JP2001120948A - Wet stack gas desulfurizing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wet stack gas desulfurizing device capable of effectively uniformalizing the gas flow in an absorption tower by a simple means without increasing the pressure loss in the absorption tower and pump power. SOLUTION: An absorbing solution spraying part 4 of the absorption tower 2 is arranged at the upper side of a waste gas inlet 3, and a guide plate 20 arranged at the position placed oppositely to the waste gas inlet 3 in the absorption tower 2 while inclining upward from the horizontal direction toward a wall surface at the position placed oppositely to the waste gas inlet 3 from the waste gas inlet 3 side and arranged by providing a space between the wall surface of the absorption tower 2 at the gas inlet 3 side and a partition plate 21 arranged by standing almost in the vertical direction from the bottom part of a circulation tank 5 are provided. The waste gas introduced into the absorption tower 2 is to the upper side by colliding with the guide plate 20 and the gas flow in the absorption tower 2 is uniformalized without increasing the pressure loss in the tower. Sulfurous acid is oxidized to sulfuric acid at an absorbing solution oxidizing region 15 of the circulation tank 5 divided by the partition plate 21 while keeping pH at 2-4 and the reaction to gypsum is proceeded without precipitating calcium sulfite, and the lowering the desulfurization performance and the lowering in the purity of gypsum due to insufficient oxidation can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas desulfurization apparatus for removing sulfur oxides (hereinafter referred to as SOx) in exhaust gas using a slurry absorbing solution containing a desulfurizing agent such as limestone.
In particular, the present invention relates to a method for preventing gas drift in an absorption tower.

[0002]

2. Description of the Related Art In recent years, the natural environment surrounding the earth has been deteriorating. In particular, in thermal power plants and the like installed around the world, SO2 contained in exhaust gas generated by the combustion of fossil fuels has increased.
x and dust are one of the main causes of environmental problems such as air pollution.

[0003] In particular, recently, while the demand for lowering the concentration of SOx and dust has been required, the capacity of boilers has been increasing, and the demand for the development of a high-performance and low-cost flue gas desulfurization system has been urgently required. Have been.

FIG. 5 shows an example of a conventional flue gas desulfurization apparatus. The flue gas desulfurization device includes an absorption tower main body 2, a gas inlet 3, an absorbing liquid spraying part 4, a circulating tank 5, a circulating pump 6, a stirrer 7, an air blowing pipe 8, a mist collecting part 9, an absorbing liquid extracting pipe 10, It mainly includes a circulating liquid pipe 11, a gypsum dewatering device 12, a limestone supply pipe 13, and a recovery pipe 14.
Exhaust gas 1 is introduced from the gas inlet 3 and the absorbing liquid spray 4
The gas comes into gas-liquid contact with the absorbing liquid sprayed from the mist, and becomes a clean gas. After the mist entrained by the mist collecting unit 9 is removed, the gas is discharged.

[0005] Further, the absorbing liquid in gas-liquid contact descends in the absorption tower main body 2 and is temporarily retained in the circulation tank 5. In the circulation tank 5, the air supplied from the air blowing pipe 8 is miniaturized by the stirrer 7,
oxidizes x. The absorbing liquid in the circulating tank 5 is sucked by the circulating pump 6, pressurized, and sprayed by the absorbing liquid spray unit 4 via the circulating liquid pipe 11. During this time, the absorption liquid containing calcium carbonate sent by the circulation pump 6 is sprayed from the absorption liquid spray unit 4 arranged in the absorption tower main body 2, and the absorption liquid and the exhaust gas are brought into gas-liquid contact in the absorption tower main body 2. . At this time, the absorbent selectively absorbs SOx in the exhaust gas, generates sulfurous acid (H ₂ SO ₃ ), stays in the lower circulation tank 5, reacts with limestone (CaCO ₃ ), and reacts with calcium bisulfite (Ca ( HSO ₃ ) becomes sulfite ions in the _two liquids).

