JPS6347790B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dust collection method. More specifically, the dust collection water used in dust collectors for exhaust gas discharged from blast furnaces, converters, sintering furnaces, etc., and environmental dust collectors used for environmental purification in workplaces where dust and various reactive gases are present. This paper relates to a dust collection method aimed at improving performance. It is economically undesirable to discharge the collected water used in exhaust gas dust collectors after one use, so it is normally used for circulation. However, if it is used for circulation as it is, scale will adhere to it and cause damage to pumps, piping, dust collectors, etc. There will be financial damage caused by the blockage. Conventionally, in order to eliminate such damage, a thickener was installed in the circulation path of the collected dust water to coagulate and precipitate suspended substances in the collected dust water, and polyphosphates and relatively low molecular weight substances were added to the collected dust water. Attempts have been made to prevent scale adhesion by adding polyacrylic acid or its salts. However, although polyphosphates are effective in preventing and dispersing scale precipitation, they are hydrolyzed into orthophosphates during use and rapidly lose their effectiveness. Moreover, the generated orthophosphate reacts with metal ions such as calcium ions, magnesium ions, and zinc ions dissolved in the dust collection water to form water-insoluble phosphates (calcium phosphate, magnesium phosphate, zinc phosphate, etc.). This forms and precipitates as crystal particles, which in turn promotes the formation of sludge and scale. In addition, polyphosphates can cause red tides in the ocean if dust water containing them is released. On the other hand, when polyacrylic acid or its salts are used, various advantages have been recognized, including that they do not contain phosphorus and are more effective than polyphosphates in preventing and dispersing scale precipitation in cooling water systems. ing. However, although a considerable amount of metal compounds have been removed from the exhaust gas dust collection water through coagulation and sedimentation treatment,
When the collected dust water is treated with an alkali, the hydroxides of iron and zinc produced by the alkaline treatment are light and therefore do not settle sufficiently in the thickener and remain in the collected water. In addition, the compounds formed by the reaction between carbon dioxide contained in the exhaust gas and metal ions in the dust collection water when they come into contact with the exhaust gas have considerable solubility in water, so they may not be completely dissolved by coagulation and precipitation. cannot be captured. If the dust collection water contains metal compounds such as hydroxides and carbonates, the polyphosphates, polyacrylic acids, or their salts that have been used so far do not always have a sufficient scale suppression effect. do not have. Therefore, there is currently a demand for the development of effective scale inhibitors in this field. In view of the current situation, the present inventors have conducted intensive research to develop a scale inhibitor that is effective in preventing and dispersing scale in collected dust water containing metal compounds. The inventors have discovered that this has particularly excellent effects, and have completed the present invention. Therefore, it is an object of the present invention to provide a dust collection method that causes less scale adhesion even when the collected dust water contains metal compounds. That is, the dust collection method of the present invention uses a general formula for circulating water used in a dust collection device. (However, in the formula, m and n are 0 or positive integers, and m+n
= 1 to 100, and (-C ₂ H ₄ O)- unit and (-C ₃ H ₆ O)-
Units may be combined in any order. )
Polyalkylene glycol monoallyl ether () represented by, and general formula (However, in the formula, R ₁ represents hydrogen or a methyl group,
X represents hydrogen, a monovalent metal, a divalent metal, an ammonium group or an organic amine group. ) (meta)
Copolymerizing the acrylic acid monomer () using a polymerization initiator at a ratio such that () is 0.1% by weight or more and less than 5.0% by weight with respect to the total of () and (),
It is characterized in that, if necessary, a water-soluble polymer obtained by further neutralizing with an alkaline substance is added and recycled. The polyalkylene glycol monoallyl ether () used in the present invention is represented by the above general formula, and the number m+n of added moles of alkylene oxide is 1 to 100. When the number of added moles m+n is 0, the effect of preventing scale precipitation and dispersing scale of the obtained copolymer is not fully satisfied. On the other hand, if it exceeds 100, the copolymerization reactivity of such polyalkylene glycol monoallyl ether is low, and a water-soluble polymer that is effective in preventing scale precipitation and dispersing scale cannot be obtained. Polyalkylene glycol monoallyl ether () is produced by converting ethylene oxide and/or allyl alcohol into allyl alcohol using an alkali such as KOH or NaOH as a catalyst.
