WO2016139837A1

WO2016139837A1 - Method for cleaning furnace wall tube of once-through boiler

Info

Publication number: WO2016139837A1
Application number: PCT/JP2015/078193
Authority: WO
Inventors: 馬渡　憲次; 宏樹大久保; 翔下田
Original assignee: 三菱日立パワーシステムズ株式会社
Priority date: 2015-03-04
Filing date: 2015-10-05
Publication date: 2016-09-09
Also published as: JP6363037B2; TWI593929B; CN107208879B; SG11201706388PA; CN107208879A; JP2016161255A; TW201636557A

Abstract

Provided is a method for cleaning a furnace wall tube (5) of a once-through boiler in a water supply system in which oxygen treatment is applied, wherein the method for cleaning a furnace wall tube (5) of a once-through boiler involves chemical cleaning to selectively remove powder scale (PS), which has lower thermal conductivity than does self-oxidizing scale (HS), the self-oxidizing scale (HS) and powder scale (PS) having been produced on the inner surface of the furnace wall tube (5).

Description

Cleaning method of furnace wall tube of once-through boiler

The present disclosure relates to a method of cleaning a furnace wall tube of a once-through boiler.

In a thermal power generation system in which oxygen treatment is applied to a boiler water supply system, an event occurs in which the metal temperature of the furnace wall tube of the once-through boiler rises, and the occurrence of boiler water leakage due to furnace wall tube breakage becomes a problem. When the metal temperature of the furnace wall tube rises, iron elutes from the low pressure feed water heater drain system or the piping of the water supply system to form hematite (Fe ₂ O ₃ ), and hematite adheres and deposits on the inner surface of the furnace wall tube. The cause is that the heat conduction is deteriorated (hereinafter, hematite is referred to as powder scale due to its property).

In order to prevent the above-mentioned leak nonconformity of the furnace wall pipe, chemical cleaning of the furnace wall pipe is regularly performed to completely remove the scale made of iron-based oxide deposited on the inner surface of the pipe.

For example, Patent Document 1 discloses chemical cleaning comprising an acid cleaning step of dissolving and removing scale with an acid (inorganic acid or organic acid), a subsequent water cleaning step, and a subsequent rustproofing step. There is. In the acid washing step, the acid solution is circulated to the boiler.

Further, for example, Patent Document 2 discloses a method of cleaning a natural circulation drum type boiler having a coal saving device, a furnace and a heater. In such a cleaning method, after a cleaning liquid to which a dispersant is added is injected from the cleaning system temporarily installed in the economizer excluding the heater and the boiler including the furnace into the boiler, it is not possible to hold the cleaning liquid in the boiler. Bubbling by injecting an active gas.

Further, for example, Patent Document 3 discloses a powder scale discharge method including a water filling step, a pressing step, and a pressure reducing step. The water filling step is a step of supplying water to the space to be cleaned, such as an evaporation pipe, with the cleaning fluid into which the microbubbles have been introduced, for water filling. In the pressurizing step, after leaving the state of the water filling step for a predetermined time, the cleaning fluid pressure in the closed space is increased to increase the cleaning fluid pressure, thereby contracting the microbubbles in the cleaning fluid to achieve relative Small micro bubbles and nano bubbles. The depressurization step is to expand the bubbles in the cleaning fluid in the form of relatively small microbubbles and nanobubbles by contracting in the pressurization step.

JP 2012-24735 A JP-A-8-105602 JP, 2014-142154, A

The methods disclosed in Patent Documents 1 to 3 require a long time to clean the inner surface of the furnace wall tube, which increases the construction cost and extends the construction period.

In view of the above-described circumstances, at least one embodiment of the present invention aims to provide a method of cleaning a furnace wall tube of a once-through boiler capable of shortening the cleaning time.

(1) A method of cleaning a furnace wall tube of a once-through boiler according to at least one embodiment of the present invention,
A method for cleaning a furnace wall tube of a once-through boiler, wherein oxygen treatment is applied to a water supply system,
Of the autoxidized scale and the powder scale formed on the inner surface of the furnace wall tube, the powder scale having a thermal conductivity lower than that of the autoxidized scale is selectively removed by chemical cleaning.

