Method for producing alkali metal bicarbonates from combustion exhaust gases

Abstract

This invention provides a method for producing high-purity alkali metal bicarbonates using combustion exhaust gas. [Solution] A method for producing an alkali metal bicarbonate, comprising subjecting combustion exhaust gas containing at least one acidic component selected from the group consisting of HF, HCl, and SO2, and CO2, to a preliminary treatment to remove at least a portion of the acidic component to obtain a preliminary treatment exhaust gas, and then performing a contact treatment in which the preliminary treatment exhaust gas is brought into contact with an aqueous solution (a) containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates to obtain an alkali metal bicarbonate.

Description

[Technical Field]

[0001] The present invention relates to a method for producing alkali metal bicarbonates from combustion exhaust gas. [Background technology]

[0002] Combustion exhaust gases generated at thermal power plants, waste incineration facilities, biomass power plants, and other similar facilities contain large amounts of carbon dioxide. Since carbon dioxide is a greenhouse gas, methods for its capture have been explored.

[0003] Patent Document 1 discloses an exhaust gas treatment system for treating exhaust gas generated by combustion, comprising an acid gas removal device that removes acidic gas components contained in the exhaust gas by dry treatment, a temperature reduction device, and a device for separating and recovering carbon dioxide.

[0004] Patent Document 2 discloses a method for producing sodium bicarbonate using carbon dioxide derived from combustion exhaust gas from a boiler, which has been diluted with an inert gas.

[0005] Patent Document 3 discloses a method for producing sodium bicarbonate from a carbon dioxide-containing product generated by the combustion of a carbonaceous raw material.

[0006] Thus, while it has been shown that carbon dioxide can be recovered from combustion exhaust gases and sodium bicarbonate can be produced from carbon dioxide, the purity of sodium bicarbonate has not been considered. Sodium bicarbonate is used in a variety of applications, including pharmaceuticals, food additives, animal feed, neutralizing agents, and incineration exhaust gas treatment, and in some applications, high purity is required. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 7242774 [Patent Document 2] Patent No. 5934003 [Patent Document 3] Patent No. 7446312 [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention has been made in view of the above circumstances, and aims to provide a method for producing high-purity alkali metal bicarbonates using combustion exhaust gas. [Means for solving the problem]

[0009] As a result of diligent research, the inventors discovered that high-purity alkali metal bicarbonates can be produced by removing some or all of the acidic components from combustion exhaust gas containing at least one of the acidic components (HF, HCl, SO2) and CO2, and then contacting the gas with an aqueous solution of an alkali metal hydroxide or carbonate. This led to the completion of the present invention. The present invention encompasses the following embodiments. [1] Combustion exhaust gas containing at least one acidic component selected from the group consisting of HF, HCl, and SO2, and CO2 is subjected to a pretreatment to remove at least a portion of the acidic component, thereby obtaining pretreated exhaust gas. The pre-treated exhaust gas is subjected to a contact treatment in which an aqueous solution (a) containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates is brought into contact with the pre-treated exhaust gas to obtain an alkali metal bicarbonate. A method for producing alkali metal bicarbonates, including the following. [2] The method for producing alkali metal bicarbonate according to [1], wherein in the pre-treated exhaust gas, the molar ratio of HF to CO2 (HF / CO2) is 0.00023 or less, the molar ratio of HCl to CO2 (HCl / CO2) is 0.00406 or less, and the molar ratio of SO2 to CO2 (SO2 / CO2) is 0.00220 or less. [3] In the slurry obtained by the contact treatment, based on the mass of the slurry, the fluorine concentration is 6.4 ppm or less, the chlorine concentration is 212 ppm or less, and the SO4 2- concentration is 311 ppm or less, the method for producing an alkali metal hydrogen carbonate according to [1] or [2]. [4] In the alkali metal hydrogen carbonate obtained by the contact treatment, based on the total mass of the alkali metal hydrogen carbonate, the fluorine concentration is 6.0 ppm or less, the chlorine concentration is 200 ppm or less, and the SO4 2- concentration is 330 ppm or less, the method for producing an alkali metal hydrogen carbonate according to any one of [1] to [3]. [5] The pretreatment is performed by a wet method using an aqueous solution (b) of at least one alkali metal compound selected from the group consisting of an alkali metal hydroxide, an alkali metal carbonate, and an alkali metal hydrogen carbonate, or a dry method using a powder of an alkali metal hydrogen carbonate. The method for producing an alkali metal hydrogen carbonate according to any one of [1] to [4]. [6] The pretreatment is performed using the alkali metal hydrogen carbonate obtained by the contact treatment. The method for producing an alkali metal hydrogen carbonate according to any one of [1] to [5]. [7] After the pretreated exhaust gas is made into fine bubbles, the contact treatment is performed. The method for producing an alkali metal hydrogen carbonate according to any one of [1] to [6]. [Advantages of the Invention]

[0010] According to the present invention, it is possible to provide a method for producing a high-purity alkali metal hydrogen carbonate using combustion exhaust gas. [Brief Description of the Drawings]

[0011] [Figure 1] In the present invention, it is a flowchart showing an example of a step of removing an acidic component from combustion exhaust gas containing an acidic component and CO2 gas using a wet scrubber. [[ID=第二十八条]] [[ID=第二十九条]] [Figure 2] [[ID=第三十条]] In the present invention, it is a flowchart showing an example of a step of removing an acidic component from combustion exhaust gas containing an acidic component and CO2 gas by a dry method. [Figure 3] This is a flow chart showing an example of a process for producing an alkali metal hydrogen carbonate from combustion exhaust gas containing CO2 gas from which an acidic component has been removed in the present invention. [Figure 4] This is a schematic diagram showing an example of drying equipment used when drying a cake of an alkali metal hydrogen carbonate.

