KR20130035643A - Corrosion preventive method of heat exchange facilities or boiler - Google Patents

Abstract

PURPOSE: A heat exchange device or a method for preventing an outer surface of a boiler from rusting are provided to obtain soundness of exterior surface exposed to exhaust gas of the boiler using fossil fuel by suppressing corrosion of a base material with anticorrosive agent. CONSTITUTION: A liquid additive composition is comprised of magnesium ion, dispersing agent, anticorrosive agent, emulsifier, and solvent. The magnesium ion is included in a form of magnesium chloride or magnesium hydroxide. The dispersing agent is anionic surfactant which the number of carbon is over 25. The anticorrosive agent is one or more kinds selected from group comprised of hexadecyl pyridinium compound, thiourea, and triclosan. [Reference numerals] (AA) First step; (BB) Second step;

Description

Corrosion preventive method of heat exchange facilities or boiler

The present invention relates to a method for preventing external corrosion of a heat exchanger or a boiler.

Hot and cold corrosion caused by the exhaust gas occurs differently depending on the fuel. In particular, sulfur oxides generated by sulfur in fossil fuels have a significant effect on low temperature corrosion. For example, SO ₃ generated in heavy oil combustion is generated in the boiler furnace and the exhaust gas flow path. The conditions and the design of the furnace in the furnace have a great influence on the generation of SO ₃ , and a lot of slag is generated at the high temperature of the exhaust gas. It increases corrosion and SO ₃ conversion rate, and SO ₃ is condensed at low temperature to corrode metal iron and increase AH temperature.

In order to effectively remove this, a method of using finely divided and dispersed magnesium compound as an additive for lubricating oil or fuel oil (high sulfur heavy oil) is widely practiced in foreign countries.

In addition, a method of using magnesium in the form of slurry is disclosed in Korea.

The magnesium compound can control the corrosive SO ₃ in the boiler exhaust by the following three actions.

1) Control the catalysis that promotes the conversion of SO ₂ → SO ₃ caused by deposits (V2O5) on the outside of the boiler tube.

2) Neutralize sulfuric acid condensed at low temperature through the formation of magnesium sulfate

3) Magnesium sulfate is formed by removing gaseous SO ₃ by gas-solid reaction

However, when using a slurry form, reactivity is a problem and poor workability. In addition, since it is used in combination with fuel oil, it is inevitably limited.

The method of using magnesium in the form of the slurry is disclosed in Korean Patent Publication No. 10-2005-0043355. As in the above patent, in the conventional patent, in order to solve the corrosion problem generated in a power plant using high sulfur heavy oil as a fuel, the main purpose is to add magnesium in the form of slurry to the fuel additive. The use of magnesium in the form of a slurry in oil is excessively expensive compared to the purpose, and incidentally, excessive additives remain in the lower part of the boiler or in the low temperature part, resulting in adhesion problems (waste treatment, increase in bottom part). In addition, the additive is designed to dissolve only in oil, so it is difficult to remove or prevent corrosion products on the power plant using water to improve combustion, or on the outer surface of the tube where the unevenness and corrosion are advanced.

The prior art is mainly limited to use as additives for liquid fuels, and currently there are insufficient measures for the generation of sulfur oxides in solid fuels. There is a need for anti-corrosion additives that can be used in coal-fired boilers, wood-fired pellets, many other solid fuels, and gas-fired boilers.

The present invention is a chemical composition (liquid additive composition or solid additive) added to the liquid and solid fuel in order to remove the external corrosion products of the steel structure consisting of the irregularities and overlapping structure, such as HRSG fin tube It relates to a method for removing corrosive organisms and base metal corrosion using the composition.

The present invention relates to liquid additive compositions containing magnesium ions, dispersants, preservatives, emulsifiers and solvents.

Hereinafter, the additive composition according to the present invention will be described in more detail.

Ionic magnesium compounds according to the invention contain magnesium ions, dispersants, preservatives, emulsifiers and solvents.

In the present invention, magnesium ions may act to neutralize corrosion products. In the present invention, by using magnesium ions, it can be used in a facility of a variety of structures compared with the magnesium oxide used in the prior art, it is advantageous in terms of cost because of high reactivity.

