WO2020137496A1

WO2020137496A1 - Method and apparatus for cleaning and maintaining boiler plant

Info

Publication number: WO2020137496A1
Application number: PCT/JP2019/048147
Authority: WO
Inventors: 貴行和田; 陽一真保; 良典野口; 瑞希大塚
Original assignee: 三菱日立パワーシステムズ株式会社
Priority date: 2018-12-27
Filing date: 2019-12-09
Publication date: 2020-07-02
Also published as: TWI796533B; TW202041812A; JP2020106199A; JP7150594B2; KR20210034040A

Abstract

The purpose of the present invention is to provide a method and an apparatus for cleaning and maintaining a boiler plant, by which, in a period between chemical cleaning and initiation of normal operation, it is possible to subject parts of a boiler to be cleaned to a rust-proofing treatment at low cost and in a short time, and to maintain the boiler. This method for maintaining a boiler plant includes: a step (S2) for subjecting parts to be cleaned, which have scale attached thereto, to neutral cleaning at room temperature using a neutral cleaning liquid containing a rust preventive agent; a step (S4) for circulating an aqueous solution of an ammonia-based compound having a pH of 9.8 or more at room temperature to the parts to be cleaned; and a step (S5) for blowing the aqueous solution of an ammonia-based compound from the parts to be cleaned.

Description

Cleaning and storage method and cleaning storage device for boiler plant

The present disclosure relates to a cleaning storage device for cleaning and storing a boiler plant and a cleaning storage method thereof.

When storing a boiler plant equipped with a boiler that has a drum and an exhaust heat recovery boiler (HRSG) for several days, such as when it is out of operation, the dissolved oxygen in the feed water or boiler water becomes a cause of corrosion of boiler plant components. Therefore, during storage of the boiler plant, corrosion is prevented by using an anticorrosive agent (see Patent Document 1). As the anticorrosive agent, hydrazine having deoxidizing ability is used.

Conventionally, at the time of storage such as shutdown of the boiler plant, the operating water (supply water and boiler water) in the boiler plant components is replaced with hydrazine water as the storage water, and when the boiler plant is restarted, it is the storage water. There is work that replaces hydrazine water with operating water.

A large amount of pure water is used to replace hydrazine water with operating water. Wastewater treatment is required to dispose of hydrazine water and operating water discharged during replacement work. Therefore, replacement of hydrazine water with operating water becomes a factor that increases the load on the wastewater treatment facility.

Furthermore, hydrazine is a carcinogen, so there is a problem in wastewater treatment when switching to operating water. Therefore, without using hydrazine, it is possible to divert the stored water to operating water without draining the stored water, and it is preferable to use a storage method for a boiler plant that can prevent corrosion of plant components for several days or longer. Has become.

As a method to prevent corrosion of boiler plant components without using hydrazine, it is known to adjust the concentration of ammonia added to feed water and boiler water to increase the pH of feed water as storage water and boiler water. (See Patent Document 2). When the pH of feed water and boiler water is set to 9.8 or higher, it becomes possible to prevent corrosion in plant components without adding hydrazine during storage of the boiler plant. For example, if the pH of feed water and boiler water is set to 10, it is possible to store the boiler plant without adding hydrazine.

Further, Patent Document 3 discloses a method for cleaning an exhaust heat recovery boiler, in which cleaning is performed at a low temperature (without heating/normal temperature) using a cleaning liquid containing a neutral rust remover.

[Patent Document 4] discloses a cleaning method in which a heated cleaning liquid is circulated in the heat transfer tube in a state where the exhaust gas supply port and the exhaust gas outlet of the exhaust heat recovery boiler are closed.

JP-A-62-233606 JP, 2014-159925, A JP, 2005-105786, A JP-A-11-37405

Exhaust heat recovery boiler consists of multiple steam drums and evaporators. When cleaning a plurality of parts, as shown in FIG. 12, there is a method in which a cleaning liquid from a cleaning facility 30 is put into a economizer 31, a steam drum 32, and an evaporator 33 from a water supply system to perform cleaning.

ㆍGenerally, fin tubes with high heat dissipation are used for the evaporator of the exhaust heat recovery boiler. However, in the cleaning method using the heated cleaning liquid as disclosed in Patent Document 4, for example, it is difficult to maintain the temperature of the cleaning liquid at a high temperature (50° C. to 90° C.) due to heat radiation from the fin tube, so that the cleaning effect decreases. As a countermeasure against this, in Patent Document 3, the evaporator is cleaned using a neutral rust remover without heating the cleaning liquid to a high temperature.

Fig. 13 shows a process diagram of a conventional chemical cleaning method. In the conventional chemical cleaning method, first, a temporary system is connected to the cleaning target (S31). Next, after chemically cleaning (S32) at a high temperature (50° C. to 90° C.), the cleaning liquid is blown (S33) and washed with water (S34).

　Since the scale is removed by the chemical cleaning process and the exposed base material easily reacts with oxygen, the inner surface of the heat transfer tube is easily rusted. After rinsing with water, some rust is generated, so the rust that has occurred is washed off with a rinse liquid (acid with a low concentration) (S35, 20°C to 90°C). After that, after neutralizing the inside of the system (S36, 20°C to 90°C) and adding hydrazine water to prevent rusting (S37, 80°C to 90°C) to form a rustproof film on the inner surface of the heat transfer tube , Blow (S38). Finally, the temporary system is disassembled (S39).

The above rustproof treatment is carried out at 80°C to 90°C by adding hydrazine water in order to prevent rusting during the period from washing to normal operation. However, the rustproofing treatment at a low temperature as in Patent Document 3 does not form a sufficient rustproof film. In an insufficient state, rust may occur on the inner surface of the heat transfer tube after blowing the anticorrosion treatment liquid. Rust on the inner surface of the heat transfer tube is not preferable from the viewpoint of cleaning work quality, water quality during operation, and facility reliability.

