JP5721888B1 - Chemical cleaning method and chemical cleaning apparatus - Google Patents

Abstract

The present invention provides a chemical cleaning method and a chemical cleaning apparatus capable of performing chemical cleaning for removing hematite at a low cost and shortening a maintenance work period. A cleaning liquid containing a neutral rust preventive agent is directly supplied to a cleaning target device 10 having a member to which hematite is attached through a chemical liquid supply line 102. At least the region where hematite is adhered is immersed in the cleaning liquid, and the chemical reduction is performed while maintaining the oxidation-reduction potential of the cleaning liquid at a value at which hematite is eluted in the cleaning liquid, so that hematite is eluted and removed from the member. [Selection] Figure 1

Description

  The present invention relates to a chemical cleaning method and a chemical cleaning apparatus for removing hematite adhering to an inner surface of a furnace wall tube in a thermal power generation system.

  A thermal power generation system 1 illustrated in FIG. 13 includes a once-through boiler 10. As a boiler water supply system, a condenser 20, a condensate demineralizer 21, a ground steam condenser 22, a low-pressure feed water heater 23, a deaerator 24, a high-pressure feed water heater 25, and a economizer 26 are installed. The As the steam system of the boiler, a steam separator 30, a superheater 31, a turbine 32, and a reheater 33 are installed. As the turbine 32, a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine may be installed.

In the thermal power generation system 1 in which oxygen treatment is applied to the boiler feed water system, an event occurs in which the metal temperature of the furnace wall tube of the once-through boiler 10 increases, and leakage of boiler feed water due to furnace wall tube breakage becomes a problem. Yes. The metal temperature rise in the furnace wall tube is caused by the elution of iron from the low pressure feed water heater drain system 27 or the piping of the feed water system to generate hematite (Fe ₂ O ₃ ), and hematite adheres to and accumulates on the inner wall of the furnace wall tube. This is due to poor heat conduction.

  In order to prevent the above-mentioned leakage incompatibility of the furnace wall tube, chemical cleaning of the furnace wall tube is periodically performed to remove scales composed of iron-based oxides such as hematite deposited on the inner surface of the tube. Yes. In conventional chemical cleaning, a circulation path is installed between the economizer 26 and the steam separator 30, and an acidic cleaning liquid (hydrochloric acid or the like) heated to about 60 to 80 ° C. is circulated in the circulation path. Then, the inside of the furnace wall tube is cleaned (see, for example, Patent Document 1).

  Patent Document 2 discloses a method for removing sludge and the like generated in a reactor steam generator. Patent Document 3 discloses a method for cleaning and removing iron oxide scale from a metal filter used in a thermal power plant or a nuclear power plant. In the method of Patent Document 3, the iron oxide scale is peeled off from the filter and removed by dissolving only the iron in the attached portion of the iron oxide attached to the filter.

JP-A-8-105602 JP-T-2004-535546 JP2013-71111A

  As in Patent Document 1, in the conventional chemical cleaning, the installed circulation path needs to be filled with the cleaning liquid. Moreover, since hydrogen gas is generated during cleaning by using an acidic cleaning liquid, chemical cleaning cannot be performed in parallel with mechanical and electrical work using fire. Thus, during the chemical cleaning, there is a problem that the maintenance work cannot be performed not only on the equipment immersed in the cleaning liquid but also on other equipment, and the maintenance cannot be performed efficiently. .

  In the conventional chemical cleaning method, it is necessary to circulate the cleaning liquid at a high flow rate in order to remove the scale composed of the iron-based oxide. Moreover, in order to obtain a sufficient flow rate, it is necessary to connect to a large-diameter pipe, but the upstream pipe and the downstream pipe of the once-through boiler 10 are small-diameter pipes and are not suitable for connecting a chemical cleaning device. is there. For this reason, as specifically shown in Patent Document 1, there is no choice but to connect a circulation path to the upstream side pipe of the economizer 26 and the pipe in the steam separator 30, and there are restrictions on the apparatus.

Hematite is a poorly soluble oxide, and conventional acidic cleaning liquids (for example, hydrochloric acid-based and citric acid-based) are difficult to dissolve in the cleaning liquid and sludge is generated by chemical cleaning.
In addition, a magnetite layer that is a natural oxide scale is formed on the surface of the pipe or the metal filter disclosed in Patent Document 3. In the method of Patent Document 3, only the magnetite layer is dissolved without dissolving the attached iron oxide scale, and the scale is peeled off. Therefore, if the method disclosed in Patent Document 3 is used, sludge is generated.

Since the furnace wall pipe of the once-through boiler 10 in the thermal power generation system 1 has a long and complicated pipe shape, when sludge is generated, it may accumulate in a part of the pipe and block the inside of the pipe.
For this reason, in the conventional chemical cleaning, it was necessary to remove sludge from the cleaning liquid. As a method for removing sludge, a filter is provided in the middle of the portion through which the cleaning liquid passes to collect sludge floating in the cleaning liquid, or a part of the piping of the equipment to be cleaned after chemical cleaning is cut and piped. There is a method of inspecting the inside, removing it by a physical method such as suction cleaning, and then welding the pipe again.

  Further, in the conventional chemical cleaning using an acidic cleaning liquid, it is necessary to heat the cleaning liquid as described above, and it is necessary to separately install a temperature raising equipment for heating the cleaning liquid. Moreover, the inside of the apparatus immersed in the acidic cleaning liquid has to be neutralized after cleaning, and a large amount of neutralized water is required.

  As in the thermal power generation system shown in FIG. 13, when there is a superheater 31 having stainless steel parts on the downstream side of the steam / water separator 30, there is a risk of corrosion when the stainless steel parts come into contact with an acidic cleaning liquid such as hydrochloric acid. is there. For this reason, in conventional chemical cleaning, it is necessary to pressurize and pressurize water in the non-cleaning system adjacent to the downstream side of the equipment to be cleaned to prevent intrusion of the cleaning liquid. It was installed.

  As described above, when performing conventional chemical cleaning, a large amount of cleaning liquid and water for water filling and neutralization are required, and a large-scale facility and its installation work are required, and the construction period is long. Therefore, the high maintenance cost has been a problem.

  The present invention has been made in view of the above circumstances, and includes a chemical cleaning method capable of performing chemical cleaning for removing hematite at a low cost in a short time, and a chemical cleaning apparatus for performing the chemical cleaning method. The purpose is to provide.

In the chemical cleaning method according to the first aspect of the present invention, a cleaning liquid containing a chelating agent, a reducing agent, or a rust inhibitor that is a mixture of the chelating agent and the reducing agent has a member having hematite attached thereto. The cleaning liquid supply step supplied to the target device, and at least the region of the member to which the hematite is attached is immersed in the cleaning liquid, and the oxidation-reduction potential of the cleaning liquid is maintained at a value at which the hematite elutes in the cleaning liquid, A cleaning step in which the hematite is removed from the member, and the chelating agent is one of an aminocarboxylic acid chelating agent, an oxycarboxylic acid chelating agent, and an organophosphorus chelating agent, and the reducing agent is , metal ions, sulfite, oxalic acid, formic acid, ascorbic acid, pyrogallol, hydrazine is either hydrogen, pH of the cleaning solution 8 is within the range of.

A chemical cleaning apparatus according to a second aspect of the present invention is a chemical cleaning apparatus for chemically cleaning an apparatus to be cleaned having a member to which a hematite scale is attached, and includes a chelating agent, a reducing agent, or the chelating agent. It is a mixture with the reducing agent, the chelating agent is one of an aminocarboxylic acid chelating agent, an oxycarboxylic acid chelating agent and an organophosphorus chelating agent, and the reducing agent is a metal ion, sulfite, A chemical tank that contains a rust preventive agent that is any one of oxalic acid, formic acid, ascorbic acid, pyrogallol, hydrazine, and hydrogen , and that contains a cleaning liquid having a pH in the range of 4 to 8, and the equipment to be cleaned and the chemical tank A chemical liquid supply line that supplies the cleaning liquid to the member, a pump installed in the chemical liquid supply line, the cleaning target device, and the chemical liquid A chemical solution discharge line for discharging the cleaning liquid from the member, means for immersing at least the region where the hematite is adhered in the member, and the oxidation-reduction potential of the cleaning liquid during cleaning. Means for maintaining the value at which the hematite elutes in the cleaning liquid, and the chemical liquid tank, the chemical liquid supply line and the pump are means for supplying the cleaning liquid to the member.

