JPS599207B2 - Detoxification treatment method for liquids containing imidodisulfonic acid ions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detoxifying nitrogen compounds generated in an absorption liquid during wet simultaneous treatment of sulfur oxides (SOx) and nitrogen oxides (NOx) in flue gas. More specifically, the present invention relates to a treatment method and apparatus for decomposing absorbed NOx into harmless nitrogen in a method of absorbing NOx in the form of imidodisulfonic acid ions (NH(SO3)1).

In recent years, SOx and N have been included in exhaust gas emitted from thermal power plants, various chemical factories, steel mills, and automobiles.
In order to prevent air pollution caused by Ox, various methods for removing these harmful gases have been proposed in various fields.

Among these, as one of the wet desulfurization and denitrification treatment methods,
There is a method in which it is absorbed into an absorption liquid in the form of imidodisulfonic acid ions.

This method is currently known, and involves adding metal ions or metal ions to the desulfurization solution of so-called double-alkali desulfurization methods such as the limestone-gypsum method, the soda-gypsum method, the acetic acid-soda-gypsum method, etc., to simultaneously perform denitration treatment. A metal complex is added as a catalyst.

All of these absorption liquids are strongly cyclic, and the nitrogen compounds produced when NOx is absorbed are NH(SO3)2-
It was found that the ions were dissolved in the form of ions.

In addition, these nitrogen compounds are normally highly soluble, and when they accumulate in the absorption liquid and turn the SOx absorption into gypsum, they cause problems such as deterioration of the quality and precipitation within the equipment. Post-treatment is required, such as converting the nitrogen compounds equivalent to the absorbed NOx into a by-product or nitrogen gas to render them harmless.

The inventors have considered this point, and as a result of research experiments,
The above-mentioned absorption liquid that has absorbed NOx is mixed with slaked lime (Ca(
Calcium N-Na-imidodisulfonate (N-Na (SO3)
)2Ca) can be separated from the liquid as a solid, and furthermore, if this solid is heated to 300°C or higher in either an oxidizing or reducing atmosphere,
It was discovered that the nitrogen content can be decomposed into nitrogen gas, thereby rendering it harmless.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for detoxifying a liquid containing imidodisulfonic acid ions produced by simultaneous wet desulfurization and denitrification treatment by utilizing the above-mentioned phenomenon.

The first feature of the present invention to achieve the above object is that S
After absorbing Ox and NOx and recovering SOx as gypsum, a calcium compound is added to the absorption liquid containing a transition metal complex and a sodium compound, and if necessary, an alkaline substance is added to adjust the absorption liquid to a pH of 7 or higher. , the solid substance is taken out and the solid substance is thermally decomposed at 300 to 500°C to produce nitrogen, mirabilite, and gypsum.The second feature is, in addition to the first feature, the mixing of mirabilite and gypsum. The third feature is that the solid matter is treated with water to extract the gypsum without solid matter.In addition to the second feature, the third feature is that the gypsum is heated to 1050°C or higher and separated into sulfur dioxide gas and quicklime, and sulfur dioxide gas is extracted. The gas is returned to the absorption liquid for simultaneous SOx and NOx treatment, and the quicklime is used as the added calcium compound mentioned in the first feature.

For example, the desulfurization and denitrification reaction in the acetic acid soda gypsum method is
Sodium acetate (CH3COONa) absorbs sulfur dioxide gas, producing sodium sulfite (Na2S03) and acetic acid, and further producing imidodisulfonic acid ions (NH(SO3)2-) in the presence of transition metal complexes.

NH(SO3) generated in the absorption liquid in this way
2, by directly contacting some or all of the absorbed liquid with a calcium compound such as slaked lime or quicklime, the pH is adjusted to 7.
As described above, calcium N-Na imidodisulfonate (N-Na(SO3)2Ca) is precipitated as a solid by performing the reaction under alkaline conditions, preferably at pH 8 to 9.

