KR20060001283A - Wastewater disposal method in flue gas desulfurization system by using scale preventer - Google Patents

Abstract

The present invention relates to a method for treating flue gas desulfurization wastewater using a scale generation inhibitor.

The present invention (a) after introducing the flue gas desulfurization wastewater into the primary reactor 306, while injecting sodium nitrite for decomposition of the COD component and at the same time to prevent scale formation, chromium reduction, fluorine removal and treatment efficiency improvement Reacting by injecting a production inhibitor; (b) flowing the flue gas desulfurization wastewater passed through the primary reactor 306 into the secondary reactor 312, adjusting the pH to 9.0 to 10.0 by injecting sodium hydroxide, and then injecting a chelate to remove heavy metals. Reacting; (c) introducing the flue gas desulfurization wastewater that has passed through the secondary reactor 312 into a filtration device 322 to finally filter the suspended solids; And (d) flowing the flue gas desulfurization wastewater through the filtration device 322 into the fluorine adsorption tower 328 and finally removing fluorine using an ion exchange resin regenerated by hydrochloric acid and sodium hydroxide. It provides a flue gas desulfurization wastewater treatment method using a scale generation inhibitor.

According to the present invention, a novel flue gas desulfurization wastewater treatment method using a scale generation inhibitor prevents the generation of scale generated during the wastewater treatment process, and reduces the treatment cost (installation cost, chemical cost, etc.) due to a simpler treatment process and The processing time can be shortened and the processing efficiency can be improved.

Boilers, Flue Gases, Sulfur Oxides, Desulfurization, Scales, Wastewater Treatment Processes, Scale Generation Inhibitors

Description

Wastewater Disposal Method in Flue Gas Desulfurization System by Using Scale Preventer

1A is a view for explaining the flow of flue gas generated in a boiler such as a thermal power plant,

Figure 1b is a view showing a system for the treatment of wastewater discharge and gypsum slurry generated in a conventional desulfurization facility,

2 shows a typical desulfurization wastewater treatment procedure in a coal fired power plant,

3 is a view showing a flue gas desulfurization wastewater treatment process using a scale generation inhibitor according to a preferred embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

302: primary flocculation tank 304: primary precipitation tank

306: primary reactor 308: daily wastewater reservoir

310: temporary wastewater storage tank 312: secondary reactor

314: secondary flocculation tank 316: secondary precipitation tank

318: sand filter 320: activated carbon filter

322: filtration device 324: primary pH adjustment tank

326: filtration tank 328: fluorine adsorption tower

330: secondary pH adjustment tank 332: monitoring tank

334: treatment tank 336: sludge thickening tank

338: gypsum dewatering tank 340: G.H.C

342: gypsum dehydrator 344: sludge treatment apparatus

346: filtrate tank 348: absorption tower

The present invention relates to a method for treating flue gas desulfurization wastewater using a scale generation inhibitor. More specifically, it is possible to prevent the generation of scale generated at the initial stage of the wastewater treatment process by injecting a scale generation inhibitor into the primary reactor, and to reduce and treat treatment costs (facility installation costs, chemical costs, etc.) through a simplified treatment process. The present invention relates to a method for treating flue gas desulfurization wastewater using a scale generation inhibitor aimed at reducing time and improving treatment efficiency.

In general, flue gas generated in a boiler such as a thermal power plant or an ironworks is not only ash generated by the reaction of fuel and oxygen in the air, but also sulfur oxides such as sulfur dioxide (SO ₂ ) or sulfur trioxide (SO ₃ ). (SOx), which includes not only air pollution but also acid rain, so in thermal power plants, etc., flue gas desulfurization to remove sulfur oxides contained in flue gas for environmental compliance and environmentally friendly power plant operation. The facility is in operation.

1A is a view for explaining the flow of flue gas generated in a boiler such as a thermal power plant.

The flue gas generated in the boiler 100 passes through an electrostatic precipitator (EP) 102 to remove dust contained therein, and a sulfur oxide contained therein through a desulfurization facility such as an absorption tower 106. After it is removed, it is discharged to the outside via the stack (Stack, 108). In this process, the flue gas passes through a gas-gas heat exchanger (GGH) 104 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. 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 accessories. 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 force in the stack 108 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 electrostatic precipitator 102 to remove dust, and then the flue gas is contacted with the limestone slurry in the absorption tower 106. 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).

Subdividing the above process, an exhaust gas comprising an absorption tower 106 and a gas-gas heat exchanger 104 which prevents corrosion and visible white smoke of the material and reheats the desulfurized flue gas for smooth diffusion of the flue gas. Limestone handling system for making limestone slurry and supplying it to absorption tower 106, Gypsum slurry for concentration and dehydration of absorption slurry reaction product, Gypsum handling system for making gypsum and wastewater treatment for wastewater generated from various systems It can be divided into lines.

Among these systems, the gypsum handling system and wastewater treatment system will be briefly described as follows.

FIG. 1B is a diagram illustrating a system for treating gypsum slurry and wastewater discharge generated in a conventional desulfurization facility.

Gypsum generated during the desulfurization process in the absorption tower 106 is withdrawn from the absorption tower 106 through the gypsum withdrawal pump 110 in the form of a slurry. The gypsum slurry drawn out by the gypsum take-off pump 110 is recycled according to the water level including the gypsum slurry in the absorption tower 106.