Alternatively, it can be synthesized by a known method of directly adding propylene oxide. The (meth)acrylic acid monomer () is represented by the general formula above, and specifically includes acrylic acid, methacrylic acid, and their monovalent metal salts,
Mention may be made of divalent metal salts, ammonium salts and organic amine salts. and one or two of these
More than one species can be used. The water-soluble polymer used in the dust collection method of the present invention is polyalkylene glycol monoallyl ether () and (meth)acrylic acid monomer ().
are copolymerized using a polymerization initiator in a specific ratio. Copolymerization can be carried out by methods such as polymerization in a solvent or bulk polymerization. Polymerization in a solvent can be carried out either batchwise or continuously, and the solvents used in this case include water,
Examples include lower alcohols, mixed solvents of water and lower alcohols, aromatic hydrocarbons, aliphatic hydrocarbons, ketone compounds, and ethyl acetate. As the polymerization catalyst, various water-soluble polymerization initiators, peroxides, hydroperoxides, combinations of these and polymerization promoters, or azo compounds are used depending on the solvent used. The polymerization temperature is appropriately determined depending on the solvent and polymerization initiator used, but it is usually carried out within the range of 0 to 120°C. When water is used as a solvent, sodium hydrogen sulfite-oxygen may be used as a polymerization catalyst. In this case, the polymerization is carried out by blowing oxygen gas or a mixed gas of oxygen and an inert gas into the solvent while adding sodium hydrogen sulfite to the solvent containing the raw material monomer.
This can be carried out by proceeding the polymerization reaction within a temperature range of ~80°C. Bulk polymerization uses peroxide as a polymerization initiator,
It is carried out using hydroperoxide or an azo compound at a temperature of 50 to 150°C. When producing a water-soluble polymer in this way, the charging ratio of polyalkylene glycol monoallyl ether () and (meth)acrylic acid monomer (), the amount of polymerization initiator used, the polymerization temperature,
In the case of polymerization in a solvent, the molecular weight of the resulting water-soluble polymer can be adjusted as appropriate by adjusting the type and amount of the solvent. The molecular weight of the water-soluble polymer used in the dust collection method of the present invention is not particularly limited, and a wide range of molecular weights can be used, but those in the range of 500 to 50,000 are particularly effective. In addition, the water-soluble polymer thus obtained can be used as it is in the dust collection method of the present invention, but
If necessary, it may be further neutralized with an alkaline substance. Such alkaline substances include hydroxides, chlorides and carbonates of monovalent and divalent metals;
Preferred examples include ammonia and organic amines. Although the water-soluble polymer used in the dust collection method of the present invention is sufficiently effective when used alone, it can also be used in combination with other known scale inhibitors, such as polyphosphates, if necessary. Furthermore, it can also be used in combination with ordinary water treatment agents such as anti-corrosion agents and slime control agents. In order to use the water-soluble polymer in the dust collection method of the present invention, it may be used continuously or by adding it to the dust collection water at an appropriate time, and there are no particular restrictions on the method or timing of addition. The dust collector, piping equipment, dust collecting water supply circulation method, etc. can be performed using known devices and methods. As an example of the dust collection method of the present invention, the following method can be mentioned. However, the scope of the present invention is not limited by such examples. For example, when treating blast furnace exhaust gas, the blast furnace exhaust gas discharged from the top of the blast furnace is guided to a dust collector such as a ventilate scrubber, where the exhaust gas and dust collection water are brought into contact and the dust in the exhaust gas is captured by the dust collection water. The collected dust water is led to a thickener, where the suspended matter is separated by precipitation, and a water-soluble polymer is added to the separated treated water,