As a result of studies by the present inventors, in the cleaning methods disclosed in Patent Documents 1 and 2, it is necessary to clean for a long time in order to remove all the scale formed on the inner surface of the furnace wall tube, and the construction cost is high. It has been found that not only the construction period is extended, but also the inner surface of the furnace wall pipe may be damaged. On the other hand, in the cleaning method disclosed in the patent document, pure water supplied with microbubbles is used as the cleaning fluid, but the pressure of the working fluid is pressurized from the normal pressure state and boosted, while the boosted pressure is reduced. It has been found that the pressure must be lowered to make efficient cleaning difficult.

In this respect, according to the above method (1), among the autoxidized scale and the powder scale generated on the inner surface of the furnace wall tube, the powder scale having a thermal conductivity lower than that of the autoxidized scale is selectively removed by chemical cleaning. Therefore, the cleaning time can be shortened compared to the case of removing all of the autoxidized scale and the powder scale as in the prior art. In addition, since the autoxidized scale is not removed, the cleaning solution will not damage the inner surface of the furnace wall tube.

(2) In some embodiments, in the method of (1) above,
A cleaning test step for determining cleaning conditions of the chemical cleaning for selectively removing the powder scale;
And the washing step of selectively removing the powder scale under the washing conditions determined in the washing test step.

As a result of studies by the present inventors, acid cleaning and chelate cleaning are effective for chemical cleaning, but when the cleaning conditions are high concentration, the cleaning temperature conditions are high temperatures, and the cleaning time conditions are long, the cleaning power is It is too strong to partially damage the self-oxidizing scale, and there are concerns about heat transfer inhibition due to floating of the self-oxidizing scale and corrosion due to the cleaning liquid remaining on the floating portion.

In this respect, according to the method (2) described above, chemical cleaning conditions for selectively removing the powder scale are determined, and the powder scale is selectively removed under the determined cleaning conditions. It is possible to efficiently select and remove powder scale that has lower thermal conductivity than a self-oxidizing scale.

(3) In some embodiments, in the method of (2) above,
The cleaning conditions include at least one of a cleaning solution composition condition, a cleaning solution concentration condition, a cleaning temperature condition, and a cleaning time condition.

According to the method of the above (3), since the washing conditions include at least one of the washing liquid composition conditions, the washing liquid concentration conditions, the washing temperature conditions or the washing time conditions, the thermal conductivity is higher than that of the self-oxidizing scale under appropriate washing conditions. Powder scale can be selected and removed efficiently.

(4) In some embodiments, in the method of (2) or (3) above,
The cleaning test process chemically cleans a test body constituted by a part of the furnace wall tube of the once-through boiler to be cleaned or a sample imitating the furnace wall tube, and the cleaning condition is capable of selectively removing the powder scale. Ask for

According to the above method (4), a test body constituted by a part of the furnace wall tube of the once-through boiler to be cleaned or a sample imitating the furnace wall tube can be chemically cleaned to selectively remove the powder scale. Since the cleaning conditions are determined, the cleaning conditions suitable for each of the flow-through boilers having different operating environments can be determined.

(5) In some embodiments, in the method of (4) above,
In the washing test step, the particle concentration in the washing liquid used for chemical washing of the test body is monitored to determine the completion timing of the selective removal of the powder scale, and the washing condition is determined based on the completion timing. .

According to the above method (5), the particle concentration in the washing liquid used for chemical washing of the test body is monitored to determine the completion timing of the selective removal of the powder scale, and the washing condition is determined based on the completion timing. Therefore, the washing conditions can be determined qualitatively.

(6) In some embodiments, in the method of (5) above,
In the cleaning test step, the timing at which the increase rate of the particle concentration is less than a threshold is defined as the completion timing.

