KR102217897B1 - Wet Flue Gas Desulfurization Equipment - Google Patents

Abstract

Disclosed is a wet flue gas desulfurization device comprising a gas cooling and water evaporation tower (hereinafter, referred to as a ″water evaporation tower″), and an absorption tower. In the wet flue gas desulfurization device according to the present invention, an exhaust gas containing a sulfurous acid gas flows into an exhaust gas inlet unit of the water evaporation tower, is cooled, and then is discharged to the upper part of the water evaporation tower. An exhaust gas discharged to the upper part of the water evaporation tower flows into an exhaust gas inlet unit of the absorption tower and then is discharged to the upper part of the absorption tower, and at this time, desulfurization is performed. A part of a circulating absorption liquid of the absorption tower is introduced into the water evaporation tower and is sprayed downward to the exhaust gas flowing upward from the water evaporation tower to cool the exhaust gas, and is converted into a concentrated liquid having a concentration of sulfate higher than that of a circulating absorption liquid flowing into the water evaporation tower as water in the circulating absorption liquid is evaporated. The concentrated liquid is partially discharged from the water evaporation tower. The wet flue gas desulfurization device according to the present invention can be stably operated without a scrubber closure due to the precipitation of MgSO_3 compounds during a wet flue gas desulfurization process. A sulphate, which is a by-product generated during the wet flue gas desulfurization process, is concentrated to have a commercially usable high concentration by using the heat of an exhaust gas without using a separate heat source. Wastewater does not have to be discharged, or a wastewater amount can be reduced even when wastewater is discharged.

Description

Wet Flue Gas Desulfurization Equipment

The present invention relates to a wet flue gas desulfurization device, and more particularly, concentrates the sulfate salt, which is a by-product generated in the wet flue gas desulfurization device, to a high concentration that is commercially available using the heat of exhaust gas without using a separate heat source By doing so, it is not necessary to discharge wastewater or even if it is discharged as wastewater, it relates to a wet flue gas desulfurization apparatus capable of reducing the amount of wastewater.

The flue gas desulfurization system absorbs sulfur components such as sulfurous acid gas (SO ₂ ) contained in the exhaust gas that is emitted when burning fuel containing sulfur components such as coal or bunker C oil in boilers or melting furnaces at industrial sites. It is a device that removes it. The emission of sulfurous acid gas is strictly regulated under the Environmental Conservation Act.

Among the methods of removing sulfurous acid gas from exhaust gas, a method of removing sulfur components by dry spraying and contacting powders such as slaked lime or activated carbon, which are neutralizing agents to the exhaust gas during the exhaust gas discharge process, is called the dry desulfurization method, and caustic soda, magnesium hydroxide or A method of removing sulfur components by using an aqueous slurry of limestone as a neutralizing agent and spraying an absorbent liquid into contact with exhaust gas is called a wet desulfurization method.

In general, a wet desulfurization apparatus is configured as shown in FIG. 1. The wet desulfurization device injects sulfur-containing exhaust gas discharged from the combustion device 1 into the lower part of the absorption tower 7 through the exhaust gas inlet device 11, and sprays the absorbent liquid 12 from the upper part of the absorption tower. By making it contact at (9), the sulfur component reacts with the absorbent liquid and is absorbed into the absorbent liquid. This absorbent liquid is converted into an acidic component and falls to the bottom of the tower, and the lower absorbent liquid is neutralized with a neutralizing agent so that only the exhaust gas 10 from which the sulfur component has been removed is discharged from the top of the tower. Here, the absorbent layer 9 may use a filler such as a Rasching Ring, and various types of equipment such as a Sieve tray or an empty tower shape are used.

As shown in FIG. 1, the conventional wet absorption tower has a structure in which washing water is sprayed onto a single tower and onto a multistage or single layer of packing material. Process water or scrubber circulating water is injected through the cooling water injection nozzle of the exhaust gas intake device 11 in order to prevent thermal deformation of the internal structure of the scrubber by the high temperature exhaust gas. The high-temperature exhaust gas is cooled by evaporation of the cooling water injected from the exhaust gas inlet 11 and passes through the desulfurization zone. The water remaining after evaporation used for cooling is combined with the circulating water at the bottom of the existing scrubber. When the scrubber circulating water is used as cooling water, there have been cases in which salt lumps are formed by splashing on the wall surface of the exhaust gas inlet device 11 and drying.

