JPS6012559B2 - How to remove deposits from boilers, heat exchangers, etc. - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for removing deposits from boilers, heat exchangers, etc., which solves the drawbacks of this type of removal method by using a special cleaning liquid. This invention relates to improvements in removal methods.

BACKGROUND OF THE INVENTION The outer surfaces of boilers, heat exchangers, etc. of thermal power plants and other steam generation plants are contaminated by ash adhering to combustion gas. In particular, the outer surface of superheater tubes in large marine boilers is heavily contaminated with adhering ash as the fuel oil deteriorates, causing problems such as blockage of superheater gas passages and high-temperature corrosion of tube support fittings. Generally, deposits on the outer surface of superheater tubes are removed by the water washing method shown in Table 1. Table 1 Note) The values in the table are based on the case where deposits on the outside surface of the boiler superheater tube of a 200,000 ton class tanker are removed using the water washing method.
That's a can.

Fig. 1 shows this water washing system together with an outline of the boiler. 1 is a burner, 2 is a furnace water wall, 3 is a superheater, 4 is an evaporator tube, 6 is a steam drum, 6 is a water drum, and 7 is a It is a muscle charcoal machine.

In FIG. 1, two cleaning systems are available: a high-pressure jet cleaning system with a capacity of 100 to 120 k9/ground and a fresh water spray cleaning system with a capacity of 3 to 5 k9/ground.

In the jet cleaning system, clean water for cleaning in a tank 8 installed on the upper deck passes through a valve 9 and is sent from a pump 10 to a hose 11 at high pressure, and from a jet cleaning nozzle 12 attached to the tip of the high-pressure hose to a superheater. 3, and removes deposits with high-pressure jet cleaning. On the other hand, in the low-pressure fresh water spray cleaning system, fresh water is sent from the pump 10 to the hose 13 at a low pressure, and is sprayed from the spray nozzle 14 attached to the end of the hose to the superheater 3 to moisten and soften deposits. Further, the cleaning waste liquid from these two systems is stored in an outboard tank 16 via a hose 15 from the drain of the furnace. In the cleaning method using these two systems, as shown in Table 1, the first step is to perform the first jet cleaning using the jet cleaning system to remove soot and dirt deposits.
In the b-th step, fresh water spray cleaning is performed in a spray cleaning system to moisten and soften the remaining deposits, and in the m-th step, the moistened and softened deposits are removed by a second jet cleaning.
Further, the deposits not removed in the first to mth steps are removed in the sickle W step using a hand tool such as a pneumatic hammer or a chisel. The conventional method operated in this manner has the following drawbacks.

Since most of the deposits on the outer surface of the superheater tube with a '1' steam temperature of about 400 qo or less are soft porous and mainly composed of Na2S04, they can be removed by the conventional water washing method or by long-term washing.

However, the components adhering to the high temperature area above about 400℃ are V, Fe,
Since the deposited layer is dense and contains a large amount of Ni-based compounds, it is almost impossible to remove the deposits using the conventional method even if cleaning is performed for a long time. Therefore, in the W step, the remaining deposits are removed using a hand tool such as an air hammer or a chisel, which requires a large number of man-hours. ■ In the conventional method, the amount of waste liquid is large because it takes a long time, especially for clean water spray cleaning in the 0th step.
It has a weak acidity of about 5.5 and contains pollutants, and requires treatment such as sedimentation and separation after neutralization, but the cost is high because the amount of waste liquid to be treated is large.

'31 Working with hand tools such as air hammers and chisels inside the furnace causes problems such as the generation of dust and poor ventilation, which is a health issue for the workers and damages the outer surface of the pipes, so maintenance is important. undesirable.

As a result of numerous experimental studies to eliminate the drawbacks of the conventional method, the present inventors have discovered that instead of the clean water spray cleaning, which is the 0th step of the conventional method, spraying with a cleaning solution containing a chemical solution of a specific composition has been carried out. By doing this, wetting, softening,
The scale dissolves and powders the deposits that are difficult to remove in a short time, making the use of air hammers, chisels, etc. in Step W of the conventional method unnecessary, and reducing the amount of waste liquid generated. It was confirmed that the scales were reduced.

The present invention was completed based on the above knowledge, and the heat transfer surfaces of boilers, heat exchangers, etc. are first jet-cleaned using high-pressure water to remove soot-like deposits and foreign deposits. Next, the deposits remaining on the heat transfer surface are treated with hydrogen peroxide,
It is characterized by spraying a cleaning solution containing ammonium nitrate and ammonium chloride to dissolve the deposits or turning them into powder and pieces, and then jet washing with high-pressure water to remove the remaining deposits that have turned into powder and pieces. The gist of this article is a method for removing deposits from boilers, heat exchangers, etc.

