JPS594661A - Heat-resistant type anti-corrosive film - Google Patents

Abstract

PURPOSE:To form a heat-resistant type anti-corrosive film having improved economic efficiency, corrosion resistance, and durability, by applying a mixture containing an alkaline earth metal carbonate to the surface of pipes of the high- temperature part of a heat transfer device such as a boiler for burning garbage with a silicate-based binder. CONSTITUTION:The surface 1 of pipes of the high-temperature part of a heat transfer device such as a boiler using only heavy oil for combustion, a boiler for burning garbage, etc. is coated with a mixture containing one or more carbonates of alkaline earth metal such as Mg, Ca, Ba, Be, etc. using a silicate- based binder (e.g., sodium sulicate, etc.), to form the heat-resistant type anti- corrosive film 2. EFFECT:The corrosive scale 3 is reacted with the alkaline earth metal carbonates, the voids 2a in the anti-corrosive film 2 are filled, the contact between the scale 3 and the metal 1 is prevented, and corrosion is suppressed.

Description

[Detailed description of the invention] The present invention is a heavy oil-fired boiler, a power generation boiler, and a soda cycle 1p.
(This relates to a heat-resistant anti-corrosion coating that is adhered and formed on the surface of heat exchanger tubes in high-temperature parts of boilers, garbage incineration boilers, etc.)

In recent years, in heavy oil-fired boilers, etc., combustion ash adhering to the surface of heat exchanger tubes in high-temperature areas has increased due to factors such as an increase in the temperature at the top of the furnace due to improved combustion methods for NOx countermeasures and the adoption of high-sulfur fuel due to the spread of desulfurization equipment. Corrosion of the high-temperature heat exchanger tubes is occurring due to this.

The combustion ash that adheres to the surface of the heat exchanger tube in the high temperature section contains V, Na
, highly corrosive v2o6-Na whose main component is 8.0
It is known that it is a 2SO4-based substance. Here, the high temperature part is a temperature range in which the surface temperature of the attached combustion ash is 200 to 1000°C.

As is well known, countermeasures against corrosion caused by adhering combustion ash can be broadly classified into two types.

l) Improving the material of the high temperature section heat transfer tube 2) Improving the combustion ash adhering to the high temperature section heat transfer tube surface (low S
3) Methods for surface treatment of high-temperature heat transfer tubes are currently being researched and developed in various fields, but all methods are economically efficient and corrosion-resistant. There are problems in terms of performance, durability, etc.

The present invention has been made to eliminate the drawbacks of the conventional methods, and according to the above-mentioned classification, it relates to the improvement of 3) by applying 2).

In other words, 9 The present invention has a heat exchanger tube surface in a high temperature section such as a boiler,
A mixture containing one or more alkaline earth metal carbonates such as Mg, Ca, Ba, and Be was deposited using a silicate binder. This is a heat-resistant anti-corrosion coating characterized by the following.

The present invention will be explained with reference to FIG. In Figure 1, 1
2 is the metal on the surface of the high-temperature heat exchanger tube, 2 is the Mg, Ca,
A heat-resistant anticorrosive coating containing one or more alkaline earth metal carbonates such as Ba and Be.

2a is a void existing inside the heat-resistant anti-corrosion coating 2, and 8 is a highly corrosive V2 attached to the surface of the heat-resistant anti-corrosion coating 2.
06- Na2804 scale.

In this Figure 1, 2 is Mg, Ca, Ba, B
In the case of a heat-resistant anticorrosion coating that does not contain an alkaline earth metal compound such as a, when 3 is heated to a high temperature, it melts, penetrates and penetrates 2a present inside 2Q, and eventually reaches the surface of 1. Here, the metal surface is locally oxidized and sulfided according to reaction formulas (1) and (2) described later, and this expands to destroy the boundary between 1 and 2, and corrosion progresses.

However, Mg is added to the heat-resistant anti-corrosion coating mentioned above.

