KR19980071934A - How to clean the superheater and reheater - Google Patents

Abstract

The present invention cleans the superheater and the reheater, which is the middle part of the power generation equipment, which performs physical cleaning through a finish steam blowing after chemical cleaning including a water washing process, a main washing process, a washing process, a neutralizing process, and a rust prevention process. This method is to reduce the construction cost by reducing the construction air compared to the conventional method of cleaning only by steam blowing, to minimize the noise pollution, and to reduce the metal oxide or It can minimize the amount of other foreign matter, minimize the risk of damage to the peripherals or human life, and can improve the performance of the power plant with excellent cleanliness.

Description

How to clean the superheater and reheater

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a power plant, and more particularly, to a method for chemically and physically cleaning a superheater and a reheater, which are intermediate parts of a newly installed power plant. In particular, in the present invention, the main purpose is the cleaning of the once-through boiler.

In order to prevent accidents during operation and to maximize operating efficiency, the power generation equipment should be thoroughly cleaned inside the equipment before starting normal operation. Oils, metal oxides, and other solid materials that are well known as foreign substances that exist inside the power plant that can reduce operating efficiency and cause accidents are well known.

Among them, oils and fats are bending oil, cutting oil, etc. which are buried in the manufacturing process of equipment, and rust preventive oil coated to prevent oxidation of metal which may occur during installation period. Metal oxides are polishing scales produced during iron material production. (mill scale) and rust generated during production, preservation and installation. Other solid foreign substances are mainly composed of soil, sand, welding residues and other foreign substances introduced during the preservation and installation process.

The power plant can be divided into four parts.

Water supply part: boiler supply water tank and line

Water pipe part: economizer, evaporator, boiler

Middle part: superheater, reheater, turbine

Multiple parts: condenser

Until now, only the water supply part, the water pipe part, and the plural parts have been targeted for chemical cleaning among the above-mentioned power generation equipment parts, and it has been understood that the superheater and the reheater, which are the middle parts, cannot be chemically cleaned. Therefore, when cleaning them, only the physical cleaning method using high pressure steam (hereinafter referred to as steam blowing) has been adopted.

However, it takes a long time to clean the superheater and reheater with cleanliness suitable for normal operation only by steam blowing, and as a result, construction air is delayed, a lot of manpower is required, and fuel consumption is large, resulting in a large construction cost.

In addition, the steam blowing is very noisy and the environmental problem is high due to the high noise. Therefore, it is difficult to resolve civil complaints of neighboring residents every time a power plant is constructed, and the workers involved in the construction work do not work normally during the steam blowing process. There is also a problem that can not be done. Steam blowing also releases metal oxides and other debris into the area surrounding the power plant, causing severe crop damage and even fatal hazards.

Another drawback of steam blowing is that dirt, dust, sand, construction materials and debris can be easily removed, but there is a problem that it is difficult to remove a firmly adhered grinding scale and rust.

Therefore, the present invention, in view of the above problems of the prior art, can reduce the construction cost by reducing the construction air, minimize the noise pollution, and minimize the amount of metal oxides or other foreign substances discharged to the surrounding area It is possible to minimize the risk of damage to the peripheral equipment, human life damage, etc., and to provide a method for cleaning the superheater and reheater, which is the middle part of the new power plant with excellent cleanliness and improved performance.

According to the present invention as a method for achieving the above object, in the cleaning of the superheater and reheater, which is an intermediate part of the power plant, a power plant characterized in that the finishing steam blowing after the chemical cleaning including the following processes further comprises: Methods of cleaning are provided:

(a) Flushing

This process is carried out to remove solid foreign matter that can be easily removed by washing with water, and hydrazine ( ) Administer 100 ~ 300ppm of solution.

(b) Main cleaning process

This process is carried out to remove metal oxides and fats and oils, one or two or more mixtures selected from the group consisting of citric acid, formic acid and hydroxyacetic acid (HAA), Alternatively, use a chemical cleaning solution consisting of tetraammonium EDTA or diammonium EDTA and a disintegrating agent, a surfactant, and a corrosion inhibitor.

(c) Rinsing

After the chemical cleaning solution used in the cleaning process is discharged, the washing process is performed, followed by rinsing with the hydrazine solution.

(d) Neutralization Preparation Process

Contains 0.1-0.3% citric acid.