Chemicals used to collect sulfurous acid gas in a wet scrubber include caustic soda (NaOH), sodium carbonate (Na ₂ CO ₃ ), and magnesium hydroxide [Mg(OH) ₂ ]). The salt concentration is operated within 3 ~ 10% to prevent the scrubber from being closed due to it. In particular, in the case of magnesium hydroxide, which is the cheapest desulfurization agent, the solubility of magnesium sulfite (MgSO ₃ ), an intermediate product during the desulfurization process, is only a maximum of 10 g/ℓ at 40°C as shown in FIG. 2 (Source: Encyclopidia of Chemical Engineering) It is so low that it has a limit to operating a high salt concentration. Therefore, if the salt concentration in the circulating water is high, it has the advantage of reducing the amount of wastewater generated even if the wastewater cannot be reused, but for stable operation, the concentration of MgSO ₄ in the scrubber circulating water is maintained at 3-6%. .

Exhaust gas discharged from the combustion process passes through a heat recovery device at the front end, and is usually introduced into the scrubber in the range of 100 to 200°C. In the wet scrubber, water sprayed by the amount of heat held by the gas flowing into the scrubber evaporates, and the temperature of the gas decreases due to the latent heat of evaporation. The operating temperature of the scrubber is determined according to the temperature of the inlet gas and the concentration of water retained, and is operated in the range of 40 ~ 75℃. For example, when the exhaust gas 13,000N㎥ with a moisture content of 9.1% at 180℃ passes through a scrubber operated at a general salt concentration, about 950Kg of water evaporates and the temperature decreases to 57℃.

The final product of the desulfurization process, such as magnesium sulfate or sodium sulfate, is a compound that is easily concentrated enough to have a value of 25% or more at a scrubber operating temperature of 40° C. or higher, as shown in FIG. 3.

In order to use magnesium sulfate as a by-product in the flue gas desulfurization process for commercial use, it is necessary to concentrate it to a concentration of at least 10%. Considering the transportation cost, it must be concentrated to at least 15% for economical use. This means that it is necessary to maintain the Mg ion concentration three times higher than the MgSO ₄ concentration of 3-6% of the general desulfurization process. In some processes, the operation of maintaining the MgSO ₄ concentration above 7% was performed for the purpose of reducing the amount of wastewater generated, but the scrubber closure phenomenon due to the formation of MgSO ₃ compound crystals or the SO low enough to not generate MgSO ₃ compounds. _{3 Because} of the limitations such as lowering the desulfurization efficiency due to the ion concentration, it was not possible to operate at all times.

Patent Registration No. 10-0421463 (registered on February 23, 2004)

Accordingly, it is an object of the present invention to perform stable operation without a scrubber closing phenomenon due to precipitation of MgSO ₃ compounds during the wet flue gas desulfurization process, and to exhaust sulfate, which is a by-product during the wet flue gas desulfurization process, without using a separate heat source. It is to provide a wet flue gas desulfurization apparatus capable of reducing the amount of wastewater even if it is not required to discharge wastewater by concentrating it to a high concentration that is commercially available using the heat of gas.

The wet flue gas desulfurization apparatus according to the present invention for achieving the above object includes a gas cooling and moisture evaporation tower (hereinafter, referred to as a “water evaporation tower” ) and an absorption tower.

In the wet flue gas desulfurization apparatus of the present invention, the exhaust gas including sulfurous acid gas generated by combustion of a fuel containing a sulfur component by a combustion device is introduced into the exhaust gas inlet of the moisture evaporation tower and cooled, and then the moisture evaporation tower Is discharged to the top of.

