JPS61113780A - Anticorrosive for heating surface - Google Patents

Abstract

PURPOSE:To obtain an anticorrosive for the heating surface of a boiler tube or the like producing a significant corrosion preventing effect by dispersing and suspending an Mn compound and a water soluble synthetic resin in water to prepare an emulsion. CONSTITUTION:An Mn compound such as MnO2, MnCO2, Mn(OH)2 or a fatty acid salt of Mn and a water soluble synthetic resin such as an acrylate polymer or a vinyl polymer are dispersed and suspended in water to prepare an emulsion. At this time, a surfactant such as polyoxyethylene alkyl ether is used as an emulsifier. When the heating surface of a boiler tube liable to corrode is coated with the emulsion, the emulsion produces a significant corrosion preventing effect.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a corrosion inhibitor for heat transfer surfaces in boiler furnaces, etc.
This invention relates to a corrosion inhibitor that is especially effective when applied to boilers that use asphalt or petroleum coke as fuel.

(Conventional technology) Fuel ash adheres and accumulates in boiler furnaces that burn heavy oil and crude oil, and in some cases, high-temperature exposed tubes such as superheaters and reheaters suffer severe corrosion and thinning. Sometimes. The cause of this is that elements such as sodium, sulfur, and vanadium contained in the fuel react with each other to form compounds with low melting points and strong accelerated oxidation effects, which cause severe corrosion on the pipe walls during boiler operation. This is because it exerts its effect. Examples of this type of corrosive compound include the following. Since the compound contains vanadium, the accelerated oxidation corrosion effect described above is also called vanadium attack. The numbers in parentheses indicate the melting point.

1ON-0.7v! 0W (574℃') Na10・2
720g (614℃)2 Nano ・5'Tl2
01. (565℃) 5Na, OV, O, -11'
7.0g (535℃)h~(670℃) Na1E+
04 (884℃) The low melting point indicates that it is likely to exist in a molten state in the tube wall temperature environment during boiler operation, and in the molten state, the activities of various chemical reaction factors become active and are generated on the boiler tube surface. This suggests that the corrosion rate of pipes is accelerated by destroying the protective oxide film. Also Na180. (sulfuric acid) I
Jum) forms a eutectic with vanadium compounds, lowering the melting point and exhibiting strong corrosive properties. (For example, 50%h06
．． (A mixture of 50% Na2804 melts at approximately 600°C.) As is clear from the above corrosion reactions, when accelerated oxidation corrosion occurs, it is necessary that the compound exhibiting the corrosive action be in an electrically molten state. . If the melting point of a compound that exhibits corrosive action is raised to a solid state, the corrosion reaction rate will be severely reduced to such an extent that it will not pose a practical problem. Based on this idea, compounds with high melting points such as calcium and magnesium are added to the fuel and reacted with low melting point compounds in the combustion environment, raising the melting point and thereby preventing corrosion reactions. method is being carried out. Incidentally, OaO has a melting point of 2200° C. MgO has a high melting point of 2800° C. When these react with vanadium compounds, compounds with high melting points as shown below are produced.

MgO"7101+ (671℃) 0aO-V,
O, (618℃) Mg0・2VtOg (835℃)
Oao・2VHO6 (778℃) Mg() 5V2
01? (1191℃)CaO・3v! oII (1016
℃) As a calcium compound, Oa 0C)s XCa
(OH)x, as a magnesium compound MgO,'
g('H)tsMgcICb, Mg as both elemental compounds
There is OOH-CaCOl (dolomite).In addition, kaolin, All OHX81%, etc. have been tested for the above purpose, but currently MgO1Mg(oa) is used from the point of view of injection effect (the purpose can be achieved with a small amount). * is the most commonly used.

Meanwhile, asphalt and petroleum coke have begun to be used as fuel for boilers in order to effectively utilize energy sources and reduce operating costs. However, these fuels contain large amounts of vanadium and sulfur compounds, as well as carbonaceous substances that have a slow burning rate. For this reason, it is difficult to achieve complete combustion using a burner for heavy oil or crude oil, so improved burners are used for combustion, but even with this, complete combustion does not occur in the combustion area, and the boiler It is observed that combustion continues even after some of the fuel has accumulated on the bottom of the furnace or superheater. In these combustion parts (the parts where the particles are deposited or are burned after being deposited), oxygen is consumed for combustion, resulting in an environment where the partial pressure of oxygen is locally low. In such an environment with a low oxygen partial pressure, the accelerated oxidation effect of the vanadium compound does not occur, and the vanadium oxide itself has a high melting point of V, O, (both have melting points of 1900°C or higher). V, 0II (which is a higher oxide and has a low melting point)
670° C.), so even if a large amount of vanadium compounds are contained, vanadium attack will not occur.

