JPS63166981A - Aqueous composite antiscale agent for boiler - Google Patents

Abstract

PURPOSE:To produce an aqueous composite antiscale agent which effectively prevent the corrosion of a boiler and the sticking of scales by compounding it with the specific ratio of a specified deoxidizer and a catalyst thereof, scale dispersing agent and catalytic promoter for the prevention of chelating. CONSTITUTION:15-30wt.% sulfite as the deoxidizer, 0.003-0.01wt.% cobalt salt as the catalyst, 2-5wt.% sodium polyacrylate (1,000-5,000mol.wt) as a scale dispersing agent and 2-4wt.% nitrate of calcium or magnesium as the catalytic promoter for the prevention of the chelating of polyacrylic acid and cobalt are compounded to prepare the aqueous composite antiscale agent. The corrosion of the boiler and the sticking of the scales can be effectively prevented by using the antiscale agent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] This invention relates to a composite boiler cleaning agent.

[Prior Art] As boilers become more efficient, problems caused by water quality, such as boiler corrosion and scale adhesion, are becoming more complex.

Conventionally, water treatment has been carried out assuming that the temperature and concentration inside the boiler can are the same at all parts, but in small, high-efficiency boilers such as once-through boilers, the part where the feed water flows and the part where the steam flows are different. There are large differences in temperature and concentration at the site of excretion, resulting in complex symptoms. In other words, at the feed water inlet, the temperature is low, so the deoxidizing power does not work sufficiently, and low-temperature corrosion is likely to occur, and the heat transfer surface is highly concentrated, so scale is likely to adhere.

Therefore, both an oxygen scavenger that acts quickly at low temperatures and a scale dispersant that has high dispersion power are essential for can cleaning agents.

Through previous research, the inventors selected sulfite as an oxygen scavenger that is effective at low temperatures, and found that cobalt salt is effective as a catalyst. When added, polyacrylic acid was found to interfere with catalysis. This is considered to be due to the chelation of cobation and polyacrylic acid.

[Summary of the Invention] As a result of many experiments and studies, the inventors found that the above-mentioned interference was eliminated by adding a calcium or magnesium salt to the 11tI salt-cobalt salt-sodium polyacrylate system. We found out what can be prevented.

In this case, since calcium and magnesium are both components of scale, scale adhesion was expected due to the addition of the above-mentioned salt. However, according to the inventors' considerations, sodium with a molecular weight of 1,000 to 5,000 has the ability to dissolve scale components with a weight of more than 10 times its own concentration, so polyacrylic acid The weight concentration ratio of sodium and calcium or magnesium salt is 1 to 1.2.
: If set to 1, scaling can be sufficiently prevented.

In addition, the calcium or magnesium salt is 6 to iopp.
In order to exhibit a sufficient effect at m as caC'03, it is preferable to reduce the amount to 10 ppm or less from the viewpoint of preventing scale.

Calcium or magnesium salts generally have low solubility, but nitrates have high solubility compared to other salts, so
It is best to use nitrates as a component of can cleaning agents. In addition, if sulfite has a fast-acting oxygen scavenging ability at low temperatures, storage stability will deteriorate, so potassium sorbate is used as a stabilizer (about 1.5% of sulfite in terms of weight and darkness ratio).
is preferable.

The composite can cleaning agent of the present invention, which includes all of the above elements, has a fast deoxidizing power and a high dispersion power at low temperatures, and can effectively prevent boiler corrosion and scaling.

[Example of the Invention] The oxygen scavenging ability of Composition A which does not contain calcium nitrate as a catalyst aid and Composition B which contains it was confirmed.

Composition A (%) Composition B (%) KOH
4,5KOH4,5 to 2 CO34,7K2 CO34,7KIS
O328,3K2 803 28.3 Sorbic acid Potassium sorbate 0.47 Potassium 0.47C
O8Oa O,005C08OA 0.0
05 Polyacrylic acid Sodium polyacrylate 4.7 Sodium 4.7Ca (NO3)
2 Pure water 57.325 Pure water 55
．． 325 Conditions Water temperature: 30°C Water: Distilled water Chemical input amount: 300fItg/i The results of this example are shown in Figure 2.

As is clear from this, the presence of calcium in the above composition greatly increases the rate of removal of dissolved oxygen.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for measuring dissolved oxygen, and FIG. 2 is a graph showing the relationship between time and dissolved oxygen concentration when compositions A and 8 were added. Patent applicant: Miura Kogyo Co., Ltd. 0 1 2
3 (minutes) Time from chemical injection

Claims (1)

[Claims] Sulfite as an oxygen scavenger, cobalt salt as its catalyst,
Contains sodium polyacrylate (molecular weight 1,000-5,000) as a scale dispersant, calcium or magnesium salt as a catalyst aid to prevent chelation of polyacrylic acid and cobalt, and the proportions of each are A water-based composite can cleaning agent characterized by having the following weight percent: Sulfite 15-30 Cobalt salt 0.003-0.01 Sodium polyacrylate 2-5 Calcium or magnesium nitrate 2-4