According to the method of (6) above, the timing at which the rate of increase of the particle concentration is less than the threshold is taken as the completion timing, so that the washing conditions can be determined quantitatively.

According to at least one embodiment of the present invention, there is provided a method of cleaning a furnace wall tube of a once-through boiler capable of shortening the cleaning time.

It is a conceptual diagram which shows schematic structure of the thermal-power-generation plant by which oxygen treatment is applied to a boiler feed water system. It is a conceptual diagram which shows the state which installed the washing | cleaning circulation path | route in the thermal-power-generation plant shown in FIG. It is a schematic diagram which shows the outline of the furnace wall pipe which the scale adhered and deposited on the inner surface. It is the figure which showed the relationship between the thickness of a scale, and metal temperature. It is a figure showing the relation between the operation time of the once-through boiler and the thickness of the autoxidation scale. It is a conceptual diagram which shows the presumed structure of the furnace wall pipe of the once-through boiler in which the self-oxidation scale and the powder scale were produced | generated on the inner surface. It is a figure which shows the washing | cleaning conditions which can selectively remove a powder scale. It is a conceptual diagram which shows the outline of the washing | cleaning test apparatus which calculates | requires the washing | cleaning conditions which can selectively remove a powder scale. It is a figure which shows the relationship between the washing | cleaning time and the increase rate of particle concentration and particle concentration in a washing | cleaning liquid.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as the embodiments or shown in the drawings are not intended to limit the scope of the present invention to this, but are merely illustrative. Absent.

For example, a representation representing a relative or absolute arrangement such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” is strictly Not only does it represent such an arrangement, but also represents a state of relative displacement with an angle or distance that allows the same function to be obtained.

Further, for example, the expression expressing a shape such as a quadrilateral shape or a cylindrical shape not only represents a shape such as a rectangular shape or a cylindrical shape in a geometrically strict sense, but also an uneven portion The shape including a chamfer etc. shall also be expressed.

On the other hand, the expressions "comprising", "having", "having", "including" or "having" one component are not exclusive expressions excluding the presence of other components.

FIG. 1 is a conceptual view showing a schematic configuration of a thermal power plant 1 to which oxygen treatment is applied to a boiler water supply system.

The method of cleaning the furnace wall tube 5 of the once-through boiler according to at least one embodiment of the present invention is a method of cleaning the furnace wall tube 5 of the once-through boiler in which oxygen treatment is applied to the water supply system.

As shown in FIG. 1, the thermal power plant 1 to which oxygen treatment is applied to the boiler water supply system includes a turbine condenser 11, a condensate pump 12, a condensate processing unit 13, a condensate pressure pump 14, and a low pressure feedwater heater 15. The deaerator 16, the boiler feed pump 17, the high pressure feed heater 18, the furnace economizer 19, the super heater 20, and the reheater 21 are provided. The furnace economizer 19 includes an economizer 22, a furnace 23, a gas-liquid separator 24, a gas-liquid separation tank 25, and a boiler circulation pump 26.

FIG. 2 is a conceptual diagram showing a state in which the cleaning and circulation route 3 is installed in the thermal power plant 1 shown in FIG.

As shown in FIG. 2, in the cleaning circulation path 3, the scale S (see FIG. 3) in which the cleaning solution circulates from the economizer 22 to the gas-liquid separator 24 and adheres to the inner surface of the furnace wall pipe 5 It is to be cleaned and includes a buffer tank 31, a circulation pump 32, a heater 33, and a waste tank 34. These are mutually connected by temporary piping 35.

The cleaning liquid is stored in the buffer tank 31, and the cleaning liquid stored in the buffer tank 31 is delivered by the circulation pump 32. The cleaning liquid delivered by the circulation pump 32 is heated by the heater 33, passes through the economizer 22, the furnace 23, and the gas-liquid separator 24, and is collected in the buffer tank 31. As a result, the cleaning liquid stored in the buffer tank 31 circulates from the economizer 22 to the gas-liquid separator 24 and cleans and removes the scale S adhering to and deposited on the inner surface of the furnace wall pipe 5 (chemical cleaning) .

