JPS5933837B2 - 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 conventional removal methods of this type by using a special cleaning liquid. Concerning improvements in removal methods.

The outer surfaces of boilers, heat exchangers, etc. in 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 due to the deterioration of fuel oil, causing problems such as blockage of superheater gas passages and high-temperature corrosion of tube support fittings. The deposits on the outside of the superheater tubes were removed by the water washing method shown in Table 1.

Figure 1 shows this water washing system together with an overview of the boiler, where 1 is a burner, 2 is a furnace water wall, 3 is a superheater, 4 is an evaporator tube, 5 is a steam drum, 6 is a water drum, and 7 is a It is a energy saver.

In Figure 1, the cleaning system is 9/c from 100 to 120.
1? L high pressure jet cleaning system and 3~5kg/CI?
Two systems of T's fresh water spray cleaning system can be used.

In the jet cleaning system, fresh 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 a low-pressure fresh water spray cleaning system, fresh water is supplied to pump 1.
Water is fed to the hose 13 at a low pressure from 0, and is sprayed from a spray nozzle 14 attached to the end of the hose to the superheater 3, moistening and softening 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.

The cleaning methods using these two systems are as shown in Table 1.
As a process, the first jet cleaning is performed using a jet cleaning system to remove soot-like and soft deposits, and in the second step, fresh water spray cleaning is performed using a spray cleaning system.
The remaining deposits are moistened and softened, and in the second step, the moistened and softened deposits are removed by a second jet cleaning.

Further, the deposits not removed in the first to (2) steps are removed in the (2) step using a hand tool such as an air hammer or a chisel.

The conventional method operated in this manner has the following drawbacks.

1) Since most of the deposits on the outer surface of superheater tubes where the steam temperature is about 400° C. or lower are soft porous and mainly composed of Na2SO4, they can be removed by washing for a long time using only the conventional water washing method.

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 step (2), the remaining deposits are removed using hand tools such as an air hammer or a chisel, which requires a large number of man-hours.

2) In the conventional method, the amount of waste liquid is large because it takes a long time especially for the clean water spray cleaning in step ①, and these waste liquids have a pH of about 2 to 5 due to the dissolution of compounds such as S and ② in the deposits. It is weakly acidic and contains pollutants, so it 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.

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

As a result of numerous experimental studies in order to eliminate the drawbacks of the above-mentioned conventional method, the present inventors have discovered that instead of the fresh water spray cleaning, which is the step (1) of the above-mentioned conventional method, a spray using a cleaning solution containing a chemical solution of a specific composition has been developed. By doing this, wetting, softening,
Scales that are difficult to remove are dissolved and powdered in a short period of time, making the use of air hammers, chisels, etc. in step ① of the conventional method unnecessary, and reducing the amount of waste liquid generated. It was confirmed that 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 soft deposits, and then For the deposits remaining on the heat transfer surface, spray a cleaning solution containing hydrogen peroxide and ammonium chloride to dissolve the deposits or turn them into powder and fine pieces. Then, jet cleaning with high-pressure water is performed to remove the powder and fine pieces. The gist of this paper is a method for removing deposits from boilers, heat exchangers, etc., which is characterized by removing fragmented residual deposits.

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 The chemical cleaning solution for removing deposits is formulated so that two types, hydrogen peroxide and ammonium chloride, can be used together.

Also, the concentration is such that it contains 0.5 to 10 parts of hydrogen peroxide and 1 to 10 parts of ammonium chloride.

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 component is contained in a ratio of 10 or more, no significant effect on dissolving or pulverizing deposits can be obtained, which is not preferable from an economical point of view.

2) Operating temperature: 20 to 40°C As the temperature rises, the reaction of dissolving and powdering the deposits becomes faster, but on the other hand, the corrosion of the steel surface increases, a heat source is required for heating, and the generated steam makes workability difficult. The temperature is preferably 200C or more and 40C or less, since problems such as deterioration of the temperature may occur.

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

The components of the deposits are Na, S, V, Fe, Ni, etc., and the combination state is that in water-soluble deposits, the main component is Na2SO4, and in the deposits that are difficult to dissolve in water, the main component is Na10 V24064
ffNa2O-v2o4. ”V2O5,I'Ja
o, 33v2o5, Na-V- such as NaV6O13
Among the CJ-based compounds, the proportions of Fe and Ni-based compounds are also higher than in the case of water-soluble deposits.