In the chemical cleaning method and the chemical cleaning apparatus of the above aspect, since the cleaning liquid is supplied only to the equipment to be cleaned, the amount of the cleaning liquid required for the chemical cleaning can be greatly reduced.
Furthermore, since the use of washing solution containing an anti-rust agent, even if a device having a stainless steel component on the downstream side of the cleaning target device is disposed, there is no need to carry out water Zhang, etc. for preventing corrosion of members, Equipment for water filling becomes unnecessary, and the device configuration is simplified. In addition, since no hydrogen is generated during cleaning, chemical cleaning can be performed in parallel with mechanical and electrical work using fire, and inspection and maintenance work for each part can be performed in parallel. Can be shortened.
Thus, the use of the chemical cleaning method and the chemical cleaning apparatus of the present invention is advantageous because the cost required for maintenance such as equipment costs and chemical costs can be greatly reduced.

In the chemical cleaning method, the cleaning step is performed while the value is maintained within a range of −0.8 V or more and −0.4 V or less with respect to a silver-silver chloride electrode.
In the chemical cleaning method, the value may be adjusted by supplying a reducing atmosphere gas to the device to be cleaned.

The chemical cleaning apparatus includes a reducing atmosphere adjusting unit that adjusts the oxidation-reduction potential of the cleaning liquid during cleaning to a value within a range of −0.8 V or more and −0.4 V or less with respect to a silver-silver chloride electrode.
In the chemical cleaning apparatus, the reducing atmosphere adjusting unit may supply reducing atmosphere gas to the cleaning target device.

  By maintaining the reduced state as the oxidation-reduction potential, hematite is dissolved and removed in the cleaning liquid. The solid matter such as sludge is hardly generated by the cleaning, and even when a slight amount of solid matter is generated, it can be easily discharged from the cleaning target device together with the cleaning liquid. Further, since no equipment for removing sludge is required, the equipment cost can be reduced.

  In the chemical cleaning method, it is preferable that the temperature of the cleaning liquid in the cleaning step is in a range of an ambient temperature around the member and a temperature that is 10 ° C. higher than the ambient temperature.

In the chemical cleaning apparatus, it is preferable that the temperature of the cleaning liquid supplied to the member is in a range of an ambient temperature around the member and a temperature that is 10 ° C. higher than the ambient temperature.
The chemical cleaning apparatus further includes a circulation loop that connects the chemical liquid supply line on the upstream side and the chemical liquid supply line on the downstream side across the pump, and a part of the cleaning liquid that has passed through the pump is the circulation loop. It is preferable to be conveyed to the upstream side of the pump via

According to the present invention, hematite can be removed at a lower temperature than when an acidic cleaning solution is used, and it is not necessary to positively raise the temperature of the cleaning solution, and it is extremely easy to maintain the temperature at the ambient temperature.
If the temperature of the cleaning liquid is raised to a temperature that is 10 ° C. higher than the environmental temperature, the cleaning power can be further increased. For example, the temperature of the cleaning liquid can be easily raised by using heat generated during pump operation. Since the configuration of the present invention does not actively cool, the temperature of the cleaning liquid can be maintained higher than the environmental temperature for a long time.
According to the present invention, it is possible to perform cleaning at a lower temperature than the conventional method using an acidic cleaning liquid. As a result, it is possible to reduce equipment costs and cleaning costs.

In the chemical cleaning method, the region is immersed in the cleaning liquid while the cleaning liquid is left standing.
During the cleaning, the chemical cleaning apparatus stops the supply of the cleaning liquid to the member and the discharge of the cleaning liquid from the member to allow the cleaning liquid to stand.
According to the chemical cleaning method and the chemical cleaning apparatus described above, it is not necessary to install a large circulation path for the cleaning liquid, which is advantageous because the cleaning is performed in a simple process.

The chemical cleaning method further includes a water supply step between the cleaning liquid supply step and the cleaning step, wherein a predetermined amount of the cleaning liquid is supplied to the cleaning target device in the cleaning liquid supply step, and in the water supply step A predetermined amount of water is supplied to the device to be cleaned, and the region is immersed in the cleaning liquid.
The chemical cleaning apparatus further includes a water supply unit including a water tank that stores water, a water supply line that connects the water tank and the device to be cleaned, and a water pump installed in the water supply line. Prepare.

  According to the chemical cleaning method and the chemical cleaning apparatus, the cleaning liquid layer and the water layer can be separated in the cleaning target device. If the area where hematite is adhered is immersed in the cleaning liquid and the other part is immersed in water, the amount of the cleaning liquid used for chemical cleaning can be greatly reduced.

  In the chemical cleaning method, the cleaning liquid may be accommodated in a capsule made of a water-soluble polymer, and the capsule may be supplied to the device to be cleaned.

  In the chemical cleaning apparatus, the cleaning liquid may be stored in a capsule made of a water-soluble polymer, the chemical liquid tank may store the capsule, and the capsule may be supplied from the cleaning liquid tank to the device to be cleaned.

  According to the present chemical cleaning method and chemical cleaning apparatus, for example, a region where a large amount of hematite is generated can be easily immersed in the cleaning liquid, so that the amount of the cleaning liquid to be used can be greatly reduced.

  In the chemical cleaning method, the cleaning liquid is repeatedly discharged from the member and the discharged cleaning liquid is supplied to the member during the cleaning step, and the cleaning liquid is disposed in the vicinity of the region. Move the liquid level.

  In the chemical cleaning apparatus, during cleaning, the cleaning liquid in the member is discharged toward the chemical liquid tank through the chemical liquid discharge line, and the cleaning liquid in the chemical liquid tank is supplied to the member through the chemical liquid supply line. To repeat.

  According to the present chemical cleaning method and chemical cleaning apparatus, since the flow rate is given to the cleaning liquid and the cleaning liquid is stirred in the region where hematite is adhered, the cleaning power is improved, which is advantageous.

  In the above chemical cleaning method, during the cleaning step, the cleaning liquid passes through the member and is discharged from the upstream end of the member, and the discharged cleaning liquid is directly discharged to the downstream end of the member. Circulated.

  In the chemical cleaning apparatus, the circulation line includes a circulation line that connects an upstream end and a downstream end of the member, and a circulation pump installed in the circulation line, and the circulation line is used during cleaning. Then, the cleaning liquid discharged from the front downstream end is circulated to the upstream end.

  Also with the present chemical cleaning method and chemical cleaning apparatus, a flow rate is given to the cleaning liquid in the region where hematite adheres and the cleaning liquid is stirred, so that the cleaning power is improved. In addition, since the cleaning liquid is heated when passing through the pump and cleaning is performed in a state higher than the environmental temperature around the member, the cleaning power is improved.

According to the present invention, the amount of cleaning liquid used can be reduced as compared with the conventional chemical cleaning method, and the configuration of the chemical cleaning apparatus is simplified, so that the cost required for chemical cleaning can be greatly reduced.
Further, in the present invention, since the cleaning liquid is not supplied to other equipment and hydrogen is not generated during cleaning, it is possible to perform other operations simultaneously with chemical cleaning. For this reason, this invention has the advantageous effect that a maintenance work period is shortened compared with a prior art.

It is the schematic explaining the chemical cleaning apparatus which concerns on 1st Embodiment. It is the schematic of an example of a once-through boiler. It is the schematic of an example of a once-through boiler. It is the schematic explaining the chemical cleaning method of 1st Embodiment. It is a SEM photograph of the cross section of the furnace wall tube before the cleaning liquid immersion. It is a SEM photograph of the cross section of the furnace wall tube after chemical cleaning. It is the schematic explaining the chemical cleaning apparatus which concerns on 2nd Embodiment. It is the schematic explaining the chemical cleaning apparatus which concerns on 3rd Embodiment. It is the schematic explaining the chemical cleaning apparatus which concerns on 4th Embodiment. It is the schematic explaining the chemical cleaning apparatus which concerns on 5th Embodiment. It is the schematic explaining the chemical cleaning apparatus which concerns on 8th Embodiment. It is the schematic explaining the chemical cleaning apparatus which concerns on 9th Embodiment. It is the schematic of a thermal power generation system.