Embodiments for Carrying Out the Invention

[0012] The meanings of the terms in this specification are as follows. A numerical range represented by "~" means a numerical range having the numerical values before and after ~ as the lower limit value and the upper limit value. "Combustion exhaust gas" means, for example, exhaust gas generated as a result of combustion in a thermal power generation facility, a waste combustion treatment facility, a biomass power generation facility, or the like. "d10", "d50", and "d90" respectively refer to the 10% diameter, 50% diameter (median diameter), and 90% diameter in the cumulative distribution curve of the volume of bubbles with respect to the size of the bubbles.

[0013] Hereinafter, the present invention will be described, but the present invention is not limited by the examples in the following description.

[0014] In the method of the present invention, combustion exhaust gas containing at least one acidic component selected from the group consisting of HF (hydrogen fluoride), HCl (hydrogen chloride), and SO2 (sulfur dioxide) and CO2 (carbon dioxide) is subjected to a pretreatment for removing at least a part of the acidic component to obtain pretreated exhaust gas (hereinafter, sometimes referred to as "pretreated CO2-containing exhaust gas"). A contact treatment is performed by bringing the pretreated exhaust gas into contact with an aqueous solution (a) containing at least one alkali metal compound selected from the group consisting of an alkali metal hydroxide and an alkali metal carbonate (hereinafter, sometimes referred to as "aqueous solution (a) of an alkali metal compound") to produce a high-purity alkali metal hydrogen carbonate.

[0015] 《Pretreatment》 In the method of the present invention, first, a combustion exhaust gas containing at least one acidic component selected from the group consisting of HF, HCl, and SO2, and CO2 is subjected to a preliminary treatment to remove at least a portion of the acidic component, thereby obtaining a pre-treated exhaust gas. In the present invention, the combustion exhaust gas is combustion exhaust gas generated in a thermal power plant, waste incineration facility, biomass power plant, etc., and has a CO2 concentration of about 8 to 12 volume percent. The concentration of acidic components contained in this combustion exhaust gas depends on the type and amount of substances burned in the facility, but is approximately HF concentration = 25 to 40 volume ppm, HCl concentration = 500 to 1500 volume ppm, and SO2 concentration = 250 to 2000 volume ppm.

[0016] In the present invention, the extent to which acidic components are removed by pretreatment from combustion exhaust gas containing at least one of the acidic components (HF, HCl, SO2) and CO2 is preferable, such that the composition of the pretreated exhaust gas has an HF / CO2 molar ratio of 0.00023 or less, an HCl / CO2 molar ratio of 0.00406 or less, and an SO2 / CO2 molar ratio of 0.00220 or less, in order to obtain a high-purity alkali metal bicarbonate. By using pre-treated combustion exhaust gas from which acidic components have been removed within this range, the acidic component content in the produced alkali metal bicarbonate can be reduced to: fluorine (F) concentration = 6.0 ppm or less, chlorine (Cl) concentration = 200 ppm or less, SO4 2- The sulfate ion concentration can be reduced to 330 pm or less.

[0017] The preferred range for removing acidic components from combustion exhaust gas by pretreatment is such that the gas composition of the pretreated exhaust gas has an HF / CO2 molar ratio of 0.00011 or less, an HCl / CO2 molar ratio of 0.00205 or less, and an SO2 / CO2 molar ratio of 0.00120 or less. By using pretreated exhaust gas from which acidic components have been removed within this range, the content of acidic components in the alkali metal bicarbonate produced is such that the F concentration is 3.0 ppm or less, the Cl concentration is 100 ppm or less, and SO4 2- = Can be reduced to 184 ppm or less.

[0018] A more preferable range for removing acidic components from combustion exhaust gas by pretreatment is when the gas composition of the pretreated exhaust gas has an HF / CO2 molar ratio of 0.00003 or less, an HCl / CO2 molar ratio of 0.00084 or less, and an SO2 / CO2 molar ratio of 0.00040 or less. By using pretreated exhaust gas from which acidic components have been removed within this range, the content of acidic components in the alkali metal bicarbonate produced is such that F concentration = 1.0 ppm or less, Cl concentration = 40 ppm or less, and SO4 2- = Can be reduced to 67 ppm or less.

[0019] In the present invention, the method for removing acidic components from combustion exhaust gas containing CO2 is not particularly limited, and examples include a wet method using an aqueous solution (b) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates, or a dry method using slaked lime or alkali metal bicarbonate powder. Examples of alkali metals in the alkali metal compounds and alkali metal bicarbonates include lithium, sodium, and potassium. The concentration of the alkali metal compound in the aqueous solution (b) is not particularly limited as long as a predetermined amount of the acidic component is removed as described above, but it is typically in the range of 1 to 10% by mass.