 Although rust prevention treatment that fills the inside of the system with storage water containing a high concentration of ammonia can be considered, it is necessary to drain the storage water for dismantling construction of the temporary system. Therefore, it may be unfavorable to fill the storage water with water from the viewpoint of the degree of freedom of construction (partial disconnection of the system and restoration of the disconnected part).

The present disclosure has been made in view of the above problems, and during the period from chemical cleaning to the start of normal operation, rust prevention treatment is performed on the cleaning target portion of the boiler at low cost and in a short time, and the boiler is stored. An object of the present invention is to provide a cleaning storage method and a cleaning storage apparatus for a boiler plant that can be used.

In order to solve the above problems, the cleaning storage method and cleaning storage apparatus of the boiler plant of the present disclosure adopt the following means.

A first aspect of the present disclosure includes a step of neutrally cleaning a cleaning target site having scale attached thereto at room temperature with a neutral cleaning solution containing a rust remover, and a pH of 9. Provided is a method for cleaning and storing a boiler plant, which includes a step of circulating an ammonia-based compound aqueous solution at room temperature of 8 or more and a step of blowing the ammonia-based compound aqueous solution from the cleaning target site.

According to the first aspect, since the cleaning is performed at room temperature, the temperature rising facility and the preheating process of the cleaning liquid are unnecessary, and it is not necessary to monitor the temperature drop of the cleaning liquid due to cooling during the cleaning process. This makes it possible to reduce the cleaning cost and cleaning time. The "normal temperature" means about room temperature, and is a temperature at which preheating or heating is not performed from the outside. Specifically, it is 5°C to 50°C, more preferably 15°C to 30°C.

After the ammonia-based compound aqueous solution having a pH of 9.8 or higher is circulated on the surface of the base material of the cleaning target site after the scale is removed, the ammonia-based compound aqueous solution is blown from the cleaning target site, and the surface contains ammonia-containing water. Covered with a membrane. As a result, it becomes possible to suppress rusting until the start of operation. The main component of the ammonia-containing water film is ammonia water, which is the same as the feed water treatment chemical used when operating the boiler plant. From this, it is not necessary to remove the ammonia-containing water film at the start of the operation, and therefore the operation can be started as it is after the boiler plant is stored. As a result, working time can be shortened and cost can be reduced. Furthermore, since rusting can be suppressed without using hydrazine, it is excellent in environmental friendliness.

In the first aspect, in the step of neutral cleaning, the neutral cleaning solution is circulated in the cleaning target site, iron ions in the circulated neutral cleaning solution are analyzed, and the neutral cleaning solution is analyzed. It is desirable to finish the neutral cleaning after confirming that the change in iron ion concentration in the cleaning liquid shows a saturation tendency.

The fact that the iron ion concentration change in the cleaning liquid tends to be saturated means that the scale to be cleaned has been removed and the scale dissolution amount has decreased. By confirming this and determining the end of cleaning, the maximum cleaning effect can be obtained in the shortest possible time.

In the first aspect, it is desirable to provide a step of performing acid cleaning at room temperature with an acidic cleaning liquid before the step of circulating the aqueous ammonia compound solution.

Depending on the operation of the plant, scale components include calcium (Ca), aluminum (Al), copper (Cu), etc. Since Ca, Al, and Cu have low solubilities in the vicinity of neutrality, these scale components may not be completely dissolved/removed by low-temperature cleaning using a neutral rust remover. The scale that cannot be removed may remain as sludge in the system. The residual sludge can be discharged to the outside of the system to some extent by blowing the cleaning liquid or washing with water after cleaning, but it is difficult to discharge the whole sludge and may remain in the system. In particular, in a gas vertical flow type exhaust heat recovery boiler, the heat transfer tubes are arranged horizontally and the length is large at 20 m class, and it is difficult to discharge sludge at the flow velocity of the water flow at the time of cleaning and discharging (blowing). Particular attention is required. The remaining sludge becomes a factor of lowering the heat transfer performance of the heat transfer tube and causing corrosion due to sludge-containing components.

In acid cleaning, these scale components (Ca, Al, Cu, etc.) that are difficult to dissolve in a neutral cleaning solution can be removed, and the amount of sludge remaining on the cleaning target site can be reduced.

In the first aspect, in the step of performing the acid cleaning, the acidic cleaning solution is circulated in the cleaning target site, iron ions in the circulated acidic cleaning solution are analyzed, and iron in the acidic cleaning solution is analyzed. It is desirable to finish the acid cleaning after confirming that the change in ion concentration shows a saturation tendency.

In the first aspect, further comprising a step of extruding and blowing the acidic cleaning liquid using the aqueous ammonia compound solution after the acid cleaning, and in the step of extruding and blowing, the acidic cleaning liquid of the extruding blow is After blowing almost the entire amount and circulating the aqueous ammonia compound solution in the cleaning target site, the pH of the aqueous ammonia compound compound is analyzed, and the extrusion blow and the ammonia are analyzed until the analyzed pH becomes a reference value or more. It is desirable to continue the circulation of the aqueous system compound solution.

　In extrusion blow, the acidic cleaning liquid is extruded and replaced with an aqueous ammonia compound solution. By judging the duration of the extrusion blow based on the pH of the blow liquid, it is possible to avoid spending extra time.

In the first aspect, after the neutral cleaning, the method further comprises a step of extruding and blowing the neutral cleaning liquid using the aqueous solution of the ammonia-based compound, and in the step of extruding and blowing, the Blowing almost the entire amount of the cleaning liquid, after circulating the ammonia-based compound aqueous solution in the cleaning target site was analyzed for components derived from the rust remover in the ammonia-based compound aqueous solution, of the components derived from the analyzed rust remover It is desirable to continue the extrusion blow and the circulation of the aqueous solution of ammonia compound until the concentration becomes equal to or lower than the reference value.