Further, by dispersing the air introduced from the air blowing pipe 8 in the circulation tank 5 by the stirrer 7, the calcium bisulfite is oxidized and finally gypsum (C)
aSO ₄ · _2H 2 O) to generate the. Most of the gypsum is removed by a gypsum dewatering device 12 through a recovery system pipe 14 branched from the absorbent extraction pipe 10. Normally, the gas inlet 3 is arranged to be inclined upward from the horizontal as it moves upstream so that the sprayed absorbent does not flow back upstream of the gas inlet 3.

In order to reduce the cost of the absorption tower of the recent desulfurization apparatus, the number of absorption liquid spray nozzles arranged in four to six stages is increased by increasing the number of nozzles provided per stage to two to three.
It has been reduced step by step.

However, since the resistance to the gas flow rising in the absorption tower is reduced by reducing the number of spray nozzles, the exhaust gas 1 introduced from the gas inlet 3 as shown in FIG. The flow rate of the exhaust gas to the wall surface side of the absorption tower main body 2 facing the gas inlet 3 increases because the flow tends to flow toward the wall surface side of the absorption tower main body 2 and the liquid level of the circulation tank 5. Also, recently, there has been a tendency to reduce the diameter of the absorption tower main body 2 in order to reduce the cost and the site area inside the absorption tower main body 2, thereby increasing the gas flow rate in the absorption tower main body 2. The drift will be further promoted. The spray amount of the absorbing liquid required for the SOx absorption efficiency is determined by the flow rate of the exhaust gas and the SOx in the exhaust gas.
Since it is determined according to the concentration, the deviation of the exhaust gas flow rate as described above causes a decrease in the absorption efficiency in the absorption tower main body 2 or a facility cost of the circulation pump 6 due to an increase in the spray amount of the absorption liquid,
It appears as an increase in operating costs.

As a conventional technique for preventing such a situation, there is a technique in which a porous gas dispersion plate 22 is arranged below the absorbing liquid spray section 4 as shown in FIG. However, in order to prevent the above-described drift of the exhaust gas by the gas dispersion plate 22, the aperture ratio of the gas dispersion plate 22 must be reduced. However, when the aperture ratio of the gas dispersion plate 22 is reduced, a large increase in pressure loss is inevitably caused.

[0010]

The above prior art increases the pressure loss in the absorption tower and the power of the pump when the number of spray nozzles and the tower shape are reduced in order to make the absorption tower compact. No consideration has been given to means for preventing gas drift in the absorption tower without any problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to reduce the pressure loss in the absorption tower and the gas flow in the absorption tower without increasing the power of the pump by simple means. It is an object of the present invention to obtain a wet exhaust gas desulfurization apparatus for making the gas uniformly uniform.

[0012]

The above object of the present invention is attained by the following constitution. That is, an absorption tower having an exhaust gas inlet for introducing sulfur oxide-containing exhaust gas discharged from a boiler or the like and an absorbent spraying section for spraying an absorbing liquid onto the introduced exhaust gas, and is disposed at a lower portion of the absorption tower. A circulation tank for storing the absorbing solution that has absorbed the sulfur oxides in the absorption tower,
A wet exhaust gas desulfurization apparatus having an absorption liquid circulation flow path for circulating a part of the absorption liquid in the circulation tank to the absorption liquid spray section of the absorption tower, wherein the absorption liquid spray section of the absorption tower is located above the exhaust gas inlet section. Arranged at a position in the absorption tower facing the exhaust gas inlet, inclined upward from the horizontal direction from the exhaust gas inlet side toward the absorption tower wall surface at a position facing the exhaust gas inlet,
In addition, a flat guide plate is arranged at an interval between the absorption tower wall on the side of the exhaust gas and the wall inclined upward from the horizontal direction toward the absorption tower wall on the side of the exhaust gas, and circulation is performed. In the tank, the circulation tank located below the exhaust gas inlet of the absorption tower and the circulation tank opposed to the exhaust gas inlet and below the gap provided between the guide plate and the absorption tower wall on the gas inlet side A partition plate is set up in the vertical direction from the bottom of the circulation tank to partition the inside of the tank. In the region in the circulation tank opposite to the oxidation region partitioned by the plate, an absorption liquid extracting portion connected to the absorption liquid circulation channel was arranged, and an alkaline desulfurizing agent supply portion was provided above the region. This is a wet exhaust gas desulfurization unit with a neutralization zone.