Only the liquid is separated from this mixed liquid, returned to the original absorption liquid for simultaneous desulfurization and denitrification treatment, and recycled for use.

The above is exactly the same when using an absorption liquid for simultaneous desulfurization and denitrification treatment in which a transition metal complex, such as an iron complex, is added to limestone slurry or sodium sulfite solution.

In this way, the solid N-Na(SOs)2Ca separated by removing the liquid from the solution in which calcium N-Na imidodisulfonate was precipitated is then heated in an oxidizing or reducing atmosphere. , decomposed by heat treatment at a temperature of 300°C or higher, preferably 350 to 500°C, to produce nitrogen gas, mirabilite, and gypsum (CaS04).

In this way, the NOx content absorbed by the absorption liquid is rendered harmless.

By dissolving the resulting mixture of Glauber's salt and gypsum with water, only the Glauber's salt dissolves and the gypsum remains undissolved.

This is separated into solid and liquid, and the liquid is returned to the simultaneous desulfurization and denitration treatment equipment.

Most of the undissolved solids separated in the above-mentioned dissolution process of the Glauber's salt recovery pot are called calcined gypsum, which can be used as a raw material for anhydrous gypsum plaster.

This product also has temperatures above 1050°C, preferably 1100°C.
By heating at ~1250℃ humidity, SO2 and C
It can be decomposed into aO, and the SO2 can be sent to the absorption tower of the simultaneous desulfurization and denitrification treatment equipment, and the CaO can be used as the calcium compound for the above-mentioned alkali treatment.

The above are the steps according to the present invention.

An embodiment of the process of the present invention will be specifically described below using six system diagrams.

In the system diagram, the detoxification treatment of the imidodisulfonic acid ion-containing liquid, which is the residual liquid after recovering SOx from the absorption-gypsum conversion apparatus 10 of the desulfurization and denitrification simultaneous treatment apparatus as gypsum, is as follows:
Alkaline reaction tank 20 for NOx solidification, solid-liquid separator 30
, 60, thermal decomposition furnaces 40, 70, melting tank 50, etc.

In the absorption-gypsum processing apparatus 10, the solid content of the imidodisulfonic acid ion-containing slurry after treating SOx and NOx-containing flue gas by using the iron complex-containing limestone slurry as an absorption liquid for simultaneous desulfurization and denitrification treatment is converted into a solid liquid. The product separated and removed by the separator is sent through line 11 into an alkali reaction tank 20 for solidifying N content.

Slaked lime, which is a calcium compound, supplied from a line 21 and quicklime produced in a thermal decomposition furnace 70, which will be described later, are fed into this alkaline reaction tank 20, and the pH is maintained at 8 to 9 with these alkaline agents. , N-Na(SO3)2
Ca is reacted and produced.

The reaction liquid slurry is transferred to the solid-liquid separator 3 as shown by line 22.
Sent to 0.

The liquid separated by the solid-liquid separator 30 is returned to the absorption liquid of the desulfurization, denitrification, and simultaneous absorption treatment apparatus through a line 31.

Solidified N-Na (SO3) containing nitrogen
2 is supplied to the thermal decomposition furnace 40 via the CFL purine 32.

This thermal decomposition furnace may be one that is generally suitable for firing solid materials, such as a rotary kiln.

Here, it is heated at a temperature of 300 to 500°C to decompose it, and the nitrogen content is converted into nitrogen gas and rendered harmless.

The mixed solid of Glauber's salt and gypsum produced here is supplied to the dissolution tank 50 via line 41, the Glauber's salt is dissolved by the water supplied from line 51, and the gypsum mixed solution is supplied to the dissolving tank 50 through line 41.
2 to the solid-liquid separator 60 for solid-liquid separation.
is returned to the absorbent solution.

The solid gypsum is removed through line 62.

This is further heated to 1100 to 125
It can be thermally decomposed at 0°C to form SO2 and CaO.

S02 is the desulfurization and denitrification simultaneous absorption treatment equipment 1 through the line 72.
It can be recovered as gypsum by returning it to the 0 absorption tower.

For CaO, the line 71 sends it to the alkali reaction tank 20.
It can be used as a calcium compound for producing solidified nitrogen compounds.

Examples of the present invention will be described below.

Example 1 The composition (initial stage) of the absorption liquid in the simultaneous desulfurization and denitrification treatment apparatus 10 shown in FIG.
2 Na FeS04: 0. IMNa2SO
4: 0.5MCaC03
: IM is added in order to maintain pH 6, while the composition of SOx and NOx containing gas is N.
o: 1500 ppm SO2: 3000 ppm O2: 5% Ar 2 The remainder was synthesized in a cylinder.

The absorption liquid (liquid amount: 400,771/cm) was put into an absorption tower (glass reaction tube of 6φXH300) and SOx, NOx
The contained gas is brought into contact, SOx is converted into CaSO3 and taken out as CaSO4, and the residual liquid after taken out contains Ca(OH
)2 was added to adjust the pH to 8.5.

After reacting under these conditions, the solid matter (N-Na
Calcium monoimidodisulfonate) was obtained.

When this solid was heated to 300°C or higher, nitrogen was decomposed and a solid decomposition product was obtained.

Analysis of this solid decomposition product by X-ray diffraction revealed that CaSO
4 and Na2SO4.

Note that as shown in FIG. 2 (air atmosphere, heating time 120 minutes), the nitrogen removal rate hardly changes even when the temperature is 500°C or higher, so it is appropriate to decompose under heating conditions of 300 to 500°C.

In this example, the pH of the absorption liquid was set to 8.5 by adding Ca(OH)2, but in order to extract it as a solid substance of calcium N-Na-imidodisulfonate, the pH of the absorption liquid was adjusted to 8.5. Figure 3 shows that it is necessary to set the value to 7 or more.

If the pH is preferably set to 7 to 9.5, Ca solids can be taken out without precipitating Fe.

Therefore, if adding a calcium compound alone is insufficient to raise the pH of the absorption liquid to 7 or more, it is necessary to add an alkaline substance.

Example 2 The solid decomposition products (CaS04 and Na2SO4) obtained in Example 1 were washed with water to form Na2SO4.
was dissolved to obtain solid CaS04.

Example 3 Since CaS04 obtained in Example 2 was anhydrite, it was difficult to dissolve and did not become a hydrate.

Therefore, it is undesirable for the gypsum (CaSO4.2H20) produced as a by-product in the simultaneous desulfurization and denitration treatment equipment 10 shown in FIG. By heating in a furnace, it was decomposed into CaO and SO2.

The decomposition reaction of anhydrite is known to be a reduction reaction.

Industrially, by using a kiln or a tunnel furnace as a heating method, thermal decomposition is performed once in an air-deficient state, and additional air is introduced near the outlet to easily produce CaO and SO.
It can be broken down into two parts.

As explained above, according to the method and apparatus of the present invention,
It has the following effects.

That is, as an effect of the first invention, the imidodisulfonic acid ion-containing liquid after exhaust gas absorption treatment containing SOx and NOx can be rendered harmless by converting it into nitrogen and solids (gypsum and mirabilite).

As an effect of the second invention, in addition to the effect of the first invention, the solid material can be extracted as gypsum by water treatment, while the dissolved mirabilite is returned to the absorption liquid for simultaneous desulfurization and denitrification treatment to form sodium compounds. It can be used for the addition of

In addition to the effects of the first and second inventions, the effect of the third invention is that gypsum is thermally decomposed to produce quicklime and sulfur dioxide gas, and the quicklime is used as an added calcium compound in the residual liquid containing imidodisulfonate ions, The gas can be returned to the absorption liquid for simultaneous desulfurization and denitrification treatment and recovered as gypsum, making it possible to create a completely closed system.