In extrusion blow, the neutral cleaning solution is extruded and replaced with an aqueous ammonia compound solution. By determining the duration of extrusion blow due to the decrease in the concentration of the components derived from the rust remover in the blow liquid, it is possible to avoid spending extra time.

In the first aspect, after the step of blowing the aqueous ammonia compound solution, a solid vaporizable ammonia compound can be introduced into the site to be cleaned.

The solid of the vaporizable ammonia compound that has been input is vaporized in the cleaning target site, is quickly diffused, and is taken into the ammonia-containing water film. When the portion to be cleaned is stored for a long period of time after the formation of the ammonia-containing water film, the ammonia component escapes from the ammonia-containing water film, but the rust preventive effect of the water film can be maintained by introducing the vaporizable ammonia compound solid.

In the first aspect, at least one of the acidic cleaning liquid and the neutral cleaning liquid may be filtered during circulation.

Sludge can be removed by filtering the circulating cleaning solution. As a result, the amount of sludge remaining generated during cleaning can be reduced, and therefore the heat transfer performance of the heat transfer tube due to sludge residue and the risk of corrosion due to sludge-containing components can be reduced.

In the first aspect, the cleaning target portion may be an evaporator of the exhaust heat recovery boiler. By limiting the part to be cleaned to the evaporator, the amount of cleaning liquid used can be suppressed and the amount of drainage can be reduced.

According to a second aspect of the present disclosure, a circulation part configured to circulate a fluid in a portion to be cleaned to which scale is attached, and a neutral cleaning liquid supply for supplying a neutral cleaning liquid containing a rust remover to the circulation part. Section, an ammonia-based compound aqueous solution supply section for supplying an ammonia-based compound aqueous solution containing an ammonia-based compound having a pH of 9.8 or more to the circulation section, and a blow channel for discharging the ammonia-based compound aqueous solution from the circulation section. Provided is a cleaning and storage device for a boiler plant equipped with the same.

In the second aspect, the circulation unit has a circulation flow path whose both ends are connected to an inlet/outlet of the cleaning target site, a pump provided in the middle of the circulation flow path, and the downstream side of the pump. And a filtering device provided in the middle of the circulation flow path.

In the second aspect, one end is connected to at least one of the circulation part, the inlet and the outlet of the cleaning target site, and the other end is the acidic cleaning liquid supply part, the neutral cleaning liquid supply part, and the ammonia-based compound aqueous solution. You may further provide the blow flow path connected to at least one of the supply parts.

According to the second aspect, since the blow liquid can be returned to at least one of the acidic cleaning liquid supply unit, the neutral cleaning liquid supply unit, and the ammonia-based compound aqueous solution supply unit, the installation of the drain tank can be omitted.

According to the present disclosure, in a period from chemical cleaning to the start of normal operation, rust prevention treatment is performed on a cleaning target portion of a boiler at low cost and in a short time, and a boiler plant cleaning storage method and cleaning storage that can store a boiler It becomes a device.

It is process drawing of the cleaning storage method which concerns on 1st Embodiment. It is a graph which illustrates the amount of sludge in neutral washing. FIG. 3 is a schematic diagram showing changes in the cleaning time and the Fe ion concentration in the neutral cleaning liquid in the first embodiment. It is a schematic diagram of an ammonia-containing water film. It is a schematic diagram at the time of specific part washing. It is process drawing of the cleaning storage method which concerns on 2nd Embodiment. It is a graph which illustrates the sludge amount in acid cleaning and neutral cleaning in 2nd Embodiment. FIG. 7 is a schematic diagram of changes in the cleaning time and the Fe ion concentration in the cleaning liquid in the second embodiment. It is process drawing of the cleaning storage method which concerns on 3rd Embodiment. It is a schematic diagram which shows an example of a washing storage apparatus. It is a schematic diagram which shows an example of a washing storage apparatus. It is a schematic diagram at the time of washing multiple parts. It is process drawing of the conventional chemical cleaning method.

Hereinafter, an embodiment of a cleaning and storing method and a cleaning and storing apparatus for a boiler plant according to the present disclosure will be described with reference to the drawings.

The following embodiments exemplify a method for cleaning and storing an exhaust heat recovery boiler. In each step of the cleaning and storing method according to the following embodiment, the inside of the cleaning target device (cleaning target portion) is cleaned using a cleaning liquid at room temperature without heating. "Normal temperature" means about room temperature, and is a temperature at which preheating or heating is not performed from the outside. The “normal temperature” is specifically 5 to 50° C., more preferably 15° C. to 30° C.

[First Embodiment]
FIG. 1 shows a process diagram of a method for cleaning and storing a boiler plant according to this embodiment. The cleaning storage method according to the present embodiment includes step 1 (S1) to step 6 (S6) in order.

(S1) Connection of Temporary System (Cleaning/Storage Device) First, a temporary system for supplying the cleaning liquid into the device to be cleaned is connected. After that, the cleaning liquid or the like is injected into the device to be cleaned via the temporary system.

(S2) Neutral Cleaning After a neutral cleaning solution containing a rust remover is injected from the temporary system to fill the inside of the equipment to be cleaned with the neutral cleaning solution, the neutral cleaning solution is circulated in the system at room temperature. The wash solution is not warmed during circulation.

The pH of the neutral cleaning solution containing the rust remover is 4 to 8. The rust remover is a chelating agent, a reducing agent, or a mixture of a chelating agent and a reducing agent, and is an object to be removed that has adhered to the inside of the equipment to be cleaned (for example, a scale containing metal oxides or metal salts, rust hump). Etc.) can be removed. “Rusty humps” are hump-like corrosion products (see JIS Z 0103 1050) that occur on the surface of steel. The neutral cleaning liquid is appropriately adjusted in concentration of the chelating agent, the reducing agent and the corrosion inhibitor so as to obtain a desired cleaning capacity and cleaning time.

Examples of the chelating agent include aminocarboxylic acids such as EDTA, BAPTA, DOTA, EDDS, INN, NTA, DTPA, HEDTA, TTHA, PDTA, DPTA-OH, HIDA, DHEG, GEDTA, CMGA, EDDS, and salts thereof. Carboxylic acid type chelating agents, oxycarboxylic acids such as citric acid, gluconic acid, hydroxyacetic acid and salts thereof, oxycarboxylic acid type chelating agents such as ATMP, HEDP, NTMP, PBTC and EDTMP, and salts thereof. It is an organic phosphorus chelating agent such as. Examples of the reducing agent include various metal ions such as Fe ²⁺ and Sn ²⁺ , nitrites such as sodium sulfite, organic compounds such as oxalic acid, formic acid, ascorbic acid and pyrogallol, hydrazine and hydrogen. A corrosion inhibitor may be added to the neutral cleaning liquid.

(S3) Extrusion Blow After analyzing the Fe ions in the liquid of the neutral cleaning liquid that has been circulated and confirming that the change in the Fe ion concentration in the liquid tends to saturate, the ammonia-based compound at room temperature is placed in the device to be cleaned. The neutral cleaning solution is extrusion blown while pouring the aqueous solution. The saturation tendency means that the change width of the Fe ion concentration in the liquid is 100 mg/L or less as compared with the previously measured Fe ion iron concentration in the liquid. The amount of the aqueous ammonia compound solution used for extrusion blow is, for example, about 1 to 1.5 times the capacity of the device to be cleaned.

The aqueous ammonia-based compound solution contains the ammonia-based compound at a concentration such that the pH is 9.8 to 11, preferably pH 9.8 to 10.5. The ammonia-based compound is, for example, a volatile amine selected from 2-amino-2-methyl-1-propanol, monoethanolamine, monoisopropanolamine, cyclohexylamine, diethylethanolamine, morpholine, 3-methoxypropylamine, and ammonia. It is a compound.

(S4) Circulation of Ammonia-Based Compound Aqueous Solution In (S3) above, after substantially all of the neutral cleaning liquid is extruded and blown with the ammonia-compound aqueous solution, the extrusion-blowing is temporarily stopped and the ammonia-based compound aqueous solution in the device to be cleaned is circulated. .. During the circulation of the aqueous ammonia compound solution, the aqueous ammonia compound solution is not heated.

After circulating the ammonia-based compound aqueous solution, analyze the ammonia-based compound aqueous solution to confirm the components in the solution that are derived from the rust remover.

For example, if the neutral cleaning solution contains organic phosphoric acid as a chelating agent, analyze phosphorus (P) in the aqueous ammonia compound solution. P analysis can be carried out by the molybdenum blue absorptiometry described in JIS K 0102 Industrial Wastewater Testing Method 46.3 Total Phosphorus, ion chromatography, ICP mass spectrometry or atomic absorption.

Repeat steps (S3) and (S4) until the rust remover-derived component in the liquid falls below the standard value. The reference value is set in advance by a preliminary test. Confirm that the components derived from the rust remover in the liquid are below the standard values.

(S5) Blow Ammonia-Based Compound Aqueous Solution After the above (S4), the ammonia-based compound aqueous solution is blown from inside the cleaning target device to form an ammonia-containing water film on the inner surface of the cleaning target device. This ammonia-containing water film portion has a rust preventive effect.

(S6) Dismantling the temporary system After the above (S5), the temporary system is dismantled.

-The above steps 2 to 5 may be performed only once, or may be performed multiple times.

If the equipment to be cleaned has a permanent cleaning and storage device, (S1) and (S6) above are omitted.

Fig. 2 exemplifies (S2) the amount of sludge (standard value) before and after neutral cleaning. In the figure, the vertical axis represents the amount of sludge remaining in the equipment to be cleaned. (S2) About 90% of sludge can be removed only by neutral cleaning.

(S2) Fe scale is dissolved and removed by neutral cleaning. FIG. 3 shows a schematic diagram of changes in the cleaning time and the Fe ion concentration in the cleaning liquid. In the figure, the horizontal axis represents the cleaning time, the vertical axis represents the Fe ion concentration, and the broken line represents the transition during neutral cleaning. In the neutral cleaning, when the cleaning progresses to some extent, the scale to be cleaned is removed, the Fe scale dissolution amount decreases, and the Fe ion concentration change in the cleaning liquid tends to be saturated. In the above cleaning and storing method, by confirming the saturation tendency of the change in Fe ion concentration and ending each cleaning step, it is possible to avoid continuation of cleaning more than necessary and carry out neutral cleaning in the necessary minimum time. Thereby, extension of each cleaning time can be suppressed.

According to the above-described cleaning storage method, after the neutral cleaning liquid is washed away, the ammonia-based compound aqueous solution is circulated in the system, so that the ammonia having a high pH (9.8 or more) is applied to the surface of the base material 10 of the cleaning target device. The contained water film 11 is formed (see FIG. 4). The high pH water film portion has a rust preventive effect, and the effect is maintained after the restoration of the cleaning equipment temporary pipe is completed after the aqueous solution of the ammonia compound is blown. Since the pH of the ammonia-containing water film 11 is 9.8 or higher, the rust-preventing effect is obtained even without hydrazine, so that hydrazine is not required and the environment is excellent.