[0020] Examples of wet methods include a method in which combustion exhaust gas containing acidic components and CO2 is injected into the aqueous solution (b), and a method in which combustion exhaust gas containing acidic components and CO2 is supplied while circulating the aqueous solution (b) in a tower using a scrubber as shown in Figure 1. In Figure 1, the scrubber 1 consists of a tower section 2 and a circulating liquid storage tank 3. The inside of the tower section 2 is filled with packing material 4 such as pole rings. The circulating liquid storage tank 3 contains circulating liquid 5, which is the aqueous solution (b) described above. In particular, the filtrate 29 in the alkali metal bicarbonate production apparatus shown in Figure 3, which will be described later, is a saturated aqueous solution of alkali metal bicarbonate, so using this is preferable from the viewpoint of resource recycling. By starting the circulating liquid pump 6, the circulating liquid 5 is sent to a spray nozzle 7 installed in the upper part of the tower and sprayed into the inside of the tower. Meanwhile, combustion exhaust gas containing acidic components and CO2 gas is introduced below the packing material 4 in the tower via the combustion exhaust gas introduction pipe 8. The introduced combustion exhaust gas comes into contact with the circulating liquid 5 on the surface of the packing material 4, removing the acidic components, and is discharged from the top of the tower via the combustion exhaust gas outlet pipe 9.

[0021] In the dry method, as shown in Figure 2, combustion exhaust gas 10 containing acidic components and CO2 is introduced into a heat exchanger called an economizer 11 and cooled by heat exchange with water. Then, in the economizer outlet pipe 12, a neutralizing agent powder 13 such as slaked lime or alkali metal bicarbonate is added. This neutralizing agent powder 13 reacts with the acidic components in the combustion exhaust gas and is captured and removed by a dust collector 14, so that the pre-treated exhaust gas from which the acidic components have been removed is discharged through the combustion exhaust gas outlet pipe 15.

[0022] Regardless of whether the pretreatment method for removing acidic components from combustion exhaust gas is a wet or dry method, it is preferable from the standpoint of resource recycling if it uses alkali metal bicarbonates obtained by the contact treatment described later. The method of the present invention may include a step of recovering combustion exhaust gas generated at a thermal power plant, waste incineration facility, or biomass power plant before the aforementioned preliminary treatment.

[0023] Contact Processing A method for obtaining high-purity alkali metal bicarbonate from the aforementioned pre-treated CO2-containing exhaust gas includes contacting the pre-treated CO2-containing exhaust gas with an aqueous solution (a) containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates to precipitate alkali metal bicarbonate, filtering the slurry, and then drying it. The CO2 concentration in the aforementioned pre-treated CO2-containing exhaust gas is also approximately 8-12% by volume.

[0024] <Aqueous solution of alkali metal compound (a)> Aqueous solution (a) is an aqueous solution containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates. Examples of alkali metals in the alkali metal compound include lithium, sodium, and potassium. When these alkali metals are used, the target product of the method of this embodiment is a bicarbonate such as lithium bicarbonate, sodium bicarbonate, or potassium bicarbonate.

[0025] The upper limit of the concentration of the alkali metal compound in aqueous solution (a) is the saturation concentration of the alkali metal compound. The concentration of the alkali metal compound in aqueous solution (a) is preferably 3% or more, and more preferably 5% or more. Regarding the lower limit of the concentration of the alkali metal compound in aqueous solution (a), it is preferable that the concentration exceeds the solubility of the alkali metal bicarbonate at 0°C when the alkali metal compound reacts with CO2 to produce the alkali metal bicarbonate. In particular, when the alkali metal compound in aqueous solution (a) is sodium carbonate, its concentration is preferably 6-25%, and more preferably 10-20%. If it is above the lower limit, when sodium bicarbonate is produced by reaction with carbon dioxide, the amount tends to exceed the solubility of sodium bicarbonate, and sodium bicarbonate tends to precipitate. If it is below the upper limit, the amount of sodium bicarbonate in the slurry containing the produced sodium bicarbonate is appropriate, and the viscosity of the slurry does not become too high, making it easy to handle. The solid content concentration of the slurry is preferably 3-25%, and more preferably 8-20%.

[0026] <Method of contacting pre-treated CO2-containing exhaust gas with an aqueous solution of an alkali metal compound (a)> The method for contacting the pre-treated CO2-containing exhaust gas with the aqueous solution (a) is not particularly limited, and one method is to blow the pre-treated CO2-containing exhaust gas into the aqueous solution (a) through a nozzle, but a method of supplying fine bubbles of the pre-treated CO2-containing exhaust gas is preferred. This is because the production of alkali metal bicarbonates is carried out by dissolving CO2 in the aqueous solution (a), and by atomizing the CO2 and increasing the dissolution rate, the utilization rate of CO2 can be increased, and the production rate of carbonates and bicarbonates can be increased. The higher the utilization rate of CO2, the less pre-treated CO2-containing exhaust gas can be used, so the amount of impurities mixed into the obtained alkali metal bicarbonate can be reduced, and a high-purity alkali metal bicarbonate can be obtained. The preferred range for the utilization rate of CO2 is 90% or more, more preferably 95% or more, and it is possible to achieve up to 100%.

[0027] When alkali metal bicarbonates are produced using a method in which fine bubbles of pre-treated CO2-containing exhaust gas are supplied to the aqueous solution (a), the entire amount of acidic components contained in the pre-treated CO2-containing exhaust gas is contained in the slurry containing alkali metal bicarbonates. Therefore, the content of components derived from acidic components relative to the mass of the slurry containing alkali metal bicarbonates can be defined according to the degree of removal of acidic components. In the gas composition of the pre-treated CO2-containing exhaust gas, if the HF / CO2 molar ratio is 0.00023 or less, the HCl / CO2 molar ratio is 0.00406 or less, and the SO2 / CO2 molar ratio is 0.00220 or less, then the content of components derived from acidic components relative to the mass of the total slurry is F = 6.4 ppm or less, and Cl = 212 ppm or less, SO4 2- = 311 ppm or less.