[0013]

According to the present invention, since the guide plate is arranged to be inclined upward from the gas inlet to the direction facing the gas inlet, the guide plate will flow toward the side wall of the absorption tower facing the gas inlet. Is guided upward by colliding with the guide plate. That is, since the gas flow direction is guided upward without narrowing the gas flow path as in a gas dispersion plate or the like, the gas flow in the absorption tower can be made uniform without increasing the pressure loss in the absorption tower.

When the guide plate is formed into a grid or a porous shape, the air blown from the air blowing section tends to stay in the space between the guide plate and the liquid level in the circulation tank. Since it has a porous shape, it can also serve as an air vent.

[0015] When the concentration of SOx in the exhaust gas increases, the concentration of sulfurous acid in the absorbing solution increases to 10 to 20 mmol / l, but when the pH of the ordinary absorbing solution is 5 to 5.5, it exceeds the limit value of the concentration of dissolved sulfurous acid. Therefore, SOx absorbed in the absorbing solution precipitates as calcium sulfite (CaSO ₃ ). Since the precipitated calcium sulfite is no longer oxidized by oxygen, it is circulated while remaining in the absorbing solution, which causes a decrease in desulfurization performance and a decrease in purity of the recovered gypsum.

Accordingly, SOx is absorbed so that it does not precipitate as calcium sulfite even when the sulfurous acid concentration becomes 10 mmol / L or more, and is oxidized in an absorbing solution whose pH has been lowered to about 2 to 4, so that SOx is absorbed. The partition plate is provided in the circulation tank as a configuration for reacting with oxygen in the air before reacting with the limestone. Then, the sulfurous acid is oxidized by oxygen in the air blown from the air blowing part to become sulfuric acid (H ₂ SO ₄ ), which is supplied with limestone over the partition plate, and is supplied to the neutralized region where the absorbing liquid extracting part is also installed. Be guided. The neutralization zone gypsum by reacting sulfuric acid with limestone (CaSO ₄ · 2H
₂ O), where the pH first recovers to 5 or higher.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific examples of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. FIG. 1 is a sectional view of a wet exhaust gas desulfurization device for an absorption tower according to an embodiment of the present invention. In FIG. 1, reference numerals 1 to 14 indicate the same components as those of the prior art. In such a structure, the guide plate 20 has a flat plate shape, is above the liquid level of the circulation tank 5, and is arranged to be inclined upward as it goes from the gas inlet 3 to the inside of the absorber main body 2. The guide plate 20 has an opening on the gas inlet 3 side (between the absorption tower side wall and the tip of the guide plate 20).
have.

With this structure, the exhaust gas 1 supplied into the absorption tower main body 2 can be made to collide with the guide plate 20 so that the flow direction of the exhaust gas can be directed upward. As a result, even if the number of stages of the absorbing liquid spray unit 4 is reduced to two to three stages as compared with the conventional absorbing tower to reduce the resistance of the internal structure to the gas flow in the absorbing tower 2, the absorbing liquid spray unit 4 does not The sprayed absorbent and the exhaust gas 1 are in gas-liquid contact uniformly. Since the absorbent and the exhaust gas 1 are in uniform contact, the absorption efficiency of sulfur oxides in the exhaust gas 1 can be improved without increasing the pressure loss.