The cleaning liquid used in the chemical cleaning method and the chemical cleaning system of the present invention is an aqueous solution comprising a corrosion inhibitor.
Anti Sabizai, the chelating agent is an admixture of a reducing agent, or a chelating agent and a reducing agent. Chelating agents include, for example, aminocarboxylic acids such as EDTA, BAPTA, DOTA, EDDS, INN, NTA, DTPA, HEDTA, TTHA, PDTA, DPTA-OH, HIDA, DHEG, GEDTA, CMGA, and EDDS, and amino such as salts thereof. Carboxylic acid chelating agents, oxycarboxylic acid chelating agents such as citric acid, gluconic acid, hydroxyacetic acid and the like, and salts thereof, organic phosphoric acids such as ATMP, HEDP, NTMP, PBTC, EDTMP and their salts Organic phosphorus chelating agents such as Examples of the reducing agent include various metal ions such as Fe ²⁺ and Sn ²⁺ , sulfites such as sodium sulfite , organic compounds such as oxalic acid, formic acid, ascorbic acid, and pyrogallol, hydrazine, and hydrogen. Cleaning liquid containing antirust agent, pH is 4 to 8, preferably pH 5 to 7.

It may be added corrosion inhibitor in corrosion inhibitor. In the cleaning liquid, the concentrations of the chelating agent, the reducing agent, and the corrosion inhibitor are appropriately adjusted so that a desired cleaning power and cleaning time can be obtained.

  The cleaning liquid may or may not contain an antifoaming agent for preventing foaming. In this embodiment, a known antifoaming agent can be used.

  Hereinafter, embodiments of the chemical cleaning method and the chemical cleaning apparatus of the present invention will be described by taking a thermal power generation system as an example. However, the present invention is not limited to a thermal power generation system, and can be applied to other devices to which hematite adheres.

[First Embodiment]
FIG. 1 is a schematic view for explaining a chemical cleaning apparatus according to the first embodiment. FIG. 1 shows a case where a chemical cleaning apparatus 100 is installed in the thermal power generation system 1 during maintenance. The configuration of the thermal power generation system 1 is the same as that shown in FIG. In the thermal power generation system 1, hematite, which is a powdery scale, adheres to the inside of the heat transfer pipe such as the furnace wall pipe of the once-through boiler 10, and the heat conductivity of the heat transfer pipe is lowered. Therefore, the once-through boiler 10 is a cleaning target device in order to recover the heat transfer performance.

  The chemical cleaning apparatus 100 according to the first embodiment includes a chemical tank 101, a chemical supply line 102 that connects the chemical tank 101 and the once-through boiler 10, a chemical discharge line 103 that connects the chemical tank 101 and the once-through boiler 10, and a control. Part 104. The chemical tank 101 contains the above-described cleaning liquid. The control unit 104 is a computer, for example.

  FIG. 2 is an example of a once-through boiler. 2A is a schematic view of the once-through boiler, and FIG. 2B is an enlarged view of a portion surrounded by a circle A in FIG. 2A. The once-through boiler 10a of Fig.2 (a) is comprised by the combustion chamber 11a enclosed by the wall surface 12a, and several furnace wall pipes. The furnace wall tube 13a of the once-through boiler 10a is a straight tube extending along the wall surface 12a in a direction perpendicular to the cross section of the combustion chamber 11a. A plurality of furnace wall tubes 13a are arranged in the horizontal direction along the wall surface 12a. A lower header 14a is installed in the lower part of the combustion chamber 11a, and the lower ends of the plurality of furnace wall tubes 13a are connected to the lower header 14a. An upper header is installed in the upper part of the combustion chamber 11a, and the upper ends of the plurality of furnace wall tubes 13a are connected to the upper header 15a.

FIG. 3 shows another example of the once-through boiler. 3A is a schematic view of a once-through boiler, and FIG. 3B is an enlarged view of a portion surrounded by a circle B in FIG. 3A. 3 is different from the once-through boiler 10a of FIG. 2 in the shape of the furnace wall tube. In the once-through boiler 10b, a plurality of furnace wall tubes 13b are spirally disposed along the wall surface 12b below the combustion chamber 11b. The furnace wall tube 13b branches into a plurality of tubes at a midway position in the vertical direction of the combustion chamber 11b (branch portion 16). The branched furnace wall tube 13b is straight and extends upward in the vertical direction along the wall surface 12b with respect to the cross section of the combustion chamber 11a.
The lower header 14b is installed in the lower part of the combustion chamber 11b, and the lower ends of the plurality of furnace wall tubes 13b are connected to the lower header 14b. An upper header is installed in the upper part of the combustion chamber 11b, and the upper ends of the plurality of furnace wall tubes 13b are connected to the upper header 15b.

In the chemical cleaning apparatus 100 of the first embodiment, the chemical solution supply line 102 and the chemical solution discharge line 103 are connected to the lower headers 14a, 14b of the once-through boiler 10 (10a, 10b).
The chemical solution supply line 102 is provided with a pump 105 and a valve V1. A valve V <b> 2 is installed in the chemical solution discharge line 103. The pump 105 and the valves V1 and V2 communicate with the control unit 104.

  The place where hematite adheres depends on how the furnace wall tube is arranged. Hematite tends to adhere to a place where the flow rate of boiler feed water changes in the furnace wall pipe. For example, in the once-through boiler 10a of FIG. 2, more hematite adheres to the inner surface of the furnace wall tube 13a located below the combustion chamber 11a than the other parts. In the once-through boiler 10b of FIG. 3, hematite adheres more to the inner surface of the furnace wall tube 13b of the branch portion 16 than to the other portions.

  The chemical cleaning apparatus 100 according to the first embodiment further includes a reducing atmosphere adjusting unit. In the chemical cleaning apparatus 100 of the first embodiment, the reducing atmosphere adjustment unit is the reducing atmosphere gas supply unit 110. The reducing atmosphere gas supply unit 110 in FIG. 1 includes a reducing atmosphere gas storage unit 111 and an air supply line 112. The chemical cleaning apparatus 100 includes an exhaust line 113. Valves V3 and V4 are installed in the air supply line 112 and the exhaust line 113, respectively. The air supply line 112 and the exhaust line 113 are connected to the upper headers 15a and 15b of the once-through boiler 10 (10a and 10b). The valves V3 and V4 are connected to the control unit 104.

  The reducing atmosphere gas storage unit 111 is a cylinder that stores the reducing atmosphere gas. The reducing atmosphere gas is a gas for adjusting the cleaning liquid to a reduced state. Specifically, the reducing atmosphere gas is nitrogen, argon, steam, carbon dioxide, combustion exhaust gas, or the like. The purity of the reducing atmosphere gas does not have to be a high-purity gas, and any gas can be used as long as the oxidation-reduction potential of the cleaning liquid during the cleaning process described later can be maintained within a predetermined range. When nitrogen is used as the reducing atmosphere gas, a nitrogen injection facility that is already installed in the thermal power generation system 1 can be used as the reducing atmosphere gas supply unit 110, or a nitrogen injection facility may be temporarily or newly installed. Steam or combustion exhaust gas as the reducing atmosphere gas can be steam or combustion exhaust gas generated in a boiler of another adjacent thermal power generation system.

A chemical cleaning method for cleaning and removing hematite attached in the once-through boiler using the chemical cleaning apparatus 100 of the first embodiment will be described below.
The chemical cleaning method of the present embodiment is performed, for example, during a periodic inspection of the thermal power generation system, during a process of constructing a scaffold in the furnace and a process of constructing equipment other than the equipment to be cleaned (the once-through boiler 10).
In carrying out the chemical cleaning method of the present embodiment, a valve installed in a pipe connecting the once-through boiler 10 and the economizer 26 is closed.