On the other hand, if there are environmentally trapped calcium and magnesium compounds that contain such unburned carbon and have a low oxygen partial pressure, (
In an attempt to prevent vanadium attack, Oa,
, when Mg compounds are added) and sulfide corrosion occurs, accelerating wear and tear on boiler tubes. The corrosion reaction in this case is roughly as follows. Taking Mg(OH)x as an example, the formula (1
) to (6).

Mg(OH)t added to the fuel is heated to a high temperature in the combustion region and is dehydrated.

Mg(01, --→MgO(1)) Since the combustion region contains B"x and SOx gases, it reacts with these to produce sulfate.

MgO+E? False +1/20. -MgSO4(2)MgO
+801-Mg11?04 (3
) This is contained in the fuel ash, and in an environment where the unburned carbon is being burned, 2Mg5o, + 50 → 2Mg0 + 3(X),
+ 28 (4) M-1-8-→M 8
(5) MgSO4-)-3ME+-→MgO+! +M
The reaction O+4ET (6) occurs. Here, M indicates a boiler tube.

It can be seen that Mg(oH)t, which is injected into the fuel to prevent vanadium attack, actually causes corrosion. A similar cause of corrosion may occur when calcium compounds are injected.

For these reasons, the corrosion prevention method by injecting calcium and magnesium compounds, which is used in boilers that burn heavy oil or crude oil, is not recommended for asphalt or petroleum coke, especially when the latter fuel is used. There is a drawback that it cannot be done.

(Problems to be Solved by the Invention) It is an object of the present invention to solve the problem in that the fuel ash containing unburned carbon adheres to the bottom of the furnace and the boiler tubes, and The objective is to provide a corrosion inhibitor for heat transfer surfaces that prevents corrosion damage caused by continued combustion.

(Means for Solving the Problems) The motive of the present invention is to achieve the above objectives by coating locations where problems are expected to occur with a corrosion inhibitor containing a manganese compound that is more likely to form sulfides than boiler pipes. This is because we have experimentally confirmed that this can be achieved.

That is, after dispersing a corrosion inhibitor containing a manganese compound, which is more likely to form sulfides than all the components of boiler tubes, into an emulsion containing a water-soluble synthetic resin, this is applied to the tubes where corrosion is expected to occur. It is to be coated.

Therefore, the present invention relates to a corrosion inhibitor for boiler heat transfer surfaces, which is made of an emulsion in which a Mn compound and a water-soluble synthetic resin are dispersed in water and kept moist. Furthermore, the present invention provides A/,
The present invention also relates to a corrosion inhibitor for boiler heat transfer surfaces comprising an emulsion in which at least one compound of elements selected from the group of Si and Fe, a Mn compound, and a water-soluble synthetic resin are dispersed and suspended in water.

Examples of the water-soluble resin used in the present invention include acrylic ester copolymers, polyacetic acid and neil, polyethylene polyethylene, and styrene-butadiene copolymers. Surfactants used when emulsifying water-soluble resins include organic compounds such as polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, trimetheraminoethyl alkylamide halogenide, and alkyl betaine. There are rust conductors, etc.

Examples of the Mn compound used in the present invention include “°-
・“°00...”n(OH)2 is the fourth fatty acid “no!
5. Organic compounds can also be used.

As the compound of the element selected from the group of Mu/, Si, and Fe used in the present invention, a compound of Mu: AtRol
, A/(OH), , Sl compound: 8101, ether silicate, methyl silicate naphthenic acid, Fe compound:
Fe101°? θ0OH1Fes04, iron acetate, A/
and Sl compound dikaolin (A/ff1O, 8102
・2H, O), etc.

By the way, if too much A/, Si, etc. is added, the surface of the boiler tube constituting the combustion chamber will become 1/(A/, 81, etc.) and the heat reflection will be strong and the heat absorption of the boiler tube will be reduced. This has the disadvantage that the temperature of the combustion flame is maintained at a high state, and the formation of NOx, which is considered the most important form of exhaust gas pollution, is promoted.In other words, even if there is a corrosion prevention effect, From an operational point of view, it can be said that adding a large amount is not preferable.

However, if a Mn compound (colored) is allowed to coexist, whitening will be suppressed and the above-mentioned problem of Hox generation will be eliminated.

The content range of each component of the corrosion inhibitor of the present invention is Mn01
20 to 100% by weight is preferred. Also, 1tn in this range
AI! 20s is 10-50% critical,
Elo, 10-50% by weight, Fe, 0320-30% by weight are preferred.

Note that the presence of OaO and MgO in an amount of up to 10% by weight is permissible.

Furthermore, the content of the water-soluble synthetic resin is not particularly stipulated, as long as it is enough to coat the boiler pipes with the corrosion inhibitor, and the selection should be made at a concentration that is easy to work with (for example, for feather treatment spraying). Bye. If it has a high resin content and is highly sticky and has poor workability, it may be diluted by adding water.

The features of the present invention are listed below.

■ Manganese easily reacts with sulfur compounds, and by turning itself into sulfide, it lowers the sulfur partial pressure in the environment and alleviates its corrosivity.

