JPH06170153A - Treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To provide a method for treating exhaust gas economically and favorably in the case of performing dust removal and desulfurization treatment of exhaust gas in a scrubber by decreasing trouble of corrosion in a route of exhaust gas and avoiding trouble in loss of an alkali agent. CONSTITUTION:Dust removal and desulfurization are performed by introducing exhaust gas G into many pieces of scrubbers 1 (1A-1E) arranged in a row and bringing a processing solution containing a desulfurizing agent consisting of water and an alkali agent into contact therewith. In the case of leading exhaust gas G' derived from the respective scrubbers 1 (1A to 1E) to a stack 7 through the respective fans 5 (5A to 5E) and discharging it to the atmosphere, a treatment flow path 9 is formed by which the processing solutions of the respective scrubbers 1 (1A to 1E) are successively transferred to the adjacent scrubber sides. The whole amount of the desulfurizing agent necessary for the respective scrubbers is supplied to the initial scrubber 1A side in the treatment flow path 9. pH of the processing liquid in the final scrubber 1E side is regulated to about 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas discharged from a coal combustion boiler or the like, and more particularly to a method for dedusting and desulfurizing ash contained in exhaust gas and sulfur oxides such as SO _2. It is a thing.

[0002]

2. Description of the Related Art Dedusting and desulfurization of this type are usually carried out in this order, but it is desirable to carry out at the same time in consideration of the installation site and equipment costs. The simultaneous treatment method involves contacting the exhaust gas introduced into the scrubber with a treatment liquid containing a desulfurizing agent consisting of water and an alkaline reagent to capture the ash in the exhaust gas and simultaneously reacting sulfur oxides with the alkaline reagent. There is a method of removing it as a desulfurization product.

In a power plant and the like, a large number of boilers are operated at the same time, so the exhaust gas discharged from each boiler is dedusted and desulfurized as described above in separate scrubbers. The exhaust gas is collected by each blower into one flue and discharged into the atmosphere from one chimney.

By the way, in such an exhaust gas treating method, the desulfurization reaction in the scrubber is carried out by using the desulfurizing agent as Mg.
In the case of (OH) _2, the following formulas (1) and (2); Mg (OH) ₂ + SO ₂ + H ₂ O = MgSO ₃ + H ₂ O (1) MgSO ₃ + SO ₂ + H ₂ O = Mg (HSO ₃ ) reaction of ₂ ... (2) occurs. Both reactions depend on the pH of the treatment solution,
When H is low, the reaction of the formula (2) is mainly and Mg (HS
A large amount of O ₃ ) ₂ is produced, and when PH is high, the reaction of the formula (1) is mainly produced and a large amount of MgSO ₃ is produced. Therefore, the ratio of MgSO ₃ / Mg (HSO ₃ ) _{2 in} the treatment liquid is, for example, 1/10 at PH 5.8, 1/1 at PH 6.8, P
It seems that it will be 10/1 at H7.8.

Here, if the pH of the treatment liquid is set to the above-mentioned 5.8, when some mist escapes to the exhaust path of the exhaust gas, the drain becomes a liquid containing a high concentration of Mg (HSO ₃ ) _2. This causes the reaction of oxygen in the exhaust gas with the following formula (3); Mg (HSO ₃ ) ₂ + O ₂ = MgSO ₃ + H ₂ SO ₄ (3) to generate sulfuric acid. As a result, the pH of the drain drops to about 2 and corrodes the blower, flue, and chimney in the exhaust path. Therefore, the material of the blower and the like is not made of stainless steel but must be an expensive acid resistant material, and the flue and chimney must also be provided with an expensive acid resistant lining.

On the other hand, if the pH of the treatment liquid is set to 7.8, the drain in the exhaust path contains a large amount of MgSO ₃ , so that sulfuric acid is not produced by the reaction of the above formula (3). . Therefore, there is no concern about corrosion of the blower, etc., and it can be handled with inexpensive materials such as stainless steel and lining. However, if the PH is increased in this way, CO ₂ mixed in the exhaust gas by about 10 to 15%,
The following formula (4): Mg (OH) ₂ + 2CO ₂ + H ₂ O = Mg (HCO ₃ ) ₂ + H ₂ O (4) will occur, and the bicarbonate produced by this reaction Since it is discharged to the outside, it becomes a loss of the desulfurizing agent.

