JPH0377697A - Sequestering agent for water system of boiler - Google Patents

Abstract

PURPOSE:To prevent the formation of scale in the water system of a boiler by preparing a sequestering agent contg. a terpolymer of (meth)acrylic acid with (meth)acrylamide and itaconic acid or a specified itaconate as an effective component. CONSTITUTION:Prescribed amts. of (meth)acrylic acid, (meth)acrylamide and itaconic acid or an itaconate represented by formula I (where each of R1 and R2 is H or 1-8C alkyl) are dissolved in a solvent to about 10-60mol% total concn. to prepare a comonomer soln. A polymn. initiator is added to the soln. and mixed by stirring at about 40-120 deg.C for about 2-8hr in a flow of an inert gas to synthesize a terpolymer. A sequestering agent for the water system of a boiler is prepd. by blending the terpolymer as an effective component. The pref. wt. average mol.wt. of the terpolymer is about 1,000-100,000.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ion sequestering agent for boiler water systems for preventing the formation of scale in boiler water systems and for removing scale that has once formed.

[Prior Art] In a boiler water system, dissolved ions contained in the feed water are concentrated and further exposed to high temperatures of 150° C. or higher, so relatively poorly soluble compounds become supersaturated and precipitate as scale on heat transfer surfaces. When scale is deposited on the heat transfer surface, the thermal conductivity decreases, which not only increases the amount of fuel used and reduces the amount of steam generated, but also increases the temperature of the heat transfer surface due to scale accumulation, which reduces the strength of the metal material. The boiler may explode due to a drop in the temperature. In recent years, as the performance of boilers has improved, the amount of evaporation per unit heat transfer surface has tended to increase, and the tendency for scale formation has increased.

Conventionally, phosphates and alkalis were used to insolubilize calcium and magnesium as suspended solids in the form of calcium phosphate and magnesium hydroxide, respectively, to prevent scaling problems caused by precipitation of poorly soluble compounds on heat transfer surfaces. Natural polymers such as tannin, lignin, and starch are used to prevent the formation of suspended solids.
A method has been adopted in which dispersants such as anionic synthetic polymers such as poly(meth)acrylic acid and styrene sulfonic acid-maleic acid copolymers are used in combination. This type of treatment works by generating solids inside the can to prevent scale, so the scale prevention effect is insufficient, and metals derived from corrosion products in the condensate system and water supply system are No effect was shown on the deposition run-up of components.

So-called threshold treatments, in which organic phosphonic acids and anionic synthetic polymers are treated in amounts far lower than needed to sequester calcium ions in the water, have not been successful in high-temperature water systems such as boilers. On the other hand, ED
The method using a chelating agent such as TA or NTA has an excellent scale prevention effect because the chelating agent forms a stable chelate compound with metal ions such as calcium, magnesium, iron, etc. in water and solubilizes it. Adding a chelating agent in excess of the amount necessary to chelate metal ions in water has the disadvantage of accelerating corrosion of the boiler steel surface.

To overcome the corrosion problem caused by chelating agents, attempts have been made to use anionic polymers containing carboxylate functional groups as sequestering agents for metal ions in water, instead of existing chelating agents. JP-A-56-2897 discloses a scale control agent containing an itaconic acid polymer. Further, JP-A-56-20169 discloses a scale control agent containing an itaconic acid copolymer consisting of 75 mol% itaconic acid and 25 mol% or less of other unsaturated monomers. Such itaconic acid-based polymers had an excellent scale control effect on calcium-based scale, but were poor in their control effect on magnesium-based scale. JP-A-58-84099 discloses a method of using polyacrylic acid or an acrylic acid-acrylamide copolymer as an ion sequestering agent for boilers. Not only do these polymers have an insufficient sequestering effect, but if the amount added is insufficient, the polymer itself reacts with calcium to form a poorly soluble calcium salt of the polymer.

[Problem M to be solved by the invention] Is the problem of the present invention the above-mentioned problems I? An object of the present inventor is to provide an improved ion sequestering agent for boiler water systems that eliminates FYg and can effectively control both calcium scale and magnesium scale as well as metals other than alkali metals at the same time. utilized synthetic techniques to synthesize a large number of copolymers with different combinations of monoethylenically unsaturated monomers and different copolymerization composition ratios, and investigated the relationship between their molecular compositions and school prevention effects. The present invention was arrived at as a result of systematic classification and extensive experimental research.

