JPS62121620A - Process of exhaust gas desulfurization and denitration - Google Patents

Abstract

PURPOSE:To effectively desulfurize and denitrate by absorbing SOx and NOx with the absorbent of Mg water solution in the first and second absorption columns, oxidizing part of the liquid from the first absorption column in the oxidization column with neutralizing agent added, and filtering the crystallized sulfate. CONSTITUTION:The off-gas containing SOx and NOx is fed from the flue 10 into the first absorption column 1, and O3 is fed from the line 13 to oxidize NO into NO2. The absorption of the first absorption column has pH4.5-5.5 and absorbs NOx and SOx. Then, the off-gas out of the first absorption column comes into the second absorption column and absorbs the remaining NOx and SOx. The solution extracted out of the first absorption column 1 is sent to the oxidization column 4, and oxidized with the neutralizing agent MgO and air. MgSO4 thus produced is filtered by the crystallization separator 5, and the crystals are taken out of the line 19, while the filtrate is sent through the line 17, MgO being added therein by the absorbent controlling tank 6, and sent into the second absorption column to be used again as absorbing solution.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a flue gas desulfurization and denitrification method. It relates to a method of removal.

Conventional technology The conventional method for flue gas desulfurization using magnesium (Mg) is as follows:
The absorption liquid is oxidized to form an aqueous solution of magnesium sulfate (Mgso), and the entire amount is discarded. Also, sulfur dioxide (S
As a method of removing nitrogen monoxide (NO) at the same time as O2), ozone (03) is injected into the flue gas, and the NO is oxidized to nitrogen dioxide (No2), which is then removed by an absorption tower.

Problems to be Solved by the Invention As mentioned above, the conventional method of removing NO at the same time as removing SO2 involves injecting 03 into the flue gas, oxidizing the NO to NO2, and removing it in an absorption tower. However, this method has a problem in that the removal efficiency of nitrogen oxides is low, and in order to increase the efficiency, it is necessary to introduce a large amount of 03, which is not economical.

Another way to increase the denitrification efficiency is to add additives to the absorption liquid, which can significantly reduce the amount of 03 used.However, if the entire amount of absorption liquid is discarded, the additive becomes disposable, This is not only uneconomical, but also has the problem of causing wastewater pollution because the waste contains additives. The present invention attempts to solve these problems. That is, the present invention enables the use of additives when simultaneously removing sulfur oxides and nitrogen oxides from flue gas, increases desulfurization efficiency and denitrification efficiency, and reduces the amount of 03 used. It is an object of the present invention to provide a flue gas desulfurization and denitrification method that can reduce the amount of gas, is economically superior, and does not cause pollution problems.

The only way to solve the problem is to carry out the ozone oxidation wet simultaneous desulfurization and denitrification method.
A first absorption tower and a second absorption tower are installed, and the first absorption tower absorbs most of the NO2 and some SO2 using a magnesium aqueous solution, and the remaining NO□ and most of the 802 are absorbed in the second absorption tower. In addition, the liquid from the first absorption tower was oxidized to precipitate and crystallize sulfate, and then the crystals and liquid were separated, and the p liquid was reused as an absorption liquid without being discarded. . That is, 1 the configuration of the present invention is to use an alkaline absorbent and at least one of magnesium oxide and magnesium hydroxide in an ozone oxidation wet simultaneous desulfurization and denitrification process for removing sulfur oxides and nitrogen oxides in flue gas, By absorbing sulfur oxides and nitrogen oxides in the absorption tower and the second absorption tower, the hydrogen ion index of the liquid in the first absorption tower is reduced to 45.
to 5.5, and a part of this is oxidized with air in an oxidation tower while adding a neutralizing agent to precipitate and crystallize the sulfate in the liquid.
This is led to a separator to separate the crystals, and the P liquid is used for the absorption liquid (
The feature is that it can be reused.

Function NO in the exhaust gas is converted to NO2 in 03 and converted to Mg in the first absorption tower.
The system aqueous solution removes NO2 and some S02, and
The absorption tower removes leaked No2 and most of SO2. In addition, the bleed liquid from the first absorption tower is oxidized to precipitate and crystallize the sulfate in the liquid, and then the crystals and the liquid are separated in a separator, and the P liquid is reused as an absorption liquid.

Embodiment FIG. 1 shows an example of flue gas desulfurization and denitrification equipment for implementing the present invention. In Figure 1, 1 is the first absorption tower and 2 is the second absorption tower.
Absorption tower, 3 ozone generator, 4 oxidation tower, 5 crystal separator, 6 absorbent adjustment tank, 7 first pump, 8 second
pump, 9 is the third pump, 10 is the first flue, 11 is the second
Flue, 12 is the third flue, 13 is the ozone injection line, 14
15 is an air blowing line, 15 is an additive supply line, 16 is a magnesium oxide supply line, 17 is a separated liquid return line, 18 is a drainage line, and 19 is a crystal extraction line.

That is, the flue gas containing sulfur oxides and nitrogen oxides enters the first absorption tower 1 through the first flue 10. This flue gas is mixed with a necessary amount of 03 from the ozone generator 3 through the ozone injection line 13.