 The magnesium ions may be included in the additive composition in the form of magnesium chloride or magnesium hydroxide. The magnesium chloride or magnesium hydroxide is present in the ionic state in the additive composition by a dispersant described below. The magnesium ion may be included in an amount of 10 to 30 parts by weight, and preferably in an amount of 15 to 20 parts by weight, based on 100 parts by weight of the liquid additive composition. If the content is less than 10 parts by weight, there is a fear that the corrosion protection effect is insignificant, if it exceeds 30 parts by weight, magnesium ions that do not participate in the neutralization reaction is discharged to the outside causing environmental pollution, there is a fear that the material price may rise. .

The dispersant in the present invention allows the magnesium ions to be uniformly dispersed in the additive. As the dispersant, an anionic surfactant having 25 or more carbon atoms may be used. Specifically, at least one selected from the group consisting of olefin-sodium maleate and condensed phosphate may be used.

In the present invention, the dispersant may be included in an amount of 5 to 20 parts by weight, and preferably in an amount of 10 to 15 parts by weight, based on 100 parts by weight of the liquid additive composition. If the content is less than 5 parts by weight, the dispersing effect of magnesium ions may be insignificant. If it exceeds 20 parts by weight, the material price may increase.

In the present invention, the corrosion inhibitor serves to suppress corrosion of the base material exposed on the surface, thereby ensuring the integrity of the outer surface exposed to the exhaust gas. As the preservative, a general preservative used in the art may be used without limitation, and specifically, at least one selected from the group consisting of hexadecylpyridinium compound, thiourea, and triclosan may be used. In addition, the corrosion inhibitor may be included in an amount of 0.01 to 1.0 parts by weight based on 100 parts by weight of the liquid additive composition, preferably may be included in an amount of 0.1 to 0.3 parts by weight. If the content is less than 0.01 part by weight, there is a fear that the corrosion protection effect of the base material is insignificant.

In the present invention, an emulsifier is used to facilitate mixing of magnesium ions and a solvent. As the emulsifier may be used a general emulsifier used in the art, specifically, one or more selected from the group consisting of lauryl alcohol, lauryl alcohol sulfate ester, sodium salt, oleic acid and glycerin. In addition, the emulsifier may be included in an amount of 0.01 to 1.0 parts by weight, and preferably in an amount of 0.1 to 0.3 parts by weight, based on 100 parts by weight of the liquid additive composition. If the content of the emulsifier is less than 0.1 part by weight, there is a fear that the emulsification is not properly, if it exceeds 0.3 parts by weight, there is a possibility that it is excessively injected, not suitable for economics.

In the present invention, the solvent may be used a general solvent used in the art, specifically, may be used at least one selected from the group consisting of water and alcohol, preferably a mixture of water and alcohol. At this time, the mixing ratio of water and alcohol may be 7: 3 to 9: 1. The solvent may be included in an amount of 60 to 80 parts by weight based on 100 parts by weight of the liquid additive composition, and preferably may be included in an amount of 64.4 to 74.8 parts by weight.

The liquid additive composition according to the present invention has the following effects.

First, vanadium pentoxide, which is generated mainly in the combustion process, is converted into a vanadium compound having a high melting point to prevent accumulation in the boiler, thereby preventing the generation of sulfur trioxide due to the catalytic reaction.

The melting point of the vanadium pentoxide is about 600 ℃ easily melted in the boiler and attached to the inner wall of the boiler causes the scale generation. This vanadium pentoxide not only becomes a catalyst for the generation of sulfur trioxide as described above, but also oxidizes the boiler outer wall.

When the liquid additive composition according to the present invention is added during the combustion process, magnesium ions react with vanadium pentoxide to form magnesium sulfate, and the magnesium sulfate is discharged to the outside of the boiler together with the exhaust gas to accumulate the vanadium pentoxide in the boiler. prevent. Accordingly, the amount of sulfur trioxide generated during the combustion process can be reduced. The magnesium sulfate may neutralize sulfuric acid condensed at a low temperature portion.

In addition, when the liquid additive composition is applied to the surface of a solid raw material such as coal, scattering of the solid raw material can be prevented.

The liquid additive composition described above in the present invention may be used as a solid additive by mixing with dry ice.