<Gas supply process>
The control unit 104 opens the valves V2 and V3. A reducing atmosphere gas (such as nitrogen gas) is fed from the reducing atmosphere gas storage unit 111 to the furnace wall tubes 13a and 13b of the once-through boiler 10 via the air supply line 112. Air in the furnace wall tubes 13 a and 13 b is discharged out of the system via the chemical solution discharge line 103. By this step, the air in the furnace wall tubes 13 a and 13 b in the once-through boiler 10 is discharged through the chemical solution discharge line 103. The furnace wall pipes 13a and 13b are filled with the reducing atmosphere gas by the gas supply process.
After a sufficient time for gas replacement has elapsed, the control unit 104 closes the valves V2 and V3.

<Cleaning liquid supply process>
The control unit 104 activates the pump 105 and opens the valve V1. The control unit 104 opens the valve V4. The cleaning liquid in the chemical liquid tank 101 is fed to the once-through boiler 10 via the chemical liquid supply line 102. As a result, the inner surfaces of the furnace wall pipes 13a and 13b are immersed in the cleaning liquid, and the purge gas in the furnace wall pipes 13a and 13b, such as nitrogen having a volume corresponding to the supplied cleaning liquid, is discharged out of the system through the exhaust line 113.

  In this embodiment, since the valve of the pipe connecting the once-through boiler 10 and the economizer 26 is closed, the cleaning liquid supplied from the chemical liquid supply line 102 to the lower headers 14a and 14b flows into the economizer 26. There is nothing.

  In the present embodiment, at least the area where hematite adheres on the inner surfaces of the furnace wall tubes 13a and 13b is immersed in the cleaning liquid. In particular, on the inner surfaces of the furnace wall tubes 13a and 13b, a region where hematite adheres in a larger amount than other portions is always immersed in the cleaning liquid. For example, as shown in FIG. 4, the control unit 104 supplies the cleaning liquid so that the liquid level 18 of the cleaning liquid is located above the region 17 where hematite is attached more than the other parts. Considering the cost of chemical cleaning, the cleaning liquid is filled with the upper ends of the plurality of furnace wall tubes 13a and 13b (connection portions with the upper headers 15a and 15b) as the upper limit. In this embodiment, the cleaning liquid does not reach the downstream steam separator 30 beyond the once-through boiler 10. That is, in the present embodiment, the cleaning liquid is supplied only to the once-through boiler 10 that is the cleaning target device.

  The region where hematite adheres, in particular, the region 17 where hematite adheres more than other parts is specified in advance, so that the hematite adherence region can be immersed from each size of the furnace wall tubes 13a and 13b. Necessary amount can be determined. The control unit 104 stores the required amount of cleaning liquid, and supplies a predetermined amount of cleaning liquid according to the required amount of steam to the once-through boiler 10 in the cleaning liquid supply process.

<Washing process>
When the region to which hematite is attached is immersed in the cleaning liquid, the control unit 104 stops the pump 105 and closes the valves V1 and V4. In a state where the cleaning liquid is allowed to stand, the hematite is immersed in the cleaning liquid and the cleaning process is performed.
The soaking time (cleaning time) depends on the amount of hematite generated, but is, for example, 24 hours or longer. During this cleaning process, the pressure in the furnace wall tubes 13a and 13b hardly changes and is constant.

  In this embodiment, since the cleaning liquid is allowed to stand during the cleaning process, the temperature of the cleaning liquid during the cleaning process is approximately the same as the environmental temperature around the furnace wall tubes 13a and 13b. For example, the environmental temperature around the furnace wall tubes 13a and 13b is about 20 to 40 ° C. Since the environmental temperature is close to the outside air temperature and does not change greatly during the cleaning process, the cleaning liquid temperature is also maintained at substantially the same level as the environmental temperature.

Since the reducing atmosphere gas is filled in the space inside the furnace wall pipes 13a and 13b by the gas supply process, the cleaning liquid during the cleaning process is maintained in a reduced state. Specifically, the oxidation-reduction potential of the cleaning liquid during the cleaning process can be measured using an oxidation-reduction potentiometer in the middle of the chemical liquid discharge line 103, for example. The oxidation-reduction potential is maintained at −0.8 V or more and −0.4 V or less on the basis of the silver-silver chloride electrode. According to the pH-potential diagram, by setting the oxidation-reduction potential to −0.4 V or less, the dissolution reaction efficiency of the iron oxide is increased and hematite is dissolved in the cleaning liquid. On the other hand, Fe ⁰ occurs as the redox potential decreases. When the oxidation-reduction potential is less than −0.8 V, Fe ⁰ is generated, sludge is precipitated, and iron adheres to the furnace wall tubes 13a and 13b.

When the oxidation-reduction potential deviates from the predetermined range, the reducing atmosphere gas is refilled so as to maintain the oxidation-reduction potential of the cleaning liquid. Specifically, the valves V2 and V3 are opened. Thereby, the reducing atmosphere gas is supplied from the reducing atmosphere gas storage unit 111 to the once-through boiler 10, and the cleaning liquid is supplied to the chemical liquid tank 101 via the chemical liquid discharge line 103. Thereafter, the valves V2 and V3 are closed, the valves V1 and V4 are opened, and the pump 105 is started, so that the cleaning liquid in the chemical tank 101 is supplied to the once-through boiler 10. Alternatively, the valves V3 and V4 are opened while the valves V1 and V2 are closed, and the reducing atmosphere gas is supplied from the reducing atmosphere gas storage unit 111 to the once-through boiler 10 to be refilled with the reducing atmosphere gas.
When the oxidation-reduction potential deviates from a predetermined value, the above-described reducing agent may be added to the cleaning liquid. Specifically, the cleaning liquid is returned to the chemical liquid tank 101 in the same manner as described above, and after the reducing agent is added in the chemical liquid tank 101, the cleaning liquid is supplied to the once-through boiler 10.
The maintenance of the oxidation-reduction potential may be automated based on an instruction from the control unit 104 that monitors the oxidation-reduction potential, or an operator may manually detect and maintain the oxidation-reduction potential.

5 and 6 show the results of verifying the effect of the chemical cleaning method of the present embodiment on a furnace wall tube collected from an actual machine. The furnace wall tube to which hematite was adhered was collected from the actual machine and immersed (soaked) in the above-described cleaning liquid (pH 5 to 7) while maintaining at 25 ° C. The components of the cleaning liquid are appropriately selected between 3 to 5% by weight of the chelating agent and 1.5 to 2.5% by weight of the reducing agent.
The inner surface of the furnace wall tube before immersion of the cleaning solution was red, and an auto-oxidation scale (magnetite (Fe ₃ O ₄ )) and hematite were confirmed in the SEM photograph (FIG. 5). On the other hand, the inner surface of the furnace wall tube after chemical cleaning was black, and only the self-oxidation scale was confirmed in the SEM photograph (FIG. 6).

  The cleaning effect of the cleaning solution was verified using hematite. A cleaning solution (pH 5 to 7) to which hematite powder was added was put in a container, and the upper portion of the cleaning solution was purged with nitrogen and sealed. The oxidation-reduction potential during the test period was in the range of -0.8 V to -0.4 V on the basis of the silver-silver chloride electrode. The components of the cleaning liquid are appropriately selected between 3 to 5% by weight of the chelating agent and 1.5 to 2.5% by weight of the reducing agent. As a result of keeping the washing liquid at 25 ° C. while standing for 8 hours, the washing liquid changed from opaque reddish brown to almost transparent. This means that hematite was dissolved in the cleaning liquid by soaking.

<Discharge process>
After the cleaning process is performed for a predetermined time, the control unit 104 opens the valve V2. The cleaning liquid in the furnace wall pipes 13 a and 13 b is fed from the lower headers 14 a and 14 b to the chemical tank 101 through the chemical discharge line 103 and collected. Thereby, the chemical cleaning method of this embodiment is completed.
If it recovered cleaning solution long as the corrosion inhibitor residual, cleaning component (concentration of corrosion inhibitor) readjusted to be reused in the next chemical cleaning.

