JPH11141804A - Method of chemically cleaning boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemical cleaning method which raises the temperature by recovering heat from cleaning waste fluid, and shortens the extrusion washing process and also lessens the calorific value required for the heating in the next process, by raising the extrusion washing efficiency hereby, and besides can lessen the quantity of cooling water and also can lessen the capacity of storage of waste fluid, by lowering the temperature of the cleaning waste fluid, and can make the cleaning efficient by making the cooling by FDF needless hereby shortening the cleaning time. SOLUTION: Chemical cleaning liquid is led in a boiler 1 through a valve V2 by a pump 2, and it is circulated through valves V3 and V1 so as to perform chemical cleaning, and after finish of cleaning, cleaning water is passed through a valve V5 from a water supply path 7, and it is heated with a heat exchanger 11 and is poured into the boiler, and the cleaning liquid is pushed out for cleaning, and the cleaning waste fluid is cooled with the heat exchanger 11 from a valve V6 and is let flow in a waste fluid tank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical cleaning method for a boiler, and more particularly, to a chemical cleaning method in which a chemical cleaning liquid is introduced into a boiler to clean the boiler in a heated state, and then cleaning water is introduced to perform extrusion cleaning. Things.

[0002]

2. Description of the Related Art In a water tube type boiler such as a once-through boiler and a variable-pressure once-through boiler, an acid solution is introduced into the boiler as a chemical cleaning solution, circulated in a heated state to perform a cleaning process, and then pure water is introduced as cleaning water. To carry out the extrusion water washing process. In the washing step, the scale is removed by heating to 80 to 90 ° C. and circulating the washing liquid, and in the extrusion water washing step, washing water is introduced, and the washing drainage is extruded without circulation.
Extrusion of washing wastewater and washing with water are performed.

FIG. 3 is a flowchart showing a conventional cleaning method, wherein 1 is a boiler, 2 is a pump, and 3 is a drainage storage tank. In the chemical cleaning method, the cleaning liquid is introduced into the boiler 1 from the liquid supply path 4 by the pump 2, taken out from the discharge path 5, and circulated through the circulation path 6 by opening the valve V ₁ to perform cleaning. After the washing step ends closing valve V _1, and supplies the washing water to the boiler 1 from the water supply passage 7, carries out the extrusion washing step is allowed to flow into the wash effluent to the draining tank 3 from drains 8. The drainage in the drainage storage tank 3 is sent from a drainage path 9 to a drainage treatment device (not shown).

[0004] The purpose of the extrusion water washing step is to discharge (extrude) the washing waste liquid in which the scale has been dissolved out of the system, wash away the washing liquid adhering to the pipe wall, and prepare for the next step, for example, the rust prevention treatment step Is to arrange. In this case, if the cleaning liquid is first discharged, and then the cleaning water is introduced and washed with water, corrosion occurs due to the introduction of air.Therefore, the cleaning liquid is extruded by introducing the cleaning water without introducing air, and then the water is washed. That is being done.

[0005] In the conventional extrusion water washing process, the washing wastewater is simply extruded by introducing the washing water and the washing operation is performed, so that the washing water enters the boiler at a low temperature (normal temperature) and receives heat from the pipe wall. However, the water is washed at a relatively low temperature, so that the solubility of the dissolved scale component is reduced, so that it takes a long time to wash the water, which requires a large amount of washing water (pure water) and a large amount of water. Wash drainage occurred.

[0006] On the other hand, the washing waste liquid has a high temperature of about 90 ° C,
If this is allowed to flow into the drainage storage tank as it is, the resin (PVC etc.) piping in the tank and the epoxy resin coating or rubber lining on the tank wall will be damaged, so a large amount of cooling water must be introduced into the tank in advance. The wastewater had to be introduced and cooled and diluted, requiring a large amount of cooling water and a large storage tank.

[0007] To avoid this, FDF (Forced Draft)
Fan) sends air to the boiler's fire side to cool it, which increases the cleaning time. In addition, it is necessary to remove scaffolds for boiler periodic inspections in order to operate the FDF, and it is necessary to shorten the periodic inspection process. Inconveniences such as occur.