In the present invention, by using a solid additive including dry ice, it is easy to remove external corrosive, no contaminants remain, and as the dry ice evaporates, a liquid corrosion inhibitor may remain to prevent further corrosion.

In the present invention, the liquid additive composition may be included in an amount of 1 to 20 parts by weight based on 100 parts by weight of the solid additive, and dry ice may be included in an amount of 80 to 99 parts by weight based on 100 parts by weight of the additive.

Liquid additive composition in the present invention can be prepared by mixing the above-described magnesium ions, dispersants, preservatives, emulsifiers and solvents using common mixing methods used in the art.

In addition, the solid additive including the liquid additive composition and dry ice may be prepared using rapid freezing through a lyophilization method.

The present invention also relates to an external corrosion prevention method comprising the step of contacting the above-described liquid additive composition or solid additive with an iron structure.

In the present invention, the steel structure may be a boiler or a heat exchanger having an uneven structure, and specifically, may be a heat recovery steam generator (HRSG). The heat recovery steam generator (HRSG) is used to recover energy in the high-temperature exhaust gas discharged after combustion in a gas turbine, etc., and has a cylindrical tube shape. Specifically, in order to improve the heat exchange ability of the tube, which is an iron structure, the heat recovery steam generator closely arranges a structure (pin tube) in which a pin is inserted to the outside of the cylinder at regular intervals in a cylindrical tube, and at the top thereof. A stack of pin tubes of the same shape are staggered and composed of overlapped pin tubes. In the heat recovery steam generator, a high temperature exhaust gas may flow through the outside of the cylinder, and a heat medium such as water or steam may pass through the inside of the cylinder.

Conventionally, in order to prevent corrosion of the heat recovery steam generator (HRSG) constituting the composite structure, a method of washing the tube using high pressure water at the top and collecting the corrosion products dropped off from the outlet, overlapping with the unevenness In the structure consisting of the washing water is difficult to be evenly sprayed, only loose corrosion of the surface directly in contact with the water is removed, even this is difficult to completely remove the exhaust was discharged to the outside along with the exhaust gas when operating the boiler. Accordingly, the corroded portion generates a continuous corrosion causing a lot of problems in the stable operation of the equipment.

On the other hand, the liquid additive composition or the solid additive according to the present invention may have an excellent corrosion protection effect by being in contact with the outer surface of the cylinder of the heat exchanger, in particular, the heat recovery steam generator having the uneven structure.

Specifically, the additive may be injected into the outer tube of the boiler or heat exchanger through a nozzle or the like. At this time, the injection pressure is not particularly limited and may be 10 kg / cm ^{2 or} more. At this pressure, the additive may be evenly sprayed on the uneven surface. The upper limit of the injection pressure may be 100 kg / cm ² .

In the present invention, the liquid additive composition or the solid additive may preferably be injected at the outlet of the gas turbine where the fuel is combusted. Since the steel structure (boiler and heat exchanger) used in the present invention is installed at the rear end of the gas turbine, it is possible to easily prevent corrosion of the steel structure by injecting a liquid additive composition or a solid additive at the outlet of the gas turbine.

In addition, the liquid additive composition or the solid additive of the present invention can be applied to the surface of a solid fuel such as coal to neutralize the sulfuric acid produced during the combustion of the solid fuel, thereby preventing scattering of the solid fuel, particularly coal.

In the present invention, by using a liquid additive composition or a solid additive, the corrosion product is neutralized and the base metal exposed on the surface is inhibited by a corrosion inhibitor, thereby ensuring the integrity of the outer surface exposed to the exhaust gas of the boiler using fossil fuel. Can be. Corrosion inhibitors of magnesium oxide in the form of a conventional slurry can be used in various structures, and the ionic phase is very advantageous in terms of cost by increasing the reactivity by using magnesium.

When the liquid additive composition or the solid additive is injected into the heavy oil power plant, the operating cost is reduced by 30% compared to the slurry type currently in operation, and the total savings of KRW 7.8 billion / year / three units can be achieved. As there are only 10 large boilers among domestic heavy oil power plants, it can save about 20 billion won, and in terms of chemical cost of additives used in coal-fired power plants, the annual drug consumption cost per unit reaches hundreds of millions of won. Since more than 50 units are operating on a boiler basis, annual chemical costs of about 30 billion won can be reduced by about 30%.