The exhaust gas discharged to the top of the moisture evaporation tower is introduced into the exhaust gas inlet of the absorption tower and then discharged to the top of the absorption tower. At this time, the circulating absorbent liquid is sprayed downward to the exhaust gas flowing upward so that the sulfurous acid gas contained in the exhaust gas is absorbed by the circulating absorbent liquid, and is neutralized by a neutralizing agent at the bottom of the absorption tower to convert to sulfate and sulfite, thereby absorbing the The concentration of the sulfurous acid gas contained in the exhaust gas in the tower is lowered. That is, desulfurization is performed.

A portion of the circulating absorbent liquid of the absorption tower is introduced into the moisture evaporation tower and sprayed downward on the exhaust gas flowing upward from the moisture evaporation tower to cool the exhaust gas, and the moisture in the circulating absorbent liquid is evaporated, resulting in the concentration of sulfate. Is converted into a concentrate higher than the circulating absorption liquid flowing into the moisture evaporation tower, and the concentrate is partially discharged from the moisture evaporation tower.

An oxidizing air supply device is installed in the moisture evaporation tower, and an air diffuser is disposed at the bottom of the moisture evaporation tower, so that oxidizing air is aerated in the concentrate to oxidize sulfite ions contained in the concentrate to oxidize bisulfate ions (HSO It is switched ^to) _4.

It is preferable that the pH of the concentrate is 3 or less.

An oxidizing air supply device is installed in the absorption tower, and an air diffuser is disposed at the bottom of the absorption tower, so that the oxidizing air is aerated in the circulating absorption liquid, and sulfite ions contained in the circulating absorption liquid are oxidized to oxidize bisulfate ions (HSO It is switched ^to) _4.

It is preferable that the concentration of SO ₃ ions in the circulating absorption liquid of the absorption tower is 4 to 8 g/ℓ, and the pH is 5 to 6.

The neutralizing agent is Mg(OH) ₂ , the concentration of MgSO ₄ in the circulating absorption liquid of the absorption tower is 3 to 6%, and the concentration of MgSO ₄ in the concentrate discharged from the moisture evaporation tower is preferably 10% or more.

The temperature of the exhaust gas flowing into the moisture evaporation tower may range from 100 to 200 °C, and the operation temperature of the absorption tower may range from 40 to 75 °C.

The wet flue gas desulfurization apparatus according to the present invention enables stable operation without a scrubber closure phenomenon due to precipitation of MgSO ₃ compounds during the wet flue gas desulfurization process, and does not use a separate heat source for sulfate, a by-product generated during the wet flue gas desulfurization process. It is not necessary to discharge wastewater by concentrating it to a high concentration that is commercially available using the heat of the exhaust gas, or even if it is discharged as wastewater, the amount of wastewater can be reduced.

1 is a view schematically showing a wet absorption tower of a conventional wet flue gas desulfurization apparatus.
2 is a graph showing the solubility of MgSO ₃ according to temperature.
3 is a graph showing the solubility of MgSO ₄ and Na ₂ SO ₄ according to temperature.
4 is a view showing a schematic configuration of a wet flue gas desulfurization apparatus according to an embodiment of the present invention.
5 shows the results of a thermal stability test of hydrotalcite prepared using a high-concentration MgSO ₄ compound, a by-product obtained by a flue gas desulfurization process of a wet flue gas desulfurization apparatus according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.

The wet flue gas desulfurization apparatus according to the present invention includes a gas cooling and moisture evaporation tower (hereinafter referred to as'water evaporation tower' ) 2 and an absorption tower 7, as shown in FIG. 4.

The exhaust gas 3 flows into the moisture evaporation tower 2. At this time, the exhaust gas 3 includes sulfurous acid (SO ₂ ) gas generated by combustion of a fuel containing a sulfur component by the combustion device 1. Typically, the inflowing exhaust gas 3 is at a high temperature of about 100 to 200°C, and the operation temperature of the absorption tower is 40 to 75°C. The exhaust gas 3 is introduced through the exhaust gas inlet device 11 provided at the exhaust gas inlet of the moisture evaporation tower 2. The exhaust gas inlet portion is disposed at a position higher than the circulating concentrated liquid collecting portion in the bottom portion of the moisture evaporation tower 2. The exhaust gas 3 is cooled by spraying of the circulating concentrated liquid in the exhaust gas inlet device 11 and the moisture evaporation tower 2 and then discharged to the upper portion of the moisture evaporation tower 2. The circulating concentrate will be described in more detail below.

