JPH09173765A - Flue gas desulfurizer using magnesium hydroxide as absorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To incorporate a MgSo3 oxidizing tower separately installed before into an absorber to simplify a desulfurization system and reduce the cost in a desulfurizer using magnesium hydroxide as an absorbent by dividing the liquid accumulation part of the absorber in two by a partition wall. SOLUTION: A flue gas desulfurizer 10 uses magnesium hydroxide as a slurry absorbent 6 and is constituted so that the slurry absorbent 6 can be sprayed from the upper part of an absorber to bring it into contact with waste gas 5 and desulfurize it. In this case, a liquid accumulation part 2 of the slurry absorbent 6 in the lower part of the absorber 1 is divided in two by a partition wall 3, and one liquid accumulation part 2A is provided with a slurry feeding means 14 for feeding the slurry absorbent 6 containing magnesium hydroxide thereto and is provided with a circulating line 4b for circulating the slurry absorbent in a spray pipe 4a in the upper part of the absorber, and the other liquid accumulation part 2B is provided with an oxidizing air blow-in means 7.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a flue gas desulfurization apparatus for desulfurizing SO _X contained in exhaust gas from a boiler using magnesium hydroxide as an absorbent, and particularly to a magnesium sulfite produced as a by-product in an absorption tower. The present invention relates to a flue gas desulfurization device in which an oxidation tower is omitted by oxidizing inside.

[0002]

2. Description of the Related Art Sulfur oxides in exhaust gas generated after combustion of fuel in a boiler are desulfurized by an absorbent in a desulfurizer.

FIG. 2 shows a desulfurizer 20 using magnesium hydroxide as an absorbent, according to the prior art. In the desulfurization device 20, the sulfur oxides (mainly SO ₂ , SO ₂
First, the exhaust gas containing ₃ ) is introduced into the absorption tower 8, where the absorbent slurry containing magnesium hydroxide is injected from the upper part of the absorption tower to contact with the exhaust gas, and the sulfur oxides in the exhaust gas are converted into the absorbent slurry. Desulfurizes by absorbing and removing.
Here, SO ₂ and SO ₃ , which are the main sulfur oxides, combine with magnesium hydroxide in the absorbent slurry to form magnesium sulfite and magnesium sulfate as shown in the following formula.

Mg (OH) ₂ + SO ₂ → MgSO ₃ + H ₂ O ...... (1) Mg (OH) ₂ + SO ₃ → MgSO ₄ + H ₂ O ・ ・ ・ (2) Formula (2) Although magnesium sulfate can be discharged as it is, magnesium sulfite produced by the formula (1) is CO
Since D (chemical oxygen demand) is high, it is discharged after oxidizing air is blown in the oxidation tower 9 to form magnesium sulfate.

MgSO ₃ + 1 / 2O ₂ → MgSO ₄ (3)

[0006]

However, if the oxidation tower 9 is installed separately from the absorption tower 8, the system becomes large and complicated, and the cost for installation and maintenance is also high. If the absorption tower 8 can oxidize magnesium sulfite, the oxidation tower 9 can be omitted, which is very advantageous in terms of downsizing of the system and cost reduction. However, it is not desirable to simply omit the oxidation tower 9 and blow the oxidizing air directly into the liquid reservoir of the absorbent slurry of the absorption tower 8 to completely oxidize the magnesium sulfite in the absorption tower 8. The reason will be described below.

[0007] For SO ₂ based on the equation (1) is reacted with Mg (OH) ₂ is dissolved in H ₂ O of SO ₂ is first slurry solution the need for sulfite, sulfite Is unstable and easily returns to SO ₂ by a reversible reaction.

H ₂ O + SO ₂ → H ₂ SO ₃ → H ₂ O + SO ₂ (4) However, if magnesium sulfite is present, SO ₂ becomes Mg (HSO ₃ based on the following formula (5). ) ₂ is stably incorporated into H ₂ O.

MgSO ₃ + SO ₂ + H ₂ O → Mg (HSO ₃ ) ₂ (5) In other words, the existence of MgSO ₃ is indispensable for the above equation (1) to proceed smoothly, and therefore it is not possible to completely oxidize magnesium sulfite in the absorption tower. Desulfurization effect deteriorates. Therefore, some of the magnesium sulfite is always absorbed to some extent in the absorption tower 8.
It is desirable to oxidize magnesium sulfite while leaving it inside.

Therefore, an object of the present invention is to omit the oxidation tower for oxidizing the absorbent slurry after absorbing SO _X , while improving the inside of the absorption tower to add Mg in addition to the conventional function as an absorption tower.
It is to be able to oxidize SO ₃ (however, at this time, a part of MgSO ₃ is left unoxidized).

[0011]

In order to achieve the above object, the invention of claim 1 uses magnesium hydroxide as an absorbent slurry, and the absorbent slurry is injected from the upper part of the absorption tower and brought into contact with exhaust gas. In a flue gas desulfurization device for desulfurization, the liquid reservoir of the absorbent slurry at the bottom of the absorption tower is divided into two by a partition wall,
A slurry supply means for supplying an absorbent slurry containing magnesium hydroxide is provided in one of the liquid reservoirs, a circulation line for circulating the slurry in the spray pipe above the absorption tower is provided, and an oxidizing air blowing means is provided in the other liquid reservoir. Is configured.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

In a system for treating exhaust gas containing high-concentration sulfur oxides, exhaust gas 5 from a boiler (not shown)
Is introduced into desulfurization device 10 shown in FIG. 1 through known devices (not shown) and desulfurization treatment is performed.

