JPH0630789B2 - Scale prevention method for high temperature and high pressure water system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Object of the Invention [Field of Industrial Application] The present invention relates to a scale prevention method for a high-temperature high-pressure water system. More specifically, various industrial water systems using high-temperature and high-pressure water of 150 ° C or higher, such as geothermal hot water system of geothermal power plant, boiler water system, wood cooking process of paper and pulp industry, etc. The present invention relates to a scale prevention method useful for preventing system scale generation.

[Prior art]

In a geothermal power plant that uses geothermal hot water ejected along with steam, the geothermal fluid ejected from underground is separated into steam and geothermal hot water by a steam separator, and steam is used for power generation and geothermal water is heat exchanged. It is used for a variety of purposes such as agriculture, tourism, and district heating, and is returned to the basement from a return well.

Such geothermal water is supplied from the geothermal well through various transportation pipes and valves to the steam separator and heat exchanger, and is normally
Although it is high-temperature high-pressure water of 150 ° C or higher, at this time, scale, especially calcium-based scale, adheres to the transportation pipes and valve devices, which lowers transportation efficiency and lowers power plant output and heat exchange rate. There was a problem in that the system was blocked or the system was closed in some cases.

Further, there is a problem of calcium-based scale in a boiler water system using high temperature and high pressure water of 150 ° C. or higher or a wood cooking process in a paper-pipe factory which is also a high temperature and high pressure system.

Therefore, it has been desired to prevent the generation of scale in such a high temperature and high pressure water system.

In general, a method of adding various scale inhibitors to prevent water-based scales is known, and it is said that some of these scale inhibitors can be used in high-temperature high-pressure water systems. For example, it is proposed to add an aqueous solution of polyacrylic acid or its alkali metal salt in order to prevent calcium carbonate scale in a geothermal hot water system (JP-A-58-12209).
No. 6), polycarboxylic acid-based polymers such as polyacrylic acid, polymethacrylic acid, and polymaleic acid, and organic phosphorus compounds such as phosphonic acid and phosphonocarboxylic acid are added to prevent scale from adhering to the heat transfer surface of the boiler. Are proposed (Japanese Patent Publication No. 53-20475, Japanese Patent Publication No. 58-53034 and Japanese Patent Laid-Open Publication No. 55-1897).

[Problems to be solved by the invention]

However, the effects of conventional agents, which are said to have a scale preventing effect under high temperature and high pressure as described above, are actually 150
It cannot be said that it is sufficient in high-temperature and high-pressure water exceeding ℃, and especially under the severe conditions such as the above-mentioned geothermal hot water at high temperature and high pressure and where calcium-based scales are easily generated, the scale inhibitor is more conventional than before. It has been considered difficult to prevent scales by the addition of, and it has reached to the present day without being sufficiently solved.

Also, in the wood digestion process in paper and pulp mills, chips that are normally crushed wood are digested at high temperature and high pressure using a chemical solution containing sodium sulfide and sodium hydroxide. Due to the peculiarity of the cooking liquor (high alkali, large amount of organic substances, etc.), it has not been treated with an effective scale inhibitor until now.

As a result of intensive studies conducted by the present inventors on such a cause, polycarboxylic acid-based polymers and phosphonic acid-based compounds as described above, which were considered to be stable even at high temperatures by thermal analysis, etc. 150 ℃ ~ 250 ℃ under high pressure
In high temperature water, the effect was reduced to 1/2 or less in a short time due to some change, and this was one of the causes, leading to the finding that calcium scale was not sufficiently prevented.

The present invention has been made under such circumstances, and it is an object of the present invention to provide a method for remarkably suppressing the generation of scale in a high temperature and high pressure water system. The present inventors intend to provide a method capable of ideally preventing the calcium-based scale in a high-pressure water system. The present inventors further conducted research on various drugs that are generally considered to have the scale-preventing ability. As a result, they found that the specific bis (poly-2-carboxyethyl) phosphinic acid or its salt selectively exerts an excellent calcium-based scale inhibiting effect in high-temperature high-pressure water of 150 ° C to 250 ° C. It was The fact that these bis (poly-2-carboxyethyl) phosphinic acids generally have scale-inhibiting ability at a temperature of about 40 to 100 ° C is described in JP-B-54-29316 and JP-A-55-11092. It is known, but the effect of preventing calcium-based scale in high temperature and high pressure water exceeding 150 ° C. has not been known at all.

