JP7065161B2 - Desulfurization method and desulfurization equipment - Google Patents

Description

The present invention relates to a jet bubbling type desulfurization method and a desulfurization apparatus.

Combustion exhaust gas emitted from coal-fired furnaces and coal-fired power plants contains sulfur oxides (SOx), and these sulfur oxides are removed by desulfurization equipment. Jet bubbling method and spray method are known as desulfurization devices that remove sulfur oxides from combustion exhaust gas containing sulfur oxides, but jet bubbling type desulfurization devices are widely used because they have excellent desulfurization performance. Has been done. The jet bubbling type desulfurization device removes sulfur oxides by bubbling exhaust gas containing sulfur oxides into an alkaline agent-containing liquid in a reaction vessel and reacting the sulfur oxides with oxygen and an alkaline agent. be.

In the jet bubbling type desulfurization device, the gypsum produced by the reaction is accumulated in the reaction tank, so that the slurry containing the produced gypsum is extracted from the reaction tank. Then, the extracted slurry is solid-liquid separated, and gypsum, which is a solid content, is recovered. On the other hand, at least a part of the recovered residual liquid after the gypsum is recovered by solid-liquid separation is discharged from the desulfurization apparatus.
Here, the liquid contained in the slurry extracted from the reaction vessel contains an oxidizing substance and hexavalent selenium (Se ⁶⁺ ) because it has a high oxidizing atmosphere and a high pH. Oxidizing substances cause deterioration of wastewater treatment equipment, and hexavalent selenium is regulated in various countries around the world. Therefore, wastewater treatment is performed by a wastewater treatment device to remove oxidizing substances and hexavalent selenium. However, since the installation cost of the wastewater treatment device and the treatment time are required, it is desired to reduce the oxidizing substances and hexavalent selenium, and the atmosphere in the system is changed from a high oxidizing atmosphere to a low oxidizing atmosphere (reducing atmosphere). Many attempts have been made to bring it to a near state.

For example, in the jet bubbling type wet desulfurization apparatus described in Patent Document 1, a partition wall is provided in the reaction vessel to provide a complete oxidation region in which sufficient oxygen is supplied and an incomplete oxidation region in which sufficient oxygen is not supplied. The reaction tank is partitioned into. According to the desulfurization apparatus according to Patent Document 1, a high desulfurization rate is ensured in the complete oxidation region, and an oxidative substance is reduced in the incomplete oxidation region.
However, in the desulfurization apparatus of Patent Document 1, a partition wall that divides the reaction tank into a complete oxidation region and an incomplete oxidation region, an oxygen supply means capable of supplying different amounts of oxygen to each region, and a stirrer provided in each region. It is necessary to provide many additional members inside the reaction vessel. In addition, the mechanism of the reaction tank in which these additional members are provided is complicated.

On the other hand, in the jet bubbling type wet desulfurization apparatus described in Patent Document 2, the slurry having a high oxidizing atmosphere once extracted from the reaction vessel is reduced by coming into contact with the combustion exhaust gas containing sulfur oxides, resulting in a low oxidizing atmosphere. After that, it is taken out from the reaction tank again and discharged / recovered to the outside of the device. That is, the slurry extracted from the reaction vessel again is reduced to a lower oxidizing atmosphere than when it was first extracted from the reaction vessel by coming into contact with the combustion exhaust gas containing sulfur oxides. Therefore, according to the desulfurization apparatus according to Patent Document 2, it is possible to suppress the load on the wastewater treatment apparatus and achieve high recovery rate and high purity of the product with a simple configuration.
However, in recent years, wastewater regulations have been tightened more and more, and by making the atmosphere even lower, the production of oxidizing substances and hexavalent selenium is suppressed, and jet bubbling has excellent desulfurization performance and is a simple configuration. A method of desulfurization method and desulfurization equipment is strongly desired.

Japanese Patent No. 4269379 Japanese Unexamined Patent Publication No. 2015-71141

Therefore, it is an object of the present invention to provide a desulfurization method and a desulfurization apparatus having an excellent desulfurization performance and a simple structure while suppressing the production of oxidizing substances and hexavalent selenium.

In the desulfurization method according to the embodiment of the present invention, a gas to be treated containing a sulfur oxide is introduced into an alkaline agent-containing liquid contained in a reaction vessel, and oxygen is supplied to the alkaline agent-containing liquid. From the contact step of precipitating the product produced by the reaction of the sulfur oxide, the oxygen, and the alkaline agent in the alkaline agent-containing liquid into the alkaline agent-containing liquid, and the first region in the reaction vessel. The slurry is reduced from the first extraction step of extracting the slurry containing the alkaline agent-containing liquid and the precipitated product, and the second region in the reaction vessel or in communication with the reaction vessel. A mixing step of mixing the second extraction step of extracting the produced fluid, the slurry extracted in the first extraction step, and the fluid extracted in the second extraction step, and the mixing thereof. It is characterized by comprising a separation and recovery step of separating and recovering solid content from a mixture of the slurry and the liquid mixed in the step.

Further, the desulfurization apparatus according to another embodiment of the present invention includes a gas to be treated gas introduction path, a gas to be treated gas introduction chamber into which a gas to be treated containing a sulfur oxide is introduced from the gas introduction path to be treated, and the subject to be treated. An alkaline agent-containing liquid chamber provided below the treatment gas introduction chamber and accommodating the alkaline agent-containing liquid in the lower portion thereof, and the treated gas introduced into the treated gas introduction chamber into the alkaline agent-containing liquid chamber. A reaction vessel having a gas descent tube for supplying into the contained alkaline agent-containing liquid, an oxygen supply tube for supplying oxygen to the alkaline agent-containing liquid contained in the alkaline agent-containing liquid chamber, and the above-mentioned Among the products produced by the reaction of the alkaline agent-containing liquid, the sulfur oxide, the oxygen, and the alkaline agent in the alkaline agent-containing liquid from the first region in the alkaline agent-containing liquid chamber, the alkaline agent. A gas capable of reducing the slurry is extracted from a first extraction portion for extracting the slurry containing the precipitates precipitated in the containing liquid and a second region in the reaction vessel or in communication with the reaction vessel. A mixing tank that mixes the extraction portion of 2, the slurry extracted by the first extraction portion, and the fluid extracted by the second extraction portion, and the slurry and the above mixed in the mixing tank. It is characterized by comprising a separation and recovery unit for separating and recovering solid content from a mixture with a fluid.

According to the present invention, it is possible to provide a desulfurization method and a desulfurization apparatus having an excellent desulfurization performance and a simple structure while suppressing the production of an oxidizing substance and hexavalent selenium.

It is a schematic diagram which shows an example of the jet bubbling type desulfurization apparatus which concerns on 1st Embodiment of this invention. It is a graph which shows an example of the relationship of the amount of oxygen with respect to the supply amount of the gas to be processed in a mixing tank. It is a graph which shows an example of the relationship between the amount of oxygen, and the redox potential with respect to the supply amount of the gas to be processed in a mixing tank. It is a schematic diagram which shows an example of the jet bubbling type desulfurization apparatus which concerns on 2nd Embodiment of this invention. It is an enlarged view of the main part of the desulfurization apparatus shown in FIG. (A) It is a schematic cross-sectional view which shows the structure of the desulfurization apparatus which concerns on 2nd Embodiment of this invention. (B) It is a schematic cross-sectional view which shows the structure of the modification of the desulfurization apparatus which concerns on 2nd Embodiment of this invention. It is a graph which shows the relationship of the concentration of an oxidizing substance with respect to the redox potential of an alkaline agent-containing liquid. It is a graph which shows the relationship of the redox potential of a mixing tank with respect to the supply amount of a slurry. It is a schematic diagram which shows an example of the jet bubbling type desulfurization apparatus which concerns on 3rd Embodiment of this invention.