When an alkaline earth metal compound such as Ca, Ba, Ba, etc. is present, 8 is heated to a high temperature and melts as shown in Figure 1.
Even if 3 penetrates into 2a existing inside 2a, Mg, Ca, and Ba of 2 will be absorbed into the void surface while passing through 2a.

9 For example, when the alkaline earth metal compound is an Oa compound, OaO is obtained by incorporating an alkaline earth metal compound such as Be.
-Vha5 Because it changes to the Na2804 scale,
The melting point of 8 increases and solidifies within the void.

Next, phosphate-based and silicate-based binders are known as binders that allow inorganic substances such as Al, Si, and Zn to adhere to metal surfaces. Regarding the silicate binder, the present inventors have investigated various methods for depositing the above-mentioned alkaline earth metal compound on the surface of a tube of a high-temperature heat exchanger such as a boiler. As a result, they found that the alkaline earth metal carbonate was well dispersed in a silicate binder, such as an aqueous sodium silicate solution, and that the coating after coating had good adhesion, uniformity, and density. And Arca L,, kind, Wa,,). I-eight, cuff.

When mixed with sodium silicate aqueous solution, silium, sulfuric acid, etc. solidify and cannot be applied to metal surfaces.

As described above, 1 the present invention reacts with corrosive scale and alkaline earth metal carbonate to close the voids in the heat-resistant anticorrosive coating,
It is characterized by suppressing corrosion by cutting off the contact between corrosive scale and metal, and by using a silicate binder as a method of coating and molding alkaline earth metal carbonate onto the metal surface.

In addition, in the present invention, Mg, Ca, Ha, Be
Alkaline earth metal carbonates such as J, 8i, Zn,
Even if metals such as Zr and their oxides are added, the same effect can be obtained.

And, as alkaline earth metal carbonates such as Mg, Ca, Ba, Be, etc., limestone (CaO02), chalk (0aOO3) + calcite (0a0
03), aragonite (CaC03), marble (CaC0
3), dolomite (CaCO3・0aCO3), rhomboidite (
Ores such as MgC03), doxite (DaCO3), etc. may also be used.In addition, silicate binders include sodium silicate, Oa, AI, Zn, Co, Fa,
Ba, RO, Mg.

It goes without saying that a combination of silicates such as Mn and Li and their Class 2a or higher may also be used.

reaction formula % formula % (2) However, R: unspecified reducing agent M: Metal Next, the present invention will be specifically illustrated by examples.

The scale that had adhered to the high-temperature heat exchanger tube of the heavy oil-fired boiler that caused the corrosion accident was collected, and after crushing, a corrosion test was conducted by immersing the test pieces of Grades 1 to N1 & 18 in Table 1 into this corrosive scale. I did it.

The test conditions were: oxygen concentration: 5 VO 1%, carbon dioxide concentration: 15 VO 1%, sulfur dioxide concentration: 0.5 VO.
1%, remaining nitrogen gas atmosphere, test temperature: 650℃
, test time = 200 hours.

Also, the test piece is 20 mm x 50 mm x 5 m
Using 24 m S TBA machines, the heat-resistant anti-corrosion coating is 50W.
A solution containing 50 wt % of thorium silicate aqueous solution and 50 wt % of calcium carbonate powder was applied to the test piece.

Adhesive molding was used.

Table 1 Corrosion test piece Table 2 Corrosion test results The results are as shown in Table 2.9Heat-resistant anti-corrosion coating (N3) in which alkaline earth metal carbonate such as Ca is adhered and molded with a silicate binder according to the present invention It can be seen that the corrosion weight loss is about 1/4 compared to the conventional inorganic paint film (No. 2), and the corrosion resistance is significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the present invention. 1...Metal, 2...Heat-resistant anti-corrosion coating, 2a...2
The void that exists inside the 3... scale.

Claims (1)

[Claims] Mg, Oa,
Ba. A mixture containing 1 m or more of an alkaline earth metal carbonate such as I3e was deposited using a silicate binder. A heat-resistant anti-corrosion coating characterized by: