KR20080065394A - Scale preventer and scale preventing method for wastewater disposal facility in flue gas desulfurization system using sodium hypochlorite - Google Patents

Abstract

A scale preventing agent and a scale preventing method for reducing and preventing scales generated and adhered to a desulfurizing wastewater treatment apparatus by using sodium hypochlorite as a principal treatment chemical are provided. A scale preventing agent for a desulfurizing wastewater treatment apparatus comprises citric acid, a water-soluble complexing agent, a negative charge coating agent, and a scale disintegrating agent as effective components. The scale preventing agent comprises 7.7 wt.% of the citric acid, 5.7 wt.% of the water-soluble complexing agent, 4.2 wt.% of the negative charge coating agent, 3.2 wt.% of the scale disintegrating agent, and the balance of water. The scale preventing agent further comprises 11.1 wt.% of lithium carbonate and 4.2 wt.% of acetic acid. A scale preventing method of a desulfurizing wastewater treatment apparatus using sodium hypochlorite as a principal treatment chemical comprises injecting 450 to 500 ppm of the scale preventing agent into a second reaction tank(222) and a third reaction tank(224) of the desulfurizing wastewater treatment apparatus using the sodium hypochlorite as the principal treatment chemical. Further, the water-soluble complexing agent is diethylene triamine pentaacetic acid or methylene phosphonic acid, the scale disintegrating agent is 1-hydroxy ethylidene-1 or 1-phosphonic acid, and the negative charge coating agent is aminotrimethyl phosphonic acid.

Description

Scale Preventer and Scale Preventing Method for Wastewater Disposal Facility in Flue Gas Desulfurization System Using Sodium Hypochlorite}

1 is an exemplary view for explaining a typical flow of flue gas generated in a boiler such as a thermal power plant,

2 is an exemplary view showing the configuration of a conventional desulfurization wastewater treatment apparatus in a coal fired power plant.

The present invention relates to a scale inhibitor and a scale prevention method for a desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent. More specifically, citric acid, water-soluble complexing agent, negative charge coating agent and scale disintegrating agent to prevent and remove scale generated and attached to the desulfurization wastewater treatment apparatus using sodium hypochlorite (NaClO) as the main treatment agent An anti-scaling agent and an anti-scaling method are included as active ingredients.

Flue gas generated in boilers such as thermal power plants and steel mills contains sulfur (S0 _X ) such as sulfur dioxide (S0 ₂ ) or sulfur trioxide (S0 ₃ ), as well as ash generated by the reaction of fuel and oxygen in the air. ) Is included. Since the sulfur oxides are not only a source of air pollution but also an acid rain, the fossil fuel process includes a flue gas desulferization (FGD) process for removing sulfur oxides contained in the flue gas.

1 is an exemplary view for explaining a typical flow of flue gas generated in a boiler such as a thermal power plant.

The flue gas generated in the boiler 110 removes dust contained therein through an electrostatic precipitator (EP) 120 and removes sulfur oxides contained therein through a desulfurization facility such as an absorption tower 130. Then, it is discharged to the outside through the stack (Stack, 150). In this process, the flue gas passes through a gas-gas heat exchanger (GGH) 140 in which heat exchange is performed between the flue gas before the desulfurization process and the flue gas undergoing the desulfurization process.

In the flue gas desulfurization process, sulfur compounds including sulfur oxides contained in flue gas after combustion are removed by processes such as absorption, oxidation, reduction and adsorption using reactants and catalysts. Can be divided into By the way, in general, a wet desulfurization method capable of economical efficiency, fast reaction speed, and miniaturization of equipment is mainly used.

In the wet desulfurization method, the flue gas is washed with water or an alkaline solution to absorb sulfur oxides contained in the flue gas, and the primary product is in the form of a solution or slurry. The wet desulfurization method has the advantage of fast reaction speed and miniaturization of the accessory. However, the wet desulfurization method has a disadvantage in that a low temperature of the gas discharged after the process is low, so that the rising power in the stack 150 is low, and thus a reheating process is required, and a large amount of wastewater is generated according to the process. In general, the wet desulfurization method that is widely used is a process using lime or limestone as an absorption reaction agent, which can generally remove 90% or more of sulfur oxides.

A typical wet limestone flue gas desulfurization process is as follows. The flue gas generated in the combustion system is passed through the electric dust collector 120 to remove dust, and then the flue gas is contacted with the limestone slurry in the absorption tower 130. Thus, sulfur oxides are reacted with limestone (CaCO ₃ ) to generate a slurry comprising a solid precipitate such as CaSO ₃ or CaSO ₄ . Finally, forced oxidation air is injected into the lower part of the absorption tower to produce gypsum (CaSO ₄ · H ₂ O).