[Means for Solving the Problems] The ion sequestering agent for boiler water systems of the present invention comprises (meth)acrylic acid, (meth)acrylamide and the following formula: CH, -C
-0-R.

C1,=C C-0-R.

1 (Here, R3 and R2 are each independently hydrogen or carbon number l
-8 alkyl group. ) is composed of a terpolymer consisting of itaconic acids shown as the active ingredient. A more preferable configuration is 20 to 80 of (meth)acrylic acid.
mol%, 5 to 65 mol% of (meth)acrylamide, and the following formula% (where R, , R, are each independently hydrogen or carbon number 1
-8 alkyl group. ) itaconic acid 5
~40 mol%, or 5 to 30 mol% of itaconic acid ester, and a terpolymer selected from the composition ratio within the area surrounded by ABCDEF or A'BCDEF' in the triangular diagram of FIG. constitutes as an active ingredient.

Here, (meth)acrylic acid may be acrylic acid, methacrylic acid, or both, but acrylic acid is preferable. Further, (meth)acrylamide may be either acrylamide or methacrylamide or both, but acrylamide is preferable. Itaconic acids include itaconic acid, itaconic acid mono- or dimethyl ester, and itaconic acid monos include diethyl ester, itaconic acid mono- or dipropyl ester, itaconic acid mono- or dibutyl ester, itaconic acid mono- or di(2-ethylhexyl) ester, etc. However, these may be used alone or in combination of two or more, and may be a copolymer containing another monoethylenically unsaturated monomer as the fourth component, but the comonomer composition ratio The ion sequestering agent of the present invention can be produced by a known radical polymerization method.For example, a predetermined amount of monomers is added to a total monomer concentration of 10 to 60 mol%. A polymerization initiator and, if necessary, a chain transfer agent are added to a comonomer solution dissolved in a suitable solvent, and the mixture is stirred for about 2 to 8 hours while maintaining the temperature at 40 to 120°C under a stream of inert gas. It is obtained by Solvents are usually water, lower alcohols such as isopropyl alcohol, ethyl alcohol, methyl alcohol, and mixed solvents of these. Polymerization initiators include persulfates (including sodium salts, potassium salts, and ammonium salts), peroxides. Hydrogen, peroxides such as t-butyl hydroperoxide and benzoyl peroxide, and various azo compounds (e.g. 2.2'
-Azobis(2-amidinopropane) hydrochloride) etc. can be used, and a redox catalyst system may also be used.The optimal amount of polymerization initiator varies depending on the type of initiator, but is usually based on the total amount of monomers. 0.1 to 10
Use g.

The weight average molecular weight of the copolymer is 1,000 to 100.00
It is preferably in the range of 0, more preferably z, o
o.

~50,000. Here, the weight average molecular weight is determined by gel permeation chromatography <apc>
It is measured using polyethylene glycol of known molecular weight as a standard.

The molecular weight of the copolymer can be controlled by adjusting the amount of a chain transfer agent used. As chain transfer agents, known compounds such as thioglycolic acid and its esters, β-mercaptopropionic acid and its esters, mercapto compounds such as alkylmercaptans, (
Allyl compounds such as meth)allylsulfonic acid and (meth)allyl alcohol, hypophosphites, bisulfites, and the like are used.

Another method for controlling the molecular weight of the copolymer is to continuously feed a comonomer solution and a polymerization initiator solution separately at a constant flow rate into a reaction vessel whose temperature is maintained constant. In this method, the molecular weight can be adjusted by changing conditions such as the rate of initiator and monomer addition, reaction temperature, initiator concentration, and comonomer solution concentration.

Produced by the known radical polymerization method as described above (
The terpolymer consisting of meth)acrylic acid, (meth)acrylamide and itaconic acids is a linear random polymer.

A preferable amount of the ion sequestering agent of the present invention is to add the terpolymer as an active ingredient to 1 part of the metal component contained in the water to be treated.
The range is from 2 to 301)911 ppm, and more preferably from 4 to 20ppe+.

Here, metal components refer to alkali metals such as calcium, magnesium, iron, zinc, copper, manganese, aluminum, etc. that exist in the form of ionic or finely suspended particles (oxides, hydroxides, various salts, etc.) in boiler water. Indicates the metal components to be excluded.