■ Manganese sulfide MnE+ (melting point 1160℃),
The Mn-MnS eutectic (1580°C) has a high melting point, and even if sulfide is generated, it will not melt even during boiler operation (and MnS will not cause corrosion.

■ A/: The anti-corrosion effect of Si is that it does not have a direct chemical reaction with the S compound, so by coexisting with the S compound, it dilutes the 0 degrees of the S compound and prevents it from coming into contact with boiler pipes, etc. . Furthermore, fuel ash containing A/Si generally accumulates on the heat transfer surface immediately after it is peeled off from the boiler tube, and rarely prevents heat absorption.

(2) Although the Fe compound reacts with 8 compounds compared to A/ and Si (see Table 2 of Examples below), A/.

1gi, a strong sulfide corrosive Ca compound, M
It was found that when allowed to coexist with compound g, it exhibits a corrosion inhibiting effect (see D1E in Table 1 of Examples). SaraKF
Since the e compound belongs to the same class of colored compounds as the Mn compound, it similarly has the effect of suppressing the Box generation phenomenon.

■ Boiler tubes where corrosion is expected to occur
Because it targets only the tubes that show signs of corrosion damage, it costs less than injecting this type of corrosion inhibitor into the fuel.

■ Since a manganese compound is added to the emulsified liquid using a water-soluble resin, there is no risk of flame or hygienic problems when coating.

Moreover, since it forms a water-impermeable and elastic film after drying, solid substances such as manganese compounds are completely coated on the tube.

■ Because of the above properties, it is possible to form a thick film by repeating coating.

(9> Also, the coating can be applied by coating, spraying, etc.

〔Example〕

The effects of the present invention were investigated by applying it to a boiler operating using petroleum coke as fuel.

i) The composition of the corrosion inhibitor of the present invention as shown in Table 1 was prepared. In this test, Oa and Mg compounds, which are conventionally used to prevent high-temperature corrosion in heavy oil-fired boilers, were prepared using the same method as in the present invention (for comparison). ■ in Table 1 indicates the product without coating with this type of additive.

Weigh 5 kg of each of the ingredients listed in Table 1, and add 7 kg of water.
．． 1 kg of acrylic acid ester copolymer, 0.2 kg of methyl cellulose, and 0.2 kg of a commercially available nonionic surfactant (polyoxyethylene nonylphenol) were added to a well-mixed aqueous solution, and the mixture was further stirred to make adjustments. finished.

11) Properties of petroleum coke and operating conditions of boiler tubes tested for corrosion The corrosive components in petroleum coke are 4.5% sulfur, 830 ppm of basicum, and 110 ppm of sodium. The operating conditions of the boiler tubes tested are: tube wall temperature. 510℃～530℃
, the combustion gas temperature is 870-850°C.

111) Coating work with corrosion inhibitor After completely removing the fuel ash that had adhered to the boiler pipes with Sandplus to give it a golden appearance, apply the corrosion inhibitor prepared in the above manner to a spray that is used for spraying agricultural chemicals, etc. It was applied evenly using a machine. The application was repeated three times at 24 hour intervals.

It was confirmed that a dry film of water-soluble resin was formed almost uniformly on the surface of the boiler tube coated with the corrosion inhibitor of the present invention, and that various components were retained in the dry film.

iv) Test results: Approximately 5 months have passed since the boiler was operated, and at the time of operation, the process described in (a) is carried out again. After approximately 4 months have passed, the fuel ash adhering to the tube surface is removed and the sulfidity level of the tube surface is determined. investigated.

To investigate the degree of sulfidation, monochrome printing paper was immersed in 5% sulfuric acid and then stuck on the tube surface for about 10 minutes.

Afterwards, the photographic paper was washed with water, and the degree of sulfidation was compared based on the brown coloration on the stamp surface and its distribution.

This determination of sulfidity is based on the fact that if sulfide is generated on the tube surface, it reacts with sulfuric acid to generate hydrogen sulfide gas. This technique takes advantage of the impression that this gas reacts with the silver halide on the photographic paper, fixing brown silver sulfide on the screen.

As is clear from the above, the corrosion inhibitor of the present invention cannot be applied to heat transfer surfaces such as inside boilers, especially conventional corrosion inhibitors that are mainly composed of calcium compounds or magnesium compounds and are resistant to vanadium attack. It can be used as a heat transfer surface in boilers that use asphalt or petroleum coke as fuel, and has a large corrosion-preventing effect, which is advantageous.

Sub-agent: 1) Akira Sub-agent Ryo Hagi Hara -

Claims (2)

[Claims] (1) Dispersing Mn compound and water-soluble synthetic resin in water,
Corrosion inhibitor for boiler heat transfer surfaces consisting of a suspended emulsion (2) Corrosion inhibitor for boiler heat transfer surfaces made of an emulsion in which at least one compound of elements selected from the group of Al, Si, and Fe, a Mn compound, and a water-soluble synthetic resin are dispersed and suspended in water.