KR20220101980A - Method To Dispose Of Waste Derived From Dry Type Flue Gas Desulfurization Equipment - Google Patents

Abstract

Provided is a method for treating waste derived from a dry type flue gas desulfurization facility, comprising the steps of: mixing, with water, dust waste of a dry flue gas desulfurization facility containing sulphate of soda and carbonate of soda to dissolve soluble substances contained in the waste in the water and thus to form an aqueous solution; removing insoluble substances contained in the waste from the aqueous solution; and removing carbonate and bicarbonate components dissolved in the aqueous solution by adding an acidic material to the aqueous solution. The method for treating the waste derived from the dry type flue gas desulfurization facility according to the present invention not only can reduce the amount of landfill waste by more than 85 % by treating dust waste discharged from dry flue gas desulfurization facility such as steel mills and sintering plants harmlessly to the environment, but also can reduce secondary environmental pollution due to leachate for the landfill waste.

Description

Method To Dispose Of Waste Derived From Dry Type Flue Gas Desulfurization Equipment

The present invention relates to a waste treatment method derived from a dry flue gas desulfurization facility, and more particularly, to a dry flue gas desulfurization facility that harmlessly treats dust waste discharged from a dry flue gas desulfurization facility such as an iron and sinter plant. It relates to a waste treatment method.

The flue gas generated in the sintering process contains a large amount of various heavy metal dust, HCl, SO ₃ gas, etc., so it is difficult to collect the gas with a general wet scrubber. Therefore, in the desulfurization of such an exhaust gas, a dry capture method using sodium bicarbonate (NaHCO ₃ ) is used. The dust collected by the dry collection method contains a large amount of red pepper (Na ₂ SO ₄ ), salt (NaCl), sodium sulfite (Na ₂ SO ₃ ), unreacted carbonate (Na ₂ CO ₃ , NaHCO ₃ ), and the like. Table 1 is an analysis table for the dust of such a dry flue gas desulfurization process.

In Table 1, the sum of the components does not reach 100%, which is a result of not being reflected by the analysis, such as the number of crystals included in the salt water (Na ₂ SO ₄ ), etc. in addition to the measurement error.

Since waste dust is industrial waste, it is generally disposed of by methods such as landfill. However, as shown in Table 2, most of the dust components can be easily dissolved and eluted by rainwater even if they are buried. In this case, it can weaken the landfill ground and cause collapse or secondary damage due to large amounts of harmful leachate. When Na ₂ SO ₃ component is present in the leachate, the biochemical oxygen demand (COD) of the leachate increases, and when Na ₂ CO ₃ is present, the water becomes strongly alkaline, which can affect the survival of aquatic organisms.

Therefore, it was necessary to find a way to treat such waste dust without landfilling.

Patent Publication No. 10-2009-0054859 (published on Jun. 01, 2009) proposes a method of using such waste dust as a concrete activator. However, since the waste dust contains about 10% of salt (NaCl), the proposed method is not widely used. It is common knowledge that the presence of salt in concrete can accelerate cracking of concrete by corroding reinforcing bars.

Since about 50,000 tons of dust, which is difficult to landfill, is generated a year, it would be useful if a method to discharge the dust without burdening the environment or to recycle part of the dust waste is proposed by treating the dust so that the harmful components in the dust are converted harmlessly. will be.

The present invention has been devised to solve the problems of the prior art.

Accordingly, it is an object of the present invention to provide a waste treatment method derived from a dry flue gas desulfurization facility that harmlessly treats dust waste discharged from a dry flue gas desulfurization facility such as an ironmaking plant or a sinter plant.

More specifically, it is an object of the present invention to not only reduce the amount of landfilled waste by 85% or more by treating the dust waste discharged from dry flue gas desulfurization facilities such as iron and sinter plants harmlessly to the environment, but also To provide a waste treatment method from a dry flue gas desulfurization facility capable of preventing secondary environmental pollution caused by leachate.

In order to achieve the above object, the waste treatment method derived from the dry flue gas desulfurization facility according to the present invention mixes the dust waste of the dry flue gas desulfurization facility containing sorghum and sodium carbonate with water to remove the soluble substances contained in the waste. Dissolving in water to form an aqueous solution, removing insoluble substances contained in the waste from the aqueous solution, and adding an acidic substance to the aqueous solution to remove carbonate and bicarbonate components dissolved in the aqueous solution .