The fact that such bis (poly-2-carboxyethyl) phosphinic acid or a salt thereof exhibits an excellent scale-inhibiting effect which is not inferior to that at room temperature under high temperature and high pressure is similar to that of a polyamine chemically similar to this. This is a surprising point in view of the fact that acrylic acids, phosphonic acids, phosphonocarboxylic acids, etc. significantly reduce their effects under high temperature and high pressure.
The present invention has been made based on this finding.

(B) Structure of the Invention Thus, according to the present invention, bis (poly-2-carboxyethyl) phosphinic acid having a molecular weight of about 300 to 1300 or a salt thereof is added to high-temperature high-pressure water at 150 ° C. to 250 ° C. Provided is a method for preventing scale in a high-temperature high-pressure water system, which is characterized by preventing or suppressing scale generation in high-pressure water.

Bis (poly-2-carboxyethyl) used in this invention
Phosphinic acid is generally of the formula: (N and m are integers), and those having a molecular weight of about 300 to 1300 as an average molecular weight by the GPC method are preferable from the viewpoint of the scale prevention effect. Examples of the salt of bis (poly-2-carboxyethyl) phosphinic acid include alkali metal salts and ammonium salts, but it is usually preferable to use sodium salt.

Examples of the high-temperature high-pressure water system of 150 ° C. to 250 ° C. to which the present invention is applied include, as described above, a geothermal hot water system, a boiler water system, a wood cooking water system in a paper / pulp mill, and the like.

The addition amount of the compound used in the present invention varies depending on the target system, but when the boiler water system is targeted, it is suitable to add 0.1 to 500 mg / in the boiler feed water.
100 mg / is preferable, and in the case of geothermal hot water system, 0.1% of geothermal hot water from a part of the geothermal hot water transport pipe.
~ 200mg / suitable for press-fitting, 1 ~ 50mg /
Is preferred, and when it is intended for a wood cooking water system, it is suitable to add 0.1 to 200 mg / in the cooking liquor in the digester, preferably 0.1 to 50 mg /. By such addition, the calcium-based scale, especially the calcium carbonate-based scale that can be generated under high temperature and high pressure can be significantly suppressed as compared with the conventional one.

In addition, in the addition, it is preferable to use an aqueous solvent solution of the compound, especially an aqueous solution, and at this time, other agents, for example, an anticorrosive agent and a scale-preventing agent other than the calcium-based scale are allowed to coexist. It is also possible.

The present invention will be described below with reference to test examples and examples.

[Test example] Stability test of each compound under high temperature and high pressure by autoclave Enclose 2 ml of aqueous solution of each compound in a glass tube and heat at 10 kgf / cm ² · 183 ° C and 35 kgf / cm ² · 241 ° C in autoclave.
Leave for 24 hours under high pressure. Then cool to room temperature,
Using the aqueous solution of the taken out compound, the following calcium carbonate ion dispersion test was tested.

Calcium ion 250mg / and M alkalinity 600mg / cm ²
Calcium chloride and sodium bicarbonate were added to pure water so that The pH of the liquid was 8.3. The test liquid 1
Each compound was added at the specified concentration to 60 ° C, and the internal temperature was maintained at 60 ° C using a magnetic stirrer at a rotation speed of 100 rpm.
Stir for an hour. After the test, the solution is filtered using Toyo filter paper No. 6 and the calcium ion in the filtrate is measured.

The percentage of the calcium ion concentration after the test to the calcium ion concentration before the test was defined as the calcium ion dispersion ratio of the reagent. The results of this test and the results of the calcium carbonate ion dispersion test at 60 ° C. of each compound that has not been subjected to the heating operation are also shown in Table 1.

