JPS5939328A - Desulfurization of exhaust gas - Google Patents

Abstract

PURPOSE:To attain to reduce utility and to simplify an installation, by a method wherein an absorbing liquid withdrawn from an absorbing process is guided to an ejector and subjected to gas-liquid contact with the part of exhaust gas containing sulfur dioxide gas and oxygen. CONSTITUTION:Exhaust gas 101 is guided to a dust removing tower 1 to be introduced into an absorbing tower 3 and sulfur oxide in the exhaust gas 101 is absorbed and removed by a calcium type absorbent slurry 22. The reaction slurry is guided to an ejector 8 and the gas 33 from which dust is removed in the dust removing tower is absorbed with said slurry 22 passing through the ejector 8. In this case, the unreacted absorbent in the reaction slurry is reacted with SO2 in the gas to be converted to sulfite which is, in turn, oxidized by O2 in the gas along with sulfite formed in the absorbing process to be converted to sulfate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas desulfurization method, and more particularly to a wet exhaust gas desulfurization method for recovering sulfates by reacting and oxidizing an absorbent slurry using gas after exhaust gas removal.

The wet desulfurization process generally uses solutions or suspensions of hydroxides and carbonate oxides of alkali metals, alkaline earth metals, etc. to absorb and remove sulfur oxides from gases, and As a raw product, sulfate like gypsum is obtained.

FIG. 1 shows a typical example of a conventional desulfurization process in which calcium sulfate (gypsum) is produced as a by-product and recovered using a calcium (C-) based absorbent as an alkaline agent. In the figure, exhaust gas from boilers, etc., 1o1 is the dust removal tower log) 3
1 to the dust removal tower 1, where it is removed and cooled,
The scattered mist is removed by the mist eliminator 2.
After sulfur oxides in the exhaust gas 101 are absorbed and removed by the calcium-based absorbent slurry 22 in the absorption tower 3, the clean gas 102 is discharged through the duct 32. The calcium-based absorbent 22 that has absorbed sulfur oxides is converted into calcium sulfite in the absorption tower 3 and the absorption tower circulation tank 5. Part of it is oxidized by oxygen in the exhaust gas and becomes gypsum, and part of it is unreacted and absorbed. It remains in the slurry as an agent. This reaction slurry is supplied to the reaction tank 9 via a conduit 13 by a pre-de-bonpf, and the unreacted absorbent is added with sulfuric acid 23 to adjust the pH to a suitable value for oxidation. The partially produced slurry containing gypsum is then fed via conduit 15 to the silica oxidation tower 10, where the calcium sulfite is air oxidized and further
After solid-liquid separation, the solid slurry is dehydrated in a centrifugal separator 20 and gypsum is recovered. On the other hand, filtrate water during solid-liquid separation and dehydration is recycled and reused.

1. However, in this conventional technology, when oxidizing sulfite in the slurry extracted from the absorption process, the unreacted absorbent in the slurry is reacted, and the pH is adjusted to a pH suitable for oxidation.
These utilities and equipment are required because sulfuric acid is added to oxidize the slurry and air is used to oxidize the sulfite in the slurry.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to use sulfuric acid for the reaction of unreacted absorbent in the absorbent extracted from the absorption process and for the oxidation of sulfite in the absorbent. The present invention provides a wet desulfurization process that can recover gypsum as a byproduct without using air.

The present invention uses an ejector to bring the absorption liquid extracted from the absorption process into gas-liquid contact with the exhaust gas containing sulfur dioxide gas (S 02) and oxygen (02) after removing dust in a dust removal tower, so that the exhaust gas The 802 inside converts the unreacted absorbent into sulfite, and the 02 in the exhaust gas converts it into sulfate (gypsum).
It is a turtle that was made to look like this.

In the present invention, it is important to bring the exhaust gas after dust removal into contact with the absorption liquid in the ejector. Exhaust gas from coal-fired boilers, etc., contains a lot of dust and halides such as H(1, HF), so adjusting the pH of the absorption liquid with 802 in the exhaust gas before dust removal is a good way to prevent by-product gypsum. This will not only reduce the quality but also affect the corrosion of the equipment's materials.Thus, these dusts and
It is important to contact the gas containing SO2,02 with the absorption liquid after removing the 0-genides in the scrubbing tower in order to obtain high-quality gypsum.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 2 is a flow sheet showing an embodiment of the wet exhaust gas degassing method of the present invention. Exhaust gas 101 from a boiler or the like is led from a dust removal tower input rod duct 31 to a dust removal tower 1, where it is removed and cooled, after which scattered mist is removed by a mist eliminator 2, and water is led to an absorption tower 3. Here, the calcium-based absorbent slurry 22 absorbs and removes sulfur oxides in 10"l of exhaust gas. The top duct 3 of the absorption tower 3
Clean gas 102 is discharged from 2. The calcium-based absorbent 22 that has absorbed sulfur oxides becomes sulfite in the absorption tower 3 and the absorption tower circulation tank 5, and some of it is oxidized by oxygen in the exhaust gas and becomes gypsum, and some of it is unreacted and absorbed. It remains in the slurry as an agent.