When the water level of the absorption tower 106 is high, the gypsum slurry taken out by the gypsum take-off pump 110 is sent to the gypsum dewatering tank 118 through the gypsum discharge pipe 114 until it is lowered to a certain level. On the other hand, when the water level of the absorption tower 106 falls below a certain level, the extracted gypsum slurry is transferred to the absorption tower 106 through the total amount of the recirculation pipe (112). Whether to deliver or circulate to the gypsum discharge pipe 114 and the recirculation pipe 112 is adjusted by an on-off valve (not shown).

On the other hand, when the concentration of impurities in the gypsum slurry is high, the gypsum slurry is delivered to the primary cyclone 124 through the impurity discharge pipe 116, the operator is to operate the discharge valve (not shown) manually as needed. .

Heavy particles in the primary cyclone 124 are sent back to the absorption tower through the return pipe 126, the light particles and water is passed through the wastewater discharge pipe 128 to the wastewater treatment system. In FIG. 1B, the wastewater as the wastewater treatment system is shown to be delivered to the desulfurization wastewater treatment plant 138 through the wastewater discharge tank 130. However, in some cases, the desulfurization wastewater treatment plant 138 is not directly passed through the wastewater discharge tank 130. Sometimes it is discharged.

On the other hand, the gypsum slurry delivered through the gypsum discharge pipe 114 is delivered to the gypsum centrifuge 120 via the gypsum dewatering tank 118. In the gypsum centrifuge 120, the gypsum is separated and discharged to the gypsum dehydrator 122, and about 90% of the wastewater remaining after separating gypsum is transferred to the filtrate tank 136 through the filtration tank delivery pipe 132, The remaining 10% of the wastewater is discharged to the desulfurization wastewater treatment plant 138 through the wastewater delivery pipe 134. At this time, in some cases, before the wastewater is discharged to the desulfurization wastewater treatment plant 138, a secondary cyclone (not shown) may be installed to separate solid matter in the wastewater once again.

The desulfurized wastewater is composed of COD component, suspended solids (SS, Suspended Solids), fluoride (F) and various heavy metals (Cr, Zn, Hg, etc.) from minerals such as coal and limestone. In the desulfurization wastewater treatment plant 138, COD components, suspended solids, fluorine, heavy metals, etc. are removed through physical and chemical treatments, and then discharged to the outside after being treated within an environmental regulation range.

The desulfurization wastewater treatment process in the desulfurization wastewater treatment plant 138 is as follows.

FIG. 2 shows a typical desulfurization wastewater treatment procedure in a coal fired power plant.

The desulfurization wastewater delivered to the desulfurization wastewater treatment plant 138 is first mixed with a coagulant adjuvant (PAA (+), 0.1%) in the primary coagulation tank 202, and then mixed with heavy particles in the primary sedimentation tank 204. Precipitates. After heating to about 50 ° C. in the primary reactor 206 and adjusting the pH to 2.0, sodium nitrite (NaNO ₂ ) or hypochlorous acid (NaOCl) is injected and reacted to oxidize the COD component and simultaneously sulfuric acid. Ferrous iron (FeSO ₄ ) is injected and reacted to reduce highly toxic Cr ⁺⁶ to less toxic Cr ⁺³ .

The desulfurized wastewater passed through the primary reactor 206 is temporarily stored in the daily wastewater reservoir 212 via the distribution tank 210 after the pH is adjusted in the primary pH adjustment tank 208. In some cases, it may be delivered from the distribution tank 210 to the temporary wastewater storage tank 214.

Next, the desulfurization wastewater is sent to the secondary reaction tank 216, and calcium chloride (CaCl ₂ ) for fluorine removal, chelate for heavy metal removal, sodium hydroxide (NaOH) and hydrochloric acid (HCl) for pH adjustment are introduced. Fluorine, heavy metals or suspended solids in the wastewater passed through the secondary reactor 216 are aggregated in the secondary flocculation tank 218 by the flocculating aid (PAA (-), 0.1%) and sent to the secondary precipitation tank 220. Precipitates.

The desulfurization wastewater that has passed through the secondary precipitation tank 220 is again passed through the tertiary reaction tank 222, the tertiary flocculation tank 224, and the tertiary precipitation tank 226 to remove heavy metal components, suspended solids, and the like. Thereafter, the pH is adjusted in the secondary pH adjusting tank 228 and then transferred to the filtering device 232 via the equalizing tank 230. In the filtration device 232, the desulfurized wastewater is passed through a sand filter, an activated carbon filter, a fluorine adsorption column, and the like to finally remove contaminants, and then passed through a fourth pH adjustment tank 234, a monitoring tank 236, and a treatment tank 238. Discharged to the outside.

On the other hand, the sludge that passed through the primary sedimentation tank 204, the secondary sedimentation tank 220 and the tertiary sedimentation tank 226 is concentrated in the sludge treatment apparatus 240, and then dehydrated. To be disposed of.

However, in the conventional method of treating flue gas desulfurization wastewater, there are some problems as follows.

First, a large amount of scale is generated during the reaction of chemical chemicals injected for waste water treatment and desulfurization waste water, and scale is attached inside the waste water treatment facility, thereby increasing the maintenance and repair cost of the facility. It caused serious obstacles to the stable operation of the equipment, and in particular, a large amount of scale was attached to the first reaction tank 206, the first pH adjusting tank 208, and the daily waste water storage tank 208 where chemical treatment of the desulfurization waste water was first performed. As a result of frequent problems such as stirrers and measuring instruments, the quality of the treated water is deteriorated. Therefore, there is a need to periodically remove the scale.

However, since the descaling work is performed manually in a confined space, the remaining chemicals threaten the worker's health, increase the risk of asphyxiation of the worker by hydrogen sulfide gas, and delay the wastewater treatment due to the long time required for the descaling work. Several serious problems have arisen, such as an increase in the concentration of impurities in the absorption tower.

Second, the processing cost (facility installation cost, chemical cost, etc.) due to the complex treatment process and excessive use of chemicals is generated, which adds to the economic burden, requires a long treatment time, and the low efficiency of treatment ensures compliance with the environmental regulations. There was a difficult problem.

Third, in the conventional flue gas desulfurization wastewater treatment method, the sludge passed through the primary sedimentation tank 204, the secondary sedimentation tank 220, and the tertiary sedimentation tank 226 is concentrated in the sludge treatment apparatus 240, and then dewatered. At that time, a large amount of dehydrated cake is generated and disposed of as waste. As a result, waste disposal costs are required, resulting in environmental pollution caused by waste.

Therefore, the present invention has been invented to solve the above problems, and through the new method of flue gas desulfurization wastewater treatment method using a scale generation inhibitor to prevent scale generation in the early stage of the wastewater treatment process, The purpose is to reduce treatment costs (facility installation costs, chemical costs, etc.) due to the treatment process, shorten the treatment time, and improve treatment efficiency.

In order to achieve the above object, the present invention (a) after introducing the flue gas desulfurization wastewater into the primary reactor 306, while injecting sodium nitrite for decomposition of COD components, preventing the formation of scale, chromium reduction, fluorine removal And reacting by injecting a scale generation inhibitor for improving treatment efficiency; (b) flowing the flue gas desulfurization wastewater passed through the primary reactor 306 into the secondary reactor 312, adjusting the pH to 9.0 to 10.0 by injecting sodium hydroxide, and then injecting a chelate to remove heavy metals. Reacting; (c) introducing the flue gas desulfurization wastewater that has passed through the secondary reactor 312 into a filtration device 322 to finally filter the suspended solids; And (d) flowing the flue gas desulfurization wastewater through the filtration device 322 into the fluorine adsorption tower 328 and finally removing fluorine using an ion exchange resin regenerated by hydrochloric acid and sodium hydroxide. Provided is a method for treating flue gas desulfurization wastewater using a scale generating inhibitor.

Hereinafter, preferred embodiments of the present invention will be described in detail. 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.

3 is a view showing a flue gas desulfurization wastewater treatment process using a scale generation inhibitor according to a preferred embodiment of the present invention.

Desulfurization wastewater from flue gas desulfurization processes includes COD components, suspended solids (SS), pH, fluoride (F), various heavy metals (Cr, Zn, Hg, etc. Among them, the COD component is a form of N, S, O, and H that are hydrogen-bonded and contains a large amount of nitrogen oxides (NOx) and sulfur oxides (SOx), which are very strong. It is difficult to decompose with weak oxidizing agent because it is a hard treatment material that cannot be removed by general wastewater treatment method.

Therefore, in order to effectively treat the flue gas desulfurization waste water, the flue gas desulfurization waste water treatment method using a scale generation inhibitor according to a preferred embodiment of the present invention comprises the following steps.

First, the flue gas desulfurization wastewater is introduced into the primary flocculation tank 302, followed by the coagulation reaction by injecting a coagulant aid (PAA), and then entering the primary precipitation tank 304 to precipitate heavy particles. At this time, the precipitated sludge is transferred to the sludge concentration tank 336 and concentrated.

Meanwhile, the flue gas desulfurization wastewater in which heavy particles are filtered through the precipitation reaction is introduced into the primary reactor 306, and then sodium nitrite (NaNO ₂ ) and scale formation prevention, chromium reduction, fluorine removal and treatment efficiency for decomposition of COD components. It reacts by injecting the anti-scaling agent for improvement. At this time, the reaction conditions are preferably in a temperature of 55 to 60 ° C, pH 2-3.

First, a scale generation inhibitor for preventing scale generation, chromium reduction, fluorine removal and treatment efficiency will be described in detail.

The scales generated in the primary reactor 306 and the daily wastewater reservoir 308 are estimated to be generated through various paths. Among the causes of the scale generation, there are those which can be improved and those which cannot be improved. Among them, the cause of improvement of scale is ferrous sulfate (FeSO ₄ · 7H ₂ O), a chromium reducing agent, and hydrochloric acid (HCl), a pH regulator for optimizing the reaction.

First of all, widely used pH regulators are hydrochloric acid, sulfuric acid (H ₂ SO ₄ ), etc. Since sulfuric acid (H ₂ SO ₄ ) contains SO ₄ ^2- ions, it is likely to cause scale formation of another pathway. In the flue gas desulfurization wastewater treatment method according to a preferred embodiment of the present invention, hydrochloric acid was used as a pH adjusting agent.

