JP6743558B2 - Boiler chemical cleaning method - Google Patents

Description

The present invention relates to a chemical cleaning method for a boiler, and more particularly to a chemical cleaning method for a boiler that heats a cleaning liquid.

Iron oxide scale grows on the inner surface of the evaporation tube of the boiler over many years, which is a factor that deteriorates the thermal efficiency. Therefore, the scale is dissolved and removed by periodic chemical cleaning, and it is necessary to maintain or raise the temperature of the cleaning liquid during this chemical cleaning (Patent Document 1).

Patent Document 1 describes that steam is blown into the cleaning liquid to heat it (paragraph 0013).

JP, 11-141804, A

In the temperature rise and temperature maintenance by the direct heating method by injecting steam into the cleaning liquid, the following problems were caused by steam injection.
(1) Dilution of the cleaning liquid by steam drain occurs, and the scale dissolving ability decreases.
(2) If the concentration of the cleaning liquid is set to a high value in consideration of the diluted amount of the cleaning liquid, the amount of cleaning chemicals increases.
(3) When the amount of chemicals increases, the burden on wastewater treatment increases.

The present invention provides a chemical cleaning method for a boiler that solves the above-mentioned problems by performing at least a part of heating with a steam heat exchanger, instead of performing only the injection of steam for cleaning the boiler. To aim.

A chemical cleaning method for a boiler according to the present invention is a chemical cleaning method for a boiler in which cleaning liquid is passed through a boiler evaporation pipe for cleaning, and in the chemical cleaning method for heating the cleaning liquid, at least heating of the cleaning liquid is performed. It is characterized in that a part is performed by a steam heat exchanger.

In one aspect of the present invention, the cleaning liquid is heated by using both direct heating in which steam is injected into the cleaning liquid and indirect heating using a steam heat exchanger.

In one aspect of the present invention, a step of injecting steam into the cleaning water to raise the temperature of the cleaning water to a predetermined temperature while circulating the cleaning water in the boiler, and then adding a cleaning chemical to the cleaning water to supply the cleaning liquid to the boiler. And the step of heating the cleaning liquid with a steam heat exchanger.

In the method for chemically cleaning a boiler of the present invention, a steam heat exchanger is used for at least a part of heating for maintaining or raising the temperature of the cleaning liquid. This makes it possible to prevent or suppress the dilution of the cleaning liquid due to the injection of steam when the cleaning liquid is heated.

According to one aspect of the present invention, when cleaning a boiler, an operator installs a steam heat exchanger in a cleaning liquid circulation system for chemical cleaning of a boiler evaporation pipe, and lays piping so as to allow indirect heating. Then, during the temperature raising step, the cleaning liquid is directly heated by steam injection to raise the temperature to a predetermined cleaning temperature. Then, a chemical is injected and a chemical cleaning process is performed. In this chemical cleaning step, indirect heating by a steam heat exchanger is performed in order to maintain the cleaning liquid temperature.

By doing so, the temperature can be raised to the predetermined temperature in a short time by direct heating by steam injection. Then, a cleaning chemical is added, and the boiler is chemically cleaned by performing indirect heating with a steam heat exchanger. In this case, since the steam is not injected after the cleaning chemical is added, the cleaning liquid is not diluted by the steam drain, and the scale dissolving ability of the cleaning liquid does not decrease.

Further, since the cleaning liquid is not diluted, it is not necessary to set the cleaning chemical concentration to a high value, and the increase of the cleaning chemical amount can be prevented. In addition, the load of wastewater treatment does not increase.

It is a schematic system diagram which shows the chemical cleaning method of the boiler of this invention.

Hereinafter, an embodiment will be described with reference to FIG.

In order to chemically clean the evaporation pipe of the boiler 1, a circulation line consisting of a circulation pump 2, a circulation feed pipe 3, a circulation return pipe 4, a steam heat exchanger 5 and a circulation return pipe 6 is connected to the evaporation pipe of the boiler 1. ing.

A cleaning chemical or pure water injection pipe 14 is connected to the circulation feed pipe 3 via a valve V ₁ .

A bypass line including a pipe 7, a mixing heater 8 and a pipe 9 is provided so as to bypass the steam heat exchanger 5 and connect the pipes 4 and 6. Valves V _{2 to} V ₅ are provided in the pipes 4, 6, 7 and 9 respectively to switch the flow of the pipe 4, the steam heat exchanger 5 and the pipe 6 and the bypass flow bypassing the flow.

The steam heat exchanger 5 is for indirectly heating the cleaning liquid, and the mixing heater 8 is for directly heating the cleaning liquid with steam.

The steam from the pipe 10 connected to the steam source (for example, a small boiler) can be injected into the mixing heater 8 via the valve V ₆ and the pipe 11, and the steam heat exchange via the valve V ₇ and the pipe 12. It can be introduced to the heat source fluid side of the container 5. The drain from the steam heat exchanger 5 is drained through the pipe 13.

To the circulation return pipe 6, a cleaning waste liquid discharge pipe 15 having a valve V ₈ is connected.

In the first aspect of the present invention, the cleaning liquid is heated only by indirect heating. In this case, the valves V ₄ and V ₅ for bypass and the valve V ₆ for supplying steam to the mixing heater 8 are closed. The valve V _{8 is} also closed.

The cleaning liquid is supplied to the boiler 1 via the pipes 14 and 3. After a sufficient amount of the cleaning liquid is supplied, the valve V ₁ is closed, the circulation pump 2 is started to circulate the cleaning liquid, and the valve V ₇ is opened to supply the steam to the steam heat exchanger 5 to supply the cleaning liquid. To warm. After the temperature of the cleaning liquid has risen to a predetermined temperature, the amount of steam supplied to the steam heat exchanger 5 is controlled to maintain the cleaning liquid temperature at the predetermined temperature. After the lapse of a predetermined cleaning time, the valve V ₈ is opened and the cleaning liquid is discharged through the pipe 15. Then, the valve V ₁ is opened, pure water is supplied to the boiler 1 through the pipes 14 and 3, and the remaining cleaning liquid and scale are pushed out.