[First Embodiment]
<Desulfurization equipment>
The jet bubbling type desulfurization apparatus according to the first embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a schematic view showing an example of a jet bubbling type desulfurization apparatus according to the first embodiment of the present invention. In the jet bubbling method, the gas to be treated and oxygen are introduced into the alkaline agent-containing liquid contained in the lower part of the reaction vessel, and the gas to be treated and the alkaline agent-containing liquid are brought into gas-liquid contact to form a floss layer. This is a method of reacting these to remove sulfur oxides.

(Sulfur oxide, gas to be treated)
Examples of the sulfur oxide (SOx) in the present invention include sulfur dioxide gas and various forms of sulfur dioxide such as those in which sulfur dioxide gas is dissolved in water. Examples of the gas containing sulfur oxides (gas to be treated) include combustion exhaust gas discharged from a coal-fired furnace and a coal-fired power plant. For example, coal-derived selenium is generally contained in a certain amount in the combustion exhaust gas of coal, and the present invention suppresses the production of selenium-derived hexavalent selenium contained in such a gas to be treated. One of the purposes is to do. Therefore, the gas to be treated in the desulfurization apparatus according to the embodiment of the present invention is not limited to the combustion exhaust gas of coal, for example, the combustion exhaust gas of a fuel other than coal and containing selenium and sulfur oxides. Etc., various exhaust gases may be included in the target.

(Reaction tank)
As shown in FIG. 1, the jet bubbling type desulfurization apparatus 100 has a jet bubbling type reaction tank 11. Although the reaction tank 11 in the first embodiment is cylindrical, the reaction tank 11 is not limited to a cylindrical shape, and may have an arbitrary shape such as a box shape (rectangular parallelepiped shape).
The reaction tank 11 has a gas to be introduced chamber 14, an alkaline agent-containing liquid chamber 16, and a gas to be discharged chamber 17. Further, the reaction tank 11 is provided with a gas to be treated gas introduction path 12 and a gas to be treated gas discharge port 13.

The gas to be introduced passage 12 is provided so as to project near the central portion of the side wall of the reaction tank 11, and the gas to be treated is introduced into the gas to be introduced chamber 14.
The gas to be introduced chamber 14 is provided in the central portion in the vertical direction inside the reaction tank 11, and the gas to be treated containing sulfur oxides is introduced from the gas to be introduced passage 12.
The alkaline agent-containing liquid chamber 16 is provided below the gas introduction chamber 14 to be treated, and has a structure capable of accommodating the alkaline agent-containing liquid 15 in the lower portion.
The gas to be treated gas discharge chamber 17 is provided on the upper side of the gas to be treated gas introduction chamber 14 and communicates with the gas to be treated gas discharge port 13.
The gas to be treated gas discharge port 13 is provided so as to project above the side wall of the reaction tank 11, and the gas to be desulfurized in the alkaline agent-containing liquid chamber 16 is discharged from the gas to be treated gas discharge chamber 17.

The gas to be introduced chamber 14 and the alkaline agent-containing liquid chamber 16 are separated by a first partition wall 18 that crosses the reaction vessel 11. Further, the gas to be treated gas introduction chamber 14 and the gas to be treated gas discharge chamber 17 are separated by a second partition wall 19 that crosses the reaction tank 11.

The first partition wall 18 also serves as the bottom surface of the gas to be introduced chamber 14. The first partition wall 18 is provided with a plurality of gas descent pipes 22 extending downward and reaching below the liquid level 21 of the alkaline agent-containing liquid 15, and the gas descent pipe 22 has a gas to be introduced chamber 14 and an alkaline agent. It communicates with the containing liquid chamber 16. Therefore, the gas to be treated introduced into the gas to be introduced chamber 14 is supplied to the alkaline agent-containing liquid 15 housed in the alkaline agent-containing liquid chamber 16 via the plurality of gas descending pipes 22. A plurality of small openings are provided on the lower side of the gas descending pipe 22, and the gas to be treated ejected from the gas descending pipe 22 is dispersed in the alkaline agent-containing liquid 15.

The second partition wall 19 also serves as the bottom surface of the gas discharge chamber 17 to be processed. The second partition wall 19 is provided with a communication pipe 25 that extends downward and penetrates the horizontal central portion of the gas introduction chamber 14 to reach the alkaline agent-containing liquid chamber 16, and the communication pipe 25 contains an alkaline agent. The liquid chamber 16 and the gas discharge chamber 17 to be processed are communicated with each other. Therefore, the desulfurized gas to be treated in the alkaline agent-containing liquid chamber 16 is discharged from the space 26, which is a space on the liquid surface 21 in the alkaline agent-containing liquid chamber 16, via the communication pipe 25. It reaches 17 and is discharged from the gas discharge port 13 to be processed.
The gas to be discharged chamber 17 and the communication pipe 25 are omitted, a gas discharge port 13 to be treated is provided so as to communicate with the space 26, and the space 26 provides the gas discharge chamber 17 to be treated as shown in FIG. You may also use it.

In the gas to be treated gas introduction path 12, an industrial water supply pipe 32 for spraying the industrial water via the pipe 31 onto the gas to be treated is provided. Industrial water is used as a humidifying liquid for humidifying the gas to be treated, and humidifies and cools the gas to be treated. The humidifying liquid sprayed in the gas to be treated gas introduction path 12 is not limited to industrial water, and is not particularly limited as long as it is a liquid that can humidify the gas to be treated, such as water. The pipe 31 and the industrial water supply pipe 32 do not necessarily have to be provided. Further, in the gas introduction path 12 to be treated and the gas introduction chamber 14 to be treated, other members for supplying the humidifying liquid may be provided in addition to the industrial water supply pipe 32.

The reaction tank 11 is provided with a stirrer 27 for stirring the alkaline agent-containing liquid 15. The stirrer 27 rotates at a predetermined rotation speed to stir the alkaline agent-containing liquid 15 contained in the alkaline agent-containing liquid chamber 16.

(Oxygen supply pipe)
One end of the oxygen supply pipe 38 is laid near the bottom of the alkaline agent-containing liquid chamber 16 of the reaction tank 11. The other end of the oxygen supply pipe 38 is connected to an oxygen supply source (not shown) outside the reaction vessel 11. Oxygen is supplied to the alkaline agent-containing liquid 15 housed in the alkaline agent-containing liquid chamber 16 by the oxygen supply pipe 38.
The oxygen supplied into the alkaline agent-containing liquid 15 reacts with the alkaline agent and the sulfur oxide dissolved in the alkaline agent-containing liquid 15. A part of the product produced by the reaction of oxygen, the alkaline agent and the sulfur oxide is precipitated in the alkaline agent-containing liquid 15 and becomes a precipitate. Hereinafter, the alkaline agent-containing liquid in which the precipitate is suspended (the alkaline agent-containing liquid containing the precipitate at a high concentration) is referred to as a slurry.
The oxygen supply pipe 38 may supply a liquid or gas containing oxygen from the oxygen supply source into the alkaline agent-containing liquid 15, but it is preferable to supply air from an economical point of view.

(1st extraction part, 1st area)
A pipe 33 connected to the pump 34 is provided at the bottom of the side wall of the alkaline agent-containing liquid chamber 16 that houses the slurry inside. The pump 34 extracts the slurry from the inside of the alkaline agent-containing liquid chamber 16 via the pipe 33. One end of the pipe 35 is connected to the outlet side of the pump 34, and the other end of the pipe 35 is connected to the mixing tank 36 whose details will be described later. Therefore, the slurry extracted from the alkaline agent-containing liquid chamber 16 is housed in the mixing tank 36 via the pipe 33, the pump 34, and the pipe 35.
The pipe 33, the pump 34, and the pipe 35 form the first extraction portion. Further, in the alkaline agent-containing liquid chamber 16, the vicinity of the position where the pipe 33 is provided is the first region, and the slurry is extracted from this first region by the first extraction portion.