Next, chromium reducing agents are widely used as sodium bisulfite (NaHSO ₃ ), ferrous sulfate, and the like. Ferrous sulfate reacts with chlorine ions contained in the wastewater to produce ferric hydroxide (FeCl ₃ ) and ferric oxide. In order to prevent (Fe ₂ O ₃ ) to prevent this, by replacing with sodium bisulfite and acetic acid (CH ₃ COOH), as shown in Formula 1, reduced to trivalent chromium from hexavalent chromium is treated by precipitation.

2H ₂ CrO ₄ + 3CH ₃ COOH + ₃ NaHSO ₃ → Cr ₂ (SO ₄ ) ₃ + 3CH ₃ COONa + 5H ₂ O

Cr ₂ (SO ₄ ) ₃ + ₃ NaOH → Cr (OH) ₃ ↓ + 3Na ₂ SO ₄

In addition, in order to remove the fluorine component in the waste water, as shown in Chemical Formula 2, calcium chloride (CaCl ₂ ) and sodium hydroxide (NaOH) are reacted to convert calcium chloride to Ca (OH) ₂ , and then reacted with fluorine to react with fluorite (CaF ₂ ). Precipitation is carried out.

CaCl ₂ + 2NaOH → Ca (OH) ₂ + 2NaCl

However, sodium chloride (NaCl) is produced during the conversion of calcium chloride to Ca (OH) ₂ , increasing chlorine ions in the wastewater by about 400ppm, causing corrosion of the piping, and two chemicals to produce Ca (OH) ₂ . In order to improve the economic efficiency of injecting calcium chloride and sodium hydroxide, it is replaced with lithium carbonate (Li ₂ CO ₃ ) as in Chemical Formula 3 and treated with a fine precipitate of lithium fluoride (LiF ↓).

2HF + Li ₂ CO ₃ → 2LiF ↓ + H ₂ CO ₃

However, in the above process, lithium carbonate has a small solubility in water, and thus acetic acid (CH ₃ COOH) is added as shown in Chemical Formula 4.

2HF + 3 / 2Li ₂ CO ₃ + CH ₃ COOH → 2LiF ↓ + CH ₃ COONa + 3 / 2H ₂ CO ₃

On the other hand, since most of the scales generated in the primary reactor 306 and the daily wastewater storage tank 308 are inorganic, formic acid (HCOOH) is added which is effective for removing inorganic scales such as calcium salts.

As described above, the anti-scaling agent for preventing scale formation, chromium reduction, fluorine removal, and improving treatment efficiency includes formic acid, lithium carbonate, hydrochloric acid, acetic acid, and sodium bisulfite as active ingredients, and in some cases, a dispersant and a penetrant are added. It can be included as.

As the dispersant, nonionic surfactants which are dissolved without being ionized in water are used. As nonionic surfactants, both nonylphenol (NP) surfactant and octylphenol (OP) surfactant can be used. Such dispersants serve to promote penetration, dispersion, emulsification, and the like of the scale inhibitor. It is preferable to add 0.5 to 2.5 weight% of the dispersant. When the dispersant is less than 0.5% by weight, the ability to penetrate, emulsify, and disperse is reduced, and thus, scale formation prevention action is lowered. On the contrary, when the dispersant is more than 2.5% by weight, storage stability is decreased and bubbles are generated.

On the other hand, the penetrant prevents the scale from adhering to the wall surface of the primary reactor 306 or the like.

Hereinafter, the Example and actual use example of a scale generation inhibitor are demonstrated.

Example 1

The anti-scaling effect was tested for 1 liter of the wastewater sample by formulating a anti-scaling agent with 0.18 g of sodium bisulfite, 2.95 g of acetic acid and residual water with respect to 100 g of total weight.

The test results are shown in Table 1.

division Test Items COD (ppm) SS (ppm) sample 257 145 Wastewater Treatment by Existing Method 111 86 Input of scale generation inhibitor 10 ml 53 28 7 ml 61 27 3 ml 56 28

In the case of the anti-scaling agent consisting of sodium bisulfite and acetic acid, the COD value and the SS value decrease as shown in Table 1. In particular, it can be seen that the level of suspended matter, which is a direct cause of scale generation, is significantly reduced.

Example 2

The anti-scaling effect was tested for 1 liter of the wastewater sample by formulating a anti-scaling agent with 0.18 g of sodium bisulfite, 2.95 g of acetic acid, 0.175 g of lithium carbonate, 4.27 g of hydrochloric acid, and the remaining water with respect to 100 g of total weight.

The test results are shown in Table 2.

division Test Items COD (ppm) SS (ppm) sample 257 145 Wastewater Treatment by Existing Method 111 86 Input of scale generation inhibitor 10 ml 64 51 7 ml 68 47 3 ml 74 42

In the case of Example 2 also showed that the COD value and the suspended matter value was decreased than before, but the decrease is less than the case of Example 1.

However, the composition of Example 2 has a greater effect on the removal of fluorine ions contained in the desulfurization wastewater, and thus, the composition of Example 2 in which lithium carbonate and hydrochloric acid are added is more preferable than the composition according to Example 1. In particular, due to the effect of removing fluorine ions there is an effect that can reduce the amount of calcium chloride that is added to the secondary reaction tank 216 for the removal of fluorine ions.