According to the above method, since the cleaning liquid containing the neutral rust preventive agent is used, even if the cleaning process is carried out in the soaking state, the inner surfaces of the furnace wall tubes 13a and 13b immersed in the cleaning liquid corrode. Hematite can be dissolved in the cleaning solution without doing so.
As described with reference to FIGS. 5 and 6, in this embodiment, since it is not a method of separating and removing hematite by eluting a magnetite layer which is a natural oxide scale, generation of sludge is suppressed. In particular, in the thermal power generation system 1, since the piping shape of the furnace wall tube of the once-through boiler 10 is long and complicated, when sludge is generated, the sludge may accumulate in the middle of the piping and close the piping. If hematite is dissolved in the cleaning liquid and removed from the furnace wall tubes 13a and 13b as in the present embodiment, the hematite eluted together with the cleaning liquid after chemical cleaning can be discharged. Therefore, for example, in the thermal power generation system 1 adopting the present embodiment, a facility for removing sludge such as a filter is unnecessary, and a process such as another cleaning for removing sludge is also unnecessary.

[Second Embodiment]
FIG. 7 is a schematic view illustrating a chemical cleaning apparatus according to the second embodiment.
In the chemical cleaning apparatus 200 according to the second embodiment, the chemical solution supply line 202 and the chemical solution discharge line 203 are connected to the lower headers 14a and 14b of the once-through boiler 10 as in the first embodiment. The chemical solution supply line 202 and the chemical solution discharge line 203 are connected to the chemical solution tank 201. An exhaust line 213 is connected to the upper headers 15a and 15b of the once-through boiler.

  The chemical cleaning apparatus 200 includes a reducing atmosphere gas supply unit 210 as a reducing atmosphere adjustment unit on the downstream side of the pump 205 of the chemical solution supply line 202. The reducing atmosphere gas supply unit 210 is connected to the control unit 204.

  The reducing atmosphere gas supply unit 210 of the second embodiment is a microbubble generator. A microbubble generator is an apparatus that injects bubbles into a liquid. In the present embodiment, the gas injected into the liquid (cleaning liquid) as bubbles is the reducing atmosphere gas listed in the first embodiment.

  Although not shown in FIG. 7, a reducing atmosphere gas storage unit and an air supply line connected to the once-through boiler 10 may be installed as in FIG. 1.

  A chemical cleaning method using the chemical cleaning apparatus 200 of the second embodiment will be described below. Also in the present embodiment, when the chemical cleaning method is performed, a valve installed in a pipe connecting the once-through boiler 10 and the economizer 26 is closed.

<Cleaning liquid supply process / gas supply process>
The control unit 204 closes the valve V2. The control unit 204 activates the pump 205 and the reducing atmosphere gas supply unit 210 and opens the valve V1. The cleaning liquid in the chemical tank 201 is conveyed to the reducing atmosphere gas supply unit 210 via the chemical supply line 202. The reducing atmosphere gas supply unit 210 injects bubbles of the reducing atmosphere gas into the cleaning liquid. A cleaning liquid containing bubbles is supplied to the furnace wall tubes 13 a and 13 b of the once-through boiler 10 via the chemical liquid supply line 202.

  Bubbles in the cleaning liquid are discharged from the cleaning liquid in the furnace wall tubes 13a and 13b and stored in the upper space of the cleaning liquid supplied in the furnace wall tubes 13a and 13b. The control unit 204 opens the valve V4, and the air in the furnace wall tubes 13a and 13b is released outside the system through the exhaust line 213. Thus, the furnace wall pipes 13a and 13b are replaced with the reducing atmosphere gas from the purge gas atmosphere.

  Thus, in the second embodiment, an independent gas supply process is not required as in the first embodiment, and the replacement of the gas in the furnace wall tubes 13a and 13b is performed together with the cleaning liquid supply process.

<Washing process>
When at least a region to which hematite has adhered (particularly region 17 to which hematite has adhered more than the other portion) is immersed in the cleaning liquid, the control unit 204 stops the pump 205 and the reducing atmosphere gas supply unit 210 and switches the valves V1 and V4. Close. In the state where the cleaning liquid is allowed to stand, the hematite is soaked and cleaned. Also in the present embodiment, the cleaning liquid in the furnace wall tubes 13a and 13b is approximately the same as the ambient temperature around the furnace wall tubes 13a and 13b, and the oxidation-reduction potential is −0.8 V or more on the basis of the silver-silver chloride electrode. It is maintained at 0.4V or less.

<Discharge process>
After the cleaning process is performed for a predetermined time, the cleaning liquid in the furnace wall tubes 13a and 13b is collected in the chemical tank 201 in the same process as in the first embodiment. Thereby, the chemical cleaning method of this embodiment is completed.

  When a cleaning liquid that does not contain an antifoaming agent is used in the chemical cleaning methods of the first and second embodiments, the cleaning liquid is foamed by supplying the cleaning liquid to the furnace wall tubes 13a and 13b, and bubbles are generated in the region where hematite is generated. A sticky cleaning solution adheres. Detergency is improved by increasing the contact time between hematite and the foam-like cleaning liquid. Moreover, the usage-amount of a cleaning liquid reduces by making a cleaning liquid into foam.

[Third Embodiment]
FIG. 8 is a schematic view illustrating a chemical cleaning apparatus according to the third embodiment.
In the chemical cleaning apparatus 300 of the third embodiment, the chemical liquid supply line 302 and the chemical liquid discharge line 303 are connected to the lower headers 14a and 14b of the once-through boiler 10 as in the first embodiment. The chemical solution supply line 302 and the chemical solution discharge line 303 are connected to the chemical solution tank 301.

The chemical cleaning apparatus 300 includes a reducing atmosphere adjusting agent supply unit 310 as a reducing atmosphere adjusting unit. The reducing atmosphere adjusting agent supply unit 310 includes a reducing atmosphere adjusting agent storage unit 311 and a reducing atmosphere adjusting agent supply line 312. The reducing atmosphere adjusting agent storage unit 311 stores the reducing atmosphere adjusting agent. The reducing atmosphere adjusting agent is, for example, hydrazine, L-ascorbic acid, sulfur-based reducing agent and the like.
The reducing atmosphere adjusting agent supply unit 310 is connected to the chemical solution supply line 302 on the downstream side of the pump 305. A valve V5 is installed in the reducing atmosphere adjusting agent supply line 312. The valve V5 is connected to the control unit 304.

  Although not shown in FIG. 8, a reducing atmosphere gas storage unit, an air supply line, and an exhaust line that are connected to the once-through boiler 10 may be installed as in FIG. 1.

  A chemical cleaning method for cleaning and removing hematite attached in the once-through boiler using the chemical cleaning apparatus 300 of the third embodiment will be described below. In carrying out the chemical cleaning method of the present embodiment, a valve installed in a pipe connecting the once-through boiler 10 and the economizer 26 is closed.

<Cleaning liquid supply process>
The control unit 304 closes the valve V2. The control unit 304 activates the pump 305 and opens the valves V1 and V5. While the cleaning liquid in the chemical liquid tank 301 passes through the chemical liquid supply line 302, the reducing atmosphere adjusting agent is introduced into the cleaning liquid from the reducing atmosphere adjusting agent supply unit 310. The cleaning liquid charged with the reducing atmosphere adjusting agent is fed to the furnace wall tubes 13 a and 13 b of the once-through boiler 10.

<Washing process>
When at least the region to which hematite is attached is immersed in the cleaning liquid, the control unit 304 stops the pump 305 and closes the valves V1 and V5. In the state where the cleaning liquid is allowed to stand, the hematite is soaked and cleaned.

  Also in this embodiment, the cleaning liquid in the furnace wall tubes 13a and 13b is at the same level as the ambient temperature around the furnace wall tubes 13a and 13b. By introducing the reducing atmosphere adjusting agent from the reducing atmosphere adjusting agent supply unit 310 to the cleaning liquid, the oxidation-reduction potential of the cleaning liquid is maintained at −0.8 V or more and −0.4 V or less with respect to the silver-silver chloride electrode. The control unit 304 adjusts the opening of the valve V5 in order to obtain a reducing agent input amount that provides a steam oxidation-reduction potential.

<Discharge process>
After the cleaning process is performed for a predetermined time, the cleaning liquid in the furnace wall tubes 13a and 13b is collected in the chemical liquid tank 301 through the chemical liquid discharge line 303 in the same process as in the first embodiment. Thereby, the chemical cleaning method of this embodiment is completed.

  When a large amount of hematite is adhered, the fluctuation of the oxidation-reduction potential due to the dissolution of hematite increases. By additionally adding a reducing atmosphere adjusting agent to the cleaning liquid as in this embodiment, the oxidation-reduction potential can be easily adjusted within the range of -0.8 to -0.4V.