The absorbing liquid sprayed in the absorbing liquid spraying section 4 comes into gas-liquid contact with the exhaust gas 1 so that the S
After Ox is absorbed, it falls onto the guide plate 20 and falls
Flows down in the direction of the opening according to the inclination of the opening, and falls into the circulation tank 5 from the opening. In the circulation tank 5, it reacts with limestone (CaCO ₃ ) to react with calcium bisulfite (Ca
(HSO ₃ ) becomes sulfite ions in the _two liquids), and the air introduced from the air blowing pipe 8 is dispersed in the absorption liquid in the circulation tank 5 by the stirrer 7, so that calcium bisulfite is is allowed oxidized by oxygen in the air ultimately produce gypsum _{(CaSO 4 · 2H 2 O)} . Most of the gypsum is removed by the gypsum dewatering device 12 through the recovery system pipe 14 branched from the absorbent extraction pipe 10.

In the exhaust gas desulfurization apparatus shown in FIG. 1, the absorption liquid in the circulation tank 5 is divided into an oxidation zone 15 and a neutralization zone 16 so that the oxidation tank 15 can be effectively oxidized. A characteristic feature is that a partition plate 21 is provided at the center in a substantially vertical direction from the bottom of the tank.

The interior of the circulation tank 5 is divided by a partition plate 21 into a space on the side where the absorbing liquid flows down from the guide plate 20 and a space on the absorption extraction pipe side of the circulation pump 6. A stirrer 7 and an air blowing pipe 8 are provided on the side where the absorbing liquid flows down from the opening of the guide plate 20, and the stirrer 7 atomizes the air and oxidizes sulfurous acid in the absorbing liquid. Therefore, this space is referred to as an oxidation zone 15.

On the other hand, the absorbent drain pipe 1 of the partition plate 21
The limestone supply pipe 1 is located in the neutralization zone 16 in the circulation tank 5 on the 0 side.
The absorbing solution oxidized from sulfurous acid to sulfuric acid in the oxidation zone 15 flows over the upper part of the partition plate 21 and flows into the neutralization zone 16. The neutralizing zone 16 is also provided with a stirrer 7, which only needs to stir the absorbing liquid in the neutralizing zone 16 so as not to deposit on the bottom of the solids circulation tank 5. A part of the absorbing solution in the neutralization zone 16
Gypsum dewatering device 12 from the middle of
Sent to

FIG. 4 shows the relationship between the pH of the absorbing solution and the concentration of dissolved sulfurous acid.
000 ppm, and the SOx concentration (sulfurous acid concentration) absorbed in the absorbing solution in this case is 1-2 mmol / liter. The pH of a normal absorbing solution is operated in the range of 5 to 5.5. At this time, the concentration of sulfurous acid that can be dissolved in the absorbing solution is about 2 to 2.
Since it is 4 mmol / liter, the absorbed SOx all dissolves sulfite ions and is easily oxidized by oxygen in the air blown into the circulation tank 5 and reacts with limestone to form gypsum.

However, in recent thermal power plants, the concentration of SOx in exhaust gas tends to increase due to diversification of fuels and the like, and the concentration of SOx in high exhaust gas is 4000 ppm or more. When the SOx concentration becomes high, the sulfurous acid concentration in the absorbing solution increases to 10 to 20 mmol / liter. However, when the pH of the normal absorbing solution is 5 to 5.5, the dissolved sulfurous acid concentration exceeds the limit value. S absorbed in liquid
Ox precipitates out as calcium sulfite (CaSO ₃ ). Since the precipitated calcium sulfite is no longer oxidized by oxygen, it is circulated while remaining in the absorbing solution, which causes a decrease in desulfurization performance and a decrease in purity of the recovered gypsum.

Therefore, in order to prevent precipitation as calcium sulfite even when the sulfurous acid concentration becomes 10 mmol / liter or more, it is sufficient to oxidize the absorbing solution at a low pH. That is, if it reacts with oxygen in the air before reacting with the limestone that has absorbed SOx, it becomes sulfuric acid by an oxidation reaction, and then it becomes gypsum by reacting with limestone.