Example 3

The final anti-scaling agent based on the results of Examples 1 and 2 was 25.0-30.0 wt% formic acid, 10.0-15.0 wt% lithium carbonate, 8.0-12.0 wt% hydrochloric acid, 5.0-10.0 wt% acetic acid, sodium bisulfite It is preferably composed of 1.0 to 4.0% by weight and residual water.

According to this composition, 1.40% by weight of a penetrant and a dispersant were added to 28.1% by weight of formic acid, 13.12% by weight of lithium carbonate, 10.0% by weight of hydrochloric acid, 8.56% by weight of acetic acid, and 2.53% by weight of sodium bisulfite, and the remaining amount was water. Injecting 400 to 500 ppm in (306) and the effect thereof is shown in Table 3.

The reaction temperature of the primary reaction tank 306 is 55-60 degreeC, and pH is 2-3. On the other hand, the analysis results of the suspended solids according to the conventional treatment method and the injection of the scale generation inhibitor is for the outlet water of the primary reactor (306).

division Wastewater Existing Treatment Method After injection of scale inhibitor Remarks COD (ppm) 1,100 113 7 Side effects SS (ppm) 20,000 1,730 62 Scale creation prevention effect Cr ⁺⁶ (ppm) 2.0 Not detected Not detected F ^- (ppm) 150 60 14 Side effects

As shown in Table 3, continuous injection of the scale generation inhibitor into the primary reactor 306 for reducing the COD value and reducing the hexavalent chromium ion during the desulfurization wastewater treatment process results in the reduction of the suspended solids. And the scale that is attached to the daily wastewater reservoir 308 can be prevented. In addition, as a side effect, the COD value is reduced and the fluorine ion is also reduced.

On the other hand, the conventional treatment method for the removal of the COD component is treated by injecting sodium nitrite (NaNO ₂ ) corresponding to 10 times the inlet COD component to the first reaction tank, and then to process the residual NO ₂ ^_ by the formula (5) adding the NaOCl On the other hand, the addition of NaHSO ₃ to process the residual ClO ^_ and final treatment.

NO ₂ ^_ + NaOCl → NO ₃ ^_ + NaCl

ClO ^_ + H ⁺ + NaHSO ₃ → NaHSO ₄ + HCl

However, the excess reaction of NO ₂ ^_ itself has the NO _x group, rather it increases the COD.

Example 4

In order to determine the optimal injection concentration of NaNO ₂ for the removal of COD components, 130 ppm of COD was introduced into the first reactor 306 and 500 ppm of scale generation inhibitor was injected together to perform a Jar Test.

The test results are shown in Table 4.

division                                              NaNO ₂ injection concentration (ppm) Remarks 150 200 250 400 COD (ppm) 74 73 68 90 -1st reactor inlet COD (130ppm)-500ppm injection of scale generation inhibitor

As shown in Table 4, the injection of NaNO ₂ , which is about twice the inflow COD while simultaneously injecting 500 ppm of the scale generation inhibitor, was found to have an optimal COD removal effect.

Example 5

In order to determine the necessity of an auxiliary reaction (NaOCl and NaHSO ₃ ) to treat the existing excess of sodium nitrite by injecting NaNO ₂ at an optimal concentration, the auxiliary reaction was omitted and approximately 500 ppm of the scale-generating agent and about twice the influent COD The change of COD when only NaNO _{2 was} injected and treated was examined.

The test results are shown in Table 5.

division Primary reactor influent 1st reaction tank number Daily wastewater reservoir Secondary Precipitator Outlets Final treatment COD (ppm) according to conventional treatment 545 180 150 85 45 COD (ppm) when side reaction is omitted 622 65 30 15 13

As shown in Table 5, the COD analysis result shows that the COD removal rate is improved compared to the conventional treatment method when treated with only sodium nitrite and scale generation inhibitor corresponding to twice the inflow COD while omitting the secondary reaction. In addition, since the residual NO ₂ ^_ is oxidized by aeration in the daily wastewater storage tank 308 to produce NO ₃ ^_ and the reaction proceeds with nitric acid, the flue gas desulfurization wastewater treatment using the scale generation inhibitor according to the preferred embodiment of the present invention. The method does not inject the NaOCl and NaHSO ₃ drugs for the auxiliary reaction.

Next, the flue gas desulfurization wastewater passing through the primary reactor 306 is stored in at least one of the daily wastewater reservoir 308 or the temporary wastewater reservoir 310. This is for storing the flue gas desulfurization waste water in another reservoir when the cleaning operation for either the daily waste water reservoir 308 or the temporary waste water reservoir 310 is in progress. At this time, the reaction in the primary reaction tank 306 of the flue gas desulfurization waste water described so far is continued in the daily waste water storage tank 308 or the temporary waste water storage tank 310.

On the other hand, in some cases, the gas-gas heat exchanger (GGH) cleaning wastewater is additionally introduced into the temporary wastewater storage tank 310 and stored therein. The gas-gas heat exchanger cleaning wastewater is introduced into the secondary reaction tank 312 together with the flue gas desulfurization wastewater to undergo a later step.