The present invention is applicable to boilers such as thermal power plants and chemical plants.
It can be applied to a method for cleaning deposits on heat exchangers, etc.

Hereinafter, the composition of the cleaning liquid of the present invention and the temperature at which the cleaning liquid is used will be further explained in detail.

'1' Combination and Concentration Range of Cleaning Solution As a chemical cleaning solution for removing deposits, hydrogen peroxide, ammonium nitrate, and ammonium chloride are mixed so that they can be used together.

The concentration is such that hydrogen peroxide is 0.5 to 10%, ammonium nitrate is 1 to 10%, and ammonium chloride is 1 to 10%. A concentration lower than this requires a long time for cleaning and is not practical from a work standpoint. On the other hand, even if each of them is contained in an amount of 10% or more, no significant effect on dissolving or pulverizing deposits can be obtained, which is not preferable from an economic point of view. [2] If the operating temperature is 20 to 40 mm, the melting of deposits and powdering reaction will be delayed, but on the other hand, the corrosion of the steel surface will increase, a heat source for heating will be required, and the generated steam will Since problems such as poor workability occur, the temperature is preferably 20°C or higher and 4 pi or lower.

Next, the action of the cleaning liquid used in the present invention will be explained.

The components of deposits are Na, S, V, Fe, Ni, etc., and their combination state is Na2S04 as the main component in water-repellent deposits, and Na as the main component in deposits that are difficult to dissolve in water.

V240 lost, N also ○, V204, V205, N too. Sword V
Na-V-○ type compounds such as 205・NaV60,5,
The proportions of Fe and Ni-based compounds are also higher than in the case of water-soluble deposits. The dissolving and pulverizing effects of the cleaning liquid comprising hydrogen peroxide, ammonium nitrate, and ammonium chloride used in the present invention on the above-mentioned deposits can be considered as follows. Hydrogen peroxide strongly oxidizes deposits to the maximum oxidation state, while decomposing them while actively generating oxygen on the surface of the deposits.

In this process, the deposits are decomposed and powdered due to the volume change due to oxidation and the oxygen gas pressure generated on the surface of the deposits.
Furthermore, since most of the deposits contain some water-soluble components, although the degree may vary, as a result of these, the liquid gradually penetrates and the deposits are washed and removed. In addition, ammonium nitrate and ammonium chloride can be used to purge aqueous solutions with acid salts.
Although it is made weakly acidic such as H4-5, an aqueous solution containing only these salts has almost no dissolving effect on deposits. However, in the coexistence of hydrogen peroxide, which is a strong oxidizing agent, these acid salts act as corresponding acids on Na-V-○ compounds and oxides such as Fe and Ni in the deposits, causing the deposits to deteriorate. As the dissolution of hydrogen peroxide progresses, the aforementioned hydrogen peroxide alone decomposes the deposits,
It is thought that together with the powdering action, the deposits are dissolved, powdered, and removed. As a result, according to the present invention, the following effects can be achieved.

'1' Using an aqueous solution containing hydrogen peroxide, ammonium nitrate, and ammonium chloride, deposits can be dissolved and powdered in a small amount of liquid in a short time.

{21 Therefore, since the remaining deposits after cleaning with the cleaning solution of the present invention are powdered and fragmented, they can be easily removed by high-pressure water cleaning, and the work time and man-hours can be reduced significantly. .

{3' Since the amount of washing waste liquid is small, the cost of waste liquid treatment such as neutralization, sedimentation, and separation is low.

■ It is preferable from the safety and health standpoint of the workers because it is not necessary to carry out manual work using hammers, chisels, etc. in a dusty furnace with poor ventilation, and no tin is produced on the surfaces to be cleaned.

FIG. 2 shows a chemical cleaning system using a chemical cleaning solution used in the method of the present invention. In Figure 2, 1 to 7 are boiler components, 8 to 12 are high-pressure water jet cleaning systems, and 15 to 16 are cleaning waste liquid lines, which are the same as in Figure 1 above. However, in FIG. 2, the chemical cleaning solution spray cleaning system of the present invention is installed in place of the conventional clean water spray cleaning system.