[Fourth Embodiment]
FIG. 9 is a schematic diagram illustrating a chemical cleaning apparatus according to the fourth embodiment.
Similarly to the chemical cleaning apparatus of the first embodiment, the chemical cleaning apparatus 400 according to the fourth embodiment is a chemical tank 401, a chemical supply line 402, a chemical discharge line 403, a control unit 404, a pump 405, and a reducing atmosphere gas supply unit 410. As a reducing atmosphere gas storage unit 411, an air supply line 412, and an exhaust line 413.
In the chemical cleaning apparatus 400, a circulation loop 406 is installed across the pump 405 of the chemical solution supply line 402.
A circulation loop can also be provided for the chemical cleaning apparatuses of the second embodiment and the third embodiment.

  By passing through the pump 405 in the cleaning liquid supply process, the temperature of the cleaning liquid rises. Part of the cleaning liquid that has passed through the pump 405 flows into the circulation loop 406 and is conveyed to the chemical liquid sharing line upstream of the pump 405. By doing so, the heated cleaning liquid is supplied to the furnace wall tubes 13a and 13b of the once-through boiler 10, and the temperature is higher than that of the first to third embodiments (specifically, the furnace wall tubes). The cleaning step is performed at a temperature higher than the ambient temperature around 13a and 13b and less than or equal to ambient temperature + 10 ° C.

  The higher the temperature of the cleaning process, the more the reaction between the cleaning liquid and hematite and the dissolution in the cleaning liquid are promoted. According to this embodiment, the temperature of the cleaning liquid can be increased with a simple configuration without installing a temperature increasing facility. Further, since the temperature difference between the environmental temperature and the cleaning liquid temperature is small, the configuration of the present embodiment can maintain the temperature of the cleaning liquid higher than the environmental temperature for a long time. As a result, the cleaning power can be further increased.

[Fifth Embodiment]
FIG. 10 is a schematic view for explaining a chemical cleaning apparatus according to the fifth embodiment.
Similar to the chemical cleaning apparatus of the first embodiment, the chemical cleaning apparatus 500 according to the fifth embodiment is a chemical tank 501, a chemical supply line 502, a chemical discharge line 503, a control unit 504, a pump 505, and a reducing atmosphere gas supply unit 510. As a reducing atmosphere gas storage section 511, an air supply line 512, and an exhaust line 513.
The chemical cleaning apparatus 500 further includes a water supply unit 520. The water supply unit 520 includes a water tank 521 and a water supply line 522. The water tank 521 contains water therein. A water supply pump 523 and a valve V6 are installed in the water supply line 522. The water supply line 522 is connected to the lower headers 14a and 14b.

  A chemical cleaning method for cleaning and removing hematite adhered in the once-through boiler using the chemical cleaning apparatus 500 of the fifth embodiment will be described below. In carrying out the chemical cleaning method of the present embodiment, a valve installed in a pipe connecting the once-through boiler 10 and the economizer 26 is closed.

<Gas supply process>
In the same process as in the first embodiment, the reducing atmosphere gas is supplied from the reducing atmosphere gas storage unit 511 through the air supply line 512 into the furnace wall tubes 13a and 13b, and the inside of the furnace wall tubes 13a and 13b is reduced atmosphere gas. Filled with.

<Cleaning liquid supply process>
The control unit 504 activates the pump 505 and opens the valves V1 and V4. The cleaning liquid in the chemical liquid tank 501 is supplied to the once-through boiler 10 via the chemical liquid supply line 502.

  After the predetermined amount of cleaning liquid is supplied, the control unit 504 stops the pump 505 and closes the valve V1. Next, the control unit 504 activates the water-filled pump 523 and opens the valve V6. As a result, the water in the water tank 521 is supplied to the furnace wall tubes 13 a and 13 b of the once-through boiler 10 through the water supply line 522.

  By adjusting the flow rate of the cleaning liquid and water, the furnace wall is in a state where the cleaning liquid layer is on the upper side in the vertical direction, the water layer is on the lower side in the vertical direction, and the cleaning liquid layer and the water layer are at least partially separated. The water level in the pipes 13a and 13b rises. In the present embodiment, the control unit 504 supplies a predetermined amount of cleaning liquid and water respectively to the chemical solution so that the region 17 where hematite adheres more than the other portions in the furnace wall tubes 13a and 13b is immersed in the cleaning liquid layer. The fuel is supplied from the tank 501 and the water tank 521 to the furnace wall pipes 13a and 13b.

<Washing process>
When the region 17 where hematite adheres more than the other part is immersed in the cleaning liquid, the control unit 504 stops the water-filled pump 523 and closes the valves V4 and V6. The hematite is soaked and washed in a state where the washing liquid is left still. Also in this embodiment, the cleaning liquid temperature during the cleaning process is approximately the same as the environmental temperature around the furnace wall tubes 13a and 13b, and the oxidation-reduction potential of the cleaning liquid during the cleaning process is −0.8 V or more and −0.4 V or less. (Silver-silver chloride electrode standard).

<Discharge process>
After the cleaning process is performed for a predetermined time, the cleaning liquid in the furnace wall tubes 13a and 13b is supplied to the chemical tank 501 in the same process as in the first embodiment. Thereby, the chemical cleaning method of this embodiment is completed.
Cleaning liquid collected in the liquid tank 501 is antirust agent concentration is reduced. Therefore, a new cleaning liquid is added and the cleaning liquid is reused, or the cleaning liquid is discharged from the chemical liquid tank 501 and discarded.

  According to the method of the present embodiment, since the region 17 where hematite adheres more than the other part is immersed in the cleaning liquid and concentratedly removed, the amount of the cleaning liquid to be used can be greatly reduced. Cleaning costs can be reduced.

[Sixth Embodiment]
The chemical cleaning apparatus of the sixth embodiment has the same configuration as that of the first embodiment except that the cleaning liquid is accommodated in the microcapsules.
A microcapsule is one in which the above-described cleaning liquid is packaged in a water-soluble capsule. The capsule material of the microcapsule is a water-soluble polymer such as dextrin, processed starch, gelatin, gum arabic, sodium alginate, and carrageenan. The size of the microcapsule is about 0.5 mm to 2 mm in diameter, for example. The microcapsules are produced by, for example, a spray drying method, a spray cooling method, or the like.

  In the chemical cleaning apparatus of the sixth embodiment, a microcapsule supply unit is installed on the upstream side of the pump 105 in the chemical solution supply line 102. The microcapsule supply unit has a tank that accommodates the microcapsules. The microcapsules are stored in a tank in a state of being dispersed in a transport liquid (for example, water).

  In the sixth embodiment, the gas supply process, the cleaning liquid supply process, the cleaning process, and the discharge process are performed as in the first embodiment. In the cleaning liquid supply process of the sixth embodiment, in the cleaning liquid in which the transport liquid including the microcapsules circulates through the chemical liquid supply line 102 by the activation of the pump installed in the flow path connecting the microcapsule supply unit and the chemical liquid supply line 102. The cleaning liquid containing microcapsules is supplied to the furnace wall tubes 13a and 13b. The microcapsules move upward in the furnace wall tubes 13a and 13b and accumulate near the liquid surface. When the capsule of the microcapsule is dissolved in the transport liquid, the cleaning liquid is released, and a foam-like cleaning liquid layer is formed in the vicinity of the liquid surface. In particular, the dispersion concentration of the microcapsules (amount of cleaning liquid) and the liquid surface height (amount of transport liquid supplied by the control unit 104) are set so that the region 17 where hematite adheres more than the other part is immersed in the cleaning liquid layer. Adjust as appropriate.

  According to the method of this embodiment, since the region where hematite is generated more than the other part can be easily immersed in the cleaning liquid, the amount of the cleaning liquid to be used can be further greatly reduced, and the cleaning cost is further increased. It is possible to reduce.

  The sixth embodiment can also be applied to the chemical cleaning methods and chemical cleaning apparatuses of the second to fifth embodiments.