The end of the pipe 33 opposite to the end on the pump 34 side is not limited to the configuration connected to the bottom of the side wall of the alkaline agent-containing liquid chamber 16, and the slurry in the alkaline agent-containing liquid chamber 16 is not limited. There is no particular limitation as long as the configuration is provided at a position where the above can be extracted. However, since the slurry having a highly oxidizing atmosphere can be extracted even in the alkaline agent-containing liquid chamber 16, the end of the pipe 33 is larger than the bottom of the alkaline agent-containing liquid chamber 16 (the gas lowering pipe 22 for supplying the gas to be treated). It is preferably provided in a region close to the oxygen supply pipe 38 for supplying oxygen). Since the bottom of the alkaline agent-containing liquid chamber 16 has a high concentration of oxygen in the slurry and a high oxidizing atmosphere, the concentration of oxidizing substances and hexavalent selenium is high, but it does not contain reduced substances and there is little soot and dust. This is a particularly suitable area for extracting good gypsum. The slurry extracted from this can be mixed with a fluid capable of reducing the slurry (details will be described later), and the reduction of oxidizing substances and hexavalent selenium can be achieved at the same time.
The pipe 33 may be provided on the bottom portion of the bottom portion of the alkaline agent-containing liquid chamber 16, but it is more preferable that the pipe 33 is provided on the side wall portion. Further, the lower end of the pipe 33 is set to the slurry sedimentation height when the stirrer 27 is stopped so that the pipe 33 is less likely to be blocked by the sedimented gypsum when the stirrer 27 is stopped and the gypsum of good quality can be extracted. It is especially preferable to match.

(Second extraction part, second area)
On the other hand, the reaction tank 11 is provided with an end of a pipe 37 for extracting a fluid capable of reducing the slurry extracted by the pump 34, and a gas introduction path 12 to be processed in the side wall of the gas introduction chamber 14 to be processed. It is provided at a position opposite to the position. The other end of the pipe 37 extends to the inside of the mixing tank 36, which will be described in detail later. Therefore, the gas to be treated extracted from the gas to be treated gas introduction chamber 14 is supplied to the slurry housed in the mixing tank 36 via the pipe 37.
That is, in the first embodiment, the gas to be treated extracted from the gas introduction chamber 14 to be treated and supplied to the mixing tank 36 via the pipe 37 is a fluid capable of reducing the slurry. Further, the pipe 37 constitutes a second extraction portion. At this time, in the gas introduction chamber 14, the vicinity of the position where the pipe 37 is provided is the second region, and the gas to be treated, which is a fluid capable of reducing the slurry, is extracted from this second region. Is done.

The fluid capable of reducing the slurry extracted from the first extraction portion is not limited to the gas to be treated. The fluid is not particularly limited as long as it is a fluid that can be extracted from the outside of the reaction tank 11 or the reaction tank 11 that communicates with the reaction tank 11 and that can reduce the slurry extracted from the first extraction portion. For example, the floss fluid may be extracted from the floss layer 28 in the alkaline agent-containing liquid chamber 16 and used as a fluid capable of reducing the slurry. An example of extracting the floss fluid from the floss layer 28 and using it as a fluid capable of reducing the slurry will be described later.

When the gas to be treated is used as the fluid capable of reducing the slurry, the gas to be treated before being supplied into the alkaline agent-containing liquid 15 contained in the alkaline agent-containing liquid chamber 16 can be extracted from the installation location of the pipe 37. There is no particular limitation as long as it is a position. For example, in the case of the reaction tank 11, the pipe 37 may be provided at an arbitrary position in the gas to be introduced chamber 14 or at an arbitrary position in the gas descent pipe 22. Further, for example, in the case of the outside of the reaction tank 11 communicating with the reaction tank 11, the communication tank 11 communicates with the reaction tank 11 at an arbitrary position of the gas to be introduced path 12 communicating with the reaction tank 11 or via the gas introduction path 12 to be treated. Therefore, it may be provided at an arbitrary position in a communication path (not shown) that connects the external device that generates the gas to be treated to the gas introduction path 12 to be treated.
Further, the gas to be treated in the gas to be introduced chamber 14 is supplied to the slurry in the mixing tank 36 via the pipe 37 by the self-pressure in the gas to be introduced chamber 14, but a compressor or the like is provided. May be supplied.

(Mixing tank)
A mixing tank 36 is provided outside the reaction tank 11.
One end of the pipe 35 is connected to the mixing tank 36, and the other end is connected to the pump 34 for extracting the slurry from the alkaline agent-containing liquid chamber 16. Therefore, the slurry is supplied to the mixing tank 36 by the pump 34.
Further, one end of the pipe 37 is connected to the mixing tank 36 and extends to the inside of the mixing tank 36, and the other end is connected to the side wall of the gas to be treated gas introduction chamber 14. Therefore, the gas to be processed is supplied to the mixing tank 36 via the pipe 37.

For example, in the case of 700 MW boiler exhaust gas and the concentration of SO ₂ in the exhaust gas is 700 ppm, one PVC (polyvinyl chloride) pipe having a diameter of 4 inches (10.16 cm) is provided as the pipe 37. The flow rate of the gas to be processed flowing through the pipe 37 is set to 300 to 600 Nm ³ / h-wet.

A stirrer 41 for mixing the slurry and the gas to be processed is provided in the mixing tank 36, and the mixture is rotated at a predetermined rotation speed.

Further, one end of the pipe 49 is connected to the upper part of the mixing tank. The other end of the pipe 49 is connected to the upper part of the side wall of the alkaline agent-containing liquid chamber 16 (the side wall portion corresponding to the space portion 26 above the floss layer 28). Therefore, the gas to be treated after being sufficiently gas-liquid contacted with the slurry in the mixing tank 36 to be desulfurized enters the space 26 in the alkaline agent-containing liquid chamber 16 from the upper part in the mixing tank 36 via the pipe 49. Will be supplied.

The mixing tank 36 is not particularly limited as long as it is a mixture of the slurry extracted by the first extraction portion and the fluid extracted by the second extraction portion. In the mixing tank 36, the slurry having a highly oxidizing atmosphere is reduced by the gas to be treated, which has a lower oxidizing atmosphere than the slurry, and the oxidizing substance and hexavalent selenium are reduced.

The reduction reaction in the mixing tank 36 will be described in more detail.
Since the desulfurization reaction that occurs in the alkaline agent-containing liquid chamber 16 requires dissolved oxygen, oxygen is supplied from the oxygen supply pipe 38. However, if the oxidation reaction caused by oxygen proceeds too much, tetravalent selenium (Se ⁴⁺ ) is oxidized to produce hexavalent selenium (Se ⁶⁺ ), and the amount of oxidizing substances increases. Therefore, hexavalent selenium and oxidizing substances tend to increase in the slurry in the alkaline agent-containing liquid chamber 16, and in particular, since the vicinity of the oxygen supply pipe 38 has a highly oxidizing atmosphere, hexavalent selenium and oxidizing substances High concentration. However, the slurry at the bottom of the alkaline agent-containing liquid chamber 16 contains good gypsum, which has a high concentration of oxidizing substances and hexavalent selenium, but does not contain reduced substances and has little soot and dust.
On the other hand, in the reaction tank 11 or outside the reaction tank 11 communicating with the reaction tank 11, there is a fluid capable of reducing the slurry extracted by the first extraction portion.

Therefore, in the first embodiment, a part of the gas to be treated is extracted from the gas introduction chamber 14 to be treated and mixed with the slurry having a highly oxidizing atmosphere contained in the mixing tank 36. Since the gas to be treated has an oxidizing atmosphere lower than that of the slurry, the slurry having a highly oxidizing atmosphere is reduced in the mixing tank 36. As a result, hexavalent selenium is reduced to tetravalent selenium in the mixing tank 36, and oxidizing substances are reduced. Further, since a desulfurization reaction occurs in the mixing tank 36 at this time, the gas to be treated supplied in the mixing tank 36 is bubbled in the slurry and sufficiently desulfurized, and then contains an alkaline agent via the pipe 49. It reaches the space 26 in the liquid chamber 16.
Therefore, the desulfurization apparatus of the first embodiment sufficiently causes a reduction reaction and a desulfurization reaction in the mixing tank 36 to suppress the production of oxidizing substances and hexavalent selenium, and has excellent desulfurization performance. , Can be realized with a simple configuration.