Further, in the rust preventive treatment step following the extrusion water washing step, it is necessary to heat the rust preventive treatment liquid, and thus it is necessary to inject a larger amount of steam, which is disadvantageous in terms of thermal efficiency. there were.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to recover the heat from the washing effluent to raise the temperature of the washing water, thereby increasing the efficiency of the extrusion water washing and shortening the extrusion water washing step, as well as shortening the next step. By reducing the amount of heat required for heating the chiller and lowering the temperature of the washing drainage, the amount of cooling water can be reduced and the capacity of the drainage storage tank can be reduced.
An object of the present invention is to provide a chemical cleaning method that does not require cooling by F, thereby shortening the cleaning time and improving efficiency.

[0010]

According to the present invention, there is provided a cleaning step of introducing a chemical cleaning liquid into a boiler and circulating and cleaning it in a heated state, introducing cleaning water into the boiler, extruding a cleaning drainage and washing with water. In the extrusion water washing step, the washing wastewater discharged from the boiler and the washing water to be introduced are introduced into a heat exchanger to exchange heat, and the washing wastewater is cooled and discharged, and the washing water is discharged. A chemical cleaning method for a boiler, comprising heating and performing extrusion water cleaning with cleaning water in a heated state.

The boiler to be cleaned in the present invention is used as a steam generator, and is not particularly limited, but a water tube type boiler such as a once-through boiler or a variable-pressure once-through boiler used in a thermal power plant or the like. However, it is suitable as a cleaning target, and in particular, a boiler that performs chemical cleaning in a heated state is suitable as a target.

The chemical cleaning solution used in the present invention is 1 to 10
An acid washing solution comprising an aqueous solution of an organic acid such as hydrochloric acid, sulfuric acid or the like, or an organic acid such as citric acid or malic acid is generally used, but a washing solution for washing in a heated state with a chelating agent or the like is also included. Auxiliary agents such as surfactants and corrosion inhibitors are added to these cleaning liquids in addition to acids and the like as main agents.

The chemical cleaning using these cleaning liquids is carried out in a heated state, generally at 70 to 98 ° C., preferably at 80 to 95 ° C.
The heating is performed while circulating the cleaning liquid. The cleaning liquid is generally heated by blowing steam, but can be heated by electric heating or other heating means. The circulation is performed by a pump through a circulation system. As the washing process proceeds, the acid concentration decreases, and the eluted scale component, for example, the iron ion concentration, increases to a constant value. At this point, the circulation is stopped and the washing process is terminated.

In the extrusion water washing step, generally, pure water is introduced as a washing to extrude washing waste liquid and washing is performed with water.
At this time, the washing water and the washing waste liquid are introduced into a heat exchanger, and heat exchange is performed through a heat exchange wall. Thereby, the washing water is heated and introduced into the boiler, and the washing waste liquid is cooled and flows into the waste liquid storage tank. In this case, the washing water is 3
It is heated to 0 to 50 ° C, and the washing effluent is cooled to 50 to 70 ° C.

When extruded water washing is performed by introducing heated washing water into a boiler, the solubility of scale components is increased, so that the washing efficiency is increased, the extruded washing step is shortened, and the amount of washing water is reduced. Further, since the temperature drop of the boiler is small, the amount of heating of the rust preventive solution in the next step is small, and the thermal efficiency is high.

On the other hand, since the washing waste liquid is cooled and discharged, it can flow into the waste liquid storage tank as it is, and cooling with cooling water becomes unnecessary. For this reason, the conventional cooling water amount can be limited, and the capacity of the drainage storage tank can be small. Also F
As compared with the case where the cleaning liquid is cooled by the DF, a long cooling step is eliminated, the cleaning time can be shortened, and the regular inspection work is not affected.