The exhaust gas discharged to the top of the moisture evaporation tower 2 is introduced into the exhaust gas inlet of the absorption tower 7. The exhaust gas inlet portion is disposed at a position higher than the circulating absorbent liquid collecting portion in the bottom portion of the absorption tower 7. Exhaust gas flowing into the absorption tower 7 is discharged to the top as exhaust gas 10. At this time, the circulating absorbent liquid 12 is sprayed downward to the exhaust gas flowing upward so that sulfurous acid gas contained in the exhaust gas is absorbed by the circulating absorbent liquid. When sulfurous acid gas is absorbed in the circulating absorbent, it is acidified. This circulating absorbent falls down and is neutralized by a neutralizing agent in the circulating absorbent collection unit, thereby converting to sulfite and oxidized to convert to sulfate. Accordingly, the concentration of sulfurous acid gas contained in the exhaust gas in the absorption tower 7 is lowered. That is, desulfurization is performed.

In order to implement the above-described desulfurization in the absorption tower 7, a neutralizing agent aqueous solution in which the neutralizing agent 5 is dissolved in water is supplied to the circulating absorbent liquid collection unit provided at the bottom of the absorption tower 7. As a neutralizing agent, NaOH, Mg(OH) ₂ , NH ₄ OH, Na ₂ CO ₃ and the like may be used. The neutralizing agent aqueous solution supplied to the circulating absorbent liquid collecting unit is supplied to the spray nozzle 8 installed at a higher position than the exhaust gas inlet, sprayed, and then collected again by the circulating absorbent liquid collecting unit. Therefore, the neutralizing agent aqueous solution circulated in this way may be referred to as the circulating absorption liquid 12. The neutralizing agent aqueous solution is stored in the chemical storage tank 6 in which the neutralizing agent 5 and water are mixed, and then supplied to the absorption tower 7, the supply amount and supply method can be determined according to application to a general wet flue gas desulfurization process. . The absorption layer 9 may be installed on the absorption tower 7 to better absorb sulfurous acid gas from the exhaust gas. The operating temperature of the absorption tower 7 is generally set to the temperature of the circulating absorbent liquid 12 collected in the circulating absorbent liquid collecting unit, and this generally matches the temperature of the exhaust gas 10. The operation temperature of the absorption tower 7 is generally maintained at about 40 to 75°C.

On the other hand, it is known that the concentration of SO ₃ ions (SO ₃ ^2- ions and HSO ₃ ^- ions) absorbed and dissolved in the circulating absorption liquid 12 in the absorption tower 7 plays an important role in determining the flue gas desulfurization performance. have. In general, the scrubber circulating water after normal desulfurization, i.e., circulation absorbent 12, maintains a salt concentration of about 5% based on MgSO ₄ and a concentration of SO ₃ ions of 4 to 8 g/ℓ (0.05 to 0.1 mol/ℓ). do. In addition, it may contain hundreds to thousands of mg/ℓ of suspended matter depending on the type of drug used as a neutralizer. If necessary to maintain the concentration of the circulating absorbent liquid 12 as described above, the process water 4 may be additionally supplied from the upper portion of the absorption tower 7.

In order to properly maintain the salt concentration in the circulating absorbent liquid 12 as described above, an oxidizing air supply device 13 is installed in the absorption tower 7, and a diffuser 14 is provided at the bottom of the absorption tower 7 It is placed. When the diffuser 14 to the air oxidation by aeration in the circulating absorption liquid sulfite ions contained in the circulating absorption liquid is oxidized bisulfate ion (HSO ₄ ^-) is converted to. Therefore, for example, the scrubber clogging phenomenon does not occur due to crystal precipitation due to excessive formation of the MgSO ₃ compound. Meanwhile, the aeration operation should be performed so that the above-described SO ₃ ion concentration can be maintained.