As an example, the concentration of SO ₂ in exhaust gas is set to 6
When the concentration of CO _{2 is} 00 ppm and the concentration of CO ₂ is 10%, the ratio of the loss as the discharged bicarbonate is about 2% at PH6, and about 6.3% at PH6.3 with respect to the net Mg (OH) ₂ used as the desulfurizing agent.
About 4%, PH 6.6 about 8%, PH 6.7 about 10
%, PH 7.0 is about 20%. Therefore, in terms of economic efficiency, the above loss is about 2-4% P
It is desirable to treat at about H6 to 6.3, but in this case, as described above, there arises a problem of corrosion of the blower of the exhaust path, the flue, the chimney, and the like.

In the above, as the desulfurizing agent, Mg (O
H) ₂ has been described as an example, but other CaO, Ca
This is almost the same when using compounds such as (OH) ₂ containing Mg and Ca, as well as caustic soda and caustic potash, and this is an unavoidable problem as long as an alkaline reagent is used as a desulfurizing agent.

[0009]

As described above, in the conventional treatment method for dedusting and desulfurizing exhaust gas in the scrubber, if the alkaline reagent which is a desulfurizing agent is reduced and the pH of the treating solution is kept low. , The problem of corrosion occurs in the exhaust path after the scrubber, and it is necessary to use expensive acid-resistant materials etc. as a countermeasure against it, and conversely, if the amount of alkaline reagent is increased and the pH of the processing liquid is set high, All of them had to be economically disadvantageous, such as causing the problem of loss.

In view of the above circumstances, the present invention reduces the problem of corrosion in the exhaust passage when dedusting and desulfurizing exhaust gas in a scrubber, and avoids the problem of alkali reagent loss. The purpose is to provide an economically advantageous treatment method.

[0011]

Means for Solving the Problems The present inventor has conducted extensive studies in order to achieve the above-mentioned object, and as a result, as described above, exhaust gas discharged from a large number of boilers in a power plant or the like is separated into separate scrubbing chambers. -Dust removal and desulfurization inside, and the exhaust gas after this treatment was collected into one flue by each blower and discharged from one chimney into the atmosphere. In the method of treating exhaust gas using
In the exhaust gas discharged from each scrubber, by creating a processing flow path that sequentially transfers the processing liquid discharged from each scrubber to the adjacent scrubber side and devising the method of adding the alkaline reagent to this processing flow path. The inventors have found that the problem of corrosion in the exhaust path due to the mist can be reduced and the problem of loss of the alkaline reagent can be avoided, and have completed the present invention.

That is, according to the present invention, an exhaust gas containing ash and sulfur oxides is introduced into a large number of parallel scrubbers, and a treatment liquid containing a desulfurizing agent consisting of water and an alkaline reagent is brought into contact with the scrubber to remove the exhaust gas. Dedust and desulfurize,
Next, when the exhaust gas discharged from each scrubber is guided to the chimney by each blower and discharged into the atmosphere, a processing flow path is formed to sequentially transfer the processing liquid of each scrubber to the adjacent scrubber side. The total amount of desulfurizing agent required for each scrubber is supplied to the first scrubber side in the route, and the pH of the treatment liquid on the final scrubber side is about 6
The present invention relates to a method for treating exhaust gas, which is characterized in that it is arranged before and after.

[0013]

In the present invention, since the entire amount of the desulfurizing agent necessary for each scrubber is supplied to the first scrubber side in the processing flow path connecting the scrubbers, the treatment is performed before reaching the final scrubber side. The pH of the liquid is kept at a high value of about 7 or more due to the excess alkaline reagent, and the mist of the exhaust gas discharged from the corresponding scrubber does not acidify the drain and corrodes the blowers directly connected. Don't worry.

On the other hand, when the high PH is set as described above,
Each Sukuratsuba - salts such as Mg (HCO _{3) 2} by reaction with CO ₂ comes contains a large amount in the processing solution discharged from, but this compound final Sukuratsuba - when there was Itaritsu the side, the processing solution Since the pH is set to around 6, it is used for decomposition in the desulfurization reaction and is rarely discharged as a bicarbonate to the outside of the system, and the loss of the alkaline reagent is suppressed as much as possible.

Further, when the final scrubber side is set to around PH6, the exhaust gas mist derived from this scrubber contains a high concentration of Mg (HSO ₃ ) _{2 and the} like, which is a cause of acidification of the drain. As a result, the corresponding blower or duct may be corroded. For this reason, these blowers and ducts need to be made of expensive acid-resistant material or have an expensive acid-resistant lining, but the cost increase due to this is that of all blowers and ducts of all scrubbers. As it is a small part, it is not a big cost up as a whole.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an apparatus to which the exhaust gas treating method of the present invention is applied.