Next, the flue gas desulfurization wastewater is introduced into the secondary reactor 312 from the daily wastewater storage tank 308 and the temporary wastewater storage tank 310, and then adjusted to pH 9.0 to 10.0 by injecting sodium hydroxide to remove heavy metals. Inject the chelate for reaction.

In the conventional treatment method, heavy metals are precipitated by forming an insoluble salt by the formula (6) in an alkaline state of pH 10.5.

^{Al 3+ + 3NaOH + Me → Al} (OH) 3 · Me ↓ + 3Na +

Fe ³⁺ + ₃ NaOH → Fe (OH) ₃ ↓ + 3Na ⁺

Cr ³⁺ + 3NaOH → Cr (OH) ₃ ↓ + 3Na ⁺

Me + 3NaOH → Me (OH) ₃ ↓ + 3Na ⁺ (Me: Heavy Metal)

However, when the pH is adjusted to 10.5 as in the conventional treatment method, sludge containing 70 to 80% of water is generated about 90% of the sample volume, and there is a difficulty in flocculation and sedimentation due to the sludge generated and difficulty in clogging the pipe. This results in unstable plant operation.

Example 6

The pH of the secondary reactor 312 was adjusted down from 10.5 to 9.5 to analyze the heavy metal content of the treated water.

The test results are shown in Table 6.

division draft chrome cadmium Mercury arsenic zinc lead 'A' regional emission limit 1 or less 2 or less 0.1 or less 0.005 or less 0.5 or less 5 or less 1 or less Analysis 0.88 0.10 Not detected Not detected 0.04 0.13 0.03

As shown in Table 6, even if the pH of the secondary reactor 312 is treated by adjusting the pH down from 10.5 to 9.5, since heavy metals are treated within the emission allowance standard, flue gas desulfurization wastewater using a scale generation inhibitor according to a preferred embodiment of the present invention. In the treatment method, by adjusting the pH of the secondary reactor 312 to 9.5, the treatment of heavy metals, as well as stable plant operation, and the reduction of chemical consumption according to the pH control were intended.

Next, the flue gas desulfurization wastewater which passed through the secondary reaction tank 312 flows into the secondary flocculation tank 314, injects flocculation aid, and coagulates the reaction, and then flows into the secondary precipitation tank 316 for precipitation reaction. At this time, the precipitated sludge is transferred to the sludge concentration tank 336 and concentrated.

Next, the flue gas desulfurization wastewater undergoing the precipitation reaction in the secondary sedimentation tank 316 is introduced into the filtration device 322 to finally filter the suspended matter. The filtration process in the filtration device 322 will be described in detail. First, the suspended particulate matter is filtered through the sand filter 318, and then the unfiltered particles are not filtered in the sand filter 318 through the activated carbon filter 320. Finally, small suspended solids are filtered.

On the other hand, the filtration wastewater containing suspended solids generated in the filtration process through the sand filter 318 and the activated carbon filter 320 is transferred to the daily wastewater storage tank 308, and then the secondary reaction tank 312 together with the flue gas desulfurization wastewater. It is introduced into the process and goes through the process described so far.

Next, the flue gas desulfurization wastewater filtered through the filtration device 322 is introduced into the primary pH adjusting tank 324, and then hydrochloric acid is injected to adjust the pH to 2.5 to suit the appropriate reaction conditions in the fluorine adsorption tower 328. After adjusting to 3.5, the fluorine adsorption column 328 is introduced into the fluorine adsorption tower 328 through a filtered water tank 326 to finally remove fluorine using an ion exchange resin regenerated by hydrochloric acid and sodium hydroxide.

Meanwhile, in the process of regenerating the ion exchange resin for fluorine removal, the ion exchange resin regeneration waste water is generated. The ion exchange resin regeneration waste water is transferred to the daily waste water storage tank 308, and then the secondary reaction tank together with the flue gas desulfurization waste water. 312 is sequentially passed through the process described so far.

Next, after introducing the flue gas desulfurization wastewater passing through the fluorine adsorption tower 328 into the secondary pH adjustment tank 330, sodium hydroxide is injected to adjust the pH to 6.0 to 8.0 to meet the discharge discharge standard. 332) to determine whether the discharge is suitable.

At this time, the flue gas desulfurization wastewater which has been determined to be suitable for discharge in the monitoring tank 332 is recycled to the ash treatment plant water through the treatment tank 334. That is, since ash is collected in the dry state in the electric dust collector, since water is needed as a means for transferring ash to the ash processing plant for treating the ash, the flue gas desulfurization which has been determined to be suitable for discharge in the monitoring tank 332. Wastewater is recycled to the treatment plant water.

However, the flue gas desulfurization wastewater that has been determined to be unsuitable for discharge in the monitoring tank 332 is not only suitable for recycling into the ash of the treatment plant, but also causes a problem of environmental pollution when discharged directly to the outside, and thus, the daily treatment through the treatment tank 334. After being transferred to the wastewater storage tank 308, it is introduced into the secondary reactor 312 together with the flue gas desulfurization wastewater to sequentially pass through the process described so far.