Examination of Test Results As shown in Test Nos. 6 to 10, even if the compound is considered to have excellent calcium ion dispersion effect at 60 ° C. and stable at high temperature by thermal analysis, 10
kgf / cm ² · 183 ℃, in heating and after pressurization at high temperature and pressure conditions of 35kgf / cm ² · 241 ℃, calcium ion dispersion effect of each compound was compared to the heating and pressurization 10kgf /
cm ² · 183 ° C decreased to 1/2 to 1/3, and 35 kgf / cm ² · 241 ° C decreased to 1/3 to 2/15, and the effect is close to the test result without drug addition. Recognize.

In comparison with these, as shown in Test Nos. 2 to 5, it is understood that the calcium ion dispersing effect of the compound of the present invention has a good effect even after pressurizing and heating the autoclave.

Example 1 The effect of chemicals on geothermal hot water of a geothermal power plant was investigated using an autoclave. That is, a predetermined amount of chemicals similar to the geothermal hot water of a certain geothermal power plant (see water quality in Table 2) was added and charged in an autoclave. After sealing the autoclave,
While stirring at 100 rpm, a test was carried out for 18 hours under pressure heating conditions of 15 kgf / cm ² and 200 ° C. By collecting test water after the test and analyzing the total calcium concentration in the test water before and after the test,
The amount of adhered calcium was calculated. The test results are shown in Table 3.

The same applies to the following experimental examples.

[Discussion] As shown in Test Nos. 4 to 9, it is understood that even known scale inhibitors do not have a sufficient scale inhibiting effect on the calcium scale of geothermal hot water.

More specifically, as shown in Test No. 6, Japanese Patent Publication No. 53-
Polymaleic acid, which is effective in high temperature and high pressure applications such as boilers according to JP 20475, is not effective in calcium scale of geothermal hot water, and its addition concentration is 5 times as shown in Test Nos. 7 and 8. It can be seen that even if it is increased 10 times, a sufficient effect cannot be obtained.

Further, as shown in Test No. 9, phosphonocarboxylic acid and polyacrylic acid, which are effective under high temperature and high pressure in a boiler or the like according to Japanese Patent Publication No. 58-53034, are similar in structure to the compounds of the present invention. It can be seen that even when used together, it is not effective for the calcium scale of geothermal hot water.

As shown in Test No. 5, JP-A-58-122096 shows that polyacrylate, which is the only known calcium carbonate scale inhibitor in geothermal hot water, is not sufficiently effective.

As described above, the bis (poly-2-carboxyethyl) phosphinic acid of the present invention and its salt shown in Test Nos. 2 and 3 are small in amount in comparison with the scale suppressing effect of the above-described known scale inhibitors in geothermal hot water. It can be seen that the added concentration sufficiently suppresses the calcium scale of geothermal hot water.

These facts are considered to be stable at high temperatures by experiments such as differential heat, and even scale inhibitors that were actually effective under high temperature and high pressure, such as boilers, are not effective against the calcium scale of geothermal water. It is shown that even if the added concentration is increased, it is not always effective and only the compound of the present invention has a remarkable scale-inhibiting effect on the calcium scale of geothermal hot water with a small added concentration,
Even if the compound of the present invention is generally known to have a scale-inhibiting effect, it is considered to be an unexpected effect which cannot be easily predicted.

Example 2 The effect of chemicals in a digester in a paper / pulp mill was examined using the same autoclave as in Example 1. A predetermined amount of chemicals was added to 2000 ml of test water (see water quality in Table 4) similar to black liquor in a digester of a certain company, and the mixture was charged into an autoclave. After sealing the autoclave, stirring at 100 rpm, 10 kgf / cm
^The test was conducted for 48 hours under pressure and heating conditions of 2.183 ° C. After the end of the test, sampled water was collected, and in the same manner as in Example 1,
The amount of adhered calcium was calculated. The test results are shown in Table 5.

[Discussion] As shown in Test Nos. 4 to 8, it is understood that even known scale inhibitors do not have a sufficient scale inhibiting effect on the calcium scale in the digester.

More specifically, as shown in Test No. 6, Japanese Patent Publication No. 53-
Polymaleic acid, which is effective under high temperature and high pressure in boilers according to JP 20475, is not effective for calcium scale in a digester, and its addition concentration is doubled as shown in Test Nos. 7 and 8. It can be seen that a sufficient effect cannot be obtained even if the amount is increased by 4 times.