ㆍAmmonia component escapes from the ammonia-containing water film 11 when the restoration process of the temporary connection of the cleaning equipment is prolonged and the opening time becomes long. Therefore, (S6) during the dismantling of the temporary system, a solid substance of an ammonia compound that is vaporizable at room temperature and pressure may be additionally charged into the equipment to be cleaned to supplement the ammonia gas. The introduced ammonia compound is quickly vaporized to generate an ammonia-based gas. Ammonia-based gas diffuses in the system and is dissolved in the ammonia-containing water film. As a result, the pH of the ammonia-containing water film 11 can be maintained at a high level, so that the deterioration of the rust preventive effect of the ammonia-containing water film 11 due to the pH decrease can be reduced.

The water film of the aqueous ammonia compound solution or the solids of the ammonia compound remaining at the start of operation is easily dissolved in the operating water. In the exhaust heat recovery boiler, ammonia is used to adjust the pH of the feed water during operation. The ammonia-based compound aqueous solution used for forming the water film in the above embodiment does not need to be removed at the start of operation of the exhaust heat recovery boiler because the main component is ammonia. Therefore, after the exhaust heat recovery boiler is stored, the operation can be started as it is, so that the working time can be shortened, the plant operation rate can be improved, and the chemical cost and the wastewater treatment cost can be reduced.

⿟ Neutral cleaning solution may be filtered during circulation. As a result, the amount of sludge remaining at the time of cleaning can be reduced, and thus the risk of deterioration of heat transfer performance of the heat transfer tube due to sludge remaining and the risk of corrosion generation due to sludge-containing components can be reduced.

The cleaning storage method according to the above embodiment is suitable for cleaning the boiler water system of the exhaust heat recovery boiler. In particular, as shown in FIG. 5, the cleaning target equipment requiring cleaning is specified in a specific portion where scale easily adheres (for example, a heat transfer tube of an evaporator where scale easily adheres due to temperature and pressure conditions). However, the amount of cleaning liquid used and the working time for cleaning can be reduced, which is more preferable.

[Second Embodiment]
FIG. 6 shows a process diagram of the boiler plant cleaning and storing method according to the present embodiment. This embodiment differs from the first embodiment in that an acid cleaning step is performed before neutral cleaning. The cleaning storage method according to the present embodiment includes step 11 (S11) to step 19 (S19) in order.

(S11) Connection of Temporary System (Cleaning/Storage Device) Similar to (S1) of the first embodiment, first, a temporary system for supplying the cleaning liquid into the device to be cleaned is connected. After that, the cleaning liquid or the like is injected into the device to be cleaned via the temporary system.

(S12) Acid Cleaning After the acidic cleaning liquid is injected from the temporary system to fill the inside of the cleaning target device with the acidic cleaning liquid, the acidic cleaning liquid is circulated in the cleaning target device at room temperature. The wash solution is not warmed during circulation. The acidic cleaning liquid may be an inorganic acid solution or an organic acid solution capable of dissolving Ca, Al, Cu and the like. The pH of the acidic cleaning liquid is preferably 4 or less, more preferably 3 or less. For example, a 1% by mass to 10% by mass aqueous hydrochloric acid solution can be used as the acidic cleaning liquid.

(S13) Blow of acidic cleaning solution Iron (Fe) ions in the circulated acidic cleaning solution are analyzed, and after a saturation tendency of changes in Fe ion concentration is confirmed, the cleaning solution is blown to complete the acid cleaning. The saturation tendency means that the change width of the Fe ion concentration in the liquid is 100 mg/L or less as compared with the previously measured Fe ion iron concentration in the liquid.

Iron ions in the liquid are phenanthroline absorptiometry, flame atomic absorption, electric heating atomic absorption or ICP emission spectrophotometry described in JIS K 0101 Industrial water test method 60 iron (Fe), or boiler of JIS B 8224. Water supply and boiler water-Test method 26 1,10-phenanthroline absorptiometry described in Iron (Fe), 2,4,6-tri-pyridyl-1,3,5-triazine (TPTZ) absorptiometry, flame It can be analyzed by an atomic absorption method, an electric heating atomic absorption method, an ICP emission spectroscopic analysis method, an ICP mass spectrometric method, a sulfosalicyl absorptiometry method, or the like. JIS is an abbreviation for Japanese Industrial Standards.

(S14) Washing with water After the inside of the device to be cleaned is filled with water, the water is circulated at room temperature to replace the acidic cleaning liquid remaining in the device to be cleaned with water. This step may be omitted.

(S15) Neutral Cleaning After blowing the water of (S14) above, the inside of the equipment to be cleaned is filled with a neutral cleaning liquid containing a rust remover, and the neutral cleaning liquid is circulated in the system at room temperature. The wash solution is not warmed during circulation. As the neutral cleaning liquid, the same one as in the first embodiment can be used.

(S16) Extrusion Blow Similar to (S3) of the first embodiment, Fe ions in the circulating neutral cleaning liquid were analyzed, and it was confirmed that the change in Fe ion concentration in the liquid tended to be saturated. After that, the neutral cleaning liquid is extruded and blown while injecting the ammonia-based compound aqueous solution at room temperature into the device to be cleaned. The same aqueous ammonia solution as in the first embodiment can be used.

(S17) Circulation of Aqueous Solution of Ammonia Compound In the same manner as (S4) of the first embodiment, in (S16), after substantially all the amount of the neutral cleaning solution is extruded and blown with the aqueous solution of ammonia compound, the extruded blow is temporarily stopped, The ammonia compound aqueous solution in the equipment to be cleaned is circulated. During the circulation of the aqueous ammonia compound solution, the aqueous ammonia compound solution is not heated.

After circulating the ammonia-based compound aqueous solution, analyze the ammonia-based compound aqueous solution to confirm the components in the solution derived from the rust remover.

Repeat the above steps (S16) and (S17) until the content of the rust remover-derived component in the solution is below the standard value. The reference value is set in advance by a preliminary test. Confirm that the components derived from the rust remover in the liquid are below the standard values.