FIG. 3 is a schematic view showing an outline of the furnace wall pipe 5 in which the scale S is adhered and deposited on the inner surface.

As shown in FIG. 3, the scale S adhering to and deposited on the inner surface of the furnace wall pipe 5 is configured to include the autoxidation scale HS and the powder scale PS. The self-oxidizing scale HS is deposited on the inner surface of the furnace wall tube 5 to form a dense layer, and the powder scale PS is porous with a small particle diameter and attached to the surface of the self-oxidizing scale HS.

FIG. 4 is a diagram showing the relationship between the thickness of the scale S and the metal temperature.

As shown in FIG. 4, the increase in metal temperature is largely influenced by the thickness of the powder scale PS, and is small by the thickness of the autoxidized scale HS. The metal temperature of the furnace wall pipe 5 is controlled below the control temperature, but the self-oxidizing scale HS does not grow to a predetermined value (hereinafter referred to as “HS thickness limit value”), and the metal of the furnace wall pipe 5 The temperature never reaches the control temperature.

FIG. 5 is a view showing the relationship between the operation time of the once-through boiler and the thickness of the self-oxidation scale HS.

As shown in FIG. 5, the growth rate of the self-oxidation scale HS is relatively slow, and the thickness is equal to or less than the HS thickness limit value even after about 10 years. Therefore, even if the self-oxidation scale HS is left as it is, the metal temperature of the furnace wall pipe 5 does not reach the control temperature in about 10 years.

On the other hand, powder scale PS has a smaller thermal conductivity than autoxidized scale HS, and if the thickness grows to a predetermined value (hereinafter referred to as "PS thickness control value"), the metal temperature of furnace wall pipe 5 reaches the control temperature Therefore, the thickness of the powder scale PS is required to be controlled to the PS thickness management value or less.

In addition, powder scale PS is brought in from boiler feed water, adheres and grows, and depends on the water quality of the feed water. Therefore, depending on the quality of the water supplied, the furnace wall pipe 5 may reach the control temperature in two years, or may reach the control temperature in 10 years.

Therefore, in the method of cleaning the furnace wall tube 5 of the once-through boiler according to some embodiments, the thermal conductivity of the autoxidation scale HS and the powder scale PS generated on the inner surface of the furnace wall tube 5 is higher than the autoxidation scale HS. The low rate powder scale PS is selectively removed by chemical cleaning.

In the embodiment illustrated in FIG. 2, the cleaning solution is performed until the powder scale PS having a thermal conductivity lower than that of the autoxidized scale HS is selectively removed by chemical cleaning among the scales S deposited and deposited on the inner surface of the furnace wall pipe 5. Circulate.

According to the cleaning method of the furnace wall tube 5 of the once-through boiler according to some embodiments described above, the self-oxidation scale HS and the powder scale PS generated on the inner surface of the furnace wall tube 5 are more than the self-oxidation scale HS. Since the powder scale PS having low thermal conductivity is selectively removed by chemical cleaning, the cleaning time can be shortened as compared with the case of removing all of the autoxidized scale HS and the powder scale PS as in the prior art. In addition, since the self-oxidation scale HS is not removed, the cleaning solution will not damage the inner surface of the furnace wall tube 5.

FIG. 6 is a conceptual view showing a presumed structure of the furnace wall pipe 5 of the once-through boiler in which the autoxidation scale HS and the powder scale PS are generated on the inner surface.

The surface layer of the powder scale PS has weak adhesion and can be partially removed by washing with water. On the other hand, in the vicinity of the interface between the powder scale PS and the autoxidation scale HS, it has an adhesion which is difficult to remove by washing with water. As shown in FIG. 6, this means that powder scale PS and powder scale PS, and powder scale PS and autoxidation scale HS use magnetite etc. as binder B, and the surface of autoxidation scale HS is microscopically rough, It is estimated that the powder scale PS is physically held. Therefore, in the selective removal of powder scale PS, it is necessary to dissolve at least the surface layer of the autoxidation scale HS or the binder B.