The ion sequestering agent of the present invention not only has the effect of sequestering metal ions present in water, but also has the effect of removing scale that has already adhered inside the boiler without corroding the steel surface of the boiler. The ion sequestering agent of the present invention does not promote corrosion of boiler iron surfaces even when injected in excess.The ion sequestering agent of the present invention is a polymer electrolyte and exhibits not only an ion sequestering effect but also a good dispersion effect, so the ion sequestering effect is sufficient. It is suitable for maintaining the generated precipitated particles in a dispersed state even when the particles are not dispersed.

The ion sequestering agent of the present invention is usually used in a neutralized form with an alkali metal hydroxide such as caustic soda or caustic potassium, or an alkali compound such as ammonia or various amines. The amount of alkali used for neutralization is the pH of boiler feed water and canned water.
is preferably adjusted to be within the range of 7 to 12, more preferably 9 to 12.

The ion sequestering agent of the present invention can be used in combination with known boiler treatment agents such as oxygen scavengers, condensate-based neutralizing agents, condensate-based film-forming corrosion inhibitors, dispersants, and antifoaming agents. Furthermore, it has been found that when the ion sequestering agent of the present invention and an oxygen scavenger are used in combination, the corrosion of the boiler steel surface is significantly reduced compared to when the oxygen scavenger is used alone. Examples of such oxygen scavengers include hydrazine, sulfites, carbohydrazides, polyacrylic acid hydrazide, erythorbic acid, L-ascorbic acid, diethylhydroxylamine, and the like.

[Example] Example 1 332.8 g of water was charged into a glass reaction vessel equipped with a thermometer, a stirrer, a nitrogen gas inlet tube, and a reflux condenser, and 22.5 L of acrylic acid, 45 g of acrylamide, and 22.5 g of dimethyl itaconate were added. ．． The comonomer solution prepared by adding was heated to 55° C. under a nitrogen gas stream.

β-mercaptopropionic acid 2.25. After quickly adding a solution of sodium persulfate 5.02 dissolved in 15 g of water, the temperature was maintained at 55°C while removing the reaction heat.
50% caustic soda ss, ay was added to the 0 reactant, which was then heated at 80°C for 2 hours to complete the reaction, and then water was added to form an aqueous solution 562 with a polymer active content concentration of 16%.
I got y. The pH of this solution was 13. The Brookfield viscosity at 25°C was 15 cp.

Example 2 160 g of water was placed in the same glass reaction vessel as in Example 1, and 12.5 g of acrylic fi, 259 acrylamide, and itaconic acid tz, sg were added to a comonomer solution prepared, and 1.0 g of β-mercaptopropionic acid and persulfuric acid were added. A solution of 3 g of sodium dissolved in 20 g of water was added and heated to 60°C under a stream of nitrogen gas. At the initial stage of the reaction, 60°C was maintained by heating for 2 hours while removing the reaction heat, and then heated at 80°C for 1 hour. The reaction was completed by heating for 0
50% caustic soda to the reactant 36.4. was added, and then water was added to form an aqueous solution 312.5. with a polymer active ingredient concentration of 16%.
I got it. The pH of this solution was 12, and the Brookfield viscosity at 9.25°C was 32 cp.

Examples 3 to 8 Using the same reaction vessel and method as in Example 1, the comonomer composition ratio of acrylic acid, acrylamide, and dimethyl itaconate, and the type of chain transfer agent (β-mercaptopropionic acid, sodium hypophosphite, We synthesized copolymers with varying concentrations of either of the following) and chain transfer agents.

Examples 9 to 14 Using the same reaction vessel and method as in Example 1, copolymers were synthesized by changing the comonomer composition ratios of acrylic acid, acrylamide, and itaconic acid and the concentration of the chain transfer agent.

The compositions and physical properties of the copolymers synthesized in Examples 1 to 14 and the copolymers of Comparative Examples 1 to 11 synthesized in the same manner with the comonomer composition ratios shown in the table below are summarized in Table 1 below. .

(2) The viscosity measurement method is as follows.

The viscometer used for the measurement was a BL type viscometer manufactured by Tokyo Keiki Co., Ltd., and the measurement was carried out under the conditions of No. 120-Y and 60 rpm.