The step of removing the insoluble material contained in the waste from the aqueous solution includes the steps of separating a supernatant of the aqueous solution from the precipitating material when the precipitating material contained in the waste is precipitated and activated carbon or diatomaceous earth in the aqueous solution from which the precipitating material is removed It is preferable to include the step of introducing fine suspended substances suspended in the aqueous solution as insoluble substances contained in the waste to the activated carbon or diatomaceous earth, and then filtering the activated carbon or diatomaceous earth to which the fine suspended substances are adsorbed. .

The precipitable material settles within 30 minutes when the aqueous solution is left standing, and the step of separating the supernatant of the aqueous solution from the precipitable material may be performed within 30 minutes after mixing the waste and the water.

The settling material may be formed in less than 7% of the total weight of the waste.

A heavy metal adsorbent having a -SH functional group may be added to the aqueous solution to form a precipitate in a state in which the precipitable material is adsorbed to the heavy metal adsorbent.

The insoluble material removed in the step of removing the insoluble material contained in the waste from the aqueous solution may be disposed of by landfilling.

The separated precipitable material may be used as a raw material for an iron making process.

It is preferable to further include the step of oxidizing the sulfite contained in the waste to sulfate by supplying air to the aqueous solution.

The aqueous solution in which the carbonate and bicarbonate components are neutralized may be discharged by adjusting the pH to 5.8 to 8.5.

The waste treatment method derived from the dry flue gas desulfurization facility according to the present invention is capable of reducing the amount of waste to be landfilled by 85% or more by treating the dust waste discharged from dry flue gas desulfurization facilities such as iron and sinter plants harmlessly to the environment. In addition, it is possible to prevent secondary environmental pollution caused by leachate for landfilled waste.

1 is a diagram schematically illustrating a waste treatment method derived from a dry flue gas desulfurization facility according to an embodiment of the present invention.

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

Dust, dust waste and waste referred to in this specification should be understood to mean dust waste discharged from a dry flue gas desulfurization facility unless otherwise specified or otherwise interpreted in context.

As seen in Table 1, a significant portion of the components constituting the dust is Mangocho (Na ₂ SO ₄ ). When sodium sulfite (Na ₂ SO ₃ ) is also oxidized, it can be oxidized, and when the carbonate compound is neutralized with sulfuric acid, it can be oxidized. Accordingly, the soluble substances dissolved in water in the dust do not harm the environment even if they are discharged as wastewater after oxidizing sodium sulfite and neutralizing carbonate compounds.

Most of the heavy metal components contained in the dust precipitate in the form of metal hydroxides when the pH of the aqueous solution exceeds 10. On the other hand, when the aqueous solution is acidified, the heavy metal component is dissolved in the water. Accordingly, the insoluble material contained in the dust, particularly the heavy metal component, is dissolved during the neutralization reaction with sulfuric acid and cannot be separated from the Mangocho (Na ₂ SO ₄ ) component, and then such wastewater cannot be discharged. Therefore, insoluble substances contained in the dust must be removed before the neutralization reaction with sulfuric acid.

However, among the insoluble substances contained in the dust, fine insoluble dust particles are not only not soluble in water when the dust is dissolved, but also float in the solution due to poor sedimentation. These suspended solids are very difficult to separate from solution. In general, when suspended substances in water form flocs using an organic or inorganic coagulant, a clear supernatant can be obtained through rapid precipitation, which is widely used in water treatment processes. However, due to the carbonates present in the waste dust, there is a problem that the coagulation performance cannot be exhibited by using a general inorganic or organic coagulant. There is also a method of filtering the entire amount of the solution in which the dust is dissolved, but if a large amount of suspended matter forms a cake, the filtration speed is slowed down, so excessive equipment is required. Accordingly, it is necessary to introduce an efficient method for removing suspended solids.

Therefore, in order to complete the present invention, it is necessary to reduce the amount of landfill waste by sufficiently dissolving the dust first. That is, the dust waste of the dry flue gas desulfurization facility should be formed separately from landfill waste and waste water. And in order to remove COD from wastewater, sulfite ions must be removed.

In addition, the dust contains about 1% iron. When the water-soluble component is removed from the dust and the obtained sludge is dried, the iron content increases to about 20%. Currently, steel mills separately collect blast furnace dust with an iron content of around 30%, reduce it, and use it as a raw material for the steelmaking process.

An object of the present invention is to reduce the landfill amount of waste from dry flue gas desulfurization facilities amounting to 50,000 tons per year by 85% or more, and to enable the landfill waste to be safely landfilled or recycled for other purposes.

Accordingly, the waste treatment method of the present invention comprises the steps of mixing the dust waste of a dry flue gas desulfurization facility containing sorghum and sodium carbonate with water to dissolve the soluble material contained in the waste in the water to form an aqueous solution, in the waste removing the included insoluble substances from the aqueous solution, and adding an acidic substance to the aqueous solution to remove carbonate and bicarbonate components dissolved in the aqueous solution.

In the present invention, the soluble material contained in the dust is dissolved in water by first mixing the dust waste with water. At this time, it is preferable to stir in order to achieve dissolution quickly. For example, as shown in FIG. 1, the dust stored in the dust storage facility may be put into the water of the dissolution tank and stirred to dissolve the soluble material contained in the dust in the water.

In the step of dissolving waste in water, the ratio of water to waste may be 10:1 (in winter) to 4:1 (in summer). In particular, in the case of midwinter, when the water temperature approaches 0°C, the solubility of mulberry is significantly lowered, so it is desirable to increase the water temperature to around 10°C using steam to save water. Most of the soluble substances are dissolved with just stirring for 10 to 20 minutes.

When the waste is dissolved in water, the resulting aqueous solution becomes alkaline due to the dissolved carbonate component and its pH is about 10 or higher.

When the soluble material of the waste is completely dissolved in water, the aqueous solution containing the insoluble material may be transferred from the dissolution tank to the settling tank, for example, as shown in FIG. 1 . In the sedimentation tank, the water in which the waste is dissolved is very turbid to the extent of tens of thousands of mg/L of suspended matter, and it is impossible to cleanly remove the suspended matter using various organic and inorganic coagulants of general concentration. This is thought to be because ionic substances such as dissolved sodium carbonate and sodium bicarbonate cause a chemical reaction with the inorganic coagulant to prevent it from acting as a coagulant.

More than 90% of insoluble substances generated during the dissolution of waste are substances with rapid sedimentation, such as iron or siliceous substances. Therefore, in the first precipitation step, the simplification of the equipment can be achieved by roughly precipitating only the precipitating substances that are heavy and settling quickly in a short time. Therefore, according to the present invention, it is possible to achieve the miniaturization of equipment, efficiency and ease of removal of suspended substances by classifying the insoluble substances contained in the waste into sedimentary substances and floating substances and processing them in stages. Specifically, in the case of precipitating only such heavy fast-settling material, after stirring is completed for dissolution of the waste, that is, after stopping the stirring and standing still, for example, within 30 minutes after moving to the sedimentation tank, the amount of sediment is 7% of the total waste It can sink to a lower level, so the sedimentation and dewatering equipment can be downsized. Therefore, in the present specification, the precipitable material may be understood to settle within 30 minutes when the aqueous solution is left standing. When the settling material is precipitated, as shown in Figure 1, the supernatant of the aqueous solution in the settling tank is transferred to the oxidizing tank, while the precipitated settling material is discharged from the settling tank and can be discarded after work-up, e.g., filtering have. For example, such settling material may be buried with the separated suspended solids described below. On the other hand, since such a precipitated material contains about 20% of iron, it may be used as a raw material for an ironmaking process after reduction treatment.

When the pH of the aqueous solution exceeds 10 in the precipitation tank, most of the heavy metal components contained in the dust are precipitated in the form of metal hydroxides. However, if the precipitated heavy metal hydroxide is acidified by rainwater when buried, it may be re-eluted. To prevent this possibility, a heavy metal adsorbent having a -SH functional group may be used together. That is, as shown in FIG. 1, when an appropriate amount of a heavy metal scavenger, that is, a heavy metal adsorbent having a -SH functional group, is added to the dissolution tank, the precipitation material is adsorbed to the heavy metal adsorbent to form a precipitate in the electrochemical tank. The heavy metal adsorbent having a -SH functional group may include H ₂ S and various organic compounds, and generally known ones may be used.