For this purpose, acid washing and chelate washing etc. are effective, but when the washing conditions are high concentration, washing temperature conditions are high temperature and washing time conditions are long, washing power is too strong and the self-oxidation scale HS is partially And the heat transfer inhibition due to the floating of the autoxidation scale HS and the corrosion due to the cleaning liquid remaining on the floating portion.

Therefore, the method of cleaning the furnace wall tube 5 of the once-through boiler according to some embodiments includes a cleaning test step and a cleaning step.

The washing test step is for obtaining washing conditions for chemical washing for selectively removing the powder scale PS, and the washing step is for selectively removing the powder scale PS under the washing conditions obtained in the washing test step.

According to the cleaning method of the furnace wall tube 5 of the once-through boiler according to some embodiments described above, chemical cleaning conditions for selectively removing the powder scale PS are determined, and the powder scale PS is selectively eliminated under the determined cleaning conditions. Therefore, the powder scale PS having a thermal conductivity lower than that of the autoxidation scale HS can be efficiently selected and removed among the autoxidation scale HS and the powder scale PS.

FIG. 7 is a view showing washing conditions capable of selectively removing powder scale.
As shown in FIG. 7, the cleaning conditions according to some embodiments include at least one of a cleaning solution composition condition, a cleaning solution concentration condition, a cleaning temperature condition, and a cleaning time condition.

As shown in FIG. 7, in a typical chemical cleaning procedure for cleaning the furnace wall tube of the once-through boiler, an organic acid such as citric acid or hydroxy acid is used for the composition of the cleaning solution. The concentration of the cleaning solution is 3% to 10%, and the number of times of cleaning depends on the amount of the scale S adhering to the inner surface of the furnace wall tube 5. The temperature of the washing solution is 80 ° C. to 90 ° C., and the washing time is about 6 hours to 10 hours.

A typical chemical cleaning procedure is suitable for removing all the scale S deposited and adhered to the inner surface of the furnace wall tube 5, but is not suitable for selectively removing the powder scale PS. That is, in a typical chemical cleaning procedure, not only powder scale PS but also autoxidation scale HS will be removed.

On the other hand, the cleaning condition 1 is a reduction in the temperature of the cleaning solution, and the composition of the cleaning solution, the concentration of the cleaning solution, and the cleaning time are the same as the above-described typical chemical cleaning procedures. The temperature of the cleaning solution is, for example, normal temperature, which is advantageous in that it is not necessary to heat the cleaning solution. The washing under the washing condition 1 suppresses the damage of the autoxidized scale HS and enables selective removal of the powder scale PS.

The washing condition 2 is obtained by shortening the washing time, and the composition of the washing solution, the concentration of the washing solution, and the temperature of the washing solution are the same as the typical chemical washing procedure described above. The washing time is, for example, one hour, which is advantageous in that the washing is completed in a short time. The washing under the washing condition 2 suppresses the damage of the autoxidized scale HS and enables selective removal of the powder scale PS.

The cleaning condition 3 is a reduction in the concentration of the cleaning solution, and the composition of the cleaning solution, the temperature of the cleaning solution, and the cleaning time are the same as the above-described typical chemical cleaning procedures. The concentration of the washing solution is, for example, less than 3%, which is advantageous in that the amount of washing solution (stock solution) is reduced. The washing under the washing condition 3 suppresses the damage of the autoxidized scale HS and enables selective removal of the powder scale PS.

The washing condition 4 is an arbitrary modification of the above-mentioned typical chemical washing procedure, and the composition of the washing solution uses an organic acid such as EDTA, malonic acid or hydroxyacetic acid. The concentration of the cleaning solution is 3% to 10% or less than 3%, and the number of cleanings depends on the amount of the scale S adhering to the inner surface of the furnace wall tube 5, but the cleaning is usually performed multiple times. The temperature of the cleaning solution is 80 ° C. to 90 ° C., or normal temperature, and the cleaning time is about 6 hours to 10 hours, or less than 1 hour. The washing under the washing condition 4 suppresses the damage of the autoxidized scale HS and enables selective removal of the powder scale PS.