■, The chelation value is measured by the following method.

l Experimental equipment 1) Orion IJI-CH Ion Analyzer E
^940 type 2) Horn Calcium measurement electrode 9
3-20 type 3) 77 Pole for divalent cation measurement 93-32 type 4) 17 Ag/
^9 C1 reference electrode 90-02 type 5) Toa Denpa p
H meter 88-18ET type 6〉 Horn pH
Stat ll5M-10^ type A, Calcilla 14 chelation value measurement method a, reagent 1> Calcium standard solution - +CaCj! 2, z112
A 45.7971 solution of O was standardized by N/100 EDT^, and the Ca concentration of this solution was determined. This solution is also diluted with pure water so that the Ca concentration is 10,000 ppet (as CaCO3). Also, add KCl to 62/l during dilution.

2) Standard solution for creating a calibration curve → Add calcium standard solution to C4 (
6g #) solution to create a solution containing 10,100.1000 pp theory as calcium hardness.

3) Polymer solution → Precisely weigh synthetic product 52 and add KCl (6
50 companies with g#resolution.

b. Add N/1 O-KOH to measure and record the ion concentration after adjusting pl() to 10. Plot the relationship between the amount of polymer added and the ion concentration on a graph, and determine the chelation 1( The amount of calcium complexed by 1 g of polymer (in terms of CaCO3) was determined.

Δ[Ca”]]/Δ-1: Initial gradient: Sample collection 1?150wfX0.18 B, Magnesium chelation value measurement method a, Reagent l) Magnesium standard solution → Dissolve HgC116HzO in pure water and make 14gH as 10000 ρp Prepare it so that it becomes a kabura.

2> Standard solution for creating a calibration curve → Dilute the magnesium standard solution with pure water to create a 10° 100 pp solution of MgH.

3) Polymer solution → Accurately weigh 5 g of the synthetic product and add 5 g of pure water.
Increase to 0-1.

b. Measurement After adding N/1O-NaOfl and adjusting 98 to 9, measure and record the ion concentration. The magnesium chelation value is determined from the initial slope in the same way as the calcium chelation value.

Example 15 Test agents having the concentrations shown in Table 2 were added to 100 mf of deionized water, and the pH was adjusted to 11.8 with 0 and 0.5N sodium hydroxide in which the reagents shown below were dissolved.

HgC1z, 6tL0 30.6mg#! NaH
COz 840+*y#Na25iO,
,511□0 1060B/1Na2SOa
444tag/lFeCl3
29Arag/l This solution has a calcium hardness of 22p
pm (8.8pp- as calcium), magnesium hardness 14ppm (3.4pp- as magnesium)
Contains 9.5 ppm total iron, 300 ppm silica, 300 ppm sulfate ion, and 500 ppm alkalinity.

This solution was set in an autoclave and allowed to stand in a constant temperature oil bath maintained at a temperature of 180°C. After 18 hours, the autoclave was cooled and the contents were taken out, and the concentration of calcium and magnesium in the p liquid that was filtered through a 0.45μ membrane filter was measured by atomic absorption spectrometry, and the inhibition rate was calculated using the following formula.

Here, CA: Measured value of calcium or magnesium when the test agent is added. CB: Measured value of calcium or magnesium when the test agent is not added. Co: The initial concentration test results of calcium or magnesium are shown in Table 2.

Example 16 The experiment was conducted using the experimental boiler shown in Figure 1.

Boiler heat exchanger tube (9) has a diameter of 28 mm and a length of 345 m.
It has a cylindrical shape and is made of carbon steel (S25C).

An electric heater of 3.5 to 10 mm was inserted inside the heat exchanger tube to continuously heat the tube. Boiler pressure is 10kyf/ell
The amount of steam generated was approximately 3.71/h, and the temperature of the canned water was 180°C. Water having the quality shown in Table 3 was used as make-up water.

Table 3 Mixed water was automatically fed to the experimental boiler (8) by a feed pump (4) to maintain a constant liquid level.

Continuous blowdown was not carried out, but boiler can water was sampled at regular intervals to determine the concentration (ratio of chloride ion concentration of feed water to can water) and the suppression rate of calcium and magnesium using the same method as in Example 15. I asked for The test time was 8 hours. Table 4 shows the results of the scale weight attached to the heat transfer tube (9), and Table 5 shows the results of the concentration degree and inhibition rate of canned water.

Make-up water was provided in the water supply tank (3) using the treatment agent shown in Table 4 and the same experimental equipment as in Example 17 and Example 16 at a boiler pressure of 20 k.
gf/am” and a can water temperature of 210° C. The water quality shown in Table 6 was used as make-up water.