In FIG. 1, reference numeral 1 (1A to 1E) denotes five parallel scrubbers, which are boilers 2 (2B to 2E).
Exhaust gas is introduced from the water injection pipe 3 (3A to 3E)
Also, by adding water and water slurry of Mg (OH) ₂ from the desulfurizing agent storage tank 4 and bringing them into contact with each other, the exhaust gas is dedusted and desulfurized.

5 (5A to 5E) is a scrubber 1 (1
The exhaust gas derived from A to 1E) is collected in the flue 6 and
This is a blower that is emitted from the chimney 7 of the book into the atmosphere. 8 (8
A-8E), the blower 5 (5A-5
A duct with E), which is connected to the flue 6 described above.

Reference numeral 9 denotes a processing flow path for sequentially transferring the processing liquid of each of the scrubbers 1A to 1E to the adjacent scrubber side by a pipe 10 (10A to 10E). Each scrubber 1 on the side of the scrubber 1A
All the desulfurizing agents required for A to 1E are supplied from the desulfurizing agent storage tank 4 through the pipe L. The supply amount of the desulfurizing agent is about 6 when the pH of the treatment liquid on the final scrubber 1E side is about 6 It is adjusted by automatic control so that the front and rear, that is, about 5.7 to 6.3.

The above-mentioned scrubber-1 (1A-1E) is
In this example, it is composed of a bench-yuri scrubber. FIG. 2 shows the configuration of the scrubber 1A. The other scrubbers 1B-1E are exactly the same. Figure 2
Inside, 11 is a bench lily tube, 12 is a tower type cyclone,
Reference numeral 13 is a connection pipe, 14 is a processing liquid receiving tank, 15 is a classifier (hydrocyclone), and 16 is a pump.

In this type of scrubber, the exhaust gas G is introduced from the open end side of the bench-free pipe 11 and is made into a high-speed air flow at its narrowed portion to disperse the water supplied from the water injection pipe 3 (3A) into fine droplets. Then, dust particles made of ash in the exhaust gas are made to collide with and adhere to the water droplets, and the adhered water droplets are introduced tangentially to the lower portion of the cyclone 12 through the connecting pipe 13 by the gas flow, and are caught by the tower wall by centrifugal force. Drop it to the bottom of the tower.
Separately, in the connection pipe 13, Mg which is a desulfurizing agent is used.
A treatment liquid containing (OH) ₂ is supplied to cause a reaction with sulfur oxides in the exhaust gas to obtain a desulfurized product, and the desulfurized product is dropped to the bottom of the cyclone together with the captured dust.

The treatment liquid thus trapping the ash and containing the desulfurization product is transferred from the bottom of the tower to the receiving tank 14, where it is oxidized by the air sent from the sparger 17 if necessary. After that, it is supplied to a classifier (hydrocyclone) 15 by a horn 16, the fine slurry from which the captured ash is removed is circulated and supplied to the connection pipe 13, and the coarse slurry containing the captured ash is supplied to the pipe 10 (10).
By A), it is transferred to (the receiving tank for) the adjacent Scrubber-1 (1B). The classifier 15 described above may use a shockener instead of the liquid cyclone.

According to such an apparatus configuration, each boiler is
Exhaust gas G discharged from 2A to 2E is introduced into the corresponding scrubbers 1A to 1E and subjected to dedusting and desulfurization treatment as described above. At that time, the scrubbers 1A to 1E are treated.
The total amount of desulfurizing agent required for E is supplied from the storage tank 4 to the scrubber 1
It is supplied only to the A side, and this is the scrubber 1B →
Because of the shift from 1C → 1D → 1E, SCRATSUBA 1D
Sufficient alkali reagent, namely Mg
There will be (OH) ₂ .

For this reason, since the PH of the treatment liquids of the scrubbers 1A to 1D is maintained at a high value of about 7 or more, the exhaust gas G discharged from the scrubbers 1A to 1D after being subjected to dedusting and desulfurization treatments. 'Is MgSO in the mist
_It will contain a large amount of ₃ , and the drain will not be acidified. Therefore, the blower 5A carrying this exhaust gas G '
.About.5D and ducts 8A to 8D have no particular concern about corrosion, and may be made of an inexpensive stainless steel material or may be provided with a normal lining.

If the high PH is set as described above,
CO in the treatment liquid discharged from the scrubber 1A to 1D.
_A large amount of salts such as Mg (HCO ₃ ) ₂ are included in the reaction with ₂ , but when this reaches the final side of the scrubber 1E (reception tank 14), the pH of the treatment liquid is about 6 Since it is set before and after, it can be decomposed and utilized well for desulfurization reaction,
It is not discharged outside the system as bicarbonate.

Therefore, this final Scratuba-1E
The treatment liquid discharged from the (classifier 15) side to the outside of the system through the pipe 10E contains all the ash content captured by each of the scrubbers 1A to 1E as the main solid content, and contains magnesium sulfate or the like in the liquid. A water slurry containing desulfurization products,
It is discharged to the outside of the system with the loss of the alkaline reagent being suppressed as much as possible, and appropriately disposed or collected.

On the other hand, the exhaust gas G'which is dedusted and desulfurized from the final scrubber 1E and is discharged is P of the treatment liquid.
Since H is set at around 6, high-concentration Mg (HSO ₃ ) ₂ etc. is contained in the mist, which causes acidification of the drain, so the blower 5E carrying this exhaust gas G '
And the duct 8E may be corroded. Therefore,
For these, it is necessary to take measures such as using an expensive acid resistant material or applying an expensive acid resistant lining, but as already mentioned, other blowers 5A to 5D and ducts 8A to 8D are used.
Since it is possible to use low cost materials etc., the overall cost does not increase, and economical equipment cost can be covered.

Moreover, as shown in this embodiment, when all the exhaust gases G'guided from the ducts 8A to 8E are collected in the flue 6 and discharged into the atmosphere from one chimney 7, the duct 8A side is the chimney 7. Position closest to, in other words duct 8
If the E side is located farthest from the chimney 7, the exhaust gas G ′ containing the acidic mist discharged from the duct 8E is diluted by the exhaust gas G ′ containing the alkaline mist discharged from the ducts 8D to 8A. Will be done.

Therefore, even if the acid-resistant lining is required on the duct 8E side of the flue 6, the ducts 8D to 8D thereafter are provided.
A does not require a very expensive lining, and the chimney 7 is almost unaffected by the acid mist. Therefore, a normal lining is sufficient, and this is also a great economical advantage.

In the above embodiment, the boiler-2A-
Exhaust gas discharged from 2E is used for each scrubber 1A to 1E.
Introduced in the example, the boiler-2A
When the amount of exhaust gas is extremely large, it may be divided and introduced into each of the scrubbers 1A to 1E. Further, the scrubber 1 is not limited to the above bench Yury scrubber, and various scrubbers known as a wet method such as a perforated plate type scrubber can be used, and the number thereof is not limited to the above five, Any number of 2 or more, preferably 3 or more can be selected.

Alkaline agents used as desulfurizing agents include CaO and Ca (O) in addition to the above Mg (OH) _2.
Various compounds containing Mg and Ca such as H) ₂ can be used, and caustic soda and caustic potash may be used. Regardless of which alkaline reagent is used, the same action and effect as described above can be obtained.

[0032]

As described above, according to the present invention, it is possible to reduce the problem of corrosion of the blower and the like in the exhaust path, avoid the problem of alkali reagent loss, and provide an economically advantageous exhaust gas treatment method. Can be provided.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus to which an exhaust gas treating method of the present invention is applied.

FIG. 2 is a schematic configuration diagram of a scrubber used in the exhaust gas treatment method of the present invention.

[Explanation of symbols]

1 (1A to 1E) Scrubber 3 (3A to 3E) Water injection pipe 4 Storage tank of desulfurizing agent consisting of Mg (OH) ₂ water slurry 5 (5A to 5E) Blower 7 Chimney 9 Processing flow path 10 (10A to 10E) ) Piping for transferring the treatment liquid to the adjacent scrubber side G Exhaust gas before treatment G ′ Exhaust gas after treatment

Claims (1)

[Claims] 1. Dedusting and desulfurization of exhaust gas by introducing exhaust gas containing ash and sulfur oxides into a large number of parallel scrubbers and contacting this with a treatment liquid containing a desulfurizing agent consisting of water and an alkaline reagent. Then, in guiding the exhaust gas discharged from each scrubber to the chimney by each blower and releasing it into the atmosphere, a processing flow path for sequentially transferring the processing liquid of each scrubber to the adjacent scrubber side is formed, The first scrubber side in this treatment channel is supplied with the total amount of desulfurizing agent required for each scrubber so that the pH of the treatment liquid on the final scrubber side is about 6 or less. Exhaust gas treatment method.