Figure 1 shows the main reaction zone where the neutralization reaction takes place on the tube surface of the heat exchanger.
Figure 2 shows the boiler tube outer surface slagging jang additive injection position.
3 shows a method for injecting a liquid additive composition according to the invention and injecting it into a boiler furnace.
Figure 4 shows a micrograph of the emulsification test results of the liquid additive composition prepared by the example.

The content of the present invention will be described in detail with reference to the following drawings.

In the present invention, Figure 1 shows the main reaction zone in which neutralization occurs in the tube surface of the heat exchanger.

Liquid additive composition containing magnesium ions is injected to remove the corrosion and various obstacles in the device caused by the corrosive substances contained in the exhaust gas generated by the combustion of fossil fuel, and the injection amount of the additive composition is to neutralize the corrosive substances. It should be the minimum amount necessary for the supply, and if the injection amount is large, the material price will rise and it will be discharged through the chimney, causing environmental pollution.

The liquid additive composition injected into the neutralizing material may be sprayed because it is mixed with a solvent. However, it is technically nearly impossible to continuously and evenly spray an additive through an area of 5 m in width and length (eg HRSG) of a tube of a heat exchanger having an uneven structure that is continuously operated. Expected technical difficulties are as follows.

As shown by the distribution of the flow field, the flow of exhaust gases is very stable. In a stable exhaust gas flow, the additive composition has very small particles (droplets), so that the momentum force caused by the particle injection is very small, so that the particles injected from the nozzles do not spread widely but are affected by the flow of the exhaust gas. To be scattered. Thus, the additive may not be evenly distributed into the HRSG.

At present, the number of nozzles must be increased to a large number to evenly distribute the injected additive composition. However, if the additive composition is sprayed in several nozzles, the amount of spraying per nozzle is so small that difficulty in distribution of the flow rate occurs, and the problems of increasing the cost and resistance of the exhaust gas flow due to the installation of the multiple nozzles Derived.

The neutralization zone can be divided into the previous stage of the heat exchanger zone, the zone in which the heat exchanger tube banks are located, or the zone where the two zones are combined. The most effective neutralization zone is the first stage reaction zone shown in FIG. . Corrosion in the heat exchanger tube group that is a problem in the first stage reaction zone can be prevented. However, the location where the spray nozzle can be installed is generally located close to the first stage reaction zone. It is difficult to obtain a smooth particle distribution in the first stage reaction zone under the stable state of exhaust gas flow.

In principle, the best way to solve this problem is to spray from a part far from the position of the first stage reaction zone (HRSG) to maximize the neutralization reaction in the first stage reaction zone. In this case, the contact time of the exhaust gas and the additive composition is also long, and since the flow of the exhaust gas is more complicated than the position where the nozzle is currently installed, it is determined that the diffusion effect of the particles is greater. It is determined that the best position is the rear end of the turbine, and when the neutralizing material (liquid additive composition) is injected into the rear end of the turbine, the neutralization reaction of the corrosive gas is promoted by smooth mixing with the exhaust gas.

Figure 2 is a view showing the injection position of the additive composition for preventing corrosion of the outer surface of the boiler tube, specifically the position where the additive is injected to neutralize the exhaust gas of the thermal boiler. If the injection position of the additive is low, the coating phenomenon occurs on the outer surface of the boiler tube near the flame. In FIG. 2, the exhaust gas flows along the flow, and a region where the adhesion rate of various foreign substances in the exhaust gas is high is indicated at a specific portion.

In addition, Figure 3 shows a method for injecting the additive composition according to the present invention by injection into a furnace of a boiler or a heat exchanger.

As shown in FIG. 3, the additive composition may be sprayed in various forms according to the type of nozzle, and the nozzle may be sprayed at a position away from the first stage reaction region (see FIG. 1).

Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples, but the scope of the present invention is not limited by the following examples.

Example 1

(1) Preparation of Liquid Additives Composition

20 parts by weight of magnesium ions, 10 parts by weight of Triton X100 (dispersant), 0.3 parts by weight of ascorbic acid (anticorrosive), 0.3 parts by weight of lauryl alcohol (emulsifier), 69.4 parts by weight of a solvent having a ratio of 8: 2 of water and alcohol To prepare a liquid additive composition.