[0028] If the exhaust gas composition after the aforementioned pretreatment is within the preferred range described above, with an HF / CO2 molar ratio of 0.00011 or less, an HCl / CO2 molar ratio of 0.00205 or less, and an SO2 / CO2 molar ratio of 0.00120 or less, then the content of components derived from acidic components relative to the mass of the total slurry is F = 3.1 ppm or less, Cl = 107 ppm or less, and SO4 2- = 169 ppm or less.

[0029] If the exhaust gas composition after the aforementioned pretreatment is within the more preferable range described above, with an HF / CO2 molar ratio of 0.00003 or less, an HCl / CO2 molar ratio of 0.00084 or less, and an SO2 / CO2 molar ratio of 0.00040 or less, then the content of components derived from acidic components relative to the mass of the total slurry is F = 0.8 ppm or less, Cl = 44 ppm or less, and SO4 2- = 56 ppm or less.

[0030] The following describes a case in which the contact treatment is performed by supplying fine bubbles of the pre-treated CO2-containing exhaust gas to the aqueous solution (a). In this specification, "fine bubbles" refers to a general term encompassing microbubbles with a diameter of approximately 1 to 150 μm and nanobubbles with a diameter of less than 1 μm. Furthermore, in this specification, the process of creating fine bubbles may be referred to as "fine bubble formation." When a large number of microbubbles are generated in water, it appears as turbidity. On the other hand, because nanobubbles are extremely small, the water remains clear. In this embodiment, it is preferable that the size (bubble diameter) of the fine bubbles in the pre-treated CO2-containing exhaust gas is such that d50 is 100 μm or less and d90 is 150 μm or less. By using fine bubbles with such a bubble diameter, the utilization rate of CO2 can be sufficiently increased. Furthermore, from the viewpoint of ensuring the effects of the present invention are more reliable, d50 is preferably 50 to 90 μm, more preferably 60 to 80 μm, and d90 is preferably 100 to 150 μm, more preferably 100 to 130 μm. In this invention, so-called nanobubbles with a diameter of 1 μm or less are not required. The minimum value of the fine bubble diameter is not particularly limited, but from the viewpoint of ease of fine bubble preparation, it is preferable that it is greater than 1 μm or 10 μm or more. According to the method of this invention, the utilization rate of carbon dioxide can be sufficiently increased even without the presence of fine bubbles with a diameter of 1 μm or less.

[0031] The size (bubble diameter) of fine bubbles in pre-treated CO2-containing exhaust gas can be measured, for example, using a particle size analyzer (product name: Particle Track G400) manufactured by Mettler Toledo, Inc., which employs FBRM (Focused Beam Reflectance Measurement).

[0032] The devices used to create such fine bubbles are not particularly limited, but include the following: (Example 1) A device that supplies gas to the suction side of a pressure pump and converts the inhaled gas into fine bubbles using mixing blades that rotate at high speed inside the pressure pump. An example is the "Vortex Turbo Mixer Pump" (product name) manufactured by Nikuni Co., Ltd. (Example 2) A device that creates a low-pressure region in a liquid flow by using the Venturi effect (narrowing the flow path of a pressurized liquid to increase the flow velocity and create a low-pressure region), and then supplies gas to that region to create fine bubbles. Examples include the "YJ Nozzle" (product name) manufactured by Envirovision Co., Ltd. and the "Aqua Transfer Nozzle" (product name) manufactured by Waternavi Co., Ltd. (Example 3) A device that creates a negative pressure zone in the center by ejecting water radially from a high-speed rotating disc, and then draws in gas to create fine bubbles. An example is "Spinor" (product name) manufactured by Waternavi Co., Ltd.

[0033] When the alkali metal compound is an alkali metal hydroxide, the temperature of the aqueous solution (a) when supplying the pre-treated CO2-containing exhaust gas is not particularly limited, but is preferably 0°C to 80°C. The lower the temperature, the greater the solubility of CO2 in the aqueous solution (a) of the alkali metal hydroxide, but a temperature of 0°C or higher is preferable because there is no risk of freezing. On the other hand, the higher the temperature, the less the solubility of CO2 in the aqueous solution (a) of the alkali metal hydroxide, and a temperature of 80°C or lower is preferable because the rate of alkali metal bicarbonate formation is faster. The temperature of the aqueous solution (a) is more preferably 20 to 60°C, and even more preferably 30 to 50°C.

[0034] When the alkali metal compound is an alkali metal carbonate, the temperature of the aqueous solution (a) when supplying the pre-treated CO2-containing exhaust gas is not particularly limited, but is preferably 0°C to 80°C. The lower the temperature, the greater the solubility of CO2 in the aqueous solution of alkali metal carbonate, but temperatures above 0°C are preferable because there is no risk of freezing. On the other hand, the higher the temperature, the less the solubility of CO2 in the aqueous solution (a) of alkali metal carbonate, and temperatures below 80°C are preferable because the rate of alkali metal bicarbonate formation increases. Furthermore, the higher the temperature, the greater the solubility of the generated alkali metal bicarbonate, but temperatures below 80°C are preferable because the amount of alkali metal bicarbonate precipitated increases. The temperature of the aqueous solution (a) is more preferably 20 to 70°C, and even more preferably 25 to 50°C. Regarding the time for supplying the pre-treated CO2-containing exhaust gas to the aqueous solution (a), there are no particular restrictions as long as the desired reaction can proceed sufficiently, but it is generally 0.2 to 16 hours, and preferably 0.5 to 8 hours.

[0035] Next, with reference to Figure 3, an example of an apparatus for producing high-purity alkali metal bicarbonates from pre-treated CO2-containing exhaust gas will be described. The crystallization tank 20 contains liquid 22. Liquid 22 in the crystallization tank is an aqueous solution of alkali metal hydroxide or carbonate (aqueous solution (a)). This liquid is sent to the YJ nozzle 24 using a circulation pump 23 and circulated through the circulation piping 25. Meanwhile, pre-treated CO2-containing exhaust gas is sent to the YJ nozzle 24 through a CO2-containing gas supply piping 26 to create fine bubbles. As the CO2-containing gas is supplied, the aqueous solution of alkali metal hydroxide or carbonate in the crystallization tank is bicarbonated, and alkali metal bicarbonates precipitate. Once the alkali metal bicarbonates have precipitated, the supply of CO2-containing gas can be stopped.

[0036] Next, the liquid 22 in the crystallization tank, in which the alkali metal bicarbonate has precipitated, is sent through the supply pipe 27 to the filter 28 for filtration. The dewatered cake of alkali metal bicarbonate, separated from the filtrate 29 by the filter, is sent through the supply pipe 30 to the drying equipment 31, where it is dried to obtain alkali metal bicarbonate powder 32.

[0037] To obtain high-purity bicarbonates with a low content of components derived from acidic components in combustion exhaust gas, it is advantageous to increase the solid content concentration in the dehydrated cake of alkali metal bicarbonates during this filtration process. This is because these impurity components tend to exist at a higher concentration in the mother liquor than in the solid alkali metal bicarbonates in the liquid in which the alkali metal bicarbonates have precipitated. The dehydrated cake of alkali metal bicarbonates consists of solid alkali metal bicarbonates and a mother liquor, and impurities contained in the mother liquor in the dehydrated cake are carried over directly into the alkali metal bicarbonate powder after drying in the subsequent stage. The solid content concentration in the dehydrated alkali metal bicarbonate cake is preferably 40% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. Methods of filtration to obtain such a dehydrated cake with a high solid content include, in addition to vacuum filtration, pressure filtration, methods using a centrifugal dehydrator, and methods using a filter press.

[0038] A common method for drying alkali metal bicarbonate cakes obtained by centrifugal dehydration is heating them to over 80°C in an atmosphere containing CO2 gas. Alkali metal bicarbonates undergo a decomposition reaction to alkali metal carbonates when exposed to high temperatures above 80°C in air for extended periods, as shown in equation (1). Therefore, drying in an atmosphere containing CO2 gas is necessary. However, this method has the problem of requiring equipment to recover the CO2 gas emitted from the drying facility. 2MHCO3→ M2CO3+ CO2+ H2O...Equation (1) (In the formula, M represents an alkali metal.)

[0039] Separately, drying can be done in air without using CO2 gas if the drying time is short. Examples of such equipment include airflow dryers and fluidized bed dryers. Examples of airflow dryers include the Flash Jet Dryer manufactured by Seishin Corporation and the Jet Turbo Dryer manufactured by Hiraiwa Iron Works Co., Ltd. Examples of fluidized bed dryers include the Slit Flow manufactured by Okawara Manufacturing Co., Ltd., the Fluidized Bed Dryer manufactured by Kurimoto Iron Works Co., Ltd., and the Tornesh Dryer manufactured by Nara Machine Works Co., Ltd.

[0040] Figure 4 shows the equipment for drying alkali metal bicarbonate cake using a flash jet dryer manufactured by Seishin Corporation. Hot air 41 is introduced into the flash jet dryer 40. When alkali metal bicarbonate cake 42 is supplied quantitatively to it, it is instantly dried and becomes an airflow containing alkali metal bicarbonate powder, which is introduced into the cyclone 43 and collected as powder in a recovery container 45 installed at its bottom. [Examples]

[0041] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0042] (Carbon dioxide utilization rate) The carbon dioxide utilization rate (UR) (%) during alkali metal bicarbonate precipitation was defined as the ratio (B) of the calculated amount of carbon dioxide gas required to convert all the carbonates in the alkali metal carbonate aqueous solution into bicarbonates to the actual amount of carbon dioxide gas supplied for alkali metal bicarbonate precipitation (A). That is, the carbon dioxide utilization rate (UR) can be calculated using the following formula (1). Carbon dioxide utilization rate (UR) (%) during alkali metal bicarbonate precipitation = Calculated amount of carbon dioxide gas required to convert all alkali metal carbonate to bicarbonate (B, unit: L) / Actual amount of carbon dioxide gas supplied (A, unit: L) × 100 Equation (1)

[0043] (Analysis method for determining the content of components derived from acidic components in combustion exhaust gas in alkali metal bicarbonate powder) [Method for analyzing fluoride content] Measurement using a fluoride ion-selective electrode 5.0 g of alkali metal bicarbonate powder was dissolved in phenolphthalein solution, neutralized with (1:1) nitric acid, and the powder was dissolved. After confirming that the powder was dissolved, pure water was added to make a total volume of 50 ml, which was the sample solution. 20 ml of this sample solution was taken and placed in a beaker. 20 ml of TISAB buffer solution for fluoride ion concentration measurement was also taken and placed in a beaker. A fluoride ion-selective electrode was immersed in the sample solution, and the value was read when the potential became stable. The potential was measured with four standard solutions of a predetermined fluoride ion concentration to create a calibration curve, and the fluoride ion concentration in the sample solution was determined from this calibration curve, and the concentration in the powder of the alkali metal hydrogen carbonate was calculated.