Compared to the effect of these known scale inhibitors for preventing calcium scale in digesters, bis (poly-2-carboxyethyl) phosphinic acid of the present invention and its salts shown in Test Nos. 2 and 3 were added in a small amount. It can be seen that the concentration sufficiently suppresses the calcium scale in the digester.

As described above, by experiments such as differential heat, it was considered that the scale inhibitor was safe at high temperature in the past, and even a scale inhibitor that was actually effective under high temperature and high pressure in a boiler, etc. was added to the calcium scale in the digester. Notwithstanding the fact that increasing the concentration is not always effective, only the compounds according to the invention have a significant scale-inhibiting effect on the calcium scale in the digester with a small addition concentration, even though the invention Even if a compound is generally known to have a scale-inhibiting effect, it is considered to be an unexpected effect that cannot be easily predicted.

Example 3 An autoclave equipped with a steam outlet and a makeup water inlet was used and a test was conducted for 2 days while supplying water from Osaka City.
The concentration rate was 10 times, and the pressure was 10 kgf / cm ² . After the completion of the test, sample water was collected and the same method as in Examples 1 and 2 was used.
The amount of adhered calcium was calculated. The test results are shown in Table 6.

[Discussion] As shown in Test Nos. 4, 5, 8 and 9, it is understood that even known scale inhibitors do not have a sufficient scale inhibiting effect at a low addition concentration.

More specifically, tests commonly known as scale inhibitors
Even with phosphonocarboxylic acids and polyacrylic acids shown as NO.
It can be seen that the addition concentration of 10 mg / is required to exert the effective scale preventing effect as shown in O.6 and 7.

And, as shown in Test No. 8, even in the combination of phosphonocarboxylic acid and polyacrylic acid, which is effective in preventing the scale of the boiler according to JP-B-58-53034, effective scale prevention is achieved at a low addition concentration. You can see that it is not effective.

Further, as described in Test No. 9, polymaleic acid which is effective in preventing boiler scale according to Japanese Patent Publication No. 53-20475 is not effective at a low addition concentration,
As shown in Test Nos. 10 and 11, it is understood that the addition concentration of 10 mg / is necessary in order to exert the effective scale preventing effect.

As described above, bis (poly-2-carboxyethyl) phosphinic acid and its salt, which are the compounds of the present invention shown in Test Nos. 2 and 3 in comparison with the scale preventing effect of the above-mentioned known scale inhibitors, are 3 mg / It can be seen that the calcium scale is sufficiently suppressed at a concentration of about 1/3 or less of the addition concentration of the known scale inhibitor shown in Test Examples 7 and 11.

(C) Effect of the Invention According to the method of the present invention, the generation of high-temperature and high-pressure calcium-based scale can be significantly suppressed or prevented by using a specific compound. Such effects are remarkably excellent in proportion to conventional scale inhibitors for high-temperature high-pressure water systems and similar compounds, and can be said to be selective effects. And the method of the present invention has been a conventional problem.
It is possible to easily solve the scale trouble of high temperature and high pressure water system of 0 ℃ to 250 ℃ at low concentration, especially the scale trouble in the geothermal heat water transport pipe, wood cooking water system and boiler water system in the geothermal power plant. It can be resolved.

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Claims (5)

[Claims] 1. A molecular weight of about 150 ° C. to 250 ° C. in high temperature high pressure water.
A method for preventing scale in a high-temperature high-pressure water system, comprising adding 300 to 1300 bis (poly-2-carboxyethyl) phosphinic acid or a salt thereof to prevent or suppress the generation of scale in the high-temperature high-pressure water. 2. The method according to claim 1, wherein the scale is a calcium-based scale. 3. The method according to claim 1, wherein the high-temperature high-pressure water is geothermal hot water. 4. The method according to claim 1, wherein the high-temperature high-pressure water is a cooking liquor in a digester for digesting wood in a paper / pulp mill. 5. The amount added to high-temperature high-pressure water is 0.1 to 500 mg /
The method of claim 1 wherein: