JPS588889B2 - High Gas Datsuryu Datsushi Youhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for treating sulfur oxides (SOx) and nitrogen oxides (NOx).
) Wet flue gas desulfurization and denitrification method for simultaneously removing SOx and NOx from general flue gas emitted from boiler heating furnaces, sintering furnaces, roasting furnaces, converters, melting furnaces, incinerators, etc. Regarding.

The present inventors have conducted intensive research and development on SOx and NOx removal processes and devices to eliminate air pollution caused by SOx and NOx. hydroxide)
SOx and N in combustion exhaust gas are removed using a cleaning solution containing sulfites and sulfites.
A patent application was filed for a process for simultaneously removing Ox (see Japanese Patent Laid-Open No. 27763/1983).

However, in this method, when treating exhaust gas with relatively high oxygen concentration, the denitrification sulfite cleaning agent itself does not produce NOx.
In addition to the reaction with the gas, a large amount is consumed by the oxygen in the gas, making it uneconomical.

Therefore, an object of the present invention is to minimize the consumption of the cleaning agent by oxygen in the exhaust gas in a desulfurization and denitrification method using the sulfite as a denitrification agent, and to reduce SOx and NOx in the exhaust gas.
An object of the present invention is to provide a wet desulfurization and denitration process that desulfurizes and denitrates x at a high removal rate.

In the first embodiment of the exhaust gas desulfurization and denitration method according to the present invention, for example, chlorine dioxide (C10) is contained in the exhaust gas.

) or ozone (03) is introduced to oxidize nitrogen monoxide (NO) contained in the exhaust gas to nitrogen dioxide (NO2),
Next, the exhaust gas is treated with an aqueous solution having a pH of 5 or higher and containing an alkali metal or ammonium hydroxide or carbonate, an alkali or ammonium metal sulfite, and thiourea, the sulfite being 0. It consists of desulfurization and denitrification by bringing a cleaning solution containing a concentration of 1 mol/l or more into gas-liquid contact using a cleaning tower.

A second aspect of the exhaust gas desulfurization and denitration method according to the present invention? First, for example, C102 or 03 is introduced into the exhaust gas to convert nitrogen monoxide (NO) contained in the exhaust gas to nitrogen dioxide (No.
), and then oxidizing the exhaust gas to an alkali metal or ammonium hydroxide or carbonate, an alkali metal or ammonium sulfite, thiourea, and at least one of copper ions and iron ions. An aqueous solution with a pH of 5 or higher, containing the sulfite at 0. 1mol/l
It consists of desulfurization and denitrification by bringing the cleaning solution containing the above concentration into gas-liquid contact using a cleaning tower.

The desulfurization reaction in this process is expressed by the following formula (1) or (2).
As shown in

(In the formula, M represents an alkali metal such as sodium or potassium or ammonium.

same as below. )2MOH+SO2-M2SO3+H20
・・・・・・・・・(1) M2CO3+S02-M2S
03+CO2 ・・・・・・・・・(2) That is, sulfur dioxide gas (S02) is absorbed into the cleaning liquid as an alkali metal or ammonium sulfite by adding an alkali metal or ammonia hydroxide or carbonate to the cleaning liquid. do.

However, in reality, a large amount of carbon dioxide (CO2) contained in the combustion exhaust gas is dissolved in the circulating cleaning solution, so the replenished alkali metal or ammonium hydroxide or carbonate reacts with the dissolved CO2 in the cleaning solution. Immediately add bicarbonate M
It becomes HCO3 and reacts with SO2 in the exhaust gas in the form of bicarbonate according to the following formula (3).

2MHC03+SO2→M2SO3+2CO2+1I2
0...(3) Next, the denitrification reaction in this process is complicated, but its main reaction is as shown by the following formula (4).

N02+2M2S03→2M2SO4+-+N2 ・
...(4) That is. For example, chlorine dioxide gas (C102
) or ozone (03) is added to oxidize nitrogen monoxide (NO) to nitrogen dioxide (NO2), and then this NO2 and the NO2 originally contained in the exhaust gas are treated with alkali metal or ammonium sulfite. The aqueous solution containing thiourea and a cleaning solution containing thiourea and copper ions and/or iron ions are used to remove the thiourea.

Furthermore, since the alkali metal or ammonium sulfite which is the reducing agent for NO2 can be used as it is as it is produced in the desulfurization reactions (1) to (3), the exhaust gas contains a considerably larger amount of SOx than NOx. It has the advantage that there is no need to add sulfite when desulfurizing and denitrating.

The copper ions and iron ions used in the cleaning solution of the process of the present invention are, for example, in the form of copper sulfate, copper chloride, iron sulfate, iron chloride, etc., or in the form of copper chelate compounds, iron chelate compounds, or copper complex compounds, iron complex compounds. It can be used in the form of

In the present invention, the pH of the cleaning solution needs to be 5 or more, so in order to make copper ions or iron ions exist in the cleaning solution in an ionic state rather than as an insoluble compound, a copper chelate compound, an iron chelate compound, or a copper complex compound is used. , is preferably added in the form of an iron complex compound.

As a chelating agent, ethylenediaminetetraacetic acid (EDT
A) ((CH2)2・N2・(CH2COOH)4
), citric acid (Ca Hs 07 ), ? Tartaric acid (C
General chelating agents such as 4H6 06 ) and gluconic acid (CaHt07) can be used, and are added as copper and iron chelate compounds, respectively.

In addition, as complex compounds of copper and iron, copper/ammonia complex (Cu(NH3)+': l2+, iron/cyan complex CFe
(CN)a ]'- etc. are used.

In the desulfurization and denitrification method according to the present invention, the pH of the cleaning solution is 5.
Above, preferably 6.5 to 8.5, and the sulfite concentration is 0.
It is assumed to be 1 mol/l or more.