[0044] [Analysis method for Cl content] Analysis by turbidimetry Analysis was performed based on JIS K 8001 5.7 [Chloride (Cl)] (1) (turbidimetry). Approximately 10 ml of pure water was added to 5.0 g of the powder of the alkali metal hydrogen carbonate, and after adding (1:1) nitric acid to dissolve the powder, distilled water was added again to make the total volume 50 ml. Approximately 10 g of this solution was weighed out, 1 ml of (1+2) nitric acid and 1 ml of an aqueous silver nitrate solution with a concentration of 20 g / l were added, and it was shaken. As a calibration curve, 0, 0.2, 0.4, 0.6, 0.8, and 1.0 ml of a chloride standard solution with a concentration of 0.01 mg-Cl / ml were weighed out respectively, the total volume was made 10 ml with pure water, then 1 ml of (1+2) nitric acid and 1 ml of an aqueous silver nitrate solution with a concentration of 20 g / l were added, and it was shaken. After leaving it in the dark, the turbidity of the sample solution was compared with the chloride standard, and the chloride ion concentration in the sample solution was determined from this turbidity, and the concentration in the powder of the alkali metal hydrogen carbonate was calculated.

[0045] [SO4 2- [Analysis method for content] Analysis by ICP emission spectrometry 1 ml of nitric acid and pure water were added to 1.0 g of the powder of the alkali metal hydrogen carbonate to make the total volume 100 ml, and solution (a1) was obtained. Solution (a1) was dispensed in 10 ml portions, and SO4 2- standard solution was added respectively so that the concentration became 0, 0.1, 0.5, 1.0, and 3.0 μg / ml to prepare a sample solution. The obtained sample solution was designated as solution (b1). Solution (b1) was subjected to an ICP emission spectrometer to measure the intensity of S atoms, and the concentration of SO4 2- was determined, and the concentration in the powder of the alkali metal hydrogen carbonate was calculated.

[0046] Tables 1 and 2 show the production conditions for alkali metal bicarbonates and the content of components derived from acidic components in the obtained alkali metal bicarbonate powder. Example 1 is a comparative example, and Examples 2 to 7 are examples.

[0047] (Example 1) Production of sodium bicarbonate from combustion exhaust gas that has not had acidic components removed. Sodium bicarbonate powder was produced from combustion exhaust gas containing acidic components and CO2 using the apparatus shown in Figure 3. This combustion exhaust gas was before the acidic components were removed, and the concentrations of each component were as follows: CO2 = 10 vol%, HF = 30 vol ppm, HCl = 560 vol ppm, and SO2 = 300 vol ppm. Expressed as molar ratios relative to CO2, the HF / CO2 molar ratio was 0.0003, the HCl / CO2 molar ratio was 0.0056, and the SO2 / CO2 molar ratio was 0.003. In a crystallization tank 20 with an internal volume of 5 L, 400 g of sodium carbonate powder and 2000 g of deionized water were placed and stirred with a stirring device 21 to obtain 2400 g of a 16.7% sodium carbonate aqueous solution. This aqueous solution was circulated at a flow rate of 20 L / min through a circulation pipe 25 using a circulation pump 23. A YJ nozzle 24 was installed in the circulation pipe. The YJ nozzle used was a YJ-6 inline type (product name). Immediately after starting circulation, combustion exhaust gas of the above composition was supplied to the YJ nozzle 24 at a rate of 4 L / min, encapsulated in fine bubbles. Here, the d50 of the fine bubbles was 80 μm and the d90 was 145 μm. The temperature of the aqueous solution when carbon dioxide was introduced was 25-35°C. 211 minutes after starting to supply combustion exhaust gas, after supplying 845 L, the inside of the crystallization tank became a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. The content of components derived from acidic components in the combustion exhaust gas added to the sodium bicarbonate slurry at this time was F=8.4 ppm, Cl=292 ppm, SO4 2- The result was 424 ppm. The sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrator 28 used was a H-110F model manufactured by Kokusan Co., Ltd. The centrifugal dehydrated cake was dried in a drying facility 31 under a carbon dioxide atmosphere at 80°C to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The content of components derived from acidic components in the combustion exhaust gas in the obtained sodium bicarbonate powder was F=7.8 ppm, Cl=276 ppm, SO4 2- The level was high at 448 ppm.

[0048] (Example 2) Production of sodium bicarbonate from combustion exhaust gas from which acidic components have been removed Acidic components were removed from the combustion exhaust gas of Example 1 using the wet scrubber shown in Figure 1. The combustion exhaust gas of Example 1 was supplied through the combustion exhaust gas introduction pipe 8. A sodium bicarbonate aqueous solution was used as the circulating fluid. After the removal of the acidic components, the concentrations of each component were CO2 = 10 vol%, HF = 2.0 vol ppm, HCl = 37 vol ppm, and SO2 = 20 vol ppm. Expressed as molar ratios to CO2, the HF / CO2 molar ratio was 0.00002, the HCl / CO2 molar ratio was 0.00037, and the SO2 / CO2 molar ratio was 0.00020. Sodium bicarbonate powder was produced in the same manner as in Example 1, except that the combustion exhaust gas from which the acidic components had been removed was used. 211 minutes after the start of supplying the combustion exhaust gas from which the acidic components had been removed, and after supplying 845 L, the crystallization tank contained a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. The content of components derived from the acidic components in the combustion exhaust gas added to the sodium bicarbonate slurry at this time was F=0.6 ppm, Cl=19 ppm, SO4 2- The concentration was 28 ppm. In the same manner as in Example 1, this sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying equipment 31 to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The content of components derived from acidic components in the combustion exhaust gas in the obtained sodium bicarbonate powder was F=0.8 ppm, Cl=17 ppm, SO4 2- A very low concentration of 37 ppm was obtained, resulting in a high-purity sodium bicarbonate powder.