This reaction liquid slurry is pressurized by the bleed pump 7 and guided to the ejector 8 through the conduit 13.

When the reaction liquid slurry supplied to the ejector 8 passes through the ejector, the gas 33 after dust removal in the dust removal tower is sucked. At this time, the unreacted absorbent in the reaction slurry reacts with S02 in the gas to become sulfite, and this sulfite is oxidized by 02 in the gas together with the sulfite generated in the absorption process. It becomes sulfate. The oxidation performance in this case is much better than air oxidation using a conventional oxidation tower atomizer, so the amount of oxygen in the exhaust gas from the boiler, etc. However, if the 02 concentration in the exhaust gas is low or if the oxidation rate needs to be further increased, the oxidation rate can be increased by blowing air into part of the exhaust gas from the line 36. .

The slurry reacted and oxidized in the ejector 8 and containing a lot of sulfate is sent to the Shirafuna 11 through the conduit 16, where solid-liquid separation is performed, and the solid slurry is passed through the conduit 18 to the dehydrator 2.
0, where it is dehydrated and recovered as sulfate particles (gypsum) 40. It is desirable that the Shirafuna 11 has a structure that performs gas-liquid separation at the same time as solid-liquid separation. By returning the gas separated by the Shirafuna 11 to the absorption tower 3 via the conduit 34, the system can be simplified without requiring any special treatment. The filtered water of the Shirafuna 11 is taken out by a conduit 19 and recycled to the original device.

Next, specific examples of the present invention will be described.

In the embodiment according to the flow sheet of FIG. 2, the dust removal tower inlet exhaust gas fi13,0OON+n"/h,
□Concentration 1,000p, H2O in gas: 10 Voj
Wet limestone operating at 2%, 02:6 Voj2% -
In the gypsum method desulfurization equipment, unreacted calcium carbonate in the reaction liquid slurry extracted from the absorption process was approximately 59 f), but after this slurry was led to the ejector and dust removed in the dust removal tower, As a result of suctioning exhaust gas of 150 N+++'/h with an ejector and causing a reaction, gypsum with a purity of 99.6% was recovered from the reaction liquid slurry of the absorption step.

As described above, according to the present invention, S02.02 in the exhaust gas generates sulfite, adjusts the pH of the liquid, and oxidizes the absorption liquid to sulfate in the ejector. An oxidation tower having an atomizer is no longer necessary, and utilities can be reduced and equipment simplified. In addition, the slurry that reacts and oxidizes in the ejector can be separated into solid and liquid using Shirafuna to recover high-quality byproduct gypsum.Furthermore, by separating the accompanying gas from the ejector into gas and liquid using Shirafuna and returning it to the absorption tower, No special gas processing equipment is required, and the entire system can be streamlined.

[Brief explanation of drawings]

FIG. 1 is a flow sheet of a conventional wet desulfurization process, and FIG. 2 is a flow sheet of a wet desulfurization process showing an embodiment of the present invention. 1... Dust removal tower, 2... Mist eliminator, 3... Absorption tower, 4... Demister, 5... Absorption tower circulation Tank, 6...
Circulation pump, 9... Bleed pump, 8...
...Ejecta 1, 11...Shirafuna.

Claims (1)

[Scope of Claims] (1) In an exhaust gas desulfurization method having an absorption process in which exhaust gas is brought into contact with an absorption liquid to absorb and remove sulfur oxides in the gas, the absorption liquid extracted from the absorption process is introduced to an ejector. A part of the exhaust gas containing arsenic acid gas and oxygen from the fc ridge is brought into gas-liquid contact to react and oxidize the unreacted absorbent and juxtaposed acid salts in the absorption liquid. An exhaust gas desulfurization method characterized by using sulfate. (2. In claim 1, the exhaust gas desulfurization method is characterized by blowing air into a part of the exhaust gas. (3) In claim 1 or 2, separation of sulfate (4) In any one of claims 1 to 17, claim 3, the gas obtained by gas-liquid separation of the gas entrained in the ejector is subjected to an absorption step. An exhaust gas desulfurization method characterized by returning the gas.