(S18) Blow Ammonia-Based Compound Aqueous Solution Similar to (S5) of the first embodiment, after (S17) described above, the ammonia-based compound aqueous solution is blown from the inside of the equipment to be cleaned to form an ammonia-containing water film on the inner surface of the equipment to be cleaned. Form. This ammonia-containing water film portion has a rust preventive effect.

(S19) Temporary system dismantling Similar to (S6) of the first embodiment, after (S18), the temporary system is dismantled.

The cleaning from steps 12 to 18 of the above cleaning storage method may be carried out only once or plural times.

If the device to be cleaned has a permanent storage device, steps (S11) and (S19) above are omitted.

According to the above cleaning and storing method, after the scale that is difficult to dissolve in the neutral cleaning liquid such as Ca, Al and Cu is removed by (S12) acid cleaning, the sludge remaining in the cleaning target device is (S15) neutral cleaning. To remove. By using a neutral cleaning solution, it is possible to dissolve and remove the remaining scale while suppressing the base material corrosion of the target equipment as much as possible, and reduce the amount of sludge residue.

Fig. 7 exemplifies the residual sludge amount (standard value) in (S12) acid cleaning and (S15) neutral cleaning. In the figure, the vertical axis represents the amount of sludge remaining in the cleaning target device (100 before acid cleaning). As shown in FIG. 2, about 20% of the sludge remains in the acid cleaning at room temperature, but about 70% of the remaining 20% of the sludge could be removed by the neutral cleaning.

Fe scales are also dissolved and removed in both (S12) acid cleaning and (S15) neutral cleaning. FIG. 8 shows a schematic diagram of changes in the cleaning time and the Fe ion concentration in the cleaning liquid. In the figure, the horizontal axis represents the cleaning time, the vertical axis represents the Fe ion concentration, the solid line represents the transition during acid cleaning, and the broken line represents the transition during neutral cleaning. In the acid cleaning and the neutral cleaning, when the cleaning progresses to a certain extent, the scale to be cleaned is removed, the Fe scale dissolution amount decreases, and the Fe ion concentration change in the cleaning liquid tends to be saturated. In the cleaning storage method according to the present embodiment, by confirming the saturation tendency of the Fe ion concentration change and ending each cleaning step, it is possible to avoid excessive cleaning continuity and perform acid cleaning and neutral cleaning in the necessary minimum time. it can. Thereby, extension of each cleaning time can be suppressed.

According to the cleaning and storing method according to the present embodiment, after washing the neutral cleaning liquid, the aqueous ammonia compound solution is circulated in the system, so that the surface of the base material 10 of the cleaning target device has a high pH (9.8). The above-mentioned ammonia-containing water film 11 is formed. The high pH water film portion has a rust preventive effect, and the effect is maintained after the restoration of the cleaning equipment temporary pipe is completed after the aqueous solution of the ammonia compound is blown. Since the pH of the ammonia-containing water film 11 is 9.8 or higher, the rust-preventing effect is obtained even without hydrazine, so that hydrazine is not required and the environment is excellent.

ㆍAmmonia component escapes from the ammonia-containing water film 11 when the restoration process of the temporary connection of the cleaning equipment is prolonged and the opening time becomes long. Therefore, (S19) during the dismantling of the temporary system, a solid substance of a vaporizable ammonia compound at room temperature and normal pressure may be additionally charged into the device to be cleaned to supplement the ammonia gas. The introduced ammonia compound is quickly vaporized to generate an ammonia-based gas. Ammonia-based gas diffuses in the system and is dissolved in the ammonia-containing water film. As a result, the pH of the ammonia-containing water film 11 can be maintained at a high level, so that the deterioration of the rust preventive effect of the ammonia-containing water film 11 due to the pH decrease can be reduced.

At least one of the acidic cleaning solution and the neutral cleaning solution may be filtered during circulation. As a result, the amount of sludge remaining at the time of cleaning can be reduced, so that the heat transfer performance of the heat transfer tube is reduced due to the sludge remaining and the risk of corrosion generation due to the sludge-containing component can be reduced.

[Third Embodiment]
FIG. 9 is a process diagram of the boiler plant cleaning and storing method according to the present embodiment. This embodiment is different from the first and second embodiments in that the step of acid cleaning is performed after neutral cleaning. The cleaning storage method according to the present embodiment includes step 21 (S21) to step 28 (S28) in order.

(S21) Temporary System (Storage Device) Connection Similar to (S1) of the first embodiment, first, a temporary system for supplying the cleaning liquid into the cleaning target device is connected. After that, the cleaning liquid or the like is injected into the device to be cleaned via the temporary system.

(S22) Neutral Cleaning As in (S2) of the first embodiment, a neutral cleaning liquid containing a rust remover is injected from the temporary system to fill the inside of the cleaning target device with the neutral cleaning liquid, and then Circulate a cleaning solution that is water-soluble in the system at room temperature. The wash solution is not warmed during circulation. As the neutral cleaning liquid, the same one as in the first embodiment can be used.

(S23) Blow of Neutral Cleaning Solution Iron (Fe) ions in the circulating neutral cleaning solution are analyzed, and if a saturation tendency of the change in Fe ion concentration is confirmed, the cleaning solution is blown to complete the neutral cleaning.

(S24) Acid Cleaning After blowing the neutral cleaning liquid in (S23), the inside of the equipment to be cleaned is filled with an acidic cleaning liquid containing a rust remover, and the acidic cleaning liquid is circulated in the system at room temperature. The wash solution is not warmed during circulation. As the acidic cleaning liquid, the same one as in the second embodiment can be used.

(S25) Extrusion Blow After analyzing the Fe ions in the liquid of the circulated acidic cleaning liquid and confirming that the change in the Fe ion concentration in the liquid tends to be saturated, an aqueous ammonia compound solution at room temperature is placed in the equipment to be cleaned. The neutral cleaning liquid is extrusion blown while being injected. The same aqueous ammonia solution as in the first embodiment can be used.