[Brief explanation of drawings]

Figure 1 is a processing system diagram explaining the method and equipment arrangement of the present invention, Figure 2 is a graph showing the relationship between heating temperature and nitrogen removal rate, and Figure 3 is a graph showing the relationship between the pH of the absorption liquid and the concentration of Ca and Fe. It is a graph showing the relationship between 10... Simultaneous desulfurization and denitrification treatment equipment, 20...
...Alkali reaction tank, 30,60...Solid-liquid separator, 40,70...Heating decomposition furnace, 50...
...Dissolution tank.

Claims (1)

[Scope of Claims] 1. An absorption liquid containing a sodium desulfurizing agent such as caustic soda or sodium acetate and a transition metal complex, or an absorption liquid containing a transition metal complex obtained by adding a sodium compound to a calcium desulfurizing agent such as limestone. SOx in exhaust gas using
(a) Calcium compounds and alkaline substances are added to the imidodisulfonic acid ion-containing residual liquid after absorbing and removing NQx and recovering the SOx content in the absorption liquid as gypsum by adding calcium compounds as necessary. By adding at least a calcium compound, the pH can be adjusted to 7.
With the above, a step of precipitating calcium N-Na-imidodisulfonate, separating the solid calcium N-Na-imidodisulfonate, and circulating the liquid content back to the absorption liquid for simultaneous desulfurization and denitrification treatment; (1) An imidodisulfone characterized by comprising a step of thermally decomposing the separated solid N-Na-imidodisulfonate calcium at a temperature of 300 to 500'C to produce nitrogen, Glauber's salt, and gypsum. A method for detoxifying liquids containing acid ions. 2. Using an absorption liquid containing a sodium-based desulfurization agent such as caustic soda or sodium acetate and a transition metal complex, or an absorption liquid containing a transition metal complex obtained by adding a sodium compound to a calcium-based desulfurization agent such as limestone, SOx
(a) Calcium compounds and alkaline substances are added to the imidodisulfonic acid ion-containing residual liquid after absorbing and removing SOx and NOx, and collecting the SOx content in the absorption liquid as gypsum by adding calcium compounds as necessary. It is recommended to add at least a calcium compound, pH 7.
With the above, the step of precipitating calcium N-Na-imidodisulfonate, separating the solid calcium N-Na-imidodisulfonate, and circulating the liquid content back to the absorption liquid for simultaneous desulfurization and denitrification treatment; ) The separated solid calcium N-Na-imidodisulfonate is thermally decomposed at a temperature of 300 to 500°C,
a step of converting nitrogen, mirabilite, and stone into a stone building; 1. A method for detoxifying a liquid containing imidodisulfonic acid ions. 3. Using an absorption liquid containing a sodium-based desulfurization agent such as caustic soda or sodium acetate and a transition metal complex, or an absorption liquid containing a transition metal complex obtained by adding a sodium compound to a calcium-based desulfurization agent such as limestone, SOx
(a) Calcium compounds and alkaline substances are added to the imidodisulfonic acid ion-containing residual liquid after absorbing and removing SOx and NOx, and collecting the SOx content in the absorption liquid as gypsum by adding calcium compounds as necessary. By adding at least a calcium compound, the pH can be adjusted to 7.
2, a step of precipitating calcium N-Na-imidodisulfonate, separating the solid calcium N-Na-imidodisulfonate, and circulating the liquid component back to the absorption liquid for simultaneous desulfurization and denitrification treatment. (C]) A step of thermally decomposing the separated solid calcium N-Na-imidodisulfonate at a temperature of 300 to 500°C to produce nitrogen, Glauber's salt, and gypsum; (C) The thermal decomposition (d) heating the separated gypsum at a temperature of 10,500 C or higher; An imidodisulfone characterized by comprising a step of decomposing it into sulfur dioxide gas and quicklime, returning the sulfur dioxide gas to the absorption liquid for simultaneous desulfurization and denitrification treatment, and reusing the quicklime as a calcium compound used in the above step (a). A method for detoxifying liquids containing acid ions.