[Seventh Embodiment]
A chemical cleaning method according to the seventh embodiment will be described using the chemical cleaning apparatus 100 of FIG. In the chemical cleaning method of the seventh embodiment, the gas supply process, the cleaning liquid supply process, and the discharge process are performed in the same manner as in the first embodiment except for the cleaning process.

  In the cleaning step in the chemical cleaning method of the seventh embodiment, when the region to which hematite is attached is immersed in the cleaning liquid, the control unit 104 stops the pump 105 and closes the valves V1 and V4.

  The control unit 104 opens the valve V2. Since the cleaning liquid is fed back to the chemical tank 101 through the chemical discharge line 103 by opening the valve V2, the liquid level of the cleaning liquid in the furnace wall tubes 13a and 13b is lowered. Next, the control unit 104 closes the valve V2 and opens the valve V1 to start the pump 105. As a result, the cleaning liquid in the chemical liquid tank 101 is supplied to the furnace wall pipes 13a and 13b of the once-through boiler 10 via the chemical liquid supply line 102, and the liquid level of the cleaning liquid in the furnace wall pipes 13a and 13b rises. The control unit 104 performs the discharge and supply of the cleaning liquid at a predetermined cycle.

The discharge amount of the cleaning liquid here may be a part or all of the cleaning liquid. If the discharge amount of the cleaning liquid is changed, the change amount of the liquid level can be changed. The discharge amount of the cleaning liquid, that is, the amount of change in the liquid level is preferably set appropriately in consideration of the size of the region where hematite adheres more than the other part, the cleaning efficiency, and the like. The control unit 104 discharges and feeds a predetermined amount of cleaning liquid according to the liquid level change amount.
Moreover, the period which repeats discharge | emission and supply of a washing | cleaning liquid, and a stationary period may be implemented alternately alternately.

  When the discharge and the supply of the cleaning liquid are repeated, the cleaning liquid is agitated near the liquid surface in the furnace wall tubes 13a and 13b, and a flow rate is given to the cleaning liquid. As a result, the cleaning power is improved, and the cleaning efficiency of hematite is increased.

  In addition, the chemical cleaning method of this embodiment is applicable also when using the chemical cleaning apparatus of 2nd Embodiment-4th Embodiment.

[Eighth Embodiment]
FIG. 11 is a schematic view illustrating a chemical cleaning apparatus according to the eighth embodiment.
Similar to the chemical cleaning apparatus of the first embodiment, the chemical cleaning apparatus 600 according to the eighth embodiment is a chemical liquid tank 601, a chemical liquid supply line 602, a chemical liquid discharge line 603, a control unit 604, a pump 605, and a reducing atmosphere gas supply unit 610. As a reducing atmosphere gas storage section 611, an air supply line 612, and an exhaust line 613. The chemical cleaning apparatus 600 further includes a pump 606 in the chemical solution discharge line 603.
A chemical cleaning method according to the eighth embodiment will be described with reference to FIG. In the chemical cleaning method of the eighth embodiment, the gas supply process, the cleaning liquid supply process, and the discharge process are performed in the same manner as in the first embodiment except for the cleaning process.

  In the cleaning step in the chemical cleaning method of the eighth embodiment, when the region to which hematite is attached is immersed in the cleaning liquid, the control unit 604 stops the pump 605 of the chemical liquid supply line 602 and closes the valves V1 and V4.

  The control unit 604 opens the valves V2 and V3 and operates the pump 606. When the valve V3 is opened, the reducing atmosphere gas is supplied from the reducing atmosphere gas reservoir 111 to the furnace wall tubes 13a and 13b of the once-through boiler 10 through the air supply line 112, and the gas pressure in the space above the cleaning liquid level increases. To do. At the same time, by opening the valve V2 and starting the pump 606, the cleaning liquid inside the furnace wall pipes 13a and 13b is supplied to the chemical liquid tank 601 via the chemical liquid discharge line 603, and the liquid level of the cleaning liquid inside the furnace wall pipes 13a and 13b Decreases.

  Next, the control unit 604 closes the valves V2 and V3 and opens the valves V1 and V4. The control unit stops the pump 606 and starts the pump 605. Thereby, the cleaning liquid in the chemical liquid tank 601 is supplied to the furnace wall pipes 13a and 13b of the once-through boiler 10 via the chemical liquid supply line 602, and the liquid level of the cleaning liquid in the furnace wall pipes 13a and 13b rises.

  Since pressurization of the cleaning liquid level with gas and discharge of the cleaning liquid using a pump are used, the flow rate at the time of discharging the cleaning liquid is higher than that in the seventh embodiment, and the cleaning liquid is near the liquid level in the furnace wall tubes 13a and 13b. Is easily stirred. For this reason, a cleaning power improves rather than 7th Embodiment and the cleaning efficiency of hematite rises.

  The chemical cleaning apparatus and the chemical cleaning method of the present embodiment can also be applied to a case where a pump is installed in the chemical solution discharge line as compared with the second to fourth embodiments.

[Ninth Embodiment]
FIG. 12 is a schematic view illustrating a chemical cleaning apparatus according to the ninth embodiment.
Similar to the chemical cleaning apparatus of the first embodiment, the chemical cleaning apparatus 700 according to the ninth embodiment is a chemical tank 701, a chemical supply line 702, a chemical discharge line 703, a control unit 704, a pump 705, and a reducing atmosphere gas supply unit 710. As a reducing atmosphere gas storage unit 711, an air supply line 712, and an exhaust line 713. The chemical cleaning apparatus 700 further includes a circulation line 720. In addition, it is possible to install the same circulation line also with respect to the chemical cleaning apparatus of 2nd Embodiment-4th Embodiment.

  The circulation line 720 is connected to the lower headers 14a and 14b as one end side of the once-through boiler and to the upper headers 15a and 15b as the other end side. A circulation pump 721 is installed in the middle of the circulation line 720. The circulation line 720 and the circulation pump 721 may be temporarily installed.

  The direction of circulation of the cleaning liquid is not particularly limited. In the configuration of FIG. 12, the cleaning liquid is circulated in the furnace wall tubes 13 a and 13 b from the bottom to the top, but the cleaning liquid may be circulated from the top to the bottom.

  In this embodiment, the temperature of the cleaning liquid is around the ambient temperature, and the circulation flow rate may be a small flow rate that circulates at least once during the cleaning process. Therefore, the discharge pressure of the circulation pump 721 may be low.

  A chemical cleaning method using the chemical cleaning apparatus 700 of the ninth embodiment will be described below. In the chemical cleaning method of the ninth embodiment, the gas supply process and the discharge process are performed in the same manner as in the first embodiment.

<Cleaning liquid supply process>
The control unit 704 activates the pump 705 and opens the valves V1 and V4. The cleaning liquid in the chemical liquid tank 701 is supplied to the once-through boiler 10 via the chemical liquid supply line 702. In the ninth embodiment, the cleaning liquid is supplied to all of the lower header, the furnace wall tube, the upper header, and the circulation line 720 in the once-through boiler 10. The control unit 704 stores an amount of cleaning liquid that can immerse all of the lower header, the furnace wall tube, the upper header, and the circulation line 720, and supplies a predetermined amount of cleaning liquid to the once-through boiler 10 in the cleaning liquid supply process.

  Here, a valve installed in a pipe connecting the once-through boiler 10 and the steam separator 30 is closed. By doing so, the cleaning liquid can be prevented from flowing into the steam separator 30 which is a device adjacent on the downstream side of the once-through boiler 10.

<Washing process>
When a predetermined amount of cleaning liquid is supplied to the once-through boiler 10, the control unit 704 stops the pump 705 and closes the valves V1 and V4. Next, the control unit 704 activates the circulation pump 721. When the circulation pump 721 is activated, the cleaning liquid passes through the lower headers 14a and 14b, the furnace wall tubes 13a and 13b, the upper headers 15a and 15a, and the circulation line 720. That is, in the present embodiment, the cleaning liquid is circulated without flowing into other equipment (the economizer 26 and the steam separator 30) adjacent to the once-through boiler 10. Circulation is performed at a flow rate that allows the cleaning liquid to circulate between the once-through boiler 10 and the circulation line 720 at least once during the cleaning process. Note that the rotational speed of the circulation pump 721 may be increased or decreased at a predetermined cycle. By doing so, the flow rate of the cleaning liquid flowing through the furnace wall tubes 13a and 13b varies, and the cleaning capability is further improved.