In this first mode, since steam is not directly injected, vibration and noise due to steam injection do not occur. Further, it is not necessary to partially blow the cleaning liquid due to the vapor drain generation, and the work load is reduced.

In the second aspect of the present invention, the cleaning liquid is heated by direct heating and indirect heating. In the case of direct heating, the cleaning liquid is circulated through the loop of the pipe 3, the boiler 1, the pipes 4 and 7, the mixing heater 8, the pipes 9 and 6, and the circulation pump 2. Since the steam is injected into the mixing heater 8, the cleaning water is rapidly heated. If necessary, the valve V ₈ is opened and the amount of water commensurate with the amount of steam drain water is discharged from the pipe 15. In the case of indirect heating, the bypass valves V ₄ and V ₅ and the vapor supply valve V ₆ to the mixing heater 8 are closed. The valve V _{8 is} also closed. Further, the valves V ₂ , V ₃ and V ₇ are opened. As a result, steam is supplied to the steam heat exchanger 5 through the pipes 10 and 12, and the circulating cleaning liquid is maintained at a predetermined temperature. Others are the same as the first aspect.

In the third aspect of the present invention, first, the pipes 3, 4, and 6, the circulation pump 2, the steam heat exchanger 5, and the bypass line, which form a circulation line with cleaning water containing no cleaning chemical (for example, pure water). The constituent pipes 7 and 9 and the mixing heater 8 are respectively filled.

Then, the valves V ₁ , V ₂ , V ₃ , V ₇ , and V ₈ are closed, the valve V ₆ is opened, the circulation pump 2 is operated, and cleaning water is supplied to the pipe 3, the boiler 1, the pipes 4, 7, and mixing. The heater 8, the pipes 9 and 6, and the loop of the circulation pump 2 are circulated. Since steam is injected into the mixing heater 8, the cleaning water is rapidly heated. If necessary, the valve V ₈ is opened and the amount of water commensurate with the amount of steam drain water is discharged from the pipe 15.

If the water temperature rises to a predetermined chemical cleaning temperature, the valve _{V 4, V 5, V 6} closed, and the valves _{V 2, V 3, V 7} opens. Further, a cleaning chemical is injected from the pipe 14. As a result, the cleaning liquid in which the cleaning chemicals are dissolved is circulated through the boiler 1, and the boiler 1 is chemically cleaned. During this time, steam is supplied to the steam heat exchanger 5 through the pipes 10 and 12, and the circulating cleaning liquid is maintained at a predetermined temperature.

After performing this chemical cleaning for a predetermined time, the valve V ₈ is opened and the cleaning liquid is discharged through the pipe 15 as in the first embodiment. Then, the valve V ₁ is opened, pure water is supplied to the boiler 1 through the pipes 14 and 3, and the remaining cleaning liquid and scale are pushed out.

Also in the second and third aspects, since the direct injection of steam is shorter than that in the conventional case, vibration and noise due to the injection of steam are reduced. Further, a part of the cleaning liquid is not blown due to the generation of steam drain, and the work load is reduced.

Hereinafter, the effects of the present invention will be described more specifically with reference to Examples 1 and 2.

[Example 1]
Example 1 is an example in which chemical cleaning of a boiler is performed according to the first aspect. The amount of cleaning liquid was 55 m ³ , the heat transfer area of the steam heat exchanger was 15 m ² , and the cleaning temperature was 85°C. By the application of the present invention, in the conventional method, the cleaning liquid was diluted with steam at a chemical concentration of 0.6%, whereas in Example 1, the steam was not directly enclosed in the cleaning liquid, so that there was no dilution by temperature rise. Further, it was possible to raise the initial temperature of the cleaning liquid from 30° C. to 85° C. in 4 hours. The subsequent cleaning time was 6 hours.

In addition, the problem of noise and vibration, which had been a problem in the conventional construction method for the boiler, was solved by applying the construction method of the present invention.

[Example 2]
Example 2 is an example of chemically cleaning a boiler according to the third aspect. The mixing heater 8 was used to raise the temperature of the washing water to 85°C. In this case, the temperature rising time from the initial temperature of 30° C. to 85° C. was 2.5 hours.

After that, the use of the mixing heater 8 was stopped, the cleaning chemicals were injected, the temperature of the cleaning liquid was kept warm by the steam heat exchanger 5, and the boiler was cleaned with this cleaning liquid for 6 hours.

As a result, the total chemical cleaning of the boiler 1 was completed in 8.5 hours, which was shorter than that in Example 1.

1 Boiler 2 Circulation pump 5 Steam heat exchanger 8 Mixing heater

Claims (2)

A chemical cleaning method for a boiler, in which a cleaning liquid is passed through a boiler evaporation pipe for cleaning, wherein at least a part of heating of the cleaning liquid is performed by a steam heat exchanger in the chemical cleaning method for heating the cleaning liquid. A chemical cleaning method for boilers,
Injecting steam into the cleaning water while circulating the cleaning water in the boiler to raise the temperature of the cleaning water to a predetermined temperature;
After that, a cleaning chemical is added to the cleaning water to circulate the cleaning liquid in the boiler, and the circulating cleaning liquid is heated by a steam heat exchanger.
A method for chemically cleaning a boiler, comprising: The chemical cleaning method for a boiler according to claim 1, wherein the cleaning liquid is heated by using both direct heating for injecting steam into the cleaning liquid and indirect heating using a steam heat exchanger.

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