The water is recycled and used again as dust collection water. The water-soluble polymer used in the dust collection method of the present invention is preferably added to a predetermined concentration from any position in the pipe that circulates the treated water precipitated and separated in the thickener to the dust collector. The amount to be added cannot be absolutely determined depending on the use, purpose, etc., but it is usually in the range of 0.1 to 100 ppm based on the collected dust water. According to the dust collection method of the present invention, even when the dust collection water contains metal compounds such as calcium, magnesium, iron, zinc, etc., or when the pH value of the dust collection water is high, the water-soluble polymer allows the pump to pump. Precipitation of scale and dispersion of scale in pipes, dust collectors, etc. can be effectively carried out, and therefore long-term operation is possible by circulating the collected dust water. In addition, dissolved metal compounds may condense and scale may precipitate due to long-term operation, but even in this case, the precipitated scale is soft due to the action of water-soluble polymers, so it is not easily resistant to water flow. It can be removed by twisting. In addition, the polyalkylene glycol moiety in the molecule of a water-soluble polymer is bonded to the main chain of the polymer through an ether bond, so it can be used for long periods of time at high temperatures, in boiling water, or in high pH ranges. Hydrolysis does not occur at all, and excellent performance can be maintained over a long period of time. Furthermore, since the water-soluble polymer is a synthetic product, it has the advantage that it can be stably supplied with a constant quality compared to natural products. Examples will be described in more detail below, but it goes without saying that the present invention is not limited only to these examples. In addition, unless otherwise specified in the examples, parts represent parts by weight, and % represents weight %. All viscosities in the examples were measured using a Bismethron viscometer manufactured by Seiki Kogyo Kenkyusho at 25°C.
Measurement was performed at 60 rpm. Furthermore, the molecular weight was measured using gel permation chromatography (Model 244, manufactured by Waters). Reference Example 1 Polyethylene glycol monoallyl ether (containing an average of 5 ethylene oxide units per molecule) was placed in a glass reaction vessel equipped with a thermometer, stirrer, dropping funnel, gas introduction tube, and reflux condenser.
7.5 parts and 389.9 parts of water were charged, and the inside of the reaction vessel was purged with nitrogen while stirring, and heated to 95°C in a nitrogen atmosphere. Then, 38% sodium acrylate aqueous solution
506.6 parts and 80 parts of 5% ammonium persulfate aqueous solution were each added over 120 minutes. 16 more after addition
of 5% ammonium persulfate aqueous solution was added over 20 minutes. 95 for 120 minutes after the addition of monomer aqueous solution is completed.
The polymerization reaction was completed while maintaining the temperature at °C to obtain a water-soluble polymer (1). A 40% aqueous solution of this water-soluble polymer (1) had a pH of 7.3 and a viscosity of 267 cps. Moreover, the molecular weight was 4100. Reference Example 2 In the same reaction vessel as Reference Example 1, add 9.8 parts of polyethylene glycol monoallyl ether (containing an average of 10 ethylene oxide units per molecule) and water.
After charging 441.7 parts, the inside of the reaction vessel was purged with nitrogen while stirring, and heated to the boiling point in a nitrogen atmosphere. Then, 500.5 parts of a 38% sodium acrylate aqueous solution and 40 parts of a 5% ammonium persulfate aqueous solution were added.
