 18 until its pH reaches 6-8.5, the formation of calcium carbonate in the solid 5 is stopped, and carbon dioxide can be immobilized to a pH where calcium carbonate does not dissolve, thereby maximizing the amount of differential carbon dioxide immobilized.

[0026] Furthermore, since it can utilize the large amount of lime residue that was previously discarded as waste 3, it contributes to reducing carbon dioxide emissions while effectively utilizing waste 3. Similarly, by utilizing exhaust gas from the combustion equipment, it contributes to reducing carbon dioxide emissions while effectively utilizing exhaust gas 4. Therefore, it can be recycled, reducing the environmental burden.

[0027] Since powder 2 does not use concrete sludge as a raw material, it can be manufactured in large quantities regardless of the amount of concrete sludge generated.

[0028] Since the production of powder 2 is essentially completed within the reaction vessel 10, equipment costs can be reduced, making lower-cost production possible.

[0029] The manufactured powder 2 can be suitably used as a chemical product, for example, as an admixture for fresh concrete or concrete mixing, a filler for asphalt compounds, or a raw material for plastics.

[0030] In this way, by using lime residue and exhaust gas containing carbon dioxide to fix carbon dioxide, a powder 2 containing calcium carbonate and magnesium carbonate can be produced and made available for use in the applications described above. This makes a significant contribution to carbon neutrality (reduction of total carbon dioxide emissions) and is industrially advantageous. [Examples]

[0031] An embodiment of this example will be described.

[0032] In this embodiment, a 100L reaction tank 10 was used as the manufacturing apparatus 1. 4 kg of lime residue powder as waste 3 and 80 L of water 12 were added to the reaction tank 10 to form a slurry of a strongly alkaline intermediate 18. Exhaust gas from a city gas boiler generated at the factory was introduced into the reaction tank 10 as gas 4 and stirred while aerating.

[0033] In this embodiment, aeration and stirring were continuously carried out for 6 hours until the pH of the intermediate 18 in the reaction vessel 10 was neutralized, from pH 13 to pH 8.5.

[0034] After neutralization, the intermediate 18 was left to stand for a certain period of time. The solid 5 was then separated from the unreacted waste 3 with carbon dioxide using solid-liquid separation, and dried to obtain powder 2. The analysis results of the obtained powder 2 are shown in Table 1. Table 1 also includes an example of powder produced by adding water to concrete sludge, supplying a gas containing carbon dioxide to fix the carbon dioxide, generating a calcium carbonate-containing solid, and then performing solid-liquid separation.

[0035] [Table 1]

[0036] Thus, compared to the comparative example, powder 2 produced by the manufacturing method of this embodiment had a larger particle size and a smaller BET specific surface area, resulting in good dewatering properties, a shorter drying time, and the ability to be manufactured with less energy.

[0037] Furthermore, while the amount of carbon dioxide fixed by calcium carbonate was the same in both the example and the comparative example, in this example, since magnesium carbonate was also produced in addition to calcium carbonate, the amount of carbon dioxide fixed by magnesium carbonate was added, resulting in the production of powder 2 with a higher carbon dioxide fixation amount than the comparative example. [Explanation of Symbols]

[0038] 1. Carbon dioxide fixation device 2 powder 3. Waste 4 gas 5. Solids 10 reaction vessels 11. Stirring means 12 water 15. Gas introduction means 16 Outlet 18 Intermediates

Claims

1. A slurrying process to produce a strongly alkaline intermediate by mixing powdered waste containing calcium and magnesium with neutral water without adding an alkaline agent, This slurrying process involves an immobilization process in which a solid containing calcium carbonate and magnesium carbonate is produced by reacting the calcium and magnesium eluted from the waste with a gas containing carbon dioxide in the intermediate produced by this slurrying process. A separation and drying step is performed to produce a powder in which carbon dioxide is immobilized by solid-liquid separation of the solid material generated by this immobilization step together with the waste material that has not reacted with carbon dioxide, and then drying the solid material. A method for fixing carbon dioxide, characterized by comprising the following features.

2. In the immobilization process, the gas is reacted until the pH of the intermediate reaches 6 to 8.

5. The carbon dioxide fixation method according to claim 1, characterized by its features.

3. The waste is lime residue generated during the manufacturing process of magnesium hydroxide. A carbon dioxide fixation method according to claim 1 or 2, characterized by the features described herein.

4. A reaction vessel into which powdered waste containing calcium and magnesium and neutral water are introduced, A stirring means for mixing the waste introduced into this reaction vessel with the neutral water to produce a slurry of a strongly alkaline intermediate, A gas introduction means for blowing a gas containing carbon dioxide into the reaction vessel to react with the calcium and magnesium leached from the waste, An outlet for discharging precipitate from the reaction vessel, A carbon dioxide fixation device characterized by comprising the following features.

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