The supernatant from which most of the precipitating material has been removed is transferred, for example, from the precipitation tank to the oxidation tank for COD removal, and the SO ₃ component contained in the supernatant in the oxidation tank is oxidized. Oxidation of SO ₃ ions is determined by the amount of oxidizing air injected according to the amount of the SO ₃ compound to be input. The air required to oxidize 100Kg of sulfite ions to sulfate ions per hour is 100(Kg/Hr SO ₃ ^2- ) ÷ 80(Kg/Kmol SO ₃ ^2- ) × 16(Kg/Kmol O) ÷ 100% reaction basis. 32(Kg/Kmol O ₂ ) × 22.4 ㎥/Kmol ÷ 0.21 (oxygen ratio in air) = 66.7 ㎥/Hr. In the case of a diffuser that injects air through a hole with a diameter of 6 mm in the pipe, the efficiency of oxygen utilization varies depending on the depth of the aerated water. If more than 4.5 times the amount of air is injected, most of SO ₃ is oxidized. Therefore, in order to save energy and keep the facility area narrow, it is necessary to maintain the depth of the oxidation tank deep. However, in order to maintain the water depth of 6 m or more, the power required to overcome the high water pressure increases, so it is preferable to maintain a water head of about 4 to 5 m.

After removing SO ₃ ions, it is necessary to remove fine suspended matter suspended in the aqueous solution as insoluble substances contained in the waste. For this purpose, for example, the aqueous solution after the oxidation process in the oxidation tank is transferred to the mixing tank. In the mixing tank, activated carbon or diatomaceous earth is added at 500~1,500 mg/L to remove chromaticity substances and fine suspended substances present in the solution. Then, the color material and fine suspended matter are adsorbed to the activated carbon or diatomaceous earth. Then, if the entire solution is filtered through a filter, an aqueous solution from which fine suspended matter is removed is obtained. Filtration aids such as activated carbon or diatomaceous earth help to speed up filtration because they can adsorb fine suspended matter and make it into relatively larger particles than fine suspended matter. Because the amount of suspended matter is small and the particle size of the filter aid is large, the differential pressure is hardly generated, so the filtration speed is very fast, and filtration is possible even with a simple liquid bag filter type equipment, thereby simplifying the equipment. As a filtration facility that can simply filter a large amount of solution containing a small amount of suspended matter and discharge sludge, a product called Funda Bag Filter is commercially available.

After filtering the activated carbon or diatomaceous earth, the aqueous solution is transferred to, for example, an acid treatment tank for acid treatment. Acid treatment may be performed by adding a strong acid such as sulfuric acid or hydrochloric acid to the aqueous solution. According to the acid treatment, carbonate and bicarbonate contained in the aqueous solution may be converted into sulfate or salt. After acid treatment, the aqueous solution may be discharged by neutralizing it so that the pH is between 5.8 and 8.5.

The equipment shown in FIG. 1 is merely an exemplary equipment for implementing the method of the present invention, and the method of the present invention may be implemented by a facility configuration different from that shown in FIG. 1 .

Hereinafter, the present invention will be specifically illustrated by way of Examples. However, since the following examples are only examples of the present invention, it should not be understood that the scope of the present invention is limited by the following examples.

<Example 1>

While stirring 2ℓ of water at 13°C, 200.7 g of dust containing waste forget-me-not (having a composition according to the primary analysis in Table 1) generated in the flue gas desulfurization process is slowly added to dissolve in water. As the solute dissolves, there is little change in temperature. Stir for about 20 minutes to allow complete dissolution. The entire amount of the solution was filtered through a reduced pressure filtration device to obtain 18.96 g of sludge and 2,080 ml of a filtrate. The filtration time was 27 minutes.

The pH of this filtrate was 10.3 and the COD was 400 mg/L. This solution was placed in a 2L beaker, and aeration was performed at a rate of 2L per minute to an effective head of 15 cm to proceed with oxidation of SO ₃ ions. After aeration for about 160 minutes, the oxidation is completed to the extent that SO ₃ ions are hardly detectable.

Thereafter, the aqueous solution is acid-treated using hydrochloric acid or sulfuric acid to remove carbonate and bicarbonate contained in the aqueous solution, and then neutralized to a pH range of 5.8 to 8.5 and discharged. The concentration of heavy metals in the effluent was found to be 1/2 to 1/10 of the regulation value.

<Example 2>

While stirring 2ℓ of water at 12 ° C., 208 g of dust containing waste ragweed (having a composition according to the secondary analysis in Table 1) generated in the flue gas desulfurization process is slowly added to dissolve in water. Stir for about 20 minutes to allow complete dissolution. If this solution is left still, all coarse particles are precipitated within 20 minutes. When the supernatant is separated, it becomes about 1.9 L. Filtration of the precipitate produced 23.7 g of sludge. The filtration time was 4 minutes. The supernatant and the filtrate were combined to make 2 L, and then aeration was performed to oxidize SO ₃ ions.