On the other hand, if necessary, the absorption tower 7 may be provided with a head monitoring device 15 for monitoring the height of the circulating absorbent liquid, and in order to prevent the height of the circulating absorbent liquid from being excessively increased, the circulating absorbent liquid overflow device 17 is provided. Can be provided.

Part of the circulating absorbent liquid 12 of the absorption tower 7 flows into the moisture evaporation tower 2 and is sprayed downward on the exhaust gas 3 flowing upward from the moisture evaporation tower 2. To this end, a spray nozzle 8 is installed in the moisture evaporation tower 2 at a higher position than the exhaust gas inlet device 11. At this time, it may be sprayed into the exhaust gas inlet device 11 as well. When the absorbed liquid introduced in this way is sprayed onto the exhaust gas 3 in the moisture evaporation tower 2, the exhaust gas 3 is cooled and moisture is evaporated from the absorbed liquid introduced. Therefore, the absorbent liquid circulating in the moisture evaporation tower (2) is converted to a concentrated liquid that is higher than the circulating absorbent liquid (12) of the absorption tower (7) before the concentration of sulfate is introduced into the moisture evaporation tower (2). do. Then, the concentrated liquid is partially discharged from the moisture evaporation tower 2 by the operation of the concentrated liquid discharge valve 18. The discharged high-concentration sulfate aqueous solution can be discharged as wastewater through a separate neutralization, precipitation or filtration facility or can be commercially reused.

The moisture evaporation tower 2 converts the low concentration of the circulating absorbent liquid 12 for sulfate into a high concentration concentrated liquid circulating in the absorption tower 7 by cooling the exhaust gas and evaporating moisture without absorption of sulfurous acid gas. The purpose. That is, in the moisture evaporation tower 2, only the cooling and moisture evaporation of the exhaust gas 3 must occur, and it is necessary to be adjusted so that the sulfur dioxide gas is not collected. When the sulfurous acid gas is collected in the moisture evaporation tower 2, for example, the concentration of the MgSO ₃ compound increases and precipitates as crystals, which is not preferable because the moisture evaporation tower 2 may be closed. In addition, when more than necessary sulfur dioxide is collected in the moisture evaporation tower 2, it is not preferable because the absorption tower 7 cannot secure an appropriate concentration of SO ₃ ions, which may impede the desulfurization efficiency.

In the flue gas desulfurization process, it is a known fact that if the pH is kept acidic or if SO ₃ ions are not present, the sulfur dioxide gas is not collected. Therefore, the present inventors pay attention to the fact that water evaporates by the heat of exhaust gas in a general wet absorption tower (scrubber) and the condition in which sulfur dioxide gas is not collected in the flue gas desulfurization process, By arranging the water evaporation tower (2) in the present invention, it was recognized that it was possible to form a high-concentration sulfate solution using only the heat of the exhaust gas without using a separate heat source.

In order to prevent the sulfurous acid gas from being collected in the moisture evaporation tower 2, an oxidizing air supply device 13 is installed in the moisture evaporation tower 2. Further, a diffuser 14 is disposed at the bottom of the moisture evaporation tower 2. When the diffuser 14 to the air oxidation by aeration to concentrate sulfite ions contained in the concentrate is oxidized bisulfate ion (HSO ₄ ^-) it is converted to. At this time, the pH of the concentrate is maintained at 3 or less. Therefore, in the present invention, the concentrated liquid circulating in the moisture evaporation tower 2 does not contain sulfite ions substantially and has an acidity of pH 3 or less, so that the moisture evaporation tower does not collect sulfurous acid gas and is caused by salt precipitation. The closing phenomenon of (2) does not occur.

Weak acid of bisulfite (HSO ₃ ^-) ions are oxidative strong acid a bisulfate (HSO ₄ ^-) is discarded if the ion has a pH of it is previously known to be rapidly decreased (Japanese Patent Application Laid-Open No. 7-136453, 1995. 5. 30 . open). If a separate neutralizing agent is not supplied to the moisture evaporation tower 2, most of the sulfur dioxide gas cannot be collected due to the acidic pH and flows into the desulfurization section, that is, the absorption tower 7.