(S26) Circulation of Ammonia-Based Compound Aqueous Solution In the above (S25), after substantially all of the acidic cleaning solution is extruded and blown with the ammonia-compound aqueous solution, the extrusion-blowing is temporarily stopped and the ammonia-based compound aqueous solution in the equipment to be cleaned. Circulate. During the circulation of the aqueous ammonia compound solution, the aqueous ammonia compound solution is not heated.

ㆍAfter circulating the ammonia-based compound aqueous solution, analyze the ammonia-based compound aqueous solution to confirm the pH value of the ammonia-based compound aqueous solution.

Repeat the above (S25) and (S26) until the pH of the aqueous solution of the ammonia-based compound becomes equal to or higher than the reference value. The reference value is set in advance by a preliminary test. Confirm that the pH of the aqueous ammonia-based compound solution is above the reference value. The reference value is, for example, pH 9.8 or more, which has an anticorrosive effect even without hydrazine.

(S27) Blow Ammonia-Based Compound Aqueous Solution Similar to (S5) of the first embodiment, after the above (S26), the ammonia-based compound aqueous solution is blown from the inside of the equipment to be cleaned to form an ammonia-containing water film on the inner surface of the equipment to be cleaned. Form. This ammonia-containing water film portion has a rust preventive effect.

(S28) Temporary System Dismantling Similar to (S6) of the first embodiment, after (S27), the temporary system is dismantled.

The above steps 22 to 27 may be carried out only once or a plurality of times.

Next, cleaning when the device to be cleaned is the evaporator of the exhaust heat recovery boiler will be described with reference to FIGS. 10 and 11.

FIG. 10 is a schematic diagram of a temporary system (cleaning storage device 2). In FIG. 10, the cleaning target device is the heat transfer tube of the evaporator 1. In FIG. 10, for simplification of the drawing, only the inlet header 1a and the outlet header 1b of the heat transfer pipe to which the cleaning/storage device 2 is connected are shown. In FIG. 10, the arrow entering the inlet header 1a represents the connection from the evaporator drum, and the arrow exiting the outlet header 1b represents the connection to the evaporator drum.

The cleaning storage device 2 includes a circulation unit 3, a chemical liquid tank 4, a chemical liquid pump 5, a makeup water tank 6, a drainage tank 7, and pipes L ₁ to L ₄ connecting them. The circulation unit 3 includes a circulation flow path (pipe L ₁ ) and a pump 8.

One end of the circulation flow path (pipe L ₁ ) is connected to the inlet side of the heat transfer tube (inlet header 1 a) and the other end is connected to the outlet side of the heat transfer tube (outlet header 1 b ). A pump 8 is provided in the middle of the circulation flow path (pipe L ₁ ), and is configured to circulate a cleaning liquid or the like in the heat transfer tube. Valves V ₁ to V ₄ are installed in the circulation flow path (pipe L ₁ ).

The chemical liquid tank 4 is connected in the middle of the circulation flow path (pipe L ₁ ) via the pipe L ₂ and the chemical liquid pump 5. A valve V ₅ and a valve V ₆ are arranged in the pipe L ₂ so as to sandwich the chemical liquid pump 5. In the chemical liquid tank 4, a chemical liquid to be circulated (acid, rust remover or ammonia-based compound aqueous solution) can be stored. The chemical liquid tank 4 may be a tank truck including the chemical liquid tank 4. In FIG. 10, since there is one chemical liquid tank 4, the chemical liquids in the chemical liquid tank 4 are replaced in order.

A makeup water tank 6 is connected to the circulation flow path (pipe L ₁ ) via a pipe L ₃ . A valve V ₇ and a valve V ₈ are arranged in the pipe L ₃ . The connection position of the makeup water tank 6 may be either upstream or downstream of the circulating position of the connection position of the chemical liquid tank 4. Water such as pure water is stored in the makeup water tank 6.

The drainage tank 7 includes a connecting pipe (not shown) connected to both ends of the circulation flow path (pipe L ₁ ) and the inlet port 1a of the heat transfer tube or the inlet port of the heat transfer tube via the lines L ₄ to L _6. It is connected to the. A valve V ₉ and a valve V ₁₀ are arranged in the pipe L ₄ . A valve V ₁₁ and a valve V ₁₂ are arranged in the pipe L ₅ . A valve V ₁₃ and a valve V ₁₄ are arranged in the pipe L ₆ .

In the cleaning storage device 2 of FIG. 10, the filtration device 9 is provided in the circulation flow path (pipe L ₁ ) on the circulation downflow outlet flow side of the pump 8. The filtration device 9 is a device that removes fine solids by a filter or membrane filtration. Since the sludge generated in the neutral cleaning step and the acid cleaning step can be recovered by providing the filtering device 9 and the residual sludge amount during cleaning can be reduced, the risk of corrosion trouble due to residual sludge can be reduced.

Since the cleaning/storage device 2 of FIG. 10 operates at room temperature, no means for adjusting the temperature of the fluid is installed.

FIG. 11 is a schematic diagram of a temporary system (cleaning storage device 20) different from FIG. The same components as those in FIG. 10 are denoted by the same reference numerals. In the cleaning storage device 20 of FIG. 11, a plurality of chemical liquid tanks 24a to 24c are connected in parallel, and a blow channel L ₂₁ for returning drainage (blowing liquid) to one of the chemical liquid tanks 24a to 24c instead of the drainage tank 7. Is provided. A valve V ₂₇ is arranged in the blow passage L ₂₁ .