[0049] (Example 3) Production of sodium bicarbonate from combustion exhaust gas from which acidic components have been removed The combustion exhaust gas used was a mixture of the combustion exhaust gas before the removal of acidic components used in Example 1 and the combustion exhaust gas after the removal of acidic components using a wet scrubber used in Example 2, in a volume ratio of 3:7. The concentrations of each component in this mixed gas were CO2 = 10 vol%, HF = 10 vol ppm, HCl = 187 vol ppm, and SO2 = 100 vol ppm. Expressed as molar ratios relative to CO2, the HF / CO2 molar ratio was 0.00010, the HCl / CO2 molar ratio was 0.00187, and the SO2 / CO2 molar ratio was 0.00100. Sodium bicarbonate powder was produced in the same manner as in Example 1, except that the combustion exhaust gas from which the acidic components had been removed was used. 211 minutes after the start of supplying the combustion exhaust gas from which the acidic components had been removed, and after supplying 845 L, the crystallization tank contained a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. The content of components derived from the acidic components in the combustion exhaust gas added to the sodium bicarbonate slurry at this time was F=2.8 ppm, Cl=97 ppm, SO4 2- The concentration was 141 ppm. In the same manner as in Example 1, this sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying equipment 31 to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The content of components derived from acidic components in the combustion exhaust gas in the obtained sodium bicarbonate powder was F=2.8 ppm, Cl=91 ppm, SO4 2- A sodium bicarbonate powder with a low concentration of 155 ppm was obtained, which is higher purity than that obtained in Example 1.

[0050] (Example 4) Production of sodium bicarbonate from combustion exhaust gas from which acidic components have been removed The combustion exhaust gas used was a mixture of the combustion exhaust gas before the removal of acidic components used in Example 1 and the combustion exhaust gas after the removal of acidic components using a wet scrubber used in Example 2, in a volume ratio of 6:4. The concentrations of each component in this mixed gas were CO2 = 10 vol%, HF = 19 vol ppm, HCl = 354 vol ppm, and SO2 = 190 vol ppm. Expressed as molar ratios relative to CO2, the HF / CO2 molar ratio was 0.00019, the HCl / CO2 molar ratio was 0.00354, and the SO2 / CO2 molar ratio was 0.00190. Sodium bicarbonate powder was produced in the same manner as in Example 1, except that the combustion exhaust gas from which the acidic components had been removed was used. 211 minutes after the start of supplying the combustion exhaust gas from which the acidic components had been removed, and after supplying 845 L, the crystallization tank contained a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. The content of components derived from the acidic components in the combustion exhaust gas added to the sodium bicarbonate slurry at this time was F=5.3 ppm, Cl=185 ppm, SO4 2- The result was 268 ppm. In the same manner as in Example 1, this sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying equipment 31 to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The content of components derived from acidic components in the combustion exhaust gas in the obtained sodium bicarbonate powder was F=5.0 ppm, Cl=174 ppm, SO4 2- A sodium bicarbonate powder with a low concentration of 287 ppm was obtained, which is higher purity than that obtained in Example 1.

[0051] (Example 5) Production of sodium bicarbonate from combustion exhaust gas from which acidic components have been removed In Example 4, the sodium bicarbonate slurry was filtered using a centrifugal dehydrator, but instead, it was filtered using a filter press, resulting in 550 g of dehydrated cake and 2016 g of filtrate 29. The dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying apparatus 31, yielding 440 g of sodium bicarbonate powder. The solid content concentration in the dehydrated cake was calculated to be 80%. The content of components derived from acidic components in the combustion exhaust gas in the obtained sodium bicarbonate powder was F=3.2 ppm, Cl=115 ppm, SO4 2- The result was 99 ppm, yielding a higher purity sodium bicarbonate powder than in Example 4.

[0052] (Example 6) Production of sodium bicarbonate from combustion exhaust gas from which acidic components have been removed In the dry method apparatus shown in Figure 2, sodium bicarbonate powder was used as the alkaline neutralizing agent powder 13 to remove the acidic components from the combustion exhaust gas of Example 1. After the removal of the acidic components, the concentrations of each component were CO2 = 10 vol%, HF = 1.6 vol ppm, HCl = 29 vol ppm, and SO2 = 16 vol ppm. Expressed as molar ratios relative to CO2, the HF / CO2 molar ratio was 0.00002, the HCl / CO2 molar ratio was 0.00030, and the SO2 / CO2 molar ratio was 0.00016. Sodium bicarbonate powder was produced in the same manner as in Example 1, except that the combustion exhaust gas from which the acidic components had been removed was used. 211 minutes after the start of supplying the combustion exhaust gas from which the acidic components had been removed, and after supplying 845 L, the crystallization tank contained a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. The content of components derived from the acidic components in the combustion exhaust gas added to the sodium bicarbonate slurry at this time was F=0.4 ppm, Cl=15 ppm, SO4 2- The concentration was 22 ppm. In the same manner as in Example 1, this sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying equipment 31 to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The content of components derived from acidic components in the combustion exhaust gas in the obtained sodium bicarbonate powder was F=0.6 ppm, Cl=13 ppm, SO4 2- A very low concentration of 31 ppm was obtained, resulting in a high-purity sodium bicarbonate powder.