In the present invention, when Mg(OH) ₂ is used as the neutralizing agent, the concentration of MgSO ₄ in the circulating absorption liquid 12 of the absorption tower 7 is 1 to 8%, preferably 3 to 6%, The concentration of MgSO ₄ in the concentrate discharged from the moisture evaporation tower 2 through the concentrate discharge valve 18 may be in the range of 10% to 20%, particularly 15% or more. That is, in the present invention, it is possible to discharge a high concentration sulfate aqueous solution of 15% or more while stably performing the desulfurization process. This means that compared to the conventional flue gas desulfurization process, the amount of wastewater generated can be reduced to 1/3 or less, and the present invention can utilize such a high-concentration sulfate aqueous solution as an industrial raw material for the production of other products instead of discharging it as wastewater. There is an advantage.

Hereinafter, the present invention will be specifically illustrated through examples. However, since the following examples are only examples of the present invention, it should not be understood that the scope of the present invention is limited by the following examples.

<Example 1> Scrubber operation

The water evaporation tower (2) has a tower diameter of 2.5 m, water injection volume of 100㎥/Hr, and a packing material thickness of 20cm to treat exhaust gas with gas volume 24,000N㎥/Hr, moisture content 1.9%, SO ₂ 1,040ppm, temperature 132℃. It was installed in the form of a scrubber. The absorption tower 7 was installed with a scrubber having a tower diameter of 3m, a water injection amount of 250㎥/Hr, and a packing material thickness of 50cm. For other chemical supply facilities and aeration facilities, the standard of the general flue gas desulfurization process was applied.

The operation conditions of the absorption tower 7 were operated at pH 5.7, Mg ion concentration 0.4 mol/ℓ (MgSO ₄ equivalent concentration about 4.8%) SO ₃ ion concentration 6.5 g/ℓ, and absorption tower 7 operating temperature was 45°C. , The concentration of sulfurous acid gas discharged was 33 ppm. At this time, the input process water was 2.5㎥ per hour, and 30% Mg(OH) ₂ 192 Kg was used for chemicals. The discharged desulfurization wastewater was 2.7㎥ per hour. This wastewater was continuously introduced into the moisture evaporation tower (2), and the discharged water discharged from the moisture evaporation tower (2) was 0.8㎥ per hour, and the concentration in terms of MgSO ₄ was 15.5%. 20 Kg of 30% Mg(OH) ₂ per hour was used to neutralize the acidic MgSO ₄ concentrated water.

<Example 2> Preparation of magnesium carbonate using magnesium sulfate

893 g of a 15.3% magnesium sulfate solution obtained by filtering the magnesium sulfate produced in Example 1 was placed in a 2 liter beaker, adjusted to 40° C., and 787 g of a 15% solution of sodium carbonate (Na ₂ CO ₃ ) was slowly added for 30 minutes while stirring. When the resulting MgCO ₃ precipitate is heated at 90 to 95°C for 4 hours while stirring, 4MgCO ₃ ·Mg(OH) ₂ ·4H ₂ O is obtained. The precipitate was filtered, washed, and dried to obtain 997 g of basic magnesium carbonate. The produced product has the following characteristics.

standard Existing imports Examples of the present invention MgO 41% or more 41.76 42.97 CaO 0.45% or less 0.35 0.35 SiO ₂ 0.1% or less 0.06 0.06

<Example 3> Preparation of hydrotalcite using magnesium sulfate

455 g of 15.3% magnesium sulfate produced in Example 1 was placed in a 2 L beaker and stirred. Separately, 232 g of aluminum hydroxide (62% of Al ₂ O ₃₎ and 82 g of 50% NaOH are added and heated to make 370 g by adding water when all the aluminum hydroxide is dissolved, and then slowly added to a beaker containing magnesium sulfate solution over about 30 minutes. . Thereafter, 132 g of a 15% Na ₂ CO ₃ solution was added and stirred well, and then transferred to a high-temperature high-pressure reactor and reacted at a pressure of 165° C. 6-7 Kg/cm 2 for 4 hours. After cooling, the reaction product was filtered, washed, and dried to obtain 48 g of hydrotalcite (Mg ₄ Al ₂ CO ₃ (OH) ₁₂ · 4H ₂ O).