The mixture was added over a period of 120 minutes, and after the addition was completed, 8 parts of a 5% aqueous ammonium persulfate solution was added over a period of 20 minutes. After the addition of the monomers was completed, the temperature was maintained at the boiling point for 120 minutes to complete the polymerization reaction, yielding a water-soluble polymer (2). A 40% aqueous solution of this water-soluble polymer (2) has a pH of 7.5 and a viscosity of
It was 348cps. Moreover, the molecular weight was 4700. Reference Example 3 In the same reaction vessel as Reference Example 1, prepare an azeotropic composition of 1 part of polypropylene glycol monoallyl ether (containing on average 2 propylene oxide units per molecule) and isopropyl alcohol (hereinafter abbreviated as IPA) with water. (IPA/water = 87.4/12.6 (weight ratio))
495.5 parts were charged, and the inside of the reaction vessel was purged with nitrogen while stirring, and heated to the boiling point. then acrylic acid 199
1 part, 6 parts of benzoyl peroxide and 298.5 parts of IPA-water azeotrope was added over 120 minutes. After the addition was complete, the temperature was maintained at the boiling point for 120 minutes to complete the polymerization reaction. Then 40% caustic soda aqueous solution
Neutralization was performed using 276.2 parts, and IPA was distilled off to obtain a water-soluble polymer (3). A 45% aqueous solution of this water-soluble polymer (3) had a pH of 8.5 and a viscosity of 830 cps. Moreover, the molecular weight was 2800. Reference Example 4 In the same reaction vessel as in Reference Example 1, 285 parts of isopropyl alcohol (hereinafter abbreviated as IPA) was charged, the inside of the reaction vessel was purged with nitrogen while stirring, and the mixture was heated to the boiling point in a nitrogen atmosphere. Thereafter, a mixture of 4.5 parts of polyalkylene glycol monoallyl ether (containing an average of 18 ethylene oxide units and 2 propylene oxide units per molecule), 295.5 parts of acrylic acid, 3 parts of benzoyl peroxide, and 300 parts of IPA was added over 120 minutes. After the addition was completed, 0.6 parts of benzoyl peroxide dispersed in 11.4 parts of IPA was added in two portions every 30 minutes. After the addition of the monomer mixture was completed, the temperature was maintained at the boiling point for 120 minutes to complete the polymerization reaction. Thereafter, the mixture was neutralized with 410.1 parts of a 40% caustic soda aqueous solution, and then IPA was distilled off to obtain a water-soluble polymer (4). This water-soluble polymer (4)
The pH of a 45% aqueous solution of was 8.5 and the viscosity was 1920 cps. Moreover, the molecular weight was 3000. Reference example 5 438.8 parts of water was charged in the same reaction vessel as in reference example 1,
While stirring, the inside of the reaction vessel was purged with nitrogen and heated to 95°C. Thereafter, 63 parts of a 10% aqueous solution of polyethylene glycol monoallyl ether (containing an average of 30 ethylene oxide units per molecule), 378.2 parts of a 38% aqueous solution of partially neutralized sodium acrylate (80 mol% neutralization) and 5% filtrate were added. Ammonium sulfate aqueous solution
120 parts were added in 120 minutes each. After addition
The temperature was held at 95° C. for 120 minutes to complete the polymerization reaction. Thereafter, it was completely neutralized with a caustic soda aqueous solution to obtain a water-soluble polymer (5). . 40% of this polymer (5)
The pH of the aqueous solution was 9.0 and the viscosity was 403 cps. or,
The molecular weight was 4800. Example 1 In a beaker, 750 ml of deionized water, 50 ml of a 0.58% aqueous solution of calcium chloride, 50 ml of an aqueous solution containing 200 ppm of the water-soluble polymer (1) obtained in Reference Example 1, and 50 ml of a 0.44% aqueous solution of sodium hydrogen carbonate were stirred. and then PH8.5 with 0.01N aqueous sodium hydroxide solution.
After adjusting to 1000 g, add deionized water
A 5 times supersaturated aqueous solution of calcium carbonate at 25°C was prepared. This 5-times supersaturated aqueous solution was divided into four equal parts, each placed in a glass bottle, sealed tightly and allowed to stand at 60°C. After 5 hours, 10 hours, 20 hours, and 40 hours, the test solution was taken out and cooled to 25°C. The test solution was passed through Toyo Paper quantitative paper No. 5C and tested by atomic absorption spectrometry (422.7 nm). The concentration of calcium ions remaining therein was measured, and the amount of precipitated calcium carbonate was calculated. The results are shown in Table 2. Examples 2 to 5 In Example 1, the water soluble polymers (2) to (5) obtained in Reference Examples 2 to 5 were used instead of the water soluble polymer (1), and the other conditions were the same as in Example 1. It was tested as follows. The results are shown in Table 1. Comparative Example 1 The amount of precipitated calcium carbonate was investigated in the same manner as in Example 1, except that commercially available sodium polyacrylate (molecular weight 5000) was used instead of the water-soluble polymer (1). The results are shown in Table 1. Comparative Example 2 In Example 1, the amount of precipitated calcium carbonate was investigated in the case where the water-soluble polymer (1) was not used. The results are shown in Table 1.