Since the cleaning conditions according to some embodiments described above include at least one of cleaning solution conditions, cleaning solution concentration conditions, cleaning temperature conditions, or cleaning time conditions, the heat conduction is higher than that of the self-oxidizing scale HS under appropriate cleaning conditions. The powder scale PS with a low rate can be selectively removed.

FIG. 8 is a conceptual view showing an outline of a washing test apparatus for obtaining washing conditions capable of selectively removing powder scale PS.

As a washing solution for selectively removing the powder scale PS, at least one of an inorganic acid (hydrochloric acid), an organic acid (citric acid, hydroxyacetic acid, malonic acid, etc.), or a chelating agent can be used.

Then, it is desirable to maintain the integrity of the self-oxidizing scale HS by completing the washing when the binder or holder of the powder scale PS is dissolved or the powder scale PS is peeled off.

However, the time required for dissolution of powder scale PS or exfoliation of powder scale PS varies depending on the washing liquid composition condition, the washing temperature condition, and the adhesion state of powder scale PS.

The cleaning test process according to some embodiments chemically cleans a sample TP constituted by a part of the furnace wall pipe 5 of the once-through boiler to be cleaned or a sample imitating the furnace wall pipe 5, and the powder scale Determine washing conditions that can selectively remove PS.

In the embodiment illustrated in FIG. 7, the scale dissolution test apparatus 6 is used to test a test body TP which constitutes a part of the furnace wall pipe 5 of the once-through boiler to be cleaned. The scale dissolution test apparatus 6 includes a warm tank 61, a circulation pump 62, a circulation tank 63, and a particle counter 64. The test body TP is immersed in the hot tank 61, and the cleaning liquid stored in the circulation tank 63 is fed out by the circulation pump 62. The cleaning fluid delivered by the circulation pump 62 passes through the test body TP and is collected in the circulation tank 63. Thus, the cleaning liquid stored in the circulation tank 63 circulates the test body TP, and cleans the scale S (powder scale PS) attached to the inner surface of the test body TP.

According to the cleaning test process according to some embodiments described above, the test body TP constituted by a part of the furnace wall pipe 5 of the once-through boiler to be cleaned or the sample imitating the furnace wall pipe is chemically cleaned Since the washing conditions capable of selectively removing the powder scale PS are determined, the washing conditions suitable for each of the through-flow boilers having different operating environments can be determined.

FIG. 9 is a diagram showing the relationship between the cleaning time and the particle concentration in the cleaning liquid and the rate of increase of the particle concentration. The relationship shown in FIG. 9 is merely an example.

Powder scale is an iron oxide called hematite (Fe ₂ O ₃ ), which is less soluble compared to the autoxidized scale HS, and it is difficult to completely dissolve it even by chemical cleaning, and its particles are in the cleaning solution. Suspend in floating or stagnant areas. In addition, as the cleaning time increases, the number of particles suspended in the cleaning solution increases, and eventually stagnates in the retention portion.

Therefore, in the cleaning test process according to some embodiments, the completion timing of the selective removal of the powder scale PS is determined by monitoring the particle concentration in the cleaning liquid used for the chemical cleaning of the test object TP, and the completion timing is determined. Determine the washing conditions based on the above.

In the embodiment illustrated in FIG. 8, the particle concentration is monitored using the particle counter 64 to determine the completion timing of the selective removal of the powder scale PS, and the cleaning time is determined based on the completion timing. The particle diameter of the particles to be monitored using the particle counter 64 is set to a predetermined value (for example, 10 μm), and the disturbance due to the foreign matter or the exfoliation sludge from the self-oxidation scale HS is eliminated.

The particle concentration is the number of particles in the cleaning solution, and the increase rate of the particle concentration is {(number of particles at n time)-(number of particles at n-1 hour)} / (particle at n time) It is calculated by the following equation) * 100.