Hydrotalcite is a product used as a thermal stabilizer such as PVC, and the results of the thermal stability test of the hydrotalcite manufactured by the method of Examples were similar to those of the existing products.

1: Combustion device 2: Gas cooling and water evaporation tower
3: exhaust gas 4: process water
5: neutralizing agent 6: storage tank
7: absorption tower 8: spray nozzle
9: absorption layer 10: exhaust gas
11: exhaust gas inlet device 12: circulating absorbent liquid
13: oxidizing air supply device 14: diffuser
15: head detection device 16: control valve for discharging circulating absorbent liquid
17: circulating absorbent liquid overflow device 18: concentrated liquid discharge valve

Claims (7)

It is a wet flue gas desulfurization device including a gas cooling and moisture evaporation tower (hereinafter referred to as a'water evaporation tower' ) and an absorption tower,
Exhaust gas including sulfurous acid gas generated by combustion of the fuel containing sulfur component by the combustion device is introduced into the exhaust gas inlet of the moisture evaporation tower, cooled, and then discharged to the top of the moisture evaporation tower,
The exhaust gas discharged to the top of the moisture evaporation tower flows into the exhaust gas inlet of the absorption tower and is discharged to the top of the absorption tower. At this time, the circulating absorption liquid is sprayed downward on the exhaust gas flowing upward to the exhaust gas. The sulfurous acid gas contained in the gas is absorbed by the circulating absorption liquid, neutralized by a neutralizing agent at the bottom of the absorption tower, and converted into sulfate and sulfite, thereby lowering the concentration of the sulfurous acid gas contained in the exhaust gas in the absorption tower. , That is, desulfurization takes place,
A portion of the circulating absorbent liquid of the absorption tower is introduced into the moisture evaporation tower and sprayed downward on the exhaust gas flowing upward from the moisture evaporation tower to cool the exhaust gas, and the moisture in the circulating absorbent liquid is evaporated, resulting in the concentration of sulfate. Is converted into a concentrate higher than the circulating absorbent liquid flowing into the moisture evaporation tower, and the concentrate is partially discharged from the moisture evaporation tower,
An oxidizing air supply device is installed in the moisture evaporation tower, and an air diffuser is disposed at the bottom of the moisture evaporation tower, so that oxidizing air is aerated in the concentrate to oxidize sulfite ions contained in the concentrate to oxidize bisulfate ions (HSO ₄ ^- converts to ),
The pH of the concentrate is 3 or less, and the concentrate circulated in the moisture evaporation tower does not contain sulfite ions and does not collect sulfurous acid gas in the exhaust gas,
An oxidizing air supply device is installed in the absorption tower, and an air diffuser is disposed at the bottom of the absorption tower, so that the oxidizing air is aerated in the circulating absorption liquid, and sulfite ions contained in the circulating absorption liquid are oxidized to oxidize bisulfate ions (HSO ₄ ^- converts to ),
SO ₃ ion concentration in the circulating absorption liquid of the absorption tower is 4 to 8 g/ℓ, pH is 5 to 6,
The neutralizing agent is Mg(OH) ₂ , the concentration of MgSO ₄ in the circulating absorption liquid of the absorption tower is 3 to 6%, and the concentration of MgSO ₄ in the concentrate discharged from the moisture evaporation tower is 10% or more. Flue gas desulfurization device. delete delete delete delete delete The method of claim 1,
A wet flue gas desulfurization apparatus, characterized in that the temperature of the exhaust gas flowing into the moisture evaporation tower is in the range of 100 to 200 °C, and the operating temperature of the absorption tower is in the range of 40 to 75 °C.

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