After adding 0.73 g of powdered activated carbon to the solution from which SO ₃ ions have been removed, it is stirred for 10 minutes. Activated carbon adsorbs fine particles, making filtration very fast and at the same time diluting the color of the solution. The entire amount of the solution was filtered through a reduced pressure filter. 2.6 g of sludge was generated and the filtration time was 3 minutes. The pH of the filtrate was 10.12.

Thereafter, the aqueous solution is acid-treated using hydrochloric acid or sulfuric acid to remove carbonate and bicarbonate contained in the aqueous solution, and then neutralized to a pH range of 5.8 to 8.5 and discharged. The concentration of heavy metals in the effluent was found to be 1/2 to 1/10 of the regulation value.

<Example 3>

While stirring 16 liters of water at 12 ° C., 1,610 g of dust containing waste fermented plants (having a composition according to the tertiary analysis in Table 1, and the iron content was 1.15%) generated in the flue gas desulfurization process is slowly added to dissolve in water. . Stir for about 20 minutes to allow complete dissolution. The solution was allowed to stand to precipitate all coarse particles.

When the supernatant was separated, it became about 15 L, and when the precipitate was filtered, 171 g of sludge was produced. When the sludge was dried, it was 106 g. The iron content was 17.4%.

This process was performed once more to obtain 30 L of an aqueous solution. The COD of this solution was 360 mg/L. Separately, a pipe with a diameter of 15 cm was cut to a length of 2 m, and a cylinder-shaped oxidation reaction vessel with one side closed was prepared, and 30 liters of solution was placed there. At this time, the water level reached 170 cm. Oxidation of SO ₃ ions was carried out by performing aeration at a rate of 2 L per minute. After aeration for about 160 minutes, the oxidation was completed to the extent that SO ₃ ions were hardly detectable.

After oxidation of SO ₃ ions, the same procedure as in Example 2 was performed.

Claims (9)

Forming an aqueous solution by mixing the dust waste of a dry flue gas desulfurization facility containing red pepper and sodium carbonate with water to dissolve the soluble substances contained in the waste in the water; removing the insoluble substances contained in the waste from the aqueous solution and adding an acidic material to the aqueous solution to remove carbonate and bicarbonate components dissolved in the aqueous solution. According to claim 1,
The step of removing the insoluble material contained in the waste from the aqueous solution includes the steps of separating a supernatant of the aqueous solution from the precipitating material when the precipitating material contained in the waste is precipitated and activated carbon or diatomaceous earth in the aqueous solution from which the settling material is removed to the activated carbon or diatomaceous earth to adsorb fine suspended substances suspended in the aqueous solution as insoluble substances contained in the waste, and then filtering the activated carbon or diatomaceous earth to which the fine suspended substances have been adsorbed. A waste treatment method from a dry flue gas desulfurization facility. 3. The method of claim 2,
The precipitable material is to settle within 30 minutes when the aqueous solution is left standing, and the step of separating the supernatant of the aqueous solution from the precipitable material is a dry flue gas desulfurization facility, characterized in that it is performed within 30 minutes after mixing the waste and the water Waste treatment methods derived from 4. The method of claim 3,
The sedimentation material is a waste treatment method derived from a dry flue gas desulfurization facility, characterized in that formed in less than 7% based on the total weight of the waste. 5. The method according to any one of claims 2 to 4,
A waste treatment method derived from a dry flue gas desulfurization facility, wherein a heavy metal adsorbent having a -SH functional group is added to the aqueous solution to form a precipitate in a state in which the precipitated material is adsorbed to the heavy metal adsorbent. 6. The method according to any one of claims 1 to 5,
The method for treating waste from a dry flue gas desulfurization facility, characterized in that the insoluble material removed in the step of removing the insoluble material contained in the waste from the aqueous solution is disposed of by landfill. 6. The method according to any one of claims 1 to 5,
The method for treating waste from a dry flue gas desulfurization facility, characterized in that the separated precipitable material is used as a raw material for an ironmaking process. 8. The method according to any one of claims 1 to 7,
The waste treatment method derived from a dry flue gas desulfurization facility, characterized in that it further comprises the step of oxidizing the sulfite contained in the waste to sulfate by supplying air to the aqueous solution. 9. The method according to any one of claims 1 to 8,
A waste treatment method derived from a dry flue gas desulfurization facility, characterized in that the aqueous solution in which the carbonate and bicarbonate components are neutralized is adjusted to a pH of 5.8 to 8.5 and discharged.

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