The gypsum produced by the absorption tower 130 is used as high-purity industrial gypsum after dehydration, in which fine particles and water in the gypsum are discharged. At this time, the discharged water is transferred to the desulfurization wastewater treatment apparatus 200 to be described later as desulfurization wastewater, and is discharged.

2 is an exemplary view showing the configuration of a desulfurization wastewater treatment apparatus using sodium hypochlorite as a main treatment chemical in a coal-fired power plant.

The desulfurization wastewater treatment device 200 is a device for treating wastewater discharged from a desulfurization facility. The desulfurization wastewater treatment device 200 includes suspended solids (SS), heavy metals, chemical oxygen demand (COD) components through physical and chemical treatment. Remove and process within environmental limits and discharge.

The desulfurization wastewater delivered from the absorption tower 130 to the desulfurization wastewater treatment device 200 is first precipitated with heavy gypsum particles in the desulfurization wastewater in the pretreatment tank 210 to separate and remove some of them, and then the first reactor 220 to the first reactor. It is oxidized with sodium hypochlorite in the first reactor 220 of the three reactors 224 to lower the chemical oxygen demand.

The desulfurized wastewater that passed through the first reactor 220 is removed excess sodium hypochlorite by NaHSO ₃ from the third reactor 224 through the second reactor 222, and the toxic hexavalent chromium ( Cr ⁶⁺ ) is reduced to trivalent chromium (Cr ³⁺ ), which is relatively toxic.

After the desulfurization wastewater discharged from the third reactor 224 is temporarily stored in the daily tank 230, caustic soda (NaOH) and a flocculant are added and reacted in the fourth reactor 240 and the fifth reactor 242, and then reacted. In the first precipitation tank 250, fluorine, heavy metals, etc. are precipitated and removed.

The desulfurization wastewater passing through the first settling tank 250 is introduced into the sixth reactor 260 and the seventh reactor 262, the caustic soda, sodium carbonate (Na ₂ again) in the sixth reactor 260 and seventh reactor (262). After the CO ₃ ) and the flocculant are injected and reacted, calcium ions and residual heavy metals are precipitated and removed in the second precipitation station 270, and the pH (acidity) is neutralized in the first PH adjusting tank 280 and the filter tower The pH is lowered to acidic (about 3 PH to 4 PH) again in the second PH adjusting tank 292 via 290, and then fluorine is removed from the fluorine absorption tower 294. The desulfurized wastewater from which fluorine has been removed (in which case the wastewater becomes treated water almost treated) is neutralized in the final PH adjusting tank 296, and then discharged and discharged to the outside.

On the other hand, desulfurization wastewater contains a variety of components such as coal ash, fine gypsum particles, chlorine ions, heavy metals, suspended solids, COD components, such as waste water treatment process, especially the inner wall of the third reactor 224, agitator, measuring instrument, etc. It is attached heavily, such a scale is attached, the treatment capacity of the reaction vessel is reduced, the reaction efficiency is lowered, such as malfunction of the measuring instrument, there is a problem that the quality of treatment of desulfurization waste water is deteriorated and the throughput is also reduced. In addition, each device of the desulfurization wastewater treatment device 200 increases the risk of damage or failure, and the operation of the desulfurization wastewater treatment device 200 must be repeatedly stopped in a short cycle in order to physically remove the attached scale. There are various serious problems, such as removing the scale from a closed space, which greatly threatens worker safety.

In order to solve this problem, a scale inhibitor for a desulfurization wastewater treatment apparatus using sodium nitrite (NaNO ₂ ) and ferrous sulfur (FeSO ₄ ) as a main treatment chemical for treating desulfurization wastewater has been developed and used.

However, this conventional anti-scaling agent is to stop the use of ferrous sulfate (FeSO ₄ ) and to replace with sodium bisulfite (NaHSO ₃ ) to prevent the growth of adhesion of calcium particles (eg gypsum particles) as fine particles. In the desulfurization wastewater treatment apparatus 200 in which sodium hypochlorite, which is a compound of silicon (Si) and calcium (Ca), hardly soluble in strong acids or strong alkalis, is used as a main treatment medicine, There is a problem that can not be removed.

In order to solve this problem, the present invention is to provide a scale preventing agent and a scale preventing method for reducing and preventing the scale generated and attached to the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent. have.

In order to achieve this object, the present invention is characterized in that, in the scale inhibitor of the desulfurization wastewater treatment apparatus, citric acid, a water-soluble complexing agent, a negative charge coating agent, and a scale disintegrating agent are used as active ingredients, and sodium hypochlorite is used as the main treatment drug. It provides a scale inhibitor for the desulfurization wastewater treatment apparatus.

