KR20040067443A - Method for desulfurizing fluegas - Google Patents

Abstract

PURPOSE: Provided is a method for desulfurizing exhaust gas which uses limestone wastes as an absorbing agent of sulfur oxides. CONSTITUTION: The method comprising steps of (a) introducing exhaust gas containing sulfur oxides to an absorbing tower; (b) contacting the exhaust gas with limestone slurry to desulfurize; (c) making the air let in an absorption treating agent slurry stored in the lower part of the absorbing tower to make gypsum slurry from the limestone slurry; (d) recovering a part of the gypsum slurry; and (e) recirculating residue as an absorbing solution of the sulfur oxides is characterized in that the limestone slurry is prepared by suspending limestone wastes.

Description

Wet flue gas desulfurization method {METHOD FOR DESULFURIZING FLUEGAS}

The present invention relates to a wet flue gas desulfurization method for removing sulfur oxides in exhaust gas generated by combustion in a thermal power plant, a plant, an incinerator, or the like.

Flue gas desulfurization, also called exhaust gas desulfurization, means the removal of sulfur components, particularly sulfur dioxide, from the exhaust gases emitted from factories and thermal power plants.

With the development of modern industry, harmful gases such as SO _X and NO _X emitted from various factories, thermal power plants, and incinerators cause serious air pollution, causing various diseases such as respiratory disease, asthma and lung cancer in our bodies. In particular, sulfur dioxide (SO ₂ ) is the main cause of air pollution, and many ways around the world have been studied to remove these harmful gases.

The flue gas desulfurization method is classified into a wet method and a dry method according to the type and use type of the absorbent treatment agent of the exhaust gas.

The wet method is a method of removing harmful gases by contact reaction with liquid absorption agents such as ammonia water, sodium hydroxide solution, lime oil, etc. and is used for thermal power plants and large incinerators because of its high efficiency and stable operation of the equipment.

In the dry method, particles and powders such as activated carbon and carbonate are contacted with the exhaust gas and removed by adsorbing or reacting sulfur dioxide. The absorbent is directly dried on the exhaust gas as a solid absorbent in a dry powder state rather than in a liquid state. It is somewhat inferior in efficiency due to contact, but it is mainly used in small incinerators because of low equipment cost because it does not require an apparatus such as an absorption tower or a scrubber.

The wet method includes sodium carbonate as an absorbent (Na ₂ CO _3), sodium bicarbonate (NaHCO _3), calcium carbonate (limestone minutes, CaCO ₃₎ to which the like is widely used, but are excellent in reactivity with the SO ₂ advantage since expensive price Flue gas desulfurization treatment costs a lot of problems.

Accordingly, the present invention has been made to solve the problem of the high cost of the conventional wet flue gas desulfurization method, to find a new material as an absorbent of sulfur oxide in the wet flue gas desulfurization method to reduce the cost required for flue gas desulfurization and In addition, it aims to provide a wet flue gas desulfurization method that is conducive to environmental development.

In the wet flue gas desulfurization method of the present invention for achieving the above object, a sulfur oxide-containing combustion exhaust gas is introduced into an absorption tower, and the sulfur flue gas is contacted with a limestone slurry to desulfurize, and the air is blown into the absorbent slurry stored under the absorption tower. In the wet flue gas desulfurization method of making a limestone slurry into a gypsum slurry, recovering a part thereof, and recycling the residue as an absorbent of sulfur oxide, the limestone slurry is characterized in that the limestone slurry is suspended in water. .

Limestone waste is discharged as a large amount of by-product from chemical factories, waste water treatment plants, and steel mills, such as soda factories.It is a strong alkaline industrial waste that can be scattered dust or polluted streams and surroundings by rain, but it is an environmental pollutant. Difficult to discard

Therefore, by using the limestone waste as the sulfur oxide absorbent by the wet flue gas desulfurization method as in the present invention, it is possible to see various effects of recycling of resources and prevention of environmental pollution.

1 is a block diagram showing a general wet flue gas desulfurization apparatus.

* Explanation of symbols for main parts of the drawings

1: absorption tower 2: spray nozzle

3: circulation pump 4: circulation tank

5: Oxidation Agitator 6: Air Suction Tube

7: mist eliminator 8: limestone slurry tank

9: thickener 10: centrifuge

11: slurry extraction pump 12: solid concentrate tank

13: plaster 14: spray stage

Hereinafter, the wet flue gas desulfurization method of the present invention will be described in detail.

In the wet flue gas desulfurization method according to the present invention, sulfur oxide-containing combustion exhaust gas is introduced into an absorption tower, which is contacted with a limestone slurry to desulfurize, and the air is blown into the absorbent slurry stored under the absorption tower to plaster the limestone slurry. In the wet flue gas desulfurization method of making a slurry, recovering a part thereof, and recycling the residue as an absorbent of sulfur oxide, the limestone slurry is characterized by using a suspension of limestone waste.

Limestone waste is discharged as a by-product from soda plants, chemical plants, wastewater treatment plants and steel mills. Limestone waste contains large amounts of calcium carbonate and calcium oxide. As a result of investigating the components of limestone waste discharged to the sodium carbonate (Na ₂ CO ₃ ) manufacturing process, CaCO ₃ 24.1wt%, CaO 10.9wt%, MgO 4.6wt%, CaCl ₂ 5.8wt%, CaSO ₄ 3.5wt%, Fe ₂ 1.2 wt% of O ₃ , _2.3 wt% of Al ₂ O ₃ , 3.6 wt% of NaCl, 4.0 wt% of SiO ₂ , and 40.0 wt% of moisture. It can be seen that CaCO ₃ and CaO account for about 58 wt% of the total weight except for water. In the conventional wet flue gas desulfurization method, limestone used as a sulfur oxide absorbent is used in the form of limestone powder or heavy calcium carbonate prepared by crushing limestone with a crusher and then crushed with a hammer crusher, and usually about 53% or more of calcium carbonate ( CaCO ₃ ) content.