In FIG. 1, the absorbing solution that has contacted with the exhaust gas 1 and absorbed SOx becomes sulfurous acid (H ₂ SO ₃ ), and the pH drops to about 2 to 4. Immediately after absorbing the SOx, the absorbent falls toward the circulation tank 5, but collides with the guide plate 20 installed above the circulation tank 5 and advances along the inclination of the guide plate, and the absorbent in the circulation tank 5 It falls into the oxidation zone 15 on the side wall of the circulation tank 5 facing the extraction pipe 10 side. At this point, the sulfite in the absorbing solution is still limestone (C
Since it has not reacted with aSO ₃ ), the pH is maintained at 2 to 4. Next, the sulfurous acid is oxidized by oxygen in the air blown from an air blowing pipe 8 provided in the circulation tank 5 to become sulfuric acid (H ₂ SO ₄ ). On the other hand, since the limestone is supplied to the absorption liquid extraction pipe 8 side of the circulation tank 5, the sulfuric acid is guided to the neutralization zone 16 where the limestone is supplied, and reacts with the limestone to form gypsum (CaSO ₄ .2).
H ₂ O), where the pH first recovers to 5 or higher. The above reaction is shown below.

Absorption reaction: SOx + H₂O = H₂SO₃ Oxidation reaction: H₂SO₃+ 1 / 2O₂= H₂SO₄ Neutralization reaction: CaCO₃+ H₂SO₄+ H₂O = CaSO
₄・ 2H₂O + CO ₂

That is, SO absorbed in the unit absorbing solution
Even if the amount of x becomes 5 mmol / liter or more, the absorbed SOx is oxidized while maintaining the pH at 2 to 4 until it reacts with limestone, so that the reaction can proceed to gypsum without precipitation of calcium sulfite. it can. Therefore, a decrease in desulfurization performance and a decrease in gypsum purity due to insufficient oxidation can be prevented.

Next, FIG. 2 shows an embodiment in which the guide plate 20 is formed in a grid shape or a perforated plate. The other members denoted by reference numerals in the figure are the same as those in FIG. In the case of the apparatus shown in FIG. 2, the effect of preventing the gas drift in the absorption tower is the same as that of the flat guide plate 20 shown in FIG. 1, but the guide plate 20 having the shape of a grid or a perforated plate is provided. Also serves as a vent. That is, some air blown from the air blowing pipe 8 tends to stay in the space between the guide plate 20 and the liquid level of the circulation tank 5, but the air is evacuated from the guide plate 20 to the upper part of the absorption tower. Can be missed. Further, the absorbent containing sulfurous acid that falls on the guide plate 20 has an effect of contacting air on the guide plate 21, on the surface of the grid inside the guide plate 20, or on the surface of the holes to oxidize the sulfurous acid.

Next, the structure shown in FIG. 3 shows an embodiment in which the guide plate 20 and the partition plate 21 are integrated. Reference numeral 23 denotes an air vent hole, and reference numeral 24 denotes a baffle. Other symbols are the same as those in FIG.

In the case of FIG. 3, the function of the partition plate 21 is the same as that described in FIG. 1, but the liquid in the oxidation zone 15 passes through the space between the partition plate 21 and the bottom of the circulation tank 5 and is neutralized. It is led to 16. Therefore, an air vent hole 23 is provided to prevent the air supplied from the air blowing pipe 8 from being entrained by the liquid guided to the neutralization region 16 and remaining in the neutralization region 16. In addition, the air entrained in the neutralization zone 16 is used to remove the absorbent extraction pipe 10.
When entrained by the liquid extracted from the circulating fluid, the liquid is drawn into the circulating pump 6, which causes a reduction in absorption performance due to a shortage of circulating liquid. Therefore, the baffle 24 is connected to the absorbent drain pipe 10.
To prevent air entrapment.

[0032]

As is clear from the above description, according to the present invention, the gas flow can be made uniform without increasing the pressure loss in the absorption tower, and the sulfurous acid concentration in the absorbing solution is 5 mmol / Even if it is higher than 1 liter, it can be oxidized without precipitating calcium sulfite, and it is possible to prevent a decrease in desulfurization performance and a decrease in gypsum purity.