As shown in FIG. 1, the desulfurization apparatus 10 comprises an absorption tower 1 which introduces the exhaust gas 5 from the side and discharges it from the top.
A spray pipe 4 a for injecting the absorbent slurry 6 of Mg (OH) ₂ is provided. In the lower part of the absorption tower 1, the slurry liquid 6 after injection is injected.
A liquid reservoir 2 for storing the liquid is formed.
It is divided into two by. An Mg (OH) ₂ absorbent slurry supply device 14 is connected to one of the liquid reservoirs 2A,
A circulation line 4b for circulating the absorbent slurry 6 through the circulation pump 4 to the spray pipe 4a is connected to the lower part of the.

Further, the other liquid reservoir 2B is provided with an oxidizing air blowing means 7 for injecting oxidizing air from the bottom thereof, and is connected with a withdrawal line 15 for withdrawing the liquid from the liquid reservoir 2B.

The liquid reservoir 2A corresponds to a conventional liquid reservoir. The absorbent Mg (OH) ₂ slurry 6 is introduced from the absorbent slurry supply means 14 into the liquid reservoir 2A of the absorption tower 1, and is injected by the circulation pump 4 from the spray pipe 4a above the absorption tower 1 via the circulation line 4b. To be done. Then Mg (OH) as an absorbent
₂ Slurry liquid 6 drops SO ₂ and SO _{3 in} exhaust gas 5 while falling
(See equations (1) and (2) described in the prior art),
MgSO ₃ and MgSO ₄ are produced. The absorbent slurry 6 containing these salts is poured into the liquid reservoirs 2A and 2B. The absorbent slurry 6 returned to the liquid reservoir 2A is again injected from the spray pipe 4a above the absorption tower 1 by the circulation pump 4, and the above process is repeated.

The absorbent slurry 6 in the liquid reservoir 2B is injected by the spray pipe 4a above the absorption tower 1 as described above.
Further, the liquid naturally overflows from the liquid reservoir 2A beyond the partition wall 3 and collects in the liquid reservoir 2B. Oxidizing air is blown into the liquid reservoir 2B by an air blowing means 7 composed of a tube or a perforated plate to oxidize MgSO _{3 of the} absorbent slurry. That is, the liquid reservoir 2B corresponds to the oxidation tower in the conventional technique. Thus, the MgSO _{3 of the} absorbent slurry is air-oxidized to MgSO ₄ . MgSO ₄ (Mg
The SO _{3 that} is oxidized and the one that is directly generated from SO ₃ are extremely well dissolved in water and harmless, so that they are directly extracted by the extraction line 15 and discharged.

According to the present invention, since the liquid reservoir 2 is divided into two by the partition wall 3, not only the conventional oxidation tower 9 can be omitted by oxidizing MgSO _{3 in} one liquid reservoir 2B. A part of MgSO ₃ is always secured in the other liquid reservoir 2A and is sprayed from the spray pipe 4a, followed by Mg (OH) 2
_In the reaction between the ₂ slurry liquid 6 and SO ₂ , the smooth absorption of SO _{2 into} the Mg (OH) ₂ slurry liquid (see the above formulas (1) and (5)) is guaranteed.

The division of the liquid reservoir portion 2 by the partition wall 3 does not necessarily have to be equally divided, and if the SO ₂ concentration in the exhaust gas 5 is relatively low and the amount of MgSO ₃ produced is small, as much MgSO 4 as possible will be produced.
_{In order} to secure ₃ and promote the reaction of the above formula (5), the liquid reservoir 2A may be enlarged. On the other hand, when the SO ₂ concentration in the exhaust gas is relatively high and a large amount of MgSO ₃ is produced, on the contrary, MgSO ₃
The liquid reservoir 2B, which is an oxidizing air blowing part, may be enlarged in order to promote the oxidation of the liquid.

Thus, in the present invention, in the absorption tower
Since MgSO ₃ can be oxidized, the conventional oxidation tower can be omitted, and there is no effect on the desulfurization efficiency, and the sulfur oxides in the exhaust gas can be desulfurized at a desulfurization efficiency of about 95%.

In short, according to the present invention, the liquid storage section 2 of the absorption tower 1 is divided into two by the partition wall 3, so that the MgSO ₃ oxidation tower, which is conventionally installed separately, is incorporated into the absorption tower. The desulfurization system can be simplified and the cost can be reduced.

[0022]

In summary, according to the flue gas desulfurization apparatus of the present invention, the liquid storage section of the absorption tower is divided into two by the partition wall, so that the MgSO ₃ oxidation tower which has been separately installed is absorbed. By incorporating it in the tower, it has the excellent effect of simplifying the desulfurization system and reducing costs.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flue gas desulfurization apparatus using magnesium hydroxide of the present invention as an absorbent.

FIG. 2 is a view showing a conventional flue gas desulfurization apparatus using magnesium hydroxide as an absorbent.

[Explanation of symbols]

1 Absorption Tower 2A Liquid Reservoir A 2B Liquid Reservoir B 3 Liquid Reservoir Partition 4 Circulation Pump 4a Injection Spray Pipe 4b Circulation Line 5 Exhaust Gas 6 Absorbent (Mg (OH) ₂ ) Slurry 7 Oxidized Air Injection Means 14 Absorbent Slurry Supplying means 10 Desulfurization equipment

Claims (1)

[Claims] 1. A magnesium hydroxide absorbent slurry,
In a flue gas desulfurization device that desulfurizes by injecting this absorbent slurry from the upper part of the absorption tower and contacting it with the exhaust gas, the liquid storage part of the absorbent slurry in the lower part of the absorption tower is divided into two by a partition wall One part is provided with a slurry supply means for supplying an absorbent slurry containing magnesium hydroxide, and a circulation line for circulating the spray tube in the upper part of the absorption tower, and the other liquid reservoir part is provided with an oxidizing air blowing means. Flue gas desulfurization equipment using magnesium hydroxide as an absorbent.