The make-up water in Table 6 is mixed with the treatment agent shown in Table 7 and 3.5 ppm of hydrazine as an oxygen scavenger in the water supply tank (3), and the concentration of one can of water supplied to the experimental boiler (8>) is 5. Continuous blowdown was performed to double the amount.

The test time was 10 hours. Table 7 shows the experimental results.

As is clear from Table 2, the terpolymer consisting of acrylic acid, acrylamide, and itaconic acid monomers exhibited a remarkable ion sequestering effect on both calcium and magnesium ions. - A binary copolymer lacking any one of the monomers constituting the crab copolymer was only effective against either calcium or magnesium ions.

From Tables 4, 5, and 7, it can be seen that the ion sequestering agent of the present invention exhibits a good scale prevention effect even when used in boiler water conditions where the concentration of hard substances in the water is extremely high.

In Tables 5 and 7, the calcium suppression rate of the ion sequestering agent of the present invention exceeds 100%, which indicates that the scale that had already adhered inside the boiler was removed. - On the other hand, the magnesium inhibition rate was around 50%, but since no scale was observed in the boiler heat exchanger tubes, it is thought that the dispersion effect was at work in addition to the ion sequestration effect.

Furthermore, from Table 7, when the copolymer of Example fiI42 and hydrazine were used in combination, a corrosion improving effect was observed compared to when treated with hydrazine alone.

[Effects of the Invention] As shown in the examples, the ion sequestering agent of the present invention has a superior scale prevention effect in high-temperature water systems compared to conventional known scale inhibitors, contributes to the safe operation of boilers, and improves transmission. Since it is possible to improve thermal efficiency and increase the concentration of boiler canned water, it is possible to significantly reduce fuel consumption. Furthermore, since it not only prevents scale but also removes existing scale, it is possible to reduce the cost and construction period required for chemical cleaning.

Furthermore, by using it in combination with a known oxygen scavenger, corrosion of the boiler iron surface can be improved.

[Brief explanation of drawings]

FIG. 1 shows a flowchart of an experimental boiler used in Examples and Comparative Examples of the present invention. FIG. 2 shows the copolymer composition ratio of the preferred terpolymer of the ion sequestering agent for boiler water systems of the present invention. (1>... Makeup water tank (2)... Makeup water pump (3>... Water tank (4)... Water supply pump (5)... Feed water heater (6>... Chemical solution Tank (7>...Chemical injection hole pump (8)...Experimental boiler (9)...Heat transfer tube (10)...
・Electric heater (11)...Liquid level gauge (12)
)...Automatic liquid level regulator (13)...Blow water cooler (14)...Mist separator (15)...Pressure gauge (16)...Automatic pressure regulator (17)...・Pressure control valve (18>...
・Condenser 2 (Figure Ida)

Claims (1)

[Claims] 1. (meth)acrylic acid, (meth)acrylamide, and the following formula, ▲ Numerical formula, chemical formula, table, etc. ▼ (Here, R_1 and R_2 each independently represent hydrogen or carbon number 1 to 8 An ion sequestering agent for boiler water systems, characterized in that it contains as an active ingredient a terpolymer of itaconic acids (which is an alkyl group of ). 2. 20-80 mol% of (meth)acrylic acid, (meth)
5 to 65 mol% of acrylamide, and itaconic acid represented by the following formula ▲ Numerical formula, chemical formula, table, etc. ▼ (Here, R_1 and R_2 are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms.) A of the triangular diagram in Figure 2.
An ion sequestering agent for boiler water systems, characterized in that it contains as an active ingredient a preferable terpolymer selected from the composition ratio within the area surrounded by BCDEF. 3. 20-80 mol% of (meth)acrylic acid, (meth)
5 to 65 mol% of acrylamide, and itaconic acid represented by the following formula ▲ Numerical formula, chemical formula, table, etc. ▼ (Here, R_1 and R_2 are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms.) It is characterized by containing as an active ingredient a preferable terpolymer consisting of 5 to 30 mol% of ester and selected from the composition ratio within the area surrounded by A'BCDEF' in the triangular diagram of FIG. An ion sequestering agent for boiler water systems. 4. The terpolymer, which is an active ingredient of the ion sequestering agent for boiler water systems according to any one of claims 1 to 3, is added to 1 p of metal components (excluding alkali metals) contained in the water to be treated.
A method for preventing scale in a boiler, characterized in that the amount is used in a range of 2 to 30 ppm based on pm.