When the extrusion water washing step is completed, post-steps such as a rust prevention treatment step are performed. In the rust prevention treatment step, rust prevention treatment is performed by introducing and circulating a rust prevention treatment liquid.
At this time, heating is performed by blowing steam or the like. However, the amount of heating heat is small because the temperature is not reduced so that efficient processing can be performed.

When the post-treatment such as the rust prevention treatment is completed, the extruded water is washed again with the washing water. At this time, the heat exchange between the rust prevention treatment drainage and the washing water also increases the washing efficiency. Washing time is reduced. Further, since the boiler temperature drop is small, the next drying step is also shortened, and the overall cleaning time is shortened.

Since the rust-prevention treatment waste liquid is also cooled, it can flow directly into the waste liquid storage tank, and cooling water at this time is not required. Although the washing water in the final washing step is discharged as it is, since the temperature is considerably lowered, there is no problem even if it flows into the drainage storage tank. Drying is performed after washing water is drained,
The drying time is reduced because the boiler is not cooled.

[0020]

According to the present invention, since the cleaning waste water and the cleaning water are heat-exchanged, heat is recovered from the cleaning waste water to increase the temperature of the cleaning water, thereby increasing the efficiency of the extrusion water cleaning. In addition to shortening the extrusion water washing process, the amount of heat required for heating in the next process is reduced, and the temperature of the washing drainage is reduced, so that the amount of cooling water can be reduced and the capacity of the drainage tank can be reduced. Also, cooling by the FDF is not required, thereby shortening the cleaning time and improving the efficiency.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are flowcharts showing a chemical cleaning method according to another embodiment. The same reference numerals as in FIG. 3 denote the same or corresponding parts, and reference numeral 11 denotes a heat exchanger.

The chemical cleaning method shown in FIG. 1 uses the valves V ₁ , V ₂ , V ₃
Is opened (the others are closed), the cleaning liquid is introduced into the boiler 1 by the pump 2 from the liquid supply path 4, taken out from the extraction path 5, and circulated through the circulation path 6 to perform chemical cleaning. During that time, the cleaning liquid is kept in a heated state by blowing steam or the like. As the washing proceeds, the scale in the water tube dissolves, and the acid concentration of the washing liquid decreases, and the scale component concentration, for example, the iron ion concentration increases. At the stage when these concentrations have become constant, the washing step is completed and the process proceeds to the extrusion water washing step.

In the extrusion water washing step, the valves V _{1 to} V ₃ are closed and V ₄ to V ₃
Open V _7, by supplying pure water as the cleaning water from the water supply passage 7 through valve V _4, the heat exchanger 11 from the valve V ₅ by a pump 2
Through the boiler 1, the cleaning liquid in the boiler 1 is extruded as cleaning drainage, and the inside of the boiler 1 is washed with water. The cleaning waste liquid exchanges heat from the valve V ₆ through the heat exchanger 11, flows into the waste liquid storage tank 3 through the valve V ₇ , and is further sent from the discharge passage 9 to the waste liquid treatment device.

Since the washing water entering from the water supply channel 7 is heated in the heat exchanger 11, the solubility of the scale component when introduced into the boiler 1 increases, thereby increasing the washing efficiency and the washing time. And the temperature of the boiler 1 is prevented from lowering. On the other hand, the washing waste liquid discharged from the boiler 1 is cooled by the heat exchanger 11, so that it can flow directly into the waste liquid storage tank 3, and there is no need to fill cooling water in advance. The end point of the extrusion water washing can be determined by measuring the acid concentration or the scale component concentration in the washing effluent, for example, the iron ion concentration.

At the end of the extruding water washing step, the valves V _{4 to} V ₇ are closed, and the valves V _{1 to} V ₃ are opened to circulate the liquid while pouring the rust preventive agent, thereby performing the rust preventive treatment. At this time, the rust preventive solution circulating by blowing steam is heated, but the amount of heat applied here is small because the temperature drop of the boiler in the extrusion water washing step is small.