Further, according to another object of the present invention, in the scale prevention method of the desulfurization wastewater treatment apparatus, a scale inhibitor comprising citric acid, a water-soluble complexing agent, a negative charge coating agent and a scale disintegrating agent as an active ingredient, sodium hypochlorite as the main treatment drug Provided is a 450 ppm to 500 ppm injection into the second and third reactors of the desulfurization wastewater treatment apparatus to be used to provide a scale prevention method of the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are designated as much as possible even if displayed on different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

The scale inhibitor for the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent according to a preferred embodiment of the present invention is one of citric acid (C ₆ H ₈ O ₇ ), a water-soluble complexing agent, a negative charge coating agent and a scale disintegrating agent or Including a plurality of combinations to suppress the generation of the scale, to remove the generated scale, further includes lithium carbonate (Li ₂ CO ₃ ) and acetic acid (CH ₃ COOH) to remove fluorine, using water as a solvent It is characterized by.

Here, citric acid is first combined with calcium ions (Ca ²⁺ ) of the desulfurized wastewater to produce citrate, so that it can be dissolved well in neutral cooling water, so that calcium ions are combined with other inorganic ions and hard scale particles. It is not only possible to prevent the reaction, but also to prevent corrosion of the desulfurization wastewater treatment device, and to be harmless to the human body, so it is very preferable as an active ingredient of the scale inhibitor.

In addition, the water-soluble complexing agent contains iron ions (Fe ³⁺ ) and aluminum ions (AL ³⁺ ), which are highly viscous, and condensate particles of hard silicon (Si) and calcium compounds to promote scale adhesion. By producing water-soluble complexes, iron and aluminum ions are prevented from binding and scaling with other molecules. As such a water-soluble complexing agent, it is preferable to use diethylene triamine pentaacetic acid (DTPA) or methylene phosphonic acid (Methylene Phosphonic Acid), but is not limited thereto.

In addition, the negatively-charge coating agent causes the silicon and calcium compounds and other hard compound particles to be negatively charged, thereby preventing them from condensing to grow and scale. As the negative charge coating agent, aminotrimethylene phosphonic acid (ATMP: Aminotrimethyl Phosphonic Acid) or the like is preferably used, but is not limited thereto.

In addition, the scale disintegrating agent is a kind of threshold effect agent, which not only prevents the scale from being generated by disintegrating the crystal itself when the Suspended Solids (SS) are stuck together or attached to the scale, but also prevents the scale from being generated. Remove it. As the scale disintegrating agent, it is preferable to use 1-hydroxy ethylidene-1 (1-Hydroxy Ethylidene-1), 1-phosphonic acid, or the like, but is not limited thereto.

Hereinafter, examples and practical use examples of a scale inhibitor and a scale prevention method for a desulfurization wastewater treatment apparatus using sodium hypochlorite as a main treatment agent according to a preferred embodiment of the present invention will be described.

In order to understand the anti-scaling and removing effect of the anti-scaling agent for the desulfurization wastewater treatment apparatus using sodium hypochlorite as a main treatment drug according to a preferred embodiment of the present invention, by preparing a anti-scaling agent having a composition ratio as shown in Table 1 The second reactor 222 and the third reactor 224 of the desulfurization wastewater treatment apparatus using sodium chlorate as the main treatment chemical were injected with 450 ppm to 500 ppm with respect to 200 ml of the sample of the desulfurization wastewater.

Table 1 shows the composition ratio and the purpose of use of the active ingredient contained in the anti-scaling agent for the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment drug according to a preferred embodiment of the present invention. Here, lithium carbonate and acetic acid are for removing fluorine in the desulfurization wastewater and may be added as necessary.

As described above, the experimental results when the scale prevention rag having a composition ratio as shown in Table 1 is injected into the desulfurized wastewater sample is shown in Table 2.

Table 2 compares the experimental results before and after the use of the anti-scaling agent for the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent according to a preferred embodiment of the present invention.

As shown in Table 2, after using the scale inhibitor for the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent according to a preferred embodiment of the present invention, fine particles and chemical oxygen demand (COD: Chemical Oxygen Demand, Hereafter referred to as 'COD' can be reduced. In particular, it can be seen that the microparticles that provide a direct cause for the generation and attachment of scale are significantly reduced.

In order to further understand the anti-scaling and removing effect of the anti-scaling agent for the desulfurization wastewater treatment apparatus using sodium hypochlorite as a main treatment drug according to a preferred embodiment of the present invention, the anti-scaling agent of the composition ratio of the active ingredient shown in Table 1 While continuously injecting the second reactor 222 and the third reactor 224 of the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent for about two months, the flow rate of the desulfurization wastewater was checked to confirm the optimum injection amount. 250 ppm, 350 ppm, 450 ppm, 550 ppm, 650 ppm were injected.