In FIG. 11, the makeup water tank 6, the chemical liquid tank 24a, the valve V _25a , the valve _V26a , the chemical liquid pump 5, the pipe L ₂ and the valve V ₆ are the acidic cleaning liquid supply unit, the makeup water tank 6, the chemical liquid tank 24b, the valve V _25b , The valve V _26b , the chemical liquid pump 5, the pipe L ₂ and the valve V ₆ are the neutral cleaning liquid supply unit, the makeup water tank 6, the chemical liquid tank 24c, the valve V _25c , the valve V _26c , the chemical liquid pump 5, the pipe L ₂ and the valve V _6. Is an ammonia compound aqueous solution supply part.

Acid is stored in the chemical liquid tank 24a. A neutral rust remover is stored in the chemical liquid tank 24b. Aqueous ammonia compound solution is stored in the chemical tank 24c.

By providing chemical liquid tanks 24a to 24c for each chemical liquid, the blow liquid in each step of acid cleaning liquid blowing, water washing, extrusion blow, and ammonia compound aqueous solution blowing can be returned to any of the chemical liquid tanks 24a to 24c.

Note that the cleaning

storage devices

2 and 20 of FIGS. 10 and 11 are either a detachable type that can be attached to a cleaning target device when used and can be detached from the cleaning target device when not in use, or a permanent type. Good.

FIG. 10 can be applied to the cleaning and storing method of the boiler plant of the first to third embodiments. FIG. 11 can be applied to the cleaning and storing method of the boiler plant of the first to third embodiments. FIG. 11 is particularly suitable for the cleaning and storing method of the boiler plant of the second and third embodiments.

1 Evaporator 1a Inlet heading 1b Outlet heading 2 Cleaning storage device 3 Circulating

part

4, 24a, 24b, 24c Chemical liquid tank 5 Chemical liquid pump 6 Makeup water tank 7 Drainage tank 8 Pump 9 Filtration device 10 Base material 11 Ammonia-containing water film

Claims

A step of neutrally cleaning the portion to be cleaned with the scale attached thereto at room temperature with a neutral cleaning liquid containing a rust remover,
Circulating an aqueous solution of an ammonia-based compound containing ammonia-based compound at room temperature and having a pH of 9.8 or higher,
A method for cleaning and storing a boiler plant, comprising a step of blowing the aqueous solution of an ammonia-based compound from the cleaning target portion.
In the step of neutral cleaning,
Circulating the neutral cleaning liquid in the cleaning target site,
Analyzing iron ions in the circulated neutral cleaning solution,
The method for cleaning and storing a boiler plant according to claim 1, wherein the neutral cleaning is terminated after confirming that the change in the iron ion concentration in the neutral cleaning liquid shows a saturation tendency.
The method for cleaning and storing a boiler plant according to claim 1 or 2, further comprising a step of performing acid cleaning with an acidic cleaning liquid at room temperature before the step of circulating the aqueous ammonia compound solution.
In the step of acid cleaning,
Circulating the acidic cleaning liquid in the cleaning target site,
Analyzing iron ions in the circulated acidic washing solution,
The method for cleaning and storing a boiler plant according to claim 3, wherein the acid cleaning is terminated after confirming that the change in the iron ion concentration in the acidic cleaning liquid shows a saturation tendency.
After the acid cleaning, the method further comprises a step of extruding and blowing the acidic cleaning solution using the aqueous ammonia compound solution,
In the extrusion blowing step,
Blow almost the entire amount of the acidic cleaning liquid by the extrusion blow, analyze the pH of the ammonia-based compound aqueous solution after circulating the ammonia-based compound aqueous solution in the cleaning target site,
The method for cleaning and storing a boiler plant according to claim 3 or 4, wherein the extrusion blow and the circulation of the aqueous ammonia compound solution are continued until the analyzed pH becomes a reference value or more.
After the neutral cleaning, the method further comprises a step of extrusion-blowing the neutral cleaning liquid using the aqueous ammonia compound solution,
In the extrusion blowing step,
Blow almost the entire amount of the neutral cleaning liquid in the extrusion blow, analyze the components derived from the rust remover in the ammonia-based compound aqueous solution after circulating the ammonia-based compound aqueous solution in the cleaning target site,
The boiler plant cleaning and storage according to any one of claims 1 to 4, wherein the extrusion blow and the circulation of the ammonia-based compound aqueous solution are continued until the concentration of the analyzed component derived from the rust remover becomes a reference value or less. Method.
The method for cleaning and storing a boiler plant according to any one of claims 1 to 6, wherein after the step of blowing the aqueous solution of the ammonia compound, a solid of a vaporizable ammonia compound is introduced into the cleaning target site.
The method for cleaning and storing a boiler plant according to any one of claims 1 to 7, wherein at least one of the acidic cleaning solution and the neutral cleaning solution is filtered during circulation.
The method for cleaning and storing a boiler plant according to any one of claims 1 to 8, wherein the cleaning target portion is an evaporator of an exhaust heat recovery boiler.
A circulation unit configured to circulate a fluid in the cleaning target area to which the scale is attached,
A neutral cleaning liquid supply unit that supplies a neutral cleaning liquid containing a rust remover to the circulation unit,
An ammonia-based compound aqueous solution supply unit that supplies an ammonia-based compound aqueous solution containing an ammonia-based compound and having a pH of 9.8 or more to the circulation unit;
A blow flow path for discharging the ammonia-based compound aqueous solution from the circulation unit,
Boiler plant cleaning storage equipment equipped with.
The circulation unit,
A circulation channel whose both ends are connected to the inlet and outlet of the cleaning target portion,
A pump provided in the middle of the circulation flow path,
A filtering device provided in the middle of the circulation flow path on the downstream side of the pump,
The cleaning and storing apparatus for a boiler plant according to claim 10, further comprising:
One end of the blow passage is connected to the circulation unit, at least one of an inlet and an outlet of the cleaning target portion, and the other end is connected to at least one of the neutral cleaning liquid supply unit and the ammonia-based compound aqueous solution supply unit. The cleaning/storage device for a boiler plant according to claim 10 or 11, which is connected.