[Brief description of the drawings]

FIG. 1 is a sectional side view of an absorption tower showing one embodiment of the present invention.

FIG. 2 is a sectional side view of an absorption tower showing one embodiment of the present invention.

FIG. 3 is a sectional side view of an absorption tower showing one embodiment of the present invention.

FIG. 4 shows the relationship between the pH of the absorbing solution and the concentration of sulfurous acid dissolved in the absorbing solution.

FIG. 5 is a cross-sectional side view of an absorption tower showing an example of the related art.

FIG. 6 is a cross-sectional side view of an absorption tower showing an example of the prior art.

FIG. 7 is a cross-sectional side view of an absorption tower showing an example of the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Exhaust gas 2 Absorption tower 3 Gas inlet part 4 Absorbing liquid spray part 5 Circulation tank 6 Circulating pump 7 Stirrer 8 Air blowing pipe 9 Mist collection part 10 Absorbing liquid extraction pipe 11 Circulating liquid pipe 12 Gypsum dewatering device 13 Limestone supply pipe 14 Recovery system piping 15 Oxidation zone 16 Neutralization zone 20 Guide plate 21 Partition plate 22 Gas dispersion plate 23 Air vent hole 24 Baffle

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor: Naruto Takamoto No. 3-36, Takara-cho, Kure-shi, Hiroshima Pref. F-term in Babcock Hitachi, Ltd. GA02 GB02 GB09 4D020 AA06 BA02 BA09 BB05 CB25 CB27 CC04 CC07 CC08 CD01 DA02 DA03 DB03 DB08

Claims (4)

[Claims] An absorption tower having an exhaust gas inlet for introducing a sulfur oxide-containing exhaust gas discharged from a boiler or the like, an absorbent spraying section for spraying an absorbing liquid onto the introduced exhaust gas, and a lower part of the absorption tower. A circulating tank for storing the absorbing solution that has absorbed the sulfur oxides in the absorption tower, and an absorbing solution circulating flow path for circulating a part of the absorbing solution in the circulating tank to the absorbing solution spray portion of the absorbing tower. In the wet exhaust gas desulfurization system provided, the absorption liquid spray part of the absorption tower is arranged above the exhaust gas inlet, and a position in the absorption tower facing the exhaust gas inlet, facing the exhaust gas inlet from the exhaust gas inlet side Inclined upward from the horizontal direction toward the wall surface of the absorption tower, and inclined upward from the horizontal direction toward the absorption wall surface on the exhaust gas inlet side, and between the absorber wall surface on the gas inlet side. Is a flat guide plate with an interval In the circulation tank, the inside of the circulation tank located below the exhaust gas inlet portion of the absorption tower and the exhaust gas inlet portion are opposed, and the lower portion of the space provided between the guide plate and the absorption tower wall surface on the gas inlet portion side. The partition inside the circulation tank, a partition plate that stands almost vertically from the bottom of the circulation tank is arranged, and the region in the circulation tank on the exhaust gas inlet side partitioned by the partition plate is an oxidation region provided with an air blowing part. An area in the circulation tank opposite to the oxidation area partitioned by the partition plate is provided with an absorbent extraction section connected to the absorbent circulation flow path, and an alkaline desulfurizing agent supply section is provided above the area. A wet exhaust gas desulfurization unit characterized by a neutralization zone provided. 2. The wet exhaust gas desulfurization apparatus according to claim 1, wherein the guide plate is formed of a grid or a perforated plate. 3. The wet exhaust gas desulfurization apparatus according to claim 1, wherein a space is provided in which the absorbing liquid is sent from the oxidation zone to the neutralization zone over the opening of the partition plate or above the partition plate. 4. The liquid separating device according to claim 3, wherein the guide plate and the partition plate have an integral structure, and a liquid separating means having a space between the partition plate and the bottom of the circulation tank is provided.
A wet exhaust gas desulfurization apparatus as described in the above.