SO ₂ removal reaction using calcium carbonate (CaCO ₃ ) is as follows.

_{SO 2 (g) + H 2} O → H + + HSO 3 - ( absorption reaction)

CaCO₃(s) + H⁺→ Ca²⁺+ HCO₃ ^-(Neutralization reaction)

_{^{HCO 3 - + H + → H}} 2 0 + CO 2

^{_{HSO 3 - + ½O 2 (aq}} ) → SO 4 2- + H + ( oxidation)

Ca ²⁺ + SO ₄ ^2- + 2H ₂ O → CaSO ₄ · 2H ₂ O Gypsum growth (crystallization reaction)

CaCO ₃ (s) + SO ₂ (g) + 2H ₂ O + ½O ₂ → CaSO ₄ 2H ₂ O (s) + CO ₂ (g) (total reaction)

The SO ₂ removal reaction using calcium oxide (CaO) is as follows.

SO ₂ (g) + CaO → CaSO ₃

2CaSO ₃ + O ₂ → 2CaSO ₄

Limestone wastes contain large amounts of CaCO ₃ and CaO, making them excellent absorbers of sulfur oxides.

Hereinafter, the wet flue gas desulfurization method of the present invention will be described through examples.

1 is a block diagram showing a general wet flue gas desulfurization apparatus.

The wet flue gas desulfurization apparatus comprises a spray stage (14) having a plurality of spray nozzles (2) for spraying limestone slurry adsorbing sulfur oxides in exhaust gas, a circulation tank (4) for storing a plurality of sulfur oxides and limestone slurries; And a limestone slurry circulation pump 3 for transferring the limestone slurry of the circulation tank 4 to the spray nozzle 2 of the spray stage 14, and installed in the circulation tank 4 to promote oxidation of sulfur oxides. The oxidizing stirrer 5, the air suction pipe 6 for supplying oxygen into the circulation tank 4, and the exhaust gas from which the sulfur oxides have been removed are discharged through the spray stage 14. In order to recover the fine mist mixed, the mist eliminator 7 installed at the upper end of the absorption tower 1, the limestone slurry tank 8 mixing water with the limestone, and the limestone slurry taken out from the circulation tank 4 Diluted water and solid limestone of waste A thickener (9) for separating, a solid component concentrate tank (12) for concentrating the solid component sent from the thickener (9), and a centrifuge (10) for finally extracting water from the solid component ), And a slurry extraction pump 11 which takes out limestone slurry from the circulation tank 4 and sends the limestone slurry to the sealer 9.

First, limestone waste discharged as a large amount of by-products from chemical plants, wastewater treatment plants, steel mills, etc. is mixed with water and stored in the limestone slurry tank 8 as a suspension, that is, limestone waste slurry. The limestone waste slurry stored in the limestone slurry tank 8 is transferred to the circulation tank 4 through a pump. The limestone waste slurry of the circulation tank 4 is sprayed through the plurality of spray nozzles 2 of the spray stage 14 through the circulation pump 3.

The exhaust gas is introduced into the absorption tower 1 by the inlet duct, and gas-liquid contact is made with the limestone waste slurry sprayed from the spray nozzle 2.

The limestone waste slurry absorbs SO ₂ in the exhaust gas, forms calcium sulfite, is stored in the circulation tank 4, oxygen is supplied into the circulation tank 4 through the air suction pipe 6, and the oxidation agitator 5 ), Calcium sulfate, that is, gypsum crystallization, is achieved.

Part of the slurry collected in the circulation tank 4 in which limestone waste and gypsum coexist is sent to the spray nozzle 2 again by the circulation pump 3 and goes through the above process several times.

The limestone waste is mixed with water in the limestone slurry tank 8 to form a slurry and periodically supplied to the circulation tank 4, while a part of the slurry from the circulation tank 4 is taken out by the extraction pump 11. It is sent to the thinner (9), in which the solid component in the limestone and gypsum slurry is naturally precipitated and separated from the supernatant water, and the separated solid component is sent to the concentrate tank (12).

The concentrate in the concentrate tank 12 is transferred to a centrifuge 10 by a pump where it is finally dehydrated and recovered as gypsum 13.

In addition, the small droplet diameter of the adsorbed liquid atomized by the spray nozzle 2 is mixed with the exhaust gas, but is recovered by the mist eliminator 7 installed above the absorption tower to remove the exhaust gas harmful to the human body.

As described above, in the wet flue gas desulfurization method using the limestone waste according to the present invention, since limestone waste discharged as a by-product from chemical plants, waste water treatment plants, steel mills, etc. is used as an absorbent, conventional limestone powder or heavy calcium carbonate Compared to flue gas desulfurization, the cost is significantly reduced, and the recycling of limestone waste, which is difficult to treat as strong alkaline industrial waste, has a significant effect on the utilization of resources and above all, the current pollution prevention.

Claims (1)

An exhaust gas containing sulfur oxides is introduced into an absorption tower, which is contacted with a limestone slurry to desulfurize, air is blown into the absorbent slurry stored at the bottom of the absorption tower to make a limestone slurry into a gypsum slurry, and a part thereof is recovered. The wet flue gas desulfurization method of recycling a residue as an absorbent of sulfur oxides, wherein the limestone slurry is suspended in limestone waste.