The results of these experiments are shown in Tables 3-5.

Table 3 shows the results of analyzing the water quality of the desulfurized wastewater before and after use for each concentration of the anti-scaling agent for the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment drug according to a preferred embodiment of the present invention. Here, the water quality of the desulfurization wastewater before using the scale inhibitor was determined by the content of COD and fluorine (F) in the inflow water of the first reaction tank 220, and the water quality of the desulfurization wastewater after using the scale inhibitor was the first precipitation tank 250. It was judged by the content of COD and fluorine in the influent of.

As shown in Table 3, since the content of COD and fluorine is minimized when the injection concentration of the scale inhibitor is 450 ppm to 500 ppm, it is most preferable to inject the scale inhibitor of the injection concentration of 450 ppm to 500 ppm.

Table 4 shows the results of continuous injection of 450 ppm anti-scaling agent for the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment drug according to the preferred embodiment of the present invention.

450 ppm of scale inhibitor was continuously injected into the second reactor 222 and the third reactor 224, so that the inflow of the influent flowing into the first precipitation tank 250 and the discharged water finally discharged before and after using the scale inhibitor were used. Comparing the content of COD, fine particles, fluorine, it can be seen that the content is reduced as shown in Table 4.

Table 5 shows the results of the scale measurement before and after using the anti-scaling agent for the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent according to a preferred embodiment of the present invention.

As a result of measuring the scale of the inner wall of the third reactor 224 immediately before using the scale inhibitor, the thickness of the scale was about 2 cm, and after about two months after using the scale inhibitor, the scale of the inner wall of the third reactor 224 was used. As a result, the thickness of the scale was reduced to 1.5 cm.

From the results shown in Table 5, it can be seen that the anti-scaling agent plays a role of removing the generated and attached scale as well as preventing the scale from being generated and attached.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

As described above, according to the present invention, in the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent, the scale can be prevented from being formed and attached, and the scale generated and attached can be removed.

In addition, by stopping the injection of sodium carbonate (Na ₂ CO ₃ ), which has been injected into the seventh reactor to remove calcium ions, it is possible to prevent adhesion of the soft scale accumulated on the inner wall of the seventh reactor.

This eliminates the need to physically remove the scale, thereby ensuring a stable and smooth treatment of desulfurization wastewater, maintaining a better quality of the final treated water, and allowing operators to physically remove the scale. Inefficiency can be prevented, and safety accidents (choking accidents, etc.) that can occur while the worker removes the scale can be prevented in advance.

Claims (8)

In the anti-scaling agent of the desulfurization wastewater treatment apparatus, An anti-scaling agent for a desulfurization wastewater treatment apparatus using sodium hypochlorite as a main treatment agent, comprising citric acid, a water-soluble complexing agent, a negative charge coating agent, and a scale disintegrating agent as active ingredients. The method of claim 1, wherein the anti-scaling agent, Sodium hypochlorite as the main treatment agent comprising 7.7% by weight of the citric acid, 5.7% by weight of the water-soluble complexing agent, 4.2% by weight of the negatively charged coating agent, 3.2% by weight of the scale disintegrant and the balance water Anti-scaling agent for desulfurization wastewater treatment equipment. The method of claim 1, wherein the anti-scaling agent, An anti-scaling agent for a desulfurization wastewater treatment apparatus using sodium hypochlorite as a main treatment agent, further comprising lithium carbonate and acetic acid. The method of claim 3, wherein The lithium carbonate is 11.1% by weight, wherein the acetic acid is 4.2% by weight anti-scaling agent for desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment drug. The method of claim 1, wherein the water-soluble complexing agent, An anti-scaling agent for desulfurization wastewater treatment apparatus using sodium hypochlorite as a main treatment agent, which is Diethylene Triamine Pentaacetic Acid (DTPA) or Methylene Phosphonic Acid (DTPA). The method of claim 1, wherein the scale disintegrating agent, For desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment agent, characterized in that it is 1-hydroxy ethylidene-1 (1-Hydroxy Ethylidene-1) or 1-phosphonic acid (1-Phosphonic Acid) Scale inhibitors. The method of claim 1, wherein the negative charge coating agent, An anti-scaling agent for desulfurization wastewater treatment apparatus using sodium hypochlorite as a main treatment agent, characterized in that it is aminotrimethylene phosphonic acid (ATMP). In the scale prevention method of a desulfurization wastewater treatment apparatus, The hypochlorite acid is injected into the second and third reactors of the desulfurization wastewater treatment apparatus using sodium hypochlorite as the main treatment drug at 450 ppm to 500 ppm. Method for preventing scale in desulfurization wastewater treatment apparatus using sodium as the main treatment agent.

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