Example 7

Comparison of the efficiency of the anti-scaling agent by changing the COD component, suspended solids (SS), chromium and fluorine content when 400 ppm of the anti-scaling agent is continuously injected into the primary reactor 306 is compared with that of the conventional treatment method. And analyzed.

The test results are shown in Table 7.

division Process by the existing treatment method Treatment by injecting scale inhibitor COD                                              SS                                              Cr                                              F COD SS Cr F 'Ga' Regional Emission Limits (ppm) 20 or less 20 or less 2 or less 15 or less 20 or less 20 or less 2 or less 15 or less Primary reactor influent (ppm) 558 174 0.47 69.8 596 170 0.42 64.1 Final treated water (ppm) 150 10 0.02 7.2 12 0 0.10 10.6 % Removal 73                                              94 96 90 98 100 76 83

As shown in Table 7, the removal rate of suspended solids (SS), COD and fluorine, including chromium reduction, were all well within the emission limits, and COD was 73% removed by conventional treatment methods. Treatment resulted in 98% removal efficiency.

Meanwhile, the precipitated sludge precipitated in the primary settling tank 304 and the secondary settling tank 316 flows into the sludge thickening tank 336 and is concentrated. At this time, the supernatant generated in the concentration process is transferred to the daily wastewater storage tank 308, and then flows into the secondary reaction tank 312 together with the flue gas desulfurization wastewater to pass through the process described so far.

The precipitated sludge concentrated through the sludge thickening tank 336 is treated with gypsum through the sludge treatment apparatus 344 and recycled. The treatment process through the sludge treatment device 344 will be described in detail. After mixing the concentrated sediment sludge with the gypsum slurry produced in the absorption tower 348, the gypsum hydrocyclone (GHC) is introduced into the gypsum dehydration tank 338. Gypsum Hydrocyclone (340) and gypsum dehydrator (342) produce gypsum less than 10% moisture.

By treating the concentrated sediment sludge with gypsum and recycling it, the problem of waste disposal cost and environmental pollution caused by a large amount of dehydration cake generated in the existing treatment method has been solved.

Meanwhile, about 90% of the wastewater left after separating gypsum through the gypsum hydrocyclone 340 is recycled to the desulfurization facility water through the filtrate tank 346, and the remaining about 10% is passed through the filtrate tank 346. After being transferred to the secondary coagulation tank 302 and subjected to coagulation / precipitation reaction together with the flue gas desulfurization wastewater, the secondary reactor 312 is introduced into the secondary coagulation tank 302 to sequentially pass through the above-described processes.

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, a new method of flue gas desulfurization wastewater treatment method using a scale generation inhibitor prevents generation of scale which occurs at an early stage of the wastewater treatment process and seriously affects the wastewater treatment process. The treatment efficiency can be improved by improving the treatment water quality and shortening the descaling operation time, which is required for a long time.

In addition, by greatly simplifying the treatment process, it is possible to drastically reduce equipment installation costs, maintenance costs, and chemical treatment costs, and shorten the treatment time.

In addition, by recycling the concentrated sediment sludge with gypsum, it is possible to solve the problem of waste disposal costs and environmental pollution due to the large amount of dehydration cake generated in the existing treatment method.

Claims (23)