FIG. 2 is a graph showing an example of the relationship between the amount of oxygen and the amount of gas to be processed in the mixing tank 36.
In the case of 700 MW boiler exhaust gas and the concentration of SO ₂ in the exhaust gas is 700 ppm, one PVC (polyvinyl chloride) pipe with a diameter of 4 inches (10.16 cm) is provided as the pipe 37, and the pipe 37 is provided. The amount of oxygen in the mixing tank 36 when the flow rate of the gas to be processed was changed was measured and shown in FIG.
According to FIG. 2, by changing the flow rate of the gas to be treated, an oxidizing atmosphere in which oxygen is present in the region above the dotted line in the graph and a reduction in which oxygen is not present in the region below the dotted line. It can be seen that the sexual atmosphere and the sexual atmosphere can be transferred to each other.

Further, FIG. 3 is a graph showing an example of the relationship between the amount of oxygen and the redox potential with respect to the supply amount of the gas to be processed in the mixing tank 36. In the same manner as in FIG. 2, the amount of oxygen in the mixing tank 36 and the oxidation-reduction potential (ORP) when the flow rate of the gas to be treated was changed were measured and shown in FIG. In FIG. 3, the dotted line shows the ORP in the mixing tank 36, and the solid line shows the amount of dissolved oxygen in the mixing tank 36.
According to FIG. 3, it can be seen that ORP of 200 mV or less can be achieved by changing the flow rate of the gas to be treated. When the ORP is 200 mV or less, that is, when the introduced amount of the gas to be treated is 400 Nm ³ / h-wet or more in FIG. 3, the dissolved oxygen amount in the mixing tank 36 is close to 0 or less, and the oxidizing atmosphere. It can be seen that the slurry is reduced to a reducing atmosphere or a state close to a reducing atmosphere.

(Measurement unit)
The mixing tank 36 is provided with an ORP measuring unit 50 which is a measuring unit for measuring the redox potential of the mixture in the mixing tank 36. The ORP measuring unit 50 is not particularly limited as long as it can measure the redox potential of the mixture in the mixing tank 36. The redox potential measured by the ORP measuring unit 50 is sent to a control unit (not shown) whose details will be described later.

(Separation and collection section)
A pipe 42 connected to the pump 43 is provided on the side wall of the mixing tank 36. The mixture of the slurry and the gas to be processed mixed in the mixing tank 36 is extracted from the inside of the mixing tank 36 by the pump 43 via the pipe 42. One end of the pipe 44 is connected to the outlet side of the pump 43, and the solid-liquid separator 46 is connected to the other end of the pipe 44. The solid-liquid separator 46 separates the mixture extracted from the mixing tank 36 into solid and liquid, and separates and recovers the solid content. The solid-liquid separator 46 is a separation / recovery unit.

(Wastewater treatment equipment)
A wastewater treatment device is connected to the rear stage of the solid-liquid separator 46. The wastewater treatment device is supplied with the recovered residual liquid after the solid content is recovered by the solid-liquid separator 46 via the pipe 45 connected to the solid-liquid separator 46. The wastewater treatment device removes nitrogen compounds, COD (Chemical Oxygen Demand) components, hexavalent selenium, etc. from the recovered residual liquid so that it can be discharged as wastewater.

(Alkaline agent introduction part)
The pipe 47 branched from the pipe 45 is connected to the alkaline agent-containing liquid chamber 16 of the reaction tank 11. The pipe 47 is provided with an alkaline agent introduction portion 48 for introducing an alkaline agent such as limestone in the middle. The alkaline agent introduction unit 48 introduces the alkaline agent into a part of the recovered residual liquid separated by solid and liquid, and makes it usable again as the alkaline agent-containing liquid 15 in the alkaline agent-containing liquid chamber 16.
The pipe 47 and the alkaline agent introduction portion 48 do not necessarily have to be provided.

(Control unit)
As described above, the redox potential of the mixture in the mixing tank 36 measured by the ORP measuring unit 50 is sent to the control unit (not shown).
The control unit controls a valve (not shown) provided in the pipe 37 based on this redox potential, and the amount of the gas to be processed (the amount of the fluid capable of reducing the slurry) extracted from the gas introduction chamber 14 to be processed. ) Can be adjusted to any amount.
The control unit can also control the amount of slurry extracted from the alkaline agent-containing liquid chamber 16 in addition to the amount of the gas to be processed extracted from the gas to be treated chamber 14. The control unit can control the pump 34, a valve (not shown) provided in the pipes 33, 35, or the like to adjust the amount of slurry extracted from the alkaline agent-containing liquid chamber 16 to an arbitrary amount.

The control unit preferably controls the amount of the gas to be extracted so that the redox potential measured by the ORP measuring unit 50 is 200 mV or less, and more preferably 0 mV or more and 150 mV or less. preferable.

After the ORP of the mixture in the mixing tank 36 is adjusted as described above, the solid content is separated and recovered by the solid-liquid separator 46.

According to the desulfurization apparatus of the first embodiment described above, it is possible to suppress the production of oxidizing substances and hexavalent selenium and to realize excellent desulfurization performance with a simple configuration.

<Desulfurization method>
Next, a desulfurization method using the above-mentioned desulfurization apparatus 100 will be described with reference to FIG. Here, the desulfurization method of the first embodiment includes at least a contact step, a first extraction step, a second extraction step, a mixing step, and a separation / recovery step. Hereinafter, each step will be described in order.

(Contact process)
In the contact step, the gas to be treated containing sulfur oxides is introduced into the alkaline agent-containing liquid 15 contained in the reaction vessel 11, oxygen is supplied to the alkaline agent-containing liquid 15, and the sulfur oxides and oxygen ( The product produced by the reaction between the dissolved oxygen) and the alkaline agent in the alkaline agent-containing liquid 15 is deposited in the alkaline agent-containing liquid 15.

In the example shown in FIG. 1, first, the gas to be treated containing the sulfur compound is introduced into the gas to be treated gas introduction path 12 provided in the reaction tank 11. The gas to be treated introduced into the gas to be treated gas introduction path 12 comes into contact with the industrial water sprayed from the industrial water supply pipe 32. Industrial water is a humidifying liquid that humidifies and cools the gas to be treated. When the gas to be treated comes into contact with the humidifying liquid, the gas to be treated is humidified and the generation of scale due to drying in the apparatus can be suppressed.

Next, the humidified gas to be treated flows into the gas descending pipe 22 via the gas to be treated gas introduction chamber 14. The gas to be treated that has flowed into the gas lowering pipe 22 reaches the alkaline agent-containing liquid chamber 16 and is located below the liquid level 21 of the alkaline agent-containing liquid 15 housed in the alkaline agent-containing liquid chamber 16. It spouts from multiple holes located near the lower end of the. The gas to be treated ejected from a plurality of holes located near the lower end of the gas descending pipe 22 becomes bubbles, is dispersed in the alkaline agent-containing liquid 15, and rises while in gas-liquid contact with the alkaline agent-containing liquid.

In this way, the floss layer 28, which is a gas-liquid contact layer composed of the gas discontinuous phase of the gas to be treated and the liquid continuous phase of the alkaline agent-containing liquid, is formed on the liquid surface 21 of the alkaline agent-containing liquid 15. Since oxygen is supplied to the alkaline agent-containing liquid 15 from the oxygen supply pipe 38, the sulfur oxide contained in the gas to be treated reacts with the oxygen and the alkaline agent in the alkaline agent-containing liquid 15 in the floss layer 28. .. In a series of flows, sulfur oxides such as SO ₂ in the gas to be treated are dissolved in the alkaline agent-containing liquid and removed from the gas to be treated.