(e) neutralization with ammonia water,

(f) Passivation

Contains 200-500 ppm of hydrazine.

After completion of this chemical cleaning, a limited finishing steam blowing is performed to further remove sediment or other remaining foreign matter during chemical cleaning, ensuring the cleanliness of medium-term parts such as superheater or reheater in the power plant.

Hereinafter, the present invention will be described in more detail.

The water washing step (a) of the chemical cleaning process of the present invention is carried out using a hydrazine solution, and this washing is preferably performed until the turbidity becomes 3.0 NTU or less. If the turbidity is high, pickling is affected, so it is necessary to perform turbidity below 3.0 NTU.

In this washing step (b), degreasing and degreasing are performed, wherein the chemical cleaning liquid used is one or two or more mixtures selected from the group consisting of citric acid, formic acid and HAA, or tetraammonium EATA and diammonium EDTA. One selected from the group consisting of is used.

Preferred is a mixture of 2-5% citric acid and 1-3% formic acid, 3-7% citric acid alone, or 2-5% citric acid and 1-3% HAA. Depending on the nature of the scale and the material of the equipment to be cleaned, the most preferred chemical cleaner is one selected from the group consisting of tetraammonium EDTA and diammonium EDTA (which may be selected instead of these organic acids).

In addition to the above components, the cleaning liquid may contain a degradable agent, an activator, a surfactant, a corrosion inhibitor, ammonium bifluoride, and sorbic acid as a reducing agent. .

In the present invention, another type of organic acid or inorganic acid may be used instead of the above organic acid, but according to the present cleaning process, the above kind is most preferably used.

This cleaning is suitable to be carried out in the temperature range of 80 ± 5 ℃, except in case of using tetraammonium EDTA, the temperature condition of 150 ℃ should be given.

In this cleaning process, pH, , The oil and fat concentration should be checked every hour. When the iron concentration reaches a certain level, this cleaning is considered to be finished.

In the washing process (c), the hydrazine solution is carried out using 100 to 300 ppm in order to suppress re-resurfacing. The temperature is preferably 50 ° C. or more, and is preferably carried out until the oil content concentration is 0 ppm and the turbidity is 3.0 NTU or less. Do.

Preliminary neutralization preparation step (d) is carried out using a 0.1 ~ 0.3% solution of the citric acid solution, the treatment temperature is 80 ± 5 ℃ is appropriate.

The neutralization step (e) is preferably carried out by neutralizing with ammonia water so that the pH is 9 to 10 and is appropriate when the temperature is about 80 ° C. The operation at this time is preferably a cyclic operation condition.

The antirust process (f) is the most desirable condition when hydrazine solution (around 0.05%) is used and sodium nitrite (Sodium Nitrite) ₂ ) can also be used.

When comparing the method of the present invention and the conventional steam blowing method for each item as follows.

(1) In terms of safety, the existing method is a serious problem of safety disaster during steam blowing period, but this method solves the problem of safety disaster.

(2) In noise, the existing method is difficult to promote normal work due to excessive noise. For example, the noise tolerance standard is less than 50㏈, but the existing method is very high, even with a silencer, 70-90㏈. On the other hand, according to this method, since the steam blowing is reduced by more than 80%, the noise pollution is solved.

(3) In terms of quality, it is impossible to completely remove the rust and scale inside the line during steam blowing, so that there is a high risk of damage to the equipment parts such as valves and turbine blades during normal operation.However, according to this method, hardenability that cannot be removed by steam blowing alone. It is also possible to remove and remove scales to prevent erosion damage during operation and to improve performance.

(4) In the working method, the existing method requires 17 ~ 18㎏ / ㎠ · G, high temperature above 200 ~ 300 ℃ (HPS), and a large amount of water is required, but low temperature work is possible in this method. And the water can be drastically reduced.

(5) In terms of damage, the existing method has inherent safety and damage factors, but this method has no damage factor, and is safe for materials such as carbon steel and SUS copper, guarantees corrosion resistance, and decomposes at high temperatures during operation. There is no influence.

(6) In the amount of steam, the existing method requires a large amount of high temperature and high pressure steam, but in the case of this method, some low temperature and low pressure steam is required for cleaning.

(7) In the working time, the existing method takes 20-30 days to clean. However, in this method, it is possible to shorten the air by 20-25 days per unit in 5-10 days.