In the reaction N O+ 0s-No2+02, No is oxidized to NO2. The absorption liquid in the first absorption tower 1 has a hydrogen ion index (pH) of 4.5 to 5.5.
It absorbs N02 and SO□ in flue gas. The flue gas leaving the first absorption tower 1 enters the second absorption tower 2 through the second flue 11.

The remaining NO2 and S02 are absorbed with an absorption liquid (pH approximately 5.5 to 6.5).

The desulfurization reaction in the second absorption tower 2 is expressed by the following formula.

Mg(OH)2 +SO2→Mg fE 03 +H2
0. . . (1) MgSOs +SO2+H2O-M
g (I(SO3)2 . . . . (2) Here, there are many reactions of the above formula (1), but there are few reactions of the above formula (2).

Further, the desulfurization reaction in the first absorption tower 1 is expressed by the following formula.

M gS 03 + S02 + H20-Mg (H
803) 2 ・ ・ ・ (3) On the other hand, NO2 is absorbed in the first absorption tower 1 and the second absorption tower 2 and reduced by sulfite ions. At this time, the additive functions to promote the absorption of NO2, but when the liquid pH exceeds about 5.8 to 6.0, it changes from liquid to solid and loses its ability to promote absorption. The pH of the liquid in the first absorption tower 1 and the second absorption tower 2 needs to be 5.8 or less.

Then, the liquid extracted from the first absorption tower 1 is sent to the oxidation tower 4, and is oxidized by blowing air into it while adding a neutralizing agent MgO. In other words, it becomes as follows.

Mg S 03 + 20□→Mg1EO4・・・・
(4) Mg(H3O3)2 +02-Mg(H8O,)
2...(5) Mg(H8O4)2 +MgO→2M
g504 +H20... (6) In this way, MgSO4 produced in the oxidation tower 4 causes its concentration to exceed its solubility, precipitates, and exists as crystals in the liquid. The crystals are separated by the crystal separator 5, the crystals are taken out by the crystal take-out line 19, and most of the P liquid is sent from the liquid return line 17 to the absorbent adjustment tank B, where MgO is replenished, and the second liquid is used as the absorbent liquid. It is sent to absorption tower 2 and used.

Note that since the pH of the liquid in the oxidation tower 4 is maintained at 5.8 or less, the additive is returned to the absorbent adjustment tank B together with the P liquid without being precipitated. In addition, a part of the absorption liquid whose pH has been lowered by absorbing SO2 and NO
02 and NO2 are absorbed using the above formula (3) to lower the pH.

In Figure 2, 5 is plotted on the horizontal axis X and the denitrification rate O is plotted on the vertical axis y.Curve A in the figure shows the case with additives, and curve B shows the case without additives. There is. That is, when there is an additive, compared to when there is no additive,
It can be seen that the denitrification rate is high. Note that the method of increasing the denitrification rate by adding additives to the absorption liquid is also a known method.

Effects of the Invention The present invention provides an ozone oxidation wet simultaneous desulfurization and denitrification process for removing sulfur oxides and nitrogen oxides from flue gas. absorbs sulfur oxides and nitrogen oxides, and
A portion of the liquid from the absorption tower is oxidized with air while adding a neutralizing agent in an oxidation tower to crystallize the sulfate in the liquid, the crystals are separated in a separator, and the filtrate is recycled as an absorption liquid. Since this is the method used, in the first absorption tower, most of the No. and some SO□
is removed, and the remaining N02 and most of the SO2 are removed in the second absorption tower, making it possible to easily achieve the targeted desulfurization and denitration as a whole. In addition, without discarding the entire amount of filtrate from the separator, the entire amount or close to the total amount of the filtrate is reused as an absorbent, making it possible to use additives and improving the denitrification rate. This makes it possible to reduce the amount of Os used, making it economical. Also, after lowering the pH of the liquid in the first absorption tower to 4.5 to 5.5, a part of the liquid is led to the oxidation tower and oxidized, so the oxidation tower lowers the pH of the liquid to 5.8 or less. There is no precipitation of additives and catalyst components in the liquid, all of which can be reused, which is economically advantageous.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of equipment for implementing the present invention;
FIG. 2 is an explanatory diagram showing the relationship between the presence or absence of additives and the denitrification rate. 1... First absorption tower, 2... Second absorption tower, 5... Ozone generator, 4... Oxidation tower, 5°... Crystal separator, 6
...Absorbent adjustment tank.

Claims (1)

[Claims] 1. In the ozone oxidation wet simultaneous desulfurization and denitrification process that removes sulfur oxides and nitrogen oxides from flue gas, at least one of magnesium oxide and magnesium hydroxide is used as an alkaline absorbent, and the first absorption tower and the second absorption tower By absorbing sulfur oxides and nitrogen oxides in the tower, the hydrogen ion index of the liquid in the first absorption tower is lowered to 4.5 to 5.5, and a part of this is absorbed in the oxidation tower while adding a neutralizing agent. A flue gas desulfurization and denitrification method characterized by oxidizing with air to precipitate and crystallize sulfate in the liquid, introducing it to a separator to separate the crystals, and reusing the filtrate as an absorption liquid.