When the rust prevention process is completed, the same extrusion water washing process as the previous process is performed. In this case, the valves V _{1 to} V ₃ are closed and the valve V ₄
~V ₇ introducing pure water as wash water open, the heat exchanger 1
1 and is introduced into the boiler 1, and the washing wastewater is supplied to the heat exchanger 11.
Through the drainage tank 3. Also in this case, the washing efficiency is increased by heating the washing water, and the temperature of the boiler is suppressed from being lowered. In addition, since the washing waste liquid is cooled, it becomes possible to directly flow into the waste liquid storage tank 3.

After the final extruding water washing step is completed, the boiler 1 is drained and dried. At this time, since the temperature of the boiler 1 is prevented from lowering, the drying time is shortened. The discharged washing wastewater is usually collected in a system other than the drainage storage tank. However, even when the washing wastewater is allowed to flow into the drainage storage tank 3, it can be directly collected in the drainage storage tank 3 because the temperature is considerably reduced. it can.

The method shown in FIG. 1 is an example in which the cleaning water is sucked by the pump 2 and injected. FIG. 2 shows an example in which pure water as the cleaning water is supplied at a considerable pressure. After introducing a cleaning liquid to the boiler 1 by 2 in the pump 2 from the water supply pipe 7 by opening the valve V _8, the circulation path by closing the opening valve V ₈ with the valve V ₁ 6
Circulates through to perform chemical cleaning.

In the extrusion washing step, the valves V ₁ are closed, V ₈ and V ₉ are opened, pure water is supplied from the water supply channel 7 as washing water, heated through the heat exchanger 11 and injected into the boiler 1 by the pump 2. . The washing waste water is cooled from the valve V ₉ through the heat exchanger 11 and flows into the drainage storage tank 3. The heat exchanger 11 may be a co-current type or a counter-current type. The rust prevention treatment step, the final extrusion water washing step, and the drying step are performed in the same manner as described above.

[0030]

Embodiments of the present invention will be described below. Example 1 A once-through boiler having an evaporation amount of 1710 tons / hr was chemically cleaned by the method shown in FIG. Chemical cleaning solution is citric acid 1.5% by weight
And an organic acid aqueous solution containing 1.5% by weight of glycolic acid and a corrosion inhibitor, the temperature in the washing step is 90 ° C., and the washing time is 6 hours.
Time. After the above-mentioned washing step, the process was moved to an extrusion washing step, pure water was supplied as washing water, and heat was exchanged in the heat exchanger 11 to carry out extrusion and washing. Table 1 shows the temperature changes at the inlet and outlet of the heat exchanger (HE) of the washing water and the washing wastewater after the start of the extrusion water washing.

[0031]

[Table 1]

According to the results shown in Table 1, the washing water was heated to a substantially constant temperature of about 35 ° C., and the washing drainage was heated to about 60 ° C. (70 ° C.).
It can be seen that it has been cooled to a substantially constant temperature in the following.
In addition, since the extrusion cleaning time is 60 to 75 minutes when heat exchange is not performed, it can be seen that the time is reduced by about 15 to 30 minutes. In the next rust prevention treatment step, the heating time was short, and the time was shortened by two hours.

[Brief description of the drawings]

FIG. 1 is a flowchart of a chemical cleaning method according to an embodiment.

FIG. 2 is a flowchart of a chemical cleaning method according to another embodiment.

FIG. 3 is a flowchart of a conventional chemical cleaning method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Boiler 2 Pump 3 Drainage storage tank 4 Liquid supply path 5 Extraction path 6 Circulation path 7 Water supply path 8 Drainage path 9 Drainage path 11 Heat exchanger

Claims (1)

[Claims] 1. A cleaning step of introducing a chemical cleaning liquid into a boiler and circulating and cleaning it in a heated state, and an extruding water washing step of introducing washing water into the boiler, extruding washing wastewater and washing with water, In the extrusion water washing process, the washing wastewater discharged from the boiler and the washing water to be introduced are introduced into a heat exchanger to exchange heat, and the washing wastewater is cooled and discharged, and the washing water is heated. A chemical cleaning method for a boiler, wherein the extruder is washed with water.