That is, the chemical cleaning solution of the present invention is sent from the tank 17 through the valve 18 to the low pressure pump 19 through the hose 201, and then to the superheater 3.
is guided to the gas side and inside of the superheater 3 from a spray nozzle 22 attached to the header 21 at the top thereof,
Dissolves deposits into powder and pieces in a short time. The parts indicated by broken lines are used to circulate the chemical cleaning solution of the present invention in order to make effective use of it, and 23 is the injection line for the concentrated cleaning solution, and 24 is the recovery line for the cleaning solution. Next, experimental examples and examples of the present invention will be given.

Experimental Example 1 Table 2 shows examples of the results of the dissolution test of the chemical cleaning liquid used in the method of the present invention, together with the results of the dissolution test of water.

The test method is to determine the amount of deposits on the outer surface of marine boiler superheater tubes 2.0
~2.2 Weigh out the solution, place it in a polyethylene net with a 12-mesh mesh, and immerse it in a beaker containing 100ml of liquid. Immediately after leaving it at room temperature for 5 hours, the deposits remaining on the polyethylene net were dried at 110°C, and the amount dissolved was determined from the difference in weight before and after the test. As can be seen from Table 2, the chemical cleaning solution used in the method of the present invention has deposits A to C of 90 to 1
00% dissolved.

In addition, 50 to 85% of the brood-soluble deposits D and E, which dissolve in water at a rate of 10% or less, are dissolved, and the deposits remaining on the polyethylene net are quite brittle, so they can be easily washed with high-pressure water. Can be fragmented and removed. Table 2 Note: Deposits A to E were separated from the outer surface of the boiler superheater tubes of five 200,000 ton class tankers.

Experimental Example 2 Table 3 shows an experimental example in which changes in dissolution rate were investigated by varying the concentration of the chemical cleaning solution used in the method of the present invention.

In the case of 0.5% hydrogen peroxide, 1% ammonium nitrate, and 1% ammonium chloride, the dissolution rate is 75% for deposit B and 30% for deposit E, but all deposits remaining on the polyethylene net are oxidized. Even if it cracks or cracks,
It can be almost removed by washing with high-pressure water after the chemical washing according to the method of the present invention. However, concentrations lower than this are not practical because the dissolution rate is poor and chemical cleaning requires a long time. Moreover, no significant effect is observed even if the content exceeds 10% hydrogen peroxide, 10% ammonium nitrate, and 10% ammonium chloride, so higher concentrations are not preferred from an economic standpoint.

Table 3 Note) Deposits B and E are the same as in Experimental Example 1.

Table 4 of Examples shows the deposit removal process when spray cleaning was performed using a chemical cleaning solution according to the present invention instead of the conventional clear water spray cleaning. Table 4 Note) The values in the table are for the case where deposits on the outer surface of the boiler superheater tube of a 200,000 ton class tanker are removed by the method of the present invention, and the values in the table are for one can.

The composition of the chemical cleaning solution is an aqueous solution at room temperature containing 3% hydrogen peroxide, 5% ammonium nitrate, and 5% ammonium chloride. In the conventional method shown in Table 1, it took 10 to 7 hours for clean water spray cleaning in step D, and the amount of waste liquid was 20 to 200 g. , the cleaning time is 5 hours, and the amount of waste liquid is 10 hours even with a 1-pass method.
This can be reduced further by using a circulating system.

In addition, since the deposits are thoroughly dissolved and powdered by spray cleaning with the chemical cleaning solution of the present invention, the removal of remaining deposits in step W in Table 1, which was performed in the conventional method, is no longer necessary. Ta. In the end, with the cleaning method of the present invention, the amount of waste liquid was reduced to 1/40 of the conventional method, and the required number of days was reduced from 3 to 7 days of the conventional method to 1 day.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a water washing system according to a conventional method together with an outline of a boiler, and FIG. 2 is an explanatory diagram showing a chemical cleaning system according to the present invention together with an outline of a boiler. Figure 1 Figure 2

Claims (1)

[Claims] 1 Heat transfer surfaces of boilers, heat exchangers, etc. are first jet-cleaned with high-pressure water to remove soot-like deposits and soft deposits, and then any deposits remaining on the heat transfer surfaces are cleaned with excess water. Spray a cleaning solution containing hydrogen oxide, ammonium nitrate, and ammonium chloride to dissolve deposits or remove powder.
A method for removing deposits from boilers, heat exchangers, etc., characterized in that after fragmentation, jet cleaning is performed using high-pressure water to remove powder and fragmented residual deposits.