(8) From an environmental point of view, this method can prevent civil noise caused by high noise by drastically reducing the number of steam blowing and the period, and prevent damages to nearby crops by iron oxide and foreign substances that can be discharged during steam blowing. It is possible to prevent the occurrence of the problem in advance, and noise generation is alleviated, so that the worker's hearing impairment is eliminated.

(9) From an economic point of view, if the middle part is chemically cleaned before steam blowing, it can save about 1 billion won per unit for the direct cost, which is fuel and pure cost of steam blowing, compared to steam blowing alone. .

Features and other advantages of the present invention as described above will become more apparent from the embodiments described below. However, the present invention is not limited to the following examples.

Example 1

The superheater (SH) and the reheater (RH) of the power plant shown in Table 2 below were chemically cleaned under the conditions shown in Table 1 below. The treatment period for each device is shown in Table 2 below.

TABLE 2

[Comparative Example]

The superheater (capacity about 90M ³ ) and reheater (capacity about 740M ³ ), which are the mid-term parts, were cleaned for the Taean Thermal Power Plant Units 1-4 using only the steam blowing method. Steam blowing periods and costs are shown in Table 3 below.

division unit Unit 1 Unit 2 Unit 3 Unit 4 Total days Work 34 37 31 27 Total Blows time 49 52 45 38 Total net usage ton 42,535 40,335 37,382 26,224 Average net water consumption ton / time 868 775 830.7 690.1 Total fuel usage ℓ 4,167,967 3,542,316 3,184,768 2,656,533 Average fuel consumption ℓ / time 85,060 68,121 70,773 69,909 ^* Fuel Cost + Pure Water Cost 1000 won 2,486,833 2,116,264 1,903,386 1,584,452

* 1998. 4. Unit price: Pure water = 652 won per ton, Fuel = 590 won per liter

Example 2

Using the same chemical cleaning method as in Example 1, the superheater (capacity about 90M ³ ) and the reheater (capacity about 740M ³ ), which are the mid-term parts, of the Taean Thermal Power Plant No. 4 and the generator of the same model were cleaned.

The average chemical cleaning unit price was 1.5 million won per M ³ , 1,110,000 (1,000 won) for the entire 740M ³ , and at least 1.5 times more than that of Comparative Example 2, resulting in cost savings.

As described above, according to the present invention, when the chemical cleaning is performed in parallel, as compared to the case of performing the pre-cleaning process only by steam blowing as in the past, the problem that is greatly reduced can be greatly reduced and excellent quality without damage to the base material. As it is guaranteed, corrosion factors of power generation facilities can be reduced and operation efficiency can be maximized.

Claims (3)

In the cleaning of the superheater and the reheater, the steam part of the power plant, a cleaning method characterized by further performing a finish steam blowing after chemical cleaning comprising the following steps: (a) Flushing Solid foreign material removal process, hydrazine (to prevent rust prevention) ) Administer 100 ~ 300ppm of solution. (b) Main cleaning process Degreasing and degreasing processes; One or two or more mixtures selected from the group consisting of citric acid, formic acid, and hydroxyacetic acid (HA), tetraammonium EDTA or diammonium EDTA and disintegrating agents, surfactants, and corrosion inhibitors. Main cleaning by chemical cleaning solution consisting of, (c) Rinsing After flushing the chemical cleaning liquid used in this cleaning, this washing process is performed and rinsing with hydrazine solution is performed. (d) Neutralization Preparation Process Contains 0.1-0.3% citric acid. (e) neutralization with ammonia water, (f) passivation, Sodium Nitrite containing 200-500ppm of hydrazine ₂ ) can also be used. The cleaning method according to claim 1, wherein the chemical cleaning liquid of the main cleaning step (b) contains one or two or more mixtures selected from the group consisting of an activator, ammonium fluoride and sorbic acid. The chemical cleaning solution according to claim 1, wherein the chemical cleaning liquid of the main cleaning step (b) is a mixture of 2 to 5% citric acid and 1 to 3% formic acid, 3 to 7% citric acid alone, or 2 to 5% citric acid A washing method comprising one selected from the group consisting of a mixed acid of 3% hydroxyacetic acid, mixed acid of formic acid 1-3% and 1-3% hydroxyacetic acid, tetraammonium EDTA or diammonium EDTA .