KR102331750B1 - Treatment method for process water - Google Patents

Abstract

The present invention relates to a method for treating process water containing hydrocarbon impurities, slag, and the like. The present invention exhibits excellent coagulation and precipitation efficiency.

Description

Treatment method for process water

The present invention relates to a method for treating process water containing hydrocarbon impurities, slag, and the like.

As a method of treating wastewater containing impurities, a method of aggregating and precipitating impurity particles using a polymer coagulant is used. In the case of food processing wastewater, sewage wastewater, etc., since the main components contained in wastewater are solid particles having a negative charge, a cationic polymer coagulant having an opposite charge to these solid particles suspended in water is used to conduct an electrical neutralization reaction. It is possible to effectively remove it. However, the process water generated from gasification facilities such as coal gasification combined cycle power plants contains hydrocarbon impurities and suspended substances in water such as slag, and these impurities have a positive charge, so the conventional treatment method using a polymer flocculant has a problem in that it is difficult to effectively process solid particles.

When a large amount of suspended substances exist in water because aggregation and precipitation of solid impurities are not effectively performed, the precipitation of the hardness component (Ca ²⁺ ) is accelerated, and the calcium compounds (CaCO ₃ , CaSO _{4 ,} etc.) in the pipe increase These compounds adhere to the piping and equipment and cause scale, which may eventually lead to clogging of the piping. Therefore, there is a need for a technology that quickly aggregates, precipitates, and removes the solids present in water, ^{and effectively prevents precipitation of the hardness component (Ca 2+ ).}

In addition, the conventional polymer flocculant mainly acts effectively in the acidic region, and thus may have a negative effect on the subsequent biological treatment process. Therefore, after the coagulation and precipitation reaction using the polymer coagulant, the adverse effect on the microbial activity can be prevented only by going through a process of adjusting the pH from an acidic to a neutral range. Such an additional process for adjusting the pH complicates the entire water treatment process, and thus an increase in cost is inevitable, so a technique for omitting this process is required.

The present invention provides a process water treatment method that can use both a cationic polymer and an anionic polymer as a polymer flocculant, and exhibits excellent coagulation and precipitation efficiency even in a neutral environment.

The process water treatment method of the present invention includes the step of adding a composite coagulant containing poly aluminum chloride (PAC) and a polymer coagulant to the process water.

The process water treatment method according to the present invention can use both a cationic polymer and an anionic polymer as a polymer flocculant, and has excellent coagulation and precipitation efficiency compared to the conventional method using a polymer flocculant alone. In addition, since the process water treatment method of the present invention works effectively even in a neutral environment, the pH drop occurs less than the conventional method using a cationic polymer flocculant in which agglomeration and precipitation reactions occur in an acidic region. As a result, it does not adversely affect the subsequent biological process, and it is not necessary to necessarily go through a pH adjustment step, so it is economical and has excellent field applicability.

Hereinafter, the present invention will be described in detail. However, it is not limited only by the following content, and each component may be variously modified or selectively mixed as needed. Accordingly, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

The process water treatment method of the present invention includes the step of adding a composite coagulant containing polyaluminum chloride and a polymer coagulant to the process water. Polyaluminum chloride generates fine flocs by minimizing the electric double layer repulsion between impurities suspended in water. to remove As such, by mixing the polyaluminum chloride and the polymer coagulant, it is possible to increase the coagulation and sedimentation rates for turbidity-inducing substances.

As the polyaluminum chloride, a compound represented by the following Chemical Formula 1 may be used.

[Formula 1]

[Al ₂ (OH) _n Cl _6-n ] _m

in the above formula

n is an integer from 1 to 6

m is an integer of 10 or less.

The polyaluminum chloride may have an Al ₂ O ₃ content of 10 to 18%.

The polymer coagulant may be a cationic polymer, an anionic polymer, or a mixture thereof. As the cationic polymer, polyethyleneimine, dialkyldimethylammonium salt, diaminoalkoxylammonium salt, imidazolium salt, etc. can be used, and as the anionic polymer, sodium alkylate, sodium carboxymethyl cellulose, sodium polyacrylate, etc. Can be used. The polymer coagulant may be used alone or in combination of two or more.

The mixing ratio (weight ratio) of the polyaluminum chloride and the polymer flocculant may be 7: 3 to 2.5: 7.5, for example, 5.5: 4.5 to 3: 7, and in another example 4: 6 to 3: 7. When the blending ratio of the polymer coagulant to the polyaluminum chloride is less than the above-mentioned range, the agglomeration and precipitation of the fine floc may not be sufficiently achieved, so that the turbidity improvement (impurity removal) effect may be insufficient. On the other hand, when it exceeds the above-mentioned range, the turbidity improvement (impurity removal) effect may be insufficient because the content of polyaluminum chloride is insufficient to sufficiently form fine flocs.

The dosage of the complex coagulant may be increased or decreased depending on the pH or turbidity of the process water. As an example, the complex coagulant may be added at a concentration of 100 to 300 ppm in the process water, but when the pH of the process water is alkaline beyond neutral or has high turbidity, it is necessary to input in an amount exceeding 300 ppm On the contrary, when the pH of the process water is acidic or the turbidity is low, it can be added in an amount of less than 100 ppm.

The step of adding the complex coagulant to the process water may be performed in a neutral environment, for example, pH 6.5 to 7.5. Therefore, compared to the conventional method using a cationic polymer flocculant in which agglomeration and precipitation reactions occur in an acidic region, a drop in pH occurs less. As a result, it does not adversely affect the subsequent biological process, and it is not necessary to necessarily go through a pH adjustment step, so it is economical and has excellent field applicability.

The process water treatment method of the present invention may further include the step of adding a scale inhibitor including acetic acid after the step of adding the complex coagulant to the process water. The scale inhibitor serves to prevent scale precipitation by increasing the solubility of the hardness component (Ca ^{2+ ).} Accordingly, the formation of scale in the pipe is prevented, thereby reducing the amount of work and labor costs due to frequent maintenance and replacement of equipment. In addition, the scale inhibitor acts as a nutrient for microorganisms in the biological treatment tank, thereby exerting a synergistic effect of increasing the total nitrogen and phosphorus treatment efficiency.

The concentration of acetic acid in the scale inhibitor may be adjusted according to the pH of the process water and the content of Ca ions. For example, the concentration of acetic acid in the scale inhibitor may be 5 to 30%. When the concentration of acetic acid is less than the above-mentioned range, the amount of Ca ions that can be bound is reduced, and when the concentration of acetic acid exceeds the above-mentioned range, the pH of the process water increases and the aggregation efficiency may decrease.

The scale inhibitor may further include a corrosion inhibitor, a surfactant, and the like. As the corrosion inhibitor, a phosphate or silicate-based corrosion inhibitor may be used, and the surfactant may be a nonionic or anionic surfactant, but is not limited thereto.

The dosage of the scale inhibitor may be adjusted according to the pH of the process water and the content of Ca ions. For example, the scale inhibitor may be added at a concentration of 35 to 220 ppm in the process water.

In one example, the process water treatment method of the present invention comprises the steps of: adding a composite coagulant comprising polyaluminum chloride and a polymer flocculant to the process water; settling and settling steps; separating the precipitate; adding a scale inhibitor containing acetic acid; and recycling the process water.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are provided to help the understanding of the present invention, and the scope of the present invention is not limited to the examples in any sense.

[Production Example 1-5]

A composite coagulant of each Preparation Example was prepared with the composition shown in Table 1 below.

Polyaluminum chloride: High base polyaluminum chloride (DK-HIMAX1, Daekyung Polychem Co., Ltd.)

Polymer Flocculant: Cationic Polymer Flocculant (SUPERFLOC C-8398, Ecotech Korea)

[Experimental Example 1]

After each 300 ppm of the coagulant according to Table 2 was added to the process water, changes in turbidity were observed. The experiment was performed a total of 4 times, and the results are shown in Table 2 below. As shown in Table 2 below, when the composite coagulant of the present invention is used, it can be confirmed that the turbidity reduction effect of the process water is excellent when compared with Comparative Example 1 in which the polymer flocculant is used alone.