As exemplified in FIG. 9, the particle concentration generally increases as the washing time increases, and the increase rate of the particle concentration decreases. By monitoring these, the selective removal of powder scale PS is completed. The timing is determined, and the cleaning condition (cleaning time) is determined based on the completion timing.

According to the cleaning test process according to some embodiments described above, the completion timing of the selective removal of the powder scale PS is judged by monitoring the particle concentration in the cleaning liquid used for the chemical cleaning of the test object TP, and completed. Since the cleaning conditions are determined based on the timing, the cleaning conditions can be determined qualitatively.

In the cleaning test process according to some embodiments, the timing at which the increase rate of the particle concentration is less than the threshold is taken as the completion timing.

In the embodiment illustrated in FIG. 9, the threshold is 10% / time, and the timing at which the increase rate of the particle concentration is less than 10% / hour is the completion timing.

According to the cleaning test process according to some embodiments described above, since the timing when the rate of increase of the particle concentration is less than the threshold is the completion timing, the cleaning conditions can be quantitatively determined.

Although the particle concentration is monitored using the particle counter 64 in the embodiment illustrated in FIG. 8, a simplified monitoring method performed at the time of plant construction or plant startup may be used. Specifically, after filtering sample water using a membrane filter, a method may be used to estimate the iron concentration by the color of the filter. In this case, the timing at which the increase in the concentration of particles contained in the cleaning liquid is not recognized is taken as the completion timing.

The present invention is not limited to the above-described embodiments, and includes the embodiments in which the above-described embodiments are modified or the embodiments in which these embodiments are appropriately combined.

DESCRIPTION OF SYMBOLS 1 Thermal power generation plant 11 Turbine condenser 12 Condensing pump 13 Condensing water treatment apparatus 14 Condensate pressure rising pump 15 Low pressure feed water heater 16 Deaerator 17 Boiler feed water pump 18 High pressure feed water heater 19 Fire furnace economizer 20 Super heater 21 Reheater 22 Economizer 23 furnace 24 gas-liquid separator 25 gas-liquid separation tank 26 boiler circulation pump 3 cleaning circulation route 31 buffer tank 32 circulation pump 33 heater 34 waste tank 35 temporary piping 5 furnace wall pipe 6 scale dissolution test equipment 61 hot water tank 62 Circulation pump 63 Circulation tank 64 Particle counter S scale HS Self oxidation scale PS Powder scale B Binder TP sample

Claims

A method for cleaning a furnace wall tube of a once-through boiler, wherein oxygen treatment is applied to a water supply system,
The furnace wall of a once-through boiler characterized by selectively removing the powder scale having a thermal conductivity lower than that of the self-oxidizing scale among the self-oxidizing scale and the powder scale formed on the inner surface of the furnace wall tube. How to clean the tube.
A cleaning test step for determining cleaning conditions of the chemical cleaning for selectively removing the powder scale;
The method according to claim 1, further comprising: a cleaning step of selectively removing the powder scale under the cleaning conditions determined in the cleaning test step.
The method according to claim 2, wherein the cleaning conditions include at least one of a cleaning solution composition condition, a cleaning solution concentration condition, a cleaning temperature condition, and a cleaning time condition.
The cleaning test process chemically cleans a test body constituted by a part of the furnace wall tube of the once-through boiler to be cleaned or a sample imitating the furnace wall tube, and the cleaning condition is capable of selectively removing the powder scale. The method for cleaning a furnace wall tube of a once-through boiler according to claim 2 or 3, wherein:
In the washing test step, the particle concentration in the washing liquid used for chemical washing of the test body is monitored to determine the completion timing of the selective removal of the powder scale, and the washing condition is determined based on the completion timing. The method for cleaning a furnace wall tube of a once-through boiler according to claim 4, characterized in that:
In the said washing | cleaning test process, the timing to which the increase rate of the said particle concentration becomes less than a threshold value is made into the said completion timing. The washing | cleaning method of the furnace wall pipe of the once-through boiler of Claim 5 characterized by these.