[Table] As is clear from the results shown in Table 1, the water-soluble polymer used in the dust collection method of the present invention has an excellent effect on preventing scale precipitation of calcium carbonate. Example 6 180 ml of deionized water was placed in a glass bottle, and while stirring, 25 ppm of the water-soluble polymer (1) obtained in Reference Example 1 was added to the deionized water, and then 2.8 ml of a 5% aqueous sodium hydrogen carbonate solution was added. 2.16 ml of a 1% aqueous zinc chloride solution was added, followed by deionized water to bring the total amount to 200 g. After standing still for 24 hours, this test solution was passed through Toyo Paper quantitative paper No. 5C, and the concentration of zinc ions remaining in the test solution was measured by atomic absorption spectrometry (2138.6 nm), and the amount of precipitated zinc compounds was calculated. . The results are shown in Table 2. Examples 7 to 10 In Example 6, the same procedure as in Example 6 was carried out except that the water-soluble polymers (2) to (5) obtained in Reference Examples 2 to 5 were used instead of the water-soluble polymer (1), respectively. I did a test.
The results are shown in Table 2. Comparative Example 3 The amount of precipitated zinc compound was investigated in the same manner as in Example 6, except that commercially available sodium polyacrylate (molecular weight 5000) was used instead of the water-soluble polymer (1). The results are shown in Table 2. Comparative Example 4 In Example 6, the amount of precipitated zinc compound was investigated in the case where the water-soluble polymer (1) was not used.
The results are shown in Table 2.

[Table] As is clear from the results shown in Table 2, the water-soluble polymer used in the dust collection method of the present invention has an excellent effect on preventing scale precipitation of zinc compounds. Example 11 In the circulating water system for blast furnace exhaust gas dust collection water, a test short pipe (3/8 inch diameter, 150 mm length) was installed in the middle of the circulation of thickner treated water to the dust collector, and Reference Example 2
Add the water-soluble polymer (2) obtained in 0.5ppm to the circulating water.
The weight and adhesion rate of scale adhering to the short test tube were measured by continuous operation for 30 days while continuously adding the solution at the thickener outlet to achieve a concentration of . The test conditions were as follows. The results are shown in Table 3. Water temperature 35-40℃ Flow rate 1.5m/sec PH 7-8 (no particular adjustment) Comparative example 5 In Example 11, commercially available sodium polyacrylate (molecular weight 5000) is used instead of water-soluble polymer (2). The weight of the scale adhering to the short test tube and its adhesion rate were measured in the same manner as in Example 11. The results are shown in Table 3. Comparative Example 6 In Example 11, continuous operation was performed for 15 days in the case where water-soluble polymer (2) was not added, and the amount and rate of scale adhesion were measured. The results are shown in Table 3.

[Table] As is clear from the results shown in Table 3, the water-soluble polymer used in the dust collection method of the present invention has an excellent effect on preventing scale precipitation in collected dust water during continuous operation.

Claims (1)

[Claims] 1 General formula for circulating water used in a dust collector (However, in the formula, m and n are 0 or positive integers, and m+n
= 1 to 100, and (-C ₂ H ₄ O)- unit and (-C ₃ H ₆ O)-
Units may be combined in any order. )
Polyalkylene glycol monoallyl ether () represented by, and general formula (However, in the formula, R ₁ represents hydrogen or a methyl group,
X represents hydrogen, a monovalent metal, a divalent metal, an ammonium group or an organic amine group. ) (meta)
Acrylic acid monomer () is copolymerized using a polymerization initiator at a ratio such that () is 0.1% by weight or more and less than 5.0% by weight based on the total of () and (), and if necessary, an alkaline substance is further added. A dust collection method characterized by adding and circulating a water-soluble polymer obtained by neutralizing with water.