The concentration of thiourea added to the cleaning solution is 0. 0 3
mol/l or more, preferably 0.05-0. 4 m
ol/l, copper ion or iron ion concentration is 0.0 0
3 mol/l or more, preferably 0.01 to 0.04 mol
It is desirable to set it to l/l.

This means that if the pH of the cleaning solution is less than pll5.0, is there sulfur in the cleaning solution? This is because the presence of hydrogen sulfite ions becomes noticeable in the equilibrium between ions and hydrogen sulfite ions, reducing both the deflow rate and the denitrification rate.Also, if the pH of the cleaning solution exceeds 85, CO, which is inevitably contained in the exhaust gas, decreases. This is because a large amount of alkali is consumed to neutralize the gas, which is undesirable.

Also, the sulfite concentration is 0. If it is less than 1 mol/l, the denitrification rate will decrease, which is not preferable, and if the thiourea concentration is 0.
If it is less than 0.03 mob/l, the denitrification rate will decrease and the value will decrease to 0.03 mob/l. If it exceeds 4 mol/l, the catalytic effect of the denitrification reaction reaches saturation, which is not economical.

Furthermore, the concentration of copper ions or iron ions is also 0. 0 0
Below 3 mol/l, the denitrification rate decreases to 0.04 m
Even if it exceeds ol/l, the denitrification effect remains unchanged and it is not economical, which is not preferable.

Hereinafter, the method of the present invention will be explained in more detail with reference to Examples.

Example 1 0. Using an absorption solution containing only a 2 mol/l sulfite aqueous solution and an absorption solution containing thiourea, 200
A sulfite oxidation test was conducted by blowing air containing NO2 into the absorption liquid.

In the experiment, 500 ml of each of the above absorption liquids was placed in an absorption bottle, and air containing NO2 was added to the bottle at 10 l/min for 3
I blew it for 0 minutes.

The residual sulfite concentration after the test was measured by 12 titration to determine the oxidation rate of sulfite in the absorption liquid, and the oxidation inhibiting effect of thiourea was confirmed.

The results are shown in Table 1.

? Example 2 0. 1 8 mol/l sodium sulfite and 0.2
An absorption liquid containing mol/l of sodium carbonate and thiourea, a copper EDTA compound, or thiourea and copper EDT.
Using various absorption liquids containing compound A, oxidized with C102 gas, 500% NO2 gas and 10% S02 gas
An absorption test for NO2 gas and SO2 gas was conducted by blowing air containing 0.00 ppm into the absorption liquid.

In the test, 500 ml of each of the above absorption liquids was placed in an absorption bottle, and NO gas and SO? of the above concentration were added to the bottle. 10% of air containing
The air was blown at l/min.

The NO2 gas concentration and SO2 gas concentration at the inlet and outlet of the absorption bottle were measured using a chemiluminescent nitrogen oxide measuring device and a solution conductivity type sulfur oxide measuring device, respectively.
The absorption efficiency of 02 gas was determined.

In addition, the sulfite ion concentration in the absorption liquid was measured, and the rate of decrease in the sulfite ion concentration was determined.

These results confirmed the absorption efficiency increasing effect of thiourea and copper EDTA compounds and the antioxidant effect of sulfite ions.

The results are shown in Table 2. ? Example 3 NO 2 50 ppm, NO 100 ppIn and S
10,000 Nm3/H including O2450
Sulfur oxides and nitrogen oxides in factory exhaust gas were removed by the method of the present invention.

First, 130 ppm of CIO gas is injected into the exhaust gas in the exhaust gas supply duct to oxidize NO in the exhaust gas to N02, and then the exhaust gas is heated to a leakage shelf (a perforated plate shelf with no weir or overflow part) with a perforation rate of 38%. ) It was sent to the bottom of a single leaking shelf absorption tower consisting of three stages and brought into countercurrent contact with the circulating absorption liquid under the following conditions.

Gas superficial velocity 5 m/sec Liquid gas ratio (L
/G) 4 Circulating absorption liquid pH 6.8 Circulating absorption liquid composition (NH4)2CO 30. 5 mol/l (NH
4)2 S O s 0. 5mol
/l Thiourea 0. 1mol/lE
DTA-C u2+0. 0 3 mol/l (NH
4) 2803 Replenishment Amount Okg/H The NOx concentration in the leaking shelf absorption outlet gas was t5ppm or less, and the SO2 concentration was 10ppm or less.

In addition, except for using a circulating absorption liquid that does not contain thiourea and EDTA-Cu2+, the gas superficial velocity, liquid-gas ratio, circulating absorption liquid pHN circulating liquid ammonium sulfite concentration (0.5
When desulfurization and denitration experiments were conducted under the same conditions (mol/l) as before, the SOx concentration of the treated gas was 10 ppm or less, and the NOx concentration was 30 ppm or less.

In this case, the amount of (NH4)2 SO3 supplied is 230 kg.
/H was consumed in large quantities.

Claims (1)

[Claims] 1. In a method for wet removal of sulfur oxides and nitrogen oxides contained in combustion exhaust gas, nitrogen monoxide contained in the exhaust gas is first oxidized to nitrogen dioxide, and then alkali metal or ammonium is oxidized. An aqueous solution having a pH of 5 or more and containing a hydroxide or carbonate, an alkali metal or ammonium sulfite, and thiourea, the sulfite being 0.
A method for desulfurizing and denitrating an exhaust gas, characterized in that the cleaning solution containing a concentration of 1 mol/l or more and the exhaust gas are brought into gas-liquid contact using a cleaning tower to perform desulfurization and denitration. 2. The exhaust gas desulfurization and denitration method according to claim 1, wherein the cleaning liquid further contains at least one of copper ions and iron ions.