In the method of treating the flue gas desulfurization wastewater discharged from the flue gas desulfurization equipment for removing the sulfurous acid gas in the flue gas generated when burning the fuel containing sulfur in a boiler such as a thermal power plant or steel mill, (a) After introducing the flue gas desulfurization wastewater into the primary reaction tank 306, while injecting sodium nitrite for decomposition of COD components, a scale generation inhibitor for preventing scale formation, chromium reduction, fluorine removal, and improving treatment efficiency. Reacting by injecting; (b) flowing the flue gas desulfurization wastewater passed through the primary reactor 306 into the secondary reactor 312, adjusting the pH to 9.0 to 10.0 by injecting sodium hydroxide, and then injecting a chelate to remove heavy metals. Reacting; (c) introducing the flue gas desulfurization wastewater that has passed through the secondary reactor 312 into a filtration device 322 to finally filter the suspended solids; And (d) introducing the flue gas desulfurization wastewater passed through the filtration device 322 into the fluorine adsorption tower 328 and finally removing fluorine using an ion exchange resin regenerated by hydrochloric acid and sodium hydroxide. Flue gas desulfurization wastewater treatment method using a scale generation inhibitor comprising a. The method of claim 1, The flue gas desulfurization wastewater flowing into the primary reaction tank 306 first flows into the primary flocculation tank 302, injects the flocculent aid, causes the flocculation reaction, and then flows into the primary precipitation tank 304 and undergoes precipitation reaction. Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that the waste water. The method of claim 1, As an intermediate step between step (a) and step (b), Storing the flue gas desulfurization wastewater that passed through the primary reactor 306 in any one or more of the daily wastewater storage tank 308 or the temporary wastewater storage tank 310 further comprises a flue gas using a scale generation inhibitor Desulfurization wastewater treatment method. The method of claim 1, As an intermediate step between (b) and (c), Including the flue gas desulfurization wastewater passed through the secondary reaction tank 312 into the secondary flocculation tank 314 and agglomeration reaction by injecting the coagulant aid, and then entering the secondary precipitation tank 316 to precipitate the reaction. Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that. The method of claim 1, As an intermediate step between the step (c) and the step (d), After generating the flue gas desulfurization wastewater filtered through the filtration device 322 into the primary pH adjustment tank 324, the scale generation further comprises the step of adjusting the pH to 2.5 to 3.5 by injecting hydrochloric acid Flue gas desulfurization wastewater treatment method using an inhibitor. The method of claim 1, As a next step of step (d), The flue gas desulfurization wastewater that passed through the fluorine adsorption tower 328 is introduced into the secondary pH adjustment tank 330, injected with sodium hydroxide, adjusted to pH 6.0-8.0, and then flows into the monitoring tank 332 to determine whether the discharge is suitable. Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that it further comprises a step. The method of claim 1, The scale generation inhibitor is formic acid, lithium carbonate, hydrochloric acid, acetic acid and sodium bisulfite as an active ingredient, flue gas desulfurization wastewater treatment method using a scale production inhibitor. The method of claim 7, wherein The anti-scaling agent comprises 25.0 to 30.0% by weight of the formic acid, 10.0 to 15.0% by weight of the lithium carbonate, 8.0 to 12.0% by weight of the hydrochloric acid, 5.0 to 10.0% by weight of the acetic acid, 1.0 to 4.0% by weight of the sodium bisulfite, and the remaining water Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that. The method of claim 7, wherein The scale generation inhibitor further comprises a dispersing agent and a penetrant, flue gas desulfurization wastewater treatment method using a scale generation inhibitor. The method of claim 9, The dispersing agent and the permeation agent is 0.5 to 2.5% by weight flue gas desulfurization wastewater treatment method using a scale generation inhibitor. The method according to any one of claims 7 to 10, Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that the injection concentration of the scale generation inhibitor is 400 ~ 500ppm. The method of claim 1, The injection concentration of sodium nitrite injected in the step (a) for the decomposition of the COD component is 1.5 to 2.5 times the concentration of the inlet COD component, flue gas desulfurization wastewater treatment method using a scale generation inhibitor. The method of claim 1, Sodium hydroxide for pH control in the step (b) is a flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that the reaction conditions of the secondary reactor 312 is injected to maintain a pH of 9.5. The method of claim 3, wherein The gas-gas heat exchanger (GGH) cleaning wastewater is additionally introduced into the temporary wastewater storage tank 310 to flow into the secondary reactor 312 together with the flue gas desulfurization wastewater to cause the reaction of step (b). Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that it further comprises the step of. The method of claim 1, Step (c) is (c1) filtering the suspended particulate matter through the sand filter 318; And (c2) filtering the suspended solid material having small unfiltered particles in the sand filter 318 through the activated carbon filter 320. Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that carried out including. The method of claim 3, wherein A method for treating flue gas desulfurization wastewater using a scale generation inhibitor further comprising the step of transferring the filtration wastewater containing suspended solids, which is generated during the filtration process of the filtration device 322, to the daily wastewater storage tank 308. . The method of claim 3, wherein A method of treating flue gas desulfurization wastewater using a scale generation inhibitor further comprising the step of transferring the ion exchange resin regeneration wastewater generated in the process of regenerating the ion exchange resin to the daily wastewater storage tank (308). The method of claim 6, A method of treating flue gas desulfurization wastewater using a scale generation inhibitor further comprising the step of recycling the flue gas desulfurization waste water that has been determined to be suitable for discharge in the monitoring tank 332 through the treatment tank 334. The method of claim 6, The flue gas desulfurization waste water that has been determined to be ineligible in the monitoring tank 332 is transferred to the daily waste water storage tank 308 through the treatment tank 334, and then, to the secondary reactor 312 together with the flue gas desulfurization waste water. Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that further comprising the step of introducing to cause the reaction of step (b). The method according to claim 2 or 4, The sludge settled in the first settling tank 304 or the second settling tank 316 is concentrated by entering the sludge thickening tank 336, and the concentrated settled sludge is treated with gypsum through the sludge treatment apparatus 344. Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that it further comprises the step of recycling. The method of claim 20, After transferring the supernatant water generated in the concentration process of the sludge thickening tank 336 to the daily wastewater storage tank 308, the secondary water is introduced into the secondary reactor 312 together with the flue gas desulfurization wastewater to cause the reaction of the step (b). Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that it further comprises the step of. The method of claim 20, The treatment step through the sludge treatment device 344, after mixing the concentrated sediment sludge with the gypsum slurry produced in the absorption tower 348 to enter the gypsum dehydration tank 338, gypsum hydrocyclone 340 and Flue gas desulfurization wastewater treatment method using a scale generation inhibitor, characterized in that the step of producing a gypsum less than 10% moisture through the gypsum dehydrator (342). The method of claim 22, About 90% of the wastewater remaining after separating gypsum through the gypsum hydrocyclone 340 is recycled to the desulfurization facility water through the filtrate tank 346, and the remaining about 10% is passed through the filtrate tank 346 to the primary. After the transfer to the coagulation tank 302, the coagulation aid is injected into the coagulation reaction, the coagulation reaction is introduced into the first precipitation tank 304, the precipitation reaction, and then flows into the primary reaction tank 306 together with the flue gas desulfurization waste water (the A method of treating flue gas desulfurization wastewater using a scale-generating agent, further comprising the step of causing a reaction of step a).

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