Comparative Example 1: Cationic polymer (SNF Korea)

Example 1: Composite coagulant of Preparation Example 4

[Experimental Example 2]

After each 100 ppm of the composite coagulant of each preparation was injected into process water (turbidity 306 NTU), changes in turbidity were observed, and the results are shown in Table 3 below. As shown in Table 3 below, all of Examples 2-6 using the composite coagulant of the present invention exhibited an excellent turbidity reduction effect. In particular, as the blending ratio of the polymer coagulant increases, it can be seen that the effect of reducing the size and turbidity of the floc is further increased.

Example 2: Composite coagulant of Preparation Example 1

Example 3: Composite coagulant of Preparation Example 2

Example 4: Composite coagulant of Preparation Example 3

Example 5: Composite coagulant of Preparation Example 4

Example 6: Composite coagulant of Preparation Example 5

d1: 0-1 mm, d2: 1-2 mm, d3: 2-3 mm, d4: 3-4 mm, d5: 4-5 mm

[Experimental Example 3]

_{CaCO 3} 500 ppm (Ca concentration: 200 ppm) was added to two 1,000 mL beakers, respectively, and pure water was added, and then 600 ppm of acetic acid solution was added to the other beaker while leaving one beaker as it is. After acetic acid was added, the mixture was stirred at 40° C. at 250 rpm for 30 minutes, left still for 10 minutes, and the Ca ion concentration according to the elapsed time was measured, and the results are shown in Table 4 below. As shown in Table 4 below, when pure water was administered, the concentration of Ca ions in the solution did not increase even after 150 minutes, whereas when acetic acid solution was added, the concentration of Ca ions was similar to the concentration (200 ppm). It was. From the above results, it can be confirmed that the acetic acid solution increases the solubility of calcium ions.

[Experimental Example 4]

_{CaCO 3} 2,500 ppm (Ca concentration: 1,000 ppm) was added to two 1,000 mL beakers, respectively, and pure water was added. Then, one beaker was left and 3,000 ppm of acetic acid solution was added to the other beaker. After acetic acid was added, the mixture was stirred at 40° C. at 250 rpm for 30 minutes, left still for 10 minutes, and the Ca ion concentration according to the elapsed time was measured, and the results are shown in Table 5 below. As shown in Table 5 below, when pure water was administered, the concentration of Ca ions in the solution did not increase even after 150 minutes, whereas when acetic acid solution was added, the concentration of Ca ions was similar to the concentration (1,000 ppm). It was. From the above results, it can be confirmed that the acetic acid solution increases the solubility of calcium ions. In particular, it can be confirmed that the effect of the addition of acetic acid is effectively exhibited even when the Ca ion concentration is very high.

[Experimental Example 5]

The process water of the coal gasification power plant was collected at different sampling locations, and 75 ppm of an acetic acid solution was added to each, and then the Ca ion concentration in the solution before and after the input was measured. The average value of the Ca ion analysis concentration of the process water collected weekly for one month before acetic acid input was expressed as the concentration before acetic acid input, and the average value of the Ca ion analysis concentration measured weekly for 2 months after acetic acid input was expressed as the concentration after acetic acid input. indicated. As shown in Table 6 below, it can be seen that the Ca ion concentration in the process water was significantly increased when the acetic acid solution was added. From the above results, it can be confirmed that as the acetic acid solution is administered, the hardness component (Ca ²⁺ ) is solubilized to suppress scaling.

Claims (5)

adding a composite coagulant containing polyaluminum chloride and a polymer coagulant to the process water; and
Process water treatment method comprising the step of adding a scale inhibitor containing acetic acid after the step. The process water treatment method according to claim 1, wherein the polymer flocculant is a cationic polymer, an anionic polymer, or a mixture thereof. The process water treatment method according to claim 1, wherein the mixing ratio of the polyaluminum chloride and the polymer coagulant is 7: 3 to 2.5: 7.5 by weight. delete delete