In the reaction between sulfur oxides, oxygen and an alkaline agent, sulfur oxides such as SO ₂ contained in the gas to be treated react with the alkaline agent and oxygen, and a part of the product produced by the reaction is the alkaline agent-containing liquid 15. Precipitate inside.
For example, when the sulfur oxide contains SO ₂ and limestone (CaCO ₃ ) is used as the alkaline agent, the reaction of the following formula (1) occurs. That is, in the reaction of the following formula (1), gypsum (CaSO _{4.2H 2} O), which is a product, is produced, and a part of the gypsum is deposited as a precipitate in the alkaline agent-containing liquid 15. On the other hand, sulfur oxides are removed from the gas to be treated.
SO ₂ + 2H ₂ O + 1 / 2O ₂ + CaCO ₃ → CaSO _{4.2H 2} O + CO ₂ (1)

The alkaline agent contained in the alkaline agent-containing liquid is a neutralizing agent that neutralizes the acid, and examples thereof include calcium carbonate and sodium hydroxide. Moreover, water is mentioned as a solvent of the alkaline agent-containing liquid.

The gas to be treated from which the sulfur oxide has been removed is discharged from the gas discharge port 13 to be treated via the space 26 above the alkaline agent-containing liquid chamber 16, the communication pipe 25, and the gas discharge chamber 17 to be treated. ..

(First extraction process)
Then, in the first extraction step, an alkaline agent-containing liquid containing a high concentration of the product generated and precipitated by the desulfurization reaction from the first region in the reaction tank 11 (alkaline agent-containing liquid chamber 16) (hereinafter, Extract the slurry). The first region is a region having a higher oxidizing atmosphere than the second region described later.
In the example shown in FIG. 1, the region near the bottom of the side wall in the alkaline agent-containing liquid chamber 16 is the first region. At this time, in the first extraction step, the slurry is extracted from the region near the bottom of the side wall in the alkaline agent-containing liquid chamber 16 via the pipe 33 by the pump 34. The extracted slurry is housed in the mixing tank 36 via the pipe 35. However, the present invention is not limited to the configuration shown in FIG.

In the first extraction step, the slurry may be extracted from a region other than the bottom of the side wall in the alkaline agent-containing liquid chamber 16. The region for extracting the slurry, that is, the first region is not particularly limited as long as it is a region in which the slurry can be extracted in the alkaline agent-containing liquid chamber 16. However, since the bottom of the alkaline agent-containing liquid chamber 16 has a high concentration of oxygen in the slurry and a high oxidizing atmosphere, the concentration of oxidizing substances and hexavalent selenium is high, but it does not contain reduced substances and is dust. It is a particularly suitable area for extracting good gypsum. The slurry extracted from this can be mixed with a fluid capable of reducing the slurry (details will be described later), and the reduction of oxidizing substances and hexavalent selenium can be achieved at the same time.

(Second extraction process)
On the other hand, in the second extraction step, a part of the gas to be treated introduced into the reaction tank 11 is extracted from the second region of the gas introduction chamber 14. The second region is a region of an atmosphere in which the slurry extracted in the first extraction step can be reduced.
In the example shown in FIG. 1, the vicinity of the side wall in the gas to be treated gas introduction chamber 14 is the second region. At this time, in the second extraction step, a part of the gas to be processed in the gas to be treated chamber 14 is extracted from the region near the side wall in the gas to be introduced chamber 14 by the pipe 37. The extracted gas to be treated is supplied into the slurry housed in the mixing tank 36. Since the gas to be treated has an oxidizing atmosphere lower than that of the slurry, the slurry can be reduced. However, the present invention is not limited to the configuration shown in FIG.

The second extraction step is not particularly limited as long as the fluid capable of reducing the slurry extracted in the first extraction step can be extracted from the outside of the reaction tank 11 or the reaction tank 11 communicated with the reaction tank 11. Therefore, in the second extraction step, a fluid other than a part of the gas to be processed may be extracted as a fluid capable of reducing the slurry extracted in the first extraction step. Further, the region for extracting the fluid capable of reducing the slurry in the second extraction step, that is, the second region may be a region other than the vicinity of the side wall in the gas introduction chamber 14 to be treated, and may be a region in the reaction tank 11. It may be an area other than the treatment gas introduction chamber 14, or may be outside the reaction tank 11 communicating with the reaction tank 11.

When extracting the gas to be processed, it is preferable that a part of the gas to be processed before being introduced into the alkaline agent-containing liquid 15 is extracted in the second extraction step. In the second extraction step, a part of the gas to be treated before being introduced into the reaction tank 11 may be extracted, or a part of the gas to be treated after being introduced into the reaction tank 11 may be extracted. .. Therefore, the second extraction step communicates with the reaction tank 11 in the gas descending pipe 22, the gas introduction chamber 14 to be processed, the gas introduction path 12 to be processed, or the gas introduction path 12 to be processed. The gas to be processed can be extracted from the communication path (not shown) connecting the external device for generating the gas to be processed to the gas introduction path 12 to be processed.

(Mixing process)
In the mixing step, the slurry extracted from the first region in the first extraction step and the fluid capable of reducing the slurry extracted from the second region in the second extraction step are mixed.
In the example shown in FIG. 1, the mixing step is performed in the slurry extracted from the alkaline agent-containing liquid chamber 16 housed in the mixing tank 36 and subjected to the treatment extracted from the gas introduction chamber 14 to be processed. These are mixed by supplying a part of the gas and bubbling. Further, in the mixing step, it is preferable to rotate the stirrer 41 provided in the mixing tank 36 at a predetermined rotation speed to promote the mixing of the slurry and the gas to be processed.
In the mixing step, the slurry having a highly oxidizing atmosphere is reduced by the gas to be treated, which has a lower oxidizing atmosphere than the slurry, and the oxidizing substance and hexavalent selenium are reduced. Further, the gas to be treated mixed with the slurry in the mixing step is desulfurized by gas-liquid contact in the slurry, and is introduced into the space 26 in the alkaline agent-containing liquid chamber 16 via the pipe 49.

(Measurement process)
Further, it is preferable that the measuring step measures the redox potential of the mixture obtained in the mixing step.
In the example shown in FIG. 1, the ORP measuring unit 50 for measuring the redox potential is provided in the mixing tank 36, and the measuring step is to oxidize the mixture (the slurry and the gas to be treated) in the mixing tank 36. Measure the reduction potential. Then, in the control step described in detail later, it is preferable to control the amount of slurry extracted in the first extraction step based on the measured redox potential.

(Separation and recovery process)
In the separation / recovery step, the solid content is separated and recovered from the mixture of the slurry and the fluid mixed in the mixing step.
In the example shown in FIG. 1, in the separation / recovery step, the solid content is separated and recovered from the mixture of the slurry and the gas to be treated mixed in the mixing tank 36 by the solid-liquid separator 46. The recovered residual liquid after the solid content is separated and recovered from the mixture is supplied to the wastewater treatment apparatus via the pipe 45 connected to the outlet side of the solid-liquid separator 46, and is treated with wastewater by the wastewater treatment apparatus. (Wastewater treatment process).

(Wastewater treatment process)
In the wastewater treatment step, nitrogen compounds, COD, hexavalent selenium and the like are removed from the recovered residual liquid after the solid content (precipitate) is separated and recovered by the solid-liquid separator 46. Wastewater treatment is performed by a wastewater treatment device installed outside.
The recovered residual liquid after the solid content is separated and recovered by the solid-liquid separator 46 is supplied to the wastewater treatment device via the pipe 45. Since the amount of oxidizing substances and hexavalent selenium is reduced in this recovered residual liquid, it is not necessary to install a new wastewater treatment device, or the load of wastewater treatment can be reduced.

(Alkaline agent introduction process)
Further, in the alkaline agent introduction step, an alkaline agent such as limestone can be introduced into a part of the recovered residual liquid from which the solid content has been separated by the solid-liquid separator 46, and can be supplied again into the alkaline agent-containing liquid chamber 16. The alkaline agent-containing liquid 15 is preferable.
In the example shown in FIG. 1, a pipe 47 branched from the pipe 45 connected to the outlet side of the solid-liquid separator 46 is provided, and in the alkaline agent introduction step, an alkaline agent such as limestone is provided in the middle of the pipe 47. It is introduced into a part of the recovered residual liquid by the alkaline agent introduction unit 48. A part of the recovered residual liquid into which the alkaline agent is introduced is stored in the alkaline agent-containing liquid chamber 16 via the pipe 47 and used as the alkaline agent-containing liquid 15.