The action of the cleaning liquid consisting of hydrogen peroxide and ammonium chloride used in the present invention to dissolve and powderize the above-mentioned external surface deposits is 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.

During this process, the deposits are decomposed and powdered due to the volume change due to oxidation and the gas pressure of oxygen generated on the surface of the deposits, and most deposits contain some water-soluble components, although there are differences in degree. As a result, the liquid gradually penetrates and the deposits are washed and removed.

In addition, ammonium chloride is an acidic salt and the aqueous solution has a pH of 4 to 5.
However, 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 the corresponding acids, causing Na-
-Acts on 〇-based compounds and oxides such as Fe, Ni, etc., and dissolves the deposits. Combined with the above-mentioned decomposition and pulverization effect of hydrogen peroxide alone on the deposits, the deposits are dissolved, pulverized, and removed. It is considered that the

As a result, according to the present invention, the following effects can be achieved.

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

2) Therefore, since the undesired substances remaining after cleaning with the cleaning solution of the present invention are powdered and fragmented, they can be easily removed by high-pressure water cleaning, which can significantly shorten the working time and reduce the number of man-hours. .

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

4) It is preferable from the standpoint of safety and health for the workers, as it is not necessary to use hand tools such as hammers and chisels in a poorly ventilated furnace where dust is generated, and the surface to be cleaned does not get scratched.

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 pump 17 through the valve 18 to the low-pressure pump 19 to the hose 20, guided to the gas side and inside of the superheater 3, and then from the spray nozzle 22 attached to the header 21 at the top thereof. It is sprayed into the superheater 3 and melts the deposits into powder and pieces in a short time.

The parts indicated by broken lines are used to circulate the chemical cleaning liquid of the present invention in order to make effective use of it, and 23 is a concentrated cleaning liquid injection line, and 24 is a cleaning liquid recovery line.

Next, experimental examples and examples of the present invention will be given.

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

The test method was to determine whether the mass of deposits on the outer surface of a marine boiler superheater tube was 2.0.
~2.2 g was accurately weighed, placed in a polyethylene net with 12 meshes, and immersed in a beaker containing 100 TL of liquid.

After being left 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 dissolved 94 to 100 percent of deposits A to C.

In addition, there are hardly soluble deposits that dissolve in water at a rate of 10% or less, and 35 to 60% of deposits are dissolved in E, 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.

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 parts of hydrogen peroxide, the dissolution rate is 49 parts for deposit B and 28 parts for deposit E, but since all the deposits remaining on the polyethylene net are brittle due to oxidation and cracking, It can be almost removed by washing with high-pressure water after the chemical washing according to the invention method.

However, concentrations lower than this are not practical because the dissolution rate is poor and chemical cleaning requires a long time.

Furthermore, even if hydrogen peroxide or ammonium chloride is contained in amounts of 10 parts or more, no significant effect is observed, and therefore higher concentrations are not preferred from an economical point of view.

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.

In the conventional method shown in Table 1, it took 10 to 70 hours to spray clean water in step ① and the amount of waste liquid was 20 to 200 m'', but if spray cleaning is performed using the chemical cleaning solution of the method of the present invention, The cleaning time is 5 hours, and the amount of waste liquid is 1 ion.
”, and can be further reduced by using a circulating system.

Furthermore, since most of the deposits are dissolved and powdered by the chemical cleaning solution spray cleaning of the present invention, the work of removing the remaining deposits in step (2) of Table 1, which was performed in the conventional method, is no longer necessary.

In the end, the cleaning method of the present invention reduces the amount of waste liquid to 1.
/2 to 1/40, and the required number of days was reduced by 1 field from 3 to 7 days in the conventional method.

[Brief explanation of the drawing]

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.

Claims (1)

[Claims] 1 Heat transfer surfaces of boilers, heat exchangers, etc. are first jet-cleaned using high-pressure water to remove soot-like deposits and soft deposits, and then peroxide is applied to the deposits remaining on the heat transfer surfaces. After spraying a cleaning solution containing hydrogen and ammonium chloride to dissolve the deposits or turn them into powder or pieces,
A method for removing deposits from boilers, heat exchangers, etc., which further includes jet cleaning with high-pressure water to remove residual deposits in the form of powder and fragments.