  Further, the temperature of the cleaning liquid is raised when passing through the circulation pump 721. For this reason, for example, as compared with the case where the cleaning liquid is allowed to stand during the cleaning process as in the first embodiment (specifically, higher than the environmental temperature around the furnace wall tubes 13a and 13b, the environmental temperature + 10 ° C. The cleaning step is performed in the following).

  During the cleaning process, the flow path of the cleaning liquid (the lower headers 14a and 14b, the furnace wall pipes 13a and 13b, the upper headers 15a and 15b, and the circulation line 720) constitutes a closed space. The potential is maintained at −0.8 V or more and −0.4 V or less (silver-silver chloride electrode standard).

  According to this embodiment, a flow rate is given to the cleaning liquid, the cleaning liquid is stirred, and further, the cleaning liquid is heated during the cleaning process. Therefore, the cleaning power is improved as compared with the first embodiment in which no circulation line is provided, and hematite The cleaning efficiency increases.

DESCRIPTION OF SYMBOLS 1 Thermal power generation system 10,10a, 10b Through-flow boiler 11a, 11b Combustion chamber 12a, 12b Wall surface 13a, 13b Furnace wall pipe 14a, 14b Lower header 15a, 15b Upper header 16 Branch part 100,200,300,400,500 , 600, 700 Chemical cleaning apparatuses 101, 201, 301, 401, 501, 601, 701 Chemical liquid tanks 102, 202, 302, 402, 502, 602, 702 Chemical liquid supply lines 103, 203, 303, 403, 503, 603 703 Chemical solution discharge line 104, 204, 304, 404, 504, 604, 704 Control unit 105, 205, 305, 405, 505, 605, 606, 705 Pump 110, 210, 410, 510, 610, 710 Reducing atmosphere gas supply Part 111,411,511,611 711 Reducing atmosphere gas storage unit 112, 412, 512, 612, 712 Supply line 113, 213, 413, 513, 613, 713 Exhaust line 310 Reducing atmosphere adjusting agent supply unit 311 Reducing atmosphere adjusting agent storage unit 312 Reducing atmosphere adjusting agent Supply line 406 Circulation loop 520 Water supply unit 521 Water tank 522 Water supply line 523 Water-filled pump 720 Circulation line 721 Circulation pump

Claims (19)

A cleaning liquid supply step in which a cleaning liquid containing a chelating agent, a reducing agent, or a rust preventive agent that is a mixture of the chelating agent and the reducing agent is supplied to a cleaning target device having a member to which hematite is attached
A cleaning step in which at least the region where the hematite is adhered in the member is immersed in the cleaning liquid, and the oxidation-reduction potential of the cleaning liquid is maintained at a value at which the hematite is eluted in the cleaning liquid, and the hematite is removed from the member And
The chelating agent is any one of an aminocarboxylic acid chelating agent, an oxycarboxylic acid chelating agent and an organic phosphorus chelating agent,
Wherein the reducing agent is a metal ion, sulfite, oxalic acid, formic acid, and the ascorbic acid, pyrogallol, hydrazine, or hydrogen,
A chemical cleaning method wherein the pH of the cleaning liquid is within a range of 4 to 8.   2. The chemical cleaning method according to claim 1, wherein the cleaning step is performed while the value is maintained within a range of −0.8 V or more and −0.4 V or less on a silver-silver chloride electrode basis.   The chemical cleaning method according to claim 1, wherein the value is adjusted by supplying a reducing atmosphere gas to the device to be cleaned.   The chemical cleaning method according to any one of claims 1 to 3, wherein a temperature of the cleaning liquid in the cleaning step is in a range from an ambient temperature around the member to a temperature not higher than 10 ° C higher than the ambient temperature. .   The chemical cleaning method according to claim 1, wherein the region is immersed in the cleaning liquid in a state where the cleaning liquid is left standing. Further comprising a water supply step between the cleaning liquid feeding step and the cleaning step,
The predetermined amount of the cleaning liquid is supplied to the cleaning target device in the cleaning liquid supply step, the predetermined amount of water is supplied to the cleaning target device in the water supply step, and the region is immersed in the cleaning liquid. The chemical cleaning method according to claim 5.   The chemical cleaning method according to claim 1, wherein the cleaning liquid is accommodated in a capsule made of a water-soluble polymer, and the capsule is supplied to the cleaning target device.   During the cleaning step, the step of discharging the cleaning liquid from the member and the step of supplying the discharged cleaning liquid to the member are repeated to increase the level of the cleaning liquid near the region. The chemical cleaning method according to claim 1, wherein the chemical cleaning method is moved.   The cleaning liquid passes through the member and is discharged from the upstream end of the member during the cleaning step, and the discharged cleaning liquid is circulated directly to the downstream end of the member. The chemical cleaning method according to claim 4. A chemical cleaning apparatus for chemically cleaning a device to be cleaned having a member to which a hematite scale is attached,
A chelating agent, a reducing agent, or a mixture of the chelating agent and the reducing agent, and the chelating agent is one of an aminocarboxylic acid chelating agent, an oxycarboxylic acid chelating agent and an organophosphorus chelating agent The reducing agent contains a rust preventive agent that is any one of metal ions, sulfites, oxalic acid, formic acid, ascorbic acid, pyrogallol, hydrazine, and hydrogen , and contains a cleaning solution having a pH in the range of 4-8. A chemical tank,
A chemical supply line for connecting the cleaning target device and the chemical tank and supplying the cleaning liquid to the member;
A pump installed in the chemical supply line;
A chemical solution discharge line for connecting the cleaning target device and the chemical solution tank, and discharging the cleaning solution from the member;
Means for immersing at least the region of the member to which the hematite is adhered in the cleaning liquid;
Means for maintaining the redox potential of the cleaning liquid during cleaning at a value at which the hematite elutes in the cleaning liquid;
The chemical cleaning apparatus, wherein the chemical liquid tank, the chemical liquid supply line, and the pump are means for supplying the cleaning liquid to the member.   The chemical cleaning apparatus according to claim 10, further comprising a reducing atmosphere adjustment unit that adjusts the value to a value within a range of −0.8 V or more and −0.4 V or less based on a silver-silver chloride electrode reference.   The chemical cleaning apparatus according to claim 11, wherein the reducing atmosphere adjusting unit supplies a reducing atmosphere gas to the cleaning target device.   The chemical cleaning according to any one of claims 10 to 12, wherein a temperature of the cleaning liquid supplied to the member is in a range not less than an ambient temperature around the member and not more than 10 ° C higher than the ambient temperature. apparatus. A circulation loop connecting the upstream chemical liquid supply line and the downstream chemical liquid supply line across the pump;
The chemical cleaning apparatus according to claim 10, wherein a part of the cleaning liquid that has passed through the pump is conveyed to the upstream side of the pump through the circulation loop.   The chemical cleaning apparatus according to claim 10, wherein during the cleaning, the supply of the cleaning liquid to the member and the discharge of the cleaning liquid from the member are stopped and the cleaning liquid is allowed to stand.   The water supply part provided with the water tank which accommodates water, the water supply line which connects the said water tank and the said washing | cleaning object apparatus, and the water supply pump installed in the said water supply line is further provided with the water supply part. Item 16. The chemical cleaning apparatus according to any one of Items 15. The cleaning liquid is contained in a capsule made of a water-soluble polymer,
The chemical cleaning apparatus according to any one of claims 10 to 16, wherein the chemical liquid tank accommodates the capsule, and the capsule is supplied from the cleaning liquid tank to the cleaning target device.   During the cleaning, the cleaning liquid in the member is discharged toward the chemical liquid tank through the chemical liquid discharge line, and the cleaning liquid in the chemical liquid tank is supplied to the member through the chemical liquid supply line. The chemical cleaning apparatus according to any one of claims 10 to 13. A circulation section comprising a circulation line connecting the upstream end and the downstream end of the member, and a circulation pump installed in the circulation line;
The chemical cleaning apparatus according to any one of claims 10 to 13, wherein the cleaning liquid discharged from the front downstream end through the circulation line is circulated to the upstream end through the circulation line.