An emulsion test apparatus was used to inject a predetermined concentration (500 ppm relative to fuel) of the prepared ionic magnesium compound, heavy oil, and water to test the properties of the emulsion formed.

The stability test of the samples tested in the emulsifying performance device was measured by the sedimentation rate method and the shape of the particles was observed under a microscope.

When the emulsifier concentration and the test method (sedimentation rate method) were the same, the performance of the emulsifier was confirmed to be maintained for 24 hours.

Figure 4 shows a micrograph of the sample tested in the emulsifying device.

Specifically, in FIG. 4, when the additive + heavy oil + water (ionic magnesium) uses the liquid additive prepared according to the above example as an additive, the additive + heavy oil + water uses a conventional additive (magnesium oxide instead of ionic magnesium). ), Heavy oil + water shows a micrograph of the result of emulsification test when no additive is used. As shown in FIG. 4, when the additive containing magnesium ions is used, it can be confirmed that the emulsification performance is excellent as compared with the case where the additive and the additive containing magnesium oxide are not used.

(2) manufacture of solid additives

10 parts by weight of the liquid additive composition prepared in (1) and 90 parts by weight of dry ice were mixed, followed by rapid freezing using a freeze drying method to prepare a solid additive.

The additives prepared above are sprayed on a structure with high unevenness to eliminate corrosion, and corrosion inhibitors and ionic magnesium compounds are deposited on the surface by evaporation of dry ice to protect the base metal and neutralize sulfur oxides to inhibit corrosion. .

Example 2.

Coal low coal in the coal loading station is coated with a solution containing 10 parts by weight of the liquid additive composition of Example 1 (1) on a predetermined amount surface (1 kg / m ² ), and a certain amount of additive is injected into the transfer line during coal transfer (1 kg / m ² ) to neutralize the sulfur oxides generated during coal combustion, and to prevent the scattering of coal dropped.

Claims (14)

Liquid additive composition containing magnesium ions, dispersants, preservatives, emulsifiers and solvents.
The method of claim 1,
Magnesium ion is a liquid additive composition that is included in the form of magnesium chloride or magnesium hydroxide.
The method of claim 1,
The dispersant is a liquid additive composition which is an anionic surfactant having 25 or more carbon atoms.
The method of claim 1,
The corrosion inhibitor is at least one liquid additive composition selected from the group consisting of hexadecylpyridinium compound, thiourea and triclosan.
The method of claim 1,
Emulsifier is at least one liquid additive composition selected from the group consisting of lauryl alcohol sulfate, sodium salt, oleic acid and glycerin.
The method of claim 1,
And the solvent is at least one liquid additive composition selected from the group consisting of water and alcohols.
The method of claim 1,
Liquid additive composition containing 10 to 30 parts by weight of magnesium ions, 5 to 20 parts by weight of dispersant, 0.01 to 1.0 part by weight of corrosion inhibitor, 0.01 to 1.0 part by weight of emulsifier, and 60 to 80 parts by weight of solvent, based on 100 parts by weight of the liquid additive composition. .
Liquid additive compositions containing magnesium ions, dispersants, preservatives, emulsifiers and solvents; And
Solid additives including dry ice.
The method of claim 8,
Solid additive comprising 1 to 20 parts by weight of the liquid additive composition and 80 to 99 parts by weight of dry ice with respect to 100 parts by weight of the solid additive.
A method of preventing corrosion of an iron structure comprising the step of contacting the additive composition according to claim 1 or the solid additive according to claim 8 with the steel structure.
11. The method of claim 10,
Steel structures are corrosion protection methods for steel structures that are heat exchangers or boilers.
11. The method of claim 10,
A method for preventing corrosion of steel structures by injecting a liquid additive composition or a solid additive into an outlet of a gas turbine where fuel is combusted.
11. The method of claim 10,
A method of preventing external corrosion of steel structures by applying a liquid additive composition or a solid additive to the steel structures at a pressure of 10 kg / cm ² or more.
A method of preventing scattering of coal, comprising applying the liquid additive composition according to claim 1 or the solid additive according to claim 8 on a surface of coal.

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