(Control process)
Next, the above-mentioned control process will be described in detail with reference to specific examples of the control method.
As described above, the control step controls the amount of slurry to be extracted in the first extraction step based on the redox potential measured in the measurement step.
In the example shown in FIG. 1, the ORP measuring unit 50 is provided in the mixing tank 36, and the control step is the mixture in the mixing tank 36 sent from the ORP measuring unit 50 received by the control unit (not shown). The amount of the gas to be treated (the amount of the fluid capable of reducing the slurry) to be extracted in the second extraction step is controlled based on the redox potential of.
The control step can also control the amount of slurry extracted in the first extraction step in addition to the amount of gas to be extracted in the second extraction step.

In the control step, it is preferable to control the amount of the gas to be extracted so that the redox potential measured by the ORP measuring unit 50 in the measuring step is 200 mV or less, and it is controlled to be 0 mV or more and 150 mV or less. Is more preferable.

According to the desulfurization method of the first embodiment described above, it is possible to suppress the production of oxidizing substances and hexavalent selenium and to realize excellent desulfurization performance with a simple configuration.

[Second Embodiment]
FIG. 4 is a schematic view showing a jet bubbling type desulfurization apparatus according to the second embodiment of the present invention. FIG. 5 is an enlarged view of a main part of the desulfurization apparatus shown in FIG. 4, and shows the configuration of the overflow weir 60 and its vicinity. Hereinafter, the second embodiment will be described, but the same members as those in the first embodiment are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIGS. 4 and 5, the desulfurization apparatus 200 of the second embodiment includes an overflow weir 60 and a pipe 71 in place of the pipe 37 in the desulfurization apparatus 100 of the first embodiment shown in FIG. .. Therefore, when the desulfurization apparatus 200 of the second embodiment and the desulfurization apparatus 100 of the first embodiment are compared, the second extraction unit (second extraction step) is different, and the control unit (not shown) is omitted. The control process) is also different. The desulfurization apparatus 200 of the second embodiment and the desulfurization apparatus 100 of the first embodiment are the same except for the second extraction unit and the control unit.
Hereinafter, the second extraction unit (second extraction step) and the control unit (control process) of the desulfurization apparatus 200 will be described in detail.

(Second extraction section, second extraction process, second area)
In the second embodiment, an overflow weir 60 extending from a position below the liquid level 21 of the alkaline agent-containing liquid 15 to above the liquid level 21 is provided in the vicinity of the side wall in the alkaline agent-containing liquid chamber 16. There is. The floss fluid constituting the floss layer 28 formed on the liquid surface 21 of the alkaline agent-containing liquid 15 overflows the overflow weir 60 and flows into the side wall side of the alkaline agent-containing liquid chamber 16. On the other hand, since the alkaline agent-containing liquid 15 located at the lower part of the floss layer 28 is blocked by the overflow weir 60, it does not flow above the overflow weir 60 (does not overflow), and the alkaline agent-containing liquid chamber 16 does not flow. It does not flow into the side wall.

The overflow weir 60 will be described in more detail with reference to FIG.
The overflow weir 60 of the second embodiment includes a side plate 61 and a bottom plate 62 having an opening 62a. Further, an ascending flow suppression plate 63 is provided below the overflow weir 60.

The side plate 61 extends above the static liquid surface of the alkaline agent-containing liquid 15, blocks the alkaline agent-containing liquid 15, and causes the floss fluid to overflow from the floss layer 28. Therefore, it is preferable that the side plate 61 extends above the static liquid level of the alkaline agent-containing liquid 15 and below the upper end of the floss layer 28. Specifically, the side plate 61 preferably extends 50 mm or more above the static liquid level (standard liquid level height), and more preferably 100 mm or more and 300 mm or less.
Here, the static liquid level is a stationary liquid level before the gas to be processed is ejected from the gas descending pipe 22. The static liquid level is located slightly above the liquid level 21.

When the flue gas desulfurization apparatus 200 is stopped, the solid matter in the floss layer 28 may be deposited on the bottom plate 62 of the overflow weir 60, which may impair the overflow function during the operation of the flue gas desulfurization apparatus 200. Therefore, the bottom plate 62 is arranged so as to be inclined in the example shown in FIG. 5, and has an opening 62a. By providing the opening 62a, the solid matter in the floss layer 28 is discharged to the outside of the overflow weir 60, and sedimentation can be suppressed.
The shape of the opening 62a is not particularly limited, but is, for example, a circular shape having a diameter of 25 mm or more and 50 mm or less. In the example shown in FIG. 5, one opening 62a is provided, but a plurality of openings 62a may be provided.

The ascending flow suppression plate 63 is provided below the opening 62a. In the ascending flow suppression plate 63, the ascending flow of the alkaline agent-containing liquid 15 outside the overflow weir 60 generated by the stirrer 27 near the side wall of the alkaline agent-containing liquid chamber 16 passes through the opening 62a and is above the bottom plate 62. Inflow (mixing into the overflow weir 60) can be suppressed. Further, the ascending flow suppression plate 63 can also suppress the gas supplied from the oxygen supply pipe 38 from flowing into the upper part of the bottom plate 62 through the opening 62a.

One end of the pipe 71 for extracting the floss fluid overflowing from the overflow weir 60 is provided on the side wall of the alkaline agent-containing liquid chamber 16. The other end of the pipe 71 extends to the inside of the mixing tank 36. Therefore, in the slurry housed in the mixing tank 36, the floss fluid extracted via the overflow weir 60 in the alkaline agent-containing liquid chamber 16 is supplied via the pipe 71.

That is, in the second embodiment, the floss fluid extracted from the alkaline agent-containing liquid chamber 16 via the pipe 71 and supplied to the mixing tank 36 is a fluid capable of reducing the slurry. Further, in the second embodiment, the overflow weir 60 and the pipe 71 form the second extraction portion. At this time, in the alkaline agent-containing liquid chamber 16, the vicinity of the position where the pipe 71 is provided, that is, the region partitioned by the overflow weir 60 and the side wall of the alkaline agent-containing liquid chamber 16 is the second region. Is. The second extraction section extracts the floss fluid, which is a fluid capable of reducing the slurry, from the second region. Although the floss fluid can be directly extracted from the pipe 71 without providing the overflow weir 60, the overflow weir 60 may be mixed with a large amount of the alkaline agent-containing liquid 15 located at the lower part of the floss layer 28. It is preferable to provide a floss fluid to enclose the floss fluid. Further, although the floss fluid is composed of two phases of gas and liquid, it is preferable to provide the overflow weir 60 because the ratio of gas is high and it is easier to secure an effective amount of liquid than to directly withdraw from the pipe 71.

The installation location of the pipe 71 is not particularly limited as long as it is at a position where the floss fluid overflowing the overflow weir 60 can be extracted, but is above the liquid level 21 (standard liquid level height) of the alkaline agent-containing liquid 15. Moreover, it is preferable that the floss layer 28 is provided on the side wall of the alkaline agent-containing liquid chamber 16 below the upper end. Specifically, the pipe 71 is provided within the range of the side wall of the alkaline agent-containing liquid chamber 16 100 mm below to 200 mm above the static liquid level (standard liquid level height) of the alkaline agent-containing liquid 15. preferable.

The floss fluid constituting the floss layer 28 contains precipitates generated and precipitated by the desulfurization reaction, an alkaline agent-containing liquid, and a gas to be treated that has been desulfurized by the desulfurization reaction, and is further contained in the gas to be treated. It also contains impurities such as soot and dust contained in. A floss fluid containing such various components is supplied to the mixing tank 36 via the pipe 71.

In the second embodiment, the desulfurization apparatus 200 includes a plurality of overflow weirs 60. In FIGS. 4 and 5, for the sake of understanding the invention, only one overflow weir 60 is shown, and the others are omitted.
FIG. 6A is a schematic cross-sectional view showing the configuration of the desulfurization apparatus according to the second embodiment. In FIG. 6A, for the sake of understanding the invention, the configurations other than the side wall of the reaction tank 11 and the overflow weir 60 are not shown.
As shown in FIG. 6A, four overflow weirs 60 are provided at equal intervals along the side wall of the cylindrical reaction tank 11. The number of overflow weirs 60 is not limited to four, and any number can be provided. It is preferable that the plurality of overflow weirs 60 are arranged at equal intervals.

Further, FIG. 6B is a schematic cross-sectional view showing the configuration of a modified example of the desulfurization apparatus according to the second embodiment. Also in FIG. 6B, for the sake of understanding the invention, the configurations other than the side wall of the reaction tank 11 and the overflow weir 60 are not shown.
As shown in FIG. 6B, four overflow weirs 60 are provided at equal intervals along the side wall of the rectangular parallelepiped-shaped reaction tank 11. At this time, in the horizontal cross section of the reaction tank 11, the overflow weirs 60 may be provided at the four corners of the reaction tank 11, but they may be provided near the midpoints of each side of the rectangular cross section. preferable. When the overflow weir 60 is provided near the midpoint, the flow of the floss fluid is better than that at the four corners, and the replacement of the floss layer 28 and the alkaline agent-containing liquid 15 is further promoted, which is preferable. ..

(Control unit, control process)
In the second embodiment, the control unit controls the pump 34, valves (not shown) provided in the pipes 33, 35, and the like based on the redox potential of the mixture in the mixing tank 36, and contains an alkaline agent. The amount of slurry extracted from the liquid chamber 16 can be adjusted to an arbitrary amount.
The control unit can also control the amount of floss fluid extracted from the alkaline agent-containing liquid chamber 16 in addition to the amount of slurry extracted from the alkaline agent-containing liquid chamber 16. The control unit can control a valve (not shown) provided in the pipe 71 to adjust the amount of floss fluid extracted from the floss layer 28 in the alkaline agent-containing liquid chamber 16 to an arbitrary amount.

The control unit preferably controls the amount of the slurry extracted so that the redox potential measured by the ORP measuring unit 50 is 200 mV or less, and more preferably 0 mV or more and 150 mV or less.

According to the desulfurization method of the second embodiment according to the present invention described above, it is possible to realize suppression of the production of oxidizing substances and hexavalent selenium and excellent desulfurization performance with a simple configuration.

Here, in the desulfurization apparatus 200 of the second embodiment, the fact that the oxidizing substance can be reduced by controlling the amount of the slurry extracted from the alkaline agent-containing liquid chamber 16 will be described in more detail with reference to specific examples.
FIG. 7 is a graph showing the relationship between the redox potential of the alkaline agent-containing liquid and the concentration of the oxidizing substance, and shows the case of pH = 4 (solid line) and the case of pH = 5 (dotted line).
According to FIG. 7, it can be seen that the concentration of the oxidizing substance in the alkaline agent-containing liquid changes depending on the redox potential. As is clear from FIG. 7, when the redox potential is 200 mV or less, almost no oxidizing substance exists.

On the other hand, FIG. 8 shows the inside of the mixing tank 36 (alkaline agent-containing liquid in the mixture) with respect to the amount of slurry extracted from the alkaline agent-containing liquid chamber 16 when desulfurization is performed by the desulfurization apparatus 200 of the second embodiment. It is a graph which shows the relationship of the redox potential of. At this time, desulfurization was performed with 700 MW of boiler exhaust gas under the condition that the concentration of SO ₂ in the exhaust gas was 700 ppm.
As is clear from FIG. 8, by controlling the amount of slurry extracted from the alkaline agent-containing liquid chamber 16, the redox potential can be set to 200 mV or less, and as a result, almost no oxidizing substance is present. I understand.

(Effect / mechanism of action of the second embodiment)
By the way, the floss fluid constituting the floss layer 28 contains soot dust as described above, but by reducing the soot dust contained in the floss layer 28, the effect of suppressing the generation of scale in the apparatus can be obtained. It turned out to be. Therefore, in the second embodiment, in addition to the effect of the first embodiment, the effect of suppressing the generation of scale in the apparatus is obtained. The mechanism of action at which this effect is obtained will be described below.

Since soot and dust are very fine particles, they have planktonic properties due to their fine shape. Therefore, the soot dust trapped in the floss layer 28 adheres and stays on the surface of the foam bubbles.
Here, in the conventional desulfurization apparatus, since the slurry (alkaline agent-containing liquid) is extracted only from the bottom of the alkaline agent-containing liquid chamber, most of the floss fluid is not directly discharged to the outside, and therefore, The concentration of fine soot dust inevitably increases in the floss layer with the desulfurization treatment, resulting in a high concentration. The high-concentration soot dust exists in a state of being concentrated in air bubbles, but a part of it is peeled off by the flow of the gas to be treated and adheres to the surface of the member downstream of the desulfurization device to generate scale. Causes. Further, the high-concentration soot dust peeled off from the foam bubbles may accompany the flow of the gas to be treated toward the gas discharge port to be treated, and the soot concentration of the gas discharged to the outside of the scrubbering apparatus may increase.
Therefore, in the second embodiment, the soot dust captured in the floss layer 28 adheres and stays on the surface of the foam bubbles, but is extracted by the pipe 71 or the like. As a result, since the concentration of soot on the surface of the foam bubbles of the floss layer 28 can be reduced, the generation of scale derived from soot dust can be suppressed in the second embodiment, and the flue gas desulfurization apparatus is used accordingly. It is possible to reduce the soot concentration of the gas (cleaned gas) discharged to the water.

Further, in the second embodiment, the floss fluid is effectively used. Since the slurry in the alkaline agent-containing liquid chamber 16 has a high pH in a highly oxidizing atmosphere, there are many oxidizing substances and hexavalent selenium, but the floss fluid in the floss layer 28 has a low pH in a low oxidizing atmosphere. Therefore, tetravalent selenium, which has no oxidizing substances and is advantageous for wastewater treatment, is the main component. By positively using the floss fluid having such properties, the load on the wastewater treatment apparatus can be reduced.

[Third Embodiment]
FIG. 9 is a schematic view showing a jet bubbling type desulfurization apparatus according to a third embodiment of the present invention. Hereinafter, the third embodiment will be described, but the same members as those in the second embodiment are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIG. 9 , in the desulfurization apparatus 300 of the third embodiment, in addition to the desulfurization apparatus 300 of the second embodiment shown in FIG. 4, the pipe 81, the pump 82, the pipe 83, the solid-liquid separator 84, A pipe 85 is provided. Therefore, when the desulfurization apparatus 300 of the third embodiment and the desulfurization apparatus 200 of the second embodiment are compared, in the third embodiment, the third extraction unit (third extraction step) and the sub-separation / recovery unit. (Sub-separation and recovery step) is different in that it is provided, and is the same except for this point.
Hereinafter, the third extraction unit (third extraction step) and the sub-separation / recovery unit (sub-separation / recovery step) of the desulfurization apparatus 300 will be described in detail.

(Third extraction part, third extraction process)
A pipe 81 connected to the pump 82 is branched and provided in the pipe 33 constituting the first extraction portion. The pump 82 pulls out the slurry from the pipe 33 via the pipe 81. This slurry is a part of the slurry extracted from the alkaline agent-containing liquid chamber 16 by the pump 34.
One end of the pipe 83 is connected to the outlet side of the pump 82, and the other end of the pipe 83 is connected to the solid-liquid separator 84. Therefore, the solid content of the slurry extracted from the pipe 33 via the pipe 81 branched is separated and recovered by the solid-liquid separator 84. This separation and recovery will be described later.

The pipe 81, the pump 82, and the pipe 83 form a third extraction portion. Further, in the example shown in FIG. 9 , the slurry is extracted from the branch position of the pipe 33 to the pipe 81 by the third extraction portion. The pipe 81 may be provided at any location as long as it is between the alkaline agent-containing liquid chamber 16 and the mixing tank 36. In other words, there is no particular limitation as long as a part of the slurry extracted in the first extraction step can be extracted before being subjected to mixing in the mixing step.

Further, the pipe 81 may be connected to the alkaline agent-containing liquid chamber 16. That is, the slurry housed in the alkaline agent-containing liquid chamber 16 may be extracted through the pipe 81 by the pump 82 and supplied to the solid-liquid separator 84 via the pipe 83. At this time, the vicinity of the position where the pipe 83 of the reaction tank 11 (alkaline agent-containing liquid chamber 16) is provided is the third region, and the slurry is extracted from the third region by the third extraction portion. ..

(Sub-separation and recovery section, sub-separation and recovery process)
The slurry extracted by the third extraction portion is supplied to the solid-liquid separator 84 via the pipe 83 connected to the outlet side of the pump 82. The solid-liquid separator 84 separates the slurry extracted by the third extraction unit into solid and liquid, and separates and recovers the solid content. The solid-liquid separator 84 is a sub-separation / recovery unit. The recovered residual liquid after the solid content is recovered by the solid-liquid separator 84 returns to the alkaline agent-containing liquid chamber 16 via the pipe 85 and the pipe 47.
Unlike the mixture supplied to the solid-liquid separator 46, the slurry supplied to the solid-liquid separator 84 does not contain the floss fluid constituting the floss layer. That is, there is little soot in the slurry supplied to the solid-liquid separator 84. Therefore, since the amount of soot and dust mixed in the solid content separated by the solid-liquid separator 84 is small, very high-quality gypsum can be obtained. According to the sub-separation and recovery unit (sub-separation and recovery step), the gypsum separated and recovered from the floss fluid by the solid-liquid separator 46, that is, the gypsum of the floss fluid, apart from the relatively low-quality gypsum having a high content of soot and dust. High-quality gypsum having a low content, that is, a low content of soot and dust, can be separately recovered by the solid-liquid separator 84.

In the conventional desulfurization apparatus, only the slurry extracted from the lower part of the alkaline agent-containing liquid chamber is solid-liquid separated and recovered as gypsum. At this time, since fine soot dust is hardly discharged as described above, the soot dust in the alkaline agent-containing liquid and the floss layer has a high concentration. Therefore, since soot dust is present in a high concentration in the slurry extracted from the alkaline agent-containing liquid chamber, the quality of the gypsum derived from this slurry is deteriorated. When the main component of soot and dust is unburned carbon, this tendency becomes remarkable and the hue deteriorates.
However, in the third embodiment, by extracting the floss fluid from the floss layer 28 and discharging it, the concentration of soot and dust in the slurry sent to the solid-liquid separator 84 is reduced, so that the quality of gypsum is improved.

According to the third embodiment described above, gypsum having a low content of soot and dust can be separately collected, so that high-quality gypsum can be obtained. This high-grade gypsum can also be used by appropriately mixing it with a relatively low-grade gypsum containing soot and dust. Further, also in the third embodiment, as in the second embodiment, the recovered residual liquid after the solid content is recovered by the solid-liquid separator 46 has reduced oxidizing substances and hexavalent selenium. , A part or all of this recovered residual liquid can be sent to the wastewater treatment device.

11 Reaction tank; 12 Processed gas introduction path; 13 Processed gas discharge port; 14 Processed gas introduction chamber; 15 Alkaline agent-containing liquid; 16 Alkaline agent-containing liquid chamber; 17 Processed gas discharge chamber; 18 First partition; 19 Second partition; 21 Liquid level; 22 Gas descent pipe; 25 Communication pipe; 26 Space part; 27 Stirrer; 28 Fross layer; 31 Pipe; 32 Industrial water supply pipe; 33 Pipe; 34 Pump; 35 Pipe; 36 Mixing Tank; 37 pipes; 38 oxygen supply pipes; 41 stirrer; 42 pipes; 43 pumps; 44 pipes; 45 pipes; 46 solid-liquid separator; 47 pipes; 48 alkaline agent introduction part; 49 pipes; 50 ORP measurement part; 60 Overflow dam; 61 Side plate; 62 Bottom plate; 62a Opening; 63 Upflow suppression plate; 71 Piping; 81 Piping; 82 Pump; 83 Piping; 84 Solid-liquid separator; 85 Piping; 100 Degassing equipment; 200 Degassing equipment; 300 Desulfurization equipment

Claims (8)

A gas to be treated containing a sulfur oxide is introduced into an alkaline agent-containing liquid contained in a reaction vessel, oxygen is supplied to the alkaline agent-containing liquid, and the sulfur oxide, the oxygen and the alkaline agent are contained. A contact step of precipitating the product produced by the reaction with the alkaline agent in the liquid into the alkaline agent-containing liquid, and
A first extraction step of extracting a slurry containing the alkaline agent-containing liquid and the precipitated product from the inside of the reaction vessel to the outside of the reaction vessel.
A second extraction step of extracting a part of the gas to be treated before being introduced into the alkaline agent-containing liquid in the contact step to the outside of the reaction vessel, and a second extraction step.
A mixing step of mixing the slurry extracted in the first extraction step and a part of the gas to be processed extracted in the second extraction step outside the reaction vessel.
A desulfurization method comprising: a separation / recovery step of separating a gas component from a mixture of the slurry mixed in the mixing step and a part of the gas to be treated and separating and recovering the solid content. A measurement step for measuring the redox potential of the mixture obtained in the mixing step, and a measurement step.
At least one of the amount of the slurry extracted in the first extraction step and the amount of a part of the gas to be extracted in the second extraction step based on the redox potential measured in the measurement step. The desulfurization method according to claim 1, further comprising a control step for controlling the above. The desulfurization method according to claim 2, wherein the control step is controlled so that the redox potential measured in the measurement step is less than 200 mV. The desulfurization method according to any one of claims 1 to 3, wherein the first extraction step extracts the slurry from the bottom of the reaction vessel. An alkali agent-containing liquid provided below the gas to be treated gas introduction path, the gas to be treated gas introduction chamber into which the gas to be treated containing sulfur oxide is introduced from the gas introduction path to be treated, and the gas to be treated gas introduction chamber is provided. An alkaline agent-containing liquid chamber housed in the lower portion thereof, and a gas descent tube for supplying the treated gas introduced into the treated gas introduction chamber into the alkaline agent-containing liquid housed in the alkaline agent-containing liquid chamber. And, with a reaction vessel,
An oxygen supply pipe that supplies oxygen to the alkaline agent-containing liquid contained in the alkaline agent-containing liquid chamber, and an oxygen supply pipe.
From the alkaline agent-containing liquid chamber
With the alkaline agent-containing liquid
Of the products produced by the reaction of the sulfur oxide, the oxygen, and the alkaline agent in the alkaline agent-containing liquid, the slurry containing the precipitates precipitated in the alkaline agent-containing liquid is extracted from the reaction vessel. The first extraction part and
A second extraction section for extracting a part of the gas to be treated out of the reaction vessel from the gas introduction path to be processed or the gas introduction chamber to be processed.
A mixing tank in which the slurry extracted by the first extraction portion and a part of the gas to be processed extracted by the second extraction portion are mixed outside the reaction vessel.
A desulfurization apparatus comprising: a separation / recovery unit that separates a gas component from a mixture of the slurry mixed in the mixing tank and a part of the gas to be treated and separates and recovers the solid content. A measuring unit that measures the redox potential of the mixture, and
At least one of the amount of the scrubber extracted by the first extraction unit and the amount of a part of the gas to be processed extracted by the second extraction unit based on the redox potential measured by the measurement unit. The desulfurization apparatus according to claim 5, further comprising a control unit for controlling. The desulfurization apparatus according to claim 6, wherein the control unit controls the redox potential measured by the measurement unit to be 200 mV or less. The desulfurization apparatus according to any one of claims 5 to 7, wherein the first extraction unit extracts the slurry from the bottom of the alkaline agent-containing liquid chamber.

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