[0053] [Table 1]

[0054] (Example 7) Production of potassium bicarbonate Potassium bicarbonate powder was produced from combustion exhaust gas containing acidic components and CO2 using the apparatus shown in Figure 3. The specific procedure was as follows: Acidic components were removed from the combustion exhaust gas of Example 1 using the wet scrubber shown in Figure 1. The combustion exhaust gas of Example 1 was supplied through the combustion exhaust gas introduction pipe 8. A sodium bicarbonate aqueous solution was used as the circulating fluid. After the removal of the acidic components, the concentrations of each component were CO2 = 10 vol%, HF = 2.0 vol ppm, HCl = 37 vol ppm, and SO2 = 20 vol ppm. Expressed as molar ratios to CO2, the HF / CO2 molar ratio was 0.00002, the HCl / CO2 molar ratio was 0.00037, and the SO2 / CO2 molar ratio was 0.00020. In a crystallization tank 20 with an internal volume of 5 L, 635 g of potassium carbonate powder and 1217 g of deionized water were placed and stirred with a stirring device 21 to obtain 1852 g of a 34.3% potassium carbonate aqueous solution. This aqueous solution was circulated at a flow rate of 20 L / min through a circulation pipe 25 using a circulation pump 23. A YJ nozzle 24 was installed in the circulation pipe. The YJ nozzle used was a YJ-6 inline type (product name). Immediately after starting circulation, combustion exhaust gas of the above composition was supplied to the YJ nozzle 24 at a rate of 4 L / min in the form of fine bubbles. The temperature of the aqueous solution when carbon dioxide was introduced was 25-35°C. 258 minutes after starting to supply combustion exhaust gas, after supplying 1031 L, the inside of the crystallization tank became a cloudy potassium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. The content of components derived from acidic components in the combustion exhaust gas added to the potassium bicarbonate slurry at this time was F=0.9 ppm, Cl=29 ppm, SO4 2- The concentration was 43 ppm. The potassium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1174 g of filtrate 29. The centrifugal dehydrator 28 used was an H-110F model manufactured by Kokusan Co., Ltd. The centrifugal dehydrated cake was dried in a drying facility 31 under a carbon dioxide atmosphere at 80°C to obtain 440 g of potassium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The content of components derived from acidic components in the combustion exhaust gas in the obtained potassium bicarbonate powder was F=1.1 ppm, Cl=26 ppm, SO4 2- The concentration was 57 ppm.

[0055] [Table 2] [Explanation of Symbols]

[0056] 1 Scrubber 2 Tower 3 Circulating fluid storage tank 4 Filling 5 Circulating fluid 6. Circulating fluid pump 7. Spray nozzle 8, 10 Combustion exhaust gas introduction piping 9, 15 Combustion exhaust gas outlet piping 11 Economizer 12 Economizer outlet piping 13. Powdered alkaline neutralizing agent 14 Dust collector 20 Crystallization tank 21. Stirring device 22 Liquid in the crystallization tank 23 Circulation pump 24 YJ nozzles 25 Circulation piping 26. Supply piping for gas containing CO2 27 Supply piping 28 Filter 29 Filtrate 30 Feeding pipe for dehydrated alkali metal bicarbonate cake 31 Drying equipment 32. Alkali metal bicarbonate powder 40 Flash Jet Dryer 41 Hot air 42. Alkali metal bicarbonate cake 43 Cyclone 44 Collection containers

Claims

1. HF, HCl, and SO ２ At least one acidic component selected from the group consisting of and CO ２ The combustion exhaust gas containing the above is subjected to a preliminary treatment to remove at least a portion of the acidic components, thereby obtaining the preliminary treated exhaust gas. A contact treatment is performed on the pre-treated exhaust gas by contacting it with an aqueous solution (a) containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates to obtain an alkali metal bicarbonate. A method for producing alkali metal bicarbonates, including the following.

2. In the pre-treated exhaust gas, the molar ratio of HF to CO ２ is 0.00023 or less, the molar ratio of HCl to CO ２ is 0.00406 or less, and the molar ratio of SO ２ to CO ２ is 0.00220 or less, the method for producing an alkali metal hydrogen carbonate according to claim 1. ２ The CO of ２ The molar ratio of SO to CO ２ / CO ２ is 0.00220 or less.

3. In the slurry obtained by the above contact treatment, the fluorine concentration is 6.4 ppm or less and the chlorine concentration is 212 ppm or less, based on the total mass of the slurry. ４ ２－ A method for producing an alkali metal bicarbonate according to claim 1 or 2, wherein the concentration is 311 ppm or less.

4. In the alkali metal bicarbonate obtained by the above contact treatment, the fluorine concentration is 6.0 ppm or less and the chlorine concentration is 200 ppm or less, based on the total mass of the alkali metal bicarbonate, and SO ４ ２－ A method for producing an alkali metal bicarbonate according to claim 1 or 2, wherein the concentration is 330 ppm or less.

5. A method for producing an alkali metal bicarbonate according to claim 1 or 2, wherein the pretreatment is carried out by a wet method using an aqueous solution (b) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates, or by a dry method using powder of alkali metal bicarbonate.

6. A method for producing an alkali metal bicarbonate according to claim 1 or 2, wherein the preliminary treatment is performed using the alkali metal bicarbonate obtained by the contact treatment.

7. A method for producing an alkali metal bicarbonate according to claim 1 or 2, wherein the pre-treated exhaust gas is converted into fine bubbles, and then the contact treatment is performed.

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